Rare earth magnet and method for manufacturing rare earth magnet

Abstract

The invention provides a rare earth magnet and a method of manufacturing the same. The rare earth magnet achieves high magnetic performance and low eddy current loss. The rare earth magnet includes coated magnet powder particles, each coated magnet powder particle including a rare earth magnet powder particle and an insulating material coating on a surface of the rare earth magnet powder particle, where the insulating material includes nanoparticles coated with the rare earth magnet powder particle. A method of manufacturing a rare earth magnet includes a coating operation including adding an insulating material to rare earth magnet powder particles such that each coated magnet powder particle includes a rare earth magnet powder particle and an insulating material coating layer on a surface of the rare earth magnet powder particle, wherein the coating operation comprises spraying a nanoparticle dispersion solution comprising nanoparticles and a binder to the rare earth magnet powder particles caused to roll and flow.

Description

Technical Field

[0001] The present invention relates to a rare earth magnet and a method for manufacturing a rare earth magnet. Background Art

[0002] In recent years, efforts to achieve a low-carbon or decarbonized society have become more active, and for vehicles, research and development related to electrification technologies are also being carried out in order to reduce carbon dioxide emissions and improve energy efficiency. Methods for improving energy efficiency include improving the efficiency of motors used as power sources. Recently, rare earth magnets have been increasingly used to improve the efficiency of motors. Since rare earth magnets are metal magnets, their resistance is usually low, which leads to the problem that incorporating rare earth magnets into motors increases eddy current losses, which reduces the efficiency of the motors. Regarding how to reduce eddy current losses, various proposals have been made.

[0003] Patent Document 1 discloses a rare earth magnet capable of reducing eddy current losses, which has rare earth magnet powder particles, and each rare earth magnet powder particle is covered with a film-like coating containing a rare earth oxide. Binding portions containing rare earth oxide particles are interposed between the coated rare earth magnet powder particles. A method for producing a rare earth magnet includes: performing high-temperature and high-pressure forming of a mixture of a rare earth oxide and rare earth magnet powder particles coated with the rare earth oxide.

[0004] Patent Document 2 discloses a method for manufacturing a rare earth magnet, which includes: mixing Nd-Fe-B magnet powder with an oxide such as CaO and a nitride such as BN or a fluoride such as CaF2 for the purpose of high resistance; and processing the resulting mixture by thermoplastic molding to produce an anisotropic magnet.

[0005] Patent Document 3 discloses a first method for manufacturing a rare earth magnet, which includes: preparing isotropic rapidly cooled powder particles such as Nd-Fe-B magnet powder particles; mixing the isotropic rapidly cooled powder particles with a predetermined composite for forming an insulating layer; processing the mixture by cold molding to produce a cold-molded product (temporary molding); and processing the cold-molded product by hot molding (densification); and processing the resulting product by thermoplastic molding (imparting anisotropy) to produce a rare earth magnet, and discloses that the magnet thus produced generally includes stacked Nd-Fe-B rapidly cooled powder particles with a composite powder material therebetween, each particle having a long side length of 100 μm to 400 μm and a thickness of 20 μm to 40 μm.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: JP4784173B

[0009] Patent Document 2: JP2003 - 022905A

[0010] Patent Document 3: JP2010 - 027852A Summary of the Invention

[0011] Technical Problem

[0012] In order to minimize the deterioration of the magnetic properties of a rare - earth magnet, it is desirable to reduce the amount of an insulating composite material to be mixed with magnet powder particles. However, since each of the magnet powder particles is flaky, the magnet powder particles are usually stacked in the step of densifying the mixture of the magnet powder particles and the insulating composite material. Therefore, when performing the method of manufacturing a magnet of the prior art, the thermoplastic molding (densifying) process causes the magnet powder particles and the insulating composite material to deform and spread in a direction perpendicular to the pressing direction (i.e., along the main surface of the magnet powder particles). This means that during the thermoplastic molding process, a reduced amount of the insulating composite material may cause fractures in the insulating layer, thereby forming an electrical connection between magnet powder particles that should be separated by the insulating layer. In this case, larger eddy - current paths (less effective in disrupting eddy - current paths) are formed in the produced magnet, which results in larger eddy - current losses during the operation of a motor using the magnet.

[0013] The present invention has been made in view of the above problems of the prior art, and the main object of the present invention is to provide a rare - earth magnet and a method for manufacturing a rare - earth magnet that achieve both high magnetic properties and low eddy - current losses.

