Fuji Photo Film Company, Limited

Fujifilm Corporation

Kouichi Masaki

Toshihiko Miura

Yasuo Tamai

Tatsuji Kitamoto

Hiroo Inaba

Hiroshi Ogawa

Yasushi Hattori

Kiyomi Ejiri

Goro Akashi

Nobuo Yamazaki

Mikihiko Kato

Toshio Kawamata

Yasushi Endo

Chiaki Mizuno

Koukichi Waki

Masaaki Suzuki

Koji Sasazawa

Takeshi Harasawa

Hideaki Kosha

Takako Ozawa

Toshiyuki Suzuki

Kideaki Kosha

Koyotaka Fukino

Kiyoma Ejiri

Teruya Shinjo

Shinichiro Dezawa

Ferromagnetic nanoparticles which are produced by reducing, in the presence of a polymer, two or more metals having different reduction potentials twice or more, using two or more reducing agents having different reduction potentials, a material coated with a dispersion of ferromagnetic nanoparticles in which the ferromagnetic nanoparticles are dispersed, and a magnetic recording medium which has a magnetic layer consisting of the material. The ferromagnetic nanoparticles having a holding power Hc of 95.5 kA/m or more, the material coated with the dispersion of ferromagnetic nanoparticles having excellent industrial coatability, and the magnetic recording medium using the dispersion are provided.

Ferromagnetic nanoparticles, material coated with dispersion of ferromagnetic nanoparticles, and magnetic recording medium using the material

To provide a magnetic recording medium which undergoes little effect of thermal fluctuation and provides a high short wavelength output and C/N ratio when reproduction is conducted using MR head, the magnetic recording medium includes a non-magnetic layer having a non-magnetic powder dispersed in a binder provided on a support and a magnetic layer having a ferromagnetic powder dispersed in a binder provided on the non-magnetic layer, wherein the ferromagnetic powder comprises a hexagonal ferrite magnetic powder having an average diameter of from 10 to 35 nm and a coercive force of from 135 to 400 kA/m; the magnetic layer has a coercive force of from 135 to 440 kA/m; and a product of an anisotropic magnetic field of the magnetic layer and an average particle volume of the hexagonal ferrite magnetic powder is from 1.2&#xd7;10to 2.4&#xd7;10kA/m&#xb7;nm.

Magnetic recording medium

A magnetic recording medium comprising: a support; and at least a magnetic layer comprising a hexagonal ferrite powder and a binder, wherein the hexagonal ferrite powder is of magnetoplumbite type and has an average diameter of 15 to 35 nm and an alkaline earth element to iron ratio of 0.10 to 0.15 in terms of peak intensity ratio analyzed by electron spectroscopy for chemical analysis.

A magnetic recording medium comprising a support having provided thereon a nonmagnetic layer containing a nonmagnetic powder dispersed in a binder and a magnetic layer containing a ferromagnetic powder dispersed in a binder provided on the nonmagnetic layer, wherein the magnetic layer comprises a hexagonal ferrite powder having an average tabular diameter of from 10 to 35 nm, a coercive force (Hc) of from 135 to 400 kA/m, SFD (Switching Field Distribution) (25&deg; C.) of from 0.40 to 0.90, and &Dgr; SFD &lsqb;SFD (100&deg; C.)&minus;SFD (25&deg; C.)&rsqb; of from 0.15 to 0.20.

A magnetic recording medium comprises a non-magnetic layer containing a non-magnetic powder abd a binder provided on a support, and a magnetic layer containing a ferromagnetic powder and a binder provided on the non-magnetic layer, wherein the magnetic layer contains a hexagonal ferrite magnetic powder having an average tabular diameter of 10 to 28 nm and has a coercive force (Hc) of 135 to 400 kA/m, a ratio (Hc/Hk) of the Hc to an anisotropic magnetic field (Hk) of 0.3 to 0.6, and a maximum value of &Dgr;M of 0 to 0.10.

Magnetic recording medium comprising a magnetic layer exhibiting low &Dgr;M value

A method of producing hexagonal (system) ferrite, wherein the hexagonal (system) ferrite having an average tabular diameter of 10 to 40 nm and a coercive force (Hc) of 135 to 400 kA/m is treated with an organic compound containing a polar group having an acid dissociation constant (pKa) of 4 or below and/or a salt thereof when the ferrite is recovered and washed, and a magnetic recording medium comprising a support having thereon a non-magnetic layer comprising a non-magnetic powder and on the non-magnetic layer a magnetic layer comprising a ferromagnetic powder, wherein the ferromagnetic powder comprises a hexagonal (system) ferrite magnetic powder having an average tabular diameter of 10 to 40 nm and a coercive force (Hc) of 135 to 400 kA/m and being subjected to treatment with an organic compound containing a polar group having an acid dissociation constant (pKa) of 4 or below and/or a salt thereof.

Method of producing hexagonal ferrite and magnetic recording medium using said hexagonal ferrite

A ferromagnetic metal powder for magnetic recording containing iron as the main constituent and MAl O (wherein M is a transition metal), wherein the coercive force (Hc) thereof is from 135 to 240 kA/m, the saturation magnetization (&sgr;s) is from 100 to 150 A&middot;m /kg, the average major axis length of the particles thereof is from 30 to 80 nm, the average acicular ratio of the particles is from 4.0 to 8.0, and the variation coefficient of the major axis lengths is from 3 to 25%. A magnetic recording medium having on a support a non-magnetic layer and at least a magnetic layer containing the above-described ferromagnetic metal powder, said medium has good short wavelength output and good S/N.

