| 摘要 |
PURPOSE:To improve dimensional stability and flatness, by setting the tension of a polyester film after the completion of biaxial orientation in the longitudinal direction of said film to a specific value or less and heating the central part and side edge parts of the film to specific temps. to hold said temps. CONSTITUTION:A film 4 after the completion of biaxial orientation is sent into a heat treatment apparatus and successively passed through a heating zone 1, a cooling zone 2 and a tension separation zone 3 to be taken up. As a heating means, an infrared heater is used and the temp. of the central part of the film is heated to 150 deg.C or more while each of the side edge parts of said film is heated to temp. 10 deg.C more higher than that of the central part. In order to make a heat shrinkage value sufficiently low in the longitudinal direction by heat treatment, the tension of the film in the longitudinal direction within the heating zone 1 is set to 10kg/m or less. After heating, the film is gradually cooled in the cooling zone 2 to eliminate the strain generated by heat treatment. The cooled film is released from tension and taken up on and after under proper tension.
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