Rare-earth bonded magnet compound and method for producing rare-earth bonded magnet using the same

Abstract

To provide a rare-earth bonded magnet compound having high flowability when a binder is molten.SOLUTION: A rare-earth bonded magnet compound (10) is obtained by kneading rare-earth magnet powder (11) and a resin binder (12). The rare-earth magnet powder is obtained by mixing coarse powder (111) having a D50 of 240 μm or more and less than 380 μm and fine powder (112) having a D50 of 35 μm or less. D90 / D10, which is a ratio of D90 to D10 in a particle size distribution of the entire rare-earth magnet powder, is 28 or more and 37 or less. Herein, D50, D90 and D10 refer to particle diameters at which cumulative distributions relating to the particle diameter of powder (a proportion of the volume (which is proportional to weight) occupied by particles having a particle diameter smaller than a certain particle diameter in the entire powder) measured by a laser diffraction / scattering method are 50%, 90% and 10%, respectively.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a compound for rare earth bonded magnets, which is made by kneading rare earth magnet powder containing rare earth elements as the main constituent elements with a binder (binding agent), and a method for manufacturing rare earth bonded magnets using said compound. The rare earth magnets covered by the present invention include RFeN-based rare earth magnets whose main constituent elements are rare earth elements (R), iron (Fe), and nitrogen (N), RFe-based rare earth magnets whose main constituent elements are rare earth elements and iron, RFeB-based rare earth magnets whose main constituent elements are rare earth elements, iron, and boron (B), and RCo-based magnets (RCo5-based, R2Co ... 17 rare earth magnets, etc. [Background technology]

[0002] Bonded magnets are generally manufactured by kneading magnet powder with a resin binder (after mixing the two, or while mixing, kneading while heated to a temperature higher than the melting point of the binder) to produce a bonded magnet compound (hereafter abbreviated as "compound"), heating the compound to melt the binder, and solidifying it in a mold. Molding methods include compression molding, extrusion molding, injection molding, etc., and among these, injection molding has the advantage of allowing a high degree of freedom in the shape of the bonded magnet that can be manufactured.

[0003] When manufacturing bonded magnets by injection molding, if the compound has low fluidity when injected into a mold, the compound will not spread throughout the entire mold, making it impossible to obtain a bonded magnet of the desired shape. For this reason, compounds with high fluidity are required.

[0004] Patent Document 1 describes the production of rare earth bonded magnets using a compound for rare earth bonded magnets made by kneading RFeN rare earth magnet powder, a binder, and a coupling agent. In general, the coupling agent adheres to the surface of magnet powder particles while chemically bonding with the binder molecules when the binder is in a molten state, thereby making it easier for the magnet powder particles to flow together with the molten binder. There are various types of coupling agents, but Patent Document 1 describes a coupling agent having the general formula R (4-n) -Si-X (n) (wherein R is a hydrocarbon group or one or more organic groups having a functional group, X is a hydrolyzable group (alkoxy group, glycol group, etc.), and n is an integer in the range of 1 to 3) is used. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-092262 A [Non-patent literature]

[0006] [Non-Patent Document 1] Akio Minegishi, "Fundamentals of Slurry Rheology: Relationship between Particle Size, Particle Shape, and Zeta Potential", [online], February 19, 2018, Spectris Corporation, [Retrieved October 4, 2023], Internet<URL:https: / / www.materials-talks.jp / files / 20180226142620_0.pdf> Summary of the Invention [Problem to be solved by the invention]

[0007] The fluidity of a compound varies depending on various conditions, including the presence or absence of a coupling agent and the type of coupling agent. In some cases, the fluidity of the compound may decrease despite the addition of a coupling agent. The problem that the present invention aims to solve is to provide a compound for rare earth bonded magnets that has high fluidity when the binder is in a molten state, regardless of the presence or absence of a coupling agent. [Means for solving the problem]

[0008] The compound for rare earth bonded magnets according to the present invention, which has been developed to solve the above problems, is a mixture of rare earth magnet powder and a resin binder, The rare earth magnet powder is a mixture of coarse powder having a D50 of 240 μm or more and less than 380 μm and fine powder having a D50 of 35 μm or less, and the ratio of D90 to D10 in the overall particle size distribution of the rare earth magnet powder, D90 / D10, is 28 or more and 37 or less. It is characterized by:

[0009] In the present invention, "D50" refers to the particle size at which the cumulative distribution of particle size of a powder measured by a laser diffraction / scattering method (the ratio of the volume (proportional to the weight) of particles smaller than a certain particle size to the entire powder) is 50%. Similarly, "D90" and "D10" refer to the particle sizes at which the cumulative distribution is 90% and 10%, respectively.

