JPH02232902A - Manufacture of magnetic metal powder for magnetic recording - Google Patents

Abstract

PURPOSE:To obtain a magnetic powder having an excellent oxidation-resisting property by a method wherein a specific organic acid metal compound is hydrolyzed in a specific alkaline atmosphere, the decomposed substance is coated on the surface of magnetic metal powder, the moisture contained therein is removed using a specific solvent, a specific heat treatment is conducted, and the magnetic metal powder is coated with a uniformly densed oxidation- resistant film. CONSTITUTION:Co, Ni, Cu and Mn slat of organic acid such as acetic acid, oxalic acid and the like, having C6 or lower, are hydrolyzed in the state wherein ammonia water, and the surface of magnetic metal powder grains of iron alloy is coated with a metal hydroxide. Besides ammonia water, ammonia and organic amine may be used. Also, as a polarity organic solvent to be used for a liquid-phase treatment, 5C or lower monovalent aliphatic alcohol, polyhydric alcohol, esters, ethylene glycol monoether and ketones can be selected. After the prescribed quantity of ammonia water, which is the neutralization equivalent of organic metal compound or more, has been added to the slurry which is obtained by suspending the magnetic powder of substrate grains, organic acid metal compound is added. After the above-mentioned material has been washed with methyl alcohol and the like, it is treated in N2 at 250 to 500 deg.C and then it is subjected to a slow oxidation in an O2/N2 less than 1vol.%. Using the above-mentioned constitution, the magnetic powder for magnetic recording, having excellent oxidation-resistant property, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for producing a metal magnetic powder having excellent oxidation resistance and suitable for magnetic recording.

[Technical background of the invention and its problems]

In recent years, there has been a growing trend towards smaller size and higher performance magnetic recording media due to higher recording densities. In conjunction with this, iron or iron-based metal magnetic powders (hereinafter referred to as metal magnetic powders) are used as magnetic powders for magnetic recording, which have a higher saturation magnetization and are easier to achieve high magnetic retention than conventional iron oxide-based magnetic powders. It is attracting attention, and digital audio tape and 8m/m
Although efforts are being made to put it to practical use in video tapes and the like, in recent years, there are even more expectations for its application to high-performance recording media such as high-definition video tapes and high-density disks.

By the way, such metal magnetic powder usually has a thickness of about 0.5μ.
It is desirable that the particles be fine particles with a diameter of 1.5 m or less (longer diameter), and more preferably 9.3 μm or less, and have excellent dispersibility, orientation in a coating film, filling property, etc. when used as a magnetic paint. It is hoped that However, such fine particles have strong surface activity, and as a result, oxidation progresses over time, resulting in a decrease in magnetic properties such as saturation magnetization and coercive force, resulting in so-called stability over time (hereinafter referred to as oxidation resistance). ) may be unavoidable. In even more severe cases, if the oxidation reaction proceeds rapidly, spontaneous combustion may occur.
This can cause various problems in handling operations and process control, such as combustion.

