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Dynamic Controls for Static

(December 2012) posted on Tue Feb 12, 2013

Learn about what static electricity is, the factors that affect it, and the methods available to counteract it.

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By Screen Printing's Solution Sourcebook

If your prints suffer from ink-adhesion problems caused by surface contamination from dust and particulates, or if you’re having issues with media sticking, binding, or misrouting, you may be shocked to learn that your issues are likely rooted in static electricity.

What is static electricity?
When a material or object holds a net electrical charge, either positive or negative, it is said to have a static charge. The term static is a relative one, as in many cases static charges will slowly decrease over a period of time. The length of time depends on the resistance of the material. For practical purposes the two extremes can be taken as plastics and metal. Plastics generally have very high resistivity. This allows them to maintain static charges for long periods of time; on the other hand, metals have very low resistances and an earthed (grounded) metal object will hold its charge for an imperceptibly short period of time.

Factors that affect static electricity
Many factors affect the generation and maintenance of a static charge. Among them are humidity, the type of material, repetition, and change in temperature.

Type of material Some materials are more readily charged than others. For example, materials such as acetate gain a charge very readily, while glass gains a charge less readily. Also the relative position of materials on the triboelectric series will determine whether a material charges positively or negatively dependent on the other material with which it has come into contact. For example, hard rubber, when rubbed against nylon, will become negatively charged but will become positively charged when rubbed against polyethylene.

Humidity Generally speaking, the dryer the environment, the higher the level of static charge and, conversely, the higher the humidity, the lower the static charge. In relative terms, water is a significantly better conductor of electricity than most plastics. Atmospheric humidity deposits small quantities of water on all surfaces in the environment; therefore, surface static charges on materials have a tendency to dissipate to earth by current flow through the surface moisture.

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.


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