Method for manufacturing composite magnet powder

Abstract

To provide a method for producing composite magnet powder in which the deterioration of magnetic properties in the presence of water is suppressed. [Solution] A method for producing composite magnet powder containing rare earth transition metal magnet powder and polystyrene, comprising the following steps: a raw material mixture preparation step of preparing a raw material mixture containing rare earth transition metal magnet powder and styrene monomer, and a polymerization step of subjecting the raw material mixture to a grinding treatment to promote the polymerization reaction of the styrene monomer contained in the ground raw material mixture, thereby obtaining a product containing composite magnet powder.

Description

[Technical Field]

[0001] This invention relates to a method for producing composite magnet powder. [Background technology]

[0002] Rare-earth transition metal magnets, such as samarium iron nitrogen (SmFeN) magnets and neodymium iron boron (NdFeB) magnets, possess excellent magnetic properties. Therefore, they are used in general electrical appliances, medical equipment, and general industrial equipment, and are particularly important as magnetic force sources in motors. Such rare-earth transition metal magnets are used in the form of sintered magnets or bonded magnets. Sintered magnets are manufactured by molding and sintering rare-earth transition metal magnet powder. Bonded magnets are manufactured by mixing, kneading, and molding rare-earth transition metal magnet powder and resin. Of these, bonded magnets offer the advantage of obtaining molded bodies with high dimensional accuracy, ease of post-processing, and a high degree of freedom in shape.

[0003] Incidentally, one application of motors equipped with magnets is in pumps that circulate water or antifreeze used to regulate the temperature of equipment. For example, in engine-powered automobiles, electric pumps are used to cool the engine. In electric vehicles, electric pumps are used to regulate the temperature of the battery, charging and discharging circuits, and equipment. There is a demand for miniaturization and weight reduction in on-board electric pumps, and the use of rare-earth bonded magnets, which have high magnetic properties and a large degree of freedom in shape, is expected.

[0004] However, rare-earth bonded magnets have a problem in that their magnetic properties deteriorate significantly when exposed to water for extended periods. This is because the rare-earth transition metal magnet powder contained in the rare-earth bonded magnets is easily oxidized by water. Oxidation reduces magnetization and forms a low-coercivity phase, making it easier for the magnetization to reverse, resulting in a decrease in coercivity. Therefore, the magnet powder used in the manufacture of rare-earth bonded magnets is required to have high water resistance.

[0005] To prevent a decrease in magnetic properties in the presence of water and to impart high water resistance, a technique has been proposed to apply a protective coating to the surface of the particles constituting the magnetic powder for bonded magnets. For example, Patent Document 1 discloses a method for producing highly weather-resistant magnetic powder in which iron-based magnetic alloy powder containing rare earth elements is pulverized in an organic solvent, phosphoric acid is added during the pulverization of the magnetic powder to form a protective coating on the surface of the magnetic alloy powder, and then the powder is further heat-treated (Claim 1 of Patent Document 1, etc.).

[0006] Patent Document 2 proposes a technique for coating the surface of a rare-earth magnet material with a polymer protective film by applying a liquid containing an organic crosslinked polymer to a molded article of rare-earth magnet material and irradiating it with an electron beam (e.g., claims 1 to 10 of Patent Document 2). Patent Document 3 proposes a technique for coating the surface of a rare-earth magnet material with a polymer protective film by immersing it in a polyolefin-xylene dilution solution (e.g., claim 1 of Patent Document 3). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 3882490 [Patent Document 2] Japanese Patent Publication No. 2005-294417 [Patent Document 3] Japanese Patent Application Publication No. 4-257202 [Overview of the project] [Problems that the invention aims to solve]

[0008] Although technologies for forming protective coatings have been proposed for some time, further improvements in water resistance are required when rare-earth bonded magnets are used in even harsher aquatic environments. Conventional technologies have limitations in achieving further improvements in water resistance.

[0009] In view of these problems, the inventors conducted thorough research. As a result, they found that when radical polymerization of styrene monomer is performed in the presence of pulverized rare-earth transition metal-based magnet powder, the radicals generated on the surface of the magnet powder can be used as the starting point for polystyrene polymerization of the styrene monomer. They also found that a composite magnet powder containing a compound of rare-earth transition metal-based magnet powder and polystyrene can be obtained, and that the obtained composite magnet powder is particularly excellent in terms of hydrophobicity (water resistance), and the deterioration of magnetic properties in the presence of water is significantly suppressed.

