Rare earth bonded magnet mixture and method for manufacturing rare earth bonded magnet using same

Abstract

The present invention relates to a rare earth bonded magnet mixture, the mixture comprising: a rare earth magnet powder comprising a coarse powder and a fine powder; and a resin binder, in which the rare earth bonded magnet mixture is obtained by kneading a rare earth magnet powder and the resin binder, the rare earth magnet powder is obtained by mixing a coarse powder and a fine powder, the coarse powder has a D50 of 240 [mu] m or more and less than 380 [mu] m, the fine powder has a D50 of 35 [mu] m or less, and the D90 / D10 of the rare earth magnet powder is 28 or more and 37 or less. D90 / D10 is the ratio of D90 to D10 in the particle size distribution of the entire rare earth magnet powder.

Description

Technical Field

[0001] The present invention relates to a rare earth bonded magnet mixture obtained by kneading a binder and a rare earth magnet powder containing a rare earth element as a main constituent element, and a method for producing a rare earth bonded magnet using the mixture. Examples of the rare earth magnet used in the present invention include RFeN-based rare earth magnets containing rare earth elements (R), iron (Fe) and nitrogen (N) as main constituent elements, RFe-based rare earth magnets containing rare earth elements and iron as main constituent elements, RFeB-based rare earth magnets containing rare earth elements, iron and boron (B) as main constituent elements, and RCo-based (RCo-based, RCo5-based, R2Co5-based) rare earth magnets containing rare earth elements and cobalt (Co) as main constituent elements. 17 Base) rare earth magnet. Background Art

[0002] Bonded magnets are generally prepared by kneading magnet powder and resin binder to prepare a bonded magnet mixture (hereinafter referred to as "mixture"), that is, after or when the magnet powder and the resin binder are mixed, the magnet powder and the resin binder are kneaded in a state where the magnet powder and the resin binder are heated to a temperature higher than the melting point of the binder, the mixture is heated to melt the binder, and the mixture is solidified in a mold. Examples of molding methods include compression molding, extrusion molding, and injection molding. Among them, injection molding has the advantage of allowing the shape of the bonded magnet that can be produced to have a high degree of freedom.

[0003] In the case of producing a bonded magnet by injection molding, if the fluidity of the mixture is low when the mixture is injected into the mold, the mixture does not spread over the entire mold and a bonded magnet having a predetermined shape cannot be obtained. Therefore, a mixture having high fluidity is required.

[0004] Patent document 1 describes the production of a rare earth bonded magnet by using a rare earth bonded magnet mixture obtained by kneading RFeN-based rare earth magnet powder, a binder, and a coupling agent. Generally, the coupling agent chemically bonds to the molecules of the binder while adhering to the surface of the magnet powder particles in a molten state of the binder, so the action of the coupling agent makes the magnet powder particles easily flow together with the molten binder. Examples of coupling agents include those made of various materials, and in Patent document 1, a coupling agent composed of the general formula R (4-n) -Si-X (n) A silane coupling agent represented by , wherein R represents one or two or more organic groups having a hydrocarbon group or a functional group, X represents a hydrolyzable group such as an alkoxy group or a diol group, and n represents an integer in the range of 1 to 3.

[0005] Patent Document 1: JP2016-092262A

[0006] Non-patent document 1: Akinari Minegishi "Fundamentals of Slurry Rheology: Relationship between Particle Size, Particle Shape, and Zeta Potential" [online], February 19, 2018, Spectris Co., Ltd., [Search on July 5, 2023], Internet<URL:https: / / www.materials-talks.jp / files / 20180226142620_0.pdf> Summary of the invention

[0007] The fluidity of the mixture depends not only on the presence or absence of a coupling agent and the type of coupling agent, but also on various conditions. In some cases, the fluidity of the mixture is reduced even if a coupling agent is added. The object of the present invention is to provide a rare earth bonded magnet mixture which has high fluidity when the binder is melted, regardless of the presence or absence of a coupling agent.

