Corona Charging and Charge Decay Characteristics of Non-Woven Filter Media

The surface potential decay measurement techniques are commonly employed for adjustment of Xerox-photography processes, development of electrets, and assessment of polyethylene films for cable insulation. In all these situations, it is important to evaluate the surface charge density and compare it to the limit imposed by the dielectric rigidity of atmospheric air. The aim of this paper is to enhance the efficiency of corona charging of non-woven filter media for heat, ventilation and air conditioning applications. In a first set of experiments, samples of non-woven polypropylene fibrous medias were exposed to positive and negative corona discharges from a wire electrode. The current-voltage characteristics of the electrode system in the presence of the media, corroborated with the results of both surface potential decay plots and charge measurements clearly show that the surface charge is limited by the local discharges that occur inside the fibrous dielectric in contact with a grounded plate electrode. The second set of experiments pointed out that the use of a triode-type electrode arrangement may reduce the variability of corona-charging of non-woven medias, though it does not significantly increase the surface charge density.