JP5061995B2 - Magnet manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a magnet, and more particularly to a method for manufacturing a magnet by wet molding.

  As a method for producing a sintered magnet obtained by sintering magnetic powder, a wet molding process in which a slurry obtained by mixing magnetic powder as a raw material of a magnet with a solvent such as oil is molded and then sintered. The method of going through is known. Among magnets, rare earth magnets containing rare earth elements have excellent magnetic properties, and thus are applied to applications that require high magnetic properties even though they are small in size. A production method by wet molding is effective.

  In manufacturing a magnet by wet molding, a magnetic field is applied during molding to orient the magnetic powder (magnetic field orientation), thereby enhancing the magnetic properties. In general, the higher the degree of orientation of the magnetic powder, the more excellent the magnetic properties (particularly the residual magnetic flux density (Br)) can be obtained. Therefore, various methods for improving the degree of orientation of the magnetic powder have been studied.

For example, in Patent Document 1 below, magnetic powder (fine powder) is recovered in a liquid composed of oil and a nonionic surfactant or an anionic surfactant to obtain a slurry-like molding raw material. It is described to form. Patent Document 2 listed below discloses a liquid containing magnetic powder and a lubricant comprising a monohydric alcohol ester of a fatty acid, a monohydric alcohol ester of a polybasic acid, a fatty acid ester of a polyhydric alcohol, or a derivative thereof. It is described that a slurry is produced by collecting the inside. It is shown that a high degree of orientation can be obtained by the slurry obtained as described above.
JP 2001-210508 A JP 2002-164238 A

  When the slurry obtained by recovering the magnetic powder in an oil containing a surfactant, a lubricant or the like as in the above prior art is used, the degree of orientation in the magnet is improved. However, in recent years, there is a tendency for magnets to have higher Br with the same composition, and for this reason, it is necessary to increase the degree of orientation of the magnets more than before.

  This invention is made | formed in view of such a situation, and it aims at providing the manufacturing method of the magnet which can obtain the magnet which has high Br.

The method for producing a magnet according to the present invention is for producing a rare earth magnet having an R—Fe—B composition containing a rare earth element R. The magnetic powder and a liquid dispersant are kneaded and kneaded. A kneading step for obtaining a product, a slurry preparing step for adding a solvent to the kneaded product to obtain a slurry having a solid concentration of 60 to 80% by mass, a molding step for molding the slurry to obtain a molded product, and firing the molded product And a firing step.

  According to the magnet manufacturing method of the present invention, by kneading the magnetic powder and the liquid dispersant, the aggregation of primary particle aggregates (secondary particles, etc.) in the magnetic powder can be sufficiently crushed. The dispersant can be sufficiently adhered to the surface of the primary particles of the magnetic powder. As a result, in the kneading step, the dispersant can be dispersed widely and uniformly in the magnetic powder. The term “kneading” as used herein means an operation of repeatedly applying pressure to a mixture having fluidity that can maintain a lump shape.

  Moreover, in this invention, a kneaded material and a solvent are mixed in a slurry preparation process, and a slurry with a solid content concentration of 60-80 mass% is obtained. By mixing the kneaded material and the solvent, a slurry in which the magnetic powder is highly dispersed in the solvent can be obtained. Since the dispersant is sufficiently attached to the primary particles of the magnetic powder, the state in which the magnetic powder is highly dispersed is maintained even in the solvent. Moreover, by adjusting the solid content concentration of the slurry to a predetermined value (60 to 80% by mass), the fluidity of the slurry can be made suitable for performing the subsequent molding step.

  The magnet manufacturing method according to the present invention includes a kneading step of kneading magnetic powder and a liquid dispersant to obtain a kneaded product, mixing the kneaded product and the liquid dispersant, and a solid content concentration of 60. The 1st slurry preparation process which obtains the 1st slurry of -80 mass%, the pressing process which removes a part of liquid content contained in the 1st slurry, and the processed material and solvent obtained through the pressing process , A second slurry preparing step for obtaining a second slurry having a solid content concentration of 60 to 80% by mass, a molding step for molding the second slurry to obtain a molded body, and firing for firing the molded body And a process.

