M&R Professional Screen Printing Series

Citation preview

Level

M&R Professional Screen Printing Series Authored by Joe Clarke and Colleen C. Lynch

1

Textiles

M&R Professional Screen Printing Series Authored by Joe Clarke and Colleen C. Lynch

Level

1

Textiles

M&R Professional Screen Printing Series: Level 1 Ó2001 by First Aid Ltd. All rights reserved. No part of this book shall be reproduced, stored in a retrieval system, or transmitted by any means (electronic, mechanical, photocopying, recording, or otherwise) without written permission from the authors. No patent liability is assumed with respect to the use of the information contained herein. Although every precaution has been taken in the preparation of this book, the publisher and authors assume no responsibility for errors or omissions. Neither is any liability assumed for damages resulting from the use of the information contained herein. First Printing March 2001 English Version Book Part # MAN-PSPM-1.0 English Version CD Part # MAN-PSPM-1.0/CD Trademarks All terms mentioned in this book that are known to be trademarks, service marks or copyrights have been so acknowledged. The publisher and authors can not attest to the accuracy of this information. Use of a term in this book should not be regarded as affecting the validity of any trademark, service mark or copyright. Warning and Disclaimer Every effort has been made to make this book as accurate as possible. In an effort to limit the length of the book, a certain level of general screen print knowledge has been assumed. The reader should use due diligence before using any of the information contained in this book in a production setting. The reader should also refer to the M&R Operator’s Manual for additional press information. The information contained in this book is on an “as is” basis. The authors and publisher shall have neither liability nor responsibility to any person or entity with respect to any loss or damages arising from the information contained in this book, CD or web site postings.

Publisher M&R Printing Equipment Project Manager First Aid Ltd. Authors Joe Clarke Colleen C. Lynch Editor Colleen C. Lynch with direction from Mark Bucanan Photography Steve LaMonica CAD Drawings Frank Laurendi Cover Design Colleen C. Lynch Interior Design & Layout Colleen C. Lynch

Forward Dear Friend: The garment printing industry was the cornerstone of our company. I felt the best way to express our gratitude was to help you use your equipment to its full potential whether or not it is M&R's brand name. The CD (or book) you are reading is our way of saying “thank you” for your support. M&R, is comitted to raising the level of education avaiable to the screen printer, therefore any profits derived from sales of this manual will be returned to the industry. Our intention with this handbook is education, not advertising, so to keep ourselves honest, we contracted an independent consulting firm, First Aid Ltd. to author this publication, under our supervision.

Richard C. Hoffman, CEO

The 250-page handbook is divided into of six chapters, Screens, Stencils, Inks, Press Calibration, Flashing and Costs. All of our experience indicates that if these six areas are in order, increased productivity, quality and profits are the natural result. The handbook offers straight foreword "how-to" information. It is unique in the fact that its recommendations for all major elements of production, dovetail into a functional system for success. The information is current and most has never before been published. It has elements of value for veterans as well as newcomers to our industry. This English version of our Professional Screen-Printing Series is another in a line of educational products and services. Please let us know what you think of the handbook. You may contact Mike Sweers at 1-800-888-8888 or if calling from outside the continental US or wanting to contact by mail or email, please refer to the contact information listed in the acknowledgements section of this manual. Thank you for being a part of this growing industry.

Sincerely,

Richard C. Hoffman CEO M&R Printing Equipment

About The Authors First Aid Ltd. was the project manager for this book. First Aid has been in business since January 1998. They are a consulting firm that specializes in process-screen printing, but are diverse enough to offer services in the areas of research and new product development, sales and marketing, production costing, site location, hands-on training and seminars. First Aid’s expertise extends far beyond the covers of this book. They assist their clients with on-site training and implementation of HiRes AccuColor printing on dark or light textiles, graphics process printing, high tolerance printing and the newest addition, direct printing of large format lenticular images. First Aid Ltd. has been able to differentiate itself by using math, science and statistics as the foundation for a screen printing system. Over the years they have accumulated a library of calculations and algorithms used to set specifications. They have integrated these into an internal software package they use to assist their clients in setting customized specifications for the screen printing system. You will find the results of many of those algorithms in the charts and tables found in this manual. Joe Clarke, Technical Director for First Aid Ltd. was primary author. He has been involved in the screen-print industry for over 32 years. He owned his own print shop at a young age, has had the opportunity to work in an ink lab and design equipment for the industry. He has aided mesh , emulsion, ink, and equipment manufacturers in product design. He has given numerous seminars, writes monthly for several trade magazines, is a three-time Swormstedt Award winner for best technical paper of the year and is a member of the Academy of Screen Print Technology. Colleen C. Lynch, President of First Aid Ltd. was co-author, editor and layout design. She has over ten years experience in the screen-print industry. She was part of the startup team for DYNAMESH Inc., American distribution for NBC Mills mesh. She has gained additional experience working as National Sales Manager for Chicago Decal Company and Vice President for Toyo America. Her areas of expertise within the industry lie in HiRes AccuColor© separations, screens and stencils. Ms. Lynch is responsible for the systematic approach First Aid has taken to the process of screen screen printing.

Acknowledgements For a project of this scope to come to fruition, it takes the cooperation and aide of many people. The following companies and people came to our aide, either in providing materials, photographs or illustrations, data, and testing. We are grateful for their contributions and support. Adam Scaife of Pleiger Plastics for technical additions. Al Anderson of the S.G.I.A. for technical insights. Autotype USA, for technical input and use of their Exposure Calculator. Cary Pucilla of SaatiPrint (formerly Majestech) for digital files and tech sheets. Dale Scott of Liberty Screen Print for High Density samples. Dynamesh, manufacturers of screen mesh, for technical data and mesh samples. Encore Engineering for digital files and tech support on squeegees and sharpeners. Genevive Munden for technical input and comments on the ink chapter. Gino and Bernadette Battaglia of Blue Chicago for permission to use photos of the John Carroll Doyle tee shirt images. Haden-Horne Ink Company for ink samples and specifications on plastisols. Hunter Labs for the Hunter L*a*b* Color Solid. First Aid Ltd. for their Mesh Counter films, Printer’s Color Wheel and various charts, graphs and flowcharts. Kiwo for extensive lab work, photomicrographs and technical support. Laura Unterbrink of Kiwo USA for patience even the third time we lost her digital files. M&R Printing Equipment: Mike Sweers for unwavering assistance on an abundance of issues, scanning and retouching photos, building custom files, retrieving archived information, proof reading and editing and a variety of other tasks too numerous to mention. Without Mike's involvement, the quality of the handbook would have been compromised. Frank Laurendi constructed original CAD drawings that lend clarity and scale precision to the handbook. He supplied files on many components of the presses and process. Andy Oleson and Jeff Hefner for screens both prepared and loaned and their total cooperation, Joel Glassner for being sure that the showroom press was in spec and ready for a photo session or research use. Mike Correnti for art and sympathy for anyone wanting to put Microsoft tables and Excel graphs into Quark. Special thanks to those who proofed and edited the manuscripts; it is this group who insures clarity and accuracy.

Acknowledgements SaatiPrint for technical assistance and permission to show their metering equipment. Mark Buchanan, Executive Editor, Printwear Magazine for journalistic guidance. Murakami Screen USA for photomicrographs, technical data and mesh samples. National Business Media, Printwear Magazine, for supplying digital files of artwork. NuArc Inc. for photographs and technical information. Photo Research for the Color Chromaticity Diagram. Pleiger Plastics for squeegee blades used in our testing and supplemental tech support. Promotions Chicago for printed samples. “Spike” Wolf of Target Graphics for appearing in the photo inspecting HiRes AccuColorÓ garments. Steve LaMonica for an abundance of high quality photography with quick copy turnaround. Stretch Devices for roller frames used in the photos and during testing. Ross Balfour of SaatiPrint for technical guidance on stencil coating methods. Target Graphics Ltd. for Hi-Res AccuColor© tee shirts and permission to use their specifications.

Contact Information Autotype USA Schaumburg, IL. 60173 Phone 847-303-5900 Fax 847-303-5225 Toll Free 800-323-0632 www. autotype-americas.com Blue Chicago 736 N. Clark St. Chicago, IL 60601 Phone 312-642-6261 Fax 312-661-1814 Dynamesh 155 W. Hawthorne Unit 4E

West Chicago, IL. 601 Phone 630-293-5454 Fax 630-293-5647 Toll Free 800-235-5056 www.dynamesh.com Encore Engineering 5404 Ashton Ct. Suite D Sarasota FL. 34233 Phone 941-921-5138 Fax 941-921-5434 Toll Free 800-922-5138 www.encoreenginc.com First Aid Ltd. 1314 Elm St. St. Charles IL. 60174-4131 Phone 630-377-7699

Fax 630-377-6867 E-mail [email protected] www.FirstAidLimited.com Haden-Horne Ink Company 2471 North Forest Dr. Marietta, GA. 30062 Phone 770-642-7773 Fax 770-649-7687 E-mail [email protected] Hunter Labs Reston, VA. 22090 Phone 703-471-6870 Fax 703-4714237 E-mail [email protected] www.hunterlab.com

Acknowledgements KNC Marketing 86 Irongate Dr. Waldorf, MD 20602 Phone 301-843-1896 Fax 301-843-7649 Toll Free 800-627-8264 wwwknc.com Kiwo USA 1929 Marvin Cir. Seabrook, TX. 77586 Phone 281-474-9777 Fax 281-474-7325 Toll Free 800-549-6872 www.kiwo.com Liberty Screen Print 320 Gibson Dr. Madison, NC. 27025 Phone 336-548-6071 Fax 336-548-1866 www.libertyembroidery@aol. com M&R Printing Equipment 1 N 372 Main St. Glen Ellyn, IL 60134 Phone 630-858-6101 Fax 630-858-6134 Toll Free 800-736-7431 www.mrprint.com Murakami Screen USA 745 Monterey Pass Rd. Monterey Park, CA 91754 Phone 323-980-0662 Fax 323-980-0659 Toll Free 800-562-3534 E-mail [email protected] www.murakamiscreen.com

NuArc Inc. 6200 W. Howard St. Niles, IL 60714 Phone 847-967-4400 Fax 847-967-9664 Toll Free 800-962-8883 E-mail [email protected] www.nuarc.com Photo Research 9731 Topanga Canyon Place Chatsworth, CA 91311-4135 Phone 818-341-5151 Fax 818-341-7070 www.photresearch.com Pleiger Plastics Company Crile Rd. P. O. Box 1271 Washington, PA 15301 Phone 724-228-2244 Fax 724-228-2253 Toll Free 800-753-4437 E-mail [email protected] www.pleiger.com Printwear Magazine National Business Media 2800 W. Midway Blvd. Broomfield, CO 80020 Phone 303-469-0424 Fax 303-469-5730 E-mail pweditor@nbm www.nbm.com/printwear Promotions Chicago 904 Westgate St. Addison, IL. 60101 Phone 630-628-7890 Fax 630-628-7891 E-mail [email protected]

S.G.I.A. 10015 Main St. Fairfax, VA. 22031 Phone 703-385-1335 Fax 703-273-0456 www.sgia.org SaatiPrint USA (formerly Majestech ) 247 Route 100 P.O. Box 440 Somers, NY 10589 Phone 914-232-7781 Fax 914-232-4004 Toll Free 800-431-2200 E-mail majestech@ majestech.com www.saati.com Steve LaMonica Photographer 2623 N. Drake Ave. Chicago, IL 60647 Phone 773-772-6895 Fax 773-772-6896 E-mail [email protected] Stretch Devices 3401 North I Street Philadelphia, PA 19134 Phone 215-739-3000 Fax 215-739-3011 Toll Free 800-523-3694 Target Graphics 29 W 707 North Aurora Rd. Naperville, IL 60563 Phone 630-357-7468 Fax 630-357-8287 Toll Free 800-689-6461 E-mail [email protected]

Table Of Contents Chapter One: Screens.............................................................1.1 Chapter Two: Stencils..............................................................2.1 Chapter Three: Inks....................................................................3.1 Chapter Four: Press Calibration.............................................4.1 Chapter Five: Flashing.............................................................5.1 Chapter Six: Costing..............................................................6.1

Terminator

Ultimate

Challenger II

Formula

Gauntlet R/S

Gauntlet II

Part Number MAN-PSPM-1.0

I. Published Specifications Are Not All The Same Clarification of Published Specifications II. Properties Of Test Screen Fabric Applications Specifications Ink Transfer Tensioned Geometry Halftone Suitability Conclusion III. Frame Properties Frame Size Size Exceptions Frame Strength And Flatness Conclusion IV. Tensioning Goals Low Elongation Screen Fabric Tensioning Instructions V. Troubleshooting Screen Life Mesh Bursting Mesh Ripping Tension Counter Measures Tension Limits Tension And Off-C Contact Distance

Chapter

1

SCREENS

Screens Published Specifications Are Not All The Same Whether you look at a mesh-manufacturer’s catalogue, its invoices, hang tags or the coding on its product’s selvage, you get specifications. These are intended to give you some level of certification that the mesh you’re looking for is the mesh you receive—but these specifications can be misleading if you do not have enough information. The mesh, in fact, may be far from the product you are expecting. It is important to note that are no standards in the way mesh manufacturers offer up specifications. Some information is nominal, some theoretical, some actually measured. You will want to know the ± tolerance of nominal and measured information, the equipment used to take measurements, if it was measured or calculated in metric or English measurements and if any conversions were made—theoretical specifications should come with the calculations, for you to know how they arrived at that information. Specifications are based on relaxed mesh or pre-woven threads. This is not in itself a problem, unless you try to use this information to determine angles to avoid moiré or to predict ink mileage. When selecting mesh, this pre-woven, relaxed-mesh information should be used as comparative information only. However, the variance in how the specifications are given make even this a challenge. We urge you to carefully read the specification sheets. They will generally divulge methods used to gather the data. If you’re still uncertain, talk to the manufacturer. It should be able to give you all the information you require. When you’ve gathered sufficient information, you will need to make up your own comparison sheet that uses that same calculations for all the theoretic specifications, and includes the ± tolerances of nominal or measured specifications. This is the only way to get a fair comparison between mesh manufacturers. There are four types of information available on screen mesh: nominal, theoretical, measured and absent. Each of these has some utility, but all are vastly different. Nominal … means the name and has little to do with the precise dimension or measurement. For example, a 230 mesh is seldom an exact 230; just as infrequently as it is the same count in the warp as in the weft. Find out the ± tolerance of the mesh count. This will tell you the range you can expect when ordering this count. And remember, this specification is for relaxed—non-tensioned— mesh. Similarly, low-elongation (LE) is not as much a specification as it is a general tendency for the mesh to develop tension with relatively lower elongation. PAGE 1 . 3

Chapter 1 You require the mesh’s SS (stress-strain) curve to know this specification. Theoretical … information is that which is developed as a calculation. Many theoretic values are calculated using a pre-woven thread diameter and a nominal mesh count. For example, a 41-micron thread diameter is listed (and shown) as a cylindrical cross section but, in fact, it is not a circle at all. The thread diameter becomes oval-shaped during weaving and finishing—one reason why the fabric thickness is always less than two times the thread diameter. Measured … information is based on actual measurements taken on either the bolt or the mill-run of fabric—in its relaxed state. It is not to be taken as absolute, for there are variances in the measurement processes; it can be an average, or other approximation. For example, some manufacturers list the measured fabric thickness with each bolt of mesh. Fabric thickness is a composite of thread diameter; mesh count and finishing conditions, so it is difficult to calculate. While this it is by far the most informative data that can be given, here again, you will want to be aware of the ± tolerance of this measurement. Absent … information is, obviously, the worst of all. What you don’t know can hurt you. Do you remember the “twill-mesh reality” of a few years ago? No one (outside of the weavers) knew that twill mesh was being arbitrarily substituted for plain-woven goods! Today’s missing data pertains to the stress/strain relationship of the mesh—its SS curve. It has been deemed by some as trivial but, as an example, if the SS is imbalanced, you have the option to lose tension during a press run or to end up with moiré in your halftone work. Your choice. The real world knows that, “If it ain’t broke (not costing you money), don’t fix it.” But—fixing or not fixing aside—wouldn’t you agree that it’s critical to know if your materials are broken? If not, you may make a decision based on wrong (or absent) information and, in such a case, there is no predicting the results. The “truths” upon which you’ve been relying may be based upon a lack of quality information. Thus, we encourage you to get “live” specifications whenever possible so that you can set standards and predict your printed results. We help you begin this by identifying basic screen-mesh properties. Note that specific details are omitted in these definitions—with reason—but are covered later in this chapter. Clarification of Published Specifications As we stated above, all such data has utility. The point is that you should not confuse the name of something with its size or other physical property. Many of the PAGE 1 . 4

Screens published specifications are useful for one purpose—comparison. For example, if you have one mesh with a 45-micron thread and another of the same count but a larger mesh opening, it is fair to plan on improved ink flow and, perhaps, higher elongation. A problem arises if and when specification names are taken as precision measurements. Below we explain the utility of each of the most frequently used specification names. Mesh count … is nominal and defines the target number of threads and openings per linear inch in either direction. In the real world, the count is not too often exactly on target and rarely is the count the same in both directions. This is not an inherent problem. Rather, the manufacturers have a specification (or tolerance range) within which they work and, at times, that range may be inadequate for our purposes. Also, as the fabric is stretched, the count literally drops, based on the amount of elongation. The on-press mesh count is the only one that really matters to you. Thus, mesh count should never be relied upon as a singular entity for the reasons above and those to follow. Thread diameter … is nominal and defines the target diameter of the filament as they arrive from the yarn spinner; there is no guarantee that your bolt was composed of precisely the named thread diameter. Once the fabric is woven then finished, the threads are oval in shape. They do not significantly change diameters in the tensioning process, particularly with low-elongation fabric. The thread diameter sets the range for fabric thickness and, other than that, only connects the stencil to the frame. If there was another way to secure the stencil to the frame, you would want to eliminate the mesh, because the threads only get in the way. Thinner threads offer far less interference in the forms of printed resolution, ink passage, moiré and artifacts, but are not as strong as thicker threads.

TD

Virgin Thread Diameter

Figure 1.1 Shows a line drawing of a fabric thread in its cross sectional form. The yarn (thread) is spun in a cylindrical form. In the manufacturing and finishing processes it becomes ovaled. The “thread diameter” is given as though the yarn was still cylindrical in form

PAGE 1 . 5

Chapter 1 Mesh opening … is theoretical and defines the average—not the minimum— distance between adjacent threads. It is not often square as indicated by the fact that the mesh count is not usually equal, warp to weft. Further, it becomes enlarged as the fabric is stretched. You should monitor the stretched distance (percentage of elongation) of your fabric in order to know just how “un-square” the mesh opening has become. When the mesh opening is large enough, it allows the ink to pass with a minimum of effort. There are three ways to enhance this: coarser mesh, higher elongation, or thinner, stronger threads. We recommend the last of these options.

Thread Opening

300s Mesh

Figure 1.2 This a photomicrograph of a thin thread 300 S fabric compliments of Murakami Screen US Inc. The dark areas of the photo represent the mesh opening. Even though this fabric would print very well, you can readily see that the opening is quite small. Just imagine the aperture if the thread was a T or HD, ink passage becomes very restricted.

Percent open area … is theoretical and, unfortunately, is based on a calculation that uses a thread diameter that is round and a mesh opening that is square. Again, as a comparative factor used prior to in-plant testing, this may have some utility. Generally, we recommend the highest percentage of open area per mesh count. While it does have a proportional relationship to the flow rate and pressure drop of the mesh, as a single entity this measurement offers little more than comparative value. Theoretical ink volume … is, again, very theoretical, as its name suggests. This specification is best used for general comparison of ink volume within a single count of differing diameters. Any more creative comparisons become less accurate. Fabric thickness … is offered in two forms, nominal and measured. Naturally, the measured form should be far more accurate (depending on the accuracy of the test methods versus the variance from nominal data used to established the PAGE 1 . 6

Screens target). Fabric thickness roughly describes the length of the “tunnel” through which you will have to pump ink. This is of considerable significance to the tee shirt printer for a few reasons; white constitutes approximately 45% of the inks used. It must be deposited in a sufficient film thickness to be opaque. It has a dilatent (shear thickening) flow property so the harder you push it the less it flows. Whites like a large opening and a thin tunnel. Weave type …options include plain and twill weaves, as well as multi-filament, which is infrequently used today. Plain woven is the only fabric that should be used for high quality screen-printing. Most of the manufacturers and or dealers have at one time or another swapped twill weave fabric for plain and not announced this to the public. The attitude may have been that the screen printer will never know the difference. But the fact is the printer will notice a difference, but identifying the mistaken twill mesh as the culprit, can be time consuming and difficult. You should be aware of the problems twill weave fabric causes and develop a system for verification of your incoming materials. Generally it is precisely the wrong type of geometry, a small opening and thick threads. Blue Jeans should be twill woven for strength, but for printability screen mesh should not.

Plain Woven Mesh Construction End View of Weft Threads Figure 1.3 This a cross sectional view of plain-woven screen mesh. From the left, the warp yarns are separated and a weft yarn is shot between for the width of the bolt and held under tension. Next the warp yarns are again separated and are wrapped around the weft yarn. Next the process is shown as it continues. Drawings courtesy of Printwear Magazine.

