Diafoil Company, Ltd.

Kichinojo Tomitaka

Shigeo Utsumi

Tomoyuki Kotani

Masumi Koizumi

Kazuo Endo

Chikakazu Kawaguchi

Masashi Inagaki

Toshifumi Takisawa

Yoshio Meguro

Masahiko Fujimoto

Nobuyasu Shudo

Kenji Kato

Kazuyuki Akatsu

Shigeyuki Watanabe

A biaxially oriented polyester film simultaneously satisfying the following formulas (I) to (III):

Low-shrinkage polyester film and preparation thereof

The present invention provide a biaxially oriented polyester film for use in a floppy disc, which has a coefficient of thermal expansion (.alpha..sub.T) in film plane of (1.0.+-.0.5).times.10.sup.-5 mm/mm/.degree.C. and a heat shrinkage of not higher than 0.09% after treatment the film for 72 hours under conditions of a temperature of 60.degree. C. and a humidity of 80% RH in any directions in film plane, and simultaneously satisfies the following equations (1) to (5):

Biaxially oriented polyester film for use in floppy disc

A polyester film suitable for a base of high density magnetic recording medium containing barium ferrite as a magnetic material characterized in that the centerline average roughness (Ra) is not more than 0.025 .mu.m and the F.sub.5 value in the longitudinal direction is not less than 14 kg/mm.sup.2 is disclosed wherein the polyester film exhibit excellent better durability when used with barium ferrite as a magnetic material.

Polyester film for high density magnetic recording medium

Disclosed herein is a polyester film containing specific fine spherical silica particles. The film of the present invention is especially suitable as a base film for a magnetic recording medium or dielectric for a capacitor. The films of the present invention have the markedly improved properties such as surface properties, electromagnetic properties, electrical properties, etc. due to the excellent dispersibliity of the particles in the film.

Polyester films, magnetic recording media and film capacitors produced

A biaxially stretched polyester film which satisfies the following equations (1) to (4):

Process of making a biaxially stretched polyester film and biaxially

A biaxially oriented polyester film for floppy disks which has an in-plane thermal expansion coefficient (.alpha..sub..gamma.) of (1.7.+-.0.8).times.10.sup.-5 /.degree.C. and a shrinkage of not more than 0.03% after 72-hour treatment under the conditions of 60.degree. C. and 80% RH, and which simultaneously satisfies the following relationships (1) to (6):

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Yokohama, Japan

Kichinojo Tomitaka