  In such a manufacturing method, since the magnetic powder and the liquid dispersant are kneaded, most of the magnetic powder in the kneaded product can be composed of primary particles. A dispersant can be deposited. In the first slurry preparation step in the manufacturing method, since the first slurry is prepared by further adding a dispersant to the kneaded product after the kneading step, the dispersant is more sufficiently attached to the surface of the primary particles of the magnetic powder. Can be made. As a result, the magnetic field orientation of the magnetic powder in the slurry occurs very well during molding, and a magnet having an excellent degree of orientation and thereby high Br can be obtained.

  The pressing step is performed to remove a part of the liquid component (dispersant) contained in the first slurry and facilitate the preparation of a second slurry suitable for molding. If the dispersant is excessively present in the second slurry, there may be a situation in which a molded body cannot be obtained and a magnet cannot be manufactured.

  According to the present invention, a magnet having a high Br can be manufactured.

  Hereinafter, preferred embodiments of the present invention will be described. In the following description, a method of manufacturing a rare earth magnet particularly suitable for the present invention will be described. However, the method of manufacturing a magnet of the present invention is not limited to a rare earth magnet, and can be obtained by sintering magnetic powder such as other metal magnets. Any sintered magnet can be used without any particular limitation.

  FIG. 1 is a flowchart showing a manufacturing process of a rare earth magnet according to a preferred embodiment.

  In manufacturing the rare earth magnet, first, an alloy is prepared so that a rare earth magnet having a desired composition can be obtained (step S11). In this process, for example, a simple substance, an alloy, a compound, or the like containing an element such as a metal corresponding to the composition of the rare earth magnet is dissolved in an inert gas atmosphere such as vacuum or argon, and then used for casting or stripping. An alloy having a desired composition is manufactured by performing an alloy manufacturing process such as a casting method.

  Here, examples of rare earth magnets include those containing mainly Nd and Sm as rare earth elements, and those having a composition in which a rare earth element and a transition element other than the rare earth element are combined are suitable. Specifically, the rare earth element (represented by “R”) contains at least one of Nd, Pr and Dy in an amount of 26 to 33% by mass, B contains 0.5 to 1.5% by mass as an essential element, And what has the composition of the R-Fe-B type | system | group whose remainder is Fe is preferable. Such a rare earth magnet has a composition further containing other elements such as Co, Ni, Mn, Al, Nb, Zr, Ti, W, Mo, V, Ga, Zn, Cu, and Si as required. You may do it.

  Next, the obtained alloy is coarsely pulverized to obtain particles having a particle size of about several hundred μm (step S12). The coarse pulverization of the alloy is performed by using a coarse pulverizer such as a jaw crusher, a brown mill, a stamp mill, or the like, or after the alloy has occluded hydrogen, it is self-destructive based on the difference in hydrogen occlusion between different phases. It can be performed by causing pulverization (hydrogen occlusion pulverization). After the coarse pulverization and before the fine pulverization described later, a pulverization aid may be added to facilitate the pulverization of the magnetic powder. Examples of the grinding aid include the same dispersants as described later.

  By further finely pulverizing the powder obtained by coarse pulverization (step S13), a raw material powder (magnetic powder) of a magnet having a particle diameter of preferably about 1 to 10 μm, more preferably about 3 to 5 μm is obtained. Fine pulverization is performed by further pulverizing the coarsely pulverized powder using a fine pulverizer such as a jet mill, a ball mill, a vibration mill, and a wet attritor while appropriately adjusting conditions such as pulverization time. To do.

  The pulverized magnetic powder and the liquid dispersant are mixed to obtain a mixture (step S14; mixing step). The dispersant is a component for suppressing reaggregation of these particles by adhering to the particles constituting the magnetic powder. For example, surfactant, fatty acid, fatty acid alcohol, fatty acid alcohol ester, polybasic An alcohol ester of an acid, a fatty acid of a polyhydric alcohol or a derivative thereof can be applied. Of these, polyhydric alcohol fatty acids and derivatives thereof are preferred. In view of work efficiency and the like, in the mixing step, it is preferable to mix the magnetic powder and the liquid dispersant.

