Rare earth magnet and method for manufacturing rare earth magnet

Abstract

To provide a rare earth magnet that can achieve both high magnetic properties and low eddy current loss, and a method for manufacturing the same.SOLUTION: A rare earth magnet 1 includes a coated magnet powder 5 in which a coating 4 made of an insulating material is formed on the surface of a rare earth magnet powder 2, the insulating material includes nanoparticles that coat the surface of the rare earth magnet powder 2. The method for manufacturing the rare earth magnet 1 includes adding an insulating material to the rare earth magnet powder 2 such that a coating 4 is formed on the surface of the rare earth magnet powder 2, and in the step of obtaining the coated magnet powder 5 with the coating 4 formed, the insulating material is added by spraying a nanoparticle dispersion liquid containing nanoparticles and a binder onto the tumbling and fluidizing rare earth magnet powder 2.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] In recent years, efforts to realize a low-carbon or carbon-free society have become more active, and research and development into electrification technologies is being conducted to reduce CO2 emissions and improve energy efficiency in vehicles. One method for improving energy efficiency is to improve the efficiency of the motor used as the power source. In recent years, rare earth magnets have been widely used to improve motor efficiency. Because rare earth magnets are metallic magnets, their electrical resistance is low, but when they are incorporated into motors, eddy current loss increases, which can reduce motor efficiency. Various proposals have been made with the aim of reducing eddy current loss.

[0003] Patent Document 1 discloses a rare earth magnet capable of reducing eddy current loss, which has rare earth magnet powder covered with a film-like coating layer containing rare earth oxide. The particles of the magnet powder coated with the rare earth oxide have binders containing rare earth oxide particles interposed between them. The rare earth magnet is produced by high-temperature pressure molding of a mixture of the rare earth magnet powder coated with the rare earth oxide and the rare earth oxide.

[0004] Patent Document 2 discloses a method for producing a rare earth magnet in which, for the purpose of achieving high electrical resistance, Nd-Fe-B based magnet powder is mixed with an oxide such as CaO, a nitride such as BN, or a fluoride such as CaF2, and this mixture is then subjected to hot plastic working to obtain an anisotropic magnetic material.

[0005] Patent Document 3 discloses a first method for producing rare earth magnets, which includes the steps of preparing an isotropically quenched powder such as Nd-Fe-B magnet powder, mixing the isotropically quenched powder with a predetermined compound that will form the insulating layer, cold-forming (pre-forming) the mixture, hot-forming (densifying) the cold-formed body, and hot plastic working (anisotropizing).The document describes that the magnets produced by this method are composed of Nd-Fe-B quenched powders with long sides of 100 to 400 μm and thicknesses of 20 to 40 μm, generally stacked with compound powders in between. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4784173 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-22905 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-27852 Summary of the Invention [Problem to be solved by the invention]

[0007] To prevent the magnetic properties of rare-earth magnets from deteriorating, it is better to mix a small amount of insulating compound into the magnet powder. However, because the magnet powder is flaky, the magnet powder generally forms a layered structure during the densification process of the mixture of the magnet powder and insulating compound. Therefore, when magnets are manufactured using conventional manufacturing methods, the magnet powder and insulating compound deform during the hot plastic working process, spreading in a direction perpendicular to the pressure direction (i.e., along the main surface of the magnet powder). Therefore, if the amount of insulating material is reduced, the insulating layer is broken during hot plastic working, and the magnet powder particles that were separated by the insulating layer become electrically connected. This increases the eddy current path (reducing the effect of disrupting the eddy current path), resulting in increased eddy current loss during motor operation.

[0008] In view of the above background, the present invention aims to provide a rare earth magnet that can achieve both high magnetic properties and low eddy current loss, and a method for manufacturing such a rare earth magnet, which will ultimately contribute to improving energy efficiency. [Means for solving the problem]

[0009] In order to solve the above problems, one aspect of the present invention is a rare earth magnet (1) that includes a coated magnet powder (5) in which a coating (4) made of an insulating material is formed on the surface of rare earth magnet powder (2), the insulating material including nanoparticles that coat the surface of the rare earth magnet powder.

