| 摘要 |
PROBLEM TO BE SOLVED: To effectively utilize the full width of a biaxially stretched polyester film in consideration of the orienting property of the film and to reduce cost by cutting the film having a specified difference in the orientation angle between the central and edge parts, in such a way that the difference in the angle of orientation between both edges is reduced to a specified value or smaller and then carrying out heat treatment. SOLUTION: A biaxially stretched polyester film having 30 deg. or higher difference in the angle of orientation between the central and edge parts in the width direction after film formation is cut into two or more, in such a way that the difference in the angle of orientation between both edges is reduced to 25 deg. or smaller, and then heat treatment is carried out at 60-200 deg.C under 0.01-60 kg/cm2 tension in conveyance before coating with photographic constituent layers, including a photosensitive layer and after coating with an undercoat layer. The polyester film undergoes 0.01 g/cm3 or smaller density change, a birefrigence change of 0.005 or smaller and an elastic modulus change of 0.75-1.2 in the longitudinal direction before and after the heat treatment.
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