2024 Volume 37 Issue 1 Pages 63-68
To realize sustainable societal growth, the automotive industry is currently transitioning from gasoline-powered vehicles to electric ones. Consequently, there is a growing need for the development of compact electric motors with high energy conversion efficiency. Although a rectangular motor coil with a high occupancy ratio has been developed, it is not easy to protect the surface of the coil using conventional dipping methods. As an alternative method, we previously proposed an electrophoretic deposition (EPD) method using polyimide (PI) with high heat resistance as an insulating material. An EPD material based on the ammonium salt of a polyamide acid PAA(PMDA/ODA) as PI precursor has been developed; however, it was subjected to hydrolysis, and the lifetime was quite low. Therefore, a polyamide ester, PAE(PMDA/ODA), was synthesized to protect the carboxylic acids in PAA. The EPD solution of PAE with boehmite alumina successfully resulted in a 53 µm thickness deposition coating by EPD. After baking the coating film for the imidization of PAE, we obtained a 10% weight-loss temperature and Coulomb efficiency of 580 °C and 82 mg/C, respectively, indicating high EPD ability and heat resistance.
