Bonded magnet and compound

Abstract

This bonded magnet comprises: magnetic particles; a binder that binds the magnetic particles together; and elastomer particles, wherein a part of the elastomer particles is located in at least a part between the magnetic particles. This compound used for the production of the bonded magnet contains magnetic particles, a resin, and elastomer particles.

Description

Bonded magnets and compounds

[0001] This disclosure relates to bonded magnets and compounds.

[0002] Bonded magnets, which include magnetic particles and a binder, have an advantage over sintered magnets in terms of their greater freedom in shape. For example, Patent Document 1 discloses a method for manufacturing bonded magnets using magnetic particles and epoxy resin.

[0003] International Publication No. 2024 / 142174

[0004] When bonded magnets are molded from a compound containing magnetic particles and resin, the coercivity of the resulting bonded magnets is inferior to the coercivity expected from the performance of the magnetic particles. In recent years, there has been a demand for higher performance in bonded magnets, and it would be useful to be able to obtain bonded magnets with even greater coercivity.

[0005] One aspect of this disclosure aims to provide a bonded magnet in which the reduction in coercivity is suppressed, and a compound that can be used to obtain such a bonded magnet.

[0006] It is known that when processing magnetic particles, impacts during processing can cause damage to the surface of the magnetic particles, leading to oxidation of the magnetic particles, or distortion of the crystal structure of the magnetic particles. When forming bonded magnets from a compound, the compound is compressed during the manufacturing process. Collisions between magnetic particles occur within the compound, resulting in similar damage to the coating on the surface of the magnetic particles and distortion of the crystal structure within the bonded magnet. Furthermore, it has been found that oxidation of the magnetic particles due to coating damage and distortion of the crystal structure prevent the resulting bonded magnets from exhibiting the coercivity expected from the magnetic particles. The invention disclosed herein is based on these findings.

[0007] This disclosure includes the following aspects: [1] A bonded magnet comprising magnetic particles, a binder that binds the magnetic particles together, and elastomer particles, wherein a portion of the elastomer particles is located at least a portion of the space between the magnetic particles. [2] A compound used in the manufacture of a bonded magnet, comprising magnetic particles, a resin, and elastomer particles. [3] The compound according to [2], wherein the resin comprises an epoxy resin and further comprises a curing agent. [4] The compound according to [2] or [3], wherein the elastomer particles comprise at least one selected from the group consisting of butadiene rubber and silicone rubber. [5] The compound according to any one of [2] to [4], wherein the magnetic particles comprise an Sm-Fe-N alloy. [6] The compound according to any one of [2] to [5], wherein the content of the elastomer particles is 0.2 parts by mass or more per 100 parts by mass of the amount of magnetic particles. [7] The compound according to any one of [2] to [6], wherein the average particle diameter of the elastomer particles is smaller than the average particle diameter of the magnetic particles. [8] The compound according to any one of [2] to [7], wherein the ratio of the average particle diameter of the elastomer particles to the average particle diameter of the magnetic particles is 0.3 or less. [9] The compound according to any one of [2] to [8], wherein the magnetic particles are covered with a resin layer containing the resin.

[10] The compound according to any one of [2] to [9], wherein the elastomer particles are dispersed in the resin.

[11] The compound according to [9], wherein the resin layer contains the elastomer particles.

[12] The compound according to [9], wherein the elastomer particles are attached to the resin layer.

[0008] According to one aspect of this disclosure, it is possible to provide a bonded magnet in which the reduction in coercivity is suppressed, and a compound that can be used to obtain such a bonded magnet.

[0009] Figure 1 is a schematic cross-sectional view showing one embodiment of a bonded magnet. Figure 2 is a schematic cross-sectional view showing one embodiment of the particles constituting the compound. Figure 3 is a schematic cross-sectional view showing one embodiment of the particles constituting the compound.

[0010] Embodiments of the present disclosure will be described below, with reference to the drawings as appropriate. However, the following embodiments are illustrative examples for illustrating the present disclosure and are not intended to limit the present disclosure to the following. In the description, the same reference numerals will be used for the same element or element having the same function, and redundant explanations will be omitted as appropriate. Furthermore, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings unless otherwise specified. In addition, the dimensional ratios of each element are not limited to the ratios shown. "(meth)acrylic resin" means at least one of acrylic resin and the corresponding methacrylic resin.

[0011] One embodiment of a bonded magnet according to this disclosure comprises magnetic particles, a binder that binds the magnetic particles together, and elastomer particles. In the bonded magnet, a portion of the elastomer particles is located between at least some of the magnetic particles. The remaining portion of the elastomer particles may be located elsewhere than between the magnetic particles.

