Tdk Corporation

Takashi Handa

Kiminori Tamai

Katsuhiko Yamazaki

Akinori Nishizawa

Tsutomu Ide

The present invention provides a magnetic recording medium which has a thin film magnetic layer considerably excellent in surface smoothness, and is excellent in electromagnetic conversion property. A magnetic recording medium comprising a non-magnetic support, a lower non-magnetic layer comprising at least a non-magnetic powder and a binder resin on one surface of the non-magnetic support, and a magnetic layer comprising at least a ferromagnetic powder and a binder resin on the lower non-magnetic layer, wherein when the magnetic recording medium is subjected to extraction treatment with water, 7 to 23 &#x3bc;g of POions are extracted per 10 mmof the volume of the lower non-magnetic layer of the magnetic recording medium. A magnetic recording medium comprising a non-magnetic support, a lower non-magnetic layer comprising at least a non-magnetic powder and a binder resin on one surface of the non-magnetic support, and a magnetic layer comprising at least a ferromagnetic powder and a binder resin on the lower non-magnetic layer, wherein when the magnetic recording medium is subjected to extraction treatment with water, 8 to 22 &#x3bc;g of Mgions are extracted per 10 mmof the volume of the lower non-magnetic layer of the magnetic recording medium.

Magnetic recording medium

An object is to provide magnetic recording medium having a densely packed, highly oriented magnetic layer by enhancing the dispersibility of magnetic powder having a carbon or iron carbide base surface. Magnetic powder is pretreated by kneading and dispersing it with an organic solvent and optionally, an anionic or ampholytic surfactant and a fatty acid, and a resin containing an amino group or ammonium salt group is used as a binder.

A magnetic layer containing a magnetic powder whose surface is composed mainly of carbon and/or iron carbide and a binder is provided on a non-magnetic substrate, the magnetic layer further contains an organic dye compound having at least one polar group selected from the group consisting of a hydroxyl group, a carboxylic acid group, a sulfonic acid group and a salt thereof, and the binder contains an amino group and/or an ammonium salt group. Due to the improved dispersibility of a magnetic paint, the magnetic recording medium of the invention is improved in surface morphology, magnetic properties, and electromagnetic properties.

Magnetic recording medium comprising a magnetic layer containing

Iron carbide particles are heat treated in a nitrogen atmosphere to form magnetic particles each comprising an iron base core and a carbon base surface. This magnetic particle powder having increased saturation magnetization .sigma.s is mixed with a binder to form a magnetic layer on a substrate, thus providing a magnetic recording medium which exhibits improved remanence Br and reproduces increased outputs.

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Nagano, Japan

Takashi Handa