JP4276098B2 - Rare earth magnet and manufacturing method thereof - Google Patents

Description

  The present invention relates to a rare earth magnet and a method for producing the same, and more particularly to a rare earth magnet having a protective layer on the surface and a method for producing the same.

  Conventionally, rare earth magnets are known as high performance permanent magnets. These are not only used for household appliances such as conventional air conditioners and refrigerators, but are also being applied to drive motors for industrial machines, robots, fuel cell vehicles, hybrid cars, etc. It is expected that energy saving can be realized. Among such rare earth magnets, R—Fe—B (R is a rare earth element) type magnet has attracted attention because it has particularly high magnetic properties. As such R—Fe—B rare earth magnets, for example, those described in Patent Document 1 and Patent Document 2 below are known.

  These R—Fe—B rare earth magnets are high-performance magnets exhibiting a high energy product exceeding 25 MGOe. However, since it contains rare earth elements and iron as the main components of the magnet, it is very easily oxidized and has low temperature resistance. For this reason, these magnets tend to have low corrosion resistance, and it has been difficult to avoid deterioration of magnetic characteristics over time due to long-term use.

  In recent years, attempts have been made to form a protective layer on the surface of a magnet body for the purpose of improving the corrosion resistance of such R—Fe—B rare earth magnets. For example, Patent Document 3 listed below describes a rare earth magnet in which an oxidation-resistant metal film is formed on the surface of a magnet body by plating, thereby improving the oxidation resistance of the magnet.

Patent Document 4 listed below describes a rare earth magnet in which a resin film is formed on the surface of a magnet body, thereby improving the oxidation resistance of the magnet. Furthermore, the following Patent Document 5 describes a rare earth magnet in which a dense coating made of a metal oxide is formed on the surface of a magnet body by a sol-gel method, thereby improving the corrosion resistance and alkali resistance of the magnet. Yes.
JP 59-46008 A JP-A-60-9852 JP-A-60-54406 JP-A-60-63901 JP 2001-76914 A

  Since the rare earth magnet according to the above prior art has various protective layers on the surface of the magnet body, it has higher corrosion resistance than when the magnet body is used alone. However, these rare earth magnets have insufficient corrosion resistance due to insufficient properties of the protective layer itself, and are still practical for applications where severe conditions such as high temperature conditions are imposed. It was scarce.

  For example, the metal film formed by plating described in Patent Document 3 tends to have a pinhole. Thus, if even a slight pinhole or the like is present in the protective layer, the corrosion resistance of the entire magnet is remarkably reduced, for example, the magnet body is corroded by a salt spray test.

  Further, since the protective layer in the rare earth magnet described in Patent Document 4 is made of resin, the moisture permeability is not perfect, and therefore, external moisture may slightly permeate the protective layer. It was. When external moisture permeates the protective layer in this way, the moisture comes into contact with the magnet body and corrodes the contact area, or moisture enters between the protective layer and the magnet body to peel off the protective layer. May cause inconveniences such as promoting Furthermore, the protective layer composed of the resin in this way often has insufficient heat resistance, and thus it has been difficult to use a magnet having such a protective layer under high temperature conditions.

  Furthermore, in the rare earth magnet described in Patent Document 5, the sol solution for film formation is heated at the time of forming the protective layer, thereby causing solvent evaporation, polymerization or thermal decomposition reaction. In the process, the applied sol liquid tends to cause large volume shrinkage. In this case, the protective layer has a stress due to the volume shrinkage, and cracks are likely to be generated in the protective layer. This tendency is particularly great when a thick protective layer is to be formed or when the magnet surface has irregularities. Thus, when a crack arises in a protective layer, the corrosion resistance of a rare earth magnet will become extremely low like the case of the pinhole mentioned above.

  The present invention has been made in view of the circumstances of these prior arts, and provides a rare earth magnet capable of exhibiting high corrosion resistance by providing a protective layer having excellent characteristics on the surface, and a method for producing the same. For the purpose.

  The inventors of the present invention have made extensive studies to achieve the above object, and when a so-called organic-inorganic hybrid material using a combination of an organic material and an inorganic material is applied to a protective layer for a magnet, It is possible to form a protective layer having the above characteristics at the same time, and such a protective layer has superior characteristics as compared to a protective layer formed by using an organic material or an inorganic material alone as in the above-described conventional technology. I found that I have.

  Further, when a further detailed study was made on such a protective layer, it was found that the organic layer and the inorganic material were simply mixed with each other as in the conventionally known organic-inorganic hybrid material. It was confirmed that phase separation between components and inorganic components may occur. For this reason, it has been found that a protective layer made of such a mixture cannot exhibit uniform characteristics over the entire protective layer.

  Based on these findings, the present inventors applied a material containing a compound having a predetermined interaction between both components as an organic-inorganic hybrid material combining an organic component and an inorganic component to the protective layer. The present inventors have found that a rare earth magnet having extremely excellent corrosion resistance can be obtained.

That is, the rare earth magnet of the present invention comprises a magnet body made of a sintered body containing a rare earth element and a protective layer formed on the surface of the magnet body. A compound and an inorganic polymer compound, one of the organic polymer compound and the inorganic polymer compound has a proton-donating functional group, and the other has a proton-accepting functional group. In addition, the protective layer is characterized in that a hydrogen bond between the organic polymer compound and the inorganic polymer compound is formed at least partially.

  In the protective layer of the rare earth magnet, a hydrogen bond is formed between the organic polymer compound and the inorganic polymer compound. For this reason, in the protective layer, these compounds rarely cause phase separation, and the organic polymer compound and the inorganic polymer compound are uniformly dispersed. As a result, the protective layer has a dense structure and uniform characteristics over the entire film.

