JP2000309802A - Rare earth magnetic powder, method for surface treatment of the same and rare earth bond magnet using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain rare earth magnetic powder of high quality improved in oxidation resistance, simultaneously free from deterioration in magnetic properties even in the case of the improvement of the oxidation resistance and free from being influenced by the environment of high temp.-high pressure at the time of kneading it with a resin, or the like. SOLUTION: In a method in which a silica coating thin film is formed on the surface of rare earth magnetic powder composed of an alloy or an intermetallic compd. contg. rare earth elements in the compsn., the magnetic powder is mixed with a silica sol produced from the hydrolysis of an alkyl silicate with a base as a catalyst, and this mixture is heated in an inert atmosphere. Desirably, the thickness of the silica thin film lies in the range of 0.01 to 3 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for improving the oxidation resistance of a magnetic powder by forming a thin film of silica on the particle surface of the rare earth magnetic powder.

[0002]

2. Description of the Related Art At present, rare earth magnets having high magnetic properties enable the use of materials which are indispensable for miniaturization of electronic products, such as communication equipment and information processing equipment, which enable reduction in size and size of magnets. Has become. In particular, rare earth bonded magnets have excellent shape workability, and can be formed into thin and minute shapes, and thus the amount of rare earth bonded magnets used is steadily increasing.

[0003] Typical rare earth bonded magnets include Sm-C
o-based, Nd-Fe-B-based, and Sm-Fe-N-based magnetic materials are used, each of which has high magnetic properties. However, since these rare-earth magnets contain a rare-earth element as a component, and the rare-earth element is an element that is easily oxidized, a rare-earth magnet that contains the rare-earth element in its composition is basically easily oxidized. Therefore, in order to obtain a practical rare-earth bonded magnet, it is basically necessary to overcome oxidation resistance.

Such a rare earth magnet is disclosed in
Japanese Patent Publication No. -280404 discloses a method of depositing silica glass on the surface of a sintered magnet or a bonded magnet by a sol-gel method using tetraethoxysilane.
However, providing such a special coating on the surface of the magnet molded product is not a measure that complicates the manufacturing process and increases the manufacturing cost. In contrast, Japanese Patent Application Laid-Open No. 62-152107
Japanese Patent Application Laid-Open No. 2-265222 discloses a method of coating the particle surface of a rare-earth magnetic powder itself with a silicate such as sodium silicate. Japanese Patent Application Laid-Open No. 8-111306 discloses a method for mechanically attaching silica powder, and a method for forming a protective film of silicon dioxide on the surface of an NdFeB-based alloy powder by a sol-gel reaction using ethyl silicate as a raw material or a plasma chemical vapor deposition method. Have been.

However, the protective film obtained by these methods is in the form of fine particles, and in order to obtain excellent oxidation resistance, the protective film on the surface of the magnetic powder must be thickened to fill the gap. As a result, the original magnetic properties of the magnetic powder are significantly reduced. That is, in these techniques, the oxidation resistance and the magnetic properties have a trade-off relationship, and are not sufficiently satisfactory in that respect. Even if a uniform coating is formed in the form of particles, the magnetic powder is exposed to a high temperature and high pressure environment in a high temperature and high pressure during the subsequent resin bonding process during the production of the bonded magnet or the compound of the raw material, and the coating peels off. Therefore, there is a problem that the effect cannot be exhibited.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems and to improve the oxidation resistance of rare-earth magnetic powder and at the same time to improve the magnetic properties even if the oxidation resistance is improved. It is an object of the present invention to obtain a high-quality rare-earth magnetic powder that does not decrease and is not affected by a high-temperature and high-pressure environment during kneading with a resin or the like.

[0007]

In order to solve the above-mentioned problems, the inventors of the present invention have applied a coating having oxidation resistance to the surface of rare earth magnetic powder particles more uniformly than the conventional method. It is thought that it can be solved by doing, and after diligently examining various coating materials, an alkyl silicate represented by ethyl silicate (silicate compound,
Silica sol obtained by hydrolyzing silicon alkoxide under a basic catalyst is mixed uniformly with rare earth magnetic powder in an inert atmosphere, and then heated to further condense, resulting in a strong and dense colloid. It was found that a silica-like thin film was formed, and the silica film had a remarkable oxidation resistance effect.

That is, the rare earth magnetic powder of the present invention comprises:
It is characterized in that silica obtained by hydrolyzing an alkyl silicate adheres to the particle surface of the rare earth magnetic powder in a thin film form.

The surface treatment method for a rare earth magnetic powder according to the present invention is a method for forming a silica coating on the surface of a rare earth magnetic powder composed of an alloy or an intermetallic compound containing a rare earth element in the composition. A silica sol produced from the hydrolysis of an alkyl silicate using the catalyst as a catalyst, and heating in an inert atmosphere.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The alkyl silicate used in the present invention is a silicate ester represented by the following general formula. SinO (n-1) (OR) (2n + 2), wherein R is an alkyl group, for example, a methyl group, an ethyl group, a propyl group, a butyl group and the like can be used. As the alkyl group, ethyl silicate using an ethyl group can be preferably used because the cost is particularly low, and since it is nontoxic and easy to handle. The value of n is related to the molecular weight of the alkyl silicate, and n = 1 to 10 is preferably used. If n is larger than 10, it becomes difficult to obtain dense silica.

