| 摘要 |
PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film suitable for optical applications capable of producing a high quality release film for producing a polarizing plate which has sufficient winding characteristics, chargeability and slipperiness and can perform highly precise inspection in the crossed Nicol method even when coated with a release layer at a high speed, for example, when used as a substrate of a release film for producing a polarizing film.SOLUTION: There is provided a polyester film having a layered structure of at least three layers containing at least two kinds of particles having different average particle diameter on both outer layers, wherein the value (St/Sa) obtained by dividing the maximum cross-sectional roughness (St) on both surfaces of the film by the average roughness (Sa) is in the range of 65 to 90, the orientation angle is 15° or less and the polyester film satisfies the following expression: 2≤&Dgr;P/&Dgr;n≤7 (wherein, &Dgr;P means a plane orientation degree and &Dgr;n means a birefringent index.) |