  Moreover, since the protective layer contains the organic polymer compound and the inorganic polymer compound together as described above, it has the following characteristics. For example, even when a stress that causes the volume of the layer to shrink by performing solvent evaporation, polymerization, or the like is generated during the formation of the protective layer, such a stress is contained because the flexible organic polymer compound is contained. Can be relaxed. The protective layer formed in this way has very few pinholes and cracks.

  Furthermore, since the protective layer contains an inorganic polymer compound, the protective layer has significantly higher heat resistance and moisture resistance than a protective layer formed only of an organic polymer compound. . A rare earth magnet having such a protective layer has characteristics that can withstand use under high temperature conditions, and corrosion of the magnet body due to moisture hardly occurs.

  Thus, the protective layer having the above-described configuration has excellent corrosion resistance as compared with a conventional protective layer formed by using either an organic material or an inorganic material alone. In addition to such effects, the protective layer has a property of high adhesion to the rare earth magnet. Although this cause is not necessarily clear, it is considered to be based on the following reasons. That is, the rare earth element contained in the magnet body has a characteristic of high reactivity with oxygen. Moreover, the inorganic polymer compound which is a constituent component of the protective layer often has an oxygen atom in the molecule. Therefore, when such a protective layer containing an inorganic polymer compound is applied as a protective layer of a magnet body containing a rare earth magnet, the rare earth element and the protective layer are chemically bonded via oxygen, thereby Improved adhesion. However, the action is not limited to these.

  One of the organic polymer compound and the inorganic polymer compound in the protective layer of the rare earth magnet has a proton-donating functional group and the other is a proton in order to form a hydrogen bond between them. It preferably has an accepting functional group.

  In particular, the organic polymer compound preferably has a proton-accepting functional group in the molecule, and the inorganic polymer compound preferably has a proton-donating functional group in the molecule. . By such a combination, a strong hydrogen bond is formed between both polymer compounds, and a protective layer having excellent characteristics can be obtained.

The proton-accepting functional group that the organic polymer compound has is preferably an amide group. The amide group is excellent in proton acceptability in hydrogen bonding. For this reason, in such a configuration, hydrogen bonds between the organic polymer compound and the inorganic polymer compound are more likely to occur. In particular, the amide group preferably has a structure in which a hydrogen atom in a nitrogen atom is substituted with an organic group. In the present invention, in the amide group, in addition to the group represented by —CONH ₂ , the hydrogen atom of the group represented by the structure is substituted with another functional group (for example, a carbon atom of a hydrocarbon group). Is also included.

  More specifically, the organic polymer compound is preferably at least one compound selected from the group consisting of polyvinylpyrrolidone, polyoxazoline, and polyacrylamide derivatives. An organic polymer compound containing these as monomer units has an amide group excellent in proton acceptability. As with the definition of the amide group described above, the polyacrylamide derivative includes polyacrylamide and polyacrylamide in which the hydrogen atom of the amide group bonded to the main chain is substituted with another functional group. Here, the latter is preferable as the polyacrylamide derivative to be contained as the organic polymer compound.

  The inorganic polymer compound contained in the protective layer is preferably a compound having a main chain formed by alternately bonding metal atoms and oxygen atoms. An inorganic polymer compound having such a configuration has a characteristic of being stable. For this reason, the corrosion resistance of the protective layer containing this inorganic polymer compound is also improved.

  More specifically, the metal atom constituting the main chain of the inorganic polymer compound contains at least one element selected from the group consisting of Si, Al, Ti, Zr, Ta, Mo, Nb and B. It is preferable. In particular, it is preferable that Si is contained. Inorganic polymer compounds containing these elements are more stable and can further improve the corrosion resistance of the protective layer.

As such an inorganic polymer compound having Si, the following formula (1);
[Chemical 1]
R ¹ _m Si (OR ² ) _4-m (1)
(In the formula, R ¹ represents an organic group having 1 to 8 carbon atoms, R ² represents an alkyl group having 1 to 5 carbon atoms or an acyl group having 1 to 4 carbon atoms, and m is 1 or 2. R ¹ or R ² present may be the same or different.)
A compound obtained by condensing or co-condensing a compound represented by the formula (1) and / or a hydrolysis product thereof is preferred.

The method for producing a rare earth magnet according to the present invention is a method for simply producing the rare earth magnet of the present invention, wherein the organic polymer compound having a proton-accepting functional group and a proton-donating functional group are converted. Coating solution for preparing coating solution through mixing with inorganic monomer having group to be formed or proton donating functional group and / or inorganic polymer precursor containing polymerization product (oligomer or polymer) of this inorganic monomer A preparation step, a coating step in which this coating solution is applied onto the surface of a magnet body made of a sintered body containing a rare earth element, and an organic polymer compound and an inorganic polymer compound are contained in the coating solution. And a protective layer forming step of forming a protective layer in which a hydrogen bond between the organic polymer compound and the inorganic polymer compound is formed at least partially . Here, the protective layer forming step includes a case where the protective layer is formed simultaneously with the application to the magnet body.

  In the rare earth magnet manufacturing method, the protective layer is formed by a so-called wet method in which a coating solution to be a protective layer is applied to the magnet body. According to such a method, it is possible to form a protective layer having a uniform thickness under mild conditions without using a complicated apparatus or the like.

  Further, when the inorganic polymer precursor is a compound capable of further polymerization reaction, that is, the precursor is the inorganic monomer, or an oligomer or polymer obtained by polymerizing this monomer, and can be further polymerized. In the case where any of those in a state is included, the inorganic polymer precursor is preferably polymerized in at least one of the coating liquid preparation step, the coating step, and the protective layer forming step.

  As the organic polymer compound, a compound in which the proton-accepting functional group is an amide bond is preferably used. As described above, the amide group is excellent in proton acceptability when a hydrogen bond is generated. For this reason, in such a configuration, hydrogen bonds between the organic polymer compound and the inorganic polymer compound are more likely to occur. As a result, the corrosion resistance of the protective layer obtained is further improved.

