JP6600875B2 - Method for producing RTB-based sintered magnet - Google Patents

Description

  The present disclosure relates to a method for manufacturing an RTB-based sintered magnet.

R-T-B system sintered magnets mainly composed of R ₂ T ₁₄ B-type compounds are known as the most powerful magnets among permanent magnets, and include hard disk drive voice coil motors (VCM), It is used for various motors such as motors for hybrid vehicles and home appliances.

The _RTB -based sintered magnet has an irreversible thermal demagnetization because its intrinsic coercive force H _cJ (hereinafter simply referred to as “H _cJ ”) decreases at a high temperature. In order to avoid irreversible thermal demagnetization, it is required to maintain high H _cJ even at high temperatures when used for motors and the like.

The R-T-B based sintered magnet is known to improve H _cJ when a part of R in the R ₂ T ₁₄ B-type compound phase is substituted with a heavy rare earth element RH (Dy, Tb). . In order to obtain high H _cJ at a high temperature, it is effective to add a large amount of heavy rare earth element RH in the RTB-based sintered magnet. However, when the light rare earth element RL (Nd, Pr) is replaced as R in the RTB-based sintered magnet with the heavy rare earth element RH, H _cJ is improved, while the residual magnetic flux density B _r (hereinafter simply “ There is a problem that “B _r ”) is reduced. Further, since the heavy rare earth element RH is a rare resource, it is required to reduce the amount of use thereof.

In recent years, so as not to reduce the B _r, to improve the H _cJ of the R-T-B based sintered magnets have been studied with less heavy rare-earth element RH. For example, the fluoride or oxide of heavy rare earth elements RH, various metals M or M alloys, either alone or mixed, are present on the surface of the sintered magnet, and heat treatment is performed in that state, thereby increasing the coercive force. It has been proposed to diffuse the contributing heavy rare earth element RH into the magnet.

  Patent Document 1 discloses the use of R oxide, R fluoride, and R oxyfluoride powders.

  Patent Document 2 discloses that an RM (M is one or more selected from Al, Cu, Zn, Ga, etc.) alloy powder is used.

  Patent Documents 3 and 4 are RM alloys (M is one or more selected from Al, Cu, Zn, Ga, etc.), M1M2 alloys (M1M2 is one or more selected from Al, Cu, Zn, Ga, etc.), and It is disclosed that by using a mixed powder of RH oxide, it is possible to partially reduce the RH oxide with an RM alloy or the like during heat treatment and introduce the heavy rare earth element RH into the magnet.

International Publication No. 2006/043348 JP 2008-263179 A JP 2012-248827 A JP 2012-248828 A

  In the method disclosed in the above patent document, since the powder is present on the surface of the sintered magnet, typically, a slurry in which the powder is dispersed in water or an organic solvent is prepared, and the sintered magnet is contained in this slurry. After soaking, it is dried. Moreover, the method of apply | coating such a slurry by spraying can also be used.

  The present inventor examined a method of applying a paste obtained by mixing these powders with a binder to the surface of the sintered magnet, and the coating film was peeled off from the surface of the sintered magnet during the heat treatment, and the powder contained in the peeled portion. It has been found that the problem that medium elements do not sufficiently diffuse inside the sintered magnet can occur.

  The embodiment of the present disclosure diffuses a desired element from a powder particle included in a coating film into a coating object with good reproducibility by preventing the coating film from being peeled off from the surface of the sintered magnet in the course of heat treatment. Enable.

  An R-T-B system sintered magnet manufacturing method according to the present disclosure includes a step of preparing an R-T-B system sintered magnet, a mixed powder in which metal powder and metal compound powder are mixed, and a polymer composition. Forming a coating film of paste containing RTT on the surface of the RTB-based sintered magnet, and performing heat treatment on the RTB-based sintered magnet having the coating film formed on the surface And a step of diffusing a metal component in the coating film into the RTB-based sintered magnet, wherein the polymer composition is 2,2,4-trimethyl-1,3-pentanediol. A base oil containing monoisobutyrate, a binder, and a coupling agent are included.

  In one embodiment, the polymer composition further includes a dispersant.

