What's the best order to print the four colors in four-color process? A definitive conclusion has eluded even the most technical screen printers. Read on to discover how scientific experimentation has established a better answer.
Also appreciate that a low Rz (stencil roughness) is needed to stop squeegee-induced gain. This is why it’s so important never to print four-color work with a high-Rz stencil. If you have a stencil with both low EOM and low Rz, then your single-color prints are under excellent control (dot gains typically < 10% and with a total immunity to squeegee settings, print speeds, etc.) and your dot-on-dot problems are minimized.
In our study, we found no skipping, our dot gain was under good control, and the job was easy to print. The stencil also has a proven high fidelity from film to print, so we were reducing stencil-induced color shifts to a minimum.
2. Make sure you have the right CMYK intensities from your inks. We have to admit a slight error here based on our inexperience. We printed our solid inks onto our chosen substrate (a matte, coated paper) then based the inks until they reached the required ISO density standards for four-color process. What was our error? We forgot that the paper absorbed a small amount of the ink, so the intensity of the first ink down is higher than that of subsequent prints. In hindsight, we should have based the inks to a compromise value based on densities obtained by printing onto a non-absorbent plastic substrate. However, we found that we are not alone. Many printers make this error and ascribe the reduced color of sub-sequent inks to a so-called trapping effect. Simple experiments on non-absorbent substrates show that such trapping is a myth.
3. Choose a set of screens that gives zero mesh moiré. We chose to print at 80 lines/in. and used the MacDermid Autotype Mesh Moiré Calculator to determine that our C, Y, and M screens at 37.5, 82.5, and 7.5° would be free of mesh moiré on a 150-thread/in., 31-micron mesh, but that strong moiré would appear in the K at 67.5°. We therefore printed the K on a 180-thread/in., 27-micron mesh, shown on the Calculator to be moiré free at the same angle.
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