JP2005347408A - Manufacturing method of magnetic powder, and magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of magnetic powder having a minute average particle size and especially magnetic characteristics for enabling high-density magnetic recording, and to provide a magnetic recording medium. <P>SOLUTION: A reverse micelle solution (I) formed by mixing a non-aqueous organic solvent containing a surface-active agent and a reducing agent solution, and a reverse micelle solution (II) formed by mixing a non-aqueous organic solvent containing a surface-active agent, a compound solution containing rare-earth elements, and a transition metal compound solution are mixed. A transition metal compound particle containing rare-earth elements is formed, and a reducing diffusion method is executed to the transition metal compound particle containing rare-earth elements, thus obtaining rare-earth transition metal-based alloy magnetic powder whose average particle size is 5-15 nm. Then, a nitride is subjected to a nitriding reaction. The magnetic recording medium has a magnetic layer containing the magnetic powder and a binder on a nonmagnetic support. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a magnetic powder and a magnetic recording medium. The magnetic recording medium having the magnetic powder of the present invention as a component of the magnetic layer can be suitably applied particularly to a system including an MR head utilizing the magnetoresistive effect.

In recent high-density magnetic recording systems, high-sensitivity reproducing heads (MR heads) using the magnetoresistive effect have been used. In this case, the system noise is dominated by noise derived from the magnetic recording medium. In order to reduce noise originating from magnetic recording media, the miniaturization of ferromagnetic particles has been promoted. However, as the magnetic particles become finer, they become more susceptible to thermal fluctuations, and the stability of the magnetization transition region is increased. Is estimated to be a problem.
The stability of 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), and KuV / kT is 50 to 70 or more. Is preferred.

In order to overcome the problem of thermal fluctuation, it has been proposed to use a magnetic material having a large anisotropy constant (see, for example, Non-Patent Document 1). Examples of candidate magnetic materials include CoPt, Co ₃ Pt, CoCrXY (X = Ta, Pt, Y = Nb, B), FePd, FePt, MnAl, and SmCo.

Promising magnetic particle materials for improving magnetic recording density include CuAu type or Cu ₃ Au type ferromagnetic ordered alloys. It is known that the ferromagnetic ordered alloy has large magnetocrystalline anisotropy due to strain generated during ordering and exhibits hard magnetism even when the size of the magnetic particles is reduced. Magnetic particles exhibiting ferromagnetism are produced by a liquid phase method or a gas phase method. In particular, magnetic particles immediately after being produced by a liquid phase method have an irregular phase and a face-centered cubic structure. Yes.

A CuAu type or Cu ₃ Au type face-centered cubic crystal is generally not suitable for a recording medium because it exhibits soft magnetism or paramagnetism. In order to obtain a ferromagnetic ordered alloy having a coercive force of 95.5 kA / m (1200 Oe) or more, which is necessary for a magnetic recording medium, it is necessary to perform an annealing process at a temperature higher than the transformation temperature at which the disordered phase is transformed to the ordered phase. .

S. Sun et al. Have made a presentation on monodisperse FePt nanoparticles and ferromagnetic FePt nanocrystal superlattices (see, for example, Non-Patent Document 2). S. Sun, et al. Surface treated fcc structured FePt particles (non-magnetic) with oleic acid and oleylamine for stabilization and oxidation prevention, and then applied them to a SiO ₂ / Si substrate and 550 in nitrogen. Carbon coated ultrafine particle magnetic material (carbon coated ultrafine particle nanosize magnetic material) that is heat treated at 30 ° C., carbonized oleic acid and oleylamine, fixed to FePt and phase changed to fct structure FePt to develop ferromagnetism ) Aggregates were obtained and their recording / reproduction characteristics were reported. Although FePt is a promising magnetic material, it is disadvantageous to use Pt, which is a rare metal element.

In order to overcome the problem of thermal fluctuation, a rare earth permanent magnet is known as a magnetic material having a large anisotropy constant. Patent Documents 1 to 6 propose a manufacturing method in which the particle size is made equal to or smaller than a single magnetic domain and the particle diameter is made uniform to obtain a large coercive force. However, the obtained particle size is 0.1 to several μm and cannot be used for a high-density magnetic recording medium in consideration of the recording wavelength and the particle size.
Patent Documents 7 to 12 propose granular or elliptical rare earth-iron-boron magnetic powder and rare earth-iron-metalloid magnetic powder having an average particle size of 5 to 200 nm. The starting oxide is reduced with hydrogen to obtain rare earth-iron-boron magnetic powder and rare earth-iron-metalloid magnetic powder. The reduction potential of rare earth elements is −2.3 to −2.5 V, and cannot be reduced with hydrogen gas, CO, or CH ₄ -based reducing gas used for reduction of transition metals. Reduction can be achieved by mixing and heating a metal having a reduction potential lower than that of the target rare earth element. The reduction potential of alkali metal is -3.04v for Li, -2.71v for Na, -2.93v for K, and the reduction potential for alkaline earth metal is -2.37v for Mg and -2.87v for Ca. , Sr is -2.89v and Ba is -2.91v. By mixing these with a rare earth element-containing material and heating in an inert gas, the rare earth element in the particles can be reduced and alloyed. . The use of metallic calcium is most preferable in terms of handling safety and cost.

D.Meller, A.Moser, L.Folks, et al, IEEE Trans, Magnetics, 36, 10 (2000) S.Sun, C.B.Murray, D.Weller, L.Folks, A.Moser, Science, 287, 1989 (2000) Japanese Patent Laid-Open No. 11-189811 JP-A-11-241104 JP 2003-297660 A Japanese Patent Laid-Open No. 10-144509 Japanese Patent Laid-Open No. 2001-140005 JP 2004-18932 A JP 2001-181754 A Japanese Patent Laid-Open No. 2002-50508 JP 2002-50509 A JP 2002-56518 A JP 2002-121027 A JP 2003-100507 A

An object of the present invention is to provide a method for producing a magnetic powder having a fine average particle size and having magnetic characteristics capable of high-density magnetic recording.
Another object of the present invention is to provide a magnetic recording medium comprising the magnetic powder as a component of a magnetic layer, which can be particularly suitably applied to a system including an MR head.

The present invention is as follows.
(1) a reverse micelle solution (I) formed by mixing a water-insoluble organic solvent containing a surfactant and a reducing agent aqueous solution;
Mixing a water-insoluble organic solvent containing a surfactant, a rare earth element-containing compound aqueous solution, and a reverse micelle solution (II) formed by mixing a transition metal compound aqueous solution to form rare earth element-containing transition metal compound particles A method for producing a rare earth-transition metal alloy magnetic powder having an average particle size of 5 to 15 nm, wherein the rare earth element-containing transition metal compound particles are subjected to a reduction diffusion method.
(2) a reverse micelle solution (I) formed by mixing a water-insoluble organic solvent containing a surfactant and a reducing agent aqueous solution;
Mixing a water-insoluble organic solvent containing a surfactant, a rare earth element-containing compound aqueous solution, and a reverse micelle solution (II) formed by mixing a transition metal compound aqueous solution to form rare earth element-containing transition metal compound particles A method for producing a rare earth-transition metal-nitrogen based magnetic powder having an average particle size of 5 to 15 nm, wherein the rare earth element-containing transition metal compound particles are subjected to a reduction diffusion method and then nitrided.
(3) In a magnetic recording medium having a magnetic layer containing a magnetic powder and a binder on a nonmagnetic support, the magnetic powder is a rare earth-transition metal alloy obtained by the production method described in (1) above. A magnetic recording medium characterized by being a magnetic powder.
(4) In a magnetic recording medium having a magnetic layer containing a magnetic powder and a binder on a nonmagnetic support, the magnetic powder is a rare earth-transition metal-nitrogen obtained by the production method described in (2) above. A magnetic recording medium characterized by being a magnetic powder.

