JP4265168B2 - Method for manufacturing permanent magnet - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a permanent magnet that is capable of imparting various functions such as high corrosion resistance and insulation to a rare earth permanent magnet and that is free from pollution problems and is friendly to the global environment.
[0002]
[Prior art]
Rare earth permanent magnets such as R—Fe—B permanent magnets represented by Nd—Fe—B permanent magnets and R—Fe—N permanent magnets represented by Sm—Fe—N permanent magnets are In particular, R-Fe-B based permanent magnets are used in various fields today because they use abundant and inexpensive materials and have high magnetic properties.
However, since rare earth permanent magnets contain a highly reactive rare earth element: R, they are easily oxidatively corroded in the atmosphere. When used without any surface treatment, a slight amount of acid, alkali, moisture, etc. Corrosion proceeds from the surface due to the presence of rust, and rust is generated, resulting in deterioration and variation in magnet characteristics. Furthermore, when a magnet in which rust is generated is incorporated in an apparatus such as a magnetic circuit, the rust may be scattered to contaminate peripheral components.
In view of the above points, for the purpose of imparting corrosion resistance to a rare earth permanent magnet, it has long been performed to form a resin film as a corrosion resistant film on the surface thereof.
Until now, when forming a resin film on the surface of rare earth permanent magnets, electrodeposition coating, spray coating, dip coating, and roll coating methods can be applied to coating solutions prepared by dissolving the resin that is the coating component in an organic solvent. A method of applying a resin film by applying heat treatment to the surface of a magnet by means of heat treatment has been adopted. The resin film forming method using such a coating liquid is very useful in that the process is simple. However, this method has a problem that the organic solvent evaporates from the film in the process of forming the resin film by heat treatment, so that there is a problem that pinholes are easily generated in the film and a yield of the coating liquid is poor. However, it cannot be said to be a satisfactory method in terms of performance and cost as a corrosion resistant coating. Also, this method using an organic solvent is not desirable in terms of improving the global environment. Therefore, as an alternative method of forming a resin film using such a coating liquid, a method of forming a resin film on the surface of a rare earth permanent magnet by electrostatic powder coating using a powder coating has already been proposed. (Japanese Patent Laid-Open No. 11-238620).
[0003]
[Problems to be solved by the invention]
The method of forming a resin coating on the surface of rare earth permanent magnets by electrostatic powder coating using powder coating is a rare earth permanent permanent powder coating that is negatively charged by an electrostatic coating gun or the like. This is a method in which the powder coating is melted to form a resin film by applying heat treatment after being applied to the surface of the magnet, and the resin film formed is more corrosion resistant than the resin film forming method using a coating liquid. Excellent in that it can be recovered and reused because it can be recovered and reused, and there is no pollution problem because it does not use organic solvents. Although it is a method, in order to satisfy the high corrosion resistance requested | required of recent rare earth permanent magnets, the further improvement is required.
In recent years, rare earth permanent magnets have been required to have various functions such as insulation as well as high corrosion resistance depending on the application field, and an excellent method that can impart various functions to rare earth permanent magnets. Is anxious.
Accordingly, an object of the present invention is to provide a method for producing a permanent magnet that is free from pollution problems and can be imparted to rare earth-based permanent magnets with various functions such as high corrosion resistance and insulation.
[0004]
[Means for Solving the Problems]
As a result of various investigations in view of the above points, the present inventor has found that a fine particle-dispersed resin coating is applied to the surface of a rare earth permanent magnet by electrostatic powder coating using a powder coating composed of inorganic fine particles and a resin. It was found that the above-mentioned purpose can be achieved by forming.
[0005]
The present invention has been made based on the above findings, the manufacturing method of a permanent magnet of the present invention, as claimed in claim 1, a powder coating comprising a fine inorganic particles and a resin, the average as fine inorganic particles A powder coating material containing zinc fine particles having a particle size of 0.01 μm to 20 μm in an amount of 25% by weight to 95% by weight and having an average particle size of 10 μm to 50 μm with the zinc fine particles exposed on the surface. It is characterized in that an inorganic fine particle-dispersed resin film is formed on the surface of a rare earth permanent magnet by electrostatic powder coating .