[0008] In order to solve the above problems, the rare earth bonded magnet mixture according to the present invention is a rare earth bonded magnet mixture obtained by kneading rare earth magnet powder and a resin binder, wherein the rare earth magnet powder is obtained by mixing coarse powder with D50 greater than or equal to 240 μm and less than 380 μm and fine powder with D50 less than or equal to 35 μm, and D90 / D10 is greater than or equal to 28 and less than or equal to 37, D90 / D10 is the ratio of D90 to D10 in the particle size distribution of the entire rare earth magnet powder.

[0009] In the present invention, "D50" refers to the particle diameter at which the cumulative distribution related to the powder particle diameter is 50%, measured by a laser diffraction / scattering method using a particle size distribution analyzer (MT3300EX manufactured by MicrotracBEL Corp.). The cumulative distribution related to the powder particle diameter represents the volume ratio (proportional to the weight) of particles having a particle diameter smaller than a specific particle diameter in the entire powder. Similarly, "D90" and "D10" refer to the particle diameters at which the cumulative distribution is 90% and 10%, respectively.

[0010] In the rare earth bonded magnet mixture according to the present invention, a mixture of coarse powder and fine powder each having the above-mentioned D50 range and different particle diameters is used as rare earth magnet powder. Generally, it is known that in a slurry obtained by mixing a powder and a liquid, when a powder containing particles having different particle diameters is used, the viscosity of the slurry is lower than the viscosity of a slurry containing a powder made of particles having a uniform particle diameter (for example, see non-patent document 1). In the present invention, the coarse powder and the fine powder are mixed with each other, and then the D90 / D10 of the entire rare earth magnet powder after mixing is set to be greater than or equal to 28 and less than or equal to 37. Therefore, when the binder is melted, the fluidity of the rare earth bonded magnet mixture can be higher than the case where a rare earth magnet powder having another particle size distribution is used.

[0011] In the case where the D50 of the coarse powder is less than the above range or the D50 of the fine powder is greater than the above range, the difference between the particle diameters of the coarse powder and the fine powder is reduced, and the fluidity of the rare earth bonded magnet mixture cannot be fully increased. On the other hand, in the case where the D50 of the coarse powder is greater than the above range, the coarse particles may aggregate in the rare earth bonded magnet mixture in which the binder is melted, and the fluidity is reduced. There is no particular limit to the lower limit of the D50 of the fine powder, but too small a D50 makes it difficult to produce fine powder. Therefore, the D50 of the fine powder can be smaller within the range possible for fine powder production.

[0012] In the rare earth bonded magnet mixture according to the present invention, RFeN-based rare earth magnet powder, RFe-based rare earth magnet powder, RFeB-based rare earth magnet powder, RCo-based rare earth magnet powder, etc. can be used as rare earth magnet powder. In particular, among RFeN-based rare earth magnets, SmFeN-based rare earth magnets in which the rare earth element R is Sm have a small coercive force change with respect to temperature, and can be preferably used for driving an electric motor of an automatic vehicle whose temperature rises to about 130°C during use, and therefore, SmFeN-based rare earth magnet powder can also be preferably used in the present invention.

[0013] In the rare earth bonded magnet mixture according to the present invention, the rare earth magnet powder can be made of flat particles having a flat shape. Generally, a magnet mixture in which the magnet powder is made of flat particles has lower fluidity than a magnet mixture in which the magnet powder is made of spherical particles, and is not suitable for molding, such as injection molding. However, in the magnet mixture according to the present invention, since the fluidity can be increased by mixing coarse powder and fine powder, the magnet mixture according to the present invention can be used for molding, such as injection molding, even when the magnet powder is made of flat particles. In the present invention, "flat particles" refer to particles whose size in a direction perpendicular to a certain direction (thickness direction) is twice or more the size of the particle in the thickness direction. The magnet powder made of such flat particles is obtained by, for example, dripping molten metal on the surface of a high-speed rotating roller to prepare a strip alloy, and then crushing the strip alloy, the molten metal being obtained by melting an alloy as a rare earth magnet material.

