JPS6272528A - Production of magnetic powder - Google Patents

Abstract

PURPOSE:To produce the titled magnetic powder having excellent dispersibility by heat-treating an amorphous material obtained from a mixture of the essential component of hexagonal ferrite, a substituent component and a vitrifying compo nent, reheating the material and then quenching the material. CONSTITUTION:A mixture of (A) the essential component of hexagonal ferrite, (B) the substituent component (e.g., TiO2) for reducing coercive force and (C) the vitrifying component is heated, melted and then quenched to obtain the amorphous material. The amorphous material is packed in a heat-resistant vessel and heat-treated to deposit a hexagonal ferrite crystal and a sintered body is obtained. The sintered body is then pulverized, heated at temps. of (250-350 deg.C) which are below the Curie point of the ferrite and then quenched to provide thermal strain. The vitreous phase in the sintered body is released from the ferrite crystal phase at their interface and cracks are formed on the vitreous phase side. Then the fine powder of the sintered body is treated with a dilute acid to dissolve and remove the vitreous substance, then washed with water until the pH is controlled to >=6 and dried.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention 1 The present invention relates to a method for producing magnetic powder used in the production of high-density magnetic recording media, and particularly relates to a method for producing magnetic powder using a sintered powder containing hexagonal ferrite in high yield. The present invention relates to a method for producing magnetic powder that can extract orthogonal ferrite from a body in a uniformly dispersed state.

[Technical background of the invention and its problems] Conventionally, when manufacturing perpendicular magnetic media by a coating method using fine particles of hexagonal ferrite, a single hexagonal ferrite has a large coercive force. During recording, the magnetic head becomes saturated and magnetic recording becomes impossible, so by replacing some of the constituent atoms of hexagonal ferrite with specific other atoms, the corner retention force is reduced to a value suitable for perpendicular magnetic recording. It is being done to

Further, if the grain size of the hexagonal ferrite fine particles used for such perpendicular magnetic recording is less than 0.01 μm, it cannot exhibit strong magnetism comparable to magnetic recording,
If the thickness exceeds 311 Ill, it is difficult to advantageously perform perpendicular magnetic recording as high-density recording, so a thickness in the range of 0.01 to 0.3 μm is suitable.

The method for producing magnetic powder that meets the above conditions is to mix the basic component of hexagonal ferrite, a substitute component for reducing coercive force, and a glass-forming component, heat and melt the mixture, and then melt this. The method used is to rapidly cool the material to make it amorphous, heat-treat it to precipitate hexagonal ferrite fine particles, and then treat it with dilute acid to separate and extract the ferrite.

However, in such conventional methods, the amorphous material takes on a thin flake shape, and in particular, the total amount of the basic components and substituted components of the hexagonal crystal ferrite 1 is smaller than the sum of these and the glass-forming components Φ. In the case of a high yield exceeding 40% by weight, the spacing of the phase n of the produced ferrite fine particles becomes close, and the flaky amorphous material hardly changes its shape even after heat treatment, so dilute acid There was a problem in that it was difficult to pulverize into a shape suitable for processing. In other words, when a flaky amorphous material with a high proportion of hexagonal ferrite is pulverized using a rotating disk type pulverizer, the flaky amorphous material is thin, so it slips between the disks and becomes a fine powder. As a result, even after pulverization, the glass-forming components remain sandwiched between closely spaced ferrite particles, making it difficult for dilute acid to permeate and dissolve them, making it impossible to form ferrite particles with good dispersibility. There wasn't.

[Object of the Invention] The present invention has been made to solve these conventional difficulties, and involves reheating a heat-treated sintered body at a temperature below one curie point, and then rapidly cooling it to apply thermal strain. With a simple operation, peeling and cracking is generated at the interface between the glass phase of the flaky amorphous material and the hexagonal ferrite crystal phase, which improves the permeability of dilute acids and the ability to be crushed by ultrasonic waves. It is an object of the present invention to provide a method for producing magnetic powder that makes it possible to obtain hexagonal ferrite with improved dispersibility.

[Summary of the Invention] In order to achieve the above-mentioned object, the present invention has been made by (a) heating and melting a mixture of a basic component of hexagonal ferrite, a substitute component for reducing coercive force, and a glass-forming component; a step of rapidly cooling to form an amorphous body; (b) a step of subjecting the amorphous body to heat treatment to precipitate crystals of hexagonal crystal ferrite 1; and (c) a sintering step in which crystals are precipitated by heat treatment. After finely pulverizing the body and reheating it at a temperature below one curie point, it is rapidly cooled and thermally strained, and (d) the fine powder of the thermally strained sintered body is treated with dilute acid. and extracting hexagonal ferrite crystals.

In the present invention, in order to obtain the desired magnetic powder, first, a starting material of magnetobrambite-type ferrite, a starting material of a replacement component to obtain the coercive force required for a magnetic powder for magnetic recording media, and a glass The forming components are mixed in a predetermined ratio. In other words, when replacing some of the 1:65+ ions in magnetobrambite barium ferrite with CO1+ ions and Ti4+ ions, -1)
3BO3,3a C03, Fe2O:+, Ti0z, C
Weigh out OO in a predetermined ratio and mix uniformly. Next, these mixtures are heated and melted, and this melt is poured onto water-cooled twin rolls and rapidly cooled to produce an amorphous body. Further, this amorphous body is filled into a heat-resistant container, placed in an electric furnace, and crystals of substituted barium ferrite are precipitated under predetermined temperature conditions to form a sintered body. In this way, the sintered body (q) is
The powder is finely pulverized and heated again to a temperature of about 250 to 350° C., which is below the curie point (about 350° C.) of barium ferrite, and then put into, for example, cold water to be rapidly cooled.

