JPH08143903A - Formability improver for rare earth sintered permanent magnet alloy powder - Google Patents

Abstract

(57) [Summary] (Modified) [Objective] The present invention provides a formability improving agent for rare earth sintered permanent magnet alloy powders, which reduces the oxidizing action of rare earth elements on higher fatty acid salts and is excellent in formability. . [Composition] Aromatic amine compounds, phenol derivatives, gallic acid esters, tocol derivatives, flavonoids, dibutylhydroxytoluene (BHT) and dibutylhydroxyanisole (BHA) selected as antioxidants for 100 parts by weight of higher fatty acid salts. At least one of 0.5
A moldability improving agent for rare earth permanent magnet alloy powder, characterized by being mixed in an amount of up to 50 parts by weight.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a formability improving agent for rare earth sintered permanent magnet alloy powders having excellent magnetic properties, which are useful as materials for various electric machines and electronic devices.

[0002]

2. Description of the Related Art Rare earth permanent magnets are generally manufactured by a powder metallurgy method, and the steps thereof are raw material melting, casting heat treatment, pulverization, magnetic field forming, sintering and aging. Coarse pulverization and fine pulverization are performed on the ingot of the target composition to obtain a pulverized magnetic powder of about several μm, but the additive-free powder that does not use any formability improver during and after pulverization has very poor formability. Due to friction with the side surface of the die at this time, flaws, peeling, cracks and the like are likely to occur on the die surface and the surface of the molded body. Further, in order to mold the additive-free powder, a very high molding pressure is required, and in such high-pressure molding, not only is it necessary to increase the size of the press machine, but the resulting molded body tends to crack. However, it was a big problem in terms of quality and product yield. In order to improve such moldability, conventionally, a binder such as paraffin wax, higher fatty acid or various higher fatty acid salts represented by zinc stearate, and a lubricant have been added and blended. However, paraffin wax has a small effect of improving formability, and if a large amount of paraffin wax is used, the orientation of the alloy powder in the magnetic field is obstructed and it becomes difficult to anisotropy. There was a defect of causing deterioration of characteristics. Further, in the case of higher fatty acid, the lubricity and orientation are good, but there is a problem that the strength of the molded product is significantly deteriorated. On the other hand, the higher fatty acid salt represented by zinc stearate has a great effect of significantly reducing the friction between the die surface and the molded product due to its excellent lubricity and has a high effect of improving the moldability, and also has an excellent orientation in a magnetic field. In addition, since the compact has high compact strength, it has excellent properties as a compactibility improver for rare earth sintered permanent magnet alloy powder. However, when the higher fatty acid salt is mixed with the active rare earth magnet fine powder of several μm, the catalytic effect of the metal ions of the magnetic powder and the higher fatty acid salt causes autoxidation of the higher fatty acid salt, and the higher fatty acid increases with time from the mixing. Oxidation of salt proceeds. Thus, the oxygen contained in the higher fatty acid salt in a large amount is combined with the rare earth element during the subsequent sintering step and taken into the magnet sintered body, resulting in a decrease in the effective rare earth amount in the magnet and a coercive force, This causes a decrease in energy product and deterioration of the BH curve in a rectangular shape. As described above, the higher fatty acid salt is an excellent moldability improving agent, but on the other hand, it works as an oxidizing agent for rare earth elements, so that it has a big problem that oxidation must be prevented.

[0003]

Despite being a higher fatty acid salt having excellent properties as a moldability improver for rare earth magnets, oxygen is present in the formability improver due to autoxidation generated by the catalytic effect of magnet fine powder. It has a problem that it is easily contained. The autoxidation of higher fatty acid salts is the same as in the case of general fatty acid esters. Here, a general autoxidation process of fatty acid is shown below (where R represents a fatty acid alkyl residue). Start RH → R ・ + H ・ ・ ・ ・ (1) RH + O ₂ → ROO ・ + H ・ ・ ・ ・ (2) Growth R ・ + O ₂ → ROO ・ ・ ・ ・ (3) ROO ・ + RH → ROOH + R · · · (4) Stop R · + R · → RR · (5) R · + ROO · → ROOR · · (6) ROO · + ROO · → ROOR + O ₂ · · (7) The metal ions generated from the fine powder and the higher fatty acid salt during the pulverization of the rare earth metal alloy contribute as a catalyst for the generation of active free radicals of the fatty acid salt in the initiation stage and cause the subsequent chain reaction. Therefore, the fatty acid salt contains a large amount of oxygen over time, and this oxygen causes deterioration of the characteristics of the rare earth sintered magnet. Therefore, it is necessary to prevent the oxidation of the higher fatty acid salt by inactivating the metal ion which is a catalyst for the generation of active free radicals in the oxidation mechanism. The present invention has been made in order to solve the above problems, and an object thereof is to provide a formability improving agent for a rare earth sintered permanent magnet alloy powder which has a reduced oxidizing effect and is excellent in formability.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that a higher fatty acid salt is blended with an antioxidant and mixed with a rare earth sintered permanent magnet alloy powder. It was found that the excellent moldability of higher fatty acid salts can be retained by molding in a magnetic field, sintering, and aging treatment, and the present invention was completed by establishing various conditions. Aromatic amine compounds, phenol derivatives, gallic acid esters as antioxidants for 100 parts by weight,
A moldability-improving agent for rare earth permanent magnet alloy powder, which comprises 0.5 to 50 parts by weight of at least one selected from flavonoid, dibutylhydroxytoluene (BHT) and dibutylhydroxyanisole (BHA). is there.

The present invention will be described in detail below.