  In a certain embodiment, the ratio of the said mixed powder with respect to the said whole paste is 70 mass% or more and 90 mass% or less.

  In one embodiment, the mixed powder includes a powder of an RLM alloy (RL is Nd and / or Pr, M is one or more selected from Cu, Fe, Ga, Co, and Ni), and RH fluoride (RH is Dy). And / or Tb), RH oxyfluoride, and at least one powder of RH oxide.

  In one embodiment, the RLM alloy powder is not less than 5 mass% and not more than 96 mass% of the entire mixed powder.

  In one embodiment, the base oil has a weight loss starting temperature of 100 ° C. to 300 ° C. by thermogravimetry.

  In one embodiment, after forming the coating film on the surface of the RTB-based sintered magnet, before diffusing the metal component in the coating film into the RTB-based sintered magnet. And a drying step for reducing the content of the base oil contained in the coating film, and a binder removal step for reducing the content of the binder contained in the coating film.

  According to the embodiment of the present disclosure, the coating film of the paste in which the powder and the polymer composition are mixed is prevented from being peeled off during the heat treatment, so that a desired element is diffused from the powder in the coating film to the object. Can be realized with a high yield. In an aspect of an embodiment, since the coating film of the paste in which the powder and the polymer composition are mixed is suppressed or prevented from being peeled off from the surface of the sintered magnet, the desired metal element in the powder is sintered with a high yield. The effect of improving the coercive force can be obtained.

FIG. 2 is a cross-sectional view schematically showing a state after a paste coating film 200 is formed on the surface of an R-T-B sintered magnet 100 and a drying process is performed. It is sectional drawing which shows the coating film 200 after performing a binder removal process. It is sectional drawing which shows the state of the coating film 200 after hold | maintaining at the temperature more than melting | fusing point of the metal powder particle 22 by heat processing. 4 is a cross-sectional view schematically showing a state in which the heat treatment temperature is increased and the metal in the coating film 200 is diffused from the surface of the RTB-based sintered magnet 100 into the magnet. FIG. It is sectional drawing which shows typically the part in which peeling of the coating film 200 produced in the middle of heat processing. It is sectional drawing which shows typically the state which the temperature of heat processing rose in the part in which peeling of the coating film 200 produced. It is a perspective view which shows the position of the magnet piece cut out from the RTB system sintered magnet 100 in order to measure a magnet characteristic with a broken line.

  As described above, the present inventor has intensively studied to solve the problem that the coating film for diffusing the metal element is peeled off during the heat treatment, and the diffusion component in the coating film is not sufficiently diffused into the magnet. As a result, it is possible to suppress peeling of the coating film by making the polymer composition contain a base oil containing 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, a binder, and a coupling agent. The present inventors have found that it can be prevented and have come up with the present invention.

  First, after forming a coating film of a paste containing the mixed powder and the polymer composition on the surface of the RTB-based sintered magnet, how the coating film changes through drying and heat treatment. Will be explained.

  FIG. 1A is a cross-sectional view schematically illustrating a state after a paste coating film 200 is formed on the surface of an RTB-based sintered magnet 100 and a drying process is performed. In the coating film (dry film) 200, a large number of metal powder particles 22 and metal compound powder particles 24 exist in the polymer composition 20 that spreads in a film shape along the surface of the RTB-based sintered magnet 100. ing. The coating film 200 immediately after coating has an appropriate viscosity that is easy to apply and still maintains sufficient fluidity, but the base oil in the polymer composition 20 is vaporized and fluidized by performing the drying process. Sex is lost. Although the base oil is a constituent element of the polymer composition 20, for convenience, the coating film 200 will be described using the term “polymer composition” as it is for the residue after the base oil is removed. There is.

  FIG. 1B shows a cross section of the coating film 200 after performing the binder removal process at the temperature T1. Although most of the polymer composition 20 of the coating film 200 is lost due to thermal decomposition or evaporation due to the binder removal step, the metal powder particles 22 and the metal compound powder particles 24 in the coating film (dried film) 200 are lost due to the remaining portion. Is retained. The coating film (dry film) 200 is adhered or fixed to the surface of the RTB-based sintered magnet 100.

