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Print on Synthetics

(December 1999) posted on Sun Dec 19, 1999

Make your job stick

By Mark Goodridge

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Back in the dawn of textile screen printing (the '70s), a customer once asked me, "Can you print on nylon jackets?" In a moment of thoughtlessness I replied, "Sure." Months later, after thousands of dollars worth of wasted labor, supplies, and jackets, I realized that my procedure for printing on knit cotton wasn't going to work on nylon. But through trial and error, I eventually learned how to modify the ink, press setup, and printing procedures to achieve an acceptable print. This was my introduction to the wonderful world of printing on synthetic fabrics.

Synthetic fabrics are knit or woven textiles with yarns made from chemical compounds with names that often begin with "poly." These fabrics bear little resemblance to the jersey-knit cotton T-shirts and fleece goods so prevalent in our industry. Synthetic fabrics are typically very sensitive to heat and the source of serious dye-migration or dye-sublimation problems. Additionally, they have smooth, tight surfaces that offer little texture for ink adhesion. To make matters worse, synthetic fabrics are often found in very expensive customer-supplied garments.

For a shop accustomed to printing cotton T-shirts, the changes required to print onto dazzle cloth, Supplex, Lycra, nylon mesh, or other unfamiliar fabrics can come as a shock. Standard inks and production procedures won't get the job done. So when the customer asks you to print onto a fabric that you've never printed before, where do you begin?

Start with the fabric

Before printing on an unfamiliar fabric, find out exactly what it is. Ideally, fabric information will appear on the neck tag, or the customer will provide it for you (or at least name the garment distributor or manufacturer). More likely, however, is that you'll have to determine fabric characteristics yourself. Here are the areas to consider:

Fabric construction Determine if the fabric is knit or woven by inspecting it with an 8-10x magnifying glass. Most synthetic fabrics are woven, meaning that threads cross each other at right angles in a tic-tac-toe pattern (Figure 1A). Knit fabrics, such as traditional cotton T-shirts, have threads that loop around each other (Figure 1B). In general, plastisols adhere to knit fabrics better than woven because they penetrate the knit more effectively.

Using the magnifying glass, also note the construction of the fabric's yarn. If the yarn is a bundle of long, smooth fibers and the weave is tight, then ink adhesion is likely to be a problem. Conversely, if the threads are fuzzy and the fabric has an uneven surface with lots of open areas between threads, plastisols will penetrate and adhere well.

Finally, check to see if the fabric is a composite of different material layers laminated together. Alternately, the garment may be constructed with panels of different materials (Figure 2). When printing onto either type of composite material, your problems may multiply because you must evaluate the elasticity, heat sensitivity, and other attributes of more than one fabric.

Fabric elasticity Test the elasticity of the fabric by stretching a sample in the same direction as the grain, across the grain, and on the bias (diagonal to the grain). Compare the stretch of the unknown fabric with the stretch of a piece of jersey-knit T-shirt material. The more the fabric stretches, the more likely the ink film will crack and separate from the fabric when the garment is worn.

Fabrics that stretch more than T-shirt material will usually require a highly elastic ink that has been specifically designed to stretch with the fabric. Fabrics that stretch the same amount or less than T-shirt material will not require an especially elastic ink.

Several specialty water-based inks provide enough elasticity after curing to keep up with all but the most elastic fabrics. Some plastisol inks are also designed for printing on elastic materials, and ink additives are available to increase the elasticity of standard plastisols.

Often, printing a thick layer of plastisol onto the fabric can control fabric elasticity. When properly cured, the ink film is strong enough to limit fabric stretch to the maximum stretchability of the ink itself. However, on athletic garments where both extreme stretchability and breathability are important, this solution may not be acceptable.

Fabric coating Check for waterproof coatings by placing a swatch of the fabric over a cup and pushing the fabric down to form a small pocket. Pour a few teaspoons of water into the pocket and observe how long it takes for the water to wet and penetrate the fabric. The time required can range from a few seconds to many hours. The slower the fabric absorbs water, the more likely that the fabric has a coating that resists ink adhesion.

Heat resistance Nylon is not the only fabric that shrinks significantly when heated. Run a swatch of any synthetic fabric through the dryer and note if it shrinks, deforms, or melts under normal curing temperatures. Find out if the fabric is damaged by heat before production. If heat damage does occur, use plastisols formulated for lower temperature curing, or water- or solvent-based inks that cure at room temperature.

Ink selection

When printing onto synthetics, you must learn to select the correct ink from among a bewildering variety of plastisol, water-based, sublimation, and solvent-based inks. You'll also need the skill to make accurate, repeatable ink modifications.

