Compound for bond magnet and compact for bond magnet

Abstract

To provide a compound for a bond magnet that can produce a compact for a bond magnet with superior mechanical strength.SOLUTION: The compound for a bond magnet includes a magnetic powder, a resin composition containing an epoxy resin, a curing agent, and a coupling agent having a functional group that can react with glycidyl groups. The compound contains the epoxy resin and the curing agent so that the amount of hydroxyl groups per 1 g of cured material represented by the following formula (1) is 3.0 mmol / g or more. The amount of hydroxyl groups per 1 g of cured material=curing agent content [g]×1000 / (hydroxyl group equivalent of curing agent A×(epoxy resin content [g]+curing agent content [g])) ...(1)SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a compound for a bonded magnet and a compact for a bonded magnet. [Background technology]

[0002] A bonded magnet is a magnet made by mixing magnetic powders such as ferrite, alnico, and rare earth with binders such as resin and molding them under high pressure into a specific shape. Bonded magnets have a greater degree of freedom in shape than sintered magnets, making them easy to mold into a variety of shapes such as thin rings, high dimensional accuracy, excellent mechanical properties that make them less likely to crack or chip, and the ability to mold them integrally with other components. In addition, the presence of resin, an insulator, between the magnet powder particles results in magnets with high electrical resistance. For this reason, they are used in a wide variety of products, including automobiles, general home appliances, communication and audio equipment, medical equipment, and general industrial equipment.

[0003] Such bonded magnets are manufactured by compression molding a mixture of resin and magnet powder, called a compound. Compounds are manufactured by kneading magnetic powder, the particle size of which is adjusted to increase the density of the magnet, with a binder such as resin. For applications requiring heat resistance, thermosetting resins are being widely considered as binders.

[0004] A technical problem in applications where heat resistance is important is the reduction in mechanical strength due to softening of the resin, and in particular the mechanical strength is significantly reduced when heated. Patent Document 1 shows that the mechanical strength of a bonded magnet at high temperatures can be improved by using a binder for rare earth bonded magnets that contains a certain ratio of epoxy resin and polybenzimidazole. Patent Document 2 shows that the mechanical strength of a bonded magnet at high temperatures can be improved by using a dihydrobenzoxazine compound and a mixture of a dihydrobenzoxazine compound and an epoxy resin or a phenolic resin as a binder for rare earth bonded magnets. Patent Document 3 shows the improvement of mechanical strength at high temperatures by using polyamideimide. Patent Document 4 shows that a bonded magnet with high density can be obtained by obtaining a green compact that is less likely to crack even when a raw material powder with a reduced amount of resin is molded under high pressure. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-273916 [Patent Document 2] JP 2001-214054 A [Patent Document 3] JP 2004-31786 A [Patent Document 4] JP 2012-209484 A Summary of the Invention [Problem to be solved by the invention]

[0006] Various studies have been conducted to improve the mechanical strength, but the current situation is that further improvement is required, particularly in mechanical strength at high temperatures.

[0007] The present invention aims to provide a compound for bonded magnets that can produce bonded magnet green bodies having superior mechanical strength, and also aims to provide a bonded magnet green body produced by molding the compound. [Means for solving the problem]

[0008] As a result of intensive research, the inventors of the present invention have focused on the possibility that the type of coupling agent contained in the resin composition and the amount of hydroxyl groups (OH group amount) in the cured product of the resin composition may affect the mechanical strength. They have found that by using a specific coupling agent and blending an epoxy resin and a curing agent so that the amount of hydroxyl groups in the cured product (resin composition after curing) is 3.0 mmol / g or more, it is possible to improve the mechanical strength of the molded body for bonded magnets at room temperature and further suppress the decrease in mechanical strength at high temperatures.

[0009] The present invention provides a compound for bonded magnets, comprising a magnetic powder, and a resin composition containing an epoxy resin, a curing agent, and a coupling agent having a functional group capable of reacting with a glycidyl group, the epoxy resin and the curing agent being contained in such an amount that the amount of hydroxyl groups per gram of the cured product, represented by the following formula (1), is 3.0 mmol / g or more. Amount of hydroxyl groups per 1 g of hardened material = Hardener content [g] × 1000 / (Hydroxyl equivalent A of hardener × (Epoxy resin content [g] + Hardener content [g])) (1)

[0010] In one embodiment, the epoxy resin may include a naphthalene-type epoxy resin.

