Patent ID: 7153547

Claim:
A birefringent optical film comprising at least two kinds of polymer materials, wherein Σ(Cn×Wn) as a total of products Cn and Wn satisfies a numerical formula (1): Σ( Cn×Wn )≦30×10 −8 cm 2 /N (1) where Cn and Wn denote respectively a photoelastic coefficient and a volume fraction of each polymer material, and at least one of the polymer materials has a photoelastic coefficient value of at least 60×10 −8 cm 2 /N, wherein the birefringent optical film comprises a laminate of at least two polymer layers formed of at least one kind of the polymer materials, wherein the birefringent optical film comprises a polymer layer of the polymer material having a photoelastic coefficient of at least 60×10 −8 cm 2 /N and a polymer layer of a polymer material other than the polymer material having a photoelastic coefficient of at least 60×10 −8 cm 2 /N, and wherein nx, ny and nz in a polymer layer of the polymer material having a photoelastic coefficient of at least 60×10 −8 cm 2 /N satisfy numerical formulae (3) and (4): nx≧ny>nz (3) 0.005≦( nx−nz )≦0.1 (4) where nx and ny denote main refractive indices in two directions in the plane of the polymer layer and nz denotes a refractive index in the thickness direction of the polymer layer.