According to the present invention, a magnetic powder having an average particle size of 5 to 15 nm and a magnetic property capable of high density magnetic recording can be obtained.
In addition, according to the present invention, it is possible to provide a magnetic recording medium that can be particularly suitably applied to a system including an MR head.

The present invention will be further described below.
The magnetic powder obtained by the production method of the present invention has ferromagnetism, ultrafine particles having an average particle size of 5 to 15 nm, and a high coercive force of 125 to 400 kA / m. Therefore, a magnetic recording medium having a magnetic characteristic capable of high-density magnetic recording and having this in the magnetic layer can be particularly suitably applied to a system including an MR head.

  Magnetic powders for high-density magnetic recording media must have fine particles and a small particle size distribution. To this end, the particle size distribution of starting materials (rare earth element-containing transition metal compound particles) for producing magnetic powders must be reduced. It is necessary to. Such a starting material can be produced by a gas phase method or a liquid phase method, but a liquid phase reduction method is preferred in view of excellent mass productivity and monodispersibility. As the liquid phase reduction method, various conventionally known methods can be applied. Among the liquid phase reduction methods, the reverse micelle method is particularly preferable because the particle size is easily controlled and the monodispersity is excellent.

In the production method of the present invention, first, a reverse micelle solution (I) formed by mixing a water-insoluble organic solvent containing a surfactant and a reducing agent aqueous solution, a water-insoluble organic solvent containing a surfactant, a rare earth A reverse micelle solution (II) formed by mixing an element-containing compound aqueous solution and a transition metal compound aqueous solution is mixed to form rare earth element-containing transition metal compound particles.
In the present invention, the reverse micelle refers to a state in which a structure in which the aqueous solution is enclosed in a microsphere surrounded by a hydrophilic group of a surfactant is dispersed in a water-insoluble organic solvent.

  In the reverse micelle solution (I), an oil-soluble surfactant is used as the surfactant. Specifically, sulfonate type (for example, aerosol OT (manufactured by Wako Pure Chemical Industries)), quaternary ammonium salt type (for example, cetyltrimethylammonium bromide), ether type (for example, pentaethylene glycol dodecyl ether) and the like can be mentioned. It is done. The amount of the surfactant in the water-insoluble organic solvent is preferably 20 to 200 g / liter.

  Preferred examples of the water-insoluble organic solvent that dissolves the surfactant include alkanes, ethers, and alcohols. The alkane is preferably an alkane having 7 to 12 carbon atoms. Specifically, heptane, octane, isooctane, nonane, decane, undecane, dodecane and the like are preferable. As the ether, diethyl ether, dipropyl ether, dibutyl ether and the like are preferable. As the alcohol, ethoxyethanol, ethoxypropanol and the like are preferable.

Examples of the reducing agent in the reducing agent aqueous solution include alcohols; polyalcohols; H ₂ ; HCHO, S ₂ O ₆ ²⁻ , H ₂ PO ₂ ⁻ , BH ₄ ⁻ , N ₂ H ₅ ⁺ , H ₂ PO ₃ ^−. Are preferably used alone or in combination of two or more. The amount of the reducing agent in the aqueous solution is preferably 3 to 50 mol with respect to 1 mol of the transition metal compound used.

  Here, the mass ratio (water / surfactant) between water and the surfactant in the reverse micelle solution (I) is preferably 20 or less. If the mass ratio exceeds 20, precipitation may easily occur and particles may be uneven. The mass ratio is preferably 15 or less, and more preferably 0.5 to 10.

Next, reverse micelle solution (II) is prepared. The conditions of the surfactant and the water-insoluble organic solvent (substance used, concentration, etc.) in the reverse micelle solution (II) are the same as in the reverse micelle solution (I).
In addition, the component of reverse micelle solution (II) can use the same kind or different kind of thing as reverse micelle solution (I). The mass ratio of water and surfactant in the reverse micelle solution (II) is the same as that in the reverse micelle solution (I), and may be the same as or different from the mass ratio of the reverse micelle solution (I). May be.

In the rare earth element-containing compound aqueous solution, the amount of rare earth element used is preferably 0.10 to 0.13 mol% with respect to the transition metal.
The rare earth element used in the present invention is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu. , Sm, Nd, Tb.

In the transition metal compound aqueous solution, the transition metal compound is mainly used as a transition metal salt, and the concentration thereof is preferably 0.1 to 1000 μmol / ml, and preferably 1 to 200 μmol / ml as the transition metal salt concentration. More preferred.
As the transition metal, Fe, Co, and Ni exhibiting ferromagnetism are preferable.

Subsequently, the prepared reverse micelle solutions (I) and (II) are mixed and subjected to a reduction reaction to form rare earth element-containing transition metal compound particles. The mixing method is not particularly limited, but it is preferable to add and mix the reverse micelle solution (I) while stirring the reverse micelle solution (II) in consideration of the uniformity of the reduction reaction. .
The reduction reaction is allowed to proceed after completion of the mixing, and the temperature at that time is preferably in the range of −5 to 30 ° C. and constant.
When the reduction temperature is less than −5 ° C., there arises a problem that the aqueous phase condenses and the reduction reaction becomes non-uniform. When the reduction temperature exceeds 30 ° C., aggregation or precipitation is likely to occur and the system may become unstable. A preferable reduction temperature is 0 to 25 ° C, more preferably 5 to 25 ° C.
Here, the “constant temperature” means that when the set temperature is T (° C.), the T is in the range of T ± 3 ° C. Even in this case, the upper and lower limits of T are in the range of the reduction temperature (−5 to 30 ° C.).

  The time for the reduction reaction needs to be appropriately set depending on the amount of the reverse micelle solution and the like, but is preferably 1 to 30 minutes, and more preferably 5 to 20 minutes.

  Since the reduction reaction has a great influence on the monodispersity of the particle size distribution, it is preferable to carry out the reduction reaction while stirring as fast as possible. A preferred stirring device is a stirring device having a high shearing force. Specifically, the stirring blade basically has a turbine-type or paddle-type structure, and a sharp blade is provided at the end of the blade or at a position in contact with the blade. It is an attached structure and is a stirring device that rotates a blade by a motor. Specifically, devices such as a dissolver (manufactured by Special Machine Industries), an omni mixer (manufactured by Yamato Kagaku), and a homogenizer (manufactured by SMT) are useful. By using these apparatuses, it is possible to synthesize monodisperse rare earth element-containing transition metal compound particles as a stable dispersion.

  In at least one of the reverse micelle solutions (I) and (II), at least one type of dispersant having 1 to 3 polar groups is added in an amount of 0.00 per mole of the rare earth element-containing transition metal compound particles to be produced. It is preferable to add 001-10 mol.

  By adding such a dispersant, it is possible to obtain particles that are more monodispersed and have no aggregation. If the addition amount is less than 0.001 mol, the monodispersity of the rare earth element-containing transition metal compound particles may not be further improved, and if it exceeds 10 mol, aggregation may occur.