[0014] Technical Solution

[0015] As a solution to the above - mentioned task to be completed, one aspect of the present invention provides a rare - earth magnet 1, which includes coated magnet powder particles 5. Each of the coated magnet powder particles includes a rare - earth magnet powder particle 2 and a coating layer 4 of an insulating material on the surface of the rare - earth magnet powder particle. Among them, the insulating material contains nanoparticles, and the rare - earth magnet powder particles are coated with the nanoparticles.

[0016] In this configuration, since the insulating material contains nanoparticles, the coating layer formed on the surface of the rare - earth magnet powder particle becomes thin and uniform, which prevents the occurrence of fractures in the coating layer. This allows the coated magnet powder particles to achieve both high magnetic properties and low eddy - current losses.

[0017] Preferably, the rare earth magnet may be further configured such that the nanoparticles are made of an alkali metal fluoride or an alkaline earth metal fluoride (CaF₂) and have a particle size of 1 nm to 100 nm.

[0018] This configuration minimizes the reaction between the coating formed of the alkali metal fluoride or the alkaline earth metal fluoride and the rare earth in the material of the rare earth magnet powder particles. This prevents deterioration of the magnetic properties of the rare earth magnet powder particles and deterioration of the insulating properties of the coating.

[0019] Preferably, the rare earth magnet may be further configured such that the coating containing the nanoparticles has a thickness of 200 nm to 2000 nm.

[0020] In this configuration, the nanoparticles form multiple layers, which prevents the nanoparticles from dispersing and causing fractures in the coating, and also prevents the occurrence of fractures in the coating due to insufficient nanoparticles during the molding operation for compressing and deforming the coated magnet powder particles. This suppresses an increase in eddy current loss.

[0021] As a solution to the above task to be completed, another aspect of the present invention provides a method for manufacturing a rare earth magnet 1, the method comprising: performing a coating operation, the coating operation comprising: adding an insulating material to rare earth magnet powder particles 2 to produce coated magnet powder particles 5 such that each of the coated magnet powder particles in the coated magnet powder particles includes one rare earth magnet powder particle in the rare earth magnet powder particles 2 and a coating 4 of the insulating material on the surface of the rare earth magnet powder particles ( Figure 1 in (B)); and performing a molding operation, the molding operation comprising: placing the coated magnet powder particles in a mold configured to allow pressurization, and applying pressure to the coated magnet powder particles in the mold, thereby compressing and deforming the coated magnet powder particles to produce the rare earth magnet ( Figure 1 in (C) and Figure 1 in (E)), wherein the insulating material contains nanoparticles, and wherein the coating operation comprises: spraying a nanoparticle dispersion solution containing the nanoparticles and a binder onto the rare earth magnet powder particles caused to tumble and flow, thereby adding the insulating material.

[0022] In this configuration, the coating operation including spraying a nanoparticle dispersion solution containing nanoparticles and a binder onto the rare earth magnet powder particles caused to tumble and flow results in a thin and uniform coating formed on the surface of the rare earth magnet powder particles. This prevents the occurrence of fractures in the coating. This allows the coated magnet powder particles to achieve both high magnetic properties and low eddy current loss.

[0023] Preferably, the above method can also be configured such that the nanoparticle dispersion solution is prepared by mixing nanoparticles made of an alkali metal fluoride or an alkaline earth metal fluoride and having a particle size of 1 nm to 100 nm, a solvent, and the binder.

[0024] This configuration ensures that the nanoparticles are uniformly attached to the surface of the rare earth magnet powder particles by the binder, thereby preventing the nanoparticles from becoming discrete and causing fractures in the coating. This configuration also inhibits the reaction between the alkaline earth metal fluoride or alkali metal fluoride contained in the coating and the rare earth that is the material of the rare earth magnet powder particles.

[0025] Preferably, the above method can also be configured such that the coating operation includes adding the insulating material to the rare earth magnet powder particles such that the coating of the rare earth magnet containing the nanoparticles has a thickness of 200 nm to 2000 nm.

[0026] In this configuration, the nanoparticles form multiple layers, which prevents the nanoparticles from becoming discrete and causing fractures in the coating, and also prevents the occurrence of fractures in the coating due to insufficient nanoparticles during the molding operation for compression deformation of the coated magnet powder particles. This inhibits an increase in eddy current loss.

[0027] Preferably, the above method can also be configured such that the binder is an acrylic binder that decomposes at a temperature lower than the heat input temperature during the molding operation.

[0028] This configuration ensures that the nanoparticles are attached to the surface of the rare earth magnet powder particles and prevents the binder from remaining as a residue in the rare earth magnet.

