Composite magnet powder and method for manufacturing the same

Abstract

To provide a composite magnet powder in which the deterioration of magnetic properties in the presence of water is suppressed, and a method for producing the same. [Solution] A method for producing composite magnet powder containing rare earth transition metal magnet powder and polystyrene, comprising the following steps: a surface treatment step of mixing rare earth transition metal magnet powder and a phosphoric acid compound in a solvent to produce phosphoric acid treated magnet powder; a raw material mixture preparation step of preparing a raw material mixture containing the phosphoric acid treated magnet powder and styrene monomer; and a polymerization step of advancing the polymerization reaction of the styrene monomer contained in the raw material mixture to obtain a product containing composite magnet powder.

Description

[Technical Field]

[0001] The present invention relates to composite magnet powder and a method for producing the same. [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. 38824090 [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 light of these problems, the inventors conducted thorough research. As a result, they found that when styrene polymerization is performed in the presence of phosphoric acid-treated 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 composite magnetic powder in which the deterioration of magnetic properties in the presence of water is suppressed, and a method for producing the same. [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 surface treatment process for producing phosphoric acid-treated magnet powder by mixing rare earth transition metal magnet powder and a phosphoric acid compound in a solvent. A raw material mixture preparation step of preparing a raw material mixture containing the phosphate-treated magnet powder and styrene monomer, and A method is provided that includes a polymerization step to advance the polymerization reaction of styrene monomer contained in the raw material mixture, thereby obtaining a product containing composite magnet powder.

[0013] According to another aspect of the present invention, a composite magnet powder manufactured by the method described above, A composite magnetic powder is provided, containing phosphorus (P) in an amount of 0.3% to 0.9% by mass and carbon (C) in an amount of 0.05% to 1.50% by mass. [Effects of the Invention]

[0014] According to the present invention, there are provided composite magnet powders with suppressed deterioration of magnetic properties in the presence of water and a method for producing the same.

Embodiments for Carrying Out the Invention

[0015] Specific embodiments of the present invention (hereinafter referred to as "the present embodiments") will be described below. However, the present invention is not limited to the following embodiments, and various modifications are possible without changing the gist of the present invention. Also, in this specification, as long as technical consistency can be achieved, any combination of preferred embodiments can be adopted. For example, any combination of one and the other of preferred numerical ranges can be made.

[0016] <<1. Method for Producing Composite Magnet Powder>> The present embodiments are directed to a method for producing a composite magnet powder containing a composite of a rare earth-transition metal-based magnet powder and polystyrene. This production method includes the following steps: a surface treatment step of mixing a rare earth-transition metal-based magnet powder and a phosphoric acid compound in a solvent to produce a phosphoric acid-treated magnet powder, a raw material mixture preparation step of preparing a raw material mixture containing the phosphoric acid-treated magnet powder and a styrene monomer, and a polymerization step of promoting the polymerization reaction of the styrene monomer contained in the raw material mixture to thereby obtain a product containing the composite magnet powder. Further, the production method of the present embodiments may further include a recovery step of recovering the composite magnet powder from the product obtained in the polymerization step and a drying step of performing a heat drying treatment on the product or the composite magnet powder. Details of each step will be described below.

[0017] <Composite Magnet Powder> The composite magnet powder contains a rare earth-transition metal-based 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-based magnet powder (hereinafter sometimes referred to as "magnet particles") is modified with polystyrene. As long as the rare earth-transition metal-based magnet powder and polystyrene are composited and contained, the specific existence form of the composite magnet powder is not limited. For example, it may be a form in which all or part of the surface of the magnet particles is coated with polystyrene. It may be a form in which spherical or amorphous polystyrene particles adhere to all or part of the surface of the magnet particles. It may be a form in which magnet particles are encapsulated inside the polystyrene particles. Or it may be a form in which the magnet particles and the polystyrene particles are composited in a浑然一体 way.

[0018] The 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 excellent water resistance. Therefore, the composite magnet powder containing the 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.