As the dispersant, an organic compound having a group that adsorbs on the surface of the rare earth element-containing transition metal compound particles is preferable. Specifically, it has 1 to 3 amino groups, carboxy groups, sulfonic acid groups or sulfinic acid groups, and these can be used alone or in combination.
As structural formulas, R—NH ₂ , NH ₂ —R—NH ₂ , NH ₂ —R (NH ₂ ) —NH ₂ , R—COOH, COOH—R—COOH, COOH—R (COOH) —COOH, R —SO ₃ H, SO ₃ H—R—SO ₃ H, SO ₃ H—R (SO ₃ H) —SO ₃ H, R—SO ₂ H, SO ₂ H—R—SO ₂ H, SO ₂ H— R (SO ₂ H) —SO ₂ H, wherein R is a linear, branched or cyclic saturated or unsaturated hydrocarbon.

  It is also preferable to age after the reduction reaction, and the temperature of the solution after the reaction is raised to the aging temperature. The aging temperature is preferably a constant temperature of 30 to 90 ° C., and the temperature is higher than the temperature of the reduction reaction. The aging time is preferably 5 to 180 minutes. Further, it is preferable to add an element such as Ti or B which enhances the stability of the rare earth element-containing transition metal compound particles to the starting material.

  The reaction product after completion of the reduction reaction is preferably washed with a mixed solution of water and primary alcohol to remove impurities. The primary alcohol used for washing is not particularly limited, but methanol, ethanol and the like are preferable. The volume mixing ratio (water / primary alcohol) is preferably in the range of 10/1 to 2/1, and more preferably in the range of 5/1 to 3/1. When the ratio of water is high, the surfactant may be difficult to remove, and conversely, when the ratio of primary alcohol is high, aggregation may occur. After washing, the solvent is replaced to make an aqueous system.

Subsequently, the surface of the rare earth element-containing transition metal compound particles is preferably covered with an alkaline earth metal hydroxide layer. With this coating, when the rare earth element is alloyed by the reduction diffusion method described later, the reduction rate can be controlled and sintering between particles can be prevented. Among them, the alkaline earth metal hydroxide is preferably Ca (OH) ₂ . The alkaline earth metal hydroxide layer can be coated, for example, by adding and mixing an alkaline earth metal hydroxide and an alkaline aqueous solution such as NH ₄ OH to the rare earth element-containing transition metal compound particles. The alkaline aqueous solution may be an aqueous solution of KOH or NaOH in addition to the NH ₄ OH aqueous solution. However, if these are used, the salt of K or Na remains in the starting material, which deteriorates the corrosion resistance of the magnetic powder. It is not preferable.
The coating amount of the alkaline earth metal hydroxide is preferably 1: 0.3 to 1: 5 as a mass ratio of the rare earth element-containing transition metal compound particles: alkaline earth metal hydroxide. More preferably, it is 1: 0.5-1: 3. When the mass ratio of the alkaline earth metal hydroxide is less than 0.3, the coating thickness is small, and when the alloy is formed by the reduction diffusion method described later, the sintering prevention effect is poor. The recovery efficiency is inferior, which is not preferable.

Next, the particles covered with the alkaline earth metal hydroxide layer may be heated to oxidize the alkaline earth metal hydroxide. For example, when Ca (OH) ₂ is used as the alkaline earth metal hydroxide, if it is changed to CaO by oxidation, the water produced in the subsequent reduction reaction can be absorbed and a uniform reduction reaction can proceed. In this oxidation reaction, particles coated with the alkaline earth metal hydroxide layer are separated and dried, and then heated at 550 ° C. or higher, for example, 550 to 600 ° C.

Subsequently, the particles obtained above are preferably pulverized to a size of about 0.05 to 100 μm and subjected to a reduction diffusion method to alloy rare earth elements. The reduction diffusion method in the present invention is a reaction well-known in the art, for example, also described in Patent Document 1 described above. The metal used in the reduction diffusion method is a metal having a lower reduction potential than the rare earth element used.
The metal reducing agent having a reduction potential that is more negative than that of the rare earth element is used in the form of particles or powders. From the viewpoint of cost, granular metal calcium having a particle size of 4 mesh or less is suitable. These reducing agents have a reaction equivalent (the stoichiometric amount necessary to reduce the rare earth element oxide, including the amount required to reduce the transition metal if it is partially oxidized). The amount is 1.1 to 5 times, preferably 1.5 to 3 times. The reaction temperature is preferably 900 to 1200 ° C., the reaction time is 10 to 100 minutes, and the reaction atmosphere is preferably an inert gas atmosphere.
At this time, the reaction product is a mixture of by-produced CaO, unreacted excess Ca, and the generated magnetic powder, which are in a lump state in which these are combined. This product is poured into cooling water to remove CaO and metallic Ca from the magnetic powder as a Ca (OH) ₂ suspension. Further, residual Ca (OH) ₂ is removed by washing the magnetic powder with acetic acid or hydrochloric acid. When the product in a lump state is put into cooling water, the lump state is collapsed and pulverization proceeds due to oxidation of metal Ca by water and hydration reaction of by-product CaO. It is also preferable to add an organic substance that strongly adsorbs to the magnetic powder at the later stage of washing with water. The organic substance to be adsorbed is preferably an organic substance containing a polar group having a pKa smaller than a fatty acid (pKa is 4.2 or more) added during the production of the magnetic recording medium and a salt thereof. Examples of the functional group having a pKa of 4 or less include PO (OH) ₂ , OPO (OH) ₂ , SO ₃ H, CONHOH, and SO ₂ NHOH. The amount of adsorption is preferably an amount that completely covers the particle surface, but the effect is recognized even when a part of the surface is covered.

  In the present invention, the magnetic powder after the reduction diffusion method may be further nitrided. The nitriding conditions include a condition in which the powder is heated to 400 to 600 ° C. in nitrogen gas, nitrogen gas containing a small amount of hydrogen, ammonia gas, or a mixed gas of ammonia and hydrogen.

  The rare earth-transition metal alloy of the present invention thus produced is granular with an average particle size of 5 to 15 nm or spheroidal with an acicular ratio of, for example, 1.1 to 1.8, and dispersed. Excellent in properties.

The present invention also provides a magnetic recording medium having a magnetic layer containing a magnetic powder and a binder on a nonmagnetic support, wherein the magnetic powder is a magnetic powder obtained by the above-described production method. To do.
For the production of such a magnetic recording medium, an ordinary coating type magnetic recording medium manufacturing method can be applied. 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. The thermoplastic resin has a glass transition temperature of −100 to 150 ° C., a number average molecular weight of 1,000 to 200,000, preferably 10,000 to 100,000, and a degree of polymerization of about 50 to 1,000.

  Such binder resins include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic ester, styrene, butadiene, ethylene, vinyl butyral. , Vinyl acetal, vinyl ether, etc. as a constituent unit, polymers or copolymers, polyurethane resins, and various rubber resins.

  Thermosetting resins or reactive resins include phenolic resins, epoxy resins, polyurethane curable resins, urea resins, melamine resins, alkyd resins, acrylic reactive resins, formaldehyde resins, silicone resins, epoxy-polyamides. Resin, a mixture of polyester resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, a mixture of polyurethane and polyisocyanate, and the like.

In order to obtain a better dispersion effect of the magnetic powder and durability of the magnetic layer in the binder resin, COOM, SO ₃ M, OSO ₃ M, P═O (OM) ₂ , O— P = O (OM) ₂ (wherein M is a hydrogen atom or an alkali metal base), OH, NR ₂ , N ⁺ R ₃ (R is a hydrocarbon group) an epoxy group, SH, CN, etc. One or more polar groups are preferably introduced by copolymerization or addition reaction. The amount of such a polar group is 10 ⁻¹ to 10 ⁻⁸ mol / g, preferably 10 ⁻² to 10 ⁻⁶ mol / g.

