Manufacturing method for compound and bonded magnets

Abstract

To provide a compound that exhibits excellent fluidity and increases the bulk density of bonded magnets manufactured from the compound. [Solution] Compound 10 comprises a first magnet powder consisting only of a plurality of first magnet particles 1, and granulated powder. The first magnet powder and granulated powder are mixed. The particle size of the first magnet powder is smaller than the particle size of the granulated powder. Each of the plurality of granulated particles 3 constituting the granulated powder comprises one or more second magnet particles 2, and a resin composition 4 covering one or more second magnet particles 2. The plurality of first magnet particles 1 are an alloy containing samarium, iron, and nitrogen. The one or more second magnet particles 2 are an alloy containing samarium, iron, and nitrogen. The resin composition 4 contains a thermosetting resin.

Description

Technical Field

[0001] The present disclosure relates to a compound and a method for manufacturing a bonded magnet.

Background Art

[0002] Sm-Fe-N-based permanent magnets (samarium-iron-nitrogen-based permanent magnets) can be manufactured from inexpensive raw materials compared to other rare-earth magnets such as Nd-Fe-B-based permanent magnets (neodymium-iron-boron-based permanent magnets), and have excellent magnetic properties. However, since the crystal structure of Sm-Fe-N-based permanent magnets is liable to deteriorate at high temperatures (about 500°C), it is difficult to manufacture sintered magnets from Sm-Fe-N-based permanent magnets. Therefore, Sm-Fe-N-based permanent magnets are used as raw materials for bonded magnets that can be manufactured by heating at a low temperature at which the crystal structure is maintained (thermosetting of the resin composition mixed with the magnet powder) (see Patent Document 1 below).

[0003] As a raw material for bonded magnets, a compound containing magnet powder (a large number of magnet particles made of a permanent magnet) and a resin composition is used. For example, in the manufacture of bonded magnets, a molding process of heating and compressing the compound in a mold is carried out. If necessary, a magnetic field may be applied to the compound in the mold during the molding process. By this molding process, a molded body made of magnet powder and a resin composition is formed from the compound. By thermosetting the resin composition in the molded body, the molded body becomes a bonded magnet.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The smaller the particle size of the magnetic powder contained in the compound, the easier it is for the magnetic powder to densely fill the bonded magnet, and the easier it is for the bulk density of the bonded magnet to increase. As the bulk density of the bonded magnet increases, the residual magnetic flux density and mechanical strength of the bonded magnet tend to increase. However, the smaller the particle size of the magnetic powder, the larger the specific surface area of ​​the magnetic powder, and the easier it is for the magnetic powder to aggregate. Therefore, the smaller the particle size of the magnetic powder, the less fluid the compound containing the magnetic powder becomes. It is difficult to transport a compound with poor fluidity, and it is also difficult to process a compound with poor fluidity precisely. For example, it is difficult to transport and inject a compound with poor fluidity into the inside of a mold for compression molding. A compound with poor fluidity is difficult to fill into the mold, and a gap may be created between the compound and the inner wall of the mold. As a result, it becomes difficult to precisely adjust the dimensions and shape of the molded body using the mold. It is also difficult to process compounds with poor fluidity using injection molding.

[0006] Instead of conventional compounds (simply mixtures of magnet powder and resin composition), granulated powder formed from a mixture of magnet powder and resin composition may be used as a raw material for bonded magnets. The particle size of the granulated powder is larger than the particle size of the magnet powder itself. Furthermore, the resin composition in the granulated powder suppresses contact and aggregation between multiple magnet particles in the granulated powder. Therefore, the granulated powder is less prone to aggregation and more fluid than magnet powder and conventional compounds. The larger the particle size of the granulated powder, the less prone to aggregation and the more fluid it is. However, the larger the particle size of the granulated powder, the more difficult it is for the granulated powder to densely fill the bonded magnet, and the more likely the bulk density of the bonded magnet is to decrease. Along with the decrease in bulk density of the bonded magnet, the residual magnetic flux density and mechanical strength of the bonded magnet decrease.

[0007] One aspect of this disclosure is to provide a compound that has excellent fluidity and increases the bulk density of bonded magnets manufactured from the compound, and a method for manufacturing bonded magnets using the compound. [Means for solving the problem]

[0008] For example, one aspect of this disclosure relates to a compound relating to any one of the following [1] to [4], and to a method for manufacturing a bonded magnet relating to the following [5].

[0009] [1] comprising a first magnet powder consisting only of a plurality of first magnet particles, and granulated powder, The first magnet powder and the granulated powder are mixed together. The particle size of the first magnet powder is smaller than the particle size of the granulated powder. Each of the plurality of granulated particles constituting the granulated powder comprises one or more second magnetic particles and a resin composition covering one or more of the second magnetic particles, The plurality of first magnetic particles are an alloy containing samarium, iron, and nitrogen. One or more of the second magnetic particles are an alloy containing samarium, iron, and nitrogen. The resin composition includes a thermosetting resin. Compound.