Many proposals have already been made to improve these problems. For example, (1) the particle surface of the metal magnetic powder immediately after being produced by reduction may be slowly oxidized to form a thin oxide film, or (2) the particle surface of the metal magnetic powder may be coated with, for example, a silicon-based compound or a higher fatty acid-based compound. There are known methods in which (3) a corrosion-resistant metal compound is deposited on the surface of the metal magnetic powder particles by various wet or dry methods. However, even with these methods, the oxidation resistance cannot be fully satisfied, and when trying to impart sufficient oxidation resistance, it is difficult to obtain the excellent magnetic properties of metal magnetic powder such as high saturation magnetization and high coercive force, or to make it into a paint. There are still many problems that need to be improved, such as the difficulty in dispersing time. In particular, in conjunction with the demand for higher S/N ratios and higher outputs, there is a trend toward finer particles of metal magnetic powder, and there is a strong desire to solve the above problems. [Object of the Invention] An object of the present invention is to solve the above-mentioned problems and provide a method for producing metal magnetic powder suitable for use in magnetic recording media with excellent oxidation resistance. [Summary of the Invention] The present inventors have been conducting various studies for some time in order to solve the above-mentioned problems without impairing the inherent excellent properties of metal magnetic powders, but they have We focused on the extremely important importance of uniformly depositing various metal hydroxides and oxides onto metal magnetic powder particles, and proceeded with further investigation. As a result, when carrying out uniform adhesion treatment from a liquid phase system, when heating and drying a filter cake after treatment, or when heat-treating a dried product,
Oxidation tends to proceed rapidly due to water vapor generated by the moisture contained in the cake brought in from the adhesion treatment system, and a large drop in magnetic properties such as coercive force and saturation magnetization cannot be avoided. The use of easily hydrolyzable processing agents such as alkoxides is attracting attention in order to impart oxidation resistance by depositing hydroxides or oxides, but the cost of the processing agents is high, and the treatment It was found that there were many problems that still needed improvement, such as low storage stability of the drug. The present invention has been made in view of the various problems described above, and involves hydrolyzing a specific organic acid metal compound in a specific alkaline atmosphere and converting the decomposition product into metal magnetic material. It adheres to the surface of powder particles, and then the adhered material is washed with a solvent of a specific composition to efficiently remove water content, and this material is heat-treated under specific conditions. The present invention has been completed based on the knowledge that oxidation resistance can be easily imparted by forming a uniform and dense oxidation-resistant coating in an economically advantageous manner.

That is, the present invention provides the following features: (1) A metal magnetic powder is treated in a liquid phase system with CoINx + at least one organic acid metal compound of Cu and Mn and an alkali to form a hydroxide of the metal on the particle surface of the metal magnetic powder. After coating, the resulting coating treatment slurry is filtered, washed with a mixed solvent containing the organic solvent having an azeotropic composition of a polar solvent and water, and then washed under a non-oxidizing atmosphere. 1. A method for producing metal magnetic powder for magnetic recording, the method comprising heating at 250 to 500°C.

<<2>> The method for producing a metal magnetic powder for magnetic recording according to claim {1}, wherein the organic acid metal compound is a metal salt of an organic acid having 6 or less carbon atoms.

<3) The method for producing a metal magnetic powder for magnetic recording according to claim (2), wherein the organic acid metal compound is a metal salt of acetic acid. <<4>> The method for producing a metal magnetic powder for magnetic recording according to claim (1), <2>, or (3), wherein the organic acid metal compound is a Co metal salt.

(5) The method for producing a metal magnetic powder for magnetic recording according to claim <1>, wherein the alkali is ammonia, aqueous ammonia, or an organic amine.

(6) The method for producing a metal magnetic powder for magnetic recording according to claim <5>, wherein the alkali is aqueous ammonia.

<<7>> The method for producing a metal magnetic powder for magnetic recording according to claim (1), wherein the polar organic solvent is a monohydric alcohol, a polyhydric alcohol, an ester, an ether, or a ketone.

(8) The method for producing a metal magnetic powder for magnetic recording according to claim (7), wherein the monohydric alcohol is an aliphatic alcohol having 5 or less carbon atoms.

(9) The method for producing a metal magnetic powder for magnetic recording according to claim (7), wherein the ether is ethylene glycol monoether.

A claim characterized in that after heat treatment in a non-oxidizing atmosphere, the treated product is subjected to gradual oxidation treatment in an oxidizing atmosphere (
1) A method for producing a metal magnetic powder for magnetic recording according to item 1).

In the present invention, the metal magnetic powder (hereinafter referred to as base particles) used as the object to be treated is a metal magnetic powder of iron or iron-based alloys mainly composed of iron, which is manufactured by various methods, and the most commonly used In addition to the above-mentioned needle-shaped crystals, various shapes such as spindle-shaped, rice grain-shaped, spherical, rod-shaped, plate-shaped, dice-shaped, etc. can be used. Can be done. It should be noted that these base particles may be subjected to gradual oxidation treatment, for example, with an oxygen-containing gas, if necessary, prior to the supporting treatment.