  More specifically, as the organic polymer compound, it is preferable to use at least one compound selected from the group consisting of polyvinylpyrrolidone, polyoxazoline, and polyacrylamide derivatives. An organic polymer compound containing these as monomer units has an amide group excellent in proton acceptability.

  The inorganic polymer precursor includes an inorganic monomer in which a polymerizable functional group is bonded to at least one metal atom selected from the group consisting of Si, Al, Ti, Zr, Ta, Mo, Nb and B; It is preferable that a polymerization product (oligomer, polymer, etc.) of this monomer is contained. In particular, it is preferable to use a metal atom of Si. Since these inorganic polymer precursors easily generate an inorganic polymer compound by heating or the like, the protective layer can be easily formed. In addition, since the inorganic polymer compound having these metal atoms in the main chain is stable, the corrosion resistance of the protective layer obtained is further improved.

More specifically, the inorganic polymer precursor preferably contains a compound represented by the following formula (1) and / or a hydrolysis product thereof. By doing so, polysiloxane having excellent stress relaxation properties is introduced into the inorganic polymer compound. And the protective layer containing such an inorganic high molecular compound becomes a thing which does not produce a crack etc. easily.
[Chemical 2]
R ¹ _m Si (OR ² ) _4-m (1)
(In the formula, R ¹ represents an organic group having 1 to 8 carbon atoms, R ² represents an alkyl group having 1 to 5 carbon atoms or an acyl group having 1 to 4 carbon atoms, and m is 1 or 2. R ¹ or R ² present may be the same or different.)

  According to the present invention, it is possible to provide a rare earth magnet having a protective layer on the surface, which has both the characteristics of both an organic polymer compound and an inorganic polymer compound, and hardly causes phase separation. Is possible. Such rare earth magnets have extremely excellent corrosion resistance and are suitable as permanent magnets used in applications that are used under high temperature conditions, such as drive motors for fuel cell vehicles and hybrid cars.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.

  First, an embodiment of the rare earth magnet of the present invention will be described with reference to FIGS. FIG. 1 is a perspective view showing a rare earth magnet according to a preferred embodiment. FIG. 2 is a cross-sectional view taken along line II-II of the rare earth magnet shown in FIG. A rare earth magnet 1 shown in FIGS. 1 and 2 has a configuration in which a protective layer 4 is formed on the surface of a magnet body 2. Hereinafter, the components constituting the protective layer 4 and the magnet body 2 will be described.

  First, the components of the protective layer 4 will be described. The protective layer 4 contains an organic polymer compound and an inorganic polymer compound, and these are partly bonded by hydrogen bonds. “Hydrogen bond” means a bond formed by interposing hydrogen between two atoms, and is generally represented by XH... Y. Here, X and Y represent two atoms bonded by a hydrogen bond, and XH represents a covalent bond between the X atom and hydrogen. Thus, a hydrogen bond is formed between the group represented by XH and the Y atom.

  The organic polymer compound and the inorganic polymer compound contained in the protective layer 4 have a functional group in the molecule that can form a hydrogen bond with each other in order to form a hydrogen bond. Here, the functional group capable of forming a hydrogen bond is a proton-donating functional group (a group represented by the above XH) that donates hydrogen in a hydrogen bond and a proton acceptor that accepts hydrogen in a hydrogen bond. Combination of functional groups (groups containing Y described above).

  The organic polymer compound and the inorganic polymer compound may have either a proton-donating property or a proton-accepting functional group, respectively. However, when preferred, the organic polymer compound is a proton-accepting functional group. And the inorganic polymer compound has a proton-donating functional group.

  Hereinafter, each polymer compound will be described. The organic polymer compound can be used without particular limitation as long as it has a proton-accepting functional group in the molecule. Examples of the proton-accepting functional group include functional groups having a large electronegative oxygen atom, nitrogen atom, fluorine atom, chlorine atom and the like. Specifically, an amide group, an imide group, a carbonate group, and a urethane group are preferable.

Among these, an amide group is particularly preferable because it can exhibit high proton acceptability when forming a hydrogen bond. Further, in the organic polymer compound, among the amide groups, those having a configuration in which the hydrogen atom of the group represented by —CONH ₂ is substituted with another functional group (more preferably, an organic group) are more preferable. . If it carries out like this, the hydrogen bond of the amide groups in an organic polymer compound which had a possibility of generating when the nitrogen atom of an amide group has a hydrogen atom will hardly be formed. As a result, phase separation between the organic polymer compound and the inorganic polymer compound in the protective layer is further reduced.

  The organic polymer compound having an amide group may be any compound having at least an amide group in the molecule. From the viewpoint of generating a stronger hydrogen bond, each monomer unit in the polymer is an amide group. It is preferable to have.

  Examples of such organic polymer compounds include polyvinyl pyrrolidone, polyoxazoline, polyacrylamide derivatives, poly (N-vinylcaprolactone), polyvinyl acetamide, nylon derivatives, and the like. The organic polymer compound may be a copolymer obtained by copolymerizing monomers constituting these polymers in any combination.

  More specifically, examples of polyvinyl pyrrolidone include poly (1-vinyl-2-pyrrolidone). Examples of the polyoxazoline include poly (2-methyl-2-oxazoline), and examples of the polyacrylamide derivative include poly (N, N-dimethylacrylamide).

  On the other hand, an inorganic polymer compound is a compound having a main chain (skeleton) composed of elements other than carbon atoms and having a proton-donating functional group in the molecule. The main chain of such an inorganic polymer compound contains a metal atom, and in a preferred case, has a structure in which metal atoms and oxygen atoms are alternately bonded.

