JP2002157727A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic recording medium low in noise, having a large area and using super fine particles coated with carbon by improving dispersibility of the super fine particles in a coating liquid. SOLUTION: (1) A magnetic recording medium wherein a magnetic layer is formed by applying a magnetic paint containing magnetic powder formed by subjecting ferromagnetic powder consisting of the super fine particles coated with carbon to surface oxidation treatment and a bonding agent onto a substrate. (2) A magnetic recording medium wherein a magnetic layer is formed by applying a magnetic paint containing the ferromagnetic powder consisting of the super fine particles coated with carbon, a dispersing agent and a bonding agent onto a substrate. (3) A magnetic recording medium wherein a magnetic layer is formed by applying a magnetic paint containing magnetic powder formed by subjecting the ferromagnetic powder consisting of the super fine particles coated with carbon to surface oxidation treatment, a dispersing agent and a bonding agent onto a substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic tape and a magnetic disk, and more particularly, to a method of forming a magnetic layer by applying a magnetic paint mainly composed of a ferromagnetic powder or a binder onto a non-magnetic support. The present invention relates to a coated magnetic recording medium formed, and more particularly to a coated magnetic recording medium particularly suitable for application to a system using an MR head utilizing a magnetoresistance effect for reproduction. The present invention also relates to a magnetic recording medium for high-density recording using carbon-coated ultrafine ferromagnetic powder.

[0002]

2. Description of the Related Art Magnetic recording technology requires that a medium can be used repeatedly, signals can be easily digitized and a system can be constructed by combining with peripheral devices, and signals can be easily modified. It has been widely used in various fields such as video, audio, and computer applications because it has excellent features not found in other recording methods. Conventionally, video tapes, audio tapes,
Magnetic recording media such as magnetic disks include ferromagnetic iron oxide,
Co-modified ferromagnetic iron oxide, chromium dioxide, ferromagnetic metal powder,
A material in which a magnetic layer in which hexagonal ferrite or the like is dispersed in a binder is coated on a nonmagnetic support is widely used. In order to achieve high recording density of magnetic recording media, the use of shorter wavelength signals has been strongly promoted, but the length of the signal recording area is comparable to the size of the magnetic material used. When the size becomes large, a clear magnetization transition state cannot be created, so that recording becomes substantially impossible. For this reason, it is necessary to develop a magnetic substance having a sufficiently small particle size with respect to the shortest wavelength to be used.

[0003] Metal powders for magnetic recording have needle-like particles and impart shape anisotropy to obtain a desired coercive force.
It is well known to those skilled in the art that it is necessary to reduce the surface roughness of a medium by reducing the size of a ferromagnetic metal powder for high-density recording. However, in the metal powder for magnetic recording, the acicular ratio decreases with miniaturization, and a desired coercive force cannot be obtained.

Recently, a data recording system for a computer includes a high-sensitivity reproducing head utilizing a magnetoresistance effect.
(MR head) is used, in which case the system noise is dominated by noise originating from the magnetic recording medium. Ferromagnetic particles are being miniaturized to reduce noise derived from the medium, but as the ferromagnetic particles become finer, they become more susceptible to thermal fluctuations, and the stability of the magnetization transition region becomes a problem. It is estimated that
The stability of the magnetization is evaluated by KuV / kT (Ku is the magnetic anisotropy constant, V is the particle volume, k is the Boltzmann constant, and T is the absolute temperature). KuV / kT must be 50 to 70 or more. Is preferred. Regarding the particle volume and thermal fluctuation of metal tape, there is a report by Toshiyuki Suzuki et al. (IEICE Technical Report MR97-55 P33-40 Nov. 21, 1997). IEEE Trans. Ma to overcome the problem of thermal fluctuation
g. vol36 (1), p10-15 (2000) proposed the use of magnetic materials with large anisotropy constants. CoPt, Co3Pt, CoCrXY (X = Ta, Pt, Y = NB, B), FePd, FePt, M
Examples are nAl and SmCo.

Also, S. Sun et al.
No. 287, 1989-1992 (2000) has published a paper on monodisperse FePt nanoparticles and ferromagnetic FePt nanocrystal superlattices. S.Sun and colleagues reported that fcc F
After surface treatment of ePt particles (non-magnetic) with oleic acid and oleylamine,
This is coated on a SiO2 / Si substrate, and heat-treated at 550 ° C for 30 minutes in nitrogen to carbonize oleic acid and oleylamine, fix it on FePt, and change the phase to fct FePt to develop a ferromagnetic carbon coating. An aggregate of fine particle magnetic material (carbon coated ultrafine particle nano size magnetic material) is obtained. Although this method can produce a magnetic recording medium having a relatively small area such as a hard disk, it is not suitable for manufacturing a magnetic recording medium requiring a large area such as a magnetic tape. In order to obtain a large-area magnetic recording medium, a method of preparing a powder of a carbon-coated ultrafine magnetic material, dispersing it in a solvent together with a binder, and coating the powder on a support is conceivable. As a result, no magnetic recording medium having poor dispersibility and good characteristics was obtained by this method. Also, Sun (S.Sun)
In these methods, since there is a step of heat treatment at a high temperature of 500 ° C. or more, a support having poor heat resistance could not be used.

[0006]

The proposal by S. Sun et al. Is an ambitious study to create an HDD without using vacuum technology, but the film is distorted by heat treatment. However, it was difficult to produce a magnetic recording medium having a large area, and it was difficult to apply the magnetic recording medium to a support having low heat resistance. Even if a magnetic coating material in which a carbon-coated ultrafine particle magnetic material is dispersed in a solvent is prepared to apply a large area, a good magnetic recording medium cannot be obtained because the dispersibility is extremely poor. SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems of the prior art, and provides a low-noise, large-area magnetic recording medium by improving the dispersibility of a carbon-coated ultrafine particle magnetic material in a coating solution. It is intended to be.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and is intended to realize a magnetic recording medium having a large area using a magnetic material coated with ultra-fine particles of carbon coated with high Ku. In addition, as a result of various studies on a surface treatment method of a carbon-coated nano-sized magnetic material which realizes a high dispersibility suitable for it, a method capable of improving the dispersibility of a coating solution containing a magnetic material was found. On the basis thereof, a magnetic recording medium having a magnetic layer formed by applying a stable highly dispersible coating solution on a support was obtained, and the object of the invention was achieved. That is, the present invention is as follows.

[0008] 1. A magnetic recording medium comprising a magnetic layer formed by applying a magnetic paint containing a binder and a magnetic powder obtained by oxidizing the surface of carbon-coated ultrafine ferromagnetic powder to a support.

