Patent ID: 8211345

Claim:
A process for producing an optical film comprising at least one type of plasticizer and being produced in a roll form, the process comprising the steps of: casting a dope, prepared by dissolving a raw material resin in a solvent, on an endless support to form a web; peeling the web from the endless support; and drying and winding the peeled web, wherein, prior to peeling the web from the endless support, the center portion in a transverse direction and edge portions on both sides of the web are heated at different temperatures; and a heating temperature of the center portion is lower than a heating temperature of the edge portions in an anterior portion of the endless support, and a heating temperature of the center portion is higher than a heating temperature of the edge portions in a posterior portion of the endless support; and wherein the optical film has a total width of 1500 mm-4000 mm; value X and value X′ differ from each other, provided that value X is calculated by Expression 1 using value A which is an amount of a plasticizer present in a center portion on a front surface side of the optical film determined via TOP-SIMS (time of flight secondary ion mass spectrometry) and value B which is an amount of a plasticizer present in a center portion on a rear surface side of the optical film determined via TOF-SIMS, and value X′ is calculated by Expression 2 from value A′ which is an amount of a plasticizer present in an edge portion on the front surface side of the optical film determined via TOF-SIMS and value B′ which is an amount of a plasticizer present in an edge portion on the rear surface side of the optical film determined via TOF-SIMS; and value X is larger than value X′: X={A/(A+B)}×100 Expression 1 X′={A′/(A′+B′)}×100 Expression 2.