JPH04362018A - Production of magnetic powder - Google Patents

Abstract

PURPOSE:To provide a production method for magnetic hexagonal ferrite powder having high dispersibility. CONSTITUTION:When hexagonal ferrite powder is produced by a glass crystallizing method, an extracted slurry contg. fine hexagonal ferrite particles is dried so that the water content of dried hexagonal ferrite powder is regulated to 0.5-5.0wt.%. Since strong cohesion force among the fine ferrite particles is relieved, ferrite powder having high dispersibility is obtd.

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 magnetic powder suitable for magnetic recording media, and more particularly to a method for producing magnetic powder with good dispersibility by a glass crystallization method.

0002

[Prior Art] Coating type magnetic recording media are obtained by coating magnetic powder such as γ-ferrite or iron powder together with a resin binder on a substrate such as a polyester film. Magnetic recording was performed using directional magnetization. However, when trying to improve the recording density with this magnetic recording method that uses in-plane longitudinal magnetization, there is a problem that the recording and reproducing output decreases due to the increase in the demagnetizing field within the medium in the high frequency range. . Therefore, there is a limit to the improvement in recording density in this method.

[0003] Therefore, in order to meet the recent demand for higher recording densities in magnetic recording media, one of the ways to significantly improve the magnetic recording density is to use perpendicular magnetization, which uses magnetization in a direction perpendicular to the coated surface of the base of a magnetic recording medium. Magnetic recording methods have been developed. A magnetic recording medium based on this method is suitable for high-density recording because it does not have the problem of demagnetizing field in a high frequency range, compared to a conventional recording method using magnetization in the longitudinal direction within the coated surface.

[0004] As a magnetic recording medium suitable for this perpendicular magnetic recording, for example, a magnetic paint mainly composed of hexagonal ferrite powder and a resin binder, which tends to orient the axis of easy magnetization in a direction perpendicular to the substrate, is coated on the substrate. Examples include coated magnetic recording media. For example, the hexagonal ferrite powder used in coated magnetic recording media has the chemical formula BaFe12O.
Examples include M-type barium ferrite represented by 19.

By the way, when manufacturing a perpendicular magnetic recording medium by a coating method using fine particles of hexagonal ferrite,
Hexagonal ferrite has a large coercive force that saturates the magnetic head during recording, so it is necessary to reduce the coercive force to a value suitable for perpendicular magnetic recording by replacing some of the constituent atoms with specific atoms. . As a hexagonal ferrite in which some of the constituent atoms are replaced with specific atoms, for example, the chemical formula BaMe2 Fe16O27 (M
W-type barium ferrite, which contains M-type ferrite and spinel ferrite at the same time, and hexagonal ferrite in which some of these atoms are replaced with other elements. can be given.

[0006] The above-mentioned hexagonal ferrite crystals preferably have a grain size in the range of 0.01 to 0.3 μm. The reason is that the grain size of the crystal is 0.01 μm.
If it is less than 0.3, it cannot exhibit the strong magnetism required for magnetic recording.
This is because if it exceeds μm, it is difficult to perform perpendicular magnetic recording as high-density recording advantageously. If the particle size is within this range,
Sufficient recording and reproduction can be performed in the recording wavelength region of 1 μm or less, which makes it clear that the perpendicular magnetic recording method is superior to the longitudinal magnetic recording method.

[0007] As methods for producing the above-mentioned hexagonal ferrite powder, there are generally coprecipitation methods, hydrothermal synthesis methods, glass crystallization methods, etc. Among them, the glass crystallization method is more effective than other methods. is known as a preferred method for obtaining hexagonal ferrite with good dispersibility.

This glass crystallization method heats and melts a raw material mixture containing a hexagonal ferrite basic component, a substitution component for reducing coercive force, and a glass-forming component/modifying component.
The process consists of four steps: the resulting melt is rapidly cooled to produce an amorphous body, the amorphous body is then heat-treated to precipitate hexagonal ferrite, and this is extracted. There is.

[0009]

[Problems to be Solved by the Invention] However, even when hexagonal ferrite fine particles such as barium ferrite are produced by the above-mentioned glass crystallization method, they do not lose their cohesive properties and remain solid due to their high surface activity. Since agglomerates may be formed, it has been difficult to stably produce ferrite particles with good dispersibility.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a method for stably producing highly dispersed hexagonal ferrite magnetic powder.

[0011]

[Means for Solving the Problems] In order to achieve the above objects, the present invention controls the drying process of hexagonal ferrite to adjust the moisture content in the powder, thereby reducing the agglomeration of hexagonal ferrite. This improves the dispersibility when forming into a medium. That is, a raw material mixture containing a hexagonal ferrite basic component, a substitution component for reducing coercive force, and a glass forming component is heated and melted, and the resulting melt is rapidly cooled to produce an amorphous body. Then, this amorphous body is heat-treated to precipitate hexagonal ferrite, and then subjected to acid treatment to separate and extract the hexagonal ferrite. A slurry containing the extracted hexagonal ferrite fine particles is After drying, the amount of water contained in the hexagonal ferrite powder is 0.4.
It is characterized by having a content of ~5.0 wt%.

