Compound and bonded magnet

Abstract

This compound contains a magnetic powder, an epoxy resin, and imidazole. However, this compound does not contain a phenolic curing agent. The magnetic powder is an alloy containing samarium, iron, and nitrogen.

Description

Compound and bonded magnets

[0001] The present disclosure relates to compound and bonded magnets.

[0002] Sm—Fe—N permanent magnets (samarium-iron-nitrogen permanent magnets) can be produced from cheaper raw materials than other rare earth magnets such as Nd—Fe—B permanent magnets (neodymium-iron-boron permanent magnets), and they have excellent magnetic properties. However, the crystal structure of Sm—Fe—N permanent magnets is prone to deterioration at high temperatures (approximately 500°C), making it difficult to produce sintered magnets from them. Therefore, Sm—Fe—N permanent magnets are used as raw materials for anisotropic bonded magnets, which can be produced by heating at low temperatures (thermal curing of thermosetting resins mixed with magnet powder) at which the crystal structure is maintained.

[0003] The raw material for anisotropic bonded magnets is a compound containing magnet powder (numerous magnet particles consisting of permanent magnets) and a thermosetting resin (see Patent Document 1 below). In manufacturing anisotropic bonded magnets, the compound is fed into a mold. The compound in the mold is heated and compressed while a magnetic field generated by a coil is applied to the compound in the mold. After the compound is heated and compressed, an anisotropic bonded magnet made from the hardened compound is manufactured. Each magnet particle in the anisotropic bonded magnet (magnetic domains in each magnet particle) is magnetized and oriented along the magnetic field.

[0004] Patent No. 7298804

[0005] If the thermosetting resin in the molded body formed in the mold is not cured sufficiently, the molded body is likely to break when it is removed from the mold. Furthermore, if the thermosetting resin in the molded body is not cured sufficiently, it is difficult to increase the bulk density of the molded body, and it is also difficult to increase the residual magnetic flux density of the final bonded magnet. The longer the molded body is heated in the mold, the more rapidly the thermosetting resin in the mold is cured. Therefore, the longer the molded body is heated and compressed in the mold, the more likely it is that damage to the molded body will be suppressed, the more likely the bulk density of the molded body will increase, and the more likely the residual magnetic flux density of the bonded magnet will increase. However, the longer the molded body is heated and compressed in the mold, the lower the productivity of the bonded magnet.

[0006] An object of one aspect of the present invention is to provide a compound that hardens easily in a short time and increases the residual magnetic flux density of a bonded magnet produced from the compound, and a bonded magnet that includes a hardened product of the compound.

[0007] For example, the present invention relates to a compound according to any one of [1] to [7] below, and a bonded magnet according to [8] or [9] below.

[0008] [1] A compound comprising: a magnet powder that is an alloy containing samarium, iron, and nitrogen; an epoxy resin; and imidazole; and no phenol-based hardener.

[0009] [2] The compound according to [1], wherein the imidazole is at least one selected from the group consisting of 2-ethyl-4-methylimidazole, 2-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, and 1-aminopropyl-2-methylimidazole.

[0010] [3] The compound according to [1] or [2], wherein the epoxy resin is at least one selected from the group consisting of biphenyl-type epoxy resins, dicyclopentadiene-type epoxy resins, naphthalene-type epoxy resins, and cresol novolac-type epoxy resins.

[0011] [4] The compound according to any one of [1] to [3], wherein the phenolic curing agent is at least one selected from the group consisting of phenolic resins and phenolic novolac resins.

[0012] [5] The compound according to any one of [1] to [4], which is in the form of a powder, a tablet, or a paste.

[0013] [6] The compound according to any one of [1] to [5], which is a raw material for a bonded magnet.

[0014] [7] The compound according to any one of [1] to [5], which is a raw material for an anisotropic bonded magnet in which the magnetization direction of each of the plurality of magnetic particles that make up the magnetic powder is aligned.

[0015] [8] A bonded magnet comprising a cured product of the compound according to any one of [1] to [5].

[0016] [9] An anisotropic bonded magnet comprising a cured product of the compound according to any one of [1] to [5], wherein the magnetization direction of each of the plurality of magnetic particles constituting the magnetic powder is aligned.

[0017] According to one aspect of the present invention, there is provided a compound that hardens easily in a short time and that increases the residual magnetic flux density of a bonded magnet produced from the compound, and a bonded magnet that includes a hardened product of the compound.

[0018] FIG. 1 is a schematic cross-sectional view of a bonded magnet according to one embodiment of the present invention.

[0019] (Outline of Compound and Bonded Magnets) Preferred embodiments of the present invention will be described below with reference to the drawings. In the drawings, equivalent components are designated by equivalent reference numerals. The present invention is not limited to the following embodiments. X, Y, and Z shown in Figure 1 represent three coordinate axes that are orthogonal to one another.

[0020] The compound according to this embodiment includes magnet powder, epoxy resin, and imidazole, but does not include a phenolic curing agent. The compound may be referred to as a mixture including epoxy resin and imidazole, but not including a phenolic curing agent. The compound may consist only of magnet powder, epoxy resin, and imidazole. The compound may be in the form of a powder, tablet, or paste at room temperature (e.g., 20°C ± 15°C). The compound according to this embodiment may be a raw material for a bonded magnet (e.g., an anisotropic bonded magnet). The magnet powder is an alloy containing samarium (Sm), iron (Fe), and nitrogen (N). The magnet powder may be referred to as a plurality of magnet particles made of an alloy containing samarium, iron, and nitrogen. The alloy containing samarium, iron, and nitrogen may be referred to as a Sm-Fe-N permanent magnet. The Sm-Fe-N permanent magnet may have anisotropy. In other words, each magnet particle (magnetic domain within each magnet particle) constituting the magnet powder of the Sm-Fe-N permanent magnet can have an easy axis of magnetization (crystal axis) extending in one direction. Epoxy resin is a type of thermosetting resin. Imidazole may be a curing agent that hardens the epoxy resin when heated. For example, an addition reaction between the epoxy resin (epoxy group) and imidazole (nitrogen in the five-membered ring) may promote polymerization of the epoxy resin, polymerization or crosslinking between epoxy resins via imidazole. Imidazole is superior to other curing agents (e.g., phenolic curing agents) in that it can easily harden the epoxy resin in a shorter time. Some or all of the epoxy resin in the compound may be uncured (uncured epoxy resin). Some or all of the epoxy resin in the compound may be semi-cured (B-stage epoxy resin). Some of the epoxy resin in the compound may be uncured, and the remaining epoxy resin in the compound may be semi-cured. When the epoxy resin is thermally cured, the multiple magnet particles contained in the compound are bound together by the cured epoxy resin. In other words, the epoxy resin functions as a binding material (binder) that binds the multiple magnet particles that make up the magnet powder together.

