JPH10177907A - Method for producing metal magnetic powder and magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a fine metallic magnetic powder having good magnetic properties, which prevents sintering of particles during heat treatment in a reducing atmosphere and maintains a needle-like shape. . SOLUTION: In the present invention, first, a needle-like fine powder mainly composed of iron oxyhydroxide is mixed in a non-reducing gas with a pressure of 40%.
The temperature is raised to a certain temperature from 0 ° C to 620 ° C. next,
At this constant temperature, a heat treatment is performed by introducing a mixed gas of a reducing gas and a non-reducing gas. In the step of performing the heat treatment, the mixing ratio of the non-reducing gas is initially reduced,
The mixing ratio of the non-reducing gas is increased stepwise. For example, the mixing ratio of the non-reducing gas is initially set to 33% by volume or less, and finally to 50% by volume or more. As the non-reducing gas, a non-reducing gas composed of an element having an atomic number of 7 or more is used. Next, a slow oxidation treatment is performed.

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 magnetic metal powder and a method for producing a magnetic recording medium using the magnetic metal powder. More specifically, the present invention relates to a needle-like fine powder having excellent shape anisotropy. The present invention relates to a method for producing a metal magnetic powder and a method for producing a magnetic recording medium having excellent electromagnetic conversion characteristics using the metal magnetic powder.

[0002]

2. Description of the Related Art As recording media used in audio devices, video devices, computer devices, etc., magnetic powders, organic binders and various additives are dispersed in an organic solvent.
A so-called coating type magnetic recording medium is used, in which a magnetic coating prepared by kneading is coated on a non-magnetic support and dried to form a magnetic layer. Since the coating type magnetic recording medium is excellent in productivity and versatility, it is still the mainstream of magnetic recording media even at present.

In these various magnetic recording / reproducing devices,
In recent years, miniaturization, weight reduction, high image quality, and long time have been promoted, and accordingly, there has been a strong demand for high density recording of the above-mentioned coating type magnetic recording medium.

In order to achieve high-density recording in a coating type magnetic recording medium, it is first important to control the magnetic properties of the magnetic powder and the shape of each particle. That is, the magnetic powder for a coating type magnetic recording medium that enables high density recording includes:
Characteristics such as high coercive force, high saturation magnetic flux density, and uniform fine particles are required.

As magnetic materials meeting this demand, γ-Fe ₂ O ₃ or Co-modified γ-Fe ₂
Instead of iron oxide-based magnetic powders such as O _3, metal magnetic powders mainly composed of iron have been used.

The metal magnetic powder is composed of fine particles having a stabilized structure in which, for example, a needle-shaped core portion mainly composed of iron is covered with a thin clad layer mainly composed of iron oxide. Metal magnetic powder having such a structure is obtained by using iron oxyhydroxide or iron oxide obtained by dehydrating the same as a raw material, and reducing these raw materials to a metal state by performing a heat treatment in a reducing atmosphere.
It is manufactured by gradually oxidizing this to form a thin oxide film on the surface of the metal particles and stabilizing it. Therefore, it is possible to obtain both a high saturation magnetization specific to a ferromagnetic metal and a large high coercive force utilizing shape anisotropy.

[0007]

Although the metal magnetic powder is suitable for high-density recording in principle as described above, in order to achieve a higher density, a fine powder having excellent magnetic properties and excellent shape is required. It needs to be particles. However, miniaturization of the particles works to increase the volume ratio of the surface oxide film due to the increase in the specific surface area and to decrease the saturation magnetic flux density. Furthermore, there is a possibility that the oxidation resistance and the dispersibility in the magnetic paint are impaired due to the fineness of the particles, and it is extremely difficult to satisfy all the conditions required for a high-density recording medium at the same time.

Among them, it is effective to increase the Bohr magneton with respect to the saturation magnetization by adopting an Fe—Co alloy composition containing iron as a main component and adding about 40 mol% or less of cobalt thereto.

Regarding the shape of the metal magnetic powder, the shape of the acicular particles becomes dull during the heat treatment step, causing the aspect ratio to deteriorate.
It is necessary to prevent phenomena in which the shape anisotropy and dispersibility of the particles are reduced by sintering the particles to form a bridge.