[0010] This invention was completed based on such findings, and aims to provide a method for producing composite magnetic powder in which the deterioration of magnetic properties in the presence of water is suppressed. [Means for solving the problem]

[0011] The present invention encompasses the following embodiments. In this specification, the expression "~" includes the numerical values ​​at both ends. That is, "X~Y" is synonymous with "X or greater and Y or less".

[0012] According to one aspect of the present invention, a method for producing a composite magnet powder comprising a rare earth transition metal-based magnet powder and polystyrene, comprising the following steps: A raw material mixture preparation step for preparing a raw material mixture containing rare earth transition metal magnet powder and styrene monomer, and A method is provided which includes a polymerization step in which the raw material mixture is subjected to a grinding process to promote the polymerization reaction of styrene monomer contained in the ground raw material mixture, thereby obtaining a product containing composite magnet powder. [Effects of the Invention]

[0013] The present invention provides a method for producing composite magnet powder in which the deterioration of magnetic properties in the presence of water is suppressed. [Modes for carrying out the invention]

[0014] Specific embodiments of the present invention (hereinafter referred to as "these embodiments") are described below. However, the present invention is not limited to the following embodiments, and various modifications are possible without altering the essence of the invention. Furthermore, in this specification, any combination of preferred embodiments can be adopted as long as technical consistency can be maintained. For example, one of the preferred numerical ranges can be arbitrarily combined with the other.

[0015] <<1. Method for manufacturing composite magnet powder>> This embodiment relates to a method for producing composite magnet powder containing rare earth transition metal magnet powder and polystyrene. This production method includes the following steps: a raw material mixture preparation step in which a raw material mixture containing rare earth transition metal magnet powder and styrene monomer is prepared; and a polymerization step in which the raw material mixture is subjected to a grinding treatment to promote the polymerization reaction of the styrene monomer contained in the ground raw material mixture, thereby obtaining a product containing composite magnet powder. Furthermore, the production method of this embodiment may further include a recovery step in which the composite magnet powder is recovered from the product obtained in the polymerization step, and a drying step in which the product or composite magnet powder is subjected to a heat drying treatment. Details of each step are described below.

[0016] <Composite magnet powder> The composite magnet powder contains a compound of rare earth transition metal magnet powder (hereinafter sometimes referred to as "magnet powder") and polystyrene. In other words, the surface of the particles constituting the rare earth transition metal magnet powder (hereinafter sometimes referred to as "magnet particles") is modified with polystyrene. As long as the composite magnet powder contains a compound of rare earth transition metal magnet powder and polystyrene, the specific mode of existence of the composite magnet powder is not limited. For example, it may be a mode in which polystyrene coats all or part of the surface of the magnet particles. It may be a mode in which spherical or amorphous polystyrene particles are attached to all or part of the surface of the magnet particles. It may be a mode in which magnet particles are embedded inside polystyrene particles. Alternatively, it may be a mode in which magnet particles and polystyrene particles are compounded together as a single unit.

[0017] Rare earth-transition metal-based magnet powder is excellent in magnet properties such as magnetization, coercive force, and maximum energy product. Also, polystyrene has the advantages of being excellent in transparency, mechanical strength, electrical insulation, chemical resistance, heat resistance, and moldability, as well as water resistance. Therefore, the composite magnet powder containing the composite of rare earth-transition metal-based magnet powder and polystyrene has the characteristic of being excellent in various properties such as water resistance while maintaining high magnet properties.

[0018] The rare earth-transition metal-based magnet powder is composed of an alloy containing at least a rare earth metal (Re) and a transition metal (TM), and is a powder showing magnet properties, that is, hard magnetic properties. Here, the alloy is a concept including not only solid solutions but also eutectics and intermetallic compounds. As intermetallic compounds, compounds having crystal structures such as CaCu5 type, Th2Zn 17 type, Th2Ni 17 type, TbCu7 type, ThMn 12 type, NaZn 13 type, Nd2Fe 14 B type, MgCu2 type, etc. are exemplified. Also, in this specification, the powder means an aggregate of a large number of particles. That is, a large number of particles aggregate to form the powder. The particle diameter of the particles constituting the rare earth-transition metal-based magnet powder is not particularly limited. However, it is preferable that the particle size distribution of the particles is uniform. The powder is preferably composed of particles having a particle diameter in the range of 5 μm or more and 80 μm or less, for example. The particle diameter is measured by a known measuring instrument such as a dry particle size distribution measuring instrument or a wet particle size distribution measuring instrument.

