JPH0684263B2 - Method for producing anisotropic oxide permanent magnet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing an oxide permanent magnet, and more particularly to a lubricant for ferrite magnet powder used in wet magnetic field molding.

[Prior art and its problems]

There are two known methods for producing anisotropic magnets, in which ferrite magnet fine powder having a magnetoplumbite structure is oriented in a magnetic field, a dry method and a wet method. The dry method is to mix fine powder of ferrite magnet with polyvinyl alcohol, vinyl acetate, camphor, starch powder, etc. as a binder, and press-mold the dry powder in a magnetic field. Compared with the wet method, this method has the advantages that the time required for molding is shorter, the equipment is smaller, and it is also suitable for molding of complicated shapes. However, the dry magnetic field molding method has a drawback in that the ferrite magnet powder has a lower orientation than the wet method, and therefore the performance of the magnet is reduced.

On the other hand, the wet method uses ferrite magnet powder with water as a dispersion medium,
A polyvinyl alcohol aqueous solution, alcohol, etc. are added and suspended, and magnet powder is aligned in a magnetic field in a mold and molded. 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. When the molding time is shortened by forced drainage,
The molding equipment is larger than the dry method. Also,
When the molding pressure is increased, cracks are likely to occur in the molded product, making it difficult to obtain a molded product with a complicated shape. However, the wet magnetic field molding method can produce anisotropic ferrite magnets with high performance that cannot be obtained by the dry method.

As explained above, the moldability of conventional ferrite magnet powder and the magnetic field orientation, which is a factor in magnet characteristics, tend to contradict each other.

[Object of the Invention]

Therefore, an object of the present invention is to obtain a method for producing an oxide permanent magnet which is excellent in formability at the same time in the above-mentioned wet method in which high magnet characteristics are obtained.

[Means for solving problems]

In order to achieve the above object, it was considered important to improve the lubricant of the magnet powder, and as a result of various attempts, it was found that it is preferable to use liquid paraffin as the lubricant.

That is, according to the present invention, the oxide magnet powder is coated and mixed with 0 to 4.5 wh% (however, 0 is not included) of paraffin as a lubricant, and the slurry obtained by dispersing this in a liquid is pressure-molded in a magnetic field. After that, a method for producing an anisotropic oxide magnet is obtained, which is characterized by being fired.

〔Example〕

 The present invention will be described in detail below with reference to examples.

Example 1 Strontium carbonate (SrCO ₃ ) and ferric oxide (Fe ₂ O ₃ ) were mixed at a molar ratio of 1: 5.7, calcined at 1250 ° C. for 2 hours, and pulverized to about 0.8 μm with a pole mill. did. This powder was dried to give an experimental powder.

The above powder contains 0 to 5 wt% of liquid paraffin with respect to the magnet powder.
The toluene solution prepared so as to be 100% was mixed and dried. The powder obtained by coating and mixing the liquid paraffin was dispersed in ethyl alcohol.

This slurry was molded into a disk with a diameter of 20 mm and a height of 10 mm in a magnetic field of about 10 kOe at a sample pressure of 0.3 ton / cm ² and then subjected to main firing at 1210 ° C. for 2 hours to examine the magnetic properties.

The results are shown by circles and solid lines in the figure. A magnet having a higher energy product than the uncoated powder was obtained when the coating mixture amount of liquid paraffin was 0 to 4.5 wt% (not including 0). (BH) max
The increase of B corresponds to the improvement of Br, and the improvement of Br corresponds to the improvement of the C-plane orientation degree of the crystal grains by the liquid paraffin coating. Further, reduction of Br and _B H _C with increasing the mixing amount of the liquid paraffin is related to the amount of carbon was decomposed by paraffin remaining in the magnet.

Example 2 The strontium ferrite magnet powder produced in Example 1 was mixed with 1.5 wt% of liquid paraffin to coat it. This powder was dispersed in an aqueous solution in which an alkyl ether nonionic surfactant was dissolved by 0.5 wt%.

The slurry was molded into a disk with a diameter of 20 mm and a height of 10 mm in a magnetic field of about 10 kOe at a sample pressure of 0.3 ton / cm ² and then subjected to main firing at 1220 ° C. for 1 hour to examine the magnetic properties. The results are shown in the table below.

By coating the strontium magnet powder with liquid paraffin, the magnet orientation was improved and Br was increased.
A significant improvement in (BH) max was achieved.

As is clear from Examples 1 and 2, liquid paraffin is added to strontium ferrite fine powder in an amount of 0 to 4.5 wt%.
It is possible to manufacture a high-performance oxide permanent magnet with high anisotropy by coating and mixing (not including 0) and press-molding a slurry obtained by dispersing this in a liquid in a magnetic field.

It should be noted that in the above-mentioned Examples, only the use of an aqueous solution of ethyl alcohol and an alkyl ether-based nonionic surfactant as a dispersion medium is described as a method of dispersing powder mixed with liquid paraffin by coating in a liquid. There is no particular limitation as long as the dispersibility is not reduced. In this embodiment, a surfactant is used to reduce the water repellency of liquid paraffin, and ethyl alcohol having a small surface tension is used for dispersion.

Further, in the above two embodiments, only the strontium ferrite magnet was described, but the present invention relates to the improvement of the orientation of the ferrite magnet in the magnetic field. It is also applicable to a magnetoplumbite anisotropic magnet containing one or more of barium, strontium, calcium, lead and the like.

[Brief description of drawings]

The figure shows the relationship between the coating amount of liquid paraffin on strontium magnet powder and magnet characteristics in Example 1.

Claims (1)

[Claims] 1. A mixture of oxide magnet powder coated with liquid paraffin as a lubricant in an amount of 0 to 4.5 wt% (not including 0), and a slurry obtained by dispersing this in a liquid is pressure-molded in a magnetic field, A method for producing an anisotropic oxide magnet, which is characterized by firing.