[0010] [2] The particle size of the first magnet powder is 1 μm or more and 5 μm or less, The particle size of the granulated powder is 30 μm or more and 100 μm or less. The compound described in [1].

[0011] [3] The median diameter of the first magnet powder is smaller than the median diameter of the granulated powder, The median diameter of the first magnet powder is 1 μm or more and 5 μm or less. The median diameter of the granulated powder is 30 μm or more and 100 μm or less. The compound described in [1] or [2].

[0012] [4] The content of the first magnet powder is 5% by mass or more and 20% by mass or less, The content of the granulated powder is 80% by mass or more and 95% by mass or less. The compound listed in any one of [1] to [3].

[0013] [5] A method for manufacturing a bonded magnet from a compound according to any one of [1] to [4], comprising a molding step of forming a molded body from the compound in the mold by heating and compressing the compound in the mold. A method for manufacturing a bonded magnet.

Advantages of the Invention

[0014] According to one aspect of the present disclosure, there are provided a compound having excellent fluidity and increasing the bulk density of a bonded magnet manufactured from the compound, and a method for manufacturing a bonded magnet using the compound.

Brief Description of the Drawings

[0015] [Figure 1] FIG. 1 shows a schematic cross-section of a specific example of a compound according to the present disclosure.

Modes for Carrying Out the Invention

[0016] Hereinafter, preferred embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same reference numerals are assigned to the same components. The present disclosure is not limited to the following embodiments. X, Y, and Z shown in FIG. 1 mean three coordinate axes orthogonal to each other.

[0017] (Overview of Compound and Method for Manufacturing Bonded Magnet) The compound according to this embodiment is a raw material for bonded magnets. As shown in Figure 1, the compound 10 according to this embodiment includes a first magnet powder consisting only of a plurality of first magnet particles 1, and a granulated powder consisting only of a plurality of granulated particles 3. The first magnet powder and the granulated powder in the compound 10 are mixed. The particle size of the first magnet powder is smaller than the particle size of the granulated powder. In other words, the particle size of each of the plurality of first magnet particles 1 is smaller than the particle size of each of the plurality of granulated particles 3. For example, the median diameter (D50) of the first magnet powder may be smaller than the median diameter of the granulated powder. Each of the plurality of granulated particles 3 constituting the granulated powder includes one or more second magnet particles 2 and a resin composition 4 that covers part or all of the surface of each of the one or more second magnet particles 2. That is, one granulated particle 3 includes one or more second magnet particles 2 and a resin composition 4 that covers the surface of each second magnet particle 2. The compound 10 may be described as a mixture. Compound 10 may be in powder form at room temperature (for example, 20°C ± 15°C).

[0018] The method for manufacturing a bonded magnet according to this embodiment may include a molding step in which a molded body is formed from a compound in a mold by heating and compressing the compound in the mold. If necessary, a magnetic field may be applied to the compound in the mold during the molding step. The molded body becomes a bonded magnet by the thermal curing of the resin composition in the molded body.

[0019] Conventional compounds that do not contain granulated powder (simply a mixture consisting of magnet powder and resin composition) are difficult to flow because they contain magnet powder that is prone to agglomeration. It is difficult to transport compounds with poor fluidity, and it is also difficult to process compounds with poor fluidity precisely. However, the compound 10 according to this embodiment contains not only the first magnet powder but also granulated powder. The particle size of the granulated powder is larger than that of the first magnet powder, and the granulated powder is less prone to agglomeration than the first magnet powder. Therefore, the compound 10 containing granulated powder is less prone to agglomeration and flows more easily than conventional compounds that do not contain granulated powder. It is easy to transport the compound 10 with excellent fluidity during the manufacturing process of bonded magnets, and it is also easy to process the compound 10 with excellent fluidity precisely during the manufacturing process of bonded magnets. Compounds consisting solely of granulated powder are coarser than conventional compounds containing small-particle magnet powder (simply a mixture of magnet powder and resin composition). Therefore, compounds consisting solely of granulated powder are difficult to densely pack in a molded body, and numerous voids are easily formed between multiple granulated particles in the molded body. As a result, the bulk density of bonded magnets manufactured from compounds consisting solely of granulated powder is lower than that of bonded magnets manufactured from conventional compounds. However, the compound 10 according to this embodiment includes not only granulated powder but also first magnet powder. The first magnet particles 1, which have small particle sizes, are easily packed between multiple granulated particles 3, which have larger particle sizes. Therefore, the compound 10 according to this embodiment is easily densely packed in a molded body, and the bulk density of bonded magnets manufactured from the compound 10 according to this embodiment is higher than that of bonded magnets manufactured from compounds consisting solely of granulated powder. As described above, the granulated powder in compound 10 improves the fluidity of compound 10, and the first magnet powder in compound 10 increases the bulk density of the bonded magnet.

