| 摘要 |
PURPOSE:To obtain the titled film having minute ruggedness at its surface, excellent in strength, flatness and lubricatability and useful for a magnetic tape or the like, by a method wherein stretching in the first axial direction, stretching in the second axial direction perpendicular to the first direction and restretching in the first direction are conducted at specified temperatures and with specified draw ratio. CONSTITUTION:The polyester film is stretched in the first axial direction at a temperature of 90-150 deg.C with a draw ratio of not lower than about 3.2, is then stretched in the second axial direction perpendicular to the first direction at a temperatue of approximate to or higher than the temperature of the stretching in the first direction with a draw ratio in the range of about 3.0-4.5, and, if required, it is subjected to an intermediate heat treatment in a temperature range of 140-200 deg.C. Further, the film is restretched in the first axial direction at a temperature of 120-170 deg.C with a draw ratio of 1.2-2.5 to obtain the objective film wherein a plurality of rugged patterns comprised of minute projections 21 and recesses 24 at the peripheries of the projections 21 are provided at the surface of the film and the ratio of the major diameter (a) to the minor diameter (b) of the recess is in the range of 1:1-2:1. |