Properties Of Test Screen Fabric Now let us build on the basic information we have identified. We offer a model (refer to figures 1.4 and 1.5) based on information of the theoretical category— measured SS curves, and measured fabric thickness. The model is not intended as an absolute, but to give you a variety of perspectives to help illustrate the causeand-effect relationship of the mesh specifications. The table in figure 1.4 lists comparative factors of four test mesh counts used in PAGE 1 . 7

Chapter 1 How We Developed The Mesh Model We selected fabrics that were lowelongation, whenever possible, and obtained SS data to support our choices. We selected fabric that had the selvage edge on both sides so we knew our bolt was not cut from a larger woven width. The filament in all possible cases were colored to reduce light scatter (halation) during exposure. The threads were thin as was the fabric thickness, and they all had a proportionately large mesh opening. Such geometry allows the fast and unrestricted transfer of the thickest plastisols. The fabrics were all relatively flat to permit fast squeegee speeds. Finally, we published the model of the fabrics once they were tensioned, in order to make the information as real world as possible.

this manual (and explained on pages 1.8 through 1.14). The data below is computed after the noted percent elongation and resulting tension level. Some of the criteria used were a 65-lpi for modeling halftone equivalents and 10-ips (inches per second) squeegee speed for modeling pressure drop and flow rate. The SS information was based on 45” dyed mesh. Applications The four fabrics are 80/71, 150/45, 230/40 and 305/35 thread. These were chosen for a variety of reasons, including that they address a good cross section of printing needs and offer good mesh geometry. For inventory and real-world control, you will want to keep some distance between mesh counts and limit the number of counts you use. The mesh manufacturers usually use a single thread to weave four mesh counts; it is economical and provides a wide range of products from which you may choose. The thread diameters are “nominal”—that is, given a name. These are not absolute dimensions nor do they need to be. The “tried and untrue” mesh count is just that. It is rare that a published count is the actual number of threads, in either direction. Further, the count is not usually the same in warp and weft directions. If you are ordering strictly by the count of the mesh, you are probably getting a fabric with a thick thread and a small opening—such is the least expensive for the weaver to manufacture. Last but definitely not least, the warp direction may not build tension as fast as the weft, and no tension meter will report that reality. All in all, you may not know what you are buying, particularly if your reference is the manufacturers catalog. We will, however, try to help you get to the bottom of the mesh. The 80/71 can be used for athletic printing, high-density graphics, and metallic and puff-ink designs. It will deposit a thick-but-smooth layer of even the tackiest of inks with a minimum of squeegee force. The 150/45, in the context of these four fabrics, is the workhorse; it will print most wet-on-wet applications with a reason-

PAGE 1 . 8

Screens able hand and drape. The print speed on this fabric is excellent. It is fine for the brightest of underbases and clears well on both fleece and jersey-knit T's. The 230/40 mesh offers finer detail, softer hand but higher print speed only with the proper ink, intended for high-speed, automatic printing. Naturally, the ink mileage on this fabric is excellent and it performs well for overprinted colors. The 305/35 is traditionally intended for halftones and process color, but even serves well as an underbase for high-detail work. Its flow rate and pressure drop allow it to fill the knit in the garment at high speeds and still provide details for 65-lpi and above. Many of the specifications in the tables below are defined as “nominal.” These are target dimensions and, per manufacturer, are to be within a published or unpublished range. The use of this data allows us to anticipate results of certain printing conditions with a minimum of testing prior to production. From this data we have constructed models of printing performance. The model is a simulation of what can be expected from a fabric with particular properties. We encourage you to test for yourself and determine the best product for your needs. Meanwhile, use the tables below to jump start your process. Following is a detailed explanation of the variables for the first six columns—the mesh specifications of Part 1.

Mesh Count

Thread Diameter

N/cm²

Percent Elongation

Actual Mesh Count

Fabric Color

Fabric Thickness

Mesh Opening.

Open Area

Ink Height

Flow Rate

Pressure Drop

Mesh Model Part 1

80S 150S 230S 305T

71m 45m 40m 35m

25 23 25 24

3.9ST 5.6LE 5.0LE 6.1LE

77 141 216 291

White Amber Amber Amber

119 72 60 53

247 124 70 48

60% 54% 41% 34%

4.0 2.5 1.5 1.0

.223 .126 .102 .070

3.5% 10.3% 19.8% 27.6%

Figure 1.4 This table lists the properties of our four sample screens (details follow in the text). The 80S for example has a 71 micron thread diameter, was tensioned to 25 Newton’s per square centimeter, the ST elongation fabric was taken to 3.9% elongation. The actual count as woven and finished was a 77 average mesh. The cloth was white with a thickness of 119 microns, a mesh opening of 247 microns and an open area of 60%. Its nominal ink height is 0.004” or four mils, with a flow rate of 0.223 L/cm2/S and a pressure drop of 3.5%. Note that the flow rate and pressure drop can be used at this stage for comparative purposes. They are used more appropriately after the mesh is tensioned.

PAGE 1 . 9

Chapter 1 Actual Mesh Count

StressStrain

StressStrain Variance

Cross Section

Actual Mesh Opening

FlatnessAngle

Open Dot

TonalRange

AlphaAngle

MoiréAngle

Moiré Frequency

Ideal Lpi

Mesh Model Part 2

77 141 216 291

6.4 4.1 5.0 3.9

< 1.0% < 0.5% < 0.5% < 0.5%

120 88 106 110

272 145 83 57

11.3° 12.9° 17.4° 19.8°

------50.5 37.2

---19% 62% 77%

84.3° 79.8° 75.3° 72.0°

---27.5° 17.5° 12.9°

.033 .016 .013 .012

7.6 24.9 54.9 89.8

Figure 1.5 This is a list of the performance properties of the four sample mesh counts. Row Three shows a 216 mesh as tensioned. The stress-strain variance was less than 1/2%, which is agreeable. It has a cross section of 106 with an actual open area of 83 microns with a flatness angle of 17.4°. The open dot area for a 65-line halftone is 50.5%, substantially greater than the 41% open area. Its geometry represents a tonal range of 62% (excluding the stencil) and the optimal angle of intersection is 75.3°. Symmetry is found at 17.5° to forestall radial moiré and its tendency to cause moiré based on the 65 Lpi is 0.013. The ideal Lpi for ink transfer and symmetrical balance is 54.9 lines per inch.

Specifications These are the terms applied to the mesh that you buy. As we described above, many of them are nominal—or simply “names”—and should not be mistaken for dimensions or specifications. Depending on the manufacturer, you may be able to get actual measurements—or even a Certificate of Analysis (C of A) to specify the measurements on the actual bolt of material. Mesh count … means the number of threads and openings in a linear inch in either direction. It is nominal because the fabric is frequently of a different count than labeled. For example, the 305 mesh may have a weft count equal to 301 and a warp count equal to 306 so that the stress strain can be balanced. (refer to page 1.16 for explanation). The letter designation next to the nominal count is a relative diameter of the thread and should be used as a reference only; for real-world comparisons use the thread diameter data provided in microns instead. Thread diameter … refers to a nominal thread diameter in microns. You should realize that this name is based on a cylindrical (unwoven) filament. The actual filament become ovaled during the weaving process. So, if you realize that the thread acts to obstruct details and ink passage, then coarse-thread fabrics are even worse than this data might suggest. Further, there is little change in thread diameter at any tension level. N/cm² (Newton per square centimeter) … is a measure of the average tension of the test screen in either direction, based on the percent elongation to keep a balanced SS relationship (refer to page 1.15). This tension level was a result of a percentage of elongation, which allowed us to maintain a square mesh PAGE 1 . 10

Screens opening as well as a balance of strain on both the warp and weft. Percent. elongation … is the percentage of elongation for warp and weft threads, required to take the mesh to a Figure 1.6 This is a photomicrograph compliments of Murakami Screen US Inc. It is an specified tenenlargement of a 420 S mesh count. The count should be given in both the warp and weft directions for two reasons; the mesh count from all manufacturers is nominal, it is rarely a persion level. If fect 420. Secondly the warp and weft do not always match identically. You want the manufacthe fabric is balturer to tell you both actual, not published, mesh counts. If these are too different or move from anced, this perthe target too far, you may have problems with moiré and registration. centage is the same in both the warp and weft directions. Otherwise, you compromise the shape of the opening or the tension between stroke and non-stroke directions (refer to figure 1.24, on page 1.30 for details.) a. Virgin-before weaving.

b. Finishedafter weaving and finishing.

Figure 1.7 This is a cross sectional illustration of the changes in the thread “diameter” from virgin to finished to tensioned. The top illustration shows the relationship when the threads are cylindrical, in a virgin state. The middle illustration shows the mesh as finished in manufacturing. The threads have been ovaled, there fore the opening is smaller. The bottom illustration shows the results of the mesh once it is tensioned. The opening has increased in size. Note that the theoretical data does not show such differences but when used as intended it is very representative of the relationships between one mesh and another related mesh.

c. Tensioned-after stretching.

PAGE 1 . 11

Chapter 1 Low elongation… is noted in the same column and indicates the modulus of the fabric—we refer to it colloquially as “low elongation.” Note that it is less a specification than a tendency, and each manufacturer’s “LE” properties differ. LE fabric actually has a higher modulus of elasticity; that is, it develops tension at a higher rate. This is the only type of fabric that you should use for high-quality printing. Not only does it get to tension faster, but it retains that tension level better than traditional (lower modulus) mesh. With low-elongation fabric, the purpose of retensioning became less of a factor in a high quality print and the concept of work hardening screen mesh applied to conventional mesh much more than low elongation (refer to figure 1.8 below for details). Figure 1.8 This is a graph of four relative possibilities of percentage of elongation. The vertical axis indicates tension while the horizontal axis indicates stretch or elongation as a percentage. From left to right, the first mesh is a low elongation fabric at a relatively high-tension level. The next is a low elongation fabric taken to a low-tension level. Number three is a fabric taken to high tension that required a great deal of stretch. And the last fabric is a high elongation fabric that was never taken to high tension. For stable on press geometry and consistent openings, one or two are best suited. The level of tension should be to support the proper off-contact distance refer to page ___ for details. Graph compliments of Printwear Magazine.

Actual mesh count … is based on the nominal count, and percentage of elongation. For example, if the fabric starts at 230 and is elongated five percent, the resultant count would be 218.5. As elongation increases, the count continues to drop. This is critical information when you are aligning images specific to the mesh in order to eliminate radial moiré or fluctuations in printed-line thickness (see figure 1.36 on page). Fabric color … is most often a factor with finer mesh counts (that have dyed filament), while the coarser counts are typically white (undyed). The colored filament inhibit light scatter or halation from costing detail in the image. The manuPAGE 1 . 12

Screens facturer logic is that the dying allows you a greater window of exposure latitude at a longer exposure time. Additional manufacturer logic is that no one (so they think) wants finer detail on lower mesh counts. Be wary of both. Some fabrics lose their SS balance because they’ve been dyed as woven material; and many of the white fabrics are not production friendly when it comes to detail. Fabric width (not listed in chart) … may, if changed, also affect your SS balance. Once you set your standards, do not arbitrarily switch widths without corresponding data on the balance of that width. Also, you want to be sure the manufacturer does not cut your cloth from a wider bolt or you will never know what you have. Ink Transfer The next six elements deal with the ability of the tensioned mesh to transfer ink both at a high rate of speed and with minimal obstructions. Note that there is an ink height but no theoretical ink volume listed. The reason is that the specific volume is greatly affected by the fabric mass of the garment. Fabric thickness … is the thickness of the woven cloth. Depending on the manufacturer it may be a measured (versus computed) number. This aspect has a primary influence on the ink-deposit height and smoothness of the print. You want the fabric to be as thin as possible so that it is easier to pump ink through the tunnel of the mesh, as measured by its thickness. This is most important when the ink in question is white. White ink is shear thickening—its viscosity actually increases under shear—and does not travel well or far on its own. Thus, the solution for white ink is as thin a mesh as possible.

Mesh Opening

Fabric Thickness

Ovaled Thread Diameter

Figure 1.9 This is a cross sectional illustration of the basic geometry of the fabric. Labeled is the ovaled thread “diameters” the mesh opening and the fabric thickness. Since the fabric thickness is based on the initial (cylindrical) thread diameter and the crimp angle, it may wise to have an actual measurement taken from time to time.

PAGE 1 . 13

Chapter 1 Mesh open … is the average dimension from thread to thread prior to tensioning. Once the fabric is stretched, the mesh opening becomes enlarged. The opening increases in direct proportion to the elongation, but it is not proportional to the measured tension level. A larger opening allows larger-particle and higher tack-level inks to transfer. Open area … is a percentage of mesh area. As a single entity, it has little relevance to the printer other than the rule of thumb that bigger is better in virtually all cases. In our context, it allows a comparison to the “Open dot area,” below. The open dot area is calculated for the 230 and 305 fabrics only. You may note from the table that the percentage open area runs nearly parallel to pressure drop (but it is not a linear relationship). Nominal ink height … is the nominal ink height in mils, deposited by the tensioned mesh. The substrates, the inks themselves and the press settings also affect the ink height. The numbers shown are reasonable and can be used for comparison, but are not intended for precise mileage calculations. Actual thickness is quite specific to the ink used. Flow rate … is expressed in liters per square centimeter per second and is a key factor in the printing process. It is the rate that a quantity of ink can transfer through the mesh, and is bounded by the geometry of the tensioned mesh. Our model is based on a blade speed of 10 inches per second. You want to select a mesh with as high a flow rate as possible, per actual fabric thickness. Pressure drop … lists the percentage of change in hydrostatic pressure on the ink due to the mesh geometry and based on a squeegee interface greater than 1/MC.Graphically, the mesh is shaped like an hourglass, wide open on the top and on the bottom with a narrow passage in the middle. It is the particular shape of the hourglass that must be dealt with. Either by using ink that is very thin to accommodate the hourglass or by better mesh selection. It is preferable to have a lower pressure-drop number. This number can be used to compare various mesh

PAGE 1 . 14

Actual Mesh Count

StressStrain

StressStrain Variance

Cross Section

Actual Mesh Opening

FlatnessAngle

Open Dot

TonalRange

AlphaAngle

MoiréAngle

Moiré Frequency

Ideal Lpi

Mesh Model Part 2

77 141 216 291

6.4 4.1 5.0 3.9

< 1.0% < 0.5% < 0.5% < 0.5%

120 88 106 110

272 145 83 57

11.3° 12.9° 17.4° 19.8°

------50.5 37.2

---19% 62% 77%

84.3° 79.8° 75.3° 72.0°

---27.5° 17.5° 12.9°

.033 .016 .013 .012

7.6 24.9 54.9 89.8

Screens specifications. A lower-pressure-drop mesh will allow a more bodied ink to transfer through it. Our model is based on a blade speed of 10 inches per second. Mesh Model Part 2, has been repeated on the previous page for your convenience and lists the same four mesh counts and considers the 230 and the 305 mesh counts for process color printing of a 65-lpi halftone. Tensioned Geometry The printer needs to know the nature of the mesh on press. To help you view this, we obtained the SS curves on the mesh so that we could build the model. If the tension level were changed, the model would be quite different. For example if the tension were less, the elongation would be less. The mesh opening would be smaller and all attributes would change. Actual count …of the mesh is taken after the percentage of elongation. Note that it is imperative that the elongation is the same in both directions and that the actual mesh count is known prior to tensioning. As the elongation or tension increases, the count is reduced. Strain -Stress … is a coefficient indicating how rapidly the mesh will develop tension at our area of interest. It is the strain - tension, divided by the stress - the percentage of elongation. For example, if the mesh takes five percent elongation to reach 20-N/cm², the S/S is 4.0. A four percent to the same tension is a 5.0. The higher number indicates that it develops tension with less stretch. This index should be compared to the SS variance as higher modulus fabrics typically have a smaller window of opportunity. Component

Warp

Weft

Variance

Result

Match

%E

N/cm²

MC

%E

N/cm²

MC

%E

N/cm²

MC

1

MC

6.0

26.0

282

7.5

32.2

282

1.5

6.8

----

2

N/cm²

6.0

26.0

282

4.3

26.0

291

1.7

----

9.0

3

Match %E

6.0

26.0

282

6.0

26.5

286

----

0.5

4.0

Due to: Register and/or Tension Loss Frequency and Radial Moiré Register and/or Radial Moiré

Figure 1.10 There are three possibilities for tensioning mesh and they are shown in the table above. The nominal mesh count is a 305 / 35. The actual woven count is 299-warp by 304-weft. Number one is to match the MC (mesh count); two is to match N/cm² (the tension); and number three is to match the %E (percentage of elongation) of the mesh. The first heading is warp and under it is %E (percentage of elongation); N/cm² (tension); and MC (mesh count). The point is that if you option for one with an unbalanced mesh the other two will suffer. The variance column shows how much in error the mesh will be. If you match the mesh count,but the elongation and tension are far off–you will experience tension loss on press. If you match the tension, but the elongation and mesh count are far off–you may experience frequency and radial moiré. If you match the elongation, but the tension and mesh count are off–you may experience frequency moiré. None of these choices is ideal because the mesh is imbalanced. PAGE 1 . 15

Chapter 1 SS variance … is the disparity between warp and weft threads and their tension levels at equal elongation. The variance is taken at the tension level we used for the test screens. Equal elongation allows us to maintain a square opening and also to reduce registration jumps during production. A good rule of thumb is to hold warp and weft to one and a half percent variance, none of the mesh manufacturers do this every time with all counts and widths. Murakami SS Curve 150S Mesh 50

45

40

Tension (N/cm^2)

35

30

25

20

15

10

Warp and weft curves are precisely superimposed.

Figure 1.10 This is a reproduction of a stress strain curve provided by Murakami Screen US Inc. The particular mesh is a 150 S thread (per inch) the horizontal axis shows the percentage of elongation from 1% to 8%. The vertical axis shows the tension in Newton per square centimeter from 0 to 50 N/cm². The dense black line shows both the warp and the weft curves. For example if you stretch 5% in either direction, the resulting tension will be 32 N/cm². This is an ideal situation when both warp and weft are superimposed. It means that the square ness of the woven fabric can be maintained during tensioning. If the two curves do not overlap, equal stretch will not result in equal tension. The result is a distorted mesh opening and tension loss on press.

Cross Section … (given in 000’s) takes the thread diameter and the threads per inch and computes fabric density per lineal inch. When evaluated with the S/S it allows accurate comparison of the elastic nature of the fabric and it is unaffected by the screen dimensions. You will note from the table that even though the counts vary radically, the cross sections are similar.

Actual opening … is a measure of the mesh opening at the noted percentage 1 2 3 4 5 6 7 8 of elongation. It increases Percentage of Elongation as the fabric is elongated and allows passage of the ink particulate a larger opening (per mesh count) is always preferable. This dimension is critical to the transfer of long, or needle-like particles like the pigments used for blues and blacks. If those colors are hanging up in the screen, particularly around the perimeter of the image, check the actual open area of the mesh. 5

0

Flatness angle … is a measure of the slope of the threads, which is a constraint to squeegee speed and stencil Rz (flatness). You can expect to see a better Rz (stencil flatness) with a flatter woven screen mesh. Of course this angle should be as low as possible and established once the fabric is tensioned. A flatter fabric is always preferable and when used in conjunction with high yield ink, permits higher squeegee speeds. PAGE 1 . 16

Screens Flatness Angle

Figure 1.12 This drawing shows a cross sectional illustration of the flatness angle of the mesh. The flatness angle is based on the relative pitch of the warp thread as shown. Flatter mesh permits higher squeegee speeds and allows a superior stencil Rz (flatness).

Halftone Suitability The proper selection of a screen fabric is perhaps never more critical than when used in the production of process colors. The next six elements deal with the fabric’s inherent ability to hold a dot, tonal range and to run free of moiré for a given Lpi. Open dot … is the average open dot area on the mesh specified. In our case we have used a 65 Lpi halftone with a computed minimum highlight diameter. The dot is placed directly upon the thread, knuckle and opening and the three areas are evaluated and then the average is taken. This shows a relationship between the frequencies of the mesh and the halftone and should never be less than the percentage of open area of the mesh. Tonal range … is based on a computed highlight and shadow dot diameters and is always far short of the practical range but allows fair comparison between similar mesh geometry. The longest tonal range possible is preferable for most halftone printing. Alpha angle … describes that relationship between the mesh and any geometric shape (lines, dots. squares) and their optimal reference. It is based on the elongated mesh and is the best angle to avoid fluctuations in the reproduction of the image. For process color printing it is usually advantageous to put the chaining PAGE 1 . 17

Chapter 1 direction cyan halftone at this reference. The reason for the cyan is that it is low luminosity (very easy to see), it will always run full range in the image and its pigment particles are the most difficult to transfer through the mesh.

a.

b.

c.

Percent Open Dot Area Figure 1.13 This drawing illustrates the gamut of possible dot positions of a minimum computed highlight dot superimposed over the screen mesh in question. In each of three positions the area of the exposed dot is computed. The three positions are a. Centered over a mesh opening. b. Centered over a knuckle and c. Centered over the middle of a thread. Since all other positions will fall between these constraints, the average of the three is taken. The percentage should always be greater than the open mesh area calculations. This verifies a proper relationship between the minimum dot and the mesh geometry. It is much more relevant to the selection of Lpi and screen mesh than comparing a dot to a thread.

Moiré angle … is computed from the tensioned fabric and creates a symmetrical balance of the chaining and non-chaining direction of the halftone, to eliminate radial moiré in process color. It can be used with the Alpha Angle to compute ideal relationships between halftones and mesh frequencies. Note that although there are other forms of moiré, radial is one of the most prevalent and this angle, when used on a balanced screen mesh eliminates this facet of moiré. Moiré frequency … is the frequency of the moiré based on zero angling of the halftone on the elongated mesh. It is used to compare the halftone to the Lpi for similar mesh counts. A lower frequency is desirable and below 0.002 it is virtually non-existent. Note that although none of the test cases are below 0.002 with a 65 Lpi halftone, that is why the dots are precisely angled with respect to the mesh. Ideal Lpi … is computed for the least risk of both frequency and radial moiré between the mesh and the line count. It is derived from the Alpha angle and the Moiré Angle, and is achieved if and when the two angles match each other. This mesh to Lpi relationship has a symmetrical relationship that corresponds with the optimal angle for image resolution. PAGE 1 . 18

Screens Figure 1.14 This drawing illustrates a screen, a overlaid film positive with an angle marked with a dotted line. Several assumptions have been made for the symmetry angle to eliminate radial moiré, first that the mesh is tensioned at a right angle to the frame. Second that the warp and weft threads are tensioned to nearly the same count. If these are the case, then there is an angle that will eliminate radial moiré. These are calculated in the tables above.

