Sumitomo Bakelite Announces Development of High Tracking Resistant Epoxy Resin Powder Coating

Sumitomo Bakelite Co., Ltd. (Head Office: Shinagawa-ku, Tokyo; Representative Director and President: Shinichi Kajiya) has developed a powder coating for electrical insulation with high tracking resistance*1. This material has a Comparative Tracking Index (CTI)*2 of 900V and is a solvent-free epoxy resin-based insulating coating suitable for insulating high-voltage conductors such as busbars. *1 Tracking resistance: Refers to the resistance to the "tracking phenomenon," where a conductive path (track) is formed on the surface of an insulator due to electrical discharge, leading to a short circuit (dielectric breakdown) between wirings. *2 Comparative Tracking Index (CTI): A standardized index for evaluating the tracking resistance of insulating materials. A higher CTI indicates superior tracking resistance. Background of Development To extend the cruising range of EVs and shorten charging times, the 800V electrification of EV electrical systems (receiving and feeding sides) is progressing, especially in Europe and the United States. Beyond EVs, high voltage is also expected to advance in mobile applications such as eVTOLs*3 and electric vehicles, aiming for higher output and lighter weight. Furthermore, 1kV-class applications are expanding in industrial machinery, offshore wind power generation vessels, solar power generation-linked inverters, and large-scale battery systems. As the number of high-voltage products is expected to increase, a higher level of tracking resistance than conventional materials is predicted to be required for conductor insulation coatings to ensure long-term reliability and safety. To meet these needs, our company has developed an epoxy resin powder coating with a CTI 900V performance. *3 eVTOL: Abbreviation for "Electric Vertical Take-Off and Landing," referring to an aircraft that can take off and land vertically using electric power. Features of High Tracking Resistant Epoxy Resin Powder Coating High Tracking Resistant Epoxy Resin Powder Coating

Generally, in addition to liquid coatings, powder coatings are widely used to provide insulation to conductor surfaces. From the perspective of environmental protection, shape stability, and productivity, solvent-free powder coatings are superior to liquid coatings. Furthermore, among powder coatings, those based on thermoplastic resins do not generate adhesion between the coated conductor and the film, which carries a risk of insulation performance degradation in the operating environment. In contrast, our powder coating is based on a thermosetting epoxy resin, and a reaction occurs with the conductor during the coating process, resulting in strong adhesion and improved reliability of insulation performance. Typically, the dielectric breakdown voltage of an epoxy resin powder coating film is very high, at 30-40kV/mm, but the CTI, one of the indicators of insulation durability, is generally around 300-600V. In contrast, for this product, based on the UL standard UL2597 for tracking resistance, and in accordance with the STT*4 test, we measured the actual CTI performance of our developed epoxy resin powder coating. The results confirmed that this developed product achieved CTI 900V, demonstrating its capability to meet the trend of higher voltages (see Figure 1).

Figure 1: CTI comparison with existing products

*4 STT test: Refers to the Surface Tracking Test, a test standard for evaluating the tracking resistance of insulating materials used at voltages exceeding 600V. Advantages in Development and Production This product has a low risk of insulation performance degradation even with long-term use under 900V energized conditions, allowing for shorter creepage distances between conductors. This contributes to the miniaturization and higher efficiency of electrical systems and components. Furthermore, it enables thin insulating coating on various conductor shapes without the need for molds. Future Plans In recent years, the trend towards 800V system voltage in EVs is progressing, particularly in Europe and the United States, and the demand for high tracking resistance performance is increasing. While the initial application for this product is envisioned for EV battery busbars, we aim to enter other applications where high tracking resistance performance is required. This product has been confirmed to have a CTI 900V performance, and sample provision is scheduled to begin soon. Going forward, we will focus on product development to meet needs in a wide range of applications, including not only EVs but also busbars and bus rings used in motors for drones and wind power generators. Inquiries regarding this matter Sumitomo Bakelite Co., Ltd. Materials Solution Sales Division, Composite Materials & Molded Products Sales Department TEL: 03-5462-4757 Inquiry form here