Also, the manufacturing method according to claim 2 is the manufacturing method according to claim 1, wherein the resin is an epoxy resin.
Also, the manufacturing method according to claim 3, wherein, in the method according to claim 1 or 2, wherein the film thickness of the inorganic fine particle dispersed resin coating is characterized by a 10 m to 50 m.
Moreover, the permanent magnet of this invention was manufactured with the manufacturing method of Claim 1 as described in Claim 4 .
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The method for producing a permanent magnet of the present invention is characterized in that an inorganic fine particle-dispersed resin film is formed on the surface of a rare earth permanent magnet by electrostatic powder coating using a powder coating comprising inorganic fine particles and a resin. Is. A method of forming an inorganic fine particle-dispersed resin film using a coating solution prepared by dispersing inorganic fine particles in a solution obtained by dissolving a resin in an organic solvent is already known, but is formed by the method of the present invention. The inorganic fine particle-dispersed resin film is superior in adhesion to the surface of the rare earth permanent magnet, and the inorganic fine particle dispersed in the resin film is more than the inorganic fine particle-dispersed resin film formed by a method using a coating liquid. It has an effect that could not be expected from the previous knowledge that its function is higher.
[0007]
The inorganic fine particles serving as a constituent component of the powder coating material are appropriately selected according to the function to be imparted to the rare earth permanent magnet. For example, for the purpose of imparting high corrosion resistance, zinc fine particles, aluminum fine particles, magnesium fine particles, or the like may be selected. Since these metal fine particles have a lower potential than the surface substrate of the rare earth permanent magnet, when the resin film in which these metal fine particles are dispersed is formed on the surface of the rare earth permanent magnet, the metal fine particles in the resin film By exhibiting an electrochemical sacrificial anticorrosive action, high corrosion resistance can be imparted to the rare earth permanent magnet as the entire coating. For the purpose of imparting insulation, fine particles of metal oxide such as SiO ₂ or Al ₂ O ₃ may be dispersed in the resin film. Further, if the anatase type TiO ₂ fine particles are dispersed in the resin film, the photocatalytic function can be imparted to the rare earth permanent magnet.
[0008]
The average particle size of the inorganic fine particles is desirably 0.01 μm to 20 μm. If the average particle size is less than 0.01 μm, the aggregation of inorganic fine particles is likely to occur, making it difficult to uniformly disperse the inorganic fine particles in each powder, and consequently the inorganic fine particles on the surface of the rare earth permanent magnet. This is because it becomes difficult to form a resin film in which a uniform dispersion is made, and thus high corrosion resistance may not be imparted to the rare earth permanent magnet. On the other hand, if the average particle size exceeds 20 μm, the film thickness of the formed film becomes too thick, and it may be difficult to provide a small magnet having excellent dimensional accuracy and to secure the effective volume of the magnet. It is.
[0009]
Examples of the resin that is a constituent of the powder coating include resins generally used as constituents of the powder coating such as epoxy resin, acrylic resin, polyester resin, polyamide resin, polyimide resin, and polyamideimide resin. Among these, epoxy resins are excellent resins in terms of corrosion resistance and handling properties, and polyimide resins are resins excellent in terms of insulation properties, gas resistance and heat resistance. Therefore, these resins are preferably used in the present invention. Adopted.
[0010]
The content of inorganic fine particles in the powder coating is preferably 25% by weight to 95% by weight. If the amount is less than 25% by weight, the effect of dispersing the inorganic fine particles in the resin film may not be sufficiently exhibited. On the other hand, if the amount exceeds 95% by weight, the essential function of the resin film may be impaired. This is because the intended function may not be imparted to the rare earth-based permanent magnet due to the loss of smoothness.
[0011]
The powder coating material composed of inorganic fine particles and resin is a known powder coating manufacturing technology, that is, for example, when a resin curing agent (epoxy resin is used as necessary) for inorganic fine particles and resin as raw materials. In general, aromatic amines, acid anhydrides, dicyandiamide derivatives, and the like are used, and various additives, catalysts, and the like are uniformly mixed, and then manufactured through melt dispersion, cooling, pulverization, and sieving steps. The average particle size of the powder coating material thus produced is desirably 10 μm to 50 μm. The reason is that, as will be described later, the inorganic fine particle-dispersed resin film formed on the surface of the rare earth permanent magnet preferably has a film thickness of 10 μm to 50 μm, which is convenient for forming a film having such a film thickness. Because it is good.