[0011] In one embodiment, the naphthalene-type epoxy resin may include a trifunctional or tetrafunctional epoxy resin.

[0012] In one embodiment, the ratio of the hydroxyl equivalent of the curing agent to the epoxy equivalent of the epoxy resin may be 1.0 to 1.4.

[0013] In one embodiment, the functional group capable of reacting with a glycidyl group may comprise a succinic anhydride group.

[0014] The present invention provides a compact for a bonded magnet obtained by molding the above compound. Effect of the Invention

[0015] According to the present invention, it is possible to provide a compound for a bonded magnet that can produce a bonded magnet green body having superior mechanical strength, and also to provide a bonded magnet green body obtained by molding the compound.

[0016] The bonded magnet compact obtained from the bonded magnet compound of the present invention has excellent mechanical strength at room temperature and exhibits little loss in mechanical strength at high temperatures. The molded product has excellent mechanical strength, particularly crushing strength. Therefore, it has the special effect of making it easier to apply the bonded magnet to applications where it is exposed to high temperatures. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Preferred embodiments of the present invention will be described in detail below, however, the present invention is not limited to the following embodiments.

[0018] <Compound for bonded magnets> The bonded magnet compound includes a magnetic powder and a resin composition including an epoxy resin, a curing agent, and a coupling agent having a functional group capable of reacting with a glycidyl group.

[0019] [Resin composition] The organic components in the bonded magnet compound excluding the magnetic powder, i.e., the mixture of epoxy resin, hardener, coupling agent capable of reacting with glycidyl group, etc., are called the resin composition. The resin composition functions as a binder for the magnetic powder that constitutes the bonded magnet, and is the source of mechanical strength. In the bonded magnet compact obtained by compression molding and heating the bonded magnet compound, the hardened resin composition functions as a strong binder between the magnetic powder.

[0020] (Epoxy resin) The epoxy resin is not particularly limited as long as it has two or more epoxy groups in one molecule. Specific examples of the epoxy resin include biphenyl type epoxy resins, stilbene type epoxy resins, diphenylmethane type epoxy resins, sulfur atom-containing type epoxy resins, novolac type epoxy resins, dicyclopentadiene type epoxy resins, salicylaldehyde type epoxy resins, naphthalene type epoxy resins (epoxy resins having a naphthalene structure), naphthylene ether type epoxy resins, β-naphthol type epoxy resins, copolymer type epoxy resins of naphthols and phenols, epoxidized products of aralkyl type phenolic resins, bisphenol type epoxy resins, glycidyl ether type epoxy resins (e.g., glycidyl ether type epoxy resins of alcohols, paraxylylene and / or Examples of the epoxy resins include glycidyl ether type epoxy resins of meta-xylylene-modified phenolic resins, glycidyl ether type epoxy resins of terpene-modified phenolic resins, cyclopentadiene type epoxy resins, glycidyl ether type epoxy resins of polycyclic aromatic ring-modified phenolic resins, and glycidyl ether type epoxy resins of naphthalene ring-containing phenolic resins), glycidyl ester type epoxy resins, glycidyl or methylglycidyl type epoxy resins, alicyclic type epoxy resins, halogenated phenol 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.

[0021] Among the above epoxy resins, from the viewpoint of high strength and heat resistance, naphthalene type epoxy resins can be used, and in particular, naphthalene type epoxy resins that are solid at room temperature can be used. From the same viewpoint, trifunctional naphthalene type epoxy resins, tetrafunctional naphthalene type epoxy resins, β-naphthol type epoxy resins, etc. can be used as naphthalene type epoxy resins. Examples of commercially available naphthalene type epoxy resins include HP-4700, HP-4710, HP-4770, EXA-5740, EXA-7311-G4, etc., manufactured by DIC Corporation. These may be used alone or in combination of two or more. In addition, HP-4032 and HP-4032D, which are bifunctional naphthalene type epoxy resins, can be used in combination with the above epoxy resins.