[0020] Compound 10 may consist only of the first magnet powder and the granulated powder. Compound 10 may further contain other components in addition to the first magnet powder and the granulated powder. For example, the other component may be a resin composition different from the resin composition 4 contained in the granulated powder (an uncured or semi-cured resin composition that does not constitute the granulated powder). Each of the multiple granulated particles 3 may consist only of one or more second magnet particles 2 and the resin composition. Each of the multiple granulated particles 3 may contain multiple second magnet particles 2. The number of second magnet particles 2 contained in each of the multiple granulated particles 3 may be the same. The number of second magnet particles 2 contained in any one granulated particle 3 may be different from the number of second magnet particles 2 contained in another granulated particle 3.

[0021] Multiple first magnetic particles 1 are alloys containing samarium (Sm), iron (Fe), and nitrogen (N). One or more second magnetic particles 2 contained in each granulated particle 3 are also alloys containing samarium, iron, and nitrogen. The composition of the second magnetic particles 2 may be the same as that of the first magnetic particles 1. The composition of the second magnetic particles 2 may be different from that of the first magnetic particles 1, as long as the first magnetic particles 1 and the second magnetic particles 2 are alloys containing samarium, iron, and nitrogen.

[0022] Each of the multiple granulated particles 3 contains a resin composition 4 which includes a thermosetting resin. As described later, the resin composition 4 may further contain one or more components other than the thermosetting resin. Part or all of the resin composition 4 may be uncured. Part or all of the resin composition 4 may be semi-cured (stage B resin composition). Part of the resin composition 4 may be uncured and the remainder of the resin composition 4 may be semi-cured. When a single granulated particle 3 contains multiple secondary magnet particles 2, the resin composition 4 in the granulated particle 3 functions as a binder that binds the multiple secondary magnet particles 2 together. The resin composition 4 in the molded body and bonded magnet functions as a binder that binds multiple magnet particles together in the molded body and bonded magnet. For example, the resin composition filled between multiple magnet particles binds them together. Furthermore, the heat curing of the resin composition causes the cured product to bind the multiple magnet particles together more firmly. In other words, the resin composition imparts mechanical strength to the molded body and bonded magnet manufactured from the compound.

[0023] For example, the particle size of the first magnet powder (multiple first magnet particles 1) may be 1 μm or more and 5 μm or less, or 2 μm or more and 3 μm or less. When the particle size of the first magnet powder is 1 μm or more, the fluidity of the compound 10 tends to improve. When the particle size of the first magnet powder is 5 μm or less, the bulkiness of the bonded magnet manufactured from the compound 10 tends to increase. For similar reasons, the median diameter of the first magnet powder may be 1 μm or more and 5 μm or less. The particle size of the first magnet powder may be irregular as long as it is smaller than the particle size of the granulated powder. The particle size of one or more secondary magnet particles 2 contained in each granulated particle 3 may be the same as the particle size of the first magnet powder. The particle size of the secondary magnet particles 2 may be different from the particle size of the first magnet powder. For example, the particle size of the secondary magnet particles 2 may be 0.5 μm or more and less than 100 μm, 1 μm or more and 10 μm or less, 1 μm or more and 5 μm or less, or 2 μm or more and 3 μm or less. The particle sizes of one or more secondary magnet particles 2 contained in each granulated particle 3 may be irregular.

[0024] For example, the particle size of the granulated powder (multiple granulated particles 3) may be 30 μm or more and 100 μm or less, or 30 μm or more and 70 μm or less. When the granulated powder is 30 μm or larger, the fluidity of the compound 10 tends to improve. When the granulated powder is 100 μm or smaller, the bulkiness of the bonded magnet manufactured from the compound 10 tends to increase. For similar reasons, the median diameter of the granulated powder may be 30 μm or more and 100 μm or less, or 30 μm or more and 70 μm or less. The particle size of the granulated powder may be uneven as long as the particle size of the first magnet powder is smaller than the particle size of the granulated powder.

[0025] For example, the content of first magnet powder (multiple first magnet particles 1) in compound 10 may be 5% by mass or more and 20% by mass or less, and the content of granulated powder (multiple granulated particles 3) in compound 10 may be 80% by mass or more and 95% by mass or less. When the content of first magnet powder is 5% by mass or more and the content of granulated powder is 95% by mass or less, the density of the bonded magnet produced from compound 10 tends to increase. When the content of first magnet powder is 20% by mass or less and the content of granulated powder is 80% by mass or more, the fluidity of compound 10 tends to improve.

[0026] For the reason that the bulk density, mechanical strength, and residual magnetic flux density of bonded magnets tend to increase, the content of "total magnet particles" in compound 10 may be 90.0% by mass or more and 99.9% by mass or less, 95.0% by mass or more and 99.5% by mass or less, or 96.0% by mass or more and 98.0% by mass or less. "Total magnet particles" in compound 10 refers to all first magnet particles 1 and all second magnet particles 2 in compound 10. The bulk density and residual magnetic flux density of bonded magnets tend to increase with increasing content of total magnet particles in compound 10. The mechanical strength of bonded magnets tend to increase with decreasing content of total magnet particles in compound 10. The content of resin composition 4 in compound 10 may be 0.1% by mass or more and 10.0% by mass or less, 0.5% by mass or more and 5.0% by mass or less, or 2.0% by mass or more and 4.0% by mass or less. As the content of resin composition 4 in compound 10 decreases, the bulk density and residual magnetic flux density of the bonded magnet tend to increase. As the content of resin composition in compound 10 increases, the mechanical strength of the bonded magnet tend to increase.

