This article highlights some of the most important variables in the process and offers tips for achieving consistency.
Thinking of oneself as a manufacturer of screen printing rather than as a screen printer can be the conceptual key to standardizing and ultimately upgrading production. Successful manufacturers try to leave nothing to chance. They purchase reliable raw materials from reliable suppliers. As they make production improvements, they measure and document everything. Once they optimize production, they document work procedures and insist on check-offs at each step in the manufacturing regimen. Let’s take a look at factors that influence stencilmaking and how to standardize these factors for best results.
Most jobs don’t require clean-room conditions, but all shops can benefit from daily dusting and a few laps with a wet mop to reduce airborne dirt, dust, and lint. Temperature and relative humidity should be controlled, because they can affect exposure time directly, as well as dimensional stability and registration and the ink behavior on press.
Into the stretch
Successful stencils begin with several important elements that, strictly speaking, don’t involve making stencils at all. Mesh should be selected for the requisite ink deposit, with a mesh count that correlates with fineness of line and halftone detail, and be stretched properly on a frame that will not yield.
Stretching affects the off-contact distance—and, therefore, the amount of stencil flexing during printing and consequent stencil wear—and the dimensional stability of the stencil, which ultimately affects registration. Mesh manufacturers publish information on optimal stretching for every screen mesh they manufacture. Just ask. Arbitrary terms such as tight or bongo-drum-head tight aren’t good enough. Measure mesh tension with a tensiometer (Figure 1).
Dmax, Dmin, and delineation
Most shops don’t use CTS imaging yet and, therefore, must use intermediate artwork. The art should have sufficient density—a Dmax of 4.0, measured on a densitometer, is ideal—to block light from the image areas, sufficient clarity (a low Dmin) to transmit light into the stencil material’s non-image areas, and sharp edge definition (acutance) between the two.
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