[0010] According to this aspect, since the insulating material contains nanoparticles, the coating formed on the surface of the rare earth magnet powder is thin and uniform, and the coating is prevented from being broken down, which makes it possible to simultaneously improve the magnetic properties of the coated magnet powder and reduce eddy currents.

[0011] In the above aspect, the nanoparticles may be made of an alkali metal fluoride or an alkaline earth metal fluoride (CaF2) and have a particle diameter of 1 to 100 nm.

[0012] According to this aspect, the alkali metal fluoride or alkaline earth metal fluoride that constitutes the coating is prevented from reacting with the rare earth that constitutes the rare earth magnetic powder, thereby preventing a deterioration in the magnetic properties of the rare earth magnetic powder and the insulating properties of the coating.

[0013] In the above aspect, the thickness of the coating containing the nanoparticles of the coated magnet powder may be 200 nm to 2000 nm.

[0014] According to this aspect, the nanoparticles are formed in multiple layers, which prevents the coating from being broken due to the nanoparticles becoming sparse, or the coating from being broken due to a lack of nanoparticles during compression molding of the coated magnet powder, thereby suppressing an increase in eddy currents.

[0015] In order to solve the above problems, one aspect of the present invention is a method for manufacturing a rare earth magnet (1), which includes the steps of adding an insulating material to rare earth magnet powder (2) so that a coating (4) is formed on the surface of the rare earth magnet powder, thereby obtaining coated magnet powder (5) with the coating (FIG. 1(B)); and placing the coated magnet powder inside a pressurizable mold and compressing the coated magnet powder using the mold. The above in an unmagnetized state and a molding process (Fig. 1(C) and (E)) to obtain a rare earth magnet, in which the insulating material includes nanoparticles. In the process to obtain the coated magnet powder, the insulating material is added by spraying a nanoparticle dispersion liquid containing the nanoparticles and a binder onto the rolling-fluidized rare earth magnet powder.

[0016] According to this aspect, by spraying a nanoparticle dispersion containing nanoparticles and a binder onto the rolling-fluidized rare earth magnet powder, a thin and uniform coating of nanoparticles can be formed on the surface of the rare earth magnet powder. This prevents the coating from being broken during the compacting process. This makes it possible to simultaneously improve the magnetic properties of the coated magnet powder and reduce eddy currents.

[0017] In the above aspect, the nanoparticle dispersion may be obtained by mixing the nanoparticles made of alkali metal fluoride or alkaline earth metal fluoride and having a particle size of 1 to 100 nm, a solvent, and a binder.

[0018] According to this embodiment, the nanoparticles can be reliably and uniformly attached to the surface of the rare earth magnet powder via the binder, which prevents the nanoparticles from becoming sparse and the coating from being broken down.Furthermore, the alkali metal fluoride or alkaline earth metal fluoride that makes up the coating is prevented from reacting with the rare earth that makes up the rare earth magnet powder.

[0019] In the above aspect, in the step of obtaining the coated magnet powder, the insulating material may be added so that the thickness of the coating containing the nanoparticles in the rare earth magnet is 200 nm to 2000 nm.

[0020] According to this aspect, the nanoparticles are formed in multiple layers, which prevents the coating from being broken due to the nanoparticles becoming sparse, or the coating from being broken due to a lack of nanoparticles during compression molding of the coated magnet powder, thereby suppressing an increase in eddy currents.

[0021] In the above embodiment, the binder may be an acrylic binder that is thermally decomposable at or below the heat input temperature during molding.

[0022] According to this embodiment, it is possible to reliably adhere the nanoparticles to the surface of the rare earth magnet powder, and also to prevent the binder from remaining as a residual component on the rare earth magnet.

[0023] In the above-described embodiment, the molding step includes a primary molding step (FIG. 1(C)) in which the coated magnet powder is placed inside the mold capable of applying pressure in a first direction, and the mold applies pressure to the coated magnet powder in the first direction to obtain a primary molded product of the rare earth magnet; and a secondary molding step in which the primary molded product is plastically deformed by applying pressure in a second direction intersecting the first direction, Unmagnetized state It is preferable to include a secondary molding step (FIG. 1(E)) to obtain the rare earth magnet.