[0027] (Details of the first and second magnetic particles) As described above, the first and second magnetic particles are alloys containing samarium (Sm), iron (Fe), and nitrogen (N). Alloys containing samarium, iron, and nitrogen can be referred to as Sm-Fe-N permanent magnets. Sm-Fe-N permanent magnets exhibit magnetic anisotropy. In other words, the magnetic domains contained in the first and second magnetic particles each have an easy magnetization axis (crystal axis) extending in one direction. The "SmFeN powder" described below is a general term for the first and second magnetic particles.

[0028] For example, SmFeN powder has Sm2Fe as the main phase. 17 The powder may contain N3 (alloy). For example, at least a portion of the SmFeN powder may be an anisotropic magnetic powder containing Th2Zn type crystals (rhombohedral crystals) as the main phase. An anisotropic magnetic powder is a magnetic powder in which the individual magnetic particles constituting the magnetic powder are single crystals, or a magnetic powder in which the individual magnetic particles constituting the magnetic powder are composed of a large number of fine single crystal grains (magnetic domains), and the direction of the easy magnetization axis of each crystal grain is aligned in a specific direction. For example, at least a portion of the SmFeN powder may be an isotropic magnetic powder containing TbCu7 type crystals (hexagonal crystals) as the main phase. An isotropic magnetic powder is a magnetic powder in which the individual magnetic particles constituting the magnetic powder are composed of a large number of fine single crystal grains (magnetic domains), and the direction of the easy magnetization axis of each crystal grain is disordered. In addition to the SmFeN powder, the magnetic powder may further contain powders made of other permanent magnets.

[0029] The method for producing SmFeN powder is not limited. For example, a method for producing SmFeN powder may include the steps of forming an alloy powder containing Sm and Fe by a mechanical alloying method, and obtaining SmFeN powder by heating the alloy powder in nitrogen gas. SmFeN powder may also be produced by a rapid solidification method. In the rapid solidification method, 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. SmFeN powder is obtained by crushing the solidified alloy. SmFeN powder may also be produced by the HDDR (Hydrogenation Disproportion Desorption Recombination) method.

[0030] For example, as the SmFeN powder, unground powder (spherical magnetic powder) obtained by Nichia Corporation's build-up method may be used. The surface of each magnetic particle constituting the SmFeN powder may be covered with an inorganic film by surface treatment. For example, the inorganic film may contain phosphate or silica-based compounds.

[0031] The particle sizes of the first and second magnetic particles may be adjusted in the manufacturing method described above, or they may be adjusted by classification using a sieve. Commercially available magnetic powders whose particle sizes have already been adjusted to a desired range may be used as the first and second magnetic particles.

[0032] (Details of the resin composition) The resin composition may consist of the non-volatile components of the compound excluding the first magnetic powder and a plurality of second magnetic particles. As described above, the resin composition includes a thermosetting resin. The thermosetting resin may be the main component of the resin composition. In addition to the thermosetting resin, the resin composition may further contain one or more components selected from the group consisting of a curing agent, a curing accelerator (curing catalyst), a coupling agent, a wax (lubricant), a reactive diluent, and a flame retardant.

[0033] For example, the thermosetting resin may be one or more resins selected from the group consisting of epoxy resins, maleimide compounds (e.g., bismaleimide), polyimides, polyamides, and polyamideimides.

[0034] For example, the curing agent may be one or more compounds selected from the group consisting of phenolic resins, phenol novolac resins, imidazole, dicyandiamide (DICY), aromatic polyamines, acid anhydrides, aliphatic polyamines, polyaminoamides, and polymercaptans. When the resin composition contains a phenolic resin (especially a phenol novolac resin) as a curing agent together with the epoxy resin, the heat resistance (mechanical strength at high temperatures) of the bonded magnet tends to improve. When the resin composition contains an amine (e.g., imidazole) as a curing agent together with the epoxy resin, the resin composition tends to cure quickly during the molding process described later.

[0035] For example, the curing accelerator may be one or more compounds selected from the group consisting of imidazole and tetrasubstituted phosphonium / tetrasubstituted borate.

[0036] For example, the coupling agent may be any coupling agent that reacts with the glycidyl groups present in the resin composition. The coupling agent improves the adhesion between the magnet particles and the resin composition, thereby improving the mechanical strength of the bonded magnet. The coupling agent that reacts with the glycidyl groups may be, for example, a silane compound (silane coupling agent).