[0012] In the bonded magnet described above, the decrease in coercivity is suppressed. The following factors are presumed to be the reason for this. However, the factors are not limited to those listed below. When a bonded magnet is obtained from a compound, the magnetic particles are bonded together by the resin contained in the compound. At this time, some of the elastomer particles are located at least partially between the magnetic particles, which mitigates the impact caused by collisions between magnetic particles and prevents damage to the coating on the surface of the magnetic particles. As a result, deterioration such as oxidation of the magnetic particles is suppressed. In addition, the elastomer particles reduce the stress between magnetic particles during collisions, suppressing the generation of strain in the crystal structure within the magnetic particles. It is presumed that, through these actions, deterioration of the magnetic particles and strain in the crystal structure are suppressed in the bonded magnet described above, and the decrease in coercivity is suppressed.

[0013] Figure 1 is a schematic cross-sectional view showing one embodiment of a bonded magnet. The bonded magnet 1 shown in Figure 1 comprises a plurality of magnetic particles 10, a binder 12 that binds the magnetic particles 10 together, and elastomer particles 14. In Figure 1, of the elastomer particles 14, elastomer particles 14a located between at least some of the magnetic particles 10 buffer collisions between the magnetic particles 10. Of the elastomer particles 14, elastomer particles 14b are located outside the spaces between the magnetic particles 10. In Figure 1, elastomer particles 14a are shown in a deformed, flattened shape due to the proximity of the magnetic particles 10, but deformation is not necessarily required, and they may maintain a shape similar to that of elastomer particles 14b.

[0014] The magnetic particles 10 may be composed of permanent magnets. The permanent magnets may contain alloys. Examples of alloys include samarium-cobalt alloys (Sm-Co alloys), neodymium-iron-boron alloys (Nd-Fe-B alloys), samarium-iron-nitrogen alloys (Sm-Fe-N alloys), iron-cobalt alloys (Fe-Co alloys), and Al-Ni-Co alloys. Preferably, the magnetic particles 10 contain an Sm-Fe-N alloy. When the magnetic particles 10 are composed of permanent magnets, the particle size of the magnetic particles 10 may be, for example, 1 μm or more, or 2 μm or more, and may be 30 μm or less, or 20 μm or less.

[0015] The magnetic particles 10 may be composed of a soft magnetic material. The soft magnetic material may contain at least one metal selected from the group consisting of pure iron and iron-containing alloys. Examples of iron-containing alloys include Fe-Cr alloys (stainless steel), Fe-Ni-Cr alloys (stainless steel), Fe-Si alloys, Fe-Si-Al alloys (Sendust), Fe-Ni alloys (Permalloy), Fe-Cu-Ni alloys (Permalloy), Fe-Cr-Si alloys (electromagnetic stainless steel), and Fe-Ni-Mn-C alloys (Invar). The soft magnetic material may be amorphous. The soft magnetic material may be an Fe amorphous alloy. The magnetic particles 10 composed of a soft magnetic material may be composed of amorphous iron or carbonyl iron. When the magnetic particles 10 are composed of a soft magnetic material, the particle size of the magnetic particles 10 may be 60 μm or more and 150 μm or less.

[0016] The magnetic particles 10 may contain multiple types of metallic elements. In addition to the above elements, the magnetic particles 10 may further contain at least one element selected from the group consisting of base metal elements, noble metal elements, transition metal elements, and rare earth elements. The magnetic particles 10 may further contain at least one element selected from the group consisting of copper (Cu), titanium (Ti), manganese (Mn), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), tin (Sn), chromium (Cr), barium (Ba), strontium (Sr), lead (Pb), silver (Ag), oxygen (O), beryllium (Be), phosphorus (P), boron (B), and silicon (Si).

[0017] The bonded magnet 1 may contain one type of magnetic particle, or it may contain multiple types of magnetic particles. The bonded magnet 1 may contain multiple types of magnetic particles with different average particle diameters (median diameter (D50) measured by a laser diffraction particle size distribution analyzer). The magnetic particles 10 may be, for example, spherical, flattened, or needle-shaped.

[0018] The content of magnetic particles 10 may be 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or 96% by mass or more, based on the total amount of bonded magnet 1, from the viewpoint of increasing the residual magnetic flux density of the bonded magnet. The content of magnetic particles 10 may be 96.4% by mass or less, 96.3% by mass or less, 96.1% by mass or less, or 96% by mass or less, based on the total amount of bonded magnet 1, from the viewpoint of further suppressing the decrease in coercivity in the bonded magnet.

[0019] The magnetic particles 10 may have a coating containing an inorganic compound. The inorganic compound may be a metal oxide or the like. The coating containing the inorganic compound may be a film composed of a metal oxide or the like, from the viewpoint of improving bonding with the binder 12. Examples of inorganic compounds include phosphates and silica.