[0019] 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, CaCu5 type, Th2Zn 17 type, Th2Ni 17 type, TbCu7 type, ThMn 12 type, NaZn 13 type, Nd2Fe 14Examples include compounds having crystalline structures such as type B and MgCu2 type. In this specification, powder refers to an aggregate of many particles; that is, many particles aggregate to form powder. The particle size 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 is uniform. The powder is preferably composed of particles with a particle size in the range of 5 μm to 80 μm. The particle size is measured using known measuring instruments such as dry particle size analyzers and wet particle size analyzers.

[0020] Rare earth metals (Re) are a general term for metals (elements) that make up the group consisting of scandium (Sc) with atomic number 21, yttrium (Y) with atomic number 39, and lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71. The rare earth metals (Re) contained in the magnetic powder are not particularly limited. However, it is preferable to have 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). In particular, from the viewpoint of obtaining a magnetic material with excellent magnetic properties, it is more preferable to have one or more selected from the group consisting of samarium (Sm), neodymium (Nd), and praseodymium (Pr). Particularly preferable is that the magnetic powder contains either samarium (Sm) or neodymium (Nd) or both. The rare earth metal contained in the magnetic powder may be of one type or multiple types.

[0021] Transition metals (TM) are a general term for metals (elements) located between Group 3 and Group 11 of the periodic table. The transition metals (TM) contained in magnetic powder are not particularly limited. However, from the viewpoint of magnetic properties, one or more selected from the group consisting of iron (Fe), manganese (Mn), and cobalt (Co) are preferred, with iron (Fe) being the most preferred. The transition metals contained in magnetic powder may be one type or multiple types.

[0022] The rare-earth transition metal-based magnet powder may contain only rare-earth metals (Re) and transition metals (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 . Alternatively, the alloy powder may contain other metal elements or non-metal elements other than rare-earth metals (Re) and transition metals (TM). Examples of such alloy powders include samarium iron nitride (SmFeN) powder and neodymium iron boron (NdFeB) powder. Samarium iron nitride powder is a permanent magnet material having a basic composition of Sm2Fe 17 N x , and neodymium iron boron powder is a permanent magnet material having a basic composition of Nd2Fe 14 B.

[0023] Preferably, the rare-earth transition metal-based magnet powder is samarium iron nitride (SmFeN) powder. Samarium iron nitride-based powder is excellent in heat resistance and weather resistance and is useful as a magnet powder for bonded magnets. The composition of samarium iron nitride powder is not particularly limited as long as magnet characteristics can be obtained. However, from the viewpoint of magnet characteristics, the samarium (Sm) content in the powder is preferably 14% by mass or more and 27% by mass or less, and more preferably 15% by mass or more and 25% by mass or less. Also, in the basic composition (Sm2Fe 17 N x ), the saturation magnetization is maximized when x = 3. Therefore, x is preferably 2.5 or more and 3.5 or less, and more preferably 2.8 or more and 3.2 or less.

[0024] <Phosphoric acid treatment step> In the phosphoric acid treatment process, rare earth transition metal-based magnet powder and a phosphoric acid compound are mixed in a solvent to produce phosphoric acid-treated magnet powder. The phosphoric acid-treated magnet powder comprises magnet powder and a phosphoric acid coating applied to the particle surface of the magnet powder. Here, phosphoric acid-treated magnet powder refers to rare earth transition metal-based magnet powder that has been treated with phosphoric acid. The phosphoric acid coating is a coating mainly composed of a phosphoric acid compound. The phosphoric acid coating has the effect of preventing oxidation of the magnet powder. It also plays a role in forming radicals that promote the polymerization reaction of styrene monomer in the subsequent polymerization process.

[0025] The details of the rare-earth transition metal-based magnetic powder are as described above. Specifically, the rare-earth transition metal-based magnetic powder is a hard magnetic material powder consisting of an alloy containing at least a rare-earth metal (Re) and a transition metal (TM). The rare-earth transition metal-based magnetic powder may contain only the rare-earth metal (Re) and the transition metal (TM), or it may contain other metallic or non-metallic elements other than the rare-earth metal (Re) and the transition metal (TM).