[0037] For example, the wax may be one or more compounds selected from the group consisting of synthetic waxes, saturated fatty acids, saturated fatty acid salts, and saturated fatty acid esters. Due to the lubricating properties of the wax, multiple magnetic particles in the compound slide easily against each other. Therefore, in the molding process described later, each magnetic particle rotates easily due to the magnetic field, and each magnetic particle is easily oriented along the magnetic field. As a result, the residual magnetic flux density of the bonded magnet tends to improve.

[0038] 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. For example, the reactive diluent may be at least one selected from the group consisting of alkyl monoglycidyl ethers, alkylphenol monoglycidyl ethers, and alkyl diglycidyl ethers.

[0039] For example, the flame retardant may be one or more compounds selected from the group consisting of brominated 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.

[0040] The resin composition may include other resins, such as thermoplastic resins, in addition to thermosetting resins. For example, the other resins may be one or more resins selected from the group consisting of polyphenylene sulfide resins, acrylic resins, methacrylic resins, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyethylene terephthalate, and silicone resins.

[0041] (Method for producing granulated powder) The method for producing granulated powder is not limited. For example, granulated powder may be produced by the following method. The term "secondary magnetic powder" as used below means magnetic powder consisting only of a plurality of secondary magnetic particles.

[0042] A resin solution containing the dissolved resin composition is prepared by uniformly stirring and mixing the uncured resin composition (all components constituting the resin composition) with an organic solvent. The organic solvent is not limited as long as it is a solvent in which the resin composition can be dissolved. For example, the organic solvent may be one or more compounds selected from the group consisting of acetone, methyl ethyl ketone, methyl isobutyl ketone, benzene, toluene, xylene, N-methylpyrrolidinone (N-methyl-2-pyrrolidone), γ-butyrolactone, dimethylformamide, and dimethyl sulfoxide. The organic solvent may be a liquid at room temperature. For example, the boiling point of the organic solvent may be between 60°C and 150°C.

[0043] Granulated powder is obtained by thoroughly removing the organic solvent from the resin solution while stirring and mixing the above resin solution and second magnet powder. As the organic solvent is removed, the resin composition solidifies on the surface of one or more second magnet particles, forming granulated particles consisting of one or more second magnet particles and the resin composition. Granulated particles consisting of multiple second magnet particles bound to each other via the resin composition may also be formed. The resin composition may cover part or all of the surface of each second magnet particle. Granulated particles consisting of one or more second magnet particles and the resin composition, with their magnetization direction oriented along the magnetic field, may be formed by thoroughly removing the organic solvent from the mixture of resin solution and second magnet powder in a magnetic field.

[0044] For drying the granulated powder (removal of organic solvent), the granulated powder may be formed in a vacuum. To suppress oxidation of the second magnetic powder, the granulated powder may be formed in an inert gas. For example, the inert gas may be nitrogen gas or a noble gas (such as argon). For drying the granulated powder (removal of organic solvent), the second magnetic powder and resin solution may be heated at a temperature above the boiling point of the organic solvent and below the curing temperature of the thermosetting resin, while stirring. The stirring method for the second magnetic powder and resin solution may be stirring by vibration, stirring by airflow, mechanical stirring, or stirring by a magnetic field. The particle size of the granulated powder may be controlled by the particle size of the second magnetic powder, the concentration and viscosity of the resin solution, the boiling point of the organic solvent, and the drying temperature.

[0045] The particle size and particle size distribution of the granulated powder may be adjusted by classification. For example, the classification means may be a sieve. The mesh size of the sieve is not limited. For example, nominal mesh sizes of sieves according to JIS Z8801-1 are 25 μm, 32 μm, 38 μm, 45 μm, 53 μm, 63 μm, 75 μm, 90 μm, 106 μm, 125 μm, 150 μm, 212 μm, 250 μm, 300 μm, 355 μm, 425 μm, 500 μm, 600 μm, 710 μm, 1 mm, 1.18 mm, 1.4 mm, and 1.7 mm, 2 mm, etc. Granulated powder can be classified using sieves having these nominal mesh sizes. By classifying granulated powder using one type of sieve, granulated powder with a particle size below a desired value (sieve opening) may be recovered. By classifying granulated powder using two types of sieves with different openings, the particle size of the granulated powder may be adjusted to a predetermined range.

[0046] (Method of manufacturing bonded magnets) For example, a method for manufacturing bonded magnets includes at least a molding step. The method for manufacturing bonded magnets may further include a cooling step, a demagnetization step, a thermosetting step, and a magnetization step as steps following the molding step. Details of each step are described below.

[0047] Before the start of the molding process, the compound is supplied and filled into the mold (cavity). The temperature of the compound itself supplied and filled into the mold may be room temperature or ambient temperature. The compound is easily manufactured by mixing the first magnetic powder and granulated powder before the molding process.