[0021] The bonded magnet according to this embodiment includes a hardened compound. The bonded magnet may consist solely of a hardened compound. For example, as shown in FIG. 1, the bonded magnet according to this embodiment may be an anisotropic bonded magnet (2A) in which the magnetization direction m of each of the multiple magnetic particles 3 that make up the magnetic powder is aligned. However, the magnetization direction of each of the multiple magnetic particles in the bonded magnet does not have to be aligned.

[0022] Phenolic curing agents are well known as a typical example of conventional curing agents for curing epoxy resins. However, contrary to conventional wisdom, compounds containing imidazole but not a phenolic curing agent can be fully cured in a shorter time than compounds containing both a phenolic curing agent and an imidazole. Furthermore, compounds containing imidazole but not a phenolic curing agent can be fully cured in a shorter time than compounds containing a phenolic curing agent and a conventional curing agent other than imidazole (compounds without imidazole). For example, the conventional curing agent other than a phenolic curing agent and imidazole may be at least one curing agent selected from the group consisting of organic phosphoric acid, organic phosphate, organic boric acid, and organic borate. Furthermore, compounds containing imidazole but not a phenolic curing agent can be fully cured in a shorter time than conventional compounds containing a phenolic curing agent but not imidazole.

[0023] Because the compound according to the present embodiment contains imidazole but no phenolic curing agent, when the compound according to the present embodiment and a conventional compound are heated at the same temperature, the epoxy resin in the compound according to the present embodiment is likely to cure sufficiently in a shorter time than the epoxy resin in the conventional compound. As a result, the bulk density and mechanical strength of a bonded magnet (green body) formed from the compound according to the present embodiment are likely to be higher than those of a bonded magnet formed from a conventional compound. Since the remanence of a bonded magnet increases as the bulk density of a bonded magnet increases, the remanence of a bonded magnet formed from the compound according to the present embodiment is likely to be higher than those of a bonded magnet formed from a conventional compound. For example, when a bonded magnet (green body) is formed from the compound according to the present embodiment by heating and compressing it in a mold, the bulk density and mechanical strength of the bonded magnet formed in the mold are likely to be sufficiently high. As a result, damage and deformation of the bonded magnet that accompanies removal from the mold is suppressed, and the bulk density, mechanical strength, and residual magnetic flux density of the final bonded magnet are likely to be increased. Because the compound according to this embodiment hardens in a shorter time than conventional compounds, the time required to heat and compress the compound in the mold is shortened, the occurrence of defective products in the molding process is suppressed, and the yield rate of the bonded magnet is increased. As a result, the productivity of the bonded magnet is improved. Because the viscosity of phenolic curing agents tends to be higher than that of epoxy resins, conventional compounds containing phenolic curing agents are more difficult to mold than the compound according to this embodiment. Therefore, the bulk density, mechanical strength, and residual magnetic flux density of bonded magnets formed from conventional compounds containing phenolic curing agents tend to be lower than the bulk density, mechanical strength, and residual magnetic flux density of bonded magnets formed from the compounds according to this embodiment.

[0024] (Details of the Compound) <Resin Composition Comprising Epoxy Resin and Imidazole> In the present invention, the term "resin composition" refers to the remaining portion (non-volatile components) of the compound excluding the magnet powder. The resin composition contains at least an epoxy resin and imidazole, but does not contain a phenolic curing agent. The resin composition may further contain at least one component selected from the group consisting of a coupling agent, a wax (lubricant), a reactive diluent, and a flame retardant. The compound may further contain an organic solvent in addition to the magnet powder and the resin composition. The resin composition may consist only of an epoxy resin and imidazole. The compound may consist only of the magnet powder and the resin composition.

[0025] The resin composition containing epoxy resin and imidazole functions as a binder that binds together the magnet particles that make up the magnet powder. In other words, the resin composition imparts mechanical strength to the bonded magnet produced from the compound. For example, the resin composition filled between the magnet particles binds them together. Furthermore, when the resin composition is thermally cured, the cured resin composition binds the magnet particles together even more firmly.

[0026] The mass of the magnet powder in the compound may be expressed as Mm (unit: g). The mass of the entire resin composition in the compound may be expressed as Mr (unit: g). The content (unit: mass%) of the magnet powder in the compound may be defined as Mm / (Mm + Mr) × 100. The content (unit: mass%) of the resin composition (e.g., epoxy resin and imidazole) in the compound may be defined as Mr / (Mm + Mr) × 100. Because the bonded magnet produced from the compound tends to have high bulk density, mechanical strength, and residual magnetic flux density, the content of the magnet powder in the compound may be 90.0% by mass or more and 99.9% by mass or less, preferably 95.0% by mass or more and 99.5% by mass or less, and more preferably 96.0% by mass or more and 98.0% by mass or less. As the content of the magnetic powder increases, the bulk density and residual magnetic flux density of the anisotropic bonded magnet tend to increase. As the content of the magnetic powder decreases, the mechanical strength of the anisotropic bonded magnet tends to increase. The content of the resin composition in the compound may be 0.1% by mass or more and 10% by mass or less, preferably 0.5% by mass or more and 5% by mass or less, and more preferably 2% by mass or more and 4% by mass or less. For example, the total content of the epoxy resin and imidazole in the compound may be 0.1% by mass or more and 10% by mass or less, preferably 0.5% by mass or more and 5% by mass or less, and more preferably 2% by mass or more and 4% by mass or less. As the content of the resin composition decreases, the bulk density and residual magnetic flux density of the anisotropic bonded magnet tend to increase. As the content of the resin composition increases, the mechanical strength of the anisotropic bonded magnet tends to increase.

