Toray Industries, Inc.

Kazuhiro Tanaka

Satoyuki Minami

Takeshi Nishioka

Masahiko Motegi

Toshiya Yoshii

Saburo Fujita

Ken-ichi Kawakami

The present invention relates to a polyethylene terephthalate film having the sum of F-5 values in longitudinal and transverse directions of 3500 to 5000 kg/cm.sup.2, absolute heat shrinkages in longitudinal and transverse directions at 100.degree. C. of up to 2.5% and amorphous orientation factor of -1.5 to 0.5, a process for the production thereof and a magnetic recording medium containing the film as a base. The polyethylene terephthalate film useful as a magnetic recording medium having super high-tensile-strength in both longitudinal and transverse directions and a low heat shrinkage is provided, while it has been considered that such properties could not be obtained in polyethylene terephthalate film.

Production of polyethylene terephthalate film for magnetic recording

Polyethylene terephthalate film, process for the production thereof and

A magnetic recording disk is disclosed, which comprises (1) a three-layered laminate consisting of a core layer of a biaxially oriented polyolefin film which has a birefringence of not more than 0.01 and an amorphous-region orientation coefficient of not more than 0.2 and two outer layers of a biaxially oriented polyester film adhereed to the core layer, and (2) a magnetic layer formed on at least one side of the laminate. This magnetic recording disk undergoes only a slight dimensional change with a variation in humidity and temperature, and the dimensional change is isotropic in the plane.

Magnetic recording disk

The present invention relates to a process for preparing a polyester film which has not only uniaxially enhanced mechanical properties but also biaxially enhanced mechanical properties. The process involves heat-setting a biaxially oriented polyester film at a temperature above that used for the machine and transverse direction stretching and above that used for the machine direction re-stretching, but at least 10.degree. C. below the melting point of the polyester, then re-stretching the film in both the machine and transverse directions, and re-heat-setting the film.

Method for manufacturing polyester films

Growing community of inventors

Ohtsu, Japan

Kazuhiro Tanaka