Preparation And Performance Of Sandwich Structured HBP-BOPP-HBP Dielectric Composite Film

Although the dielectric constant of biaxially oriented polypropylene(BOPP)is low,it has a high breakdown strength,so it has important applications in polymer film capacitors.In this paper,through the functional modification of the surface of BOPP film,a HBP-BOPP-HBP dielectric composite film with a sandwich structure was designed and prepared,and the effect of the graft layer thickness on the dielectric properties of the composite film was systematically studied.In order to improve the energy storage density of the BOPP film,a high breakdown strength(?500 MV/m)BOPP film(d=9.8 ?m)is used as the intermediate layer.The branch layer was used as the upper and lower layers,and a HBP-BOPP-HBP dielectric composite film with a sandwich structure was successfully prepared.BOPP is used as an intermediate layer to provide high breakdown strength,and HBP is used as a surface layer to increase the dielectric constant.The grafting of HBP on the upper and lower surfaces of the BOPP film includes two steps:first,a polyacrylic acid(PAA)graft layer is constructed on the surface of the BOPP film by means of visible light graft polymerization,and then the PAA graft layer surface carboxyl group and 3,5-diaminobenzoic acid are used(DABA).The polycondensation reaction of the amino groups in the BOPP film builds the HBP graft layer.The experimental results show that after grafting the HBP grafting layer with a thickness of 2.06 ?m,the dielectric constant has increased significantly from 2.2 to 5.5 for pure BOPP films(an increase of approximately 1.5 times),while the dielectric loss remains very low(<0.03).Moreover,all sandwich structure HBP-BOPP-HBP dielectric composite films have higher energy storage density than unmodified BOPP films.For example,at an electric field strength of 400 kV/mm,the discharge energy density of HBP-BOPP-HBP(1-20-1)film is as high as 2.38 J/cm3,which is higher than that of pure BOPP film(1.75 J/cm3)about 36%.At the same time,the charge and discharge efficiency remains about 90%.