Therefore, a method for preventing the deterioration of the shape in the reduction step by applying a shape-retaining agent during heat treatment to the surface of iron oxyhydroxide or iron oxide is disclosed in, for example, JP-A-6-36265. It has been disclosed. As such a shape maintaining agent, Al, Si, a rare earth element, a compound thereof, and the like are known.

[0011] However, it is difficult to stably produce the ultrafine needle-like metal magnetic powder with good shape only by the effect of the shape retaining agent. In particular, in the case of a mother tape having a high coercive force used in a magnetic field transfer system, a metal magnetic powder having further improved shape and magnetic properties is required.

The present invention has been made in view of such conventional circumstances, and it is an object of the present invention to provide a method for producing a fine metal magnetic powder excellent in magnetic properties, which preserves a needle-like shape well. And

Further, the present invention provides a magnetic recording medium which exhibits good dispersibility and orientation when such a metal magnetic powder is prepared as a magnetic coating material, thereby obtaining excellent electromagnetic conversion characteristics in the field of high density magnetic recording. It is an object to provide a method for manufacturing a medium.

[0014]

Means for Solving the Problems In order to achieve the above object, a method for producing a metal magnetic powder of the present invention comprises: When performing the heat treatment at 400 to 620 ° C., at least one kind of non-reducing atmosphere gas having an atomic number of 7 or more is introduced, and the introduction ratio of the reducing atmosphere gas and the non-reducing atmosphere gas is changed in the reduction step. It is characterized by performing a gradual oxidation treatment.

The non-reducing gas having an atomic number of 7 or more employed in the present invention includes N ₂ , Ne, Ar, Kr, Xe and Rn.
It is preferable that at least one selected from the group consisting of

The iron oxyhydroxide employed in the present invention includes α-FeOOH, β-FeOOH, γ-FeOOH
OOH and the like, in particular, α-FeOOH, γ-Fe
OOH is preferred. These iron oxyhydroxides include Co, N
i, Cr, Mn, Mg, Ca, Ba, Sr, Zn, T
A metal compound such as i, Mo, Ag, or Cu may coexist, and an aluminum compound or a rare earth element compound may be present on the surface. In the present invention, iron oxide which is an intermediate product obtained by dehydration of these iron oxyhydroxides is also included in the concept of iron oxyhydroxide.

Since the shape of these iron oxyhydroxides is reflected in the shape of the metal magnetic powder as the final product, the major axis length is, for example, about 0.05 μm to 0.3 μm, and the axial ratio (aspect ratio) is 3 μm to 3 μm. It is preferably about 20 and has a needle-like, column-like, spindle-like or rod-like outer shape.

Further, the magnetic recording medium of the present invention has a structure in which a magnetic recording layer mainly composed of a metal magnetic powder produced by the above-described method for producing a metal magnetic powder and an organic binder is formed on a nonmagnetic support. Having.

As the organic binder used in the present invention, any of those used in a usual coating type magnetic recording medium can be used, and a polyvinyl copolymer resin, a polyester polyurethane resin, a polycarbonate polyurethane resin, a nitrocellulose resin or Examples thereof include a mixture of these resins. If necessary, additives such as a lubricant, an abrasive, and an antistatic agent may be added to these organic binders. As these additives, any conventionally known materials can be used, and there is no particular limitation.

As the material of the non-magnetic support employed in the present invention, any of those used in ordinary coating type magnetic recording media can be used, and polyesters such as polyethylene terephthalate and polyolefins such as polyethylene and polypropylene can be used. , Cellulose derivatives such as cellulose triacetate, cellulose diacetate, and cellulose butyrate; vinyl resins such as polyvinyl chloride and polyvinylidene chloride; plastics such as polycarbonate, polyimide and polyamide imide; and light metals such as aluminum alloys and titanium alloys And ceramics such as alumina glass. When a rigid substrate such as an Al alloy plate or a glass plate is used for the non-magnetic support, an oxide film such as alumite treatment or a Ni-P film is formed on the substrate surface so that the surface is hardened. You may.

