Is static standing in the way of quality and productivity in your shop? This discussion will help you identify sources of static electricity as well as the types of systems available to eliminate it from your production process.
By David Rogers
Repetition Repeated actions, such as friction or separation, increase the level of charge found on a material. For example, a plastic web moving over a series of Teflon rollers will increase its surface charge after every roller.
Battery effect The combination of many charged items can lead to extremely high charges. For instance, individual sheets of plastic with relatively low surface charges when stacked together can generate extremely high voltages.
Change in temperature As a material cools down it has a tendency to generate charge. The action of the cooling is to leave a net charge on the material throughout its entire volume. If the material is a very good insulator the internal (volumetric) static charge can be maintained for extremely long periods of time. However, over time this charge normally migrates to the surface, at which point it becomes a surface static charge. An example of this is an injection molding that is seemingly neutral when hot but can subsequently be found to have a large surface charge once cool.
Common electrostatic problems
The main static-related difficulties printers face include electrostatic attraction, material misbehavior, and operator shocks. Electrostatic attraction (ESA) involves the attraction of airborne particles to charged surfaces—or the attraction of charged airborne particles to surfaces that may be totally free of any charge. This problem affects most plastics-based applications. The ESA effect can attract dust to substrate surfaces and ultimately damage print finishes.
Material misbehavior is another form of ESA. The problem manifests itself in the form of the product itself, usually in the form of material webs, fibers, or sheets sticking to themselves or equipment, misrouting, or repelling inks and coatings. Automated printing processes are particularly prone to this problem.
Operator or personnel shocks are becoming increasingly significant as companies look to improved safety standards. These shocks can be painful, though the effects are usually quite safe and short lived. However, in extreme cases, the debilitating effects can cause personnel collision or entrapment with associated machinery or can even initiate a fire or an explosion in hazardous areas.
Methods of elimination
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