In the present invention, the organometallic compounds used include various Go. Ni+Cu+Mn
The processing agent for these compounds is an organic acid metal salt of
The above-mentioned organic acid metal salts, which may be used alone or in combination of two or more, are preferably metal salts of aliphatic hydrocarbon organic acids having 6 or less carbon atoms. Specific examples of these include Co, Ni, such as acetic acid, oxalic acid, and citric acid. Cu. Mention may be made of Mn salts.
Further, in order to deposit the hydroxide of the metal on the particle surface of the metal magnetic powder using the organic acid metal compound, the organic acid metal compound is applied in the presence of an alkaline substance in a liquid phase system containing the base particles. This can be done by hydrolysis. Various alkaline substances can be used as the alkaline substance, but preferably ammonia, aqueous ammonia,
Organic amines, particularly preferably aqueous ammonia and ammonia, can be used, and these can also be used in combination. Examples of the solvent used in the liquid phase treatment include polar organic solvents such as ketones, ethers, esters, and alcohols, water, and aqueous media containing these polar organic solvents. They can also be used together.

The liquid-phase deposition treatment method can be carried out by various methods, but preferably, for example, a slurry in which metal magnetic powder of the base particles is suspended in the liquid-phase treatment solvent, Either a predetermined amount of an alkaline substance equal to or greater than the neutralization equivalent of the organometallic compound is added, and then an organic acid metal compound is added, or the organometallic compound and the predetermined amount of the alkaline substance are added to the suspension slurry of the base particles. This can be done by adding simultaneously. In the above-mentioned deposition treatment system, for example 8
It is preferable to carry out the process at a temperature of 0°C or lower, preferably 60°C or lower. Co. as previously described. The slurry treated with Ni, Cu or Mn metal hydroxide is, if necessary, aged and filtered, and the filtered cake is then filtered into a slurry containing an organic solvent having an azeotropic composition higher than that of a polar organic solvent and water. Washing with a mixed solvent removes unreacted substances in the filtered cake, and
The contained water is replaced with a mixed solvent. Various kinds of polar solvents can be used as the polar solvent, but monohydric alcohols, polyhydric alcohols, esters, ketones, etc. are preferable, and in particular monohydric alcohols having 5 or less carbon atoms are preferred. Aliphatic alcohols, such as methyl alcohol, ethyl alcohol, isoprobioalcohol, butyl alcohol, isoamyl alcohol, and ethers include ethylene glycol monoethers, such as ethylene glycol ethyl ether, ethylene glycol methyl ether, ethylene glycol monobutyl ether, etc. can. If the composition of the mixed solvent contains more water than the azeotropic composition, oxidation of the base particles is likely to proceed rapidly due to generated water vapor in the subsequent drying and heat treatment steps. etc., which is undesirable. Incidentally, following the washing with the mixed solvent described above, further washing with a small amount of a polar solvent can be carried out if necessary.

Further, the mixed solvent used in the washing can be recovered by distillation and reused by supplementing a small amount of organic solvent as necessary, which can reduce processing costs and is very industrially advantageous. In the present invention, the amount of the metal hydroxide deposited varies depending on the shape, size, specific surface area, etc. of the metal magnetic powder particles of the base particles, and cannot be definitively stated, but with respect to the weight standard of the base particles. , Co., Ni. The content of Cu and Mn as metals is 1 to 30%, preferably 3 to 20%. If the amount of coating is too much than the above range, magnetic properties such as saturation magnetization may be easily damaged, which is not preferable.

