JPH0669011A - Manufacture of metal magnetic powder - Google Patents

Abstract

PURPOSE:To notably enhance the oxidation resistance of the metal magnetic powder by performing surface oxidizing step using a low oxygen concentration gas containing steam in specific concentration at specific temperature. CONSTITUTION:As for a metallic oxide mainly comprising iron, a spinel compound having no dehydrating hole at all bored by heating step in an inert gas atmosphere after particle surfaces are coated with a mixture layer containing at least dihydric transition metallic compound is used. Next, a metallic iron produced by reducing this metallic oxide using a reducing gas is surface oxidized. As for this oxidizing step, the reduced metallic iron is oxidized at the temperature of 60-120 deg.C in an inert gas containing moisture content at the partial steam pressure of 20-50mmHg and 100-2500ppm of oxygen. This surface oxidizing step, despite a simple one, can notably enhance the oxidation resistance thereby enabling the manufacturing method of metal magnetic powder having excellent magnetic characteristics to be devised.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a metal magnetic powder used for magnetic recording, and more specifically, it stabilizes the surface oxidation after reducing the metal powder precursor to metallize it with a specific concentration of water vapor. TECHNICAL FIELD The present invention relates to a method for producing a metal magnetic powder having excellent oxidation resistance by using a low oxygen concentration gas containing it and performing it in a specific temperature range.

[0002]

2. Description of the Related Art In recent years, various recording systems have been remarkably developed, but in particular, progress has been made in reducing the size and weight of a magnetic recording / reproducing apparatus. Along with this, there is an increasing demand for higher performance of magnetic recording media such as magnetic tapes and magnetic disks.

In order to satisfy such requirements for magnetic recording, magnetic powder having high coercive force and high saturation magnetization is required. Conventionally, as magnetic powder for magnetic recording, generally needle-shaped magnetite or maghemite or so-called cobalt-containing iron oxide obtained by modifying these magnetic iron oxide powders with cobalt is used, but in order to obtain a medium with higher output. Has started to use ferromagnetic metal powders with higher coercive force and saturation magnetization, so-called metal magnetic powders.

Various methods have been proposed as a method for producing such metallic magnetic powder, but they are generally obtained by heating and dehydrating needle-shaped goethite or it because of its economical advantage. A method is used in which the iron oxide particles obtained are heated in a reducing gas atmosphere such as hydrogen to reduce them to metallic iron.

However, the metal magnetic powder thus obtained has a serious problem. That is, the magnetic metal powder has the drawback that it is chemically unstable and its saturation magnetization decreases with the passage of time. Various proposals have been made to solve this drawback, for example, surface oxidation in a solvent (for example, JP-A-59-16901, JP-A-5-19501).
No. 9-170201) and a method of oxidizing in a gas phase while changing the temperature in multiple stages (Japanese Patent Laid-Open No. 1-21022), but sufficient performance has not been obtained yet. High temperature (200 ~ 600
Although a method of performing oxidation at (° C.) (Japanese Patent Laid-Open No. 60-26602) has also been proposed, it cannot be said to be a desirable method because it causes deterioration of magnetostatic characteristics as described later.

[0006] An object of the present invention is to provide a method for producing a metal magnetic powder, which has a significantly improved oxidation resistance and is excellent in magnetic properties by a simple surface oxidation treatment in order to solve the above problems.

[0007]

In order to achieve the above-mentioned object, the present inventors have studied the oxidative stabilization of a magnetic metal powder obtained by reducing a metal oxide mainly composed of iron. It was found that the oxidation resistance of the metal magnetic powder can be greatly improved by performing the surface oxidation treatment at a specific temperature using a low oxygen concentration gas containing a specific concentration of water vapor, resulting in completion of the present invention. It was

That is, the gist of the present invention is a method for producing a metal magnetic powder by reducing a metal oxide containing iron as a main component with a reducing gas and subjecting the obtained metal iron to a surface oxidation treatment. , Steam reduction of metallic iron after reduction 20
The present invention relates to a method for producing a magnetic metal powder, characterized in that it is oxidized at a temperature of 60 to 120 ° C. in an inert gas containing water of ˜50 mmHg and oxygen of 100 to 2500 ppm. In addition, in the production method of the present invention, the iron-based metal oxide is inactive after coating the mixture layer containing at least a divalent transition metal compound on the particle surface of the acicular hydrous iron oxide particles. The effect of the present invention is particularly effective when a spinel compound obtained by heating in an atmosphere and having substantially no dehydration pores is used.

