Enameled Wire Having Polyimide-silica Hybrid Insulation Layer Prepared by Sol-gel Process

Heat resistant enameled wire that possessed a polyimide-silica hybrid insulation layer prepared using the sol-gel process was prepared. Tetraethoxysilane (TEOS) was hydrolyzed, followed by polycondensation in polyamic acid varnish, and the varnish was then used as an enamel. Conductor wire was coated with the enamel through a die to control the coating thickness. The wire was then passed through an oven for solvent evaporation and imidation. Interconnected uniform silica globules with a diameter of 50 nm were observed in the insulation layer by scanning electron microscopy (SEM). The enameled wire showed higher breakdown voltage than that without silica after thermal deterioration at 300 °C or 400 °C.