| 摘要 |
PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film having a low heat shrinkage factor in all directions, satisfying high transparency and take-up or feed workability at the same time and always enabling plate making not generating color shift when used in a photographic photosensitive material using a thermal developing system. SOLUTION: A biaxially oriented film, of which the temperature coefficient of expansion and humidity coefficient of expansion simultaneously satisfy formulae; 1×10-6<=αt<=25×10-6 (1) and 5×10-6<=αh<=25×10-6 (2) [wherein,αt is the temperature coefficient of expansion (cm/cm/ deg.C) of the film before thermal slackening treatment andαh is the humidity coefficient of expansion (cm/cm/% RH) of the film before thermal slackening treatment], is subjected to thermal slackening treatment once or more to manufacture the biaxially oriented polyester film.
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