[0010] In the rare earth bonded magnet compound according to the present invention, a mixture of coarse and fine powders with different particle sizes, each having a D50 in the above range, is used as the rare earth magnet powder. It is generally known that in a slurry made by mixing powder and liquid, the viscosity of the slurry is lowered when a powder containing particles with different particle sizes is used rather than a powder consisting of particles with a uniform particle size (see, for example, Non-Patent Document 1). In the present invention, the coarse and fine powders are mixed, and the D90 / D10 of the entire rare earth magnet powder after mixing is set to 28 to 37. This makes it possible to increase the fluidity of the rare earth bonded magnet compound in a state in which the binder is molten, compared to the case of using rare earth magnet powders with other particle size distributions.

[0011] If the D50 of the coarse powder is smaller than the above range or if the D50 of the fine powder is larger than the above range, the difference in particle size between the coarse powder and the fine powder is small, and the fluidity of the rare earth bonded magnet compound cannot be sufficiently increased. On the other hand, if the D50 of the coarse powder is larger than the above range, the coarse particles tend to aggregate in the rare earth bonded magnet compound in which the binder is melted, and the fluidity decreases. There is no particular limit to the D50 of the fine powder, but if it is too small, it becomes difficult to manufacture the fine powder. Therefore, the D50 of the fine powder should be small within the range that allows manufacturing.

[0012] In the rare earth bonded magnet compound according to the present invention, the rare earth magnet powder can be RFeN rare earth magnet powder, RFe rare earth magnet powder, RFeB rare earth magnet powder, RCo rare earth magnet powder, etc. In particular, among RFeN rare earth magnets, SmFeN rare earth magnets in which the rare earth element R is Sm have a small change in coercivity with temperature and can be suitably used in automobile traction motors whose temperatures rise to about 130°C during use, so SmFeN rare earth magnet powder can also be suitably used in the present invention.

[0013] In the rare earth bonded magnet compound according to the present invention, the rare earth magnet powder may be made of flat particles having a flat shape. Generally, a magnet compound in which the magnet powder is made of flat particles has lower fluidity than a magnet compound in which the magnet powder is made of spherical particles, and is not suitable for use in molding such as injection molding. However, in the magnet compound according to the present invention, the fluidity can be increased by mixing coarse powder and fine powder, so that even if the magnet powder is made of flat particles, it can be used for molding such as injection molding. In the present invention, the "flat particles" refer to particles whose size in one direction perpendicular to a certain direction (thickness direction) is at least twice as large as the size of the particles in the thickness direction. Such magnet powder made of flat particles can be obtained, for example, by dropping a molten alloy, which is a material of a rare earth magnet, onto the surface of a roll rotating at high speed to produce a ribbon-shaped alloy, and then pulverizing the ribbon-shaped alloy.

[0014] The rare earth bonded magnet compound according to the present invention is characterized by its high fluidity and can be used particularly suitably when manufacturing rare earth bonded magnets by injection molding. In injection molding, a thermoplastic resin is generally used as a binder, so the binder contained in the rare earth bonded magnet compound according to the present invention is preferably a thermoplastic resin. However, the rare earth bonded magnet compound according to the present invention may also be used when manufacturing rare earth bonded magnets by methods other than injection molding, such as compression molding or extrusion molding, in which case a thermosetting resin binder may be used.