<Addition amount of alkyl silicate> The addition amount of alkyl silicate required for forming a silica thin film is as follows.
Although it depends on the type of ethyl silicate, the type, shape, and particle size of the magnetic powder, it is preferable to add 1 to 10 parts by weight based on 100 parts by weight of the rare earth magnetic powder having an average particle diameter of 1 to 10 μm. .

<Hydrolysis of Alkyl Silicate and Basic Catalyst> The most characteristic feature of the present invention is that the hydrolysis of alkyl silicate is carried out in a basic catalyst. It is known that the mechanism of hydrolysis and condensation of alkyl silicate in a basic aqueous solution is fundamentally different from that of an acidic aqueous solution. In the case of a basic aqueous solution, the alkoxy group of the alkyl silicate is simultaneously replaced with a hydroxyl group. Therefore, S
A siloxane bond grows three-dimensionally from i, and a silica sol having a condensed network structure is formed. Ammonia, an alkali metal or alkaline earth metal hydroxide, or a metal hydroxide in which the hydroxide exhibits basicity can be used as the basic catalyst, but all the ammonia volatilizes in the subsequent heating step and does not remain. Therefore, it can be used most preferably. The hydrolysis and condensation reaction of an alkyl silicate under a basic catalyst takes place in a wide range, but in the present invention, a basic having a hydrogen ion concentration (pH) of 7.5 or more is preferable, and a range of 8 to 13 is more preferable. preferable.

FIG. 1 shows the relationship between pH and heat resistance when coating Sm 2 Fe 17 N 3 -based magnetic powder with silica formed by hydrolysis from an alkyl silicate, based on the magnetic properties of the magnetic powder. It is known that the magnetic properties of Sm2Fe17N3-based magnetic powder are significantly reduced when oxidized.

From this figure, it is found that the coercive force and the residual magnetization are low when the pH is 6 or less, but both characteristics are greatly improved when the pH is 7.5 or more. Here, the magnetic properties of the magnetic powder were determined by packing the magnetic powder in a sample case together with paraffin wax, melting the paraffin wax with a drier, and then measuring 20k.
The axis of easy magnetization is aligned with the orientation magnetic field of Oe, and the magnetization magnetic field 40
VSM with pulse magnetization of kOe and maximum magnetic field of 20 kOe
It is a relative value obtained by measuring magnetic properties with a (vibrating sample magnetometer).

The amount of water added to the hydrolysis is 0.1 to 3 times the theoretical amount required for the hydrolysis of the alkyl silicate. If the amount is less than this range, a dense silica thin film cannot be obtained. If the amount is more than this range, the rare-earth magnetic powder is oxidized. Therefore, the addition amount of water is preferably 0.5 to 2 times, and the addition of a stoichiometric amount is most preferable.

At the time of hydrolysis, alcohol may be added simultaneously with addition of ammonia and water. Alcohol acts as a surfactant to enhance the dispersibility of water in the alkyl silicate.

<Mixing of Magnetic Powder and Silica Sol> The treatment agent is coated on the surface of the magnetic powder in a high-speed shear mixer in a dry manner. The coating does not depend only on the wettability of the silica sol, but uses the shear force of the mixer to apply the silica sol uniformly to the surface of the magnetic powder particles while strongly stirring and dispersing the magnetic powder. At this stage, dispersing the silica sol as uniformly and uniformly as possible greatly affects the oxidation resistance of the subsequent silica film.

For this purpose, a more uniform coating can be achieved by previously dispersing and coating ethyl silicate uniformly on the magnetic powder and then adding and mixing a basic aqueous solution. The mixing conditions also depend on the stirring speed, the capacity of the mixer, and the size and shape of the blades, and it is difficult to specify them. However, the conditions should be set so that the entire system is uniformly mixed in each system.

<Heat treatment> A silica thin film having a three-dimensional network structure is formed on the particle surface of the rare-earth magnetic powder. However, by heating, the remaining SiOH undergoes a polycondensation reaction and is stabilized to form a stronger silica thin film. I do. The processing temperature required for this condensation is 60 to 250 ° C., preferably 1 to 250 ° C.
00-250 ° C.

The silica thin film thus obtained has a thickness of 0.1 mm.
When coated with a thickness in the range of 01 to 3 μm, the oxidation resistance can be improved without impairing the magnetic performance.

In the present invention, the wettability between the magnetic powder and the resin,
A coupling agent can be used for the purpose of improving the strength of the magnet. The coupling agent is selected according to the type of the resin.