Film Positive

Dot Chaining Direction

Square Mesh Opening

Moiré Symmetry Angle

Conclusion You will want to select fabrics comparable or superior to these in specification and performance. They were chosen specifically to offer high quality prints, and to accept virtually all ink systems at top press speeds. Your fabrics should be plain woven, as flat as possible, of a consistent width with dyed monofilament polyester. The SS curve should be in balance and the square opening should remain square after tensioning. Per count the mesh should have a large opening, a thin thread which produces a thin fabric. This type of geometry will optimize the transfer of ink and the accuracy of the image. Get a certificate of analysis on the fabric that you purchase. It lists the specifications of the specific bolt that you paid for, not just nominal dimensions from a book - the Certificate of Analysis is the real world story. You will find the most durable fabrics do not print very well and the best screens come from fabrics that need to be handled with care. Care consists of calibrating the press (refer to page 4.15), proper off-contact and peel settings (refer to page 4.10), proper squeegee and flood bar settings (refer to page 4.25) and proper tenPAGE 1 . 19

Chapter 1 How To Instructions

Identifying Quality Fabric Verify the following properties: 1. Monofilament polyester.

sioning (refer to page 1.33). The choice is yours. You can have both a long lasting screen and high quality print results if you apply the methods contained in this manual.

2. Low elongation. 3. Plain weave.

Frame Properties

4. Dyed filament.

The selection of a frame is often compromised by the desire to cut costs, but noth6. Balanced SS curve. ing could be further from the 7. Consistent width with selvage. truth. If you cut corners on All other performance properties will be in check if the the size, strength or quality of above seven are specified. the frame—the decision will come back to haunt you with press problems. Following we offer a detailed recipe for frame selection to optimize productivity and deliver quality print results fron the press. 5. Thin thread.

Frame Size The standard frame sizes for M&R presses are engineered and specified to allow the highest quality printing with easy registration on your press. It is unwise to standardize on a size other than what is recommended. Frames that are too large will not fit properly in the screen holders front-to-rear and side-to-side, nor allow room for micro-registration. Frames that are too small often intended to “save” the company money in mesh and initial investment, but usually do just the opposite. Ink Well And Registration

Ink well is the minimum distance between the end of the squeegee and the sidewall of the frame. It is the minimum of both the squeegee length (side-to-side ink well) as well as squeegee stroke length (front-to-rear ink well). As the size of the ink well decreases, accurate registration becomes less likely (at a fixed offcontact distance) and the pressure between the end and the midpoint of the blade becomes less balanced. To maintain the registration tolerance with smaller ink wells the off contact must be reduced, however this often leads to ink transfer problems between the end and the midpoint of the blade, even with a high tensioned screen. PAGE 1 . 20

Screens Squeegee Holder

Rear Ink Well Squeegee Blade

Side Ink Well

Front Ink Well

Screen Frame

Platen Surface

Off Contact Distance Essentials of Press Set-Up

Figure 1.15 This drawing illustrates the platen, screen frame and squeegee and the main components of the following section. You may want to review Chapter 5 for detailed discussions of these components from an on-press perspective.

Image registration is composed of two elements: accuracy and repeatability. Accuracy is the extent to which the original has been duplicated in size. This is not usually a concern for the garment printer. For example if the image is to be 18-inches long, we don’t often care if it turns out to be 18 1/8-inches long but we do care that all of the colors that build the image line up. That is if they all turn out to be precisely 18 1/8-inches long. If you are running close tolerance work, process color or cut-piece stock to be sewn after printing, the off-contact setting is crucial (refer to page 4.4 for complete details on offcontact distances).

Consequences Of Using Smaller Frames Smaller length or width frames will force the screen holders to sit on the platen or hang suspended at an angle and result in extreme print problems such as blurring, smearing and premature mesh fatigue. Using smaller frames than the recommended size, (squeegee and off-contact distance being constant) will cause the following problems: 1. Force the frame holders to sit on the platens. 2. Reduce the range of acceptable off-contact settings. 3. Force you to print a smaller image. 4. Will cause the mesh and stencil to fatigue and breakdown faster. 5. Make registration very difficult.

Image Tolerance

The table (figure 1.18, page 1.23) and graph (figure 1.19, page 1.24) present a nominal off-contact distance of 1/8” (0.125”) and various sized inkwells to demonstrate what happens to the tolerance of the image as the size of the ink well diminishes. For a working reference we have listed the Lpi or ruling of the halftone that can be run at these settings. Bear in mind that PAGE 1 . 21

Chapter 1

Schematic For Standard Gauntlet Frame Figure 1.16 This is a schematic of the platen, image sizes and frame dimensions for a standard Gauntlet Press. With each press comes a maintenance manual and included is a drawing for the specifications on your particular press. It is wise to adhere to the maximum dimension allowable for the format of your press

the constraint to image registration tolerance is not usually the M&R press but the screen settings. As you can see from the chart in figure 1.19, the registration tolerance improves as the off-contact is reduced, but two things must happen to reduce the off-contact distance: First, the tension level must permit the reduction in the off-contact distance or image stretch, in the stroke direction will occur. Second, as the distance is reduced, it becomes more difficult to equalize the pressure between the ends and the midpoint of the blade: unequal deposits may result. The off contact is best run at the maximum within tolerance levels: run as high as you and still PAGE 1 . 22

Screens

Schematic For Standard Challenger Frame Figure 1.17 This is a Challenger Press schematic for image positioning on a standard frame size. Shipped with every press is a detailed maintenance manual with schematics particular to your press size and configuration. For the highest image tolerance, it is best to use the standard screen size recommended for your press.

1/8-inch (0.125”) Off-Contact Distance. Ink Well

1.0”

1.5”

2.0”

2.5”

3.0”

3.5”

4.0”

4.5”

Tolerance in Mils

7.7

5.1

3.9

3.1

2.6

2.2

1.9

1.7

Lpi Equivalent

22

33

45

56

67

79

90

101

Figure 1.18 This table lists the relative combinations of minimum inkwell, halftone Lpi and image tolerance at an offcontact distance of one-eighth of an inch. The inkwells often have four different dimensions, front, rear, left and right. The only inkwell dimension that counts in the tolerance of the image is the smallest one of the four. It is this one that causes the greatest stretch of the image and can make or break registration. From the top row the ink well is given in increments of one-half inch from one-inch to four and one-half inches. At one-eighth of an inch off-contact distance the tolerance in mils, is listed from 7.7 mils, to 1.7 mils, (0.0077” to 0.0017”). The bottom row lists the relative Lpi printable with that level of distortion. For example at one-eighth of an inch off-contact distance, and a 3.5-inch minimum ink well, the tolerance is 2.2 mils, (0.0022”) and the stretch will permit a 79 Lpi halftone to be printed. PAGE 1 . 23

Chapter 1 meet the image tolerance required. When the off-contact distance is sufficient the ink deposit becomes more consistent. At 1/8" Ink Well and Image Tolerance

Image Tolerance in Mils

9.0 8.0 7.0

At 1/8" as the inkwell increases, the image tolerance improves.

6.0 5.0 4.0 3.0 2.0 1.0 0.0 1.0

1.5

2.0

2.5

3.0

Ink Well in Inches

3.5

4.0

4.5

Figure 1.19 This illustrates the relationship between image tolerance and ink well for an arbitrary offcontact distance of oneeighth of an inch. As the ink well becomes larger, the image tolerance improves. For example if you are at 1.5-inches minimum ink well the best case tolerance is approximately 5.0 mils, (0.005”). But if you leave an ample distance of 4.0inches, the tolerance possible is just more than 2.0 mils,. The point is to warn you that a larger frame and a smaller squeegee are always wise for a close tolerance print.

The ink well and tolerance for the maximum image size have been noted for both the Gauntlet and Challenger at an off-contact distance of 1/8-inch (0.125) above and for 1/16-inch (0.063) below. To show the difference in a closer off-contact setting, the table below has the same inkwells and resulting tolerances with an off-contact distance of 1/16-inch (0.063). If you choose to run a closer off-contact distance it will become even more critical to have your press properly calibrated. And as in the case above, you will need to adjust tension levels and be prepared to contend with the fact that ink transfer from the end of the blade to its midpoint will be compromised (refer to page 4.40 for details). If you have established the proper conditions you may be able to run at a closer off-contact distance. For example at a distance of 1/16-inch but you cannot just arbitrarily drop the off-contact distance. Be sure that you have checked the list below to see if any changes will permit closer off-contact distance. 1. 2. 3. 4. PAGE 1 . 24

Larger frame. Shorter squeegee. Shorter squeegee stroke. Higher tension.

Screens The next graph uses a nominal 1/16-inch off-contact distance and compares various ink well sizes to the respective image tolerance. The range is from an extremely close one-inch ink well to four and one half inches, which is also impractical. Note that the Lpi listed is for reference and is far superior to the one-eighth inch off-contact distance table above. 1/16-inch (0.063”) Off-Contact Distance

Ink Well

1.0”

1.5”

2.0”

2.5”

3.0”

3.5”

4.0”

4.5”

Tolerance in Mils

1.9

1.3

0.9

0.7

0.6

0.5

0.4

0.4

Lpi Equivalent

89

133

x

x

x

x

x

x

Figure 1.20 This is similar to the table above but with an off-contact distance of 1/16th-inch (0.063’). With this closer distance the tolerance improves greatly. For example at a minimum inkwell of 1.5-inches the tolerance is 1.3 mils, (0.0013”) but do not be misled, there is more to the story. At this close off-contact distance it is difficult to develop contact pressure between the blade and the mesh at the midpoint of the blade. Even the highest tension levels improve but do not guarantee the contact pressure. You may want to review chapter five before you make this decision.

The graph in figure 1.22, includes both the 1/8-inch and the 1/16-inch off-contact distances so that you can compare the inkwell and image tolerances for both. Obviously the closer distance has appeal when shown in this context. Be wary of being too close, the telltale signs are image stretch and poor ink transfer, particularly in the center of the mesh. M&R equipment will allow you to run in the real world as close as 0.020-inch with proper calibration but beware that closer is not better for most cases. You will need to assess your inks, press calibration, tension level, and squeegee parameters in addition to the frame size. Size Exceptions Note that there are several options for frame sizes on the Challenger and Challenger II. The Challenger series presses are available with long stroke options on some or all press heads. This means that a standard 22-inch stroke length Challenger can be fitted to print a 30-inch or 36-inch stroke length. There are opportunities and limitations to how you can configure the press. If you want a longer stroke than standard, reduce the width of the image and frame. If you need to maintain the width and increase the length, it is possible by restricting the number of colors used. Customer service will be happy to assist you in understanding all possible configurations to make your Challenger series press even more versatile.

PAGE 1 . 25

Chapter 1 Figure 1.21 This is similar to the last chart; this one compares inkwell and image tolerance but this time 2.0 at an off-contact distance of 1.8 At 1/16-inch, as the inkwell increases in 1/16th-inch (0.0016”). 1.6 The curve shows that as the size, the image tolerance improves. 1.4 ink well increases the tolerance improves. At approxi1.2 mately four inches the toler1.0 ance has reached diminishing 0.8 returns; a larger inkwell 0.6 only makes a marginal 0.4 improvement in tolerance. 0.2 Note that screen stretch due to inkwell and off-contact 0.0 distance is 0.4 mils, 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 (0.0004”) with this off-contact setting. Move cautiously Ink well in Inches though, off-contact is only half of the issue, contact pressure between the blade and the mesh does better with greater off-contact distances. Review chapter five for details on offcontact inkwells and image tolerances.

Image tolerance in Mils

At 1/16" Ink Well and Image Tolerance

Figure 1.22 For your convenience we have plotted both off-contact distances on the same 9.0 chart. Note that the rel8.0 ative shape of the curves is similar because they 7.0 At 1/8-inch off-contact distance are both bound by the 6.0 reality of improved tol5.0 erance with a larger (minimum) inkwell. 4.0 However the closer off3.0 contact setting shows a 2.0 marked improvement at At 1/16-inch off-contact distance any inkwell distance. 1.0 But as we have cau0.0 tioned you above, do not 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 jump to the conclusion that you should set the Ink Well in Inches off-contact distance closer. Review chapter five for the details on setting the proper distance. The first thing that this chart should tell you is that you need a full sized screen and the minimum squeegee length for high tolerance work.

Image Tolerance in Mils

At 1/8" & 1/16" Ink Well and Image Tolerance

PAGE 1 . 26

Screens Frame Strength And Flatness The frame you select should have the integrity to withstand your intended tension level. You want the frame to resist weakness in two areas: torsion twisting and internal deflection. Any twisting in the corners causes the frame to be racked or not flat. This condition creates the same problem as a press that is not calibrated. Worse yet if you put such a frame into a press that is not calibrated: the only predictable result is too much downtime. There is no type of squeegee, off-contact setting, peel rate or tension level that will solve this problem. If you are using a roller frame you can and should be careful to flatten it prior to tensioning. If your tensioning procedures cause the frame to rack again, contact the manufacturer. If you take the racking out of a frame that has already been tensioned, you are creating isolated stresses on the mesh. This stress will come back to haunt you in the form of a rip or tension loss or Figure 1.23 This illustrates some of the opportunities on a Challenger Press. There is a standard screen width for each Challenger Press and it is listed in the operations manual. both. However there are a variety of sizes that you can use if your image permits fewer colors or a frame that is even more rectangular. If your image is long and narrow, for example a long vertical stripe, you may be able to use a frame that is narrower side to side but longer than “standard” front to rear. Also if you can run fewer colors you can utilize frames that are wider side-to-side and longer front to rear than the standard. As you can see in the illustration, a frame that is only 28-inches long could be as wide as 32-inches, far over the standard. If you have a need to print oversized and have long stroke possibilities, call us at the factory and let us help you engineer your printing.

If your frame deflects internally it will create a pulsing action during production. It will be as though you rapidly took the mesh to a higher tension level and then released it, over and over again. This may occur at the rate of 800 or 900 times per hour on a Challenger or Gauntlet press and will typically jump as much as three to four N/cm². When the frame has bowed inward it “pulses” right at the edge of the mesh and will lead to a rip at the center of the longer frame wall. This jump from static (resting) tension to dynamic (printing) tension causes a proportional tension loss and will have to be dealt with. There are a few options: PAGE 1 . 27

Chapter 1 Keeping R oller Frames Flat Typically the warp(threads run the length of the bolt) allows a greater percentage of elongation than the weft. Weft (threads run the width of the bolt) are lower elongation and require more force. This fact may lead the roller frames. Roller frames may have a tendency to twist while you are tensioning them. It seems as though you need to be an octopus to hold down the other side while you are tightening the bolts. An easy solution to this dilemma is to mount a U-shaped aluminum channel to the end of your stretching table. Remember to measure the highest part of the frame when determining the size of the channel and add room to line the channel with foam to protect the mesh. Now just slide the far end of the frame you are tensioning into the channel. It will keep the frame flat no matter how high you take the tension.

1. Find a more robust frame. 2. Reduce the level of tension. 3. Reduce the squeegee width and stroke. 4. Reduce the off-contact distance. Conclusion Too often the decision is made to use a screen that is too small to function properly on the press. The logic is that one can save mesh, emulsion, exposure times and print speed. These supposed savings are an illusion; ironically mesh dollars are actually lost. The frame must be flat and not bow inward in production or image quality and mesh life are immediately lost. Remember that the press is your “racecar”, your way to make money, do nothing to slow it down. Smaller frames will do just that.

Tensioning In this country, most tee shirt printers are using retensionable roller frames for automatic production. The reason is that most of the inks are very tacky and require a great deal of force to transfer. Most of the frames are small for the image size leaving very small inkwells. Finally too few of the presses are regularly calibrated. With these conditions, retentioning can be a blessing. But whatever your conditions or frame type, there are certain obligations that the tensioning results should meet or exceed. This is the focus of the following section.

Goals There are five fundamental goals that should be met in the tensioning process. Excluding any of these can be the cause of severe problems on press. 1. Maintain a square mesh opening. 2. Avoid any areas of isolated stress. 3. Allow the off-contact distance to achieve image tolerance.

PAGE 1 . 28

Screens 4. Permit zero screen lag. 5. Equalize contact pressure between blade and mesh.

Selecting The Proper Frame

How To Instructions

Choose one that: 1. Is as wide as the press will permit.

Maintain Square Opening

2. Is as long in the stroke direction as the press will

permit. It should be the goal of the fabric weavers to offer a fab3. Is as robust as the frame design permits and the tenric that can maintain a square sion level requires. mesh opening. The primary 4. Does not twist at its corners. reason is that a distorted 5. Does not bow inward. shape weakens the mesh, creates misregistration, leads to 6. Holds the mesh securely. probable moiré, and won’t 7. Maintains a square mesh opening at any tension transfer ink as well. level. Unfortunately the tension 8. Does not create isolated stress. meter never really knows if the opening is square, because 9. Permits off-contact for image tolerance. it is not designed or intended 10. Prints with zero mesh lag. to pick up the difference. 11. Helps equalize blade/mesh contact pressure. Below are details on percentage of elongation as a technique to be used in addition to reading tension with a meter. There is an accurate method of testing to find the final actual (tensioned) mesh count in either direction and that is a TPI (thread per inch) mesh counter (refer to page 1.43 for photo). By laying the test film on the tensioned fabric, you can evaluate whether or not your opening is square. Simply backlight the screen as on a light table and lay the film on the impression side. Rotate the film until interference fringes are precisely horizontal. This moiré pattern will allow you to identify the specific mesh count.

Avoid Areas Of Isolated Stress

As elongation increased to achieve higher and higher tension levels, the need to reduce stress in the corners became more obvious. This technique called softening, keeps the mesh from ripping but can be used to improve overall tension levels and make them more consistent. Use a tension meter at an angle and slide it from the corner to the center of the mesh. (see figure 1.38 on page 1.44). Watch for any spikes in the reading. If the tension level of the mesh is higher PAGE 1 . 29

Chapter 1 near the corner than it is in the center, that area will be the first to rip. (Refer to page ___ for details). Further, if there are high stress areas then there are also low stress areas. These are the ones that lose tension during the production run. 1. Square Opening- 2. Rectangular Opening- 3. Rectangular OpeningImbalanced Weave Imbalanced Elongation Ideal Weave

Figure 1.24 This drawing illustrates three possible mesh openings and counts. The far left illustration shows a mesh with a square opening. This one would have the same mesh count for warp and weft and would by definition be ideal. The second drawing shows a rectangular opening as woven. Its opening is not square so the count differs between warp and weft It will be very difficult to tension this mesh properly. The third drawing shows a tensioned version of the rectangular weave it is unlikely that you can achieve a moiré free screen that will not lose tension on press with this mesh.

Contact Distance To Achieve Image Tolerance Allow The Off-C

The tension level of the mesh must be sufficient to allow an off-contact distance that accommodates the tolerance of the images that you print (refer to page 1.49 for complete details). The off-contact distance is constrained by the minimum ink well, screen tension and image tolerance. The first two are internal issues; the third will be obvious to your customer. Tension and ink well should accommodate the tolerances that your customer needs. Tension must be high enough to prevent image stretch and yet low enough to prevent reproportioning and fabric degradation. Figure 1.25 This drawing illustrates the problem of isolated stress. Lets say that at the corner of the frame the tension level is 10 N/cm² because the corner was softened to prevent ripping during tensioning. Then we check the tension a little further from the corner and get a 20 N/cm² reading. Further from the corner again and we peak at 25 N/cm² and still further we return to 20 N/cm². This screen will most assuredly rip at the 25 N/cm² line. Once the isolated stress exists the ratio of stress to strain (stretch to tension) diminishes. The solution is to progressively soften the corners as described on page 1.35. Drawing compliments of Screen Graphics Magazine.

Frame l

10 N/CM2 l 20 N/CM2 8

2

25 N/CM Isolated Stress l

22 N/CM l

2

20 N/CM

2

Isolated Stress Tension Loss & Ultimate Burst at 25 N/CM2 PAGE 1 . 30

Screens Permit Zero Screen Mesh Lag

Due to the off-contact distance, after the squeegee passes, the screen should “snap back” at the same rate as the squeegee speed at the midpoint of the stroke. This condition is called zero screen lag . Negative lag occurs with excessive tension, peel rates or off-contact distances. Positive lag (snap back slower than the blade speed) occurs with the opposite settings and is far more obvious and equally destructive (see figure 1.26). If you have the proper tension for your press conditions you will automatically get zero screen lag. If you have positive lag raise the off contact, negative lag lower the off contact. This is a temporary fix only, to be used when you are on the press. To eliminate the problem next time you tension screens (press condition remaining constant) for positive lag, increase tension levels, for negative lag, decrease tension levels.

a. Positive Lag

b. Zero Lag

Figure 1.26 illustrates the range of lag possible just by varying the offcontact distance. The top drawing shows the frame too close to the platen and the result is positive mesh lag–the screen will tend to stick to the platen and not snap back. It will be particularly noticeable in the central areas as mesh marks or will force you to use thin ink. The middle drawing shows the ideal, as the stroke continues the speed at which the screen lifts is precisely the same as the squeegee speed–the condition is zero mesh lag. The bottom drawing shows negative mesh lag. It is due to overtension for the off-contact distance. It will be obvious by ripped and burst screens.

c. Negative Lag

Equalize Contact Pressure Between Blade And Mesh

It is not in the purview of the tension level to singularly reach the targeted cpntact pressure. The inkwell must be large enough to allow equal pressure between PAGE 1 . 31

Chapter 1 How To Instructions

Checking For Isolated Stress To check for isolated stress follow these steps: 1. Tension your screen as normal. 2. Put the meter in the corner, facing outward. 3. Angle the meter approximately 45°. 4. Slide the meter slowly toward the center of the frame. 5. Tap the meter periodically if necessary. 6. Observe for any high points in the tension. 7. If so these are areas of isolated stress. 8. They should be relieved before you go to press.

the blade and mesh across the entire surface of the blade. Unfortunately this size inkwell is an anomaly – it doesn’t happen too often. It is worst when the tension extreme–too high or too low. Low Elongation Screen Fabric With the introduction of “low elongation” screen fabric, all of the rules in the print shop changed. Low elongation is the generic name for mesh that has been manufactured to have a higher modulus of elasticity. That means that with less stretch, you get higher tension and supposedly less tension loss prior to and on press.