  The proton-donating functional group is a functional group having a structure represented by, for example, —OH or —NH. Specific examples of the functional group containing such a structure include a hydroxyl group and an amino group. In particular, a hydroxyl group is preferable because a hydrogen bond can be favorably formed with the above-described proton-accepting functional group.

  As the metal atom of the main chain of the inorganic polymer compound, at least one element selected from the group consisting of Si, Al, Ti, Zr, Ta, Mo, Nb and B is preferable, and Si is particularly preferable. . More specifically, the inorganic polymer compound is preferably a polysiloxane having a main chain formed by a bond represented by -Si-O-. Such a polysiloxane has an advantage that polymers having various structures can be formed because the precursor is relatively stable and can be synthesized relatively easily. In the present specification, the metal atom includes Si and B.

Examples of the polysiloxane include those obtained by condensation or cocondensation of a compound represented by the following formula (1) and / or a hydrolysis product thereof. In the following formulae, R ¹ represents an organic group having 1 to 8 carbon atoms, R ² represents an alkyl group having 1 to 5 carbon atoms or an acyl group having 1 to 4 carbon atoms, and m is 1 or 2. A plurality of R ¹ or R ² may be the same or different.
[Chemical formula 3]
R ¹ _m Si (OR ² ) _4-m (1)

When such a compound is condensed, a polysiloxane having a bond represented by -Si-O- in the main chain is generated. Further, at the time of condensation, the functional group represented by OR ² is hydrolyzed to generate a hydroxyl group. As a result, a polysiloxane having a main chain composed of —Si—O— bonds and having a hydroxyl group that is a proton-donating functional group is obtained. The polysiloxane thus obtained has excellent stress relaxation properties. For this reason, the protective layer 4 containing this polysiloxane does not easily cause cracks or the like.

  In the protective layer 4, it is preferable that the organic polymer compound and the inorganic polymer compound are contained in the following compounding ratio. That is, the content of the organic polymer compound is preferably 20 to 100 parts by mass with respect to 100 parts by mass of the inorganic polymer compound. When the content of the organic polymer compound is less than 20 parts by mass, the stress relaxation property of the protective layer to be obtained tends to be small and cracks tend to occur in the protective layer. On the other hand, when the content of the organic polymer compound exceeds 100 parts by mass, the heat resistance and moisture resistance of the protective layer tend to decrease.

In addition to the organic polymer compound and the inorganic polymer compound described above, the protective layer 4 includes, as trace components, fine metal powders such as Al, Mg, Ca, Zn, Si, and Mn, resin components such as epoxy resins, and montmorillonite. Clay minerals such as SiO ₂ , ZrO ₂ , Al ₂ O _{3 and} other metal oxide oxides.

  In the protective layer 4 having the above-described configuration, whether a hydrogen bond is formed between the organic polymer compound and the inorganic polymer compound is confirmed by, for example, a Fourier transform infrared spectrometer (FT-IR). be able to. Specifically, when the protective layer 4 is peeled from the magnet body 2 and this peeled piece is analyzed by FT-IR, when hydrogen bonds are formed in the protective layer 4, the functions contributing to the hydrogen bonds The group normally exhibits absorption at a position shifted from the absorption wave number obtained in a state where it is not involved in hydrogen bonding.

For example, when the organic polymer compound has an amide group and contributes to hydrogen bonding as in the preferred example described above, the amide carbonyl usually found in the vicinity of 1650 cm ^−1. The stretching vibration of the group is observed in a state shifted to the low wavenumber side by about 20 cm ⁻¹ .

  Next, the constituent material of the magnet body 2 in the rare earth magnet 1 will be described. The magnet body 2 is a permanent magnet containing a rare earth element. In this case, the rare earth element means an element belonging to the third period of the long-period periodic table and an element belonging to the lanthanoid, and examples of such rare earth elements include yttrium (Y), lanthanum (La), cerium ( Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium ( Tm), ytterbium (Yb), lutetium (Lu) and the like.

  Examples of the constituent material of the magnet body 2 include those containing the rare earth element and the transition element in combination. In this case, as the rare earth element, at least one element selected from the group consisting of Nd, Dy, Pr and Tb is preferable, and these elements include La, Sm, Ce, Gd, Er, Eu, Tm, Yb and Y. More preferably, it further contains at least one element selected from the group consisting of:

  More specifically, examples of the constituent material of the magnet body 2 include those having an R—Fe—B (R is a rare earth element) type or R—Co type structure. In the material having the former structure, R is preferably Nd, and in the material having the latter structure, R is preferably Sm.

  Especially, as a constituent material of the magnet body 2 in the rare earth magnet 1, a material having an R—Fe—B structure is preferable. Such a material has a main phase having a substantially tetragonal crystal structure, and a rare earth-rich phase having a high rare earth element content in the grain boundary portion of the main phase, and a boron atom content ratio. Has a high boron-rich phase. These rare earth-rich phase and boron-rich phase are nonmagnetic phases that do not have magnetism, and such a nonmagnetic phase is usually contained in an amount of 0.5 to 50% by volume in the magnet constituting material. Moreover, the particle size of the main phase is usually about 1 to 100 μm.

  In the constituent material of the magnet body 2 having such a configuration, the rare earth element content is preferably 8 to 40 atomic%. When the rare earth element content is less than 8 atomic%, the crystal structure of the main phase becomes almost the same as that of α-iron, and the coercive force (iHc) tends to decrease. On the other hand, if it exceeds 40 atomic%, a rare earth-rich phase is excessively formed, and the residual magnetic flux density (Br) tends to be small.

  Further, the Fe content is preferably 42 to 90 atomic%. When the Fe content is less than 42 atomic%, Br decreases, and when it exceeds 90 atomic%, iHc tends to decrease. Furthermore, the content of B is preferably 2 to 28 atomic%. When the content of B is less than 2 atomic%, a rhombohedral structure is likely to be formed, and this tends to reduce iHc. When it exceeds 28 atomic%, a boron-rich phase is excessively formed. Br tends to be small.