[0012] If the amount of water contained in the hexagonal ferrite powder after drying is less than 0.4 wt%, it is not preferable because the cohesive force between the ferrite particles acts strongly and tends to form solid aggregates. Furthermore, if the water content exceeds 5%, the final dispersibility of the magnetic powder into the resin binder during media production will decrease, and the magnetic properties of the resulting media will deteriorate.
This is not preferable because it causes deterioration of characteristics due to environmental changes.

[0013]

[Operation] The operation of the above structure will be explained.

The hexagonal ferrite fine particles are tabular and tend to aggregate in the direction of the axis of easy magnetization perpendicular to the plane of the plate. When there is little moisture adhering to the powder surface, the cohesive force between the ferrite fine particles appears strong, making it easier to form solid aggregates. On the other hand, when the amount of water is large, the excessive water suppresses the adsorption of the dispersant during the preparation of the medium, thereby reducing the dispersibility of the magnetic powder into the resin binder. therefore,
By controlling the water content in ferrite within an appropriate range, the dispersibility of hexagonal ferrite fine particles is improved.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below with reference to a specific example in which it is applied to a hexagonal ferrite, such as a magnetoplumbite barium ferrite.

Examples 1 to 4 Some of the Fe3+ ions in barium ferrite were replaced with Co2
Chemical formula BaFe10.4T with coercive force required for magnetic powder for magnetic recording media by replacing +, Ti4+ ions
A ferrite represented by i0.8 Co0.8 O19 was produced. During production, the ferrite component Fe2O3 of barium ferrite, the substitution component TiO2 for reducing coercive force, CoO, and the glass forming components BaO, B2
Composition ratio by weight percentage: Fe2 O3
31.2%, TiO2 2.58%, CoO
2.42%, BaO 46.9%, B2O3
16.9%, Fe2O3, TiO
2, CoO, BaCO3, and H3BO3,
was weighed.

The above raw materials were thoroughly mixed, placed in a platinum container, and heated and melted at 1350° C. using a high frequency heating device. After that, the diameter is 50 cm, the rotation speed is 500 rpm, and the linear pressure is 5.
The above-mentioned melt was poured onto a ton of water-cooled twin rolls and rapidly cooled by rolling to produce an amorphous body. This amorphous material was then filled into a predetermined container and crystallized in an electric furnace under appropriate temperature conditions. The obtained sintered body was pulverized using a dry pulverizer such as a Braun type crusher to a pulverized particle size of 100 mesh or less, and then wet-pulverized using a ball mill.

From the thus obtained pulverized material, BaO.
The B2O3 phase and BaO phase were dissolved and removed. After the acetic acid treatment was completed, washing with water was repeated until the pH reached 6.0 or higher. The barium ferrite slurry that had been washed with water was placed in a hot air dryer and dried. Changes in moisture content during drying were monitored using a Karl Fischer type infrared absorption moisture meter. Measurement conditions were N2 gas flow, 175
It was ℃.

Four types of hexagonal ferrite powders were prepared by changing the amount of water in the ferrite during drying, and these were designated as Examples 1 to 4 of the present invention.

Comparative Examples 1 and 2 In addition, two types of hexagonal ferrite powders were prepared in the same manner as in the example except that the water content in the ferrite was set to less than 0.4 wt%, and these were compared. Examples 1 and 2
And so.

Table 1 below shows the water content and secondary agglomeration diameter of the hexagonal ferrite powders obtained in Examples 1 to 4 and Comparative Examples 1 and 2. Furthermore, the characteristics of magnetic recording media produced using these magnetic powders according to conventional methods are also shown.

[0022]

[Table 1]

As is clear from Table 1, the barium ferrite fine particles of Examples 1 to 4 of the present invention had extremely good dispersibility, and the medium coercive force and squareness ratio were increased.

[0024] In Examples 1 to 4, Ti and Co were added as substitute components to barium ferrite, but other substitute components Sn, Zn, Ni, Mn, Nb, T
Almost similar results were obtained even when a was added.

[0025]

As explained above, the present invention is a method for producing magnetic powder suitable for high-density magnetic recording media, and the water content in ferrite powder is reduced to 0.4 to 5.0 during the drying process.
By controlling the content within the range of wt%, the strong cohesive force between the hexagonal ferrite fine particles is relaxed, so that a highly dispersible hexagonal ferrite powder can be obtained.

Claims (1)

[Claims] Claim 1: A raw material mixture containing a hexagonal ferrite basic component, a substitution component for reducing coercive force, and a glass forming component is heated and melted, and the resulting melt is rapidly cooled to form an amorphous material. This amorphous body is then heat-treated to precipitate hexagonal ferrite, and then subjected to acid treatment to separate and extract the hexagonal ferrite. A method for producing a magnetic powder, comprising drying a slurry containing the hexagonal ferrite powder so that the amount of water contained in the dried hexagonal ferrite powder is 0.4 to 5.0 wt%.