Putting Synthetic Substrates to the Test
Davis explains how to identify and overcome the most troublesome characteristics of synthetics.
Textile screen printers routinely work with specialty and synthetic fabrics. Handling these often challenging materials is accepted as a part of doing business. Even though textile-manufacturing technology has become quite sophisticated, many of the issues involved with printing fabrics such as nylon and polyester have remained. This month, I'd like to examine the properties and behaviors of these two materials and discuss ways you can test these fabrics and avoid problems during production.
In my experience, there are two kinds of screen printers when it comes to nylon: those who excel at working the material because they've taken the time to test and those who rush into nylon work, fail, and ultimately avoid nylon jobs altogether.
The greatest challenge that printers face in printing nylon is ensuring that inks properly adhere to the fabric. In the case of nylon jackets, the challenge is that the majority of jacket materials are treated with waterproofing chemicals. So you either have to ensure that the coating is removed prior to printing or modify your inks to enhance their ability to adhere to the treated fabric.
Wiping down the nylon with rubbing alcohol to remove the coating from the fabric's surface typically works. But keep in mind that alcohol may affect the fabric's color and create a shade variation where the fabric was wiped down. Another effective method is to introduce an adhesion promoter into your plastisols. This approach eliminates the possibility of chemically changing the fabric's surface.
As with any fabric that you attempt to screen print for the first time, you should carefully test nylon materials prior to production. Doing so helps ensure that you'll be able to achieve the desired results rather than produce costly mistakes. If you do not have access to the fabric for testing before you go to press, then you should immediately contact the fabric/garment manufacturer and inquire about decorating instructions. If they don't have the information you need, check with your ink manufacturer for guidance.
Different fabrics and treatments call for different precautions, printing techniques, and curing methods. The material composition or method of manufacture may require you to shorten curing times to avoid issues, such as shrinkage. Because nylon is highly prone to shrinkage when it's flash cured, it can be valuable to experiment with preshrinking the material before printing to alleviate the problem.
For most textile screen printers, printing on polyester is limited to printing 50/50 cotton/polyester T-shirt fabrics. Printing on such materials is typically not an issue when using a good bleed-resistant plastisol or bleed-resistant white as an underbase on dark 50/50 garments. The challenges mount, however, for athletic printers that work with specialty woven fabrics that not only are 100% polyester, but also have a higher degree of elongation than standard T-shirt materials. Here again, testing prior to printing is the key to determining the best production practices to employ with the material. Some key aspects to consider include the following:
The fabric's potential for shrinkage when exposed to heat Like nylon, polyester is a heat-sensitive fabric that can shrink when exposed to excessive heat. The degree to which the material may shrink depends a lot on the construction of the fabric. One wise practice to follow when working with polyester fabrics is to use low-temperature or fast-fusing plastisols in order to reduce the total heat to which the material is subjected. These inks typically will fuse in the 280°F range, as opposed to the 320°F range commonly used for standard plastisols. Again, it is always wise to conduct tests to discover the fabric's exact limitations.
The fabric's potential for dye migration and sublimation Dye migration is a common issue with 100%-polyester materials. A manufacturer's choice of dyeing processes, as well as the dyes used in coloring the polyester, can make dye migration a major problem. Additionally, polyester dyes can sublimate into the ink film when temperatures grow high enough.
If you're working with a woven 100%-polyester material that has a high elongation factor, you'll need to test it with a bleed-resistant, high-elongation plastisol. The test prints should be produced well in advance of the planned production run because bleeding may take a week or more to appear. If it does occur, you may need to consider switching to another ink or reducing drying temperatures. Once again, consult the fabric and ink manufacturers for other recommendations that will help you achieve the desired results.
An option that can dramatically reduce the potential for bleeding is to select 100%-polyester fabrics that are dyed with cationic polyester colorants. These dyes are locked into the polyester fibers and resist migration. However, even though these fabrics are a good insurance policy against migration, it is still wise to test anyway so that you can ensure that your inks and production techniques will lead to successful prints.
To check the material's potential for sublimation, take a 1-sq-in. piece of the fabric and place it between two pieces of white Pellon. Then use a heat-transfer system and press the fabric/Pellon combination for 30 sec at 270°F. Remove the sample and Pellon from the press and inspect the Pellon for any discoloration caused by sublimation. If none is present (and there shouldn't be at 270°F), increase the transfer-press temperature 10° and repeat the process. Continue this process in 10° increments until you reach 320°F. If you do not notice any discoloration of the Pellon at this point, you can be confident that sublimation will not be an issue. If discoloration occurs at any point in the test, you'll know what temperature is the highest that the fabric can reliably withstand.
The ink's ability to bond to the fabric You can perform a number of ink-adhesion tests to test the fabric's receptivity to your inks. In my experience, wash testing the printed fabric is the best way to gauge the level of ink adhesion. When working with a material that is new to your facility, it is best to wash test printed samples at least five times to ensure good print performance.
The ink's ability to meet the fabric's elongation characteristics You can make your life easier when printing onto a fabric that has an unusual degree of stretch or elongation by using a high-elongation plastisol. This type of ink is more resilient and resistant to cracking than conventional plastisols and can help prints remain intact on stretchable fabrics. Not all athletic polyester fabrics stretch to the same degree, so it is again beneficial to test the ink/fabric combination beforehand to make sure that prints perform as expected.
New fabrics enter the market all the time. Each presents its own challenges in terms of printability and comes with its own set of processing limitations. To get successful results with synthetic fabrics in your facility, you must devote time to testing so that you can identify the ideal ink and production parameters for any each job you face.