[0026] As the phosphoric acid compound, known compounds used for surface treatment of magnetic powder can be used. Examples include phosphoric acids such as orthophosphoric acid, phosphorous acid, hypophosphoric acid, pyrophosphoric acid, linear polyphosphoric acid, and cyclic metaphosphoric acid; and phosphates such as sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, zinc phosphate, and calcium phosphate. One compound may be used alone, or multiple compounds may be used in combination.

[0027] In the phosphoric acid treatment, the magnet powder and the phosphoric acid compound are mixed in a solvent. Specifically, the phosphoric acid compound is dissolved in a solvent to prepare a dilution solvent, and the magnet powder is added to this dilution solvent and stirred. Alternatively, the phosphoric acid compound may be added to the solvent containing the magnet powder and stirred. The magnet powder may also be pulverized during the phosphoric acid treatment. An organic solvent and / or water may be used as the solvent. There are no particular restrictions on the organic solvent, and alcohols, ketones, lower hydrocarbons, aromatics, or mixtures thereof can be used. In addition, lower alcohols such as methanol, ethanol, and 2-propanol (isopropyl alcohol) can be used as alcohols.

[0028] The amount of phosphate compound added should be adjusted to the optimal amount according to the particle size and surface area of ​​the magnetic powder. However, it is generally preferable to use 0.1 mol / kg to 2.0 mol / kg relative to the magnetic powder, more preferably 0.15 mol / kg to 1.5 mol / kg, and even more preferably 0.2 mol / kg to 0.4 mol / kg.

[0029] The phosphorus (P) content of the phosphate-treated magnet powder is preferably 0.1% to 2.0% by mass, and more preferably 0.3% to 0.9% by mass. By moderately increasing the phosphorus content, it is possible to fully utilize the antioxidant effect of the magnet powder and the polymerization-promoting effect of styrene monomer based on the phosphate coating. Furthermore, if the phosphate coating is excessively thick, radicals may decrease, and polymerization of styrene monomer may be suppressed. By moderately suppressing the phosphorus content, such polymerization suppression can be avoided.

[0030] The particle size of the magnet powder after phosphate treatment (phosphate-treated magnet powder) is not particularly limited. However, the average particle size (D50) is preferably between 1 μm and 100 μm, and more preferably between 1 μm and 10 μm. Note that D50 is the cumulative 50% diameter determined from the volume-based particle size distribution curve, and can be obtained by measuring the magnet powder with a particle size distribution analyzer equipped with an agglomeration and disintegration mechanism (for example, HELOS&LODOS manufactured by Sympatec).

[0031] <Raw material mixture preparation process> In the raw material mixture preparation step, a raw material mixture containing the obtained phosphate-treated magnet powder and styrene monomer (SM) is prepared. At this time, it is preferable to uniformly mix the phosphate-treated magnet powder and styrene monomer. To achieve a more uniform mix, an organic solvent may be added to the raw material mixture. The method of mixing the raw materials is not particularly limited. However, it is preferable to use a mixer with a stirring mechanism. The optimal mixing time is difficult to determine in general as it depends on the processing volume, but it is generally between 5 minutes and 30 minutes.

[0032] The styrene monomer is not particularly limited as long as it is used as a radical polymerizable monomer. However, in order to prevent oxidative degradation of the magnetic powder, the moisture content of the styrene monomer is preferably less than 0.1% by mass.

[0033] The amount of styrene monomer in the raw material mixture is preferably 120 parts by mass or more and 4000 parts by mass or less, and more preferably 200 parts by mass or more and 600 parts by mass or less, per 100 parts by mass of phosphate-treated magnet powder. A higher amount of styrene monomer results in a higher amount of polystyrene (PS) modification in the final composite magnet powder. As a result, the water resistance of the composite magnet powder becomes even better. On the other hand, if the amount of polystyrene modification is excessive, the magnet powder may aggregate or the non-magnetic component may increase, which can reduce the magnetic properties of the composite magnet powder. By moderately controlling the amount of styrene monomer, the reduction in magnetic properties can be suppressed.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] As will be described later, in the manufacturing method of this embodiment, the metal phosphate contained in the phosphate coating is thought to act as a polymerization initiation site for the styrene monomer. Therefore, the polystyreneization of the styrene monomer proceeds sufficiently even without the use of a polymerization initiator.