[0020] The coating containing the above inorganic compound may be formed by treating the magnetic particles 10 with a surface treatment agent, and may contain compounds derived from the surface treatment agent. Examples of surface treatment agents include silane coupling agents, titanate coupling agents, aluminate coupling agents, and zirconate coupling agents.

[0021] Examples of silane coupling agents include 8-methacryloxyoctyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropyltrimethoxysilane.

[0022] The binder 12 may contain a cured product of a thermosetting resin, a thermoplastic resin, or both. Examples of thermosetting resins include epoxy resins, phenolic resins, bismaleimide resins, polyimide resins, and polyamideimide resins. Examples of thermoplastic resins include (meth)acrylic resins, polyolefins (e.g., polyethylene and polypropylene), polystyrene, polyvinyl chloride, and polyethylene terephthalate. The binder 12 preferably contains a cured product of an epoxy resin.

[0023] The weight-average molecular weight of binder 12 may be 200 or more, or 300 or more, and may be 10,000 or less, or 5,000 or less.

[0024] In this specification, "weight-average molecular weight" refers to the value obtained by measuring using GPC (Gel Permeation Chromatography) and converting it using a calibration curve with standard polystyrene. The measurement conditions for weight-average molecular weight are shown below.

[0025] Instrument name: HLC-8320 (manufactured by Tosoh Corporation) Column: TSKgel SuperMultipore HZ-M (3 columns) (manufactured by Tosoh Corporation) Detector: RI Column temperature: 40°C Eluent: A solvent that dissolves the target substance can be selected. For example, tetrahydrofuran can be used as a solvent. Flow rate: 0.35 mL / min Standard substance: Polystyrene

[0026] The content of the binder 12 may be 1% by mass or more, 2% by mass or more, or 3% by mass or more, and may be 20% by mass or less, 10% by mass or less, 7% by mass or less, or 5% by mass or less, based on the total amount of the bond magnet 1.

[0027] The amount of binder 12 may be 1 part by mass or more, 2 parts by mass or more, or 3 parts by mass or more, and may be 20 parts by mass or less, 10 parts by mass or less, 7 parts by mass or less, or 5 parts by mass or less, per 100 parts by mass of magnetic particles 10.

[0028] The elastomer particles 14 described above may contain a rubber component. Examples of rubber components include butadiene rubber (butadiene rubber, 1,2-polybutadiene, and styrene-butadiene rubber, etc.), diene rubber (chloroprene rubber and isoprene rubber, etc.), acrylic rubber (acrylic acid ester / 2-chloroethyl vinyl ether copolymer and acrylic acid ester / acrylonitrile copolymer, etc.), silicone rubber, olefin rubber (polyisobutylene and ethylene propylene rubber, etc.), and urethane rubber. Preferably, the elastomer particles 14 contain at least one selected from the group consisting of butadiene rubber and silicone rubber.

[0029] The weight-average molecular weight of the rubber component may be 100 or more, or 200 or more, and may be 100,000 or less, 50,000 or less, 10,000 or less, 5,000 or less, or 1,000 or less.

[0030] Examples of elastomer particle shapes 14 include spherical, flattened, and needle-shaped.

[0031] The average particle diameter of the elastomer particles 14 may be 1 nm or more, 10 nm or more, 30 nm or more, 50 nm or more, or 80 nm or more, from the viewpoint of further suppressing the decrease in coercivity in the bonded magnet. The average particle diameter of the elastomer particles 14 may be 300 nm or less, 200 nm or less, 170 nm or less, 150 nm or less, or 120 nm or less, from the viewpoint of improving the mechanical strength of the bonded magnet.

[0032] The average particle diameter of the elastomer particles 14 may be smaller than the average particle diameter of the magnetic particles 10. The ratio of the average particle diameter of the elastomer particles 14 to the average particle diameter of the magnetic particles 10 may be 0.001 or more, 0.01 or more, 0.015 or more, 0.02 or more, or 0.025 or more, from the viewpoint of further suppressing the decrease in coercivity in the bonded magnet. The ratio of the average particle diameter of the elastomer particles 14 to the average particle diameter of the magnetic particles 10 may be 0.6 or less, 0.4 or less, 0.3 or less, 0.2 or less, 0.15 or less, 0.1 or less, or 0.05 or less, from the viewpoint of improving the mechanical strength of the bonded magnet.

[0033] In this specification, the average particle size of elastomer particles is determined as follows: Scanning electron microscope (SEM) images of the cross-section of the bonded magnet and energy-dispersive X-ray analysis (EDX) results of the cross-section of the bonded magnet are obtained, and elastomer particles in the images are identified based on the analysis results. Then, in image analysis of the SEM images, the particle size is measured for 20 arbitrary particles, and the arithmetic mean of the obtained particle sizes is taken as the average particle size. If the shape of the particle is not spherical, the particle size is taken as the diameter of the circle circumscribing the particle in the SEM image.