  As a surfactant that can be applied as a dispersant, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and a nonionic surfactant can be appropriately selected and used. Examples of the fatty acid alcohol ester include those in which the hydrogen of the carboxyl group in a fatty acid such as capric acid, myristic acid, lauric acid, caprylic acid, stearic acid, oleic acid and the like is substituted with an alkyl group. Furthermore, examples of the alcohol ester of polybasic acid include those in which the hydrogen of the carboxyl group in adipic acid or phthalic acid is substituted with an alkyl group. Furthermore, examples of the fatty acid or ester thereof of polyhydric alcohol include sorbitan threolate.

  Thereafter, the mixture containing the magnetic powder and the dispersant is kneaded to obtain a kneaded product (step S15; kneading step). The kneading can be performed using, for example, a pressure kneader, an open kneader, a twin screw extruder, a planetary mixer, or the like.

  In the kneading step, the content of the magnetic powder in the mixture (magnetic powder concentration) is preferably 85 to 95% by mass, more preferably 88 to 94% by mass with respect to the total mass of the mixture. I do. When the magnetic powder concentration of the mixture in the kneading step is less than 85% by mass, the fluidity of the mixture increases, the load applied to the mixture decreases, and the magnetic powder in the mixture is less likely to contact and collide with each other. Sometimes, there is a tendency that the aggregates of the primary particles of the magnetic powder are not sufficiently crushed. On the other hand, if it exceeds 95% by mass, the mixture is not sufficiently wetted by the solvent of the magnetic powder, and kneading itself becomes difficult and it tends to be difficult to obtain a good kneaded product.

  In the kneading step, the magnetic powder concentration (solid content concentration) of the mixture may be gradually changed by adding a liquid dispersant or the like. In this case, during the kneading step, the mixture does not always need to have the above-described suitable magnetic powder concentration, and may have a suitable magnetic powder concentration for at least a certain time.

  Here, the fixed time is a time that can sufficiently crush the aggregates of primary particles contained in the mixture. Conditions such as pressure and shear force applied to the mixture, and aggregation of the magnetic powder before kneading. It depends on the degree. For example, in the case of a mixture prepared under normal conditions, in order to sufficiently break up the aggregate of the magnetic powder, at least 5 minutes, preferably 10 minutes or more, more preferably 20 minutes or more, as described above. It is preferable to perform kneading at a magnetic powder concentration. When this time is less than 5 minutes, kneading becomes insufficient and the aggregates of primary particles tend not to be sufficiently crushed.

  After the kneading step, a dispersant is further added to the obtained kneaded product to obtain a dispersant-containing slurry (first slurry) having a solid content concentration smaller than that of the kneaded product (step S16; first slurry preparing step). . By carrying out this step, a sufficient amount of dispersant can be adhered to the surface of the primary particles of the magnetic powder. The solid content concentration of the dispersant-containing slurry is 60 to 80% by mass (more preferably 65 to 75% by mass). When the solid content concentration of the dispersant-containing slurry exceeds 80% by mass, the amount of the dispersant attached to the surface of the primary particles of the magnetic powder becomes insufficient. In order to attach a sufficient amount of the dispersant to the primary particles of the magnetic powder, the solid content concentration of the dispersant-containing slurry may be 80% by mass or less, but the solid content concentration of the dispersant-containing slurry is 60% by mass. If it is less than%, it takes time to obtain a processed product having a desired solid content concentration in the pressing step described later, and the working efficiency is lowered.

  The dispersant-containing slurry can be prepared, for example, by adding a liquid dispersant while stirring the kneaded product obtained in the above-described kneading step. The dispersant used in this step may be the same as or different from the dispersant used in the mixing step.

  The three steps of the mixing step, the kneading step, and the slurry preparation step described above may be performed independently or as a series of operations. That is, mixing of magnetic powder and liquid dispersant, kneading of the mixture, and slurry preparation by further addition of the dispersant may be performed in separate tanks, and mixing and kneading may be performed in one tank. After performing, only slurry preparation may be performed in different tanks, and all of mixing, kneading and dilution may be performed in one tank. However, since it is difficult to move the mixture in which only the dispersant is added to the magnetic powder, it is preferable to perform mixing and kneading by at least a series of operations. In this case, for example, mixing and kneading can be continuously performed by adding a liquid dispersant while stirring the magnetic powder, or adding the magnetic powder while stirring the liquid.