  In the constituent materials described above, a part of Fe in R—Fe—B may be substituted with Co. Thus, if a part of Fe is replaced by Co, the temperature characteristics can be improved without deteriorating the magnetic characteristics. In this case, it is desirable that the amount of substitution of Co not be larger than the content of Fe. When the Co content exceeds the Fe content, the magnetic properties of the magnet body 2 tend to be reduced.

  A part of B in the constituent material may be substituted with an element such as C, P, S or Cu. By replacing a part of B in this way, the magnet body can be easily manufactured and the manufacturing cost can be reduced. At this time, the substitution amount of these elements is desirably an amount that does not substantially affect the magnetic properties, and is preferably 4 atomic% or less with respect to the total amount of constituent atoms.

  Further, from the viewpoint of improving iHc and reducing manufacturing costs, in addition to the above-described structure, Al, Ti, V, Cr, Mn, Bi, Nb, Ta, Mo, W, Sb, Ge, Sn, Zr, Ni , Si, Ga, Cu, Hf and other elements may be added. These addition amounts are also preferably in a range that does not affect the magnetic properties, and are preferably 10 atomic% or less with respect to the total amount of constituent atoms. In addition, O, N, C, Ca, etc. are conceivable as components inevitably mixed, and these may be contained in an amount of about 3 atomic% or less with respect to the total amount of constituent atoms.

The magnet body 2 having such a configuration can be manufactured by powder metallurgy. In this method, first, an alloy having a desired composition is produced by a known alloy production process such as a casting method or a strip casting method. Next, this alloy was pulverized to a particle size of 10 to 100 μm using a coarse pulverizer such as a jaw crusher, a brown mill, or a stamp mill, and then further pulverized by a fine pulverizer such as a jet mill or an attritor. The particle size is 5 to 5 μm. The powder thus obtained is preferably molded at a pressure of 0.5 to ⁵ t / cm ² in a magnetic field having a magnetic field strength of 600 kA / m or more.

  Thereafter, the obtained compact is preferably sintered in an inert gas atmosphere or under vacuum at 1000 to 1200 ° C. for 0.5 to 10 hours and then rapidly cooled. Further, the sintered body is subjected to heat treatment at 500 to 900 ° C. for 1 to 5 hours in an inert gas atmosphere or vacuum, and then the sintered body is processed into a desired shape to obtain the magnet body 2. .

  The rare earth magnet 1 according to a preferred embodiment of the present invention has a structure in which the protective layer 4 described above is provided on the surface of the magnet base body 2 described above. In the rare earth magnet 1, the thickness of the protective layer 4 is preferably 0.1 to 100 μm, and more preferably 5 to 50 μm. When this thickness is less than 0.1 μm, it tends to be extremely difficult to sufficiently cover the magnet surface. On the other hand, when the thickness exceeds 100 μm, the protective layer is likely to be cracked or peeled off, and the reliability as the protective layer tends to be lowered. In this case, the thickness of the protective layer 4 means the average thickness of the protective layer 4 formed on the surface of the magnet body 2.

  Further, the rare earth magnet 1 may include one or more layers other than the protective layer 4 on the surface of the magnet body 2. For example, an inorganic oxide layer or a metal layer may be provided as a base layer of the protective layer 4, and a resin coat layer or the like may be further provided on the surface of the protective layer 4.

  Next, an embodiment of a method for producing the rare earth magnet 1 configured as described above will be described. The manufacturing method of the rare earth magnet 1 includes a step of preparing a coating solution for forming the protective layer 4 (coating solution preparation step), a step of applying a coating solution on the surface of the magnet body 2 (coating step), and this coating It has the process (protective layer formation process) which forms the protective layer 4 from a liquid.

  In the method for producing the rare earth magnet 1, first, in the coating liquid preparation step, as a raw material, an organic polymer compound having a proton-accepting functional group, and a group to be converted into a proton-donating functional group or proton donation An inorganic polymer precursor containing an inorganic monomer having a functional group and / or a polymerization product of this monomer is prepared, and these are mixed in a state dissolved or dispersed in a predetermined solvent.

  The organic polymer compound used in the coating liquid preparation step can be obtained, for example, by polymerizing a monomer of an organic compound having a proton-accepting functional group. As such an organic compound, a compound having a polymerizable double bond (for example, a carbon-carbon double bond or a carbon-nitrogen double bond) and a proton-accepting functional group in the molecule is preferable. For example, when synthesizing the above-described polyvinyl pyrrolidone, polyoxazoline, polyacrylamide derivative, and the like, the organic compounds that are raw materials thereof are vinyl pyrrolidone, oxazoline, acrylamide derivatives, and the like.

  As said organic polymer compound, that whose weight average molecular weight is 2000 or more is preferable, What is 2000-1 million is more preferable, What is 10000-5000000 is still more preferable.

  On the other hand, the inorganic polymer precursor includes an inorganic monomer having a proton-donating functional group or a group to be a proton-donating functional group, and a polymerizable functional group bonded to a metal atom. And a polymerization product which is an oligomer or polymer of this monomer. The latter polymerization product has a proton-donating functional group in the molecule. Examples of the metal element of the inorganic monomer include Si, Al, Ti, Zr, Ta, Mo, Nb, and B.

  Examples of the proton donating functional group in the inorganic polymer precursor include a hydroxyl group and an amino group. An example of the group that should be a proton-donating functional group is an alkoxy group. The alkoxy group is a functional group that is hydrolyzed to give a hydroxyl group that is a proton-donating functional group. Such a hydrolysis reaction proceeds, for example, with a polymerization reaction of an inorganic monomer having an alkoxy group. .

