Study On Preparation And Performance Of TiO₂/NA-PI Impregnating Varnish

Nano-TiO₂had excellent strength rigid and electrical properties, when addedto PI matrix, it could effectively improve heat resistance and dielectric propertiesof polymer, so TiO₂was doped into PI matrix to improve properties of compositematerials.The surface of nano-TiO₂was modified by silane coupling agent KH560.Polyamic acid was synthesized with technology of in situ polymerization, whenpyromellitic dianhydride and3,3’-two ethyl4,4’-two amino two phenyl methanewere used as organic monomer, nadic anhydride was used as end capping agent,and then nano-TiO₂/NA-PI impregnating varnish was synthesized with thermalimide method.The organic degree and structure changes of nano-TiO₂were described byFT-IR, SEM, TEM and weight methods. The results showed that the organicdegree of nano-TiO₂was2.97%, surface-treated nano-TiO₂grafted uniformly inboth end of coupling agent, the surface of nano-TiO₂and silane coupling agenthappened chemically bonded, formed a relatively smooth particles, regular smallspherical particles, the dispersion of nanoparticles became more uniform and thephenomenon of cluster became weaker.Scanning electron microscope （SEM） was used to indicate the aggregationstructure of materials, the chemical structure of the materials was characterizedby Fourier transform infrared spectrometer （FT-IR）, using thermal gravimetricanalysis （TGA） has tested the thermal properties of materials, electronicuniversal tensile testing machine and adhesion tester were used to measure themechanical properties of the materials, and using pressure tester and dielectricspectroscopy to research and analysis the electrical properties of the impregna-ting varnish. The results showed that: nanometer TiO₂was dispersed uniform inthe polyimide matrix, the absorption peaks of Si-O-Si bond appeared at1110cm-1, and this also showed that the surface of nano-TiO₂has been grafted with thecoupling agent KH560. At around1459cm-1, the peak shape of Infraredspectroscopy of the pure PI and PI doped with TiO₂were significantly different,showed that the titanium dioxide and organic matrix has generated cross-linking.With the increase in the amount of inorganic doping, the thermal decompositiontemperature of TiO₂/NA-PI impregnating varnish showed a monotonic upwardtrend, decline in tensile strength, dielectric constant, dielectric loss factor wasincreased, the level of adhesion of the impregnating varnish were all A grade.The breakdown field strength of TiO₂/NA-PI impregnating varnish was lowerthan pure polyimide, but the breakdown field strength of it was250%times ofthe standard （70kV/mm） of silicone impregnating varnish （JB/T3078-1999） andthe Epoxy doping imine impregnating varnish （JB/T7095-1993）.