| 摘要 |
An aspect of the invention provides a heat treatment method of a thermoplastic resin film comprising running a strip shaped thermoplastic resin film in a longitudinal direction and heating the thermoplastic resin film while holding the edge of the film in a width direction to conduct a heat treatment, wherein a tension of the thermoplastic resin film in the width direction is controlled to be constant. According to the aspect of the invention, since a thermoplastic resin film during a heat treatment is held with a constant tension in a width direction, the thermoplastic resin film during the heat treatment can be prevented from sagging or pulling excessively. Therefore, occurrence of variability of optical characteristics can be prevented, and thus a thermoplastic resin film excellent in optical characteristics can be produced.
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