JPH0834145B2 - Method for producing metal magnetic powder for magnetic recording - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for producing a metal magnetic powder suitable for magnetic recording, particularly a metal magnetic powder for magnetic recording having improved oxidative stability.

[Technical background of the invention and its problems]

In recent years, magnetic recording media have become more and more compact and have higher performance due to higher recording capacities. Together with this, as magnetic powder for magnetic recording, iron-based metal magnetic powder of iron or iron-based alloys having a larger saturation magnetization and a higher coercive force than the conventional iron oxide-based magnetic powder (hereinafter referred to as metal magnetic powder). ) Is attracting attention, and audio tapes and
In addition to being attempted to apply to 8m / m video tapes,
The application to high-performance recording media such as high-definition video tapes, digital audio tapes, and high-density discs, which have been recently developed, is further expected.

By the way, such metal magnetic powder is usually about 0.5 μm.
Furthermore, fine particles having a particle size of 0.3 μm or less are desired.Such fine particles have strong surface activity, and as a result, oxidation progresses over time and magnetic characteristics such as saturation magnetization decrease with it. Deterioration of the oxidative stability is unavoidable, and in severe cases, various troubles are unavoidable in handling operations and process control such as spontaneous ignition and combustion when the oxidation reaction rapidly progresses.

Various proposals have already been made in order to improve these problems. For example, (1) a method of alloying by adding a metal component other than iron to an aqueous iron salt solution or hydrated iron oxide during the production of the metal magnetic powder, (2) a surface of the metal magnetic powder particles of various inorganic or There have been attempts such as a method of coating with an organic treatment agent. However, the method (1) limits the metals that can be alloyed by substituting iron, and it is necessary to increase the amount of the substituting metal in order to improve the oxidation stability, and the magnetic properties such as coercive force and saturation magnetization are significantly In the method (2), the amount of coating must be considerably increased in order to impart sufficient oxidative stability, and as a result, a decrease in saturation magnetization cannot be avoided and a magnetic coating composition is used. There are many problems such as impairing the dispersibility and easily lowering the strength of the magnetic recording medium.

Further, as a method of imparting the above-mentioned oxidation resistance, various methods of forming an oxide film on the surface of the magnetic metal powder particles have been proposed. For example, (1), a method of introducing a trace amount of oxygen-containing gas to slowly oxidize the particle surface (for example, JP-B-51-5608, JP-A-48-25662, JP-B-52-19541),
(2) A method of oxidizing the surface of particles in an atmosphere of nitrogen gas containing water vapor (for example, Japanese Examined Patent Publication 35-3862 and Japanese Patent Publication 45-986).
9, Japanese Examined Patent Publication No. 61-36044), (3) A method of oxidizing the surface of particles in an oxygen-containing gas atmosphere containing water vapor (see, for example, Japanese Patent Laid-Open Publication No.
56-55503, JP-A-56-69301), (4) A method of oxidizing the particle surface in a hydrogen gas atmosphere containing water vapor (for example, JP-B-58-241, JP-B-58-52522, JP-A-60-26602). Are known. However, the above method (1) is
Since the amount of heat generated during the oxidation reaction is large and it is not easy to control the temperature distribution in the reactor uniformly, it is necessary to carry out the treatment for an extremely long time while controlling the gas flow rate finely. The method of
The iron oxide formed on the surface of the particles is likely to become hematite, and in order to obtain a uniform stable film, the film thickness must be increased and the saturation magnetization cannot be lowered. Further, in the method (3), although the oxidation reaction can be carried out even at a relatively low temperature, hydrated oxides are easily formed and the effect of imparting oxidation resistance is not substantially brought about. In the method (4), although a magnetite coating with a relatively small decrease in saturation magnetization is easily formed on the particle surface, it is necessary to increase the water vapor concentration in order to obtain a sufficient magnetite film thickness, and as a result, the oxidation reaction Excessively progresses, hematite and wustite are easily mixed in, and formation of a uniform coating of magnetite is easily impaired.

As mentioned above, in the case of the stabilization treatment by the conventional method,
If it is not possible to impart sufficient oxidation resistance, or if it is attempted to impart sufficient oxidation resistance, the excellent magnetic properties such as high saturation magnetization and high coercive force of the metal magnetic powder, and dispersibility at the time of coating can be obtained. It is easy to be impaired, and further, it is not easy to control the process operation in the oxidation reaction treatment, and therefore there are many problems that still need improvement, such as large variations in quality performance due to stabilization treatment, and its solution is desired. There is. In particular, with further demands for higher S / N ratio and higher output, further reduction of the particle size of the magnetic metal powder is aimed at, and there is a strong demand for solving the above problems.

