JPH07297013A - Manufacture method of magnetic powder - Google Patents

Abstract

PURPOSE:To manufacture magnetic powder having excellent magnetic characteristics by crushing an interfacial activator added magnetic material in a liquid. CONSTITUTION:An interfacial activator added magnetic material is crushed in a liquid. At this time, the interfacial activator adsorbs on the surface of the crushed magnetic material. The interfacial activator composed of long chain molecules can avoid the cohesion.-agglutination (physical coupling) of the magnetic material particles by magnetism thereof. Accordingly, the magnetic material can be crushed to single magnetic domains thereby enabling the magnetic particles having high residual magnetizing force and coersive force to be manufactured. This interfacial activator is at least one kind of elements out of stearic acid, ricinoleic acid, derivative of stearic acid or at least one kind of the derivatives of the ricinoleic acid. Finally, 0.1-30wt.% of this interfacial activator is to be added to the 100wt.% of the magnetic material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing magnet powder which can be used for bonded magnets and the like.

[0002]

2. Description of the Related Art Currently, magnets include sintered magnets and bonded magnets. Of these, the sintered magnet is the magnet powder 100.
%, Which has a high magnetic property. Therefore, sintered magnets are used where high magnetic properties are required.

On the other hand, a bonded magnet is a composite material of magnet powder and resin, and is used where a complicated shape is required. Specifically, it is used for thin-walled rings such as stepping motors.

By the way, many magnetic materials are brittle and have low mechanical strength. Therefore, their processing is one of the major problems. There are some magnetic materials with excellent mechanical strength, but the rare earth magnet, which is the most high-performance magnet,
Brittleness and low mechanical strength. Bonded magnets are composite materials developed to compensate for these drawbacks. That is, since it is excellent in shape-imparting property due to the addition of the resin, it is easier to manufacture a complex-shaped component or a thin-walled component as compared with a sintered magnet.

In order to improve the performance of such bonded magnets and sintered magnets, it is necessary to improve the performance of the raw material magnet powder. For example, in a bonded magnet, Sm ₂ Fe ₁₇
N ₃ is considered as one of the candidate materials for higher performance. In particular, Sm ₂ Fe ₁₇ N ₃ can be expected to have higher performance than Nd-Fe-B based magnets and Sm-Co based magnets when (1) bonded magnets are used. (2) Burning because it decomposes at 600 ° C or higher Inability to tie (10 for sintering this kind of material
Therefore, it is expected as a bonded magnet material. Further, since the magnetic characteristics are high, the device can be downsized. However, the actually obtained Sm ₂ Fe ₁₇ N ₃
The powder has not yet been put to practical use because its magnetic properties are not sufficiently high.

The reason why the magnetic properties of the obtained Sm ₂ Fe ₁₇ N ₃ powder are not sufficiently high will be described below.

As a conventional method for producing magnet powder such as Sm ₂ Fe ₁₇ N ₃ powder, the raw material is pulverized mainly by a mechanical method. However, the magnetic properties of the obtained powder are not sufficiently high and are not sufficient for practical use. It is considered that the magnetic properties are improved when the single domain particles of several μm are used, but when the raw material is pulverized, the magnetic powder causes aggregation and adhesion due to its magnetic force, and the pulverization effect is not fully utilized. Is.

That is, since the particle size of the magnet raw material obtained by pulverization is extremely small and the magnetization and coercive force are generated, the individual particles become strong magnets, and the magnetic force causes strong agglomeration (physics) between the particles. Binding) occurs. Further, in a mechanical pulverization method such as a ball mill, these agglomerated particles are bound together more strongly and are accompanied by a chemical bond. Therefore, even if the grinding time is lengthened, the particle size does not become fine, and the particle size tends to increase after reaching the minimum value at a certain grinding time. For example, in order to obtain high remanence and high coercive force with Sm ₂ Fe ₁₇ N ₃ based magnetic powder, it is necessary to grind to a single domain particle diameter of about 1 μm. However, the conventional pulverization does not reach the single magnetic domain grain size, and the magnetic properties are low. Even if the pulverization is further advanced, only large secondary particles that are aggregated and adhered are formed, and the magnetic characteristics are not improved.