Plastisol inks Familiarize yourself with plastisol inks that feature low curing temperatures and above-average adhesion and elongation capabilities. Test a variety of low-bleed white and yellow plastisols, because inks that resist bleeding on one fabric will not necessarily do so on all fabrics. Also, stock plastisol ink additives such as viscosity modifiers (thinners and thickeners), adhesion-promoting additives, and additives that reduce the cure temperature of the ink.

Adhesion-promoting additives Although some plastisol inks are designed to adhere to nylon fabrics without the use of adhesion promoters, they will not adhere to all synthetic fabrics--not even all nylons. The only way to be sure of ink adhesion is to test various fabric/ink combinations.

In cases where adhesion is questionable, using an adhesion promoter is a form of cheap insurance. But if such additives are used improperly, you might do more harm than good. Using too little additive can lead to inks that don't adhere well, and too much can reduce the ink's viscosity so that it loses opacity and is difficult to print.

Typically, adhesion-promoting additives are mixed with plastisols at 10-15% by weight. Use more additive when printing onto nylon with heavy water- or stain-resistant coatings or when using a high-opacity ink, but never exceed 15%. If you don't have an ink scale, measure the additive by volume, using one part additive to five parts standard-opacity plastisol ink. When mixing with high-opacity inks, add one part additive to four parts ink.

It takes up to 72 hours after printing and drying for adhesion promoters to fully react with the ink. So if the print is tested for adhesion immediately after curing or even a day later, the results may be disappointing. Don't despair. Simply wait for the full three-day cure period to elapse, then check adhesion--and make sure customers are aware of the cure period as well.

Water-based inks Synthetic fabric printing is no place for printers with a phobia about water-based inks. Contrary to what you may have been told, water-based inks are not more difficult to use than plastisols, just different.

Water-based inks provide lower cure temperatures (many even cure at room temperature), better adhesion, and much better elasticity than any plastisol. Sublimation transfers, which are made with water-based screen-printing inks (as well as inks and toners on several types of digital-imaging systems), are the preferred method of decorating white polyester and some other synthetic fabrics.

Remember that water-based screen-printing inks have different emulsion, mesh, and printing requirements. Learn how to use them properly, and stock a supply of the inks before you have to print a rush job on customer-supplied synthetic garments.

Solvent-based inks They're somewhat rare, but a few solvent-based inks are intended for textile printing. These inks have special features that make them useful in a plastisol-dominated industry. Some are resistant to laundry and dry-cleaning chemicals; others dry quickly at room temperature or adhere well to difficult fabrics. For some materials in certain production situations, solvent-based inks are the best solution.

Special production requirements

Synthetic fabrics usually require special production procedures, including attachments or modifications to the press (e.g., jacket hold-downs and special platens), special printing procedures (e.g., coating the surface of the platen with paper), and regular production checks. If the best ink for a fabric is water-based, your screen department will have to learn how to make water-resistant screens.

Above all else, you must be able to set drying and curing temperatures exactly and consistently throughout a production run and from job to job. Complete and accurate production records are invaluable for this type of printing.

The following list contains an assortment of synthetic fabrics with specific job setup and printing suggestions unique to each. Because of the enormous diversity of fabrics available to your customers, the procedures outlined here must be carefully tested in your plant before you use them in production.

• Acrylic fleece Acrylic fleece is uncommonly heat sensitive and can shrink as much as 12% when heated. As the fabric temperature increases, the material becomes limp, and, if handled while hot, can be stretched permanently out of shape.

When printing acrylic fleece, use a water-based ink with a cross-linking additive to enhance low-temperature curing. If you print with plastisol inks, select one with a low fusing temperature. Print a thin ink layer by using high mesh count and high-tension screens. Use the lowest possible flash and curing temperatures. Control or prevent heat buildup by using cool-down stations on the press and by placing fans near the flash-curing unit and at the unloading end of the dryer.

Dye migration is possible with acrylic fleece, but not common. Choke the underbase and adjust the artwork to allow for fabric shrinkage. If possible, avoid using designs with large solid areas.

• CoolMax CoolMax, a lightweight fabric used in cycling and running wear, consists of fibers that wick perspiration away from the body and provide a cooling effect through rapid evaporation of the moisture. Plastisols are not recommended for use on CoolMax since the ink would at least partially block this evaporation process.

CoolMax is generally white, so you should consider decorating the fabric with sublimation transfers, which won't affect the hand or moisture absorbency of the fabric. As mentioned previously, the transfers can be either screen printed or digitally imaged. Apply the image to the garment with a heat-transfer press, making sure the heat required to transfer the image won't harm the fabric--CoolMax has a melting point of 493°F (256°C). For direct printing, use a soft-hand water-based ink.