[0024] According to this aspect, in the secondary molding process, the coated magnet powder of the primary molded product is stretched in a third direction perpendicular to the first and second directions, while being compressed in the second direction, so that the thickness of the coating on the main surface of the rare earth magnet powder (i.e., the thickness in the first direction) is less likely to become thin. This prevents the coating from being broken, which in turn prevents an increase in eddy current loss. This means that the amount of insulating material added to the rare earth magnet powder can be reduced, thereby preventing a decrease in the magnetic properties of the rare earth magnet caused by the addition of insulating material. [Effects of the Invention]

[0025] According to the above aspects, it is possible to provide a rare earth magnet that can achieve both high magnetic properties and low eddy current loss, and a method for manufacturing the rare earth magnet. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is an explanatory diagram of a method for manufacturing a rare earth magnet according to an embodiment; [Figure 2] Schematic diagram of a rolling fluidization device [Figure 3] Schematic diagram of coated magnet powder [Figure 4] SEM image showing nanoparticle coating [Figure 5] SEM photo of the cross section of a rare earth magnet primary molding after primary molding [Figure 6] 1A is a cross-sectional view showing a primary molded product and a secondary molded product of a nanoparticle coating according to the present invention, and FIG. 1B is a cross-sectional view showing a bulk coating according to a comparative example. [Figure 7] SEM photographs showing (A) the nanoparticle coating according to the present invention and (B) the bulk coating according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0028] First, a method for manufacturing a rare earth magnet 1 according to an embodiment will be described. Figure 1 is an explanatory diagram of the method for manufacturing a rare earth magnet 1 according to an embodiment. As shown in Figure 1(A), first, rare earth magnet powder 2 is manufactured. Through this process, rare earth magnet powder 2 is obtained.

[0029] The raw material of the rare earth magnet powder 2 is not limited to this, but for example, a neodymium magnet (Nd-Fe-B magnet, more precisely NdFe 14 B) may be used. The method for obtaining the rare earth magnet powder 2 from the rare earth magnet raw material is, for example, the melt spinning method. The melt spinning method is a manufacturing method for producing fine flake-shaped (thin piece) magnetic powder for magnets containing Nd—Fe—B crystals by spraying an alloy molten at high temperature onto a cooled roll and rapidly cooling it.

[0030] The rare earth magnet powder 2 obtained in this process is an isotropic quenched powder with no uniform crystal orientation, and due to its flake shape, has two main surfaces 2a. In this specification, the main surfaces 2a are defined as the largest of a pair of flat surfaces facing in opposite directions. When viewed perpendicular to the main surfaces 2a, the rare earth magnet powder 2 has an aspect ratio of approximately 1 (e.g., 0.7 to 1.0). The aspect ratio is the ratio of the minor axis (minor axis) to the major axis (long axis diameter) of a particle, and is expressed as b / a, where a is the major axis and b is the minor axis. The major axis (major axis diameter) refers to the maximum Feret diameter, and the minor axis (minor axis diameter) refers to the minimum Feret diameter. The measurement method for the major and minor axes complies with the provisions of JIS Z8890:2017, "Evaluation of the Particle Properties of Powders."

[0031] Next, as shown in Figure 1(B), an insulating coating process is performed to form an insulating coating on the surface of the rare earth magnetic powder 2. In this process, an insulating substance is added to the rare earth magnetic powder 2 so that a coating 4 is formed on the surface of the rare earth magnetic powder 2, thereby obtaining a coated magnetic powder 5 on which the coating 4 is formed.

[0032] The insulating material is preferably, but not limited to, an alkali metal fluoride or an alkaline earth metal fluoride. In this embodiment, calcium fluoride (CaF2), which is an alkaline earth metal fluoride, is used as the insulating material. The insulating material is not limited to calcium fluoride, and may be an alkaline earth metal fluoride such as magnesium fluoride, barium fluoride, or strontium fluoride, or an alkali metal fluoride such as lithium fluoride. Alternatively, the insulating material may be a mixture of these.