[0009] 2. A magnetic recording medium comprising a magnetic layer formed by applying a magnetic paint containing carbon-coated ultrafine ferromagnetic powder, a dispersant and a binder to a support.

[0010] 3. A magnetic recording medium comprising a magnetic layer formed by applying a magnetic coating material containing a magnetic powder obtained by oxidizing a surface of a carbon-coated ultrafine ferromagnetic powder, a dispersant and a binder to a support.

Hereinafter, specific embodiments of the present invention will be described in detail. The metal constituting the magnetic material is preferably a simple metal or an alloy thereof, or an intermetallic compound generally used in a permanent magnet.Specifically, Co, CoPtCr, Co ₃ Pt, FePd, FeP
Preferred metals include t, CoPt, MnAl, Fe ₁₄ Nd ₂ B, SmCo ₅ , and TbFeCo. The average particle size of the metal fine particles is preferably 2 to 15 nm, more preferably 3 to 10 nm. Further, it is also preferable to use the morphological control agent to form acicular or plate-like particles. In the case of a needle shape, the minor axis is 2 to 5 n
It is preferable that the number of needles (long axis / short axis) be 2 to 15 in m.

The above-mentioned nano-sized metal fine particles are ultra-fine particles which can be called a precursor of carbon-coated ultra-fine particles, and the ultra-fine particles are coated with carbon. In the case of ultra-fine particles of carbon-coated FePt, the method is as follows: (1) The precursor of the magnetic material of ultra-fine particles of carbon-coated ultra-high Ku is synthesized by a known method such as a sputtering method or a vapor deposition method, and vaporized as a carbon source. The precursor is coated by introducing a neutral organic compound into the system. This is heated at 525 to 600 ° C using a stationary, rotary or fluidized bed heating furnace in an inert gas atmosphere, and then pulverized and classified to obtain a carbon-coated nano-sized magnetic material. (2) By wet reduction As a method, a metal ion is reduced to fine metal particles, an organic compound (for example, a surfactant) is allowed to act on the fine particles, and the magnetic material is adsorbed on the fine metal particles. The magnetic material is placed in the stationary, rotary or fluidized bed heating furnace. Spray drying the precursor, and further heating at 525 to 600 ° C. in an inert gas atmosphere to obtain a carbon-coated ultrafine particle. The method of producing carbon-coated ultrafine particles of other metal species also depends on the firing temperature,
Conditions such as reaction time and gas atmosphere need to be adjusted,
A similar method can be applied.

Examples of the carbon source for coating include alkanols such as 1,2-hexanediol, ethers such as dioctyl ether, fatty acids such as oleic acid, fatty acid amides such as stearylamide, carbon such as polyvinylpyrrolidone, oxygen, and the like. In some cases, an organic compound comprising nitrogen or a polymer dispersant is used. In the case of other carbon-coated metal ultrafine particles, the carbonization heating temperature differs depending on each metal, and the organic compound of the carbon source can be appropriately selected from organic compounds and polymer dispersants composed of carbon, oxygen and optionally nitrogen. In substantially the same manner. The amount of carbon fixed to the metal surface is preferably 30 to 80% by volume, more preferably 30 to 70% by volume, based on the metal magnetic material.

An appropriate temperature for the carbonization heating temperature is selected in the range of 100 to 800 ° C., preferably 200 to 600 ° C. according to the type of the metal fine particles. In addition, from room temperature to 20
It is also possible to adopt a two-step system in which the organic compound is adsorbed on the surface of the particles at about 0 ° C. and then coated with carbon at 200 to 800 ° C. The heating time also depends on the temperature and the type of metal ultrafine particles,
Further, an appropriate time is appropriately selected depending on the carbon source compound, but it is usually preferably from 10 minutes to 120 minutes.

The carbon-coated ultrafine particle magnetic material thus obtained is obtained as independent particles. In order to further improve the acidity, the surface of the particles is oxidized or a dispersant is added. Either or both of them are added to form a coating solution in a state of being dispersed in a binder.

The oxidizing method is a method in which an oxidizing agent is acted on the obtained carbon-coated ultrafine particle magnetic substance in a gas phase or a liquid phase to reduce the coated carbon layer and to introduce a surface functional group. Thereby, the dispersibility in the magnetic paint can be improved. As the gas phase oxidizing agent, air, ozone, nitrogen oxide, nitric acid and a mixture thereof are preferable, and as the liquid phase oxidizing agent, nitric acid, potassium permanganate, hypochlorous acid, sodium hypochlorite, aqueous bromine solution ,
Ozone aqueous solution can be used. If the weather resistance of the nano-sized magnetic material is sufficiently excellent, the oxidation treatment may be performed in either a liquid phase or a gas phase. However, when the magnetic material is active against water, it is preferable to use the gas phase treatment. preferable.

In order to cause a uniform reaction in the coating layer, it is necessary to keep the nano-sized magnetic material in a fluidized state, and a fluidized bed system fluidized with an oxidizing gas and a fixed bed system which can always be agitated. , Or use a rotary kiln system. In addition to the introduction of functional groups on the surface containing the oxidizing agent, which increases the interaction with the binder and improves the dispersibility, the oxidizing agent selectively oxidizes relatively low crystallinity parts. It is preferable to perform the treatment because primary particles are easily generated. The oxidation treatment temperature is determined by the combination with the oxidizing agent, and it is also preferable to combine the oxidation treatment. For example, a method in which an oxidation treatment is performed at 30 to 150 ° C. with dry air and ozone, and a carbon layer covering the particle surface is oxidized at 150 to 250 ° C. using NO ₂ can be used. As the oxidation treatment time, an optimum time is selected based on a combination of the oxidizing agent and the oxidation temperature. The time is generally between 3 and 60 minutes.

Further, as described above, the dispersibility of the carbon-coated ultrafine particle magnetic material can be improved by using a dispersant. It is preferable to use a carbon black dispersant as the dispersant, and it is particularly preferable to use a pigment dispersant in order to enhance dispersibility. Examples of the pigment dispersant that can be used in the present invention include a pigment dispersant using an organic dye as a raw material. As the organic dye serving as a raw material of the pigment dispersant of the present invention, a commercially available dye or pigment can also be used. For example, anthraquinone dyes, azo dyes, phthalocyanine dyes, quinacridone dyes, dioxazine dyes, anthrapyrimidine dyes, anthanthrone dyes, indanthrone dyes,
Pigments or dyes such as flavanthrone dyes, pyranthrone dyes, perinone dyes, perylene dyes, thioindigo dyes, triphenylmethane dyes, and isoindolinone dyes. Specifically, pigment dispersants described in, for example, Color Material Engineering Handbook (edited by the Color Material Association, 1989, p. 319) and JP-A Nos. 1-232524 and 6-259758 are preferable. These pigment dispersants may be used alone or in combination of two or more. In improving the dispersibility of the carbon-coated ultrafine particle magnetic material, the above-described surface oxidation treatment or the addition of a dispersant may be used alone or in combination.

