Patent ID: 7828997

Claim:
A method for producing a cellulose acylate film by melt film formation, including discharging a molten cellulose acylate resin melted in an extruder on a running or rotating cooling support through a die in a form of a sheet, thereby solidifying the discharged molten resin by cooling, the method comprising: measuring an in-plane a retardation (Re) of a slow axis which is a lengthwise direction of the cellulose acylate film and a retardation (Rth) of the cellulose acylate film in thickness direction; and controlling the temperature of the molten resin at an outlet of the die to a range of glass transition temperature Tg+70° C. to Tg+150° C. so that the measured retardations Re and Rth fall into the range of −10 nm to 80 nm and 0 to 60 nm, respectively; and controlling a lip clearance ratio (D/W), which is a ratio of a lip clearance (D) of the die to a thickness (W) of the molten resin extruded through the die, to a range of 1.5 to 10, wherein the extruder employs conditions of a screw compression ratio of 2.5 to 4.5, an L/D (the ratio of cylinder length (L) to cylinder bore diameter (D) of the extruder) of 20 to 70, and a temperature of the molten resin at an outlet of the extruder of 190° C. to 245° C.