[0039] <Polymerization process> In the polymerization process, the polymerization reaction of styrene monomer contained in the raw material mixture is carried out, thereby obtaining a product containing composite magnet powder.

[0040] The manufacturing method of this embodiment is characterized by the fact that the polymerization reaction of styrene monomer is carried out in the presence of phosphoric acid-treated magnet powder. In other words, normally, polymerization initiators such as radical polymerization initiators and redox initiators are used to promote the polymerization of styrene monomer. In contrast, in the manufacturing method of this embodiment, the polymerization of styrene monomer proceeds sufficiently even without the use of polymerization initiators. The following mechanism is considered to be the reason for this, although it should not be interpreted as limiting.

[0041] As mentioned earlier, phosphate-treated magnet powder has a phosphate coating formed on the surface of the magnet powder particles. This phosphate coating contains metal phosphates, specifically transition metal and rare earth metal phosphates generated during phosphate treatment. That is, during phosphate treatment, the metals (rare earth metals, transition metals) contained in the magnet powder (rare earth transition metal magnet powder) react with phosphate compounds to produce metal phosphate salts. These metal phosphate salts then adhere to the surface of the magnet powder particles, forming a phosphate coating. For example, if the magnet powder is SmFeN powder, iron phosphate or samarium phosphate is contained in the phosphate coating. It is speculated that unpaired electrons and ions in these metal phosphates, especially transition metal phosphates (such as iron phosphate), act as polymerization initiation sites for styrene monomer, resulting in the radical polymerization of styrene monomer.

[0042] 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 metal phosphate contained in the phosphate-treated magnet powder acts as the polymerization initiation site 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.

[0043] 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 will 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.

[0044] Next, the polymerization reaction of styrene monomer is carried out. Specifically, to avoid polymerization inhibition by oxygen, the raw material mixture is kept under an anaerobic atmosphere. At this time, it is preferable to stir the raw material mixture to promote uniform and sufficient radical polymerization. Furthermore, it is difficult to determine the optimal conditions such as processing temperature and processing time, as these vary depending on conditions such as the amount of raw material mixture. However, it is preferable to carry out the polymerization reaction of styrene monomer at a temperature of 50°C to 90°C for 1 hour to 48 hours.

[0045] A polymerization inhibitor may be added to the raw material mixture (product) after a predetermined time has elapsed. This will terminate the polymerization reaction of styrene monomer. Examples of polymerization inhibitors include hydroquinone derivatives, nitrosamines, 4t-butylcatechol, and TEMPO.

[0046] 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.

[0047] <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.

[0048] <Drying process> If necessary, a step of heat drying treatment (drying step) may be provided for the product or composite magnet powder. 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 between 90°C and 170°C. In addition, to promote drying, heat drying may be performed under an inert gas or reduced pressure atmosphere.

[0049] <Post-processing steps> 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.

[0050] 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.

[0051] <<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.

[0052] 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 surface treatment step of mixing rare earth transition metal magnet powder and a phosphate compound in a solvent to produce phosphate-treated magnet powder; a raw material mixture preparation step of preparing a raw material mixture containing the phosphate-treated magnet powder and styrene monomer; and a polymerization step of advancing the polymerization reaction of the styrene monomer contained in the raw material mixture to obtain a product containing composite magnet powder.

[0053] The composite magnet powder of this embodiment preferably contains phosphorus (P) in an amount of 0.3% to 0.9% by mass and carbon (C) in an amount of 0.05% to 1.50% by mass. 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.

[0054] 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]

[0055] 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.