As the binder resin for the magnetic layer in the magnetic recording medium of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof can be used. As a thermoplastic resin, the glass transition temperature is -100 to 150.
° C, the number average molecular weight is 1,000 to 200,000, preferably 10,000 to 100,000, and the degree of polymerization is 50 to 1,000.
Is used.

Examples of the thermoplastic binder resin include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acuric acid, acrylic ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic ester, styrene, butadiene, ethylene, Examples thereof include polymers or copolymers containing a monomer selected from vinyl butyral, vinyl acetal and vinyl ether as constituent monomers, polyurethane resins, and various rubber resins.

The thermosetting resin or the reactive resin includes a phenol resin, an epoxy resin, a polyurethane curable resin, a urea resin, a melamine resin, an alkyd resin, an acrylic reaction resin, a formaldehyde resin, and a silicone resin. , An epoxy-polyamide resin, a mixture of a polyester resin and an isocyanate prepolymer, a mixture of a polyester polyol and a polyisocyanate, and a mixture of a polyurethane and a polyisocyanate.

In order to obtain a better dispersion effect of ferromagnetic powder and durability of the magnetic layer in the binder resin, COOM, SO ₃ M, OSO ₃ M, P = O (O
_{M) 2, O-P =} O (OM) 2, M per (or a hydrogen atom or an alkali metal _{salt,), OH, NR 2,} N + R 3
(R ₂ and R ₃ are alkyl groups, alkenyl groups, acyl groups, allyl groups), at least one polar group selected from groups such as epoxy group, SH, CN, etc. introduced by copolymerization or addition reaction. It is preferable to use The amount of such a polar group is from 10 ^-8 to 10 ^-1 mol / g, preferably from 10 ^-6 to 10 ^-2 mol / g.

The binder resin used in the magnetic recording medium of the present invention is used in an amount of 5 to 50% by mass, preferably 10 to 30% by mass, based on the ferromagnetic powder. It is preferable to use 5 to 100% by mass when using a vinyl chloride resin, 2 to 50% by mass when using a polyurethane resin combination, and 2 to 100% by mass for polyisocyanate.

In the present invention, when polyurethane is used, the glass transition temperature is -50 to 100 ° C., and the elongation at break is 1
00-2000%, breaking stress 0.05-10 kg / c
m ² and the yield point are preferably 0.05 to 10 kg / cm ² .

The polyisocyanate used in the present invention includes tolylene diisocyanate, 4-4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, and naphthylene-1. ,
5-diisocyanate, o-toluidine diisocyanate
, Isophorone diisocyanate, triphenylmethane triisocyanate and other isocyanates; products of these isocyanates and polyalcohols; and polyisocyanates formed by condensation of isocyanates. -And the like can be used. Commercially available trade names of these isocyanates are Nippon Polyurethane Co., Ltd., Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR.
Millionate MTL, Takeda Pharmaceutical Co., Ltd., Takenate D-1
02, Takenet D-110N, Takenet D-20
0, Takenate D-202, Desmodur L, Desmodur IL, Desmodur N Desmodul HL, manufactured by Sumitomo Bayer, etc. These are used alone or by utilizing the difference in curing reactivity. One or more combinations can be used.

In the magnetic layer of the magnetic recording medium of the present invention, various functions such as a lubricant, an abrasive, a dispersant, an antistatic agent, a dispersant, a plasticizer, a fungicide and the like are usually provided. Materials to be contained according to the purpose.

As the lubricant used in the magnetic layer of the present invention, a dialkyl polysiloxane (where alkyl is
5), dialkoxypolysiloxane (alkoxy has 1 to 4 carbon atoms), monoalkylmonoalkoxypolysiloxane (alkyl has 1 to 5 carbon atoms, alkoxy has 1 to 4 carbon atoms), phenylpolysiloxane, fluoro Silicone oil such as alkylpolysiloxane (alkyl is 1 to 5 carbon atoms); conductive fine powder such as graphite; inorganic powder such as molybdenum disulfide, tungsten disulfide; polyethylene, polypropylene, polyethylene vinyl chloride copolymer, poly Plastic fine powder such as tetrafluoroethylene; α-olefin polymer; saturated fatty acid which is solid at normal temperature (carbon number of 10 to 22); unsaturated aliphatic hydrocarbon which is liquid at normal temperature (carbon having terminal n-olefin double bond Compound having about 20 carbon atoms; monobasic fatty acid having 12 to 20 carbon atoms and Fatty acid esters consisting of 3 to 12 monovalent alcohol prime, fluorocarbons and the like can be used.

Of the above, saturated fatty acids and fatty acid esters are preferred, and both are more preferred. Ethanol, butanol, phenol, benzyl alcohol, 2
-Methyl butyl alcohol, 2-hexyldecyl alcohol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether, dipropylene glycol monobutyl ether, diethylene glycol monobutyl ether, s-butyl alcohol, etc., monoalcohols, ethylene glycol, diethylene glycol, neopentyl glycol , Glycerin, sorbitan derivatives and the like. Similarly, fatty acids include acetic acid, propionic acid, octanoic acid, 2-ethylhexanoic acid, lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, arachiic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, and palmitoleic acid And the like or a mixture thereof.

Specific examples of the fatty acid ester include butyl stearate, s-butyl stearate, isopropyl stearate, butyl oleate, amyl stearate, 3-methylbutyl stearate, 2-ethylhexyl stearate, and 2-hexyldecyl. Stearate, butyl palmitate, 2-ethylhexyl myristate,
A mixture of butyl stearate and butyl palmitate, butoxyethyl stearate, 2-butoxy-1-propyl stearate, dipropylene glycol monobutyl ether acylated with stearic acid, diethylene glycol dipalmitate, hexamethylene diol to myristic acid And various ester compounds such as glycerin oleate.

Furthermore, in order to reduce the hydrolysis of fatty acid esters which often occur when the magnetic recording medium is used under high humidity, the fatty acids and alcohols used as raw materials are branched / straight chain, isomer structure such as cis / trans, branch position. A choice is made. These lubricants are added in the range of 0.2 to 20 parts by mass with respect to 100 parts by mass of the binder.

The following compounds can also be used as the lubricant. That is, silicon oil, graphite, molybdenum disulfide, boron nitride, fluorinated graphite, fluorinated alcohol, polyolefin, polyglycol, alkyl phosphate, tungsten disulfide and the like.

