| 摘要 |
PURPOSE:To decrease the dependence of retardation on an angle by shrinking a stretched thermoplastic resin film or sheet in a stretching axis direction while suppressing the elongation in the directions parallel with the plane of the film or sheet perpendicular to the stretching axis at the time of thermally relieving the above- mentioned film or sheet. CONSTITUTION:The stretched thermoplastic film or sheet shrinks in a stretching direction when this film or sheet is thermally relieved in a non-restrained state at the temp. above the glass transition temp. of the thermoplastic resin film or sheet. The film or sheet necks in and shrinks in the directions parallel with the plane of the film or sheet and perpendicular to the stretching axis at the time of the stretching and, therefore, the film or sheet tends to elongate in the directions parallel with the plane of the film or sheet and perpendicular to the stretching axis at the time of thermal relieving. The film or sheet shrinks in the stretching axis direction and its thickness increases and in addition, the dependence of the retardation on the angle is ameliorated when the elongation in the directions parallel with the plane of the film or sheet and perpendicular to the stretching axis is suppressed to the length shorter than the length at which the film or sheet can elongate in the non-restrained state at the time of thermally relieving. |