[0014] Due to its high fluidity, the rare earth bonded magnet mixture according to the present invention can be particularly preferably used for producing rare earth bonded magnets by injection molding. In injection molding, thermoplastic resins are generally used as adhesives, and therefore, the adhesive contained in the rare earth bonded magnet mixture according to the present invention is preferably a thermoplastic resin. However, the rare earth bonded magnet mixture according to the present invention can be used to produce rare earth bonded magnets by methods other than injection molding, such as compression molding or extrusion molding, and in this case, a thermosetting resin adhesive can be used.

[0015] In the rare earth bonded magnet mixture according to the present invention, it is preferred that the binder has a viscosity of 25 Pa·s or less at a temperature of 310° C. The viscosity is determined according to ISO 11443 at a shear rate of 1000 sec. -1 , the ratio L / D of the length L of the capillary to its inner diameter D is 30 / 1 and the measurement time is 5 minutes. Therefore, when the binder melts, the fluidity of the rare earth bonded magnet mixture can be further increased. Examples of binder materials that meet these conditions include polyphenylene sulfide (PPS).

[0016] According to the present invention, it is not necessary to add a coupling agent to the rare earth bonded magnet mixture. However, it is permitted to add a coupling agent to the rare earth bonded magnet mixture according to the present invention.

[0017] A method for manufacturing rare earth bonded magnets according to the present invention, the method comprising: preparing a rare earth bonded magnet mixture by kneading rare earth magnet powder and a binder (mixture preparation step), the rare earth magnet powder being a mixture of coarse powder with a D50 greater than or equal to 240 μm and less than 380 μm and fine powder with a D50 less than or equal to 35 μm, and the D90 / D10 of the rare earth magnet powder being greater than or equal to 28 and less than or equal to 37, and D90 / D10 being the ratio of D90 to D10 in the particle size distribution of the entire rare earth magnet powder; and melting the binder kneaded into the rare earth bonded magnet mixture, and then injecting the rare earth bonded magnet mixture into a mold (injection molding step).

[0018] According to the method for producing a rare earth bonded magnet of the present invention, by using the rare earth bonded magnet mixture according to the present invention, the fluidity of the rare earth bonded magnet mixture in the injection molding step can be improved. Therefore, the rare earth bonded magnet mixture can be more reliably spread over the entire mold, and a bonded magnet having a predetermined shape can be more reliably obtained.

[0019] According to the present invention, when the binder is melted, a rare earth bonded magnet mixture having high fluidity can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figures 1A to 1C Schematic diagram showing a method for producing a rare earth bonded magnet mixture according to an embodiment of the present invention.

[0021] Figure 1D is a schematic diagram illustrating a method for producing a rare earth bonded magnet using a rare earth bonded magnet mixture.

[0022] Figure 2 : is a graph showing an example of the cumulative distribution of the particle diameters of the coarse powder and the fine powder contained in the rare earth bonded magnet mixture of the present embodiment.

[0023] Figure 3 : is a graph showing an example of the particle diameter distribution of the coarse powder and the fine powder contained in the rare earth bonded magnet mixture of the present embodiment.

[0024] Figure 4 : is a graph showing an example of the cumulative distribution of the particle diameters of the rare earth magnet powder contained in the rare earth bonded magnet mixture of the present embodiment.

[0025] Figure 5 : is a graph showing the results of measuring the fluidity of various rare earth bonded magnet mixtures of this embodiment and comparative examples having different D90 / D10 values ​​of contained rare earth magnet powder. DETAILED DESCRIPTION

[0026] Will refer to Figures 1A to 5Embodiments of a rare earth bonded magnet mixture according to the present invention and embodiments of a method of producing a rare earth bonded magnet using the rare earth bonded magnet mixture are described.