As the abrasive used in the magnetic layer of the present invention, particles having an average particle diameter of 2 to 150 nm are effective.
Preferably it is 5 to 100 nm. α-alumina, γ-alumina, artificial diamond, fullerene including ⁶⁰ C, carbon nanotube, α-Fe ₂ O ₃ , ZrO _2, etc. are used. Examples of these abrasives include Sumitomo Chemical's α-alumina HIT-100, Hit82, HIT-80, HIT70, artificial diamond with an average diameter of 4 to 10 nm that is made by mixing graphite and explosives, and MD-100 made by Tomei Diamond. (Average diameter up to 100 nm), α-Fe ₂ O ₃ DN-001 (average diameter up to 10 nm), DN-002 (average diameter up to 20 nm) manufactured by Toda Kogyo, ZrO ₂ HZ-N manufactured by Hokuko Chemical (average diameter up to 30 nm) ), HZ
-Y 3M (average diameter ~ 40nm) and so on.

It is preferable to use not only a single polishing agent but also two or more types of polishing agents. In the case of fine diamond particles, by using together with another polishing agent, the amount added to the magnetic material can be reduced to zero. .1%.
The total amount of these abrasives is 1 to 100 parts by mass of the magnetic material.
-20 parts by mass, preferably 1-15 parts by mass. If the amount is less than 1 part by mass, sufficient durability cannot be obtained, and if it is more than 20 parts by mass, the surface properties and the degree of filling deteriorate. These abrasives may be added to the magnetic paint after dispersion treatment with a binder in advance.

Since the magnetic recording medium of the present invention uses a ferromagnetic metal powder whose surface is coated with carbon, it is often necessary only to add the nonmagnetic powder. Conductive particles can also be included as an inhibitor. However, in order to maximize the saturation magnetic flux density of the upper layer, the addition to the uppermost layer should be reduced as much as possible.
It is preferably added to a coating layer other than the upper layer. It is particularly preferable to add carbon black as an antistatic agent in terms of lowering the surface electric resistance of the entire medium.

Carbon black usable in the present invention may be furnace black for rubber, thermal black for rubber, black for color, conductive carbon black, acetylene black, or the like. Specific surface area is 5-50
0m ² / g, DBP oil absorption 10 ~ 1500ml / 100
g, particle size is 5 to 300 nm, PH is 2 to 10, water content is 0.1 to 10%, tap density is 0.1 to 1 g / cm3,
Is preferred. Specific examples of carbon black used in the present invention include BLACKPEAR manufactured by Cabot Corporation.
LS 2000, 1300, 1000, 900, 80
0,700, VULCAN XC-72, manufactured by Asahi Carbon Co., Ltd., # 80, # 60, # 55, # 50, # 35, manufactured by Mitsubishi Chemical Corporation, # 3030B, # 3040B, # 3050B,
# 3230B, # 3350B, # 9180B, # 270
0, # 2650, # 2600, # 2400B, # 230
0, # 950B, # 900, # 1000, # 95, # 3
0, # 40, # 10B, MA230, MA220, MA
77, CONDUCTEX manufactured by Konrombia Carbon
SC, RAVEN 150, 50, 40, 15, Ketjen Black EC, Ketjen Black ECDJ-500, Ketjen Black ECDJ manufactured by Lion Aguso
-600 and the like.

Carbon black may be surface-treated with a dispersant or the like, oxidized on the surface, or grafted with a resin. Is also good. Further, carbon black may be dispersed in a binder before adding it to the magnetic paint. When carbon black is used for the magnetic layer, the amount is preferably 0.1 to 30% by mass based on the magnetic material. Further, the non-magnetic layer preferably contains 3 to 20% by mass of the entire non-magnetic powder.

In general, carbon black functions not only as an antistatic agent but also to reduce the coefficient of friction, impart light-shielding properties, and improve film strength, and these vary depending on the carbon black used. Therefore, these cars used in the present invention
Bon blacks can be used in different types, amounts and combinations depending on the purpose based on the above-mentioned various properties such as particle size, oil absorption, conductivity and pH. Carbon black that can be used can be referred to, for example, "Carbon Black Handbook" edited by Carbon Black Association.

In the magnetic recording medium of the present invention, the non-magnetic layer when formed below the magnetic layer is a layer in which non-magnetic powder is dispersed in a binder resin. Various non-magnetic powders can be used for the non-magnetic layer. For example, α-alumina, β-alumina, γ-alumina, 90% or more α-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, getite, corundum, silicon nitride, titanium carbide
Bites, titanium oxide, silicon dioxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate and the like are used alone or in combination. Α-iron oxide, goethite, titanium oxide, and zinc oxide are preferred as fine and uniform particles. The particle size of these non-magnetic powders is preferably 0.01 to 1 μm. However, if necessary, non-magnetic powders having different particle sizes may be combined, and a single non-magnetic powder may have the same effect by broadening the particle size distribution. Can also. In order to increase the interaction with the binder resin to be used and to improve the dispersibility, the non-magnetic powder to be used may be surface-treated.

As the surface-treated material, silica, alumina,
Treatment with an inorganic substance such as silica-alumina or treatment with a coupling agent may be used. Tap density is 0.3-2
g / cm ³ , water content 0.1-5% by mass, pH 2-1.
1, The specific surface area is preferably 5 to 100 m ² / g. The shape of the nonmagnetic powder may be any one of a needle shape, a spherical shape, a die shape, and a plate shape. Specific examples of the non-magnetic powder used in the lower layer of the magnetic recording medium obtained by the present invention include Nanotite manufactured by Showa Denko, HIT-100 manufactured by Sumitomo Chemical, and HI
T-80, α-iron oxide DPN-250BX manufactured by Toda Kogyo,
DPN-245, DPN-270BX, DPN-550
BX, DPN-550RX, DBN-450BX, DB
N-650RX, DAN-850RX, Titanium oxide TTO-51B, TTO-55A, TTO-55 manufactured by Ishihara Sangyo
B, TTO-55C, TTO-55S, TTO-55
D, SN-100, Titanium Oxide STT-4
D, STT-30D, STT-30, STT-65C,
TEIKA made titanium oxide MT-100S, MT-100T,
MT-150W, MT-500B, MT-600B, M
T-100F, MT-500HD, Sakai Chemical FINEX
-25, BF-1, BF-10, BF-20, ST-
M, Dowa Mining Iron Oxide DEFIC-Y, DEFIC-
R, AS2BM, TiO ₂ P25 manufactured by Nippon Aerosil, 100A, 500A manufactured by Ube Industries, and baked products thereof.

