Thin, largescale processed, high-temperature resistant capacitor films based on polypropylene/cycloolefin copolymer blend

In recent decades, enhancing the high-temperature resistance of capacitor films was a research focus, but largescale-producing high-temperature resistant films remains a difficult issue. Herein, we illustrate a series of biaxially orientated polypropylene (BOPP)/cycloolefin copolymer (COC) blended films with a thickness of 3.8 μm prepared by biaxial-stretching. The structural evolution from casting to biaxial stretching was investigated to assess the feasibility of its largescale- processing. The addition of COC improves the orientation-inducing effect of the shearing and stretching field on polypropylene (PP) crystallization, leading a notable increase in lamellar thickness. Meanwhile, the rigid COC increases the activation energy of chain segment movement and decelerates chain relaxation dynamic, thereby increasing trap depth & density to inhibit the migration of charge carriers which reduces the probability of electric breakdown at high temperature. At 120 °C, the blend films exhibited a breakdown field strength 60 % higher than that of the pure BOPP film (from 252.1 MV/m to 402.8 MV/m). When the pure BOPP film completely failed at 105 °C, the blended films still achieved 78 % discharge efficiency and an energy density of 1.31 J/cm³ at 110 °C & 450 MV/m. Coupled with device capacitance and durability, these films are expected to achieve practical industrial-scale processing.