Modulation of surface electrical properties of epoxy resin insulator by changing fluorination temperature and time

In order to systematically investigate the modulating role of fluorination temperature and time on surface electrical properties of the epoxy resin insulator, epoxy resin sheets were surface fluorinated in a laboratory vessel using a F₂2/N₂2 mixture with 12.5% F₂2 by volume at 0.1 MPa and different temperatures of 25–95 °C for different times of 5–120 min. Conductivity measurements have shown that the intrinsic surface conductivity of the epoxy resin insulator could be modulated from an even lower value to a nearly four orders of magnitude higher value than the value prior to fluorination by changing the fluorination temperature and time. Surface conductivity increased with increasing fluorination temperature at the same fluorination time, while decreased to some extent with increasing fluorination time at a given fluorination temperature. Surface potential decay measurements showed consistent results with the surface conductivity measurements. ATR-IR analyses revealed substantial changes in surface chemical composition and structure, depending on the fluorination temperature and time. SEM images clearly showed an increase of the fluorinated layer thickness with increasing fluorination temperature and time. Surface cracks appeared only at elevated fluorination temperatures and increased with fluorination temperature, while the surface became compact with the duration of the fluorination. These results, compared with the previous results on an epoxy resin insulator made of DGEBA epoxy resin with a lower epoxy value, also indicated a significant influence of the epoxy resin insulator itself or the epoxy resin raw material on surface electrical properties and surface physicochemical characteristics after fluorination.