[0029] Preferably, the above method can also be configured such that the molding operation includes performing a first molding operation that includes placing the coated magnet powder particles in the mold configured to allow pressurization in a first direction and applying pressure to the coated magnet powder particles in the mold in the first direction, thereby compressing and deforming the coated magnet powder particles to produce a first molded product ( Figure 1 (C) in); and performing a second molding operation that includes applying pressure to the first molded product in a second direction intersecting the first direction, thereby plastically deforming the first molded product to produce the rare earth magnet ( Figure 1 (E) in).

[0030] In this configuration, in the second forming operation, when compressed in the second direction, the coated magnet powder particles of the first formed product expand in a third direction perpendicular to the first direction and the second direction. This prevents the thickness of the coating on the main surface of the rare earth magnet powder particles (i.e., the thickness in the first direction) from being prone to thinning. This also prevents the occurrence of breaks in the coating, thereby suppressing an increase in eddy current loss. Therefore, this configuration allows a reduction in the amount of insulating material to be added, thereby minimizing the deterioration of the magnetic properties of the rare earth magnet caused by the addition of the insulating material.

[0031] Advantageous effects

[0032] As described above, the present invention can be embodied as a rare earth magnet and a method for manufacturing a rare earth magnet, which achieve high magnetic properties and low eddy current loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is an explanatory diagram showing a method for manufacturing a rare earth magnet according to an embodiment of the present invention, and includes Figure 1 of (A) to Figure 1 of (E);

[0034] Figure 2 shows a schematic diagram of a tumbling device;

[0035] Figure 3 shows a schematic diagram of coated magnet powder particles;

[0036] Figure 4A and Figure 4B shows SEM images including nanoparticle coatings and SEM images including nanoparticle coatings;

[0037] Figure 5 shows an SEM image of a cross-section of a first formed product of a rare earth magnet after a first forming operation;

[0038] Figure 6A shows schematic cross-sectional views of (1) a first formed product and (2) a second formed product both having the nanoparticle coating of the present invention, and Figure 6B shows schematic cross-sectional views of (1) a first formed product and (2) a second formed product both having a bulk coating of a comparative example; and

[0039] Figure 7A is an SEM image showing the nanoparticle coating of the present invention, and Figure 7B is an SEM image showing the bulk coating of a comparative example.

[0040] LIST OF REFERENCE NUMERALS

[0041] 1: Rare earth magnet

[0042] 2: Rare earth magnet powder particles

[0043] 2a: Main surface

[0044] 4: Coating

[0045] 5: Coated magnet powder particles

[0046] 6: First formed product

[0047] 10: First mold

[0048] 15: Second mold

[0049] 20: Tumbling device Detailed implementation manners

[0050] The embodiments of the present invention will be described below with reference to the accompanying drawings.

[0051] First, a method for manufacturing the rare earth magnet 1 according to the embodiments of the present invention will be described below. Figure 1 is an explanatory diagram showing a method for manufacturing the rare earth magnet according to the embodiments of the present invention. As Figure 1 shown in (A) of, the first process is a step of producing rare earth magnet powder particles 2. This process produces the rare earth magnet powder particles 2 to be used.

[0052] Examples of the materials of the rare earth magnet powder particles 2 include, but are not limited to, neodymium magnets (Nd-Fe-B magnets, or more precisely Nd2Fe 14 B). An example of a method for manufacturing the rare earth magnet powder particles 2 from the raw materials of the rare earth magnet is the melt spinning method. The melt spinning method includes: spraying a high-temperature molten alloy onto a cooling roll for rapid cooling, thereby producing fine magnet powder particles for magnets in the form of a sheet (thin sheet) containing Nd-Fe-B crystals.

[0053] The rare earth magnet powder particles 2 produced in this process are isotropic rapidly cooled powder particles with non-aligned crystal directions, and each of these particles is flaky and thus has a major surface 2a. The term "major surface 2a" is defined herein as each pair of the largest opposing flat surfaces. When viewed from a direction perpendicular to the major surface 2a, each of the rare earth magnet powder particles 2 has an aspect ratio of about 1 (e.g., 0.7 to 1.0). The term "aspect ratio" refers to the ratio of the short diameter (minor axis diameter) to the long diameter (major axis diameter) of an object and is expressed as b / a, where "a" is the long diameter and "b" is the short diameter. The term "major axis (major axis diameter)" refers to the maximum Feret diameter, and the term "minor axis (minor axis diameter)" refers to the minimum Feret diameter. The method for measuring the major and minor axes complies with the provisions of JIS Z 8890:2017 "Particle Characteristics of Particle Systems".

