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Dye Migration When Screen Printing Polyester Shirts

Dye Migration when Screen Printing Polyester Shirts

Dye Migration Issues, It’s Causes and What to Do About It!

Below is an explanation of dye migration which is an ongoing problem on polyester and polyester blend fabrics.  It’s a challenge from order to order and sometimes mixed results within the same order due to different manufacturing lots.

Let’s look at dye migration first. If you were to stretch out a single thread from some cotton yarn it would look kind of fibrillated or hairy.  When it’s being dyed, the dye can soak down into the thread like little fingers and grip onto it.  We call this a mechanical bond.  Natural fabrics absorb the dyes.  Polyester, on the other hand, is very different.  Stretch out a single thread of polyester and it’s really smooth, like fishing line.  There’s nothing for the dye to grip onto or soak into so the dyes are given a chemical bond that’s heat-sealed on.  The temperatures used to heat seal the dye onto the polyester fibers range from 230º to 260º Fahrenheit.  Keep these numbers in mind because these are really important ones to remember.  

Proper Ink Curing

Most plastisol inks need to reach 320º Fahrenheit (which could take up to 1 minute) to fully cure.  The correct terminology to use would actually be fusion.  There are two main elements involved in plastisol inks, resin – which is a powder, and plasticizer – which usually looks like an oily liquid.  When these two are mixed together with a pigment, you get your ink.  If stored correctly they’ll stay wet for a long, long time.  When we’re running a printed plastisol ink through the dryer, the resin swells and absorbs the plasticizer until they become fully fused, or cured.  As mentioned already, most plastisols need to hit 320º F (may take up to 1 minute) to become fully fused.  Here’s where the dye migration occurs:  When the plastisol is on its journey through the dryer and the heat passes the 260º F threshold, the polyester dyes will often get released from the thread and they will sublimate, which basically means they turn into a gas.  The molecular weight of the dye is important here.  If it’s a dye that has a low molecular weight, it means that the dye molecules are small.  If it’s a dye that has a high molecular weight, this means that they’re bigger.  The plasticizer in the ink wants to pull those dye molecules into itself in the same way that plasticizers disperse plastisol dye molecules.  The smaller dye molecules can get pulled up through resin particles and mixed into the ink.  This is what causes the ink to change color.  The heavier dye molecules won’t because they’re too big to pass through the resin particles.  This is why sometimes the garments “bleed” (or have dye migration) and sometimes they don’t.  There are several ways to combat the problem.  One is by using a low-bleed or bleed resistant ink.  But there is no such thing as a No – Bleed ink, though.

An important thing to remember though is making sure that the ink is also fully fused, otherwise it will crack and fall off after washing.  It’s a very thin line to walk:  The lower the temp the more likely a garment won’t bleed, but the ink may not fully fuse.   Ultimately the point to remember is that as far as polyester dye migration is concerned, heat is your enemy and time is your friend.  If you can get the temperature on the dryer lower, just run the garments through for longer.  This will help in attaining fusion.  Once you’re sure that the ink is cured, get those garments cooled down as fast as possible.   Even post-cure, the residual heat can entice the polyester dye molecules to come out.  Don’t lay the printed garments on top of each other until they’re cooled.  This only traps the heat longer and exacerbates the problem.  It is possible to make polyester garments that don’t bleed and to make inks that would resist bleeding, but the cost would make them completely prohibitive.  In the meantime, we’re stuck with what we’ve got.  The best recommendation is to print similar color to the shirt color or a darker color.  If possible avoid white ink on the high trouble colors which are Reds, Oranges, Purples and Black.  Why black?  Well often old color lots are over dyed black so results very.

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