| 摘要 |
An object of this invention is to provide a highly insulating film, which is excellent in the heat resistance and has increased breakdown voltage. This invention is a highly insulating film, which is characterized by comprising a biaxially stretched film containing a styrene polymer having a syndiotactic structure as a main component, containing a thermoplastic amorphous resin Y having a glass transition temperature Tg by DSC of 130° C. or higher in an amount of 5% by mass or more and 48% by mass or less, and having a plane orientation coefficient (DeltaP) represented by the following equation (1) of -0.027 or less. DeltaP=(Nx+Ny)/2-Nz (1) (Here, in the equation (1), Nx represents the minimum value of the refractive index in the plane direction of the film, Ny represents the refractive index in the direction perpendicular to Nx in the plane direction of the film, and Nz represents the refractive index in the thickness direction of the film.) |