[0027] For example, the imidazole may be at least one compound selected from 2-ethyl-4-methylimidazole, 2-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole (4-methyl-2-phenylimidazole), 2-phenyl-4-methyl-5-hydroxymethylimidazole, 1-aminopropyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, and 1-cyanoethyl-2-phenylimidazole. Commercially available imidazole products include, for example, 2MZ-H ＴＭ , C11ZＴＭ , C17Z ＴＭ , 1, 2DMZ ＴＭ , 2E4MZ ＴＭ , 2PZPW ＴＭ , 2P4MZ ＴＭ , 1B2MZ ＴＭ , 1B2PZ ＴＭ , 2MZ-CN ＴＭ , C11Z-CN ＴＭ , 2E4MZ-CN ＴＭ , 2PZ-CN ＴＭ , C11Z-CNS ＴＭ , 2P4MHZ ＴＭ , TPZ ＴＭ , and SFZ ＴＭ (These are trade names of Shikoku Chemicals Corporation.)

[0028] The relative mass of imidazole to 100 parts by mass (100 g) of epoxy resin may be 0.1 to 30 parts by mass (0.1 g to 30 g), 1 to 15 parts by mass (1 g to 15 g), or 1 to 5 parts by mass (1 g to 5 g), because this allows the compound to cure quickly and the bonded magnet produced from the compound to have increased bulk density, mechanical strength, and residual magnetic flux density. As the relative mass of imidazole increases, the compound cures more quickly. As the relative mass of imidazole decreases, deterioration of the compound during storage (for example, thermal curing of the epoxy resin during storage of the compound) is more easily suppressed.

[0029] The resin composition may contain one or more capsules (microcapsules) encapsulating at least a portion of the imidazole. For example, the capsules may be made of an organic compound (polymer). When the resin composition contains one or more capsules encapsulating at least a portion of the imidazole, contact and reaction between the imidazole and the epoxy resin is suppressed during storage of the compound, thereby easily suppressing deterioration of the compound during storage (e.g., thermal curing of the epoxy resin during storage of the compound). In other words, when the resin composition contains one or more capsules encapsulating at least a portion of the imidazole, the storage stability of the compound is improved, allowing the compound to be stored for a long period of time. All of the imidazole contained in the resin composition may be encapsulated in one or more capsules. A portion of the imidazole contained in the resin composition may be encapsulated in one or more capsules, and the remaining imidazole contained in the resin composition may not be encapsulated. The capsules may rupture or liquefy upon heating or compression of the compound during the molding process. For example, the capsule may burst due to thermal expansion of the imidazole during the molding process. For example, the capsule may burst due to pressure being applied to the capsule during the molding process. As the capsule bursts or liquefies during the molding process, the imidazole may seep out from the inside of the capsule to the outside of the capsule.

[0030] In addition to the imidazole, the compound may further contain a curing accelerator, for example, at least one compound selected from the group consisting of tetra-substituted phosphonium tetra-substituted borates, aliphatic polyamines, polyaminoamides, polymercaptans, aromatic polyamines, acid anhydrides, and dicyandiamide (DICY).

[0031] For example, the epoxy resin may be one having two or more epoxy groups in one molecule. From the viewpoint of improving the heat resistance (mechanical strength at high temperatures) of the bonded magnet, the epoxy resin is preferably a heat-resistant epoxy resin such as a naphthalene-type epoxy resin.

[0032] Examples of epoxy resins include biphenyl-type epoxy resins, stilbene-type epoxy resins, diphenylmethane-type epoxy resins, sulfur-containing epoxy resins, novolac-type epoxy resins, dicyclopentadiene-type epoxy resins, salicylaldehyde-type epoxy resins, naphthalene-type epoxy resins, naphthol- and phenol-copolymerized epoxy resins, epoxidized aralkyl-type phenolic resins, bisphenol-type epoxy resins, glycidyl ether-type epoxy resins of alcohols, glycidyl ether-type epoxy resins of paraxylylene-modified phenolic resins and / or metaxylylene-modified phenolic resins, and glycidyl ether-type epoxy resins of terpene-modified phenolic resins. The epoxy resin may be at least one selected from the group consisting of phenolic resins, cyclopentadiene-type epoxy resins, glycidyl ether-type epoxy resins of polycyclic aromatic ring-modified phenolic resins, glycidyl ether-type epoxy resins of naphthalene ring-containing phenolic resins, glycidyl ester-type epoxy resins, glycidyl or methylglycidyl-type epoxy resins, alicyclic epoxy resins, halogenated phenol novolac-type epoxy resins, cresol novolac-type epoxy resins (orthocresol novolac-type epoxy resins), hydroquinone-type epoxy resins, trimethylolpropane-type epoxy resins, and linear aliphatic epoxy resins obtained by oxidizing olefin bonds with a peracid such as peracetic acid. Examples of highly crystalline epoxy resins that may be used include hydroquinone-type epoxy resins, bisphenol-type epoxy resins, thioether-type epoxy resins, and biphenyl-type epoxy resins.

[0033] At least a portion of the epoxy resin may be a naphthalene-type epoxy resin having a naphthalene structure. Naphthalene-type epoxy resins are solid at room temperature. When the compound contains a naphthalene-type epoxy resin, the bonded magnet tends to have high mechanical strength at room temperature and high temperatures. For example, the naphthalene-type epoxy resin may be at least one epoxy resin selected from the group consisting of naphthalene diepoxy compounds, naphthylene ether-type epoxy resins, naphthalene novolac-type epoxy resins, methylene-bonded dimers of naphthalene diepoxy compounds, and methylene-bonded dimers of naphthalene monoepoxy compounds and naphthalene diepoxy compounds.

[0034] For example, the naphthalene-type epoxy resin is preferably at least one of a trifunctional epoxy resin and a tetrafunctional epoxy resin. The naphthalene-type epoxy resin is more preferably a tetrafunctional epoxy resin. When the naphthalene-type epoxy resin contained in the compound is at least one of a trifunctional epoxy resin and a tetrafunctional epoxy resin, the naphthalene-type epoxy resins are three-dimensionally crosslinked with each other as the compound is heated during the molding process, forming a strong crosslinked network. As a result, the movement of the naphthalene-type epoxy resin in the bonded magnet is suppressed at high temperatures. In other words, the glass transition temperatures of the trifunctional epoxy resin and the tetrafunctional epoxy resin are higher than the glass transition temperature of the difunctional epoxy resin. Therefore, when the naphthalene-type epoxy resin contained in the compound is at least one of a trifunctional epoxy resin and a tetrafunctional epoxy resin, the bonded magnet is likely to have high mechanical strength at high temperatures, and changes in the orientation direction of the magnet powder due to temperature increases are likely to be suppressed.