[0033] The method for forming the coating 4 on the surface of the rare earth magnet powder 2 is as follows. First, calcium fluoride nanoparticles with a particle size of 1 to 100 nm and a binder are mixed and stirred in a solvent to produce a nanoparticle dispersion. The solvent is not limited to, but may be, for example, isopropyl alcohol (2-propanol, also known as IPA). The binder is added to increase the binding strength of the nanoparticles to the rare earth magnet powder 2. The binder is preferably decomposed and removed by heating during molding of the rare earth magnet 1. Therefore, it is preferable to select a binder that exhibits good thermal decomposition properties at or below the heat input temperature during molding and leaves no residual components after molding. Although not limited to, an acrylic binder is used as the binder in this embodiment. The acrylic binder is a binder made of an acrylic polymer.

[0034] After preparing the dispersion, a rolling flow device 20 is used to roll and flow the rare earth magnet powder 2, and a nanoparticle dispersion containing nanoparticles and a binder is sprayed onto the powder, thereby adding an insulating material to the rare earth magnet powder 2.

[0035] Fig. 2 is a schematic diagram of the tumbling fluidization device 20. As shown in Fig. 2, the tumbling fluidization device 20 includes a main body case 22 that defines a fluidized bed 21, a blade rotor 23 rotatably disposed at the bottom of the fluidized bed 21, and a spray nozzle 24 provided on the lower side surface of the main body case 22. The spray nozzle 24 is attached to the main body case 22 in a horizontal position above the blade rotor 23 so that the nozzle faces the bottom of the fluidized bed 21.

[0036] Air is supplied from the bottom of the main body case 22, and the rotation of the blade rotor 23 forcibly promotes the rolling fluidization of the rare earth magnetic powder 2 in the fluidized bed 21. With the air flow and the rare earth magnetic powder 2 flowing in a swirling manner, a nanoparticle dispersion liquid is sprayed from a spray nozzle 24 onto the bottom of the fluidized bed 21, thereby efficiently coating the surface of the rare earth magnetic powder 2 with the nanoparticles.

[0037] Fig. 3 is a schematic diagram of coated magnet powder 5. As shown in Fig. 3, in the process of obtaining coated magnet powder 5, a coating 4 having a thickness of 1 μm to 40 μm is formed on the surface of rare earth magnet powder 2 by adding a nanoparticle dispersion liquid so that the thickness of coating 4 of rare earth magnet powder 2 in rare earth magnet 1 is 200 nm to 2000 nm.

[0038] An SEM photograph showing the nanoparticle coating is shown in Figure 4. As described above, the nanoparticle coating has a particle diameter of 1 to 100 nm and is coated on the surface of the rare earth magnet powder 2 to a thickness of 1 μm to 40 μm.

[0039] 1(C), the coated magnet powder 5 is subjected to primary molding. In this process, the coated magnet powder 5 is placed inside a primary molding die 10 (hot press), and the coated magnet powder 5 is compressed and deformed in a first direction by the primary molding die 10, thereby obtaining a primary molded product 6 of a rare earth magnet 1 in which the coated magnet powder 5 is densified.

[0040] The primary molding die 10 has a cylindrical die body 11 having a cross-sectional shape that matches the shape of the primary molded product 6, and an upper die 12 and a lower die 13 that can apply a compressive force in a first direction to the object inside the die body 11. That is, in this process, pressure is applied to the primary molded product 6 while the coated magnet powder 5 is constrained in a direction perpendicular to the first direction. In this embodiment, the first direction is the up-down direction, but is not limited to this.

[0041] The primary molded product 6 is formed by hot press molding, in which the primary molding die 10 is heated to a predetermined temperature and a predetermined pressure is applied for a predetermined time. When compressed and deformed by pressure, the coated magnet powder 5 in the primary molding die 10 is oriented so that the main surfaces 2a of the rare earth magnet powder 2 face a first direction, and the particles are stacked on top of each other in a direction (first direction) perpendicular to the main surfaces 2a.

