Electrostatic charge occurrence, significance and measurement

Abstract

Polymeric materials often have a resistance to earth in excess of 10 6ω. This condition results in the ability to accumulate and store electrostatic charge over significant periods of time. Once an electrostatic charge has been gained (either by tribocharging or corona discharge techniques) it reduces at a rate depending on the resistivity of the material, and on the level of charge remaining on the material. The dependence of charge decay rate on charge magnitude is described by the relaxation equation; however, charge decay values are often quoted (for a fixed time period). Such values can be ambiguous and often lead to erroneous conclusions; a new ‘performance rating’ system is introduced here, giving an accurate and easily interpreted indication of charge decay rate and charge levels involved. Measurements of surface charge are obtained by electrostatic fieldmeters, one of which is linked to a data-logger for automatic data collection for manipulation and presentation of results. This procedure enables accurate assessment of antistatic systems and atmospheric effects (such as relative humidity).