Ink (Image courtesy International Coatings Company)

Word to the Wise: Ink Curing

Kieth Stevens is the Western regional sales manager for International Coatings. He has been screen printing for over 37 years, teaching screen printing for more than 12 years and is a regular contributor to International Coatings' blogs. He also won a 2014 Golden Image Award from SGIA. For more information, visit iccink.com and read the company’s blog at internationalcoatingsblog.com.

I’ve been a hobby chef for many years, and while I’ve been in the screen print industry for more than 43 years, it’s hard not to see some similarities between the two. Bear with me. 

Recently when I was trying out a new, reasonably complicated recipe for some pastries that a friend shared with me, I noticed how much harder it would be to make if I didn’t have the right equipment or tools available in my kitchen. I have a food processor and know how to use it. I know where the mixer is, and I know what the cooking temperature and time need to be for a perfect result. After all the effort I spent to follow the instructions exactly how they were laid out, it would be unfortunate to end up with something burnt or undercooked. 

This baking process closely resembles the screen printing process. You spend time prepping the artwork. You are careful with coating and exposing of the screens. You level the platens, carefully register the different screens, and thoroughly mix up the colors before you put them into the screen. Finally, you print the shirts and carefully lay them onto the dryer. You deliver the shirts to your customer and about a week later, the phone rings. The customer complains that the ink is cracking or washing off the garment. What was overlooked? 

This problem is indicative of undercured ink. Either the cure temperature was not high enough to cure the ink or the time spent in the dryer was too short. As in my cooking example, the pastry would have a crisp outside, but a doughy inside. Similarly, when ink is undercured, the outside of the ink can feel “dry” to the touch, but the inside is not fully fused.

Too many shops overlook the importance of the ink cure. It’s not just “set it and forget it.” There are too many variables that need to be assessed like the outside temperature and humidity, the ink deposit thickness, the garment type, the ink type, and of course, the dryer temperature. Dryer temperature doesn't refer to the setting that is shown on the dryer’s temperature display but the actual temperature inside the dryer itself. You may need to use a laser temperature reader or a donut probe to get the exact temperature inside the dryer. There is also the dwell time in the dryer heat chamber, which is the actual duration that the ink spends in the heat chamber. For most plastisol inks, dwell time should be at least one full minute. 

If someone calls me to complain that they are experiencing the ink cracking or coming off the shirt, 99 percent of the time it's because the ink is not fully cured.