[0054] Next, as shown in (B) of Figure 1 an insulating coating operation is performed to form an insulating coating on the surface of the rare earth magnet powder particles 2. This operation involves adding an insulating material to the rare earth magnet powder particles 2 such that a coating 4 is formed on the surface of each rare earth magnet powder particle 2, thereby producing coated magnet powder particles 5 having the coating 4 formed thereon.

[0055] Examples of preferred insulating materials include, but are not limited to, alkali metal fluorides or alkaline earth metal fluorides. In the present embodiment, calcium fluoride (CaF2), which is an alkaline earth metal fluoride, is used as the insulating material, but the insulating material is not limited to calcium fluoride. In some cases, the insulating material can be an alkaline earth metal fluoride (e.g., magnesium fluoride, barium fluoride, or strontium fluoride), an alkali metal fluoride (e.g., lithium fluoride), or a combination thereof (i.e., a mixture).

[0056] The method for forming the coating 4 on the surface of the rare earth magnet powder particles 2 includes mixing calcium fluoride nanoparticles having a particle size of 1 nm to 100 nm and a binder with a solvent and stirring the mixture to produce a nanoparticle dispersion solution. Examples of the solvent include, but are not limited to, isopropyl alcohol (also known as 2-propanol or IPA). A binder is added to increase the bonding between the rare earth magnet powder particles 2 and the nanoparticles. The binder is preferably decomposed and removed by heating during the molding operation to produce the rare earth magnet 1. Therefore, it is preferable to select a material that exhibits good thermal decomposition, i.e., decomposes at a temperature lower than the thermal input temperature during the molding operation and does not leave any residue after molding, as the binder. In the present embodiment, an acrylic binder (which is a binder made of an acrylic polymer) is used as the binder, but it is not limited thereto.

[0057] After preparing the nanoparticle dispersion solution, the method further includes adding an adhesive to the rare earth magnet powder particles 2 by spraying the nanoparticle dispersion solution containing the nanoparticles and the adhesive onto the rare earth magnet powder particles 2 caused to tumble and flow by using a tumbling device 20.

[0058] Figure 2 A schematic view of the tumbling device 20 is shown. As Figure 2 shown, the tumbling device 20 includes a main body housing 22 defining a fluidized bed 21, a blade rotor 23 rotatably provided at the bottom of the fluidized bed 21, and a nozzle 24 provided on the lower side of the main body housing 22. The nozzle 24 is attached to the main body housing 22 in a horizontal orientation such that the nozzle faces downward toward the bottom of the fluidized bed 21 at a position above the blade rotor 23.

[0059] Air is supplied from the bottom of the main body housing 22, and the rotation of the blade rotor 23 forces the rare earth magnet powder particles 2 to tumble and flow in the fluidized bed 21. In the case where the air and the rare earth magnet powder particles 2 flow in a vortex motion, the nanoparticle dispersion solution is sprayed from the nozzle 24 onto the bottom of the fluidized bed 21 so that the surface of the rare earth magnet powder particles 2 is coated with the nanoparticles in an effective manner.

[0060] Figure 3 A schematic view of the coated magnet powder particles 5 is shown. As Figure 3 shown, the insulation coating operation for producing the coated magnet powder particles 5 includes adding the nanoparticle dispersion solution so that a coating 4 with a thickness of 1 μm to 40 μm is formed on the surface of the rare earth magnet powder particles 2, thereby enabling the production of the rare earth magnet 1, wherein the coating 4 of the rare earth magnet powder particles 2 has a thickness of 200 nm to 2,000 nm.

[0061] Figure 4A and Figure 4B A SEM image including the nanoparticle coating is shown. As described above, the nanoparticles for the coating have a particle size of 1 nm to 100 nm, and a coating with a thickness of 1 μm to 40 μm is formed on the surface of the rare earth magnet powder particles 2.

[0062] Then, as Figure 1 shown in (C) of

[0063] The first mold 10 includes a cylindrical mold body 11 having a cross-sectional shape conforming to the shape of the first molded product 6, and an upper mold 12 and a lower mold 13 that can apply a compressive force to an object in the mold body 11 along a first direction. Accordingly, the first molding operation includes applying pressure to the coated magnet powder particles 5 while restricting deformation of the coated magnet powder particles 5 in a direction perpendicular to the first direction, thereby forming the first molded product 6. In the present embodiment, the first direction is the vertical direction, but is not limited thereto.

