JP4276553B2 - 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.

  In addition, since the protective layer in the rare earth magnet described in Patent Document 4 is made of resin, the moisture permeability resistance 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, this moisture contacts 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. There is a risk of inducing inconvenience such as promotion. Furthermore, the protective layer composed of the resin in this way often has insufficient heat resistance, and therefore 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 includes a magnet body made of a sintered body containing a rare earth element, an organic polymer compound having an aromatic ring, and an inorganic polymer compound having an aromatic ring. And a protective layer formed on the surface.

  Both the organic polymer compound and the inorganic polymer compound contained in the protective layer have an aromatic ring in the molecule. Therefore, when these polymer compounds are mixed, an interaction between π electrons in each aromatic ring (π-π interaction) occurs between the organic polymer compound and the inorganic polymer compound. In this case, the organic polymer compound and the inorganic polymer compound in the protective layer are weakly bonded by the π-π interaction. As a result, phase separation of these compounds hardly occurs in the protective layer, and the organic polymer compound and the inorganic polymer compound are uniformly dispersed. Such a protective layer has a dense structure and can exhibit 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 if a stress that causes the volume of the layer to shrink by performing solvent evaporation or polymerization at the time of forming the protective layer is generated, the protective layer contains a flexible organic polymer compound. Such stress is sufficiently 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. . Therefore, such a protective layer has characteristics that can withstand use under high-temperature conditions, and very little moisture permeates.

  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.

  The aromatic ring contained in the organic polymer compound contained in the protective layer of the rare earth magnet is preferably a benzene ring. When the aromatic ring is a benzene ring, π-π interaction with the aromatic ring of the inorganic polymer compound is likely to occur, and the rigidity of the organic polymer compound is increased, so that a strong protective layer can be obtained. .

  More specifically, examples of such an organic polymer compound include a polymer having a styrene unit. These have the characteristic that π-π interaction with other aromatic rings is particularly likely to occur, whereby the phase separation from the inorganic polymer compound in the protective layer is further reduced.

  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, Si is preferable as the metal atom constituting the main chain of the inorganic polymer compound. An inorganic polymer compound containing Si in the main chain is more stable and can further improve the corrosion resistance of the protective layer.

The inorganic polymer compound having Si in the main chain preferably has at least a structural unit composed of a compound represented by the following formula (1) and / or a hydrolysis product thereof. Since the inorganic polymer compound thus obtained is very likely to cause π-π interaction with the organic polymer compound, the corrosion resistance of the protective layer obtained is further improved.
[Chemical 1]
R ¹ _n R ² _m Si (OR ³ ) _{4- (n + m)} (1)
[Wherein, R ¹ is an organic group having an aromatic ring, R ² is an alkyl group, R ³ is an alkyl group having 1 to 5 carbon atoms or an acyl group having 1 to 4 carbon atoms, n is 1 or 2, m Is 0 or 1. However, n + m is 2 or less. In addition, when it has two or more R < ¹ > or R < ³ >, each may be the same or different. ]

As the compound represented by the above formula (1), those containing a phenyl group which may have a substituent as the group represented by R ¹ are preferable. A compound having such a structure is more likely to cause a π-π interaction with the organic polymer compound, thereby further preventing phase separation in the protective layer.

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 an organic polymer compound having an aromatic ring and a polymerizable functional group having an aromatic ring are provided. A coating liquid preparation step for preparing a coating liquid by mixing with an inorganic monomer formed by bonding to a metal atom and / or an inorganic polymer precursor containing a polymer of this inorganic monomer, and the resulting coating liquid contains a rare earth element A protective layer containing an organic polymer compound having an aromatic ring and an inorganic polymer compound having an aromatic ring is formed from the coating step of coating on the surface of the magnet body made of a sintered body and the coating liquid. And a protective layer forming step. 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.

  In the method for producing a rare earth magnet, it is preferable to cause polymerization of the inorganic polymer precursor in at least one of a coating liquid preparation step, a coating step, and a protective layer formation step. By doing so, the polymerization reaction of the inorganic polymer precursor occurs, the interaction between the polymer and the magnet body occurs, and the adhesion between the protective layer and the magnet body tends to be further improved.

