August '18

For the Business of Apparel Decorating

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62 || P R I N T W E A R A U G U S T 2 0 1 8 is high shear-rate transfer, e.g., optimal gap, minimum angle and pressure, and maximum stroke speed should support these goals. The dynamic edge of the blade should fit the tensioned mesh, specifically between one mesh open- ing and one opening plus one thread. The dynamic flexion of the blade is predicated upon the required downward force on the ink. Because these two metrics are indepen- dent, the two methods of dealing with fit and flex is via laminate blades or one of several beveled edges. The goal is to eliminate the need for "t weaking" the angle and pressure on the blade and to put the control of shear-stress in the blade design. 6. Physical properties. The length of the blade should be 1" to 2" longer than the image is wide with minimum stroke length. Excessively soft blades bounce on an irregular surface, particularly on coarser mesh where they force us to use excess pressure and reduced speed. Ex- cessively hard blades bridge the surface and reduce the deposit on coarser mesh- es forcing us to use excess angle then excess pressure at reduced stroke speed. The ends of the blade should be ground down or cut to a small radius to prevent isolated stress at the edges of the stencil and the mesh. 7. Durometer vs. moduli. The chart above names a single 70-durometer blade as 100 percent moduli and then it com- pares a range of durometers according to the compressive modulus and flexur- al modulus as a percentage. Durometer units are a bit like body temperature; 5 units (think five degrees) is a ton. Once you have selected the best squee- gee, it's time to insert the blade in its holder and take proper measurements to maintain the blade. INSERTION In the U.S., standard blades are 3/8" X 2". Most of the holders are aluminum, and the elastic blades are secured with bolts. Excess force crimps the open- ing of the holder to less than 3/8" at which point a pair of Wonder Bars should be used to pry the holder open with- out damage. Do not force the blade into the holder unless you want to print with an inconsistent edge. Once the bars open the holder greater than 3/8", the blade can again be secured. Never overtighten the blade. If the holder is not corroded, use a torque wrench set to 15-ft.lbs. MAINTAINENCE The main components of blade mainte- nance are the following: 1. Wash up: Polyurethane (PUR) is vir- tually unaffected by plastisol inks, so when we print plastisol, we recom- mend the mildest wash up available. Ink degradant and a pressure washer make quick work of an ink-covered blade. If we use water-solvent based inks, especially discharge, HAS, or PUR inks, a stronger chemical is need- ed, and wash-up must be done imme- diately after the press run. Be certain not to use alcohol or solvents contain- ing alcohol in any case as these will quickly degrade the "rubber-band" phase of the blade making the blade brittle and thereby quickly leading to edge-erosion while on press. 2. Sharpening: When the ink of choice is plastisol, the blades seem to last forever. SQUEEGEES continued on page 79 (Chart courtesy the author)

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