[0064] The first molding operation includes processing the coated magnet powder particles 5 into the first molded product 6 by hot press molding, wherein the first mold 10 is heated to a predetermined temperature and a predetermined pressure is applied for a predetermined time. When compressed and deformed by the pressure, the coated magnet powder particles 5 in the first mold 10 are oriented such that the main surface 2a of each of the rare earth magnet powder particles 2 faces the first direction, causing the coated magnet powder particles 5 to stack on top of each other in a direction perpendicular to the main surface 2a (i.e., the first direction).

[0065] Figure 5 An SEM image of a cross-section of the first molded product 6 of the rare earth magnet 1 after the first molding operation is shown. As Figure 5 shown, the first molded product 6 of the rare earth magnet 1 contains rare earth magnet powder particles 2 stacked in a direction perpendicular to the main surface 2a (i.e., the first direction).

[0066] The first molding operation for forming the first molded product 6 is performed by using a hot press process, wherein the coated magnet powder particles 5 are compressed and deformed at a high temperature, and the first mold 10 is heated to a predetermined temperature. Preferably, the predetermined temperature is a temperature within the range of about 600°C to about 700°C, preferably 640°C.

[0067] After the first molding operation, a rotation operation is performed, wherein, as Figure 1 shown in (D) of, the obtained first molded product 6 is removed from the first mold 10 and rotated 90 degrees. The rotation of the first molded product 6 is performed in a horizontal plane about a rotation axis, i.e., about an axis parallel to the main surface 2a of each of the rare earth magnet powder particles 2. In the present embodiment, the rotation angle of the first molded product 6 is 90 degrees. Although the angle is not limited to 90 degrees, the rotation angle is preferably close to 90 degrees, and more preferably, 90 degrees perpendicular to the first direction.

[0068] Then, as Figure 1 shown in (E) of, a second molding operation for shaping the first molded product 6 is performed. This operation includes rotating the first molded product 6 to as Figure 1After the angle shown in (D), the first formed product 6 is placed in the second mold 15, and pressure is applied to the first formed product 6 by the second mold 15 along a second direction intersecting the first direction, which is the pressing direction in the first forming operation (i.e., the stacking direction of the rare earth magnet powder particles 2), so that the first formed product 6 is plastically deformed to produce the rare earth magnet 1 (i.e., the second formed product).

[0069] Rotation operation as shown in (D) is required because Figure 1 the pressing direction of the second forming operation shown in (E) is the same vertical direction as the pressing direction of the first forming operation. Therefore, in some cases, when the pressing direction of the second forming operation is different from the pressing direction of the first forming operation, for example, when the pressing direction of the second forming operation is the horizontal direction, the Figure 1 rotation operation shown in (D) is not required. Figure 1 rotation operation as shown in (D) is not required.

[0070] The second mold 15 includes an upper mold 16 and a lower mold 17 that face each other. The upper mold 16 and the lower mold 17 have an upper pressure surface 16a and a lower pressure surface 17a, which conform to the shape of the first formed product 6 and are capable of applying pressure to the first formed product 6 along the second direction (the vertical direction in this embodiment). Since in this embodiment, the first formed product 6 has a rectangular shape, the upper mold 16 and the lower mold 17 have an upper pressure surface 16a and a lower pressure surface 17a, which are a pair of horizontal surfaces facing each other and parallel, and are configured to apply a compressive force to the first formed product 6 along the vertical direction perpendicular to the first direction.

[0071] The second forming operation includes: pressing the first formed product 6 without restricting the deformation of the first formed product 6 in a direction perpendicular to the second direction. Therefore, in the second forming operation, the first formed product 6 is plastically deformed by compressing the first formed product 6 along the vertical direction, which is the pressing direction of the second forming operation, while allowing the first formed product 6 to deform in the horizontal direction perpendicular to the vertical direction. Specifically, for each of the rare earth magnet powder particles 2 in the rare earth magnet 1, the thickness (dimension in the first direction) becomes thicker than when it existed in the first formed product 6 before the second forming operation. The aspect ratio of each of the rare earth magnet powder particles 2 in the rare earth magnet 1 observed from the first direction becomes smaller than when it existed in the first formed product 6 before the second forming operation. Preferably, the aspect ratio of each of the rare earth magnet powder particles 2 in the rare earth magnet 1 is less than 1, for example, 0.15 to 0.5.

[0072] In a thermoplastic forming process, the rare-earth magnet powder particles 2 of the first formed product 6 generate magnetic anisotropy (uniaxial anisotropy), where the c-axis direction (easy magnetization direction) of the crystal grains is oriented parallel to the pressing direction. The rare-earth magnet powder particles 2 of the rare-earth magnet 1 are magnetized along the direction of this magnetic anisotropy.