[0019] The rare earth metal (Re) is a general term for metals (elements) that constitute a group consisting of scandium (Sc) with an atomic number of 21, yttrium (Y) with an atomic number of 39, and lanthanum (La) with an atomic number of 57 to lutetium (Lu) with an atomic number of 71. The rare earth metal (Re) contained in the magnet powder is not particularly limited. However, one or more selected from the group consisting of samarium (Sm), gadolinium (Gd), and cerium (Ce), or one or more selected from the group consisting of praseodymium (Pr), neodymium (Nd), dysprosium (Dy), and ytterbium (Yb) are preferable. Particularly from the viewpoint of obtaining a magnet material with excellent magnet properties, one or more selected from the group consisting of samarium (Sm), neodymium (Nd), and praseodymium (Pr) are more preferable. Particularly preferably, the magnet powder contains either one or both of samarium (Sm) and neodymium (Nd). The rare earth metal contained in the magnet powder may be only one type or may be a plurality of types.

[0020] The transition metal (TM) is a general term for metals (elements) existing between Group 3 elements and Group 11 elements of the periodic table. The transition metal (TM) contained in the magnet powder is not particularly limited. However, from the viewpoint of magnet properties, one or more selected from the group consisting of iron (Fe), manganese (Mn), and cobalt (Co) are preferable, and iron (Fe) is most preferable. The transition metal contained in the magnet powder may be only one type or may be a plurality of types.

[0021] The rare earth transition metal-based magnet powder may contain only the rare earth metal (Re) and the transition metal (TM). Examples of such alloy powders include samarium cobalt (SmCo) powder. Samarium cobalt powder is a permanent magnet material having a basic composition of SmCo5 or Sm2Co 17 Or the alloy powder may contain other metal elements or non-metal elements other than the rare earth metal (Re) and the transition metal (TM). Examples of such alloy powders include samarium iron nitride (SmFeN) powder and neodymium iron boron (NdFeB) powder. Samarium iron nitride powder is Sm2Fe 17 N xIt is a permanent magnet material having a basic composition, and the neodymium iron boron powder is Nd2Fe 14 It is a permanent magnet material having a basic composition of B.

[0022] Preferably, the rare earth transition metal-based magnet powder is samarium iron nitride (SmFeN) powder. The samarium iron nitride-based powder is excellent in heat resistance and weather resistance and is useful as the magnet powder of the bonded magnet. The composition of the samarium iron nitride powder is not particularly limited as long as magnetic properties can be obtained. However, from the viewpoint of magnetic properties, the samarium (Sm) content in the powder is preferably 14% by mass or more and 27% by mass or less, more preferably 15% by mass or more and 25% by mass or less. Further, the samarium iron nitride powder has a maximum saturation magnetization when x = 3 in the basic composition (Sm2Fe 17 N x ). Therefore, x is preferably 2.5 or more and 3.5 or less, more preferably 2.8 or more and 3.2 or less.

[0023] <Raw material mixture preparation step> In the raw material mixture preparation step, a raw material mixture containing a rare earth transition metal-based magnet powder and a styrene monomer is prepared. The preparation means is not limited as long as a raw material mixture can be obtained. For example, a method of charging a rare earth transition metal-based magnet powder, a styrene monomer, and, if necessary, an organic solvent and other components into a treatment container can be mentioned. Examples of the treatment container include, but are not limited to, a grinding container (such as a ball mill pot) used in subsequent grinding treatment.

[0024] The details of the rare earth transition metal-based magnet powder are as described above. That is, the rare earth transition metal-based magnet powder is a hard magnetic material powder composed of an alloy containing at least a rare earth metal (Re) and a transition metal (TM). The rare earth transition metal-based magnet powder may contain only a rare earth metal (Re) and a transition metal (TM), or may contain other metal elements or non-metal elements other than the rare earth metal (Re) and the transition metal (TM). Also, the styrene monomer is not particularly limited as long as it is generally used as a radically polymerizable monomer. However, in order to prevent oxidative degradation of the magnet powder, the water content of the styrene monomer is preferably less than 0.1% by mass.

