JPS59197506A - Preparation of metal powder for magnetic recording - Google Patents

Abstract

PURPOSE:To prepare a metal powder for magnetic recording having uniform magnetic characteristics and good in dispersibility, by a method wherein a needle like ferric oxyhydroxide particles are granulated to form granules each having a proper particle size and, after dehydration heat treatment, reducing treatment is applied to the treated granules under stirring and heating. CONSTITUTION:Needle like alpha FeOOH particles are mainly used as a start stock material and granulated along with water being a binder to obtain spherical, angular or amorphous granules each having a particle size of 1-10mm.. After the obtained granules are further coated with silicate, dehydration heat treatment is applied to the coated granules to obtain needle like alphaFe2O3. Subsequently, this granular alphaFe2O3 is subjected to heat reducing treatment under stirring hydrogen stream by a rotary kiln for a time sufficient to rapidly penetrate hydrogen into granules to perfectly reduce alphaFe2O3 and a metal powder for magnetic recording having good magnetic characteristics, free from sintering and excellent in dispersibility can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a sword-shaped magnetic powder for magnetic recording media containing iron as a main component, and particularly to a reduction method.

Conventionally, as chain magnetic particles for magnetic recording media, γ Fe 203 or CO doped or coated γ
l”e203 had not been used. However, recently, with the request for high carbon content records, Fe powder (metal'F7J) was used.
Applications to magnetic recording tapes, disks, etc. are being considered. In 1995, a high-grade cassette tape called Metal Tape was commercially available for Dave.

The sword-shaped metal powder has high saturation magnetization (・~150 emu/Q
Although it has excellent magnetic properties such as high coercivity (1000 to 15000e), it also has drawbacks, and when it comes to metal powder production, the reduction method that is the final process of production has the biggest problem. It can be said that there is C.

The reduction process is usually carried out by heating in a reducing atmosphere in hydrogen, and is mainly described by the following reaction formula. (However, metal components are collectively represented by Fe.) At low temperatures, it mainly follows the path (■), and at high temperatures, it mainly follows the path (2). If the amount of processing is small, it can be easily reduced to α
Fe is generated, but in actual production, if more than one kilogram is processed, the water vapor pressure in the atmosphere in which the treated body is placed will rise, and it will not be properly removed from the system. ) If the pressure reaches a hydrogen pressure ratio of several percent C, the reaction will stop at FeO or lcoe304,
αFa powder is not produced. If the reduction temperature is not raised to facilitate the reduction reaction, the permissible limit of the water vapor pressure will be relaxed, but the treatment 'f! It is difficult to co-supply hydrogen uniformly and efficiently to the entire powder, and in Ii, there remain some areas where the water vapor pressure is high. For example, when the reduction is carried out at 600°C, the water vapor The high-pressure part remains as FeO, and l
” Since c○ is an antiferromagnetic material, the generated Fe
This results in a significant decrease in the saturation magnetization of the powder.

As a result of the circumstances described above, the reduction method of the prior art produces only partially incompletely reduced metal powder with large variations in magnetic properties. As a result, the shape of the sword-shaped particles was distorted and sintering between the particles progressed, resulting in a metal powder with poor dispersibility.

It is an object of the present invention to improve the drawbacks of the above-mentioned prior art and to provide a new method for producing metal powder for magnetic recording, which has less variation in magnetic properties, does not require sintering, and has excellent dispersibility.

In other words, before dehydration heat treatment, granulation is performed and granules with a size of 1 to 10+ nm are used during heat reduction heat treatment, 1]
It is newly discovered that if powdering is carried out using a continuous El tarry kiln under appropriate stirring conditions, metal powder with uniform magnetic properties and good dispersibility can be produced. This is what was discovered and the present invention was made.

The first requirement constituting the present invention is that in the reduction process, 1
The objective is to obtain granular iron oxide with a size of ~10rm.

By making it into granules, the voids in the powder increase.
, the hydrogen gas efficiently contacts the powder through the voids, and the moisture generated by the reduction reaction is efficiently discharged from the system, reducing the amount of hydrogen gas in the system. l
:The reaction does not stop at eo or FeaO4 (proceeds to Fe. The size of the granules must be 1 to 10 nI. Below 1 m + n, no noticeable effect of the increase in voids can be expected. First, uneven flow of water gas (chitunneling)
occurs, and reduction partially stops proceeding. On the contrary 10 II
When I is 111 or more, the aqueous scum cannot penetrate into the inside of the granules.

The second key point 19 is to carry out the reduction reaction under stirring. As shown in the examples, if the granules are simply dripped, the degree of reduction will not be sufficiently uniform in each part of the body. Exhaust to the outside progresses efficiently.

The object of the present invention cannot be achieved without either the first or second condition. For example, even if the reaction is carried out in a granulation-μzu1] tarry kiln, the powder is produced by the reaction.
Because of the leakage water vapor, it condenses into lumps of irregular size and deposits on the furnace wall.
Hereinafter, the content of the present invention will be explained in detail based on 1. Examples.

Example 5%Nl containing major axis 0.3μ, 9.0Illllll
O003μ.

A sword-shaped αF'000H particle with an axial ratio of 10 is used as a starting source 1'81
It was used as The αFeO○1-1 was made into irregularly shaped granules with a size of about 5 mn1 using water as a binder. The α
After adding thorium metasilicate to the "Feo01" mixture, carbon dioxide gas was blown in to neutralize p)-1 with 1, thereby covering the surface of αl-COO1-1 with the S1 compound.

After washing with water and passing through the anchor, αFeO○l-1, which is covered with the S1 compound, is exposed to air at
Solid solution αF e,,03 was turned away.

The granular α'0e203 was reduced with stirring in a rotary kiln, and the processing value was 1 kL.
/'min, ,'7' The binary temperature is 500°C.

Table 1 shows 50 locations tested from the metal powder that has undergone the above process.
The graph shows the average value of the magnetic 'lZf property and the variation with -. As comparative examples, characteristics were shown for each case with and without granulation and with various reduction methods.

In the case of the combination of granulation and agitation shown in Table 1, the effects of the present invention are clear, especially in the case of J-3, which has excellent properties and packing properties.

Example 2 Same method as Example 1 (1,1-301n
The granules were reduced in a V+'IIJ rotary kiln while stirring in In, and their magnetic properties were measured. The results are shown in Table 2.

Table 2 From Table 2, it is clear that when the size of the granules is 1 to 10 m In.

As shown in the examples, the effects of the present invention are clear, and the present invention is significant in that it clarifies the special circumstances involved in large m reduction processing and newly discovers the optimal reduction pro-hyde conditions at the production level. The invention has great engineering significance.

Applicant: Hitachi Metals Co., Ltd.

Claims (1)

[Scope of Claims] 1. Mainly acicular oxyhydroxide ferric ferric particles are used as a starting material, the starting material is coated with, for example, a silicate, and then subjected to dehydration heat treatment to obtain acicular ferric iron, Furthermore, in the method for producing a monolithic magnetic powder for magnetic recording which has iron as a main component by reducing the acicular ferric iron, a metal powder for magnetic recording which is characterized in that it particularly satisfies the following two requirements is provided. Production method. ■ In the state after the dehydration heat treatment, the particle size is 1.~10
Granulation into melon-shaped, angular or irregularly shaped particles. (2) In the heat reduction treatment, the granulated granules are kept in a stirred state. . 2. A method for producing metal powder for magnetic recording, as set forth in claim 1, characterized in that stirring is carried out particularly using a rotary kiln.