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

In the present invention, when a polyurethane resin is used, the glass transition temperature is −50 to 100 ° C., the breaking elongation is 100 to 2000%, the breaking stress is 0.05 to 10 kg / mm ² (0.49 to 98 MPa), and the yield point is 0.05-10 kg / mm < ² > (0.49-98 MPa) is preferable.

  Examples of the polyisocyanate used in the present invention include tolylene diisocyanate, 4-4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5- Isocyanates such as diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate, and products of these isocyanates and polyalcohols In addition, polyisocyanate produced by condensation of isocyanates can be used. Commercially available product names of these isocyanates include: Nippon Polyurethane, Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR Millionate MTL, Takeda Pharmaceutical Co., Ltd. , Takenet D-102, Takenet D-110N, Takenet D-200, Takenet D-202, manufactured by Sumitomo Bayer, Death Module L, Death Module IL, Death Module N, Death Mod -HL, etc., and these can be used alone or in combination of two or more by utilizing the difference in curing reactivity.

  In the magnetic layer of the magnetic recording medium of the present invention, materials having various functions such as a lubricant, an abrasive, a dispersant, an antistatic agent, a dispersant, a plasticizer, an antifungal agent and the like are usually used. It is contained depending on the purpose.

  As the lubricant used in the magnetic layer of the present invention, dialkylpolysiloxane (alkyl is 1 to 5 carbon atoms), dialkoxypolysiloxane (alkoxy is 1 to 4 carbon atoms), monoalkyl monoalkoxypolysiloxane (alkyl) Are silicon oil such as phenyl polysiloxane and fluoroalkyl polysiloxane (alkyl is 1 to 5 carbon atoms); conductive fine powder such as graphite; Inorganic powder such as molybdenum sulfide and tungsten disulfide; Plastic fine powder such as polyethylene, polypropylene, polyethylene vinyl chloride copolymer and polytetrafluoroethylene; α-olefin polymer; Saturated fatty acid solid at normal temperature (10 to 22 carbon atoms) ); Unsaturated aliphatic hydrocarbon liquid at room temperature (n-olefin double) Compounds in which the bond is bonded to the terminal carbon, carbon number of about 20); fatty acid esters composed of monobasic fatty acids having 12 to 20 carbon atoms and monohydric alcohols having 3 to 12 carbon atoms, fluorocarbons, etc. are used it can.

  Among the above, saturated fatty acid and fatty acid ester are preferable, and it is more preferable to use both together. Examples of alcohols used as fatty acid ester raw materials include ethanol, butanol, phenol, benzyl alcohol, 2-methylbutyl alcohol, 2-hexyldecyl alcohol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether, dipropylene glycol monobutyl ether, diethylene glycol monobutyl ether, Examples thereof include monohydric alcohols such as s-butyl alcohol, and polyhydric alcohols such as ethylene glycol, diethylene glycol, neopentyl glycol, glycerin, and sorbitan derivatives. Similarly, fatty acids include acetic acid, propionic acid, octanoic acid, 2-ethylhexanoic acid, lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, arachidic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, palmitoleic acid. Aliphatic carboxylic acids such as, or a mixture thereof.

  Specific examples of fatty acid esters include butyl stearate, s-butyl stearate, isopropyl stearate, butyl oleate, amyl stearate, 3-methylbutyl stearate, 2-ethylhexyl stearate, 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 Examples thereof include various ester compounds such as dipalmitate, hexamethylenediol acylated with myristic acid to obtain a diol, and glycerin oleate.

Furthermore, in order to reduce the hydrolysis of fatty acid esters that often occur when the magnetic recording medium is used under high humidity, the branched / straight chain, cis / trans and other isomeric structures and branch positions of the starting fatty acid and alcohol are selected. Things are done.
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.

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

As the abrasive used in the magnetic layer of the present invention, commonly used materials are α, γ alumina, fused alumina, corundum, artificial corundum, silicon carbide, chromium oxide (Cr ₂ O ₃ ), diamond, artificial diamond, pomegranate. Stone, αFe ₂ O ₃ or the like is used. These abrasives have a Mohs hardness of 6 or more. Specific examples include Sumitomo Chemical Co., Ltd., AKP-10, AKP-15, AKP-20, AKP-30, AKP-50, AKP-1520, AKP-1500, HIT-50, HIT60A, HIT60G, HIT70, HIT80. , HIT82, HIT-100, manufactured by Nippon Chemical Industry Co., Ltd., G5, G7, S-1, chrome oxide K, UB40B manufactured by Uemura Kogyo Co., Ltd., WA8000, WA10000 manufactured by Fujimi Abrasive Co., Ltd., LS600F manufactured by LANDS 4, MD-200, MD-150, MD-100, MD-70, IRM 0-1 / 4F, IRM 0-1 / 4FF, GE 0-1 / 10, 0-1 / 4 MyPolex 1 / 10QG and 1 / 8QG manufactured by DuPont, TF100, TF140, TF180 manufactured by Toda Kogyo Co., Ltd. and the like are listed. An average particle diameter of 0.05 to 1 μm is effective, preferably 0.05 to 0.5 μm.
In addition to using the abrasive alone, it is also suitable to use two or more kinds of abrasives together. In the case of fine-grain diamond, the amount added to the magnetic powder is 0.1% by using it together with other abrasives. Can be reduced to a degree. The total amount of these abrasives is added in the range of 1 to 20 parts by mass, preferably 1 to 15 parts by mass with respect to 100 parts by mass of the magnetic powder. When the amount is less than 1 part by mass, sufficient durability cannot be obtained. When the amount is more than 20 parts by mass, the surface property and the filling degree deteriorate. These abrasives may be added to the magnetic paint after being dispersed with a binder in advance.

In addition to the magnetic powder, the magnetic layer of the magnetic recording medium of the present invention may contain conductive particles as an antistatic agent. However, in order to maximize the saturation magnetic flux density of the magnetic layer as the uppermost layer, it is preferable to add to the uppermost layer as little as possible and add it to the coating layer other than the uppermost layer. In particular, it is preferable to add carbon black as an antistatic agent in terms of lowering the surface electrical resistance of the entire medium. The carbon black that can be used in the present invention may be rubber furnace, rubber thermal, color black, conductive carbon black, acetylene black, or the like. Specific surface area is 5 to 500 m ² / g, DBP oil absorption is 10 to 1500 ml / 100 g, particle size is 5 to 300 nm, PH is 2 to 10, moisture content is 0.1 to 10%, tap density is 0.1 to 0.1%. 1 g / cm ³ is preferable. Specific examples of carbon black used in the present invention include Cabot Corporation, BLACKPEARLS 2000, 1300, 1000, 900, 800,700, VULCAN XC-72, Asahi Carbon Corporation, # 80, # 60. , # 55, # 50, # 35, manufactured by Mitsubishi Chemical Corporation, # 3030B, # 3040B, # 3050B, # 3230B, # 3350B, # 9180B, # 2700, # 2650, # 2600B, # 2400B, # 2300, # 950B # 900, # 1000, # 95, # 30, # 40, # 10B, MA230, MA220, MA77, manufactured by Colombian Carbon, CONDUCTEX SC, RAVEN 150, 50, 40, 15, Ketjen Black manufactured by Lion Azo EC, Ketjen Black ECDJ-500, Ketjemb Rack ECDJ-600 etc. are mentioned. Carbon black may be surface-treated with a dispersant, carbon black may be oxidized, or may be grafted with a resin, or may be obtained by graphitizing a part of the surface. Further, carbon black may be dispersed in advance with a binder before being added to the magnetic paint. When carbon black is used for the magnetic layer, the amount based on the magnetic powder is preferably 0.1 to 30% by mass. Further, the following nonmagnetic layer is preferably contained in an amount of 3 to 20% by mass based on the total nonmagnetic powder.