[0027] First, refer to Figures 1A to 1D The rare earth bonded magnet mixture of this embodiment, as well as a method for producing the mixture and a method for producing a rare earth bonded magnet using the mixture are described.

[0028] The rare earth bonded magnet mixture (hereinafter referred to as "mixture") 10 of this embodiment is obtained by kneading rare earth magnet powder 11 and a binder 12 made of resin. Here, the rare earth magnet powder 11 is obtained by mixing rare earth magnet coarse powder (hereinafter referred to as "coarse powder") 111 and rare earth magnet fine powder (hereinafter referred to as "fine powder") 112. Figures 1A to 1C It is shown that by mixing the coarse powder 111 and the fine powder 112 ( Figure 1A ) to prepare the rare earth magnet powder 11, and then the rare earth magnet powder 11 and the binder 12 are kneaded by the kneading machine 90 ( Figure 1B ) in the process of preparing a flake mixture 10 ( Figure 1C Alternatively, the coarse powder 111, the fine powder 112, and the binder 12 may be mixed in advance and then fed into the kneading machine 90 and kneaded, or the coarse powder 111, the fine powder 112, and the binder 12 may be fed into the kneading machine 90 simultaneously without being mixed in advance and then kneaded.

[0029] In general, examples of resins include thermoplastic resins and thermosetting resins. Thermoplastic resins are generally used for injection molding, and therefore, in this embodiment, it is also preferred to use a thermoplastic resin as a binder. In the case of molding by compression molding, extrusion molding, etc., a thermosetting resin can be used as a binder. As a thermoplastic resin of the binder 12 used in the mixture 10 of this embodiment, for example, polyphenylene sulfide (PPS), polyamide (PA), etc. can be used. In these examples, from the viewpoint that the heat resistance of the rare earth bonded magnet can be improved, PPS is preferably used because PPS has high fluidity and high heat deformation temperature. Since the binder 12 as a thermoplastic resin is solid at room temperature, the binder 12 is mixed with the rare earth magnet powder 11 after the binder 12 is powdered.

[0030] The coarse powder 111 and the fine powder 112 constituting the rare earth magnet powder 11 are each obtained by pulverizing an alloy body made of an alloy of a rare earth magnet material. Examples of such alloys include RFeN-based alloys, RFe-based alloys, RFeB-based alloys, and RCo-based alloys. RFeN-based alloys contain R (rare earth element), Fe (iron), and N (nitrogen) as main constituent elements, and have a structure obtained by introducing N into R2Fe 17 or RFe7 to obtain R2Fe 17 N xor RFe7N x The type of R in the RFeN-based alloy is not limited, and Sm (samarium) is particularly preferably used. The RFe-based alloy contains R and Fe as main constituent elements and has R2Fe 17 The type of R in the RFe-based alloy is not limited, and Sm is particularly preferably used. The RFeB-based alloy contains R, Fe, and B (boron) as main constituent elements and has R2Fe 14 The type of R in the RFeB-based alloy is not limited, and Nd (neodymium) is particularly preferably used. The RCo-based alloy contains R and Co as main constituent elements and has RCo5 or R2Co 17 The type of R in the RCo-based alloy is not limited, and Sm is particularly preferably used.

[0031] The alloy body of rare earth magnet is more preferably prepared by molten metal quenching method. In molten metal quenching method, the molten metal obtained by melting the alloy of rare earth magnet is quenched by dripping on the surface of the roller rotating at high speed, thereby preparing alloy body. The alloy body prepared by this method has a band shape. The powder made of flat particles with flat shape is obtained by crushing the band alloy body. Compared with spherical particles, flat particles are usually unlikely to flow with viscous liquid. However, coarse powder 111 and fine powder 112 of the powder made of this flat particle are obtained as described below, and mixture 10 includes coarse powder 111, fine powder 112 and adhesive 12, so when the adhesive 12 included is melted, the fluidity of mixture 10 can increase.

