微观结构对双向拉伸聚丙烯薄膜绝缘性能的影响

Correlations Between the Microstructure and the Insulating Properties of Biaxially Oriented Polypropylene Films

近年来,电网的快速发展对电力电容器提出了更高要求。作为电容器的核心介质材料——双向拉伸聚丙烯(BOPP)薄膜,其绝缘性能直接决定了电容器的储能密度和运行可靠性。为探究BOPP的微观结构对其绝缘性能的影响,选取了3种由相同PP树脂经不同厂家制作得到的BOPP薄膜,对其表面形貌、结晶特性、取向度及电学性能进行了测试分析。结果表明:结晶度、片晶厚度、取向度及玻璃化转变温度的提升使得BOPP薄膜具有更高的直流击穿场强。进一步通过电导测试获取载流子的宏观迁移特性,并采用动态热机械分析测试(DMA)和表面电位衰减测试(SPD)研究载流子的迁移过程。体积电导率的测试结果表明BOPP薄膜的电导机制以跳跃电导为主。陷阱参数和分子链段运动活化能的计算结果阐明了微观结构对BOPP薄膜绝缘性能的影响机制,有序规整的微观结构减小了BOPP薄膜的浅陷阱密度,提高了分子链段运动活化能,使载流子的跨链迁移和沿链迁移过程受到抑制,最终体现为电导率的下降与击穿场强的提高。

In recent years,the rapid development of power grids put forward higher requirements to power capacitors.The insulation performance of biaxially oriented polypropylene(BOPP)film,as the core dielectric material of capacitors,directly determines the energy storage density and operational reliability of capacitors.In order to investigate the influence of the microstructure of BOPP on its insulating properties,we selected three kinds of BOPP films made from the same PP resin by different manufacturers,and tested and analyzed their surface morphology,crystalline properties,orientation and electrical properties.The results show that the enhancement of crystallinity,lamella thickness,orientation and glass transition temperature will result in higher DC breakdown strength of BOPP films.Further conductivity tests were performed to obtain the macroscopic migration properties of carriers,and dynamic thermo-mechanical analysis tests(DMA)and surface potential decay tests(SPD)were used to investigate the carrier migration process.The volume conductivity test shows that the conduction mechanism of BOPP film is dominated by hopping conduction.The calculation results of trap parameters and activation energy of molecular segment elucidate the mechanism of microstructure influence on the insulating property of BOPP film.The ordered and regular microstructure decreases the shallow trap density of BOPP film,increases the activation energy of molecular segment movement,and then the migration process of carriers across the chains and along the chains is suppressed,which is finally reflected in the decrease of conductivity and the improvement of breakdown strength.