[0048] In the molding process, the compound in the mold is heated and compressed. For example, in the molding process, the compound in the mold may be heated at a molding temperature T and then compressed. By heating and compressing the compound, a molded body is formed from the compound in the mold. In the molding process, the compound in the mold may be heated and compressed while a magnetic field is applied to it. When the compound in the mold is heated and compressed while a magnetic field is applied to it, multiple magnetic particles (magnetic domains) in the compound are magnetized and oriented along the magnetic field, resulting in a molded body that is magnetized along the magnetic field.

[0049] For example, the molding pressure may be between 500 MPa and 2000 MPa, between 700 MPa and 2000 MPa, or between 980 MPa and 2000 MPa.

[0050] The molding temperature T can be rephrased as the temperature of the compound during the molding process. If the maximum value of the molding temperature T is equal to or greater than the thermosetting temperature of the resin composition, the thermosetting of the resin composition during the molding process forms a molded body containing the cured resin composition and magnetic powder. If the maximum molding temperature T is less than the thermosetting temperature of the resin composition, a molded body containing the uncured resin composition and magnetic powder is formed. If the molding temperature T is equal to or greater than the thermosetting temperature of the resin composition, the molded body may be a completed bonded magnet.

[0051] For example, the molding temperature T may be 60°C to 300°C, 60°C to 180°C, 60°C to 150°C, 70°C to 110°C, or 80°C to 100°C. For example, the time during which the compound in the mold is heated at the molding temperature T (molding time) may be several tens of seconds or more and several hours or less.

[0052] The magnetic field applied to the compound inside the mold may be a static magnetic field (a continuous, constant magnetic field). The magnetic field H may also be a pulsed magnetic field (a pulsed magnetic field). For example, the strength of the static magnetic field may be between 0.5 T (Tesla) and 2.5 T. For example, the time for which the static magnetic field is applied to the compound in the mold may be between 0.08 minutes and 4 minutes. For example, the intensity of the pulsed magnetic field may be between 4T and 12T. The pulsed magnetic field may be applied to compound 2 once or multiple times.

[0053] A cooling process may be carried out after the molding process. In the cooling process, the mold containing the molded body (bonded magnet) is cooled. For example, in the cooling process, the mold containing the molded body may be cooled to room temperature. The molded body (bonded magnet) inside the mold becomes more solid due to the cooling process. As a result, the mechanical strength of the molded body inside the mold increases, which suppresses deformation and damage of the molded body in each process after the cooling process, and the mechanical strength of the bonded magnet tends to increase.

[0054] A demagnetization process may be performed after the molding process. The demagnetization process may be performed after the cooling process. The demagnetization process may be performed simultaneously with the cooling process. In the demagnetization process, the molded body is demagnetized by applying a magnetic field (reverse magnetic field) in the opposite direction to the magnetic field used in the molding process. Demagnetization of the molded body suppresses deformation of the molded body caused by the magnetic force of the molded body itself. When a demagnetization process is performed, it is preferable to perform the magnetization process described later.

[0055] If the molded body obtained in the molding process contains an uncured or semi-cured resin composition, a thermosetting process may be further carried out after the molding process, cooling process, or demagnetization process. In the thermosetting process, the molded body is heated to a temperature above the thermosetting temperature of the resin composition. As a result, the thermosetting of the resin composition in the molded body proceeds further.

[0056] A magnetization process may be carried out after the demagnetization process. A magnetization process may also be carried out after the demagnetization process and the subsequent thermosetting process. In the magnetization process, a magnetic field in the same direction as the magnetic field used in the molding process may be applied to the molded body. As a result, the molded body is magnetized and becomes a bonded magnet again.

[0057] (Analysis method) The dimensions, shape, and structure of the first magnetic powder (multiple first magnetic particles), the granulated powder (multiple granulated particles), and the second magnetic particles within each granulated particle may be analyzed using an optical microscope, a scanning electron microscope (SEM), a transmission electron microscope (TEM), or a scanning transmission electron microscope (STEM). For the analysis and identification of the composition of the granulated powder, the granulated powder may be dissolved in an organic solvent, and multiple secondary magnet particles may be separated from the resin composition dissolved in the organic solvent. The separated secondary magnet particles and the resin composition may each be analyzed individually. For example, each component 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 compositions of the first and second magnetic particles may be analyzed and determined by one or more analytical methods selected from the group consisting of X-ray fluorescence analysis (XRF), inductively coupled plasma (ICP) emission spectroscopy, X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS or EDX), and mass spectrometry.