The greatest feature of the present invention is that, in autooxidation, which is a major problem of higher fatty acid salts having excellent properties as a formability improving agent for rare earth sintered magnets, an antioxidant is added to the chain of autooxidation. It is to prevent the reaction, and thereby to immediately react with the highly reactive radicals R. and ROO. Generated in the reaction initiation and growth reaction to make them inactive and stop the chain reaction. Next, the antioxidant mechanism of the antioxidant will be described by taking an alkylphenol antioxidant as an example.

[0006]

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[0007]

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By the reaction of the above chemical formula 1 or 2, the alkylphenol stabilizes the radical generated by donating hydrogen to the highly reactive radical ROO. It functions to prevent the generation of radicals and prevent the oxidation of higher fatty acid salts.

As the antioxidant to be added to the higher fatty acid salt, a compound which readily reacts with a highly reactive radical R. or ROO. And readily donates a hydrogen atom for the purpose of inactivating it, that is, phenyl-β -Naphthylamine, phenyl
-Aromatic amine compounds such as α-naphthylamine, α-naphthol, phenol derivatives such as 2,6-ditertiarybutyl-4-methylphenol and tocophenol, gallic acid isobutyl esters, gallic acid esters such as gallic acid propyl ester, flavonoids , Dibutylhydroxytoluene (BHT), dibutylhydroxyanisole (BHA), etc. are suitable. If at least one selected from these is blended in an amount of 0.5 to 50 parts by weight, preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the higher fatty acid salt, oxidation of the higher fatty acid salt can be prevented. If the amount is less than 0.5 part by weight, the amount of the antioxidant is too small to sufficiently prevent the fatty acid salt from being oxidized, and the effect is impaired. Further, if it exceeds 50 parts by weight, the amount of the antioxidant having a small effect of improving the moldability is increased to hinder the improvement of the moldability, and the antioxidant reacts with the rare earth element during sintering to reduce the magnetic characteristics of the magnet. Will end up. Further, the antioxidant effect of the antioxidant is saturated. Therefore, the amount is preferably less than 10 parts by weight in order to exert the antioxidant effect and exhibit good magnetic properties.

Examples of the higher fatty acid salt include straight chain saturated fatty acids such as lauric acid, palmitic acid, stearic acid,
The monoene unsaturated fatty acids include palmitoleic acid, oleic acid, elaidic acid, polyene unsaturated fatty acids such as sorbic acid, linoleic acid, linolenic acid, and stearidonic acid, and these higher fatty acids include Ca, Mg, Zn, Al, and C.
Metal salts of o, Ni, Cu, Pb, etc. are used, but in practice, a fatty acid Mg salt or Zn salt having a carbon number of 16 to 18 is preferably used from the viewpoint of lubricating performance and easy availability. Further, these fatty acid salts are often mixed fatty acid salts in industrial production, and in that case, they can be used.

The amount of the moldability improving agent (mixture of higher fatty acid salt and metal deactivator) of the present invention added depends on the particle size and die of the raw material alloy powder, the shape and size of the molded body, the friction area (die surface and molding). Friction between body surfaces), press conditions, etc. can be appropriately selected. A small amount of addition has a great effect of improving the formability, and the formability is greatly improved with an increase in the addition amount. On the other hand, if it exceeds 0.5 parts by weight, the magnetic properties of the permanent magnet will deteriorate significantly, and if it is less than 0.005 parts by weight, the effect of improving the formability will not be obtained.
~ 0.3 parts by weight. The addition of the moldability improver of the present invention to the magnet alloy powder may be either dry mixing or wet mixing using a solvent solution.

[0012]

EXAMPLES The embodiments of the present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. (Examples 1 to 8 and Comparative Examples 1 to 3) Nd and Fe having a purity of 99.9% by weight and B having a purity of 99.5% by weight were weighed so as to be Nd ₁₅ Fe ₇₈ B ₇ and melted and cast in a vacuum melting furnace. Then, an ingot was produced. This ingot was roughly crushed with a jaw crusher and further jet-milled in a nitrogen gas stream to obtain a fine powder having an average particle size of 3.5 μm. The moldability improver compounded as shown in Table 1 was mixed in a fluorine-based solvent, sufficiently dried, and then the fine powder was oriented in a static magnetic field of 12 kOe and pressed at a pressure of 1 ton / cm ^2. I did. Immediately after pressing and for 7 days at 22 ° C, 40% RH
Sintered at 1100 ° C for 1 hour, then at 580 ° C for 1 hour
Heat treatment was performed for an hour. The magnetic properties were measured with a BH tracer, and the results and the oxygen increase in the sintered body after 7 days from immediately after pressing are shown in Table 2. As comparative examples, three examples of those in which the moldability improving agent of the present invention was not added at all, those in which the metal deactivator was not contained, and those in which the metal deactivator was excessively added were listed together in Tables 1 and 2.

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

INDUSTRIAL APPLICABILITY The present invention significantly reduces the friction between the die surface and the molded body due to its excellent lubricity without deteriorating the magnetic characteristics of the rare earth magnet, and also has a great effect on the orientation in a magnetic field. The present invention provides a moldability improver, which makes it possible to produce excellent rare earth sintered permanent magnets useful as materials for various electric machines and electronic devices, and its industrial utility value is extremely high.

Claims (1)

[Claims] 1. An aromatic amine compound, a phenol derivative, a gallic acid ester, a flavonoid, dibutylhydroxytoluene (BHT) and dibutylhydroxyanisole (BHA) as an antioxidant with respect to 100 parts by weight of a higher fatty acid salt.
A moldability improving agent for rare earth permanent magnet alloy powder, characterized by comprising 0.5 to 50 parts by weight of at least one selected from the above.