[0032] The coarse powder 111 having a D50 of greater than or equal to 240 μm and less than 380 μm and the fine powder 112 having a D50 of less than or equal to 35 μm are obtained by setting different target particle sizes during the pulverization of the alloy body or classifying the pulverized powder according to the particle diameter. Here, D50 is a value also called a "median value" and refers to the particle diameter at which the cumulative distribution relative to the powder particle diameter is 50%. The cumulative distribution related to the powder particle diameter represents the proportion of the volume (proportional to the weight) occupied by particles with a diameter smaller than a specific particle diameter in the entire powder. Figure 2 is a graph showing an example of cumulative distribution of the coarse powder 111 and the fine powder 112 , and the graph shows positions corresponding to the values ​​of D50 of the coarse powder 111 and the fine powder 112 in this example on the horizontal axis.

[0033] Generally, the D50 of a powder can be measured by various methods, and it is known that the obtained value varies depending on the measurement method. In the present embodiment, the D50 of the coarse powder 111 and the fine powder 112 is a value measured by a laser diffraction / scattering method. When the D50 of the coarse powder 111 is too small, the difference in particle diameter between the coarse powder 111 and the fine powder 112 is reduced, and the effect of the present invention cannot be exhibited. When its D50 is too large, the magnetic powder blocks the flow path during injection molding or during fluidity evaluation. Therefore, the D50 of the coarse powder 111 is greater than or equal to 240 μm and less than 380 μm. The preferred range of the D50 of the coarse powder 111 is greater than 250 μm and less than or equal to 370 μm. When the D50 of the fine powder 112 is too large, the difference in particle diameter between the fine powder 112 and the coarse powder 111 is reduced, and the effect of the present invention cannot be exhibited. Therefore, the D50 of the fine powder 112 is less than or equal to 35 μm. The lower limit of D50 of the fine powder 112 is not limited, but is practically about 10 μm, because when D50 of the fine powder 112 is too small, it is difficult to prepare the fine powder 112 .

[0034] The coarse powder 111 and the fine powder 112 are mixed so that D90 / D10 in the particle size distribution of the rare earth magnet powder 11 after mixing is greater than or equal to 28 and less than or equal to 37. D90 / D10 is preferably greater than or equal to 28 and less than or equal to 36, and more preferably greater than or equal to 28 and less than or equal to 35. Here, D90 refers to the particle diameter when the cumulative distribution is 90%, D10 refers to the particle diameter when the cumulative distribution is 10%, and D90 / D10 refers to a value obtained by dividing D90 by D10, that is, D90 / D10 corresponds to the ratio of D90 to D10. For example, in the case where the rare earth magnet powder 111 is obtained by mixing the coarse powder 111 and the fine powder 112, the coarse powder 111 and the fine powder 112 each have a particle size distribution similar to Figure 3 The particle volume (proportional to weight) distribution related to the particle diameter shown in the curve graph of Figure 4 The cumulative distribution is shown in the curve graph. In the cumulative distribution graph, the horizontal axis represents the particle diameter, the vertical axis represents the cumulative particle volume proportional to the weight, the particle diameter when the cumulative particle volume is 90% is D90, and the particle diameter when the cumulative particle volume is 10% is D10.

[0035] When a rare earth bonded magnet is produced using the mixture 10 obtained as described above, the mixture 10 is heated to a temperature higher than the melting point of the binder 12 and then formed by injection molding apparatus 91 ( Figure 1D ) is injected into the mold 92, and the interior of the mold 92 is cooled to a temperature lower than the melting point of the binder 12, thereby solidifying the binder 12. Thus, a rare earth bonded magnet is obtained.

