What Is A Stencil Rz Value And Why Is It Important?
Rz is a measure of the roughness or smoothness of a surface. It is an important screen parameter because it measures how efficiently the print side of the stencil controls edge definition when printing demanding artwork. For example, artwork containing fine lines or halftone dots. The stencil not only carries the detail of the image to be printed, it also has to function as a gasket to prevent ink from bleeding outside the image area under pressure from the squeegee during the print stroke. Any undesirable spreading of the ink typically causes a saw-toothed appearance on the edge of detail and fine lines. Plus it will obliterate fine reverse type. It also results in star-shaped halftone dots that cause dot gain and loss of contrast and detail, and can induce localized moiré.
In order to ensure a high-quality stencil, the Rz value must be controlled within narrow limits. Too rough, and the stencil will not gasket correctly onto the substrate. Too smooth, and the vacuum formed when printing on polished substrates will cause cobwebbing and splattering of the ink. Ideal values for most high-quality printing applications fall in the range of 4-10 microns.
