Improved resistance of epoxy resin to corona discharge by direct fluorination

Our recent studies have indicated that direct fluorination can modulate surface electrical properties and suppress surface charge accumulation of epoxy resin insulators. Further, to investigate the resistance to corona discharge of the fluorinated surface layer, the surface fluorinated epoxy sample together the unfluorinated (virgin) one were corona treated in synthetic air using a multi-needle-to-plate electrode system. ATR-IR and EDS analyses and SEM surface and cross section images show that the corona treatment did not lead to cleavage of the C-F bond in the fluorinated layer and to changes in its surface morphology and thickness, although the treatment attacked the cross-linked products generated by fluorination and the weak points at which the fluorine substitution or addition reaction took place only partially. In contrast with this, the virgin surface layer was degraded by the corona treatment, likely in the form of ablation. Measurements of surface potential decay and water contact angle indicate that the corona treatment caused a decrease in surface electrical conduction of the fluorinated sample due to the attack on the cross-linked products and the weak points, but did not change its surface wettability and did not produce soluble degradation products in the fluorinated layer. On the contrary, the measurements show that the corona treatment led to an increase in surface conduction of the virgin sample, and surface conduction of the corona treated virgin sample was highly sensitive to the humidity due to the presence of soluble degradation products on the surface.