  Note that the proton-donating functional group or the group to be the proton-donating functional group may be directly bonded to the metal element in the inorganic monomer or the polymerization product thereof, or through other elements. It may be bonded to a metal element.

  Moreover, the polymerizable functional group which the inorganic monomer mentioned above has is a functional group capable of causing a polymerization reaction in the inorganic monomer. Examples of such functional groups include a hydroxyl group and an alkoxy group. When the polymerizable functional group is an alkoxy group, a polymerization reaction of the inorganic monomer is caused by a hydrolysis-condensation reaction of the alkoxy group.

As the inorganic monomer for constituting the inorganic polymer precursor, a compound made of Si to which a hydroxyl group or an alkoxy group is bonded is suitable. Specifically, a compound represented by the following general formula (1) is preferable. In the following formulae, R ¹ represents an organic group having 1 to 8 carbon atoms, R ² represents an alkyl group having 1 to 5 carbon atoms or an acyl group having 1 to 4 carbon atoms, and m is 1 or 2. A plurality of R ¹ or R ² may be the same or different.
[Chemical formula 4]
R ¹ _m Si (OR ² ) _4-m (1)

When an inorganic monomer represented by the above formula (1) and / or a polymerization product of this monomer is used as the inorganic polymer, the resulting inorganic polymer compound is represented by a plurality of OR ² in the molecule. It comes to have a group. The group represented by OR ² is a group having hydrolyzability as described above. Further, the magnet body 2 usually has a hydroxyl group derived from the constituent material of the magnet on the surface thereof. Therefore, when the above compound is used as an inorganic polymer precursor, a condensation reaction occurs between the hydrolyzable group of the obtained inorganic polymer compound and the hydroxyl group on the magnet surface, thereby protecting The adhesion of the layer 4 to the magnet body 2 tends to be remarkably good.

  In the production of the rare earth magnet 1, a coating process for coating the coating liquid on the surface of the magnet body 2 is performed following the coating liquid preparation process described above. The coating method is not particularly limited, and a known method can be appropriately selected and used. Examples thereof include a dip coating method, a spray coating method, and a spin coating method.

  At this time, the application of the coating solution takes into consideration the solvent volatilization or volume shrinkage after the application so that the thickness of the protective layer 4 to be obtained is a desired value (0.1 to 100 μm in the preferred case). It is preferable to make adjustments. For example, when the application is performed by the dip coating method, the thickness of the coating liquid to be applied is set by appropriately setting the speed and time for lifting the magnet body 2 after immersing the magnet body 2 in the coating liquid. Can be adjusted.

  In addition, from the viewpoint of performing such coating easily and improving the adhesion of the protective layer 4 to be formed, a predetermined treatment is performed on the surface of the magnet body 2 before performing the coating step. It is desirable. Examples of the predetermined treatment include a treatment in which the surface of the magnet body 2 is smoothed by barrel polishing or the like, the surface of the body is degreased, and further washed with an acid solution or washed with water. Thereby, the magnet body 2 having a clean surface is obtained, and the adhesion between the magnet body 2 and the protective layer 4 is improved.

  And after implementing the said application | coating process, in the protective layer formation process, the protective layer 4 is formed from the apply | coated coating liquid, and the protective layer 4 is formed on the magnet element body 2 surface. In the protective layer forming step, for example, the magnet body 2 coated with the coating liquid is heated or left in the air to volatilize the solvent from the coating liquid, thereby forming the protective layer 4. In this case, the temperature condition is preferably from room temperature to 300 ° C., and the treatment is preferably performed for about 1 minute to 24 hours.

  In addition, in the method for producing the rare earth magnet 1 according to the present invention, as the inorganic polymer precursor, the above-described inorganic monomer and / or oligomer or polymer which is a polymerization product of the inorganic monomer and can cause further polymerization reaction. Is used, polymerization of these inorganic polymer precursors is caused in at least one of the coating liquid preparation step, the coating step, and the protective layer forming step.

When the polymerization of the inorganic polymer precursor is caused in the coating liquid preparation step, the organic polymer compound and the inorganic polymer precursor are mixed, and then the polymerization of the inorganic polymer precursors is caused. Here, when an example of the polymerization reaction of the inorganic polymer precursor is shown, for example, when the inorganic monomer represented by the general formula (1) is applied as the inorganic polymer precursor, the polymerization reaction is caused by hydrolysis. A polycondensation reaction occurs due to condensation between the hydroxyl groups or between the hydroxyl groups and OR ² .

  The polymerization reaction of the inorganic polymer precursor in the coating liquid preparation step can be caused, for example, by heating a mixed solution containing the organic polymer compound and the inorganic polymer precursor. When this polymerization reaction is a polycondensation reaction of inorganic monomers as described above, for example, the reaction temperature is preferably 20 to 150 ° C. The reaction time is preferably 10 minutes to 48 hours.

  Moreover, when making the said polymerization reaction produce in a coating liquid preparation process, it is preferable to add water further in a reaction liquid. Further, when the inorganic polymer precursor contains Si, it is more preferable to add a catalyst because the polymerization reaction tends to progress slowly. Examples of the catalyst in this case include an acid, a base, an organometallic compound, and the like, and a base or an organometallic salt is preferable.

  On the other hand, when the inorganic polymer precursor is polymerized in the protective layer forming step, the polymerization reaction is performed by heating the magnet body 2 in a state where the coating liquid is applied in the step or by subjecting the magnet body 2 in the atmosphere to It can be caused by leaving it for a period of time. For example, when tetrabutoxyzirconium or the like is used as an inorganic monomer, the condensation reaction between these compounds is promoted by moisture in the air when left in the atmosphere.