The axial ratio and size of the metal oxide mainly composed of iron used in the present invention are not particularly limited as long as they are generally used as a raw material of metal magnetic powder.
Further, various metal elements may be contained in order to control magnetic properties and improve dispersibility and other properties. A commonly used known reduction method is applied to the reduction of the metal oxide mainly composed of iron to a metal, and for example, a method of keeping the temperature at 350 to 550 ° C. for 2 hours or more in a hydrogen stream.

Since the obtained metal powder has a very high activity and is susceptible to oxidation, the following surface oxidation treatment is carried out in the production method of the present invention. That is, the surface oxidation treatment method in the present invention is usually performed with a steam partial pressure of 20 to 50 mmH.
g of water and an inert gas containing 100 to 2500 ppm of oxygen, and preferably a water vapor partial pressure of 20 to 50 mmHg and 200 to 500 p.
An inert gas containing pm oxygen is used. If the water vapor partial pressure is lower than 20 mmHg, the effect of containing water vapor will not be seen, and if it is higher than 50 mmHg, the oxidation resistance will be rather poor. Also, the oxygen concentration is 2500 ppm
It is considered that when the value exceeds the above range, it is considered to be due to local heat generation, but it is not preferable because the magnetic characteristics are deteriorated. When the oxygen concentration is low, there is no particular problem, but it takes 100 pp from the viewpoint of workability because it takes a long time to obtain an oxide film having a predetermined thickness.
It is considered that about m is the lower limit.

Further, the oxidation temperature at the time of carrying out the oxidation is also important, and it is usually necessary to carry out at 60 to 120 ° C, preferably 70 to 90 ° C. That is, if the temperature is too low, it becomes difficult to maintain a predetermined water vapor partial pressure due to dew condensation in the piping, and if it is too high, the effect of coexisting water vapor becomes insufficient and it is difficult to obtain sufficient oxidation resistance. This is because problems such as deterioration of characteristics occur. The treatment time may be set to the time until the surface oxidation does not substantially progress,
For example, depending on the inlet oxygen concentration, the difference between the outlet oxygen concentration and the inlet oxygen concentration may be about 30 ppm or less.
Generally, when the condition is 70 ° C. and the oxygen concentration is 250 ppm, it may be carried out for about 30 hours. As described above, although the surface oxidation treatment method of the present invention is a simple method, the oxidation resistance is significantly improved.

In the manufacturing method of the present invention, after the metal oxide mainly composed of iron coats the mixture layer containing at least a divalent transition metal compound on the particle surface of the iron oxide hydroxide particles in the form of needles, A spinel compound obtained by heating in an inert atmosphere and having substantially no dehydration pores is more preferable, but such a spinel compound can be obtained as follows.

Examples of divalent transition metal compounds include Co and F.
Examples thereof include e, Zn, Cu, Cr, and Ni compounds, and are not particularly limited. As the other compound forming the mixture layer together with the divalent transition metal compound, a known compound such as silicon, aluminum, tin or titanium compound is usually used. For example, a layer composed of a mixture of a cobalt compound and a silicon compound, a cobalt compound Examples thereof include a layer formed of a mixture of aluminum compounds or a layer formed of a mixture of three kinds of compounds of cobalt compounds, silicon compounds and aluminum compounds.

In the mixture layer containing the divalent transition metal compound, the weight ratio of the divalent transition metal compound to the iron atoms in the goethite is usually 3 to 25%, preferably 7 to
Contains 20%. This is because the desired characteristics cannot be obtained if the amount of the divalent transition metal is too large or too small. Further, other compounds constituting the mixture layer, for example, silicon and aluminum atoms such as silicon compounds and aluminum compounds are similarly 0.2 to 2% by weight ratio to iron atoms in goethite, preferably 0.
It contains 5-1%. The atomic weight ratio of the divalent transition metal compound to the other compound constituting the mixture layer is usually 10: 1 to 20: 0.5.