[0035] For example, a trifunctional naphthalene type epoxy resin or a tetrafunctional naphthalene type epoxy resin is HP-4700 manufactured by DIC Corporation. ＴＭ , HP-4710 ＴＭ , HP-4770 ＴＭ , EXA-5740 ＴＭ , or EXA-7311-G4 ＴＭ The naphthalene type epoxy resin contained in the compound may be a bifunctional epoxy resin. An example of a bifunctional naphthalene type epoxy resin is HP-4032. ＴＭ Or HP-4032D ＴＭ The naphthalene type epoxy resin contained in the compound powder may be a β-naphthol type epoxy resin.

[0036] The compound may contain one of the above epoxy resins. The compound may contain multiple of the above epoxy resins.

[0037] The phenol-based curing agent not included in the compound according to this embodiment may be at least one selected from the group consisting of phenolic resins and phenolic novolac resins.

[0038] For example, the phenolic resin not contained in the compound may be at least one selected from the group consisting of aralkyl-type phenolic resins, dicyclopentadiene-type phenolic resins, salicylaldehyde-type phenolic resins, novolac-type phenolic resins, copolymerized phenolic resins of benzaldehyde-type phenols and aralkyl-type phenols, paraxylylene- and / or metaxylylene-modified phenolic resins, melamine-modified phenolic resins, terpene-modified phenolic resins, dicyclopentadiene-type naphthol resins, cyclopentadiene-modified phenolic resins, polycyclic aromatic ring-modified phenolic resins, biphenyl-type phenolic resins, and triphenylmethane-type phenolic resins. The phenolic resin not contained in the compound may be a copolymer composed of two or more of the above phenolic resins.

[0039] For example, the phenolic novolac resin not included in the compound may be a resin obtained by condensing or co-condensing phenols and / or naphthols with aldehydes under an acidic catalyst. The phenols constituting the phenolic novolac resin not included in the compound may be at least one selected from the group consisting of phenol, cresol, xylenol, resorcinol, catechol, bisphenol A, bisphenol F, phenylphenol, and aminophenol. For example, the naphthols constituting the phenolic novolac resin not included in the compound may be at least one selected from the group consisting of α-naphthol, β-naphthol, and dihydroxynaphthalene. The aldehydes constituting the phenolic novolac resin not included in the compound may be at least one selected from the group consisting of formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde, and salicylaldehyde.

[0040] For example, the coupling agent may be any coupling agent that reacts with glycidyl groups contained in resin compositions such as epoxy resins (epoxy compounds). The coupling agent improves adhesion between the magnet particles and the resin composition, thereby improving the mechanical strength of the bonded magnet. The coupling agent that reacts with glycidyl groups may be, for example, a silane-based compound (silane coupling agent). For example, the silane coupling agent may be at least one selected from the group consisting of epoxy silane, mercapto silane, amino silane, alkyl silane, ureido silane, acid anhydride silane (e.g., silane with a succinic anhydride group), methacryl silane, and vinyl silane. The compound may contain one of the above coupling agents. The compound may also contain multiple of the above coupling agents.

[0041] For example, the wax may be at least one composition selected from the group consisting of synthetic wax, saturated fatty acid, saturated fatty acid salt, and saturated fatty acid ester. During the molding process described below, the wax's lubricity allows the magnet particles to slide easily against each other, allowing each magnet particle to rotate in a magnetic field, and aligning the easy axis of magnetization of the magnetic domains within each magnet particle along the magnetic field. In other words, each magnet particle is likely to be oriented so that its magnetization direction is approximately parallel to the magnetic field. As a result, the remanence of the bonded magnet is likely to be improved. For example, the wax may be at least one wax selected from the group consisting of polyethylene wax, amide wax, and montan wax. Among the waxes listed above, montan wax (montan acid ester) is preferred because it lubricates the magnet powder during the molding process, allowing each magnet particle to rotate in a magnetic field, and improving the orientation of the magnet powder. The compound may contain one of the waxes listed above. The compound may also contain multiple of the waxes listed above.

[0042] For example, the reactive diluent may be at least one of a monoepoxy compound and a diepoxy compound. The reactive diluent may be a monofunctional epoxy resin. The reactive diluent may be, for example, at least one selected from the group consisting of alkyl monoglycidyl ether, alkyl phenol monoglycidyl ether, and alkyl diglycidyl ether. By diluting the epoxy resin with the reactive diluent, the melt viscosity of the resin composition during the molding process can be easily adjusted to a desired low value. As a result, the compound flows easily within the mold, the compound is easily filled into the mold without gaps, the magnetic powder is easily packed densely within the bonded magnet, and the magnetization direction of each magnetic particle is easily aligned along the magnetic field during the molding process. As a result, the bulk density, mechanical strength, and residual magnetic flux density of the bonded magnet produced from the compound are easily increased.

[0043] To improve the recyclability, moldability, and cost of the compound, the resin composition may contain a flame retardant. For example, the flame retardant may be at least one compound selected from the group consisting of bromine-based flame retardants, phosphorus-based flame retardants, hydrated metal compound-based flame retardants, silicone-based flame retardants, nitrogen-containing compounds, hindered amine compounds, organometallic compounds, and aromatic engineering plastics. The compound may contain one or more of the above flame retardants.

[0044] The compound may further contain another thermosetting resin in addition to the epoxy resin. For example, the compound may further contain at least one thermosetting resin selected from the group consisting of maleimide compounds, polyimides, polyamides, and polyamideimides. A part or all of the thermosetting resin in the compound may be uncured (uncured thermosetting resin). A part or all of the thermosetting resin in the compound may be semi-cured (B-stage thermosetting resin). A part of the thermosetting resin in the compound may be uncured, and the remaining part of the thermosetting resin in the compound may be semi-cured.

[0045] The resin composition may contain, in addition to the thermosetting resin, other resins such as a thermoplastic resin, etc. For example, the resin composition may further contain at least one other resin selected from the group consisting of a polyphenylene sulfide resin, an acrylic resin, a methacrylic resin, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyethylene terephthalate, and a silicone resin.

