Patent ID: 8197726

Claim:
A method for producing a cellulose acylate film, comprising: melt-casting a cellulose acylate satisfying Formulae (1) to (3) to form a film with use of a melt extruder having a screw in which a portion corresponding to 5 to 34% of the entire length of the screw from the most upstream end of the screw is cooled to a temperature of Tg or less of the cellulose acylate and the ratio of the length of a feeding zone to the length of a compression zone is in the range of 1.2:1 to 10:1, and wherein a temperature of an outlet side of a barrel including the screw of the melt extruder is higher than a temperature of an inlet side of the barrel including the screw of the melt extruder, by 5 to 80° C.: 2.6 ≦X+Y≦ 3.0; Formula (1) 0≦X≦2.8; and Formula (2) 0.3≦Y≦3 Formula (3) wherein X represents a substitution degree for an acetyl group and Y represents the sum of the substitution degrees for a propionyl group, a butyryl group, a pentanoyl group and a hexanoyl group, and wherein the number of V-shaped thickness-uneven portions having a thickness variation in the thickness direction of 0.1 to 10% of a film thickness and a width in the in-plane direction of 1 to 20 mm is in the range of 0 to 5 per 100 m in the length direction of the film.