The method of forming such a mixture layer containing a divalent transition metal compound on the surface of the acicular iron oxide hydroxide particles is used for depositing insoluble matter from a solution state, depositing colloidal compounds and the like. It is carried out by a known method. As a specific example, for example, in order to form a layer composed of a mixture of a cobalt compound and a silicon compound, after adding No. 3 silica, the system pH is adjusted to about 7 with an aqueous solution of cobalt sulfate, and a mixture of the cobalt compound and the aluminum compound is added. In order to form a layer, the aqueous solution of aluminum sulfate and the aqueous solution of cobalt sulfate are simultaneously added, and then the pH of the system is adjusted to about 7 with an aqueous alkali solution, and a mixture of three compounds of cobalt compound, silicon compound and aluminum compound is used. In order to form a layer consisting of, No. 3 sodium hydroxide is added, the pH of the system is adjusted to 7 with an aqueous solution of cobalt sulfate and aluminum sulfate, and then the pH of the system is adjusted to 10 with an aqueous alkali solution. To the system, add an acidic water-soluble compound aqueous solution such as sulfate, and then add an alkaline aqueous solution to p The method of precipitating an insoluble oxide or hydrous oxide by regulating the like.

The spinel compound referred to in the present invention is an oxide mainly composed of iron oxide and has a surface spacing of 2.97 ± 0.05,
Those having a main peak of X-ray diffraction at positions corresponding to 2.53 ± 0.05 and 2.10 ± 0.05 angstroms are shown.

Generally, when dehydration of goethite is carried out by heating in air, dehydration holes tend to be formed, which can be observed by an electron microscope. As a method for easily determining the presence or absence of a dehydration hole, there is a correlation between the specific surface area value of particles measured by a flow type automatic specific surface area measuring device (Flowsorb 2300 type, manufactured by Shimadzu Corporation) and the presence or absence of a dehydration hole. The presence / absence of dehydration holes can be determined by using the reduction rate obtained from the specific surface area value. That is, the spinel compound in the present invention, which is substantially free of dehydration pores, has a reduction rate of the specific surface area of particles of 10% before and after the high temperature heat treatment.
Of the above spinel compounds, those having less than 10% have dehydration pores. Here, the reduction rate is calculated by the following equation. Reduction rate = (specific surface area before heat treatment-specific surface area after heat treatment)
/ Specific surface area before heat treatment

In the method of the present invention, in order to form such a spinel compound having substantially no dehydration holes, the iron oxide hydroxide particles in the form of needles are heated at a high temperature in an inert gas stream. This can be easily done by processing. This treatment is performed after coating the surface of the acicular hydrous iron oxide particles with a mixture layer containing at least a divalent transition metal compound as described above. In this case, the inert gas is not particularly limited, usually nitrogen gas,
Although argon gas or the like is used, it is preferably performed in a nitrogen gas stream because it is inexpensive.

The temperature range of the high temperature heat treatment is usually 400 to
The temperature is 700 ° C, preferably 450 to 600 ° C.
If the temperature is lower than 400 ° C, hematite remains, so that dehydration holes are likely to be formed even when the treatment is performed in an inert gas stream, and if the temperature is higher than 700 ° C, particles are likely to be fused, which is not preferable. The heating time is usually 0.5 to 4 hours, preferably 1 to 2 hours, depending on the heating temperature.

Such high temperature heat treatment is disclosed in Japanese Patent Laid-Open No. 63-
When it is carried out in air as described in Japanese Patent No. 61413, a spinel compound is not formed, but only hematite having dehydration pores is formed, and cutting occurs during reduction in a hydrogen stream, resulting in needle-like properties. Be careful because it may not be retained and it may not be possible to obtain a metal magnetic powder having the desired performance.