[0046] <Magnet Powder> As described above, the magnet powder is a powder containing an Sm—Fe—N system permanent magnet (SmFeN powder). For example, the SmFeN powder contains Sm as the main phase. ２ Fe １７ N ３ For example, at least a part of the SmFeN powder may contain Th ２ An anisotropic magnet powder containing Zn-type crystals (rhombohedral crystals) as the main phase may be used. An anisotropic magnet powder is a magnet powder in which the individual magnet particles constituting the magnet powder are single crystals, or a magnet powder in which the individual magnet particles constituting the magnet powder are composed of a large number of fine single crystal grains (magnetic domains), and the magnetization easy axis of each crystal grain is aligned in a specific direction. For example, at least a portion of the SmFeN powder is TbCu ７ The compound may be an isotropic magnet powder containing a hexagonal crystal as the main phase. Isotropic magnet powder is a magnet powder in which the individual magnet particles constituting the magnet powder are composed of a large number of fine single crystal grains (magnetic domains), and the orientation of the easy axis of magnetization of each crystal grain is disordered. In addition to the magnet powder made of an Sm—Fe—N permanent magnet, the compound may further contain powder made of another permanent magnet.

[0047] The method for producing the SmFeN powder is not limited. For example, the method for producing the SmFeN powder may include a step of forming an alloy powder containing Sm and Fe by mechanical alloying, and a step of obtaining the SmFeN powder by heating the alloy powder in nitrogen gas. The SmFeN powder may also be produced by a rapid solidification method. In the rapid solidification method, a molten alloy is supplied to the surface of a rotating water-cooled roll. As a result, the molten alloy is rapidly cooled and solidified on the surface of the water-cooled roll. The solidified alloy is pulverized to obtain the SmFeN powder. Alternatively, the SmFeN powder may be produced by an HDDR (Hydrogenation Disproportion Desorption Recombination) method.

[0048] The SmFeN powder may be, for example, a non-pulverized powder (spherical magnet powder) obtained by the build-up method of Nichia Corporation. The surface of each magnet particle constituting the SmFeN powder may be coated with an inorganic film by surface treatment. For example, the inorganic film may contain a phosphate or a silica-based compound.

[0049] Average particle size or median diameter d of SmFeN powder ５０ The average particle size or median diameter d of the SmFeN powder is preferably 0.5 μm or more and 100 μm or less, more preferably 1 μm or more and 10 μm or less, and even more preferably 2 μm or more and 3 μm or less. ５０ can be measured by a laser diffraction particle size distribution analyzer.

[0050] (Method for manufacturing the compound) The compound is obtained by mixing the magnet powder with a resin composition containing an epoxy resin and imidazole. The mass of the magnet powder and the mass of each component constituting the resin composition are adjusted to match the composition of the compound described above.

[0051] First, a resin solution is prepared by uniformly stirring and mixing a resin composition containing at least an epoxy resin and imidazole in an organic solvent. In addition to the epoxy resin and imidazole, the resin solution may further contain one or more components selected from the group consisting of a curing accelerator, a coupling agent, a wax, a reactive diluent, a flame retardant, and an organic solvent. The organic solvent is not particularly limited as long as it is a liquid that dissolves the resin composition. For example, the organic solvent may be at least one solvent selected from the group consisting of acetone, N-methylpyrrolidinone (N-methyl-2-pyrrolidone), γ-butyrolactone, dimethylformamide, dimethyl sulfoxide, methyl ethyl ketone, methyl isobutyl ketone, toluene, and xylene.

[0052] The resin solution and the magnet powder may be stirred and mixed to obtain a compound. That is, the mixture (paste) of the resin solution and the magnet powder may be used as the compound.

[0053] After stirring and mixing the resin solution and magnet powder, the organic solvent is removed from the resin solution to obtain a powder consisting of magnet powder and a resin composition. The powder consisting of magnet powder and a resin composition may be used as a compound. A powder obtained by pulverizing a mixture (lump) consisting of magnet powder and a resin composition may also be used as a compound. As the organic solvent is removed from the resin solution, the resin composition adheres to the surface of each magnet particle that constitutes the magnet powder. The resin composition may adhere to the entire surface of each magnet particle. The resin composition may also adhere to only a portion of the surface of each magnet particle. The method for removing the organic solvent from the resin solution is not particularly limited. For example, the organic solvent may be removed from the resin solution by drying the mixture of the resin solution and magnet powder. For example, the method for drying the resin solution may be vacuum drying.

[0054] A compound may be obtained by further mixing the mixture of magnet powder and resin composition with wax.

[0055] The compound may be compression molded to produce a tablet made of the compound. The tablet made of the compound may be used as a raw material for a bonded magnet. The size and shape of the tablet are not particularly limited. For example, the tablet may be cylindrical.

[0056] (Method for manufacturing a bonded magnet) The method for manufacturing a bonded magnet (anisotropic bonded magnet) according to this embodiment includes at least a supplying step and a molding step. The method for manufacturing a bonded magnet may further include a cooling step, a demagnetizing step, a thermal hardening step, and a magnetizing step following the supplying step and the molding step. Each step will be described in detail below.

[0057] <Feeding Step> In the feeding step, the compound is fed into the mold (cavity). The temperature of the compound itself fed into the mold may be room temperature. The compound fed into the mold may be in the form of a powder, tablet, or paste.

[0058] <Molding Process> In the molding process, the compound in the mold is compressed while a magnetic field is applied to the compound in the mold heated to the molding temperature T. Each magnetic particle in the compound is magnetized and rotated by the magnetic field H, and the easy axis of magnetization of the magnetic domain in each magnetic particle is oriented along the magnetic field. In other words, each magnetic particle 3 in the compound 2 is oriented so that the magnetization direction m of each magnetic particle 3 is approximately parallel to the magnetic field H (see Figure 1). When each magnetic particle 3 is a single crystal grain (single magnetic domain), the magnetization direction m of each magnetic particle 3 is the same as the direction in which the easy axis of magnetization of each magnetic particle 3 extends. The molding temperature T may be equal to or higher than the thermosetting temperature of the resin composition 5 containing the epoxy resin and imidazole. The thermosetting temperature may be rephrased as the temperature at which the thermosetting of the epoxy resin begins. By thermally curing the resin composition 5 in the molding process, a molded body 2A is formed that includes the magnetic powder (plurality of magnetic particles 3) oriented along the magnetic field H and a cured product of the resin composition 5 (epoxy resin). In other words, a molded body 2A is formed that is made of a cured product of the compound 2. The magnetization direction M of the entire molded body 2A becomes approximately or completely parallel to the direction of the magnetic field H applied to the compound in the molding process.