[0015] In the rare earth bonded magnet compound according to the present invention, the binder has a viscosity of 25 Pa·s or less at a temperature of 310°C (according to ISO11443, shear rate: 1000 sec -1It is preferable to use a binder having the following characteristics (measured under the following conditions: ratio of capillary length L to inner diameter D: L / D: 30 / 1, measurement time: 5 minutes). This allows the rare earth bonded magnet compound to have higher fluidity when the binder is in a molten state. An example of a binder material that satisfies these conditions is polyphenylene sulfide (PPS).

[0016] It is not necessary to add a coupling agent to the rare earth bonded magnet compound according to the present invention, but it is permissible to add a coupling agent to the rare earth bonded magnet compound according to the present invention.

[0017] The method for producing a rare earth bonded magnet according to the present invention comprises the steps of: a compound preparation step of preparing a compound for rare earth bonded magnets by kneading rare earth magnet powder, which is a mixture of coarse powder having a D50 of 240 μm or more and less than 380 μm and fine powder having a D50 of 35 μm or less, and in which the ratio of D90 to D10 in the overall particle size distribution of the rare earth magnet powder, D90 / D10, is 28 to 37, with a binder; an injection molding step of melting the binder mixed with the rare earth bonded magnet compound and injecting the melt into a mold; has.

[0018] According to the manufacturing method of the rare earth bonded magnet of the present invention, by using the rare earth bonded magnet compound of the present invention, the fluidity of the rare earth bonded magnet compound in the injection molding process can be increased, so that the rare earth bonded magnet compound can be more reliably distributed throughout the entire mold, thereby making it possible to more reliably obtain a bonded magnet of the desired shape. Effect of the Invention

[0019] According to the present invention, it is possible to obtain a compound for rare earth bonded magnets in which the binder has high fluidity when in a molten state. [Brief description of the drawings]

[0020] [Figure 1] 1 is a schematic diagram showing a method for manufacturing one embodiment of a rare earth bonded magnet compound according to the present invention, and a method for manufacturing a rare earth bonded magnet using the rare earth bonded magnet compound; [Diagram 2] 2 is a graph showing an example of the cumulative distribution of particle sizes of coarse powder and fine powder contained in the rare earth bonded magnet compound of the present embodiment. [Diagram 3] 2 is a graph showing an example of the particle size distribution of coarse powder and fine powder contained in the rare earth bonded magnet compound of the present embodiment. [Figure 4] 3 is a graph showing an example of the cumulative particle size distribution of rare earth magnet powder contained in the rare earth bonded magnet compound of the present embodiment. [Diagram 5] 1 is a graph showing the results of measuring the fluidity of a plurality of rare earth bonded magnet compounds according to the present embodiment and comparative examples, each of which contains rare earth magnet powder with different D90 / D10 values. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] 1 to 5, an embodiment of a compound for rare earth bonded magnets according to the present invention and an embodiment of a method for producing rare earth bonded magnets using the compound will be described.

[0022] First, with reference to FIG. 1, the compound for rare earth bonded magnets of this embodiment will be described along with its manufacturing method and a manufacturing method for rare earth bonded magnets using the compound.

[0023] The compound for rare earth bonded magnets (hereinafter, abbreviated as "compound") 10 of this embodiment is obtained by kneading rare earth magnet powder 11 with a binder 12 made of resin. Here, the rare earth magnet powder 11 is obtained by mixing rare earth magnet coarse powder (hereinafter, "coarse powder") 111 and rare earth magnet fine powder (hereinafter, "fine powder") 112. FIG. 1 shows an example in which coarse powder 111 and fine powder 112 (FIG. 1(a)) are mixed to produce rare earth magnet powder 11, and then the rare earth magnet powder 11 and binder 12 are kneaded in a kneader 90 (FIG. 1(b)) to produce pellet-shaped compound 10 (FIG. 1(c)). However, it is also possible to simultaneously mix coarse powder 111, fine powder 112, and binder 12 in advance and feed them into kneader 90 and knead them, or to simultaneously feed coarse powder 111, fine powder 112, and binder 12 into kneader 90 and knead them without mixing them in advance.