In the step of reducing iron oxyhydroxide, hydrogen molecules or hydrogen atoms in a reducing atmosphere react with oxygen, which is a constituent atom of iron oxyhydroxide, to produce H as a reaction product.
₂ O (steam) is generated in large quantities. This H ₂ O has adverse effects such as suppression of the reduction reaction and promotion of sintering of the generated metal magnetic powder in a reducing atmosphere. Therefore normally set the flow rate of H ₂ to immediately remove the reactor outside the equal and generated H ₂ O increasing the flow rate of H ₂ as the reducing gas.

However, since H ₂ has a very small specific gravity, by mixing a non-reducing gas having a large specific gravity with a high H ₂ O removal / replacement effect in a reducing atmosphere,
It has been found that adverse effects such as suppression of the reduction reaction and promotion of sintering can be eliminated.

That is, a fixed amount of a non-reducing gas is mixed with a reducing gas. The mixing ratio of the non-reducing gas (the ratio of the non-reducing gas to the total amount of the reducing gas and the non-reducing gas) is desirably in the range of 50% by volume or more and 67% by volume or less.

Also, it has been found that it is most efficient to introduce the non-reducing gas stepwise. That is,
In the initial stage of reduction, the mixing ratio of reducing gas is increased in consideration of reduction efficiency, and the ratio of non-reducing gas is increased stepwise. The mixing ratio of the non-reducing gas (the ratio of the non-reducing gas to the total amount of the reducing gas and the non-reducing gas) is initially 33% by volume or less, preferably 20% by volume or less. Considering the effect of removing and replacing H ₂ O,
The proportion of non-reducing gas is increased stepwise. Finally, the mixing ratio of the non-reducing gas (the ratio of the non-reducing gas to the total amount of the reducing gas and the non-reducing gas) is 50% by volume.
As described above, preferably, 83% by volume or more was found to be good, and the present invention was completed.

Such a non-reducing gas is naturally limited from the periodic table, and any of N ₂ or a rare gas having an atomic number of 7 or more can be used.

As a result, the collapse of the shape is suppressed and the shape becomes uniform, and the crystallinity of the particle surface is improved. Therefore, the iron oxide layer after the gradual oxidation treatment is reduced, and the finally obtained metal magnetic material is obtained. The saturation magnetic flux density of the powder is increased and the oxidation stability is excellent. Moreover, the metal magnetic powder thus produced is excellent in dispersibility in a magnetic paint.

Further, in the present invention, the metal magnetic powder produced as described above is used for a coating type magnetic recording medium.

Since the metal magnetic powder retains the particle shape of the iron oxyhydroxide as a starting material, it can have desired fineness and axial ratio, and the particles have a uniform shape. In addition, a high coercive force, a high saturation magnetic flux density, and a high squareness ratio can be obtained, and excellent dispersibility and oxidation stability are also obtained. Therefore, by using such a metal magnetic powder, a magnetic recording medium exhibiting good recording / reproducing characteristics in a high density recording area can be obtained.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below with reference to the accompanying drawings. In each of Examples and Comparative Examples, the same iron oxyhydroxide to which cobalt, aluminum, and yttrium were added was used.

Example 1 First, the production of a magnetic metal powder will be described. Iron oxyhydroxide was charged in a reduction furnace, and the temperature was raised to 520 ° C. in a nitrogen atmosphere. Thereafter, a reduction was performed by flowing a mixed gas in which H ₂ and N ₂ became 4: 1 and performing a heat treatment at a temperature of 520 ° C. for 1 hour. Then H ₂ and N ₂ is 2: flowing a mixed gas such that 1, reduced by 30 minutes heat treatment at a temperature of 520 ° C., finally H ₂ and N ₂ is 1: mixture such that 1 The gas was passed and the reduction was performed at a temperature of 520 ° C. for 30 minutes. Thereafter, N ₂ was continuously flown, and after cooling to room temperature, air was gradually contained in the flowing nitrogen gas flow, and a gradual oxidation treatment was performed to stabilize the surface.

Next, the manufacture of the sample tape will be described. Each composition of the magnetic paint was weighed, kneaded and dispersed according to the following composition to prepare a magnetic paint. Magnetic coating composition Metal magnetic powder 100 parts by weight Binder resin 20 parts by weight Abrasive: Al ₂ O ₃ 3 parts by weight Antistatic agent: carbon powder 2 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 50 parts by weight And this magnetic coating material Was coated on a polyethylene terephthalate (PET) film, oriented and dried to form a magnetic layer, thereby preparing a sample tape.

