High-field dielectric property of PET film under AC ramp voltage application

Polyethylene Terephthalate (PET) is a polar polymer and is best known as the material that constitutes a soft drink bottle. PET has excellent physical properties, such as, high heat resistance, low cold resistance, solvent resistance, and so on. It is also used as an electrical insulation or a dielectric material. In previous studies of Seki et al.(2014), in stepwise method to increase the AC electric field, the simultaneous observations of the dissipation current waveforms and electroluminescence (EL) for polar polymeric film PET and nonpolar polymeric film LDPE were carried out. From the results of observations, it was found that the nonlinear dissipation current waveform on PET at 50 Hz shows not only the large peaks at the former part of positive and negative half cycle, but also the small peaks at the latter part, and the hysteresis curve of the instantaneous current density J versus the instantaneous electric field E showed the hysteresis. Furthermore, the electric field dependence of the power loss density estimated from the hysteresis curve above the electric field of 26 kV/mm at the frequency of 50 Hz was shown the trend of saturation. In order to control the electric field application history condition, the simultaneous observations under AC ramp voltage application had been developed. Here, the time for observation was set for 10 s to make an electric field application condition same. There is another advantage. The short time electric field application makes possible to apply the further higher electric field, because the risk of occurrence of PD and/or breakdown are reduced. In this study, by using the AC ramp voltage application method, the simultaneous observations up to 60 kV/mm were carried out for both PET and LDPE samples in order to grab the conduction mechanisms of polar polymer.