JP6572171B2 - Method for producing magnet alloy powder - Google Patents

Description

  The present invention relates to a method for producing a magnet alloy powder, and more particularly to a method for producing a magnet alloy powder with little reduction in coercive force when heated to a high temperature.

  Rare earth magnets are magnet materials used for various applications including motors, like ferrite magnets and alnico magnets. Generally, since these magnets are manufactured by sintering, it is difficult to form them into complicated shapes. In addition, since the shrinkage during sintering is about 15% to 20%, a product with high dimensional accuracy cannot be obtained.

  In recent years, bond magnets have been developed to solve these drawbacks. Bonded magnets are formed by solidifying magnet powder by using polyamide resin or polyphenylene sulfide resin as a binder. However, in a bonded magnet using iron-based magnet powder containing a rare earth element, there is a problem of deterioration of magnetic properties due to heating during molding. Moreover, the bond magnet may be exposed to a high temperature of 100 ° C. or higher depending on its use, and there is also a problem of deterioration of magnetic properties due to exposure to a high temperature environment during such use.

  Therefore, in order to improve the deterioration of the magnetic properties, the surface of the molded body is coated with a thermosetting resin or the like, for example, as disclosed in Patent Document 1, a coating with a phosphate-containing paint is performed. Although a method has been proposed, sufficient characteristics have not been obtained from the viewpoint of coercive force and the like.

  At present, as disclosed in Patent Document 2, when producing magnet powder by pulverizing iron-based magnet powder containing rare earth elements in an organic solvent, there is a method of adding phosphoric acid to the organic solvent. It is said that it is effective to prevent the deterioration of magnetic properties when heated to a high temperature. According to this method, it is possible to produce magnet powder in which a film containing iron phosphate is formed on the surface of the magnet powder, and the decrease in coercive force under heating conditions is suppressed.

  However, for further application expansion, it is required to further suppress the decrease in coercive force in a high temperature environment.

JP 2000-208321 A JP 2002-124406 A

  The present invention has been made in view of the above-described circumstances, and even if heated to a high temperature during the manufacturing process of a bonded magnet or used as a bonded magnet, a magnet alloy that suppresses a decrease in coercive force at room temperature after heating. It aims at providing the manufacturing method of powder.

  This inventor repeated earnest examination in order to solve the subject mentioned above. As a result, when pulverizing the iron-based magnet alloy powder, the pH of the organic solvent containing phosphoric acid and the phosphoric acid concentration are adjusted to a specific range, and an oxidizing agent is added to the organic solvent at a specific ratio. It has been found that the reduction in coercive force at room temperature after heating can be suppressed by grinding, and the present invention has been completed.

  (1) A first aspect of the present invention is a method for producing a magnet alloy powder by pulverizing an iron-based magnet alloy powder containing a rare earth element in an organic solvent containing phosphoric acid, the iron-based magnet alloy When the powder is pulverized, the pH of the organic solvent containing phosphoric acid is 1.5 or more and 8.0 or less, the phosphoric acid concentration in the organic solvent is 0.1 vol% or more and 20 vol% or less, and oxidation is performed. This is a method for producing magnet alloy powder, in which an agent is added in a concentration of 0.0001 mol / L to 1.0 mol / L in the organic solvent.

  (2) The second invention of the present invention is the method for producing magnet alloy powder according to the first invention, wherein the pH of the organic solvent containing phosphoric acid is 4.0 or more and 5.0 or less.

  (3) The third invention of the present invention is a method for producing magnet alloy powder, wherein in the first or second invention, nitric acid is added as the oxidizing agent.

  (4) A fourth invention of the present invention is a method for producing magnet alloy powder, wherein in any one of the first to third inventions, an organic compound having a molecular weight of 100 or less is used as the organic solvent.

  (5) The fifth invention of the present invention is the method for producing magnet alloy powder according to the fourth invention, wherein an organic solvent having a relative dielectric constant of 10 or more and 50 or less is used as the organic solvent.