In the production method of the present invention, the spinel compound as described above can be preferably used. However, in the present invention, the spinel compound may be coated with another compound in addition to the above-mentioned mixture layer, if necessary. It can also be used. For example, a known compound such as silicon or aluminum can be deposited on the outermost shell of the particles in order to prevent sintering between particles of the metallic magnetic powder during heating and reduction. The silicon compound layer and the aluminum compound layer, which are the outermost layers, are formed alone or in a combination of both. Among them, when the one in which the aluminum compound layer is formed after the formation of the silicon compound layer is used, the metal magnetic property finally obtained is obtained. The powder performance is particularly excellent.

In this case, the formation of the silicon and / or aluminum compound layer is 1 to 10%, preferably 2 to 6% as the weight ratio of the total of silicon and / or aluminum to the iron atoms in the goethite. This is because when the total amount of silicon and aluminum is more than 10%, the saturation magnetization of the obtained metal magnetic powder is rather low, which is not desirable. On the other hand, if it is less than 1%, the effect of coating these as the outermost layer cannot be obtained.

The mixture layer containing the divalent transition metal compound thus obtained, and the goethite having the silicon or aluminum compound layer as the inert gas as described above, for example, in a nitrogen stream at 400 to 700 ° C. When heated to, it can be converted into a spinel compound having substantially no dehydration pores, and can be used in the present invention.

The magnetic recording medium containing the metal magnetic powder excellent in oxidation resistance and magnetic properties obtained as described above can be manufactured according to a conventional method. That is, the magnetic magnetic powder is dispersed and mixed with a binder resin, an organic solvent and other necessary components to prepare a magnetic paint, and the magnetic paint is applied onto a substrate such as a polyester film by a doctor blade method, a gravure method or a reverse method. Method, roll coating, or any other suitable method, and optionally magnetic field orientation, followed by drying.

[0025]

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Example 1 An apparatus provided with a circulation line equipped with a pipeline type dispersing machine Milder (manufactured by EBARA CORPORATION) outside the reaction tank was used.
Goethite (major axis diameter: 0.18 μm, axial ratio: 8) 500
15 g of Poise 530 (manufactured by Kao Corporation)
%) To a solution of 10 liters of deionized water
Time dispersed. While continuing dispersion by Milder, 3
17.2 g of No. Keiso (SiO ₂ content 29%) was added.
Then, 1000 ml of 270 g of cobalt sulfate heptahydrate
After adding an aqueous solution dissolved in ion-exchanged water to pH 6.5 to deposit a Si / Co mixture layer on the surface, the remaining cobalt sulfate aqueous solution is added dropwise, and 1.2 mol / liter-NaOH aqueous solution is added dropwise. The pH was adjusted to 10. After that, the electric conductivity of the cleaning liquid is 10 using ion-exchanged water.
It was washed until it became 0 μS / cm or less. Furthermore, Poise 530 (15 g) was added and redispersed to this, 69 g of No. 3 sodium hydroxide (SiO ₂ content 29%) was added, and 1 hour later, dilute nitric acid was added dropwise to adjust the pH to 6.5, and the silicon compound layer was added. I put it on. Finally, add 2N NaOH to the suspension.
Immediately after adding 172 ml of the aqueous solution, 34 g of a sulfuric acid band (Al ₂ O ₃ content 9.3%) was added to ion-exchanged water 165.
An aqueous solution dissolved in g was added dropwise to apply a layer of aluminum hydroxide, and the precipitate was washed with water, filtered and dried.

The metal precursor obtained as described above was added to 48
The particles were sized to ˜64 mesh, and heat-treated at 500 ° C. for 1 hour in a nitrogen stream having a gas linear velocity of 7 cm / sec in a fluidized-bed furnace having an inner diameter of 62 mm. Then, reduction was performed in a hydrogen stream at 500 ° C. for 6 hours. After completion of the reduction, a nitrogen gas with a steam partial pressure of 34 mmHg containing 250 ppm of oxygen at 80 ° C. was supplied to a gas linear velocity of 7 c.
Aeration was performed at m / sec, and the surface was oxidized until the oxygen concentration at the outlet became 230 ppm or more. Then, it was dried in nitrogen gas to obtain a metal magnetic powder 1 of the present invention. The characteristics of the obtained metal magnetic powder are shown in other examples (Examples 2 to 3, Comparative Example 1).
Table 3 together with 3 to 3).