[0024] Generally, resins are classified into thermoplastic resins and thermosetting resins. Since thermoplastic resins are generally used in injection molding, it is preferable to use a thermoplastic resin as the binder in this embodiment as well (when molding is performed by compression molding, extrusion molding, or the like, a thermosetting resin may be used as the binder). For example, polyphenylene sulfide (PPS), polyamide (PA), etc. can be used as the thermoplastic resin of the binder 12 used in the compound 10 of this embodiment. Of these examples, it is preferable to use PPS because it has high fluidity and a high heat deformation temperature, which can increase the heat resistance of the rare earth bonded magnet. Since the binder 12, which is a thermoplastic resin, is solid at room temperature, it is powdered and then mixed with the rare earth magnet powder 11.

[0025] Both the coarse powder 111 and the fine powder 112 that make up the rare earth magnet powder 11 are obtained by pulverizing an alloy body made of an alloy that is a material for a rare earth magnet. Examples of such alloys include RFeN-based alloys, RFe-based, RFeB-based, and RCo-based alloys. RFeN-based alloys have R (rare earth element), Fe (iron), and N (nitrogen) as their main constituent elements, and are generally represented by the formula RFe 17 Or RFe7 with N introduced, R2Fe 17N x Or RFe7N x The type of R in the RFeN alloy is not limited, but Sm (samarium) is particularly preferably used. RFe alloys have R and Fe as their main constituent elements, and the formula is RFe 17 Or, RFe7. The type of R in the RFe alloy is not limited, but Sm is particularly preferably used. RFeB alloys have R, Fe, and B (boron) as main constituent elements, and have the formula RFe 14 The type of R in the RFeB alloy is not limited, but Nd (neodymium) is particularly preferred. The RCo alloy has R and Co as its main constituent elements, and is generally RCo5 or R2Coe 17 The type of R in the RCo-based alloy is not limited, but Sm is particularly preferably used.

[0026] The rare earth magnet alloy body can be suitably produced by a melt quenching method. In the melt quenching method, a molten rare earth magnet alloy is quenched by dropping the molten rare earth magnet alloy onto the surface of a roll rotating at high speed. The alloy body produced by this method has a ribbon-like shape. By pulverizing this ribbon-like alloy body, a powder consisting of flat particles having a flat shape is obtained. Flat particles generally do not flow easily with a viscous liquid as compared with spherical particles, but by obtaining coarse powder 111 and fine powder 112 from powder consisting of such flat particles as described below, the fluidity of compound 10 can be increased when binder 12 contained together with coarse powder 111 and fine powder 112 is melted.

[0027] By setting different target particle sizes when crushing the alloy body and classifying the crushed powder according to particle size, coarse powder 111 having a D50 value of 240 μm or more and less than 380 μm and fine powder 112 having a D50 value of 35 μm or less are obtained. Here, D50 is a value also called the "median" and refers to a particle size at which the cumulative distribution of the particle size of the powder (indicating the proportion of the volume (∝ weight) of particles smaller than a certain particle size in the entire powder) is 50%. Figure 2 shows an example of the cumulative distribution of the coarse powder 111 and the fine powder 112 in a graph, and the position of the horizontal axis corresponding to the D50 value of the coarse powder 111 and the fine powder 112 in this example is shown in the graph.

[0028] In general, the D50 of a powder can be measured by various methods, and it is known that the value obtained varies depending on the measurement method. In this embodiment, the D50 of the coarse powder 111 and the fine powder 112 is a value measured by a laser diffraction / scattering method. If the D50 value of the coarse powder 111 is too small, the difference in particle size between the fine powder 112 and the coarse powder 112 becomes small, and the effect of the present invention is not obtained. If the D50 value of the coarse powder 111 is too large, the magnetic powder clogs the flow path during injection molding or when evaluating fluidity. Therefore, the D50 value is set to 240 μm or more and less than 380 μm. The preferred range of the D50 of the coarse powder 111 is more than 250 μm and 370 μm or less. If the D50 value of the fine powder 112 is too large, the difference in particle size between the coarse powder 111 and the coarse powder 112 becomes small, and the effect of the present invention is not obtained. Therefore, the D50 value of the fine powder 112 is set to 35 μm or less. There is no restriction on the lower limit of the D50 of the fine powder 112, but if it is too small, it becomes difficult to produce the fine powder 112, so in practice, it is about 10 μm.