  (6) The sixth invention of the present invention is the method for producing a magnetic alloy powder in the fifth invention, wherein 2-propanol, 1-methyl-2-pyrrolidone, or a mixture thereof is used as the organic solvent. .

  (7) According to a seventh aspect of the present invention, in the sixth aspect, as the organic solvent containing phosphoric acid, 1-methyl-2-pyrrolidone and phosphoric acid in a proportion of 10% by volume or more and 14% by volume or less It is a manufacturing method of magnet alloy powder using what is contained.

  ADVANTAGE OF THE INVENTION According to this invention, the magnet alloy powder which suppressed effectively the fall of the coercive force at room temperature by being exposed to a high temperature environment can be manufactured.

  Hereinafter, a specific embodiment of the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. In addition, this invention is not limited to the following embodiment, A various change is possible in the range which does not change the summary of this invention. In this specification, the notation “X to Y” (X and Y are arbitrary numerical values) means “X or more and Y or less”.

<< 1. Manufacturing method of magnet alloy powder >>
The method for producing a magnet alloy powder according to the present embodiment is a method for producing a magnet alloy powder by pulverizing an iron-based magnet alloy powder containing a rare earth element in an organic solvent containing phosphoric acid.

Here, the iron-based magnet alloy powder containing a rare earth element has, for example, a Th ₂ Zn ₁₇ type, Th ₂ Ni ₁₇ type, or TbCu ₇ type crystal structure. These are intermetallic compounds having rhombohedral and hexagonal crystal structures. Examples of the Th ₂ Zn ₁₇ type alloy powder include Sm ₂ Fe ₁₇ N ₃ alloy and Nd ₂ Fe ₁₇ N _3. Is mentioned. Examples of the Th ₂ Ni ₁₇ type alloy powder include Gd ₂ Fe ₁₇ N _{3 and the} like.

  Examples of rare earth elements include Sm, Nd, Pr, Y, La, Ce, and Gd. These may be used alone or as a mixture, but Sm is particularly preferable. Further, the iron-based magnet alloy powder contains iron (Fe) as an essential component as a transition metal element, and a part thereof may be substituted with Co. Specifically, the Curie temperature and corrosion resistance of the fine powder can be improved by substituting 20% by mass or less of Fe with Co.

  In addition, this iron-based magnet alloy powder includes C, Al, Si, Ca, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Re, Os, Ir, Pt, Au, or the like may be included. In the iron-based magnet alloy powder, these components are contained in a proportion of, for example, 3% by mass or less, preferably 0.05% by mass to 0.5% by mass. The weather resistance and heat resistance of the bonded magnet produced using a certain magnet alloy powder can be improved.

  The iron-based magnet alloy powder can be produced, for example, by subjecting an alloy powder obtained by a reduction diffusion method, a liquid quenching method, or a HDDR (Hydrogen Decomposition Desorption Recombination) method to a nitriding heat treatment.

  In the method for producing a magnet alloy powder according to the present embodiment, when the iron-based magnet alloy powder is pulverized in an organic solvent, the pH of the organic solvent containing phosphoric acid is 1.5 or more and 8.0 or less, The phosphoric acid concentration is 0.1 vol% or more and 20 vol% or less, and an oxidizing agent is added in an organic solvent at a concentration of 0.0001 mol / L or more and 1 mol / L or less.

  According to such a manufacturing method, even when heated to a high temperature during the manufacturing process of the bonded magnet or when used as a bonded magnet, it is possible to obtain a magnet alloy powder that suppresses a decrease in coercive force at room temperature after heating. .

[Crushing in an organic solvent containing phosphoric acid]
First, film formation by adding phosphoric acid to an organic solvent will be described. In the method for producing magnet alloy powder according to the present embodiment, as described above, magnet alloy powder is produced by pulverizing iron-based magnet alloy powder containing rare earth elements in an organic solvent containing phosphoric acid.