[0034] From the perspective of further suppressing the decrease in coercive force in the bonded magnet, the content of the elastomer particles 14 may be 0.1% by mass or more, 0.15% by mass or more, 0.2% by mass or more, 0.25% by mass or more, 0.3% by mass or more, 0.4% by mass or more, 0.5% by mass or more, or 0.6% by mass or more, based on the total amount of the bonded magnet 1. From the perspective of increasing the residual magnetic flux density of the bonded magnet, the content of the elastomer particles 14 may be 5% by mass or less, 3% by mass or less, 1% by mass or less, 0.8% by mass or less, 0.7% by mass or less, 0.5% by mass or less, or 0.4% by mass or less, based on the total amount of the bonded magnet 1.

[0035] From the perspective of further suppressing the decrease in coercive force in the bonded magnet, the content of the elastomer particles 14 may be 0.1 part by mass or more, 0.15 part by mass or more, 0.2 part by mass or more, 0.25 part by mass or more, 0.3 part by mass or more, 0.4 part by mass or more, 0.5 part by mass or more, or 0.6 part by mass or more, with respect to 100 parts by mass of the amount of the magnetic particles 10. From the perspective of increasing the residual magnetic flux density of the bonded magnet, the content of the elastomer particles 14 may be 5 parts by mass or less, 3 parts by mass or less, 1 part by mass or less, 0.8 part by mass or less, 0.7 part by mass or less, 0.5 part by mass or less, or 0.4 part by mass or less, with respect to 100 parts by mass of the amount of the magnetic particles 10.

[0036] From the perspective of further suppressing the decrease in coercive force in the bonded magnet, the content of the elastomer particles 14 may be 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, 7 parts by mass or more, 9 parts by mass or more, 12 parts by mass or more, or 15 parts by mass or more, with respect to 100 parts by mass of the amount of the binder 12. From the perspective of increasing the residual magnetic flux density of the bonded magnet, the content of the elastomer particles 14 may be 40 parts by mass or less, 35 parts by mass or less, 30 parts by mass or less, 25 parts by mass or less, 17 parts by mass or less, 15 parts by mass or less, or 12 parts by mass or less, with respect to 100 parts by mass of the amount of the binder 12.

[0037] The bonded magnet according to the present embodiment may contain an additive in addition to the magnetic particles, the binder, and the elastomer particles. Examples of the additive include a flame retardant and a wax (lubricant).

[0038] The bulk density of the bonded magnet is 3 g / cm ３4 g / cm or more ３ 5 g / cm or more ３ or 6 g / cm or more ３ may be 7.7 g / cm or less ３ 7 g / cm or less ３ 6.5 g / cm or less ３ or 6.3 g / cm or less ３ may be less than or equal to the above values.

[0039] The bonded magnet may include, for example, a cured product of a compound described later, and may be composed of the cured product of the compound.

[0040] The bonded magnet may be an isotropic bonded magnet or an anisotropic bonded magnet (a bonded magnet in which the magnetization directions of magnetic particles are oriented).

[0041] An example of a method for manufacturing a bonded magnet includes a step of obtaining a molded body from a compound by heating and compressing the compound (molding step). The molding step may use a mold. The molding step may be a step of supplying the compound into the mold and heating and compressing the compound in the mold to obtain the above-mentioned molded body. The above-mentioned molded body may be a bonded magnet. <>

[0042] The heating temperature in the molding step may be 80°C or more, or 120°C or more, and may be 250°C or less, or 200°C or less. The heating time and the compression time may be 5 minutes or more, or 8 minutes or more, and may be 4 hours or less, or 小时3 hours or less.

[0043] The molding pressure in the molding step may be 500 MPa or more, 700 MPa or more, 1000 MPa or more, or 1500 MPa or more, and may be 2500 MPa or less, or 2000 MPa or less.

[0044] The molding process may be carried out while applying a magnetic field to the compound in the mold. Each magnetic particle in the compound is magnetized and rotated by the magnetic field, and the easy magnetization axis of the magnetic domain in each magnetic particle is oriented along the magnetic field. In other words, each magnetic particle in the compound is oriented so that its magnetization direction is approximately parallel to the magnetic field. If each magnetic particle is a single crystal grain (single magnetic domain), the magnetization direction of each magnetic particle is the same as the direction in which the easy magnetization axis of each magnetic particle extends.

[0045] When the resin contained in the compound includes a thermosetting resin, the compound hardens during the molding process, fixing each magnetic particle oriented in the direction of the easy magnetization axis. When the resin contained in the compound consists only of a thermoplastic resin, it is desirable to solidify the molded body by a cooling process after the molding process, and in that process, each magnetic particle oriented in the direction of the easy magnetization axis can be fixed more securely.