The non-magnetic support of the magnetic recording medium is usually
The thickness is preferably 3 to 100 .mu.m, preferably 3 to 20 .mu.m when used in a tape form, and 25 to 80 .mu.m when used as a flexible disk. It is 5.0 μm, preferably 0.5 to 3 μm. It is permissible to form layers other than the magnetic layer and the non-magnetic layer according to the purpose as long as the magnetic layer is the uppermost layer and the non-magnetic layer is the lower layer. For example, an undercoat layer for improving adhesion may be provided between the nonmagnetic support and the lower layer. This thickness is 0.01-1 μm, preferably 0.05-0.
3 μm. Further, a backcoat layer may be provided on the side opposite to the magnetic layer side of the nonmagnetic support. This thickness is
It is 0.1 to 1.0 μm, preferably 0.3 to 0.8 μm. Known materials can be used for the intermediate layer and the back coat layer.
In the case of a disk-shaped magnetic recording medium, the above-mentioned layer structure can be provided on both surfaces or both surfaces.

The non-magnetic support used in the present invention is not particularly limited, and those commonly used can be used. Examples of the material forming the nonmagnetic support include films of various synthetic resins such as polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamideimide, polyimide, polysulfone, polyethersulfone, and aluminum foil. And metal foils such as stainless steel foils.

In order to effectively achieve the object of the present invention, the surface roughness of the non-magnetic support should be 0.03 μm or less, preferably 0.02 μm in terms of center line average surface roughness Ra (cutoff value 0.25 mm). The thickness is more preferably 0.01 μm or less. Further, it is preferable that these non-magnetic supports not only have a small center line average surface roughness but also have no coarse protrusions of 1 μm or more. The surface roughness can be freely controlled by the size and amount of the filler added to the non-magnetic support as needed. Examples of these fillers include oxides and carbonates of Ca, Al, Si, Ti and the like, and fine powders of organic resins such as acrylics. The F-5 value of the non-magnetic support used in the present invention in the web running direction is preferably 5 to 50 kg / m.
m ² , F-5 value in the web width direction is preferably 3 to 30 k
g / mm ² . Generally, the F-5 value in the long hand direction of the web is higher than the F-5 value in the web width direction, but this is not particularly necessary when it is necessary to increase the strength in the width direction.

The heat shrinkage of the support in the web running direction and the width direction at 100 ° C. for 30 minutes is preferably 3% or less, more preferably 1.5% or less. The heat shrinkage at 80 ° C. for 30 minutes is preferably 1% or less, more preferably 0.5% or less. The breaking strength was 5 to 100 kg / mm ² (4.9 to 98 in both directions).
× 10 ⁷ Pa), and the elastic modulus is 100 to 2000 kg.
/ Mm ² (9.8 to 196 × 10 ⁸ Pa).

The organic solvent used in the present invention includes ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone and tetrahydrofuran, methanol and ethanol.
, Propanol, butanol, isobutyl alcohol
Alcohols such as alcohol, isopropyl alcohol and methylcyclohexanol, esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate and glycol acetate, glycol dimethyl ether,
Glycol ethers such as glycol monoethyl ether and dioxane, aromatic hydrocarbons such as benzene, toluene, xylene, cresol and chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride,
Chlorinated hydrocarbons such as chloroform, ethylene chlorohydrin and dichlorobenzene, N, N-dimethylformamide, hexane and the like can be used in any ratio. These organic solvents do not necessarily have a purity of 100%, and may contain impurities such as isomers, unreacted substances, by-products, decomposition products, oxides, and moisture in addition to the main components. The content is preferably 30% or less, more preferably 10% or less. The type and amount of the organic solvent used in the present invention can be changed between the magnetic layer and the intermediate layer if necessary. For example, use a highly volatile solvent for the first layer to improve the surface properties, use a solvent with a high surface tension (cyclohexanone, dioxane, etc.) for the first layer to increase the coating stability, and dissolve the solubility parameter of the second layer. For example, the filling degree may be increased by using a solvent having a high data rate, but it is a matter of course that the present invention is not limited to these examples.

The magnetic recording medium of the present invention is prepared by kneading and dispersing the above-mentioned ferromagnetic powder, a binder resin and, if necessary, other additives together with an organic solvent, applying a magnetic paint on a non-magnetic support, Orientation and drying according to the conditions.

The step of producing the magnetic coating material of the magnetic recording medium of the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Each step may be performed in two or more steps. All raw materials such as a magnetic substance, a binder, carbon black, an abrasive, an antistatic agent, a lubricant and a solvent used in the present invention can be added at the beginning or during any step. In addition, individual raw materials can be added in two or more steps. For example, the polyurethane may be divided into a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion, and then charged.

In kneading and dispersing the magnetic paint, various kneaders are used. For example, a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a tron mill, a sand grinder, a Szegvari, an attritor, a high-speed impeller disperser, a high-speed stone mill,
High-speed impact mill, disperser, kneader, high-speed mixer,
A homogenizer, an ultrasonic disperser or the like can be used.

In order to achieve the object of the present invention, it is a matter of course that a conventionally known manufacturing technique can be used for a part of the process. However, in the kneading process, a continuous kneader or a pressure kneader is used.
The use of a material having a strong kneading force, such as a die, makes it possible to obtain a high Br (residual magnetic flux density) of the magnetic recording medium of the present invention for the first time. When a continuous kneader or a pressure kneader is used, all or a part of the magnetic substance and the binder (however, preferably 30% or more of the total binder) and the magnetic substance 10 are used.
The kneading treatment is performed in the range of 15 to 500 parts by mass with respect to 0 parts by mass. The details of these kneading processes are described in JP-A-1-1-1.
No. 06338 and JP-A-64-79274. In the present invention, Japanese Patent Application Laid-Open No.
By using the simultaneous multi-layer coating method as disclosed in Japanese Unexamined Patent Application Publication No. H11-107, more efficient production can be performed.

The formation of two or more coating layers on a non-magnetic support is also effective in producing a magnetic recording medium having a high recording density, and the simultaneous coating method can produce an ultrathin magnetic layer. It is especially good because it can. As a specific method of the wet-on-wet method as the simultaneous application method,

(1) First, a lower layer is applied by a gravure coating, roll coating, blade coating, or extrusion coating device which is generally used as a magnetic paint, and while the layer is still wet, for example, -46186, JP-A-60-238179 and JP-A-2-2-2.
No. 65672, a method of applying an upper layer by a non-magnetic support pressurized extrusion coating apparatus,

(2) JP-A-63-88080, JP-A-2-17971 and JP-A-2-265672
A method of applying a lower layer coating liquid and an upper layer coating liquid almost simultaneously by a coating head incorporating two coating liquid passage slits as disclosed in JP

(3) A method in which an upper layer and a lower layer are coated almost simultaneously by an extrusion coating apparatus with a backup roll disclosed in JP-A-2-174965.