  Thus, the iron-based magnet alloy powder containing rare earth elements is pulverized in an organic solvent to form a film on the surface of the iron-based magnet powder. According to the pulverization of the iron-based magnet alloy powder in the organic solvent, the pulverization always causes a new surface to appear on the surface of the iron-based magnet alloy powder, so that a film is formed on the new surface as needed.

  In order to prevent the coercive force from being lowered even in a high temperature environment due to the production of a bonded magnet or the production of a magnet by sintering in such a film formation, a phosphate (such as iron phosphate and / or samarium phosphate) It is important to form a film of a rare earth phosphate), and it is essential to add phosphoric acid to an organic solvent and to grind in an organic solvent containing phosphoric acid.

It does not specifically limit as phosphoric acid added to an organic solvent, It is not necessary to be an anhydride. For example, a commercially available reagent phosphoric acid such as a first grade reagent or a special grade reagent containing about 15% by mass of water (H ₂ O) can be used.

  Here, it does not specifically limit as an organic solvent, What is necessary is just a solvent which has as a main component the organic compound which the iron-type magnet alloy powder containing rare earth elements does not melt | dissolve or wear excessively.

  Among them, from the viewpoint of suppressing the decrease in coercive force at room temperature due to exposure to high temperatures, and from the viewpoint of facilitating volatilization and removal of the organic solvent after pulverization and reducing manufacturing costs, organics having a molecular weight of 100 or less It is preferable to use a compound. Further, by using an organic solvent having a relative dielectric constant of 10 or more and 50 or less, dissolution of the magnet alloy powder in the pulverization treatment can be suppressed, and a magnetic film having excellent magnetic properties can be obtained by forming a good film. it can.

  Specifically, examples of such organic solvents include methanol, ethanol, 1-butanol, 2-butanol, 1-propanol, 2-propanol, acetonitrile, propionitrile, butyronitrile, i-butyronitrile, N-methylformamide. , N, N-dimethylformamide, 1-methyl-2-pyrrolidone, and dimethyl sulfoxide.

  Among these, it is more preferable to use 2-propanol or an organic solvent having a wider potential region than water. Examples of the organic solvent having a wider potential region than water include acetonitrile, N, N-dimethylformamide, 1-methyl-2-pyrrolidone, dimethyl sulfoxide and the like. In particular, by using 2-propanol, 1-methyl-2-pyrrolidone, or a mixture thereof, it is possible to more effectively reduce the decrease in coercive force at high temperatures.

  Specifically, as the organic solvent containing phosphoric acid, it is preferable to use 1-methyl-2-pyrrolidone containing phosphoric acid in a proportion of 10% by volume or more and 14% by volume or less. Even when exposed, high magnetic properties can be stably maintained.

[Phosphoric acid concentration]
The concentration of phosphoric acid in the organic solvent is 0.1% by volume or more and 20% by volume or less by volume. By adjusting an organic solvent containing phosphoric acid at such a concentration and pulverizing in the organic solvent to form a phosphate film, the coercive force decreases even in a high temperature environment such as bond magnet production. Can be suppressed. When the phosphoric acid concentration in the organic solvent is less than 0.1% by volume, it is impossible to form a film having good characteristics, and effectively suppresses the decrease in coercive force at room temperature due to exposure to a high temperature environment. I can't do it. On the other hand, when the phosphoric acid concentration exceeds 20% by volume, the phosphate film itself cannot be formed efficiently.

  Further, the concentration of phosphoric acid in the organic solvent is preferably a ratio of 2% by volume or more and 20% by volume or less, thereby obtaining a material having higher magnetic properties. Furthermore, it is particularly preferable that the phosphoric acid concentration in the organic solvent is a ratio of 10% by volume or more and 14% by volume or less, so that even if it is exposed to a high temperature environment, it has high magnetic properties. can get.

[PH]
When the iron-based magnet alloy powder is pulverized in an organic solvent, the pH of the organic solvent containing phosphoric acid is in the range of 1.5 to 8.0. When the pH is less than 1.5 or when the pH exceeds 8.0, a predetermined coercive force cannot be obtained in the obtained magnet alloy powder.

