Tips For Successful Prints -What to Know About Low-Cure Inks

July 25, 2019

Ink cracking after stretch test due to under-curing

In an article recently published by Printwear Magazine, Kieth Stevens lists some important tips on printing with Low-Cure inks. 

Using a low-cure ink means fusing the ink at a lower temperature than usual, typically around 275 degrees F (135°C). Typically, this means protecting either a heat-sensitive fabric from shriveling up or trying to keep the polyester dye from sublimating and migrating. Before starting a job with low curing temperatures, please be sure to check on the following essential points:

USE THE RIGHT INK

This point sounds logical, but be sure to use an ink designated as low-cure or one that can cure at lower temperatures, or use a low-cure additive when using a standard-cure ink.

PROFILE YOUR DRYER

Next, how do you know the exact temperature of your dryer? Don’t just go by what the settings indicate. Instead, always profile your dryer. I use what is called a donut probe, which is a small 3-inch plastic type ring with a couple of small bare wires crisscrossing it. This device sets on top of the printed area of a garment. The probe is then attached to a hand-held device that shows what the temperature is where the wires cross. The donut ring is connected to a thin 10- or 12-foot cable, allowing it to run through the dryer and read the temperature of the dryer in real-time.
Most dryer settings will differ from the actual temperature inside the dryer. For instance, the left side may be hotter or colder than the right. We have a good dryer at International Coatings, yet when profiling the dryer recently, I found the dryer settings are off by 5 degrees. As long as the actual variance is determined, if any, the dryer can then be adjusted and used with confidence. A donut probe thermometer is the only device that can perform this type of profiling.
Other tape type readers exist but only show how hot the tape got, not necessarily the type of information necessary to profile a dryer. There are also the laser type heat sensors available from the hardware store that are relatively inexpensive. Those are used by taking the temperature of the ink area of the garment as it exits from the dryer and it shows what that temperature is at that moment, but cannot tell how hot it got while in the dryer, an area that is out of reach of the laser’s sensor.

TEST FOR CURED INK

Equally important when curing at low temperatures is to test the cured ink for complete fusion. The chance that the ink is under-cured is high. Therefore, do not skip this important step. Testing for a complete cure can be done a few different ways.
Please note: The best way to confirm the ink is cured is to wait at least overnight and as much as 24 hours. This waiting process is especially important when using an adhesive catalyst. The catalyst will continue to catalyze over 24 hours before fully cured.
The first and easiest way is by merely stretching the cured ink. I usually hold the image with both my thumbs 1" apart and pull it to 2" apart. If I see no cracking, I’m pretty sure things are good to go. This is assuming the fabric or substrate can stretch.
What if you are printing on a non-woven polypropylene bag that does not stretch well? A simple scratch test will do the trick. Just lay the bag down on a firm table and scratch the printed cured image with a fingernail about five times to see if any of the image flakes off. If none or very little of the print comes off, then it should be good to go. Waiting overnight or 24 hours before doing the scratch test assures for better accuracy on this test.

 

One other way of confirming the ink has fully cured is to do a wash test. Wash the garment one time to see how it comes out. If the print fails right away, then obviously it is not cured. If the print comes out without any blemishes due to the ink washing off, then you're probably safe. To be extra sure, wash the garment up to five times.

Some name-brand companies require as many as 50 washes using specialized washing machines that have internal water heaters to maintain high water temperature throughout the wash cycle. Among other things, they also prescribe specific wash times and spin revolutions, etc. When I was a production manager, I always took printed garments from production home with me and washed them while I cooked and ate dinner and checked them so I could rest easier.

Another test, not frequently used, is using ethyl acetate. Place a few drops of ethyl acetate onto the back of the print on the inside of the garment. This spot of ink is then placed onto a clean unprinted fabric and then tightly held together for two minutes. If there is a transfer of ink to the unprinted area of the garment, it means the ink hasn't cured. The garment must be either re-cured at a higher temperature or for a longer duration.

One example on curing I always refer to is that of baking a cookie versus a cake. A thin layer of dough requires less time in the oven than a thick layer, cooked at the same temperature. Yes, the low-cure inks can cure at 275 degrees F, but keep in mind that the entire ink film must reach this temperature, not just the surface. Depending on the thickness of the print, it may require additional dwell time in the dryer to achieve this temperature. Standard dwell time in the drying chamber is usually 60 seconds. If it’s just one layer of ink (cookie) printed through a 156 mesh, chances are excellent all will be well. But if you have double printed through 110 mesh and then flashed, with an additional layer of color on top with a 156 mesh (cake), you may need some extra dwell time in the heat chamber to give the thick ink deposit time to fuse fully.

Kieth is the Western regional sales manager for International Coatings. He has been screen printing for over 37 years, teaching screen printing for over 12 years and is a regular contributor to our  blog. He also won a 2014 Golden Image Award from SGIA.

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