Injecting charges on large-area electret thin film by corona multi-pin discharge method

Corona discharge plays an important role in industrial and commercial applications, especially for large-area corona discharge need. It is a common method for the electrets industry. Nevertheless, achieving uniform charge distribution of the large area electret films is difficult. In order to achieve uniform surface charges distribution in large plane, the multi-pin-grid-plate electrode system which was powered from two continuously-adjustable DC high negative voltage suppliers (one for the multi-pins, the other for the grid) was employed. In this paper, electrostatic potential was measured by a large-scale automatic-controlled XY table which could efficiently measure over 30 cm × 30 cm electret materials. First of all, one pin experiment in large plane was established to find out the optimal charge range and surface potential with the temperature and relative humidity fixed. The set of associated parameters for the single pin system was identified with respect to a set of different spacing between the discharging pin and the sample. Then, the spacing that can has strong influence on the electric field applied to the film became the only parameter monitored. The surface potential measured was around 30 cm × 30 cm, which was limited by the operating ranges of the automatic-controlled XY table used. The aim of this paper is to establish the optimal distance between the multi-pins. In addition, the grid device was added to ensure uniform charge distribution within the samples.