[0029] The coarse powder 111 and the fine powder 112 are mixed so that the D90 / D10 in the particle size distribution of the rare earth magnet powder 11 after mixing is 28 to 37. D90 / D10 is preferably 28 to 36, more preferably 28 to 35. Here, D90 refers to the particle size where the cumulative distribution is 90%, D10 refers to the particle size where the cumulative distribution is 10%, and D90 / D10 refers to the value obtained by dividing D90 by D10 (corresponding to the ratio of D90 to D10). For example, the rare earth magnet powder 11 obtained by mixing the coarse powder 111 and the fine powder 112, each of which has a particle volume (∝ weight) distribution related to particle size as shown in the graph of FIG. 3, has the cumulative distribution shown in the graph of FIG. 4. In this cumulative distribution graph, the particle size, which is the value on the horizontal axis when the cumulative particle volume (∝ weight), which is the value on the vertical axis, is 90%, is D90, and the particle size when the cumulative particle volume is 10% is D10.

[0030] When manufacturing a rare earth bonded magnet using the compound 10 obtained as described above, the compound 10 is heated to a temperature higher than the melting point of the binder 12 and then injected into a mold 92 by an injection molding machine 91 (FIG. 1(d)), and the inside of the mold 92 is cooled to a temperature lower than the melting point of the binder 12 to harden the binder 12. This produces a rare earth bonded magnet.

[0031] Next, the experimental results of the compound 10 of this embodiment that was actually produced are shown. In this experiment, SmFeN powder was used as the rare earth magnet powder 11. The coarse powder 111 was prepared by grinding a plurality of types of powders having a D50 in the range of 240 μm or more and less than 380 μm, and the fine powder 112 was prepared by grinding a ribbon of alloys produced by a molten metal quenching method. The rare earth magnet powder 11 was obtained by mixing the coarse powder 111 and the fine powder 112 in the ratio described below. The binder 12 was prepared in three types, all made of PPS, with different melting points and viscosities when melted. The physical properties of these three types of binder 12 (referred to as "PPS1", "PPS2", and "PPS3") are shown in Table 1. "MFR" in Table 1 is an abbreviation for "Melt Flow Rate", a parameter that indicates the fluidity of the resin. The MFR was measured according to JIS K7210 under the conditions of a measurement temperature of 310° C., a measurement load of 980 N (100 kgf), a die diameter of φ1 mm, and a die length of 2 mm. The MFR was measured using a Shimadzu Corporation CFT-500D. [Table 1]

[0032] Compounds 10 obtained by kneading rare earth magnet powder 11 and binder 12 were prepared under a number of conditions, each of which varied in the D50 values ​​of coarse powder 111 and fine powder 112, the blending ratio of coarse powder 111 and fine powder 112, and the type of binder 12, and the fluidity was measured at 310°C. The blending ratio of rare earth magnet powder 11 and binder 12 was 87.4:12.6 in mass ratio in all examples. The preparation conditions and the measurement results of fluidity are shown in Table 2, and the measurement results are also shown in the graph of FIG. 5. In Table 2, Examples 1 to 6 satisfy the requirement that the D90 / D10 of rare earth magnet powder 11 in the compound according to the present invention is 28 or more and 37 or less, while Comparative Examples 1 to 14 do not satisfy this requirement. [Table 2]

[0033] In Examples 1 to 6, the MFR, a parameter indicating fluidity, is a high value of 300 or more, whereas in Comparative Examples 1 to 14, the MFR is below 300. The level of fluidity of binder 12 does not significantly affect the fluidity of compound 10 within the range (2090 to 3250) of binder 12 used in this experiment. Therefore, it is considered that the characteristics of rare earth magnet powder 11, particularly D90 / D10, mainly affect the fluidity of compound 10. If the MFR is 300 or more as in Examples 1 to 6, compound 10 can be spread throughout the entire mold during injection molding even when producing a bonded magnet with a complex shape, so that bonded magnets can be manufactured with a high degree of freedom.