Example 2 Iron oxyhydroxide was charged in a reducing furnace, and the mixture was charged in a nitrogen atmosphere to form a mixture of 5 parts.
The temperature was raised to 20 ° C. Thereafter, a reduction was performed by flowing a mixed gas in which H ₂ and N ₂ became 2: 1 and performing a heat treatment at a temperature of 520 ° C. for 1 hour. Then H ₂ and N ₂ :
The mixture gas was reduced to 1 and reduced at a temperature of 520 ° C. for 1 hour. Thereafter, N ₂ was continuously flown, and after cooling to room temperature, air was gradually contained in the flowing nitrogen gas flow, and a gradual oxidation treatment was performed to stabilize the surface. The manufacture of the sample tape is the same as that of the first embodiment.

Example 3 Iron oxyhydroxide was charged into a reduction furnace, and the mixture was charged in a nitrogen atmosphere to obtain a solution.
The temperature was raised to 20 ° C. Thereafter, a reduction was performed by flowing a mixed gas in which H ₂ and N ₂ became 1: 1 and performing a heat treatment at a temperature of 520 ° C. for 2 hours. Thereafter, N ₂ was continuously flown, and after cooling to room temperature, air was gradually contained in the flowing nitrogen gas flow, and a gradual oxidation treatment was performed to stabilize the surface. The manufacture of the sample tape is the same as that of the first embodiment.

Example 4 Iron oxyhydroxide was charged in a reduction furnace, and the mixture was charged in a nitrogen atmosphere to obtain a solution.
The temperature was raised to 20 ° C. After this, H ₂ and N ₂ are 0.5: 1.
The mixture was subjected to heat treatment at a temperature of 520 ° C. for 2 hours to perform reduction. Thereafter, N ₂ was continuously flown, and after cooling to room temperature, air was gradually contained in the flowing nitrogen gas flow, and a gradual oxidation treatment was performed to stabilize the surface. The manufacture of the sample tape is the same as that of the first embodiment.

Comparative Example 1 Iron oxyhydroxide was charged in a reducing furnace, and the mixture was charged in a nitrogen atmosphere.
The temperature was raised to 20 ° C. After this, H ₂ and N ₂ are 0.1: 1.
The mixture was subjected to heat treatment at a temperature of 520 ° C. for 2 hours to perform reduction. Thereafter, N ₂ was continuously flown, and after cooling to room temperature, air was gradually contained in the flowing nitrogen gas flow, and a gradual oxidation treatment was performed to stabilize the surface. The manufacture of the sample tape is the same as that of the first embodiment.

Comparative Example 2 Iron oxyhydroxide was charged into a reduction furnace, and the mixture was charged in a nitrogen atmosphere to obtain a solution.
The temperature was raised to 20 ° C. After this, only H ₂ gas is flowed,
The reduction was performed by heating at 520 ° C. for 2 hours. Thereafter, N ₂ was continuously flown, and after cooling to room temperature, air was gradually contained in the flowing nitrogen gas flow, and a gradual oxidation treatment was performed to stabilize the surface. The manufacture of the sample tape is the same as that of the first embodiment.

Example 5 Iron oxyhydroxide was charged into a reduction furnace, and the mixture was charged in a nitrogen atmosphere.
The temperature was raised to 20 ° C. Thereafter, a reduction was performed by flowing a mixed gas in which H ₂ and Ar became 4: 1 and performing heat treatment at a temperature of 520 ° C. for 1 hour. Then H ₂ and Ar are 2:
1 at a temperature of 520 ° C.
And then reduced by heat treatment, and finally H ₂ and Ar
1 at a temperature of 520 ° C.
Reduced. Then, after flowing N ₂ and cooling to room temperature, air was gradually contained in the flowing nitrogen gas stream, and a gradual oxidation treatment was performed to stabilize the surface. The manufacture of the sample tape is the same as that of the first embodiment.

