Structure And Properties Of Nano-Aluminum Sol Modified Polyimide Film

The development of modern high-tech puts forward higher requirements on the kinds and the performance of engineering dielectric materials. Because the polyimide has a series of excellent performance, and nano-technology can improve the properties of the traditional dielectric materials, nano-hybrid polyimide materials attract much attention. Kapton 100CR inorganic nano-hybrid film produced by DuPont has been widely applied in electronics and electrical fields for the outstanding corona-resistant performance and thermal conductivity.In this paper, the nano-alumina material is prepared by sol-gel method,and preparing the single-layer hybrid film and the three-layer composite film. By the aid of breakdown strength measuring system, corona discharge measuring equipment, dielectric spectrometer, SEM and so on, the film's electrical properties and surface morphology were measured and characterized respectively, and the experimental results were analyzed and discussed.Through the analysis of the experimental results, it is shown that the corona-resistant lifespan of single-layer hybrid film is significantly longer than that of pure PI film ,and the corona-resistant lifespan of the three-layer composite film with 24wt% amount of alumina is 24.3h, whose lifespan is longer than the single-layer hybrid film with same amount of alumina, but comparing with DuPont film whose corona-resistant lifespan is 43.16h under the same experimental condition, there is still some discrepancy.The breakdown strength of hybrid film and composite film is lower than that of pure film, while the breakdown strength of three-layer composite film is significantly higher than single-layer hybrid film, and it is similar to that of Kapton 100CR film. The relative dielectric constantεrof single-layer hybrid film increases as increasing of the inorganic content at the same frequency. The relative dielectric constant εrof hybrid film decreases as increasing of the frequency at the same inorganic content. The dielectric loss tanδof hybrid film increases as increasing of the inorganic content at the same frequency in low frequency region, The dielectric loss tanδof hybrid film decreases as increasing of the inorganic content at the same frequency in high frequency region. SEM of hybrid film showed that inorganic nano-particles are dispersed evenly in the polyimide matrix, it is well compatible between the organic phase and the inorganic phase. However, there is some big secondary reunited particles, the diameter of which is longer than Kapton 100CR film, that will influence the performance of the hybrid film.