Patent ID: 7740919

Claim:
A cellulose ester film, wherein R 0 of the cellulose ester film is from 30 nm to 150 nm, R t of the cellulose ester film is from 30 nm to 500 nm, and the ratio R t /R 0 is in the range of from 0.8 to 3.5, where R 0 represents a retardation in the plane of the cellulose ester film and R t represents a retardation in the thickness direction, R 0 and R t being measured at 23° C. and 55% RH employing light having a wavelength of 590 nm, and wherein the cellulose ester film comprises a polymer prepared by polymerizing an ethylenically unsaturated monomer having a weight average molecular weight of from 500 to 10,000, an acrylic polymer, or an acrylic polymer having on the side chain an aromatic ring or a cyclohexyl ring, wherein the cellulose ester film satisfies the following relationships: 0.5< R 450 /R 0 <1.0 1.0< R 650 /R 0 <1.5 where R 450 represents a retardation in the plane of the cellulose ester film, measured at 23° C. and 55% RH employing light having a wavelength of 450 nm, and R 650 represents a retardation in the plane of the cellulose ester film, measured at 23° C. and 55% RH employing light having a wavelength of 650 nm.