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Preparing Digital Files for Screen Printing

(October 2002) posted on Wed Oct 09, 2002

Learn how to make other types of artwork fit the screen-printing mold.

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By Mark A. Coudray

The most common corrected angle set for screen printing is Y = 7.5°, C = 22.5°, M = 82.5°, and K = 52.5°. These values will work for 95% of all screen-printing applications, even with the very fine line counts used by CD decorators. Also note that by using mesh with a lower thread diameter and plain weave, your chances of success increase substantially.


When rotating angles away from the default set used by the imagesetter, be aware that you may need to disable what is known as a screen filter. This is a subprogram or routine used in some RIP programs to help avoid conflicts when many different design elements are placed into a file for output.


Often the placed images will include their own halftone information, which is embedded in the overall design file. This means that each placed file could have different dot shapes, angles, and line counts than those established for the entire graphic. The screen filter makes sure that all of the image elements, including placed files, output with the same angles, dot shapes, and line counts. Unfortunately, such screen filters only apply the standard output angles for lithography and rarely support line counts below 65 lines/in.


To avoid the screen filter, you must open every placed file and make sure the screen angles and halftone information correspond to those used throughout the image. The screen filter must then be disabled on the imagesetter RIP. If you use a service bureau to output your separations, the bureau may need to restart its RIP in order to disable the feature, then turn on the feature when your separations are complete. <P><B>Proofing digital files</B>


Another challenge we confront is how to proof the images we will be printing. Since screen-printed images at 65 lines/in. or lower have color and halftone characteristics similar to lithographic prints, traditional overlay proofs, Chromalins, or Matchprints will work just fine.



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