Patent ID: 7354633

Claim:
A retardation film comprising: a polyalcohol ester, a polycarboxylic acid ester, and a cellulose ester, the polyalcohol ester being an ester of a monocarboxylic acid and a polyalcohol, wherein a total acylation degree of the cellulose ester is in the range of 2.4-2.8; a Mw/Mn value of the cellulose ester is in the range of 1.4-3.0, provided that Mw represents a weight average molecular weight and Mn represent a number average molecular weight of the cellulose ester; and an Ro and an Rt of the retardation film are defined by the following formulas and satisfy the following conditions: Ro is in the range of 30-300 nm, Rt is in the range of 100-400 nm, and Rt/Ro is in the range of 1.5-6.0, wherein Ro =( nxâˆ’ny )Ã— d and Rt =((( nx+ny )/2)âˆ’ nz )Ã— d, wherein Ro represents an in-plane retardation value, Rt represents an out-of-plane retardation value in a thickness direction; nx represents an in-plane refractive index in a slow axis direction, ny represents an in-plane refractive index in a fast axis direction, nz represents an out-of-plane refractive index in the thickness direction, and d represents a thickness of the retardation film in nanometers.