  FIG. 1C shows a state of the coating film 200 after the heat treatment is performed at a temperature (T3) exceeding the melting point (T2) of the metal powder particles 22. In this state, it is presumed that the metal powder particles 22 are melted, and at least a part of the metal powder particles 22 spreads in a film shape and is in contact with the metal compound powder particles 24. The coating film 200 is fixed to the surface of the R-T-B system sintered magnet 100 in a film state in which the residue of the polymer composition 20, the melt of the metal powder particles 22, and the metal compound powder particles 24 are mixed. ing.

  When the coating film 200 is peeled off, the coating film 200 is warped in the vicinity of the temperature T2, and peeling starts to occur. When the coating film 200 is formed on, for example, the upper surface of the RTB-based sintered magnet, the coating film 200 that starts to warp near the temperature T2 is softened in the process in which the heat treatment temperature further rises and reaches the temperature T3. Then, it may happen that it naturally adheres to the upper surface of the RTB-based sintered magnet again. However, when the coating film 200 is formed on the side surface of the R-T-B type sintered magnet, the coating film 200 that starts to warp near the temperature T2 adheres again to the side surface of the R-T-B type sintered magnet. There is nothing. Further, when the coating film 200 is formed on the lower surface of the R-T-B system sintered magnet, when the R-T-B system sintered magnet is supported on a flat surface, the R-T-B system is used. When the space is present below the RTB-based sintered magnet, such as when supported by a rod-like or mesh-like support member, although warpage and peeling are not likely to occur due to the weight of the sintered magnet, Part of the film will peel off and will not adhere again.

  FIG. 1D schematically shows a state in which the heat treatment proceeds at the temperature (T3) and the metal in the coating film 200 diffuses from the surface of the RTB-based sintered magnet 100 into the magnet. At this time, rare earth elements diffuse from the inside of the RTB-based sintered magnet 100 to the surface, and mutual diffusion occurs. In this way, the metal component in the coating film can be diffused into the R-T-B sintered magnet by performing a heat treatment on the RTB-based sintered magnet having the coating film formed on the surface. It becomes possible.

  FIG. 2 is a cross-sectional view schematically showing a part where the coating film 200 has been peeled off during the heat treatment. FIG. 3 schematically shows a state of the heat treatment temperature T3 in the portion where the coating film 200 is peeled off. As shown in FIG. 2 and FIG. 3, when peeling occurs in the coating film 200, a gap is generated between the coating film 200 and the RTB-based sintered magnet 100, so that it is included in the coating film 200. The metal component cannot be uniformly diffused into the RTB-based sintered magnet 100.

  The manufacturing method of the RTB system sintered magnet in the non-limiting exemplary embodiment of the present disclosure includes a step of preparing an RTB system sintered magnet, a mixed powder, a polymer composition, Forming a coating film of paste containing Rt on the surface of the RTB-based sintered magnet. This mixed powder is a powder in which the metal powder and the metal compound powder are mixed. The “metal” of the metal powder does not need to be composed of one kind of metal element, and may be an “alloy (metal alloy)”.

  Furthermore, the manufacturing method of the R-T-B system sintered magnet in this embodiment performs the heat processing with respect to the R-T-B system sintered magnet with the above-mentioned coating film formed in the surface, and the metal in a coating film A step of diffusing the components inside the RTB-based sintered magnet.

  Hereinafter, each process of the manufacturing method of the RTB system sintered magnet in this embodiment is explained.

(1) Paste preparation [Polymer composition]
First, the polymer composition used in the embodiment of the present invention will be described. The polymer composition in the present embodiment includes a base oil, a binder, and a coupling agent.

  The base oil is a carrier for uniformly supplying various components contained in the polymer composition to the metal product surface and powder, and demonstrates the function of coating the surface of the sintered magnet with a uniform layer of the polymer composition. To do. The base oil in the present disclosure includes 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, which is a monoisobutyrate solvent. By including 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, the wettability between the polymer composition constituting the paste and the mixed powder can be enhanced. In addition, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate is easy to apply because of its low quick-drying property at room temperature, and the binder and coupling agent are uniformly applied to the sintered magnet surface and mixed powder. It contributes suitably also to making it adsorb | suck. As a result, the paste containing the polymer composition and the mixed powder can be firmly adhered to the surface of the sintered magnet.