[0025] It is preferable to adjust the amount of styrene monomer so that the mixture contains 30 to 1000 parts by mass of styrene monomer per 100 parts by mass of rare earth transition metal magnet powder. A higher amount of styrene monomer results in a higher amount of polystyrene modification in the final composite magnet powder. This results in even better water resistance of the composite magnet powder. On the other hand, if the amount of polystyrene modification is excessive, the magnet powder may aggregate or the non-magnetic component may increase, leading to a decrease in the magnetic properties of the composite magnet powder. By moderately controlling the amount of styrene monomer, the decrease in magnetic properties can be suppressed.

[0026] The raw material mixture may contain an organic solvent. Using an organic solvent allows the subsequent grinding process to be carried out by a wet method in the organic solvent. It also enables the uniform polymerization of styrene monomer. Examples of organic solvents include primary, secondary, and / or tertiary alcohols having 1 or more carbon atoms. For example, alcohols with 1 to 8 carbon atoms such as methanol, ethanol, isopropyl alcohol (IPA), butanol, t-butyl alcohol, pentanol, hexanol, heptanol, and octanol can be used. In addition to linear and branched alcohols, cyclic alcohols such as alicyclic and aromatic alcohols may also be used. The alcohol is not limited to monohydric alcohols; dihydric or polyhydric alcohols with 2 or more carbon atoms may also be used, such as ethylene glycol, propylene glycol, and / or glycerin. Among these, isopropyl alcohol (IPA) is preferred in terms of cost and safety. Since it is desirable for the raw material mixture to be water-free, IPA with low water content is preferable, specifically with a purity of 99% or higher. Furthermore, one type of solvent may be used as the organic solvent, or a combination of multiple solvents may be used. If the raw material mixture contains an organic solvent, the amount of organic solvent added is preferably 30 parts by mass or more and 1000 parts by mass or less, and more preferably 150 parts by mass or more and 600 parts by mass or less, per 100 parts by mass of rare earth transition metal magnet powder.

[0027] The raw material mixture may contain other components besides rare earth transition metal-based magnet powder, styrene monomer, and organic solvent. Such components include dispersants, polystyrene-modified resins, surfactants, and / or foaming agents.

[0028] Dispersants enhance the dispersion stability of polystyrene produced by styrene polymerization in organic solvents. Any known compound used in styrene polymerization can be used as a dispersant, as long as it is soluble in organic solvents. For example, various nonionic water-soluble polymers such as polyvinyl alcohol and polyvinylpyrrolidone (PVP), as well as polyacrylic acid and carboxymethylcellulose, can be used.

[0029] Polystyrene-modified resins have the function of copolymerizing with styrene and modifying the resulting polystyrene into rare-earth transition metal-based magnet powders. Examples of polystyrene-modified resins include methacrylates having tertiary amino groups.

[0030] However, the raw material mixture does not have to contain a polymerization initiator. Here, a polymerization initiator is a known initiator used in styrene polymerization. Examples, though not limited to them, include radical polymerization initiators such as azo compounds and organic peroxides; redox initiators that combine oxidizing and reducing agents; and ionic polymerization initiators such as nucleophiles such as n-butyllithium, and electrophiles such as protic acids, Lewis acids, halogen molecules, and carbocations.

[0031] As will be described later, in the manufacturing method of this embodiment, the radicals on the magnetic powder pulverization surface formed during the pulverization process act as polymerization initiation sites for styrene monomer. Therefore, the polystyreneization of styrene monomer proceeds sufficiently even without the use of polymerization initiators.

[0032] <Polymerization process> In the polymerization process, the raw material mixture is subjected to a grinding treatment, and the polymerization reaction of the styrene monomer contained in the ground raw material mixture is promoted, thereby obtaining a product containing composite magnet powder.

[0033] The manufacturing method of this embodiment is characterized by its ability to promote the polymerization reaction of styrene monomer contained in the pulverized raw material mixture. Normally, polymerization initiators such as radical polymerization initiators or redox initiators are required to promote the polymerization of styrene monomer. In contrast, in the manufacturing method of this embodiment, the polymerization of styrene monomer proceeds sufficiently without the use of polymerization initiators. While this should not be interpreted as limiting, the following mechanism is considered to be the reason.

