JPH0765084B2 - Metal magnetic powder and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic metal powder and a method for producing the same,
More specifically, it relates to a metallic magnetic powder mainly composed of iron having excellent magnetic properties and a method for producing the same.

[Conventional technology]

Metal magnetic powders mainly composed of iron are usually produced by heating and reducing iron oxyhydroxide powder or iron oxide powder, and have a high saturation magnetization amount, but during heating and reduction, sintering occurs between particles. The resulting particles tend to impair the uniformity and shape of the particles, and it is difficult to obtain particles with sufficiently excellent magnetic properties.

Therefore, conventionally, in order to prevent sintering between particles during heat reduction, various sintering inhibitors have been applied to the particle surface of the reduced substance powder before heat reduction, For example, iron oxyoxide powder or iron oxide powder is dispersed in an alkaline aqueous solution in which an aluminate is dissolved, and the aluminate is hydrolyzed to form an aluminum compound coating such as an aluminum oxide coating. ing.
(Japanese Patent Publication No. 56-28967) Further, iron or an iron-based oxide powder is dipped in an alcohol solution of aluminum alkoxide prepared by dissolving aluminum chloride in alcohol such as ethylene glycol, polypropylene glycol, or glycerin. Then, after the aluminum alkoxide is deposited on the surface of the iron oxide powder, it is dispersed in water to hydrolyze the alkoxide to deposit an aluminum compound film such as aluminum oxide. (JP-A-53
-90151) [Problems to be solved by the invention] However, aluminum oxide film is formed on the particle surface of the powder to be reduced by hydrolysis of aluminate, or aluminum chloride is used as ethylene glycol, polypropylene glycol, glycerin, etc. Alcohol solution of aluminum alkoxide prepared by dissolving it in alcohol of is used, and by the conventional method of forming an aluminum oxide film on the particle surface of the substance to be reduced powder by hydrolysis of this aluminum alkoxide, Acid radical ions such as alkali metal ions and sulfate ions are mixed in, and cleaning is extremely difficult. Therefore, these impurities are contained in the aluminum oxide film on the surface of the particles of the metal magnetic powder obtained by heating and reducing it, and the aluminum oxide film becomes chemically unstable, and the structure of the aluminum oxide film also becomes Defects are likely to occur and interfere with the sintering prevention effect. In addition, when a magnetic paint is prepared using such a magnetic metal powder having an aluminum oxide film formed thereon, acid radical ions such as alkali metal ions and sulfate ions contained in the aluminum oxide film react with the binder resin to make it magnetic. The coating material gels, and a magnetic recording medium having sufficiently good magnetic properties and durability cannot be obtained.

[Means for Solving Problems] The present invention has been made as a result of various studies in order to solve such problems, and it is possible to remove aluminum isohydrate on the particle surface of powder mainly composed of iron oxyhydroxide or iron oxide. Propoxide, aluminum-t-butoxide, aluminum triethoxide, aluminum tri-n-butoxide,
Aluminum tri-sec-butoxide is contacted with vapor of aluminum alkoxide selected from butoxide, and then vapor is contacted to cause hydrolysis on the particle surface,
An aluminum oxide film is formed on the surface of particles of powder mainly composed of iron oxyhydroxide or iron oxide, or aluminum isopropoxide, aluminum is added to an aqueous suspension of powder mainly composed of iron oxyhydroxide or iron oxide. -T
-Butoxide, aluminum triethoxide, aluminum tri-n-butoxide, aluminum tri-sec-
A solution in which an aluminum alkoxide selected from butoxide is dissolved is added, and the aluminum alkoxide is hydrolyzed on the particle surface of the powder mainly composed of iron oxyhydroxide or iron oxide to oxidize the aluminum oxide film or hydrous aluminum oxide film. Iron or iron oxide-based powder particles are formed on the particle surface, and then these are reduced by heating to form a high-purity aluminum oxide film with a purity of 99% or more on the particle surface. By forming a powder, an aluminum oxide film that does not contain impurities such as acid radical ions such as alkali metal ions and sulfate ions, is chemically stable, and has good uniformity. To improve the magnetic properties of this type of magnetic metal powder, And favorably prevent the gelation of the magnetic coating is prepared by use, it is obtained by sufficiently improve the magnetic properties and durability of the magnetic recording medium obtained.