[0022] The epoxy equivalent of the epoxy resin can be 250 or less, may be 230 or less, or may be 220 or less. By using such an epoxy resin, the number of hydroxyl groups per unit weight of the cured product generated by the reaction with the curing agent increases, and strength is easily improved. In addition, resistance to hydrophobic oils is easily increased.

[0023] (hardening agent) As the curing agent, a phenol resin curing agent can be mentioned from the viewpoint of heat resistance. Epoxy resin curing agents are classified into types that cure at low to room temperature, such as aliphatic polyamines, polyaminoamides, and polymercaptans, and heat-curing types that do not cure unless the temperature is raised, such as aromatic polyamines, acid anhydrides, phenol novolac resins, and dicyandiamide (DICY). In general, epoxy resins cured with low to room temperature curing agents have a low glass transition point and become soft cured products. From the viewpoint of heat resistance, heat-curing curing agents can be used, and phenol novolac resin can be used as the curing agent. By using phenol novolac resin as the curing agent, a resin cured product with a high glass transition point can be obtained, so that a molded body for bonded magnets with excellent heat resistance and mechanical strength can be manufactured.

[0024] The phenolic resin curing agent is not particularly limited as long as it is a compound having two or more phenolic hydroxyl groups in one molecule. Specific examples of the phenolic resin include, for example, aralkyl type phenolic resin, dicyclopentadiene type phenolic resin, salicylaldehyde type phenolic resin, novolac type phenolic resin, naphthalene type phenolic resin, copolymer type phenolic resin of benzaldehyde type phenol and aralkyl type phenol, paraxylylene and / or metaxylylene modified phenolic resin, melamine modified phenolic resin, terpene modified phenolic resin, dicyclopentadiene type naphthol resin, cyclopentadiene modified phenolic resin, polycyclic aromatic ring modified phenolic resin, biphenyl type phenolic resin, triphenylmethane type phenolic resin, and phenolic resin obtained by copolymerizing two or more of these. Bisphenol A, bisphenol F, substituted or unsubstituted biphenol, bifunctional dihydroxynaphthalene, etc. can be used as a curing agent having a phenolic hydroxyl group. These may be used alone or in combination of two or more.

[0025] Examples of phenol novolak resins include those obtained by condensing or co-condensing phenols such as phenol, cresol, xylenol, resorcin, catechol, bisphenol A, bisphenol F, phenylphenol, and aminophenol, and / or naphthols such as α-naphthol, β-naphthol, and dihydroxynaphthalene, with aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde, and salicylaldehyde, in the presence of an acidic catalyst.

[0026] Examples of commercially available phenolic resins include Tamanol 758 manufactured by Arakawa Chemical Industries Co., Ltd., HP-850N manufactured by Hitachi Chemical Co., Ltd., and SN395 manufactured by Nippon Steel & Sumikin Chemical Co., Ltd. These may be used alone or in combination of two or more kinds.

[0027] In the resin composition, the mixing ratio of the epoxy resin and the curing agent is adjusted using the content of the epoxy resin and the hydroxyl equivalent (A) and content of the curing agent so that the hydroxyl amount per 1 g of the cured product, represented by the following formula (1), is 3.0 mmol / g or more. Amount of hydroxyl groups per 1 g of hardened material = Hardener content [g] × 1000 / (Hydroxyl equivalent A of hardener × (Epoxy resin content [g] + Hardener content [g])) (1)

[0028] This improves the mechanical strength of the bonded magnet molding at room temperature and prevents the mechanical strength from decreasing at high temperatures. From this viewpoint, the amount of hydroxyl groups may be 3.1 mmol / g or more, 3.2 mmol / g or more, or 3.5 mmol / g or more. The upper limit of the amount of hydroxyl groups may be 4.5 mmol / g from the viewpoint of preventing the strength of the cured product from decreasing.

[0029] The "cured product" in the above formula (1) is a product obtained by thermally curing a resin composition in accordance with the method for producing a molded body for a bonded magnet described below, and more specifically, a product obtained by heat-treating a resin composition at a temperature of, for example, 150 to 300°C for a few minutes to 4 hours.

