May '16

For the Business of Apparel Decorating

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94 || P R I N T W E A R M A Y 2 0 1 6 Printing with Plastisol Product and Performance Considerations in Plastisol B Y J O E C L A R K E I n our midst, there has been a bevy of itinerant-impostors, posing as indus- trial-toxicologists suggesting, even in- sisting, "This ink over here is 'safe'… that ink over there is not!" Yet some inks should be washed before wearing, some are loaded full of solvents, certain ones contain undesirable ingredients, and other new- comers haven't been accurately identified yet with respect to their volatility, skin ir- ritation, and toxicity. Some inks even have names which surely sound safer, yet none of them should be spread on the flower bed. No ink is health-promoting so each of them, case specific, should be handled, ex- hausted, and disposed of responsibly. Pro- viding the plastisol is phthalate-free and, solvent-free, plastisol can be considered en- vironmentally responsible, energy-efficient, and financially responsible. QUALITY PLASTISOL INKS Quality plastisol inks are ideally suited for both wet-on-wet and print-flash-print production. Since plastisols don't contain solvents, they are flash- and cure-safe. Un- paralleled for screen stability, they flash in one second without after-flash tack and without cool-down stations. Plastisol fuses between 275 degrees F and 330 degrees F, and is rarely, if barely, susceptible to wet or dry crocking. Roughly 50 percent of our ink consump- tion is white, and traditional whites cause 98 percent of our problems. As such, we will focus on white ink for the balance of this article. Traditional plastisol inks have exhibited excessive tack on press, which underpins virtually all the problems with produc- tion, including print stroke speed, clearing, bridging, matte-down, smoothness, opac- ity, thermal stability, minimum penetra- tion, flash time/after-tack, and fusion range. Traditional plastisol whites may solve one or more of these attributes at the ex- pense of another, but only the high- shear whites can solve all of them concurrently. Tack is the ratio of how much, on a molecular level, the ink is attract- ed to itself versus how much it is attracted to something else. Tack is the arch-enemy of "shear-thinning" which is the ratio of how thick the ink is flooded, versus how thin it can get as it transfers through the mesh when the ink is exposed to forces parallel to the mesh; think stroke speed. To circumnavigate the list of problems above, the white must be shear-thinning. Traditional white plastisol inks have normalized tack levels as high as 100 percent (e.g. peanut butter) and as low as 40 percent (suntan oil), whereas more recently formulated whites are high in viscosity but have very low tack like cold cream. For our white ink criteria, we'll con- sider buttering a slice of Wonder Bread with each of our four products. The 100 percent tack peanut butter is thick and very tacky. It will not want to transfer to the bread and when it does it will liter- ally destroy the untoasted slice. The 75 percent tack honey will tear in the winter weather and soak-in during the summer, but it never loses its tack; all year long it will destroy the bread. The 40 percent tack suntan oil gives us the impression that it is low-tack for two reasons. For one, we are comparing it to peanut butter and honey, and two, because the tack level is masked by its low viscosity. But, it's still tacky enough to soak the bread then ravage its soggy structure. Finally, there is 29 percent tack cold cream that flows onto the bread without destroying the surface or soaking in and then gumming up the works. Cold cream is the perfect metaphor for our ideal white ink. COLD CREAM INK Cold Cream represents the properties of a quality white ink which has a high viscos- ity to permit the fastest flood stroke, but prevents seepage into the mesh with a very low tack level of 29 percent. Notwithstand- ing, we need a tad of tack in order to get through mesh and stencil and to adhere to the shirt, but low tack allows it to print at the highest stroke speeds and the white will still whistle through any and all meshes. T-shirts blatantly disregard the first two laws for screen printing substrates; 1) flat and 2) substantive. Their topography looks like the Rockies, and the fact they are most- ly composed of air means the performance parameters for a white are to remain vis- cose-stable during the press run; to bridge the knitted construction; to matte-down the fibers; to produce a smooth surface; to not penetrate to the inside of the garment; and to maintain imprintability without lag, mottling, etc. Joe Clarke has spent the past 45 years in the lab and engineering de- partment in prepress and on press as a research and development and technical researcher as well as a man- ager of screen print production. He has received a number of print-related patents and is a member of The Academy of Screen and Digital Printing Technologies and a Specialty Graphic Imaging Associa- tion fellow. Clarke has presented hundreds of papers, written a couple books, and published more than 600 technical and man- agement articles for which he has earned numerous industry awards. Currently, he is president of Clarke Product Renovation, a Chicago-based corporation that brings product and process technology to the screen printing industry. He contributes fea- ture articles on textile screen printing exclusively to Printwear. Reach him at

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