Sony Corporation

Yuko Abe

Kazuhiko Suzuki

Masahiro Sawaguchi

Takeshi Koizumi

Hiroshi Kudo

Satsuki Yamada

An object of the present invention is to impart good running stability and durability to a magnetic recording medium comprising a combination of a polyester polyurethane resin and a phenox resin as a binder for a magnetic layer of a coating type magnetic recording medium while ensuring excellent static magnetic properties. In order to achieve the object, the present invention provides a coating type magnetic recording medium having a magnetic layer formed on a nonmagnetic support and containing a magnetic powder, a binder and a lubricant, wherein a combination of a polyester polyurethane resin and a phenox resin is use as the binder, a combination of a polyhydric alcohol ester and silicone oil is used as the lubricant, and the surface extraction of the lubricant from the coating type magnetic recording medium is 3.0.times.10.sup.-3 to 3.0.times.10.sup.-2 g/m.sup.2.

Coating type magnetic recording medium

A magnetic recording medium exhibiting not only good durability and traveling reliability but also improved static magnetic properties and electromagnetic transduction characteristics can be obtained according to the present invention. The magnetic recording medium includes a non-magnetic substrate and a magnetic layer composed of a magnetic powder, a binder and a lubricant, wherein the binder contains not less than 50% by weight of a polyester-polyurethane resin having a number-average molecular weight (Mn) of not greater than 15,000 and a ratio of a weight-average molecular weight (Mw) to the number-average molecular weight (Mn) of not smaller than 2.5.

Magnetic recording medium

There is disclosed a magnetic recording medium which are not only excellent in chemical and magnetic stability, durability and traveling reliability but also has a good time index function. The magnetic recording medium according to the present invention includes a non-magnetic substrate and a magnetic layer formed on the non-substrate, the magnetic layer being composed mainly of .gamma.--Fe.sub.2 O.sub.3 and having a coercive force of 25 to 33 KA/m, a residual magnetic flux density of not less than 130 mT and a thickness of 1.5 to 2.0 .mu.m, wherein the magnetic recording medium has a total thickness of not more than 6 .mu.m, and is capable of recording thereon and/or reproducing therefrom a low frequency signal.

An automatic focussing method and an automatic focussing device capable of performing correct focussing. The relative position between an object 4 and an objective lens 2 is measured for focussing. The laser light illuminated on the object is transmitted through a cylindrical lens 7 so as to be condensed only as to one direction. The laser light condensed as to the one direction is illuminated via the objective lens 2 on the object 4 in a linear form. The illuminated laser light reflected by the object 4 is integrated and detected by a detection unit. The relative position between the object and the objective lens is measured from the spot of the detected reflected laser light in order to perform focussing.

Growing community of inventors

Miyagi, Japan

Yuko Abe