Abstract: The polyester film roll, which is free from wrinkles and slacks generated with the passage of time and is having a good roll appearance, is provided without changing the characteristics of the film.

Abstract: A biaxially oriented layered polyester film which is excellent in suitability for winding and processability while retaining the flatness of the flat surface and which gives a magnetic recording medium, especially a metal coating type high-recording-density magnetic recording medium, having excellent electromagnetic characteristics. The biaxially oriented layered polyester film comprises a second polyester layer and superposed on one side thereof a first polyester layer containing an ester of a C12 or higher aliphatic monocarboxylic acid with a polyhydric alcohol and three inert particulate materials differing in average particle diameter. In the film, one of the Young's moduli respectively in the longitudinal direction and transverse direction is 6 GPa or higher and the other is 4 GPa or higher.

Abstract: A biaxially oriented polyester film for a high-density magnetic recording medium, particularly a high-density magnetic recoding medium of linear recording system, which has high strength in longitudinal and transverse directions, excellent dimensional stability in a crosswise direction and is flat and excellent in output characteristics and a process for producing the same. The biaxially oriented film is made from polyethylene-2,6-naphthalate and has a Young's modulus in a longitudinal direction of 8 GPa or more, a Young's modulus in a transverse direction of 6 GPa or more, a temperature expansion coefficient in the transverse direction (&agr;t) of −5×10−6/° C. to +12×10−6/° C., a humidity expansion coefficient in the transverse direction (&agr;h) of 5×10−6/%RH to 12×10−6/%RH and a thermal shrinkage factor in the transverse direction at 105° C. of −0.5 to +1.