[0030] In the resin composition, the ratio of the active group (e.g., phenolic hydroxyl group) in the curing agent that reacts with the epoxy group to one equivalent of the epoxy group in the epoxy resin, i.e., the ratio of the hydroxyl group equivalent of the curing agent to the epoxy equivalent of the epoxy resin (hydroxyl group equivalent / epoxy equivalent) can be 1.0 to 1.4, and may be 1.0 to 1.2. When the equivalent ratio is 1.0 or more, the amount of hydroxyl groups per unit weight of the cured product is easily secured, and the strength is not easily reduced. In addition, there are tendencies such as the curing speed of the resin composition (epoxy resin composition) being easily increased, the glass transition temperature of the obtained cured product being easily increased, a sufficient elastic modulus being easily obtained, and the oil resistance being not easily reduced. On the other hand, when the equivalent ratio is 1.4 or less, the strength of the cured product is not easily reduced.

[0031] (Coupling Agent) By using a coupling agent having a functional group capable of reacting with a glycidyl group, the adhesion between the resin composition and the magnetic powder surface can be increased, and the mechanical strength of the bonded magnet molding can be increased. Examples of coupling agents having a functional group capable of reacting with a glycidyl group include silane coupling agents, such as silane-based compounds such as epoxysilane, mercaptosilane, aminosilane, alkylsilane, ureidosilane, and acid anhydride-based silane. Among these, acid anhydride-based silane coupling agents can be used from the viewpoint of pot life, and in particular succinic anhydride-based silane coupling agents (i.e., coupling agents having a functional group containing a succinic anhydride group as a functional group capable of reacting with a glycidyl group) can be used. These can be used alone or in combination.

[0032] The amount of the coupling agent can be 25 to 35 parts by mass, or 28 to 32 parts by mass, per 100 parts by mass of the epoxy resin. If the amount of the coupling agent is equal to or more than the lower limit, the crushing strength is likely to be improved, and if it is equal to or less than the upper limit, the fluidity of the compound is likely to be improved. As the curing accelerator, a well-known curing accelerator other than the above-mentioned compounds may be further used.

[0033] (Cure accelerator) The resin composition may contain a curing accelerator. The curing accelerator may be a general imidazole-based compound or a phosphorus-based curing accelerator. Examples of phosphorus-based curing accelerators include triphenylphosphine-benzoquinone, tris-4-hydroxyphenylphosphine-benzoquinone, tetraphenylphosphonium tetrakis(4-methylphenyl)borate, and tetra(n-butyl)phosphonium tetraphenylborate. These may be used alone or in combination.

[0034] By using a curing accelerator, it is easier to obtain molded products with better mechanical properties. In addition, the bond magnet compound is more likely to exhibit long-term storage stability even in high-temperature and high-humidity environments.

[0035] The amount of the curing accelerator is not particularly limited as long as the curing acceleration effect can be achieved. From the viewpoint of improving the curability and flowability of the resin composition when absorbing moisture, the amount of the curing accelerator can be 0.1 to 30 parts by mass, and may be 1 to 15 parts by mass, relative to 100 parts by mass of the epoxy resin. The amount of the curing accelerator may be 0.001 to 5 parts by mass relative to 100 parts by mass of the total amount of the epoxy resin and the curing agent. When the amount of the curing accelerator is equal to or more than the lower limit, the expected curing acceleration effect is easily obtained, and when it is equal to or less than the upper limit, the storage stability of the obtained resin is unlikely to decrease. The curing accelerator includes one or more of the above-mentioned curing accelerators, and may also include well-known curing accelerators other than those mentioned above in addition to them.

[0036] [Magnetic powder] The magnetic powder (magnetic powder or powder for bonded magnet) is not particularly limited as long as it does not deteriorate the curing characteristics of the resin composition. Examples of the magnetic powder include powder for samarium-cobalt rare earth bonded magnet, powder for neodymium iron boron rare earth bonded magnet, powder for iron cobalt bonded magnet, powder for samarium iron nitride compound rare earth bonded magnet, ferrite powder, etc.

[0037] The particle size of the magnetic powder can be 20 to 300 μm, and may be 40 to 250 μm. The particle size of the magnetic powder can be calculated by weight measurement through sieving or by a particle size distribution measuring device (instrumental analysis) using laser diffraction or the like.

