Study On Preparation And Properties Of Nano-silicon/Aluminum Modified Polyimide Film

The new development of high frequency, high voltage and the use of PWM bring forward higher demands for engineering dielectric materials.Though PI, as one of the best organic insulated materials, has excellent dielectric performance, thermal stability and mechanical properties under the exchanged voltage, it can't suffice the AC motors which need to forbear impulse pinnacle voltage or corona resistance. Under the frequency of 60Hz and the 20kV/mm electric field, the corona-resistant time of Kapton 100CR which is modified by inorganic materials is 500 times than that of the pure 100HN films. According to the research, we found that the modified PI which was filled with inorganic meterials had longer corona-resistant time to stick up to the high frequency impulse pinnacle voltage.In this paper, a sequence of nano-silicon/aluminum modified PI films was prepared by the combined method of sol-gel and in situ process. The inorganic content was 20wt% and the weight ratio of silic and aluminum and the preparing technics of aluminum sol were fixed. The silicon sols were synthesized by regulating the molar ratio of the precursor, phenyltriethoxysilane (MSDS) and tetraethyl orthosilicate (TEOS). Ulteriorly, different PI/SiO2/Al2O3 films and PI/SiO2 films were prepared. The films'surface appearances were observed by SEM. The electric properties of the modified films were tested and analyzed, such as dielectric spectrometer, corona-resistant time and breakdown strength.From the SEM, we observed the inorganic particles were dispersed uniformitily in the PI. The silicon accelerated the aluminum's dispersing, but the surface appearances were different. When the molar ratios of MSDS and TEOS were 2:1 and 1:1, the surface appearance was preferably. The interface was blurry. It shown that the the permittivity (εγ) and dielectric loss ( tanδ) of modified PI films were higher than that of the pure PI. Under the same frequency, when the molar ratio of MSDS and TEOS was 1:1, theεγand the tanδwere lower than the other that the ratio of the TEOS was higher, but they are the lowest when the all precursor was MSDS. The PI/SiO2 films'corona-resistant time was 36.49h under the frequency of 50Hz and the 60kV/mm electric field when the molar ratio was 1:1, but the curve of PI/SiO2/Al2O3 ascended earlier and declined after as the molar quantity of MSDS was minished. It reached the vertex at the ratio 2:1. The pure PI films'was 3.03h in the same condition. All the modified films'breakdown strengths were lower than the pure PI when the inorganic content was 20wt%. The breakdown strength of PI/SiO2 films was the max 277kV/mm at the molar ratio 1:1. The pure film was 312kV/mm. Because the breakdown strength of films was correlatived to the molecule stack and inorganic materials'dispersing, the breakdown strength curve of PI/SiO2/Al2O3 films showed complicatied diversification trend. It needed us to do more research. From the above, we knew that the inorganic particles enhanced the PI films'corona-resistant property. The PI/SiO2/Al2O3 films properties presented definite disciplinarian as the molar ratio of silicon's precursor was changed.