It can be used in the present invention. Γ- (2-aminoethyl) aminopropyltrimethoxysilane, γ- (2-aminoethyl) as a coupling agent
Aminopropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, N-β- (N-vinylbenzylaminoethyl) -γ-aminopropyltrimethoxysilane hydrochloride, γ- Glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, vinyltriacetoxysilane, γ-chloropropyltrimethoxysilane, hexamethylenedisilazane, γ-anilinopropyltri Methoxysilane, vinyltrimethoxysilane, octadecyl [3- (trimethoxythryl) propyl] ammonium chloride, γ-chloropropylmethyldimethoxysilane, γ-mercaptopropylmethyldimethoxy Silane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, vinyltrichlorosilane, vinyltris (beta-methoxyethoxy) silane, vinyltriethoxysilane, beta-
(3,4 epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, N-β (aminoethyl) γ-aminopropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropylmethyl Dimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, oleidopropyltriethoxysilane, γ-isocyanatopropyltriethoxysilane, polyethoxydimethylsiloxane, polyethoxymethylsiloxane, bis ( Trimethoxysilylpropyl)
Amine, bis (3-triethoxysilylpropyl) tetrasulfane, γ-isocyanatopropyltrimethoxysilane, vinylmethyldimethoxysilane, 1,3,5
-N-tris (3-trimethoxysilylpropyl) isocyanurate, t-butylcarbamate trialkoxysilane, N- (1,3-dimethylbutylidene) -3-
Silane coupling agents such as (triethoxysilyl) -1-propanamine, isopropyl triisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl (N-aminoethyl-aminoethyl) titanate, isopropyl tris (dioctyl pyrophosphate) ) Titanate, tetraisopropylbis (dioctylphosphite) titanate,
Tetraisopropyl titanate, y tetraoctyl bis (trioctyl phosphite) titanate, isopropyl trioctyl titanate, isopropyl tri (dioctyl phosphate), isopropyl dimethacrylate isostearyl titanate, tetraoctyl bis (ditridecyl phosphite) titanate, tetra (2, 2-
Titanate cups such as diallyloxymethyl-1-butyl) bis (di-tridecylphosphite) titanate, bis (dioctylpyrophosphate) oxyacetate titanate, isopropylisostearoyldiacryl titanate, and bis (dioctylpyrophosphate) ethylene titanate Examples include a ring agent and an aluminum-based coupling agent such as acetoalkoxyaluminum diisopropylate. At least one or two or more of these coupling agents can be used. The addition amount is 0.01% by weight to 10% by weight. 0.01% by weight
In the following, the effect of the coupling agent is small, and at 10% by weight or more, the magnetic properties of the rare earth magnetic powder and the rare earth magnet are reduced due to aggregation of the rare earth similar powder. Further, in the present invention, a silane coupling agent is preferable in view of the reactivity between the silica thin film of the rare earth magnetic powder and the coupling agent.

In the present invention, a resin is used as a binder for a rare earth magnet, and a thermoplastic resin, a thermosetting resin,
At least one of an elastomer, a thermoplastic elastomer, etc.
Species or two or more can be used.

As the thermoplastic resin, 12-nylon,
Polyamide resin such as 6,12-nylon, 4,6-nylon, 6,10-nylon, nylon 6T, nylon MXD6, aromatic nylon, 11-nylon, amorphous nylon, copolymer nylon, polyethylene, high density Olefin resins such as polyethylene, low-density polyethylene and polypropylene Iomer resins such as ethylene-iomer resins, EEA resins such as ethylene-ethyl acrylate copolymer, acrylonitrile-acryl rubber-styrene copolymer resins, acrylonitrile-styrene copolymer resins Acrylonitrile-based resins such as acrylonitrile-butadiene-styrene copolymers, acrylonitrile-chlorinated polyethylene-styrene copolymers, polyvinyl-based resins such as ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, and acetate fibers. Polyethylene resin, polytetrafluoroethylene, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene / hexylfluoropropylene copolymer, tetrafluoroethylene / ethylene polymer, fluorine such as polyvinylidene fluoride, polyvinyl fluoride Resin, polymethyl methacrylate, acrylic resin such as ethylene / ethyl acrylate resin, polyurethane resin, aromatic polyester resin, polyacetal, polycarbonate, polysulfone, polybutylene terephthalate, polyethylene terephthalate, polyarylate, polyphenylene oxide,
Polyphenyl sulfide, polyoxypendylene, polyether ketone, polyether sulfone, polyether imide, polyamide imide, polyimide, polyallyl ether nitrile, polybenzimidal, polyaramid, polyester amide, wholly aromatic amide, semi-aromatic At least one kind or two or more kinds of engineering plastics such as liquid crystal resins such as amides and super engineering plastics can be used.

Examples of the thermosetting resin include epoxy resin, phenol resin, amide special resin, epoxy-modified phenol resin, unsaturated polyester resin, xylene resin, urea resin, melanin resin, silicone resin, alkyd resin, furan resin, and thermosetting resin. At least one kind or two or more kinds such as a curable acrylic resin and a thermosetting fluororesin can be used.

As the elastomer, natural rubber, nitrile / butyl rubber, polyisoprene rubber, silicon rubber,
Fluororubber, thermoplastic urethane elastomer such as ester, special ester ether, caprolactone, adipate, carbonate, lactone, etc., olefin thermoplastic elastomer, styrene thermoplastic elastomer, styrene / butadiene heat At least one or two or more thermoplastic elastomers such as a thermoplastic elastomer, a polyamide-based thermoplastic elastomer, a polyester-based thermoplastic elastomer, a nitrile-based thermoplastic elastomer, a hydrogenated SBS-based thermoplastic elastomer, and a fluorine-based thermoplastic elastomer can be used.