[0038] The magnetic powder can be 95 to 99.5% by mass, or may be 96 to 99% by mass, based on the total amount of the magnetic powder and the resin composition (i.e., the total amount of the bonded magnet compound), which makes it easier to obtain a bonded magnet compact that has excellent magnetic properties and is both high strength and heat resistance.

[0039] [Inorganic filler] The bond magnet compound may contain an inorganic filler. By using an inorganic filler, it is easy to obtain a bond magnet compact that has excellent mechanical strength at room temperature and that is less susceptible to deterioration in mechanical strength at high temperatures.

[0040] The inorganic filler may be composed of one type of particle or may be composed of a combination of two or more types of particles. The average particle size of the inorganic filler may be 1 to 100 μm, may be 1 to 50 μm, may be 1 to 20 μm, or may be 1.5 to 10 μm. The inorganic filler may be a mixture of multiple types of fillers having different average particle sizes. This can increase the space filling rate of the inorganic filler.

[0041] The inorganic filler may be silica particles. Examples of silica particles include spherical silica obtained by the sol-gel method, crushed silica finely pulverized by grinding, dry silica, wet silica, etc. Commercially available spherical silica products include MSR-2212, MSR-SC3, MSR-SC4, MSR-3512, MSR-FC208 (manufactured by Tatsumori Co., Ltd., product name), Excelica (manufactured by Tokuyama Co., Ltd., product name), SO-E1, SO-E2, SO-E3, SO-E5, SO-E6, SO-C1, SO-C2, SO-C3, SO-C5, SO-C6, (manufactured by Admatechs Co., Ltd., product name), etc. Commercially available crushed silica products include Crystallite 3K-S, NX-7, MCC-4, CMC-12, A1, AA, CMC-1, VX-S2, VX-SR (trade names, manufactured by Tatsumori Co., Ltd.), F05, F05-30, F05-12 (trade names, manufactured by Fukushima Ceramics Co., Ltd.), etc. Dry silica such as Reoloseal, and wet silica such as Toksil and Fineseal (trade names, manufactured by Tokuyama Co., Ltd.) can also be used.

[0042] The silica particles may be surface-treated with a silane coupling agent, which can suppress sedimentation of the silica particles and provide a resin composition with better dispersion stability. Examples of the silane coupling agent include vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, n-2-(aminoethyl)-3-aminopropylmethyldimethoxysilaneriethoxysilane, n-2-( Examples of the silane coupling agent include n-2-(aminoethyl)-3-aminopropyltrimethoxysilane, n-2-(aminoethyl)-3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride, 3-ureidopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, 3-isocyanatepropyltriethoxysilane, polycondensates of dimethylsilane, polycondensates of diphenylsilane, and copolycondensates of dimethylsilane and diphenylsilane. The silane coupling agent may be a silane coupling agent having an amino group.

[0043] The amount of inorganic filler to be blended can be 0.5 to 5 mass % and may be 1 to 3 mass % based on the total amount of the bonded magnet compound. If the amount of inorganic filler blended is above the lower limit, the crushing strength tends to increase, and if it is below the upper limit, the water absorption rate tends to decrease.

[0044] [Aliphatic metal salts] The bonded magnet compound may contain a fatty acid metal salt. By using the fatty acid metal salt, it is easy to obtain a bonded magnet molding that has excellent mechanical strength at room temperature and little loss of mechanical strength at high temperatures. As the fatty acid metal salt, a compound represented by the general formula (2) can be used. R2M (2) In the formula, R represents a saturated fatty acid group having 8 to 28 carbon atoms, and M represents Ca or Ba.

[0045] Examples of such fatty acid metal salts include calcium salts such as calcium caprylate, calcium laurate, calcium palmitate, calcium myristate, calcium stearate, and calcium montanate, and barium salts such as barium caprylate, barium laurate, barium palmitate, barium myristate, barium stearate, and barium montanate. These can be used alone or in combination.

[0046] The amount of the aliphatic metal salt can be 0.05 to 5 parts by mass, or may be 0.1 to 3 parts by mass, per 100 parts by mass of the total amount of the bonded magnet compound. If the amount of the aliphatic metal salt is above the lower limit, the molded body will be easier to remove from the die, and if it is below the upper limit, the strength of the molded body will not decrease.