[0034] The above describes embodiments of the compound for rare earth bonded magnets according to the present invention, and the manufacturing method of rare earth bonded magnets using said compound. However, the present invention is not limited to these embodiments, and various modifications are possible within the scope of the gist of the present invention.

[0035] [Aspects] It will be apparent to those skilled in the art that the above-described exemplary embodiments are illustrative of the following aspects.

[0036] (Item 1) A compound for rare earth bonded magnets according to one aspect of the present invention is a compound obtained by kneading rare earth magnet powder with a resin binder, The rare earth magnet powder is a mixture of coarse powder having a D50 of 240 μm or more and less than 380 μm and fine powder having a D50 of 35 μm or less, and the ratio of D90 to D10 in the overall particle size distribution of the rare earth magnet powder, D90 / D10, is 28 or more and 37 or less. It is characterized by:

[0037] (Item 2) The compound for rare earth bonded magnets according to item 2 is the compound for rare earth bonded magnets according to item 1, wherein the rare earth magnetic powder is made of a SmFeN-based material.

[0038] (Item 3) The compound for rare earth bonded magnets according to item 3 is the compound for rare earth bonded magnets according to item 1 or 2, wherein the rare earth magnetic powder is made of flat particles having a flat shape.

[0039] (Item 4) The compound for rare earth bonded magnet according to item 4 is the compound for rare earth bonded magnet according to any one of items 1 to 3, wherein the binder is made of a thermoplastic resin.

[0040] (Item 5) The compound for rare earth bonded magnets according to item 5 is the compound for rare earth bonded magnets according to any one of items 1 to 4, wherein the binder has a viscosity of 25 Pa·s or less at a temperature of 310°C.

[0041] (Item 6) A method for producing a rare earth bonded magnet according to one aspect of the present invention includes the steps of: a compound preparation step of preparing a compound for rare earth bonded magnets by kneading rare earth magnet powder, which is a mixture of coarse powder having a D50 of 240 μm or more and less than 380 μm and fine powder having a D50 of 35 μm or less, and in which the ratio of D90 to D10 in the overall particle size distribution of the rare earth magnet powder, D90 / D10, is 28 to 37, with a binder; an injection molding step of melting the binder mixed with the rare earth bonded magnet compound and injecting the melt into a mold; has. [Explanation of symbols]

[0042] 10...Rare earth bonded magnet compound (compound) 11...Rare earth magnet powder 111...Rare earth magnet coarse powder (coarse powder) 112...Rare earth magnet fine powder (fine powder) 12…Binder 91...Injection molding machine 92…Molding mold

Claims

1. It is a mixture of rare earth magnet powder and a resin binder, The rare earth magnet powder is a mixture of coarse powder with a D50 of 240 μm or more and less than 380 μm and fine powder with a D50 of 35 μm or less, and the ratio of D90 to D10 in the particle size distribution of the entire rare earth magnet powder, D90 / D10, is 28 or more and 37 or less. A compound for rare earth bonded magnets, characterized in that:

2. 2. The rare earth bonded magnet compound according to claim 1, wherein the rare earth magnet powder is made of a SmFeN-based material.

3. 3. The compound for rare earth bonded magnets according to claim 1, wherein the rare earth magnet powder is made of flat particles having a flat shape.

4. 3. The compound for rare earth bonded magnets according to claim 1, wherein said binder is made of a thermoplastic resin.

5. 3. The compound for rare earth bonded magnets according to claim 1, wherein the binder has a viscosity of 25 Pa·s or less at a temperature of 310°C.

6. a compound preparation process for preparing a rare earth bonded magnet compound by kneading rare earth magnet powder, which is a mixture of coarse powder having a D50 of 240 μm or more and less than 380 μm and fine powder having a D50 of 35 μm or less, and in which the ratio of D90 to D10 in the overall particle size distribution, D90 / D10, is 28 to 37, with a resin binder; an injection molding step of melting the binder kneaded with the rare earth bonded magnet compound and injecting the melted binder into a mold; A method for producing a rare earth bonded magnet having the above structure.

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