In the present invention, an antioxidant can be added for the purpose of preventing the binder resin from deteriorating due to the heat history during kneading and molding. As an antioxidant, triethylene glycol-bis- [3- (3-t-butyl-5-methyl-4)
-Hydroxyphenyl) propionate], 1,6-hexanenediol-bis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 2,4
-Bis- (n-octylthio) -6- (4-hydroxy-
3,5-di-t-butylalinino) -1,3,5-triazine, pentaerythrityl-tetrakis [3- (3,
5-di-t-butyl-4-hydroxyphenyl) propionate] 2,2-thio-diethylenebis [3- (3
5-di-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2,2 thiobis (4-methyl-6-t-butylphenol) ),
N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydroxycinamide), 3,5
-Di-butiru-4-hydroxy-benzylphosphonate-diethyl ester, 1,3,5-trimethyl 2,4,6-tris (3,5-di-t-butyl-4-
Hydroxybenzyl) benzene, tris- (3,5-di-tert-butyl-4-hydroxybenzyl) -isocyanurate, N, N′-bis [3- (3,5-di-tert-butyl-4-hydroxy) Phenyl) propionyl] hydrazine, decamethylenedicarboxylic acid disalicyloyl hydrazide, N, N-dibenzal, N, N-bis (3,5-di-t-butyl-4-hydroxyhydrocinnate)
Tris (2,4-di-t-butylphenyl) phosphite, 2,6-di-t-butyl-4-methylphenol, n-octadecyl-3- (3,5-di-butyl-4)
-Hydroxyphenyl) propionates, 2,2'-methylene-bis- (4-methyl-6-t-butylphenol), 2-t-butyl-6- (3'-t-butyl-5 '
-Methyl-2'hydroxybenzyl) -4-methylphenyl acrylate, 4,4'-butylidene-bis- (3
-Methyl-6-t-butylphenol, 4,4'-thiobis (3-methyl-6-t-butylphenol), 1,
3,5-tris (4-t-butyl-3-hydroxy-
2,6-dimethylbenzyl) isocyanurate, tetrakis [methylene-3- (3,5′-di-t-butyl-
4'-hydroxyphenyl) propionate] methane,
3,9-bis [2- (3-t-butyl-4-hydroxy-5-methylphenyl) propionyloxy] -1,1-
Dimethylethyl) 2,4,8,10-tetraoxaspiro [5,5] undecane, N, N'-diallyl-p-phenylenediamine, diauryl-3,3'-thiodipropionate, dimyristyl-3,3 '-Thiodipropineate, pentaerythritol-tetrakis (β-laurylthiopropionate), ditridecyl-3,3'-
Thiodipropionate, 2-mercaptobenzimidazal, thiophenylphosphite, tris (2,4-
Di-t-butylphenyl) phosphite, tetrakis (2,4-di-t-butylphenyl) -4,4′biphenylenephosphonite, 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- (3,5-
Di-tert-butyl-2-hydroxyphenyl) benzotriazole, 2- (3-tert-butyl-5-methyl-2-hydroxyphenyl) -5-chlorobenzotriazole,
2- (3,5-di-t-amyl-2-hydroxyphenyl) benzotriazole, poly [{6- (1,1,3,3)
3- (tetramethylbutyl) imino-1,3,5-triazine-2,4-diyl {(2,2,6,6-tetramethyl-4-piperidyl) imino}], 2- (3,5- Bis (1,2,2,6,6-pentamethyl-4-piperidyl) di-t-butyl-4-hydroxybenzyl) -2-n-butylmalonate, N, N'-bis (3-aminopropyl) Ethylenediamine-2,4-bis [N-butyl-
N- (1,2,2,6,6-pentamethyl-4-piperidyl) amino] -6-chloro-1,3,5-triazine condensate, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4 -Methoxybenzophenone, 2
-Hydroxy-4-octoxybenzophenone, 2,
2'-di-hydroxy-4-methoxybenzophenone,
2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- [2'hydroxy-3'-
(3 ″, 4 ″, 5 ″, 6 ″ -tetrahydrophthalimidomethyl) -5′-methylphenyl] benzotriazole, 2- [2′-hydroxy-3′-t-butyl-5 ′ -Methylphenyl] -5-chlorobenzotriazole, 2- (2'-hydroxy-3 ', 5'-t-butylphenyl] benzotriazole, 2- [2'-hydroxy-5'-t-octylphenyl] benzo Triazole, 2- [2′-hydroxy-3 ′, 5′-di-t-amylphenyl] benzotriazole, 1,2,3-benzotriazole, tolyltriazole, tolyltriazoleamine salt, tolyltriazole potassium salt, 3-
(N-salicyloyl) amino-1,2,4-triazole, 2,4-di-tert-butylphenyl-3 ′, 5′-dibutyl-4′-hydroxybenzoate, nickel dibutyldithiocarbamate, 1,1 -Bis- (4-hydroxyphenyl) cyclohexane, styrenated phenol, N.P. N′-diphenyl-p-phenylenediamine,
N-phenyl-N'-isopropyl-p-phenylenediamine, N-phenyl-N'-1,3-dimethylbutyl-p-phenylenediamine, 2,2,4-trimethyl-
1,2-dihydroquinoline polymer, 6-ethoxy-2,
2,4-trimethyl-1,2-dihydroquinoline, phenyl-1-naphthylamine, alkylated diphenylamine, octylated diphenylamine, 4,4 ′-(α, α
-Dimethylbenzyl) diphenylamine, p- (p-toluenesulfonylamide) diphenylamine, N, N '
-Di-2-naphthyl-p-phenylenediamine, N-phenyl-N '-(3-methacryloyloxy-2-hydroxypropyl) -p-phenylenediamine, 2,6-di-t-butyl-4-ethyl Phenol, 2,2′-methylene-bis- (4-ethyl-6-butylphenol),
4,4'-butylidenebis (3-methyl-6-t-butylphenol), 2,5-di-t-amylhydroquinone, 2-mercaptobenzimidazole, zinc 2-mercaptobenzimidazole, zinc 2-mercaptomethylbenzimidazole Salt, nickel diethyldithiocarbamate, nickel dibutyldithiocarbamate, 1,
3-bis (dimethylaminopropyl) -2-thiourea,
Examples include tributylthiourea, tris (nonylphenyl) phosphite, dilauryl thiodipropionate, and special wax.