Example 6 Iron oxyhydroxide was charged in a reduction furnace, and the mixture was charged in a nitrogen atmosphere to form a mixture of 5 parts.
The temperature was raised to 20 ° C. Thereafter, a reduction was performed by flowing a mixed gas in which H ₂ and Ar became 2: 1 and performing a heat treatment at a temperature of 520 ° C. for 1 hour. Then H ₂ and Ar are 1:
The mixture gas was reduced to 1 and reduced at a temperature of 520 ° C. for 1 hour. Then, after flowing N ₂ and cooling to room temperature, air was gradually contained in the flowing nitrogen gas stream, and a gradual oxidation treatment was performed to stabilize the surface. The manufacture of the sample tape is the same as that of the first embodiment.

Example 7 Iron oxyhydroxide was charged in a reduction furnace, and the mixture was charged in a nitrogen atmosphere to obtain a solution.
The temperature was raised to 20 ° C. Thereafter, a mixture gas such that H ₂ and Ar became 1: 1 was flowed, and the mixture was subjected to a heat treatment at a temperature of 520 ° C. for 2 hours to perform reduction. Then, after flowing N ₂ and cooling to room temperature, air was gradually contained in the flowing nitrogen gas stream, and a gradual oxidation treatment was performed to stabilize the surface. The manufacture of the sample tape is the same as that of the first embodiment.

Example 8 Iron oxyhydroxide was charged into a reduction furnace, and the mixture was placed in a nitrogen atmosphere at room temperature.
The temperature was raised to 20 ° C. After this, H ₂ and Ar are 0.5: 1.
The mixture was subjected to heat treatment at a temperature of 520 ° C. for 2 hours to perform reduction. Then, after flowing N ₂ and cooling to room temperature, air was gradually contained in the flowing nitrogen gas stream, and a gradual oxidation treatment was performed to stabilize the surface. For the production of the sample tape, see Example 1
Is the same as

Comparative Example 3 Iron oxyhydroxide was charged into a reducing furnace, and the mixture was charged in a nitrogen atmosphere to form a mixture of 5 parts.
The temperature was raised to 20 ° C. Thereafter, H ₂ and Ar is 0.1: 1
The mixture was subjected to heat treatment at a temperature of 520 ° C. for 2 hours to perform reduction. Then, after flowing N ₂ and cooling to room temperature, air was gradually contained in the flowing nitrogen gas stream, and a gradual oxidation treatment was performed to stabilize the surface. For the production of the sample tape, see Example 1
Is the same as

Example 9 Iron oxyhydroxide was charged in a reduction furnace, and the mixture was charged with nitrogen oxyhydroxide in a nitrogen atmosphere.
The temperature was raised to 20 ° C. Thereafter, a reduction was performed by flowing a mixed gas in which H ₂ and N ₂ became 4: 1 and performing a heat treatment at a temperature of 520 ° C. for 1 hour. Then H ₂ and N ₂ :
1 at a temperature of 520 ° C.
And then reduced by heat treatment, and finally H ₂ and N ₂ :
2 at a temperature of 520 ° C.
Reduced. Thereafter, N ₂ was continuously flown, and after cooling to room temperature, air was gradually contained in the flowing nitrogen gas flow, and a gradual oxidation treatment was performed to stabilize the surface. The manufacture of the sample tape is the same as that of the first embodiment.

Example 10 Iron oxyhydroxide was charged in a reducing furnace, and the mixture was charged in a nitrogen atmosphere to form a mixture of 5 parts.
The temperature was raised to 20 ° C. Thereafter, a reduction was performed by flowing a mixed gas in which H ₂ and N ₂ became 4: 1 and performing a heat treatment at a temperature of 520 ° C. for 1 hour. Then H ₂ and N ₂ :
1 at a temperature of 520 ° C.
And then reduced by heat treatment, and finally H ₂ and N ₂ :
3 at 30 ° C at a temperature of 520 ° C.
Reduced. Thereafter, N ₂ was continuously flown, and after cooling to room temperature, air was gradually contained in the flowing nitrogen gas flow, and a gradual oxidation treatment was performed to stabilize the surface. The manufacture of the sample tape is the same as that of the first embodiment.