  The organic polymer compound used in the production method is preferably a compound in which the aromatic ring is a benzene ring. When the organic polymer compound has a benzene ring, π-π interaction with the aromatic ring in the inorganic polymer compound is more likely to occur, thereby further improving the corrosion resistance of the protective layer.

  More specifically, a polymer having a styrene unit is preferably used as the organic polymer compound. The aromatic rings possessed by these organic polymer compounds have a characteristic that they are very likely to cause π-π interaction with other aromatic rings.

  Further, as the inorganic polymer precursor, it is preferable to use a precursor in which the metal atom is Si. Such an inorganic polymer precursor tends to be able to stabilize the coating solution, which facilitates the formation of a protective layer. In addition, when the above-described polymerization reaction of the inorganic polymer precursor is caused, the coating liquid can be stabilized as described above, and thus the polymerization reaction tends to be easily controlled.

More specifically, the inorganic polymer precursor preferably contains an inorganic monomer represented by the following formula (1) and / or a hydrolysis product thereof. Since the inorganic polymer compound formed from such a compound is stable, the corrosion resistance of the protective layer obtained is further improved.
[Chemical 2]
R ¹ _n R ² _m Si (OR ³ ) _{4- (n + m)} (1)
[Wherein, R ¹ is an organic group having an aromatic ring, R ² is an alkyl group, R ³ is an alkyl group having 1 to 5 carbon atoms or an acyl group having 1 to 4 carbon atoms, n is 1 or 2, m Is 0 or 1. However, n + m is 2 or less. In addition, when it has two or more R < ¹ > or R < ³ >, each may be the same or different. ]

In addition, the group represented by R ¹ in the compound represented by the above formula (1) particularly preferably contains a phenyl group which may have a substituent. In this case, a π-π interaction between the phenyl group and the aromatic ring in the organic polymer compound is extremely likely to occur, thereby further improving the corrosion resistance of the protective layer.

  According to the present invention, there is provided a rare earth magnet having a protective layer on the surface that has both the characteristics of both an organic polymer and an inorganic polymer compound, and that hardly causes phase separation of both polymer compounds. It becomes possible to do. Since the protective layer in the rare earth magnet has excellent corrosion resistance, the rare earth magnet including the protective layer also has excellent corrosion resistance. As a result, this rare earth magnet has a very small degree of deterioration over time in the magnetic characteristics. For this reason, the rare earth magnet of this invention is suitable as a permanent magnet used for the use used in high temperature conditions like the drive motor of a fuel cell vehicle or a hybrid car, for example.

  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 having an aromatic ring and an inorganic polymer compound having an aromatic ring. Between these, the π-π interaction between the aromatic rings occurs, whereby both compounds are weakly bonded. First, the former organic polymer compound having an aromatic ring will be described.

  The organic polymer compound having an aromatic ring is not particularly limited as long as it is a polymer compound having an aromatic ring in the molecule. This organic polymer compound may have an aromatic ring in either the main chain or the side chain. Here, the aromatic ring is a general term for rings belonging to the aromatic group, and for example, π electrons such as a benzene ring, a condensed benzene ring, a non-benzene aromatic ring, and a heteroaromatic ring are delocalized. It shall be a thermodynamically stable ring structure. In addition, such a definition of an aromatic ring is applied also to the inorganic polymer compound mentioned later.

  This organic polymer compound preferably produces a π-π interaction with an inorganic polymer compound, so that each repeating structural unit constituting the polymer preferably has an aromatic ring. Moreover, as an aromatic ring which the organic high molecular compound has, the benzene ring which exists in the tendency which produces the pi-pi interaction strongly with another aromatic ring is preferable.

  As such an organic polymer compound, both a thermoplastic organic polymer compound and a thermosetting organic polymer compound can be applied. Examples of thermoplastic organic polymer compounds include polystyrene, polyester, polyphenylene ether, polysulfone, polyether sulfone, polyphthalamide, polyphenylene sulfide, polyarylate, polyimide, polyamideimide, polyetherimide, and polymers thereof. Examples thereof include a copolymer having a plurality of types of monomer units to be formed.

