Increase in breakdown strength of PE film by additives of azocompounds

PE films with various additives were prepared by the solution-grown method. The thickness of the films ranged from 5 to 25 μm. Six different azocompounds were used as additives. The results show that BDS 0 for the film with additives was higher than that for the film without additives in the temperature range from -35 to 30°C. The increasing ratio of BDS depended on the composition of the additives used. Our results indicate that the breakdown of the film is induced by an electron avalanche. The conduction current through the film in the high electric field region was reduced by using the additives. The dependence of the conduction current on additives corresponds to that of BDS; a higher BDS is realized for films with additives by which the conductive current is controlled at the lower value. It was considered that the reduction of current by the additive is due to either the trapping effect or the excitation effect of the additive. The trap level for the additive and the excitation energy depend upon the type of radical connected on the benzene ring of the additive: electron-accepting or electron-donating type. The results suggested that high BDS and small current are obtained when the azocompound on which the electron-accepting radical is connected is used as the additive