Method for manufacturing R-T-B sintered magnet

Abstract

To raise the efficiency of pulverization while suppressing generation of VOC gas.SOLUTION: A method for manufacturing an R-T-B based sintered magnet comprises the steps of: obtaining fine powder by adding a lubricant resulting from liquefaction of at least one kind of fatty acid ester to roughly pulverized powder of alloy for R-T-B based sintered magnet, followed by pulverization (R represents at least one kind of rare earth element, and necessarily includes at least one kind selected from a group consisting of Nd, Pr, and Ce, and T represents at least one kind of transition metal element, and necessarily includes Fe, and B is boron); and preparing a sintered compact of the fine powder. The amount of the at least one kind of fatty acid ester in the lubricant is 65 mass% or more and 100 mass% or less. The amount of the lubricant added to the pulverized powder is 0.02 mass% or more and 0.5 mass% or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an R-T-B sintered magnet.

Background Art

[0002] An R-T-B sintered magnet (R is at least one of rare earth elements, necessarily including at least one selected from the group consisting of Nd, Pr, and Ce, T is at least one of transition metal elements and necessarily includes Fe, and B is boron) is composed of a main phase of a compound having an R2Fe 14 B-type crystal structure, a grain boundary phase located at the grain boundary portion of this main phase, and a compound phase generated by the influence of trace additive elements and impurities, and is known as the highest performance magnet among permanent magnets. For this reason, R-T-B sintered magnets are used in various applications such as motors for electric vehicles (EV, HV, PHV), voice coil motors (VCM) for hard disk drives, motors for industrial equipment, and various home appliances.

[0003] Such an R-T-B sintered magnet is manufactured, for example, through a process of preparing raw material alloy powder, a process of press-forming the raw material alloy powder to produce a powder compact, and a process of sintering the powder compact. The raw material alloy powder is produced, for example, by the following method. First, a raw material alloy is produced from molten metals of various raw materials by a method such as the ingot method or the strip casting method. The obtained raw material alloy is subjected to a pulverization process to obtain alloy powder having a predetermined particle size distribution. This pulverization process usually includes a coarse pulverization process and a fine pulverization process. The former is performed, for example, using mechanical pulverization or the phenomenon of hydrogen embrittlement, and the latter is performed, for example, using an air flow pulverizer (jet mill pulverization device).

[0004] Patent Document 1 discloses that by adding and mixing a lubricant in which at least one fatty acid ester is liquefied to the coarse pulverized powder of the raw material powder for rare earth magnets and then performing jet mill pulverization (fine pulverization process), the pulverization efficiency can be improved.

Prior Art Documents

Patent Document

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In recent years, from the viewpoint of preventing air pollution, it has been required to suppress the generation of gas containing volatile organic compounds (VOC) (hereinafter simply referred to as "VOC gas"). However, according to the study by the present inventor, it has been found that when the pulverization process is performed by the method described in Patent Document 1, a large amount of VOC gas may be generated. An embodiment of the present disclosure provides a method for manufacturing an R-T-B-based sintered magnet that solves such problems.

Means for Solving the Problems

[0007] The method for manufacturing an R-T-B-based sintered magnet of the present disclosure, in a non-limiting and exemplary embodiment, to the coarse pulverized powder of an alloy for an R-T-B-based sintered magnet (R is at least one of rare earth elements, and necessarily contains at least one selected from the group consisting of Nd, Pr, and Ce, T is at least one of transition metal elements and necessarily contains Fe, and B is boron), after adding a lubricant in which at least one fatty acid ester is liquefied, pulverize to obtain fine powder, and a step of producing a sintered body of the fine powder, wherein the amount of the at least one fatty acid ester in the lubricant is 65% by mass or more and 100% by mass or less, and the addition amount of the lubricant to the coarse pulverized powder is 0.02% by mass or more and 0.5% by mass or less.

[0008] In one embodiment, the amount of the at least one fatty acid ester is 85% by mass or more and 100% by mass or less.

[0009] In one embodiment, the addition amount of the lubricant to the coarse pulverized powder is 0.05% by mass or more and 0.15% by mass or less.

