JPH08246002A - Surface-coated mn-bi magnetic recording powder and its production - Google Patents

Abstract

PURPOSE: To obtain a surface-coated magnetic recording powder without the magnetic characteristic being deteriorated even if exposed to high temp. for a long time as well as to room temp. CONSTITUTION: An SiO2 protective film is formed on the surface of an Mn-Bi magnetic recording powder to constitute the surface-coated Mn-Bi magnetic recording powder. The SiO2 protective film is formed on the surface of the Mn-Bi magnetic powder by a sol-gel reaction using silicon alkoxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-coated Mn-Bi magnetic recording powder used in the manufacture of magnetic cards, magnetic tapes and the like (these are collectively referred to as magnetic recording media hereinafter).

[0002]

2. Description of the Related Art It is known to use Mn-Bi magnetic powder as a magnetic recording powder. This Mn-Bi magnetic powder contains Bi: 20 to 60 atomic%, and the rest is Mn and inevitable impurities. And a part of Mn or Bi may be added to Ru, Rh, Pd, A if necessary.
s, Sb, Al, Ga, Ge, In, Tl, P, Sn,
It is also known that substitution with Pb, Ti, Ir or the like can be performed at 20 mol% or less.

These Mn-Bi magnetic powders have excellent characteristics as magnetic recording powders, but are easily oxidized, and the magnetic characteristics are deteriorated with the oxidation. Therefore, Mn-B
A protective film is formed on the surface of the i-based magnetic powder (hereinafter, the Mn-Bi-based magnetic powder having the protective film formed thereon is referred to as a surface-coated Mn-Bi-based magnetic recording powder) to prevent deterioration of magnetic properties due to oxidation. I'm out. For example, Japanese Patent Publication Sho 60-571
Japanese Unexamined Patent Publication (Kokai) No. 27 describes surface-coated Mn-Bi magnetic recording powder in which an organic compound containing nitrogen is formed as a protective film on the surface of Mn-Bi magnetic powder. This surface-coated Mn on which a protective film for organic compound containing nitrogen is formed
In the -Bi magnetic recording powder, when exposed to a temperature exceeding 120 ° C for a long time, the organic compound containing nitrogen is vaporized and disappears, and the corrosion resistance is deteriorated. Therefore, it is said that it is preferable to use a magnetic recording medium made of this conventional surface-coated Mn-Bi magnetic recording powder at 120 ° C. or lower.

[0004]

However, in recent years, 120
There is a demand for a magnetic recording medium that can be used under severe conditions of high temperature exceeding ℃, and development of magnetic recording powder for producing a magnetic recording medium that can be used under such high temperature conditions has been required. It was wanted.

[0005]

Therefore, the present inventors have
From this point of view, as a result of research to obtain a surface-coated Mn-Bi magnetic recording powder that does not deteriorate in magnetic properties even when exposed to high temperatures for a long time, silicon dioxide (hereinafter referred to as S
iO ₂ and referred) surface coating Mn-Bi-based magnetic recording powder formed on the surface of the Mn-Bi-based magnetic powder coatings as a protective coating, to obtain a finding that exhibits excellent corrosion resistance even when subjected to a high temperature for a long time Of.

The present invention has been made on the basis of the above findings. (1) A surface-coated Mn-Bi magnetic recording powder in which a SiO ₂ protective film is formed on the surface of the Mn-Bi magnetic powder,
It is characterized by

The thickness of the SiO ₂ protective film of the surface-coated Mn-Bi magnetic recording powder of the present invention is 0.01 to 0.2 μm.
Is preferable because the SiO ₂ protective film has a thickness of 0.01 μm.
If it is less than m, the film thickness is too thin to obtain sufficient corrosion resistance, while if it exceeds 0.2 μm, the magnetic properties deteriorate and
This is because the coating film is cracked during the heat treatment process during production, and the effect of improving corrosion resistance is reduced, which is not preferable.

A more preferable thickness of the SiO ₂ protective film is 0.03 to 0.15 μm.

The SiO ₂ protective film of the surface-coated Mn-Bi magnetic recording powder of the present invention is formed by a sol-gel reaction using a silicon alkoxide. Therefore, the present invention provides (2) a Si alkoxide. The hydrolyzate film of Mn
After being formed on the surface of the -Bi-based magnetic powder, heat treatment is performed to cause a condensation reaction of the hydrolyzate to cause Mn-Bi.
It is also characterized by a method for producing a surface-coated Mn-Bi magnetic recording powder in which a SiO ₂ protective film is formed on the surface of the magnetic magnetic powder.

Tetraethyl orthosilicate (hereinafter referred to as TEOS) is preferable as the alkoxide of Si, and a small amount of an acid as a catalyst for the hydrolysis reaction is added to an alcohol solution prepared by dissolving this TEOS in an alcohol, and the mixture is stirred and left to stand. The hydrolysis shown in 1 occurs.

[0011]

Embedded image The acid as the catalyst for the above hydrolysis reaction may be any acid such as sulfuric acid, nitric acid, hydrochloric acid, oxalic acid, acetic acid, etc., but nitric acid is particularly preferable.

The solution in which the hydrolysis has occurred is further diluted with alcohol, but it is preferable that the diluted solution has a concentration of 0.1 to 5 wt% in terms of SiO ₂ . The reason is that if the SiO ₂ conversion concentration in the solution exceeds 5 wt%, the thickness of the SiO ₂ protective film becomes thicker than 0.2 μm, while if the SiO ₂ conversion concentration is less than 0.1 wt%, S
This is because the thickness of the iO ₂ protective film is less than 0.01 μm.

