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Conquering the everlasting-hemophilic, Teflon-coated, bungee cord

Printing Performance Fabrics

Joe Clarke has spent the past 47 years in the lab and in the engineering department, in pre-press and on-press, as an R&D / technical researcher and as a manager of screen print production. Clarke has held executive positions as President of M&R Printing Equipment and as Vice-President at Wilflex [Poly One]. He has been granted a growing number of print-related patents, including one for High-Shear printing with Smilin'Jack - he is a member of the ASDPT, is an Associate Editor for NBM and an SGIA Fellow.

Clarke has presented hundreds of technical papers, written a couple books and published over 600 technical / management articles for which he has been awarded five Swormstedts; the international standard for excellence in technical writing.

Currently Joe Clarke is the President of CPR, a Chicago-based corporation which manufactures Synergy Inks including NexGen; environmentally & financially responsible T-Shirt inks. For more information on CPR, visit http://www.cprknowsjack.com/.

Performance fabrics have introduced a whole new level of perspiration management to all types of athletes… and to anyone brazen enough to try and decorate them. The wearer cares about the macro—how these garments make them look to the spectators and how they feel when they are worn. But, as decorators, we’re forced to consider the micro—how much surface area they offer, how elastic they are, whether they will bleed and how many games they will last. The macro-view of our micro-analysis means we are about to print “the everlasting-hemophilic, Teflon-coated, bungee cord,” also known as performance or athletic wear.

The devil is in the details

The most important parameter of a performance plastisol is contained in this truth: If the ink falls off, it’s even worse than if it look bad. Ergo, elongation must be the most critical property. If the ink doesn’t stretch, the aesthetic value will degrade, and the ink is very likely to crack easily and pop off the fabric after sufficient washing and wearing. But let’s go through the whole list of parameters—from the ink maker to your shop floor.

Elongation—To elongate the ink (make the ink stretch), it must have sufficient plasticizer to stretch in one direction. However, never add plasticizer or “curable-reducer” without the explicit and precise guidance of the manufacturer. In order to stretch without cracking, the ink deposit must be sufficiently thick and completely cured. 

Specifications on the elongation of the ink and the garment are available from the respective manufacturers. If the stretch of the garment exceeds the elongation of the ink, apply sufficient thickness to the ink to prevent cracking and loss of adhesion. Realize that, as a result, the stretch of the garment will be compromised.

Elasticity—That of the ink and garment are two-directional in that each stretch and recover from stretch. Elasticity is given as a percentage of elongation, so an ink may have 100 percent elasticity at 125 percent elongation. This means that, if we were to stretch a (cured) printed 10" solid stripe of ink to 12.5", it would recover its original size and shape. Note that the garment elasticity is different when stretched vertically or horizontally. The ink must accommodate whichever of these two dimensions stretches more, either by restricting the garment or recovering its original size and shape.

Adhesion—The extent to which the ink will remain on the garment—no matter how the apparel is stretched, perspired upon, washed, dyed or scuffed—requires that the ink have sufficient plasticizer and should always be stirred just prior to printing to reduce its viscosity and improve adhesion. One caveat: all inks have an inherent surface tension. Inks formulated for these fabrics will have a very low surface tension; ask the supplier for the specs.

For good adhesion, preheat the platen to at least 140ºF. The ink moves toward heat; preheating improves mechanical adhesion. Performance fabrics are the one fabric that require a lot of squeegee pressure. If there is no ink on the platen after printing, it is sure you’ll have mechanical adhesion. 

Push hard with a hard, sharp, beveled-edge blade at or near vertical (maximum 5º) and make multiple passes. The first pass enters the garment, the added passes attach to the first and add the required volume of ink for durability, opacity, etc. Also remember that complete cure is critical. Some plastisols may require additional time in the dryer based on the thickness of the deposit. 

Gloss—Every ink has an intrinsic level of gloss. For performance fabrics, the desired level is usually high. If this is the case, use a high volume, low count and thin thread screen mesh. This will help produce a smooth finish without the tell-tale texture from the screen mesh.

If the desired result is to have the garment retain its level of gloss, be certain the printed product is completely cured. For colors with an unusually high gloss, be certain to check it for cure, scuff and bleed resistance.

Hand/drape—Based on the printed deposit and volume, a high deposit of ink may drape well. However, it is likely to feel rough unless there is enough ink volume. Use the print technique previously described for adhesion and use the mesh previously indicated for gloss. Drape may be less of an issue for customers and is predicated on the volume of ink deposited. A highly elastic ink is going to drape well. 

Blocking—One printed, hot surface has a tendency to weld itself to another as the garments exit the dryer. Using a plasticizer printed with a smooth finish and thick film increases the risk of blocking. Determine if the values of plasticizer—smooth and opaque—outweigh the need to have someone at the end of the dryer to catch each garment and allow them to cool before stacking. 