  In addition, when the kneading step and the slurry preparation step are performed as a series of operations, a slurry having a predetermined solid content concentration may be finally prepared by gradually adding a dispersant to the kneaded product. After kneading at a solid content concentration, a liquid dispersant may be further added to prepare a slurry having a desired solid content concentration.

  Following the slurry preparation step (step S16) by adding a dispersant, the slurry obtained through the step is squeezed to remove at least a portion of the liquid component (dispersant) contained in the slurry (step). S17; pressing process). The pressing process of the slurry can be performed using, for example, a centrifugal separator, a filter press machine, or the like.

  The processed product obtained through the pressing step preferably has a solid concentration of 80 to 95% by mass, more preferably 85 to 95% by mass, and still more preferably 88 to 95% by mass. When the solid content concentration of the processed product is less than 80% by mass, it tends to be difficult to obtain a suitable molded product in the molding step described later due to an excessive dispersant, and when it exceeds 95% by mass, the dispersion Aggregation of magnetic powder tends to occur due to lack of the agent.

  The processed material obtained through the pressing step and the solvent are mixed to obtain a solvent-containing slurry (second slurry) having a solid content concentration of 60 to 80% by mass (step S18; second slurry preparing step). The solvent is used to adjust the solid content concentration of the processed product to a predetermined value and prepare a slurry having appropriate fluidity. As a solvent, a solvent used for slurry preparation in wet molding of a magnet can be applied without particular limitation. Examples thereof include oils such as mineral oil, synthetic oil and vegetable oil, and organic solvents such as acetone and alcohol. Of these, oil is preferable in order to prevent oxidation of the magnetic powder. From the viewpoint of safety, among oils, those classified as third petroleums (those that are liquid at a temperature of 20 ° C. under atmospheric pressure and have a flash point of 70 ° C. or more and less than 200 ° C.) are preferable.

  As described above, the solvent-containing slurry obtained through the slurry preparation step has a solid content concentration of 60 to 80% by mass (more preferably 65 to 75% by mass). When the solid content concentration of the slurry is within the above range, the magnetic powder is easily oriented by an orientation operation such as molding described later, and the slurry is easily supplied to the molding machine. However, if the magnetic powder concentration in the slurry is too small, the magnetic powder in the slurry is likely to settle.

  Thereafter, before the molded body is molded, it is preferable to perform a step of dispersing the magnetic powder and the solvent again as necessary (step S19; dispersion step). In the solvent-containing slurry obtained by the addition of the solvent, the magnetic powder and the solvent are separated during the supply to the molding machine, and the supernatant of the solvent may be generated. If this slurry is used for molding as it is, the amount of magnetic powder charged into the molding machine may not be constant depending on the degree of separation, and as a result, the amount of magnetic powder in the compact may vary. On the other hand, if the dispersion is performed after the dilution and before the molding, the molding can be performed in a state where the separation of the slurry is small, and the variation of the molded body can be suppressed. In addition, although it is thought that the primary particle obtained by the kneading | mixing process mentioned above hardly produces aggregation again, for example, when aggregation has arisen in part, an aggregate is disintegrated also by this dispersion | distribution process. It is considered possible.

  The slurry can be dispersed by using a ball mill, ultrasonic diffusion, homogenizer, optimizer, or the like. For example, it is possible to achieve good dispersion by incorporating an apparatus for performing these operations in the middle of a supply pipe that supplies the diluted slurry to the molding machine. From the viewpoint of obtaining a good effect by the dispersion, it is preferable to perform the dispersion just before the molding as much as possible.

  The slurry obtained as described above is put into a molding machine, and the molded product is obtained by molding the slurry while applying a magnetic field (step S20; molding process). By the molding step, a molded body having a predetermined degree of orientation is obtained. The molding can be performed, for example, by press molding. Specifically, after the slurry is filled into the mold cavity, the filled slurry is pressurized so as to be sandwiched between the upper punch and the lower punch, It is processed into a predetermined shape while extracting the solvent and the like. At this time, the upper punch or the lower punch may be provided with a hole communicating with the outside in order to extract the solvent that has flowed out. However, it is preferable to place a cloth or paper filter on the punch surface, or to make the upper punch or the lower punch partly porous so that the magnetic powder does not flow out. The shape of the molded body obtained by molding is not particularly limited, and can be changed according to the desired shape of the rare earth magnet, such as a columnar shape, a flat plate shape, or a ring shape.