  Examples of the thermosetting organic polymer compound include phenol resin, epoxy resin, acrylic resin, melamine resin, alkyd resin, urea resin, and the like. Any of these thermoplastic or thermosetting organic polymer compounds has one or more aromatic rings in the repeating structural unit.

  In particular, the organic polymer compound is preferably the former thermoplastic organic polymer compound. If the organic polymer compound has thermoplasticity, the flexibility of the protective layer including the organic polymer compound tends to be improved, thereby reducing the occurrence of cracks and pinholes in the protective layer.

  Among these thermoplastic organic polymer compounds, a polymer having a styrene unit or polyphenylene ether is preferable. Examples of the polymer having a styrene unit include polystyrene and a copolymer obtained by copolymerizing a styrene compound and another polymerizable monomer. In addition to being excellent in the above-described effects, these tend to produce a relatively strong π-π interaction with the aromatic ring in the inorganic polymer compound.

  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 an aromatic ring in the molecule. The inorganic polymer compound may further have an organic group other than the aromatic ring as long as it has such a main chain. The main chain of the 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 inorganic polymer compound having such a configuration may have an aromatic ring in either the main chain or the side chain. The aromatic ring is not particularly limited as long as it falls under the above definition, but a benzene ring is particularly preferable. When both the organic polymer compound and the inorganic polymer compound have a benzene ring as an aromatic ring, the π-π interaction between the two becomes stronger.

  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 a compound having at least a structural unit composed of a compound represented by the following formula (1) and / or a hydrolysis product thereof. In the following formula (1), R ¹ is an organic group having an aromatic ring, R ² is an alkyl group, R ³ is an alkyl group having 1 to 5 carbon atoms or an acyl group having 1 to 4 carbon atoms, and n is 1 or 2, m is 0 or 1; However, n + m is 2 or less. In addition, when it has two or more R < ¹ > or R < ³ >, each may be the same or different.
[Chemical 3]
R ¹ _n R ² _m Si (OR ³ ) _{4- (n + m)} (1)

  Examples of the inorganic polymer compound having at least a structural unit comprising the compound represented by the above formula (1) and / or a hydrolysis product thereof include, for example, condensing the compound and / or the hydrolysis product alone. And condensates containing these.

Examples of the latter cocondensate include a cocondensate of a compound represented by the above formula (1) and a compound represented by the following formula (2). In the following formulae, R ⁴ is an alkyl group, preferably an alkyl group having 1 to ⁵ carbon atoms, R ⁵ is an alkyl group having 1 to ⁵ carbon atoms or an acyl group having 1 to 4 carbon atoms, and x is 1 or 2.
[Chemical 4]
R ⁴ _x Si (OR ⁵ ) _4-x (2)

  When the inorganic polymer compound is composed of a copolymer of these compounds, in the polymer compound, the structural unit having an aromatic ring, that is, the structural unit composed of the compound represented by the formula (1) is 10 mol. % Or more is preferable. When the structural unit having an aromatic ring has such a content, π-π interaction with an organic polymer compound having an aromatic ring tends to occur more effectively.

The compounds described above that engaged condensation or co-condensation, the group represented by R ¹ in the side chain, that is, has an organic group having an aromatic ring in the main chain a bond represented by -Si-O- The resulting polysiloxane is produced. 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.

The compound represented by the above formula (1) is obtained from the group consisting of a phenyl group, a benzyl group, a β-phenethyl group, a p-toluyl group, a mesityl group, and a p-stynyl group as the group represented by R ^1. It is preferable to have at least one kind of group. In addition, the benzene ring in these functional groups may further have another substituent. Among these, a compound having a phenyl group as R ¹ is particularly preferable. The inorganic polymer compound having a structural unit made of such a compound has a characteristic of excellent stability, and thereby the corrosion resistance of the protective layer 4 is further improved.