The wet cake washed as described above may be dried under aeration of an inert gas such as nitrogen or a slightly reducing gas (for example, II z / N z = 1% by volume or less), or After drying under reduced pressure, heat treatment is performed at 250 to 500°C in a non-oxidizing gas atmosphere. By performing the heat treatment, changes in magnetic properties such as saturation magnetization and coercive force over time can be made more favorable, and organic substances based on the processing solvent and processing agent used in the adhesion treatment system and cleaning system can be made more favorable. can be volatilized substantially completely, and as a result, an adverse effect on the dispersibility and the like during the preparation of magnetic paint can be avoided. Furthermore, if the heat treatment temperature is lower than the above range, the metal hydroxide in the deposited layer will not be substantially converted to metal oxide, and as a result, the desired effect described above will not be brought about. If the temperature is too high, particle sintering and further diffusion of the metal oxide of the adhered layer into the base particles are likely to occur. The decline may be unavoidable. Note that when the heat-treated metal magnetic powder is further subjected to gradual oxidation treatment in an oxidizing gas atmosphere, the oxidation resistance stability can be made even more preferable. In some cases, the gradual oxidation treatment may be performed prior to the heat treatment in a non-oxidizing atmosphere. Note that the slow oxidation treatment is performed using, for example, Ox/To
It can be carried out under a controlled gas atmosphere with a low oxygen concentration of less than 1% by volume. The metal magnetic powder produced according to the method of the present invention described above can be prepared using various binder resins,
For example, vinyl chloride-vinyl acetate copolymer resin, polyurethane resin, polyester resin, acrylic resin,
Magnetic paints are prepared by adding binder components such as cellulose resin and various additives such as dispersants, lubricants, abrasives, antistatic agents, etc., and various non-magnetic supports such as polyethylene terephthalate films and acetate films are prepared. The magnetic layer is coated on the body to a predetermined thickness (usually 2 to 5 μm after drying), and dried after orientation treatment to form a magnetic layer, and then subjected to calendering and thrifting to form a magnetic recording medium, such as a magnetic tape. Obtainable. In addition, the magnetic tape may be provided with a so-called back coat layer on the opposite surface of the support from the magnetic layer side in order to further improve antistatic properties, running stability, etc., if necessary.

The present invention will be further explained by giving examples and comparative examples below.

[Example of the present invention]

Example 1 A ferrous sulfate aqueous solution was neutralized with a sodium hydroxide aqueous solution,
Further, an oxidizing gas is introduced and oxidized to produce α-FeOOII, which is then heated and dehydrated to produce α-FeOOII. 0.
After that, the needle-shaped metal iron magnetic powder (specific surface area: IIE755 m"/g) was obtained by heating reduction in a hydrogen stream.
, average major axis particle diameter 0.16μ, average axial ratio 9, coercive force 12
370e, saturation magnetization 1B4.7emu/g - squareness ratio 0.
485) was used as a base particle, and 20 g of this material was suspended in 200 1Rl of ethylene glycomonoethyl ether (hereinafter referred to as ethyl cellosolve). This suspension was placed in a four-necked flask equipped with a stirrer, and while nitrogen gas was introduced to maintain a non-oxidizing atmosphere, aqueous ammonia (34 g/12 as N II s) was added with stirring.
1- was added, then the temperature was raised to 50°C at 4°C/min,
While maintaining this temperature, aqueous cobalt acetate solution (3.5% by weight as Go) was added to IWiZ and aqueous ammonia (N
34g/l as tl 3) to about 1.21n! /
The cobalt hydroxide was added simultaneously over a period of 1 hour at a rate of 1 minute, and then held at room temperature for 20 minutes to deposit cobalt hydroxide onto the substrate particles.

After filtering the resulting slurry, ethyl cellosolp/water (3
The sample was washed with 100rn1 of a mixed solvent (volume ratio: 5/65).
The washed cake was then air dried.

