Preparation And Properties Of Nano Silicon/Aluminum Hybrid Polyimide Film

With the rapid development of modern science and technology, the AC motors have been widely used and obtained good economic benefits, while a higher level of the electric properties of insulation material on motor are required. Introducing nano-oxide to the traditional insulating materials, not only can keep the original high-temperature performance, but also can significantly improve the electric properties, which has received much attention.In this paper, nano-SiO₂ and nano-Al₂O₃ were prepared by sol-gel process and hydrothermal process respectively, and were doped into polyamic acid then. A sequence of three-layer composite polyimide film was prepared by fixing the inorganic content and regulating the molar ratio of nano-SiO₂ and nano-Al₂O₃. Their chemical constitution, surface morphology, electric properties, optical properties and thermal stability were analyzed and measured respectively by FTIR, SEM, corona discharge measuring equipment, breakdown strength measuring system, UV-VIS spectrum and TG.The FTIR spectrum indicated there were carboxyl groups in three-layer composite polyimide film. It can be observed by the SEM, the inorganic nano-particles in polyimide matrix were more evenly distributed, nano-SiO₂ play a role in the dispersion of nano-Al₂O₃, the dispersion of inorganic nano-particles in PI/SiO₂/Al₂O₃ film was better than in PI/Al₂O₃ film. The corona-resistant lifespan of three-layer composite polyimide film was greatly longer than that of pure polyimide film, when the molar ratio of SiO₂ and Al₂O₃ was 1:9, it maximized and was 24 times longer than pure polyimide film. The dielectric strength of pure polyimide film was up to 387kV/mm, which was higher than that of three-layer composite polyimide film. Comparing with Kapton 100CR film, the dielectric strength of three-layer composite polyimide film was higher than that of Kapton 100CR film, when the molar ratio of SiO₂ and Al₂O₃ was 1:13, its dielectric strength was 358kV/mm. The UV spectrum revealed that the T% of composite films was smaller than that of pure polyimide film. The curves of weight loss with temperature showed that the thermal stability of three-layer composite polyimide film was better than that of pure polyimide film, the thermal decomposition temperature was 6⁷℃higher than that of pure polyimide film.