You should be aware that “low elongation” is not a specific entity; it is only a tendency for a screen mesh to develop more tension with less elongation. There are some fabrics for example, that develop high tension with 2% elongation. While other manufacturers of the “same” count may not achieve that tension until 5%. At first blush, the first one seems better, more for less, right? But it may not be so in the real world. The faster the fabric develops tension the more likely it is to suffer from two issues: First it may have an imbalanced SS after tensioning because of a smaller window of opportunity. Second that it may tend to lose that tension faster on press. Yes with retensionable frames, you can just “pull it back up” but the only thing that gets satisfied with this doctoring is the tension meter. The mesh opening will become erratic leading to progressive moiré and radial moiré. You will want to compare the rate that the mesh develops tension to the variance of the warp and weft SS curve (refer to figure 1.15 and page 1.16 for complete details).

PAGE 1 . 32

Screens LE Versus Conventional Fabric

Because the operator can achieve tension with less elongation, even if the SS curve is not balanced, it will perform better than conventional on press. There is less need to stage tensioning, (relax, tension, relax and so on) due to less elasticity of the fabric. The mesh manufacturers as well as the SPTF have studied rapid tensioning and the findings indicate minute advantages in retention of the initial tension levels with staged tensioning. The rule of thumb is that you will lose about 20 percent of the original tension in the first 72 hours and then the fabric will stabilize. With less elasticity you will want to run closer off-contact distances (refer to figure 1.39 on page 1.50 for details) and in doing so, you will see even more stable tension on press. Finally, the need to retention is reduced for all of the above reasons. All in all low elongation fabric is the only way to go but two caveats: You will still need a fabric that has a balanced SS-curve and it should be properly handled on press. Abuse on press with squeegee pressure and off contact extremes can fatigue and destroy even the best LE meshes.

Lo w Elongation With low elongation fabric you should expect: v

Higher tension with lower elongation.

v

Less need to stage tensioning.

v

More tension stability overall.

v

Less tension loss on press, with proper press conditions.

v

Less need to retention. You must insist upon:

v

Consistent mesh counts for warp and weft.

v

Balanced SS-curved before and after elongation.

Tensioning Instructions Building a screen is the foundation of your screen print process. You cannot correct the shortcomings with the stencil or on the press. This is the time to be sure you have a good system in place and follow it, even when you are under the gun to get production out the back door. Any corners cut in this process will come back to haunt you during the press run. Review the section on the cost of press downtime (see page6.35) if you have any doubts. Fabric Orientation

There are a lot of fish stories about which direction warp and weft should be orientated. Here is the real world truth: If the fabric is SS balanced with one and a half percent or less variance, (refer to page 1.29 for details) and the frame is square, then it would never matter. The practice of orienting the weft threads parallel to the stroke direction was to hedge one’s bet with a fabric that was imbalanced. You would have additional PAGE 1 . 33

Chapter 1 Mesh On A Bias If you are prone to running mesh on a bias we can probably save you a lot of mesh money. Refer to Chapter Two on stencils and you may find all of your detail needs are met by proper stencil methods, not by the mesh count or usually its orientation. If you do need to bias as in the case of finely woven goods with a series of thin straight opaque lines, angle the mesh to the *Alpha as shown on page 1.19. You will want to insure that your fabric has close to the same count for both warp and weft. This square mesh geometry allows you to run lines (or rows of dots) with a minimum of interference. Further, look at the flatness of the fabric that you are using. The stencil can be far flatter and hold far better detail if the mesh starts out flat. Finally, look into the thickness of thread that you are using and select the thinnest one for the count that you need. *The Alpha angle ranges between 68 and 74 degrees, depending on the mesh count, thread diameter and percent of elongation.

stretch in the warp direction, so to stretch it parallel to the squeegee direction insured more imbalance in the mesh openings and excessive stretch in the image. We highly recommend that you use a balanced fabric and as for orientation, there are two avenues open: If you are a high tension advocate, real world mesh will more often than not have greater elongation in the warp direction. So you will want to run the warp parallel to the long sides of a Challenger or Gauntlet frame. (see figure 1.29). The reason is that the short dimension of a nominal automatic tee shirt frame resists deflection, about three times as much as the long side. For the same reason, you will want to tension the warp first. If you run at reasonable tension levels – 25 to 35 N/cm², and you select balanced fabric, run the way that will give you the greatest yield from the bolt. But under no circumstances should you ever swap orientations. Once you pick an orientation, stick with it, any other antics and you are simply asking for trouble and inconsistency. Tensioning Time

With the introduction and near universal acceptance of low elongation fabric the need for all the staging required for conventional fabric no longer exists. You will find that you reach diminishing returns for waiting beyond the time it takes to tension. Low elongation fabric will lose a nominal 20 percent of its tension level in the first 72 hours. (This percentage will vary according to manufacturer mesh specifications and user procedures). Two options will allow you to rapidly tension low elongation fabric tee-shirt screens. First, stage them in groups of five to ten. Progressively tension these in stages; initial, second and third stage for final tension. This gives the filament time to equalize and prevents a shock to the system. Second, you can accelerate the relaxing process by applying a weight to the center of the screens. A steel plate ¼” thick by the image dimensions can be laid upon the screen between tensioning. This weight applies far less force than the squeegee blade and it will cause the initial drop in tension to occur in far less time.

PAGE 1 . 34

Screens Progressive Corner Softening

With the onslaught of retensionable frames and a meter in virtually every shop, came the need to “soften” the corners of the mesh. Public opinion has it so the mesh won’t rip and of course this is the case. And if you simply poke the corners to the table top, this is all you are getting but know that the corner can do more for your tension level and stability than you might think. The issue is how much to soften to allow the tension to get as close to the center of the mesh as possible while maintaining a square opening throughout the surface of the mesh. (Note with stretch and glue frames, this step is not realistic and often not necessary). The illusion of energy transfer is just that, an illusion but do not think that because you pull the mesh evenly, that the result is equal over the entire frame area. The reality is that the mesh openings can be greater at the edges nearer the tension. If you have ever stretched a screen, you may have recognized the extreme case as “stall” or no change in tension with an increase in elongation. There are several causes of these phenomena where stress is no longer proportional to strain: 1. Imbalanced SS curves on the mesh. 2. Necking of the filament. 3. Stress beyond the elastic limit of the fabric.

Figure 1.27 This illustrates a filament that is defective due to polymer necking. If this occurs during the tensioning process, a ripped screen is guaranteed. The neck is the weakest part of the mesh and is caused by too much tension too fast. It can be evidenced as isolated stress also (see page 1.38 for details). Drawing courtesy of Printwear Magazine.

The next graph shows the results of image travel based upon retensionable frame travel. It might seem that if you rolled the frame ¼-inch that that travel would translate to the center of the image and move ¼inch of fabric, not so. If you look at the graph you will see that 100 percent of the travel equated to 35 percent movement at 15-inches (nearly the center of a Challenger frame). And 3/8-inch travel took the mesh tension to dangerous levels. (Note that the total edge travel was 0.375-inch or 3/8-inch and the frame was at 25 N/cm² at the outset). As you can see from the graph, after half or 3/16-inch travel, there was little change in the mesh’s central areas. However, the mesh openings had been distort

PAGE 1 . 35

Chapter 1 Figure 1.28 This is a graph of the variance in the mesh geometry from the side of the frame to the center of the frame if the screen is retensioned. This factor can lead to all sorts of problems if the image happens to be process color. The result will be progressive moiré because the mesh is no longer consistent and if the line count is high, moiré is quite likely.

Pct. Elongation at 15-inches

Frame Travel VS Center Elongation at Half Challenger Distance 40% 35% 30% 25% 20% 15% 10% 5% 0% 100%

100% travel =3/8-inch or (0.375") =35% transfer efficiency.

86%

73%

59%

45%

31%

18%

5%

Percent Elongation at the Frame Edge Figure 1.29 This is a top view of a Stretch Devices Roller Frame and the lines for progressive softening are indicated. On a standard Challenger frame, run the warp threads parallel to the long side of the frame. Soften six-inches down the long side and five-inches along the short side. At the ends of the locking strip the slack should be 0.75-inches and 0.50-inches respectively. This will accomplish several things; First, there will be no isolated stress areas to lead to premature mesh failure. Second, the corner will be taut enough to coat with emulsion without leaving a puddle in the corner. Third, this technique permits more balanced mesh geometry and more consistent tension from corners to the center. Note the actual dimensions are based on the SS-curve and the actual elongation in the warp and weft firections.

ed–larger nearer the point of tension and smaller in the interior of the frame. For those of you doing halftone printing this condition leads to progressive moiré. So one of the keys to proper tensioning is to relax as much of the corner as is practical. On roller frames sized for Gauntlet and Challenger presses you will be able to soften 6-inches along the long side and 5 inches on the short side. (see figure 1.38). PAGE 1 . 36

Screens The amount parallel to the direction of stretch is based on the percentage of elongation of the fabric that you are using. This distance will be in the half inch to inch and a half areas for most fabrics and tension levels (refer to figure 1.29 for details). Once you have completed a frame, use the tension meter to check for isolated stress. Then use the Mesh Counter to check for distortion. If there is no isolated stress and no mesh distortion, the screen is ready to be coated for exposure, development and production. Tensioning By Percentage Of Elongation

Tensioning With Progressive Corner Softening

How To Instructions

1. Insert the mesh as prescribed by the manufacturer. 2. Use a black marker to scribe a line on the mesh against the channel for the locking strip. Do this on all four sides 3. Relax the mesh beginning at the end of the locking strip. 4. The depth of the softening should match the distance that you will turn the roller. 5. Proceed with softening toward the center of the roller. 6. Soften a distance of 6-inches for the long side of a *Challenger frame. 7. Soften a distance of 5-inches for the short side of a *Challenger frame. 8. Be sure that the black marker line is straight, without waves.

The best method of assuring a square opening is to tension 9. Repeat on all eight points. by percentage of elongation *Gauntlet frames are softened 5-inches on the long side of the mesh. Begin with a SS and 4-inches on the short side. curve, available from the mesh manufacturer, or at least find out what elongation should result in what tension. Get this information for both warp and weft directions. After loading the mesh into the frame, use a Sharpie marker to make fine lines on the screen at the following noted distances. Mark the Challenger screens at 22-inches apart, centered and going with the short length and 30-inches apart, centered and going with the long length, similarly the Gauntlet screens at 20inches and 28-inches (see figure 1.30). Use the next table (figure 1.31) to match a percentage of elongation to a distance stretched above and beyond the original marks. This table is not exclusive to a particular screen mesh – it gives the relationship between elongation and tension for all fabrics. For example at 5 percent elongation the 22-inch marks on PAGE 1 . 37

Chapter 1 31.5”

30”

22”

23.1”

Figure 1.30 This shows two frames with mesh prepared to tension by percentage of elongation. The mesh is inserted into the frame and opposing marks are placed on the top of the mesh near the edges of the frame. The fabric is then tensioned based on the Stress Strain curve and the warp and weft count. The resulting frame will have a balanced geometry to eliminate frequency moiré and balanced tension for stability on press.

the Challenger mesh would have elongated to 23.1-inches and the 30-inch marks to 31.5-inches. We took one of our test fabrics and with the use of its SS curve and modeled the tensioning profile on the Challenger screens. The graphs below are an example of the weft (top graph) and warp (bottom graph) and their resultant tension when elongated to a specific percentage. Note the fabric was marked at 22-inches and 30-inches and the percentages came from the mesh manufacturer’s SS curves. The actual change in the distance between the marks is noted on the left vertical axis. The horizontal axis lists the percentages of elongation from 2 percent to 8 percent and immediately below the percentage is the tension that would result for our test case screen mesh. Caution: all mesh counts have an elastic limit and it is specific to the use and abuse that the fabric is subjected to. The table is not to suggest that any or all fabrics should be taken to a given percentage of elongation or resulting tension. That information should come from the fabric manufacturer. The table is to be PAGE 1 . 38

Screens used to show the relationship between mesh elongation and resulting tension for a specific 230 with a 40m thread with a near zero variance in the SS relationship of the warp and weft directions. Press

Frame

Marks

2%

3%

4%

5%

6%

7%

8%

Challenger

26” 35” 23” 31”

22” 30” 20” 28”

22.4” 30.6 20.4 28.5

22.6” 30.9 20.6 28.8

22.8” 31.2 20.8 29.1

23.1” 31.5 21.0 29.4

23.3” 31.8 21.2 29.6

23.5” 32.1 21.4 29.9

23.7” 32.4 21.6 30.2

Gauntlet

Figure 1.31 This table lists the standard frame sizes for the Gauntlet and Challenger presses and their marks for tensioning by percentage of elongation. Lets say that you have a 26-inch by 35-inch Challenger frame and you have inserted and marked the mesh at 22-inches and 30-inches as described. Check the stress strain curve on the fabric; we will use the Murakami 150 Figure 1.10 on page 1.16 as an example. We see that a 5% elongation will take us to 30 N/cm² tension. If that tension is sufficient to support the off-contact distance (refer to page 1.49 for details) then pull the 22-inch marks to 23.1-inches and the pull the 30-inch marks to 31.5-inches. (Note that the same elongation gives the same tension only when the mesh is balanced. It maintains the same count only when the initial count is equal or similar.)

The graphs below continue to describe the relationship between tension and percentage of elongation. They divide the process into two discrete steps of warp tension and weft tension.

Elongation Beyond 30" Marks

230 / 40 Challenger Warp Elongation / Tension 33.0 32.5 32.0 31.5 31.0

Example: as the marks were stretched from 30" to 31.5", the elongation was 5% of the 30" and the tension in the warp direction was 23.5N/cm^2.

30.5 30.0 29.5 29.0 2%

3%

4%

5%

6%

7%

8%

7.8

13.7

19.6

23.5

29.4

35.3

39.2

Percentage Elongation Over Tension Figure 1.32 This shows a fabric that has been stretched with the warp on the long dimension of the Challenger frame. The mesh was marked as described and then tensioned to a percentage of elongation to maintain a square opening and to achieve screen stability on press. PAGE 1 . 39

Chapter 1 Elongation Beyond 22" Marks

230 / 40 Challenger Weft Elongation / Tension 24.5 24.0 23.5 23.0 22.5 As the marks were stretched from 22" to 23.1", the elongation was 5% of the 22" and the tension in the weft direction was 23.5 N/cm^2.

22.0 21.5

Figure 1.33 This shows a fabric that has been stretched with the weft on the short dimension of the Challenger frame. The mesh was marked as described and then tensioned to a percentage of elongation to maintain a square opening and to achieve screen stability on press.

21.0 2%

3%

4%

5%

6%

7%

8%

7.8

13.7

19.6

23.5

29.4

35.3

39.2

Percentage Elongation Over Tension

Four Possibilities of Tensioned Screen Mesh

a.

b.

a. b. c. c.

c.

d.

Balanced Tension–Balanced Opening Balanced Tension–Imbalanced Opening Imbalanced Tension–Balanced Opening Compromised Tension–Compromised Opening

Figure 1.34 This illustrates the four possibilities of tensioned screen mesh and there is only one outcome that is acceptable. Viewing from left to right: 1. The tension is balanced and the mesh opening (mesh count) is balanced. This is the one that you want to create it requires mesh with a balanced stress strain curve as well as closely related warp and weft counts. 2. The tension is balanced but the opening is imbalanced. This screen will be relatively stable on press but will cause problems with ink transfer and frequency moiré. 3. The tension is imbalanced but the opening is square. The screen will not be stable on press but ink transfer and image artifacts will be under control. 4. The tension and the opening are compromised is the nature of most screens made with a tension meter as the control.

PAGE 1 . 40

Screens The measured elongation procedure allows you to check the balance of your screen fabric as well as the specifics of the tensioning methods. You will find the lack of information from the meter (which may accurately measure tension) and the need to maintain fabric orientation and bolt specifications. Should you have a bolt that has an imbalanced warp and weft (variance greater than +/- 1.5%) then you have one of three choices with that fabric: First compromise the shape of the opening but, be on the look out for inescapable radial moiré if you are running halftones. Second maintain the shape of the opening but compromise the stress between warp and weft, which results in registration shift during the press run. Or third, compromise both of these parameters but this is very risky since you are subjected to both moiré and misregister. Stretch And Glue

Tensioning With Percent Of Elongation

How To Instructions

1. Attach the mesh with the warp threads running with the short side of the frame. Warp threads run lengthwise on the frame. 2. Insert the mesh in the frame so that it is flat and the threads run parallel to the frame sides. 3. Measure and mark opposing lines measurements on the warp direction (figure 1.31). 4. Measure and mark opposing lines on the weft direction. 5. Stretch the warp to half of the recommended percentage. 6. Use the notches scribed on roller frames as guides to 1/8” rotation. 7. Note the tension level and record the results. 8. Stretch the weft to half of the recommended percentage. 9. Note the tension level and record the results. 10. Finish up by stretching the warp to the final percent of elongation. 11. Note the tension level and record the results. 12.. Stretch the weft to the final percent of elongation. 13. Note the tension level and record the results.

With the popularity of the retensionable frame in the US garment printing industry, stretch and glue will be covered but only briefly. Again with the arrival of low elonPAGE 1 . 41

Chapter 1 gation fabrics, stretch and glue became more viable. The tee shirt printer however, will have to do some homework to accommodate static frames. First since retentioning is not an option, the press must be calibrated. Second the use of tarlike plastisols will not be accommodated: you will be better off with retensionable frames. Third you will need to keep a true and sharp edge on your squeegee blades. And the list continues with the tensioning procedures just as is the case with the retensionable frames. If you are using stretch and glue on a pneumatic system you will want to read how to soften corners for retensionable frames (refer to page 1.35). Although the execution differs, the principle is the same; you want the clamp or clamps to stop short of the end of the frame. The distances short are: 4 inches and 5 inches on a Gauntlet frame and 5 inches and 6 inches respectively on a Challenger frame. Of course you will want independent air control for the warp and weft directions (for details on percentage of elongation refer to page 1.37). Since the air systems are very sensitive to resistance, it is easy to calibrate your system for repeatable results. In practice take the air up to approximately two-thirds of its maximum

Figure 1.35 This is a photo of the Max Newton pneumatic screen stretcher. The system adjusts to virtually any frame thickness and size (up to its capacity). It consists of four channels that securely grip the mesh when the coated locking bar is set into position. Warp and weft can be treated independently to compensate for frame shape and mesh geometry. The locking bars can be shortened in length to accommodate higher tension levels without the risk of isolated stress. The Max Newton can be manually pulsed to expedite the tensioning process and to help accommodate imbalanced meshes. If you choose to pulse tension the fabric, do not pulse at maximum PSI. This will cause filament necking and weaken the “drum tight” fabric that you have created. For details refer to figure 1.27 on page 1.35. PAGE 1 . 42

Screens for that mesh and then turn it off. Wait a few seconds and then turn the air back on and go to complete tension. The relaxing of the knuckles and quick return allows you to accelerate the tensioning process. Note three facets of pneumatic tensioning on your log sheet: air pressure, percentage elongation and resulting tension. With these three in place, it will be simple to troubleshoot should your raw materials or your system take an unexpected turn. Measuring Tension

All of the tension meter manufacturers tout the accuracy of their meters and present it as the ultimate tool for gauging screen performance and this is just not the case. The problem is not exclusive to the design of the meters rather it is our reliance on tension as an accurate reporting of what has happened to a screen when the mesh is stretched. Tension is a form of pressure and cannot be relegated to a North-South, East-West domain. If you want “quick and easy” then a tension meter is fine but if you want to know the reality of what is occurring when you stretch the fabric, read on.

Figure 1.36 This is a photo of the ISPS Mesh Counter. The cross check for tension is the Mesh Counter. It is a film positive set to be laid on the mesh in both static form as well as tensioned form. The counter is accurate to one thread and can be used to insure a square opening and equal tension levels at all points on the mesh.

The meter isolates the mesh to be tested so that the tension reading is not affected by the proximity to the frame. The “feet” on the bottom of the meter near the ends of the base perform the isolating function. The spring-loaded probe centered in the meter forces a section of fabric downward until the resistance of the mesh is greater than the force of the spring. The meter has been calibrated or PAGE 1 . 43

Chapter 1 preset to units of pressure, Newton’s per square centimeter. If you want to know tension the best way to gauge it is perpendicular to the tensile (stretched) force and this is the way that the meters read. The meter can and should be used and there are some equally valuable but lesser practiced readings that will help your cause: If you are wise enough to identify

a. Maximum Image Size

b. Check Weft Tension

c. Check Warp Tension

Figure 1.37 This illustrates the use of the meter to check tension levels at the five marked points on the screen. It is critical that the tension be the same at the four corners and at least that high in the center. If the meter finds a perimeter reading higher than the center reading, check your procedures and try again.

a. Softened Corner

b. Corner To Center

c. Meter From Corner To Center

Figure 1.38 This illustrates the use of the tension meter to check for isolated stress. Begin at the corner and take readings from the point of little or no tension. As you move the meter toward the center of the frame be wary of any peaks in the tension level. If so you have isolated stress. First it will keep you from balancing the tension on the mesh. Second it will be the most likely place for the screen to rip. PAGE 1 . 44

Screens each screen and to compile data on them, be sure that you take tension readings on five points (see figure 1.37 on page 1.44). These include the center and the four corners of the maximum image area. Also note the tension range, which is the highest tension of the five points and the lowest.

General Tensioning Procedures

How To Instructions

1. Use LE, plain woven, dyed, mono-filament polyester. 2. Get a SS curve (or data) from your supplier. 3. Run the warp in the long direction. 4. Insert the mesh into the frame. 5. Use figure 1.31 for elongation for Challenger and Gauntlet screens.