[0058] The particle size and median diameter of the first magnetic powder may be determined based on the particle size distribution of the first magnetic powder before it is mixed with the granulated powder. The particle size and median diameter of the first magnetic powder may also be determined based on the particle size distribution of the compound. The particle size and median diameter of the granulated powder may be determined based on the particle size distribution of the granulated powder before it is mixed with the first magnetic powder. The particle size and median diameter of the granulated powder may also be determined based on the particle size distribution of the compound. The compound can be separated into first magnetic powder and granulated powder by multiple classifications of the compound using multiple sieves with different mesh sizes. The mesh sizes of the sieves used for classifying the compound may be selected based on the particle sizes of the first magnetic particles and granulated particles, respectively, as measured by observation of the compound using the above-mentioned microscope (for example, the average particle size of each particle calculated by sampling from the compound). The particle size and median diameter of multiple secondary magnet particles in the granulated powder may be determined based on the particle size distribution of the secondary magnet powder, which is the raw material for the granulated powder. Alternatively, the particle size and median diameter of multiple secondary magnet particles in the granulated powder may be determined based on the particle size distribution of multiple secondary magnet particles separated from the granulated powder by dissolving the resin composition in the granulated powder in an organic solvent. For example, the horizontal axis of each particle size distribution may represent the particle size, and the vertical axis may represent the number of particles, mass, or volume. For example, the particle size may represent the maximum width of each particle. For example, the particle size may represent the diameter of a sphere with the same volume as each particle (equivalent diameter of an isovolume sphere). For example, the particle size may represent the diameter of a sphere with the same surface area as each particle (equivalent diameter of an isosurface area sphere). For example, the particle size may represent the diameter of a sphere with the same settling velocity and density as each particle (equivalent diameter of an isosettling velocity sphere, or Stokes diameter). For example, each particle size distribution may be measured by sieving tests, laser diffraction scattering, dynamic light scattering, centrifugal sedimentation, or particle trajectory analysis. The shapes of the first magnetic particles, the second magnetic particles, and the granulated particles are not limited. For example, the shape of each particle may be approximately spherical or flattened. The shape of each particle may be irregular. The shape of each particle may be uneven. The shape of the second magnetic particles may be the same as that of the first magnetic particles. The shape of the second magnetic particles may be different from that of the first magnetic particles.

[0059] This disclosure is not necessarily limited to the embodiments described above. Various modifications to this disclosure are possible without departing from the spirit of this disclosure, and examples of such modifications are also included in this disclosure. For example, bonded magnets may be manufactured by injection molding of a compound heated (in a magnetic field). [Examples]

[0060] The present disclosure will be illustrated in detail by the following examples and comparative examples. The present disclosure is not limited to the following examples.

[0061] (Example 1) [Preparation of granulated powder] A solution of the resin composition (resin solution) was prepared by mixing a thermosetting resin, a curing agent, a coupling agent, a curing accelerator (curing catalyst), and acetone in a round-bottom flask. As a thermosetting resin, a biphenyl-type epoxy resin with an epoxy equivalent of 192 (YX-4000H manufactured by Mitsubishi Chemical Corporation) is used. TM ) was used. As a curing agent, a phenol novolac resin with a hydroxyl group equivalent of 108 (HP-850N manufactured by Resonaq Corporation) is used. TM ) was used. As a coupling agent, N-phenyl-3-aminopropyltrimethoxysilane (KBM-573, manufactured by Shin-Etsu Chemical Co., Ltd.) TM ) was used. As a curing accelerator, tetra(n-butyl)phosphonium tetraphenylborate (PX-4PB manufactured by Nippon Chemical Industrial Co., Ltd.) is used. TM ) was used. The volume of acetone was 50 ml. The volume of the pear-shaped flask was 300 ml. The mass of the thermosetting resin was 5.12 g. The mass of the hardener was 2.88 g, the mass of the coupling agent was 0.60 g, and the mass of the curing accelerator was 0.248 g.

[0062] The resin solution described above was added to the second magnet powder (multiple second magnet particles) in a polytetrafluoroethylene petri dish while stirring. A polytetrafluoroethylene stirring blade attached to a three-one motor was used to stir the second magnet powder. The second magnet powder to which the resin solution was added was stirred at room temperature for 1 hour, and then dried in a vacuum dryer to evaporate the acetone. Granulated powder was obtained by classifying the granulated powder produced by the above method using a sieve. The median diameter of the granulated powder was adjusted to 80 μm. As the second magnet powder, powder consisting of Sm-Fe-N magnets (magnet powder manufactured by Sumitomo Metal Mining Co., Ltd.) was used. The second magnet powder in Example 1 was obtained by crushing a lump of Sm-Fe-N magnets, and the shape of the second magnet powder was distorted (irregular). The median diameter of the second magnet powder was 2.5 μm. The mass of the second magnet powder contained in the granulated powder was 192 g.

[0063] The granulated powder was observed using a scanning electron microscope (SEM). Each of the multiple granulated particles that made up the observed granulated powder consisted of one or more secondary magnetic particles and a resin composition covering one or more secondary magnetic particles.

[0064] [Compound preparation] The compound (powder) of Example 1 was prepared by mixing the above-mentioned granulated powder with the first magnet powder. The first magnet powder mixed with the granulated powder was the same as the second magnet powder used to prepare the granulated powder. In other words, the median diameter of the first magnet powder was also 2.5 μm, and the particle size of the first magnet powder was smaller than that of the granulated powder. The content of the first magnet powder in the compound (unit: mass%) was adjusted to the value shown in Table 1 below. The content of the granulated powder in the compound (unit: mass%) was adjusted to the value shown in Table 1 below.