[0056] (1) Preparation of composite magnet powder [Example 1] <Surface treatment process> A ball mill pot with a media stirring mechanism was prepared, and the inside of the pot was purged with nitrogen. Next, 1 kg of SmFeN powder (manufactured by Sumitomo Metal Mining Co., Ltd.) with an average particle size (D50) of 40 μm, 1.5 kg of an organic solvent (2-propanol), and an 85% aqueous solution of orthophosphoric acid were added to the pot as raw materials. At this time, the amount of 85% aqueous solution of orthophosphoric acid was 19.0 g per 1 kg of SmFeN powder. After that, the pot containing the raw materials (SmFeN powder, etc.) was rotated at a rotation speed of 200 rpm for 2 hours. This pulverized and mixed the raw materials to form a slurry. The obtained slurry was dried in a vacuum at 150°C for 4 hours to obtain magnetic alloy powder (phosphate-treated magnetic powder). The average particle size (D50) of the obtained phosphate-treated magnetic powder was 2 μm.

[0057] <Raw material mixture preparation process> The obtained phosphate-treated magnet powder and styrene monomer (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako Special Grade) were placed in a sealed container equipped with a stirrer, and then mixed with the stirrer for 10 minutes to obtain a raw material mixture. At this time, the amount of styrene monomer added was 400 parts by mass per 100 parts by mass of phosphate-treated magnet powder.

[0058] <Polymerization process> A sealed container containing the raw material mixture was cooled with a heat transfer oil while nitrogen gas was blown into the container at a flow rate of 1 L / min (deoxygenation treatment). Next, the raw material mixture was heated to 80°C while being stirred, maintained at that temperature for 48 hours, and then cooled to room temperature. This promoted the polymerization of styrene monomer, yielding a product containing polystyrene-surface-modified SmFeN powder (composite magnetic powder).

[0059] <Recovery Process> Next, the product was filtered using a 100-mesh nylon filter to separate the composite magnet powder from the other components.

[0060] <Drying process> The remaining composite magnet powder on the nylon filter was put into a vacuum dryer and dried under reduced pressure at 100 °C for 24 hours to volatilize and remove the residual styrene monomer. Then, the inside of the dryer was cooled to room temperature, and the composite magnet powder was recovered.

[0061] [Examples 2 to 12] The blending amounts of 85% aqueous solution of orthophosphoric acid and styrene monomer were changed as shown in Table 1 below. Otherwise, the composite magnet powder was produced in the same procedure as in Example 1.

[0062] (2) Evaluation Regarding the samples obtained in Examples 1 to 12, evaluations of various properties were conducted as follows.

[0063] The amount of phosphorus (P quantitative value) contained in the phosphoric acid-treated magnet powder obtained in the surface treatment step was determined by quantitative analysis using an ICP emission spectrometer.

[0064] <C quantitative value> The amount of carbon (C quantitative value) contained in the composite magnet powder was analyzed using a CHN elemental analyzer (manufactured by LECO). Then, the obtained C quantitative value was evaluated as a guideline for the polystyrene coating amount.

[0065] <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).

[0066] <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 type 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.

[0067] (3) Evaluation results The evaluation results obtained are summarized in Table 1 below. Examples 1 and 3-12 are example samples, while Example 2 is a comparative example sample.

[0068] Example 1 is a sample prepared with a styrene monomer content of 400 parts by mass (per 100 parts by mass of SmFeN powder). In contrast, Example 2 is a sample made from conventional SmFeN powder without polystyrene coating. As can be seen from this comparison, the water resistance increased from 1 minute to 14 minutes with polystyrene coating, demonstrating the significant effect of polystyrene coating.

[0069] Examples 3-6 are samples prepared using the same phosphoric acid treatment as in Example 1. However, Example 3 is a sample with a styrene monomer content of 120 parts by weight, and Example 4 is a sample with a styrene monomer content of 4000 parts by weight. High water resistance and magnetic properties were achieved in Examples 3 and 4.

[0070] Example 5 is a sample with a styrene monomer content of 80 parts by mass, and Example 6 is a sample with a styrene monomer content of 4800 parts by mass. Example 5 had lower water resistance compared to the other example samples. Example 6 had high water resistance, but its Br was slightly lower. This is thought to be because polystyrene adhered to it more than necessary.

[0071] Examples 7 and 8 are samples in which the amount of phosphoric acid (85% phosphoric acid) in the phosphoric acid treatment process (surface treatment process) was reduced. Example 7 is a sample with a styrene monomer content of 120 parts by mass, and Example 8 is a sample with a styrene monomer content of 80 parts by mass. Example 7 showed high water resistance and magnetic properties. Example 8 had lower water resistance compared to Example 7. This is thought to be due to the lower amount of styrene monomer.

