JPH03217010A - Manufacture of powder of rare earth magnet - Google Patents

Abstract

PURPOSE:To make it possible to manufacture powder of a rare earth magnet having excellent oxidation resistance at a low cost by mixing a surface treating agent for preventing oxidation of the magnet powder into solution wherein rare-earth magnet alloy undergoes wet crushing, and forming an excellent resin film on the fine powder of the rare earth magnet by a simple treating method. CONSTITUTION:In the manufacturing method of the powder of a rare earth magnet, surface treating agent for preventing the oxidation of the magnet powder is mixed into solution wherein the rare-earth magnet alloy undergoes wet crushing. For example, alloy lump for 200g of Nd-Fe-B-based magnet is coarsely crushed with a hammer. The powder is placed into a pot for a ball mill together with balls made of superhard alloy. Meanwhile 600g of 4wt.% solution wherein powder-state polyacrylonitrile is dissolved into N.N-dimethylformamide is put into the pot. The air in the pot is evacuated with a vacuum pump. The pot is set in the rotary ball mill. The material is crushed for 8 hours and the fine powder whose average particle diameter is 5mum is obtained. After the supernatant in the ball mill pot is removed, the powder is stirred, and the pressure is reduced. Thus the N.N-dimethylformamide is removed. The neodymium magnet powder whose surface is coated with the polyacrylonitrile is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing rare earth magnet powder used in producing rare earth magnets. [Prior Art] Generally, when producing rare earth magnets, an ingot having a desired alloy composition is melted, this ingot is compacted at an appropriate temperature, and then mechanically pulverized using a grinder such as a pole mill. Obtaining magnetic powder. This rare earth magnet powder alone or mixed with plastic is molded into a desired shape magnet by compression molding or injection molding either in a magnetic field or without a magnetic field, and if necessary, this molded body is impregnated with plastic and solidified. or sintered.

In recent years, the cost of Sm--Co magnet materials has been increasing due to the instability of the cobalt raw material situation.

On the other hand, Nd-Fe-B magnets have appeared that have magnetic properties comparable to or superior to those of Sm-Co magnet materials.
Plastic magnets using Nd-Fe-B magnet materials are particularly desired because they are abundant in resources and inexpensive. However, neodymium magnets are much more easily oxidized than Sm--Co magnets due to the effects of the elements they contain, and deterioration of magnetic properties due to oxidation poses a problem. To prevent oxidation, the ingot is coarsely ground with a stamp mill, hammer mill, roller mill, etc., and then finely ground with a pole mill, jet mill in an inert gas atmosphere such as nitrogen gas or argon gas, or in a grinding container such as a pole mill. A commonly used method is to put a coarse grinding magnet inside and add a solution such as toluene for wet grinding.

[Problems to be Solved by the Invention] Rare earth alloys, especially neodymium alloy powders, are highly susceptible to oxidation, so the process of grinding them into fine powders is carried out in an inert gas such as nitrogen or an organic solvent such as toluene. However, even if such a method is used, the magnetic properties may deteriorate due to combination with inert gas or a trace amount of oxygen in the organic solvent, or the crushed magnet powder may be taken out and used in the next process, such as resin. There has been a problem in that in the process of mixing with a binder and molding a magnet, it combines with oxygen, resulting in a significant decrease in magnetic properties.

Therefore, the present invention was achieved as a result of testing various effective organic substance coating methods for magnet powder in the pulverization process for obtaining rare earth magnet powder. An object of the present invention is to form a good resin coating on fine rare earth magnet powder using a simple processing method, and to produce rare earth magnet powder with excellent oxidation resistance at a low cost.

[A Thousand Steps to Solve the Problem] In order to achieve the above object, the features of the present invention are as follows:
After coarsely pulverizing an ingot of rare earth magnet alloy, a surface treatment agent for the purpose of preventing oxidation is mixed into the solvent when finely pulverizing it using a wet pulverization method, and surface treatment is performed at the same time as pulverization to create a stable magnet. The purpose is to obtain a powder.

