JPS61222206A - Manufacture of oxide permanent magnet - Google Patents

Abstract

PURPOSE:To provide high performance magnet characteristics in wet molding in magnetic field, by pressurizing and molding in magnetic field slurry in which oxide magnet powder particles are coated with a given amount of aluminum stearate, are mixed, and dispersed in liquid, and by firing the slurry. CONSTITUTION:Slurry in which oxide magnet powder is coated with aluminum stearate below 4.5wt% (not including 0wt%) serving as adhesive lubricant, is mixed, and is dispersed in liquid, is pressured and molded in magnetic field, and is fired to result in an anisotropic oxide magnet. For example, magnetic powder in which SrCO3 and Fe2O3 are mixed by a mol ratio of 1:5.8, are tentatively fired at 1,250 deg.C, and are pulverized, is mixed in a warm toluene solution in which aluminum stearate powder of 1.5wt% against 100wt% of the magnet powder is mixed, and is dried. This powder which is coated and mixed with aluminum stearate is pulverized in a ball mill using ethyl alcohol as a dispersing agent. After sully formed in this way is pressured and molded into a disk shape in magnetic field, it is fired.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing an oxide permanent magnet.

In particular, it relates to a binding lubricant for ferrite magnet powder used in wet magnetic field molding.

[Conventional technology]

Two methods, a dry method and a wet method, are known as methods for manufacturing an anisotropic magnet in which fine ferrite magnet powder having a magnetobrambite structure is completely oriented in a magnetic field.

The dry method involves mixing polyvinyl alcohol, vinyl acetate, camphor, starch, paraffin wax, etc. as a binder with fine ferrite magnet powder, and press-molding the dried powder in a magnetic field. This method has advantages over the wet method in that it requires less time for molding, requires smaller equipment, and is suitable for molding complex shapes. However, in the dry magnetic field forming method.

Compared to the wet method, the orientation of ferrite magnet powder is low,
Therefore, it also has two drawbacks: the performance of the magnet is low. In addition, the disadvantage that ferrite magnet powder (generally 2 μm or less) has poor moldability must also be taken into consideration.

On the other hand, the wet method involves adding water, polyvinyl alcohol aqueous solution, alcohol, etc. as a dispersion medium to ferrite magnet powder, suspending it, aligning the magnet powder particles in a magnetic field in a mold, and molding. be. In this method, it is necessary to discharge the dispersion medium out of the mold during pressure molding, which increases the time required for molding. If the molding time is shortened by forced drainage, the molding equipment will be much more robust than in the dry method. In addition, when the molding pressure is increased, there are disadvantages such as the molded product is prone to cracks and it is difficult to obtain a molded product with a complicated shape. However, the wet magnetic field forming method can produce anisotropic ferrite magnets with high performance that cannot be obtained by the dry method.

As described above, conventionally, the moldability of ferrite magnet powder and the magnetic field orientation have shown contradictory tendencies, and it is important to use a binder that has good moldability and does not inhibit the orientation of the ferrite powder. is of great industrial importance.

[Problem that the invention seeks to solve]

An object of the present invention is to obtain even higher performance magnetic properties in wet magnetic field forming.

[Means for solving problems]

In wet magnetic field forming, aluminum stearate, which also has binding properties, is extremely useful as a surface coating agent for ferrite magnet powder to improve the performance of the magnet.
As a result of nine different types of research, it has been found that this method is also effective in improving the moldability of powder (improving compaction density in wet methods, diversifying the shapes of green compacts, etc.).

As a binder for ferrite magnet powder for dry magnetic field forming, Japanese Patent Publication No. 47-21197 discloses stearic acid-based M' CCHs (CH2)+aCOt) (However, 1
M' is included. Here, Ca, Ba, Sr,
Pb has a magnetobrambite crystal structure (MO*6Fez03. M=Ca,
It has Ba, Sr, Pb), and is chemically limited only to this metal stearate.

On the other hand,9 the present invention relates to improvement of magnet properties in wet magnetic field forming method.22 As a result of various studies, aluminum stearate, which is different from the concept of metal stearate mentioned above, was used as a lubricant for magnet powder as a ferrite. It has been discovered that by coating and mixing magnet powder particles with 4.5% by weight or less (excluding 0% by weight), it is possible to manufacture an anisotropic oxide magnet with higher performance.