• Dazzle cloth Dazzle cloth is an athletic fabric made from either polyester or nylon (Figure 3). The polyester variety is one of the worst fabrics known for bleeding (caused by dye migration and sublimation). Use low-bleed plastisols, and test the ink you plan to use by printing a sample of the material before you start production. Bleeding may not appear for up to a week or more after printing, so beware.

If it seems that bleeding will occur, test several low-bleed white plastisols for use in underbasing, then select the ink that produces the best results. Control flash and cure temperatures carefully because both over- and undercuring will increase bleeding. In some situations, bleeding may not be entirely preventable.

On nylon dazzle cloth, ink adhesion may be a problem if the plastisol doesn't penetrate the fabric adequately. To minimize this concern, add about 10% (by weight) of an adhesion-promoting additive to the ink prior to printing.

• Gore-Tex Gore-Tex is a durable, waterproof fabric that provides protection from wind and rain but remains "breathable," allowing perspiration to escape. Gore-Tex is laminated to a carrier fabric such as cotton or polyester, and the resulting product is frequently used to produce cold-weather gear.

The biggest concern when printing Gore-Tex is that the ink may not stick to the fabric. The best printing method to use depends on the amount of waterproofing on the fabric and the type of carrier fabric to which the Gore-Tex has been laminated. In all cases, use plastisol inks with better-than-average adhesion. Adding 10-15% adhesion-promoting additive by weight is also recommended. Again, make some test prints before starting a production run.

• Lycra/spandex The fiber is spandex, the fabric is Lycra (Figure 4), and DuPont invented it. Lycra, which is often used in swimsuits, running singlets, and cycling shorts, can stretch up to five times its relaxed length and conforms well to the body during vigorous athletic activities. The material shrinks when heated.

Although special elastic plastisols are available, the two best options for decorating this fabric are sublimation transfers (on white fabric) and highly elastic water-based inks made specifically for Lycra. When using plastisols, note that if the ink layer is thin enough to stretch well, it will still crack when the fabric is stretched. If it's printed thick to resist cracking, it will restrict the stretchability of the fabric.

• Nylon fabric Nylon is used to make flags, banners, windsocks, and jacket shells. Nylon fabric ranges in weight from 80 denier or taffeta to 1000 denier. Heavy nylon is used for durability in items such as luggage, while the lighter fabrics are typically used in garments. Finishes range from smooth to rough and from shiny to dull.

Printing nylon is easy if you follow a few basic procedures. Although most plastisols will work on nylon jackets, the combination of smooth yarns, tight weave, and water- and stain-resistant coatings makes it impossible to achieve good adhesion between the ink and the fabric unless an adhesion-promoting compound is added to the ink.

The most common screen mesh used in nylon printing is approximately 160 threads/in., but you can use as high as a 230-threads/in. mesh, depending upon the design, weight of the fabric, and color. As a general rule, higher mesh counts should be reserved for the lighter weight nylons and dark-colored inks. Lower mesh counts should be used for heavier fabrics and lighter colored inks.

One advantage of printing onto nylon is that the ink stays completely on top of the fabric; therefore, it is usually not necessary to underbase prints on dark backgrounds. Even white ink will cover nicely with one pass onto dark nylon.

The biggest drawback to nylon is that every color must be flashed. Because the ink lays on top of the fabric, any subsequent screens will ruin the previous printed color if it is not flashed. Nylon shrinks when flashed, so if you print multiple colors, you'll need to preshrink the fabric just before printing. But do not shrink the fabric one day and print onto it the next--the fabric will re-elongate overnight, and you will have to repeat the process.

Flashing nylon can be difficult. If the fabric is adhered directly to the platen, it's easy to overheat the nylon, and the fabric won't always shrink evenly. However, nylon jackets typically flash fast because the lining under the nylon absorbs the heat, which prevents it from building up on the fabric, and allows the nylon to move slightly as it shrinks.

You can accomplish the same trick with nylon panels by building up your platens with a layer of scrap fleece. The fleece will absorb, then dissipate the heat, and allow the shrinking nylon panel to move ever so slightly. Spray-tack the fleece on top of platen paper for easy removal when you're done.

• Nylon mesh Nylon mesh (e.g., micro mesh and porthole mesh) is often used in football jerseys and other sports uniforms that will experience rough use. Adhesion-promoting additives are not necessary for nylon mesh because its coarse texture provides an excellent surface on which the ink can adhere.

The wide, open knit in nylon mesh garments is a plus and a minus. It's an advantage for ink adhesion, but a disadvantage during printing because the open mesh allows ink to penetrate through the fabric and onto the platen. For nylon mesh, use a heavy deposit of properly cured plastisol printed with enough squeegee pressure to drive the ink deep into the fabric. Nylon mesh shrinks when heated (like nylon jacket shells), and this must be taken into account during both the design and printing stages.