  The pH condition is preferably in the range of 4.0 to 5.0, particularly preferably in the range of 4.4 to 4.6. Thereby, a much higher coercive force can be obtained. In addition, although the academic reason that such an optimal pH range exists is not clear, it is guessed that the reaction mechanism of the film formation on the surface of the iron-based magnet alloy powder changes depending on the pH.

  Although it does not specifically limit as a preparation method of pH of an organic solvent, For example, it is preferable to adjust using any 1 type, or 2 or more types, such as phosphoric acid, a sulfuric acid, nitric acid. For example, by first adding phosphoric acid, the pH of the organic solvent is lowered to about 4.5, and then using one or more of phosphoric acid, sulfuric acid, and nitric acid to a predetermined pH. Add until For example, when two kinds of phosphoric acid and nitric acid are used until they are added to a predetermined pH, when about 85% by mass phosphoric acid and 60% by mass to 80% by mass nitric acid are used, The solvent will contain 10% or less by volume of water.

[Oxidant]
In the present embodiment, an oxidizing agent is added to the organic solvent at a predetermined ratio, and the iron-based magnet alloy powder is pulverized in the organic solvent.

  As an oxidizing agent, an aqueous solution containing the substance in a molar concentration of 0.01 mol / L to 1.0 mol / L is prepared, and a platinum electrode (the surface is a wet SiC paper with a roughness equivalent to 1500 polishing) is naturally added thereto. It is preferable that the electric potential when immersed is 0.6 V or more based on a silver / silver chloride reference electrode. In this measurement, the measurement is performed by connecting an aqueous solution containing an oxidant and the reference electrode with a salt bridge made of a saturated aqueous potassium chloride solution and agar.

  Specific examples of the oxidizing agent include, but are not limited to, nitric acid, potassium permanganate, and potassium dichromate. Among these, when nitric acid is used as the oxidizing agent, it is possible to more effectively suppress a decrease in coercive force of the magnet alloy powder at room temperature due to exposure to a high temperature environment. For this reason, it is preferable to use nitric acid as an oxidant when exposed to a particularly high temperature environment.

  The oxidizing agent changes the redox potential (ORP) of the organic solvent. Thus, by adding an oxidizing agent to an organic solvent and pulverizing the iron-based magnet alloy powder in an organic solvent containing the oxidizing agent in a predetermined ratio, the changed redox potential is involved in the film formation and obtained. The magnetic properties of the magnet alloy powder obtained can be improved.

  At this time, the addition amount of the oxidizing agent needs to be a ratio of 0.0001 mol / L to 1.0 mol / L. When the addition amount is less than 0.0001 mol / L, the oxidation-reduction potential of the organic solvent hardly changes, so that the magnetic properties cannot be effectively improved. On the other hand, the addition amount exceeds 1.0 mol / L, conversely, the magnetic properties are degraded. For this reason, the addition amount of the oxidizing agent is 0.0001 mol / L or more and 1.0 mol / L or less, preferably 0.001 mol / L or more and 0.8 mol / L or less, and more preferably 0.01 mol / L or more and 0.001 or less. 5 mol / L. In addition, the addition amount of the oxidizing agent mentioned above shows the content rate (molar concentration) to the organic solvent in the state which does not contain phosphoric acid.

≪2. Manufacture of bonded magnets using magnetic alloy powder >>
As described above, according to the method for manufacturing a magnet alloy powder according to the present embodiment, even when heated to a high temperature during the manufacturing process of a bonded magnet or when used as a bonded magnet, Magnet alloy powder that suppresses the decrease in coercive force can be obtained.

  Specifically, the method for producing a bonded magnet using the magnet alloy powder obtained by the above-described production method is not particularly limited. For example, the magnet alloy powder is mixed with a known thermoplastic resin or additive. The obtained bonded magnet composition can be produced by molding by injection molding, compression molding, extrusion molding, rolling molding, transfer molding or the like.