[Object of the Invention]

The present invention solves the above-mentioned problems and, in industrially producing a magnetic metal powder for magnetic recording having improved oxidation resistance, which is suitable for a high-density magnetic recording medium, is extremely efficient and good in stability. It is to provide a method of obtaining.

[Outline of Invention]

The present inventors have long been conducting various studies to establish a method capable of efficiently imparting oxidation resistance without impairing the excellent magnetic properties of the metallic magnetic powder. However, in order to maintain the excellent oxidation resistance and the magnetic properties of the metal magnetic powder for practical use, a composition such as magnetite with high saturation magnetization is formed on the particle surface of the metal magnetic powder by the oxidation treatment by the so-called vapor phase method described above. Paying attention to the fact that it is very important to form an iron oxide layer having a dense and dense uniform film industrially easily, and stably and efficiently.
Further studies were conducted to solve the problems in the vapor-phase oxidation treatment. As a result, the metallic magnetic powder was diluted with an inert gas to a specific low steam partial pressure and a specific steam partial pressure / hydrogen partial pressure, and heat-treated with a prepared mixed gas, whereby the reaction system Of the metal magnetic powder can be formed with excellent stability by selectively operating a dense magnetite layer on the surface of the metal magnetic powder while effectively achieving uniform temperature distribution and removal of reaction heat. It is possible to impart desired oxidation resistance without substantially impairing the excellent magnetic properties, and further, after the heat treatment in the mixed gas system, followed by oxidation treatment with an oxygen-containing gas, the magnetite of The present invention has been completed based on the finding that only the surface portion can be effectively further oxidized and the oxidation resistance becomes more preferable.

That is, the first aspect of the present invention is to use a metallic magnetic powder mainly composed of iron in which steam and hydrogen gas are mixed with an inert gas to form a steam partial pressure.
0.1 to 30 mmHg and steam partial pressure / hydrogen partial pressure = 0.6 to
100 to 500 in a mixed gas atmosphere of 15.
A second aspect of the present invention is a method of producing a metal magnetic powder for magnetic recording, which comprises heat-treating at a temperature of ℃, and the second aspect of the present invention is to use a metal magnetic powder mainly composed of iron in an inert gas containing steam and hydrogen gas. Is mixed at a steam partial pressure of 0.1 to 30 mmHg and a steam partial pressure / hydrogen partial pressure of 0.6 to 15 at a temperature of 100 to 500 ° C., and then oxygen is added. A method for producing a metal magnetic powder for magnetic recording, which is characterized by performing an oxidation treatment with a gas.

In the present invention, the metal magnetic powder used as the object to be treated (hereinafter referred to as substrate particles) is a metal magnetic powder of iron or iron-based alloys mainly composed of iron, which is produced by various methods. It is obtained by subjecting acicular hydrated iron oxide such as α-FeOOH to heat reduction with a reducing gas such as hydrogen after heating / dehydration or without heat dehydration. In the heat treatment, in order to prevent sintering or shape collapse of the particles to be heated, for example, a silicon compound, an aluminum compound, a phosphorus compound, a boron compound, a nickel compound, a cobalt compound, a copper compound, tin is added to the particles as necessary. One or more kinds of various treating agents such as compounds and zirconium compounds may be added. The substrate particles obtained as described above are most commonly acicular crystals, but in addition to these, various shapes such as spindle-shaped, rice granular, spherical, rod-shaped, plate-shaped, and dice-shaped are also available. Can be used. The size of the particles is
Various ranges can be used, but the application to magnetic materials for high-density recording is far superior to that of fine particles.
Those having a particle size of 0.3 μm or less are preferable, and those having particularly large surface activity are more preferable in applying the oxidation resistance treatment of the present invention.