[0065] [Measuring the fluidity of the compound] The fluidity of the compound was measured by the following method based on JIS-Z2502. 50g of the compound was introduced into a funnel. The internal angle of the funnel was 60°, and the minimum diameter of the funnel (diameter of the funnel outlet φ) was 2.63mm. The time required for all of the compound introduced into the funnel to pass through the funnel outlet (flow time) was measured. The flow time (in seconds) for Example 1 is shown in Table 1 below. A shorter flow time indicates better fluidity of the compound.

[0066] [Measurement of bulk density of molded products] A molded body was formed from a compound by heating the compound, which was filled into a mold, to 100°C and compressing it at 100 MPa. The molded body was a rectangular parallelepiped. A hydraulic press was used to compress the compound. The molded body was placed in a dryer and heated from room temperature to 200°C at a heating rate of 5°C / min. The molded body was then held in the dryer at 200°C for 10 minutes. In other words, the resin composition in the molded body was cured at 200°C. The molded body was removed from the dryer and cooled to room temperature. The molded body that has undergone heating at 200°C corresponds to a bonded magnet.

[0067] The dimensions (length, width, and height) of the molded body produced by the above method were measured with a micrometer. The volume of the molded body was calculated from the measured dimensions. The mass of the molded body was measured with an electronic balance. The bulk density of the molded body was calculated by dividing the mass by the volume. (Bulk density of the molded body (unit: g / cm³)) 3 ) are shown in Table 1 below.

[0068] (Examples 2 and 3, Comparative Examples 1 and 2) The content of the first magnet powder in the compounds of Examples 2, 3, and Comparative Example 2 was adjusted to the values ​​shown in Table 1 below. The content of the granulated powder in the compounds of Examples 2, 3, and Comparative Example 2 was also adjusted to the values ​​shown in Table 1 below. The compound of Comparative Example 2 did not contain the first magnet powder and consisted only of granulated powder. Compounds and molded bodies (bonded magnets) for Examples 2, 3, and Comparative Example 2 were prepared in the same manner as in Example 1, except for the matters mentioned above. The flow time of the compounds for Examples 2, 3, and Comparative Example 2 was measured in the same manner as in Example 1. The bulk density of the molded bodies for Examples 2, 3, and Comparative Example 2 was measured in the same manner as in Example 1. The results of the various measurements for Examples 2, 3, and Comparative Example 2 are shown in Table 1 below.

[0069] In Comparative Example 1, instead of the compound (a mixture of first magnet powder and granulated powder), only the first magnet powder, which was the same as in Example 1, was used. The flow time of only the first magnet powder was measured in the same way as in Example 1. However, even after 100 seconds had elapsed since introducing the first magnet powder into the funnel, not all of the first magnet powder had passed through the outlet of the funnel. The first magnet powder in the funnel had aggregated and hardly flowed at all. A molded body of Comparative Example 1 was prepared using the same method as in Example 1, consisting solely of the first magnet powder. The bulk density of the molded body of Comparative Example 1 was measured using the same method as in Example 1. The bulk density of the molded body of Comparative Example 1 is shown in Table 1 below.

[0070] [Table 1] [Industrial applicability]

[0071] For example, a compound relating to one aspect of this disclosure may be used as a raw material for bonded magnets. [Explanation of Symbols]

[0072] 1...First magnetic particles (first magnetic powder), 2...Second magnetic particles, 3...Granulated particles (granulated powder), 4...Resin composition, 10...Compound.

Claims

1. The invention comprises a first magnetic powder consisting only of multiple first magnetic particles, and a granulated powder, The first magnet powder and the granulated powder are mixed together. The particle size of the first magnet powder is smaller than the particle size of the granulated powder. Each of the plurality of granulated particles constituting the granulated powder comprises one or more second magnetic particles and a resin composition covering one or more of the second magnetic particles, The plurality of first magnetic particles are an alloy containing samarium, iron, and nitrogen. One or more of the second magnetic particles are an alloy containing samarium, iron, and nitrogen. The resin composition includes a thermosetting resin. Compound.

2. The particle size of the first magnet powder is 1 μm or more and 5 μm or less. The particle size of the granulated powder is 30 μm or more and 100 μm or less. The compound according to claim 1.

3. The median diameter of the first magnet powder is smaller than the median diameter of the granulated powder. The median diameter of the first magnet powder is 1 μm or more and 5 μm or less. The median diameter of the granulated powder is 30 μm or more and 100 μm or less. The compound according to claim 1.

4. The content of the first magnet powder is 5% by mass or more and 20% by mass or less. The content of the granulated powder is 80% by mass or more and 95% by mass or less. The compound according to claim 1.

5. A method for manufacturing a bonded magnet from a compound according to any one of claims 1 to 4, The process includes a molding step in which a molded body is formed from the compound within the mold by heating and compressing the compound within the mold. A method for manufacturing bonded magnets.

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