Charge profiles in corona- or electrode-charged fluoropolymers

Various types of Teflon^TM homo- and copolymers (TFE, FEP, PFA, and Tefzel^TM E-TFE) were negatively or positively corona- or electrode-charged in high electric fields at temperatures of up to 200°C. Charge spreading in thin films of these polymers was studied by means of Piezoelectrically generated Pressure Steps (PPS). Depending on the charging parameters, space-charge profiles ranged from thin charge layers near the film surface to more or less uniformly spread bulk charge in both negatively and positively charged samples. Even for very high surface potentials (±5 kV) and long charging times (one hour), almost no charge spreading was observed after corona charging at room temperature. At high charging temperatures and-on negatively electrode-charged Teflon^TM FEP-at high DC fields, uniform charge spreading is found. From the calibrated results, maximum space-charge densities of up to 2400 C/m³ were observed on room-temperature corona-charged Teflon^TM polymers