Printwear

November '15

For the Business of Apparel Decorating

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2 0 1 5 N O V E M B E R P R I N T W E A R || 75 given potential ink volume. The jargon is a "thin thread" mesh. To be more specif- ic, when you're comfortable with the ink deposit, get a sample of the same thread diameter, but one count lower. When you feel you need more deposit for any reason, find the next larger thread diameter and drop two counts. If you feel the deposit is already excessive, then keep the mesh count but go with a thinner thread. Mesh count and thread diameter selec- tions are relatively plentiful in the 200 to 300 per inch areas; less than 200, howev- er, and the pickings get slim per any given manufacturer. The guidelines for concur- rent smoothness and deposit are dictated by the ink and blade but they will provide the best case for fill-rate and capacity and a smooth finish at the de- sired deposit per ink and blade. When selecting the best tension, it's important to steer clear of a screen that's "too tight." Consider two screens, one the ubiquitous 110/80 for the under-base and the other a 230/48 in the next head. Set the 110 at 40 N/cm² because you can, and the 230/48 at 25 N/cm² because you can't. There is nowhere that these two images will align on-press. First, they are both high capacity/low fill-rate meshes requiring lots of blade pressure. Second, the 110 is going to print closer to 70 N/ cm² while the 230 will hover around half that. If it's not lining up, and it won't, we should look at dynamic screen tension—a differential in static tension so that the dynamic tension on-press is consistent. Then, the images can easily be aligned. The oft asked question about the stencil is, "What percentage of mesh fabric thick- ness do you recommend for the EOM?" This is like asking, "If I drove nonstop from NYC to LA in 45 hours, how many calories did I burn along the way?" Sten- cil specifications which are based solely on EOM are fraught with danger. Suffice it to say we want EOM to be a result of the minimum flatness on the garment side [RzS1]. Anything thicker 1) doesn't help and 2) begins to get in the way of the flat- ness and smoothness of the under-base. Stencil EOM influences images about 3/16"-wide, so if the under-base has any areas greater than 3/8" (3/16" at one edge + 3/16" at the other edge), the perimeter of the image will be thicker than the cen- tral parts. This will have an adverse effect on the opacity and the surface appearance of the overprint colors. Higher EOM is a Band-Aid for excessive blade angle and errant off-contact distance, and excessive EOM will ensure a textured and unprint- able under-base. BLADE AND PRESSURE The blade should have an edge which is fitted to the tensioned mesh count and a profile which applies sufficient compres- sive-force and allows maximum shear- ing-force for a given ink/mesh combina- tion. It is always preferable but not always possible to run a near-zero angle, with minimum pressure and maximum speed. The maximum speed is dictated by the fill-rate of the mesh, the tack level of the ink, and the compressive/shearing-force ratio of the blade. Notwithstanding, speed at minimum angle and pressure with an optimal gap is the key to helping any given ink matte-down on the knitted garment surface. When we apply force to a blade we change the shape formed between the blade and the mesh. It appears this effort is the direct cause of ink transfer to the mesh—it is not. The shape and speed need to increase the fluid pressure in the ink which in turn caus- es a drop in viscosity. Then and only then does the ink enter the cells. And when we ask, "What is the best way to increase fluid pressure?" the answer is simple and singular: maximize the stroke speed. Below the "speed limit" with the optimal gap, increased speed will fill a larg- er percentage of the mesh with lower viscosity ink and a thin, flat smooth de- posit on the surface of the shirt. When we use stroke speed to produce the print, registration is automatically improved. Before defining how much image choke or spread is required, or whether we can hold registration, opti- mize the blade and press settings for max- imum speed. With the recommenda- tions herein, it is easy to run a quality white ink at maximum press speeds up to and including 80"/second stroke speed. UNDER-BASE INKS "We'll know one when we see it!" might be the singular thread which binds us to the under-base and to each other as printers. Some brave souls will take rasp- berry red, lemon yellow, and orange-orange and use them as under-base colors. This is a risky proposition. Nominal colors are as likely to be trans- parent as not, and no thickness of trans- parent color makes it sufficiently opaque to serve as an under-base. What's more, other than white, gray, or clear inks that have been formulated not to penetrate, When selecting the best tension, it's important to steer clear of a screen that's "too tight." Consider two screens, one the ubiquitous 110/80 for the under-base and the other a 230/48 in the next head. Set the 110 at 40 N/cm² because you can, and the 230/48 at 25 N/cm² because you can't. There is nowhere that these two images will align on-press. First, they are both high capacity/low fill-rate meshes requiring lots of blade pressure. Second, the 110 is going to print closer to 70 N/ cm² while the 230 will hover around half cm² while the 230 will hover around half that. If it's not lining up, and it won't, we screen tension—a differential in static tension so that the dynamic tension on-press is consistent. Then, the images can easily be aligned. The oft asked question about the stencil is, "What percentage of mesh fabric thick BLADE AND PRESSURE gap, increased speed will fill a larg er percentage of the mesh with lower viscosity ink and a thin, flat smooth de posit on the surface of the shirt. When we use stroke speed to produce the print, registration is automatically improved. Before defining how much image choke or spread is required, or whether we can hold registration, opti mize the blade and press settings for max imum speed. With the recommenda "We'll know one when we see it!" might be the singular thread which binds us to the under-base and to each other as printers. Some brave souls will take rasp Good matte-down is the first step in successful flash-cur- ing. (Image courtesy Brown Manufactur- ing Group Inc.)

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