You will want to use the 6. Mark off the recommended distance. meter to check for isolated 7. Soften the corners progressively. stress areas. (see figure 1.38). These often occur with reten8. Stretch in two stages, half from each end of sionable frames just inside the the frame. final point of corner soften9. Stretch half the distance warp first. ing. (refer to page 1.35 for 10. Stretch the weft, half the distance. details on progressive corner softening). The isolated stress 11. Record tension and percentage elongation. areas must be eliminated to 12. Complete the warp. insure stable tension on the 13. Complete the weft. press. Of course you will want to strive to achieve equi14. Use the meter to check for isolated stress. librium and the same tension 15. Adjust softening procedure if needed. over the surface of the mesh. However even with this con16. Check tension at the five points. dition, problems can ensue 17. Record tension and total elongation. and will never be detected by the tension meter because the trouble is that the meter has no idea of how much the mesh has been elongated.

Troubleshooting Screen Life It will be very helpful to identify where your screens blow out so that you can identify the more relevant question of why they blow out. There are two distinct and separate elements of total screen failure: those that burst and those that rip.

PAGE 1 . 45

Chapter 1 Mesh Bursting The mesh will be prone to burst in the center of the screen from external stresses not from the elongation or its resulting tension. The center where it is most difficult to transfer energy is subjected to the highest wear from the shearing effect of the blade. This is the point of least change from static to dynamic tension. Eventually the blade erodes the fabric and finally it bursts. Your images will mis-register due to stretch in the stroke direction. You may observe the “harp like” strings of mesh that break loose of the bonded knuckle. The tear is a laceration or rough cut and there are remedies and they are listed below. 1. Reduce the squeegee force. 2. Raise the off-contact distance. 3. Increase the size of the inkwell. 4. Calibrate the press. Mesh Ripping The mesh is prone to rip near the frame wall due to both internally and externally applied stresses. The internal stresses are imposed during the tensioning process; the highest stresses are nearest the point where the mesh is being pulled. Secondly is the very obvious abrasion from the ends of the squeegee blade, hopefully not from the flood bar. It is at the ends of the blade, near the edge of the mesh that the contact pressure between blade and mesh are at the highest. Mesh elasticity is at its lowest and blade pressure may be at its highest. Misregistration will be due to over-sizing the original image (refer to page 4.4 for details). The tear in this case is a slice and looks cleanly cut as with a knife. The remedies for ripping mesh follow: 1. Reduce the off-contact distance. 2. Radius both ends of the squeegee blades. 3. Increase the size of the inkwell. 4. Center the squeegee blade. 5. Calibrate the press. If you are experiencing both ripping and bursting mesh the most probable cause is that your press is out of calibration (refer to page 4.15 for complete details). It is probable that you have press heads that are out. The higher ones are causing PAGE 1 . 46

Screens the mesh to rip and the lower ones are causing the mesh to burst. If your press is in calibration then the dual problems are due to erratic screen tension. You will want your range of tensions of screens on any one set-up to be more closely related in other words, don’t run high and low tension extremes on any given press run. Be sure that your squeegee blades are sharp and true and centered in the screen. Tension Counter Measures To negate whatever qualities the fabric manufacturer and you put into the screen mesh, its tension and life expectancy use the following list of mesh killers: 1. Uncalibrated press. 2. Imbalanced SS curve. 3. Minimal ink well. 4. More squeegee force. 5. Rigid blades. 6. Higher off-contact. 7. Double stroke. 8. More peel.

Protecting Tensioned Screens

How To Instructions

1. Calibrate your press regularly. 2. Use the standard recommended screen sizes. 3. Use a squeegee blade 1” longer than your image width. 4. Set squeegee pressure at a minimum level to completely transfer ink. 5. Use a blade setting that accommodates your press conditions. 6. Run the off-contact distance as low as ink transfer permits. 7. Do not make a habit of double stroke - fix the problem. 8. Always try to run at zero peel, use only when absolutely necessary. 9. Always run low elongation screen mesh. 10. Do not flood as a preprint stroke. 11. Use ink with low tack level. 12. Use mesh with balanced SS curves. 13. Progressively soften the corners of each screen. 14. Establish tension levels by using elongation techniques. 15. Check for isolated stress areas with the meter. 16. Check all five-tension spots. 17. Beware of super-heated platens and their affect on the screens. 18. Seal the perimeter with permanent blockout. 19. Use a Mylar® tear resistant tape on all corners. 20. Protect the groove of the locking strip with cloth tape.

9. Non LE mesh. 10. Any flood pressure. PAGE 1 . 47

Chapter 1 Tips For Establishing Your Proper Tension Level

11. High ink tack. 12. Improper tensioning. 13. Excessively hot platens.

An insufficient tension level would create the following problems: 1. Require excessive off-contact distance. 2. Allows a positive mesh lag behind squeegee stroke. 3. Causes image stretch in the stroke direction.

The minimum tension level of the mesh has to meet several criteria: 1. It must permit an off-contact distance below image tolerance. 2. It must resist image stretch at the above off-contact distance. 3. It must resist positive lag during the print stroke.

The ideal tension level would meet or exceed the following criteria: 1. Permit minimal off-contact distance. 2. Permit zero mesh lag where snap-back equals squeegee speed. 3. Resist image stretch in the stroke direction (Continued next page.)

PAGE 1 . 48

14. Unsealed perimeter. 15. Poorly taped corners. 16. Unprotected locking grooves Tension Limits Prior to low elongation fabrics, and particularly in the US, we were preoccupied with higher and higher tension levels. There are a few reasons; in this country the tee shirt has achieved an all time high for popularity. The baby boomers and level of affluence created an unprecedented demand and therefore colossal automatic and manual machine sales. Most of these machines were not maintained very well and were sorely out of calibration. All of the machines (by necessity) are designed with small inkwells and the printer has a lot of screens. The ink of choice in the US is plastisols and most of them are very tacky, sticky and difficult to transfer through the mesh. The tees usually range from 15% to 25% fabric mass. Take highly elastic fabric, uncalibrated presses, small inkwells with an abundance of screens, tacky inks and a porous substrate and the advantages of higher tension screens are obvious. These screens took the form of retensionable frames and the dominance of the roller frame in the tee-shirt industry was unprecedented. Without low -fabrics there is a need for continuous take-up (tightening the fabric) and a lot of it. Some of the low modulus (opposite of low elongation) required elongation percentages of 10% to develop reasonable tension levels. And once you got there, even when you incurred the least bit of stress on the mesh, the tension level was lost. This made a continuous take-up retensionable frame a very logical method. Now that low elongation fabrics are available, the utility of the retensionable frame has changed.

Screens There are two camps of thought: First is the camp that allows the mesh manufacturer to spin and weave mesh to perform properly on press. It has a large mesh opening and a flat surface with a thin thread and is low elongation. It is engineered and manufactured for stability and ink transfer. The second camp says that you want to buy the strongest mesh available and tension it to a plateau to make it stable, flat and transfer ink properly. There are few in the business that have the controls in place to do the latter so we recommend that you let the mesh makers do the engineering. Use the proper tension level to achieve your goals, not as a cure all for all the other ailments of the screen printing process. The most appropriate cliche is “If the lights go out … don’t fix the plumbing.” Particularly in the US, we have used screen tension to attempt to solve a variety of problems rather than accurately identifying or solving the problems themselves. We have been plumbers groping in the darkness. It is true that excessively low-tension levels lead to misregister and poor ink transfer at a slow rate. But excessively high-tension levels, set in an attempt to resolve non-tension issues create other problems: screen bursting is one, buckling squeegee blades is another. In many conditions high tension actually creates an imbalance in the amount of ink transferred. Look to press calibration, ink tack, mesh geometry, sharp and true squeegee blades and proper frame size as their own culprits, you’ll find it an illuminating experience and a lot cheaper in the long run.

Tips For Establishing Your Proper Tension Level Continued The maximum tension level of the mesh has to meet several criteria: 1. Does not lead to image enlargement. 2. Does not cause premature fatigue. 3. Does not cause negative lag during the print stroke.

An excessive tension levels create the following problems: 1. Forces impractical off-contact distances. 2. Or results in image enlargement. 3. Creates negative mesh lag. 4. Causes premature fatigue or bursting.

Contact Distance Tension And Off-C Of course there is a relationship between tension and the amount of off-contact distance but that relationship relies upon more than just the two facets. The criteria for tension as it relates to off-contact distance is screen stretch. In other words, once you have set the off-contact distance to accommodate your image tolerance (refer to figure 4.4 and figure 4.5 on page 4.9) then your tension level must allow you to print without image stretch in the stroke direction. You will need higher tension for a given off-contact distance if the image PAGE 1 . 49

Chapter 1 stretches in the print stroke direction. The table below gives you a starting point for tension and off-contact distances. Tension Levels and Off-Contact Distances

Tension N/cm² Oc Inches *Oc Fractional

10

15

20

25

30

35

40

45

50

55

60

.375

.250

.160

.100

.069

.055

.042

.035

.026

.019

.015

3/ 8

1/4

1/6

1/1 0

1/1 4

1/1 8

1/2 3

1/2 7

1/3 8

1/5 2

1/6 6

*Fractional equivalents are approximate and are listed for reference sake only. You should use a meter for press calibration and it is most likely that the meter will be scaled in mils or thousandths of an inch. Figure 1.38 This table lists the tension level and off-contact distance combinations. This list is for reference and a starting point only. Refer to Chapter five for specific details on setting off-contact distances and then establishing the proper tension to support the off-contact. As the table shows, a 25 N/cm² screen will be needed for an off-contact distance of 0.100” or 1/10th-inch.

Begin by establishing your image tolerances and then use the tables shown on page 4.9 to determine the maximum off-contact distances. Once you have determined the off-contact distance, you can set the tension specific to that off-contact distance. Use the graph below for reference. Figure 1.39 This graphs the relationship between tension and off-contact distances. Off-contact is the first variable to be set on press. Tension along with squeegee settings must support the proper off-contact distance. Details are located in Chapter Five.

Off-Contact Distance in Inches

Tension & Off-Contact Distance 0.400 0.350 0.300 0.250 0.200 0.150 0.100 0.050 0.000 10

15

20

25

30

35

40

45

Tension in N/cm^2

PAGE 1 . 50

50

55

60

I. Stencils Emulsion Types Coating Parameters II. Coating The Stencil Coater Length Coater Edge(s) Coating Techniques EOM & Rz Importance III. Drying The Stencil Conditions And Time Factors Additional Considerations Humidity And Moisture Control IV. Exposing The Stencil Calibration Monitoring Exposure Variance Lamp Parameters V. Developing The Stencil Touch-u up Taping the Perimeter VI. Reclaiming The Stencil Haze Remover VII. Real World Results Prepared Test Screens Cost Of The Coating

Chapter

2

STENCILS

Stencils Stencils The role of the stencil is multi-faceted. It is to adhere to the mesh and resist reasonable abrasion from the squeegee and be enough elastic to allow proper off-contact distances. The stencil must be flat enough on the impression side to create a seal to the film positive during exposure, as well as provide an adequate print shoulder for accurate line reproduction in print production. It should be sufficient on the squeegee side to meter the proper volume of ink for fine-detail printing. The color should be transparent enough to encourage thorough exposure [on the inside of the screen] and yet it should be dyed to filter extraneous light rays. All of these parameters are operator dependent: that is, they can range from bad to good solely based on the way that you use them. If your preoccupation is with the lowest price pergallon, you are probably creating problems with quality and downtime that are easy to resolve, but costly nonetheless. Emulsion Types

S t encil Transparency and R egistration The visual transparency of the completed stencil is critical to the press operator. In a perfect world, you could align the image with a Tri-Loc and lock the image in place—you would never need to move it again. For those of you in the real world, there may be times that it just doesn't work that way—you need to see through the stencil to the image below. In most shops a minute of press time is worth $5.00 to $20.00 dollars—don't do anything that will waste a minute.You may want to rely on visual registration if... v you don't have a Tri-Loc. v the screen frame is racked.

There are three basic types of stencil emulsions: diazo, dualcure and pure photopolymer.

v the screen frame slips.

The diazo is the traditional coating; relatively low cost, long exposures and temperamental in many aspects due in part to moisture sensitivity.

v the original art really doesn't line up.

Pure photopolymer is at the other end of the spectrum from the diazo. It offers lightening fast exposure, is somewhat unaffected by relative humidity and darn expensive. It is well suited for those with small or weak light sources or those with high quantity and reasonable demands. If you plan to use a pure photopolymer extra caution should be taken in calibrating exposure. The latitude is very tight, which can easily lead to over or under exposure.

v the mesh fatigues.

v your press is out of calibration.

Dual-cure is generically a blend of diazo and pure photopolymer. It is most often the best choice for performance. It can be faster than diazo, but have user-friendly latitude. It’s the best resolution in the game and yet is relatively easy to reclaim. PAGE 2 . 3

Chapter 2 How To Instructions

Selecting an Emulsion Look for an emulsion with: v High solids content. v Transparency to ease registration. v Durability on the press to resist pinholes and breakdown. v Wide exposure latitude to be production friendly. v Fast drying to increase throughput. v Easy reclaimability for labor economy and screen life. v Fast exposure, specifically on your light source. And most of all, don't let price interfere with productivity.

For long life it tends to be unsurpassed. If you are not sure what to use, err on the side of dual-cure emulsions. Each of the coatings has specifications and parameters that are highlighted in the few paragraphs below. The information is to enable you to choose the best product, not to pigeon-hole you into a specific label or performance parameter. Coating Parameters

High solids content is the first parameter that you should look at to attain higher edge quality, fewer pinholes and longer life on the press. Not curiously, these higher-solid coatings cost more, since less of the product is water. Bridging, the ability of the emulsion to "bridge" over the open area of the mesh, was a hot topic long ago when both the solids content and print standards were dangerously low. It is, of course, constrained by the percent of solids (price) but is much more reliant on the particulars of the fabric and on the methods of application used. (Refer to pages 2.10 and 2.14 for details of fabrics, coating and exposure methods). The best bridging will come from multiple coats and, in fact, from coat-dry-coat techniques. “Resolution” is a term that is bandied around by all of us to cover a multitude of virtues. Many elements of the coating chemistry (such as resin particle size), account for its ability to hold detail. Unfortunately, the reason for poor detail many times is a function of usage: improper coating methods, drying, exposure and development conditions. Very few printers actually tap into the resolution capabilities of any of the emulsions. Remember that it is resolution on the print that is critical, not resolution potential in the can. Here again the optimal resolution occurs when the stencil is the flattest. This is accomplished through a balance of coat-dry-coat technique. Exposure speed can be beneficial but be sure that it is not hurting you in proPAGE 2 . 4

Stencils duction. A "faster" reacting coating will be more sensitive to time (or exposure units) and to thickness of the coating. With the faster coatings, particularly the "pure photopolymer" coatings, your conditions should be closely calibrated to insure success. (Refer to page 2.19 for calibration and monitoring). Reclaimability should not be counted as crucial as those facets of the product that slow down productivity (transparency for example, see side bar page 2.3). The cost of off-press functions should not be weighed as high as on-press functions. Nevertheless for reclaimability you may trade water resistance, but the bulk of the process is in the hands of your exposure and drying (refer to pages 2.19 and 2.25). Insufficient drying and/or under exposure can make the job of reclamation very difficult. (Note that some coatings are more difficult than others to reclaim, so check with your supplier on a starting point, then be sure you don't make the condition worse). Multiple wet coats and coat-dry-coat are cross grain to the desires of both the emulsion suppliers and screen room personnel. Some of the emulsion suppliers don't want to have to say that the best results are achieved with the coat-dry-coat method: it’s not what the printer wants to hear. And the screen-room personnel are under pressure to get the screen to the production floor: coat-dry-coat takes more time. However, for the best real-world outcome, coat-dry-coat produces superior results. Even the premium products shrink toward the knuckles of the mesh; depending on your conditions and quality standards this shrinkage may not bother you but will be affected by mesh geometry, coating thickness, type of coating and vacuum conditions. With coat-dry-coat, you allow the emulsion to shrink which forms an irregular surface; then you return after drying, probably with a thinner blade, to put a thin, flat finish coat on the surface, that fills in the valleys caused by shrinkage.

Variables Ef f ecting Selection of Coat er Length 1.

The tension level of the screen.

2.

The edge of the coater.

3.

How much force you want to apply.

4.

If you have permanent blockout around the perimeter.

5.

If you wipe up the drips of coating near the corners of the frame.

6.

The maximum image size.

Transparency of the dried emulsion is crucial for image registration on the T-shirt press. The best solution is to use the patented M&R Tri-Loc system so that any need to see through the screen is minimal. Otherwise, dyed emulsion, which is often the complimentary color to the screen mesh, will offer PAGE 2 . 5

Chapter 2 R ound vs Shar p Round-edge coaters: v allow a faster coating speed than sharp. v bridge coarser (160 and below) fabrics. v create less turbulence (air bubbles) on coarser fabrics. v apply more coating with fewer passes. v allow a wider range of [operator] force. v require more [operator] force.

the best resolution and latitude of exposure in trade for the ability to see through it with ease. Before you might under-rate this aspect, look to page 6.7 to see the value of one minute of downtime.

Coating The Stencil When you are ready to have flawlessly consistent screens, color after color, job after job and year after year, you are ready for a Digikote, digitally controlled screen coater (see figure 2.1). There are a variety of coaters on the market and, though they all look similar, Digikote has solved the one problem that exists with all other coating machines: how to apply pressure consistently (see figure 2.2). Electronic drivers on each side of the screen apply consistent pressure on the face of the screen regardless of your airflow,

v should be slightly shorter than sharp. v are less sensitive to the angle (coater to screen) of attack. Sharp-edge coaters: v work better on higher tension levels. v more accurately meter the coating onto the mesh. v are definitely best for face coating. v are generally better for finer (160 and up) mesh counts.

Figure2.1 Frontal view photograph of the Digikote automatic screen coater. PAGE 2 . 6

Stencils age of the machine or characteristics of the screen. No other coater can make that claim. All T-shirt printers print too close to the edge of the screen; it is a requirement of multi-color press screens. Now you can have a stencil that is the same thickness at the edge as in the center. Digikote is fully programmable to coat the front and/or the back of the screen. Digikote comes with two coating blade edges—a .050" and .080" (one and two mm). The .050" is typically used on finer mesh counts of 230 and up, while the .080" is Figure 2.2 Electronic pressure sensor from the Digikote. used for 230 mesh counts and down.The .050" lays down a thinner deposit and results in a smoother surface. The .080" lays down a heavier deposit, which creates a rougher surface. For the ultimate application you can use the .080" first and finish with the .050" (refer to figure 2.5). Coater Length The proper selection of a coater length depends on a few variables. If your tension is low, below a nominal 20 N/cm² (Newtons per-squarecentimeter), then a shorter coater length is recommended. If you are using a roundedge coater a shorter length is also in order. The longer the coating trough, the more force you will have to apply to get an accurate stencil— even more force if the edge is rounded. If you have permanent blockout on the perimeter

Figure 2.3 The width of the coater should be larger than the maximum image width yet leave ample room between the coater’s ends and frame for consistent coatings center-to-edge.

PAGE 2 . 7

Chapter 2 How To Instructions

of the screen, the coater should not pass over the blockout. As the length increases you will spend more time contending with runs and puddles in the corners of your retensionable screen.

Selecting a Coater 1.

Length must be 1" greater than the maximum image width.

2.

Length must be 2" (or more) shorter than the frame I.D. (interior dimension).

To be practical, the coater should be two inches longer than your maximum image 4. Challenger = 20" to 21" size (see figure 2.3). The limit 5. The edge of the coater must: of the coater length is predia. Fineness of mesh thread and count. cated upon the consistency of the coating from the very b. Resolution goals. edge to the center. You may c. Viscosity of emulsion coating. not care if the margins d. Applied force, screen tension, coater length [edges] are properly coated, and frame I.D. but consider this: as the coater gets closer to the edge, e. Intended number of passes. you need more force to create f. Intended dry time. equal pressure across the surg. Coating speed. face of the screen. If the pressure is unequal, so will be the coating—thicker in the center. Resolution is lost and most of the coating that you paid for will wash down the drain during development wash-out, due to underexposure. The consistency of the coating can be assessed by a gray scale and resolution target test. (Refer to page 2.21 and 2.23 for details). Mount one of each of the scales to the middle of the screen and one at the edge. Expose as normal, develop the images, then compare the two scales. The solid step for the center should match the solid step for the edge. 3.

Gauntlet = 17" to 18"

MC

Coating Method

Edge

Type

Rz

EOM

Step

Pos. Res.

Neg. Res.

80/71 150/45 230/40 305/35

1 Imp. - 1 Sqg. 1 Imp. - 1 Sqg. 2 Imp. - 1 Sqg. 2 Imp. - 2 Sqg. Dry - 1 Imp.

Rnd. Rnd. Rnd. Rnd. Sharp

Dual Dual Dual Dual

16.2 9.5 10.4 8.3

25.0 14.2 6.6 5.8

6 5 8 8

8.5 3.5 3.0 2.5

8.0 3.0 2.5 2.5

Figure 2.4 Test Screen Look-Up-Table PAGE 2 . 8

Stencils On a Challenger screen, the coater should be a maximum of 22" wide and, on a Gauntlet, 18" wide. If at all possible, use of a narrower coater can save you dollars. It is our recommendation that you never try to coat to the very edge of the frame. Coater Edge(s) In the battle of the blades edges, there is room for both round and sharp—it just depends what you want to accomplish (see figure 2.5). The best of all worlds is, at times, to apply the initial coats with a round-edge blade, then to finish with a sharpedge. To decide, see the coating tables, (figure 2.4) for details on how we coated the four test fabrics. The four test fabrics were choosen to allow a wide range of printing applications and all four offer excellant ink transfer and coverage. Or you can use the information contained in this section to decide for yourself, if and when to use each type of coater blade. The Digikote offers two standard blade edges, a 50-mil sharp and an 80-mil round. Available Figure 2.5 M&R will install a Delrin® knife-edge with the coating trough, you specify—a 50 mm sharp edge or an coaters in the field 80 mm round edge. This engineering plastic is virtually inderange from a 20structible and is manufactured to the precise edge required for mil sharp edge to a coating emulsions. 100-mil round edge. The general features of round and sharp blade edges can be found in the sidebar on page 2.6. Round edges are more forgiving—and can have its time and place—but, for the highest resolution imaging, while a sharp will be more demanding the results are worth the effort.