In the case of coating by a wet-on-wet method, the flow characteristics of the coating solution for the magnetic layer and the coating solution for the non-magnetic layer should be as close as possible to avoid disturbance of the interface between the coated magnetic layer and the non-magnetic layer. A magnetic layer having a uniform thickness and a small thickness variation can be obtained. Since the flow characteristics of the coating solution strongly depend on the combination of the powder particles and the binder resin in the coating solution,
In particular, it is necessary to pay attention to the selection of the non-magnetic powder used for the non-magnetic layer. In addition, the lower layer is applied by a coating device such as gravure coating, roll coating, blade coating, extrusion coating, etc., which are generally used for magnetic coating, dried, and further subjected to a calendar treatment as necessary, and then further thereon. A sequential coating method in which the magnetic layer is coated with a coating device such as gravure coating, roll coating, blade coating, or extrusion coating is also possible.

The residual solvent contained in the magnetic layer of the magnetic recording medium of the present invention is preferably 100 mg / m ² or less, more preferably 10 mg / m ² or less, and the residual solvent contained in the magnetic layer is contained in the non-magnetic layer. It is preferable that the amount is smaller than the contained residual solvent.

The porosity of the magnetic layer is preferably 30% by volume or less, more preferably 10% by volume or less, for both the lower layer and the uppermost layer. The porosity of the non-magnetic layer is preferably larger than the porosity of the magnetic layer, but may be small as long as the porosity of the non-magnetic layer is 5% by volume or more.

Although the magnetic recording medium of the present invention has a lower layer and an uppermost layer, these physical characteristics can be changed between the lower layer and the uppermost layer according to the purpose. For example, while increasing the elastic modulus of the uppermost layer to improve running durability, the elastic modulus of the lower layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head.

According to such a method, the magnetic layer applied on the support is subjected, if necessary, to a treatment for orienting the ferromagnetic powder in the layer, and then the formed magnetic layer is dried. The magnetic recording medium of the present invention is manufactured by performing a surface smoothing process or cutting into a desired shape as required. The composition for the uppermost layer and the composition for the lower layer are dispersed together with a solvent, and the obtained coating solution is applied onto a non-magnetic support, and orientation dried to obtain a magnetic recording medium.

The elastic modulus of the magnetic layer at 0.5% elongation is preferably 100 to 2000 k in both the web coating direction and the width direction.
g / mm ² (9.8 to 196 × 10 ⁸ Pa), and the breaking strength is desirably 1 to 30 kg / cm ² (9.8 to 29.6 ×).
10 ⁴ Pa), the elastic modulus of the magnetic recording medium is preferably 100 to 1500 kg / m in both the web coating direction and the width direction.
m ² (9.8 to 14.7 × 10 ⁸ Pa), the residual elongation is preferably 0.5% or less, and the heat shrinkage at any temperature of 100 ° C. or less is preferably 1% or less, more preferably 0.1% or less. It is at most 5%, most preferably at most 0.1%.

The magnetic recording medium of the present invention may be a tape for video use or audio use or a floppy (registered trademark) disk or magnetic tape for data recording use.
This is particularly effective for digital recording media where dropout of a signal due to dropout is fatal.
Further, the lower layer is a nonmagnetic layer, and the thickness of the uppermost layer is 0.5 μm.
By performing the following, a high-density, large-capacity magnetic recording medium having high electromagnetic conversion characteristics and excellent overwrite characteristics can be obtained.

[0060]

EXAMPLES The novel features of the present invention will be specifically described in the following examples, but the present invention is not limited to the examples. 1. Preparation and post-treatment of magnetic material Pt (acac) ₂ (197 g, 0.5 mol), 1,
2 Hexadecanediol (390 g, 1.5 mol) and dioctyl ether (20 liter) were mixed and heated to 100 ° C. Oleic acid (0.16 l, 0.5 mol), oleylamine (0.17 l, 0.5 mol), Fe (CO) ₅ (0.13 l, 1 mol)
Was added and the mixture was heated to 300 ° C. under reflux and held for 30 minutes. Remove the heating source and allow the reaction to cool to room temperature.
After cooling, the following operations were performed in an air atmosphere. Ethanol (about
(40 liters) was added to precipitate a black reaction product and centrifuged. The tan viscous liquid was removed and the black precipitate was washed with oleic acid (5
% Hexane with oleylamine (5% 0.05 liter)
(About 25 liters), precipitated by adding ethanol (about 20 liters), and centrifuged. Disperse the product in hexane (about 20 liters), centrifuge to remove undissolved precipitate,
Ethanol (about 15 liters) was added to form a precipitate, which was centrifuged. The centrifuged product was spray-dried in a nitrogen atmosphere spray dryer kept at 125 ° C., and the dried powder was collected. X-ray diffraction of the dried powder showed an fcc structure.

After the dried powder was placed in a firing apparatus and purged with nitrogen, the temperature was raised to 550 ° C. in 15 minutes, held for 30 minutes, and cooled in nitrogen. Observation of the obtained carbon-coated particles with a transmission electron microscope revealed that the average diameter of the metal portion was 6 nm (coefficient of variation of diameter: standard deviation / average value: 8%). X-ray diffraction of the obtained particles had an fct structure and was magnetic. The obtained magnetic particles were placed in a rotary heating furnace and post-treated while being rotated under the oxidizing agents and processing conditions shown in Table 1. Then, using a VSM, an external magnetic field of 1591 kA /
Hc and saturation magnetization were measured at m. The particle diameter and the coefficient of variation of the metal part were measured with a transmission electron microscope.

[0062]

[Table 1]

2. Nitrogen was bubbled into the preparation of the magnetic body and the post-processing CoSO ₄ solution (concentration 1 mol) 10 liters while stirring with a stirrer included in a container, NaBH ₄ aqueous solution
20 liters (1 mol) was added to produce metal Co. Then
Add 1 liter of sodium oleate solution (5%) and add metal Co
Oleic acid was adsorbed on the surface. The black precipitate was filtered, washed pure and free of salts. Oleic acid (5%
Hexane (about 2 liters) with oleylamine (5% 0.05 liters)
5 liters), precipitated by adding ethanol (about 20 liters), and centrifuged. The centrifuged product was spray-dried in a nitrogen atmosphere spray dryer kept at 125 ° C., and the dried powder was collected. X-ray diffraction of the dried powder had an fcc structure. The obtained magnetic particles were placed in a rotary heating furnace and post-treated while being rotated under the oxidizing agents and processing conditions shown in Table 2. afterwards
Hc and saturation magnetization were measured using a VSM with an external magnetic field of 10 kOe.
The particle size was measured with a transmission electron microscope.

