Advice and secrets from the screen printing know-it-alls.
During the summer in the US of A, it can get scorching hot – at least in some places. While some place is putting a shirt into a dryer at 50 degrees, some other poor soul is putting in a shirt at 115 degrees in August. I rarely see people changing their dryer temperature, but they really should be, based on all the variables that can change – particularly the temperature of the shirts going into the dryer.
If a shirt goes in on a dry 100-degree day, and it’s a thin, dark polyester shirt that was already flash-cured on press, that shirt is very hot going in. The temperature will rise quickly in the dryer. If that dryer was previously adjusted for a thick white cotton shirt with a thick coat of silver ink on a cool, humid day, that poly shirt would probably not just scorch, but could very well catch on fire!
What do you do to make sure you are not scorching your shirts? Good lighting. That’s it, visual inspection. And let me tell you, seeing a faint, faint brown on a white or gray heather shirt is not easy. In varying light or at a various angles you may not notice. Look at the examples here – the gray shirt has a scorch under the collar and the white shirt has a scorch on the collar. They look like normal shadows. Vigilance is required!
So you don’t want your dryer too hot, but how do you make sure you are curing the ink? Wash them – that’s the only way. You can gather information from all kinds of heat probes, temperature tapes, pyrometers and dryer gauges, but the only true proof is to wash the shirt and make sure the ink doesn’t come off.
In a pinch, you can turn your dryer temp up and belt speed down until the shirt scorches, then speed up the belt until it doesn’t scorch. That works on most dryers, but with a little short table-top model, you still can’t be sure.
In general, you want to put shirts in your dryer for as long as you can and as low a temperature as you can get away with. Production requirements may demand putting the shirt in for as short a time as possible, which means turning up the heat.
Keep in mind that the heat has to penetrate, and your margin for error is too tight at very high temperatures. You cannot bake a cake that needs 45 minutes at 350 by broiling it at 550 for 10 minutes. Likewise, you can’t cure ink at a super-high temperature for a short time.
Factors that require higher temperature or longer time on the belt:
- High humidity in your shop or the truck/depot when the shirts were on their way to you (especially applies to certain shirts like garment-dyed)
- Thick ink film
- Inks that contain water or solvent that has to evaporate before the remainder of the ink crosslinks
- Reflective, shiny or even light-colored inks which tend to reflect heat (particularly true with electric infrared panels)
- Cold shop
Factors that will require lower temperatures or shorter belt time:
- High shop temperature
- Dark-colored shirts or ink (which absorb heat)
- Thin ink film
- Shirts that have been flashed
- Thin shirts or shirts that heat up quickly like polyester or poly blends (heather gray is notorious for overheating)
If you do scorch a white shirt, you can fix it as long as it isn’t too bad. Buy hydrogen peroxide at the local drug store or supermarket and mix it with about 50% water. Put it in a spray bottle, spray it on a scorched shirt and run it through the dryer. If there is just a tiny bit of scorching on the surface, it will turn back to white. Sometimes, if you’re lucky, you can do a light mist and take a very fine scorch off heather gray, but usually the hydrogen peroxide only works on white; it will bleach other colors. – RR
Tom Davenport is founder and president of Motion Textile, Inc. (asi/72662). He currently serves on the Board of Directors for SGIA.
Rick Roth is the president of Mirror Image Inc. He is known for his award-winning screen printing and embroidery as well as his philanthropy. Visit The Ink Kitchen blog at www.theinkkitchen.com.