JPH01110706A - Metallic magnetic powder - Google Patents

Abstract

PURPOSE:To obtain the title metal magnetic powder having improved oxidational stability which is suitable for a high density magnetic recording medium by a method wherein the amino-substituted benzene carboxylic acid is carried on the surface of grains. CONSTITUTION:An amino-substituted benzene carboxylic acid compound is carried on the surface of grains. The various compounds shown by a general formula as shown in the diagram can be used as the amino-substituted benzene carboxylic acid compound. For example, the metal magnetic powder mainly composed of needle-like iron (obtained by heat-reducing the heat-dehydrated alpha-FeOOH using reducing gas, and it has the average length of axis of 0.3mum, coercive force (Hc) of 1302Oe, and saturated magnetization (sigma) of 127.8emu/g) is prepared. Said magnetic powder is dipped into an ethanol solution of 1000ml in which 1.5g of anthranilic acid (o-aminobenzene carboxylic acid) is dissolved, and after agitating for three hours at the room temperature while nitrogen gas is being fed, it is filtered, dried up in the air of the room temperature, and the metal magnetic powder having anthranilic acid on the surface of the grain can be obtained.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a metal magnetic powder suitable for magnetic recording,
In particular, it relates to a metal magnetic powder with improved oxidation stability.

[Technical background of the invention and its problems]

In recent years, there has been a growing trend toward smaller size and higher performance of magnetic recording media due to higher density recording capacity. In addition, as magnetic powder for magnetic recording, iron-based metal magnetic powder (iron-based metal magnetic powder of iron or iron-based alloys), which has a larger saturation magnetization and is easier to increase coercive force than conventional iron oxide-based magnetic powder ( Metal magnetic powder (hereinafter referred to as metal magnetic powder) is attracting attention, and its application to audio tapes, 8m/m video tapes, etc. has been attempted, and recently it has been applied to high-definition video tapes, digital audio chips, high-density disks, etc. There are increasing expectations for its application to high-performance recording media.

By the way, such metal magnetic powder is usually desired to have fine particles of about 1 μm or less, or even 0.5 μm or less,
Such fine particles have strong surface activity, and as a result, oxidation progresses over time, and as a result, magnetic properties such as saturation magnetization deteriorate, resulting in an unavoidable deterioration of oxidation stability, or even worse. However, if the oxidation reaction proceeds rapidly, various troubles in handling operations and process control cannot be avoided, such as spontaneous ignition and combustion.

Various proposals have already been made to improve these problems. For example, metal magnetic powders immediately after being produced by reduction may be slowly oxidized to form a thin iron oxide film, or inorganic substances such as chromium, silicon, aluminum, etc.
Mineral oil, silane coupling agent, organic phosphate ester,
Attempts have been made to coat metal magnetic powder with various organic acids including higher fatty acids. however,
Even with these methods, there are still many problems that need to be improved, such as not providing sufficient oxidation stability, or while providing oxidation stability, excellent magnetic properties such as dispersibility and saturation magnetization are easily lost. The problem remains.

In particular, in conjunction with the demand for higher SZN ratios and higher outputs, there is a trend toward finer grains of metal magnetic powders, and there is a strong desire for a solution to the above-mentioned problems.

[Purpose of the invention]

An object of the present invention is to provide a metal magnetic powder with improved oxidation stability suitable for high-density magnetic recording media.

[Summary of the invention]

The present invention was developed as a result of various studies carried out by the present inventors to solve the above-mentioned problems without impairing the inherent properties of metal magnetic powders. The metal magnetic powder, in which a substituted benzenecarboxylic acid compound is supported on the particle surface, can improve oxidation stability, such as extremely effectively preventing deterioration of magnetic properties over time, and improve dispersibility. The present invention has been completed based on the knowledge that the present invention has excellent properties and can also be safe. That is, the present invention is a metal magnetic powder characterized in that an amino-substituted benzenecarboxylic acid compound is supported on the particle surface.

In the present invention, the metal magnetic powder (hereinafter referred to as substrate constituent particles) used as the object to be treated is iron-based metal powder of iron or various iron-based alloys mainly composed of iron, produced by various methods. However, in addition to the above-mentioned needle-shaped crystals, there are
For example, various shapes such as a spindle shape, a rice grain shape, a spherical shape, a rod shape, a flat plate shape, and a dice shape can be used.