The Mn-Bi magnetic powder was immersed in the alcohol-diluted solution diluted with alcohol as described above, filtered, and dried at room temperature with stirring to dry Si (OH) _{4 on} the surface of the Mn-Si magnetic powder. Monomer film is uniformly formed, and this Si (OH) ₄ monomer film is formed on M
When the n-Bi magnetic powder is heated, the Si (OH) ₄ monomer undergoes a condensation reaction to cause SiO 2 on the surface of the Mn-Bi magnetic powder.
_{2 A} film is formed.

The heating atmosphere for causing the condensation reaction of the Si (OH) ₄ monomer is preferably vacuum or an atmosphere of an inert gas such as Ar or N ₂ gas, and the heating temperature is 150 ° C. or higher for promoting the condensation reaction. Is desirable, and 3
If the temperature exceeds 50 ° C, the metallic structure of the Mn-Bi magnetic powder changes, so the upper limit is preferably 350 ° C or less.

[0015]

EXAMPLE Mn and Bi were both charged into a high-frequency melting furnace, melted in an Ar atmosphere, and cast to prepare Mn-Bi alloy ingots having the component compositions shown in Tables 1 and 2. M
The n-Bi alloy ingot is placed in an Ar atmosphere at 400 ° C. for 100
After the heat treatment for holding for a while, the particles were pulverized in a toluene solvent with an attritor mill, and the particle size (d ₅₀ ) of the obtained Mn-Bi alloy powder was measured with a laser diffraction type particle size distribution meter. The results are shown in Tables 1 and 2.

Next, tetraethyl orthosilicate (T
EOS) is dissolved in isopropyl alcohol and 40.9
A wt% TEOS alcohol solution was prepared and this 40.9 wt
0.3wt% as catalyst for% TEOS alcohol solution
% Nitric acid aqueous solution was added and the mixture was stirred and then allowed to stand for 24 hours.

The solution thus obtained was further diluted with isopropyl alcohol to prepare alcohol diluted solutions having the concentrations shown in Tables 1 and _{2 in} terms of SiO ₂ .

Mn-Bi alloy powders having a particle size of d ₅₀ shown in Tables 1 and 2 were dipped in the diluted alcohol solution, filtered, and dried at room temperature with stirring to obtain Mn-B.
A Si (OH) ₄ film is formed on the surface of the i-based alloy powder, and then in a vacuum atmosphere of 2 × 10 ⁻⁵ torr at a temperature of 250 ° C. for 1 hour.
The surface-coated Mn-Bi magnetic recording powders of the present invention (hereinafter referred to as the recording powders of the present invention) 1 to 18 and the comparative surface-coated Mn-Bi magnetic recording powders (hereinafter referred to as the comparative recording powders) which have been heated for a time and have a SiO ₂ protective film. 1) and 2 were produced.

The recording powders 1 to 18 of the present invention and the comparative recording powders 1 to 2 were measured with a laser diffraction type particle size distribution meter, and the particle diameters (D ₅₀ ) are shown in Tables 1 and 2, and d ₅₀ and D ₅₀ The thickness of the SiO ₂ protective film: 1/2 (D ₅₀ -d ₅₀ ) was determined from the measured values, and the results are shown in Tables 1 and 2.

The obtained recording powders 1 to 18 of the present invention and the comparative recording powders 1 to 2 were heated and held in the atmosphere at the temperatures shown in Tables 1 and 2 for the times shown in Tables 1 and 2, and then the present invention. The coercive force and the saturation magnetization of the recording powders 1 to 18 and the comparative recording powders 1 and 2 were measured, and the results are shown in Tables 1 and 2.

For comparison, the Mn-Bi alloy powder was pulverized with 1.5 parts of dihexylamine nitrite and 400 parts of methyl isobutyl ketone by an attritor mill, and the surface of the Mn-Bi alloy powder had a thickness of 0.10. And a conventional surface-coated Mn-Bi magnetic recording powder having a nitrogen-containing anticorrosion coating of 0.15 μm (hereinafter referred to as conventional recording powder)
Nos. 1 and 2 were prepared, and the conventional recording powders 1 and 2 were held at the temperatures and the times shown in Table 2, and their coercive force and saturation magnetization were measured. The results are shown in Table 2.

[0022]

[Table 1]

[0023]

[Table 2]

From the results shown in Tables 1 and 2, all of the recording powders 1 to 18 of the present invention show less deterioration in magnetic characteristics than the conventional recording powders 1 and 2, especially when kept at a high temperature for a long time. Recognize. However, as can be seen from the comparative recording powders 1 and 2, it cannot be seen that a sufficient effect cannot be obtained if the SiO ₂ protective film is too thick or too thin.

[0025]

As described above, the surface coating Mn of the present invention is used.
-Of course, the Bi-based magnetic recording powder is at room temperature,
Since the magnetic characteristics do not deteriorate even when exposed to high temperature for a long time, the surface-coated Mn-Bi magnetic recording powder of the present invention can be used to provide a magnetic recording medium that can be used at room temperature and high temperature. It can greatly contribute to the development.

Claims (2)

[Claims] 1. A surface-coated Mn-Bi-based magnetic recording powder having a protective film of silicon dioxide formed on the surface of the Mn-Bi-based magnetic powder. 2. A surface-coated Mn-B, characterized in that a silicon dioxide protective film is formed on the surface of the Mn-Bi magnetic powder by a sol-gel reaction using a silicon alkoxide.
Method for producing i-based magnetic recording powder.