  As will be described later, after forming the coating film of the paste on the surface of the sintered magnet, each step of drying, binder removal, and diffusion heat treatment is performed. The base oil contained in the polymer composition in the paste is not only difficult to dry during the coating process performed at room temperature, but the drying process leaves the binder, coupling, and mixed powder in a uniform layer on the sintered magnet surface. Vaporization is required. In this respect, the inventors' experiments confirmed that a base oil containing 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate is suitable.

  From the above requirements, the starting temperature for weight loss by thermogravimetric measurement of the base oil is desirably 100 ° C to 300 ° C, and more desirably 150 to 280 ° C. If the weight loss starting temperature by thermogravimetry is less than 100 ° C., a bumping phenomenon occurs in the drying step and the binder removal step, and the adhesion strength of the coating film is lowered, which may cause peeling of the coating film. In addition, it has a low flash point and is difficult to handle. When the weight loss starting temperature by thermogravimetry exceeds 300 ° C, the base oil tends to remain in the coating film in the drying process and the binder removal process, and a bumping phenomenon occurs during the temperature rise in the diffusion heat treatment process, and the adhesion strength of the coating film. May be a cause of peeling off of the coating film.

  The weight reduction start temperature by thermogravimetry can be determined by measuring the mass change of the base oil with a thermobalance and measuring the temperature at which the change (weight loss) of the obtained TG curve starts. The thing whose boiling point can be measured corresponds to the weight loss starting temperature by thermogravimetry. The blending ratio of the base oil in the polymer composition is preferably 50% by mass to 99% by mass.

  The binder functions to hold the mixed powder on the magnet surface and to suppress non-uniformization due to separation of the paste before application. The type of binder is not particularly limited. For example, at least one kind of cellulose such as ethyl cellulose, alkyd resin, rosin, petroleum resin and the like can be used. Of these, ethylcellulose is preferable in that it can easily maintain the adhesion between the magnet surface after the drying step and the coating film, and can further prevent the coating film from peeling off during heat treatment. The blending ratio of the binder in the polymer composition is preferably 1% by mass to 30% by mass.

  The coupling agent functions to improve the adhesion between the mixed powder and the binder component. The coupling agent may include one or more of a silane coupling agent and a titanium coupling agent, and the silane coupling agent improves adhesion to the polymer composition, the mixed powder, and the magnet surface after drying. This is preferable. Of these, epoxy silane coupling agents are preferred. The blending ratio of the coupling agent in the polymer composition is preferably 0.1% by mass to 10% by mass.

  The polymer composition used in the embodiment of the present invention preferably further contains a dispersant. The dispersant acts to adsorb on the mixed powder, break up the agglomeration, and make a uniform paste. Moreover, liquid separation can be prevented and the paste can be maintained for a long time. As the dispersing agent, an ashless type dispersing agent can be used, and a succinimide-based dispersing agent is preferable in terms of good adsorption with the mixed powder. The blending ratio of the dispersant in the polymer composition is preferably 0.1% by mass to 10% by mass.

  The mixing ratio of the mixed powder and the polymer composition can be adjusted so that the mixed powder accounts for 70 to 90% by mass of the whole. The mixed powder contained in the paste is a powder in a state where the metal powder and the metal compound powder are mixed. The content of the mixed powder differs depending on what metal element is introduced into the RTB-based sintered magnet. A specific example of the mixed powder will be described below, taking the case where the heavy rare earth element RH is diffused in the R-T-B system sintered magnet as an example.

