Study On The Dielectric Property Of Nano-Inorganic-Polyimide Composite Film

Polyimide (PI) is a type of advanced polymeric material. Because of better thermal behavior, electric property and mechanical property, it was wildly used in aero, aviation, nuclear power and micro-electrics. In the meanwhile, it is more and more strictly to the requirement of PI properties due to the rapidly development of those fields. So it become more popular hot in preparation of nano-doped PI composite in the field of material technology. By widely using nano-composites in the electric industry and research, studying the effect of doped nano-particle on the polymers turn to the precondition of the application of nano-composites in electric field. Our laboratory accumulates lots of theory knowledge about dielectric and coronal resistance of nano-composite films. In this paper, the permittivity, dielectric spectra, conduction current and thermally stimulated current of nano-doped Al₂O₃- and SiO₂- Polyimide films were measured. In the other hand, the trap distributions of original polyimide (100HN) and coronal resistant polyimide (100CR) which were produced by DuPont Company in USA were studied by isothermal decaying current (IDC) method.By studying the dielectric characteristics of the nano-SiO₂-polyimide film synthesized using sol-gel method with content of 5wt%, 10wt%, 12.5wt%, 15wt% and 20wt%, and nano-Al₂O₃-polyimide film synthesized using sol-gel method with content of 5wt%, 10wt%, 15wt%, 20wt%, 25wt% and 30wt%, we can conclude below: (1)all the permittivity of composite film decrease and loss tangent increase with frequency increasing. (2)with the increase of the proportion by weight, the breakdown strength increase to a threshold and decrease; permittivity, loss tangent, conduction current increase; threshold of electric aging decrease; temperature peak of TSC shift to high temperature; density of trapped carrier of PI/SiO₂ nano-composite decrease; the density of trapped carrier of PI/Al₂O₃ decrease until content of nano-doped Al₂O₃ is 12.5wt% and turn to increase, and a percolation threshold exists between 12.5wt% and 15wt%; (3)at the same content of nano-inorganic particle, the breakdown and electric aging threshold of PI/Al₂O₃ lower than PI/SiO₂ composite; the relative permittivity, loss tangent, conduction current of PI/Al₂O₃ larger than PI/SiO₂; (4)after coronal aging, the thermally stimulated current peak of the composite film drops, temperature peak of TSC of PI/Al₂O₃ is neglected; temperature peak of TSC of PI/SiO₂ with content of 30wt% shift to low temperature.Studying the IDC curves of original and coronal resistant polyimide of DuPont, the conclusion were got: Compared the IDC curve of 100HN film, the decaying rate of 100CR film is not obvious; at same temperature, and the decaying rate of 100CR is larger than 100HN. Raising temperature, the peak of energy density distribution of both films shift to deep and energy density increase; at the same trap level, then density of 100CR is larger than 100HN's density. After aging, the decaying rate of 100CR shift down, but the rate of 100HN almost doesn't change; the peak of trap level density of 100CRshift to deep energy level, the amplitude of peak reduced; the peak of trap level density of 100HN unchanged, but the amplitude greatly increased.