[0042] Figure 5 is an SEM photograph of a cross section of a primary molded product 6 of rare earth magnet 1 after primary molding. As shown in Figure 5, in primary molded product 6 of rare earth magnet 1, rare earth magnet powder 2 is stacked in a direction (first direction) perpendicular to main surface 2a.

[0043] The primary molded product 6 is formed by hot compression processing in which the coated magnet powder 5 is compressed and deformed in a hot primary molding die 10 heated to a predetermined temperature. The primary molded product 6 is formed in a hot state with the die temperature set to 600°C to 700°C, preferably about 640°C.

[0044] After primary molding, the resulting primary molded article 6 is removed from the primary molding die 10 and rotated 90°, as shown in FIG. 1(D). The primary molded article 6 is rotated around a rotation axis on a horizontal plane, i.e., around an axis parallel to the main surface 2a of the rare earth magnet powder 2. The rotation angle of the primary molded article 6 is 90° in this embodiment, but is not limited to this. However, the rotation angle is preferably close to 90°, and more preferably 90° perpendicular to the first direction.

[0045] Thereafter, as shown in FIG. 1(E), secondary molding is performed on the primary molded product 6. In this process, the primary molded product 6 rotated at the angle shown in FIG. 1(D) is placed inside the secondary molding die 15. Next, the secondary molding die 15 applies pressure in a second direction that intersects with the first direction, which is the pressure direction of the primary molding (the lamination direction of the rare earth magnet powder 2), thereby plastically deforming the primary molded product 6. Unmagnetized state A rare earth magnet 1 (secondary formed product) is obtained.

[0046] The rotation process in Fig. 1(D) is performed because the pressure direction in the secondary molding in Fig. 1(E) is the same vertical direction as the pressure direction in the primary molding. Therefore, if the pressure direction in the secondary molding in Fig. 1(E) is a direction different from the first direction, such as a horizontal direction, the rotation process in Fig. 1(D) is not necessary.

[0047] The secondary molding die 15 is composed of an upper pressure die 16 and a lower pressure die 17 arranged opposite each other. The upper pressure die 16 and the lower pressure die 17 have upper pressure surfaces 16a and lower pressure surfaces 17a that fit the shape of the primary molded article 6 in order to pressurize the primary molded article 6 in the second direction (the up-down direction in this embodiment). Since the primary molded article 6 in this embodiment has a rectangular parallelepiped shape, the upper pressure die 16 and the lower pressure die 17 have upper pressure surfaces 16a and lower pressure surfaces 17a that are made up of a pair of opposing surfaces that extend horizontally and parallel to each other, and apply a compressive force to the primary molded article 6 in the up-down direction that is perpendicular to the first direction.

[0048] In the secondary molding, pressure is applied to the primary molded product 6 without restraining the primary molded product 6 in a direction perpendicular to the second direction. Therefore, through the secondary molding, the primary molded product 6 is compressed in the vertical direction, which is the pressure direction of the secondary molding, and plastically deforms so as to be stretched in the horizontal direction perpendicular to the vertical direction. Specifically, the thickness (dimension in the first direction) of the rare earth magnet powder 2 in the rare earth magnet 1 is thicker than the thickness of the rare earth magnet powder 2 in the primary molded product 6. When viewed from the first direction, the aspect ratio of the rare earth magnet powder 2 in the rare earth magnet 1 is smaller than the aspect ratio of the rare earth magnet powder 2 in the primary molded product 6. The aspect ratio of the rare earth magnet powder 2 in the rare earth magnet 1 is preferably smaller than 1, for example, approximately 0.15 to 0.5.

[0049] By hot plastic working, the rare earth magnet powder 2 of the primary molded product 6 exhibits magnetic anisotropy (uniaxial anisotropy) in which the c-axis direction (direction of easy magnetization) of the crystal grains is aligned parallel to the pressure direction. (Secondary molded product) is magnetized in the direction in which this magnetic anisotropy is manifested.

[0050] In this way, during secondary molding, the primary molded product 6 is pressurized in a second direction intersecting the first direction, causing plastic deformation. As a result, the rare earth magnetic powder 2 and the surrounding coating 4 are stretched in directions perpendicular to the second direction, i.e., in the first and third directions. In other words, the coating 4 between adjacent rare earth magnetic powder particles 2 in the first direction is stretched in the third direction, thinning it, but is not stretched in the second direction. This prevents the coating 4 from becoming too thin in the first direction, thereby suppressing an increase in eddy current loss. This effect will be described in more detail later.

