May '17

For the Business of Apparel Decorating

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70 || P R I N T W E A R M A Y 2 0 1 7 P lastisol inks have an array of benefits. For instance, being 100 percent solids, they emit no tox- ic fumes when the ink is flashed or cured. Plastisol ink rarely dries in the screen irrespective of pigment load or shop conditions. It easily gels and fuses. The ink functions with all meshes, stencils, blades, and press settings. It provides a full range of transparent to opaque finishes. But because of these positives, there is a gross misimpres- sion that products, parts, and processing will work equally well. This is not the case. What follows are the basics from ink transfer through ink fusion to put our plas- tisol inks to their best use. BEYOND "S" THREADS Plastisol inks prefer screen mesh with the highest transfer ratio, e.g. a high fill-rate and low capacity. The most efficient ap- proach to mesh selection is to choose the mesh based upon its optimal deposit. IDEAL STENCIL Quality inks are shear-thinning, which means they get thinner when force is ap- plied but return to their original viscosity once that force is removed. The amount of time the ink remains fluidized is called its "fluid momentum," which in the case of white ink is less than 1/1,000th of a second. Let's look at the geometry of a thick stencil. Right at the time when the white is designed to re- gain its viscosity so it can matte- down the fibers and leave a smooth surface, a thick stencil demands the ink continue to flow. Using the EOMr (emulsion over mesh ratio) to dictate coating thickness around the mesh is a bad idea. EOM is predicated on fluid-momentum of the ink, blade angle, and the pre- cision of the off-contact gap. The RzS1 should be minimized. The EOM is a result, and the RzS2 should mitigate the EOM, that's it. INK TRANSFER The ideal screen-printing inks are highly shear-thinning and have a minimal tack level. When shearing forces (e.g. "squeegee pressure") are applied to such an ink, they increase its fluid pressure, which results in a directly proportional drop in its viscos- ity. This "thinning" process allows the ink to enter the cells of the mesh, attach to the surface of the garment, and the ink in the cells of the mesh contracts to release the mesh as the ink begins to level on the sur- face. All this occurs at a speed measured in milliseconds. BLADES FLOOD/FILL AND PRINT The optimal printing blade should permit 90-degrees or near 90-degrees of operation, minimal pressure, and maximum stroke speed. It should have an edge during the print stroke which is fitted to the tensioned Want your plastisol to treat you better? Rules for Plastisols B Y J O E C L A R K E Joe Clarke is the President of Synergy Inks a Chicago based corporation which manufactures t-shirt inks. He has held prior executive positions as President of M&R Printing Equipment and as Vice- President at Wilflex [Poly One]. Clarke has spent the past 49 years in the lab and in the engineering department, in pre-press and on-press, as an R&D / technical researcher and as a manager of screen print production. He has been granted a number of print-related patents and is the inventor and patent holder of Smilin'Jack brand printing blades. He is a member of the ASDPT, an SGIA Fellow, an Associ - ate Editor for NBM and a regular contributor to the SPTF Journal. Clarke has presented hundreds of papers, written a couple books and published more than 600 technical/management articles for which he has received an unprecedented six Swormstedt Awards for best of this annual, international competition. Left: Stirring is a time and temperature activity. Slow-speed mixers generate little heat, but after days of mixing, the ink will eventually increase in tack. The high-speed mixers on an electric or pneumatic drill or drill press have the advantage of speed, but a proportionally greater risk of overheating. (Im- age courtesy Wilflex) Right: Plastisol ink shouldn't dry in the screen, yet easily gels and cures for versatility. (Image courtesy Wilflex)

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