[Metal powder]
RLM alloy powder that functions as a diffusion aid can be used. As the RL, a light rare earth element having a high effect of reducing the RH compound is suitable. Further, RL is also sometimes M also has the effect of diffused into the magnet to improve the H _cJ, tends to reduce the spread easily B _r to the main phase crystal grains inside the element should be avoided. From the viewpoint that the effect of reducing the RH compound is high and it is difficult to diffuse into the main phase crystal grains, RL is Nd and / or Pr, M is one or more selected from Cu, Fe, Ga, Co, Ni, and Al. And Among these, it is preferable to use an Nd—Cu alloy or an Nd—Fe alloy because the reducing ability of the RH compound by Nd is effectively exhibited. Further, the RLM alloy uses an alloy containing RL at 50 atomic% or more and having a melting point not higher than the heat treatment temperature. Such an RLM alloy efficiently reduces the RH compound during the heat treatment, and RH reduced at a higher rate diffuses into the R-T-B system sintered magnet and efficiently even in a small amount. The H _cJ of the sintered magnet can be improved. The particle size of the RLM alloy powder is preferably 500 μm or less.

[Metal compound powder]
A powder of an RH compound functioning as a diffusing agent (RH is Dy and / or Tb, and the RH compound is one or more selected from RH fluoride, RH oxide, and RH oxyfluoride) can be used. Among them, RH fluoride is preferable because it is easily reduced by the RLM alloy and has a large effect of improving _HcJ . The particle size of the RH compound powder is preferably 100 μm or less. In addition, the RH oxyfluoride in the present invention may be included in the RH fluoride as an intermediate substance in the production process of the RH fluoride.

  The abundance ratio (before heat treatment) of the RLM alloy and the RH compound in the powder state on the surface of the RTB-based sintered magnet may be RLM alloy: RH compound = 96: 4 to 5: 5 in mass ratio. it can. The abundance ratio may be RLM alloy: RH compound = 95: 5 to 6: 4. In the embodiment of the present disclosure, it is not necessarily excluded that a powder (third powder) other than the powder of the RLM alloy and the RH compound is present on the surface of the RTB-based sintered magnet. Care must be taken not to inhibit diffusion of RH in the RH compound into the R-T-B system sintered magnet. The mass ratio of the “RLM alloy and RH compound” powder in the entire powder existing on the surface of the RTB-based sintered magnet is desirably 70% or more.

(2) Preparation of R-T-B system sintered magnet base material An R-T-B system sintered magnet base material to be diffused of heavy rare earth element RH is prepared. In this specification, for the sake of easy understanding, an RTB-based sintered magnet that is an object of diffusion of the heavy rare earth element RH may be strictly referred to as an RTB-based sintered magnet base material. The term “RTB-based sintered magnet” includes such an “RTB-based sintered magnet base material”. As this RTB-based sintered magnet base material, a known material can be used, for example, having the following composition.

Rare earth element R: 12-17 atom%
B (a part of B (boron) may be substituted with C (carbon)): 5 to 8 atomic%
Additive element M ′ (selected from the group consisting of Al, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and Bi At least one): 0 to 2 atomic%
T (which is a transition metal element mainly composed of Fe and may contain Co) and inevitable impurities: the balance Here, the rare earth element R is mainly composed of at least one kind of light rare earth element RL (Nd, Pr) Element), but may contain heavy rare earth elements. In addition, when a heavy rare earth element is contained, it is preferable that at least one of Dy and Tb is included.

  The RTB-based sintered magnet base material having the above composition is manufactured by an arbitrary manufacturing method.

(3) Coating film formation Examples of a method for forming a coating film on the surface of the RTB-based sintered magnet base material may include a coating method (printing method), a dipping method, a spray method, and the like. The thickness of the coating film can be set, for example, in the range of 0.05 to 0.5 mm. The amount of RH element in the powder present on the surface of the RTB-based sintered magnet is preferably 0.03 to 0.35 mg per 1 mm ² of the magnet surface, and 0.05 to 0.25 mg. More preferably. The thickness of the coating film can be adjusted to realize such a value.

(4) Drying After forming the coating film on the surface of the RTB-based sintered magnet base material, the coating film is held at a temperature of, for example, 80 to 100 ° C. for 30 minutes to 3 hours and dried. By this drying step, the base oil contained in the coating film is vaporized and the content of the base oil is reduced. The content of the base oil contained in the coating film is substantially eliminated.