Tensile strength—Typically, plastisols recommended for performance fabrics will have sufficient tensile, which means how far it will stretch before it ruptures. Again, the level of cure is critical. Although this is not the gauge of durability, the two go hand-in-hand. When tensile strength is at its max, the durability will also be at or near maximum. At least one industry ink manufacturer has a couple solvent tests for tensile strength and certain press manufacturers can provide a flow chart for basic instructions on the test.

Abrasion resistance—Two mesh fabrics available from industry suppliers will help optimize the abrasion resistance, tensile strength, gloss, hand and drape, opacity, bleed resistance and adhesion of the ink. For thicker ink deposit, use the 83/70. For thinner deposits, use 123/55. Both fabrics allow for thicker ink deposits. To compare the abrasion resistance of two or more inks, use a coarse steel wool pad, press firmly and swipe the same area two dozen times. Observe the mesh for a change in gloss or for pigment or particle loss.

Bleed resistance—Ink manufacturers either take a chemical or mechanical approach to bleed resistance. To maximize mechanical and chemical resistance on press, be certain to apply sufficient deposit and volume. No matter the color, the ink film must be thick and smooth. Note that chemical bleed resistance may be color specific; just because one color is okay does not ensure all other colors will be. 

Verify with the manufacturer but, generally, it’s smart to test both various red and various blue garments. Since the most common ink color is white, use it to test all red fabrics and use yellow to test on all blue fabrics. Some superstitious folks preheat the garment, but preheating is just as likely to worsen bleed as it is to eliminate it. 

A primer coat may use different/ complementary chemistry to prevent bleed, so a primer and overprinting have a very beneficial synergistic effect (check with the ink supplier). A print-flash-print technique can help submerge the fibers of the garment. But, if the ink is sufficiently thick and smooth without fibers on the surface, an additional coat of the same material may make a marginal improvement. 

Since the surface of the ink gets the most heat, a double layer with flashing between often proves to be an inexpensive insurance. In all cases, be absolutely certain to completely cure the ink or the dyes will migrate through the plasticizer. 

Opacity—There is a myth which says “coarser mesh equals higher opacity.” This is clearly NOT the case. The best meshes allow operators to print a volume which supports the ink film height or a smooth finish. These meshes may be coarse but they will ALWAYS have thin threads. The squeegee blade is critical here; use a sharp beveled edge, hard blade so you can apply more volume without losing penetration. Once the fibers are submerged below the surface and the surface is smooth, it is not necessary to use more ink for opacity.

Stress cure

The most critical metric for success is to be sure the print is fully cured. It is imperative that the manufacturer’s specifications are followed to the letter with performance ink systems. For example, highly elastic, low-bleed ink systems will not offer optimal performance if the ink is under-cured. Durability and bleed resistance are compromised if the ink is over-cured. 

To monitor results, temperature tapes and heat guns are okay, but donut probes and a plot of the data are much better. (Editor’s note: See Printwear May for more on monitoring cure or search the article archives by author Ray Smith at printwearmag.com/articles/authors.) Solvent tests are very useful for calibration of curing parameters. 

Stretching doesn’t differentiate between tensile, elongation and cure, but I recommend any and all of these steps to hedge your bet. The best test is a wash test followed by a spin in a hot dryer. If the washed shirt shows less gloss or cracking when stretched, the garment is probably under cured.

Go forth and print

The preceding information is not intended to strike fear into the hearts of entrepreneurs, but rather, to warn those who throw a bunch of additives into the pail, are pretty sure the goods are cured, or who don’t bother washing the printed garment. Engage the manufacturer to get the real specs on the garments and inks. Listen to ink makers’ guidelines and be sure to charge for your talent, trouble and time. These garments can be either friend or foe. The choice is yours.


Why are Performance Garments so Hard to Print?

The combination of bleed, stretch, construction restrictions and wearer abuse (earning them the nickname “Slick-Willie”) suggest they are not easily emblazoned … even with screen printing. 

1. The first barrier is adhesion. Slick Willie typically consists of polyester with spandex for elasticity. The latter affords a lesser raw material cost than the nylon garments but both types are highly elastic and comprised of very thin, slick threads. This leaves precious little surface area—since plastisol inks rely on mechanical more than chemical adhesion, they love a high surface-area textile. Surface area is a scarce luxury with the low denier yarns and tight, flat construction of performance fabrics. 

2. Next is the “bungee-cord” issue: Performance fabrics wick away moisture and conform to every nook and cranny on the wearer. If the plastisol doesn’t stretch, the garment won’t form-fit the wearer. But, if it conforms, is not likely to be as durable.

3. If the garment is of the polyester persuasion, all but its bleached-white version will be dyed with colorants that consist of plasticizer—the main constituent of your plastisol ink. The caveat is that most of these garments are not white and dyed-dark goods are prone to dye migration or bleeding.

4. If this is not bad enough, just wait until you hear what they’re going to do with these goods after you print them! They will stretch them over muscle, pad or bullet-proof vest, sweat profusely in them for hours on end, scrape them on anything and everything with which they come into contact and them dump them in a high-heat wash load with a good dose of rifle-cleaning compounds (also known as laundry detergents) and expect the shirts to last at least a few seasons.