Patent ID: 7208205

Claim:
A method for forming a film comprising a fatty acid cellulose ester having an acetyl group and a propionyl group, the method comprising steps of casting a dope onto a belt or drum to form a film, peeling the film from the belt or drum, drying the peeled film by a tenter drying method, wherein a sum of degree of acetyl substitution (DSac) and degree of propionyl substitution (DSpr) of the fatty acid cellulose ester of the film is 2.8 or less, and a retardation value (Rt value) of the film in the thickness direction defined by Formula 1 is 60 to 300 nm, RT value=(( n x +n y )/2− n z )× d Formula 1 wherein n x represents a refractive index of the fatty acid cellulose ester film in the direction giving maximum refractive index in the plane of the fatty acid cellulose ester film, n y represents a refractive index of the fatty acid cellulose ester film in the direction perpendicular to the direction giving maximum refractive index in the plane of the fatty acid cellulose ester film, n z represents a refractive index of the fatty acid cellulose ester film in the thickness direction, and d (nm) represents the thickness of the fatty acid cellulose ester film.