JP2007231396A - Method for producing granule and method for producing rare earth sintered magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a rare earth sintered magnet capable of improving the dimensional precision in a compact and improving productivity using granules having excellent fluidity. <P>SOLUTION: The method for producing a granule includes: a step where a first organic liquid 2 is added to alloy grains 1 having a prescribed composition, and they are mixed, so as to be a granule precursor 100; and a step where a second organic liquid 3 having a saturation vapor pressure lower than that of the first organic liquid 2 is added to the granule precursor 100, so as to be a granule 200. By differentiating the addition timing between the first organic liquid 2 and the second organic liquid 3, the previously added first organic liquid 2 is present mainly at the inside of the granule 200, and the second organic liquid 3 added afterwards is present mainly on the surface of the granule 200. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing granules, and more particularly to a method for obtaining a rare earth sintered magnet by granulating raw material powder.

When manufacturing rare earth sintered magnets, magnetic properties such as saturation magnetic flux density and coercive force are ensured by refining the raw material powder used for sintering. However, the refinement of the raw material powder is a factor that hinders the dimensional accuracy and productivity of the molded body.
The raw material powder forms a compact by pressure molding in a magnetic field. In the molding in the magnetic field, the raw powder particles are oriented by applying a static magnetic field or a pulsed magnetic field. At the time of molding in this magnetic field, the finer the raw material powder, the lower the fluidity and the problem of filling into the mold. If the powder filling property is inferior, the powder cannot be sufficiently filled into the die, so the dimensional accuracy of the molded product cannot be obtained, or the filling of the die itself takes time and productivity. There is a problem of inhibiting. In particular, it is difficult to accurately and efficiently produce a molded body having a thin shape or a complicated shape.

Attempts have been made to granulate the raw material powder as one means for improving the fluidity of the raw material powder. For example, JP-A-8-107034 (Patent Document 1) and JP-A-8-88111 (Patent Document 2) propose to granulate by spray-drying a slurry in which a binder is added to a rare earth metal powder. Yes.
Japanese Patent Publication No. 7-6025 (Patent Document 3) proposes granulating a rare earth metal powder by applying a magnetic field.

JP-A-8-107034 JP-A-8-88111 Japanese Patent Publication No. 7-6025

According to Patent Document 3, a magnetic field application process at the time of producing a pressurizing body and an AC magnetic field application process for improving magnetic properties after filling the granules with the granules are required. Moreover, since it is the granule which applied the magnetic field, we are anxious about the fall of the fluidity | liquidity by residual magnetization.
According to Patent Documents 1 and 2, fluidity can be improved by producing granules. However, since the alloy particles are adhered to each other with a binder such as PVA (polyvinyl alcohol), the adhesion between the alloy particles is relatively strong. Even when such a strong adhesive granule is subjected to forming in a magnetic field, it is not easy to orient each alloy particle. Therefore, the rare earth sintered magnet obtained has a low degree of orientation and magnetic properties, particularly a residual magnetic flux density (Br). Further, since carbon contained in the binder causes a decrease in magnetic characteristics, a step of removing the binder is necessary.
The present invention has been made on the basis of such a technical problem. A rare earth sintered magnet capable of improving the dimensional accuracy and productivity of a molded body using granules having excellent fluidity. An object is to provide a manufacturing method.

  As described above, in the granulation technique using a conventional binder, a slurry containing a predetermined amount of a so-called organic solvent is prepared as a solvent for dissolving the binder and a dispersion medium for dispersing the alloy particles. The present inventors paid attention to this organic solvent. As a result, it is possible to produce a granule only with an organic solvent, the granule is excellent in fluidity when filled with a mold, and the granule produced only with an organic solvent has a relatively weak adhesion between alloy particles. Therefore, it was confirmed that a good orientation state can be realized by separating into alloy particles by a magnetic field applied during molding in a magnetic field. Furthermore, when producing granules only with an organic solvent (hereinafter referred to as organic liquid), the amount of organic liquid required as moisture for producing the granules and the amount of organic liquid necessary for the granules to maintain their morphology. There was a difference in quantity, and the latter was found to be less. It can be said that the influence of the organic liquid on the magnetic properties is very small compared to the binder such as the conventional PVA, but the amount of the organic liquid in the state of forming the granules affects the magnetic properties of the rare earth sintered magnet. Was also confirmed.

  If an organic liquid is added in an amount to provide moisture necessary for granule formation, the magnetic properties will be impaired at least. Of course, by providing a process for removing the organic liquid at any stage after granule formation, the problem of magnetic properties can be solved, but from the viewpoint of manufacturing cost, the organic liquid removal process is simple. It is desirable to be. In order to satisfy this requirement, it would be effective for achieving the object of the present invention to once produce a granule using an organic liquid and then remove other organic liquid while leaving an amount necessary for maintaining the shape of the granule. I found out. In other words, if a granule is prepared using an organic liquid that is easy to remove after granule formation and an organic liquid that is more difficult to remove than the organic liquid, only the organic liquid that is easy to remove thereafter can be preferentially removed from the granule, Organic liquids that are difficult to remove can remain in the granules.

  Here, from the viewpoint of magnetic properties, it is necessary to minimize the amount of the organic liquid that is difficult to remove. Therefore, the present inventors once produced what should be referred to as a granular precursor using an organic liquid (first organic liquid) that can be easily removed, and then the organic liquid that is difficult to remove from the granular precursor. By adding (second organic liquid), it was studied that the surface of the granule precursor was covered with alloy particles adhered by the second organic liquid. Since the granule precursor mainly includes a first organic liquid between the particles constituting the granule precursor, the second organic liquid added later is more likely to be on the surface of the granule precursor than to penetrate into the interior of the granule precursor. It will preferentially adhere between newly adhering alloy particles. Subsequently, when the process which removes the 1st organic liquid from this granule precursor was performed, the form of the granule was able to be maintained. This means that in order to maintain the shape of the granule, the second organic liquid does not have to be present closely between the particles constituting the center of the granule, but to adhere the alloy particles present on the surface of the granule. It suggests that it should exist. In addition, since it is sufficient that the second organic liquid has an amount enough to adhere the alloy particles present mainly on the surface of the granule, the amount added can be reduced.