Advantages of the Invention

[0010] According to an embodiment of the present disclosure, it is possible to provide a method for manufacturing an R-T-B-based sintered magnet capable of improving the pulverization efficiency while suppressing the generation of VOC gas.

Brief Description of the Drawings

[0011]

Figure 1

Embodiments for Carrying Out the Invention

[0012] The present inventor has examined in detail the generation of VOC gas and the pulverization efficiency when at least one fatty acid ester is added as a liquefied lubricant to the coarse pulverized powder of the alloy for R-T-B-based sintered magnets and then pulverized. As a result, it has been found that the generation of VOC gas is affected by the amount of at least one fatty acid ester in the lubricant and the liquid component (such as xylene, alcohol, isoparaffin, etc.) for dispersing it, and the improvement of the pulverization efficiency is greatly affected by the amount of at least one fatty acid ester. Therefore, it has been found that it is important to adjust the concentration of at least one fatty acid ester in the lubricant and the addition amount of the lubricant to the coarse pulverized powder in order to suppress the generation of VOC gas while improving the pulverization efficiency. As a result of further examination, the inventor has found that it is effective to adjust both the concentration and the addition amount of at least one fatty acid ester in the lubricant to a narrow specific range. That is, the present disclosure has found that by setting the amount of at least one fatty acid ester in the lubricant to a specific range of a large amount (65% by mass or more and 100% by mass or less) and setting the addition amount of the lubricant to the coarse pulverized powder to a specific range of a small amount (0.02% by mass or more and 0.5% by mass or less), it is possible to suppress the generation of VOC gas while improving the pulverization efficiency.

[0013] <Method for Manufacturing R-T-B-Based Sintered Magnet> Hereinafter, embodiments of a method for manufacturing an R-T-B-based sintered magnet according to the present disclosure will be described.

[0014] The present disclosure relates to a method for manufacturing an R-T-B sintered magnet. Here, R is at least one of rare earth elements, and necessarily includes at least one selected from the group consisting of Nd, Pr, and Ce, and T is at least one of transition metals and necessarily includes Fe.

[0015] This method for manufacturing an R-T-B sintered magnet (1) A step of adding a lubricant obtained by liquefying at least one fatty acid ester to the coarsely pulverized powder of the alloy for the R-T-B sintered magnet and then pulverizing to obtain fine powder; (2) A step of producing a sintered body of the fine powder.

[0016] First, the composition of a preferable R-T-B sintered magnet is shown below. R is a rare earth element and necessarily includes at least one selected from the group consisting of Nd, Pr, and Ce. Preferably, a combination of rare earth elements represented by Nd-Dy, Nd-Tb, Nd-Dy-Tb, Nd-Pr-Dy, Nd-Pr-Tb, Nd-Pr-Dy-Tb is used.

[0017] Among R, Dy and Tb are effective in improving the coercive force H cJ . Other rare earth elements such as La may be contained in addition to the above elements, and mischmetal or didymium can also be used. The R content of the R-T-B sintered magnet is, for example, 27% by mass or more and 35% by mass or less. Preferably, the R content of the R-T-B sintered magnet is 31% by mass or less (more preferably 27% by mass or more and 31% by mass or less, still more preferably 29% by mass or more and 31% by mass or less). Higher magnetic properties can be obtained.

[0018] T includes iron (including the case where T consists substantially of iron), and up to 50% of it by mass ratio may be replaced with cobalt (Co) (including the case where T consists substantially of iron and cobalt). Co is effective in improving the temperature characteristics and corrosion resistance, and the alloy powder may contain 10% by mass or less of Co. The content of T may occupy the remainder of R and B or R, B, and M described later.

[0019] The content of B can also be a known content, for example, the range of 0.9% by mass to 1.2% by mass is preferable. If it is less than 0.9% by mass, high H cJ may not be obtained, and if it exceeds 1.2% by mass, Br may decrease. The content of B is more preferably 1.0% by mass or less, and even more preferably 0.98% by mass or less. Note that a part of B can be substituted with C (carbon).

