Patent ID: 7223452

Claim:
A method for producing an optical film comprising a base and a biaxially birefringent layer, the method comprising: a step of coating a material of the birefringent layer on the base so as to form a coating film; and a step of solidifying the coating film on the base so as to form the birefringent layer, where the material that is coated on the base in the coating step is prepared as a coating solution by dispersing or dissolving the material in a solvent, and the solvent used exhibits solubility with respect to the base; wherein the base is composed of a transparent polymer, and the birefringent layer is formed of a polymer and laminated directly on the base, wherein the birefringent layer and the base together satisfy a formula (1) below, the birefringent layer satisfies formulae (2) and (3) below, and the polymer forming the birefringent layer has a weight-average molecular weight in a range between 10,000 and 400,000 inclusive; Δ n ( a )>Δ n ( b )×10 (1) 1<( nx−nz )/( nx−ny )<100 (2) 0.0005 ≦Δn ( a )≦0.5 (3) where Δn(a) denotes a birefringence of the birefringent layer and is represented by [(nx+ny)/2]−nz, wherein nx and ny and nz denote the respective indices in the X-, Y- and Z-axes directions of the birefringent layer; and Δn(b) denotes a birefringence of the base and is represented by [(nx′+ny′)/2]−nz′, wherein nx′, ny′ and nz′ denote the respective indices in the X-, Y- and Z-axes directions of the base; where the X-axis direction denotes an axial direction presenting a maximum refractive index within the birefringent layer and the base, the Y-axis direction denotes an axial direction perpendicular to the X-axis within the plane, and the Z-axis direction denotes a thickness direction perpendicular to the X-axis and Y-axis.