In the present invention, in order to carry out the oxidation resistance treatment, first, for example, nitrogen, helium, argon, etc., and one or more of various gases inert to the metal magnetic powder in the treatment are treated with hydrogen gas. A predetermined amount of water vapor is mixed to prepare a mixed gas having a desired composition. For example, an inert gas and a predetermined amount of hydrogen gas are introduced into a humidifier by a conventional method for humidification, and the steam partial pressure / hydrogen partial pressure ratio is usually 0.6 to 1
5, desirably 0.6 to 12, and steam partial pressure is usually 0.1 to 30 m
A mixed gas having a composition of mHg, preferably 1 to 20 mmHg is prepared. If the ratio of water vapor partial pressure / hydrogen partial pressure of the mixed gas system is too lower than the above range, the formation of the desired magnetite film is difficult to proceed, and at that time, if an attempt is made to raise the treatment temperature, a by-product phase such as wustite is formed. It is not possible to avoid the mixture of. On the other hand, if the content is higher than the above range, the oxidation reaction proceeds excessively and a non-magnetic non-hematite phase non-uniform coating is likely to be formed, which is not preferable. Further, if the water vapor partial pressure is too low than the above range, the amount of inert gas increases and it takes a very long time to form the magnetite film, and if it is higher than the above range, the temperature distribution in the reactor becomes uniform. However, the removal of the heat of reaction is easily impaired, and the formation of a dense magnetite layer becomes extremely difficult. The inert gas partial pressure in the mixed gas in the heat treatment is usually 600 m
If it is at least mHg, preferably at least 700 mmHg, and is too low than the above partial pressure, it becomes difficult to control the reaction and the reaction is likely to proceed rapidly, and the formation of a dense magnetite layer is impaired.

In order to perform the heat contact treatment with the metal magnetic powder by the mixed gas prepared as described above, various types of reactors such as a fluidized bed, a fixed bed and a moving bed which are used in a usual solid-gas contact reaction treatment are used. Filled with a metallic magnetic powder obtained by heating and reducing in a reducing gas, and other metallic magnetic powders produced by various methods, and the mixed gas is aerated at a predetermined supply rate under atmospheric pressure. However, the heat treatment may be performed while maintaining a temperature range of usually 100 to 500 ° C, preferably 150 to 450 ° C. If the treatment temperature is lower than the above range, it takes a very long time to form a predetermined amount of the magnetite layer on the surface of the metal magnetic powder particles, and if it is higher than the above range, the shape of the particles may be distorted or interparticle burning may occur. This is not preferable because it causes binding and impairs magnetic properties such as coercive force and squareness ratio and dispersibility. The heat treatment time is
Depending on the size of the reactor, the amount and kind of the magnetic metal powder to be treated, the composition of the aerated mixed gas, and the treatment temperature, it is generally 0.5 to 10 hours, although it cannot be generally stated.

The metal magnetic powder having the desired magnetite coating formed on the particle surface by performing the heat treatment for a predetermined time as described above may be cooled, for example, by passing an inert gas through the treatment system to cool the metal magnetic powder. Correspondingly, it can be easily taken out from the treatment step after being immersed in an organic solvent and air-dried.

In the present invention, the metal magnetic powder having the magnetite coating formed on the surface of the particles to impart desired oxidation resistance as described above is further ventilated with an oxygen-containing gas, and is usually at room temperature to
By operating at 200 ° C., only the surface portion of the magnetite layer formed on the surface of the metal magnetic powder particles can be selectively oxidized to Fe ₂ O ₃ . When performing the above-mentioned second-stage stabilization treatment, the saturation characteristics of the metal magnetic powder obtained by the first-stage heat treatment, magnetic properties such as coercive force and dispersibility are not substantially impaired. Further, it can be made more desirable as a magnetic recording material for high density recording, which has further improved oxidation resistance and is extremely stable. The first-stage treated product and the second-stage treated product may further include inorganic compounds such as phosphates and silicates, higher fatty acids, amines and amides, and anthranilic acid, if necessary. Deposition treatment of organic compounds such as chelating agents such as acetylacetone, and further Co, N
The oxidation resistance and the dispersibility can be further improved by treating the surface of the particles with a compound containing i, Zn, Mn or the like to form a ferrite.

The present invention will be further described below with reference to Examples and Comparative Examples.

Example of the present invention

Example 1 Magnetic magnetic powder mainly composed of needle-shaped iron [average major axis diameter 0.2
μm, average axial ratio 8 and specific surface area 85 m ² / g, α-FeOOH coated with silica (Si / Fe: 5.9 atomic weight%) and nickel (Ni / Fe: 0.9 atomic weight%) at 750 ° C. Α dehydrated by heating in
-Fe ₂ O ₃ was heated and reduced in a hydrogen gas atmosphere at 425 ° C to obtain an average major axis diameter of 0.145 μm, an average axial ratio of 8 and a specific surface area of 6
5m ² / g, coercive force (Hc) 1468Oe, saturation magnetization (σs) 169emu /
g: Substrate particles A] 35 g of solid fixed bed reactor (inner diameter 4.3 cm
φ, height 50 cm), and aerated with a mixed gas of the composition shown in Table 1 (nitrogen gas partial pressure is 748 mmHg) at a linear velocity of 10 cm / sec, and hold it at 425 ° C for 180 minutes to heat it slowly. Oxidized.
Then, the atmosphere was switched to nitrogen gas and cooled to room temperature.