[0020] In addition to the above elements, H cJ The M element can be added for improvement. The M element is one or more selected from the group consisting of Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, In, Sn, Hf, Ta, and W. The total addition amount of the M element is preferably 5.0% by mass or less. This is because if it exceeds 5.0% by mass, Br may decrease. Also, unavoidable impurities can be tolerated.

[0021] Also, the average crystal grain size of the R2T 14 B phase, which is the main phase of the R-T-B sintered magnet of the present disclosure, is preferably 2.5 μm or more and 7.0 μm or less, and more preferably 3.5 μm or more and 5.0 μm or less. Higher magnetic properties can be obtained. The average crystal grain size can be obtained, for example, by the number average of the equivalent circle diameters of crystal grains (5000 or more) evaluated by EBSD (Electron Back Scatter Diffraction). Next, a method for manufacturing the R-T-B sintered magnet of the present disclosure will be described.

[0022] <Example of the step of adding a lubricant in which at least one fatty acid ester is liquefied to the coarse pulverized powder of the R-T-B sintered magnet alloy and then pulverizing to obtain fine powder> The step of adding a lubricant in which at least one fatty acid ester is liquefied to the coarsely pulverized powder of the R-T-B system sintered magnet alloy and then pulverizing to obtain fine powder includes a step of preparing the R-T-B system sintered magnet alloy, a step of coarsely pulverizing this alloy by, for example, the hydrogen pulverization method or the like to obtain coarsely pulverized powder, and a step of supplying the coarsely pulverized powder to, for example, a jet mill device to perform pulverization to obtain fine powder.

[0023] A method for manufacturing an R-T-B system sintered magnet alloy is exemplified. An alloy ingot can be obtained by melting a metal or alloy previously adjusted to have the above-described composition and performing ingot casting by putting it into a mold. Further, the molten metal is brought into contact with a single roll, double roll, rotating disk, rotating cylindrical mold, or the like and rapidly cooled, and alloy flakes can be manufactured by a rapid cooling method typified by a strip casting method or a centrifugal casting method for producing a solidified alloy thinner than the alloy made by the ingot method.

[0024] In the embodiments of the present disclosure, materials manufactured by either the ingot method or the rapid cooling method can be used, but it is preferably manufactured by a rapid cooling method such as the strip casting method. The thickness of the rapidly cooled alloy produced by the rapid cooling method is usually in the range of 0.03 mm to 1 mm and is in the form of flakes. The alloy molten metal starts to solidify from the surface in contact with the cooling roll (roll contact surface), and crystals grow columnarly in the thickness direction from the roll contact surface. The rapidly cooled alloy is cooled in a short time compared with an alloy (ingot alloy) produced by the conventional ingot casting method (die casting method), so the structure is refined and the crystal grain size is small. Since the R-rich phase spreads greatly within the grain boundaries, the rapid cooling method is excellent in the dispersibility of the R-rich phase. For this reason, it is easy to break at the grain boundaries by the hydrogen pulverization method. By hydrogen-pulverizing the rapidly cooled alloy, the size of the hydrogen-pulverized powder (coarsely pulverized powder) can be made, for example, 1.0 mm or less. After adding a lubricant in which at least one fatty acid ester is liquefied to the coarsely pulverized powder thus obtained, it is finely pulverized, for example, with a jet mill device.

[0025] While referring to FIG. 1, a pulverization system for performing the pulverization of the present disclosure will be described. FIG. 1 is a diagram schematically showing a configuration example of a pulverization system 1000 in the present embodiment. In this example, the R-T-B system sintered magnet alloy pulverization system 1000 includes a jet mill device 100, a cyclone collection device 200, and a bag filter device 300.

[0026] The jet mill device 100 receives the supply of the material to be pulverized from a raw material tank (not shown) containing the coarsely pulverized powder added with a lubricant through a raw material input pipe 34. The addition of the lubricant will be described in detail later. The material to be pulverized is a coarsely pulverized powder of an alloy for R-T-B system sintered magnets with an average particle size of 10 μm or more and 500 μm or less. In the present disclosure, the average particle size (d50) can be measured, for example, using a standard sieve (JIS Z 8801).