  In order to efficiently cause the polymerization in the protective layer forming step, the magnet body 2 coated with the coating solution is preferably treated at room temperature to 300 ° C. for 1 minute to 24 hours. When these temperatures are low or the treatment time is short, sufficient polymerization reaction of the inorganic polymer precursor is difficult to occur and sufficient inorganic structural units are not generated, which tends to lower the heat resistance of the protective layer. It is in. On the other hand, when the treatment temperature exceeds 300 ° C., the organic structural unit is decomposed and the flexibility of the protective layer tends to be lowered.

  Furthermore, in one method for producing a rare earth magnet of the present invention, polymerization of the inorganic polymer precursor may occur in the coating step, in addition to the coating solution preparation step and the protective layer formation step. In this case, for example, the polymerization reaction is further promoted by applying the coating while heating the magnet body 2, and polymerization occurs at the same time as the coating liquid is applied to the magnet body 2.

  As described above, the polymerization reaction of the inorganic polymer precursor described above may be caused in any of the coating liquid preparation step, the coating step, and the protective layer forming step. However, in the method for producing the rare earth magnet 1 of the present invention, It is more preferable to cause such polymerization at least in the protective layer forming step. Thereby, the hydroxyl group etc. which accompany a polymerization reaction react with the active functional group which exists in the magnet element body 2 surface, and the adhesiveness to the magnet element body 2 of the protective layer 4 further improves.

  In a particularly preferred case, after causing a part of the polymerization reaction in the coating liquid preparation step (that is, without completely proceeding the polymerization), it remains in the coating liquid preparation step in the protective layer forming step. Further, polymerization is caused to the polymerized inorganic polymer precursor. By doing so, an inorganic polymer compound is generated in the coating liquid preparation stage, and thereby the stress generated when forming the protective layer is reduced. In addition, since the polymerization occurs in the protective layer forming step, the effect of improving the adhesion of the protective layer 4 to the magnet body 2 can be obtained.

  According to the rare earth magnet 1 configured as described above, the following effects can be obtained. That is, the rare earth magnet 1 has a protective layer 4 containing an organic polymer compound and an inorganic polymer compound in a state of being bonded by hydrogen bonds on the surface of the magnet body 2. In this protective layer 4, since both polymer compounds are bonded by hydrogen bonds, the organic polymer compound and the inorganic polymer compound are uniformly dispersed.

  As a result, the protective layer 4 also has characteristics obtained when each of the organic polymer compound and the inorganic polymer compound is used alone. For example, it is superior in moisture resistance and heat resistance compared to a protective layer formed only from an organic polymer compound, and excellent in stress relaxation compared to a protective layer formed only from an inorganic polymer compound. It has the characteristic of being. That is, it has extremely excellent corrosion resistance as compared with a protective layer formed only from an organic or inorganic polymer compound. Moreover, in the protective layer 4, since the organic polymer compound and the inorganic polymer compound are bonded by hydrogen bonds, phase separation between the two is extremely difficult to occur. For this reason, the protective layer 4 has a uniform characteristic over all the layers.

  Thus, since the protective layer 4 has extremely excellent corrosion resistance, the rare earth magnet 1 provided with the protective layer 4 has magnetic properties even when used under conditions exposed to high temperature and high humidity. It will be less likely to cause degradation of. For this reason, such a rare earth magnet 1 is extremely suitable as a permanent magnet used for a drive motor of a fuel cell vehicle or a hybrid car.

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

(Example 1)
A sintered body having a composition represented by 14Nd-1Dy-7B-78Fe (numbers are atomic ratios) prepared by powder metallurgy is subjected to heat treatment under conditions of 600 ° C. for 2 hours in an argon atmosphere. The sintered body was cut into a size of 56 mm × 40 mm × thickness 8 mm to obtain a magnet body. The magnet body was washed with an alkaline degreasing solution and further treated with a nitric acid solution to activate the surface of the magnet body, and then the surface was repeatedly washed with water.

  Separately, 20 g of polyvinylpyrrolidone having a weight average molecular weight of 40,000 was dissolved in 2-propanol, and 80 g of methyltrimethoxysilane and 17.5 g of 0.1% aqueous ammonia were added to this solution. A coating solution was prepared by heat treatment for 5 hours to cause a polycondensation reaction of methyltrimethoxysilane. In addition, a weight average molecular weight is the value calculated | required by converting with the analytical curve using standard polystyrene, after measuring by gel permeation chromatography.

  After applying this coating solution to the surface of the magnet body described above by the dip coating method, heating is performed at 150 ° C. for 20 minutes to form a protective layer on the surface of the magnet body, Obtained.

<Characteristic evaluation>
Using the obtained rare earth magnet, the thickness of the protective layer was measured, the surface was observed, and the corrosion resistance was evaluated by an acceleration test. That is, first, the average thickness of the protective layer was measured by cutting the rare earth magnet at the central portion in the width direction (in the depth direction in FIG. 1) and observing the cut surface with an electron microscope. As a result, it was confirmed that the average thickness of the protective layer was 15 μm. Next, when the surface of the rare earth magnet was observed with an electron microscope, it was found that no defects such as cracks were formed on the surface of the protective layer of the magnet.

  Next, an accelerated corrosion resistance test was performed in which the rare earth magnet was treated at 80 ° C. and 90% RH. As a result, even after 300 hours from the start of the test, no rust was observed in the magnet body, and it was found that the magnet body was not corroded.

(Comparative Example 1)
A rare earth magnet was produced in the same manner as in Example 1 except that the coating solution was prepared by the method described below. That is, after adding 68 g of methyltrimethoxysilane to 50 g of 2-propanol and mixing, 15 g of 0.1% ammonia water was added to this solution and reacted at 80 ° C. for 6 hours to prepare a coating solution.

  Using the obtained rare earth magnet, the thickness of the protective layer was measured, the surface was observed, and the corrosion resistance was evaluated by an acceleration test in the same manner as in Example 1. As a result, the thickness of the protective layer was 10 μm, and it was confirmed that cracks were generated on the surface of the protective layer in the rare earth magnet. Further, in the accelerated test, rust was generated in the magnet body after 300 hours had elapsed from the start of the test.

