| 摘要 |
PROBLEM TO BE SOLVED: To provide superior rigidity and high heat shrinkage properties and outstanding conservation stability with insignificant irreversible dimensional change due to use conditions and environments by setting the ratio of tension to Young's modulus when the film is stretched 5% at a specific value with regard to the orientation main axial direction of the film. SOLUTION: The biaxially oriented polyester film is made of a polyester which is orientated in the longitudinal and the width direction of the longer direction of the film. The orientation main axial direction of the film is a direction which shows a high refraction index and a higher orientation, of the longitudinal and the width direction. Further, with regard to the orientation main axial direction of the film, the ratio (F5/Ym) of stress during 5% stretching (F5(GP2)) to Young's modulus (Ym(GPa)) is set to be 0.025 or more and 0.034 or less. When the F5/Ym is less than 0.025 the conservation properties and the traveling endurance of a magnetic tape is deteriorated in case the film is used for the magnetic tape, due to the irreversible dimensional change of the film under use application environments. Further when the F5/Ym is 0.034 or above, the film is no longer applicable for use as the magnetic tape. |
