User login

The Print Sequence Project

(July 2007) posted on Tue Jul 24, 2007

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.


By Tricia Church

click an image below to view slideshow

Contradictions abound when it comes to the best sequence for printing CMYK. Disagreement in the industry, even among the scientists who strive to fully understand screen printing, makes it hard for printers to know what is best for them and their customers. We accept that finding the perfect answer is virtually impossible. The function of our study was to find a good compromise.

One issue on which we can all agree is dot-on-dot gain (Figure 1). With a small dot, just after the squeegee has passed, a modest amount of ink becomes ready to be printed. A larger dot makes much more ink ready to be printed. A certain amount of ink is printed when the sten-cil is nicely in contact with the substrate. More ink must be printed when the stencil is held above the substrate by the presence of a preceding dot.

The definitive study of this effect was carried out in 2001 by Eiffion Jewell’s team at Swansea University. Their study showed that the amount of gain depended on the dot size underneath. A small dot yielded small dot gain, a large dot (i.e., something approaching a solid) also gives a small gain, and intermediate dots give the largest gain. This means that no simple correction process can compensate for the effect. So we can guarantee that we will have dot-on-dot problems and that no print sequence can be perfect. Let’s move on to some other basic ideas.

The rules

A successful study is one that has the basics in place. The following five aspects of printing four-color jobs are entirely under your control. If you don’t follow these guidelines, the dot-on-dot nightmare will simply get worse.

1. Use a low-EOM, low-Rz stencil. It’s now widely appreciated that a low emulsion over mesh (EOM) gives you the smallest dots and therefore minimal dot-on-dot gain. High EOM regularly causes skipping in addition to terrible gain, and printers often confuse skip-ping and moiré. The rule is simple: Never print four-color work with a high-EOM stencil!


Terms:

Did you enjoy this article? Click here to subscribe to the magazine.