[0046] Examples of magnetic fields applied to the compound during the molding process include static magnetic fields (continuous, constant magnetic fields) and pulsed magnetic fields (pulsed magnetic fields). The strength of the static magnetic field may be 0.5T or more, 1T or more, or 2T or more, and may be 3T or less, or 2.5T or less. The strength of the pulsed magnetic field may be 4T or more, or 8T or more, and may be 20T or less, or 12T or less. The number of times the pulsed magnetic field is applied may be one or two or more times.

[0047] The above manufacturing method may further include a cooling step, a demagnetization step, a thermosetting step, and a magnetization step as steps following the molding step.

[0048] The cooling temperature in the cooling process may be 5°C or higher, 30°C or lower, or 25°C or lower. The cooling method may be natural cooling.

[0049] When a molding process is carried out while applying a magnetic field to the compound, if the molded body is not sufficiently hardened, the magnetic particles may move in the direction of the magnetic field generated in the molded body due to the alignment of the magnetization directions of the magnetic particles, causing each magnetic particle to protrude from the surface of the molded body and potentially leading to deformation of the molded body. Therefore, the above manufacturing method may include a demagnetization step to demagnetize the molded body in order to suppress this deformation. When a mold is used in the molding process, the demagnetization step may be performed before removing the molded body from the mold. The demagnetization step can more effectively suppress the deformation of the molded body. The demagnetization step may be performed after the cooling step or simultaneously with the cooling step. The demagnetization step may be performed by applying a magnetic field in the opposite direction to the magnetic field applied in the molding step.

[0050] If the compound contains a thermosetting resin, the above manufacturing method may include a thermosetting step from the viewpoint of more sufficiently advancing the curing of the thermosetting resin in the molded article. By going through the thermosetting step, the thermosetting of the thermosetting resin in the molded article progresses further, and the bulk density, mechanical strength, and residual magnetic flux density of the molded article (bonded magnet) tend to increase further. The thermosetting step may be performed after the molding step, cooling step, or demagnetization step.

[0051] The above manufacturing method may further include a magnetization step in which the molded body is magnetized after the demagnetization step, or after the demagnetization step and the thermosetting step. The details of the magnetic field applied in the magnetization step may be the same as the details of the magnetic field applied in the molding step described above.

[0052] One embodiment of the compound according to this disclosure is a compound used in the manufacture of bonded magnets, comprising magnetic particles, a resin, and elastomer particles.

[0053] The description of magnetic particles in the compound can be applied to the magnetic particles described for bonded magnets. The magnetic particles in the compound preferably include an Sm-Fe-N alloy. The magnetic particles may have a coating containing an inorganic compound. The coating containing the inorganic compound may be formed by treatment of the magnetic particles with a surface treatment agent, and may contain compounds derived from the surface treatment agent. The description of surface treatment agents in the compound can be applied to the surface treatment agents described for bonded magnets.

[0054] From the viewpoint of increasing the residual magnetic flux density of the bonded magnet, the magnetic particle content may be 70% or more by mass, 80% or more by mass, 90% or more by mass, 95% or more by mass, or 96% or more by mass, based on the total amount of compound. From the viewpoint of further suppressing the decrease in coercivity in the bonded magnet, the magnetic particle content may be 96.4% or less by mass, 96.3% or less by mass, 96.1% or less by mass, or 96% or less by mass, based on the total amount of compound.

[0055] The resin in the compound may be a thermosetting resin, a thermoplastic resin, or a mixture of a thermosetting resin and a thermoplastic resin.

[0056] Examples of thermosetting resins include epoxy resins, phenolic resins, bismaleimide resins, polyimide resins, and polyamideimide resins. The resin preferably contains an epoxy resin.

[0057] Epoxy resins include biphenyl-type epoxy resins, stilbene-type epoxy resins, diphenylmethane-type epoxy resins, sulfur atom-containing epoxy resins, novolac-type epoxy resins, dicyclopentadiene-type epoxy resins, salicylaldehyde-type epoxy resins, copolymer epoxy resins of naphthols and phenols, epoxidized aralkyl-type phenol resins, bisphenol-type epoxy resins (bisphenol A type epoxy resins and bisphenol F type epoxy resins, etc.), glycidyl ether-type epoxy resins of alcohols, glycidyl ether-type epoxy resins of paraxylylene and / or metaxylylene-modified phenol resins, and terpene-modified phenol Examples include glycidyl ether type epoxy resins of oleic 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 type or methylglycidyl type epoxy resins, alicyclic epoxy resins, halogenated phenol novolac type epoxy resins, orthocresol novolac type epoxy resins, hydroquinone type epoxy resins, thioether type epoxy resins, trimethylolpropane type epoxy resins, and linear aliphatic epoxy resins obtained by oxidizing olefin bonds with peracids such as peracetic acid.