[0073] In this way, in the second forming operation, the first formed product 6 is pressed and plastically deformed along a second direction intersecting the first direction. This causes the rare-earth magnet powder particles 2 and the coating 4 around the particles to spread in a direction perpendicular to the second direction (i.e., the first direction and the third direction). In other words, the coating 4 between the rare-earth magnet powder particles 2 adjacent to each other in the first direction becomes thinner by spreading in the third direction and not in the second direction. This prevents the coating 4 from becoming too thin in the first direction, which reduces the increase in eddy current loss. Details of this effect will be discussed later.

[0074] The second forming operation is carried out by using a hot compression process, in which the second mold 15 is heated to a predetermined temperature to compress and deform the first formed product 6. More specifically, by using a thermoplastic forming process, in which the first formed product 6 is plastically deformed at a temperature higher than that in the first forming operation. Preferably, the temperature of the second mold 15 in the second forming operation is the temperature at which some of the crystal grains of the rare-earth magnet powder particles 2 undergo a phase change to the liquid phase, such as about 850 degrees. This process allows the rare-earth magnet powder particles 2 to plastically deform at a high compaction rate. In the present embodiment, the first formed product 6 of the rare-earth magnet 1 is plastically processed at a compaction rate of about 70% in the second forming operation.

[0075] Next, the rare-earth magnet 1 manufactured as described above and the effects achieved by the method for manufacturing rare-earth magnets will be described with reference to comparative examples.

[0076] Figure 6A A schematic cross-sectional view shows both the first formed product 6 and the second formed product (rare-earth magnet 1) having the nanoparticle coating of the present invention, while Figure 6B A schematic cross-sectional view shows both the first formed product 106 and the second formed product (rare-earth magnet 101) of the comparative example having the bulk coating of the comparative example. First, the comparative example shown in Figure 6B will be described. When manufacturing the rare-earth magnet 101 (second formed product) of the comparative example, the insulation operation for forming the coating 104 is different from the insulation operation according to the embodiment of the present invention ( Figure 1 (B) in

[0077] The process of manufacturing the rare earth magnet 101 of the comparative example includes a first molding operation for producing a first molded product 106 ( Figure 1 in (C) of), in which the rare earth magnet powder particles 2 are stacked on top of each other in a direction perpendicular to the main surface 2a (i.e., the first direction), as Figure 6B shown in (1) of. In the first molded product 106, the coating 104 forms an insulating layer with a substantially uniform thickness between adjacent rare earth magnet powder particles 2. In other words, the adjacent rare earth magnet powder particles 2 are separated from each other by the coating 104 in the first molded product 106.

[0078] Subsequently, a second molding operation is performed on the first molded product 6, in which the first molded product 106 is pressed in a second direction ( Figure 1 in (E) of), such that the rare earth magnet powder particles 2 and the coating 104 are spread out along a plane perpendicular to the second direction (i.e., a plane including the left - right direction of the paper and the direction perpendicular to the paper). This process produces the rare earth magnet 101 (or the second molded product) of the comparative example as shown in Figure 6B (2) of. During the second molding operation, the coating 104 partially fails to follow the plastic deformation of the rare earth magnet powder particles 2 that are spreading out along a plane perpendicular to the second direction, resulting in fractures in the coating. When pressure is applied in the second direction in this state, the adjacent rare earth magnet powder particles 2 in the second direction are connected to each other at the points where fractures occur in the coating 104. This increases the volume of the rare earth magnet powder particles, resulting in an increase in eddy current loss when the motor operates.

[0079] In contrast, as Figure 6A shown in (1) of, in the rare earth magnet 1 of the embodiment of the present invention, the coating 104 formed of nanoparticles forms an insulating layer with a substantially uniform thickness between adjacent rare earth magnet powder particles 2 in the first molded product 106. During the second molding operation, as Figure 6A shown in (2) of, the coating 104 can follow the plastic deformation of the rare earth magnet powder particles 2 that are spreading out along a plane perpendicular to the second direction to become thinner, without fractures occurring in the coating.

[0080] Figure 7A is a SEM image showing the nanoparticle coating of the present invention, and Figure 7B is a SEM image showing the bulk coating of the comparative example. As Figure 7B shown, in the rare earth magnet 101 with the bulk coating of the comparative example, the adjacent rare earth magnet powder particles 2 in the vertical direction are connected to each other at the fractures in the coating 104. In contrast, as Figure 7AAs shown, in the rare earth magnet 1 with the nanoparticle coating of the present invention, the rare earth magnet powder particles 2 adjacent to each other in the vertical direction are kept separated from each other by the coating 4.

