PRODUCTION METHOD OF LONG DIAGONAL STRETCH FILM

PROBLEM TO BE SOLVED: To satisfactorily uniform a film thickness of a film after diagonal drawing in a width direction, and to reduce variation of an in-plane phase difference in the width direction after a heat endurance test.SOLUTION: A production method of a long diagonal stretch film includes a drawing process and a heat treatment process. In the drawing process, a long film is drawn in an oblique direction to a width direction to be made into a long diagonal stretch film F. In the heat treatment process, after the diagonal drawing, heat treatment is performed to the long diagonal stretch film F. A long film before diagonal drawing has a film thickness distribution in which at each position in a width direction, a film thickness is preliminarily increased from a reference film thickness by only an amount that compensates a film thickness deviation that occurs in the long diagonal stretch film after diagonal drawing, and that is asymmetric in the width direction. In the heat treatment process, to the long diagonal stretch film after diagonal drawing, in the width direction, heat treatment is performed so that a temperature distribution corresponding to the film thickness distribution of a long film before diagonal drawing may be obtained. 【課題】斜め延伸後のフィルムの膜厚を幅手方向に十分に均一にする。熱耐久試験後の幅手方向における面内位相差のバラツキを低減する。【解決手段】長尺斜め延伸フィルムの製造方法は、延伸工程と、熱処理工程とを有する。延伸工程では、長尺フィルムを幅手方向に対して斜め方向に延伸して長尺斜め延伸フィルムＦとする。熱処理工程では、斜め延伸後の長尺斜め延伸フィルムＦに対して熱処理を行う。斜め延伸前の長尺フィルムは、幅手方向の各位置で、斜め延伸後の長尺斜め延伸フィルムに生じる膜厚偏差を補償する量だけ基準膜厚から予め膜厚を増大させた、幅手方向において非対称な膜厚分布を持つ。熱処理工程では、斜め延伸後の長尺斜め延伸フィルムに対して、幅手方向において、斜め延伸前の長尺フィルムの膜厚分布に応じた温度分布が得られるように熱処理を行う。【選択図】図８