[0027] A plurality of valves are provided in the raw material input pipe 34, and the internal pressure of the jet mill device 100 is appropriately maintained by opening and closing the valves. The material to be pulverized introduced into the jet mill device 100 is finely pulverized by colliding with a collision plate installed to efficiently advance the mutual collision and pulverization of the materials to be pulverized by the high-speed injection of an inert gas from a nozzle pipe 36.

[0028] The powder of the alloy for R-T-B system sintered magnets is active and easily oxidized. Therefore, as the gas used in the jet mill device 100, in order to avoid the risk of heat generation and ignition and reduce the oxygen content as an impurity to improve the performance of the magnet, for example, an inert gas such as dry (high-purity) nitrogen, argon, or helium with a dew point of -60°C or lower is preferably used.

[0029] The powder particles (fine powder) finely pulverized inside the jet mill device 100 ride on the upward airflow and are guided from the upper discharge port to the inlet pipe 20 of the cyclone collector device 200. Coarse particles with insufficient pulverization are separated by a classification rotor installed for classifying the coarse particles, remain inside the jet mill device 100, and will further undergo a pulverization process by collision. For the classification of these coarse particles, a classification rotor may be used, or centrifugal separation by a swirling flow may be used. In this way, the material to be pulverized (coarse pulverized powder) fed into the jet mill device 100 is pulverized into fine powder with an average particle size (median diameter: d50) of 2.0 μm or more and 6.0 μm or less, and then moves to the cyclone collector device 200. The average particle diameter of the fine powder is preferably 2.0 μm or more and 5.0 μm or less. Higher magnetic properties can be obtained.

[0030] The cyclone collector device 200 is used to separate powder from the airflow carrying the powder. Specifically, the coarse pulverized powder of the R-T-B system sintered magnet alloy is pulverized by the previous jet mill, and the fine powder generated by the pulverization passes through the inlet pipe 20 together with the gas used for pulverization and is supplied to the cyclone collector device 200. A mixture of an inert gas (pulverization gas) and the pulverized fine powder forms a high-speed airflow and is sent to the cyclone collector device 200. The cyclone collector device 200 is used to separate these pulverization gas and fine powder. The fine powder separated from the pulverization gas is recovered by a powder collector 50 through the discharge port 40. The pulverization gas is supplied to a bag filter device 300 through the outlet pipe 30. In the bag filter device 300, very small fine particles are recovered, and clean gas is discharged to the outside from the exhaust port 32. It should be noted that for such solid-gas separation, it is also possible to use only a bag filter without using the cyclone collector device 200, but the impact on the environment and safety caused by the atmospheric dispersion of fine powder due to filter damage is large. Fine particles may be further separated by using a bag filter in combination with the gas after being separated by the cyclone collector device.

[0031] In the method for manufacturing the R-T-B sintered magnet of the present disclosure, after adding a lubricant in which at least one fatty acid ester is liquefied to the coarsely pulverized powder, it is pulverized by the pulverization system described above to obtain fine powder. The characteristic point of the present disclosure is that the amount of the at least one fatty acid ester in the lubricant is in the range of 65% by mass or more and 100% by mass or less, and the addition amount of the lubricant to the coarsely pulverized powder is 0.02% by mass or more and 0.5% by mass or less. Thereby, while suppressing the generation of VOC gas, the pulverization efficiency can be improved.

[0032] By setting the amount of the at least one fatty acid ester in the lubricant to be in the range of 65% by mass or more and 100% by mass or less, high pulverization efficiency can be obtained. Preferably, the amount of the fatty acid ester in the lubricant is 85% by mass or more and 100% by mass or less to obtain higher pulverization efficiency. Further, by setting the addition amount of the lubricant to the coarsely pulverized powder to be 0.02% by mass or more and 0.5% by mass or less, the generation of VOC gas can be suppressed. Preferably, the addition amount of the lubricant to the coarsely pulverized powder is 0.02% by mass or more and 0.3% by mass or less (more preferably, 0.02% by mass or more and 0.15% by mass or less) to further suppress the generation of VOC gas. For example, by setting the amount of at least one fatty acid ester in the lubricant to be in the range of 85% by mass or more and 100% by mass or less, and setting the addition amount of the lubricant to the coarsely pulverized powder to be 0.05% by mass or more and 0.3% by mass or less, the generation of VOC gas can be suppressed while obtaining higher pulverization efficiency.