This invention is based on the above knowledge, Comprising: The process of adding a 1st organic liquid to the raw material powder of a predetermined composition, mixing and setting it as a granule precursor, and a 1st organic liquid with respect to this granule precursor And a step of adding a second organic liquid having a lower saturated vapor pressure to form a granule.
Thus, by making the addition timings of the first organic liquid and the second organic liquid different, the first organic liquid added earlier is mainly present inside the granules, and the first organic liquid added later is added. The two organic liquids will be present mainly on the surface of the granules.

In this granule manufacturing method, the granule is produced using the first organic liquid and the second organic liquid having a lower saturated vapor pressure than the first organic liquid. The first organic liquid can be removed from the granule preferentially over the second organic liquid by exposing the granule to (including heating under). In addition, by selecting the saturated vapor pressure of the first organic liquid, the first organic liquid can be easily removed in a low-pressure reduced atmosphere, and the second organic liquid is mainly applied to the surface of the granules. Can remain.
When the first organic liquid is removed, the morphology of the granules is maintained by the second organic liquid. The amount of the second organic liquid in the form of granules affects the magnetic properties of the rare earth sintered magnet, particularly the residual magnetic flux density. Specifically, the smaller the amount of the second organic liquid, the more advantageous in obtaining a high residual magnetic flux density. However, in the present invention, as described above, the second precursor after the granule precursor is prepared with the first organic liquid. In order to add the organic liquid, the second organic liquid can be effectively attached to the surface of the granules. As a result, the amount of the second organic liquid can be suppressed to an amount necessary for maintaining the shape of the granules.

In the method for producing a granule of the present invention, the first organic liquid is 15.0 wt% or less (excluding 0) and the second organic liquid is 4.0 wt% or less (provided that 0 is not added) based on the raw material powder. It is desirable to add.
Thus, since the addition amount of the second organic liquid is small, it is desirable to dilute the second organic liquid with a solvent in advance and then add it to the granule precursor. Thereby, it becomes easy to uniformly adhere the second organic liquid to the surface of the granule precursor while suppressing the addition amount of the second organic liquid to a small amount.
In producing the granule precursor and granule, it is preferable to use a rolling granulation method or a rolling fluidized bed granulation method. In particular, according to the rolling granulation method, the granules are formed satisfactorily and a large yield can be secured.

The granule production method of the present invention can be suitably applied to the production of rare earth sintered magnets. In this case, the composition of the raw material powder is R ₂ T ₁₄ B phase (R is one or more elements selected from rare earth elements, T is one selected from transition metal elements including Fe or Fe and Co) Or two or more elements).
In order to apply the method for producing a granule of the present invention to the production of a rare earth sintered magnet, first, a granule is produced using the first organic liquid and the second organic liquid by the above-described method, and then the first A treatment for removing the organic liquid is performed. And after throwing the granule from which the 1st organic liquid was removed into a mold cavity, a magnetic field is applied to a granule, and a compact is obtained by press-molding, and by sintering this compact A rare earth sintered magnet can be produced.
The first organic liquid is removed after the granule is produced, and functions mainly as a granulation aid. On the other hand, the second organic liquid remains after the preparation of the granules and functions as a shape-retaining agent for maintaining the shape of the granules. Thus, since both functions differ, in the present invention, the addition amount of the first organic liquid is larger than the addition amount of the second organic liquid.

  According to the present invention, it is possible to efficiently produce granules having excellent fluidity. If this granule is molded, it is possible to improve the dimensional accuracy and productivity of the molded body, and to produce a rare earth sintered magnet without greatly degrading the magnetic properties.

Hereinafter, the present invention will be described in detail based on embodiments.
First, the granulation technique using an organic liquid, which is a feature of the present invention, will be described. Unless otherwise specified, the first organic liquid and the second organic liquid are collectively referred to simply as “organic liquid”.
Conventionally, for example, when preparing a granule using an organic binder, it has been considered that an organic binder exists between the particles and the particles adhere to each other. In the present invention, the first organic liquid is present between the particles in the stage of the granule precursor as an intermediate product, and the second organic liquid is present between the particles around the granule in the final product as a granule. Let
The adhesion force due to the organic liquid is extremely weak compared to the adhesion force due to the binder such as the conventional PVA. Therefore, the granules obtained by the present invention are easily disintegrated by a magnetic field applied during molding in a magnetic field and separated into alloy particles. Therefore, a high degree of orientation can be obtained. Up to now, the use of a binder has been considered as a premise for the production of granules. However, even when an organic liquid is used as in the present invention, it is highly valuable to find that granules with high fluidity can be obtained. In addition, since the organic liquid is mainly present on the surface of the granules, the adhesion of the granules to the mold is also prevented. In addition, since this granule collapses when a magnetic field is applied, it is suitable for a rare earth sintered magnet that performs molding in a magnetic field. Furthermore, the organic liquid is extremely easy to remove from the molded body as compared with a conventional binder such as PVA, and omits the binder removal step that is essential when using the conventional granule technology. And includes process advantages. Here, the organic liquid includes a substance generally called an organic solvent, but is called an organic liquid because it does not function as a solvent in the present invention.

  Hereinafter, the present invention will be described in detail in the order of manufacturing steps of the rare earth sintered magnet with reference to FIG. As shown in FIG. 1, in the method for producing a rare earth sintered magnet of the present invention, a granule is produced after the pulverization step, and this granule production method is a characteristic part of the present invention.

<Raw material alloy production process (S101)>
In the raw material alloy production step (S101), the raw material alloy can be produced by a strip casting method or other known melting methods in a vacuum or an inert gas, preferably an Ar atmosphere. In the strip casting method, a molten metal obtained by melting a raw metal in a non-oxidizing atmosphere such as an Ar gas atmosphere is ejected onto the surface of a rotating roll. The melt rapidly cooled by the roll is rapidly solidified in the form of a thin plate or flakes (scales). This rapidly solidified alloy has a homogeneous structure with a crystal grain size of 1 to 50 μm. The raw material alloy can be obtained not only by the strip casting method but also by a melting method such as high frequency induction melting. In order to prevent segregation after dissolution, for example, it can be solidified by pouring into a water-cooled copper plate. An alloy obtained by the reduction diffusion method can also be used as a raw material alloy.
When obtaining an RTB-based sintered magnet, a so-called alloy using a R ₂ T ₁₄ B crystal grain (low R alloy) and an alloy containing more R than a low R alloy (high R alloy) is used. A mixing method can also be applied to the present invention.
Note that the oxygen content of the raw material alloy is usually 300 ppm or less, and the oxygen content at this stage is low. However, the amount of oxygen increases in the subsequent pulverization process and magnetic field molding process. Therefore, in the present invention, in order to suppress an increase in the amount of oxygen in this step, it is preferable that the amount of oxygen in the atmosphere (the atmosphere in which the alloy is in direct contact) be set to 200 ppm or less in the steps before being subjected to sintering. A more preferable oxygen amount is 100 ppm or less, and further preferably 80 ppm or less.

