Dot gain is a challenge for garment screen printers, whether the job involves four-color process, simulated process, or index separations.
Dot gain is a challenge for garment screen printers, whether the job involves four-color process, simulated process, or index separations. Decorating textiles means working with surfaces that are 65-90% solid, which leaves a 10-35% chance of missing a printable surface.
Additionally, the substrate’s surface is absorbent and highly compressible, and the twisted yarn structure is highly irregular and not uniform. Forming a good gasket with the stencil in order to maintain dot integrity is almost impossible. We can’t do much about the nature of the garments, so our focus shifts to controllable variables on press.
Heads and platens
Dot gain increases as variation between heads and platens increases. In order to remedy the situation, you must have a way to determine platen-to-head distance. Numbering the heads and platens gives you a way to see what is happening between any given head or platen combination. How much distance qualifies as a step up or step down is up to us to determine based on our line count and tolerance for color variation within the run. A good starting point is to set the minimum off-contact to 0.06 in. An increase of 0.03 in. would constitute a step up to the next level. The highest level would be 0.12 in. or higher.
You also need to examine the ink. It must be suitable for use in printing halftones. A general-purpose mixing system may have too heavy a pigment load and create colors too dense for halftone printing.
Having the proper color strength measured before you even print the dot allows you to assess proper dot-gain profiles. Any change in total fabric height (thread diameter) or stencil profile (emulsion over mesh, EOM) will adversely affect the results. Use a relatively thin mesh, such as 280 or 305 threads/in. with 34-micron thread diameter in plain weave to control the physical growth of the dot that results from high ink volume. The thicker the mesh and stencil profile, the thicker the ink film. As the ink-film thickness increases, it provides physical volume that can smash and move around.
Likewise, thinner EOM and total stencil height will deliver a thinner ink film. This thinner film will appear not as dark—not as dense. The lower volume of ink means less physical dot gain.
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