In the present invention, examples of the aluminum alkoxide used for forming the aluminum oxide film on the surface of the particles of the metallic magnetic powder mainly containing iron include aluminum isopropoxide, aluminum-t-butoxide, aluminum triethoxide, and aluminum. Tri-
N-butoxide, aluminum tri-sec-butoxide and the like are preferably used. This kind of aluminum alkoxide is different from conventional aluminate,
It does not have acid radical ions such as alkali metal ions and sulfate ions in the molecule, and is easily vaporized without being thermally decomposed when heated at a temperature of 50 to 200 ° C. Also alcohol,
It dissolves easily in solvents such as ketones and esters, and is deliquescent and decomposes with water.

Then, such aluminum alkoxide is heated and evaporated, the vapor of aluminum alkoxide is deposited by contacting with the particle surface of the powder mainly composed of iron oxyhydroxide or iron oxide, and then contacted with steam, The aluminum alkoxide is hydrolyzed on the particle surface to form aluminum oxide, and the particle surface of the powder mainly composed of iron oxyhydroxide or iron oxide does not contain impurities such as alkali metal ions and acid radical ions such as sulfate ions, which is extremely high. A pure aluminum oxide coating is deposited.

Further, such an aluminum alkoxide is dissolved in an appropriate solvent, and the aluminum alkoxide solution is
When added to an aqueous suspension of powder mainly composed of iron oxyhydroxide or iron oxide and stirred, aluminum alkoxide is hydrolyzed on the surface of the particles of the powder mainly composed of iron oxyhydroxide or iron oxide to cause aluminum oxide. Alternatively, it becomes aluminum oxide hydroxide, and impurities such as acid radical ions such as alkali metal ions and sulfate ions are not mixed, and an extremely high-purity aluminum oxide film or aluminum oxide hydroxide film is mainly composed of iron oxyhydroxide or iron oxide. And formed on the particle surface of the powder.

The aluminum oxide coating or hydrous aluminum oxide coating formed on the particle surface of the powder mainly composed of iron oxyhydroxide or iron oxide by such a gas phase reaction or liquid phase reaction is adhered only on the particle surface. However, even when a large amount is deposited, it is deposited only on the particle surface to form an extremely high-purity aluminum oxide coating or hydrous aluminum oxide coating. The amount of the powder mainly composed of iron oxyhydroxide or iron oxide deposited on the particle surface is preferably within the range of 0.1 to 20% by weight in terms of Al / Fe atomic conversion weight ratio, and when too small, aluminum oxide is used. The coating film or hydrous aluminum oxide coating film is not formed well, and if it is too large, it is difficult to form an aluminum compound coating film of uniform thickness,
Also, aluminum compounds start to precipitate on other than the surface.

In this way, the iron oxyhydroxide or iron oxide on which an extremely high-purity aluminum oxide film or hydrous aluminum oxide film is formed is then heated to 150 to 6 in a hydrogen stream.
When heated and reduced at a temperature of 00 ° C, the extremely high-purity aluminum oxide film or hydrous aluminum oxide film sufficiently exerts the effect of preventing sintering, forming a high-purity aluminum oxide film with a purity of 99% or more. A magnetic metal powder mainly composed of iron is obtained, and the aluminum oxide film formed on the particle surface of the magnetic metal powder mainly composed of iron in this way is extremely dense, chemically stable, and uniform. The magnetic properties of this kind of metal magnetic powder are improved, and the gelling of the magnetic paint prepared by using this kind of metal magnetic powder is also well prevented. The magnetic characteristics and durability of the magnetic recording medium obtained by using are improved sufficiently.

As the powder mainly containing iron oxyhydroxide and iron oxide, α-FeOOH powder, B-FeOOH powder, γ-FeOOH powder,
In addition to α-Fe ₂ O ₃ powder, Fe ₃ O ₄ powder, etc., Co, Cr,
A powder containing various metal components such as Al, Mn, and Zn is preferably used.

