Aerovex Formerly Modern Solutions

Time to Revise Strippers’ Practices

For years, pinholes, air pockets, and low- and high-humidity have plagued strippers and plate-makers handling film sheets in vacuum frames, camera copy boards, and step-and-repeat equipment.

But we’ve traced much of the strippers’ struggle to self defeating steps based on incomplete understanding of the causes of problems. Also, some new devices solve many of the complications.

For example, everyone in the prepress department thinks that the way to eliminate pinholes in halftone screens and solids is to wash the glass of a vacuum frame or step-and-repeat machine with glass cleaner. The problem is, cleaning the glass creates an electrostatic charge that itself attracts airborne particles. We recommend using a spray product designed to neutralize the static charge and apply a microscopic protective coating, together with air-ionization equipment.

Based on visits to a wide variety of plants, we think many traditional stripping-room practices need to be revised today, even the ordinary method of eliminating air pockets from between film sheets that are pinned together on the stripping table or vacuum frame. The common practice is to use your hand to smooth the film sandwich from front to back with a light sweeping motion.  But you create surface friction, which attracts dust particles. We recommend flattening the film, using a special wand that’s been treated with the static neutralizing solution.

Moreover, some users of the wand report a reduction in vacuum drawdown time, in some cases down to 45 seconds, or half the normal period.

Even the longstanding practice of cleaning with cheesecloth is suspect: the fabric sheds fibers badly. It’s better to use glass cleaner and a soft, low-lint wipe to remove dirt from the glass; then, apply a microscopic protective friction-eliminating coating once or twice per shift. Between each exposure, a magnetic wiping fabric ensures against friction and static build-up and removes dirt from the glass.

A Minneapolis printer uses a combination of static-neutralizing spray and “magnetic” wiping fabric to prevent dust-related pinhole problems. A major printer in Wisconsin credits the same combination with eliminating film jams, and subsequent remakes, on its step-and-repeat machine.

Myths persist when it comes to humidity-related static problems. Many experienced printers believe that static electricity vanishes with high humidity in the summer months and that low humidity in the winter can be overcome by using a moisture spray.

The fact is, high humidity doesn’t mean static electricity isn’t present. It’s simply that the voltage generated is below the threshold of human feeling, so your fingertips don’t feel the discharge of electricity. You still have to neutralize the charge to ensure your equipment and materials are truly clean.

Another long-held belief is that, when contact-exposing film, vacuum-frame pressure should be 26 to 29 lbs per square inch. Not so; lab tests show any reading higher than 17 to 23 psi risks possible film size change.

The new quick-draw vacuum frames, which eliminate air trapping by using a combination of negative and positive pressure, create less friction than older-style units, but they still need to be cleaned and protected against static build-up.

Where platemakers and press operators have the loudest arguments about plate registration on press, we can be sure an outdated pin-register system is to blame.

We recommend that prepress personnel refresh their understanding of static electricity problems, stay up-to-date with new systems that prevent friction and static build-up problems, and check for correct vacuum pressure reading. A few moments of preventive maintenance will keep quality levels high, interdepartmental arguments low, and production anxiety levels at a manageable level.

Written By: Eugene C. Bulinski & Richard Trankle