| 摘要 |
PURPOSE:To increase the electromagnetic conversion property, by preparing a biaxially stretched polyester film that includes indentations and projections having an average diameter of 0.5-2mum in a number of 0.5X10<3>/mm.<2>, and indentations and projections having an average diameter of 5mum or above in a number of 10-2X10<3>/mm.<2>. CONSTITUTION:Particles of two different types having different average particle diameters are incorporated into a polyester film and the film is biaxially stretched with at least one surface thereof having rugged sections wherein projections are formed in indented parts and/or indented parts and projections are adjacent to each other. In this case, the number of the indented parts and the projections having an average diameter of 0.5-2mum should be 0.5X10<3>/mm.<2> or over, and the number of the indented parts and the projections having an average diameter exceeding 5mum should be 10-2X10<3>/mm.<2>. It is preferred that not only the usual coating type magnetic layer but also a ferromagnetic thin film is formed on the surface of this biaxially stretched polyester film. |
