March '15

For the Business of Apparel Decorating

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86 | PRINTWEAR M A RC H 20 1 5 Screen Tension Screen Tension mesh limits wet-film thickness, which is empirically established as appropriate. But the surface flaws aren't about the thickness. These "artifacts" are due to low ink volume at that wet-film thickness. Metaphorically, let's use a 4" X 5" X 1/4" slice of Swiss cheese as the current low-volume mesh and a slice of cheddar as the recommended high-volume mesh with the same size and gauge. Both slices have the same film thickness, but the cheddar has higher volume with fewer pinholes. It's also smoother and bet- ter mattes down the surface. Similarly, higher-volume meshes print faster with superior transfer, matte down, penetration, hand, and drape. However, proper use is necessary, so pay attention to the requirements of these superior fabrics. THE CAVEATS Using the wrong mesh and blade package and then running the press slower because it isn't calibrated is the same as run- ning kerosene in a high-performance sports car that hasn't been tuned up. There are four planes in which all stations and heads must be parallel: carriage, blade edge, screen, and platen. Once the four are perfectly parallel, the much maligned off-contact must be set. First, the off-contact does not rip screen mesh; old-fashion blades rip mesh. When using a hinged blade, you can set optimal gap without fear of mesh pops, which gives us perfect matte down with a smooth surface and excellent cov- erage. On a 23" X 31" frame at 27N/cm 2 with a 200 or so mesh, there should be a 3/16" gap, 5-degree blade angle, approxi- mately 25 PSI pressure, and maximum stroke speed. When the carriage is parallel to the screen, the flood bar carries a thin, consistent coating over the entire screen. The squeegee is paral- lel when it cleans and clears the entire mesh with minimal pres- sure. All heads are parallel when each color prints identically on Figure 2. This image shows a 330/23 screen mesh prior to the finishing process. Per cell of mesh, its cross section is an hourglass shape (1). After properly coating the screen's garment side, the hourglass becomes a funnel (2), and when both sides are coated, the funnel transforms into a tunnel (3). This coat- ed mesh may leave little time for a stencil professional to coat it properly with face and back coats, but it's well worth this invest- ment. (Images courtesy of the author) ++ Increasing Viscosity -- 1. Fluid pressure/ velocity loss 2. Fluid pressure increase/volume loss 2 +++ Increasing Viscosity --- 1. Fluid pressure/ velocity loss 3. Fluid pressure/ velocity loss 2. Fluid pressure increase/volume loss 1 + Increasing Viscosity - Maintains fluid pres- sure and velocity while it regulates paste volume. 3

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