Stop the Bleeding on Polyester and Blends

November 23, 2009

Garments woven from a blend of polyester and cotton can look and feel so much like 100% cotton that many screen printers are tempted to run blends on the same press and dryer setup that they just used to print all-cotton shirts.

Sometimes you can get lucky and nothing bad happens. However, it's much more common that you will get dye migration – or ink bleeding – unless you know a few crucial bits of information about polyester and some fail-safe techniques to print them without ink bleed.

Polyester fibers release their dye when they are heated to 270°F (132°C) – the so-called "glass transition temperature." Most printers set their conveyer dryers to 320°F (or much higher) for 100% cotton. If you're lucky, as mentioned above, running blends or all-poly shirts through will work fine because the dryer's temperature gauge measures the ambient temperature inside, not how hot the actual garment fibers get.

If only a few surface fibers reach 270°F for a brief time, then just a tiny quantity of dye will be released and, depending on color combinations, thickness (or absence) of base coats, etc., you might not see any bleeding. Real problems start when poly fibers reach 270°F and stay there for any period of time. When that happens, for instance, a red poly/cotton garment will definitely turn white lettering pure pink. Worse yet, that bleeding might not be visible for hours or even days, depending upon humidity, inks used, etc.

For prevention:
• Monitor core temperature closely with heat strips.
• Run pre-production tests.
• Apply a good base white made for polyester blends (not general purpose white ink).
• Use lower mesh count screens to offset higher viscosity of poly white inks.
• Never switch from 100% cotton production to polyester or poly/cotton production without re-configuring your press, inks and dryer setup.

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