These antioxidants may be used alone or in combination of two or more as necessary. A high synergistic effect can be obtained by using a primary antioxidant and a secondary antioxidant in combination. These antioxidants are stable at the processing temperature, and it is important to appropriately select them in consideration of the reactivity with the magnetic powder, the resin, and other additives. The addition amount is suitably from 0.01 to 5% by weight based on the total amount of the magnetic powder and the binder. If the amount of the antioxidant exceeds 5%, it is not appropriate because the slip property in the molten state is reduced and the mechanical strength of the bonded magnet is remarkably reduced. When the amount is 0.01% or less, the antioxidant effect on the binder resin hardly appears.

In the present invention, a lubricant can be added for the purpose of reducing the melt viscosity and improving the injection moldability. Usable lubricants include waxes such as paraffin wax, liquid paraffin, polyethylene wax, ester wax, polyethylene wax, polypropylene wax, ketone wax, carnauba, micro wax, stearic acid, 12-oxystearic acid, lauric acid, capric acid Fatty acids such as zinc stearate, calcium stearate, barium stearate, aluminum stearate, magnesium stearate, lithium stearate, strontium stearate, sodium stearate, potassium stearate, sodium oleate, zinc laurate, calcium laurate , Barium laurate, zinc linoleate, calcium linoleate,
Zinc 2-ethylhexoate, Lead benzoate, Para-tert-butyl zinc benzoate, Barium para-tert-butyl benzoate, Stearyl acid phosphite, Magnesium stearyl acid phosphite, Aluminum stearyl acid phosphite, Calcium stearyl acid phosphite, Zinc Metal soaps such as stearyl acid phosphite, barium stearyl acid phosphite, zinc behenyl acid phosphite, stearic acid amide, oleic acid amide, erucic acid amide, behenic acid amide, palmitic acid amide, hydroxystearic acid amide, ethylenebishydroxy Stearic acid amide, methylene bis stearic acid amide,
Ethylenebisstearic acid amide, ethylenebisisostearic acid amide, hexamethylenebisoleic acid amide, hexamethylenebisoleic acid amide, N-N'-
Dioleyl adipamide, N, N'-dioleyl sebacamide, m-xylylene bisstearic acid amide, N, N'-diisostearyl isophthalic amide,
Ethylene bislauric amide, ethylene bisoleic amide, ethylene biscapric amide, ethylene biscaprylic amide, distearyl adipamide,
Dioleyl adipamide, N-stearyl stearamide, N-oleyl stearamide, N-stearyl erucamide, N-12 hydroxystearyl stearamide, N-12 hydroxystearyl oleamide, methylol stearamide, Fatty acid amides such as methylol behenamide, N-butyl-N'-stearyl urea, N-phenyl-N'-stearyl urea, N-stearyl-N'-stearyl urea, xylylene bisstearyl urea, toluylene bis stearyl urea Substituted ureas such as hexamethylene bisstearyl urea, diphenylmethane bisstearyl urea, diphenylmethane bis lauryl urea, cetyl 2-ethylhexanoate, methyl cocoate, methyl laurate, isopropyl myristate, Michin isopropyl, 2-ethylhexyl palmitate, palm fatty acid methyl, tallow fatty acid methyl, myristate octyldodecyl, methyl stearate, butyl stearate, stearic acid 2-
Ethylhexyl, isotridecyl stearate, methyl caprate, methyl methyl myristate, methyl oleate, isobutyl oleate, octyl oleate, lauryl oleate, oleyl oleate, myristyl myristate, hexyldecyl myristate, stearyl stearate, 2-oleate Fatty acid esters such as ethylhexyl, decyl oleate, octyldodecyl oleate, octyldodecyl behenate, behenyl behenate, octyldodecyl erucate, isobutyl oleate, sorbitan monostearate, sorbitan distearate,
Alcohols such as ethylene glycol, stearyl alcohol and behenyl alcohol; polyethers such as polyethylene glycol, polypropylene glycol and polytetramethylene glycol; polysiloxanes such as silicone oil and silicone grease;
Examples include fluorine compounds such as fluorine-based grease and fluorine-containing resin powder. One or two or more of these lubricants can be used. However, if the amount is too small, the effect of improving the fluidity is small. If the amount is too large, the mechanical strength of the bonded magnet is remarkably reduced, making the magnet unsuitable for practical use. Therefore, the addition amount is 0.01 to 5 with respect to the total amount of the magnetic powder and the binder.
% By weight is preferred.