[0034] In the polymerization process, the raw material mixture is subjected to a grinding treatment. During this process, the magnetic powder contained in the raw material mixture is ground, forming active new surfaces (ground surfaces). Metal atoms such as rare earth metals and transition metals are exposed on these new surfaces. For example, if the magnetic powder is SmFeN powder, Fe atoms and Sm atoms are exposed on the new surfaces. We hypothesize that these metal atoms, especially transition metals (such as Fe atoms), act as polymerization initiation sites for styrene monomer, resulting in the radical polymerization of styrene monomer.

[0035] In the polymerization process, it is preferable to perform a deoxygenation treatment to reduce the oxygen content of the raw material mixture before proceeding with the polymerization reaction of styrene monomer. In the manufacturing method of this embodiment, it is thought that the newly formed surface of the rare earth transition metal-based magnet powder acts as the polymerization initiation point for styrene monomer. However, if oxygen is present in the raw material mixture, this oxygen may reduce the activity of the magnet powder, and the radical polymerization of styrene monomer may not proceed sufficiently. By performing a deoxygenation treatment, oxygen that hinders polymerization can be removed.

[0036] As long as the amount of oxygen in the raw material mixture is reduced, the specific method of deoxygenation is not particularly limited. Examples include irradiating the raw material mixture with ultrasound or blowing inert gases such as nitrogen or argon into the processing container holding the raw material mixture. When performing deoxygenation treatment by blowing inert gas, it is preferable to cool the mixture during processing. This is because if the temperature of the mixture rises during processing, the styrene monomer in the mixture may volatilize and be removed, resulting in an insufficient amount of polystyrene in the final composite magnet powder. The specific cooling method is not particularly limited. For example, examples include cooling the processing container holding the raw material mixture with ice water or circulating a heat transfer oil around the processing container to cool it. However, deoxygenation treatment is not an essential process. If the amount of oxygen in the raw material mixture is low enough that it does not pose a practical problem, deoxygenation treatment may not be necessary.

[0037] Next, the raw material mixture is subjected to a grinding treatment. This treatment promotes the radical polymerization of styrene monomer, resulting in a product containing composite magnet powder. The grinding method is not particularly limited as long as an active new surface of magnet powder is formed; known grinders such as ball mills, vibratory mills, paint shakers, bead mills, attritors and / or planetary mills may be used. Furthermore, the grinding may be carried out either dry or wet. However, in order to suppress oxidation and deactivation of the magnet powder, when dry grinding is performed, it is preferable to grind the raw material mixture in an inert gas atmosphere. For the same reason, when wet grinding is performed, it is preferable to grind in an inert solvent. Examples of inert solvents include organic solvents such as alcohols. Preferably, the grinding treatment of the raw material mixture is carried out by a wet method.

[0038] As long as the radical polymerization of styrene monomer proceeds, the degree of grinding during the grinding process is not particularly limited. However, it is preferable to adjust the degree of grinding using the average particle size (D50) of the magnet powder before and after grinding as an indicator. Specifically, it is preferable to adjust the degree of grinding so that the ratio (D50 after / D50 before) of the average particle size (before D50) of the rare earth transition metal magnet powder in the raw material mixture after grinding to the average particle size (before D50) of the rare earth transition metal magnet powder in the raw material mixture before grinding is preferably 0.015 to 0.50, and more preferably 0.03 to 0.25. By making the ratio (D50 after / D50 before) small, grinding and the formation of the active surface proceed sufficiently, making it possible to perform polymerization of styrene monomer more effectively. On the other hand, if the ratio (D50 after / D50 before) is too small, the magnet powder may be excessively finely ground, which can lead to problems such as a decrease in its magnetic properties or a decrease in handling properties. These problems can be avoided by making the ratio (after D50 / before D50) appropriately large. Furthermore, the average particle size (before D50) of the rare earth transition metal magnet powder in the raw material mixture before grinding is preferably 20 μm or more and 100 μm or less.

[0039] As long as the radical polymerization of styrene monomer proceeds, the temperature during radical polymerization is not particularly limited. However, the radical reaction rate increases at a certain temperature. It is desirable to carry out the radical polymerization of styrene monomer at a temperature within the range of 50°C to 90°C, more preferably 60°C to 80°C. The temperature during radical polymerization can be adjusted by controlling the temperature of the raw material mixture. The temperature of the raw material mixture can be adjusted, for example, by controlling the temperature of the processing vessel containing the raw material mixture.