As described above, the metal magnetic powder having a high purity 99% or higher purity aluminum oxide coating on the particle surface of the metal magnetic powder mainly composed of iron has good stability and uniformity of the aluminum oxide coating. As a result, the magnetic characteristics of the metal magnetic powder are improved, and when a magnetic recording medium is manufactured using this kind of metal magnetic powder, a magnetic recording medium having sufficiently improved magnetic characteristics and durability can be obtained.

〔Example〕

 Next, an embodiment of the present invention will be described.

Example 1 10 g of goethite powder having an average major axis of 0.4 μm and an axial ratio (major axis / minor axis) of 12/1 was placed in one of the flasks connected by a glass tube and deaerated with a vacuum pump. On the other hand, put about 20 g of aluminum isopropoxide in the other flask,
This was heated in an electric furnace to be evaporated, and the vapor of aluminum isopropoxide was sent to the flask containing the goethite powder to adsorb the vapor of aluminum isopropoxide. Thereafter, water vapor was introduced to hydrolyze the aluminum isopropoxide adsorbed on the surface of the particles of the goethite powder to obtain goethite powder having an aluminum oxide film formed on the surface of the particles.

Then, the obtained goethite powder, in a hydrogen stream, 500
It was heated and reduced at 4 ° C. for 4 hours to obtain a metallic iron magnetic powder provided with a high-purity aluminum oxide film having a purity of 99% or more. This metallic iron magnetic powder had an average major axis of 0.3 μm and an axial ratio (major axis / minor axis) of 10/1. Using the metallic iron magnetic powder thus obtained, 100 parts by weight of metallic magnetic iron powder VAGH (manufactured by UCC, vinyl chloride-vinyl acetate-vinyl alcohol copolymer) 10 〃 Pandex T-5201 ( Dainippon Ink and Chemicals, Inc., polyurethane, number average molecular weight 20,000-30,000) 6
〃 Myristic acid 5 〃 (HS-500 (Asahi Denka Co., Ltd., carbon black) 1 〃 Methyl isobutyl ketone 85 〃 Toluene 85 〃 Put the composition into a 3 volume steel ball mill and rotate it for 72 hours. And dispersed well to prepare a magnetic paste.
40 parts by weight of toluene and Coronate L (manufactured by Takeda Pharmaceutical Company,
2 parts by weight of a trifunctional low molecular weight isocyanate compound) was further added to prepare a magnetic paint. This magnetic paint thickness 12
4 μm coating thickness after drying on μm polyester film
After coating so as to have a thickness of .mu.m, drying, and mirror finishing treatment, it was cut into 1/2 inch width to prepare a magnetic tape.

Example 2 3 g of goethite powder having an average major axis of 0.4 μm and an axial ratio (major axis / minor axis) of 12/1 was dispersed in 400 ml of water, and aluminum isopropoxide was separately stirred while thoroughly stirring the dispersion with a disperser.
Alcohol solution of aluminum isopropoxide prepared by dissolving 5 g in ethanol 30 ml is gradually added, and aluminum isopropoxide is adhered to the particle surface of goethite powder, and at the same time, aluminum adsorbed on the particle surface of goethite powder. Hydrolyzes isopropoxide,
A goethite powder having an aluminum oxide film formed on the surface of the particles was obtained.

Then, the obtained goethite powder was heated and reduced in the same manner as in Example 1 to have an average major axis of 0.3 μm and an axial ratio (major axis / major axis).
We obtained metallic iron magnetic powder with a high-purity aluminum oxide coating with a minor axis of 10/1 and a purity of 99% or more, and made a magnetic tape.

Comparative Example 1 3 g of goethite powder having an average major axis of 0.4 μm and an axial ratio (major axis / minor axis) of 12/1 was suspended in a 1N aqueous solution of caustic soda, and stirred well, to prepare 0.5M aluminum sulfate separately prepared. 5 ml of 0.5N caustic soda solution was added. Next, this suspension was neutralized by gradually aerating carbon dioxide, and after adjusting the pH to 8 or less, it was separated by filtration and washed with pure water to obtain an aluminum oxide film on the surface of the goethite powder. Got

Then, the obtained goethite powder was heated and reduced in the same manner as in Example 1 to have an average major axis of 0.3 μm and an axial ratio (major axis / major axis).
A magnetic tape was prepared by obtaining metallic iron magnetic powder having an aluminum oxide coating with a minor axis of 6/1.

