How Do T-shirts Prints Dry?

Monday, February 29, 2016

Curing Inks On T-Shirts With A Textile Conveyor Dryer
Curing Inks On T-Shirts With A Textile Conveyor Dryer

T-Shirts Are Cured Not Dried

A common question we are asked is "how do the inks dry?" Actually, the term screen printers use is 'cure'. In most cases, we use plastisol inks, which will not dry with air. Plastisol is a suspension of PVC particles in a liquid plasticizer, with a consistency of toothpaste. Heat is required to cure the ink. The printed t-shirts are laid on a conveyor textile oven, which has a heat chamber set to 900-950 degrees. Only 320-350 degrees is actually necessary to cure the ink, but the dryer temperature is intentionally set high to speed up the process. T-shirts will exit the dryer within 1-2 minutes fully cured (dry).

The reason we use the term cure (not dry) is because the heat melts the ink, in essence a liquid vinyl, and upon cooling it becomes a solid sheet on vinyl that bonds to the t-shirt fabric. The t-shirts are immediately stacked, having cooled off enough as they exit the dryer. They are then folded into dozens, aka printers fold, and packed in boxes for shipping.

The entire process, with exception of setting up the press, is actually quite fast. In a typical hour, we can print, cure and pack 500 printed t-shirts.

Avoiding Cracked Prints and Ink Washout

Undercured Ink Plastisol T-Shirt Ink Cracking
Undercured Ink Plastisol T-Shirt Ink Cracking

If you have ever experienced imprints that crack after washing or worse yet, ink that actually washes off the shirt, then you know what happens when inks are not properly cured. Simply running t-shirts through a hot oven is not enough. A common problem is partial or surface cure, where the inks feel dry to the touch, but are not cured throughout the entire ink layer. Because only 320 degrees is needed to cure the ink and super heated drying chambers are used, printers often make the mistake of not curing the ink completely.

So those cracked prints you may have seen, were only cured on the surface, with the inner layer of the ink never reaching full curing temperature. To control this, the curing system must be monitored with a variety of steps. These steps include testing time & temperature variables to set production standards, periodic wash testing, heat measurement as shirts exit the dryer, and stretch testing.

Tip: If you happen to receive a bad batch of shirts, you can return them to your printer to have them fixed, as curing the ink can be redone.

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