S t encil Tr oubleshoo ting Loss of Highlight Dots v Add more impression-side coats. v Over-exposed. v Inadaquate vacuum. Loss of Shadow Dots v Add more impression-side coats. v Development too aggressive. v Under-exposed. Loss of Both Highlight & Shadow Dots v Add more impression-side coats. Pinholes (center of mesh open ing—not dust related) v Coating too thin. v Severe under-exposure. v Moisture content too high during exposure. Smearing or blurring during press run. v Add more impression-side coats. v Related to press settings or poor calibration. Ink Piling—due to too much ink volume in details. v Add more squeegee-side coats. v Sorely under-exposed. v Should see scumming during washout.

PAGE 2 . 9

Chapter 2 Coating Techniques. How To Instructions

Manual Stencil Coating 1.

Select the proper length coater (page 2.7).

2.

Use the prescribed coater edge (page 2.9).

3.

Use a coating rack or support the screen at a slight angle.

4.

Fill the coater to the same point frequently.

5.

Coat the impression side first.

6.

Center the coater near the bottom of the screen .

7.

Apply firm pressure from left to right and throughout the stroke.

8.

Slow and steady maintaining contact, bring the coater near the top.

9.

Do not alter the angle of the coater.

10. Make additional passes as required (page 2.14). 11. * Turn the screentop to bottom(vertically) and coat the squeegee side last. 12. Wipe the edge of the coater with a damp soft cloth. 13. Refill the coater with emulsion frequently: do not wait until almost empty. 14. Dry print side down. 15. Apply additional coats after drying if necessary (refer to the how-to onstructions on page 2.14). * Although it is recommended to flip screens vertically during manual coating, the size of the T-shirt screen rarely demands it. Flipping screen is done to compensate for inconsistent pressure from side to side or bottom to the top. Large format screens tend to show more variance in pressure (deposit) as the operator reaches the top of the screen. It gets increasingly harder to maintain even pressure as the operator gets closer to shoulder height. If you are experiencing a thickness variance in your screens, you may want to flip your screen, if not—you may choose to eliminate this step.

To gauge the potential of your coating methods, use either a meter to measure both EOM (emulsion over mesh) and Rz(flatness of the emulsion surface), (refer to pages 2.13 through 2.14) or for a lesser investment (and less quantification), use the gray scales and resolution targets described on pages 2.21 through 2.23. Proper coating techniques are a delicate balance of the emulsion parameters, ambient conditions, exposure capabilities, the mesh geometry and tension, the particulars of the coater blade, the Digikote settings and operator influence. We will assume that you have quality film positives, a wellprepared screen (refer to chapter one), and that your press is calibrated (refer to chapter four). Use the troubleshooting list in the sidebar (found on page 2.9) to assist you in adjusingt your coating methods. How To Coat With A Digikote Automatic Coater

Automatic stencil coating has been made affordable by M&R with the introduction of the Digikote. For decades PAGE 2 . 10

Stencils the most sophisticated printers have known that to get a quality print, you need a quality stencil. But until the Digikote, automatic screen coating was affordable only to the largest plants.

Automatic Stencil Coating

How To Instructions

1.. Turn the Digikote on (see manual for specifications). 2.

Place a round coater(s) in the back of the Digikote.

3.

Place a sharp coater(s) in the front of the Digikote.

4.

Insert the frame into the self-centering clamps.

5.

The impression side of the mesh should be facing the operator.

6.

Lower the top clamps to near the frame.

7.

Push the frame-locking button, located on the center of the top rail of the machine. The button rigidly locks the frame into position.

8.

Set the speed, begin at 5 ips (inches per second).

9.

Set the pressure, beginning at ___ units.

10. Set the number of coats, front and back. 11. Store this procedure in memory. 12. Fill the coating troughs to the same level and refill often to keep the level consistent. Figure 2.6 Start, stop, frame lock and release—all programming controls are conveniently located on the eye-level control panel, on the right hand side of the Digikote.

13. Refer to table 2.31on page 2.42 for mileage. 14. Measure the results as described in this chapter. 15. Push the start button to begin coating. 16. When done, release frame from holder.

The Digikote T2 accommodates one or two screens at a time with no variance in the coating (see figure 2.6). The T2 is intended for high throughput plants—over 100 screens per day. Like all Digikote units it is fully programmable for virtually any viscosity, profile or application of liquid emulsion coatings. Operating the Digikote is straightforeword; refer to the sidebar above for instructions. Your coating will be flawlessly consistent, dry times will be more predictable, PAGE 2 . 11

Chapter 2 Obstacles Of The T Shir t Screen Mak er v

exposures will be more consistent—therefore press breakdowns will be reduced. Still, T-shirt screens offer some unusual challenges for the stencil maker: Please refer to the sidebar left for further details.

Meshes range from 20 tpi (threads-per-inch to 460 tpi, however, T-sirt printers tend to use relatively coarse mesh counts.

v The image is very close to the edges of the frame. v Industry tension levels vary up to over 50 N/cm². v The quantities of [multicolor press] screens per day is very high. v The wear on multi-color screens is significant. v No other process prints weton-wet with plastisols. v No other process must deal with the heat created by flash units over the platens. Figure 2.7 The Digikote model T-2 can hold two screens and nearly double your productivity without sacrificing coating accuracy or consistency.

An intimate understanding of the T-shirt printing business allowed us to design the Digikote to adapt to all of its particular needs and more. Digikote can be automatically programmed to handle your needs: 1. One round and one sharp coater blade come with every Digikote. 2. Infinite speed control accommodates the coarsest mesh counts. 3. Only Digikote can adapt to the deflection of a textile screen. 4. Only Digikote is sensitive to the gamut of screen tensions. PAGE 2 . 12

Stencils 5. Programmable controls allow highest throughput. 6. Sufficient and repeatable EOM eliminates breakdowns.

Tips On Using The Digik o t e 1.

A smaller well requires more pressure for coating consistency.

2.

Coating too close to the edges can harm the mesh.

3.

Keep the coating trough filled to a consistent level.

4.

Begin at five ips blade speed.

5.

Higher mesh counts allow higher speeds.

6.

Mesh counts that have a flatter mesh surface allow higher speeds.

7.

If intermittent drying, use a round-edged coater first.

8.

Use a round-edge coater on the squeegee and sharp on the impression-side.

7. Proper Rz improves print quality. 8. Consistent coating weight allows consistent and thorough exposure. Perimeter Coating.

You may contact your supplier for a permanent blockout, which can be applied to the perimeter of the low-elongation mesh screen. The blockout seals the ink in and saves you time and money on processing chemistry. Often, as much as 40 percent of the screen can be stabilized. That could mean a savings of 40 percent in chemistry and the associated time for using that chemistry. For example, the amount of reclaiming solution is reduced, as is the time of reclaiming the smaller area. If you choose to seal the perimeter, be mindful that it must be a thin layer on the impression side or it will adversely affect the coating thickness. EOM (emulsion over mesh) and R z (stencil flatness) Importance These two measurements should be read in tandem and considered as a pair of data points. If you considering them singularly, it can be very misleading. Refer to the table on page 2.14 for standards on both EOM coating thickness, as well as Rz flatness. EOM

The basis for this measurement is to produce a stencil coating to overcome the irregular surface of the screen mesh. Once it has done so and the stencil has formed a gasket or relief on the underside of the screen, it is usually “thick enough”. There are always exceptions such as high-cut-pile terry towels and high-density fine-detail printing, but for the majority of T-shirt printing, the “thick enough” policy is sound advice. You may PAGE 2 . 13

Chapter 2 How To Instructions

Determining Coating Properties

choose to use a thickness gauge to meter the thickness of the coating (see figure 2.8). An inadequate coating thick-

1.

Record your coating procedures (per mesh type). a.

Edge radius.

b.

Passes per side.

c.

Drying—position and number of times.

d.

Drying—times and environmental conditions.

2.

Measure and record EOM.

3.

Measure and record Rz—both sides.

4.

Expose test screens with gray scales and resolution targets.

5.

Develop, dry and inspect.

6.

Compare results to the tables on pages 2.40 and 2.41.

7.

Interpreting results of scales:

Figure2.8 Majestech's TQM-ETG electronic stencil thickness gauge is designed specifically to measure the stencil thickness in microns. This is the best method of gauging EOM.

ness leads to pinholes, very poor image detail, poor exposure latitude and premature b. Generally low resolution of scales—improve breakdown on press. If the EOM. coating is too thick, the dosage of exposure to get the screen properly exposed (refer to page 2.19) is excessive. This leads to light diffusion and a loss in image accuracy. Further, such a coating will begin to lose its flatness (due to a reduced ability to evacuate the moisture from the screen)effecting the Rz level, as well as its ability to transfer ink (due to the long tunnel created by the too-thick stencil). The EOM reading should be used in conjunction with a flatness or Rz reading. a.

Loss at positive and negative ends of scales— improve Rz.

Rz

While you are achieving a coating that is just “thick enough”, it should be monitored for flatness. If the impression side of the stencil is not flat, it will not hold accurate detail. Even under the best vacuum, the coated screen will not develop PAGE 2 . 14

Stencils intimate contact with the film positive and light-undercutting will ensue. The most blatant cause of a poor Rz is a stencil that is too thin. In such a case, the Rz meter reads the undulations (hills and valleys) of the woven mesh, with the stencil only minimally improving the readings. Once the proper EOM is achieved (refer to page 2.13) a thicker coating can tend to become less flat. In theory, this should not happen, but in the real-world this can occur. It is generally due to the use of thicher fabrics and/or round-edge coater blades that leave thicker emuslison deposits with each pass. Moisture gets trapped within the stencil and the surface dries with a texture (not smooth). Refer to page 2.14 for standards on EOM and Rz. You may elect to use an Rz meter to establish the actual flatness of the coating (see figure 2.10). The poor-man's Rz proof is to take a credit card and lightly drag it across the surface Figure 2.9 Majestech's Pocket Surf meter allows you to determine the flatness of the of a light table or the glass on a vacuum frame. stencil on both the impression and the Then, as a comparison, drag the same card lightsqueegee sides of the screen. ly on the press-ready emulsion surface. If you feel the vibration or hear a buzzing, the surface is not flat. A happy medium is to monitor your calibrated stencils with resolution targets (refer to figure 2.17 on page 2.23 for details). Note that a flat stencil on the impression side of the screen is fundamental to a quality print. However, it can exaggerate the problem of after-flash tack. If this is your situation, you will want to fix the ink (refer to page 3.18 for details) and not resort to coarse fabrics with high crimp angles and undulated stencil coatings.

Drying The Stencil The problem with excessive moisture in the coating is multi-faceted. First, you can't expose the water out of the coating; that must be done in the drying stage. Second, the

Figure 2.10 Murakami shows a fine-line and space-configuration on a 350-screen mesh. These details are quickly lost if the screen has been preexposed to extraneous light or if the washout is insufficient. PAGE 2 . 15

Chapter 2 How To Instructions

Drying The Stencil Coating 1.

Be sure your stencil has a consistent coating for even drying..

2.

Dry stencil in a warm, clean, low-humidity room or cabinet.

3.

Dry the stencil with the print-side down.

4.

Use high-volume consistent air changes.

5.

Time the drying period.

6.

Use a moisture-content meter to verify the moisture is less than four percent before exposure.

coating won't expose properly; its cross-link density will be too low and premature breakdown is inevitable. The soft stencil will invite solvent and plasticizer penetration. Third, during development you may see scum or a cloudiness clinging to the open areas of the mesh. Fourth, the developed coating will be full of pinholes. Fifth, the stencil may be very difficult to

reclaim, particularly after it is used on press.

PAGE 2 . 16

The problem worsens as you realize that humans cannot tell if and when the screen is dry. The nominal amount of acceptable moisture is 3 percent. A screen that has 10 percent water content still feels dry, but will be a failure on press with the flaws described above. A stencil with three to four percent moisture con-

Figure2.11 Majestech's Aqua-Check meter will allow you to easily determine if the moistuer content of the stencil is below 4% and ready to expose.

Figure 2.12 Murakami shows this photomicrograph of a shadow dot structure. These dots are "islands" and the first to sink in the case of a screen loaded with moisture.

tent will perform extremely well. It is the screens in the area of five to nine percent that we are most concerned about. To gauge the performance of these, you will need a moisture content meter (see figure 2.11). The meter shown ranges from three to twenty moisture content and is labeled with green for go, yel-

Stencils low for caution and red to stop your use of the wet screen.

Exposure Calibration

Conditions And Time Factors

1.

Guesstimate that the best exposure time is one minute.

The obvious questions: Are my screens dry enough and how long should I wait? And we would love to give you a specific answer. Unfortunately it would be just that, specific and, therefore, not very helpful unless your conditions matched our test parameters exactly.

2.

Double the time and run the test for two minutes (one minute guess, times two = two minutes).

3.

The results show the best target for detail is either 50 percent or 75 percent (shown in figure 2.13).

4.

The results show my best target for color is 75 percent.

5.

Select 75 percent as the factor.

6.

Take the two minutes test time, multiple it by 75 percent, the calibrated exposure time is one and one-half minutes or one minute, 30 seconds.

How To Instructions

The fundamental conditions for drying are the coated weight of the emulsion, the surface area exposed, the vapor pressure of the coating, the vapor pressure and temperature of the surrounding air, and the nature of the air flow. The coating weight is a composite of the viscosity of the emulsion, the edge of the coater and the number and location of passes applied to the screen. The surface area of the coating exposed to the air is the second factor. Therefore, a fine- mesh screen (with lower surface area) will dry faster than a coarser-mesh screen.

Figure 2.13 Autotype's Exposure Calculator allows as few as a single test exposure to pinpoint your proper production exposure time or units. Upon close examination, you can see that the filtered areas look bleached out. This indicates under exposure. PAGE 2 . 17

Chapter 2 The evaporation of the emulsion is a function of the vapor pressure of the coating as well as the vapor pressure of the surrounding air. The vapor pressure of the emulsion is that state of equilibrium between the liquid and vapor. As temperature increases the vapor pressure increases in direct proportion. As an example, you can increase the temperature of water until it finally boils at a pressure of one atmosphere and 212° F. In your drying room or cabinet, the ambient air has its own vapor pressure and it may or not cooperate. The greater the difference in the vapor pressure of the ambient air and the vapor pressure of the coating, the faster the coating will evaporate. Be cautious if you are using warm air to accelerate the drying of your coated screens. Of course it will be very effective, but heat can partially “expose” the emulsion on its own and, with too much heat (try to stay below 110° F), the shelf life of the screens is in jeopardy. Airflow may seem so simple, but you must realize that it is extremely complex and not at all intuitive. For our purposes, we will not attempt to explain or define this aspect; rather, we will try to alert you to the existence of its subtleties. The dry time of a screen will be affected by whether the air is impinging (directed at) or flowing parallel to the surface of the screen. For this and the reasons stated above, it would be meaningless to isolate a standard “dry time” for a coating. Additional Considerations The room or drying cabinet should be as dust-free as possible and in, the typical T-shirt plant, this could be quite a challenge. Clean-room environments are beyond the scope of this book, but they are advantageous. Short of that, you may invest in washable indoor/outdoor carpet at the entrance to the room, along with tack tape for the floor to remove any dust and dirt from the bottom of your shoes. An air cleaner in the room, alongside your dehumidifier, will help immensely. Finally, at the auto-body or hardware store, pick up a supply of tack rags. These are gauze cloths coated with shellac and solvent. They are dust magnets that can be used to clean the screen and not leave anything behind. Be forewarned that screen emulsions are not totally insensitive to all yellow lights, particularly if the lights are high intensity (formulas relating to this topic may be found on page 9.1 of the appendix). If they “wash out great” when the screens are fresh, but fight washout once the screen sits in the “darkroom” for a time, then your lights may be the problem. To test, use black electrical tape, applied to both sides of the screen, forming an PAGE 2 . 18

Stencils “X-shape”. Let the coated screen sit as close to the lamp for as long as is normal—several hours is minimum and several days is typical. Then take the unexposed screen to development and remove the black tape. If you have a stray light problem, the “X” will washout more easily than the surrounding emulsion. Humidity And Moisture Control There are a few tools that will allow you to test and determine the time required for drying. The first purchase you should make is a thermometer and hygrometer for the drying room. These will show that a certain range of temperature and relative humidity can have a serious affect on the dry time. The rate of evaporation is directly proportional to an increase in temperature and a decrease in relative humidity. A moisture-content meter (refer to page ___for details) can be a lifesaver since no one can tell by sight or touch whether a screen is dry. It is possible to monitor airflow, but unless you are building a drying cabinet, the other recommended gauges should suffice.

Exposing The Stencil Stencil exposure is critical for two aspects of quality production. First is image accuracy. If the screen is over-exposed, detail is lost, the size of the image is altered and registering one screen to another or color accuracy can be a problem. Second, if the screen is under-exposed, pinholes and premature breakdown on press is assured. Before you try to establish and control proper exposure you may want to review tensioning methods (refer to page 1.43), coating (refer to page 2.14) drying (refer to page 2.16)and frame size (refer to page 1.21). Calibration There are two steps to stencilexposure control: calibration and monitoring. Calibration is the stage prior to production that accurately determines the

Figure2.14 Shown is the Autotype Exposure Calculator to help calibrate your screen exposures. This film positive effectively runs five exposure tests in one exposure. Complete instructions are included with the test film.

PAGE 2 . 19

Chapter 2 proper exposure based on a test sample of your normal conditions. Although there are several methods of calibration, we will detail the use of an exposure calculator by Autotype. These are available at a nominal charge from your supplier or provider of stencil products. The principle of the exposure calculator is the use of several highly detailed, measurable images. Behind these is a series of progressively darker filters, from clear to very dark (see figure 2.14). The filters relate to each other in that they transmit incrementally decreasing amounts of light. The first transmits all of the light and is marked “1.0”. The second transmits seventy percent of the light, and is marked “0.70”; the third, half of the light; fourth, thirty-three percent and fifth, one-quarter. Start with two screens of identical mesh and stencil, and prepare to expose the screens with the calibration target. Guesstimate your exposure in units or real time, and then double it only for this test (see how-to on page 2.17). Expose at the double time, then develop the screen as normal and view the results while the image is still wet. One image will look better than others. You are looking for two things: the cleanest detail in the star targets at the center of the scale, and a background color that resemble the color of the “Factor 1” scale (see figure Figure 2.15 Autotype's Exposure Calculator allows as few as a single 2.16). test exposure to pinpoint your proper production exposure time or units. Of the five factors, if your test is not one of the middle three, you will want to run the test again. The reason is simple: if your test indicates the “best” scale is at either end, you can't determine if more or less exposure would be better. Using an exposure calculator you will determine the correct exposure time for the mesh count/color, type of emulsion and coating procedure used during the calibration. The exposure time will allow a highly detailed screen with excellent durability on press. If any of these factors change, you should re-calibrate for the new or different conditions. There is a method of exposure calibration that is very precise. That is to use a radiometer with its probe behind the exposing screen. It works quite well with PAGE 2 . 20

Stencils diazo type coatings, as the diazo bleaches out as the crosslinking progresses. On the other hand, pure photo-polymers do not bleach at all and there is no plateau upon which to establish sufficient exposures. If you are going to evaluate dualcure coatings, approach cautiously. Cautions

You will want to resist the temptation to under-expose in order to hold detail. If you underexpose a screen, much of the coating washes down the drain and the result is a pinhole-ridden, thinner stencil that will only appear to hold superior detail. Pinholes are always in the perfect center of the mesh opening which tends to be the thinnest part of the coating. Unfortunately, this water-eroded coating is not robust enough to act as a gasket for the transfer of ink. Monitoring Once you have calibrated (above) your proper exposure times for each specific mesh and stencil, you will want to monitor the results to see if and how much they vary from the standard. There are two very inexpensive yet very accurate film-positive tests that can ensure the accuracy of every screen you shoot. Immediately after calibration, select a prepared screen identical to the one that has just been calibrated. Step Gray Scale 21-S

The first film-positive is a 21-step, transparent gray scale (shown in figure 2.16). It is a numbered gradient of 21 separate densities of gray filters. Step 1 is clear and step 21 is the most dense or opaque black. These steps are mathematically stepped, their densities related to each other. Step 1 transmits (relative Figure 2.17 to the scale) all the light. Step 21 This is a Stoffer 21step transpartransmits only 0.1 percent of the ent gray scale light. Each step is approximately 15 imaged on a screen. This scale percent more or less dense than its is processed to a neighbor. solid step number nine.

Figure 2.16 This is a Stoffer Scales 21-step transparent resolution guide. It is a film positive that can be used over and over again to gauge consistent stencil exposure.

