Electrical and Thermal Response of Layered Polyimide Films

Polyimides belong to a group of polymers that exhibit excellent thermal and chemical resistance, and good mechanical properties. Their electrical properties are improved or modified by incorporating a second layer having different dielectric properties. This paper concerns the dielectric properties of kapton¿ coated on one side with a thin layer of teflon¿. In order to understand the influence of the coating, layered and un-layered kapton¿ are studied under identical experimental conditions. Investigations on absorption, desorption and transport currents are measured in both specimens, at electric fields up to 12 MV/m, temperatures up to 200°C and two electrode materials. Two different thicknesses are employed to obtain insight into the volume effects. The experimental results indicate that the charging current decays with time in both films according to a power law having index n. Application of various conduction theories show that the mechanism of conduction in un-layered polyimide for the temperature range 50-90°C is dipolar; at higher temperatures charge carriers are generated within the volume. The results for the layered polyimide are also analyzed using known dielectric theories and the role of the layer material in the composite material is deciphered. These are the first ever investigations in the layered polyimide.