In the present invention, as the amino-substituted benzene carboxylic acid compound, various compounds represented by the general formulas below can be used, but ortho, meta or para-amino substituted benzene monocarboxylic acids or salts or esters thereof are preferable. , for example (1
) 0-aminobenzoic acid, (2) m-aminobenzoic acid, (
3) p-aminobenzoic acid, (4) O-aminobenzoic acid sodium salt, (5) m-aminobenzoic acid sodium salt, (6) p
-aminobenzoic acid sodium salt, (7) o-aminobenzoic acid methyl ester, (8) p-aminobenzoic acid methyl ester, (9) O-aminobenzoic acid ethyl ester,
α1lllp-aminobenzoic acid ethyl ester, αυp
-aminobenzoic acid n-propyl ester, (2) p-aminobenzoic acid isopropyl ester, α30-aminobenzoic acid n-butyl ester, αUp-aminobenzoic acid n
-Butyl ester 05ip-aminobenzoic acid isobutyl ester and the like can be mentioned. Note that the processing agents of these compounds may be used alone or in combination of two or more.

The amount of the amino-substituted benzenecarboxylic acid compound supported is:
The amount is 0.5 to 10%, preferably 1 to 7%, based on the weight of the metal magnetic powder. If the supported amount is too small than the above range, the desired effect cannot be obtained, and if the supported amount is too large, the magnetic properties such as saturation magnetization may be easily impaired, or even a bleeding phenomenon may occur. This is undesirable because it deteriorates the performance of the magnetic coating film.

The above-mentioned amino-substituted benzenecarboxylic acid compound can be supported on the surface of the base particles by various methods. For example, a treatment agent is dissolved in an appropriate solvent, and the solution is used to support the base particles. This can be done by wetting or soaking and then evaporating the solvent.

The suitable solvent may be any solvent as long as it is inert to the base particles and can dissolve at least part or all of the processing agent, such as methanol, ethanol, isopropanol, dioxane, etc. can be mentioned. However, the above-mentioned supporting treatment is
For example, it is preferable to carry out the process in a non-oxidizing atmosphere such as nitrogen gas to prevent oxidation as much as possible, and the wetting or dipping operations in the supporting treatment are usually carried out at room temperature, but they can also be carried out under heating if necessary. The treatment time is generally about 10 to 300 minutes. After wetting or immersing as described above, it is desirable to treat or evaporate the solvent and further dry under heat or reduced pressure. In addition, it is more preferable to carry out the treatment for supporting the treatment agent while crushing and dispersing the aggregates of the particles constituting the substrate using, for example, a ball mill or a sand mill.

The metal magnetic powder in which the amino-substituted benzene carboxylic acid compound is supported on the particle surface in this manner can be dried as described above to obtain the metal magnetic powder of the present invention.
More desirably, by heat-treating this material at a specific temperature, the stability over time of magnetic properties such as saturation magnetization and coercive force of the metal magnetic powder can be made even more preferable. The heat treatment temperature is 200 to 700°C, preferably 250 to 600°C. If the heat treatment temperature is too lower than the above range, the desired effect will not be brought about, and if it is too high than the above range, particle sintering will likely occur.
A decrease in coercive force and squareness ratio may be unavoidable. The atmosphere during the heat treatment is preferably one in which various inert gases such as helium, argon, etc. are used in addition to nitrogen, and if desired, oxygen or It is also possible to partially oxidize the particle surface by mixing a portion of an oxygen-containing gas such as air. Furthermore, the inert gas may be mixed with a small amount of non-oxidizing gas such as hydrogen gas.

The mechanism of action of the increase in the temporal stability and corrosion resistance of magnetic properties brought about by the heat treatment has not yet been fully elucidated, but the amino-substituted benzene carboxylic acid compound adsorbed on the particle surface is caused by the heat treatment. It is presumed that this will promote bonding with the surface of the substrate particles, and as a result, it will be possible to form a more uniform and stable film on the surface of the substrate particles, thereby increasing the oxidation stability by -0. . Furthermore, as is clear from the above, the oxidation-resistant film formed on the particle surface by the heat treatment becomes stronger, which, together with the increase in the stability of the magnetic properties over time, further increases the This is effective in making the dispersibility of the magnetic recording medium more favorable and in avoiding bleed-out in magnetic recording media.