[0081] In the rare earth magnet 1 of the present invention, even after being unfolded in the second molding operation, the coating 4 has a substantially uniform thickness within the range of 200 nm to 2000 nm.

[0082] In this way, the rare earth magnet 1 includes coated magnet powder particles, and each of the coated magnet powder particles includes a rare earth magnet powder particle 2 and an insulating material coating 4 on the surface of the rare earth magnet powder particle. The insulating material contains nanoparticles, and the rare earth magnet powder particle 2 is coated with nanoparticles. In this configuration, since the insulating material contains nanoparticles, the coating 4 formed on the surface of the rare earth magnet powder particle 2 becomes thin and uniform, which prevents fractures from occurring in the coating 4. This allows the coated magnet powder particles 5 to achieve both high magnetic properties and low eddy current losses.

[0083] As described above, the nanoparticles are made of alkali metal fluorides or alkaline earth metal fluorides and have a particle size of 1 nm to 100 nm. This configuration minimizes the reaction between the coating 4 formed by the alkali metal fluorides or alkaline earth metal fluorides and the rare earth in the material of the rare earth magnet powder particle 2. This prevents deterioration of the magnetic properties of the rare earth magnet powder particle 2 and deterioration of the insulating properties of the coating 4.

[0084] In the rare earth magnet 1, the coating 4 of the coated magnet powder particles 5 has a thickness of 200 nm to 2000 nm. In this configuration, the nanoparticles in the coating form multiple layers, which prevents the nanoparticles from being discrete and causing fractures in the coating 4, and also prevents fractures from occurring in the coating 4 due to insufficient nanoparticles during the molding operation for compressing and deforming the coated magnet powder particles 5. This inhibits an increase in eddy current losses.

[0085] The method for manufacturing the rare earth magnet 1 includes performing a coating operation, which includes adding an insulating material to the rare earth magnet powder particles 2 to produce coated magnet powder particles 5, as Figure 1 shown in (B) therein, where the insulating material contains nanoparticles. As Figure 2 shown, the coating operation includes spraying a nanoparticle dispersion solution containing nanoparticles and a binder onto the rare earth magnet powder particles 2 caused to tumble and flow, thereby adding the insulating material to the rare earth magnet powder particles 2. This coating operation makes the coating 4 formed on the surface of the rare earth magnet powder particles 2 thin and uniform. This prevents Figure 1 in (C) to Figure 1A fracture occurs in the coating 4 during the shaping operation shown in (E). This allows the coated magnet powder particles 5 to achieve both high magnetic properties and low eddy current losses.

[0086] As described above, a nanoparticle dispersion solution is prepared by mixing nanoparticles made of an alkali metal fluoride or an alkaline earth metal fluoride and having a particle size of 1 nm to 100 nm, a solvent, and a binder. This configuration ensures that the nanoparticles uniformly adhere to the surface of the rare earth magnet powder particles 2 by means of the binder, thereby preventing the nanoparticles from becoming discrete and causing fractures in the coating 4. This configuration also suppresses the reaction between the alkaline earth metal fluoride contained in the coating 4 and the rare earth that is the material of the rare earth magnet powder particles 2.

[0087] As Figure 1 shown in (B) and Figure 2 The coating operation shown includes adding an insulating material to the magnet powder particles to form a coating 4 in the resulting rare earth magnet 1 that is thicker than the coating 4 with a thickness of 200 nm to 2000 nm of the coated magnet powder particles 5. In this configuration, the nanoparticles form multiple layers, which prevents the nanoparticles from becoming discrete and causing fractures in the coating 4, and also prevents the occurrence of fractures in the coating 4 due to a shortage of nanoparticles during the shaping operation for plastically deforming the coated magnet powder particles 5. This suppresses an increase in eddy current losses.

[0088] As described above, the binder is an acrylic binder that decomposes at a temperature lower than the heat input temperature during the shaping operation, which ensures that the nanoparticles adhere to the surface of the rare earth magnet powder particles 2 and prevents the binder from remaining as a residue in the rare earth magnet 1.