[0036] Next, the experimental results related to the mixture 10 of the present embodiment actually prepared will be described. In this experiment, SmFeN-based powder was used as rare earth magnet powder 11. By crushing an alloy strip prepared by a molten metal quenching method, various types of coarse powder 111 and fine powder 112 were prepared, the D50 of the coarse powder 111 being greater than or equal to 240 μm and less than 380 μm, and the D50 of the fine powder 112 being 23 μm or 35 μm. The rare earth magnet powder 11 is obtained by mixing the coarse powder 111 and the fine powder 112 in the following proportions. As the binder 12, three types of binders made of PPS were prepared, which had different melting points, different viscosities during melting, etc. The physical properties of the three types of binders 12 (referred to as "PPS1", "PPS2" and "PPS 3") are shown in Table 1. "MFR" in Table 1 is an abbreviation for "melt flow rate", which is a parameter representing the fluidity of the resin. The MFR is measured according to ASTM D1238-90 under the conditions of a measuring temperature of 315° C., a measuring load of 49 N (5 kgf), and a holding time of 5 minutes.

[0037] [Table 1]

[0038]

[0039]

[0040] The mixture 10 obtained by kneading the rare earth magnet powder 11 and the binder 12 was prepared under various conditions, in which the D50 value of the coarse powder 111 and the fine powder 112, the mixing ratio of the coarse powder 111 and the fine powder 112, and the type of the binder 12 were different, and the fluidity of the mixture 10 at 310° C. was measured. In all the embodiments and comparative examples, the mixing ratio of the rare earth magnet powder 11 and the binder 12 was 87.4:12.6 in a mass ratio. The preparation conditions and the measurement results of the fluidity are shown in Table 2, and the measurement results are also shown in Table 2. Figure 5 "Fluidity MFR" in Table 2 is a parameter representing the fluidity of the mixture. According to JIS K7210:1999, the fluidity MFR of the mixture is measured under the conditions of a measuring temperature of 310°C, a measuring load of 980N (100kgf), a die diameter of 1mm and a die length of 2mm. In addition, CFT-500D manufactured by Shimadzu Corporation is used as a device for measuring the fluidity MFR. In Table 2, Examples 1 to 6 meet the requirement that D90 / D10 of the rare earth magnet powder 11 in the mixture according to the present invention is greater than or equal to 28 and less than or equal to 37, while Comparative Examples 1 to 14 do not meet this requirement.

[0041] [Table 2]

[0042]

[0043]

[0044] *Note: Only fine powder was used in Comparative Example 1

[0045] In Examples 1 to 6, the MFR, which is a parameter indicating fluidity, has a high value of 300 or more. In contrast, in Comparative Examples 1 to 14, the MFR is less than 300. Within the fluidity range (2090 to 3250) of the binder 12 used in this experiment, the fluidity of the binder 12 does not significantly affect the fluidity of the mixture 10. Therefore, it is believed that the fluidity of the mixture 10 is mainly affected by the characteristics of the rare earth magnet powder 11, especially D90 / D10. As in Examples 1 to 6, when the MFR is 300 or more, even in the case of preparing a bonded magnet having a complex shape, the mixture 10 can be spread throughout the entire mold during injection molding. Therefore, bonded magnets can be produced with a high degree of freedom.

[0046] Although the embodiments of the rare earth bonded magnet mixture according to the present invention and the method for producing a rare earth bonded magnet using the mixture have been described above, the present invention is not limited to these embodiments, and various modifications can be made within the scope of the gist of the present invention.

[0047] It is obvious to those skilled in the art that the above-mentioned embodiments are specific examples of the following aspects (1) to (6).

[0048] (1) A rare earth bonded magnet mixture, the mixture comprising:

[0049] Rare earth magnet powders, including coarse and fine powders; and

[0050] Resin binder,

[0051] wherein a rare earth bonded magnet mixture is obtained by kneading rare earth magnet powder and a resin binder,

[0052] The coarse powder and the fine powder are mixed to obtain rare earth magnet powder.

[0053] The D50 of the coarse powder is greater than or equal to 240 μm and less than 380 μm,

[0054] The D50 of the fine powder is less than or equal to 35 μm, and

[0055] The rare earth magnet powder has a D90 / D10 greater than or equal to 28 and less than or equal to 37, D90 / D10 being a ratio of D90 to D10 in a particle size distribution of the entire rare earth magnet powder.

