Garment screen printers seem to be fixated on white plastisol inks. Find out why.
By Mike Ukena
White inks are, without a doubt, the most shop-modified inks of all. Using additives to change the way your inks behave can be a sensible move. For example, when a bucket of white sits a round for several months—because the printer was using the right ink and not the low-bleed stuff for everything—it gets too thick. Well, a small amount of curable reducer brings the ink back to a very useable viscosity without any detrimental effect on the bleed resistance. However, adding soft-hand base would not be such a good idea. You’d have to dump in way too much to make a difference. And even though soft-hand base would improve the viscosity, it would do so at the expense of opacity and bleed resistance. Soft-hand extender base would be proper to use in a highlight white ink to be printed onto a light fabric. In this situation, opacity is not as important and you can save money and improve printability by adding the soft-hand base.
White ink also is the most commonly flashed ink. As such the flash characteristics of any white ink become a crucial factor in deciding whether or not to use it. In general, most printers flash too much. They either flash a print for too long, too hot, or both. The results can be catastrophic. An over-flashed underbase is actually a cured underbase. Plastisol does not stick well to cured plastisol. If the underbase is over-flashed, the inks printed on top of it may actually fall right off the first time the shirt is washed.
The phenomenon in play here is called intercoat adhesion. The object of flashing is to gel the ink, not cure it. When the ink is gelled, subsequent colors will bond properly. When flashed well beyond gelling, the ink is cured and the top colors fall right off. It is as if you were printing plastisol on a vinyl notebook.
A print is properly flashed when the ink is just past the point where any will transfer to your hand or to another garment. Most printers start out in the morning at the proper time and temperature. The problem is that as the platens warm up, the shop neglects to turn the flashes down to compensate. Flashes require constant attention. They are not set-and-forget devices.
Set your sights on whites
A little effort to use the right ink for each application will help save money, time, and improve print quality. Have multiple whites in your shop for different applications. If athletic and process-color printing aren’t part of your services, then you should only have three whites: a cotton white, a low-bleed white, and a mixing white. If you do process-color printing, but not athletic printing, then you only need to add a highlight process white to the three formulations previously mentioned. If your shop does it all, then you can justify stocking all six types of white discussed in this article. So pay more attention to the white inks that you use. Focusing your investments in white ink on the jobs you print will go a long way to keeping your company in the black.
Mike Ukena is a 15-year screen-printing veteran who has owned a textile-printing company and worked in technical services for the SGIA as the director of education. A member of the Academy of Screen Printing Technology, Ukena is a frequent speaker on technical and management topics at industry events. He is currently a technical sales representative for Union Ink Co., Inc.
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