The pressing direction during molding may be the same as the magnetic field application direction, or may be perpendicular to the magnetic field application direction, but more excellent magnetic properties can be obtained by applying pressure perpendicular to the magnetic field application direction. There is a tendency. Moreover, the magnetic field intensity at the time of shaping | molding can be 12-20 kOe (960-1600 kA / m), and a pressurization can be 0.3-3 ton / cm < ² > (30-300 MPa). Furthermore, the molding time is preferably several seconds to several tens of seconds. By forming in a magnetic field under such conditions, a rare earth magnet having good magnetic properties tends to be easily obtained.

  Next, a desolvation step is performed on the compact to remove the solvent and dispersant remaining in the compact by, for example, vacuum heating (step S21). The solvent removal is performed under such conditions that most of the solvent in the molded body can be removed. For example, the solvent is preferably heated at 100 to 160 ° C. for 1 to 5 hours under a reduced pressure of about 1 to 3000 Pa. In this solvent removal step, sintering of the molded body usually does not proceed, but partial sintering may proceed.

  Thereafter, the desolvated shaped body is fired to obtain a sintered body (step S22; firing step). Sintering can be performed, for example, by heating the molded body in a vacuum or in the presence of an inert gas at 950 to 1150 ° C. for 1 to 10 hours and then rapidly cooling.

  After sintering, the obtained sintered body is subjected to an aging treatment by heating the sintered body at a temperature lower than that during firing (step S23). The aging treatment is, for example, suitable for two-stage heating at 700 to 900 ° C. for 1 to 3 hours, further heating at 500 to 700 ° C. for 1 to 3 hours, and one-stage heating at about 600 ° C. for 1 to 3 hours. Perform under conditions. Such an aging treatment can improve the magnetic properties of the sintered body.

  And the target rare earth magnet is obtained by performing the process which cut | disconnects to the desired size with respect to the sintered compact obtained in this way, or smoothes the surface. The obtained rare earth magnet may further be provided with a protective layer for preventing deterioration of the oxide layer, the resin layer, etc. on the surface.

  According to the method for producing a rare earth magnet according to the above-described embodiment, the kneaded product is prepared by kneading the magnetic powder and the liquid dispersant. Etc.) can be sufficiently disintegrated. Therefore, through the kneading step, it is possible to obtain a kneaded product in which the dispersant is sufficiently adhered to the surface of the primary particles of the magnetic powder. Furthermore, in this embodiment, by performing the slurry preparation step (step S16) by adding a dispersant, the dispersant is more fully applied to the surface of the primary particles of the magnetic powder in the kneaded product obtained after the kneading step. Can be attached.

  As described above, when the method of adding a dispersant to the kneaded material is adopted, there is an advantage that the dispersant sufficiently adheres to the primary particles of the magnetic powder, while excessive dispersion with respect to the blending amount of the magnetic powder. Due to the presence of the agent, there may be a case where a molded body cannot be obtained in the molding process and a magnet cannot be manufactured. Therefore, in the method according to the present embodiment, an excess dispersing agent is removed by performing the pressing step (step S17), and a slurry suitable for molding can be easily obtained by the slurry preparation step (step S18) by adding a solvent. Can be prepared. In addition, by removing the excess dispersant before the step of adding the solvent (step 18), there is an effect that the recovered dispersant can be reused without performing a purification treatment or the like. .

  Moreover, in the slurry preparation process (step S18) by addition of a solvent, a slurry in which magnetic powder is highly dispersed in the solvent can be obtained by mixing the processed material and the solvent. Therefore, in the molding step, magnetic field orientation of the magnetic powder in the slurry is satisfactorily generated, thereby obtaining a molded body having a high degree of orientation. As a result, a rare earth magnet having a high Br can be obtained.

  As mentioned above, although the manufacturing method of the rare earth magnet was demonstrated as suitable embodiment of the manufacturing method of the magnet which concerns on this invention, this invention is not necessarily limited to embodiment mentioned above. For example, in the above embodiment, the method including the steps shown in FIG. 1 is exemplified, but the magnet manufacturing method according to the present invention includes a kneading step, a slurry preparation step by adding a solvent, a forming step, and a firing step. As long as the effects of the present invention are sufficiently obtained, some other steps may be omitted. For example, as shown in FIG. 2, the magnet manufacturing method according to the present invention omits step S16 (slurry preparation step by adding a dispersing agent) and step S17 (squeezing step) in the method according to the above embodiment. There may be.