[0047] <Manufacturing method for bonded magnet compounds> A resin composition solution for bonded magnets is obtained by dissolving raw materials including at least an epoxy resin, a curing agent, and a coupling agent having a functional group capable of reacting with a glycidyl group in an organic solvent. After adding and dispersing magnetic powder to this, the organic solvent is distilled off under reduced pressure, and the resulting mixture is dried to obtain a compound for bonded magnets. When an inorganic filler is added, it can be added together with the magnetic powder.

[0048] [Organic solvents] By mixing the resin composition with an organic solvent, the resin composition can be uniformly coated on the magnetic powder. This makes it possible to obtain a uniform compound. The organic solvent is not particularly limited as long as it can dissolve the organic components and disperse the inorganic components. Examples of the organic solvent include acetone, methyl ethyl ketone (2-butanone), methyl isobutyl ketone, benzene, toluene, and xylene. Considering workability, it is possible to use a solvent that is liquid at room temperature but has a boiling point of about 60°C to 150°C, such as acetone and methyl ethyl ketone.

[0049] The amount of the organic solvent can be 50 to 400 parts by mass, or may be 100 to 200 parts by mass, relative to 100 parts by mass of the total amount of the magnetic powder and the resin composition. When the amount of the organic solvent is equal to or more than the lower limit, the resin composition is easily dissolved uniformly, and when the amount is equal to or less than the upper limit, the reduced pressure distillation can be easily performed in a short time.

[0050] The organic solvent can be distilled off under reduced pressure using an evaporator while stirring the solution at room temperature. This removes most of the solvent. The dried product is then further dried using a vacuum dryer or the like to obtain a dried product, which can be pulverized as necessary to obtain a granular compound. The organic solvent can also be distilled off under normal pressure while stirring using a kneader or the like. The drying temperature can be room temperature from the viewpoint of suppressing the curing reaction of the resin composition, but when heating is performed, it can be 80°C or less, or 60°C or less.

[0051] <Manufacturing method for bonded magnet compacts> The resulting bonded magnet compound can be made into a bonded magnet green body through a molding step and a heat treatment step. When an aliphatic metal salt is used, it is mixed with the bonded magnet compound before the molding step.

[0052] The higher the molding pressure in the compacting process, the easier it is to obtain a high magnetic flux density and high strength. The compacting pressure can be 500 to 2500 MPa, and may be 1400 to 2000 MPa when considering mass productivity and die life. The density of the compact is determined based on the true density of the magnetic powder particles (for example, the alloy true density of neodymium-iron-boron-based bonded magnet powder is 7.6 g / cm3). 3 When the density of the compression molded body is in this range, it is easy to obtain a bonded magnet green body with good magnetic properties and high mechanical strength.

[0053] The heat treatment step is a step of curing the resin composition by heat-treating the compression molded body. The heat treatment temperature may be any temperature at which the resin composition can be sufficiently cured, and may be, for example, 150 to 300°C, or 175 to 250°C. By setting the heat treatment temperature at 300°C or less, it becomes easier to suppress oxidation of the magnetic powder caused by a trace amount of oxygen that is unavoidable in the production process, or deterioration of the cured resin. From this viewpoint, the holding time at the heat treatment temperature (at the maximum temperature) may be several minutes to 4 hours, or may be 5 minutes to 1 hour. The heat treatment atmosphere may be an inert atmosphere from the viewpoint of suppressing oxidation of the magnetic powder.

[0054] The glass transition temperature of the resin composition after curing (cured product) can be 150°C or higher, and may be 200°C or higher. This makes it easy to suppress the decrease in mechanical strength of the bonded magnet molding even in a harsh high-temperature environment. The upper limit of the glass transition temperature is not particularly limited, but can be 250°C from the viewpoint of performing the curing treatment at a temperature that does not deteriorate the magnetic properties of the magnetic powder. The glass transition temperature means the temperature at which tan δ reaches a peak in dynamic viscoelasticity measurement. EXAMPLES