  In general, carbon black not only serves as an antistatic agent, but also functions to reduce the coefficient of friction, impart light shielding properties, and improve film strength. These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention are changed in type, amount and combination, and depending on the purpose based on the various characteristics shown above, such as particle size, oil absorption, conductivity, and pH. Of course, it is possible to use them properly. 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, a nonmagnetic layer can be formed below the magnetic layer. In this case, the nonmagnetic layer is a layer in which nonmagnetic powder is dispersed in a binder resin. Various nonmagnetic powders can be used for the nonmagnetic layer. For example, α-alumina, β-alumina, γ-alumina, boehmite, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, goethite, corundum, silicon nitride, titanium carbide having an α conversion rate of 90% or more, 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, zinc oxide, and boehmite are preferable as those having a fine particle size. The particle size of these nonmagnetic powders is preferably 0.01 to 1 μm. However, if necessary, nonmagnetic powders having different particle sizes can be combined, or even a single nonmagnetic powder can have the same effect by widening the particle size distribution. You can also In order to increase the interaction with the binder resin to be used and improve the dispersibility, the nonmagnetic powder to be used may be surface-treated. The surface-treated product may be treated with an inorganic material such as silica, alumina, zirconia, or silica-alumina, or may be treated with a coupling agent. The tap density is preferably 0.3 to ² g / cm ³ , the water content is 0.1 to 5% by mass, the pH is 2 to 11, and the specific surface area is preferably 5 to 150 m ² / g. The nonmagnetic powder may be acicular, spherical, dice, or plate-shaped. Specific examples of the non-magnetic powder used in the lower layer of the magnetic recording medium obtained by the present invention include Showa Denko Nanotite, Sumitomo Chemical HIT-100, HIT-80, Toda Kogyo α-iron oxide DPN-250BX. , DPN-245, DPN-270BX, DPN-550RX, DBN-450BX, DBN-650RX, DAN-850RX, Ishihara Sangyo Titanium oxide TTO-51B, TTO-55A, TTO-55B, TTO-55C, TTO-55S, TTO-55D, SN-100, Titanium Industry Titanium Oxide STT-4D, STT-30D, STT-30, STT-65C, Teica Titanium Oxide MT-100 SMT-100T, MT-150W, MT-500B, MT-600B , MT-100F, MT-500HD, Sakai Chemical's FINEX-25 BF-1, BF-10, BF-20, ST-M, Dowa Mining Ltd. iron oxide DEFIC-Y, DEFIC-R, manufactured by Japan Aerosil AS2BM, TiO ₂ P25, manufactured by Ube Industries, Ltd. 100A, and fired 500A, and it Things.

  Forming two or more coating layers on a non-magnetic support is also effective for producing high recording density magnetic recording media, and the simultaneous coating method can produce ultra-thin magnetic layers. Efficiency is excellent. As a specific method of wet-on-wet method as the simultaneous application method,

(1) First, a lower layer is applied by a gravure coating, roll coating, blade coating, and extrusion coating device generally used in magnetic paints. A method of applying an upper layer with a non-magnetic support pressure type extrusion coating apparatus disclosed in Japanese Patent Laid-Open No. 60-238179 and Japanese Patent Laid-Open No. 2-265672,

(2) A coating head containing two slits for passing a coating solution as disclosed in JP-A-63-88080, JP-A-2-17971 and JP-A-2-265672, A method of applying the coating solution and the upper layer coating solution almost simultaneously,

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

  When applying the wet-on-wet method, the flow characteristics of the magnetic layer coating solution and non-magnetic layer coating solution should be as close as possible, but the thickness of the coated magnetic layer and non-magnetic layer interface will not be disturbed. A uniform magnetic layer with little 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, it is necessary to pay particular attention to the selection of the nonmagnetic powder used for the nonmagnetic layer. Further, after forming the nonmagnetic layer, a magnetic layer may be formed on the nonmagnetic layer. Since this method can further reduce the disturbance of the interface, it is a preferable method when forming a thin magnetic layer.

The nonmagnetic support of the magnetic recording medium of the present invention is usually 3 to 100 μm, preferably 2 to 15 μm when used in a tape form, and preferably 20 to 80 μm when used as a flexible disk. The nonmagnetic layer provided in a body shape is 0.5 to 3.0 μm, preferably 0.5 to 2.5 μm. In addition, the formation of layers other than the magnetic layer and the nonmagnetic layer according to the purpose is permitted as long as the magnetic layer is the uppermost layer and the nonmagnetic layer is the lower layer. For example, an undercoat layer may be provided between the nonmagnetic support and the lower layer to improve adhesion. This thickness is 0.01 to 0.7 μm, preferably 0.05 to 0.5 μm. Further, a backcoat layer may be provided on the side opposite to the nonmagnetic support side magnetic layer side. This thickness is 0.1 to 1.0 μm, preferably 0.2 to 0.8 μm. As these intermediate layer and backcoat layer, known ones can be used. In the case of a disk-shaped magnetic recording medium, the above layer configuration can be provided on both sides or one side.
The thickness of the magnetic layer is 0.01 to 0.15 μm, more preferably 0.02 to 0.10 μm.
In the case of a magnetic tape, the coercive force Hc is preferably 125 to 440 kA / m, more preferably 130 to 350 kA / m, and the squareness ratio (SQ) is preferably 0.75 to 0.90, and 0.80 to 0. .90 is more preferable, SFD is preferably 0.25 to 0.50, more preferably 0.25 to 0.47, and Mr · δ (residual magnetization × magnetic layer thickness) is 1.0 to 30 mT · μm. Is preferable, and 2.0 to 25 mT · μm is more preferable, and the center line average surface roughness Ra is preferably 0.05 to 2.5 nm, and more preferably 0.07 to 2.0 nm.
In the case of a magnetic disk, the coercive force Hc is preferably 120 to 400 kA / m, more preferably 130 to 350 kA / m, and the squareness ratio (SQ) is preferably 0.50 to 0.60, and 0.51 to 0 .58 is more preferable, SFD is preferably 0.25 to 0.70, more preferably 0.25 to 0.60, and Mr · δ (residual magnetization × magnetic layer thickness) is 1.0 to 30 mT · μm. Is preferable, and 2.0 to 25 mT · μm is more preferable, and the center line average surface roughness Ra is preferably 0.05 to 2.5 nm, and more preferably 0.07 to 2.0 nm.

  There is no restriction | limiting in particular in the nonmagnetic support body used by this invention, The normally used thing can be used. Examples of materials forming the nonmagnetic support include polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamideimide, polyimide, polysulfone, polyethersulfone, and other synthetic resin films, and aluminum foil And metal foil such as stainless steel foil.