(5) Debinding After drying, the coating film is heat-treated at a temperature (T1) of 350 to 450 ° C. for 1 to 4 hours, for example. By this heat treatment, most of the binder in the coating film disappears due to thermal decomposition or evaporation.

(6) Diffusion heat treatment Next, heat treatment is performed at a temperature (T3) exceeding the melting point (T2) of the metal powder particles contained in the coating film, for example, 500 to 1000 ° C. for 10 minutes to 72 hours. Is diffused from the surface of the RTB-based sintered magnet base material to the inside.

  In the embodiment of the present disclosure, for example, the heat treatment can be performed in a state where the powder of the RLM alloy and the powder of the RH compound are present on the surface of the RTB-based sintered magnet base material. Since the RLM alloy powder melts after the start of the heat treatment, it is not necessary for the RLM alloy to always maintain a “powder” state during the heat treatment. The atmosphere for the heat treatment is preferably a vacuum or an inert gas atmosphere.

(7) Surface grinding Next, it grinds to the depth of about 50-500 micrometers from the surface of a coating film, for example, and removes the surface layer of a coating film and a RTB system sintered magnet.

  A base oil, a binder, a coupling agent, and a dispersant were blended in the components and ratios shown in Table 1 to prepare a polymer composition. Details of each component of the base oil shown in Table 1 are as follows.

Base oil A: 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate Boiling point 253 ° C.
Base oil B: normal paraffin boiling point 210 ° C
Base oil C: Toluene 80% by mass Ethanol 20% by mass Mixed liquid boiling point 78 ° C
Base oil D: pentaerythritol tetraoleate

  In addition, the weight loss start temperature by thermogravimetric measurement of the base oil D was 300 degreeC or more. That is, a change in mass from room temperature to 300 ° C. was measured with a thermobalance, but no change indicating weight loss occurred.

  Details of the binder, coupling agent, and dispersant components shown in Table 1 are as follows.

Binder A: Ethylcellulose (5% toluene 80 / ethanol 20 liquid, 25 ° C. viscosity: 12 to 16 cps)
Binder B: Ethyl cellulose (5% toluene 80 / ethanol 20 liquid, 25 ° C. viscosity: 40 to 52 cps)
Binder C: Rosin Coupling agent A: Epoxy silane coupling agent Coupling agent B: Amino titanium coupling agent Dispersant A: Succinimide

Further, a mixed powder was prepared by mixing Nd ₇₀ Cu ₃₀ alloy particles having a particle size of 150 μm or less and TbF ₃ particles having a particle size of 100 μm or less prepared by centrifugal atomization at a mass ratio of 6: 4. This mixed powder and the polymer composition shown in Table 1 were blended at a mass ratio of 8: 2 to prepare a paste.

  In Sample 10, the viscosity of the polymer composition was very high, and a paste that could be applied could not be produced with the above blending ratio. Further, the paste of Sample 6 could be applied without any problem and the test after the heat treatment could be proceeded, but the remaining paste was separated after several hours. No such separation after several hours was observed in the pastes other than Samples 6 and 10.

  Next, an R-T-B system sintered magnet that is a target to which the paste is applied will be described.

First, by a known method, the composition ratio Nd = 13.4, B = 5.8, Al = 0.5, Cu = 0.1, Co = 1.1, and the balance = Fe (atomic%) RT -B system sintered magnet was produced. By machining this, an R-T-B system sintered magnet base material of 5.7 mm × 15.6 mm × 70.2 mm was obtained. Magnetic properties of the obtained R-T-B based sintered magnet base material where a measured by B-H tracer, H _cJ is 1052kA / m, B _r was 1.45 T. In addition, when the impurity amount of the R-T-B system sintered magnet base material was measured by the gas analyzer, oxygen was 740 ppm, nitrogen was 490 ppm, and carbon was 880 ppm.

The paste shown in Table 1 except for the sample 10 was applied to the surface of an R-T-B system sintered magnet base material having a size of 15.6 mm × 70.2 mm by screen printing. The coating amount was adjusted so that the amount of Tb per mm ² was 0.07 mg. After application, it was dried at 90 ° C. for 1 hour. Similarly, the paste was applied to the opposite surface of the RTB-based sintered magnet base material and dried. Since samples 7 and 11 were peeled off during the drying process, the test was stopped at this point.

