Patent ID: 7964127

Claim:
A method for producing an optical film comprising the steps of: melt casting a cellulose ester resin or a cycloolefin resin by extruding melt of the cellulose ester resin or the cycloolefin resin from a die onto a roll-shaped cooling drum; cooling and solidifying the extruded melt to form a film; stretching the film in a lateral direction of the film; and winding the stretched film in a roll, wherein the cooling drum has plural cooling regions divided in an axis direction of the cooling drum, and a surface temperature of each cooling region is independently controlled by different control systems to provide a difference in surface temperature among the plural cooling regions such that a variation in retardation of the stretched film is not more than 15 nm, wherein a width of the roll film is 1500 to 4000 mm, and wherein the plural cooling regions of the cooling drum constitute a central region and side regions located at both sides of the central region and the surface temperature of the central region is controlled to be lower than that of the side regions, and wherein in the stretching step, a stretching temperature is controlled such that a difference in temperature along the lateral direction of the film is not more than ±2° C.