Electret behavior of PET films in various stages of production

Based on thermally-stimulated current (TSC), laser-induced pressure pulse (LIPP), and isothermal charge decay (ICD) measurements of PET films in various stages of production, we discuss charge accumulation and dipole orientation introduced by the production process and subsequent positive or negative corona charging of such PET films. In the prefilms and in the final films, negative charge is more stable than positive charge. Negative charge is generally injected into both sample surfaces by a pinning process and by contact electrification during the production process, where the film is running over metal and other rollers. The TSC depolarization temperatures are about 80°C for the polarization, 90 to 130°C for positive charges and 110 to 140°C for negative charges