[0040] Preferably, the raw material mixture is left to stand after grinding while maintaining a constant temperature. Once the active surface (polymerization initiation point) of the magnetic powder is formed, radical polymerization of styrene monomer continues even after grinding is complete. Therefore, by leaving the raw material mixture to stand, it is possible to allow the polymerization reaction to proceed sufficiently while avoiding excessive grinding and fineness of the magnetic powder. There are no particular restrictions on the standing time. However, to minimize a decrease in productivity, it is preferable to keep the total processing time, including grinding time and standing time, to 48 hours or less.

[0041] A polymerization inhibitor may be added to the raw material mixture (product) after grinding or standing. This will terminate the polymerization reaction of styrene monomer. Examples of polymerization inhibitors include hydroquinone derivatives, nitrosamines, 4t-butylcatechol, and TEMPO.

[0042] As the polymerization reaction of styrene monomer proceeds, a composite magnetic powder containing a compound of magnetic powder and polystyrene is produced. Therefore, a product containing the composite magnetic powder is obtained.

[0043] <Recovery Process> If necessary, a step to recover the composite magnet powder from the product obtained in the polymerization step (recovery step) may be included. In addition to the target composite magnet powder, the product will contain foreign matter such as polystyrene aggregates, magnet powder aggregates, unreacted styrene monomer, and pulverization residue. Therefore, it is preferable to remove residual foreign matter by separating the product. Means of removing foreign matter include filtering a slurry containing the product and a solvent (organic solvent), or processing the slurry containing the product and solvent using a centrifuge. The filtration method is not particularly limited; for example, a filter funnel equipped with a filter cloth, filter paper, nylon filter, etc., with a mesh size that can separate the composite magnet powder from the foreign matter may be used. Filtration may be repeated, or multiple filtration methods may be combined. However, the recovery step is not a mandatory step. If the amount of residual foreign matter is small enough that it does not pose a practical problem, there is no need to include a recovery step. In this case, the product can be used as is as composite magnet powder.

[0044] <Drying process> If necessary, a step of heat drying treatment (drying step) may be provided for the product or composite magnet powder. If the grinding process is carried out by a wet method, the obtained product contains a solvent (organic solvent). Therefore, it is preferable to dry the product to remove the solvent. Examples of drying treatments include heat drying and vacuum drying. Of these, heat drying is preferred. Even if unreacted styrene monomer, which is a foreign substance, remains in the composite magnet powder, it can be removed by volatilization through heat drying. The heat drying temperature is not limited, but for example, it may be 120°C to 160°C. In addition, to promote drying, heat drying may be carried out under a vacuum atmosphere.

[0045] <Post-processing> If necessary, a post-treatment step (post-treatment step) may be provided in which post-treatment such as crushing, classification, and / or washing is applied to the product or composite magnet powder.

[0046] In this way, composite magnet powder can be obtained. By polymerizing styrene in the presence of rare earth transition metal-based magnet powder, the magnet powder is modified with polystyrene, and as a result, a composite magnet powder containing magnet powder with excellent water resistance can be obtained.

[0047] <<2. Composite Magnet Powder>> The composite magnet powder of this embodiment contains a composite of rare earth transition metal magnet powder and polystyrene. The details of the composite magnet powder are as described above. That is, as long as the composite magnet powder contains a composite of rare earth transition metal magnet powder and polystyrene, its specific form is not limited. The particle size of the composite magnet powder is also not particularly limited. However, the average particle diameter (D50) is preferably 0.1 μm or more and 5.0 μm or less, and more preferably 0.5 μm or more and 3.0 μm or less.

[0048] The composite magnet powder of this embodiment is preferably manufactured by the method described above. Specifically, it is preferably manufactured by a method comprising the following steps: a raw material mixture preparation step of preparing a raw material mixture containing rare earth transition metal magnet powder and styrene monomer, and a polymerization step of pulverizing the raw material mixture to promote radical polymerization of the styrene monomer contained in the pulverized raw material mixture, thereby obtaining a product containing composite magnet powder.

[0049] The composite magnet powder of this embodiment preferably contains carbon (C) in an amount of 0.08% by mass or more and 1.6% by mass or less. The carbon is a component derived from polystyrene contained in the composite magnet powder. By keeping the amount of carbon within the above range, it becomes possible to suppress the deterioration of the magnetic properties of the composite magnet powder while exhibiting an even more significant effect in improving water resistance.