[0033] The fatty acid ester of the present disclosure has the general formula RCOOR′ where R = C n H 2n+2 (alkane) or C n H 2n (alkene) C n H 2n-2It is represented by the structural formula of (alkyne), and examples thereof include methyl laurate, methyl caprate, methyl caprylate, and methyl caproate. Further, in order to improve the dispersibility of the lubricant in the coarsely pulverized powder, a liquid component other than the lubricant fatty acid ester may be contained. Examples of the liquid component include xylene, alcohol, and isoparaffin.

[0034] <(2) Example of the step of producing a sintered body of fine powder> In a preferred embodiment, the step of producing a sintered body of fine powder includes a step of producing a powder compact from the fine powder by pressing in a magnetic field and a step of sintering this powder compact.

[0035] · Step of producing a powder compact from the fine powder by pressing in a magnetic field In pressing in a magnetic field, it is preferable to form a powder compact by pressing in an inert gas atmosphere or by wet pressing from the viewpoint of suppressing oxidation. In particular, in wet pressing, the surface of the particles constituting the powder compact is coated with a dispersant such as an oil agent, and contact with oxygen and water vapor in the atmosphere is suppressed. Therefore, it is possible to prevent or suppress the oxidation of the particles by the atmosphere before and after the pressing step or during the pressing step.

[0036] When performing wet pressing in a magnetic field, a slurry in which a dispersion medium is mixed with the fine powder is prepared, supplied to the cavity in the mold of the wet pressing apparatus, and press-molded in a magnetic field. The dispersion medium is a liquid capable of obtaining a slurry by dispersing alloy powder therein. Preferred dispersion media for use in the present disclosure include mineral oil or synthetic oil. The type of mineral oil or synthetic oil is not specified, but if the kinematic viscosity at normal temperature exceeds 10 cSt, the binding force between alloy powders may increase due to increased viscosity, which may adversely affect the orientation of alloy powders during wet forming in a magnetic field. Therefore, the kinematic viscosity of the mineral oil or synthetic oil at normal temperature is preferably 10 cSt or less. Also, if the distillation point of the mineral oil or synthetic oil exceeds 400 °C, it becomes difficult to remove the oil after obtaining a formed body, and the amount of residual carbon in the sintered body may increase, resulting in a decrease in magnetic properties. Therefore, the distillation point of the mineral oil or synthetic oil is preferably 400 °C or less. A slurry can be obtained by mixing the obtained alloy powder and the dispersion medium.

[0037] The mixing ratio of the alloy powder and the dispersion medium is not particularly limited, but the concentration of the alloy powder in the slurry is preferably 70% or more (i.e., 70 mass% or more) by mass ratio. This is because the alloy powder can be efficiently supplied into the cavity at a flow rate of 20 to 600 cm 3 / s, and excellent magnetic properties can be obtained. The concentration of the alloy powder in the slurry is preferably 90% or less by mass ratio. The method of mixing the alloy powder and the dispersion medium is not particularly limited. The alloy powder and the dispersion medium may be prepared separately, and both may be weighed in predetermined amounts and mixed together for production. Also, when obtaining alloy powder by dry grinding coarse pulverized powder with a jet mill or the like, a container containing the dispersion medium may be arranged at the alloy powder discharge port of the grinding device such as a jet mill, and the alloy powder obtained by grinding may be directly recovered into the dispersion medium in the container to obtain a slurry. In this case, the inside of the container is preferably an atmosphere composed of nitrogen gas and / or argon gas, and the obtained alloy powder is directly recovered into the dispersion medium without being exposed to the atmosphere to form a slurry. Furthermore, it is also possible to obtain a slurry composed of the alloy powder and the dispersion medium by wet grinding the coarse pulverized powder using a vibration mill, a ball mill, an attritor, or the like while holding it in the dispersion medium.

