| 摘要 |
PURPOSE: To obtain a biaxially oriented polyester film which improves the contact state of a magnetic tape and a head, reduces the damage of a magnetic surface and has improved in electromagnetic conversion characteristics by specifying the inclination of the orientation main axis of the biaxially oriented polyester film with respect to the longitudinal direction of the film. CONSTITUTION: The orientation main axis of a biaxially oriented polyester film is inclined within a range of 3-20 deg. with respect to the longitudinal direction of the film. The stretching of the film in the longitudinal direction thereof may be performed in an one-stage fashion or a multistage fashion of two or more stages but, when the F-5 value in the longitudinal direction of an uniaxially stretched film is 17kg/mm<2> or more, it is especially suitable to perform two-stage stretching such that a polyester film is stretched by 1.2-4 times within the temp. range of Tg-(Tg+60 deg.C) of polyester and subjected to the second stage stretching of about 2-5 times at temp. equal to or lower than (first stage stretching temp. -5 deg.C) in order to obtain this inclination of the orientation main axis. Subsequently, the polyester film is laterally stretched and oriented. |