[0064]

[Table 2]

3. Manufacturing Method of Magnetic Recording Medium In order to prepare a multilayer magnetic tape using the magnetic powders A to D, the following composition of the magnetic layer and the composition of the lower non-magnetic layer were prepared.

(Material of magnetic layer) Ferromagnetic alloy powder 100 parts Binder resin 13 parts of vinyl chloride copolymer (containing 1 × 10 ⁻⁴ eq / g of —SO ₃ Na group) Polymerization degree 300 Polyester polyurethane resin 5 Part (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group containing 1 × 10 ^-4 eq / g) Artificial diamond (average particle diameter 8 nm) 1 part DN-001 ( Granular α-Fe ₂ O ₃ average particle diameter 10 nm) 4 parts Organic pigment dispersant (Table 3) 3 parts Butyl stearate 3 parts Stearic acid 3 parts Methyl ethyl ketone and cyclohexanone 1: 1 mixed solvent 340 parts

(Composition of Nonmagnetic Layer for Lower Layer) Acicular hematite 80 parts (specific surface area 55 m ² / g by BET method, average major axis length 0.10 μm, acicular ratio 7, pH 8.8, aluminum-treated Al ₂ O ₃ as a 1 wt%) carbon black 20 parts (average primary particle diameter 17 nm, DBP及油amount 80 ml / 100 g, surface area measured by the BET method 240m ² /g,pH7.5) binder resin of vinyl chloride copolymer 12 parts (Containing 1 × 10 ⁻⁴ eq / g of —SO ₃ Na group) Polymerization degree 300 polyester polyurethane resin 5 parts (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 —SO ₃ Na group 1 × 10 ^-4 eq / g containing) phenyl phosphonic acid 3 parts butyl stearate 3 parts stearic acid 3 parts Methyl ethyl ketone and cyclohexanone 1: 1 mixture Agent 280 parts

For each of the above-mentioned magnetic paint and non-magnetic paint, a pigment, polyvinyl chloride, an organic pigment dispersant, phenylphosphonic acid, and 50% by mass of a prescribed amount of each solvent are kneaded with a kneader, and then mixed with a polyurethane resin. The remaining components were added and dispersed with a sand grinder. Isocyanate was added to the resulting dispersion, and 15 parts of the coating solution for the nonmagnetic layer and 14 parts of the coating solution for the magnetic layer were added. Further, 30 parts of cyclohexanone was added to each, and a filter having an average pore size of 1 μm was used. The mixture was filtered to prepare a coating solution for forming a nonmagnetic layer and a coating solution for forming a magnetic layer.

The obtained coating solution for the lower non-magnetic layer was coated to a thickness of 7
μm on a polyethylene terephthalate support, so that the thickness after drying becomes 1.5 μm. Immediately thereafter, while the coating layer for the lower non-magnetic layer is still wet, the thickness of the magnetic layer is formed thereon. The wet simultaneous multi-layer coating was carried out so that the thickness was 0.10 μm, and while both layers were still in a wet state, they were passed through an orienting device and longitudinally oriented. At this time, the oriented magnet was passed through a rare-earth magnet (magnetic flux density of 500 mT), partially dried, and then passed through a superconducting magnet (magnetic flux density of 1.5 T). Thereafter, a back coat layer is applied, dried and wound up, and calendering is performed at a roll temperature of 90 ° C. using a seven-stage calender composed of metal rolls to obtain a web-shaped magnetic recording medium.
It was slit to 8 mm width to make a sample of 8 mm video tape. The magnetic properties, surface gloss, surface roughness, and electromagnetic conversion characteristics of the obtained sample were measured using a vibrating sample magnetometer. The magnetic properties were measured in parallel with the orientation direction with an external magnetic field of 796 kA / m using a vibrating sample magnetometer (manufactured by Toei Kogyo).

The method of measuring the electromagnetic conversion characteristics was as follows. MIG head (head gap 0.2 μm, track width 17 μm, saturation magnetic flux density 1.6 T, azimuth angle 20 °) and reproduction MR head on 8 mm deck for data recording
(SAL bias, MR element is Fe-Ni, track width 6μm, gap length 0.2μm, azimuth angle 20 °). MI
9. Using a G head, increase the relative speed between the tape and the head.
2 m / sec, the optimum recording current was determined from the input / output characteristics of 1/2 Tb (λ = 0.5 μm), and the signal was recorded with this current.
Reproduced with MR head. C / N was from the peak of the reproduction carrier to the degaussing noise, and the resolution bandwidth of the spectrumr was 100 kHz. It was expressed by the characteristics of the tape using Comparative Example-21.

The surface gloss was measured using a suga gloss meter,
The gloss of the reflection was measured. Surface roughness is measured by WYKO (U
S Arizona) Interferometric 3D roughness meter "TOPO-3
Using "D", a sample area of 250 μm square was measured. In calculating the measured values, corrections such as tilt correction, spherical surface correction, and cylinder correction were performed according to JIS-B601, and the center plane average roughness RaI was used as the surface roughness value.

[0072]

[Table 3]

Compound I

Embedded image

Compound II

Embedded image

The results in Table 3 show that the magnetic paint (magnetic powders A, B, and C) obtained by oxidizing the surface of the carbon-coated ultrafine ferromagnetic powder and a binder and the carbon-coated ultrafine ferromagnetic powder (magnetic powder) D), a magnetic paint comprising a dispersant and a binder, or a magnetic powder obtained by subjecting a carbon-coated ultrafine ferromagnetic powder to surface oxidation treatment, and a magnetic paint comprising a dispersant and a binder, each of which is not subjected to surface oxidation treatment. Dispersibility is remarkably superior to magnetic paints prepared without using a dispersant (reflected on gloss value, surface roughness), and as a result, the output of the magnetic material,
Significant improvements in electromagnetic conversion characteristics represented by C / N are shown.

3. Manufacturing Method of Magnetic Recording Medium In order to prepare a magnetic tape having a multilayer structure using magnetic powders E, F, and G, the following composition of a magnetic layer and a composition of a nonmagnetic layer for a lower layer were prepared. (Material of magnetic layer) Ferromagnetic alloy powder 100 parts Binder resin Vinyl chloride copolymer 12 parts (containing 1 × 10 ⁻⁴ eq / g of —SO ₃ K group, polymerization degree 300 polyester polyurethane resin 3 parts (Neo Pentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g included Artificial diamond (average particle diameter 8 nm) 1 part DN-002 (granular α- Fe ₂ O ₃ average particle diameter 20 nm) 3 parts Organic pigment dispersant (I) 3 parts Butyl stearate 3 parts Stearic acid 3 parts Methyl ethyl ketone and cyclohexanone 1: 1 mixed solvent 330 parts

The above magnetic paint is kneaded with a magnetic substance, polyvinyl chloride, an organic pigment dispersant and a solvent of 50% by mass of the formulation amount in a kneader, and then a polyurethane resin and the remaining components are added and dispersed with a sand grinder. did. Isocyanate is added to the resulting dispersion and 15 to the coating solution for the non-magnetic layer.
Parts and 14 parts of the coating solution for the magnetic layer, 30 parts of cyclohexanone was added to each, and the mixture was filtered using a filter having an average pore size of 1 μm to obtain a coating solution for forming the nonmagnetic layer and the magnetic layer. Each was prepared.