Further, in the conventional pulverization method, since the pulverization efficiency is not sufficiently high, strain is likely to be introduced inside the particles, resulting in deterioration of crystallinity. The decrease in crystallinity reduces the saturation magnetization and consequently the residual magnetic flux density.

In order to prevent the agglomeration / adhesion of the magnet powder, a method of pulverizing the magnet raw material at a high temperature (above the Curie temperature) at which the magnet raw material loses magnetism during pulverization has been proposed (Japanese Patent Laid-Open No. 175022/1993). Gazette).

[0011]

However, the above proposal also has the following problems.

Rare earth compounds such as Sm ₂ Fe ₁₇ N ₃ are
It is very susceptible to oxidation, so if it is crushed at a high temperature, it will easily be oxidized. For example, when Sm ₂ Fe ₁₇ N ₃ is oxidized, Sm and Fe become oxides and lose magnetic properties. In addition, as described above, Sm ₂ Fe ₁₇ N ₃ easily decomposes at high temperature. This decomposition is the following equation. Sm ₂ Fe ₁₇ N ₃ → 2SmN + 17Fe + 1 / 2N ₂

It is known that even if the decomposition is slight, α-Fe, which is soft magnetic, precipitates and the coercive force is greatly reduced. Also, Nd ₂ Fe other than Sm ₂ Fe ₁₇ N _3
Even in rare earth magnets such as ₁₄ B and Sm ₂ Co ₁₇ , when they are oxidized or decomposed in the same manner as described above, Fe and Co, which are soft magnetism, are precipitated, and the overall coercive force is greatly reduced. As described above, crushing at high temperature deteriorates the magnetic properties of the magnet powder.

Further, crushing at a high temperature requires a complicated apparatus and a high running cost.

The present invention has been made in view of the problems of the prior art, and an object of the present invention is to provide a method for producing magnet powder having excellent magnetic characteristics.

[0016]

The method for producing magnet powder of the present invention is characterized by adding a surfactant to a magnet raw material and pulverizing the magnet raw material in a liquid.

[0017]

According to the present invention, it is possible to manufacture magnet powder having excellent magnetic properties. The reason for this is not clear, but it is considered as follows.

When the magnet raw material is pulverized in a liquid, the surfactant is adsorbed on the surface of the pulverized magnet raw material powder. Since the surfactant is composed of long chain molecules, it prevents the powder of the magnet raw material from adhering / aggregating (physically binding) due to its magnetic force.

Therefore, since the magnet raw material can be pulverized to have a single magnetic domain particle size, magnet powder having high remanence and high coercive force can be obtained.

The surfactant is also considered to act as a grinding aid. Grinding efficiency is poor, and if it takes a long time to grind to a predetermined particle size, distortion is introduced into the particles, which is not desirable, but the addition of a surfactant improves the grinding efficiency and shortens the time. Since it is possible to pulverize in, it is difficult to introduce strain inside the particles. Therefore, the crystallinity of the particles is not reduced, and the residual magnetic flux density is not reduced.

[0021]

According to the present invention, magnet powder having excellent magnetic properties can be manufactured.

[0022]

EXAMPLES The inventions (other inventions) that make the present invention more specific will be described below.

(Description of Other Inventions) In the present invention, a surfactant is added to a magnet raw material and the magnet raw material is pulverized in a liquid.

The present invention can be applied to any raw material of a magnet to be pulverized, but is particularly suitable for producing magnet powder in which single domain particles are obtained by mechanical pulverization. For example, it can be applied to Sm ₂ Fe ₁₇ N _{3 and the} like. Further, it is desirable that the raw material of the magnet is pulverized in a coarse powder state according to the present invention to produce the magnet powder.