[0089] As Figure 1 shown, the shaping operation includes: performing a first shaping operation that includes applying pressure to the coated magnet powder particles 5 in a first direction, thereby plastically deforming the coated magnet powder particles 5 to produce a first shaped product 6 ( Figure 1 shown in (C)); and performing a second shaping operation that includes applying pressure to the first shaped product 6 in a second direction intersecting the first direction, thereby plastically deforming the first shaped product 6 to produce a rare earth magnet ( Figure 1(E) in the figure). In this configuration, during the second molding operation, when compressed in the second direction, the coated magnet powder particles 5 of the first molded product expand in a third direction perpendicular to the first and second directions. This prevents the thickness of the coating 4 on the main surface 2a of the rare earth magnet powder particles 2 (i.e., the thickness in the first direction) from easily becoming thinner. This further prevents cracks from occurring in the coating 4, which suppresses an increase in eddy current loss. Therefore, this configuration allows a reduction in the amount of insulating material to be added, thereby minimizing the degradation of the magnetic properties of the rare earth magnet 1 caused by the addition of the insulating material.

[0090] Some embodiments of the present invention have been described. However, the present invention is not limited to these specific embodiments and can be implemented by various modifications. For example, in the above embodiment, since the rare earth magnet 1 has a rectangular prism shape, as shown in FIG. Figure 1 As shown in (D), the first molded product 6 is rotated 90 degrees. However, as mentioned above, the rotation angle is not limited to this angle. For example, when the first molded product 6 presents an octagonal shape as viewed horizontally, the rotation angle may be 90 degrees or 45 degrees. When the first molded product 6 presents a 16-sided polygonal shape as viewed horizontally, the rotation angle may be any one of 22.5 degrees, 45 degrees, 67.5 degrees or 90 degrees. When the first molded product 6 presents a circular shape as viewed horizontally, the rotation angle may be any angle between 0 degrees and 180 degrees. Generally, without departing from the scope of the present invention, various changes and modifications may be made to the features of the embodiment, such as the specific configuration, position, quantity and material of each component or element in the embodiment. In the above-mentioned embodiment, not all elements included therein are required. Therefore, various modifications may be made to the embodiment as appropriate, including eliminating some elements.

Claims

1. A rare earth magnet comprising coated magnet powder particles, each of the coated magnet powder particles comprising a rare earth magnet powder particle and a coating of an insulating material on a surface of the rare earth magnet powder particle, in, The insulating material includes nanoparticles, and the rare earth magnet powder particles are coated with the nanoparticles.

2. The rare earth magnet according to claim 1, wherein The nanoparticles are made of alkali metal fluoride or alkaline earth metal fluoride and have a particle size of 1 nm to 100 nm.

3. The rare earth magnet according to claim 2, wherein The coating layer comprising the nanoparticles has a thickness of 200 nm to 2000 nm.

4. A method for manufacturing a rare earth magnet, comprising: performing a coating operation comprising: adding an insulating material to rare earth magnet powder particles to produce coated magnet powder particles such that each of the coated magnet powder particles includes one of the rare earth magnet powder particles and a coating of the insulating material on a surface of the rare earth magnet powder particle; and performing a molding operation, the molding operation comprising: placing the coated magnet powder particles in a mold configured to allow pressurization, and applying pressure to the coated magnet powder particles in the mold, thereby compressively deforming the coated magnet powder particles to produce the rare earth magnet, wherein the insulating material comprises nanoparticles, and The coating operation includes spraying a nanoparticle dispersion solution containing the nanoparticles and a binder onto the rare earth magnet powder particles that are caused to tumble and flow, thereby adding the insulating material.

5. The method for manufacturing a rare earth magnet according to claim 4, wherein: The nanoparticle dispersion solution is prepared by mixing nanoparticles made of alkali metal fluoride or alkaline earth metal fluoride and having a particle size of 1 nm to 100 nm, a solvent, and the binder.

6. The method for manufacturing a rare earth magnet according to claim 5, wherein: The coating operation includes adding the insulating material to the rare earth magnet powder particles so that the coating of the rare earth magnet including the nanoparticles has a thickness of 200 nm to 2000 nm.

7. The method for manufacturing a rare earth magnet according to claim 4, wherein: The adhesive is an acrylic adhesive that decomposes at temperatures below the heat input temperature during the molding operation.

8. The method for manufacturing a rare earth magnet according to claim 4, wherein: The forming operation includes: performing a first molding operation, the first molding operation comprising: placing the coated magnet powder particles in the mold configured to allow pressurization in a first direction, and applying pressure to the coated magnet powder particles in the mold in the first direction, thereby compressively deforming the coated magnet powder particles to produce a first molded product; and A second molding operation is performed, the second molding operation including applying pressure to the first molded product in a second direction intersecting the first direction, thereby plastically deforming the first molded product to produce the rare earth magnet.

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