  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 10 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 10 parts by mass, the stress relaxation property of the obtained protective layer is reduced, and cracks tend to be generated 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 fine metal components such as Al, Mg, Ca, Zn, Si, and Mn, SiO ₂ , TiO ₂ , and ZrO ₂ as trace components. Further, it may contain a metal oxide fine powder such as Al ₂ O _3, a resin component such as an epoxy resin, a clay mineral such as montmorillonite, and the like.

  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 of the present embodiment 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 production of the rare earth magnet 1, first, in the coating liquid preparation step, an organic polymer compound having an aromatic ring and an inorganic polymer precursor were prepared as raw materials, and these were dissolved or dispersed in a predetermined solvent. Mix in the state. Here, the inorganic polymer precursor is an inorganic monomer having an aromatic ring and a polymerizable functional group bonded to a metal atom, or a polymerization product (oligomer, polymer, etc.) of this inorganic monomer, or It is a mixture of these.

  The organic polymer compound mentioned above is mentioned as an organic polymer compound used in a coating liquid preparation process. As these organic polymer compounds, those having a weight average molecular weight of 500 to 100,000 are preferable.

  The inorganic monomer for constituting the inorganic polymer precursor is a compound that can form the above-described inorganic polymer compound by polymerization. For example, an aromatic ring has a polymerizable functional group bonded to a metal atom. The compound which consists of is mentioned. As a metal atom which such an inorganic monomer has, at least one element selected from the group consisting of Si, Al, Ti, Zr, Ta, Mo, Nb and B is preferable.

  The aromatic ring possessed by the inorganic monomer is preferably a benzene ring, and such a benzene ring can be a benzyl group, a β-phenethyl group, a p-toluyl group, a mesityl group, a p-stynyl group, or a phenyl group. It is preferably introduced in the form of an inorganic monomer. These groups may be directly bonded to the metal atom in the inorganic monomer, or may be bonded to the metal atom via another atom.

  Moreover, the polymerizable functional group which the inorganic monomer has is a functional group which enables a polymerization reaction with the inorganic monomer. Examples of such a functional group include a hydroxyl group and an alkoxy group. For example, when the polymerizable functional group is an alkoxy group, polymerization of the inorganic monomer proceeds by hydrolysis and condensation reaction of the alkoxy group.

More specifically, 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 formula, R ¹ is an organic group having an aromatic ring, R ² is an alkyl group, R ³ is an alkyl group having 1 to 5 carbon atoms or an acyl group having 1 to 4 carbon atoms, and n is 1 or 2 , M is 0 or 1. However, n + m is 2 or less. In addition, when it has two or more R < ¹ > or R < ³ >, each may be the same or different.
[Chemical 5]
R ¹ _n R ² _m Si (OR ³ ) _{4- (n + m)} (1)

In the above formula (1), the group represented by R ¹ is at least one group selected from the group consisting of a benzyl group, a β-phenethyl group, a p-toluyl group, a mesityl group, a p-stynyl group and a phenyl group. Preferably, a phenyl group is more preferable. When the group represented by R ¹ is a phenyl group, a π-π interaction between the obtained inorganic polymer compound and the organic polymer compound described above is more likely to occur. The inorganic polymer precursor may further contain a compound that can be co-condensed with the compound represented by the above formula (1). Examples of such a compound include those represented by the above formula (2). Are preferred.

  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 rare earth magnet 1 in which the protective layer 4 was formed on the surface of the magnet element | base_body 2 is obtained. In the protective layer forming step, for example, the magnet body 2 coated with the coating liquid is heated or left in the atmosphere to volatilize the solvent from the coating liquid, thereby removing the protective layer 4 from the coating liquid. Form. 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 the method for producing the rare earth magnet 1 of the above-described form, the inorganic polymer precursor contains the inorganic monomer and / or an oligomer or polymer that is a polymerization product of the inorganic monomer and can cause further polymerization reaction. In this case, 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 formation step.

