Diafoil Company, Ltd.

Tateo Kanesaki

Shigeo Utsumi

Kichinojyo Tomitaka

Satoshi Otonari

Takashi Kagiyama

Koichiro Ikushima

Norio Okumura

A polyester film suitable for use as a substrate for magnetic recording media, characterized in that said polyester film is a biaxially oriented polyester film having an average refractive index n and a planar orientation .DELTA.P, which respectively satisfy the following equations [I] and [II]:

Polyester films suitable for use in magnetic recording media

A polyester film for magnetic recording media having excellent flatness, slipperiness and adhesiveness of the magnetic layer thereto, said film having minute protrusions on the surface thereof including roughness units each of which consists of a minute protrusion and a recess therearound having a longer diameter of at least 3 .mu.m, wherein the number of the roughness units per square mm, A, (number/mm.sup.2), satisfies the relation (1):

Polyester film for magnetic recording media

A process for preparing high tensile strength polyester film especially suitable for manufacturing magnetic recording tapes is disclosed. A raw polyester film is first stretched longitudinally so as to have an index of birefringence of 0.015-0.055, is then further stretched in the same direction at a temperature between 95.degree. C. and 150.degree. C. while the index of birefringence of the film is prevented from exceeding 0.080, is then stretched transversely to 2.5-5 times its width and is further stretched longitudinally and/or transversely to 1.1 times or greater. The product has high tensile strength as well as excellent flatness and slipperiness properties.

Process for stretching polyester films

Process for preparing biaxially stretched polyester films

Growing community of inventors

Nagahama, Japan

Tateo Kanesaki