[0059] The compact 2A may be a completed anisotropic bonded magnet. The magnetization direction of the entire anisotropic bonded magnet is approximately or completely parallel to the direction of the magnetic field H applied to the compound in the molding process, the magnetization direction M of the entire compact 2A, and the magnetization direction m of each magnetic particle 3 in the bonded magnet. The anisotropic bonded magnet can have a high remanence due to the excellent orientation of the magnetic powder. Furthermore, the mechanical strength and remanence of the anisotropic bonded magnet are increased due to the compression of the compound in the molding process (i.e., the increase in the filling rate of the magnetic powder in the compact) and the thermal hardening of the compound.

[0060] For example, the molding temperature T may be 80°C or higher and 180°C or lower, preferably 120°C or higher and 150°C or lower. When the molding temperature T is above the lower limit, the compound according to the present embodiment tends to cure in a shorter time than conventional compounds that do not contain imidazole or conventional compounds that contain phenolic curing agents. Therefore, the bulk density, mechanical strength, and residual magnetic flux density of the bonded magnet formed from the compound according to the present embodiment tend to be higher than those of conventional compounds. When the molding temperature T exceeds the upper limit, the compound tends to cure too quickly during the molding process, leaving too little time for the rotation and orientation of the magnetic particles in the compound. As a result, it becomes difficult for the magnetic particles in the compound to orient themselves so that their magnetization direction is parallel to the magnetic field, and the residual magnetic flux density of the bonded magnet tends to decrease. Furthermore, if the molding temperature T exceeds the above upper limit, the compound during the molding process tends to harden too quickly, making it difficult for the compound to flow within the mold (cavity), making it difficult for the magnetic powder in the bonded magnet to be densely packed, and making it difficult for the compound to be packed into the mold (cavity) without gaps. As a result, the bulk density, mechanical strength, and residual magnetic flux density of the bonded magnet tend to decrease. If the molding temperature T is too high, the Sm—Fe—N permanent magnet is likely to deteriorate, and the residual magnetic flux density and coercive force of the bonded magnet tend to decrease.

[0061] For example, the time (molding time t) during which the compound in the mold is heated at molding temperature T may be 0.5 minutes or more and 15 minutes or less. Molding time t may be rephrased as the time required for the compound in the mold to sufficiently (or completely) harden. When molding time t is equal to or greater than the above-mentioned lower limit, the compound according to the present embodiment hardens more easily than conventional compounds that do not contain imidazole or conventional compounds that contain phenolic curing agents, and the bulk density, mechanical strength, and residual magnetic flux density of the bonded magnet formed from the compound according to the present embodiment are likely to be higher than those of the bonded magnet formed from the conventional compounds. Even when molding time t is equal to or less than the above-mentioned upper limit (i.e., even when molding time t is short), the bulk density, mechanical strength, and residual magnetic flux density of the bonded magnet formed from the compound according to the present embodiment are likely to be higher than those of the bonded magnet formed from the conventional compounds. In other words, when the molding time t is below the upper limit value mentioned above, the bulk density, mechanical strength, and residual magnetic flux density of bonded magnets formed from conventional compounds tend to be lower than those of bonded magnets formed from the compound according to this embodiment.

[0062] For example, the pressure (molding pressure) acting on the compound in a mold heated at molding temperature T may be 500 MPa or more and 2000 MPa or less, preferably 700 MPa or more and 2000 MPa or less, and more preferably 980 MPa or more and 2000 MPa or less. The molding pressure may be rephrased as the pressure exerted by the mold on the compound in the mold.

[0063] In the molding process, application of a magnetic field to the compound in the mold may be started before the mold is heated or before the temperature of the heated mold reaches the molding temperature T. In the molding process, application of a magnetic field to the compound in the mold may be started simultaneously with compression of the compound in the mold. Application of a magnetic field to the compound in the mold may be started earlier than compression of the compound in the mold. In the molding process, application of a magnetic field to the compound in the mold may be stopped simultaneously with the molding pressure reaching a maximum value. Application of a magnetic field to the compound in the mold may be stopped simultaneously with the completion of compression of the compound in the mold.

[0064] The magnetic field applied to the compound in the mold may be a static magnetic field (a continuous, constant magnetic field). The magnetic field may also be a pulsed magnetic field (a pulsed magnetic field). For example, the strength of the static magnetic field may be 0.5 T (tesla) or more and 2.5 T or less, preferably 1.0 T or more and 2.5 T or less, and more preferably 2.0 T or more and 2.5 T or less. For example, the time for which the static magnetic field is applied to the compound in the mold may be 0.08 minutes or more and 4 minutes or less, preferably 0.5 minutes or more and 4 minutes or less, and more preferably 1 minute or more and 4 minutes or less. For example, the strength of the pulsed magnetic field may be 4 T or more and 12 T or less, or 8 T or more and 12 T or less. The pulsed magnetic field may be applied to the compound once or multiple times.

[0065] <Cooling Process> After the molding process, a cooling process may be further carried out. In the cooling process, the mold containing the green body (bonded magnet) is cooled. For example, in the cooling process, the mold containing the green body may be cooled to room temperature. For example, the method for cooling the mold containing the green body may be natural cooling. In the cooling process, it is not necessary to apply a magnetic field to the green body in the mold. However, a magnetic field may be applied to the green body in the mold in the cooling process. The green body (bonded magnet) in the mold is more likely to solidify through the cooling process. As a result, the mechanical strength of the green body in the mold is increased, and deformation and breakage of the green body in each process after the cooling process are suppressed, making it easier to increase the mechanical strength of the bonded magnet.