As the surfactant added to the magnet raw material,
Although it may be of any type, one containing a long chain organic molecule is preferable. This is because the long chain organic molecules prevent the magnet particles from approaching each other, and efficiently prevent the particles from aggregating and adhering. Examples of the surfactant containing such an organic molecule include condensed stearic acid such as 12- (OH) -stearic acid shown in Chemical formula 1, polyglycerol condensed ricinoleic acid ester shown in Chemical formula 2, and isopropyltriiso shown in Chemical formula 3. Examples include titanate coupling agents such as stearoyl titanate. Among them, stearic acid, ricinoleic acid, derivatives of stearic acid, or derivatives of ricinoleic acid are more desirable. These are easily available and highly safe. Further, it does not contain Cl, Br, etc. that cause corrosion after pulverization. Long chain organic molecules other than these are expensive or difficult to obtain. In addition, the alkali metal-containing surfactant reduces magnetic properties by mixing alkali metal with magnetic powder. In the present invention, at least one of the above surfactants is used.

[0026]

[Chemical 1]

[0027]

[Chemical 2]

[0028]

[Chemical 3]

The amount of the surfactant added is preferably in the range of 0.1 to 30 parts by weight with respect to 100 parts by weight of the magnet raw material.
If the amount added is less than this range, the effect of preventing aggregation / adhesion of magnet particles is small. On the other hand, when the amount is more than this range, the surfactant is in the form of oil having a high viscosity, so that the handleability becomes poor and the cost becomes high. A more desirable amount of surfactant added is 1 with respect to 100 parts by weight of the magnet raw material.
The range is from 15 to 15 parts by weight.

The pulverization of the magnet raw material containing the surfactant is
Do in liquid. This liquid mainly serves as a dispersion medium for the magnet powder and the surfactant, and promotes pulverization.
Further, the atmosphere is shut off to prevent the magnet powder from being oxidized.

As the liquid, (1) to prevent oxidation,
It does not contain oxygen atoms (thus, alcohols are not desirable), (2) it has a low boiling point so that carbon does not remain, and (3) if the viscosity is too high, the grinding efficiency will drop, so the viscosity will be low. It is preferable that (4) the requirement to dissolve the added surfactant is satisfied. Therefore, n
- hexane _{(CH 3 - (CH 2)} 4 -CH 3) a hydrocarbon liquid, such as, liquid fluorocarbon of Freon are suitable.

As a crushing method, there is a wet crushing method using a ball mill, a vibration mill or the like.

As a crushing condition, it is preferable to crush to a region having high magnetic characteristics. The magnet has a grain size (single domain grain size) with which the magnetic property is highest, and the magnetic property is deteriorated when the size is larger or smaller than that. It is considered that the optimum average particle size is 1 to 5 μm for Sm ₂ Fe ₁₇ N ₃ .

Further, the narrower the particle size distribution is, the better, and preferably monodisperse (there is no particle size distribution and all particles have the same particle size). In magnet powder with a wide particle size distribution,
Since the coercive force of each particle is not uniform, H _k becomes low. If H _k is low, a high maximum energy product cannot be obtained. H _k is the external magnetic field strength when the magnetic flux density in the second quadrant of the magnetic hysteresis loop is 90% of the residual magnetic flux density. Such particles are possible in certain materials, but difficult with mechanical milling methods such as the present invention. Therefore, it is preferable to narrow the particle size distribution as much as possible. It is generally known that undersized particles adversely affect magnetic properties. Therefore, the particle size distribution should be narrow.

After crushing, the magnet powder is taken out of the liquid by filtration or the like.

When the produced magnet powder is used as a bonded magnet, it is not necessary to remove the surfactant from the magnet powder because the added surfactant works effectively during molding.

That is, in many bonded magnets, in order to improve the orientation of the magnet particles and the density of the molded body, a surfactant or a coupling agent is used as a surface modifier of the magnet particles during molding. The agent is added, and the surfactant added at the time of crushing plays this role.

On the other hand, when the manufactured magnet powder is used as a sintered magnet, it is better to remove the surfactant from the magnet powder. For example, in the case of Nd ₂ Fe ₁₄ B, since it is sintered in an inert atmosphere, the organic surfactant is carbonized and remains as an impurity of carbon or carbide. Since these impurities deteriorate the magnetic properties, it is better to remove them from the magnet powder.

The method of removing the surfactant from the magnet powder is washing with a solvent (the same as the liquid used at the time of pulverization).