Example 11 Iron oxyhydroxide was charged in a reducing furnace, and the mixture was charged in a nitrogen atmosphere to obtain a solution.
The temperature was raised to 20 ° C. Thereafter, a reduction was performed by flowing a mixed gas in which H ₂ and N ₂ became 4: 1 and performing a heat treatment at a temperature of 520 ° C. for 1 hour. Then H ₂ and N ₂ :
1 at a temperature of 520 ° C.
And then reduced by heat treatment, and finally H ₂ and N ₂ :
5 at a temperature of 520 ° C.
Reduced. Thereafter, N ₂ was continuously flown, and after cooling to room temperature, air was gradually contained in the flowing nitrogen gas flow, and a gradual oxidation treatment was performed to stabilize the surface. The manufacture of the sample tape is the same as that of the first embodiment.

Example 12 Iron oxyhydroxide was charged into a reduction furnace, and the mixture was charged in a nitrogen atmosphere to form a mixture of 5 parts.
The temperature was raised to 20 ° C. Thereafter, a reduction was performed by flowing a mixed gas in which H ₂ and N ₂ became 2: 1 and performing a heat treatment at a temperature of 520 ° C. for 1 hour. Then H ₂ and N ₂ :
1 at a temperature of 520 ° C.
And then reduced by heat treatment, and finally H ₂ and N ₂ :
2 at a temperature of 520 ° C.
Reduced. Thereafter, N ₂ was continuously flown, and after cooling to room temperature, air was gradually contained in the flowing nitrogen gas flow, and a gradual oxidation treatment was performed to stabilize the surface. The manufacture of the sample tape is the same as that of the first embodiment.

Example 13 Iron oxyhydroxide was charged into a reduction furnace, and the mixture was charged in a nitrogen atmosphere to obtain a solution.
The temperature was raised to 20 ° C. Thereafter, a reduction was performed by flowing a mixed gas in which H ₂ and N ₂ became 2: 1 and performing a heat treatment at a temperature of 520 ° C. for 1 hour. Then H ₂ and N ₂ :
1 at a temperature of 520 ° C.
And then reduced by heat treatment, and finally H ₂ and N ₂ :
3 at 30 ° C at a temperature of 520 ° C.
Reduced. Thereafter, N ₂ was continuously flown, and after cooling to room temperature, air was gradually contained in the flowing nitrogen gas flow, and a gradual oxidation treatment was performed to stabilize the surface. The manufacture of the sample tape is the same as that of the first embodiment.

Example 14 Iron oxyhydroxide was charged into a reducing furnace, and the mixture was charged with nitrogen oxyhydroxide in a nitrogen atmosphere.
The temperature was raised to 20 ° C. Thereafter, a reduction was performed by flowing a mixed gas in which H ₂ and N ₂ became 2: 1 and performing a heat treatment at a temperature of 520 ° C. for 1 hour. Then H ₂ and N ₂ :
1 at a temperature of 520 ° C.
And then reduced by heat treatment, and finally H ₂ and N ₂ :
5 at a temperature of 520 ° C.
Reduced. Thereafter, N ₂ was continuously flown, and after cooling to room temperature, air was gradually contained in the flowing nitrogen gas flow, and a gradual oxidation treatment was performed to stabilize the surface. The manufacture of the sample tape is the same as that of the first embodiment.

As described above, Examples 1 to 14 and Comparative Example 1
The coercive force Hc, saturation magnetization s, squareness ratio Rs, coercive force Hc, residual magnetic flux density Br, and squareness ratio Rs of the magnetic powder of Comparative Example 3 were measured using a sample vibration magnetometer.

Furthermore, the electromagnetic conversion characteristics of the sample tapes of Examples 1 to 14 and Comparative Examples 1 to 3 were evaluated. This electromagnetic conversion characteristic uses an 8 mm VTR,
Output OUT and carrier to noise ratio C at 7 MHz
/ N was measured. The measurement results are as shown in Table 1.

[0050]

[Table 1]

As is apparent from Table 1, Examples 1 to 4 and a metal magnetic powder or H ₂ / N ₂ mixed gas was subjected to heat treatment by H ₂ / N ₂ mixed gas as in Example 9-14 , And a magnetic metal powder heat-treated with an H ₂ / Ar mixed gas as in Examples 5 to 8 or H ₂ / H.
The metal magnetic powder that has been subjected to the heat treatment by changing the ratio of the Ar mixed gas stepwise exhibits a high coercive force and a high saturation magnetic flux density,
The magnetic recording medium exhibits high electromagnetic conversion characteristics and is practically excellent.