[0051] Furthermore, the secondary forming is performed by hot compression processing, in which the primary molded product 6 is compressed and deformed in a hot state with the secondary molding die 15 heated to a predetermined temperature; more specifically, by hot plastic processing, in which the primary molded product 6 is plastically deformed in a hot state at a temperature higher than that in the primary molding process. The temperature of the secondary molding die 15 for secondary forming is preferably a temperature at which some of the crystal grains of the rare earth magnet powder 2 change into a liquid phase, for example, about 850°C. This allows the rare earth magnet powder 2 to be plastically deformed with a high upsetting ratio. In this embodiment, during secondary forming, the primary molded product 6 of the rare earth magnet 1 is plastically processed with an upsetting ratio of about 70%.

[0052] Next, the effects of the rare earth magnet 1 produced in this manner and its manufacturing method will be described in comparison with a comparative example.

[0053] FIG. 6 is a cross-sectional view schematically showing primary molded products 6, 106 and secondary molded products (rare earth magnets 1, 101) of (A) a nanoparticle coating according to the present invention and (B) a bulk coating according to a comparative example. First, the comparative example (B) will be explained. In the rare earth magnet 101 (secondary molded product) according to the comparative example, a coating 104 is formed by a method different from that of the embodiment during the insulating coating process (see FIG. 1(B)) that forms an insulating coating on the surface of the rare earth magnet powder 2. The coating 104 may be formed by, for example, sputtering or vapor deposition. The coating 104 is a bulk insulating coating with a generally uniform thickness.

[0054] For the comparative rare earth magnet 101, primary molding (see FIG. 1(C)) results in a primary molded product 106 in which the rare earth magnetic powder 2 is stacked in a direction (first direction) perpendicular to the main surface 2a, as shown in FIG. 6(B1). In the primary molded product 106, an insulating layer of roughly uniform thickness is formed by the coating 104 between adjacent pieces of rare earth magnetic powder 2. In the primary molded product 106, adjacent pieces of rare earth magnetic powder 2 are separated from each other by the coating 104.

[0055] Then, the primary molded product 106 is pressurized in a second direction (see FIG. 1(E)) to perform secondary molding, which stretches the rare earth magnet powder 2 and coating 104 along a plane perpendicular to the second direction (left-right and perpendicular to the plane of the paper). This results in the rare earth magnet 101 (secondary molded product) of the comparative example shown in FIG. 6(B2). During secondary molding, the coating 104 is unable to follow the plastic deformation of the rare earth magnet powder 2 that stretches along a plane perpendicular to the second direction and becomes interrupted. By applying pressure in the second direction in this state, adjacent pieces of rare earth magnet powder 2 in the second direction are connected to each other at the interrupted portions of the coating 104. This increases the volume of the magnet powder, thereby increasing the eddy current loss that occurs when the motor is operating.

[0056] In contrast, in the rare earth magnet 1 according to the embodiment, as shown in Figure 6(A1), an insulating layer of roughly uniform thickness is formed by the coating 4 made of nanoparticles between adjacent rare earth magnet powders 2 in the primary molded product 6. Therefore, when pressure is applied in the second direction by secondary molding, as shown in Figure 6(A2), the coating 4 follows the plastic deformation of the rare earth magnet powder 2 that is stretched along a plane perpendicular to the second direction, and is stretched continuously while becoming thinner.

[0057] Figure 7 shows SEM photographs of (A) a nanoparticle coating according to the present invention and (B) a bulk coating according to a comparative example. As shown in Figure 7(B), in the rare earth magnet 101 with the bulk coating according to the comparative example, adjacent rare earth magnetic powder particles 2 at the top and bottom of the photograph are connected to each other at interrupted portions of the coating 104. In contrast, as shown in Figure 7(A), in the rare earth magnet 1 with the nanoparticle coating according to the present invention, adjacent rare earth magnetic powder particles 2 at the top and bottom are kept separated by the coating 4.