[0038] By molding the slurry thus obtained with a known wet press apparatus, a molded body having a predetermined size and shape can be obtained. This molded body is sintered to obtain a sintered body.

[0039] · Step of sintering the powder compact The sintering of the molded body is preferably carried out under a pressure of 0.13 Pa (10 -3 Torr) or less, more preferably 0.07 Pa (5.0×10 -4 Torr) or less, in the temperature range of 1000 °C to 1150 °C. In order to prevent oxidation during sintering, the residual gas in the atmosphere can be replaced with an inert gas such as helium or argon. It is preferable to perform heat treatment on the obtained sintered body. The magnetic properties can be improved by heat treatment. Heat treatment conditions such as the heat treatment temperature and heat treatment time can adopt known conditions. For the rare earth sintered magnet body thus obtained, a grinding and polishing process, a surface treatment process, and a magnetization process are performed as necessary, and the final rare earth sintered magnet is completed.

[0040] In a certain preferred embodiment, the method for manufacturing the R-T-B based sintered magnet of the present disclosure further includes a diffusion step of diffusing a heavy rare earth element RH (RH is at least one of Tb, Dy, Ho) from the surface to the inside of the sintered body. When the heavy rare earth element RH is diffused from the surface to the inside of the sintered body, the coercive force can be efficiently increased.

Example

[0041] The present disclosure will be described in more detail by way of examples, but the present disclosure is not limited thereto.

[0042] Example 1 An alloy for an R-T-B sintered magnet was produced by the strip casting method such that the composition of the R-T-B sintered magnet was Nd: 22.0 mass%, Pr: 8.0 mass%, Tb: 0.1 mass%, B: 0.95 mass%, Co: 2.0 mass%, Al: 0.5 mass%, Cu: 0.1 mass%, Ga: 0.5 mass%, Zr: 0.1 mass%, and the balance Fe. The obtained alloy was coarsely pulverized by the hydrogen pulverization method to obtain coarsely pulverized powder. The average particle size of the coarsely pulverized powder was measured. The average particle size was in the range of 200 μm to 400 μm. In the present disclosure, the average particle size of the coarsely pulverized powder was measured using a standard sieve (JIS Z S801).

[0043] A lubricant obtained by liquefying a fatty acid ester under the conditions shown in Table 1 was added to the coarsely pulverized powder. As the fatty acid ester, A: methyl caprylate (C9H 18 O2) or B: methyl caproate (C7H 14 O2) was used. Further, isoparaffin was used as a liquid component other than the fatty acid ester in the lubricant. No. 1 in Table 1 uses A: methyl caprylate as the fatty acid ester in the lubricant, the amount of the fatty acid ester in the lubricant is 50 mass% (50 mass% of the liquid component (isoparaffin)), and the addition amount of the lubricant to the coarsely pulverized powder is 0.10 mass%. Also, No. 12 uses B: methyl caproate as the fatty acid ester in the lubricant, the amount of the fatty acid ester in the lubricant is 100 mass% (without the liquid component (isoparaffin)), and the addition amount of the lubricant to the coarsely pulverized powder is 0.20 mass%. Examples of other Nos. are described in the same manner.

[0044] The coarsely pulverized powder to which the lubricant obtained by liquefying the fatty acid ester under the conditions shown in Table 1 was added was put into the jet mill device 100 of FIG. 1 and pulverized to obtain fine powder. In this example, nitrogen gas was used as the inert gas. The average particle size of the obtained finely pulverized powder was around 2.9 μm. Also, for Nos. 2, 4, 6, and 8 to 12, the VOC gas generated during fine pulverization by the jet mill was measured. The VOC gas was sampled from the nitrogen gas during pulverization and measured using a photoionization detector (PID). Note that the VOC gas is preferably 10 ppm or less.