The magnet powder produced according to the present invention can be used for bonded magnets, sintered magnets and the like.

For example, in the case of use in a bonded magnet, resin and magnet powder are mixed and then pressed to form a predetermined shape. The molding method includes compression molding, extrusion molding, injection molding, and the like, and molding can be performed in the same manner as molding of resin products, and therefore can be produced by the same mechanical equipment as molding of resin products.

In the bonded magnet, it is preferable that the magnetization easy axis directions of the magnet powder are the same direction (the orientation is good). Further, it is preferable that the resin and the magnet powder are uniformly dispersed. If the dispersion is too biased, the mechanical strength will decrease, and the shape-imparting property, which is an advantage of the bonded magnet, will decrease.

As described above, in the present invention, as a pulverizing method and apparatus, a general ball mill or a vibration mill can be used, and the addition of a surfactant is easy. Compared with, the handling is easier and the cost is lower.

Examples of the present invention will be described below.

Example 1 As a starting material, a purity of 99.
Using 9% Sm and 99.9% pure electrolytic iron, both were melted in a high frequency melting furnace and cast. The produced ingot was homogenized in argon at 1250 ° C. for 2 to 5 hours to obtain Sm ₂ Fe ₁₇ . Then, coarsely pulverized mechanically or by occluding hydrogen, and classified by a sieve to 106 to 212 μm was used as a sample. Next, this crude powder was placed in a tubular furnace, and nitriding was performed at 460 ° C. in a mixed gas stream of ammonia and hydrogen gas having a purity of 99.999%, and then cooled to room temperature. It was confirmed by X-ray diffraction (XRD) that the obtained powder was a single phase of Sm ₂ Fe ₁₇ N ₃ . This sample was used as a magnet raw material and pulverized as follows.

A ball mill was used as the crushing method. The pot was made of approximately 2 liters of stainless steel having a capacity of φ120 mm × 160 mm, and the ball was made of chrome steel of φ9.5 mm. 20 to 50 balls per pot
It was set to vol%. As the solvent, degassed n-hexane was used.

As shown in Tables 1 and 2, the coarse powder 40
With respect to g, condensed stearic acid, a titanate-based coupling agent, and polyglycerin condensed ricinoleic acid ester as surface active agents were added in an amount of 0.2 to 5 g (0.5 to 100 parts by weight of the magnet raw material). 12.5 parts by weight). In addition, in Tables 1 and 2, the addition amount of the surfactant is a ratio with respect to 100 parts by weight of the magnet raw material. A predetermined amount of the surfactant was dissolved in a solvent in advance, and the ball, the solvent, and the sample were put in a pot. The solvent was filled to pot to prevent oxidation. The pot was set in a ball mill device and pulverized. Grinding time is 1
It was set to 10 h.

For comparison, fine pulverization was carried out under the same conditions as above except that no surfactant was added.

With respect to the obtained magnet powder, 150 kOe
After applying the pulsed magnetic field of, magnetic characteristics were measured by VSM (vibrating sample magnetometer). The results are shown in Tables 1 and 2.

[0050]

[Table 1]

[0051]

[Table 2]

As is clear from Tables 1 and 2, it is understood that the addition of the surfactant improves the maximum energy product (BH) _max of the magnet powder. Further, when the addition amount is 5 parts by weight (ratio to 100 parts by weight of magnet raw material), the maximum energy product (BH) _max has a maximum value of 320 kJ / m.
³ (40 MGOe), when not added (BH)
About 40 compared to _max 224 kJ / m ³ (28 MGOe)
% Improvement was recognized.

Claims (3)

[Claims] 1. A method for producing magnet powder, which comprises adding a surfactant to a magnet raw material and pulverizing the magnet raw material in a liquid. 2. The method for producing magnet powder according to claim 1, wherein the surfactant is at least one selected from stearic acid, ricinoleic acid, derivatives of stearic acid, and derivatives of ricinoleic acid. 3. The method for producing magnet powder according to claim 1, wherein 0.1 to 30 parts by weight of the surfactant is added to 100 parts by weight of the magnet raw material.