[0050] The composite magnetic powder of this embodiment is characterized by its excellent water resistance while maintaining high magnetic properties. Such composite magnetic powder is suitable as a material for bonded magnets, especially in fields where water resistance is required. Specifically, it is particularly suitable as a material for bonded magnets used in motors for on-board electric pumps and general industrial water supply and drainage pumps. [Examples]

[0051] The present invention will be described in more detail using the following examples and comparative examples. However, the present invention is not limited to the following examples.

[0052] (1) Preparation of composite magnet powder [Example 1] <Raw material mixture preparation process> SmFeN powder (manufactured by Sumitomo Metal Mining Co., Ltd.) with an average particle size (D50) of 40 μm: 1 kg, organic solvent (2-propanol): 1.5 kg, and styrene monomer (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako Special Grade): 0.5 kg were prepared as raw materials and placed into the pot of a media-stirred ball mill. The media-stirred ball mill had 1.5 kg of SUSJ2 grinding balls (φ3.2 mm) in the pot. The amount of styrene monomer was 50 parts by mass per 100 parts by mass of SmFeN powder.

[0053] <Polymerization process> While cooling the pot of the ball mill with a heat transfer oil, nitrogen gas was blown into the pot at a flow rate of 1 L / min for 10 minutes (deoxygenation treatment). Next, the pot was heated to 50°C and rotated at that temperature at a rotation speed of 200 rpm for 2 hours. This pulverized the SmFeN powder in the pot and promoted polymerization of styrene monomer, yielding a slurry product. After that, the pot was left to stand for 20 hours before being cooled, and the product was removed after cooling.

[0054] <Recovery Process> Next, the product was filtered using a 100-mesh nylon filter to separate the polystyrene-surface-treated SmFeN powder (composite powder) from the other components.

[0055] <Drying process> The composite magnet powder remaining on the nylon filter was placed in a vacuum dryer and dried under reduced pressure at 100°C for 24 hours to remove residual styrene monomer by volatilization. Afterward, the dryer was cooled to room temperature, and the composite magnet powder was recovered. The average particle size (D50) of the SmFeN powder contained in the composite magnet powder was 2 μm.

[0056] [Examples 2-6] The amount of styrene monomer was changed as shown in Table 1 below. Otherwise, the composite magnet powder was prepared using the same procedure as in Example 1.

[0057] (2) Evaluation For the samples obtained in Examples 1 to 6, various properties were evaluated as follows.

[0058] <C quantification value> The amount of carbon (C quantification value) adhering to the SmFeN powder contained in the composite magnet powder was measured using a CHN elemental analyzer (manufactured by LECO Corporation). Then, the measured C adhesion amount was evaluated as a guideline for the polystyrene coating amount.

[0059] <Water resistance> The composite magnet powder (1 kg) was put into a mold with a cross-sectional area of φ10 mm, and a load of 1 t was applied for 3 minutes with a press machine to produce a compacted powder pellet. Next, one drop of ion-exchanged water was dropped onto the surface of the pellet, and the time was measured until the ion-exchanged water penetrated into the compacted powder pellet. Then, the water resistance was evaluated by the penetration time (water repellency time).

[0060] <Magnetic properties> The magnetic properties (saturation magnetic flux density Br, coercive force iHc, maximum energy product (BH)max) of the composite magnet powder were measured using a vibrating sample magnetometer (VSM). The measurement was carried out according to the Bond Magnet Test Method Guidebook BMG-2002 defined by the Japan Bond Magnet Industry Association.

[0061] (3) Evaluation results The obtained evaluation results are summarized in Table 1 below.

[0062] In Examples 1 to 6, it was found that the water repellency time was 6 minutes or more, indicating excellent water resistance. Also, in all cases, Br, iHC, and (BH)max were high, showing excellent magnetic properties. Among these, Examples 1 and 3 to 5 had a long water repellency time and were particularly excellent in terms of magnetic properties.

[0063] In Example 2, the water repellency time (water resistance) was slightly short. This is considered to be because the blending amount of styrene monomer (SM) was small, resulting in a small amount of polystyrene (PS) coating in the obtained composite magnet powder. Also, the magnetic properties were slightly reduced.

[0064] In Example 6, a slight decrease in magnetic properties was observed. This is thought to be because, although the water-repellent time was sufficiently long due to the very thick polystyrene layer of the composite magnetic powder, aggregation of the particles constituting the composite magnetic powder occurred, resulting in a decrease in orientation.

