Effect of UV Irradiation on Vacuum Flashover Properties of Different Polyimide Films

Polyimide (PI) is a critical insulating material in spacecraft, and its vacuum flashover characteristics are essential for the stable operation of spacecraft. However, prolonged exposure to ultraviolet (UV) radiation in space can adversely affect the flashover properties of PI. In this study, two commonly used commercial PI films (Kapton-HN and Upilex-S) were subjected to UV irradiation experiments to systematically investigate the impact of UV irradiation on the flashover characteristics of PI films and compare their UV resistance. Scanning electron microscopy (SEM) observations revealed the formation of nanoscale pore-like defects, granular substances, and spotty marks on the films' surface after irradiation. X-ray photoelectron spectroscopy (XPS) analysis indicated significant changes in the chemical structures of both films post-irradiation. Flashover test results showed that the flashover performance of both films decreased after irradiation, but the reduction was relatively smaller for Upilex-S, demonstrating its superior UV resistance. Additionally, UV irradiation significantly diminishd the number of shallow traps and increased the energy levels of deep traps on the surface of both films, with Upilex-S-UV exhibiting slightly higher trap energy levels than Kapton-HN-UV. These findings provide valuable insights for the application analysis of PI films in space environment.