Preparation And Properties Of High-performance Polyimide Insulating Paper

In the 1860 s, paper has been used as insulation material of electrical equipment. With the development of the society, aerospace and high-speed trains have higher request to motor, electrician equipment with miniaturization and large capacity tends to be prevailing. So the resistances to high temperature, strength properties and insulation properties of insulating paper have to be improved. As traditional insulating paper is unable to meet these requirements, insulating paper with more excellent performances should be developed. To satisfy the needs of more electrical equipment, polyimide insulating paper, which possessed above H heat resistance level, excellent strength and electrical properties, was prepared and investigated in this study.In this study, dry spinning polyimide fiber was used as raw material. The preparation technology of polyimide insulating paper was optimized. According to the result, the optimal preparation technology was as follow: the optimal dosages of aramid pulp, PEO, butyl benzene latex and CPAM were 6%, 0.06%, 8% and 0.06%, respectively. The optimal impregnation concentration of polyimide resin was 4%. The optimal hot pressing process was as follow: the first stage: 120℃, 5 MPa, 3 min; the second stage: 180℃, 10 MPa, 3 min; the third stage: 230℃, 15 MPa, 3 min. The performances of prepared polyimide insulating paper were excellent: the tensile index was 44.47 N·m/g, the tear index was 40.47 m N·m2/g, the electrical breakdown strength was 5.63 k V/mm, and the dielectric loss was 0.004.Using TG technology, based on Coast-Redfern method, this paper studied the thermal aging of polyimide paper, and the aging mechanism was analyzed by infrared detection. The results showed that, polyimide insulating paper had excellent thermal stability, and polyimide paper with larger thickness had better thermal stability. Thermal decomposition reaction series n of polyimide paper was 2. And polyimide paper with larger thickness had higher decomposition activation energy and use ceiling temperature. Heat-resisting class of polyimide insulating paper with different thicknesses was above class H. By infrared detection, we can draw a conclusion that polyimide paper treated under 600 ℃ for 30 min was damaged partly, and polyimide paper treated under 800 ℃ for 30 min was completely destroyed.We also studied the moisture absorption performance under 50%RH humidity and the water absorption performance in liquid water of polyimide paper. And we analyzed structure change before and after absorption treatment by infrared detection. The results showed that, with the extension of moisture absorption time and water absorption time, the relative absorption of paper-based materials rapidly increased, and then tended to be stable. Polyimide insulating paper with thickness of 0.06 mm had the greatest relative moisture absorption rate and relative water absorption rate. The diffusion types of water vapor and liquid water in polyimide insulating paper both were super diffusion, but the adsorption rate of liquid water in polyimide insulating paper was slower. In a certain period of time, water vapor and liquid water had little influence on the performance of polyimide insulating paper. The result of infrared detection showed that the moisture absorption of polyimide paper under 50%RH humidity could be ignored. However, polyimide paper dipped in liquid water had obvious characteristic peaks in 3335 cm^-1 and 1650 cm^-1.