[Operation: As a surface treatment agent, a polymer mainly composed of acrylonitrile forms a strong coating with low oxygen permeability on the surface of the magnet powder. Polymers mainly composed of acrylonitrile bond strongly with rare earth magnet powder, especially neodymium magnets, and due to the nature of the polymer, 02. Suppresses H20 invasion. A method for forming a coating of a polymer whose main component is acrylonitrile is to dissolve the polymer whose main component is acrylonitrile in a solvent placed in a wet grinding Pall mill container, and then grind the rare earth magnet alloy with the Pall mill. The acrylonitrile-based polymer adheres to the surface and covers the surface. Alternatively, the acrylonitrile monomer alone or it and other comonomers may be dissolved in a solvent, and the monomer etc. may be surface-polymerized or graft-polymerized on the pulverized surface while the rare earth magnet alloy is pulverized using a pole mill.

When we checked the progress of oxidation of the magnetic powder at high temperatures using an differential calorimetric analyzer on Nd14Fe80BB magnetic powder whose surface was treated with a polymer whose main component was acrylonitrile, we found that the main component was acrylonitrile. The sample that was not surface-treated with the polymer showed an oxidation tendency at about 250°C, whereas the surface-treated magnet powder showed no oxidative exothermic reaction even at temperatures exceeding 300°C. This can be attributed to the fact that a strong film of acrylonitrile resin is formed on the surface of the magnet powder, improving heat resistance and oxidation resistance. [Examples] Next, the manufacturing method of the present invention will be described based on Examples.

N d 14F e produced by vacuum arc melting
200 g of neodymium, iron, and poron alloy ingots for magnets having a component composition of 80B8 were coarsely ground with a hammer and placed in a pole mill pot with a cemented carbide pole, while powdered polyacrylonitrile was dissolved in N-N dimethylformamide. Put 600g of the 4WT% solution into the pot,
The air inside the pot was evacuated using a vacuum bomb. This pot was set in a rotary ball mill and ground for 8 hours to obtain an average particle size of 5I.
It was finely ground to Lm. After removing the supernatant liquid from the ball millbot, N-N-dimethylformamide was removed under reduced pressure while stirring to obtain neodymium magnet powder whose surface was coated with polyacrylonitrile.

Next, 12 nylon was added to the neodymium magnet powder, which had been surface-treated at the same time as wet grinding with polyacrylonitrile, and was heated and kneaded with a pressurized 21-glue to create a compound containing 55-T% of magnet powder, which was injected into a cylindrical shape of φllxlOmm. Molded.

When this cylindrical body was magnetized by applying a magnetic field of 7,000 Oe, it became a magnet with a residual magnetic flux density of 400 Gauss and an intrinsic coercive force of 2,400 Oe.

After this magnet was left in the atmosphere for one week, the residual magnetic flux density and intrinsic coercive force were measured, and no demagnetization was observed.

[Comparative example] N d 14F e 80BB (7) 200 g of alloy ingot
was coarsely ground with a hammer, placed in a ball mill pot together with a N-N-dimethylformamide solution, and rotary ground for 8 hours to obtain a magnet powder with an average particle size of 5 ILm. The procedure was exactly the same as in Example except that polyacrylonitrile was not dissolved in the solution. 12 Nylon was added to the magnet powder obtained by wet grinding in this way, and the compound was heated and kneaded with a pressurized 21 goo to create a compound containing 55 wt% of magnet powder.
It was injection molded into a cylindrical shape of mm.

When this cylindrical body was magnetized by applying a magnetic field of 7000 Oe, it became a magnet with a residual magnetic flux density of 230 Gauss and an intrinsic coercive force of 1200 Oe.

When this magnet was measured after being left in the atmosphere for one week, the residual magnetic flux density was 50 Gauss and the intrinsic coercive force was 75 Oerstedt, which were significantly lower.

[Effects of the Invention] As described above, according to the method of the present invention, when a rare earth magnet alloy is wet-pulverized, a polymer containing acrylonitrile as a main component is mixed into the solution as an antioxidant, and then crushed. An anti-oxidation coating can be formed on the magnet powder at the same time as pulverization.

In particular, by coating neodymium powder with a polymer whose main component is acrylonitrile, the oxidation resistance of the magnet can be significantly improved.

Claims (2)

[Claims] (1) A method for producing rare earth magnet powder, characterized in that a surface treatment agent for preventing oxidation of the magnet powder is mixed into a solution in which a rare earth magnet alloy is wet-pulverized. (2) The method for producing rare earth magnet powder according to claim (1), wherein the surface treatment agent is a polymer containing acrylonitrile as a main component.