[0012]
Electrostatic powder coating using a powder coating material composed of inorganic fine particles and resin may be performed by a known electrostatic powder coating technique. Further, for example, according to the electrolytic fluid electrostatic powder coating technique described in JP-A-11-57592, an inorganic fine particle-dispersed resin film can be uniformly formed on the entire surface of the rare earth permanent magnet. The film thickness of the inorganic fine particle-dispersed resin film thus formed is desirably 10 μm to 50 μm. If the film thickness is less than 10 μm, the performance as an inorganic fine particle-dispersed resin film may not be sufficiently exhibited. On the other hand, if the film thickness exceeds 50 μm, a small magnet having excellent dimensional accuracy and the effective volume of the magnet are provided. This is because it may be difficult to ensure the above.
[0013]
The rare earth permanent magnet having the inorganic fine particle dispersed resin film formed by the method of the present invention on its surface is, for example, a magnetic circuit using an organic adhesive such as an epoxy adhesive or an acrylic adhesive. Although it is incorporated into an apparatus and used, if the inorganic fine particles are dispersed in the resin film, the wettability and anchor effect of the surface of the resin film are improved. Therefore, according to the production method of the present invention, the resin film and the organic system are used. Excellent adhesion to the adhesive can also be obtained.
[0014]
【Example】
The present invention will be described in more detail with reference to the following examples, but the present invention should not be construed as being limited thereto.
In the following experiment, for example, as described in U.S. Pat. No. 4,770,723 and U.S. Pat. No. 4,792,368, a known cast ingot is pulverized, and after pulverization, molding, sintering, heat treatment, and surface treatment are performed. This was carried out using a sintered magnet (hereinafter referred to as a magnet test piece) having a length of 15 mm, a width of 10 mm, and a height of 2 mm of the composition (at%) of 14Nd-79Fe-6B-1Co obtained by the above.
[0015]
Example 1:
According to a known powder coating production technology, 13% by weight of bisphenol A type epoxy resin (Epicoat 1002: manufactured by Yuka Shell) and 7% by weight of dicyandiamide derivative (Araldite HT-2844: manufactured by Asahi Ciba) which is a resin curing agent And 80% by weight of zinc fine particles having an average particle diameter of 4 μm (Zinc Dust # 3: manufactured by Sakai Chemical Co., Ltd.) are mixed uniformly, followed by melt dispersion, cooling, pulverization, and sieving steps, and the content of zinc fine particles is 80%. %, And a powder coating material having an average particle size of 25 μm was produced.
In accordance with a known electrostatic powder coating technique, ultrasonic cleaning is performed in ethanol for 3 minutes to degrease the surface, and then the surface of the magnet body test piece is dried at 100 ° C. for 10 minutes in a vacuum using an electrostatic coating gun. After negatively charged powder coating is applied by electrostatic attraction, it is baked by heat treatment at 180 ° C. for 15 minutes in the atmosphere, and zinc fine particles having a film thickness of about 30 μm on the surface of the magnet specimen A dispersed epoxy resin film (dispersion amount of zinc fine particles in the film was 80% by weight) was formed.
When the corrosion resistance test of spraying 5% salt water at 35 ° C. was performed on the magnet specimen having the zinc fine particle dispersed epoxy resin coating obtained on the surface as described above, rusting was observed even after 100 hours. Not observed (n = 10).
[0016]
Comparative Example 1:
An epoxy resin coating solution containing zinc fine particles having an average particle diameter of 4 μm on the surface of a magnet specimen that was degreased by ultrasonic cleaning for 3 minutes in ethanol and then dried in vacuum at 100 ° C. for 10 minutes. (Epo-Roval: manufactured by Roval Co., Ltd.) was applied by spray coating, then baked by heat treatment at 180 ° C. for 15 minutes in the atmosphere, and a zinc fine particle dispersed epoxy resin having a film thickness of about 30 μm on the surface of the magnet body test piece A film (dispersion amount of zinc fine particles in the film was 96% by weight) was formed.