  Further, after the slurry preparation step by addition of a solvent, when the obtained slurry is immediately subjected to molding, when the separation of the slurry before molding is small, the dispersion step before molding can be omitted. Furthermore, when sufficient magnetic properties are obtained only by firing after the firing step, the aging treatment after the firing step is not necessarily performed. Moreover, the manufacturing method of the magnet which concerns on this invention may further include processes other than the process mentioned above as needed.

  As described above, the magnet manufacturing method according to the present invention is not limited to the rare earth magnet, and can be applied to the manufacture of magnets other than rare earth magnets such as other metal magnets and ferrite magnets. And even if it is a case where it applies to another magnet, it becomes possible to manufacture the magnet which has high orientation degree and high Br similarly to embodiment mentioned above.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples.

Example 1
<Manufacture of rare earth magnets>
First, Nd: 26.0 mass%, Dy: 5.0 mass%, Co: 0.5 mass%, Al: 0.2 mass%, Cu: 0.07 mass%, B: 0.95 mass%, A raw material metal or a raw material alloy was blended so that the amount of Zr was 0.18% by mass and the balance was Fe, and a raw material alloy thin plate was obtained through melting and casting by a strip casting method. The raw material alloy thin plate thus obtained was hydrogen crushed to obtain raw material alloy coarse powder. Next, after adding 0.10% by mass of lauric acid amide as a grinding aid to this raw material alloy coarse powder, it is finely pulverized in a high-pressure nitrogen atmosphere using an airflow type pulverizer (jet mill), and the raw material of the magnet A magnetic powder as a powder was obtained.

  After the obtained magnetic powder was mixed with oleic acid (dispersing agent) to obtain a mixture, this mixture was kneaded using a planetary mixer under the conditions of a rotation speed of 40 rpm and a treatment time of 30 minutes to obtain a magnetic powder. A kneaded product having a concentration of 91% by mass was obtained (kneading step). Then, oleic acid (dispersant) was further added to the kneaded material, followed by stirring with a planetary mixer for 10 minutes to obtain a dispersant-containing slurry having a magnetic powder concentration of 70% by mass (first Slurry preparation step).

  Next, the obtained dispersant-containing slurry was squeezed to obtain a processed product having a magnetic powder concentration of 85% by mass (squeezing step). The pressing process was performed using a centrifuge. The processing conditions were a rotational speed of 3000 rpm and a processing time of 1 minute.

  After adding mineral oil (trade name: IP Solvent 2028, manufactured by Idemitsu Kosan Co., Ltd.) as a solvent to the processed product obtained through the pressing treatment, the magnetic powder concentration is increased by stirring for 10 minutes with a planetary mixer. A solvent-containing slurry of 70% by mass was obtained (second slurry preparation step).

  Using the solvent-containing slurry obtained as described above, molding was performed in a magnetic field to obtain a molded body (molding step). Molding is performed by pressing between the upper punch and the lower punch in the cavity under a condition of 2.3 ton (230 MPa) in a magnetic field of 14 kOe (1120 kA / m). Was removed by suction. At this time, the magnetic field direction was made to coincide with the pressing direction. The dimension of the molded body was 20 mm × 18 mm × 12 mm.

  Next, the removal of the solvent and the dispersant contained in the molded body was performed by heating the molded body for 2 hours under conditions of a pressure of 1 to 20 Pa and a temperature of 150 ° C. Thereafter, the molded body was fired and aged using a firing furnace to obtain a sintered body (firing step). The temperature of the firing furnace was controlled as follows. That is, first, the temperature was raised under the condition of 8 ° C./min, and the temperature was maintained at 1030 ° C. for 4 hours. Then, it hold | maintained at 800 degreeC and 570 degreeC for 1 hour, respectively, and performed baking and an aging treatment.