〔Example〕

Examples of the present invention will be shown below.

Example 1 Strontium carbonate (SrCO3) and ferric oxide (F'
20g) at a molar ratio of 1:5.8.

12501:' for 2 hours and a ball mill to reduce the temperature to about 0.
It was finely ground to 8 μm. This powder was dried and used as an experimental powder.

The above powder was mixed with a warm toluene solution prepared so that the aluminum stearate powder was 0 to 5 Wt (i.e., 1% by weight) relative to the magnet powder.

Dry. The mixed powder coated with aluminum stearate was crushed in a ball mill for 3 minutes with ethyl alcohol added as a dispersion medium.

This slurry was heated to a diameter of 20 mm in a magnetic field of about 10 KOe.

Sample pressure 0.6tOn/crIL in a disk shape with a height of 10m
After molding at 1220 t:' for 1 hour, the magnetic properties were investigated.

The results are shown in FIG. When the aluminum stearate coating was mixed in an amount of 0 to 4.5 vrt,% (O not included), a magnet with a higher energy product than the uncoated powder was obtained. An increase in the energy product (BH) max corresponds to an increase in the residual magnetic flux density Br.

The improvement in Br corresponds to the improvement in the degree of C-plane orientation of crystal grains due to aluminum stearate coating.

In addition, a decrease in Br and an increase in coercive force BHC with an increase in the amount of aluminum stearate mixed are due to the fact that part of F@ is h
This is thought to be because it is replaced by t.

Example 2 In the experimental Sr ferrite magnet powder produced in Example 1,
1.5wt0% of aluminum stearate powder was added, mixed at about 150C, and then cooled. This powder coated with aluminum stearate was mixed with Q, 3wt of alkyl ether type nonionic surfactant in a ball mill.
Disintegration was carried out for 3 minutes using a 1% aqueous solution as a dispersion medium.

This slurry was heated to a diameter of 20M in a magnetic field of about 10KOe.

Sample pressure 0.3 t oTV/c in a disk shape with a height of 10 m
r! After molding at L2, main firing was performed at 1210 t:' for 1 hour, and the magnetic properties were examined. Table 1 shows the results.
Shown below.

Table 1 By coating Sr ferrite magnet powder with aluminum stearate, the degree of orientation of the magnet was improved, and as a result of increasing Br, a significant improvement in (BH)max was realized.

As mentioned above, as is clear from Example 1 and Example 2.

strontium ferrite fine powder is coated and mixed with aluminum stearate from 0 to 4.5 wtJ (not including O),
By press-molding a slurry in which this is dispersed in a liquid in a magnetic field, it has high anisotropy.

High performance oxide permanent magnets can be manufactured. still,
In the examples, only the use of an aqueous solution of ethyl alcohol and an alkyl ether nonionic surfactant as a dispersion medium is described as a method for dispersing powder coated with aluminum stearate in a liquid. There is no particular limitation as long as it does not reduce the properties. In this example, in order to reduce the water repellency of aluminum stearate, a surfactant was used and ethyl alcohol, which has a low surface tension, was used for dispersion.

In the above embodiments, only strontium ferrite magnets have been described; however, since the present invention is realized through the effect of a cohesive lubricant on improving the orientation of ferrite magnets in a magnetic field, it is limited thereto. without any
The present invention can also be applied to anisotropic magnets having a magnetobrambite structure containing one or more of the same type of magnet materials such as barium, strontium, calcium, and lead.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to obtain a high-performance anisotropic oxide permanent magnet with high anisotropy.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the amount of aluminum stearate coating mixed into the strontium ferrite magnet powder and the magnet properties in Example 1. Figure 1

Claims (1)

[Claims] 1. Oxide magnet powder is coated with 4.5% by weight or less (not including 0% by weight) of aluminum stearate as a binding lubricant, and a slurry made by dispersing this in a liquid is added in a magnetic field. A method for producing an oxide permanent magnet, which comprises obtaining an anisotropic oxide magnet by pressing and then firing.