[0058] In rare earth magnet 1 according to the present invention, even after being stretched by secondary molding, coating 4 has a generally uniform thickness in the range of 200 nm to 2000 nm.

[0059] Thus, in the rare earth magnet 1 according to the embodiment, the insulating material that constitutes the coating 4 formed on the surface of the rare earth magnetic powder 2 contains nanoparticles, and the nanoparticles coat the surface of the rare earth magnetic powder 2. Because the insulating material contains nanoparticles, the coating 4 formed on the surface of the rare earth magnetic powder 2 is thin and uniform, preventing discontinuities in the coating 4. This makes it possible to improve the magnetic properties of the coated magnetic powder 5 while reducing eddy currents.

[0060] As described above, the nanoparticles are made of alkaline earth metal fluoride and have a particle diameter of 1 to 100 nm. This prevents the alkaline earth metal fluoride that makes up the coating 4 from reacting with the rare earth that makes up the rare earth magnetic powder 2. This prevents a deterioration in the magnetic properties of the rare earth magnetic powder 2 and the insulating properties of the coating 4. The same effect can be achieved even if the nanoparticles are made of alkali metal fluoride.

[0061] Furthermore, in the rare earth magnet 1, the thickness of the coating 4 of the coated magnet powder 5 is 200 nm to 2000 nm. This allows the nanoparticles to be formed in multiple layers, preventing the coating 4 from being broken due to the nanoparticles becoming sparse, or preventing the coating 4 from being broken due to a lack of nanoparticles during compression molding of the coated magnet powder 5. This prevents an increase in eddy currents.

[0062] The insulating material that forms the coating 4 contains nanoparticles, and the manufacturing method of the rare earth magnet 1 according to the embodiment includes a step of obtaining the coated magnet powder 5 shown in FIG. 1(B). In this step, as shown in FIG. 2, a nanoparticle dispersion containing nanoparticles and a binder is sprayed onto the rolling-fluidized rare earth magnet powder 2, thereby adding the insulating material to the rare earth magnet powder 2. By adding the insulating material in this manner, a thin and uniform coating 4 is formed by the nanoparticles on the surface of the rare earth magnet powder 2. This prevents the coating 4 from being interrupted during the molding process shown in FIGS. 1(C) to 1(E). This makes it possible to improve the magnetic properties of the coated magnet powder 5 while reducing eddy currents.

[0063] As described above, the nanoparticle dispersion is obtained by mixing alkaline earth metal fluoride nanoparticles with particle diameters of 1 to 100 nm, a solvent, and a binder. This allows the nanoparticles to be reliably and uniformly attached to the surface of the rare earth magnet powder 2 via the binder, preventing the nanoparticles from becoming sparse and resulting in discontinuities in the coating 4. Furthermore, the alkaline earth metal fluoride that makes up the coating 4 is prevented from reacting with the rare earth that makes up the rare earth magnet powder 2.

[0064] In the process for obtaining the coated magnet powder 5 shown in Figures 1(B) and 2, an insulating substance is added to form a thicker coating 4 of the coated magnet powder 5 in the rare earth magnet 1, so that the thickness of the coating 4 is 200 nm to 2000 nm. This causes the nanoparticles to form multiple layers, preventing the coating 4 from being broken due to the nanoparticles becoming sparse, or preventing the coating 4 from being broken due to a lack of nanoparticles during compression molding of the coated magnet powder 5. This prevents an increase in eddy currents.

[0065] As described above, the binder is an acrylic binder that is thermally decomposable below the heat input temperature during molding, so that nanoparticles can be reliably attached to the surface of the rare earth magnet powder 2, and the binder is prevented from remaining as a residual component on the rare earth magnet 1.