  An RTB-based sintered magnet having a paste coating film (dried film) formed on both sides thereof was erected so that the coating surface was vertical as shown in FIG. Specifically, after raising the temperature from room temperature to 400 ° C. at 10 ° C./min, heat treatment is performed at 400 ° C. for 2 hours, and further, the temperature is raised to 900 ° C. at 10 ° C./min, and then at 900 ° C. for 8 hours. The heat treatment was performed.

  The state of coating film peeling after heat treatment was evaluated. Further, the coated surface is uniformly removed from both surfaces by machining to a thickness of 5.3 mm, and then the portion 100a to the portion surrounded by the broken line of the RTB-based sintered magnet 100 shown in FIG. A magnet piece of 3 mm × 7.0 mm × 7.0 mm was cut out and the magnetic properties were measured with a BH tracer. Table 2 shows the evaluation results of peeling (peeling = x, no peeling = o) and measured values of magnetic properties. In all the samples where peeling occurred, the portion including the hatched portion shown in FIG. 4 was peeled off (the back side surface was the same).

  As can be seen from Table 2, in Samples 1 to 6 in which the paste prepared using the polymer composition of the example was applied and heat-treated, the adhesion of the coating film was maintained and the coercive force was greatly improved. However, in Comparative Samples 7 to 12 which are outside the scope of the present invention, a paste prepared using a polymer composition was applied and heat-treated, and an applicable paste could not be prepared, or in the drying process. Even if the coating film was peeled off or the heat treatment step was performed, the upper part of the coating film was peeled off and dropped, and the degree of improvement in coercive force was small.

Since the present invention can improve the H _cJ of an _RTB -based sintered magnet with less heavy rare earth element RH, it can be used for the production of a rare earth sintered magnet that requires a high coercive force. The present invention can also be widely applied to techniques that require diffusion of metal elements other than the heavy rare earth element RH from the surface to the rare earth sintered magnet.

22 Metal powder particles 24 Metal compound powder particles 100 RTB-based sintered magnet 200 Coating film

Claims (7)

A step of preparing an R-T-B sintered magnet;
Forming a coating film of a paste containing a mixed powder obtained by mixing metal powder and metal compound powder and a polymer composition on the surface of the RTB-based sintered magnet;
A step of diffusing a metal component in the coating film into the RTB-based sintered magnet by performing a heat treatment on the RTB-based sintered magnet having the coating film formed on the surface. When,
Including
The polymer composition includes an RTB-based sintered magnet including a base oil containing 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, a binder, and a coupling agent. Manufacturing method.   The method for producing an RTB-based sintered magnet according to claim 1, wherein the polymer composition further includes a dispersant.   The manufacturing method of the RTB system sintered magnet according to claim 1 or 2 whose ratio of said mixed powder to said paste whole is 70 mass% or more and 90 mass% or less. The mixed powder is
Powder of RLM alloy (RL is Nd and / or Pr, M is one or more selected from Cu, Fe, Ga, Co, Ni);
At least one powder of RH fluoride (RH is Dy and / or Tb), RH acid fluoride, and RH oxide;
The manufacturing method of the RTB type | system | group sintered magnet in any one of Claim 1 to 3 containing this.   The RLM alloy powder manufacturing method according to claim 4, wherein the RLM alloy powder is 5% by mass or more and 96% by mass or less of the entire mixed powder.   The method for producing an R-T-B system sintered magnet according to any one of claims 1 to 5, wherein the base oil has a weight loss starting temperature of 100C to 300C measured by thermogravimetry. After forming the coating film on the surface of the RTB-based sintered magnet, before diffusing the metal component in the coating film into the RTB-based sintered magnet,
A drying step for reducing the content of the base oil contained in the coating film;
A binder removal step for reducing the content of the binder contained in the coating film;
The manufacturing method of the RTB type | system | group sintered magnet in any one of Claim 1 to 6 containing this.

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