(Comparative Example 2)
A rare earth magnet was produced in the same manner as in Example 1 except that the coating solution was prepared by the method described below. That is, first, 28 g of methyl methacrylate and 12 g of 2-ethylhexyl methacrylate were added to 40 g of 2-propanol and mixed, and then 1.6 g of 2,2′-azoisobutyronitrile was further added to this solution. The solution was reacted at 6 ° C. for 6 hours to prepare a solution containing an acrylic resin. Separately, 160 g of methyltrimethoxysilane was added to 30 g of 2-propanol and dissolved by stirring, and 35 g of 0.1% aqueous ammonia was added to this solution and reacted at 50 ° C. for 5 hours. A solution containing a polymer of trimethoxysilane was produced. A coating solution was prepared by mixing the solution containing the acrylic resin thus obtained and the solution containing the polymer.

  Using the obtained rare earth magnet, the thickness of the protective layer was measured, the surface was observed, and the corrosion resistance was evaluated by an acceleration test in the same manner as in Example 1. As a result, the thickness of the protective layer was 30 μm, and a sea-island structure having a size of about 1 μm due to phase separation was confirmed on the surface of the protective layer. Further, in the accelerated test, rust was generated in the magnet body after 300 hours had elapsed from the start of the test.

It is a perspective view which shows the rare earth magnet of suitable embodiment. It is sectional drawing along the II-II line of the rare earth magnet shown by FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Rare earth magnet, 2 ... Magnet base body, 4 ... Protective layer.

Claims (15)

A magnet body made of a sintered body containing a rare earth element, and a protective layer formed on the surface of the magnet body,
The protective layer contains an organic polymer compound and an inorganic polymer compound, and one of the organic polymer compound and the inorganic polymer compound has a proton-donating functional group, and the other Has a proton-accepting functional group, and
In the protective layer, a hydrogen bond between the organic polymer compound and the inorganic polymer compound is formed at least partially.
Rare earth magnet characterized by The organic polymer compound has a proton acceptor functional group, and the inorganic polymer compound, a rare earth according to claim 1, characterized in that it has a proton donating functional groups magnet. 3. The rare earth magnet according to claim 1, wherein the organic polymer compound has an amide group. The rare earth magnet according to any one of claims 1 to 3 , wherein the organic polymer compound is at least one compound selected from the group consisting of polyvinylpyrrolidone, polyoxazoline, and polyacrylamide derivatives. The rare earth magnet according to any one of claims 1 to 4 , wherein the inorganic polymer compound is a compound having a main chain formed by alternately bonding metal atoms and oxygen atoms. 6. The rare earth magnet according to claim 5 , wherein the metal atom contains at least one atom selected from the group consisting of Si, Al, Ti, Zr, Ta, Mo, Nb and B. The rare earth magnet according to claim 5 or 6 , wherein Si is contained as the metal atom. The inorganic polymer compound has the following formula (1):
[Chemical 1]
R ¹ _m Si (OR ² ) _4-m (1)
(In the formula, R ¹ represents an organic group having 1 to 8 carbon atoms, R ² represents an alkyl group having 1 to 5 carbon atoms or an acyl group having 1 to 4 carbon atoms, and m is 1 or 2. R ¹ or R ² present may be the same or different.)
The rare earth magnet according to any one of claims 1 to 7 , wherein the rare earth magnet is obtained by condensation or cocondensation of a compound represented by formula (1) and / or a hydrolysis product thereof. An organic polymer compound having a proton-accepting functional group, an inorganic monomer having a group to be converted to a proton-donating functional group, or an inorganic monomer having a proton-donating functional group, and / or a polymerization product of the inorganic monomer A coating liquid preparation step of preparing a coating liquid through mixing with a polymer precursor,
Applying the coating solution on the surface of a magnet body made of a sintered body containing a rare earth element ; and
A protective layer containing the organic polymer compound and the inorganic polymer compound from the coating solution , and at least partially forming a hydrogen bond between the organic polymer compound and the inorganic polymer compound Forming a protective layer, and
A method for producing a rare earth magnet, comprising: The rare earth magnet according to claim 9 , wherein the inorganic polymer precursor is polymerized in at least one of the coating liquid preparation step, the coating step, and the protective layer forming step. Method. The method for producing a rare earth magnet according to claim 9 or 10, wherein the organic polymer compound is one in which the proton-accepting functional group is an amide group. The production of a rare earth magnet according to any one of claims 9 to 11 , wherein at least one compound selected from the group consisting of polyvinylpyrrolidone, polyoxazoline and polyacrylamide derivatives is used as the organic polymer compound. Method. As the inorganic polymer precursor, the above-mentioned inorganic monomer in which a polymerizable functional group is bonded to at least one metal atom selected from the group consisting of Si, Al, Ti, Zr, Ta, Mo, Nb and B, and The method for producing a rare earth magnet according to any one of claims 9 to 12, wherein a polymerization product thereof is used. As the inorganic polymer precursor, the polymerizable functional groups, according to any one of claims 9 to 13, characterized by using a formed by bonding the inorganic monomer and / or a polymerization product to Si Method for producing rare earth magnets. As the inorganic polymer precursor, the following formula (1);
[Chemical 2]
R ¹ _m Si (OR ² ) _4-m (1)
(In the formula, R ¹ represents an organic group having 1 to 8 carbon atoms, R ² represents an alkyl group having 1 to 5 carbon atoms or an acyl group having 1 to 4 carbon atoms, and m is 1 or 2. R ¹ or R ² present may be the same or different.)
The manufacturing method of the rare earth magnet as described in any one of Claims 9-14 characterized by containing the inorganic monomer represented by these, and / or its hydrolysis product.

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