Over the years we’ve received quite a few tips for controlling static on folding machines and bindery equipment, many of which we have shared here on our Bindery Success Blog. (Click Here for last week's post on folding machine static.) The problems caused by static in printing are numerous and complex, including double sheets, sheet mis-feeds and mis-registration, sheet delivery issues, dust contamination and ink problems. It can shut down production and ruin jobs.
Is there a cure for static problems or at the very least, an effective way to control them? First, a simple overview of static. Everything is made of atoms which normally have a balanced electrical charge (the protons and electrons are equal.) Static charges result when two different materials come into contact and then pull apart, creating a surplus of protons (positive charge) or electrons (negative charge.) The protons or electrons actually move from one material to the other. In the pressroom or bindery, this contact is occurring non-stop, with paper potentially touching hundreds of metal or plastic parts during the course of printing and print finishing.
We know that moisture is a conductor of electricity. In the relatively humid warm months, the static charges dissipate almost as quickly as they are created because the moisture is available to conduct the charge away and restore balance to the charged material. In the cold, dry winter months the reduced humidity in the air makes the air more of an insulator rather than a conductor. Since the static charges now have fewer places to go they build up in either the machine or in the paper. Paper is a non-conductive (insulating) material, thus the static charges build to a greater level than in a metal, conductive material.
Depending on where the charge is happening, you then have sheets sticking to sheets, or sheets sticking to machine parts. Like charges repel, and unlike charges attract.
According to Dillon Mooney, Technical Consultant for the Printing Industries of America, (PIA) “There are numerous static control devices on the market that will help reduce static on equipment but the cause of the problem is often low relative humidity.”
Static control devices do indeed have an effect, but the outcome is closely tied to the relative humidity. Says Mooney, “Static typically becomes a problem with relative humidity below 40%; below 30% static buildup can be a disaster. The recommended relative humidity for pressroom and bindery year round is 45%-55%. I like to see 50-55% in the winter…If the RH is below 30% one can put all the static removal gadgets and tinsel on the equipment and it is not going to make much difference.” (Proper grounding of a machine also helps dissipate high static charges, and is required for proper functioning of static tinsel.)
In answer to our question above—no, there is not a cure for totally eliminating static. It’s literally a force of nature but it’s one that can be managed if you create the proper environment. Once the proper environment is achieved, the correct installation, location and use of static control devices will help you to manage the problem.
Some readily available resources:
Paper companies have guidelines on how to correctly acclimate paper to your pressroom, which is an important step in static control. Sappi Paper has a brief pdf guide here, Cause & Effects of Static Electricity in Paper.(Or search their library here if you have trouble downloading the pdf.)
The PIA also has publications available that touch on the topic of static with regard to paper, ink and press operations. Links to details on these valuable references are included below.
What the Printer Should Know About Paper
What the Printer Should Know About Ink
Sheetfed Offset Press Operating
Web Offset Press Operating
Any reputable static control manufacturer will have engineering consultants available to help you pinpoint and control your static issues. Remember that any time two different materials touch there is the potential for static. With dozens, or even hundreds of potential sources, determining the exact location and charge of static can be tedious without the right equipment such as static meters.
One thing scientists and engineers agree upon is that maintaining the correct relative humidity is a necessary ingredient for controlling static in your printing or bindery operation. Good luck and don't worry...spring is just around the corner!