[0058] The epoxy equivalent of the epoxy resin may be 100 g / eq or more, or 150 g / eq or more, from the viewpoint of increasing the mechanical strength of the bonded magnet. The epoxy equivalent of the epoxy resin may be 400 g / eq or less, or 350 g / eq or less, from the viewpoint of increasing the water resistance of the bonded magnet. The epoxy equivalent is the mass of epoxy resin containing one equivalent of epoxy groups. The epoxy equivalent is measured in accordance with JIS K 7236:2009.

[0059] Examples of thermoplastic resins include (meth)acrylic resins, polyolefins (e.g., polyethylene and polypropylene), polystyrene, polyvinyl chloride, and polyethylene terephthalate.

[0060] The weight-average molecular weight of the resin in the compound may be 100 or more, or 200 or more, and may be 10,000 or less, or 5,000 or less.

[0061] The resin content may be 1% by mass or more, 2% by mass or more, or 3% by mass or more, based on the total amount of the compound, and may be 20% by mass or less, 10% by mass or less, 7% by mass or less, or 5% by mass or less.

[0062] The resin content may be 1 part by mass or more, 2 parts by mass or more, or 3 parts by mass or more per 100 parts by mass of magnetic particles, and may be 20 parts by mass or less, 10 parts by mass or less, 7 parts by mass or less, or 5 parts by mass or less.

[0063] The above elastomer particles may contain rubber components. The explanation of rubber components in the compound, as described for bonded magnets, can be applied. The elastomer particles preferably include at least one selected from the group consisting of butadiene-based rubber and silicone rubber.

[0064] The average particle size of elastomer particles in the compound can be determined by applying the same explanation given for the average particle size of elastomer particles to bonded magnets. The ratio of the average particle size of elastomer particles to the average particle size of magnetic particles is preferably 0.3 or less.

[0065] From the viewpoint of further suppressing the decrease in coercivity in bonded magnets, the elastomer particle content may be 0.1% by mass or more, 0.15% by mass or more, 0.2% by mass or more, 0.25% by mass or more, 0.3% by mass or more, 0.4% by mass or more, 0.5% by mass or more, or 0.6% by mass or more, based on the total amount of compound. From the viewpoint of increasing the residual magnetic flux density of bonded magnets, the elastomer particle content may be 5% by mass or less, 3% by mass or less, 1% by mass or less, 0.8% by mass or less, 0.7% by mass or less, 0.5% by mass or less, or 0.4% by mass or less, based on the total amount of compound.

[0066] From the viewpoint of further suppressing the decrease in coercivity in bonded magnets, the elastomer particle content may be 0.1 parts by mass or more, 0.15 parts by mass or more, 0.2 parts by mass or more, 0.25 parts by mass or more, 0.3 parts by mass or more, 0.4 parts by mass or more, 0.5 parts by mass or more, or 0.6 parts by mass or more, per 100 parts by mass of magnetic particles. From the viewpoint of increasing the residual magnetic flux density of bonded magnets, the elastomer particle content may be 5 parts by mass or less, 3 parts by mass or less, 1 part by mass or less, 0.8 parts by mass or less, 0.7 parts by mass or less, 0.5 parts by mass or less, or 0.4 parts by mass or less, per 100 parts by mass of magnetic particles.

[0067] From the viewpoint of further suppressing the decrease in coercivity in bonded magnets, the elastomer particle content may be 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, 7 parts by mass or more, 9 parts by mass or more, 12 parts by mass or more, or 15 parts by mass or more per 100 parts by mass of resin. From the viewpoint of increasing the residual magnetic flux density of bonded magnets, the elastomer particle content may be 40 parts by mass or less, 35 parts by mass or less, 30 parts by mass or less, 25 parts by mass or less, 17 parts by mass or less, 15 parts by mass or less, or 12 parts by mass or less per 100 parts by mass of resin.

[0068] The compound may take any form, and may be a powder (compound powder), a tablet, or a paste. The magnetic particles may be coated with a resin layer containing resin, or with a mixture containing resin and elastomer particles (hereinafter also referred to as the "resin composition"). In this case, the layer composed of the resin composition is also called the resin composition layer. In the resin composition layer, the elastomer particles may be dispersed in the resin. The compound may also consist of magnetic particles, resin, and elastomer particles separately (for example, a mixture of magnetic particles, resin solids, and elastomer particles), a mixture of resin-coated magnetic particles (hereinafter also referred to as "coated particles") and elastomer particles, or a mixture of magnetic particles and solids of the resin composition. When the compound is a mixture of coated particles and elastomer particles, the elastomer particles may be attached to the surface of the coated particles.

