Factors that influence the corona charging of fibrous dielectric materials

Corona discharge has a wide range of industry applications, such as charging the photosensitive layer and the toner particles in photocopying machines, modifying the wet-ability of plastic films, and conditioning the electrets for air filters. In all these situations, it is important to evaluate the surface charge density and compare it to the dielectric rigidity of atmospheric air. Experiments were carried out on 0.3 mm and 0.8 mm thick non-woven polypropylene fibrous media (average diameter of the fibres: 20 μm) that were exposed to positive corona discharges from a wire–grid–plate electrode system. The electrode system was powered from a continuously-adjustable DC high-voltage supply, employed as constant current generator. The monitored variable was the surface potential detected by the probe of an electrostatic voltmeter. The controlled variables were the potential of the grid electrode and the pre-conditioning temperature of the samples. The results of the experiments enabled a crude evaluation of each factor effect. Research should continue, using the experimental design methodology, in order to establish the optimum operating conditions.