The present invention will be further explained below by giving Examples and Comparative Examples.

[Example of the present invention]

Example 1 Metal magnetic powder mainly composed of acicular iron (α-FeOOI)
A product obtained by heating and dehydrating I and reducing it with a reducing gas: average major axis length 0.3 μ, coercive force (llc) 1.
3020e, saturation magnetization (σs) 127.8emu/g)
Prepare 30 g of anthranilic acid (0-aminobenzenecarboxylic acid) and immerse it in an ethanol solution of 1,000 g in which 1.5 g of anthranilic acid (0-aminobenzenecarboxylic acid) has been dissolved. After stirring at room temperature for 3 hours while bubbling with nitrogen gas, treat it and then leave it at room temperature. It was air-dried. The metal magnetic powder of the present invention thus obtained is referred to as sample (A).

Example 2 A metal magnetic powder of the present invention was obtained in the same manner as in Example 1, except that a dioxane solution in which 1.5 g of anthranilic acid was dissolved was used instead of the ethanol solution in Example 1, and the mixture was immersed and stirred at 50°C. . This is designated as sample CB).

Example 3 The reason for using doaminobenzenecarboxylic acid in place of anthranilic acid in Example 1 is as follows.
The metal magnetic powder of the present invention was obtained by processing in the same manner as in the case of .

This is designated as sample (C).

Example 4 The acicular magnetic metal powder mainly composed of iron used in Example 1 was treated to support anthranilic acid in the same manner as in the same example. The obtained treated powder was heat-treated at 300° C. for 2 hours in a 77-full furnace under a nitrogen gas flow of 1β/min. This is designated as sample (D).

Example 5 The same procedure as in Example 4 was carried out except that the heat treatment was performed at 500° C. for 2 hours. This is designated as sample (E).

Comparative Example The metal magnetic powder used in the example before being treated with anthranilic acid is referred to as a comparative sample (F).

The coercive force (Hc: Oe) of the samples (A) to (F) of the above examples and comparative examples was measured using a vibrating sample magnetometer (VSM).
and saturation magnetization (σg: emu/g) were measured. Furthermore, the temperature was 60℃ to evaluate oxidation stability and corrosion resistance.
℃ and relative humidity of 80% for two weeks to accelerate aging, and then measure tic and σ again using a sample vibrating magnetometer (VSM) to determine the deterioration rate Δ of saturation magnetization due to accelerated aging as described above.
σS (%) was determined by the following formula.

These results are shown in Table-1.

(In the formula, σ, is the elongation before aging, and σ,′ is σ after aging.) As is clear from the results in Table 1, the sample treated with anthranilic acid of the present invention has a saturation magnetization. The deterioration rate Δσ, (%) of
It can be seen that the corrosion resistance has been significantly improved.

A magnetic coating material was prepared by dispersing each sample of the above-mentioned Examples and Comparative Examples in a binder mainly composed of vinyl chloride-vinyl acetate copolymer resin, and the magnetic coating material was coated and oriented on a polyester film using a conventional method to perform magnetic recording. When the media were prepared and their properties were examined, it was found that the media of the present invention had excellent oxidation stability and also had good dispersibility into magnetic recording media.

〔Effect of the invention〕

The metal magnetic powder supporting the amino-substituted benzenecarboxylic acid compound obtained by the present invention has significantly improved oxidation stability, and therefore can maintain excellent magnetic properties for a long period of time, and has excellent storage stability. It must be extremely favorable in terms of excellent handling and process control;
Furthermore, it has good dispersibility in the medium and is extremely suitable for manufacturing high-output, high-density magnetic recording media.

Claims (2)

[Claims] (1) A metal magnetic powder characterized by carrying an amino-substituted benzenecarboxylic acid compound on the particle surface. (2) The metal magnetic powder according to claim (1), wherein the metal magnetic powder supports an amino-substituted benzenecarboxylic acid compound on the particle surface and is obtained by heat treatment.