[0030]

[Function] A dense three-dimensional condensation polymer of silica is formed on the surface of the rare earth magnet powder, and when the condensation polymer is heat-treated and gelled into silica, the film is formed so that compressive stress acts on the powder. It is formed. This not only improves the oxidation resistance and corrosion resistance, but also ensures that the coating adheres strongly to the particles, and the falling off of the coating during the manufacturing process of the resin-bound magnet is drastically reduced.

Since the dense silica film adheres in close contact, the surface area of the particles hardly changes, and when kneaded with the resin, it has an advantageous effect on dispersibility and fluidity in the resin. Coupling treatment with a silane coupling agent or the like is necessary to select the optimum dispersibility in the resin, but the required amount of the coupling agent can be reduced because the silica film is uniform and smooth.

[0032]

[Example 1] S having an average particle diameter of 3 μm was added to a mixer.
300 g of m2Fe17N3 magnetic powder and 2.5 g of ethyl silicate (n = 5) were added by spraying and mixed in a nitrogen gas for 1 minute. Thereafter, a mixed solution of 1.08 g of aqueous ammonia adjusted to pH 12 and 3.24 g of ethanol was added by spraying, and mixed in a nitrogen gas for 1 minute by a mixer. The mixer used in the present invention is not particularly limited as long as the magnetic powder can sufficiently flow. When the mixing and dispersion are completed, the magnetic powder is taken out of the mixer and heat-treated at 230 ° C. for 30 minutes under reduced pressure.
An Sm2Fe17N3-based magnetic powdered silica thin film was formed.

The obtained silica-coated magnetic powder was subjected to surface analysis by XPS (X-ray photoelectron spectroscopy). As a result, a peak was observed at an arbitrary position near 103.5 eV, and the binding of Si2P to silicon dioxide was restricted. Matched energy. From this, it was confirmed that the silica coating was surely formed by the present method. Observation of this powder under a scanning electron microscope (SEM) revealed that it was as shown in FIG. 2 and that there was no difference in appearance between the powder and nothing coated as shown in FIG. Therefore, no particulate silica was observed on the particle surface of the Sm2Fe17N3 magnetic powder, and it was concluded from this that the silica produced by the above treatment was formed not in a particulate form but in a uniform thin film form.

The specific surface area of the obtained powder measured by the BET method was 0.7 m ² / g, which was 1.2 times the 0.6 m ² / g of the magnetic material before silica coating. It was increasing. That is, the increase in the specific surface area due to the silica coating is not so large.

Example 2 To 300 g of the magnetic powder obtained in Example 1, 1.2 g of a silane coupling agent (γ-aminopropyltriethoxysilane) and 0.6 aqueous ammonia
g and 3.6 g of a mixed solution of ethanol were added by spraying, and mixed in a mixer for 1 minute in nitrogen gas. The magnetic powder was taken out and heated at 90 ° C. for 30 minutes under reduced pressure to obtain a magnetic powder having a coupling agent film formed on a silica film.

[Example 3-1] Sm obtained in Example 2
9 parts by weight of nylon 12 resin (polyamide resin) was added to 100 parts by weight of 2Fe17N3 magnetic powder, and the mixture was similarly mixed for 5 minutes and kneaded at 220 ° C. with a biaxial kneader to obtain compound pellets.

This was injection-molded under the conditions of an orientation magnetic field of 9 KOe, a nozzle and a cylinder temperature of 250 ° C.
Was obtained. The resulting bonded magnet molded body was demagnetized and pulse-magnetized at 25 kOe, and the magnetic properties of the magnet were measured using a BH curve tracer. The residual magnetization Br: 7500 G, coercive force iHc: 11 kOe, B
H (max): 13M · G · Oe, which was an extremely excellent magnetic property.

In addition, 30 g of the compound was fractionated,
JIS-K7210 with a melt flow measuring device manufactured by Toyo Seiki
A, a load of 98.07 N was applied at 250 ° C., and the melt flow rate (MFR) was measured. As a result, 107 g /
The result was as high as 10 min.

The obtained compound was oriented and molded into a cylindrical shape having an outer diameter of 10 mm and a height of 7 mm using a magnetic field injection molding machine. The obtained molded body had a coercive force iHc of 10.7 kOe.

[Example 3-2] Sm obtained in Example 2
9 parts by weight of nylon 12 resin (polyamide resin) was added to 100 parts by weight of 2Fe17N3 magnetic powder, and an antioxidant N, N-bis @ 3- (3,5-di-t-butyl-4-hydroxyphenyl) was added. 0.5 parts by weight of propionyl hydrazine (manufactured by Ciba Geigy), 0.5 parts by weight of a lubricant, m-xylylenebisstearic acid amide, are mixed for 5 minutes by a mixer, and kneaded at 220 ° C. by a biaxial kneader to obtain a compound. -A pellet was obtained.