As described above, by causing the polymerization reaction of the inorganic polymer precursor in at least one of the steps, the adhesion between the obtained protective layer 4 and the magnet body 2 is improved. For example, when the inorganic monomer represented by the above formula (1) and / or the polymerization product thereof is used as the inorganic polymer precursor, the resulting inorganic polymer compound has a plurality of —OR ² in the molecule. With the group represented. The group represented by —OR ² has hydrolyzability, and the magnet body 2 usually has a hydroxyl group derived from the constituent material of the magnet on the surface thereof. For this reason, in the rare earth magnet 1, a condensation reaction occurs between the hydrolyzable group possessed by the inorganic polymer compound and the hydroxyl group on the surface of the magnet, whereby the magnet body 2 of the protective layer 4. Adhesiveness to is significantly improved. However, the action is not limited to these.

For example, when the polymerization reaction of the inorganic polymer precursor is first performed 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 precursor is performed. Cause it to occur. Here, when an example of the polymerization reaction of an inorganic polymer precursor is shown, for example, the polymerization reaction that occurs when the inorganic monomer represented by the general formula (1) is used as an inorganic polymer precursor is hydrolysis. This is a polycondensation reaction by condensation between generated hydroxyl groups or between hydroxyl groups and OR ² .

  Such a polymerization reaction in the coating liquid preparation step can be caused, for example, by heating the mixed liquid after mixing the organic polymer compound and the inorganic polymer precursor. When this polymerization reaction is the polycondensation reaction described above, 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. Furthermore, when the inorganic polymer precursor contains Si as a metal atom, the polycondensation reaction tends to progress slowly, so it is preferable to further add a catalyst or the like. 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.

  In order to efficiently cause the polymerization reaction in the protective layer forming step, the magnet body 2 coated with the coating solution is preferably coated at a temperature of room temperature to 300 ° C. and a time of 1 minute to 24 hours. It is preferable to treat appropriately according to the components contained therein. When these temperatures are low or the treatment time is short, a sufficient polymerization reaction of the inorganic polymer precursor is difficult to occur, and the inorganic polymer compound is not sufficiently formed. As a result, the heat resistance of the protective layer 4 is reduced. Tend to be low. 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 the method for producing a rare earth magnet of the present invention, in addition to the coating liquid preparation step and the protective layer formation step, polymerization of the inorganic polymer precursor may occur in the coating 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 preferable to cause a polymerization reaction 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 body 2 surface, and the adhesiveness to the magnet body 2 of the protective layer 4 comes to improve further.

  In a more preferred case, after causing a part of the condensation reaction in the coating liquid preparation step (that is, without completely condensing), in the protective layer forming step, in the coating liquid preparation step. The remaining inorganic polymer precursor in a further polymerizable state is polymerized. By doing so, an inorganic polymer compound is generated in the coating liquid preparation step, thereby reducing the stress generated when the protective layer is formed. 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 on the surface of the magnet body 2, and a π-π mutual between these polymer compounds. There is an effect. Since the organic polymer compound and the inorganic polymer compound are weakly bonded by this π-π interaction, phase separation between the two compounds hardly occurs in the protective layer 4. The compound and the inorganic polymer compound are in a uniformly dispersed state.

  In addition, since the organic polymer compound and the inorganic polymer compound are uniformly dispersed in this way, the protective layer 4 also has the characteristics obtained when these compounds are used alone. It has excellent corrosion resistance. For example, such a protective layer 4 is superior in moisture resistance and heat resistance as compared to a protective layer formed only from an organic polymer compound, and also compared with a protective layer formed only from an inorganic polymer compound. And it has the characteristic that it is excellent in stress relaxation property.

  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 washed repeatedly with water.

  Separately, 20 g of polystyrene having a weight average molecular weight of 2000 was dissolved in 80 g of tetrahydrofuran (THF), and 105 g of phenyltrimethoxysilane 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 polycondensation reaction of phenyltrimethoxysilane. 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.

  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, a coating solution was prepared by adding 105 g of phenyltrimethoxysilane and 17.5 g of 0.1% aqueous ammonia to 40 g of THF and reacting at 50 ° C. for 5 hours.

  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 average thickness of the protective layer was 15 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 methyltrimethoxysilane was used instead of phenyltrimethoxysilane.