[0028]

[Table 1]

Example 2 After the reduction of the metal precursor was carried out in the same manner as in Example 1, the partial pressure of water vapor containing oxygen of 250 ppm at 70 ° C. was 34 m.
Nitrogen gas of mHg was bubbled at a gas linear velocity of 7 cm / sec to oxidize the surface until the outlet oxygen concentration reached 230 ppm or more. Then, it was dried in nitrogen gas to obtain a metal magnetic powder 2 of the present invention.

Example 3 After the reduction of the metal precursor was performed in the same manner as in Example 1, the partial pressure of water vapor containing oxygen of 500 ppm at 70 ° C. 34
Nitrogen gas of mmHg is ventilated at a gas linear velocity of 7 cm / sec,
The surface was oxidized until the outlet oxygen concentration became 470 ppm or more. Then, it was dried in nitrogen gas to obtain a magnetic metal powder 3 of the present invention.

Comparative Example 1 After the reduction of the metal precursor was carried out in the same manner as in Example 1, nitrogen gas containing 250 ppm of oxygen and containing no water vapor was passed at 80 ° C. at a gas linear velocity of 7 cm / sec, and the outlet oxygen was discharged. The surface was oxidized until the concentration became 230 ppm or more, and a metal magnetic powder (Comparative Product 1) was obtained.

Comparative Example 2 After reducing the metal precursor in the same manner as in Example 1, a partial pressure of water vapor containing oxygen of 250 ppm at 80 ° C. of 10
Nitrogen gas of 0 mmHg was passed through at a gas linear velocity of 7 cm / sec to oxidize the surface until the outlet oxygen concentration reached 230 ppm or more. Then, it was dried in nitrogen gas to obtain a metal magnetic powder (Comparative Product 2) whose surface was oxidized.

Comparative Example 3 After the reduction of the metal precursor was performed in the same manner as in Example 1, the partial pressure of water vapor 3 containing 250 ppm of oxygen at 150 ° C. was 3
Nitrogen gas of 4 mmHg was passed at a gas linear velocity of 7 cm / sec, and the surface was oxidized until the outlet oxygen concentration reached 230 ppm or more. Then, it was dried in nitrogen gas to obtain a surface-oxidized metal magnetic powder (Comparative Product 3).

As described above, in Examples 1 to 3, a metal magnetic powder having a high coercive force (Hc) and a high squareness ratio (σr / σs) was obtained, and the obtained metal magnetic powder was 60 ° C./90%. R
High saturation magnetization (σ
It can be seen that s') is maintained and the oxidation resistance is excellent. on the other hand,
The magnetic magnetic powders obtained in Comparative Examples 1 and 2 have sufficient magnetic properties, but have a low saturation magnetization (σs ′) after being stored for 1 week in an atmosphere of 60 ° C./90% RH, and are inferior in oxidation resistance. .
Further, in Comparative Example 3, since the oxidation temperature is high, the magnetic characteristics are deteriorated.

[0035]

According to the method for producing a metal magnetic powder of the present invention, it is possible to obtain a metal magnetic powder having greatly improved oxidation resistance and excellent magnetic properties by a simple surface oxidation treatment.

Claims (3)

[Claims] 1. A method for producing a metal magnetic powder by reducing a metal oxide containing iron as a main component with a reducing gas and subjecting the obtained metal iron to a surface oxidation treatment to produce a metal magnetic powder. In an inert gas containing 20 to 50 mmHg of water vapor and 100 to 2500 ppm of oxygen,
A method for producing a metal magnetic powder, which comprises oxidizing at a temperature of 60 to 120 ° C. 2. A metal oxide mainly composed of iron is coated with a mixture layer containing at least a divalent transition metal compound on the surface of acicular hydrous iron oxide particles and then heated in an inert atmosphere. The production method according to claim 1, which is a spinel compound obtained by substantially free of dehydration pores. 3. The mixture layer containing at least a divalent transition metal compound is a layer composed of a cobalt compound and a silicon compound and / or an aluminum compound.
The manufacturing method described.