In order to effectively achieve the object of the present invention, the surface roughness of the non-magnetic support is 0.03 μm or less, preferably 0.02 μm or less, preferably centerline average surface roughness Ra (cutoff value 0.25 mm), Desirably, it is 0.01 micrometer or less. Further, it is preferable that these nonmagnetic supports not only have a small center line average surface roughness but also have no large protrusions of 1 μm or more. The roughness of the surface can be freely controlled according to the size and amount of filler added to the nonmagnetic support as required. Examples of these fillers include fine organic resin powders such as acrylic resins in addition to oxides and carbonates such as Ca, Al, Si, and Ti. The F-5 value in the web running direction of the nonmagnetic support used in the present invention is preferably 5 to 50 kg / mm ² (49 to 490 MPa), and the F-5 value in the web width direction is preferably 3 to 30 kg / mm ^2. (29.4 to 294 MPa), and the F-5 value in the longitudinal direction of the web is generally higher than the F-5 value in the width direction of the web, but particularly when the strength in the width direction needs to be increased. Not so.

The heat shrinkage rate at 100 ° C. for 30 minutes in the web running direction and width direction of the support is preferably 3% or less, more desirably 1.5% or less, and the heat shrinkage rate at 80 ° C. for 30 minutes is preferably 1%. % Or less, more preferably 0.5% or less. The breaking strength is preferably 5 to 100 kg / mm ² (49 to 980 MPa) in both directions, and the elastic modulus is preferably 100 to 2000 kg / mm ² (0.98 to 19.6 GPa).

  The organic solvent used in the present invention is an arbitrary ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, methanol, ethanol, propanol, butanol, Alcohols such as isobutyl 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 mono Glycol ethers such as ethyl ether, dioxane, aromatic hydrocarbons such as benzene, toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, Chi Ren chlorohydrin, dichlorobenzene, chlorinated hydrocarbons and the like, N, N- dimethylformamide, those hexane and the like can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, side reaction products, decomposition products, oxides, and moisture in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less. The type and amount of the organic solvent used in the present invention may be changed between the magnetic layer and the intermediate layer if necessary. The first layer uses a highly volatile solvent to improve surface properties. The first layer uses a solvent with high surface tension (cyclohexanone, dioxane, etc.) to improve coating stability. Examples of such a method include increasing the filling degree using a high solvent, but it is needless to say that the present invention is not limited to these examples.

  The magnetic recording medium of the present invention is kneaded and dispersed using an organic solvent together with the magnetic powder, binder resin, and other additives if necessary, and a magnetic coating is applied onto a nonmagnetic support, and if necessary. Obtained by orientation and drying.

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

  Various kneaders are used for kneading and dispersing the magnetic paint. For example, two roll mill, three roll mill, ball mill, pebble mill, tron mill, sand grinder, Segvari, attritor, high speed impeller disperser, high speed stone mill, high speed impact mill, disper, kneader, high speed mixer, homogenizer, ultra A sonic disperser or the like can be used.

  In order to achieve the object of the present invention, the manufacturing technique known so far can be used as a part of the process, but the kneading process is strong such as continuous kneader or pressure kneader. It is preferable to use one having a kneading force. Thereby, high Br can be obtained. When a continuous kneader or a pressure kneader is used, all or a part of the magnetic powder and the binder (preferably 30% or more of the total binder) is 15 to 500 mass with respect to 100 mass parts of the magnetic powder. The kneading process is performed within the range of the part. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-64-79274. In the present invention, it is possible to produce more efficiently by using a simultaneous multilayer coating method as disclosed in JP-A-62-212933.

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 nonmagnetic layer. Less than the solvent is preferred.

  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 nonmagnetic layer is preferably larger than the porosity of the magnetic layer, but may be small as long as the porosity of the nonmagnetic layer is 5% by volume or more.

  The magnetic recording medium of the present invention can have a lower layer and an uppermost layer, but it is easily estimated that these physical properties can be changed between the lower layer and the uppermost layer depending on the purpose. For example, the elastic modulus of the uppermost layer is increased to improve running durability, and 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.

  By such a method, the magnetic layer coated on the support is subjected to a treatment for orienting the magnetic powder in the layer, if necessary, and then the formed magnetic layer is dried. Further, the magnetic recording medium of the present invention is produced by performing a surface smoothing process or cutting into a desired shape as necessary. The above composition for the uppermost layer and the composition for the lower layer are dispersed together with a solvent, and the obtained coating solution is coated on a nonmagnetic support, and oriented and dried to obtain a magnetic recording medium.

The elastic modulus at 0.5% elongation of the magnetic layer is preferably 100 to 2000 kg / mm ² (0.98 to 19.6 GPa) in both the web application direction and the width direction, and the breaking strength is preferably 1 to 30 kg / mm ² ( 9.8 to 294 MPa), the elastic modulus of the magnetic recording medium is preferably 100 to 1500 kg / mm ² (0.98 to 14.7 GPa) in both the web application direction and the width direction, and the residual elongation is preferably 0.5% or less, The thermal shrinkage at any temperature below 100 ° C. is desirably 1% or less, more desirably 0.5% or less, and most desirably 0.1% or less.

  The magnetic recording medium of the present invention may be a tape for video applications, data recording applications, or a flexible disk or magnetic disk for data recording applications, but signal loss due to the occurrence of dropout is fatal. This is particularly effective for a digital recording medium. Furthermore, by forming the lower layer as a nonmagnetic layer and the thickness of the uppermost layer to be 0.3 μm or less, it is possible to obtain a high-density and large-capacity magnetic recording medium having high electromagnetic conversion characteristics and excellent overwrite characteristics. it can.

  EXAMPLES Hereinafter, although an Example and a comparative example further demonstrate this invention, this invention is not restrict | limited by the following example.

<Production example of magnetic powder>
Production Example 1 of Rare Earth Element-Containing Transition Metal Compound Particles
The following operation was performed in high purity N ₂ gas. An alkane solution in which 108 g of aerosol OT, 800 ml of decane, and 20 ml of oleylamine are added to an aqueous reducing agent solution in which 4.0 g of NaBH ₄ is dissolved in 160 ml of water (deoxygenation: 0.1 mg / liter or less) is mixed and reverse micelles are mixed. Solution (I) was prepared.

0.01 mol of ferrous nitrate (Fe (NO ₃ ) ₂ · 9H ₂ O), 0.00118 mol of samarium nitrate (Sm (NO ₃ ) ₃ · 6H ₂ O) dissolved in 120 ml of water (deoxygenated) An alkane solution obtained by mixing 54 g of aerosol OT and 400 ml of decane was added to the aqueous metal salt solution and mixed to prepare a reverse micelle solution (II).

  While the reverse micelle solution (I) was stirred at high speed with an omni mixer (manufactured by Yamato Kagaku) at 22 ° C., the reverse micelle solution (II) was added instantaneously. After stirring for 8 minutes while stirring with a magnetic stirrer, the temperature was raised to 35 ° C. and aged for 20 minutes. It was cooled to room temperature and taken out into the air after cooling. In order to destroy the reverse micelle, a mixed solution of 500 ml of water and 500 ml of methanol was added to separate into an aqueous phase and an oil phase. A state in which the rare earth element-containing transition metal compound particles were dispersed on the oil phase side was obtained. The oil phase side was washed 5 times with a mixed solution of 600 ml of water and 200 ml of methanol.

Thereafter, 2000 ml of methanol was added to cause flocculation of the rare earth element-containing transition metal compound particles to cause precipitation. The supernatant was removed and 100 ml of heptane was added to redisperse.
Further, precipitation by adding 1000 ml of methanol and precipitation dispersion of 100 ml of heptane were repeated twice, and methanol was added to precipitate rare earth element-containing transition metal compound particles. The supernatant was removed, and then 1000 ml of water was added to disperse, settle and remove the supernatant twice.