10 g of the coated powder obtained as described above was heat-treated at 400° C. for 2 hours while passing nitrogen gas in a tubular electric furnace to obtain the desired metal magnetic powder (Sample A). Example 2 In Example 1, deionized water was used instead of ethyl cellosolve to prepare a suspension of the substrate particles, and ethanol/cellosolve was used instead of the ethyl cellosolve/water mixed solvent for washing after filtration. The desired metal magnetic powder was obtained in the same manner as in the same example except that a mixed solvent of water (97/3 volume ratio) was used (Sample B). Example 3 In Example 1, the addition rates of cobalt acetate aqueous solution and ammonia water were 1.5 mf/min and about 1.8 mj, respectively.
/ minute, and ethyl cellosolve/water (
The desired metal magnetic powder was obtained by processing in the same manner as in the same example except that 35/65 volume ratio) was used (Sample C). Example 4 In Example 1, a suspension of substrate particles was prepared using butanol instead of ethyl cellosolve, and butanol/water (butanol/water) was used instead of the mixed solvent of ethyl cellosolve/water for washing after filtration. The desired metal magnetic powder was obtained in the same manner as in the same example except that a mixed solvent (60/40 volume ratio) was used (Sample D). Example 5 In Example 2, a suspension of substrate particles was prepared using ethanol instead of deionized water, and a mixed solvent of ethanol/water (98/2 volume ratio) was used for washing after filtration. The desired metal magnetic powder was obtained by processing in the same manner as in the same example (Sample E). Comparative Example 1 The desired metal magnetic powder was obtained in the same manner as in Example 1, except that cobalt chloride (CoC j2 z) was used in place of cobalt acetate (Sample F).
). Comparative Example 2 The desired metal magnetic powder was obtained in the same manner as in Example 2, except that deionized water was used instead of the ethanol/water mixed solvent for washing. Sample G
). Comparative Example 3 In Example 2, ethanol/water (
In addition to using a mixed solvent (50/50 volume ratio),
The desired metal magnetic powder was obtained by processing in the same manner as in the same example (Sample H). Comparative Example 4 The desired metal magnetic powder was obtained in the same manner as in Example 1, except that cobalt acetate and aqueous ammonia were not added (Sample I). Comparative Example 5 10 g of metal magnetic powder as base particles was immersed in 30 rn1 of toluene and then air-dried at room temperature (Sample J). The saturation magnetization (σs: e+++u/g), coercive force (H c : Oe), and squareness ratio (Rs) of the metal magnetic powders of the Examples and Comparative Examples were measured by conventional methods. In addition, in order to evaluate the oxidation stability, it was left for one week in an environment with a temperature of 60°C and a relative humidity of 80%, and σs, H C %
The accelerated change over time of Rs was measured, and the saturation magnetization deterioration rate ΔσS (%) was determined using the following formula.

These results are shown in Table 1. σ sO −σ S (In the formula, σS0 is σS before aging, and σS” is σS after aging.) [Effects of the Invention] The metal magnetic powder obtained by the present invention has significantly improved oxidation resistance. Therefore, it is capable of retaining excellent magnetic properties for a long period of time, has excellent storage stability, is extremely favorable in terms of handling and process control, and has good dispersibility in media. Therefore, it is extremely suitable for producing high-output, high-recording-density magnetic media.The present invention also provides an economically advantageous method for producing magnetic powder with excellent performance using relatively simple means. It is of great industrial significance.

Claims (10)

[Claims] (1) Metal magnetic powder is treated in a liquid phase system with at least one organic acid metal compound of Co, Ni, Cu, and Mn and an alkali to coat the particle surface of the metal magnetic powder with the hydroxide of the metal. After filtering the obtained coating treatment slurry, it is washed with a mixed solvent containing the organic solvent having an azeotropic composition of a polar solvent and water or higher, and then this slurry is heated for 250 min in a non-oxidizing atmosphere. A method for producing metal magnetic powder for magnetic recording, characterized by heat treatment at ~500°C. (2) The method for producing a metal magnetic powder for magnetic recording according to claim (1), wherein the organic acid metal compound is a metal salt of an organic acid having 6 or less carbon atoms. (3) The method for producing a metal magnetic powder for magnetic recording according to claim (2), wherein the organic acid metal compound is a metal salt of acetic acid. (4) The method for producing a metal magnetic powder for magnetic recording according to claim (1), (2) or (3), wherein the organic acid metal compound is a Co metal salt. (5) The method for producing a metal magnetic powder for magnetic recording according to claim (1), wherein the alkali is ammonia, ammonia water, or an organic amine. (6) The method for producing a metal magnetic powder for magnetic recording according to claim (5), wherein the alkali is aqueous ammonia. (7) The method for producing a metal magnetic powder for magnetic recording according to claim (1), wherein the polar organic solvent is a monohydric alcohol, a polyhydric alcohol, an ester, an ether, or a ketone. (8) The method for producing a metal magnetic powder for magnetic recording according to claim (7), wherein the monohydric alcohol is an aliphatic alcohol having 5 or less carbon atoms. (9) The method for producing a metal magnetic powder for magnetic recording according to claim (7), wherein the ether is ethylene glycol monoether. (10) The method for producing metal magnetic powder for magnetic recording according to claim (1), characterized in that after heat treatment in a non-oxidizing atmosphere, the treated product is subjected to gradual oxidation treatment in an oxidizing atmosphere.