  The thermoplastic resin serves as a binder for the magnet alloy powder, and the type thereof is not particularly limited, and conventionally known ones can be used. For example, 6 nylon, 6,6 nylon, 11 nylon, 12 nylon, 6,12 nylon, aromatic nylon, polyamide resin such as modified nylon obtained by partially modifying these molecules, linear polyphenylene sulfide resin, cross-linked type Polyphenylene sulfide resin, semi-crosslinked polyphenylene sulfide resin, low density polyethylene, linear low density polyethylene resin, high density polyethylene resin, ultrahigh molecular weight polyethylene resin, polypropylene resin, ethylene-vinyl acetate copolymer resin, ethylene-ethyl acrylate copolymer Resin, ionomer resin, polymethylpentene resin, polystyrene resin, acrylonitrile-butadiene-styrene copolymer resin, acrylonitrile-styrene copolymer resin, polyvinyl chloride resin, polyvinylidene chloride resin, poly vinegar Vinyl resin, polyvinyl alcohol resin, polyvinyl butyral resin, polyvinyl formal resin, methacrylic resin, polyvinylidene fluoride resin, polytrifluoroethylene resin, tetrafluoroethylene-hexafluoropropylene copolymer resin, ethylene-tetrafluoroethylene Copolymer resin, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin, polytetrafluoroethylene resin, polycarbonate resin, polyacetal resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyphenylene oxide resin, polyallyl ether allyl sulfone resin, poly Ether sulfone resin, polyether ether ketone resin, polyarylate resin, aromatic polyester resin, cellulose acetate resin, each of the above resin-based elastomers And the like, random copolymers of these homopolymers and other species monomer, block copolymers, graft copolymers, and end groups modified products with other substances.

  In addition, lubricants such as paraffin waxes and liquid paraffins, hindered amine stabilizers, antioxidants such as phenols, phosphites, and thioethers as long as the properties of the magnetic alloy powder produced are not impaired. Such as stabilizers. A conventionally well-known additive can be mix | blended.

  The mixing method of the magnetic alloy powder and each component described above is not particularly limited, for example, a blender such as a ribbon blender, tumbler, nauter mixer, Henschel mixer, super mixer, or Banbury mixer, kneader, roll, It can be performed using a kneader such as a kneader ruder, a single screw extruder, or a twin screw extruder.

  Thus, the composition for bonded magnets can be obtained by mixing each component. In addition, as a shape of the composition for bonded magnets obtained, it is a powder form, a bead form, a pellet form, or the form of these mixtures, However, The pellet form is desirable from the point of the ease of handling.

  Next, the bonded magnet composition obtained as described above is heated and melted at the melting temperature of the thermoplastic resin, and then formed into a magnet having a desired shape. Examples of the molding method include various molding methods such as an injection molding method, an extrusion molding method, an injection compression molding method, an injection press molding method, and a transfer molding method. Among these molding methods, in particular, the injection molding method and the extrusion molding method. Method, injection compression molding, and injection press molding are preferred.

  Specifically, when forming a bonded magnet using the bonded magnet composition, it is formed by injection molding under conditions of a molding temperature of 200 ° C. to 300 ° C. and a mold temperature of 100 to 150 ° C., for example.

  Thus, the magnet alloy powder is exposed to a high temperature in the manufacturing process of the bonded magnet. However, according to the above-described method for producing a magnet alloy powder according to the present embodiment, even when heated to a high temperature, a decrease in coercive force at room temperature after heating can be suppressed, and magnetic characteristics can be stably provided. Can be maintained.

  Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

(1) Component Iron-based magnet alloy powder: Sm-Fe-N-based magnet alloy powder
(Average particle size 20 μm, manufactured by Sumitomo Metal Mining Co., Ltd.)
Phosphoric acid: 85% strength aqueous solution
(Product name: phosphoric acid, manufactured by Kanto Chemical Co., Inc.)
Nitric acid: 69-70% strength aqueous solution
(Product name: Nitric acid, manufactured by Kanto Chemical Co., Inc.)
Sulfuric acid: 95% sulfuric acid
(Product name: sulfuric acid, manufactured by Kanto Chemical Co., Inc.)

