| 摘要 |
PROBLEM TO BE SOLVED: To provide biaxially oriented polyester films improved in transparency, surface smoothness, rigidity and dimension stability by ultra-finely dispersing a copolyester into a non-liquid crystalline polyester, difficult in breaking tapes and causing stress elongation deformation when used as the base films for magnetic recording tapes, excellent in running durability and shelf stability, and suitable as the base films for high density magnetic recording tapes. SOLUTION: Polyester films (C) are composed of (A) a non-liquid crystalline polyester and (B) a copolyester having a mesogen group in the main chain, and the half width in the circumferential direction of the diffraction peak of the crystal face in the direction of the polyester main chain which can be obtained by rotating the polyester film on its normal as the axis in the crystal orientation analysis by the wide angle X-ray diffractometry is 55 deg.-85 deg.. |