[0072] Examples 9 and 10 are samples with increased phosphoric acid content. Example 9 is a sample with a styrene monomer content of 400 parts by weight, and Example 10 is a sample with a styrene monomer content of 4800 parts by weight. Example 9 showed high water resistance and magnetic properties. Example 10 had lower magnetic properties compared to Example 9. This is thought to be due to the larger amount of polystyrene coating.

[0073] Example 11 is a sample with a significantly reduced amount of phosphate. In Example 11, the magnetic properties were slightly lower. This is thought to be because the reduced amount of phosphate coating resulted in less radical generation.

[0074] Example 12 is a sample with a significantly increased amount of phosphoric acid. Compared to the other example samples, Example 12 had lower water resistance. This is thought to be because most of the surface of the SmFeN fine powder was covered with phosphate, resulting in less radical generation.

[0075] [Table 1]

[0076] 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.

[0077] (1) A method for producing a composite magnet powder containing rare earth transition metal magnet powder and polystyrene, comprising the following steps: A surface treatment process for producing phosphoric acid-treated magnet powder by mixing rare earth transition metal magnet powder and a phosphoric acid compound in a solvent. A raw material mixture preparation step of preparing a raw material mixture containing the phosphate-treated magnet powder and styrene monomer, and A method comprising a polymerization step of advancing the polymerization reaction of styrene monomer contained in the raw material mixture to obtain a product containing composite magnet powder.

[0078] (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.

[0079] (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.

[0080] (4) Any of the methods (1) to (3) above, wherein the phosphorus (P) content of the phosphate-treated magnet powder is 0.1% by mass or more and 2.0% by mass or less.

[0081] (5) Any of the methods (1) to (4) above, wherein the amount of styrene monomer contained in the raw material mixture is 120 parts by mass or more and 4000 parts by mass or less per 100 parts by mass of the phosphoric acid-treated magnet powder.

[0082] (6) Any of the methods (1) to (5) above, wherein the polymerization reaction is carried out at a temperature of 50°C or higher and 90°C or lower for 1 hour or more and 48 hours or less.

[0083] (7) Any method of (1) to (6) above, further comprising a drying step of performing a heat drying treatment on the product or composite magnet powder.

[0084] (8) Any method (1) to (7) above, wherein the rare earth transition metal magnet powder contains either samarium (Sm) or neodymium (Nd) or both.

[0085] (9) A composite magnet powder manufactured by any of the methods described in (1) to (8) above, A composite magnetic powder containing phosphorus (P) in an amount of 0.3% to 0.9% by mass and carbon (C) in an amount of 0.05% to 1.50% by mass.

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 surface treatment process for producing phosphoric acid-treated magnet powder by mixing rare earth transition metal magnet powder and a phosphoric acid compound in a solvent. A raw material mixture preparation step of preparing a raw material mixture containing the phosphate-treated magnet powder and styrene monomer, and A method comprising a polymerization step of advancing the polymerization reaction of styrene monomer contained in the raw material mixture to obtain 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 phosphorus (P) content of the phosphate-treated magnet powder is 0.1% by mass or more and 2.0% by mass or less.

5. The method according to any one of claims 1 to 4, wherein the amount of styrene monomer contained in the raw material mixture is 120 parts by mass or more and 4000 parts by mass or less per 100 parts by mass of the phosphoric acid-treated magnet powder.

6. The method according to any one of claims 1 to 4, wherein the polymerization reaction is carried out at a temperature of 50°C or higher and 90°C or lower for a period of 1 hour or more and 48 hours or less.

7. The method according to any one of claims 1 to 4, further comprising a drying step of performing a heat drying treatment on the product or composite magnet powder.

8. 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.

9. A composite magnet powder manufactured by the method described in any one of claims 1 to 4, A composite magnetic powder containing phosphorus (P) in an amount of 0.3% to 0.9% by mass and carbon (C) in an amount of 0.05% to 1.50% by mass.

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