Research on drying and impregnating temperatures of PP film by the change of the sizes in thermal shrinkage test

The authors report the thermal shrinkage test results on R-type polypropylene (PP) film exposed to atmosphere (non-impregnation) and immersed in dielectric liquid (impregnation). The results show that the sizes of machine and cross directions of PP film decrease with increasing temperature in two cases, and the thickness increases, but the starting temperatures bringing about the changes of the sizes are different. The results also show that the change of the thickness may be divided into three regions and is related to the change of the sizes of the machine and cross directions. The starting temperature bringing about the cross direction shrinkage is an important transition point in the change course of the thickness and an important index for selecting the technology temperature of PP film in a power capacitor