Thermally Stimulated Discharge Currents from Corona Charged Polypyromellitimide Film

Thermally stimulated discharge current (TSDC) technique has been applied to investigate the polarization mechanism due to corona discharge in as-received and heat-treated Kapton® samples. The samples were charged on the upper free surface (non-metallized surface) by exposure to a negative corona discharge in air. Three peaks (termed as P₁, P₂ and P₃) were ob-served in the TSDC spectra. Tfie peaks P₁ and P₂ appear at 46° and 60°C, respectively and are in the normal current direction opposite to that of charging current. The heat treatment causes a decrease in the peak current which may be due to a reduction in the number of traps due to high temperature aging. The peak P₃ appears at 249°C in as-received Kapton samples and is in the normal current direction. For heat-treated samples this peak appears around 225°C and is in the abnormal current direction. For iodine doped samples the peaks P₁ and P₂ appear at 38° and 50°C, respectively and are in the normal current direction. The peak current is nearly 10 times that in as-received samples which may be due to an increase in the carrier mobility because of“handing-on”of carriers as a result of diffusion of 12 ions in the polymer matrix. The peaks P₁? P₂ have been attributed to shallow trap levels and peak P 3 to deep trap levels present in Kapton.