For example, you calibrate a screen and stencil and the very next screen washes out to a solid step 9 (see figure 2.17). Step 9 will forevermore be the proper step for screen development for the calibrated conditions. Lets say that things run for several weeks and then, to celebrate, you buy a coating PAGE 2 . 21

Chapter 2 trough that looks about the same as the old one. But its edge and length are different and it deposits a thicker coating of emulsion. It is not apparent to the naked eye and the screen goes for exposure and development. When the screen is developed, it turns out to be a solid step 8, exactly one step from the standard step 9. The step 8 screen is underManeuvering On A 21-S Step Transparent Gray Scale exposed because of its If you … Then you should … thicker coating; need to increase by one step, divide time or units by 0.70. you should refer to the need to decrease by one step, multiply time or units by 0.70. look-up table on page 2.43 and increase the need to increase by two steps, divide time or units by 0.50. exposure by need to decrease by two steps, multiply time or units by 0.50. approximately 43 percent (the same as dividneed to increase by three steps, re-calibrate. ing it by 0.70). need to decrease by three steps, re-calibrate. If you do so, the next screen will be back to a solid step 9 on the scale. The look-up table will assist you in maneuvering on a scale, without having to reshoot the exposure calculator. But beware, this is only accurate when you are one or two steps off on the 21-step grayscale. You may think a 15 percent change is not very much —and you would be correct. Such a variance can rarely be detected on a press. And that is just the point, no one will be able to tell that there is variability in the screen exposure, the results will be that accurate. But now the screen department will have evidence of accuracy and the press operators won't have to wonder. Resolution Target

Resolution is the ability of the stencil system to accurately reproduce a minimum image. A resolution target is a transparent film-positive with divergent scaled lines and spaces. This particular scale has divergent lines that range from 1/10 of an inch PAGE 2 . 22

Stencils at one end to 1/10,000 of an inch at their tips. One side is composed of black lines and clear spaces; the other has clear lines and black spaces (see figure 2.17). Your limits of resolution are many fold but will all be evidenced by a filling in of the lines and spaces or by a moiré pattern. The loss of lines and spaces is detailed immediately below. This scale can act as a crosscheck to the gray scale (described immediately above). By inspecting the limits of the lines (highlights) and spaces Figure 2.17 " is a Stoffer Scales trans(shadows) and comparing the two under a loupe, parent resolution guide. It is a film positive you can establish the degree of exposure balance. and can be used over and over again to gauge the resolution level of the screen. If the screen is properly exposed the two sides, positive and negative of this scale should be similar. For example, if the scale shows a 5-mil (0.005") line on the one side, then the other side should have a space resolution approximately equal to the 5-mil line. (figure 2.17) The two sides of the scale need to be similar, but the space or negative side of the scale is generally easier to resolve than the line or positive side.

Interpreting The Resolution Target Problem

Description

Over-exposed:

Highlight loss, shadows clearer but print poorly.

Under-exposed:

Shadow loss, highlights clearer but print poorly.

Coating too thin:

No exposure latitude, poor detail, star-like moiré in image.

Coating too thick:

Difficult to develop, tips of lines washout.

Mesh too coarse:

Abrupt stoppage of lines, very short range.

Thread too thick:

Star-like moiré patterns and jagged edges at finer ends of lines.

Stencil too wet:

Erosion causes coating to become thin; targets print poorly.

Insufficient vacuum:

Loss in highlights, gain in shadows, printed targets looks like short tonal range.

Note: It is critical that you wash out these scales just like you do the balance of the image; do not focus on or “baby” their development. You may want to turn to the sidebar on page 2.35 to review our recommended procedures for development. PAGE 2 . 23

Chapter 2 Remember that the resolution should be comparable between the positive [lines] and the negative [spaces] on the scale. Its most affective test is to gauge the stencil or coating thickness as a benchmark of detail capability. Once your detail surpasses the level of the mesh, (and such is the case in virtually all halftone printing) to sustain it now you must rely on the stencil. A coating that is too thin (the typical case) does not rise above the surface of the mesh and any detail will be lost as there is no intimate contact between stencil and positive. A coating that is too thick will require excessive exposure, and light diffusion will cause image edges to deteriorate in the print. The resolution target will help youdetermine edge acuity (the definition at the edge of an image). On a coating that is too thick or too thin, the quality of the lines will be distorted. Thin coatings will leave a ragged edged, saw-toothed line. Excessively thick coatings will leave an edge that has been exposed by diffused light so the size is altered, lines get smaller and spaces(between the lines) get larger. Exposure Variance In this chapter we will discuss many of the causes of exposure variance—low EOM and Rz, inadequate vacuum, lamp undercutting and non-integrated light sources. This segment deals with two of the results, under-exposure (the universally prevalent symptom) and over-exposure. Further, it deals with moisture content, a very common but unforeseen cause of under-exposure and stencil breakdown. Finally, it discusses the all-too-often senseless results of post-hardening, or “virtual exposure.” Proper lamp placement, adequate vacuum, balance of lamp and coating, and controlled output are the variables that are detailed in these pages. We have also recommended low-cost target films to calibrate and monitor screen exposure. Exposure is critical even where there is a minimum of detail—if a screen is under-exposed, and most are, reclamation will be back-breaking. If there is a modicum of detail in the image, watch out, exposure can mean the difference in pass or fail for the image. Exposed Under-E

This is most common because the most common method of inspection in the screen room is to hold a screen up to the light and, with the unaided eye, make a call on the quality of the exposed and developed stencil. Under-exposure is a knee-jerk reaction to a variety of problems: insufficient vacuum, poor Rz value, low EOM and a mesh that is too coarse, twill woven or has PAGE 2 . 24

Stencils threads that are too thick. Under-exposure appears to be a viable solution to holding finer (highlight) details, the circle around the register mark, the serifs on small type faces. . .and those specs that you thought would wash out. Several things occur with an under-exposed screen: much of the coating that you applied washes down the drain because, like the portions that did not get exposed to light, none of the screen got enough exposure, and is still water soluble. There is a likelihood of this scum filling some of the image areas. Fine details like highlight dots do not plug but they will print poorly because of the development-thinned stencil. Perhaps most consequential is the fact that an under-exposed screen will show an abundance of pinholes (refer to page ___) and breakdown prematurely on the press. After the press run, the under-exposed stencil will continue to haunt you. The soft, porous squeegee side of the emulsion goes into production and friction, flash heat and plasticizer (the main component of the plastisol ink) terrorize your stencil. The coating absorbs the plasticizer and, under the flash, it quickly crosslinks the coating and bonds it thoroughly to the mesh. Now you will have a difficult time reclaiming. Finally, the bulbs begin burning out as soon as they are first used. The problem is that they will remain “bright” to the human eye even after the actinic portion of the energy is nearly gone. So the bright light will require an increased time and, if your system has a light intergrator, it will compensate for the most part. Still use the scales, though to monitor (refer to page 2.21 for details). Exposed Over-E

With a flat coating (refer to page 2.14), adequate lamp distance and proper vacuum on the exposure frame, the consequences of over-exposure are relatively minimal. Because of the conditions typical in the T-shirt shop, over-exposure threatens a significant loss of detail. Once you achieve proper vacuum, the optimal light distance and a flat coating, you can calibrate your exposures and your worry of over-exposure (or underexposure) is over. Moisture Content

There are a few tools that will allow you to test and determine the time required for drying. The first purchase you should consider is a thermometer and hygrometer for the drying room. These will show that certain temperatures and relative humidity can have a serious effect on the dry time. The rate of evaporation is PAGE 2 . 25

Chapter 2 Tips For Screens And Equipment 1.

Integrate through the screen, only if all screens are virtually identical.

2.

Don't force the limits of the vacuum blanket.

3.

If the glass is hot, take a break.

4.

Don't put a fan in the box of a self-contained point-light source.

5.

Clean the ink off the frames thoroughly before exposure.

6.

Keep the glass clean—be sure that the glass cleaner does not leave behind a UV resistent film.

7.

Be sure screens are not racked before positioning.

8.

Maintain the oil level in your vacuum pump.

9.

Do not replace vacumn frame glass with tempered glass.

10. Lower than 26 psi (on the vacuum gauge) will sacrifice resolution.

directly proportional to an increase in the temperature and a decrease in relative humidity. A moisture-content meter (refer to page 2.16 for details) can be a lifesaver since no one can tell by sight or touch whether a stencil is dry. It is possible to monitor airflow but, unless you are building a drying cabinet, the recommended gauges should suffice. Contact Vacuum

Retensionable frames are quite popular in the textile-printing industry; however, many of the frames in use are racked (twisted), no longer laying flat. This condition causes vacuum frame glass to break prematurely. The use of tempered glass is not recommended as a solution, because it can obstruct the shorter wavelengths of light that expose the emulsions. One solution is to find a system that keeps the frame flat during stretching. This can be accomplished by attaching a Ushaped channel of metal to the stretching table. Line the inside of the channel with foam to protect the mesh. Be sure that the channel is large enough to slide your frame into with the foam padding. When you begin tensioning, slide the far end of the frame into this channel, it will keep the frame from twisting. It is also wise to seek a balance between breaking the glass and a proper vacuum. If you lower the vacuum too much you will see: (1) a loss of detail, (2) a shift in tonal range (halftones only), and (3) a change in image size. You may want to discuss proper settings with the manufacturer of the vacuum frame. NuArc units are shipped with a preset, but adjustable, calibration of 15 inches of vacuum. This number is based on actual testing of images with resolution common to the screen-printing industry. It is important to note that vacuum is affected by humidity and altitude. For example, on a rainy spring day in Atlantic City it will be easier to achieve 15 inches of vacuum, than in Denver on a typically dry day. Post Hardening

Post hardening is an old trick that suggests you under-expose in an attempt to hold detail; then after image development, PAGE 2 . 26

Stencils expose the screen again for a longer period of time. If you are so inclined, consult the manufacturer of the emulsion you are using to see if it has much posthardening efficiency. Many emulsions do not. Our test case emulsion offered a 30 percent improvement—but only at 600 percent post hardening time. You must investigate on a per-case basis. If the humidity level is high and the moisture content of the coating is over 4%, your screen is not ready to be exposed. There is no amount of exposure time or post hardening which will correct for excessive moisture. Refer to page 2.15 for more details. Lamp Parameters There are pros and cons to both independent and integrated light sources. The independent system can offer the most flexibility as well as the highest potential quality. It is imperative that the position of the lamp be controlled to optimize either the productivity or the image quality. Further, without integration, an independent lamp is problematic at best. The two types of self-contained exposure units are point-source and multipletube light sources. Multiple UV fluorescent tubes, self-contained unit (see figure 2.18): 1. are not readily available with light integrators on all tubes; 2. may build up heat and cross-link the stencil, prior to development; 3. are often designed so that the light energy undercuts the image; 4. do not often peak at the optimal wavelengths of today's coatings; 5. may work extremely fast or handle multiples of screens. Point-light source, self-contained exposure units (see figure 2.19): 1. are best when integrated; 2. may build up heat and cross-link the stencil, prior to development; 3. do not allow variable light-to-frame distances—check center to edge light falloff; PAGE 2 . 27

Chapter 2 How To Instructions

Determining Lamp Distance 1.

Place lamp at a distance from the screen, equal to the screen’s diagonal measurement.

2.

Use two identical screens, ready to expose.

3.

Use two factory calibrated 21-step gray scales and two resolution guides.

4.

Place one of each type of scale, centered on one screen.

5.

Place one of each at the extreme corner.

6.

a.

Corner of first screen if exposing one at a time.

b.

Corner of second screen if exposing multiples at a time.

Figure 2.18 NuArc's First Light is a multiple tube light source.

Load the screen(s) into the vacuum frame. a.

1st set of scales directly in front of the lamp.

b.

2nd set of scales at the extreme corner of the vacuum frame.

7.

Be certain that you have a minimum of 15 inches of vacuum pressure.

8.

Expose, develop, dry and inspect.

9.

Interpreting results: a.

Two sets of scales are identical. i.

And the quality excellent.

ii.

Lamp may be moved closer to permit reduce exposure time (page 2.31).

Figure 2.19 NuArc's freestanding Metal Halide exposure lamp.

iii. Use graph in figure 2.25 to estimate results of lamp movement. b.

Center scales indicate more exposure than corners. i.

Screen lacks durability and resolution.

ii.

Lamp must be moved further away.

iii. And exposure time must be increased. iv.

Use graph in figure 2.25 to estimate results of lamp movement.

Figure 2.20 NuArc's freestanding Metal Halide exposure lamp. PAGE 2 . 28

Stencils 4. have metal halide bulbs that peak at desirable wavelengths; 5. multiple-up configerations limited by the physical design. Independent-light source and vacuum frames(see figure 2.20 and 2.21): 1. best if integrated; 2. no residual heat buildup; 3. position lamp for balance in speed and productivity ; 4. have metal halide bulbs that peak at desirable wavelengths; 5. multiple-up configerations limited only by the size of the vacuum frame.

Figure 2.21 The SPVF from NuArc is available in a range of sizes to serve your needs as a companion piece to a freestanding light source..

Lamp Integration

The section below details the results of moving an independent light source closer or further from the screen. The principles for center-to-edge light falloff may be applied to self-contained point-light sources as well. If you have a single-point light source, typically a bulb with a reflector behind it, you can and should integrate the lamp. Integration is another form of monitoring the exposure of a screen and should be used in tandem with the scales described above. An integrator has three fundamental components: (1) a sensor to detect the energy from the lamp, (2) an adjustable digital meter to determine the energy level, time and again, (3) a switch to turn the lamp on and off. An integrator compensates for a wide range of variables in the exposure process. Some of these, critical to quality screen making, are: 1. altered lamp distance; 2. energy loss from voltage or lamp life (at the prescribed or preset wavelength); 3. energy falloff if the sensor is mounted on the vacuum frame. PAGE 2 . 29

Chapter 2 A seemingly minor change in the distance between the lamp and vacuum frame can have a significant affect on its exposure time. The integrator (and the sensor mounted on the vacuum frame) automatically compensates for any change in this distance (refer to page 2.31 for graphs that relate to this topic). Lamp Distance

Figure 2.22 Move closer—exposure time decreases, but the consistency from center, light-to-edge light is compromised. The minimum distance is the diagonal of the frame(s) resulting in a ratio of center-to-edge light of 70 percent.

New Exposure T ime

=

As a rule of thumb, your independent light source should be the distance of the diagonal of the frame or frames that you intend to expose at one time. For example, if your screens are 26" x 35" and you are doing two at a time in the vacuum frame, your lamp should be a minimal 62" from the surface of the vacuum frame (see figure 2.22). This ensures that the light intensity at the edges of the screens is 70 percent of the amount in the center of the glass. Keep in mind that the increase will force a longer exposure time.

Old Exposure T ime

2

New distance *

Old Distance

2

edge) Light Falloff (center-tto-e

There is a law of physics that describes the relationship between the amount of light directly in front of the lamp versus the amount in the corners (or any other point). That law dictates that, if you place the lamp at the distance of the diagonal measurement of the frame, you are assured of 100 percent of the light in the center (directly in front of the lamp) and 70 percent of that amount in the corner of the frame. Move the lamp farther and the ratio of center-to-edge light improves but the exposure will need to be increased. Conversely a closer lamp needs less exposure but will leave the corners of the image even more under-exposed. There is a tendency to think that more is better. That is not often the case here. Figure 2.27 on page 2.34 shows the consequences if one or multiple screens are PAGE 2 . 30

Stencils Figure 2.23 As you change the lamp distance (with a freestanding system) the required time of exposure changes.. The graph is based on a three minute standard at 100 percent distance. If you double the distance, multiply the exposure by four. Halve the distance and quarter the exposure.

Percent Distance Change

Time Change With Distance Change

250% 200% 150% 100% 50% 0% 1.5 1.6 1.8 2.0 2.2 2.4 2.7 3.0 3.3 3.7 4.1 4.5 5.0 5.6 6.2 Time in Minutes (Based on 3 min. @ 100% Distance)

exposed at one time. There is one real advantage to exposing more screens at once; the time for the vacuum drawing down is less, as a percentage of the total time. But even for a vacuum frame that would hold four Challenger frames, the vacuum draw-down time should be less than one minute.

Figure 2.24 This graph shows both the exposure time and lamp distance as a percentage.

Time and Distance Percentages

200% 150% 100% 50%

144%

136%

129%

123%

117%

111%

105%

100%

95%

90%

86%

81%

77%

73%

0% 70%

Percentage Time Change

250%

Percentage Distance Changes

PAGE 2 . 31

Chapter 2 Figure 2.25 Edge Light versus Time Adjust This graph will allow you to model the results of both time and resolution if you were to move the lamp distance to the screen.

Results of Changing the Lamp Distance

Less Than 1

120%

1000%

100%

800%

80%

600%

60%

400%

40%

200%

20% 0%

% Change in Time

% Edge - Center Light

Greater Than 1

0% 3.0 2.3 1.9 1.5 1.2 1.0 0.8 0.7 0.5 0.4 0.3

Ratio of Lamp Distance to Frame Diagonal

You will find two charts on page 2.34: one for Gauntlet screens and one for Challenger screens. Column One lists the number of standard-sized screens being exposed at a time. Column Two lists the overall size of those screens loaded with no space in between. Column Three is the preferred lamp distance, which is the same as the diagonal of the total frame size. Column Four lists a nominal exposure that can be used as a multiplier for your particular exposure time or units (see example immediately following). This number increases as the lamp distance increases. Column Five lists the percentage of light in the corner of the frame. In our example, it is always 70 percent since we placed the lamp at a distance equal to the diagonal of the frame. Column Six is the multiple-frame percentage of the single-frame time. By multiplying this number by your specific time for one frame you can easily select an optimum number of frames at a safe lamp distance. Example

After you have calibrated your exposure levels (refer to page 2.19) you have determined that the proper time is two minutes for a 23" x 31" Gauntlet screen, with a lamp PAGE 2 . 32

1. You must first establish proper exposure times for example 2 minutes. 2. You must be using a movable lamp. 3. It is based on a ratio of 1.0 where lamp distance equals frame diagonal. 4. This is a 100%, 2-minute exposure with 72% corner light. 5. Measure your ratio of frame diagonal to lamp distance. 6. Lets say it is one Challenger frame 44" diagonal. 7. At a lamp to glass distance of 53". 8. Your ratio is 1.20 (53 divided by 44). 9. Find the closest ratio on the horizontal axis of the graph. 10. Look upward from 1.20 on the horizontal axis to the series 1 curve. 11. This is the percentage of edge to center light or 80%. 12. Drop to the lower series 2 curve. 13. This is the percentage of exposure change or 160%. 14. 2 minutes times 160% equals 3.2 minutes or 3 min. 12 sec. 15. To improve edge lighting from 72% to 80% of the center, you will need to increase exposure from 2 minutes to 3.2 minutes for one Challenger frame.

Stencils distance at the frame’s diagonal dimension,or 38". If you were to load two frames of the same size, your exposure would be 209 percent of the 2 minutes or 4.18 minutes (4 min. 11 sec.) at a distance of 56 inches lamp-to-glass, the falloff would be identical to that with the single screen. Note that the per-frame exposure would be slightly longer but this would be offset by the vacuum draw-down time.

Exposing A Screen 1.

Use an integrated light source.

2.

Measure and standardize lamp-to-glass distance.

3.

Calibrate exposures for each set of mesh and coating specifics.

4.

Gauntlet Conclusion

a.

Measure and record EOM.

b.

Measure and record Rz.

c.

Measure and record stencil thickness.

d.

Use a calibration test film.

How To Instructions

Monitor each exposure.

Per Screen Exposure

As you can see from the table, a. 21-step gray scale. the lowest screen-exposure b. Transparent resolution guide. time is one frame per. But 5. Expose same meshes and coatings per exposure. when you consider vacuum draw-down time, the others 6. Adjust times, units and lamp placement based on developed scales. can become a bit more equitable (particularly if your blanket needs to be repaired or replaced). Given the capacity, two or four would be agreeable as long as the frames are not too close to the edge of the vacuum beading. Avoid the oddshaped three-frame configeration, as the per-screen time is prohibitive. Figure 2.26 When you expose multiples of screens with a freestanding lamp, you have the opportunity to move the lamp for higher productivity or higher quality, but the two directions are opposite. The graph shows that a multiple of three Gauntlet screens should be avoided for optimal results.

Gauntlet Per Screen Exposure 115 110 105 100 95 90 38

55

70

77

1

2

3

4

Distance / Number of Frames PAGE 2 . 33

Chapter 2 Gauntlet Screens

Overall Screen Dim.

Lamp Distance

Center Units (Based on 100%)

Corner Units

Exposure Per Frame

1 2 3 4

23 x 31 46 x 31 46 x 54 46 x 62

38 55 70 77

100% 209% 339% 412%

70% 70% 70% 70%

100 105 113 103

Figure 2.27 The table lists the data used for per screen exposure time in the graph above.

Challenger Conclusion

As is the case with Gauntlet screens, three screens should be avoided. Refer to the table and chart immediately above (figure 2.24 and 2.25) for the details on the Challenger screens. Two up is satisfactory and four is preferable if your vacuum frame capacity is sufficient. Be cautious not to get too close to the edge of the Challenger Per Screen Exposure Per Screen Exposure

Figure 2.28 With an exposure unit that will accommodate up to four screens, four Challenger screens would be the most productive quantity to shoot. Three would be the lowest productivity per screen to hold the same quality of center to edge lighting.

120 115 110 105 100 95 90 43

62

80

87

1

2

3

4

Distance / Number of Frames

vacuum blanket beading. Doing so will only stretch the components and cause leaks. The vacuum will take too long to draw-down resulting in no combination of screens that will expedite your screen exposure. Challenger Screens

Overall Screen Dim.

Lamp Distance

Center Units (Based on 100%)

Corner Units

Exposure Per Frame

1 2 3 4

23 x 31 46 x 31 46 x 54 46 x 62

38 55 70 77

100% 209% 339% 412%

70% 70% 70% 70%

100 105 113 103

Figure 2.29 The table lists the data used for per screen exposure time in the graph above.

PAGE 2 . 34

Stencils Developing The Stencil The process of developing (or washing out) the stencil receives little attention, but it can be a subtle cause of many imaging problems. The idea is to apply water to both sides of the stencil and allow the unexposed areas to act like a sponge and suck the water up. This leaves the coating very fragile and, with a light pressure, the softened areas dissolve and wash down the drain. For this to happen consistently may require some planning and preparation. Use a backlit sink for washout; to save remake time with those areas that you just can't see without illumination. A water-temperature mixer keeps the water at ± ½° F for consistent and reliable results. The temperature should be a consistent 125°. A power washer (not the force used for reclaiming) mixes air from your compressor with water to keep shrinkage to a minimum.

Developing The Stencil 1.

Use a backlighted sink.

2.

Use consistent 125° water temperature.

3.

Use an air/water mixing gun.

