Patent ID: 7130007

Claim:
An optical film obtained by stretching a polymer film comprising a polycarbonate resin and a styrene resin, said styrene resin having a weight average molecular weight of 20,000 or less: wherein a photoelastic coefficient is 2.0×10 −11 to 6.0×10 −11 m 2 /N, and a three dimensional refractive index is controlled so that an Nz coefficient represented with Nz=(nx−nz)/(nx−ny) satisfies a relationship of Nz≦0.9 and a front retardation (Re)=(nx−ny)×d satisfies a relationship of Re≧80 nm, when a direction where a refractive index in a film plane gives maximum is defined as X-axis, a direction perpendicular to X-axis as Y-axis, a thickness direction of the film as Z-axis, and when refractive indexes in each axial direction are defined as nx, ny, and nz, respectively, and a thickness of the film is defined as d (nm).