[0045]

Table 1

[0046] As shown in Table 1, in the examples of the present invention under the conditions of the present disclosure (a specific range where the amount of at least one fatty acid ester in the lubricant is large (65% by mass or more and 100% by mass or less), and a specific range where the addition amount to the coarsely pulverized powder of the lubricant is small (0.02% by mass or more and 0.5% by mass or less)), the VOC gas is 2.1 ppm or less, and the pulverization efficiency is 22.7 g / min or more, and a high pulverization efficiency (pulverization rate) is obtained while suppressing the generation of VOC gas. On the other hand, for No. 1 where the amount of fatty acid ester in the lubricant is less than 65% by mass, a high pulverization efficiency is not obtained. Also, for No. 9 and No. 10 where the addition amount to the coarsely pulverized powder of the lubricant exceeds 0.5% by mass, a large amount of VOC gas is generated.

[0047] Example 2 An alloy for an R-T-B sintered magnet was produced in the same manner as in Example 1. The obtained alloy was coarsely pulverized by a hydrogen pulverization method to obtain coarsely pulverized powder. The average particle size of the coarsely pulverized powder was measured. The average particle size was in the range of 200 μm to 400 μm.

[0048] A lubricant in which a fatty acid ester was liquefied under the conditions shown in No. 13 to 17 of Table 2 was added to the coarsely pulverized powder. As the fatty acid ester, A: methyl caprylate (C9H 18 O2) was used. Also, as the liquid components other than the fatty acid ester in the lubricant, isoparaffin was used for No. 13 to 15, and ethanol was used for No. 16 and 17, respectively.

[0049] The coarsely pulverized powder to which a lubricant in which a fatty acid ester was liquefied under the conditions shown in Table 2 was added was charged into the jet mill device 100 of FIG. 1 and pulverized to obtain fine powder. In this example, nitrogen gas was used as the inert gas. The average particle size of the obtained finely pulverized powder was around 2.8 μm. Also, the VOC gas generated during fine pulverization by the jet mill was measured. Note that the VOC gas is preferably 10 ppm or less.

[0050]

Table 2

[0051] As shown in Table 2, in the inventive examples under the conditions of the present disclosure (a specific range where the amount of at least one fatty acid ester in the lubricant is large (65% by mass or more and 100% by mass or less), and a specific range where the addition amount to the coarsely pulverized powder of the lubricant is small (0.02% by mass or more and 0.5% by mass or less)), the VOC gas is 7.5 ppm or less, and the pulverization efficiency is 23.3 g / min or more. While suppressing the generation of VOC gas, a high pulverization efficiency is obtained. Further, as shown in Table 1 of Example 1 and Table 2 of Example 2, in order to suppress the generation of more VOC gas while obtaining a high pulverization efficiency, it is preferable to set the addition amount of the lubricant to the coarsely pulverized powder to 0.02% by mass or more and 0.3% by mass or less.

Explanation of Signs

[0052] 100 ··· Jet mill device, 200 ··· Cyclone collector device, 300 ··· Bag filter device

Claims

1. A step of adding a lubricant in which at least one fatty acid ester is liquefied to coarse pulverized powder of an R-T-B system sintered magnet alloy (R is at least one of rare earth elements, and necessarily includes at least one selected from the group consisting of Nd, Pr, and Ce; T is at least one of transition metal elements and necessarily includes Fe; B is boron), and then pulverizing using an air jet mill to obtain fine powder; A step of producing a sintered body of the fine powder, The amount of the at least one fatty acid ester in the lubricant is 65% by mass or more and 100% by mass or less, The amount of the lubricant added to the coarse pulverized powder is 0.02% by mass or more and 0.5% by mass or less. A method for manufacturing an R-T-B system sintered magnet.

2. The amount of the at least one fatty acid ester is 85% by mass or more and 100% by mass or less. The method for manufacturing an R-T-B system sintered magnet according to Claim 1.

3. The amount of the lubricant added to the coarse pulverized powder is 0.05% by mass or more and 0.15% by mass or less. The method for manufacturing an R-T-B system sintered magnet according to Claim 1 or 2.

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