[0069] Figure 2 is a schematic cross-sectional view showing an example of particles constituting a compound. As shown in Figure 2, particles composed of magnetic particles, resin, and elastomer particles will hereafter be simply referred to as composite particles. The particles 2 (composite particles 2) constituting the compound shown in Figure 2 consist of magnetic particles 10 and a resin composition layer 26 covering the surface of the magnetic particles 10. The resin composition layer 26 consists of resin 22 and elastomer particles 24. In Figure 2, the composite particles 2 are shown in a configuration where the entire surface of the magnetic particles 10 is covered with the resin composition layer 26, but it is also possible that only a part of the surface of the magnetic particles 10 is covered with the resin composition layer 26.

[0070] Figure 3 is a schematic cross-sectional view showing an example of particles constituting a compound. In Figure 3, the particles 3 (composite particles 3) constituting the compound consist of magnetic particles 10, a resin 30 covering the surface of the magnetic particles 10, and elastomer particles 24 attached to the surface of the resin layer made up of the resin 30. In Figure 3, the composite particles 3 are shown in a configuration where the entire surface of the magnetic particles 10 is covered with the resin layer, but it is also possible that only a part of the surface of the magnetic particles 10 is covered with the resin layer. The resin layer in Figure 3 differs from the resin composition layer shown in Figure 2 in that it does not contain elastomer particles.

[0071] The compound according to this embodiment may contain additives in addition to magnetic particles, resin, and elastomer particles. Examples of additives include curing agents, curing accelerators (curing catalysts), coupling agents (e.g., silane coupling agents), flame retardants, waxes (lubricants), and organic solvents. The compound according to this embodiment contains an epoxy resin and may further contain a curing agent.

[0072] The curing agent may contain an imidazole compound. Examples of imidazole compounds include 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.

[0073] The hardening agent content may be 0.01% by mass or more, 0.03% by mass or more, or 0.05% by mass or more, based on the total amount of the compound, and may be 0.5% by mass or less, 0.3% by mass or less, 0.2% by mass or less, or 0.1% by mass or less.

[0074] The amount of curing agent may be 1 part by mass or more, 1.5 parts by mass or more, or 1.8 parts by mass or more, and may be 20 parts by mass or less, 10 parts by mass or less, or 5 parts by mass or less, per 100 parts by mass of resin.

[0075] Examples of organic solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, benzene, toluene, and xylene.

[0076] One example of a compound manufacturing method includes a step of mixing magnetic particles, resin, and elastomer particles (a step of obtaining a mixture). The resulting aggregate of composite particles may be a powder.

[0077] If the particles constituting the compound are composed of magnetic particles and a resin composition layer covering the surface of the magnetic particles (for example, composite particle 2 described above), the above mixing step may be replaced with a step to obtain composite particles by coating the magnetic particles with a resin composition containing resin and elastomer particles (step to obtain composite particles). The step to obtain composite particles may be carried out by dispersing the magnetic particles, resin, and elastomer particles in a solvent and then removing the solvent, or by bringing a resin melt containing resin and elastomer particles into contact with the magnetic particles. The solvent may be removed by volatilizing the solvent. The heating temperature in this case may be, for example, 25°C or higher. Examples of solvents used when preparing the resin solution include acetone, methyl ethyl ketone, methyl isobutyl ketone, benzene, toluene, and xylene.

[0078] If the particles constituting the compound are composed of magnetic particles, a resin layer covering the surface of the magnetic particles, and elastomer particles attached to the resin layer (for example, composite particle 3 described above), the above mixing step may be replaced with a step of mixing resin-coated magnetic particles (coated particles) with elastomer particles to obtain a compound (step of obtaining composite particles). The above-mentioned coated particles may be purchased and used, or may be prepared and used in-house. That is, the above manufacturing method may further include a step of obtaining coated particles by dispersing the magnetic particles and the resin in a solvent and then removing the solvent.

[0079] The method for producing the compound may further include other steps in addition to the step of obtaining a mixture or composite particles. Other steps may include, for example, a step of breaking down the aggregates of the composite particles obtained after the step of obtaining the composite particles.

[0080] The above-described method for manufacturing the compound was an example using a wet process, but the compound can also be manufactured without using organic solvents. In this case, the magnetic particles and the resin composition may be mixed in a sealed container.

[0081] Hereinafter, the present disclosure will be described in more detail based on examples. Note that the examples described below show an example of a representative example of the present disclosure, and the present disclosure is not limited to the following examples.

[0082] (Example 1) A rubber-containing resin (product name: "Kaneka Ace MX-960", manufactured by Kaneka Corporation) containing bisphenol A type epoxy resin and silicone rubber particles (elastomer particles) was prepared. The contents of the epoxy resin and the silicone rubber particles based on the total amount of the rubber-containing resin were 75% by mass and 25% by mass, respectively. In the above rubber-containing resin, the epoxy equivalent of the epoxy resin was 243 g / eq, the weight-average molecular weight of the epoxy resin was 1000, the average particle diameter of the elastomer particles was 100 nm, and the weight-average molecular weight of the silicone rubber was 500.