A magnetic recording medium having on a support a non-magnetic layer comprising a non-magnetic powder dispersed in a binder resin and on the non-magnetic layer a magnetic layer comprising a ferromagnetic powder dispersed in a binder resin, wherein the ferromagnetic powder is a Hexagonal (system) ferrite magnetic powder having an average tabular diameter of 10 to 35 nm and a coercive force (Hc) of 135 to 400 kA/m, and besides, the magnetic layer has a coercive force (Hc) of 135 to 440 kA/m, an anisotropic magnetic field of at least 358 kA/m and a rotational hysteresis loss integral of 0.5 to 0.95. Even when the magnetic recording medium is used in combination with an MR head, it can ensure high short-wavelength output, high C/N ratio and excellent recorded-magnetization stability.

A magnetic recording medium is disclosed, comprising a non-magnetic support having thereon at least one magnetic layer comprising a binder and a ferromagnetic metal powder mainly composed of iron, wherein the amount of a complex of iron with benzohydroxamic acid formed in the magnetic recording medium is from 0 to 6.0 ppm/g. Also, a magnetic recording medium is disclosed, which comprises a non-magnetic support having thereon at least two layers comprising a non-magnetic layer comprising a non-magnetic powder and a binder provided on a non-magnetic support and a magnetic layer comprising a binder and a ferromagnetic metal powder mainly composed of iron provided on said non-magnetic layer, wherein said non-magnetic powder contained in said non-magnetic layer forms a complex of iron with benzohydroxamic acid in an amount of from 0 to 10 ppm/g and has a water-soluble sodium salt content of from 0 to 150 ppm/g and a total water-soluble alkaline earth metal salt content of from 0 to 50 ppm/g. The present invention provides a magnetic recording medium excellent in practical performance such as running properties, durability and storage properties.

A magnetic recording medium is disclosed, which comprises a nonmagnetic support having thereon a magnetic layer containing at least ferromagnetic metal particles, wherein said ferromagnetic metal particles have a coercive force of from 1,700 to 3,000 Oe, an average long axis length of from 30 to 80 nm, an average acicular ratio of from 2.0 to 5.0, and a crystallinity of from 30 to 100%.

A magnetic recording medium comprising a nonmagnetic support having provided thereon at least a magnetic layer containing ferromagnetic metal particles, wherein the magnetic layer has a coercive force of 2,000 to 3,000 Oe and a Bm of 3,800 to 5,500 G, the ferromagnetic metal particles has an average major axis length of 0.05 to 0.12 .mu.m and an average aspect ratio of 4.0 to 10.0, the average number of crystallites constituting the ferromagnetic metal particles per particle is from 2.0 to 5.0, and the crystallites has an average aspect ratio of 1.0 to 2.0.

A magnetic recording medium comprising a nonmagnetic support having thereon a magnetic layer comprising a ferromagnetic metal powder and a binder resin, or having in this order thereon a nonmagnetic layer comprising a nonmagnetic material powder and a binder, and a magnetic layer comprising a ferromagnetic metal powder and a binder resin, wherein the magnetic layer exhibits a coercive force of from 2,000 to 3,000 Oe, and has a thickness of from 0.05 to 0.3 .mu.m, a surface roughness of from 1 to 3 nm, and the proportion of magnetizable components that are inverted by an external magnetic field of not less than 3,000 Oe in the magnetic layer is from 1% to (0.0225.times.(coercive force of magnetic layer)-38)% as determined by the remanence curve of the magnetic layer.

Magnetic recording medium comprising a magnetic layer of ferromagnetic

Disclosed is a magnetic recording medium comprising a nonmagnetic support, a lower nonmagnetic layer and an upper magnetic layer. The lower nonmagnetic layer is coated on the support, comprises an inorganic nonmagnetic powder dispersed in a binder, and is surface-coated with an inorganic oxide. The upper magnetic layer has a dry thickness of 1.0 micrometers or less and comprises a dispersion of a ferromagnetic powder in a binder. The upper magnetic layer is coated onto the lower nonmagnetic layer.

Magnetic recording medium comprising a lower nonmagnetic layer

A magnetic recording medium is described, comprising a nonmagnetic support having thereon a magnetic layer containing ferromagnetic particles which are a hexagonal system tabular particle, and which have an axis of easy magnetization in a direction of perpendicular to the major axis of the plate and are dispersed in a binder, wherein said ferromagnetic particles have a saturation magnetization of 60 emu/g or higher, a specific surface area (BET method) of from 25 to 70 m.sup.2 /g, an average particle diameter of from 0.01 to 0.2 .mu.m, and a coercive force of from 400 to 2000 oersteds, and said biner contains a resin having at least one kind of polar group in an amount of 1.times.10.sup.-5 eq/g or more of the polar group.

A magnetic recording medium is described, comprising a nonmagnetic support having thereon a single magnetic layer or plural magnetic layers containing ferromagnetic particles dispersed in a binder, wherein said ferromagnetic particles are ferromagnetic particles of the magnetic iron oxide type having an adsorption amount of stearic acid of from 3.times.10.sup.-6 to 6.times.10.sup.-6 mol/m.sup.2 per a surface area thereof; said binder contains at least one polymer having at least one polar group selected from the group consisting of --SO.sub.3 M, --OSO.sub.3 M, --OPO(OM').sub.2, --COOM and --PO(OM').sub.2, in which M represents Na, Li, K, a hydrogen atom, NR.sub.4 or NHR.sub.3, M' represents Na, Li, K, a hydrogen atom, NR.sub.4, NHR.sub.3 or an alkyl group, and R.sub.3 and R.sub.4 represent a lower alkyl group; and said magnetic layer further contains at least one fatty acid.

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Kanagawa, Japan

Kouichi Masaki