Effect Of Imidization Process On The Structure And Performance Of PI/Nano-Al₂O₃ Three Layer Composite Film

Due to its excellent electrical insulating properties,polyimide film is widely used in the fields of electrical insulation,micro electronics,aerospace and so on.With the continuous development of science and technology,electrical technology is gradually developed to the high voltage and ultra high voltage,miniaturization,and variable frequency speed regulation technology.The traditional polyimide films are difficult to meet the requirements,which promote the development of high performance and functional orientation of polyimide films.In this paper,a series of polyimide/Al₂O₃ three layer composite films were preparaed by choosed pyromellitic dianhydride?PMDA?and 4,4'-two amino two phenylether?ODA?as monomers,N,N-two dimethyl acetamide?DMAc?as solvent,and gas phase Al₂O₃ as doping phase.The imidization process of the first and second layer was controlled to obtain the PI/Al₂O₃ composite films with different interfaces between layers.The effect on the structure and performance of PI/nano-Al₂O₃ three layer composite film,especially the corona resistance property,were investigated.Firstly,the optimal dosage of Al₂O₃ in composite films were determined.Results show that when the Al₂O₃ content is 12 wt%,the corona resistant performance and the breakedown performance of the composite films is the best,which indicate that12 wt% is the optimal doping.Ten different imidization processes were designed on the basis of the optimum doping amount,and a series of first and two layer imidization processes were prepared.The FT-IR was used to evaluate the imidization process of the first layer of the composite films and the imidization degree was calculated.Results showed that all the infrared spectrum indicated a series of characteristic peaks of polyimide.However,when compared with the infrared spectrum of totally imidized polyinide,the peak strength of the obtained polyimide composite films was a little weak.SEM micrographs on the fractural surfaces of the composite films showed that all the composite film have typical three layer structure.In the case of low imidization degree of the first layer of composite films,the combination state between first and second layer was rather weak,and a separation was clearly found between layers.With the increase in the imidization degree,the combination between layers was also become well,and the separation disappeared.Corona resistance testing results showed that with the increase in imidization degree,the corona resistance time of the composite films also increased.Moreover,the SEM analysis on the surfaces and breakdown holes micro structure of the composite films after corona testing showed that with the increase of first and second layer imidization rate,the better of the combination degree of the composite films became better,and the stronger of the ability of corona resistant of the composite film.The results of the electrical breakdown test showed that with the increase of the imidization rate of the first and second layer of composite film,the electrical breakdown strength of composite films increased gradually;in addition,the conduction current characteristics of the composite films were tested and the corresponding electrical degradation threshold were calculated,and the results showed that with the increase of the imidization rate of the first and second layer of composite film,the electric degradation threshold of composite films increased;for the same sample,with the increase of temperature,the conduction current increased;and at the same temperature,with the increase of imidization rate,conductance current value increased.