The method for producing a metal magnetic powder of the present invention and the method for producing a magnetic recording medium using the same have been described in detail above. However, these examples are merely illustrative, and the present invention is not limited to these examples. It is not limited.

For example, N ₂ and Ar are exemplified as the non-reducing gas having an atomic number of 7 or more.
It is possible to use a rare gas such as r, Xe or Rn, or a mixed gas thereof. In addition, it is obvious that the conditions for reducing the iron oxyhydroxide and the conditions for producing the sample tape can be appropriately changed. The present invention can be applied to audio tapes, computer tapes, floppy disks, hard disks, etc., in addition to video tapes, regardless of the application.

As is clear from the above description, according to the method for producing a metallic magnetic powder of the present invention, sintering of particles during heat treatment in a reducing atmosphere is prevented, and a needle-like shape is maintained. It is possible to produce fine metal magnetic powder having excellent magnetic properties.

Further, according to the method of manufacturing a magnetic recording medium of the present invention, by employing such a metal magnetic powder, the dispersibility and orientation of the particles are improved, and the magnetic recording medium is excellent in magnetic characteristics and electromagnetic conversion characteristics. Is obtained. Therefore, the magnetic recording medium manufactured according to the present invention can be particularly suitably used not only as a magnetic recording medium for high-density recording but also as a mother tape in a magnetic field transfer system.

It should be noted that the present invention is not limited to the above-described embodiment, but can adopt various other configurations without departing from the gist of the present invention.

[0057]

As described above, according to the present invention,
It is possible to prevent sintering of particles during heat treatment in a reducing atmosphere, and to produce a fine metal magnetic powder having good magnetic properties and having a needle-like shape.

Further, according to the present invention, the dispersibility and orientation of the particles are improved, and a magnetic recording medium having excellent magnetic characteristics and electromagnetic conversion characteristics can be manufactured.

Claims (26)

