Accelerated Discharge of Corona-Charged Nonwoven Fabrics

Fibrous polymers with extremely low electrical conductivity such as polypropylene (PP), polycarbonate, polyurethane, and polyethylene are commonly employed as air-filter materials. The charge accumulated on such materials due to tribocharging effects inherent to the manufacturing process might be harmful either to the operator or to the electronic equipment of the production line. Whenever charge buildup cannot be avoided, it is important to have an effective method available in order to rapidly discharge the materials. The present work aims to evaluate the efficiency of active neutralization of charged nonwoven fabrics. The experiments have been carried out on 0.4-mm-thick PP and polyester fibrous media, with the average diameter of the two types of fibers being 28 and 19 mu m, respectively. The nonwoven fabrics were charged by exposing them to a negative corona discharge generated by a wire-grid-plate electrode system. The samples, laid on the surface of the grounded electrode or suspended at a small distance (4.6 mm) above it, were then subjected to the action of the bipolar ions generated by a commercial neutralizer (model 6430, Ion Systems Inc., Berkeley, CA). 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, the neutralization time, and the distance between the neutralizer and the media. 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 conditions for charge neutralization.