Synthesis and Electrophoretic Deposition of Polyimide with Methacrylic Groups on the Side Chain

To realize a sustainable growth society, automobiles are undergoing a shift from gasoline to electric vehicles, for which the development of a highly efficient small electric motor is critical. Recently, a rectangular motor coil with a high occupancy ratio has been developed, and an electrophoretic deposition-based coating method using polyimide (PI) has gained attention for forming an insulation film with high heat resistance. In this study, PI with methacrylic groups, PI(BPADA/AHPP), was synthesized and an electrophoretic deposition dispersion was prepared by nano-compositing it with alumina sol. The zeta potential of the dispersion was charged at +55.5 mV. A film of 122-μm thickness was deposited on the cathode via electrophoretic deposition using the dispersion. After baking, the insulating film exhibited high electrophoretic deposition ability and high heat resistance, as evidenced by the 10% weight loss temperature of 413 °C and the coulomb efficiency of 27 mg/C.