[0066] As shown in FIG. 1, the molding process includes a primary molding step (FIG. 1(C)) in which the coated magnet powder 5 is compressed and deformed in a first direction, and a secondary molding step (FIG. 1(E)) in which the primary molded product 6 is compressed and plastically deformed in a second direction intersecting the first direction. In this secondary molding step, the coated magnet powder 5 of the primary molded product 6 is stretched in a third direction perpendicular to the first and second directions, while being compressed in the second direction. This prevents the thickness of the coating 4 on the main surface 2a of the rare earth magnet powder 2 (i.e., the thickness in the first direction) from becoming thin. This prevents breaks in the coating 4, thereby preventing an increase in eddy current loss. This allows for a reduction in the amount of insulating material added to the rare earth magnet powder 2, thereby preventing a decrease in the magnetic properties of the rare earth magnet 1 due to the addition of insulating material.

[0067] While the specific embodiments have been described above, the present invention is not limited to these embodiments and modifications, and can be implemented in a wide variety of ways. For example, in the above embodiment, the primary molded product 6 is rotated 90° in FIG. 1(D) because the rare earth magnet 1 has a rectangular parallelepiped shape. However, as noted above, the rotation angle is not limited to this. For example, if the primary molded product 6 is octagonal when viewed horizontally, the rotation angle may be 90° or 45°. Furthermore, if the primary molded product 6 is hexagonal when viewed horizontally, the rotation angle may be 22.5°, 45°, 67.5°, or 90°. If the primary molded product 6 is circular when viewed horizontally, the rotation angle may be any angle greater than 0° and less than 180°. Furthermore, the specific configuration, arrangement, quantity, and materials of each component and part may be modified as appropriate without departing from the spirit and scope of the present invention. Furthermore, some or all of the configurations of the above embodiments may be combined with each other. On the other hand, not all of the components shown in the above embodiment are necessarily required, and they can be selected as appropriate. [Explanation of symbols]

[0068] 1: Rare earth magnet 2: Rare earth magnet powder 2a: Main surface 4:Coating 5: Coated magnet powder 6: Primary molded product 10: Primary molding die 15: Secondary molding mold 20: Rolling fluidization device

Claims

1. A rare earth magnet, The magnet powder contains a coated magnet powder in which a coating made of an insulating material is formed on the surface of rare earth magnet powder, the insulating material includes nanoparticles, and the nanoparticles coat the surface of the rare earth magnet powder; The nanoparticles are made of alkali metal fluoride or alkaline earth metal fluoride and have a particle size of 1 to 100 nm.

2. 2. The rare earth magnet according to claim 1, wherein the thickness of the coating containing the nanoparticles of the coated magnet powder is 200 nm to 2000 nm.

3. A method for producing a rare earth magnet, comprising: a step of adding an insulating material to the rare earth magnet powder so that a coating is formed on the surface of the rare earth magnet powder, thereby obtaining a coated magnet powder having the coating formed thereon; a molding step of placing the coated magnet powder inside a pressurizable mold and compressing the coated magnet powder using the mold to obtain the rare earth magnet in an unmagnetized state, the insulating material includes nanoparticles; In the process of obtaining the coated magnet powder, the insulating material is added by spraying a nanoparticle dispersion containing the nanoparticles and a binder onto the rolling-fluidized rare earth magnet powder.

4. 4. The method for producing a rare earth magnet according to claim 3, wherein the nanoparticle dispersion is obtained by mixing the nanoparticles, which are made of an alkali metal fluoride or an alkaline earth metal fluoride and have a particle diameter of 1 to 100 nm, a solvent, and a binder.

5. 5. The method for producing a rare earth magnet according to claim 4, wherein in the step of obtaining the coated magnet powder, the insulating material is added so that the thickness of the coating containing the nanoparticles in the rare earth magnet is 200 nm to 2000 nm.

6. 4. The method for producing a rare earth magnet according to claim 3, wherein the binder is an acrylic binder that is thermally decomposable at temperatures equal to or lower than the heat input temperature during molding.

7. The molding step includes: a primary molding step of placing the coated magnet powder inside the mold capable of applying pressure in a first direction, compressing and deforming the coated magnet powder by applying pressure in the first direction using the mold, and obtaining a primary molded product of the rare earth magnet; a secondary forming step of pressurizing the primary molded product in a second direction intersecting the first direction to plastically deform the primary molded product, thereby obtaining the rare earth magnet in an unmagnetized state.

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