[Claims] 1. a step of raising the temperature of a needle-like fine powder mainly composed of iron oxyhydroxide to a certain temperature of 400 ° C. to 620 ° C. in a non-reducing gas; A method for producing a metal magnetic powder, comprising: a step of performing a heat treatment by introducing a mixed gas of a gas and a non-reducing gas; and a step of performing a slow oxidation treatment. 2. The method according to claim 1, wherein the mixing ratio of the non-reducing gas is maintained at a certain value in the step of performing the heat treatment. 3. The method according to claim 1, wherein the mixing ratio of the non-reducing gas is maintained at a certain value in a range of 50% by volume or more and 67% by volume or less in the step of performing the heat treatment.
A method for producing the metal magnetic powder according to the above. 4. The step of performing a heat treatment, wherein the mixing ratio of a non-reducing gas composed of an element having an atomic number of 7 or more is 50
2. The method for producing a metal magnetic powder according to claim 1, wherein the metal magnetic powder is maintained at a certain fixed value within a range of not less than volume% and not more than 67 volume%. 5. The method according to claim 1, wherein the mixing ratio of the non-reducing gas is changed in the step of performing the heat treatment. 6. The metal magnet according to claim 1, wherein in the step of performing the heat treatment, the mixing ratio of the non-reducing gas is initially reduced, and the mixing ratio of the non-reducing gas is increased stepwise. Powder manufacturing method. 7. The metal according to claim 1, wherein, in the step of performing the heat treatment, the mixing ratio of the non-reducing gas is initially 33% by volume or less, and finally is 50% by volume or more. Manufacturing method of magnetic powder. 8. The mixing ratio of a non-reducing gas comprising an element having an atomic number of 7 or more in the step of performing heat treatment is initially 33% by volume or less, and finally 50% by volume or more. The method for producing a metal magnetic powder according to claim 1, wherein: 9. The metal according to claim 1, wherein in the step of performing the heat treatment, the mixing ratio of the non-reducing gas is initially 20% by volume or less, and finally is 50% by volume or more. Manufacturing method of magnetic powder. 10. The step of performing heat treatment, wherein the atomic number is 7
The method for producing a metal magnetic powder according to claim 1, wherein the mixing ratio of the non-reducing gas composed of the above-mentioned elements is initially 20% by volume or less and finally 50% by volume or more. 11. The metal according to claim 1, wherein, in the step of performing the heat treatment, the mixing ratio of the non-reducing gas is initially 33% by volume or less and finally 83% by volume or more. Manufacturing method of magnetic powder. 12. The step of performing a heat treatment, wherein the atomic number is 7
2. The method according to claim 1, wherein the mixing ratio of the non-reducing gas composed of the above elements is initially 33% by volume or less and finally 83% by volume or more. 13. The metal according to claim 1, wherein in the step of performing the heat treatment, the mixing ratio of the non-reducing gas is initially 20% by volume or less, and finally 83% by volume or more. Manufacturing method of magnetic powder. 14. The step of performing a heat treatment, wherein the atomic number is 7
2. The method for producing a metal magnetic powder according to claim 1, wherein the mixing ratio of the non-reducing gas composed of the above elements is initially 20% by volume or less and finally 83% by volume or more. 15. The non-reducing gas may be N ₂ , Ne, Ar,
3. It is at least one selected from the group consisting of Kr, Xe and Rn.
3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 1
15. The method for producing a metal magnetic powder according to 3 or 14. 16. A step of raising the temperature of a needle-shaped fine powder mainly composed of iron oxyhydroxide to a certain temperature of 400 ° C. to 620 ° C. in a non-reducing gas; A step of introducing a mixed gas of a gas and a non-reducing gas and performing a heat treatment; a step of performing a gradual oxidation treatment to obtain a metal magnetic powder; and a step of forming a magnetic layer mainly containing the metal magnetic powder and an organic binder. Forming on a non-magnetic support. 17. The heating process according to claim 16, wherein the mixing ratio of the non-reducing gas is maintained at a certain value in a range from 50% by volume to 67% by volume. A method for manufacturing a magnetic recording medium. 18. The step of performing a heat treatment, wherein the atomic number is 7
The mixing ratio of the non-reducing gas composed of the above elements is 5
17. The method for manufacturing a magnetic recording medium according to claim 16, wherein the magnetic recording medium is maintained at a certain fixed value within a range of 0% by volume to 67% by volume. 19. The magnetic method according to claim 16, wherein in the step of performing the heat treatment, the mixing ratio of the non-reducing gas is initially 33% by volume or less, and finally is 50% by volume or more. Manufacturing method of recording medium. 20. The step of performing a heat treatment, wherein the atomic number is 7
17. The method of manufacturing a magnetic recording medium according to claim 16, wherein the mixing ratio of the non-reducing gas composed of the above-mentioned elements is initially 33% by volume or less and finally 50% by volume or more. 21. The magnetic method according to claim 16, wherein in the step of performing the heat treatment, the mixing ratio of the non-reducing gas is initially 20% by volume or less, and finally is 50% by volume or more. Manufacturing method of recording medium. 22. The step of performing a heat treatment, wherein the atomic number is 7
17. The method of manufacturing a magnetic recording medium according to claim 16, wherein the mixing ratio of the non-reducing gas composed of the above elements is initially 20% by volume or less, and finally 50% by volume or more. 23. The magnetic device according to claim 16, wherein in the step of performing the heat treatment, the mixing ratio of the non-reducing gas is initially set to 33% by volume or less, and finally to 83% by volume or more. Manufacturing method of recording medium. 24. The step of performing a heat treatment, wherein the atomic number is 7
17. The method for manufacturing a magnetic recording medium according to claim 16, wherein the mixing ratio of the non-reducing gas composed of the above elements is initially 33% by volume or less and finally 83% by volume or more. 25. The magnetic method according to claim 16, wherein in the step of performing the heat treatment, the mixing ratio of the non-reducing gas is initially 20% by volume or less, and finally 83% by volume or more. Manufacturing method of recording medium. 26. The step of performing a heat treatment, wherein the atomic number is 7
17. The method for manufacturing a magnetic recording medium according to claim 16, wherein the mixing ratio of the non-reducing gas composed of the above elements is initially 20% by volume or less and finally 83% by volume or more.