Patent ID: 8859087

Claim:
A biaxially oriented insulating film which contains (i) a styrene-based polymer having a syndiotactic structure, (ii) 0.01 to 1.5 mass % of inert fine particles A4 based on 100 mass % of the film, the inert fine particles A4 having an average particle diameter of 0.2 to 3.0 μm and a relative standard deviation of particle diameter of 0.5 or less, and (iii) 1 to 3 mass % of at least one primary antioxidant selected from the group consisting of phenol-based antioxidants and amine-based antioxidants based on 100 mass % of the film, (iv) the biaxially oriented insulating film does not contain phosphorous-based antioxidants and sulfur-based antioxidants, and which has a refractive index in the thickness direction of 1.6050 to 1.6550.