Discuss the different plastisol screen printing inks and curing methods on the market. Share tips on getting the best results with the different ink manufacturers.
I am new in printing plastisol and I need some suggestions. I am doing some direct printing with plastisols with gold ink on dark navy blue shirts. As the customer has asked me to make the ink layer as think as possible, I was doing print-flash method for 4 times.
Now, my problem is that the design area is quite big and it goes almost at the corner of the flash dyer where the temperature is significantly lower than in the middle of the dryer. So, to achieve proper drying in the corners, I kept the flash on the top of the shirt for 1 minute...again and again 3 times and from my temp gun I can say that the the middle of the design was hot enough to be cured fully while the corners are not.
Now, my question is, can I try to final cure the shirts using the flash dryer again to achieve the curing by moving the dryer couple of times? Is it a problem for the area that was already cured before? Can double curing be a problem? Or triple?
It should not be problem to cure it twice the overlap area, if you let it cool down a little, so the t-shirt doesn't get scorched.
But at one minute, I think it is a little too long. If the flash dryer is at about 2,5"~3" over the t-shirt, 45 seconds may be enough.
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As Jerry used to say : Profit is not a dirty word.
It should not be problem to cure it twice the overlap area, if you let it cool down a little, so the t-shirt doesn't get scorched.
But at one minute, I think it is a little too long. If the flash dryer is at about 2,5"~3" over the t-shirt, 45 seconds may be enough.
Thank you very much for your tips; I believe I have saved the shirts by moving the dryer a little bit every after 20-25 seconds, so that the heat is not concentrated for too long. I have to say that I have already started to love printing plastisol in my very first job with the type of ink!!!! I had always been using waterbased so far!! I specially love the thickness as it sits right on the top of the lower layer and does not spread out!
There are several issues here that you must study in detail.
1. A flash unit is not a curing unit, but a device meant for gelling the ink in order to print additional colors. The flash unit may overcure the surface of the ink deposit with fully curing the bottom of the ink deposit. If it does fully cure the bottom of the deposit, it may overcure the top surface. Both overcured ink and undercured ink will crack when stretched or laundered and prove to be unsuitable to the end user.
I fully realize that infrared dryers use "flash units" to cure ink, but it is done with a conveyor belt that works completely different than a stationary flash unit. There have been vast amounts of research into this subject by others such as Ron Vinyard of Black Body Corporation who have discussed this issue. I also recently wrote a book on Flash Technology which discusses this issue in great detail.
2. A "Temp Gun" is not measuring the temperature of the ink deposit. It is measuring the ambiant air only. The reading is taken, not on a single spot, but in a bell shape, which means that at 1-inch it is reading an 8-inch circle. Pointed at the print from a distance of only a few inches and you are reading the temperature of the flash unit itself, the edge of platen and the area under the platen. The lazer beam on some units gives a false feeling of accuracy.
Ink temperature should only be measured with a donut style thermo-probe such as the one made by Atkins. You cannot rely on heat tapes, heat crayons, or ambient air test units such as the RayTek infrared gun. None of these devices will give you an accurate temperature of the ink itself.
3. Plastisol ink is cured the instant the resins absorb the liquid plastizer. This is dependent upon the resin used in the manufacturer of the ink and each manufacturer has a slightly different cure rate. Also, different colors of ink cure at a slightly different rate as the color will absorb or reflect the energy from the infrared source.
If you could get a perfect cure through the entire ink deposit from top to bottom, and you move the flash unit over a bit, you will then be reheating the ink deposit that was cured. This can cause remelting of the resins, which can subject them to failure in the laundering process. It can also cause overcuring on the previously cured section and cause failure as well.
Avoid excessive over flashing, as it can result in poor inter-coat adhesion of overprint colors. Wet plastisol ink cannot make a chemical bond to cured plastisol. There will only be surface bond that will fail in the laundering process, resulting in cracking of the brittle top surface.
Plastisol ink is made of polyvinyl chloride (PVC) which is the same material your plastic lawn furniture is made of, albeit with a plastizer to keep the ink film flexible. Just as the sun (which is an infrared energy source) can cause the furniture to become chalky, brittle and eventually fail, so can excessive heat to your plastisol inks.
4. No one can say what the distance, temperature or time can be to cure ink. Bottom line it depends on the watt density of the unit being used to cure the ink. The watt density of all infrared units is constantly changing, i.e. becoming less over time. No two units that were manufactured alike will emit the same energy after a few months of use.
Each individual must perform their own tests to assure cure.
There is much more to curing inks than meets the eye. You can find much more information in my books: Curing Plastisol Inks and Flash Technology.
Bill Hood
UltraSol Inks
Bill Hood Consulting
Bill Hood Books
Can I double cure plastisol? 
Re: Can I double cure plastisol? 