[0055] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0056] [Details of various raw materials] (Epoxy resin) HP-4700 (manufactured by DIC Corporation, product name): naphthalene-type epoxy resin (epoxy equivalent 160, softening point 90°C, functionality 4) HP-4710 (manufactured by DIC Corporation, product name): naphthalene-type epoxy resin (epoxy equivalent 170, softening point 95°C, functionality 4) HP-4770 (manufactured by DIC Corporation, product name): low viscosity naphthalene type epoxy resin (epoxy equivalent 205, softening point 72°C, functionality 4) EXA-7311-G4 (manufactured by DIC Corporation, product name): naphthylene ether type epoxy resin (epoxy equivalent 218, softening point 57°C, functionality 2) EXA-9540-P02 (manufactured by DIC Corporation, product name): β-naphthol novolac type epoxy resin (epoxy equivalent 239, softening point 84°C) N-500P-1 (manufactured by DIC Corporation, product name): orthocresol novolac type epoxy resin (epoxy equivalent 201, softening point 59°C) EPPN-502H (product name, manufactured by Nippon Kayaku Co., Ltd.): salicylaldehyde novolac type epoxy resin (epoxy equivalent: 168, softening point: 67°C) NC3000H (product name, manufactured by Nippon Kayaku Co., Ltd.): biphenyl aralkyl type epoxy resin (epoxy equivalent 290, softening point 70°C) HP7200 (manufactured by DIC Corporation, product name): dicyclopentadiene type epoxy resin (epoxy equivalent 278, softening point 61°C) (hardening agent) HP-850N (Hitachi Chemical Co., Ltd., product name): Phenol novolac resin (hydroxyl equivalent: 108) SN395 (product name, manufactured by Nippon Steel Chemical Co., Ltd.): dihydroxynaphthalene (hydroxyl equivalent: 104) (Cure accelerator) PX-4PB (product name, manufactured by Nippon Chemical Industry Co., Ltd.): Tetra(n-butyl)phosphonium tetraphenylborate (Coupling agent having a functional group capable of reacting with a glycidyl group) X-12-967C (product name, manufactured by Shin-Etsu Silicones Co., Ltd.): 3-trimethoxysilylpropylsuccinic anhydride KBM-573 (product name, manufactured by Shin-Etsu Silicones Co., Ltd.): N-phenyl-3-aminopropyltrimethoxysilane KBM-403 (product name, manufactured by Shin-Etsu Silicones Co., Ltd.): 3-glycidoxypropyltrimethoxysilane (Coupling agent having no functional group capable of reacting with a glycidyl group) KBM-1003 (product name, manufactured by Shin-Etsu Silicones Co., Ltd.): vinyltrimethoxysilane (Organic solvent) 2-Butanone (methyl ethyl ketone) (magnetic powder) MQP-B (product name, manufactured by Molycorp Magnequench): Nd-Fe-B powder (particle size 100 μm)

[0057] [Example 1] The epoxy resin, curing agent, curing accelerator, silane coupling agent, and organic solvent were added to a plastic container in the amounts (unit: parts by mass) shown in Table 1, and stirred for 60 minutes at 40 rpm using a mix rotor to obtain a resin composition solution. The blending ratio of the epoxy resin and the curing agent was adjusted using the blending amount (content) of the epoxy resin, and the hydroxyl equivalent (A) and blending amount (content) of the curing agent so that the hydroxyl group amount per 1 g of the cured product represented by the following formula (1) would be the value shown in Table 1. Amount of hydroxyl groups per 1 g of hardened material = Hardener content [g] × 1000 / (Hydroxyl equivalent A of hardener × (Epoxy resin content [g] + Hardener content [g])) (1)

[0058] Next, the resin composition solution and the magnetic powder were put into a 300 mL eggplant-shaped flask and stirred in an evaporator at 25°C for about 30 minutes. The pressure in the evaporator was then reduced to 0.1 MPa or less, and the organic solvent was distilled off. During the process, the pressure was returned to normal, the aggregated mixture was loosened in the eggplant-shaped flask, and the pressure was reduced again several times to thoroughly remove the organic solvent from the mixture. After that, the mixture was spread on a flat plate and dried in a vacuum dryer at room temperature for 8 hours, after which the aggregated dried product was coarsely crushed, and the coarse powder was removed with a 100 mesh sieve to adjust the particle size, thereby obtaining a compound for bonded magnets.

