Preparation And Properties Of Silica Alumina Co-doped Polyimide Three-layer Composite Films

Recently, more and more attention was given to the polyimide/nano-inorganic composite material and application had been enlarged. Inorganic particle is the pivotal factor to enhance polyimide's performance. At present, primary inorganic particle is SiO₂,Al₂O₃,TiO₂. These inorganic particles could improve the electrical performance of polyimide film. But mechanical performance of PI films was debased because of incorporation of inorganic particles. It brings forward higher requirements for production of PI films with better performances.In this paper, the silica sol and nano-alumina is dispersed in PAA by ultrasonic, then thermal imiditation. A series of nano Al₂O₃-SiO₂ co-doped polyimide three-layer composite films were prepared with different content and different weight ratio. To fix on the best technics and analyze the effect of temperature and time which forms the first floor of films and thickness rate of monolayer of hybrid floor and pure floor on the imidization ratio, mechanical properties, thermal stability, the dielectric loss of PI composite films, orthogonal test was designed with five factors and four levels. The analysis of extreme difference showed that the best technics was temperature and time which forms the first and second floor 260℃, 120min; the thickness rate of hybrid floor and pure floor 1:1.Their fracture morphology and chemical group were analyzed by SEM and FT-IR. SEM photo showed that the PI composite films was three-layer clearly and the dispersion of inorganic particle was influenced greatly.In this paper, the orderliness of their transmittance of UV-Vis, thermal stability, mechanical performance, electric properties and corona-resistance of PI films were measured and analyzed with different content and different weight ratio. UV-Vis transmittance analysis showed that the transmittance of pure PI films was higher than PI composite film and the curve of UV-Vis was different distinctly with different content and different weight ratio. The best film was the film of weight ratio 4, content 2wt%. The curve of TGA showed that the decomposition temperature of PI composite film was 578℃, 3℃higher than pure PI film. The thermal stability of PI composite films was influenced less by the weight ratio and content of inorganic particles. The mechanical performances of PI/SiO₂-Al₂O₃ composite film were the best with the weight ratio 4, doping amount 6wt%. The tensile strength and elongation at break of PI composite film reached 107Mpa and 14%, which were 20% and 21% higher than pure PI film respectively. The dielectric loss of PI composite films was low, but higher with the weight ratio increased. Corona-resistance time was longer in comparison with pure PI film. When the weight ratio and content of inorganic particle was 4:1 and 6wt% respectively, corona-resistance time was 58min, and 222% longer than pure PI film.