[0066] <Demagnetization Step> A demagnetization step may be further performed after the molding step. The demagnetization step may be performed after the cooling step. The demagnetization step may be performed simultaneously with the cooling step. In the demagnetization step, a magnetic field (reverse magnetic field) having a direction opposite to that of the magnetic field H used in the molding step is applied to the molded body, thereby demagnetizing the molded body. Demagnetizing the molded body suppresses deformation of the molded body due to the magnetic force of the molded body itself. For example, deformation of the molded body due to the magnetic force of the molded body itself is a phenomenon in which each magnetic particle located near the surface of the molded body protrudes from the surface of the molded body together with the resin composition, and one or more protrusions containing the magnetic particles and the resin composition are formed on the surface of the molded body. When the demagnetization step is performed while the molded body is housed in a mold, deformation and damage of the molded body that accompanies removal from the mold are suppressed. In other words, the molded body may be removed from the mold after the demagnetization step. After the molding step or the cooling step, the molded body removed from the mold may be demagnetized using a separate magnetic field application device. When the demagnetization step is performed, it is preferable to perform the magnetization step described below.

[0067] <Thermal curing step> After the molding step, cooling step, or demagnetizing step, a thermal curing step may be further carried out. In the thermal curing step, the molded body is heated to a temperature equal to or higher than the thermal curing temperature of the epoxy resin. As a result, the thermal curing of the epoxy resin in the molded body progresses further, and the bulk density, mechanical strength, and residual magnetic flux density of the molded body (bonded magnet) tend to be further increased.

[0068] <Magnetic Processing> After the demagnetization processing, a magnetic processing may be further performed. After the demagnetization processing and the subsequent thermal curing processing, a magnetic processing may be further performed. In the magnetic processing, a magnetic field in the same direction as the magnetic field used in the molding processing may be applied to the compact. As a result, the compact is magnetized and becomes an anisotropic bonded magnet again.

[0069] (Analysis Method) In order to analyze and identify the composition of a bonded magnet, a sample obtained by pulverizing the bonded magnet may be analyzed. In order to analyze and identify the composition of the compound itself retroactively from the bonded magnet, a sample obtained by pulverizing the bonded magnet may be analyzed. Furthermore, the sample obtained by pulverization may be dissolved in an organic solvent, and the magnetic powder that makes up the sample may be separated from the resin composition dissolved in the organic solvent. The separated resin composition and magnetic powder may each be analyzed individually. In the case where the composition of an uncured compound is analyzed and identified, the compound may also be dissolved in an organic solvent, and the magnetic powder may be separated from the resin composition dissolved in the organic solvent. The separated resin composition and magnetic powder may each be analyzed individually. For example, each component (such as the epoxy resin and imidazole) constituting the resin composition may be analyzed and identified by one or more analytical methods selected from the group consisting of infrared spectroscopy (IR), nuclear magnetic resonance (NMR), mass spectrometry (MS), gas chromatography (GC), and high performance liquid chromatography (HPLC). For example, the magnet powder may be analyzed and characterized by one or more analytical methods selected from the group consisting of X-ray fluorescence analysis (XRF), inductively coupled plasma (ICP) emission spectroscopy, photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS or EDX), and mass spectroscopy. The remanence Br1 of the bonded magnet and the remanence Br2 of the magnet powder itself may satisfy the following formula 1: Br1 = Br2 × (V2 / V1) × D (1) V1 in formula 1 is the volume of the entire bonded magnet. V2 in Equation 1 is the volume of the magnetic powder itself contained in the bonded magnet.V2 / V1 corresponds to the filling rate of the magnetic powder in the bonded magnet. D in Equation 1 is the degree of orientation of the magnetic powder in the bonded magnet. Based on Equation 1 above, the degree of orientation D is expressed as Br1 / {Br2 x (V2 / V1)}. In other words, the degree of orientation D can be determined based on measurements of Br1, Br2, V1, and V2. A high degree of orientation means that the easy axis of magnetization in each magnetic particle that makes up the magnetic powder contained in the bonded magnet is aligned. In other words, a high degree of orientation means that the magnetization direction of each magnetic particle that makes up the magnetic powder contained in the bonded magnet is aligned. For example, the degree of orientation D (unit: %) of the magnetic powder in the bonded magnet may be 80% or more and 100% or less.

[0070] The present invention is not necessarily limited to the above-described embodiments. Various modifications of the present invention are possible without departing from the spirit of the present invention, and these modifications are also included in the present invention.

[0071] The present invention will be described in detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples.

[0072] (Example 1) A compound (powder) of Example 1 was prepared by mixing magnet powder, epoxy resin, a coupling agent, and one type of imidazole in a plastic bottle for 1 hour. The capacity of the plastic bottle was 500 ml. The magnet powder was Sm ２ Fe １７ N ３ The mass of the magnet powder was 100 g. The epoxy resin used was a biphenyl-type epoxy resin (YX-4000H manufactured by Mitsubishi Chemical Corporation). ＴＭ The mass of the epoxy resin was 3.5 g. As a type of imidazole, 2-ethyl-4-methylimidazole (2E4MZ manufactured by Shikoku Chemical Industry Co., Ltd.) was used. ＴＭ）was used. The relative mass (unit: parts by mass) of 2-ethyl-4-methylimidazole to 100 parts by mass of epoxy resin was 1 part by mass. Hereinafter, the relative mass of 2-ethyl-4-methylimidazole to 100 parts by mass of epoxy resin will be expressed as "MI". The unit of "MI" may also be phr (per hundred resin). As a coupling agent, N-phenyl-3-aminopropyltrimethoxysilane (KBM-573 manufactured by Shin-Etsu Chemical Co., Ltd.) was used. ＴＭ The mass of the coupling agent was 0.6 g.

[0073] An anisotropic bonded magnet was produced from the compound of Example 1 by the following method.

[0074] In the feeding step, approximately 2 g of compound was fed into the mold of the molding device. The shape of the mold (cavity) was cubic, and the capacity of the mold (cavity) was 7 mm x 7 mm x 7 mm. The molding device (hydraulic press) was TM-MPH10525-10A2TM manufactured by Tamagawa Seisakusho Co., Ltd. ＴＭ was used.