You can print two ways onto nylon mesh jerseys: print to fill the holes with ink or print to leave the holes open. To fill the holes, use a low mesh count (60-83 threads/in.) and flash the print after each color, including the last color. This last flash will help bond the ink across the holes when you pull the fabric off of the platen. For open holes, use a higher mesh count (110-125 threads/in.) and don't flash after the last color. Remember to use minimal pressure because if you lay down too much ink, you will push it through to the platen and may smear it on the next shirt you put down.

If you have difficulty controlling squeegee pressure to get good prints without printing through to the platen, spray a light mist of adhesive on the platen, then place a sheet of newsprint or transfer paper over it. Next, spray a light mist of adhesive on the paper. Slip the garment onto the platen and print. Then carefully remove the garment from the platen and place it on the dryer belt. Strip the piece of paper off the platen and start your next print cycle.

• Polyester mesh Polyester mesh is similar to nylon mesh but less durable and less expensive. It is sometimes used in place of nylon in souvenir and replica athletic uniforms. As with other polyester fabrics, bleeding may be a problem. Print as you would onto nylon mesh, but test for dye sublimation and migration before starting production.

• Synthetic fleece The three major types of synthetic fleece are Microfleece, Polarfleece, and Berber. Microfleece is a lightweight version of Polarfleece. Berber has a more irregular surface. All three types of fabric are breathable, have a short pile, and wick moisture well. But they have a few key differences, too.

Printing onto these fabrics presents some of the same problems you would encounter when printing on the napped side of ordinary fleece or thick terry cloth. Since the fabric is thick, spongy, and soft, it is not appropriate for printing fine details. Water-based inks are your best choice for printing onto these fabrics because they will not damage the hand, breathability, and moisture-absorbing qualities. Use mesh counts between 110-175 threads/in.

Spray adhesives may not be effective, but if you use one, use a web spray rather than a mist spray. If the spray adhesive does not work, use a jacket hold-down device. Print with a 65-70 durometer squeegee. You may want to print an underbase layer to stabilize the fabric. It's likely that you will have to flash after every screen because the soft surface has a tendency to smear the ink.

• Supplex Supplex is a durable, wind-resistant, water-repellent nylon fabric with a supple hand. It has some elasticity, but not as much as Lycra, and is used primarily in jackets and running shorts. For best results, use a flexible and elastic plastisol ink that covers well with a thin layer to promote faster curing. Test to determine if an adhesion-promoting additive needs to be mixed with the ink. Proper dryer calibration is especially necessary with Supplex because the melting point is 375°F (190°C).

Final thoughts

Your customers generally know very little about the limitations of textile screen printing. They often assume that you can print on any garment or anything else made of cloth. Unfortunately, few shops are willing to tell customers differently.

As a result, it's common to end up with customer-supplied garments made from unknown synthetic fabrics. Without information about fabric type or sample swatches to test, your ability to print the job successfully is purely a matter of chance. Since the cost of replacing just one garment may be higher then the total profit on the job, you should probably just say "No" to such orders.

But if you want to say "Yes" and improve your success with synthetic fabrics, you need to become familiar with the materials and their effects on ink selection, printing, curing, and more. Specifically, you need to master the following areas:

• Learn to identify synthetic fabrics and the characteristics that affect their printability.

• Break out of the "plastisol-ink-through-a-110-mesh-cured-at-320-degrees" rut.

• Learn how to use plastisol additives, water-based inks, solvent-based inks, and sublimation transfers, then select the right option for each fabric that you print.

• Learn how to test for bleeding before you print a job.

• Make sure your dryer provides accurate, repeatable temperature and belt-speed settings, and learn how to maintain a variety of drying conditions for different fabric/ink combinations.

• Commit to testing fabric elasticity and other characteristics, as well as different ink/fabric combinations for adhesion. And test various production procedures to see which yields the highest print quality at the lowest practical expense.

The cost of overlooking these concerns can be enormous. Remember, you're printing on garments worth $25-50 each, and one blown job can set you back thousands of dollars. On the other hand, if you master the techniques required for printing onto synthetics, you can develop a profitable market niche, one with higher-than- average markups and lower-than-average competition. The author thanks the following personnel from Union Ink Co. for their contributions to this article: Joe Catizone, vice president sales and marketing; Sue Goodridge, technical support supervisor; Mike Llerandi, former export sales manager; Jeff Proctor, regional sales manager; Claude Rainford, ink chemist; Mike Ukena, regional sales manager, and Charlie Leach, president of the Pavonine Products division.

About the author

Mark Goodridge has worked in the screen-printing industry for 20 years. He formerly co-owned and operated a screen-printing company in Coopers Mills, ME, and from 1992-95, he worked as editor of Screenplay magazine. He is currently the marketing manager for Union Ink Co., Inc. in Ridgefield, NJ.


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