(2) Coercive force evaluation method The coercive force Hc of the magnet alloy powder was measured at room temperature with a vibrating sample magnetometer in accordance with the Bond Magnet Test Method Guidebook BMG-2002 of the Japan Bond Magnet Industry Association.

[Examples 1 to 18, Comparative Examples 1 to 6]
A 1% by mass aqueous sulfuric acid solution prepared by diluting a predetermined amount of phosphoric acid and sulfuric acid with a concentration of 95% for pH adjustment into 200 g of organic solvent 2-propanol (molecular weight: 60.1, relative dielectric constant: 18). And an organic solvent in which an aqueous nitric acid solution prepared by diluting nitric acid with a concentration of 69 to 70% as an oxidizing agent is added at a rate of 0.0001 to 2 mol / L is used as a grinding solvent. Prepared. To this pulverization medium, 100 g of Sm—Fe—N magnet alloy powder, which is an iron-based magnet alloy powder containing a rare earth element, was added and finely pulverized to a mean particle diameter of 2 μm using a medium stirring mill.

  The pulverized slurry was filtered with Nutsche and further replaced with 400 g of 2-propanol while washing away the remaining phosphoric acid. Subsequently, the obtained cake-like pulverized product was put into a mixer and dried in a vacuum at 150 ° C. for 2 hours and taken out.

  Table 1 below summarizes the types, pH, volume percent concentration of phosphoric acid, and molar concentration of nitric acid used to grind the iron-based magnet alloy powder. In addition, the molar concentration of nitric acid shows the content rate to the organic solvent in the state which does not contain phosphoric acid.

Further, the coercive force H _c1 at room temperature of the obtained magnet alloy powder was measured, and then the magnet alloy powder was heated in an electric furnace at 250 ° C. in a vacuum, and the magnet alloy powder recovered after cooling at room temperature The coercive force _Hc2 was measured. Table 1 below shows the coercive force reduction rate (1-H _c2 / H _c1 ) at this time.

[Examples 19 to 36, Comparative Examples 7 to 12]
Magnet alloy powder as in Examples 1 to 13 and Comparative Examples 1 to 6, respectively, except that 1-methyl-2-pyrrolidone (molecular weight: 99.14, relative dielectric constant: 32) was used as the organic solvent. The coercive force reduction rate was evaluated.

  As shown in Table 1, the magnet alloy powder obtained in the example can effectively suppress the decrease in coercive force at room temperature due to exposure to a high temperature environment as compared with the magnet alloy powder of the comparative example. I understand.

Claims (6)

A method for producing a magnet alloy powder by pulverizing an iron-based magnet alloy powder containing a rare earth element in an organic solvent containing phosphoric acid,
When pulverizing the iron-based magnet alloy powder,
As the organic solvent, 2-propanol or 1-methyl-2-pyrrolidone, or a mixture thereof is used.
The pH of the organic solvent containing phosphoric acid is 1.5 or more and 8.0 or less, the phosphoric acid concentration in the organic solvent is 0.1 vol% or more and 20 vol% or less, and an oxidizing agent is added in the organic solvent. The manufacturing method of the magnet alloy powder added by 0.0001 mol / L or more and 1.0 mol / L or less as a density | concentration of. The manufacturing method of the magnet alloy powder of Claim 1. The pH of the organic solvent containing the said phosphoric acid shall be 4.0 or more and 5.0 or less. The method for producing a magnet alloy powder according to claim 1, wherein nitric acid is added as the oxidizing agent. The method for producing a magnet alloy powder according to any one of claims 1 to 3, wherein an organic compound having a molecular weight of 100 or less is used as the organic solvent. The method for producing a magnet alloy powder according to claim 4, wherein an organic solvent having a relative dielectric constant of 10 to 50 is used as the organic solvent. The method for producing a magnet alloy powder according to claim 5 , wherein the organic solvent containing phosphoric acid includes 1-methyl-2-pyrrolidone containing phosphoric acid at a ratio of 10% by volume to 14% by volume.