The coating solution for the lower non-magnetic layer obtained in 2 was applied onto a 6 μm-thick polyethylene naphthalate support so that the thickness after drying was 1.8 μm, followed by drying. Roll temperature with 7-stage calender composed of metal rolls
After calendering at 80 ° C, apply a gravure method on the magnetic layer so that the thickness of the magnetic layer becomes 0.10 μm, perform smoothing treatment, and pass the magnetic layer through the alignment device while it is still wet. Was. Oriented magnets are rare earth magnets
(Magnetic flux density: 500 mT), and after partial drying, it was passed through an orientation device consisting of a superconducting magnet (magnetic flux density: 1.5 T) for longitudinal orientation. Thereafter, a back coat layer is applied, dried, wound up, and calendered at a roll temperature of 90 ° C. using a seven-stage calender composed of metal rolls to obtain a web-shaped magnetic recording medium, which is 8 mm wide. Slit to 8
mm videotape samples were made. The magnetic properties, surface gloss, surface roughness, and electromagnetic conversion properties of the obtained sample were measured in the same manner as in 2, using a vibration sample magnetometer. The results are shown by characteristics of the tape using Comparative Example-31.

[0079]

[Table 4]

The results in Table 4 show that a magnetic paint (magnetic powders E and F) obtained by subjecting a carbon-coated ultrafine ferromagnetic powder to surface oxidation treatment and a binder, a carbon-coated ultrafine ferromagnetic powder (magnetic powder G) , A magnetic paint composed of a dispersant and a binder, or a magnetic powder obtained by surface-oxidizing carbon-coated ultrafine ferromagnetic powder, and a magnetic paint composed of a dispersant and a binder are all dispersed in magnetic powder that is not subjected to surface oxidation. Dispersibility is remarkably superior to that of a magnetic paint prepared without using an agent (reflected in gloss value Re). As a result, the output of the magnetic material and the electromagnetic conversion characteristics represented by C / N are remarkably improved. It is shown.

[0081]

According to the present invention, there is provided a magnetic paint comprising a binder and a magnetic powder obtained by oxidizing the surface of a carbon-coated ultrafine ferromagnetic powder of the present invention.
A magnetic paint composed of carbon-coated ultrafine ferromagnetic powder, a dispersant and a binder, or a magnetic powder obtained by oxidizing the surface of carbon-coated ultrafine ferromagnetic powder, and a magnetic paint composed of a dispersant and a binder, all have dispersibility. An excellent, low-noise, large-area magnetic recording medium can be obtained. In particular, paints using powders that have been subjected to surface oxidation treatment remove excess carbon by oxidation, and paints using dispersants have high stability. Can be introduced to improve the dispersibility when dispersed in a binder. As a result, the surface roughness is reduced, and the output, C / N
Both can greatly improve compared to the case without treatment.

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] March 5, 2001 (2001.3.5)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction contents]

[0015] The thus obtained carbon-coated ultrafine magnetic body is obtained as the discrete particles further minute
In order to improve the dispersibility, the surface of the particles is subjected to an oxidation treatment, or a dispersant is added, or both of them are performed, and the resulting particles are dispersed in a binder to form a coating liquid.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0032

[Correction method] Change

[Correction contents]

As the abrasive used in the magnetic layer of the present invention, particles having an average particle diameter of 2 to 150 nm are effective.
Preferably it is 5 to 100 nm. α-alumina, γ-alumina, artificial diamond, Fullerenes including C _60, carbon _{nanotube, α-Fe 2 O 3,} ZrO 2 or the like is used. Examples of these abrasives include Sumitomo Chemical's α-alumina HIT-100, Hit82, HIT-80, HIT70, artificial diamond with an average diameter of 4 to 10 nm that is made by mixing graphite and explosives, and MD-100 made by Tomei Diamond. (Average diameter up to 100 nm), α-Fe ₂ O ₃ DN-001 (average diameter up to 10 nm), DN-002 (average diameter up to 20 nm) manufactured by Toda Kogyo, ZrO ₂ HZ-N manufactured by Hokuko Chemical (average diameter up to 30 nm) ), HZ
-Y 3M (average diameter ~ 40nm) etc. can be raised.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0071

[Correction method] Change

[Correction contents]

The surface gloss was measured using a Suga type gloss meter.
The gloss of the reflection was measured. Surface roughness is measured by WYKO (U
S Arizona) Interferometric 3D roughness meter "TOPO-3
D "was used to measure a 250 μm square sample area. In calculating the measured values, corrections such as tilt correction, spherical correction, and cylindrical correction were performed in accordance with JIS-B601, and the center plane average roughness Ra was used as the surface roughness value.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0080

[Correction method] Change

[Correction contents]

The results in Table 4 show that a magnetic paint (magnetic powders E and F) obtained by subjecting a carbon-coated ultrafine ferromagnetic powder to surface oxidation treatment and a binder, a carbon-coated ultrafine ferromagnetic powder (magnetic powder G) , A magnetic paint composed of a dispersant and a binder, or a magnetic powder obtained by surface-oxidizing carbon-coated ultrafine ferromagnetic powder, and a magnetic paint composed of a dispersant and a binder are all dispersed in magnetic powder that is not subjected to surface oxidation. Dispersibility is remarkably superior to that of the magnetic paint prepared without using the agent (reflected in gloss value and surface roughness ). As a result, the output of the magnetic material, C /
A remarkable improvement in the electromagnetic conversion characteristics represented by N is shown.

Claims (3)

[Claims] A magnetic recording medium comprising a magnetic layer formed by applying a magnetic coating material containing a binder and a magnetic powder obtained by oxidizing the surface of a carbon-coated ultra-fine particle ferromagnetic powder to a support. 2. A magnetic recording medium wherein a magnetic layer containing carbon-coated ultrafine particle ferromagnetic powder, a dispersant and a binder is coated on a support to form a magnetic layer. 3. A magnetic recording medium, wherein a magnetic layer containing a magnetic powder obtained by surface-oxidizing carbon-coated ultrafine particle ferromagnetic powder, a dispersant and a binder is applied to a support to form a magnetic layer. .