Garment screen printers face plenty of challenges. One of the greatest is the vast number of different substrates upon which they must print. Among them are high-elongation fabrics, which are some of the most difficult to work with. This month’s discussion will focus on printing on what is referred to generically as spandex or elastane, commonly known by the brand names Lycra, Elaspan, Linel, Dorlastan, Roica, and others.
The toughest part of decorating fabrics of this type is not so much the act of getting the ink onto the material, but getting the right ink onto the fabric and having it perform to customers’ satisfaction. A common mistake, one that many printers make when printing on fabrics of this type, is assuming that a common plastisol will do the job. The problem comes into play when the customer either puts on the piece of clothing or washes it for the first time. If standard plastisols were used, the result likely will be a print that will either crack once stretched and/or crack off in the wash.
Although plastisols in general are fine for use on high-elongation materials, the trick is to use the proper type of plastisols on these fabrics. The ink film, once cured, must be able to withstand at least a 300% elongation without cracking. A number of different components within a plastisol give the ink its stretching characteristics. They include the PVC resin (the dried, powered, plastic portion of the ink that makes up its solid components) and the plasticizer (the petroleum-based, oil-like component that makes up the liquid portion of the ink). Together, these ingredients make up the base for the ink.
Specific types of resins and plasticizers are used for high-elongation inks. The characteristics of plastisols formulated for use on high-elongation fabrics are different from those found in standard plastisols in a number of ways:
• they provide at least 300% elongation
• they have a high level of gloss
• they cure at low temperatures of approximately 270° F (132° C)
• the have lower flash or gel temperatures of 170-190° F (75-80°C)
• they can be applied to heat-sensitive fabrics
The lines of inks are sold as either fast-fusion or low-temp plastisols. The application parameters are identical to printing on jersey fabric. The actual flash and cure temperatures may vary depending on the manufacturer of the ink line.
Printing parameters
One primary consideration in the printing of high-elongation fabrics is the loading of the fabric or garment onto a platen. Keep in mind that this fabric has an elongation factor of 500% or more and is typically constructed in garment form to stretch tightly over the body. This poses a great challenge to the printer in that the press operator must know how the fabric is to stretch not only over the body, but also over the platen.
For example, if you’re printing a pair of bike shorts, the artwork will of course be representative of the image as it is intended to be once stretched. In many cases, the actual amount of stretch is minimal and little consideration need be given to distortion during the printing process. If the fabric is stretched 3-5% beyond the point where the fabric is relaxed, the distortion to the image on the fabric will be minimal.
If you are printing a fabric that’ll be stretched more than 7%, you will have to consider the possibility that adjustments to either the artwork or platen will be necessary. Such adjustments minimize the distortion to the image once the garment stretches over the body. The platen option includes a platen that stretches the garment to the estimated elongated state that it would reach when worn by a person. This would ensure that the image would be the proper size once stretched to its intended size. The misleading aspect of this is the distorted appearance of a given image prior to the garment being fitted. This part of the printing process is one that a printer can only master through time and practice.
Spot-curing considerations
Properly flashing high-elongation plastisols requires planning and care. These inks present a challenge in that they possess a very high after-flash tack. In other words, they come out from the flash unit very sticky. The excessive after-flash tack is a result of the plasticizers used in the ink. The specialty plasticizers, or hot plasticizers, are required to give the ink its elongation.
Flashing is only required when you print an underbase onto a dark fabric to increase the vibrancy of an overprinted color. A high-elongation-plastisol ink film requires additional time between flashing and printing to allow the after-flash tack to disperse from the ink film’s surface.
When printing on an automatic, you will need at least one cooling station on the press to allow the ink film sufficient time to cure prior to overprinting. Otherwise, the result could be disastrous: The screen following the flashed underbase would adhere to the hot, flashed ink film and pull the ink and fabric from the platen surface. The obvious result would be a complete loss of registration and thus the scraping of the garment. Keep in mind that as low-temperature inks cure at a lower temperature, they also flash at a lower temperature.
Curing
Even though high-elongation plastisols cure at lower temperatures than conventional formulations, you’ll still need to ensure proper cure throughout the ink film. Should the entire ink film not reach its required temperature, the results will be poor elongation and cracking due to insufficient heat, poor abrasion resistance, poor washability, and possible flaking of the ink film due to poor adhesion.
You have a number of different methods for determining the temperature the ink film reaches, but the best test to determine state of cure is to wash the garment and stretch it once it’s dried. The ink film should support at least a 300% elongation from its static state. Should the ink not stretch, or if it shows any of the previously mentioned characteristics associated with poor performance, you will know that the ink did not receive sufficient heat. The same holds true should the ink film receive excessive heat.
Stretch your printing expertise
The printing of specialty high-elongation fabrics can be productive and profitable once you identify the correct printing parameters to match the fabric characteristics. Putting the proper procedures and controls in place, as well as understanding the fundamentals associated with the material, will allow for maximum flexibility on fabrics of this type.
QUICK FACTS ABOUT SPANDEX
Spandex was first commercially produced in the US in 1959 by DuPont. The synthetic fiber is stronger than rubber and is designed to recover to almost precisely its original shape and length after repeated stretching—and it can do so to more than 500% without breaking. Spandex is a lightweight material that is heat-settable, dye-receptive, and resistant to damage from abrasion and deterioration from exposure to detergents, lotions, body oils, and more. Fibers are available in 10-2500 denier.
Rick Davis is the president of Synergy Screen Printing in Orlando, FL. A 27-year veteran of the textile-printing industry, Davis is a member of the Academy of Screen Printing Technology and has a background that spans production management, artwork engineering, application testing, and industry consulting. He is a frequent contributor to trade publications and a speaker at industry trade events.