[0083] The above rubber-containing resin, an epoxy resin (product name: "YX-4000H", manufactured by Mitsubishi Chemical Corporation, epoxy equivalent: 192 g / eq, weight-average molecular weight: 350), a curing agent (product name: "2E4MZ", manufactured by Shikoku Kasei Kogyo Co., Ltd.), and acetone were mixed to obtain a resin solution. The content of the rubber-containing resin was 1.4 parts by mass, the content of the epoxy resin was 2.45 parts by mass, and the content of the curing agent was 0.07 parts by mass. In the resin solution, 100 parts by mass of powder of an Sm-Fe-N based alloy containing a main phase composed of Sm ２ Fe １７ N ３ (spherical magnet powder, average particle diameter 3 μm) was added and dispersed. After dispersion, the resin solution was dried at 30 °C for 3 hours to obtain a compound composed of composite particles in which a resin composition layer in which elastomer particles were dispersed was provided on the surface of magnetic particles. In the obtained compound, the contents of the epoxy resin and the elastomer particles were 3.5 parts by mass and 0.35 parts by mass, respectively, with respect to 100 parts by mass of the amount of magnetic particles.

[0084] Approximately 2 g of the obtained compound was supplied into the mold of the molding apparatus. The mold had dimensions of 7 mm (length) x 7 mm (width) x 7 mm (height). A hydraulic press (product name "TM-MPH10525-10A2TM type," manufactured by Tamagawa Seisakusho Co., Ltd.) was used as the molding apparatus, and the compound was heated and compressed under the conditions of a heating temperature of 150°C, a pressure of 1800 MPa, and a compression time of 10 minutes. After heating and compression, the mold was cooled to room temperature to obtain a bonded magnet. The bulk density of the bonded magnet was 6.09 g / cm³. ３ That was the case.

[0085] (Example 2) A bonded magnet was obtained in the same manner as in Example 1, except that 2.8 parts by mass of the rubber-containing resin and 1.4 parts by mass of epoxy resin were mixed. The content of epoxy resin and elastomer particles was 3.5 parts by mass and 0.7 parts by mass, respectively, per 100 parts by mass of magnetic particles. The bulk density of the bonded magnet was 6.08 g / cm³. ３ That was the case.

[0086] (Comparative Example 1) A bonded magnet was obtained in the same manner as in Example 1, except that the above-mentioned rubber-containing resin was not mixed, and 3.5 parts by mass of epoxy resin was mixed. The bulk density of the bonded magnet was 6.10 g / cm³. ３ That was the case.

[0087] <Measurement of Residual Magnetic Flux Density and Coercivity> The residual magnetic flux density and coercivity of the bonded magnets of Examples 1 and 2 and Comparative Example 1 were measured using a high-sensitivity, superconducting magnet type (electromagnet type) vibrating sample magnetometer (VSM, product name "TM-VSM311483-HGC type", manufactured by Tamagawa Seisakusho Co., Ltd.). The results are shown in Table 1.

[0088]

[0089] 1...Bonded magnet, 2,3...Particles constituting the compound (composite particles), 10...Magnetic particles, 12...Binder, 14,14a,14b,24...Elastomer particles, 22,30...Resin, 26...Resin composition layer.

Claims

1. A bonded magnet comprising magnetic particles, a binder that binds the magnetic particles together, and elastomer particles, wherein a portion of the elastomer particles is located at least a portion of the space between the magnetic particles.

2. A compound used in the manufacture of bonded magnets, comprising magnetic particles, a resin, and elastomer particles.

3. The compound according to claim 2, wherein the resin comprises an epoxy resin and further comprises a curing agent.

4. The compound according to claim 2, wherein the elastomer particles include at least one selected from the group consisting of butadiene rubber and silicone rubber.

5. The compound according to claim 2, wherein the magnetic particles include an Sm-Fe-N alloy.

6. The compound according to claim 2, wherein the content of the elastomer particles is 0.2 parts by mass or more per 100 parts by mass of the magnetic particles.

7. The compound according to claim 2, wherein the average particle diameter of the elastomer particles is smaller than the average particle diameter of the magnetic particles.

8. The compound according to claim 2, wherein the ratio of the average particle diameter of the elastomer particles to the average particle diameter of the magnetic particles is 0.3 or less.

9. The compound according to claim 2, wherein the magnetic particles are coated with a resin layer containing the resin.

10. The compound according to claim 2, wherein the elastomer particles are dispersed in the resin.

11. The compound according to claim 9, wherein the resin layer comprises the elastomer particles.

12. The compound according to claim 9, wherein the elastomer particles are attached to the resin layer.

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