9 parts by weight of a polyamide elastomer (Pebax (Toray Co., Ltd.), 100 parts by weight of the Sm2Fe17N3 based magnetic powder obtained in Example 2;
0.5 parts by weight of N-bis {3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl} hydrazine (manufactured by Ciba Geigy) and 0.5 parts by weight of a lubricant m-xylylenebisstearic acid amide Part, mix with a mixer for 5 minutes,
Compounding by kneading at 220 ° C with a twin-screw kneader
A pellet was obtained.

Comparative Example 1 Sodium silicate was dissolved in pure water to prepare a 14 wt% sodium silicate aqueous solution. In one liter of this aqueous solution, Sm2F having an average particle size of 3 μm was used.
100 g of e17N3 magnetic powder was stirred for 30 minutes, and 0.5 liter of ethanol was added thereto, followed by stirring for 30 minutes and filtration. The obtained powder was dried under reduced pressure at 80 ° C. for 2 hours to obtain a magnetic powder having a sodium silicate film formed thereon.

The obtained silica-coated magnetic powder was subjected to surface analysis by XPS (X-ray photoelectron spectroscopy). As a result, a peak was observed at an arbitrary position near 103.0 eV. Consistent with binding energy. Observation of this powder with a SEM revealed that Sm2Fe1
Fine silicate of about 0.1 μm was observed on the particle surface of the 7N3 magnetic powder. From this, it was concluded that the above-mentioned treatment covered the particulate silicate.

The specific surface area of the obtained powder measured by the BET method was 1.9 m ² / g, which was 3.2 times the 0.6 m ² / g of the magnetic material before silica coating. Had increased. That is, the specific surface area was greatly increased by the silica coating by this method.

Comparative Example 2 Tetraethoxysilane was dissolved in isopropyl alcohol to obtain a 50 wt% tetraethoxyirane-isopropyl alcohol solution. To this solution, a 0.3 wt% aqueous nitric acid solution as an acid catalyst was added at 7 wt%, and the mixture was stirred and left for 24 hours. This solution was diluted 20 times with isopropyl alcohol to obtain a surface treatment solution.

To this surface treatment solution was added S having an average particle size of 3 μm.
The m2Fe17N3 magnetic powder was immersed and stirred. Thereafter, the mixture was filtered and dried at room temperature, and then heated at 250 ° C. under reduced pressure for 1 hour to obtain a silica-coated magnetic powder.

The obtained silica-coated magnetic powder was subjected to a surface analysis by XPS (X-ray photoelectron spectroscopy). As a result, a peak was observed at an arbitrary position near 103.5 eV, and the binding energy of silicon dioxide Si2P was observed. And matched. When this powder was observed with a SEM, as shown in FIG.
Fine silica particles of about 1 μm were observed. From this, it is concluded that the silica produced by the above treatment is covered with particulate silica

The specific surface area of the obtained powder measured by the BET method was 1.3 m2 / g, which was 2.2 m / g of 0.6 m2 / g of the magnetic material before silica coating.
Had increased twice. It can be concluded that the silica coating by this method is particulate, so that the specific surface area is greatly increased.

Comparative Example 3 Sm 2 F obtained in Comparative Example 1
The e17N3-based magnetic powder was treated with the same silane coupling agent as in Example 2, and a compound pellet and a bonded magnet were produced in the same manner.

[Comparative Example 4] A bonded magnet was produced in the same manner using Sm2Fe17N3 magnetic powder which had not been treated with a silica coating or a silane coupling agent.

In order to examine the heat resistance of the obtained magnet, the magnet was heated at 100 ° C. in the air for a predetermined time, cooled to room temperature, and the flux was measured. FIG. 5 shows the change with time of the relative flux when the value before heating was set to 100%. From this figure, it is understood that the magnetic powder subjected to the surface treatment of the present invention has extremely high stability over time.

[Example 4] A particle diameter of 40 to 30 was added to a mixer.
Magnet powder (Nd13.5Fe64.5Co16) obtained by pulverizing an NdFeB-based quenched ribbon by a melt spinning method of 0 μm.
B6) 300 g and ethyl silicate (n = 5) as 2.
5 g was spray added and mixed in nitrogen gas for 1 minute. Thereafter, a mixed solution of 1.08 g of aqueous ammonia adjusted to pH 12 and 3.24 g of ethanol was added by spraying, and mixed in a nitrogen gas for 1 minute by a mixer. When the mixing and dispersion were completed, the magnetic powder was taken out of the mixer and heat-treated at 230 ° C. for 30 minutes under reduced pressure to form an Nd2Fe14B-based magnetic powder silica thin film.

The obtained silica-coated magnetic powder was subjected to surface analysis by XPS (X-ray photoelectron spectroscopy). As a result, a peak was observed at an arbitrary position near 103.5 eV, and the binding energy of silicon dioxide Si2P was observed. And matched. From this, it was confirmed that the silica was coated by the present method. Observation of this powder with a SEM revealed that it was as shown in FIG. 6, which did not differ in appearance from the particle photograph before silica coating shown in FIG. Therefore, it is concluded that the fine particles on the surface of the magnetic powder particles are irrelevant to the silica, and that the silica produced by the above treatment is formed not in a particle form but in a uniform thin film form.

The specific surface area of the obtained powder measured by the BET method was 0.45 m2 / g, which was 3.75 times that of the magnetic material before silica coating of 0.12 m2 / g. Was. Such an increase is due to the particulate silica coating formed.