When the corrosion resistance test of spraying 5% salt water at 35 ° C. was performed on the magnet body test piece having the zinc fine particle dispersed epoxy resin coating on the surface obtained as described above, it occurred after 48 hours in all samples. Rust was observed (n = 10).
[0017]
Comparative Example 2:
In accordance with a known electrostatic powder coating technique, ultrasonic cleaning is performed in ethanol for 3 minutes to degrease the surface, and then the surface of the magnet body test piece is dried at 100 ° C. for 10 minutes in a vacuum using an electrostatic coating gun. After applying a negatively charged powder coating made of epoxy resin (Billiusia EP1000: manufactured by Nippon Paint Co., Ltd.) by electrostatic attraction, it is baked by heat treatment at 180 ° C. for 15 minutes in the atmosphere. An epoxy resin film having a thickness of about 30 μm was formed on the surface of the test piece.
When the corrosion resistance test of spraying 5% salt water at 35 ° C. was performed on the magnet body test piece having the epoxy resin coating obtained on the surface as described above, rusting was observed after 24 hours in all samples. (N = 10).
[0018]
In the zinc fine particle-dispersed epoxy resin coating formed in Example 1 and Comparative Example 1, when moisture enters the coating, a corrosion battery is formed between the surface base of the rare earth permanent magnet and the zinc fine particles, and the rare earth based Zinc fine particles with a lower potential than the surface base of the permanent magnet corrode instead of the rare earth permanent magnet, that is, in addition to the zinc fine particles exhibiting an electrochemical sacrificial anti-corrosion action, the eluted zinc is water and carbon dioxide. The zinc compound produced by the reaction with the material fills the surface of the film and voids existing in the film and densifies the film, thereby preventing the entry of corrosion factors from the outside. It is given to the system permanent magnet.
Surprisingly, the zinc fine particle-dispersed epoxy resin coating formed in Example 1 is more than the zinc fine particle-dispersed epoxy resin coating formed in Comparative Example 1 even though the amount of zinc fine particles dispersed is smaller. High corrosion resistance could be imparted to rare earth permanent magnets. The following factors can be considered as the reason for such a result. That is, since the zinc fine particles in the zinc fine particle-dispersed epoxy resin coating liquid of Comparative Example 1 are present in a state of being coated with the epoxy resin, the surface base of the rare earth permanent magnet and the zinc are formed in the formed coating. There seems to be relatively few contact parts with microparticles. However, in the powder coating of Example 1, zinc fine particles are exposed on the surface of each powder (this fact is confirmed by the present inventor through surface EPMA analysis of the powder coating), In a film formed by electrostatic powder coating using such a powder coating, it is considered that there are many contact portions between the surface base of the rare earth permanent magnet and the zinc fine particles, and thus the electric charge of the zinc fine particles is It is considered that the chemical sacrificial anticorrosive action was exerted. In addition, the large number of contact portions between the surface base of the rare earth permanent magnet and the fine zinc particles contributes to improving the adhesion of the coating to the magnet surface and effectively preventing moisture from reaching the magnet surface. it seems to do. Furthermore, in Comparative Example 1, it can be considered that pinholes are generated in the film by evaporating the organic solvent from the film in the process of forming the resin film by heat treatment. One of the factors is that this phenomenon does not occur.
[0019]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the permanent magnet which does not have a pollution problem and can give various functions, such as high corrosion resistance and insulation, to a rare earth-type permanent magnet, is kind.

Claims (4)

A powder coating material comprising inorganic fine particles and resin , each containing 25 to 95% by weight of zinc fine particles having an average particle size of 0.01 to 20 μm as inorganic fine particles and an average particle size of 10 to 50 μm A permanent-magnet dispersed resin film is formed on the surface of a rare earth permanent magnet by electrostatic powder coating using a powder coating in which zinc fine particles are exposed on the surface of the powder. Manufacturing method . The manufacturing method according to claim 1 , wherein the resin is an epoxy resin . The method according to claim 1 or 2 , wherein the inorganic fine particle-dispersed resin film has a thickness of 10 µm to 50 µm.   A permanent magnet manufactured by the manufacturing method according to claim 1.