(Examples 2 to 4)
The same raw material as in Example 1 was used, and a magnetic powder as a raw material powder for a magnet was obtained by the same method. After the obtained magnetic powder was mixed with oleic acid (dispersing agent) to obtain a mixture, this mixture was kneaded using a planetary mixer at 40 rpm for 30 minutes, and the magnetic powder concentration was a predetermined value. A kneaded product with a value was obtained (kneading step). In Examples 2 to 4, oleic acid was added to the magnetic powder so that the magnetic powder concentration of the kneaded product after the kneading step would be the values shown in the respective columns of Table 1.

  Mineral oil (trade name: IP Solvent 2028, manufactured by Idemitsu Kosan Co., Ltd.) was added as a solvent to the kneaded product without adding oleic acid (dispersant). By stirring for 10 minutes with a planetary mixer, a solvent-containing slurry having a predetermined magnetic powder concentration was obtained (slurry preparation step). In Examples 2 to 4, the mineral oil was added to the magnetic powder so that the concentration of the magnetic powder in the solvent-containing slurry was the value shown in each column of Table 1.

  Except for using the solvent-containing slurry obtained as described above, a molding process and a firing process were performed in the same manner as in Example 1 to manufacture a magnet.

(Comparative Example 1)
The same raw material as in Example 1 was used, and a magnetic powder as a raw material powder for a magnet was obtained by the same method. The obtained magnetic powder was mixed with oleic acid (dispersant) to obtain a mixture. Thereafter, this mixture was kneaded using a planetary mixer under the conditions of 40 rpm and 30 minutes to obtain a kneaded product having a magnetic powder concentration of 91% by mass.

  The kneaded product obtained as described above is further added with oleic acid (dispersant) and subsequently stirred for 10 minutes with a planetary mixer to obtain a dispersant-containing slurry having a magnetic powder concentration of 70% by mass. It was. No squeezing treatment was performed on the dispersant-containing slurry, and no solvent was added. The forming step was performed in the same manner as in Example 1 except that the dispersant-containing slurry was used as it was in the forming step instead of the solvent-containing slurry. However, in this comparative example, the dispersant could not be removed by suction during molding, and a molded product could not be obtained. Therefore, in this comparative example, a magnet could not be manufactured.

(Comparative Example 2)
Implemented except that oleic acid and mineral oil (trade name: IP Solvent 2028, manufactured by Idemitsu Kosan Co., Ltd.) were added to the kneaded product after the kneading treatment instead of adding only oleic acid (dispersant). A slurry (dispersant-containing slurry) was prepared in the same manner as in Example 2. The mixing ratio (mass ratio) between the dispersant and the solvent was 9: 5. In this comparative example, the dispersant and the solvent were removed by suction during molding, and a molded body could be obtained. The obtained molded body was fired and aged in the same manner as in Example 1 to obtain a sintered body.

<Evaluation of magnetic properties>
The magnetic characteristics of the rare earth magnets obtained in Examples 1 to 4 and Comparative Example 2 were measured using a BH tracer, and the residual magnetic flux density (Br) and the holding force (HcJ) of each magnet were calculated. Table 1 shows the measurement results of the magnetic characteristics of each magnet.

It is a flowchart which shows embodiment of the manufacturing method of the magnet which concerns on this invention. It is a flowchart which shows other embodiment of the manufacturing method of the magnet which concerns on this invention.

Claims (2)

A method for producing a rare earth magnet having an R—Fe—B composition containing a rare earth element R,
Kneading a magnetic powder and a liquid dispersant to obtain a kneaded product; and
A slurry preparation step of mixing the kneaded product and a solvent to obtain a slurry having a solid content concentration of 60 to 80% by mass;
A molding step of molding the slurry to obtain a molded body;
A firing step of firing the molded body;
A method of manufacturing a magnet, comprising: Kneading a magnetic powder and a liquid dispersant to obtain a kneaded product; and
A first slurry preparation step of mixing the kneaded material and a liquid dispersant to obtain a first slurry having a solid concentration of 60 to 80% by mass;
A pressing step for removing a part of the liquid contained in the first slurry;
A second slurry preparation step of mixing the processed product and the solvent obtained through the pressing step to obtain a second slurry having a solid content concentration of 60 to 80% by mass;
A molding step of molding the second slurry to obtain a molded body;
A firing step of firing the molded body;
A method of manufacturing a magnet, comprising:

Images