[0059] Next, 0.3 parts by mass of calcium stearate was added as a lubricant to 100 parts by mass of the bonded magnet compound, and mixed for 60 minutes in a V-type mixer. The lubricant-containing compound was molded using a hydraulic press at a molding pressure of 2000 MPa to obtain a cubic compression molded body of 7 mm x 7 mm x 7 mm. The obtained compression molded body was heated at a temperature of 200°C for 10 minutes in a constant temperature bath in a nitrogen atmosphere to produce a bonded magnet molded body.

[0060] [Other Examples and Comparative Examples] Aside from changing the raw materials used and their amounts as shown in Table 1 or Table 2, a compound for a bonded magnet and a green body for a bonded magnet were obtained in the same manner as in Example 1.

[0061] [Measurement of glass transition temperature] The resin composition solution (without magnetic powder) obtained in each example was placed in a 300 mL eggplant-shaped flask, and the pressure in the evaporator was reduced to 0.1 MPa or less at 25 ° C. to distill off the organic solvent. The resin composition was then dried in a vacuum dryer at room temperature for another 8 hours to obtain a resin composition from which the organic solvent had been sufficiently removed. The obtained resin composition was crushed, spread in a metal frame, and vacuum pressed at 180 ° C., 2 MPa, and 30 minutes to produce a plate-shaped resin plate. The obtained resin plate was cut into 2 mm × 3 mm × 25 mm to prepare a test piece, and a thermal mechanical property evaluation device (TA Instruments Co., Ltd., TMA Q400) was used to measure linear expansion at 10 ° C. / min to determine the Tg of the test piece. The inflection point between α1 and α2 was taken as Tg.

[0062] [Mechanical strength evaluation] The bonded magnet compacts obtained in each example were used as test pieces to measure the crushing strength at room temperature and at high temperatures. The results are shown in Tables 1 and 2. (Room temperature crushing strength) Using a universal compression testing machine (AG-10TBR, manufactured by Shimadzu Corporation), compressive pressure was applied from the height direction to the test specimen in an environment of 25°C, and the crushing strength (MPa) was calculated from the maximum compressive pressure at which the test specimen was destroyed by the compressive pressure. (High temperature crushing strength) The crushing strength at 150°C (MPa) was calculated in the same manner as for the room temperature crushing strength, except that the test piece was heated in a thermostatic bath at 150°C for 1 minute.

[0063] [Table 1]

[0064] [Table 2]

[0065] (Evaluation Results) The molded articles of the Examples all had high crushing strength at room temperature, and showed little decrease in crushing strength at 150° C. The molded articles of the Comparative Examples all had low crushing strength at room temperature, and showed a large decrease in crushing strength at 150° C. [Industrial Applicability]

[0066] The bonded magnet compound according to the present invention makes it possible to obtain bonded magnet green bodies having excellent crushing strength at room temperature and at high temperatures. Bonded magnet green bodies having excellent heat resistance are of great industrial value.

Claims

1. a resin composition including a magnetic powder, an epoxy resin, a curing agent, and a coupling agent having a functional group capable of reacting with a glycidyl group; The epoxy resin and the curing agent are contained in such an amount that the amount of hydroxyl groups per 1 g of the cured product represented by the following formula (1) is 3.0 mmol / g or more, A compound for molding a bonded magnet green body, wherein the resin composition after curing has a glass transition temperature of 200°C or higher. Amount of hydroxyl groups per 1 g of cured product = curing agent content [g] × 1000 / (hydroxyl group equivalent A of curing agent × (epoxy resin content [g] + curing agent content [g])) (1)

2. The compound of claim 1 , wherein the epoxy resin comprises a naphthalene-type epoxy resin.

3. 3. The compound of claim 2, wherein the naphthalene-type epoxy resin comprises a trifunctional or tetrafunctional epoxy resin.

4. The compound according to any one of claims 1 to 3, wherein the ratio of the hydroxyl group equivalent of the curing agent to the epoxy equivalent of the epoxy resin is 1.0 to 1.

4.

5. 5. The compound according to claim 1, wherein the functional group capable of reacting with a glycidyl group comprises a succinic anhydride group.

6. A compound described in any one of claims 1 to 5, wherein the amount of the coupling agent is 25 to 35 parts by mass per 100 parts by mass of the epoxy resin.

7. A bonded magnet compact obtained by molding the compound according to any one of claims 1 to 6.