Comparative Example 2 35 g of aluminum chloride (AlCl ₃ .6H ₂ O) was put into 500 g of ethylene glycol, and heated to about 80 ° C. to dissolve. Next, 150 g of goethite powder having an average major axis of 0.4 μm and an axial ratio (major axis / minor axis) of 12/1 was dispersed in this solution, the powder was filtered, and the filtered material was dispersed in water. Thereafter, this was filtered and dried to obtain a goethite powder having an aluminum oxide film formed on the surface of the goethite powder particles.

Next, the obtained goethite powder was heated and reduced in the same manner as in Example 1 to give an average major axis of 0.3 μm and an axial ratio (major axis / major axis).
A magnetic tape was prepared by obtaining metallic iron magnetic powder having an aluminum oxide coating with a minor axis of 6/1.

For the metallic iron magnetic powder having the aluminum oxide coating obtained in each Example and Comparative Example, the coercive force, the saturation magnetization, the specific surface area by the BET method was measured, and the aluminum oxide coating had an Al / Fe atomic conversion weight ratio. The contents of sulfate ion, chloride ion and sodium ion in the aluminum oxide film were measured.

The results are shown in Table 1 below.

The squareness ratio, durability and residual magnetic flux density of the magnetic tapes obtained in each of the examples and comparative examples were measured. The durability was judged by using a commercially available VTR and measuring the time until the output decreased by 3 dB when a still image was reproduced in a constant temperature room at -5 ° C.

The results are shown in Table 2 below.

[Effects of the Invention] As is apparent from Table 1 above, the metallic iron magnetic powders obtained in the present invention (Examples 1 and 2) are all conventional metallic iron magnetic powders (Comparative Examples 1 and 2). In comparison, the magnetic tape obtained by using the metallic iron magnetic powder obtained by the present invention (Examples 1 and 2) has a high coercive force, contains no impurities, and is clear from Table 2 above. 2) is a magnetic tape obtained by using the metallic iron magnetic powder obtained in Comparative Examples 1 and 2 (Comparative Examples 1 and 2),
The squareness ratio and the residual magnetic flux density are high, and the durability is good. Therefore, the metal magnetic powder of the present invention has excellent stability and uniformity of the aluminum oxide coating formed on the particle surface and excellent magnetic properties. As a result, it can be seen that the magnetic recording medium obtained by using this magnetic metal powder has further improved magnetic characteristics and hole resistance.

Claims (3)

[Claims] 1. A metal magnetic powder characterized in that a high-purity aluminum oxide film having a purity of 99% or more is provided on the particle surface of a metal magnetic powder mainly containing iron. 2. Aluminum isopropoxide, aluminum-t-butoxide, aluminum triethoxide, aluminum tri-n-butoxide, aluminum tri-sec-on the surface of particles of powder mainly containing iron oxyhydroxide or iron oxide. Aluminum alkoxide selected from butoxide is deposited by contacting with vapor of aluminum alkoxide, and then contact with steam to hydrolyze on the surface of the particle, and the surface of the aluminum oxide powder is the particle surface of iron oxyhydroxide or iron oxide. And then heat-reducing this to obtain a metallic magnetic powder mainly composed of iron having a high-purity aluminum oxide film with a purity of 99% or more formed on the particle surface. Manufacturing method 3. A powder containing iron oxyhydroxide or iron oxide as a main component is added to aluminum isopropoxide, aluminum-t-butoxide, aluminum triethoxide, aluminum tri-n-butoxide, aluminum tri-se.
Aluminum alkoxide selected from c-butoxide is added to a solution in which it is dissolved, and an appropriate amount of water is further added to hydrolyze the aluminum alkoxide on the particle surface of the powder mainly containing iron oxyhydroxide or iron oxide to give aluminum oxide. Forming a coating or hydrous aluminum oxide coating on the particle surface of powder mainly composed of iron oxyhydroxide or iron oxide, and then heat-reducing this to obtain high purity aluminum oxide with a purity of 99% or more on the particle surface. A method for producing a metal magnetic powder, characterized in that the metal magnetic powder is mainly composed of a coated iron.