[0065] [Table 1]

[0066] From the results above, it can be seen that this embodiment provides a method for manufacturing composite magnet powder in which the deterioration of magnetic properties in the presence of water is suppressed.

[0067] (1) A method for producing a composite magnet powder containing rare earth transition metal magnet powder and polystyrene, comprising the following steps: A raw material mixture preparation step for preparing a raw material mixture containing rare earth transition metal magnet powder and styrene monomer, and A method comprising a polymerization step of pulverizing the raw material mixture to promote the polymerization reaction of styrene monomer contained in the pulverized raw material mixture, thereby obtaining a product containing composite magnet powder.

[0068] (2) The method of (1) above, wherein in the polymerization step, a deoxygenation treatment is performed to reduce the amount of oxygen in the raw material mixture before proceeding with the polymerization reaction of styrene monomer.

[0069] (3) The method of (1) or (2) above, further comprising a recovery step of recovering composite magnet powder from the product obtained in the polymerization step.

[0070] (4) The raw material mixture contains 30 to 1000 parts by mass of styrene monomer per 100 parts by mass of rare earth transition metal magnet powder, according to the method of (1) to (3) above.

[0071] (5) Any of the methods (1) to (4) above, wherein the pulverization of the raw material mixture is carried out by a wet method.

[0072] (6) Any of the methods (1) to (5) above, wherein the average particle size (before D50) of the rare earth transition metal magnet powder in the raw material mixture before grinding is 20 μm or more and 100 μm or less.

[0073] (7) Any of the methods (1) to (6) above, wherein the ratio (D50 after / D50 before) of the average particle size of the rare earth transition metal magnet powder in the raw material mixture after grinding (D50 after) to the average particle size of the rare earth transition metal magnet powder in the raw material mixture before grinding (D50 before) is 0.015 or more and 0.50 or less.

[0074] (8) Any of the methods (1) to (7) above, wherein the radical polymerization of the styrene monomer is carried out at a temperature within the range of 50°C to 90°C.

[0075] (9) Any of the methods (1) to (8) above, further comprising a drying step of performing a heat drying treatment on the composite magnet powder recovered in the recovery step.

[0076] (10) Any of the methods (1) to (9) above, wherein the rare earth transition metal magnet powder contains either samarium (Sm) or neodymium (Nd) or both.

Claims

1. A method for producing a composite magnet powder containing a rare earth transition metal magnet powder and polystyrene, comprising the following steps: A raw material mixture preparation step for preparing a raw material mixture containing rare earth transition metal magnet powder and styrene monomer, and A method comprising a polymerization step of pulverizing the raw material mixture to promote the polymerization reaction of styrene monomer contained in the pulverized raw material mixture, thereby obtaining a product containing composite magnet powder.

2. The method according to claim 1, wherein in the polymerization step, a deoxygenation treatment is performed to reduce the amount of oxygen in the raw material mixture before proceeding with the polymerization reaction of styrene monomer.

3. The method according to claim 1, further comprising a recovery step of recovering composite magnet powder from the product obtained in the polymerization step.

4. The method according to claim 1, wherein the raw material mixture contains 30 to 1000 parts by mass of styrene monomer per 100 parts by mass of rare earth transition metal magnet powder.

5. The method according to any one of claims 1 to 4, wherein the grinding treatment of the raw material mixture is carried out by a wet method.

6. The method according to any one of claims 1 to 4, wherein the average particle size (before D50) of the rare earth transition metal magnet powder in the raw material mixture before grinding is 20 μm or more and 100 μm or less.

7. The method according to any one of claims 1 to 4, wherein the ratio (after D50 / before D50) of the average particle size of the rare earth transition metal magnet powder in the raw material mixture after grinding (after D50) to the average particle size of the rare earth transition metal magnet powder in the raw material mixture before grinding (before D50) is 0.015 or more and 0.50 or less.

8. The method according to any one of claims 1 to 4, wherein the radical polymerization of the styrene monomer is carried out at a temperature within the range of 50°C to 90°C.

9. The method according to any one of claims 1 to 4, further comprising a drying step of performing a heat drying treatment on the composite magnet powder recovered in the recovery step.

10. The method according to any one of claims 1 to 4, wherein the rare earth transition metal magnet powder comprises either samarium (Sm) or neodymium (Nd) or both.

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