[0056] (2) The rare earth bonded magnet mixture according to (1), wherein the rare earth magnet powder is made of a SmFeN-based material.

[0057] (3) The rare earth bonded magnet mixture according to (1) or (2), wherein the rare earth magnet powder is made of flat particles having a flat shape.

[0058] (4) The rare earth bonded magnet mixture according to any one of (1) to (3), wherein the binder is made of a thermoplastic resin.

[0059] (5) The rare earth bonded magnet mixture according to any one of (1) to (4), wherein the binder has a viscosity of 25 Pa·s or less at a temperature of 310° C.

[0060] (6) A method for manufacturing a rare earth bonded magnet, the method comprising:

[0061] A rare earth bonded magnet mixture is prepared by kneading a rare earth magnet powder and a binder, wherein the rare earth magnet powder is a mixture of a coarse powder having a D50 of 240 μm or more and less than 380 μm and a fine powder having a D50 of 35 μm or less, and the rare earth magnet powder has a D90 / D10 of 28 or more and 37 or less, wherein D90 / D10 is a ratio of D90 to D10 in a particle size distribution of the entire rare earth magnet powder; and

[0062] The binder kneaded into the rare earth bonded magnet mixture is melted, and then the rare earth bonded magnet mixture is injected into a mold.

[0063] This application is based on Japanese Patent Application No. 2023-173257 filed on October 4, 2023 and Japanese Patent Application No. 2024-117089 filed on July 22, 2024, the contents of which are incorporated herein by reference.

[0064] Reference numerals list

[0065] 10Rare earth bonded magnet mixture (mixture)

[0066] 11Rare earth magnet powder

[0067] 111 Rare earth magnet coarse powder (coarse powder)

[0068] 112 Rare earth magnet fine powder (fine powder)

[0069] 12 Adhesive

[0070] 91 Injection molding device

[0071] 92 mold

Claims

1. A rare earth bonded magnet mixture, comprising: Rare earth magnet powders, including coarse and fine powders; and Resin binder, wherein the rare earth bonded magnet mixture is obtained by kneading the rare earth magnet powder and the resin binder, The rare earth magnet powder is obtained by mixing the coarse powder and the fine powder, The D50 of the coarse powder is greater than or equal to 240 μm and less than 380 μm, The D50 of the fine powder is less than or equal to 35 μm, and The rare earth magnet powder has a D90 / D10 greater than or equal to 28 and less than or equal to 37, D90 / D10 being a ratio of D90 to D10 in a particle size distribution of the entire rare earth magnet powder. 2 . The rare earth bonded magnet mixture according to claim 1 , wherein the rare earth magnet powder is made of a SmFeN-based material. 3 . The rare earth bonded magnet mixture according to claim 1 , wherein the rare earth magnet powder is made of flat particles having a flat shape.

4. The rare earth bonded magnet mixture according to claim 1 or 2, wherein the binder is made of a thermoplastic resin. 5 . The rare earth bonded magnet mixture according to claim 1 , wherein the viscosity of the binder at a temperature of 310° C. is less than or equal to 25 Pa·s.

6. A method for producing a rare earth bonded magnet, the method comprising: A rare earth bonded magnet mixture is prepared by kneading a rare earth magnet powder and a binder, wherein the rare earth magnet powder is a mixture of coarse powder and fine powder, the coarse powder having a D50 of greater than or equal to 240 μm and less than 380 μm, the fine powder having a D50 of less than or equal to 35 μm, and the rare earth magnet powder having a D90 / D10 of greater than or equal to 28 and less than or equal to 37, D90 / D10 being a ratio of D90 to D10 in a particle size distribution of the entire rare earth magnet powder; and The binder kneaded into the rare earth bonded magnet mixture is melted, and then the rare earth bonded magnet mixture is injected into a mold.

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