In this way, the sintered fine powder containing substituted barium ferrite crystals is thermally strained by reheating and rapid cooling, so the interface between the glass phase and the barium ferrite crystal phase in the sintered body peels off. Alternatively, cracks occur on the glass phase side.

Thereafter, the powder is pulverized to a predetermined particle size by a conventional method, and glassy substances such as the 13a OB203 phase and BaO phase are dissolved and removed using an acetic acid aqueous solution. At this time, the temperature of the acetic acid aqueous solution is set to 80° C. or higher, the pulverized material is set to about 20% by weight, and if necessary, ultrasonic waves are used to promote dissolution of the glassy substance. The pulverized material treated with acetic acid is washed repeatedly with water until the pH of the liquid is 6.
When the temperature reaches the above point, washing with water is stopped, and 3a flute fine particles are obtained by filtering and drying.

In this way, in the present invention, thermal strain is applied to the finely pulverized sintered body powder for dilute acid treatment by reheating and rapid cooling, so that the glass phase and barium ferrite crystal phase in the sintered body are separated. The interface peels off or cracks occur on the glass phase side, allowing penetration of dilute acid and disintegration by ultrasonic waves to proceed efficiently. As a result, the glass phase is easily removed, resulting in fine barium ferrite powder with good dispersibility. 1q can be obtained.

Although the present invention can be used for producing magnetic powder of any particle size, it is particularly effective for producing magnetic powder with fine particles of 500 Å or less, for which good dispersibility could not be obtained by conventional methods.

[Embodiments of the Invention] Next, the present invention will be described in detail below. An example of application to powder production will be described.

Example 3a Ferrite 1 to component 1'c203 of ferrite and substituted component molecules for reducing coercive force! 02, CoO and
Glass-forming components Bao and B203 in a weight percentage of 8
2031γ,8, Ba Q45,9, Fe2O331,
6.T! 02 2.44, Co O2,29, and after thoroughly mixing them, 1
The material was melted by heating at 350° C., and the molten material was poured onto a water-cooled twin roll having a diameter of 20 cm, a rotational speed of 50 rpm, and a linear pressure of 5 tOn, and was rapidly cooled to prepare an amorphous body. Next, this amorphous body was filled into a heat-resistant container, placed in an electric furnace, and fired under predetermined hot water temperature conditions to precipitate assa ferrite crystals. Thereafter, this sintered body was crushed into a fine powder of 100 mesh or less using a Brown type crusher, and this fine powder was heated to 200 to 300°C, and immediately heated to 20°C.
The fine powder was poured into a large amount of water at a temperature below ℃ and rapidly cooled to avoid thermal distortion in the fine powder. After collecting and drying this fine powder,
% acetic acid aqueous solution to remove the BaO-8203 phase and Ba
Glassy parts such as O phase were dissolved and removed. At this time, the temperature of the acetic acid aqueous solution was 80° C. or higher, the pulverized material was concentrated at about 20% of the total, and ultrasonic waves were applied at 2 W/cc to promote dissolution. This post-treated product was repeatedly washed with water, and when the DH of the liquid reached 6 or more, it was filtered and dried.

The thus obtained 3a fluorite fine particles had extremely good dispersibility and good properties as a magnetic powder, as shown in the following table.

In addition, the comparative examples in the table are magnetic powders manufactured using the same starting material v1 and method as in the examples except that the sintered body was not subjected to heating and quenching treatment after being finely pulverized, and is a comparison with the present invention. This is what I have shown for you.

In the table, the coercive force and saturation magnetization are the values of the finally obtained magnetic powder, and the squareness ratio is the squareness ratio of the recording medium manufactured using the magnetic powder.

[Effects of the Invention] As described above, in the present invention, after pulverizing a sintered body in which crystals have been precipitated, it is reheated and rapidly cooled at a temperature below one curie point to generate thermal strain. Peeling or cracking can be generated at the interface between the glass phase of the flaky amorphous body and the hexagonal ferrite crystal phase by simply adding the following simple operations. Dilute acid easily penetrates into the peeled areas and cracked areas at these interfaces.1.
Since crushing by ultrasonic waves is easily carried out, the ferrite fine particles that are always close to each other can be further finely divided, and a magnetic powder with good dispersibility can be obtained. can.

Claims (3)

[Claims] (1) (a) A step of heating and melting a mixture of a basic component of hexagonal ferrite, a substitution component for reducing coercive force, and a glass-forming component, and then rapidly cooling it to form an amorphous body; A process of heat-treating the amorphous body to precipitate hexagonal ferrite crystals; (c) finely pulverizing the sintered body in which crystals have been precipitated by the heat treatment and reheating it at a temperature below the Curie point; It is characterized by comprising a step of rapidly cooling and applying thermal strain, and (d) a step of treating the fine powder of the thermally strained sintered body with dilute acid to extract hexagonal ferrite crystals. A method for producing magnetic powder. (2) The step (c) is characterized in that the sintered body in which crystals have been precipitated by heat treatment is reheated at a temperature of 200 to 350°C, and then placed in water to apply thermal strain. A method for producing magnetic powder according to claim 1. (3) The total amount of basic components and substituted components of hexagonal ferrite is 40% relative to the total amount of these and glass forming components.
The method for producing magnetic powder according to claim 1 or 2, wherein the amount exceeds % by weight.