Improved Breakdown Strength of Bi-Axially Orientated Polypropylene Film by the Optimization of Crystalline Properties

As the main dielectric materials of power capacitors, the breakdown strength of bi-axial orientated polypropylene (BOPP) films plays the dominant position on the energy storage density, which is largely decided by the crystalline properties. In this paper, the crystalline properties of BOPP films were optimized by the tailoring of the orientation temperature and the introduction of β-nucleating agents. The surface morphology and the aggregation structure were analyzed via scanning electron microscope, differential scanning calorimetry and wide-angle X-ray diffraction. While the dielectric properties response to the frequency and the DC breakdown strength were also tested on each BOPP film sample. Results indicated that the orientation temperature above the melting temperature of the main crystal would result in the surface structural defects of the BOPP film, and thereby caused significant deterioration of the breakdown strength. By optimizing the orientation temperature and introducing 0.09wt% β-nucleating agent, the samples exhibited the biggest breakdown strength of 620 kV/mm among all films. This work provided further insight onto the manufacturing of defect-free and performance-enhanced BOPP films.