4.

With a high volume, low pressure mist:

5.

a.

Spray the impression side thoroughly.

b.

Spray the squeegee side thoroughly.

c.

Repeat in 30 seconds.

d.

Wait an additional 30 seconds.

How To Instructions

With firm pressure and lower volume; a.

Work from the squeegee side.

b.

Maintain a 6-8" distance from the screen.

c.

Move continually from top to bottom.

d.

Neither favor nor ignore gray scales and resolution targets.

e.

Gently spray impression-side only if needed.

6.

When complete, rinse with cold water.

7.

Vacuum excess water from squeegee side.

8.

Vacuum excess water from impression side.

9.

Inspect for any residual coating in image areas.

10. If found, reapply firm pressure to that area and continue as above. 11. Process multiples for effiency. 12. If you have difficulty, review the section on storage and screen room lighting

Most of the developing should be done from the squeegee side of the screen to protect the “shoulder” of the image on the impression side. PAGE 2 . 35

Chapter 2 S t encil Finishing Tips If Touch-up takes more than 60 seconds per screen: 1.

Record the number and times on a sheet of paper.

2.

Record the reason why (films, coating, exposure, etc).

3.

Set the screens aside for hourly inspection.

4.

Return the screens to the responsible party.

5.

Notify your supervisor.

To ease the usage, application, and removal of perimeter tape: 1.

Calibrate your press and use minimum squeegee pressure.

2.

Use a proper-sized coating trough.

3.

Thoroughly dry the screen prior to exposure; this permits complete and proper exposure.

4.

Thoroughly expose the screen, being sure to “cure” the emulsion on the squeegee side.

5.

Use permanent blockout on the perimeter.

6.

Use a quality tape intended for the job.

7.

Use a tape that strips clean (without residue) and quickly (without ripping).

PAGE 2 . 36

If you find you must resort to blasting the coating off of the screen, something is wrong. This is a particular problem if the emulsion is under-exposed (refer to page 2.24 for details). The screen may have been exposed to light or heat, or could just be too old to work well. In any case, blasting is not the best answer. Up Touch-U If you subscribe to the recommendations in this manual, you will have little need for screen touch-up (also known as spotting, filling, blocking, blocking out, pinholing and many other names). The purpose of touch-up is to seal the ink from accidently printing or seeping through and ruining garments. It is not intended to be a repair station for poor films or screen processing. The greatest reason for excessive touch-up is a stencil that is too thin. There are a variety of reasons that this might occur. First is that the coating applied was too thin (refer to page 2.14). Second that the screen was under-exposed (refer to page 2.33). Dust, dirt, static electric-charge, coarse mesh, thick threads, coaters that are too large, coaters that are damaged, and “bad” emulsion are all blamed for pinholes. Of course, all of these can be culprits, but are most often secondary to a thin and under-exposed coating. Since the purpose of touch-up is not that of a repair station for poor processing, there should be a go/no-go point as a standard for passing or rejecting screens that need “mummified.” That point is 60 seconds for Challenger and Gauntlet screens. If you cannot touch-up a screen in 60 seconds, something is wrong. If you average one screen in 60 seconds (hopefully and realistically less) then one person can touch-up over 400 in a shift. Work to make your touch-up process more of a final inspection step. If you concede that this is reasonable, then you will want to initiate one of the procedures outlined in the sidebar on page 2.34.

Stencils Taping the Perimeter The taping process has sadly evolved into a “mummification” process, and the reasons are only sort of legitimate. The press operators know from experience that the stencil will break down prematurely, so they use an abundance of tape to prevent leaks. It is affective but should not be necessary. First, the stencil must be properly coated, dried and exposed (refer to pages 2.14, 2.16 and 2.33 respectively). Such a stencil will not break down rapidly. Secondly, use a quality tape intended for the purpose. “Cheap” masking tape will cost you a fortune in leaks and time to strip it from the screen. A foot of quality tape costs a nominal 8¢, which is the cost of one minute of time for a $5-per-hour employee. But your press can earn you 8¢ per second (at 40¢ per shirt and a 60dozen-per-hour cycle rate). All breakdowns take more than a minute to fix and will ruin a few shirts in the process. The key to economy is to use the tape for the purpose it is intended. There should be no need to tape the whole screen and never to tape both sides of a production screen. If you think you are taping for “strength” you may be mistaken. The tape restricts the normal flexing of the screen and does nothing to stabilize tension. Next thing you know, you need more squeegee pressure to transfer the ink...check mate.

Tips To Ease R eclaiming To make reclamation as easy as possible: 1.

Supply hot water at the prescribed pressure and volume.

2.

Use the prescribed reclaiming chemistries.

3.

Thoroughly clean and dry screens before applying reclaimer.

4.

Avoid a coating trough that is too long.

5.

Avoid coating softened corners.

6.

Thoroughly dry screens prior to exposure.

7.

Thoroughly expose the coating.

8.

Avoid solvent based "screen openers" on press.

Reclaiming The Stencil This process often takes a variety of inks and chemistries and shoots them all over a room—no wonder it seems to be a messy job. Use the appropriate hand and eye protection for your safety. Since the primary focus of this manual—and the primary goal of a press—is to run efficiently without stopping, you may want to adopt the following procedures. It is easier to find unskilled labor than semi-skilled or skilled, and we assume that some of your most skilled operators are press operators and paid accordingly. If so, all you really want them spending their time on (workload permitting) is printing and the accompanying paperwork. Any distraction can be a PAGE 2 . 37

Chapter 2 How To Instructions

Reclaiming A Screen 1.

Remove residual ink.

2.

Remove tape and tape adhesive completely from the screen.

3.

Use a screen wash that is compatible with reclaiming chemistry.

4.

Mist reclaimer on both sides of the screen.

5.

Lay screen flat— impression aide up.

6.

Wait three to five minutes.

7.

Use hot water—140° plus.

8.

Use high volume water—two to four gallons per minute.

9.

Use high-pressure water—1200 psi at two to four gpm (gallons-per-minute).

10. Work from the squeegee side. 11. Sustain a four to five inch distance from wand-toscreen. 12. If you have difficulty, review the section on proper exposure (page 2.19). 13. If you have residual haze review the ink and washup sections.

costly error in labor utilization. So it is our recommendation that the press operators do not shut the press down to clean screens, ink and blades: but they should be cleaned immediately and thoroughly before sent to reclamation. Once the screen is thoroughly cleaned with commercially available cleaners, which rinse fasr and completely, it should be allowed to dry. When dry, reclaiming chemistry should be applied to both sides and allowed to penetrate the stencil before proceeding. Since there is a waiting period of a few minutes, you may want to spray several screens at once and allow the chemistry to do its work while you are reclaiming the previous batch. (Note adding reclaimer to wet screens only dilutes its effectiveness—particularly one that is wet with screen wash).

The water temperature used to reclaim screens should be hot—150ºand flow at a nominal 2-4 gallons per minute. You will want to be sure your hot water supply can deliver this quantity of water. Take the number of screens per day and multiply that by the time per screen. Then presume that you may want to do them without stopping. For example, 50 screens per day at our recommended three minutes per screen equals 150° minutes at 2-4 gallons per minute of intermittent water at 150° F or hotter. The initial pressure of the power washer is best suited around 3000 psi and derated by changing the orifice to output 2-4 gallons per minute at or near 1200 psi. High-pressure air does not remove the stencil, high-pressure water does. PAGE 2 . 38

Stencils Many of the “bargain” pressure washers claim high-pressure but don't output much water. The active ingredient in reclaiming chemistry is sodium metaperiodate. It is normally used at 3 percent concentration (higher concentrations come out of solution readily and the SmP falls to the bottom of the pail). It is available in liquid or crystal form. If you are mixing your own to save dollars, be sure that such is really the case. Over—or under—use of the crystals could cost you far more in raw materials or conversion. For standard-sized Challenger and Gauntlet screens, you will want to allow 2-3 minutes per screen—if the conditions here are followed, that number is very attainable. (Note that it will require less time if you have used a permanent blockout on the perimeter of your screens (refer to page 2.13 for details). If you find you cannot attain this rate and you have the proper chemistry, water pressure and flow rate, read pages 2.37 through 2.38 on screen exposure. It may be that you are crosslinking the coating on press due to under-exposure. For comparison, test-reclaim a screen that has not been used on press and see if it is marginally easier.

Minimizing The Need F or Haze R emo v er 1.

Calibrate the press for minimal mesh abrasion.

2.

Sufficiently tension screens to reduce abrasion.

3.

Minimize squeegee pressure.

4.

Ensure thorough exposure.

5.

Use adequate pressure and water flow for reclaiming.

6.

Use a proper wash-up chemistry applied as directed.

7.

Clean the screens immediately after use.

Haze Remover It is often necessary to remove ink haze that should have been removed in the wash-up phase prior to reclamation (refer to page 2.40 for the details). Poor housekeeping habits in this area will cost you money. The distinct disadvantage in the use of haze remover is that it shortens the life of the screen mesh. Continued and repetitive exposure to caustics will cause enough erosion that the fabric will rip or burst prematurely. And the cost of this is extreme if it rips on press. If you can't seem to get rid of the ink haze, consider the color ink with which you are having a problem. Ink haze is a result of the inability of your wash-up to disolve the vehicle in the ink. Specifically, blues and blacks are the most notorious colors for plastisol haze. The reason—these pigment particles are PAGE 2 . 39

Chapter 2 lightweight and high in oil absorption. These properties cause the ink manufacturer to use different (polymeric) plasticizers, which are insoluble in many conventional wash-ups. Second, the dye in some of the very bright red inks, which origniallyattached to the pigment, leaves the pigment during printing and becomes attached to the mesh. The stain caused by this process may not restrict particle passage, but certainly will effect exposure time in the affected areas. Finally, is the example of white inks, which use polymeric plasticizers, however the particle size is infinitely smaller. The problem— it invades all the nooks and crannies of the mesh; resulting in the worst of all three types of ink haze. If you have haze—no matter what you have tried—get your screen chemistry and to ink supplier and ask them to find an equitable solution.

Real-World Results While it is difficult to provide exact specification for your shop (due to the variance in equipment, products, etc.), we furnish a starting point through real-word examples offered as a guideline. Our tests were conducted at Kiwo’s laboratory. They provided lab personnel and the specified emulsion. Dynamesh provided the specified screen mesh. Screens and stencils were prepare to our specifications, measurements taken on all typical parameters of the stencil—the results can be found in figure 2.30. This test gives you actual case studies, so that you can gauge the performance of your stencils. Nothing was done to force the results; no tricks or unusual techniques were used. These stencils are just as you might process in your plant. Screens Prepared Test-S Column One lists the nominal mesh count in inches. Column Two the thread diameter in microns. Column Three lists the initial tension in Newton's per square centimeter. Column Four is the method of coating used. For example if it reads: “2 imp-3 sqg.-Dry-1 imp”, the screen was coated two passes on its impresMC

TD

N/cm²

Method

Edge

Type

Dry

Moisture

Rz

EOM

80S 150S 230S 305T

71m 45m 40m 35m

25 23 25 24

1 Imp. - 1 Sqg. 1 Imp. - 1 Sqg. 2 Imp. - 1 Sqg. 2 Imp. - 2 Sqg. Dry - 1 Imp.

Rnd. Rnd. Rnd. Rnd. Sharp

Dual Dual Dual Dual

1.0 1.0 0.5 0.3

< 4% < 4% < 4% < 4%

16.2 9.5 10.4 8.3

25.0 14.2 6.6 5.8

Figure 2.30 The table shows the real-world results of our four test screens, coated, exposed, dried and developed. Although your screens, methods and results may vary, the data serves as a guideline for your stencil methods. PAGE 2 . 40

Stencils sion side, turned and given three passes on the squeegee side, dried and given one more passes on the impression side. Column Five is the edge of the coater— round or sharp. Column Six is the type of emulsion used. Column Seven is the time it was given to dry in decimal hours. That is, 0.5 hours is equal to thirty minutes. Column Eight is the moisture content as a percentage after the given dry time. Column Nine is the Rz flatness of the stencil. And Column Ten is the emulsion over mesh. These two were measured after the stated exposure time. Figure 2.31 shows the results of the exposure test on the four test-screens. Column One gives the mesh count in inches. Column Two is the thread diameter in microns. Column Three is the type of lamp used including the wattage. For MC

TD

Lamp

Distance

Units

Time

g/in²

Step

Pos. Res.

Neg. Res.

80S 150S 230S 305T

71m 45m 40m 35m

8kW 8kW 8kW 8kW

50” 50” 50” 50”

150 75 55 45

150 sec. 75 sec. 55 sec. 45 sec.

0.2 0.2 0.1 0.1

6 5 8 8

8.5 3.5 3.0 2.5

8.0 3.0 2.5 2.0

Figure 2.31 This table shows our test screens and in grams per square inch the amount of coating that was applied and then the resulting EOM and Rz for this application.

example a 5kW MH is a 5000-watt metal halide lamp. Column Four is the distance from the lamp to the vacuum frame glass during exposure. Column Five is the exposure units. Column Six is the exposure time. Column Seven is the weight of one square inch of coated mesh (the weight of the mesh is not included in this number). This will allow you to compute the cost of the product coated to this level. Column Eight is the step on a 21 step transparent gray scale. Column Nine and Ten are the positive and negative resolution in mils. The Cost Of The Coating The table shown in figure 2.32 gives the weight of the mesh alone on the four Mesh Count

Fabric g/in²

1 Coat g/in²

Pct. Gain

1+1 g/in²

Pct. Gain

1+2 g/in²

Pct. Gain

1+3 g/in²

Pct. Gain

80 S 150 S 230 S 305 T

4.0 g 4.0 g 4.1 g 4.0 g

.14 .09 .06 .04

3.5% 2.2% 1.4% 1.0%

.25 .16 .09 .06

6.2% 4.0% 2.1% 1.5%

.35 .23 .12 .08

7.9% 5.7% 2.9% 2.0%

.45 .29 .15 .10

9.9% 7.2% 3.6% 2.5%

Figure 2.32 The table shows the resulting weight of coating applied for single and multiple coats of emulsion on our four test screens.

PAGE 2 . 41

Chapter 2 test screens. We then applied several coats of emulsion, weighed the mesh after each coating was dried and recorded the increase in weight (coating only weight). The coating used has 50-percent-solids and so the dried coating is approximately half of the wet coating. Column One lists the four test screen mesh counts. Column Two lists the weight of the mesh in grams per-square-inch. Column Three is the beginning of the application of the coats, one pass only and lists the weight of that coating. Column Four lists the weight in Column Three as a percentage. Column Five lists the results of 1-plus-1-coats and so on, up to and including 1-plus-3-coats. Highlights from the table are plotted in figure 2.33 . Specifically, an 80S mesh weighs 4.0 grams per-square-inch uncoated. If you apply one pass with a round-edge coater, you are adding 0.14 grams per-squareinch. This is equal to a 3.5 percent increase over the weight of the mesh. Look at the end of the row with 1-plus-3-coats of emulsion on the uncoated screen. An addition of 0.45 grams of emulsion per-square-inch is the result, which equates to a 9.9 percent increase over the uncoated mesh. Screens Per Gallon 250

Number of Screens

200 150

80S 150S 230S 305S

100 50 0 1

1+1

1+2

1+3

Coating Method Figure 2.31 The graph shows the number of our four test screens that can be expected from the four coating methods used. Of course the single coat would yield the most screens but only at the sacrifice of resolution and press performance. PAGE 2 . 42

Stencils This data should not be construed as a limit for the number of coating you apply to your screens. That decision should be based on resolution and press performance. It is intended to help you see the results of multiple coats of emulsion applied to a given mesh count. Mesh Count

Fabric g/in²

1 Coat g/in²

Pct. Gain

1+1 g/in²

Pct. Gain

1+2 g/in²

Pct. Gain

1+3 g/in²

Pct. Gain

80 S 150 S 230 S 305 T

4.0 g 4.0 g 4.1 g 4.0 g

.14 .09 .06 .04

3.5% 2.2% 1.4% 1.0%

.25 .16 .09 .06

6.2% 4.0% 2.1% 1.5%

.35 .23 .12 .08

7.9% 5.7% 2.9% 2.0%

.45 .29 .15 .10

9.9% 7.2% 3.6% 2.5%

Figure 2.32 A 26" x 35" OD Challenger screen has a nominal coated area of 17" x 24" or approximately 400 square inches, coated with a round-edge coater, at 50 percent solids.

The table shown as figure 2.32 is an extension of the data in figure 2.30. It uses the same four screen meshes and lists incremental amounts of coating weight to each of the screens. It then estimates the number of screens that could be coated in that manner from a gallon of 50% solids emulsion.

Screen Coating Estimator 250 200 Quantity of 150 Screens 100

1 1+1 1+2 1+3

50 0 80 S

150 S

230 S

305 T

Screen Mesh Counts Figure 2.33 The Screen Coating Estimator allows you to gauge the number of screens that you can get from a US gallon of emulsion for our four test screens under the coating methods described herein.

Specifically, 305 T mesh, prepared with 1-plus-2 coats would have a coating weight of 0.35 grams per-square-inch. Such a coating weight would allow you to coat a 17" x 24" area of mesh for a yield of 108 screens-per-gallon. PAGE 2 . 43

Chapter 2 Benef its Of Pr oper Coating Thic kness 1.

Fewer pinholes—stecil bridging is improved by the thicker coating

2.

Longer press life—stencil elatisity is maintained and the thicker stencil is more resistent to squeege abrasion.

3.

Sharper printing at higher resolution is assured because along with proper EOM, comes an improved stencil flatness.

4.

Less downtime due to blurring and dot gain because the stencil “gasket” acts as a barrier to the ink filling nonimage areas.

If you alter the conditions, obviously you will change the resulting estimate of screens-per-gallon. A sharper blade, more passes, intermittent drying, a coarser mesh-count than specified, a larger coated area or a thicker thread diameter will all consume more coating. To calculate a 21" x 31" OD Gauntlet screen with an nominal coated area of 15" x 22", or approximately 330 square inches, coated as in figure 2.32, multiply the number of Challenger screens (listed in the same table) by 1.21—the result is the total number of Gauntlet screens that can be coated with a gallon of emulsion. So you would get 107, 305 T screens from a gallon coated 1-plus-3 wet-on-wet coats as applied in the table. To estimate a cost-per-screen take the number of screens and divide it by the cost-per-gallon. For example, if you coat 88305T screens with a 1-plus-3 method, as described in figure 2.32, and your cost is $75 per-gallon, your cost per -creen is approximately 85 cents. At a glance you can see that your screen cost goes up, if you put additional coats of emulsion on the screens—hardly a surprise. But you must realize that with the additional coats, there is a return on your investment. If for no other reason then press downtime, you should use the additional coats, they are a bargain regardless of your image. Refer to page 2.13 for Rz and EOM results and use these to monitor your progress.

PAGE 2 . 44

I. Ink Properties Optical Rheological Thermal II. Troubleshooting Ink Tack Build-U Up Adhesion And Surface Energy Fusion Testing Dyer Temperature Testing III. Ink Mileage

Chapter

3 INKS

Inks Ink Properties The purpose of this section is to help establish a common language between the ink compounder and the printer. These are properties that the ink maker can identify and assign a repeatable range. For the informed printer it allows a fast comparison of a variety of inks with a minimal amount of testing. We are in an industry with no standards and this is slowing our evolution. The printer cannot count on the ink printing the same time after time and is rarely sure if the ink is at fault or if the cause is the balance of the print process. Such is our world without standards. For all other applications, the plastisol manufacturers offer a Certificate of Analysis that describes any normal or special variance of the product that has been purchased. Ironically none of these alternate processes is more complex or more variable than screen printing. Ask your vendor if you are a large enough account to warrant a CofA with your ink. There are a variety of problems with some ink currently on the market. Far too often, these are “remedied” by an adjustment on the press. If the press ran slow, M&R would expect that you would call and we would do something about the problem. If the ink is forcing you to run slow, realize that ink solutions from the press may be costing you productivity and quality. The point is that what you don’t know about your ink may hurt you. If in fact the ink is problematic, the best solution is to fix the ink not to use the press, mesh, Ink Problem

Build-up After flash tack Low opacity Screen hang-up Blade hang-up Over plasticized Excess tack Thermal sensitivity Dilatent white High viscosity Poor grind

Press Compensation

Record Lost Dozens per Hour

Flash cure Cooling station or fans Double stroke, second screen Higher off-contact Lower angles, wider gap Longer flash time Higher off-contact, tension Periodic cooling breaks Slower blade speed Higher blade pressure Periodic cleaning breaks

Figure 3.1 Use the table above to record the number of dozens per hour you lose, due to the “press fix” used to compensate for ink problems. This will give you a more concrete idea of what problem ink costs you in downtime and leverage to discuss the issue with your ink manufacture. PAGE 3 . 3

Chapter 3 stencil or anything else. The problem is, you may not always know if the ink meets your specifications-you may be laboring with art, screens, stencils, press, flash or dryer to solve a problem caused solely by the ink. For our test purposes we used white ink manufactured byHaden-Horne Ink, as white is familiar to all readers and by far the most commonly used “color”. Each of the manufacturers in the market place has a “boatload” of whites and some of the companies are hard pressed to tell you which to use. Once you understand the available data on each of the whites and get comparable data from your supplier, it is simple to determine why and where you should select a white or any other color. Not all manufacturers perform all listed tests, nor do they encourage publishing the results. All of these facets of ink performance can be listed on a Certificate of Analysis. The properties listed below are offered as a starting point in your search and are divided into four categories: optical, rheological, thermal and physical. Optical The optical properties of the white are very important, as it is the color most often used as an underbase. As such it may have a strong affect on the overprinted colors, particularly if they are transparent. Further, the aesthetics of a white are critical- it must not look dirty or yellowed. Following are the standard specifications for white plastisol ink.

L*

a*

B*

92.04

-2.81

-2.65

H-Cote 9000 Optical Specifications Delta Peak Gloss Opacity E Spectral Pctg. Per Mil