[0075] In the molding process, the compound in the mold was compressed while a static magnetic field was applied to the compound in the mold heated to molding temperature T. The molding temperature T is shown in Table 1 below. The time (molding time t, unit: minutes) for which the compound in the mold was heated at molding temperature T is also shown in Table 1 below. The strength of the static magnetic field was maintained at 2.5 T. The pressure (molding pressure) acting on the compound in the mold heated to molding temperature T was maintained at 1800 MPa. A bonded magnet was formed from the compound through the above molding process. The dimensions of the bonded magnet were 7 mm length x 7 mm width x 7 mm height. In other words, the bonded magnet was cubic.

[0076] In the cooling step following the molding step, the mold containing the bonded magnet was cooled to room temperature by natural cooling. After the cooling step, the bonded magnet was removed from the mold.

[0077] (Examples 2 to 6) The relative mass MI of 2-ethyl-4-methylimidazole used in each of Examples 2 to 6 was the value shown in Table 1 below. The molding temperature T for each of Examples 2 to 6 was the value shown in Table 1 below. The molding time t for each of Examples 2 to 6 was the value shown in Table 1 below. The compound and bonded magnets for each of Examples 2 to 6 were produced in the same manner as Example 1, except for the above-mentioned points.

[0078] Comparative Example 1 No 2-ethyl-4-methylimidazole was used as a raw material for the compound of Comparative Example 1. No curing agent or curing accelerator was used as a raw material for the compound of Comparative Example 1. Except for this, the compound and bonded magnet of Comparative Example 1 were produced in the same manner as in Example 1.

[0079] Comparative Example 2 2-ethyl-4-methylimidazole was not used as a raw material for the compound of Comparative Example 2. Tetra(n-butyl)phosphonium tetraphenylborate (Bu ) was used as a raw material for the compound of Comparative Example 2 instead of 2-ethyl-4-methylimidazole. ４ P ＋ B (Ph) ４ － Tetra(n-butyl)phosphonium tetraphenylborate was used. PX-4PB manufactured by Nippon Chemical Industry Co., Ltd. ＴＭ The relative mass of tetra(n-butyl)phosphonium tetraphenylborate to 100 parts by mass of epoxy resin was 4.8 parts by mass. The molding time t of Comparative Example 2 was the value shown in Table 1 below. The compound and bonded magnet of Comparative Example 2 were produced in the same manner as in Example 1, except for the above points.

[0080] Comparative Example 3 In addition to 2-ethyl-4-methylimidazole, a phenol-based curing agent was used as the raw material for the compound of Comparative Example 2. The phenol-based curing agent was a phenol novolak resin (HP-850N manufactured by Resonac Co., Ltd.). ＴＭ) The relative mass of 2-ethyl-4-methylimidazole to 100 parts by mass of epoxy resin was 2 parts by mass. The relative mass of phenolic curing agent to 100 parts by mass of epoxy resin was 56 parts by mass. The molding time t of Comparative Example 3 was the value shown in Table 1 below. The compound and bonded magnet of Comparative Example 3 were produced in the same manner as in Example 1, except for the above-mentioned points.

[0081] <Removal of Bonded Magnet from Mold / Mechanical Strength of Bonded Magnet> In all of Examples 1 to 6 and Comparative Examples 2 and 3, the bonded magnets were not damaged or deformed when removed from the mold. In other words, in all of Examples 1 to 6 and Comparative Examples 2 and 3, the bonded magnets formed within the mold were sufficiently hardened, and had sufficiently high mechanical strength. In contrast, in Comparative Example 1, the bonded magnets formed within the mold were not sufficiently hardened, and the mechanical strength of the bonded magnets formed within the mold was significantly low. As a result, the bonded magnets of Comparative Example 1 were significantly damaged and deformed when removed from the mold, making it impossible to measure the bulk density and residual magnetic flux density of the bonded magnets of Comparative Example 1.

[0082] <Measurement of bulk density> The mass of each bonded magnet was measured using an electronic balance. The volume of each bonded magnet was calculated from the dimensions of the bonded magnet. The bulk density (unit: g / cm) of each bonded magnet was calculated by dividing the mass of each bonded magnet by the volume of each bonded magnet. ３ The bulk density of each of the bonded magnets of Examples 1 to 6 and Comparative Examples 2 and 3 is shown in Table 1 below.

[0083] <Measurement of Residual Magnetic Flux Density> The residual magnetic flux density Br (unit: tesla) of each bonded magnet was measured. A high-sensitivity normal conducting magnet type (electromagnet type) vibrating sample magnetometer (VSM) was used to measure Br. The vibrating sample magnetometer was manufactured by Tamagawa Seisakusho Co., Ltd. The residual magnetic flux density Br of each of the bonded magnets in Examples 1 to 6 and Comparative Examples 2 and 3 is shown in Table 1 below.

[0084]

[0085] For example, the compound according to one aspect of the present invention may be used as a raw material for a bonded magnet.

[0086] 2...Compound, 2A...Molded body (bonded magnet), 3...Magnet particles (magnet powder), 5...Resin composition (epoxy resin and imidazole), H...Magnetic field, m...Magnetization direction of magnet particles, M...Magnetization direction of bonded magnet.

Claims

1. A compound comprising: a magnet powder which is an alloy containing samarium, iron, and nitrogen; an epoxy resin; and imidazole; and no phenolic hardener.

2. The compound of claim 1, wherein the imidazole is at least one selected from the group consisting of 2-ethyl-4-methylimidazole, 2-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, and 1-aminopropyl-2-methylimidazole.

3. The compound according to claim 1, wherein the epoxy resin is at least one selected from the group consisting of biphenyl-type epoxy resins, dicyclopentadiene-type epoxy resins, naphthalene-type epoxy resins, and cresol novolac-type epoxy resins.

4. The compound according to claim 1, wherein the phenolic curing agent is at least one selected from the group consisting of phenolic resins and phenolic novolac resins.

5. The compound according to claim 1, which is in the form of a powder, tablet or paste.

6. The compound according to any one of claims 1 to 5, which is a raw material for a bonded magnet.

7. The compound according to any one of claims 1 to 5, which is a raw material for an anisotropic bonded magnet in which the magnetization direction of each of the multiple magnetic particles that make up the magnetic powder is aligned.

8. A bonded magnet comprising a cured product of the compound according to any one of claims 1 to 5.

9. An anisotropic bonded magnet comprising a cured product of the compound according to any one of claims 1 to 5, wherein the magnetization direction of each of the plurality of magnetic particles constituting the magnetic powder is aligned.

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