  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 average thickness of the protective layer was 15 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 (18)

A magnet body made of a sintered body containing a rare earth element;
An organic polymer compound having an aromatic ring, and an inorganic polymer compound having an aromatic ring, and a protective layer formed on the surface of the magnet body;
A rare earth magnet comprising: The rare earth magnet according to claim 1, wherein a π-π interaction between the aromatic rings occurs between the organic polymer compound and the inorganic polymer compound. The rare earth magnet according to claim 1, wherein the organic polymer compound and the inorganic polymer compound are dispersed in the protective layer. The rare earth magnet according to any one of claims 1 to 3, wherein the organic polymer compound has a benzene ring as the aromatic ring. The organic polymer compound, a rare earth magnet according to any one of claims 1-4, characterized in that it comprises a polymer having styrene units. The inorganic polymer compound, a rare earth magnet according to any one of claims 1 to 5, characterized in that a compound having a main chain and the metal atom and the oxygen atom is bonded alternately. The rare earth magnet according to claim 6 , wherein Si is contained as the metal atom. The inorganic polymer compound has the following formula (1):
[Chemical 1]
R ¹ _n R ² _m Si (OR ³ ) _{4- (n + m)} (1)
[Wherein, R ¹ is an organic group having an aromatic ring, R ² is an alkyl group, R ³ is an alkyl group having 1 to 5 carbon atoms or an acyl group having 1 to 4 carbon atoms, n is 1 or 2, m Is 0 or 1. However, n + m is 2 or less. In addition, when it has two or more R < ¹ > or R < ³ >, each may be the same or different. ]
The rare earth magnet according to any one of claims 1 to 7 , wherein the rare earth magnet has at least a structural unit comprising a compound represented by formula (1) and / or a hydrolysis product thereof. The rare earth magnet according to claim 8, wherein the group represented by R ^{1 includes a} phenyl group which may have a substituent. An organic polymer compound having an aromatic ring, an inorganic monomer having an aromatic ring and a polymerizable functional group bonded to a metal atom, and / or an inorganic polymer precursor containing a polymer of the inorganic monomer, Through the mixing, a coating solution preparation step of preparing a coating solution,
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 forming step of forming a protective layer containing the organic polymer compound having an aromatic ring and the inorganic polymer compound having an aromatic ring from the coating solution;
A method for producing a rare earth magnet, comprising: The method for producing a rare earth magnet according to claim 10, wherein a π-π interaction between the aromatic rings occurs between the organic polymer compound and the inorganic polymer compound. The rare earth magnet according to claim 10 or 11, wherein the organic polymer compound and the inorganic polymer compound are dispersed in the protective layer. The coating solution preparation step, in at least one step of said applying step, and the protective layer forming step, any one of claims 10 to 12 characterized in that the polymerization of the inorganic polymer precursor A method for producing the rare earth magnet according to 1. The method for producing a rare earth magnet according to any one of claims 10 to 13, wherein the organic polymer compound is one in which the aromatic ring is a benzene ring. The method for producing a rare earth magnet according to claim 10 , wherein a polymer having a styrene unit is used as the organic polymer compound. The method for producing a rare earth magnet according to any one of claims 10 to 15 , wherein the inorganic polymer precursor is one in which the metal atom is Si. As the inorganic polymer precursor, the following formula (1);
[Chemical 2]
R ¹ _n R ² _m Si (OR ³ ) _{4- (n + m)} (1)
[Wherein, R ¹ is an organic group having an aromatic ring, R ² is an alkyl group, R ³ is an alkyl group having 1 to 5 carbon atoms or an acyl group having 1 to 4 carbon atoms, n is 1 or 2, m Is 0 or 1. However, n + m is 2 or less. In addition, when it has two or more R < ¹ > or R < ³ >, each may be the same or different. ]
The manufacturing method of the rare earth magnet as described in any one of Claims 10-16 characterized by including the inorganic monomer represented by these, and / or its hydrolysis product. The method for producing a rare earth magnet according to claim 17, wherein the group represented by R ^{1 includes a} phenyl group which may have a substituent.

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