The obtained rare earth element-containing transition metal compound particles (starting material) were measured for composition, average particle size, and distribution (coefficient of variation). The composition was calculated by dissolving the rare earth element-containing transition metal compound particles obtained by the reaction with hydrochloric acid and measuring by ICP (Inductively Coupled High Frequency Plasma Emission Analysis).
The average particle size and distribution were determined by measuring about 500 particles photographed with a TEM (transmission electron microscope: acceleration voltage 300 kV manufactured by Hitachi, Ltd.), performing statistical processing, and calculating the average particle size by volume average. The transition metals and rare earth elements added within the experimental error were contained. The particle shape was granular, the average particle size was 5.6 nm, and the coefficient of variation was 5%. Here, granular means that the average axial ratio (average needle ratio) is about 1.0 to 1.5.

The obtained rare earth element-containing transition metal compound particles are re-dispersed in pure water, 0.1 mol of CaCl ₂ · 6H ₂ O dissolved in pure water is added, and then neutralized with NH ₄ OH. Ca (OH) ₂ was formed on the surface of the contained transition metal compound particles. The precipitate was filtered and washed with water, and then dried at 120 ° C. The dried product was dry pulverized.

Production Examples 2 to 12 of Transition Metal Compound Particles Containing Rare Earth Elements
As shown in Table 1, (0.01-x) moles of ferrous nitrate (Fe (NO ₃ ) ₂ .9H ₂ O), x moles of cobalt nitrate (Co (NO ₃ ) ₂ .6H ₂ O), 0.0024 The same operation as in Production Example 1 was performed except that an aqueous metal salt solution in which 120 mol of samarium nitrate (Sm (NO ₃ ) ₃ .6H ₂ O) was dissolved in 120 ml of water (deoxygenated) was used.

Reduction diffusion treatment 10 g of the rare earth element-containing transition metal compound particles obtained above and 1.5 g of granular metal Ca having a particle size of about 4 mm or less were mixed, placed in a steel tray, and set in an inert gas atmosphere furnace. The inside of the furnace was evacuated, heated at 600 ° C. for 30 minutes in a nitrogen stream, heated to 1050 ° C. in an argon stream, maintained for 30 minutes, and then cooled.

Nitriding treatment The powders of Production Examples 2, 4, 6, 8, 10, 11, and 12 were subsequently subjected to nitriding treatment.
After the diffusion reduction treatment, the particles were cooled to 500 ° C., evacuated once, held in a nitrogen stream for 6 hours for nitriding reaction, and then cooled to room temperature.

Recovery treatment The reaction product obtained above was put into pure water, and CaO and metallic calcium were separated from the powder as a Ca (OH) ₂ suspension. The obtained slurry was stirred and decanted to remove hydroxides such as alkaline earth metals. This operation was repeated 5 times and washed in a 3% by mass acetic acid solution to remove residual Ca (OH) ₂ . After washing with pure water twice, the magnetic powder was recovered by vacuum drying.

  The shape, average particle size, coefficient of variation, and coercive force Hc and saturation magnetization of the rare earth element-containing transition metal compound particles (starting material) obtained above and various powders (alloys) obtained by the above treatment. Table 1 shows σs. In Production Examples 11 and 12, after washing in a 3% by mass acetic acid solution, phenylphosphonic acid (3% by mass with respect to the magnetic powder) was added, washed with pure water twice, and then vacuumed. The magnetic powder is recovered by drying.

Production Examples 13 to 14 of Rare Earth Element-Containing Transition Metal Compound Particles (Comparative Example)
The following operation was performed in high purity N ₂ gas. A reducing agent aqueous solution in which 4.0 g of NaBH ₄ was dissolved in 160 ml of water (deoxygenated: 0.1 mg / liter or less) was prepared, and the mixture was stirred at a high speed with an omni mixer (manufactured by Yamato Kagaku) at 22 ° C. Metal salt aqueous solution in which ferrous nitrate (Fe (NO ₃ ) ₂ · 9H ₂ O) and 0.00118 mol of samarium nitrate (Sm (NO ₃ ) ₃ · 6H ₂ O) are dissolved in 120 ml of water (deoxygenated) Was added instantaneously. After stirring for 8 minutes while stirring with a magnetic stirrer, the temperature was raised to 35 ° C. and aged for 20 minutes. It was cooled to room temperature and taken out into the air after cooling. Using pure water, decantation was performed 3 times to remove impurities. The obtained alloy particles were measured for the composition, average particle size, and distribution (coefficient of variation) in the same manner as described above. The composition was calculated by dissolving the alloy particle-containing solution obtained by the reaction with hydrochloric acid, and measuring it by ICP (inductively coupled high-frequency plasma emission spectrometry).
The transition metals and rare earth elements added within the experimental error were contained. The particle shape was granular, the average particle diameter was 35 nm, and the coefficient of variation was 56%. The obtained particles are re-dispersed in pure water, 0.1 mol of CaCl ₂ · 6H ₂ O dissolved in pure water is added, then neutralized with NH ₄ OH, and Ca is formed on the surface of the Sm compound-containing iron fine particles. (OH) ₂ was formed. The precipitate was filtered and washed with water, and then dried at 120 ° C. The dried product was dry pulverized.
Reduction diffusion treatment, nitriding treatment (Comparative Example 2), and recovery treatment were performed in the same manner as described above. Table 1 shows the characteristics of the obtained magnetic powder (alloy). As shown in Table 1, the average particle size is large and the variation coefficient of the particle size is large, so that it is not preferable to use it as a magnetic powder for a magnetic recording medium.

  The magnetic properties of the obtained powder were measured using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) with an external magnetic field of 796 kA / m.

<Preparation of paint>
In the following examples, “parts” indicates “parts by weight”.
Magnetic liquid formula 1
Magnetic powder (shown in Table 2) 100 parts Binder resin Vinyl chloride copolymer 14 parts (containing 1 × 10 ⁻⁴ eq / g of —SO ₃ K group, degree of polymerization 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)
α-alumina (average particle size: 0.10 μm) 2 parts carbon black (average particle size: 30 nm) 5 parts butyl stearate 2 parts stearic acid 2 parts methyl ethyl ketone 125 parts cyclohexanone 125 parts

Magnetic liquid formula 2
Magnetic powder (shown in Table 3) 100 parts Binder resin Vinyl chloride copolymer 15 parts (containing 1 × 10 ⁻⁴ eq / g of —SO ₃ K group, degree of polymerization 300)
Polyester polyurethane resin 6 parts (Neopentyl glycol / Caprolactone polyol / MDI
= 0.9 / 2.6 / 1, -SO ₃ Na group: 1 × 10 ⁻⁴ eq / g)
α-alumina (average particle size: 0.10 μm) 2 parts carbon black (average particle size: 30 nm) 5 parts butyl stearate 10 parts butoxyethyl stearate 5 parts isohexadecyl stearate 2 parts stearic acid 3 parts methyl ethyl ketone 125 parts cyclohexanone 125 parts

Non-magnetic liquid formula 1
80 parts of acicular hematite (specific surface area by BET method: 65 m ² / g,
Average long axis length: 0.10 μm, average needle ratio: 7,
(pH: 8.8, aluminum treatment: 1% by mass as Al2O3)
20 parts of carbon black (average particle size: 17 nm,
DBP oil absorption: 80 ml / 100 g,
Surface area by BET method: 240 m ^{2 /} g, pH 7.5)
Binder resin 13 parts of vinyl chloride copolymer (containing 1 × 10 ⁻⁴ eq / g of —SO ₃ K group, degree of polymerization 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)
Phenylphosphonic acid 3 parts Butyl stearate 3 parts Stearic acid 3 parts Methyl ethyl ketone and cyclohexanone 1: 1 mixed solvent 280 parts