Example 5 To 300 g of the magnetic powder obtained in Example 4, 1.2 g of a silane coupling agent (γ-aminopropyltriethoxysilane) and 0.6 of aqueous ammonia
g and 3.6 g of a mixed solution of ethanol were added by spraying, and mixed in a mixer for 1 minute in nitrogen gas. The magnetic powder was taken out and heated at 90 ° C. for 30 minutes under reduced pressure to obtain a magnetic powder having a coupling agent film formed on a silica film.

Example 6 Next, 2 parts by weight of a liquid epoxy resin was mixed with 100 parts by weight of the obtained powder, and a molded product of 10φ × 7 t was obtained by compression in a mold. After the molded body was cured and magnetized, the magnetic properties were measured. As a result, residual magnetization Br: 7.4 kG, coercive force iHc: 9.5 kO
e, BHmax: 11.5 MGOe.

Comparative Example 5 Sodium silicate was dissolved in pure water to prepare a 14 wt% sodium silicate aqueous solution. In 1 liter of this aqueous solution, 100 g of the same Nd2Fe14B-based magnetic powder used in Example 2 was stirred for 30 minutes, and 0.5 liter of ethanol was added and stirred for 30 minutes.
Filtered. The powder obtained by filtration is 80 ° C. under reduced pressure,
By drying for 2 hours, a magnetic powder having a sodium silicate film formed thereon was obtained.

When the surface of the obtained magnetic powder was analyzed by XPS (X-ray photoelectron spectroscopy), a peak was observed at an arbitrary position near 103.0 eV, which coincided with the binding energy of Si2P of the silicate. did. When this powder was observed by SEM, as shown in FIG. 8, many fine particles were observed in gaps other than the magnetic particles, and it was confirmed by XPS that this was a silicate. From this,
It is concluded that the silicate produced by the above treatment is a mixture or coating of particulate silicate.

Comparative Example 6 NdFe obtained in Comparative Example 5
The B-based magnetic powder was treated with the same silane coupling agent as in Example 5, and similarly compound pellets and
A bonded magnet was produced.

[Comparative Example 7] NdFe obtained in Comparative Example 5
Compound pellets and bonded magnets were produced in the same manner without treating the B-based magnetic powder with a silane coupling agent.

[Comparative Example 8] A compound pellet and a bonded magnet were prepared in the same manner as in the case of the NdFeB-based magnetic powder which had not been treated with the silica coating or the silane coupling agent.

In order to examine the heat resistance of the obtained magnet, the magnet was heated in air at 100 ° C. for a predetermined time, cooled to room temperature, and the flux was measured. FIG. 9 shows the change over time of the relative flux when the value before heating was set to 100%. From this figure, it is understood that the magnetic powder subjected to the surface treatment of the present invention has extremely high stability over time.

FIG. 10 shows the change over time of the weight when the NdFeB-based magnetic powder is placed in the atmosphere at 200 ° C. in the atmosphere. The magnetic powder of Example 5 of the present invention, compared with the comparative example,
The heat resistance is significantly improved.

[0064]

As described above, according to the method for treating the surface of a rare earth magnetic powder of the present invention, the oxidation resistance of the rare earth magnetic powder is improved, and at the same time, the magnetic properties are not reduced even if the oxidation resistance is improved. Further, it is possible to obtain a high-quality rare-earth magnetic powder and a bond magnet that are not affected by a high-temperature and high-pressure environment during kneading with a resin or the like.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the pH when silica is coated and the magnetic properties of Sm2Fe17N3 magnetic powder.

FIG. 2 is an SEM photograph of the Sm2Fe17N3 magnetic powder of the present invention.

FIG. 3 is an SEM photograph for comparison of the present invention.

FIG. 4 is an SEM photograph for comparison of the present invention.

FIG. 5 is a characteristic diagram showing changes with time of various silica coatings and fluxes on a magnetic material.

FIG. 6 is an SEM photograph of the NdFeB-based magnetic powder of the present invention.

FIG. 7 is an SEM photograph for comparison of the present invention.

FIG. 8 is an SEM photograph for comparison of the present invention.

FIG. 9 is a characteristic diagram showing time-dependent changes of various silica coatings and fluxes on a magnetic material.

FIG. 10 is a characteristic diagram showing various silica coatings on a magnetic material and a change with time in weight change.

Claims (5)

[Claims] 1. A silica thin film obtained by hydrolyzing an alkyl silicate adheres to the surface of particles of a rare earth magnetic powder comprising an alloy or an intermetallic compound containing a rare earth element in the composition. Rare earth magnetic powder. 2. The rare earth magnetic powder according to claim 1, wherein the silica thin film has a thickness in a range of 0.01 to 3 μm. 3. The rare earth magnetic powder according to claim 1, wherein a surface of the silica thin film is coated with a silane coupling agent. 4. A rare earth magnet using the magnetic powder. 5. A method for forming a silica coating on the surface of a rare earth magnetic powder composed of an alloy or an intermetallic compound containing a rare earth element in the composition, comprising the steps of: A surface treatment method for a rare earth magnetic powder, which comprises mixing a generated silica sol and heating in an inert atmosphere.