<Coarse grinding step (S103)>
In the coarse pulverization step (S103), the raw material alloy obtained in the raw material alloy production step (S101) is coarsely pulverized. In the case of the mixing method, the low R alloy and the high R alloy are pulverized separately or together.
First, the raw material alloy is coarsely pulverized until the particle size becomes about several hundred μm. The coarse pulverization is preferably performed in an inert gas atmosphere using a stamp mill, a jaw crusher, a brown mill or the like. Prior to coarse pulverization, it is effective to perform pulverization by allowing hydrogen to be stored in the raw material alloy and then releasing it. This hydrogen release treatment is performed for the purpose of reducing hydrogen as an impurity as a rare earth sintered magnet. The temperature of heating and holding for releasing hydrogen is 200 ° C. or higher, desirably 350 ° C. or higher. The holding time varies depending on the relationship with the holding temperature, the thickness of the raw material alloy, etc., but is at least 30 minutes or longer, preferably 1 hour or longer. The hydrogen release treatment is performed in a vacuum or Ar gas flow. The hydrogen storage process and the hydrogen release process are not essential processes. This hydrogen pulverization can be regarded as coarse pulverization, and mechanical coarse pulverization can be omitted.

<Fine grinding step (S105)>
After the coarse pulverization step (S103), the process proceeds to the fine pulverization step (S105). A jet mill is mainly used for fine pulverization, and a coarsely pulverized powder having a particle size of about several hundreds of μm has an average particle size of 2.5 to 6 μm, preferably 3 to 5 μm. The jet mill releases a high-pressure inert gas from a narrow nozzle to generate a high-speed gas flow, accelerates the coarsely pulverized powder with this high-speed gas flow, collides with the coarsely pulverized powder, and collides with the target or the container wall. It is a method of generating a collision and crushing.

  In the case of the mixing method, the timing of mixing the two kinds of alloys is not limited. However, when the low R alloy and the high R alloy are separately pulverized in the pulverization step, the pulverized low R alloy powder is used. And high R alloy powder in a nitrogen atmosphere. The mixing ratio of the low R alloy powder and the high R alloy powder may be about 80:20 to 97: 3 by weight. The mixing ratio when the low R alloy and the high R alloy are pulverized together is the same. In addition, fatty acids or fatty acid derivatives and hydrocarbons for the purpose of improving the lubrication and orientation during molding, such as zinc stearate, calcium stearate, aluminum stearate, stearamide, olein, which are stearic acid and oleic acid Acid amide, ethylenebisisostearic acid amide, hydrocarbon paraffin, naphthalene and the like can be added in an amount of about 0.01 to 0.3 wt% during pulverization.

<Granule precursor preparation step (S107), granule preparation step (S109)>
The finely pulverized powder (raw material powder, alloy particles) obtained as described above is granulated through a granule precursor preparation step (S107) and a granule preparation step (S109). In the present invention, a granule is produced using two types of organic liquids, but the addition timing of the two types of organic liquids is changed to finally produce granules having a small remaining amount of organic liquid. In the following, the organic liquid will be described first, and then the characteristic addition timing of the organic liquid in the present invention will be described.

Examples of the organic liquid used in the present invention include hydrocarbon compounds, alcohol compounds, ether compounds (including glycol ether compounds), ester compounds (including glycol ester compounds), ketone compounds, fatty acid compounds, and terpene compounds. One or two of the compounds can be selected. Specific examples of such organic liquids include hydrocarbon compounds such as toluene, xylene, alcohol compounds such as ethanol, isobutyl alcohol, and ether compounds such as butyl cellosolve, cellosolve, carbitol, and butyl carbitol. Examples of ester compounds include ethyl acetate, examples of ketone compounds include acetone (dimethyl ketone), methyl isobutyl ketone, methyl ethyl ketone, and examples of terpene compounds include pinene and terpineol.
Of course, the organic liquid is not limited to the organic liquids listed here, and other organic liquids such as ethylene glycol, diethylene glycol, and glycerin can also be used.

  In the granule produced using the organic liquid, the organic liquid is present at least at the contact point between the alloy particles constituting the finely pulverized powder, and the alloy particles are adhered to each other by the liquid crosslinking force. At this time, the contact between the alloy particles does not substantially contain a solid component such as a binder for adhering the alloy particles to each other in the liquid. However, when a lubricant is added to improve the pulverization property and the orientation during molding, the solid component of the lubricant is allowed to be present in the liquid. In addition, an organic liquid is also present on the surface of the granule and can serve as a lubricant.

Granules produced using an organic liquid need to maintain their shape until a predetermined step. Once the formed granule cannot maintain its shape, the fine alloy particles dropped from the granule form a form attached to the periphery of the granule, and this form of the granule decreases the fluidity. Therefore, it is preferable that the organic liquid used in the present invention does not volatilize easily. Therefore, in the present invention, it is preferable to use an organic liquid having a saturated vapor pressure at 20 ° C. of 75 mmHg (10 kPa) or less. The saturated vapor pressure at 20 ° C. is more preferably 20 mmHg or less, and the saturated vapor pressure at 20 ° C. is more preferably 5 mmHg or less.
In addition, the organic liquid used in the present invention preferably has a boiling point of 50 ° C. or higher, more preferably 100 ° C. or higher so as not to vaporize at room temperature.

  The organic liquid used in the present invention also needs to impart sufficient adhesion, that is, shape retention, between the alloy particles to maintain the granules. Therefore, it is preferable in the present invention to specify the surface tension and viscosity of the organic liquid. The surface tension of a preferable organic liquid is 20 dyn / cm or more at 20 ° C. The surface tension at 20 ° C. is more preferably 25 dyn / cm or more, and the surface tension at 20 ° C. is more preferably 30 dyn / cm or more. The preferable viscosity of the organic liquid is 0.35 cp or more at 20 ° C. The viscosity at 20 ° C. is more preferably 1 cp or more, and the viscosity at 20 ° C. is more preferably 2 cp or more.

  Furthermore, in order to prevent oxidation of the finely pulverized powder, the organic liquid used in the present invention preferably has a low oxygen concentration and low solubility in water (water solubility).

  In the present invention, granules are produced using a first organic liquid and a second organic liquid having a saturated vapor pressure lower than that of the first organic liquid. The saturated vapor pressures of various organic liquids are shown in Table 1, and the first organic liquid and the second organic liquid may be selected based on this value. For example, as the first organic liquid, toluene, xylene, ethanol, acetone, methyl isobutyl ketone, ethyl acetate, methyl ethyl ketone, isobutyl alcohol, n-butyl acetate, dibutyl ether can be used. As the second organic liquid, a terpene compound containing pinene, menthane, terpineol, butyl carbitol acetate, cyclohexanol, ethylene glycol, butyl carbitol, diethylene glycol, carbitol, cellosolve, butyl cellosolve, propionic anhydride is used. Can do. However, this is merely an example, and does not determine the scope of the present invention. For example, among the examples exemplified as the first organic liquid, the first organic liquid and the second organic liquid can be configured, and among the examples exemplified as the second organic liquid, An organic liquid and a second organic liquid can also be configured. Table 1 also shows the physical properties of water.

  In the present invention, a step of adding and mixing the first organic liquid to the finely pulverized powder to form a granule precursor (S107), and a step of adding and mixing the second organic liquid to the granule precursor to form a granule (S109). The first organic liquid mainly functions as a granulating aid that gives moisture necessary for granule preparation to the finely pulverized powder, but is removed in a vacuum drying step (S111) described later. On the other hand, the second organic liquid mainly functions as a shape-retaining agent that imparts sufficient adhesion to maintain the shape of the granules, and remains in the granules after the reduced-pressure drying step (S111). As described above, by sharing the functions of the first organic liquid and the second organic liquid, the amount of the organic liquid remaining in the granules can be reduced before the magnetic field forming step (S113). This leads to a reduction in the amount of residual carbon in the sintered body, and finally a sintered magnet with high magnetic properties can be obtained.

In the granule precursor preparation step (S107), the first organic liquid is added to and mixed with the finely pulverized powder. The amount of the first organic liquid that functions as a granulating aid is desirably 15.0 wt% or less (excluding 0) with respect to the finely pulverized powder. Without the first organic liquid, it is difficult to give moisture necessary for granule preparation to the finely pulverized powder, and when it exceeds 15.0 wt%, the moisture becomes too much and man-hours are required for removing the first organic liquid. Will take. Therefore, the amount of the first organic liquid added is desirably 15.0 wt% or less (excluding 0). A preferable addition amount of the first organic liquid is 5 to 13 wt%, and a more preferable addition amount is 8 to 12 wt%.
By adding and mixing the first organic liquid to the finely pulverized powder, as shown in FIG. 2A, the alloy particles 1 constituting the finely pulverized powder are formed through the first organic liquid 2. An adhered granule precursor 100 is formed.

In the granule preparation step (S109), a second organic liquid having a saturated vapor pressure lower than that of the first organic liquid is added to and mixed with the granule precursor to form granules.
The amount of the second organic liquid that functions as a shape-retaining agent is desirably 4.0 wt% or less (excluding 0) with respect to the finely pulverized powder. Without the second organic liquid, the formation of granules by liquid cross-linking is not easy, while the addition of 4.0 wt% is sufficient to maintain the shape of the formed granules, and addition exceeding this is a factor that degrades magnetic properties. Become. Therefore, the amount of the second organic liquid added is preferably 4.0 wt% or less (however, not including 0). A preferable addition amount of the second organic liquid is 0.3 to 3.0 wt%, and a more preferable addition amount is 0.5 to 2.0 wt%.
Since the addition amount of the second organic liquid is small, the second organic liquid is diluted with the first organic liquid or other solvent in order to effectively attach the second organic liquid to the surface of the granule precursor. It is preferable to add them. When the second organic liquid is diluted with the first organic liquid and added, the total amount of the first organic liquid added in the granule precursor preparation step (S107) and the granule preparation step (S109) is 15. It is desirable to make it 0 wt% or less (however, not including 0).

  By adding and mixing the second organic liquid to the granule precursor, the surface of the granule precursor 100 is coated with the alloy particles 1 attached by the second organic liquid 3 as shown in FIG. Is done. At this time, a part of the second organic liquid 3 may penetrate into the granule precursor 100, but the first organic liquid 2 exists between the alloy particles 1 of the granule precursor 100, and the granule precursor Since the density of the body 100 is high, the second organic liquid 3 mainly adheres to the surface of the granule precursor 100, and constitutes a granule 200 in which a coating layer is formed by the alloy particles 1 adhered by the second organic liquid 3. Will do. When the second organic liquid 3 is diluted with the first organic liquid 2 and added, the alloy particles 1 of the coating layer adhere to the mixed liquid of the second organic liquid 3 and the first organic liquid 2. Take the form.

  FIG. 2 (b) shows that the surface of the granule precursor 100 of FIG. 2 (a) is coated with the alloy particles 1 attached by the second organic liquid 3, but the present invention is limited to this form. Not. By adding and mixing the second organic liquid 3 to the granule precursor 100, the granule precursor 100 may be split, or the granule precursors 100 may be bonded to each other. Even in such a case, the alloy particles 1 adhered by the second organic liquid 3 after the addition and mixing will coat the surface of the granule precursor 100 that has been split or bonded.

In order to produce granules by adding the first organic liquid and the second organic liquid to the finely pulverized powder at the above timing, it is preferable to use a rolling granulation method.
In order to produce granules using the rolling granulation method, a granulating apparatus (granule producing apparatus) 10 as shown in FIGS. 3 and 4 can be used.
As shown in FIGS. 3 and 4, the granulating apparatus 10 has a configuration in which a main rotor blade (main wing, rolling blade) 12 and an auxiliary rotor blade (auxiliary blade) 13 are provided in a chamber 11. ing.
The chamber 11 includes an openable / closable lid (not shown) and is hermetically sealed with the lid closed. Moreover, an organic liquid can be added to the chamber 11 by a two-fluid spray nozzle or a dropping nozzle (not shown).
The main rotor blade 12 is provided with a plurality of blade members 12b on a rotary shaft 12a, and is driven to rotate around the axis of the rotary shaft 12a by a drive motor (not shown). Similarly, the auxiliary rotor blade 13 is also provided with a plurality of blade members 13b on the rotating shaft 13a. From the drive motor (not shown) or the drive motor for rotating the main rotor blade 12, a gear, a timing belt, etc. The drive force transmitted through the drive force transmission mechanism is rotationally driven around the axis of the rotary shaft 13a.

Such a granulating apparatus 10 includes a vertical type as shown in FIG. 3 and a horizontal type as shown in FIG. 4 depending on the installation form of the main rotor blades 12.
In the vertical granulating apparatus (granule producing apparatus) 10V shown in FIG. 3, the main rotor blade 12 is provided such that the rotating shaft 12a has an axis in the substantially vertical direction in the chamber 11. The auxiliary rotor blade 13 is provided above the main rotor blade 12, and the rotating shaft 13 a is provided so as to have an axis in the horizontal direction in the chamber 11.
Further, in the horizontal granulation apparatus (granule production apparatus) 10H shown in FIG. 4, the main rotor blade 12 is provided such that the rotation shaft 12a has an axis line in a substantially horizontal direction in the chamber 11. The blade member 12b of the main rotor blade 12 extends along the peripheral wall 11a continuous in the circumferential direction of the chamber 11, and the auxiliary rotor blade 13 is provided so as to be located inward of these blade members 12b. Yes.

In such a granulating apparatus 10V, 10H, the finely pulverized powder and the organic liquid are caused to roll in the chamber 11 by the main rotor blade 12 to aggregate the finely pulverized powder through the organic liquid to form an aggregate. Then, the aggregates are loosened by the auxiliary rotor blades 13 to produce granules. More specifically, predetermined amounts of the finely pulverized powder and the first organic liquid obtained in the above-described steps are put into the chamber 11, and the main rotor blade 12 and the auxiliary rotor blade 13 are driven to rotate. Thus, the granule precursor 100 as shown in FIG. Thereafter, a predetermined amount of a second organic liquid diluted with a solvent (for example, the first organic liquid) is added, and the main rotor blade 12 and the auxiliary rotor blade 13 are rotationally driven to granulate, as shown in FIG. A granule 200 as shown is made.
In the granulating apparatuses 10V and 10H, the above granulation is performed for a predetermined time set in advance, whereby the finely pulverized powder is aggregated and granulated through the organic liquid in the chamber 11, and is shown in FIG. Granules 200 as shown in b) are produced.
Note that after the finely pulverized powder is introduced into the chamber 11, the inside of the chamber 11 is preferably replaced with an inert gas such as nitrogen in order to prevent oxidation of the finely pulverized powder. At this time, it is more preferable to rotate the main rotor blade 12 for a certain period of time to loosen the finely pulverized powder and to replace the inside of the chamber 11 with an inert gas while expelling the air present in the voids of the finely pulverized powder.

Further, the timing of charging the first organic liquid may be the same as that of the finely pulverized powder, but after the finely pulverized powder is charged as described above, the main rotor blade 12 is rotated for a predetermined time, and then the first organic liquid is discharged. It is preferable to input.
Further, even after the predetermined amount of the first organic liquid is added, the main rotor blade 12 is rotated for a certain period of time, and the finely pulverized powder is blended with the first organic liquid and granulated, as shown in FIG. After the granule precursor 100 is formed, it is preferable to add a predetermined amount of the second organic liquid diluted with a solvent (for example, the first organic liquid) and rotate the main rotor 12 again for a predetermined time. The addition amount of the second organic liquid is smaller than the addition amount of the first organic liquid as described above. Therefore, the mixing time after adding the second organic liquid (rotating time of the main rotor blade 12) is shorter than the mixing time when the granule precursor 100 is formed. Specifically, assuming that the former mixing time is 1, if the rotation conditions of the main rotor 12 are equivalent, the latter mixing time is 2 to 10, preferably 2 to 8, more preferably 3 to 5. And it is sufficient.

<Decompression drying step (first organic liquid removal step) (S111)>
In the present invention, the first organic liquid constituting the granules obtained as described above is removed. The first organic liquid has an extremely small influence on the magnetic properties as compared with a conventional binder such as PVA, and is easily removed in the sintering step (S115) described later.
The specific means for removing the first organic liquid is not particularly limited, but it is simple and effective to volatilize the granules by exposing them to a reduced pressure atmosphere. In the present invention, since the saturated vapor pressure of the second organic liquid is lower than that of the first organic liquid, it is possible to remove only the first organic liquid by adjusting the pressure of the reduced pressure atmosphere. The reduced-pressure atmosphere may be room temperature, but may be a heated reduced-pressure atmosphere. The first organic liquid can also be removed by heating at atmospheric pressure.

The pressure in the reduced-pressure atmosphere needs to be determined according to the saturated vapor pressure of the first organic liquid and the saturated vapor pressure of the second organic liquid, but if it is too high, the volatilization of the first organic liquid will not proceed sufficiently. On the other hand, when the pressure is too low, it is difficult to control the organic liquid remaining in the granules because the volatilization of the organic liquid is rapid. Therefore, in the present invention, it is preferable that the pressure of the reduced-pressure atmosphere is in the range of 10 ¹ to 10 ⁻² Torr. However, in the case of a heated reduced-pressure atmosphere, a range of 7 × 10 ² to 10 ⁻¹ Torr is sufficient.
If the heating temperature is too high, the alloy particles constituting the granule may be oxidized to cause deterioration of magnetic properties. Therefore, when heating, it is preferable that heating temperature shall be 40-80 degreeC.

  If the second organic liquid does not remain in the granules from which the first organic liquid has been removed as described above, the form of the granules cannot be maintained. On the other hand, if the amount of the second organic liquid remaining in the granules is too large, the effect of improving the magnetic properties cannot be enjoyed. Therefore, in the present invention, the amount of the second organic liquid remaining in the granules is preferably in the range of 4.0 wt% or less (excluding 0). The amount of the second organic liquid remaining in the more preferable granule is 0.3 to 3.0 wt%, and the amount of the first organic liquid remaining in the more preferable granule is 0.5 to 2.0 wt%. If this amount remains, it is possible to prevent adhesion to the mold during molding in a magnetic field, which is the next step.

  FIG. 2 (c) shows a conceptual diagram of the granule 300 after the first organic liquid is removed. This granule 300 is the final product that is subjected to molding. This granule 300 makes it possible to maintain the shape of the granule by the second organic liquid 3 continuously covering the periphery of the aggregate of the alloy particles 1.

<Molding process in magnetic field (S113)>
The granules obtained as described above are subjected to molding in a magnetic field.
Molding pressure in a magnetic field molding may be in the range of 0.3~3ton / cm ^2. The molding pressure may be constant from the start to the end of molding, may increase or decrease gradually, or may vary irregularly. The lower the molding pressure is, the better the orientation is. However, if the molding pressure is too low, the strength of the molded body is insufficient and handling problems occur. Therefore, the molding pressure is selected from the above range in consideration of this point. The final relative density of the molded body obtained by molding in a magnetic field is usually 50 to 60%.
The applied magnetic field may be about 12 to 20 kOe. By applying a magnetic field of this degree, the granules are broken down and decomposed into alloy particles. The applied magnetic field is not limited to a static magnetic field, and may be a pulsed magnetic field. A static magnetic field and a pulsed magnetic field can also be used in combination.

  Here, when forming in the magnetic field as described above, the residual amount of the organic liquid in a state where the formed body is formed is preferably 45 vol% or less (10 wt% or less). This is because the density of the molded body in the manufacturing process of the R-T-B system sintered magnet is 55 to 60%, and the remaining organic liquid can exist substantially only in the void portion of the molded body. When the residual amount of the organic liquid is more than about 45 vol%, the organic liquid is compressed by the molding pressure in the mold cavity at the time of molding, so that the molded body cannot be molded well. More specifically, since the liquid released from the molding pressure attempts to return to the original volume, the molded body may be cracked. Here, the residual amount is defined by the weight concentration (wt%) of the organic liquid present in the granules with respect to the weight of the powder forming the granules. To accurately measure the residual amount, only the organic liquid is volatilized from the granule, and its weight change is measured. At this time, in order to avoid the influence of the weight fluctuation due to the oxidation of the granule, the granule is put in a container, and this is put into a high vacuum or heated in a vacuum or an inert atmosphere to volatilize the organic liquid. It is preferable to measure the change in weight.

<Sintering step (S115)>
Next, the molded body is sintered in a vacuum or an inert gas atmosphere. Although it is necessary to adjust sintering temperature by various conditions, such as a composition, a grinding | pulverization method, the difference of an average particle diameter, and a particle size distribution, what is necessary is just to sinter at 1000-1200 degreeC for about 1 to 10 hours.

<Aging treatment process (S117)>
After sintering, the obtained sintered body can be subjected to an aging treatment. This process is an important process for controlling the coercive force. In the case where the aging treatment is performed in two stages, it is effective to hold for a predetermined time in the vicinity of 800 ° C. and 600 ° C. When the heat treatment in the vicinity of 800 ° C. is performed after sintering, the coercive force increases, which is particularly effective in the mixing method. In addition, since the coercive force is greatly increased by the heat treatment at around 600 ° C., the aging treatment at around 600 ° C. is preferably performed when the aging treatment is performed in one stage.

Of course, the present invention can be applied to granulation other than rolling granulation. For example, the present invention can be applied to rolling fluidized bed granulation. In a general rolling fluidized bed granulator, a nozzle for supplying water or a binder is installed at the upper part of the granulation tank, and a constant moisture is given by this nozzle to fluidize the raw material powder for granulation. I do. The organic liquid granule of the present invention can be produced by spraying the organic liquid from the nozzle at a predetermined timing. That is, the organic liquid granule of the present invention can be produced by adding the first organic liquid in the first half of spraying and adding the second organic liquid in the second half of spraying. The spray conditions for the first organic liquid and the second organic liquid may be the same as those in the above-described rolling granulation.
Moreover, you may apply this invention to the method of granulating by vibrating raw material powder on a sieve. In this case, first, an appropriate amount of the first organic liquid is added to and mixed with the raw material powder on the sieve, and the sieve is vibrated to produce a granule precursor having a size smaller than the intended granule. Next, an appropriate amount of the second organic liquid diluted with a solvent (for example, the first organic liquid) is added, and the mixed raw material powder is added to the granule precursor, and then on a sieve having a mesh size corresponding to the desired granule size. Vibrate. The raw material powder to be added later may be about 5 to 20 wt% with respect to the weight of the granule precursor.

Next, a rare earth sintered magnet to which the present invention is applied will be described.
The present invention is particularly preferably applied to an RTB-based sintered magnet. This RTB-based sintered magnet contains 25 to 37 wt% of a rare earth element (R). Here, R in the present invention has a concept including Y, and therefore 1 of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. It is selected from species or two or more species. If the amount of R is less than 25 wt%, the R ₂ T ₁₄ B phase, which is the main phase of the RTB-based sintered magnet, is not sufficiently generated, and α-Fe having soft magnetism is precipitated and retained. The magnetic force is significantly reduced. On the other hand, when R exceeds 37 wt%, the volume ratio of the R ₂ T ₁₄ B phase, which is the main phase, decreases, and the residual magnetic flux density decreases. Further, R reacts with oxygen, the amount of oxygen contained increases, and accordingly, the R-rich phase effective for the generation of coercive force decreases, leading to a decrease in coercive force. Therefore, the amount of R is set to 25 to 37 wt%. A preferable amount of R is 28 to 35 wt%, and a more preferable amount of R is 29 to 33 wt%.

Further, the RTB-based sintered magnet to which the present invention is applied contains 0.5 to 4.5 wt% of boron (B). When B is less than 0.5 wt%, a high coercive force cannot be obtained. On the other hand, when B exceeds 4.5 wt%, the residual magnetic flux density tends to decrease. Therefore, the upper limit of B is set to 4.5 wt%. A preferable amount of B is 0.5 to 1.5 wt%, and a more preferable amount of B is 0.8 to 1.2 wt%.
The RTB-based sintered magnet to which the present invention is applied contains Co of 2 wt% or less (excluding 0), desirably 0.1 to 1 wt%, more desirably 0.3 to 0.7 wt%. can do. Co forms the same phase as Fe, but is effective in improving the Curie temperature and improving the corrosion resistance of the grain boundary phase.

Moreover, the RTB-based sintered magnet to which the present invention is applied can contain one or two of Al and Cu in a range of 0.02 to 0.5 wt%. By including one or two of Al and Cu in this range, it is possible to increase the coercive force, increase the corrosion resistance, and improve the temperature characteristics of the obtained RTB-based sintered magnet. In the case of adding Al, a preferable amount of Al is 0.03 to 0.3 wt%, and a more preferable amount of Al is 0.05 to 0.25 wt%. In addition, in the case of adding Cu, the preferable amount of Cu is 0.15 wt% or less (not including 0), and the more preferable amount of Cu is 0.03 to 0.12 wt%.
The RTB-based sintered magnet to which the present invention is applied allows the inclusion of other elements. For example, elements such as Zr, Ti, Bi, Sn, Ga, Nb, Ta, Si, V, Ag, and Ge can be appropriately contained. On the other hand, it is preferable to reduce impurity elements such as oxygen, nitrogen, and carbon as much as possible. In particular, the amount of oxygen that impairs magnetic properties is preferably 2500 ppm or less, more preferably 2000 ppm or less. More preferably, it is 1500 ppm or less. This is because when the amount of oxygen is large, the rare-earth oxide phase, which is a nonmagnetic component, increases and the magnetic properties are deteriorated.

<First embodiment>
27.4 wt% Nd-4.6 wt% Dy-0.25 wt% Al-0.5 wt% Co-0.07 wt% Cu-1 wt% B-Bal. A raw material alloy having a composition of Fe was produced.
Next, after hydrogen was occluded in the raw material alloy at room temperature, hydrogen pulverization treatment was performed in which dehydrogenation was performed at 600 ° C. for 1 hour in an Ar atmosphere.
The alloy that has been subjected to the hydrogen pulverization treatment was mixed with 0.05 to 0.1% of a lubricant that contributes to improvement in pulverization and orientation during molding. The lubricant may be mixed for about 5 to 30 minutes using, for example, a Nauter mixer. Thereafter, a finely pulverized powder having an average particle diameter of 5 μm was obtained using a jet mill.

The above finely pulverized powder was put into a chamber of a granulator, and the inside of the chamber was filled with nitrogen to prevent oxidation. At this time, the horizontal type granulator (chamber volume is 4 liters) as shown in FIG. 4 was used.
Thereafter, the main rotor blade of the granulator was rotated at a predetermined speed to stir the finely pulverized powder. Further, the auxiliary rotor blade was rotated. As the organic liquid, ethanol was used as the first organic liquid, terpineol was used as the second organic liquid, and sprayed into the chamber for a predetermined time (spray time) using a nozzle. The spraying timing was as follows.
<Examples 1-4>
Spraying was performed in two stages. Only ethanol was sprayed in the first half of spraying, and a mixed solution of ethanol and terpineol was sprayed in the second half of spraying. The spray amount and spray time are shown in Table 2.
<Comparative Example 1>
Spraying was performed in one stage, and a mixed solution of ethanol and terpineol was sprayed for 180 seconds. The spray amount of ethanol was 9.0 wt% with respect to the finely pulverized powder, and the spray amount of terpineol was 1.0 wt% with respect to the finely pulverized powder.
<Comparative example 2>
The finely pulverized powder was sprayed with an organic liquid under the same conditions as in Comparative Example 1 except that the spray amount of terpineol was 2.0 wt% and the spray amount of ethanol was 8.0 wt%.

  Even after all the organic liquid was added, the main rotor blade and the auxiliary rotor blade were kept rotating for a certain period of time in order to blend the organic liquid and the finely pulverized powder. Thereafter, the main rotor blade and the auxiliary rotor blade were stopped, and the granules were taken out from the chamber. Subsequently, the first organic liquid contained in the removed granules, that is, ethanol was evaporated. In order to prevent oxidation of the finely pulverized powder, a vacuum chamber was used for evaporation, and evaporation was performed in a reduced pressure atmosphere. In addition, when the residual amounts of terpineol and ethanol after exposure to a reduced pressure atmosphere were confirmed, the added amount of terpineol remained almost as it was, and most of ethanol was volatilized.

The angle of repose of the granules after volatilizing the organic liquid was measured based on the following method. The results are also shown in Table 3. Table 3 also shows the angle of repose of the finely pulverized powder before granulation.
Angle of repose measurement: Granules were dropped little by little through a sieve from a certain height on a 60 mmφ circular table. The granule supply was stopped just before the granule pile collapsed. The bottom angle of the pile of granules formed on the round table was measured. The circular table was rotated by 120 °, the angles were measured at a total of three locations, and the average was taken as the angle of repose.

The resulting granules were then molded in a magnetic field. Specifically, molding was performed at a pressure of 1.4 ton / cm ^{2 in} a magnetic field of 15 kOe to obtain a molded body.
The obtained molded body was heated to 1080 ° C. in vacuum and Ar atmosphere and held for 4 hours for sintering. Next, the obtained sintered body was subjected to a two-stage aging treatment of 800 ° C. × 1 hour and 560 ° C. × 1 hour (both in an Ar atmosphere).

  Table 3 shows the results of measuring the magnetic properties of the obtained sintered magnet. Table 3 shows a sintered magnet obtained by subjecting the finely pulverized powder to molding, sintering, and aging treatment in the same manner as above without granulating the powder, and a slurry containing 0.5 wt% of PVA as a binder. The magnetic properties of sintered magnets obtained by subjecting granules obtained by spray drying to magnetic field molding, sintering and aging treatment in the same manner as above are also shown.

As shown in Table 3, the angle of repose can be set to 50 ° or less in granules granulated by a rolling method using an organic liquid. Thus, in the granule granulated by the rolling method using the organic liquid, the reflowability can be improved while the angle of repose of the finely pulverized powder is 62 °.
The angle of repose also serves as a guideline for the strength of the granule. The smaller the angle of repose, the less likely the granules are broken. Here, comparing the second organic liquid functioning as a shape-retaining agent, that is, Comparative Example 1 in which the amount of terpineol added is 1.0 wt% and Example 4 in which the amount of terpineol added is 0.5 wt%. In Example 4, although the amount of terpineol added was smaller than that in Comparative Example 1, an angle of repose smaller than that in Comparative Example 1 was obtained. This is because the granule of Example 4 has a higher talpineol concentration in the vicinity of the granule surface and thus has a higher shape retention and prevents generation of fine powder from the granule surface.
Thus, according to the present invention, it is possible to obtain a granule with high strength with a smaller amount of the second organic liquid added. In Examples 1 and 2, the angle of repose is smaller than that of Comparative Example 1 in which the amount of terpineol added is the same. This is due to the following reason. In other words, when the angle of repose is measured, the granule is dropped, so that the vicinity of the granule surface is peeled off and fine powder is generated, and the angle of repose increases. Is high, and the shape retention force by terpineol is effectively exhibited, so that the generation of fine powder can be suppressed and the angle of repose becomes small.

Further, regarding the magnetic characteristics, the residual magnetic flux density (Br) is higher in Examples 1 and 2 than in Comparative Example 1 in which the amount of terpineol as the second organic liquid is 1.0 wt%. This is because the ratio of the alloy particles in which the granules of Examples 1 and 2 are less likely to be oriented by the second organic liquid is reduced.
Moreover, it can be said that residual magnetic flux density (Br) becomes high, so that there is little addition amount of a 2nd organic liquid by the comparison of Examples 1-4.

  As described above, rather than spraying and adding a mixed solution of ethanol and terpineol in one step, ethanol is first sprayed by the method recommended by the present invention, and then terpineol is sprayed and added. It was confirmed that the angle of repose of the granule can be reduced and it is advantageous in obtaining high residual magnetic flux density (Br) and (BH) max. In particular, according to the present invention, a granule having a small angle of repose can be produced even if the amount of the second organic liquid added is small, which is effective for improving the residual magnetic flux density (Br). When granules are produced from an organic liquid, the coercive force (HcJ) is higher than that of a sintered magnet obtained by molding a finely pulverized powder in a magnetic field, and the method recommended by the present invention is the coercive force (HcJ). ).

  In particular, when a sintered magnet is produced from granules using a binder such as PVA, the magnetic properties are significantly reduced unless the binder is removed (see the magnetic properties of the sample name “spray dry” in Table 3), and the manufacturing process. The effect of the present invention that can obtain high magnetic characteristics while simplifying the above is remarkable.

In the above embodiment, ethanol is used as the first organic liquid and terpineol is used as the second organic liquid. However, the present invention is not limited to this combination, and other organic liquids can be used. Further, water may be used instead of the first organic liquid.
In addition to this, as long as it does not depart from the gist of the present invention, the configuration described in the above embodiment can be selected or changed to another configuration as appropriate.

It is a flowchart which shows the manufacturing process of the rare earth sintered magnet in this Embodiment. (A) is a diagram schematically showing a granule precursor obtained after adding and mixing the first organic liquid to the finely pulverized powder, and (b) after adding and mixing the second organic liquid to the granule precursor. The figure which shows the obtained granule typically, (c) is a figure which shows the granule after removing the 2nd organic liquid typically. It is a figure which shows the structure of a vertical rolling type granulator, (a) is a front sectional view, (b) is a top view, (c) is a right view of (b). It is a figure which shows the structure of a horizontal type | mold rolling granulator, (a) is a front sectional view, (b) is a right view of (a).

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Alloy particle, 2 ... 1st organic liquid, 3 ... 2nd organic liquid, 10, 10H, 10V ... Granulator (granule preparation apparatus), 11 ... Chamber, 12 ... Main rotor blade (main wing, rolling) Wing), 13 ... auxiliary rotor blade (auxiliary wing), 100 ... granule precursor, 200 ... granule, 300 ... granule

Claims (11)

Adding a first organic liquid to a raw material powder of a predetermined composition and mixing to form a granule precursor;
A step of adding a second organic liquid having a saturated vapor pressure lower than that of the first organic liquid to the granule precursor, and mixing them into granules;
A method for producing granules comprising:   The method for producing a granule according to claim 1, wherein the raw material powder further adheres to the surface of the granule precursor to form the granule by adding and mixing the second organic liquid.   The method for producing a granule according to claim 1 or 2, wherein the first organic liquid is mainly present inside the granule and the second organic liquid is mainly present on the surface of the granule. .   The method for producing granules according to any one of claims 1 to 3, wherein the second organic liquid is added as a mixed liquid with the first organic liquid.   The method for producing a granule according to any one of claims 1 to 4, further comprising a step of exposing the granule to a reduced-pressure atmosphere.   The method for producing a granule according to claim 5, wherein the shape of the granule is maintained by the second organic liquid.   15.0 wt% or less (excluding 0) of the first organic liquid and 4.0 wt% or less (excluding 0) of the second organic liquid are added to the raw material powder. The manufacturing method of the granule in any one of Claims 1-6 characterized by the above-mentioned.   The method for producing granules according to any one of claims 1 to 7, wherein the granule precursor and the granules are produced by a rolling granulation method or a rolling fluidized bed granulation method. The raw material powder is R ₂ T ₁₄ B phase (R is one or more elements selected from rare earth elements, T is one or two elements selected from transition metal elements including Fe, Fe and Co) The method for producing a granule according to any one of claims 1 to 8, wherein the granule has a composition containing the above element). Adding a first organic liquid to alloy particles of a predetermined composition and mixing to form a granule precursor;
A step of adding a second organic liquid having a saturated vapor pressure lower than that of the first organic liquid to the granule precursor, and mixing them into granules;
A step of removing the first organic liquid from the granules;
Placing the granules from which the first organic liquid has been removed into a mold cavity;
Applying a magnetic field to the granules, and obtaining a molded body by pressure molding;
Sintering the molded body;
A method for producing a rare earth sintered magnet.   The method for producing a rare earth sintered magnet according to claim 10, wherein the amount of the first organic liquid added is larger than the amount of the second organic liquid added.

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