What the Heck Is Dye Migration, Anyway? Screenprinting on Polyester: Questions and Answers
In today's promotional product space, shirts constructed entirely of polyester or polyester blends (tri-blends, 50/50) are becoming more and more popular because of their softness. One of the most common questions we get is: Why does it cost more to print on garments with polyester or rayon in them? The answer is that, when decorating garments consisting of polyester, the screenprint process requires a few tweaks due to an effect that can occur called "dye migration."
What is dye migration and why is it a problem?
Dye migration is the movement of particles of dye from the fabric into the ink imprinted on a garment. This causes discoloration or tinting of the imprint. For example, if you laid down plain white ink on a red polyester shirt, chances are the white will end up becoming a faded pink color instead.
When does this reaction occur?
The issue occurs in the later stages of the decoration process during the step of “curing." Curing is essentially the heating and drying of screenprinted inks to set them and ensure their durability. The printed garments are placed on a large moving belt, which passes them below a heat source usually set at 320 degrees. After being exposed to these temperatures for a controlled period of time, the ink on the apparel is now considered cured. However, this heat is also exactly what precipitates the chemical reaction behind dye migration.
Unfortunately, heat is an integral part of the way we ensure excellent quality, solid imprints that are built to last, so we are always looking for different ways to sidestep these problems in the screenprinting field.
What are the potential side steps for you and your printer?
Use the proper inks. A low-bleed polyester ink is typically common on synthetic fibers, which tend to bleed, so these inks help mitigate that risk. Most high-end low-bleed inks cure at 280 degrees compared to 320 degrees.
Be conscious of temperatures used to cure your inks. Controlling palette and dryer temperatures as well as understanding your flash times on press is critical. During the production process, make sure the flash dryers and curing drier isn’t getting too hot (290 degrees and below). Heat is the enemy when it comes to migration.
Cool the shirts down before packing. When the shirts are coming off the dryer, do not stack and pack right away. Let them cool down a bit. Some printers use fans, while others hang them before packing. Just don’t pack them hot in a box. That is the perfect environment for migration to happen.
Sometimes we are able to talk our customers into a vintage distressed look, which works great for tri-blends, etc. We don’t use an underbase white, and the dye migration actually helps achieve that washed out vintage look.