Non-magnetic liquid formulation 2
80 parts of acicular hematite (specific surface area by BET method: 65 m ² / g,
Average long axis length: 0.10 μm, average needle ratio: 7,
(pH: 8.8, aluminum treatment: 1% by mass as Al ₂ O ₃ )
20 parts of carbon black (average particle size: 17 nm,
DBP oil absorption: 80 ml / 100 g,
Surface area by BET method: 240 m ^{2 /} g, pH 7.5)
Binder resin Vinyl chloride copolymer 15 parts (containing 1 × 10 ⁻⁴ eq / g of —SO ₃ K group, degree of polymerization 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)
Phenylphosphonic acid 3 parts α-alumina (average particle diameter: 0.15 μm) 2 parts carbon black (average particle diameter: 30 nm) 5 parts butyl stearate 10 parts butoxyethyl stearate 5 parts isohexadecyl stearate 2 Part
Stearic acid 3 parts Methyl ethyl ketone and cyclohexanone 1: 1 mixed solvent 280 parts

  For each of the above magnetic liquid formulations 1 and 2 and nonmagnetic liquid formulations 1 and 2, after kneading the magnetic powder or pigment, polyvinyl chloride, phenylphosphonic acid and 50% by mass of each solvent in a kneader. The polyurethane resin and the remaining components were added and dispersed with a sand grinder. To the obtained dispersion, 15 parts of isocyanate is added to the non-magnetic liquid and 14 parts to the magnetic liquid. Further, 30 parts of cyclohexanone is added to each dispersion, and the mixture is filtered using a filter having an average pore diameter of 1 μm. Coating solutions for forming and for forming the magnetic layer were prepared, respectively.

<Preparation of tape: Examples 1 to 7 and Comparative Example 1>
The obtained coating liquid 1 for the lower nonmagnetic layer (based on the nonmagnetic liquid formulation 1) was applied on a polyethylene terephthalate support having a thickness of 7 μm so that the thickness after drying was 1.5 μm. Immediately after that, while the coating layer for the lower non-magnetic layer is still in a wet state, the wet simultaneous multilayer coating is performed so that the magnetic layer thickness after drying becomes 0.085 μm by controlling the coating amount of the magnetic layer according to the magnetic liquid formulation 1. The film was passed through an aligning apparatus and longitudinally aligned while both layers were still wet. At this time, the orientation magnet was passed through a rare earth magnet (surface magnetic flux 600 mT) and then through a solenoid magnet (magnetic flux density 1 T), dried to such an extent that the orientation did not return in the solenoid, and further dried and wound up the magnetic layer. . After that, a 7-stage calendar composed of metal rolls was used to calender the roll at 90 ° C to obtain a web-like magnetic recording medium, which was slit into a 6.45 mm width to create a 6.45 mm video tape sample. did. Using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.), the magnetic properties (square ratio (SQ), SFD, Mr (residual magnetization)) of the sample were measured in parallel with the orientation direction at an applied magnetic field of 796 kA / m. In Comparative Example 1, the coercive force was too large, and the SFD could not be calculated. Furthermore, the surface roughness was measured. For the surface roughness, a 250 μm square sample area was measured using an optical interference three-dimensional roughness meter “TOPO-3D” manufactured by WYKO (Arizona, US). In calculating the measurement values, corrections such as tilt correction, spherical correction, and cylindrical correction were performed in accordance with JIS-B0601, and the center plane average roughness Ra was set as the surface roughness value.
The results are shown in Table 2.

<Preparation of Flexible Disk: Examples 8 to 11 and Comparative Example 2>
The obtained coating solution of the lower layer nonmagnetic layer formulation 2 is coated on a 68 μm thick polyethylene terephthalate support so that the thickness after drying is 1.5 μm, dried, and then applied to the magnetic layer according to the magnetic fluid formulation 2. A magnetic layer with a thickness of 0.1 μm after drying is formed by adjusting the coating amount of the magnetic layer using a coating solution, and the magnetic field with the central magnetic field strength of 398 kA / m is counteracted while the magnetic layer is still wet. After passing through a rare earth magnet and orienting in the longitudinal direction, random orientation treatment is performed by passing through two AC magnetic field generators with a magnetic field strength of 24 kA / m at a frequency of 50 Hz and then 12 kA / m at a frequency of 50 Hz. It was. Thereby, an orientation degree ratio of 98% or more could be obtained.
The other support surface was coated and oriented in the same manner, dried, and then treated with a seven-step calender at a temperature of 90 ° C. and a linear pressure of 300 kg / cm (294 kN / m). It was punched into 3.7 mm, thermotreated (70 ° C. for 24 hours) to accelerate the curing of the coating layer, burnished with an abrasive tape, and post-treated to remove surface protrusions. Using a vibrating sample magnetometer (manufactured by Toei Kogyo), the magnetic properties of the sample were measured in parallel with the longitudinal direction of the support with an applied magnetic field of 796 kA / m. In Comparative Example 2, the coercive force was too large and the SFD could not be calculated. Furthermore, the surface roughness was measured. For the surface roughness, a 250 μm square sample area was measured using an optical interference three-dimensional roughness meter “TOPO-3D” manufactured by WYKO (Arizona, US). In calculating the measurement values, corrections such as tilt correction, spherical correction, and cylindrical correction were performed in accordance with JIS-B0601, and the center plane average roughness Ra was set as the surface roughness value.
The results are shown in Table 3.

  From the above results, it can be seen that the magnetic recording medium having a magnetic layer containing fine magnetic powder produced according to the present invention has small surface roughness and excellent high-density recording characteristics.

Claims (4)

A reverse micelle solution (I) formed by mixing a water-insoluble organic solvent containing a surfactant and a reducing agent aqueous solution;
Mixing a water-insoluble organic solvent containing a surfactant, a rare earth element-containing compound aqueous solution, and a reverse micelle solution (II) formed by mixing a transition metal compound aqueous solution to form rare earth element-containing transition metal compound particles A method for producing a rare earth-transition metal alloy magnetic powder having an average particle size of 5 to 15 nm, wherein the rare earth element-containing transition metal compound particles are subjected to a reduction diffusion method. A reverse micelle solution (I) formed by mixing a water-insoluble organic solvent containing a surfactant and a reducing agent aqueous solution;
Mixing a water-insoluble organic solvent containing a surfactant, a rare earth element-containing compound aqueous solution, and a reverse micelle solution (II) formed by mixing a transition metal compound aqueous solution to form rare earth element-containing transition metal compound particles A method for producing a rare earth-transition metal-nitrogen based magnetic powder having an average particle size of 5 to 15 nm, wherein the rare earth element-containing transition metal compound particles are subjected to a reduction diffusion method and then nitrided.   2. A magnetic recording medium having a magnetic layer containing a magnetic powder and a binder on a nonmagnetic support, wherein the magnetic powder is a rare earth-transition metal alloy magnetic powder obtained by the production method according to claim 1. A magnetic recording medium characterized by the above.   3. A magnetic recording medium having a magnetic layer containing a magnetic powder and a binder on a nonmagnetic support, wherein the magnetic powder is a rare earth-transition metal-nitrogen based magnetic powder obtained by the production method according to claim 2. A magnetic recording medium comprising: