JP7252768B2 - Method for manufacturing rare earth bonded magnet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a bonded rare earth magnet having excellent magnetic properties and strength.

Rare earth permanent magnets have high magnetic properties and are used in various fields today. Rare earth permanent magnets are broadly classified into sintered magnets and bonded magnets, depending on the raw material powder used and manufacturing method. In addition, since the resin as an insulator exists between the magnet powders, it has the advantage of high electrical resistance. However, since bonded magnets have a structure in which magnet powder is bound by a resin binder, their magnet strength is inevitably lower than that of rare earth sintered magnets, making it difficult to use them in applications requiring high magnet strength. .

In International Publication No. 2012/118001 (Patent Document 1), a compound for a bonded magnet, which is produced by setting the amount of resin and the amount of organic solvent added during kneading within a certain range, is strongly compressed to obtain a high molded body density. Also disclosed are methods of making bonded magnets with high magnetic properties.

Japanese Patent Application Laid-Open No. 2017-34097 (Patent Document 2) discloses a molding resin that can be used for normal compression bond magnets and the strongly compression bond magnet described in Patent Document 1, and has excellent mechanical strength at high temperatures. .

On the other hand, in Japanese Patent Laid-Open No. 4-27102 (Patent Document 3), a rare earth magnet powder is molded with a binder 1 containing an epoxy resin, a curing agent, and a curing accelerator that is solid at room temperature, and the binder 1 is heat-cured. A method of manufacturing a bonded magnet is disclosed in which a binder 2 containing an epoxy resin and a curing agent (imidazole compound) is vacuum-impregnated into the formed body, and the binder 2 is thermally cured.

WO 2012/118001 JP 2017-34097 A JP-A-4-27102

However, the magnetic strength of the bonded magnet described in Patent Document 1 remains practical, and it is even more difficult to adopt the bonded magnet for applications requiring high magnetic strength than the bonded magnet with a normal molded body density. Also, by adopting the resin described in Patent Document 2, although the mechanical strength is improved to some extent, it never has sufficient strength for applications such as high-speed rotating motors that require higher strength. It can not be said.

Furthermore, according to the method described in Patent Document 3, after impregnating the voids present in the molded article with an epoxy resin having an even higher strength to a molded article that has been molded and thermoset with an epoxy resin that has excellent strength, Since the magnet is cured by heat, the voids are filled with the epoxy resin, and a significant improvement in the strength of the magnet can be expected. However, the impregnating resin composition (binder 2) contains a curing agent (imidazole compound), and since it gradually begins to harden even at room temperature in the resin tank of the vacuum impregnation device, it has a pot life. It is necessary to frequently replace the impregnating resin and clean the vacuum impregnating device, resulting in poor production efficiency.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing a bonded rare earth magnet having high magnetic strength with excellent production efficiency.

As a result of intensive studies in view of the above object, the inventors of the present invention have found that, in the manufacturing process of bonded rare earth magnets, for example, an epoxy resin composition for molding used for molding bonded rare earth magnets contains an excessive amount of curing agent. After making a bonded rare earth magnet with an excess curing agent remaining, impregnating it with a resin composition that does not contain a curing agent, and curing with the remaining curing agent, a high magnet is obtained. The present inventors have found that a rare earth bonded magnet having strength can be produced with excellent production efficiency, and have arrived at the present invention.

That is, the method for producing a bonded rare earth magnet of the present invention includes:
A bond magnet molded body obtained by compressing and heat-treating a kneaded mixture of quenched rare earth alloy magnet powder, an epoxy resin and a curing agent is impregnated with an epoxy resin curable with the curing agent to form an impregnated molded body. an epoxy resin impregnation step to obtain;
a heat treatment step of heat-treating the impregnated molded body to obtain a bonded rare earth magnet,
In the bonded magnet compact, the curing agent remains,
The bonded magnet molded body and the impregnated molded body are not impregnated with a curing agent,
In the heat treatment step, the epoxy resin impregnated into the bonded magnet molded body in the epoxy resin impregnation step is cured with the curing agent remaining in the bonded magnet molded body.

Preferably, the impregnation is vacuum pressure impregnation.

According to the present invention, a bonded rare earth magnet having high magnetic strength can be produced with excellent production efficiency.

1 is a flow chart showing a method for producing a bonded rare earth magnet of the present invention; FIG.

In the method of the present invention, for example, a bonded magnet molded body molded and cured using a molding resin composition containing an excess curing agent is impregnated with an epoxy resin (impregnation resin composition) containing no curing agent. This method is characterized in that the impregnated epoxy resin is cured by the curing agent remaining in the bonded magnet compact by heating and heat-treating, and a bonded magnet with high magnetic strength can be obtained, and the curing agent is removed. The resin composition for impregnation that does not contain it has a long pot life and a long cycle of replacing the resin and cleaning the resin tank, so that the production efficiency is good.

Hereinafter, the method for producing a bonded rare earth magnet of the present invention will be described in detail with reference to FIG.

(1) Step S1 of preparing quenched rare earth alloy powder
First, a quenched rare earth alloy powder is prepared. There is no particular limitation on the quenched rare earth alloy powder that can be used in the present invention. For example, it is produced by pulverizing a quenched alloy ribbon prepared by quenching a melt of an alloy having a predetermined composition by a roll quenching method such as a melt spinning method or a strip casting method. Suitable rare earth-based quenched alloy magnet powders include, for example, Nd--Fe--B-based quenched alloy magnet powders described in US Pat. No. 4,802,931.

(2) Step S2 of preparing a resin solution for molding
Next, a molding resin composition containing an epoxy resin (molding resin) and a curing agent is dissolved in an organic solvent or the like to prepare a molding resin solution. The resin composition for molding (combination of epoxy resin and curing agent) that can be used is not particularly limited as long as the contained curing agent is a combination that can also cure the resin for impregnation (epoxy resin) described below. The resin composition for molding may contain two or more types of epoxy resins, curing accelerators, and the like. Examples of such molding resin compositions include the resin composition described in Patent Document 2, Epiclon 4050 manufactured by DIC Corporation, and JER7007P manufactured by Mitsubishi Chemical Corporation.

The blending ratio of the epoxy resin and the curing agent is set so that the curing agent contains an amount capable of completely curing both the epoxy resin for the molding resin and the epoxy resin for the impregnation resin. That is, the resin composition for molding contains an excessive amount of curing agent with respect to the amount necessary to cure the epoxy resin, and is blended so that the curing agent remains in the bonded magnet molded body obtained by the heat treatment step S5 described later. . Normally, when blending an epoxy resin and a curing agent, the blending ratio is set so that the amount of the curing agent exceeds the theoretical reaction amount to some extent so that the epoxy resin can be completely cured, which contributes to the reaction. The uncured hardener remains in the bonded magnet. Since the amount of the impregnating resin to be impregnated is very small, the impregnating resin can be sufficiently cured with the curing agent remaining after curing a typical molding resin composition.

The organic solvent is preferably a volatile organic solvent that becomes gas at room temperature. Organic solvents that can be suitably used include, for example, acetone, methyl ethyl ketone, methyl isobutyl ketone, benzene, toluene and xylene. Ketones such as methyl ethyl ketone are most preferable from the viewpoint of safety and handling.

The molding resin solution may be prepared by dissolving the molding resin composition containing the epoxy resin and the curing agent in an organic solvent as described above. or by mixing epoxy resin with a curing agent dissolved in an organic solvent. Furthermore, the epoxy resin and the curing agent are not limited to solvent-soluble resins, and water-based or solvent-free resins can also be used.

(3) Step S3 of preparing a rare earth bonded magnet compound
Subsequently, the quenched rare earth alloy powder prepared in step S1 and the molding resin solution prepared in step S2 are kneaded, and the organic solvent is volatilized to produce a rare earth bonded magnet compound. The molding resin solution used for kneading contains 0.5% by mass or more and 5.0% by mass or less of an epoxy resin and 3% by mass or more and 7% by mass or less of an organic solvent when the rare earth alloy powder to be kneaded is taken as 100% by mass. It preferably contains and If the content of the organic solvent is less than 3% by mass, the organic solvent may volatilize during kneading before the resin spreads over the surface of the magnet powder, making uniform coating impossible. In addition, if the proportion of the organic solvent exceeds 7% by mass, it takes a long time for the organic solvent to volatilize, which is undesirable from the standpoint of productivity. By kneading in such a ratio and volatilizing the organic solvent during kneading, a compound in which the surfaces of individual powder particles are thinly and uniformly coated with resin can be produced. In a preferred embodiment, the resin in the compound covers the quenched rare earth alloy magnet powder particles at a coverage rate of 90% or more, and the thickness of the resin is 0.1 μm or more and 1 μm or less. In such a compound, the magnet powder particles are thinly and uniformly coated with a high coverage rate, so even if the magnet powder particles are in contact with each other, it is difficult for them to conduct, and finally a bonded magnet having a high electrical resistance can be obtained. In order to reduce damage to the mold during subsequent compression molding, it is desirable to add or mix a lubricant such as calcium stearate to the compound.

(4) Step S4 of producing a compression molded body
Next, the compound for bonded rare earth magnets obtained in step S3 is compressed to produce a compression molded body. In this compression molding step, it is preferable to compress the rare earth bonded magnet compound so that the density of the compression molded body is in the range of 70% to 90% of the true density of the quenched rare earth alloy powder. In order to obtain such a compression molded body, the molding pressure is preferably in the range of 80 MPa to 2000 MPa, more preferably in the range of 200 MPa to 1000 MPa. If the molding pressure is less than 80 MPa, it is difficult to obtain a high magnet density. Moreover, if it exceeds 2000 MPa, the load on the mold becomes too large, which is not preferable. Examples of the press apparatus used for compression molding include a mechanical cold press machine and an ultra-high pressure powder press apparatus described in Patent Document 1. The method of the present invention is not limited to the strongly compressed high-density magnet described in Patent Document 1, but can also be applied to general-purpose compressed bond magnets. is suitably adopted for applications requiring

When the present invention is applied to general-purpose compressed bond magnets, the materials for rare earth-based bonded magnets, other manufacturing conditions, and impregnation conditions may be set in accordance with general-purpose compressed bond magnets.

(5) Step S5 of heat-treating the compression molded body to produce a bonded magnet molded body
By heat-treating the compression-molded body thus compression-molded, a bonded magnet molded body obtained by curing the molding resin is obtained. The heat treatment conditions may conform to the curing conditions of the resin used, but the heat treatment temperature is preferably 150° C. or higher and 300° C. or lower, more preferably 175° C. or higher and 250° C. or lower. When Nd-Fe-B-based quenched alloy powder is used as the rare-earth-based quenched alloy powder, it is particularly susceptible to oxidation. A non-oxidizing atmosphere such as an inert gas atmosphere such as Ar gas or nitrogen gas is preferred. Similarly, from the viewpoint of preventing oxidation, the heat treatment time (holding time at the heat treatment temperature) is preferably 1 minute or more and 4 hours or less, more preferably 5 minutes or more and 1 hour or less.

As described above, since the resin composition for molding contains an excessive amount of curing agent for curing the epoxy resin, the curing agent remains in the bond magnet molded body obtained by heat-treating the compression molded body.

(6) Step S6 of impregnating the bonded magnet molded body with an impregnating resin (epoxy resin) to produce an impregnated molded body.
Next, a resin composition for impregnation containing an epoxy resin is dissolved in an organic solvent or the like to prepare a resin solution for impregnation. This impregnating resin composition does not contain a curing agent. The impregnating resin that can be used is not particularly limited as long as it is hard to cure by itself and can be cured by a curing agent contained in the molding resin. For example, an epoxy resin can be used. Types of epoxy resins include glycidyl ether type, glycidyl ester type, glycidyl amine type, and alicyclic type. The impregnating resin preferably contains an epoxy resin, and may contain a resin other than the epoxy resin. The impregnating resin may be solid at room temperature as long as it can be dissolved in an organic solvent to form a solution. The impregnating resin solution may be further diluted with water or a solvent.

Subsequently, the bonded magnet compact obtained in step S5 is impregnated with an impregnating resin solution to produce an impregnated compact. As the impregnation method, a vacuum pressurization method, a vacuum method, a pressurization method, an immersion method, a centrifugal method, or the like can be adopted. A vacuum pressure impregnation method is particularly preferred. When the impregnation treatment is performed by these methods, it is preferable to heat the impregnating resin solution and the bonded magnet compact to perform the impregnation treatment. Heating facilitates the impregnation of the resin solution for impregnation into the bonded magnet compact.

(7) Step S7 of heat-treating the impregnated compact to produce a bonded rare earth magnet.
Subsequently, the impregnated compact produced in step S6 is heat-treated to produce a bonded rare earth magnet. Although the resin composition for impregnation does not contain a curing agent, the bonded magnet compact obtained in step S5 contains a curing agent. It is hardened by heat treatment with an agent.

When a resin composition for impregnation containing a curing agent is used as in Patent Document 3, curing of the resin for impregnation begins gradually even at room temperature. Therefore, the resin composition for impregnation has a pot life, and if the pot life is short, it is necessary to frequently replace the resin and clean the resin tank. Resin takes a long time to harden and has a high hardening temperature, resulting in poor production efficiency and possibly deteriorating magnetic properties. Thus, when using an impregnating resin composition containing a curing agent, it is difficult to achieve both pot life, production efficiency, and magnetic property deterioration rate.

On the other hand, in the method of the present invention, an excess curing agent is added to the molding resin so that the curing agent remains in the bond magnet even after the molding resin is cured. When impregnated with and heat-treated, the impregnating resin can be cured by the remaining curing agent, so that pot life, production efficiency, deterioration rate of magnetic properties, and magnet strength can all be solved.

The heat treatment conditions may conform to the curing conditions of the impregnating resin used. When Nd-Fe-B-based quenched alloy powder is used as the rare-earth-based quenched alloy powder, it is particularly susceptible to oxidation. preferably done.

The bonded magnet obtained through the above steps has a magnetic strength that is 1.2 times or more higher than that of the bonded magnet compact containing only the molding resin. In addition, since the impregnating resin used above does not contain a curing agent, it has a much longer pot life than the impregnating resin containing a curing agent, and the cycle of replacing the resin in the vacuum impregnation device and cleaning the resin tank is long. Therefore, production efficiency is high. Further, when the heat treatment for curing the impregnating resin is performed in a non-oxidizing atmosphere, the rate of deterioration of the magnetic properties of the bonded magnet compact is within 2.0%.

A step of processing the bonded magnet compact may be added between step S5 and step S6. That is, the bonded magnet compact may be processed, and the processed bonded magnet compact may be impregnated with the impregnating resin solution prepared in step S6. Further, a processing step may be added after step S7. That is, the bonded magnet produced in step S7 may be processed into a finished product. Various surface treatments may be performed after step S7. In this way, steps S1 to S7 are in the order described above, but other steps may be added after each step.

In the above embodiment, steps S1 (the step of preparing the rapidly solidified rare earth alloy powder) to S7 (the step of heat-treating the impregnated compact to produce a bonded rare earth magnet) have been described. However, the invention is not limited to the above embodiments.

For example, a bonded magnet compact obtained by compressing and heat-treating a kneaded product obtained by kneading a quenched rare earth alloy magnet powder, an epoxy resin and a curing agent is obtained, and impregnated with an epoxy resin to produce an impregnated compact. (epoxy resin impregnation step) and heat-treating the impregnated compact (heat-treatment step) to obtain a bonded rare earth magnet.

Example 1
As the rare earth-based quenched alloy powder, a Nd--Fe--B-based quenched alloy powder (MQP-13-9 manufactured by Magnequench Co., Ltd.) obtained by a melt spinning method was prepared. As the molding resin, DIC's anhydrous bisphenol A type epoxy resin Epiclon 4050, Mitsubishi Chemical's bisphenol F type epoxy resin JER4007P, and Mitsubishi Chemical's hardener DICY7 (dicyandiamide) are mixed at a mixing ratio of 45:50:5 (mass ratio). and dissolved in methyl ethyl ketone (MEK) to prepare a molding resin solution. The amount of MEK was set to 4.5% by mass based on the mass of the quenched alloy powder to be kneaded.

This molding resin solution and the Nd-Fe-B system quenched alloy powder were mixed so that the amount of resin excluding MEK was 2.0% by mass based on the mass of the quenched alloy powder, and MEK in the solution was completely volatilized. kneaded until After that, 0.07% by mass of calcium stearate was mixed with the mass of the quenched alloy powder as a reference to prepare a compound for a rare earth bonded magnet.

A compression-molded body was produced by subjecting the compound for a bonded rare earth magnet thus obtained to compression molding under a molding pressure of 1000 MPa. This compact was heat-treated in a vacuum atmosphere at a temperature of 180° C. for 2 hours to produce a bonded magnet compact having an outer diameter of 15.5 mm, an inner diameter of 9.7 mm and a height of 2.6 mm. The radial crushing strength of this bonded magnet compact was 184.8 N (average value of 5 pieces), and the magnetic force was 240.4 mT for the N pole and 243.6 mT for the S pole (average value for each of 5 pieces).

The radial crushing strength in this embodiment is the strength when a pressure is applied from the radially central portion of the bonded magnet compact or the bonded magnet using a radial crushing strength tester, and they are destroyed. The magnetic force was obtained by magnetizing the bonded magnet compact or the bonded magnet, and using a magnet analyzer manufactured by Nippon Electromagnetic Sokki Co., Ltd., to measure the central portion in the magnet thickness direction of each of the N and S poles. (All 5 averages.)

Subsequently, a resin solution for impregnation (epoxy resin F) was prepared. The blending ratio of the resin solution for impregnation was bisphenol A type epoxy resin:polypropylene glycol diglydisyl ether=1:1 (mass ratio).

A bond magnet compact was impregnated with this resin solution for impregnation by a vacuum pressure impregnation method to produce an impregnated compact. Subsequently, this impregnated molded body was heat-treated under the three conditions shown in Table 1 to cure the impregnating resin, and sample Nos. 1 to 3 of bonded rare earth magnets were produced. The radial crushing strength and magnetic force of these bonded magnets were measured, and the strength ratio and magnetic force reduction rate with respect to the bonded magnet compact were investigated. Table 2 shows the results.

注(1)：ボンド磁石成形体の圧環強度を100としたときの相対値

Note (1): Relative value when the radial crushing strength of the bonded magnet compact is 100

From Table 2, the radial crushing strength of these bonded magnets was improved by 1.2 times or more as compared with the molded bonded magnet. Moreover, the magnetic force reduction rate was within 2% for both the N pole and the S pole. It has been confirmed that the resin solution for impregnation (epoxy resin F) does not contain a curing agent and does not cure by itself. However, in this example, the epoxy resin F with which the bonded magnet compact was impregnated was hardened with sufficient hardness, and the radial crushing strength was improved by 1.2 times or more compared to the bonded magnet compact before impregnation. It is considered that F was cured by the curing agent remaining in the bonded magnet compact.

Example 2
As a comparative resin, an impregnating resin solution (epoxy resin C) containing a curing agent was prepared. The blending ratio of the resin solution for impregnation is bisphenol A type epoxy resin: polypropylene glycol diglycidyl ether: 3 or 4-methyl-1,2,3,6-tetrahydrophthalic anhydride = 1:1:2 (mass ratio). there were.

A resin solution for impregnation using epoxy resin F and a resin solution for impregnation using epoxy resin C were prepared, and pot lives were compared by comparing changes in viscosity over time. The viscosity was measured with a BH type viscometer at 23°C.

Epoxy resin F had a viscosity of 500 mP s even after 30 days, and was ready for impregnation. Epoxy resin C had a viscosity of 10,000 mP s after 5 days, making it difficult to use for impregnation. Became.

According to the present invention, it is possible to obtain a method for manufacturing a bonded rare earth magnet having high magnetic strength with excellent production efficiency.

Claims (2)

A bond magnet molded body obtained by compressing and heat-treating a kneaded mixture of quenched rare earth alloy magnet powder, an epoxy resin and a curing agent is impregnated with an epoxy resin curable with the curing agent to form an impregnated molded body. an epoxy resin impregnation step to obtain;
a heat treatment step of heat-treating the impregnated molded body to obtain a bonded rare earth magnet,
In the bonded magnet compact, the curing agent remains,
The bonded magnet molded body and the impregnated molded body are not impregnated with a curing agent,
In the heat treatment step, the epoxy resin impregnated into the bonded magnet compact in the epoxy resin impregnation step is cured with the curing agent remaining in the bonded magnet compact. In the method for producing a bonded rare earth magnet according to claim 1,
A method for producing a bonded rare earth magnet, wherein the impregnation is vacuum pressure impregnation.

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