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Dye Migration: Screen Printing Polyesters & Poly Blends
Dye migration is also known as bleeding or dye sublimation. This is a process that occurs mostly between standard plastisol inks and synthetic fibers like polyester. It is most notable with white inks on shirt colors like red, navy, maroon and even dark greens. It may appear immediately when the shirts exit the oven, when they are left to sit overnight and even two weeks later. There are two common causes of dye migration.
The real cause of dye migration is simply the fact that the dyes in the polyester fabric sublimates or turns gaseous when heated to about 330 degrees Fahrenheit during the curing of the plastisol ink. Then the dye, in gaseous form, seeps into the ink layer thus tinting it the color of the shirt. This is inherent in the dyeing process of polyester and is unavoidable but not impossible to deal with. When screen printing polyester or polyester blend garments precautions must be taken to prevent this bleeding from happening. This is what we will call the “first” cause; over curing.
Over heating your printed polyester garments during curing is inadvisable. It is important to monitor the oven temperature to ensure consistent results. This includes flash curing. Be careful not to overheat the shirt when flash curing on press. Cure all of your polyester garments under 320 degrees Fahrenheit. It is also possible to use a catalyst like Nylobond to reduce curing temperatures of plastisol inks. Lower curing temperatures are the best defense against color bleed. Thicker layers of ink will inhibit dye migration but it will also require longer heating times and temperatures.It is best to use an ink specifically designed to be low bleed or one that is made for polyester materials. White ink is the absolute worst for bleeding problems. But don't be surprised to see other inks discolor after being printed on navy or black. You could also use an under base to prevent bleeding and some ink manufacturers offer under base inks specifically for this application.
The “second” cause is basically the same problem prompted by different factors. The simple fact of the matter is that sometimes the dyeing process for the polyester garments, which is a sublimated one, is of substandard quality and the dye will tend to migrate easily from the fabric into the ink layer. This is a problem that can only be addressed at the factory where the fabric is being dyed. Good luck. Using higher quality products may help to avoid this factor.
Another part of the second cause is re-dyed shirts. This is also something that starts at the factory. Let’s say Fruit of the Loom makes more yellow shirts one spring season for some reason and then they experience larger orders for shirts like black or navy and even maroon. Can you guess what they do? That's right, a re-dye job. Any re-dyed garments will have a tendency for the dyes to bleed into the ink layer. This goes for 100% cotton shirts as well as polyester or polyester blends. Printing white ink on a 100% cotton tee shirt that has been re-dyed may also result in color bleeding into the ink layer. Using a good quality, low bleed, high opacity white ink for all of your darker colored 100% cotton shirts is recommended.
It is important to ensure the quality of your polyester garments before printing them. And there is a simple way of doing that in addition to buying a well known name brand garment. Take a clean piece of white cotton tee shirt fabric and tightly wrap it around your index finger. Then rub an area of the polyester fabric a few times with your finger. If there is a very slight color transfer, it should be alright. If there is a very significant color transfer, then I would be very cautious about printing those shirts. This test may also be repeated with the cotton fabric damp if you are unable to get readable results dry.
Finally, there are high quality garments like Under Armour® that just have a bad problem with standard plastisol inks and bleeding. They also tend to crack or flake with standard plastisol inks as well. If you are approached with an Under Armour® print job, be wary and contact your ink manufacturer for the correct ink to use. It is always a good idea to consult your ink supplier to ensure proper ink usages in your print shop.