Comparative example 1 In Example 1, it processed like the case of the same example except not containing an inert gas in mixed gas.

Comparative Example 2 In Example 1, in mixed gas (nitrogen gas partial pressure is 75
The treatment was performed in the same manner as in the case of the same example, except that 5.5 mmHg) did not contain hydrogen gas and the treatment time was 80 minutes.

Examples 2 to 5 Metallic magnetic powder mainly composed of acicular iron [average major axis diameter 0.25
μm, average axial ratio 10 and specific surface area 70 m ² / g, α-FeOOH coated with silica (Si / Fe: 4.3 atomic weight%) and nickel (Ni / Fe: 0.4 atomic weight%) at 825 ° C Α dehydrated by heating in
-Fe ₂ O ₃ was heated and reduced in a hydrogen gas atmosphere at 425 ° C to obtain an average major axis diameter of 0.17 μm, an axial ratio of 10 and a specific surface area of 53 m ² /
g, coercive force (Hc) 1320Oe, saturation magnetization (σs) 183.5emu / g:
Substrate particles B] 35 g of solid fixed bed reactor (inner diameter 4.3 cmφ,
It was charged in a height of 50 cm, and mixed gas shown in Table 2 (nitrogen gas partial pressure in Examples 2 and 3: 754.75 mmHg, Example 4: 752.
25 mmHg, Example 5: 754.75 mmHg) was aerated at a linear velocity of 10 cm / sec, and the temperature and time shown in Table 2 were maintained to carry out heat gradual oxidation treatment in a mixed system. Then, the mixture was cooled to room temperature and then immersed in toluene, and then toluene was volatilized.
(Treatment I) Next, the metal magnetic powder subjected to the heat gradual oxidation treatment in the above mixed gas system was charged into a fluidized bed reactor (inner diameter 5 cmφ, height 30 cm), and an oxygen-containing gas (oxygen-nitrogen mixed gas, oxygen). (Concentration: 1% by volume) was introduced at a linear velocity of 10 cm / sec, and the mixture was held at 30 ° C. for 5 hours for stabilization treatment. (Treatment II) Comparative Example 3 The same example as in Example 2 except that the heating gradual oxidation treatment with the nitrogen gas-steam gas-hydrogen gas-based mixed gas was not performed and the treatment II time was 10 hours. Was treated in the same manner as in.

Comparative Example 4 The same process as in Example 1 was performed except that a mixed gas having a composition of hydrogen gas partial pressure of 410 mmHg and steam partial pressure of 350 mmHg was used in Example 1.

Comparative Example 5 In Example 1, hydrogen gas partial pressure 97 mmHg, water vapor partial pressure
The same treatment as in the case of the same example was performed except that a mixed gas having a composition of 83 mmHg and a nitrogen gas partial pressure of 580 mmHg was used.

Using the magnetic metal powders of the above Examples and Comparative Examples, the following mixed compositions were mixed and dispersed to prepare magnetic paints.

Magnetic powder 5 parts by weight Polyurethane resin (30% solution) 2.96 parts by weight Dispersant 0.25 parts by weight Mixed solvent 13.4 parts by weight (toluene / MEK / cyclohexane: 4.5 / 4.5 / 1) Then, the magnetic paint is applied on a polyester film,
A magnetic tape was prepared by coating so as to have a dry film thickness of 10 μm, drying after orientation treatment.

Regarding the magnetic metal powders of the above-mentioned Examples and Comparative Examples and magnetic tapes prepared using them, saturation magnetization (σs: emu / g), coercive force (Hc: Oe), saturation magnetic flux density (B
m: Gauss), squareness ratio (Rs), orientation ratio (OR), reaction magnetic field distribution (SFD), and gloss (60 ° -60 °) were measured. Further, in order to evaluate the oxidation stability, the sample was left in an environment of a temperature of 60 ° C. and a relative humidity of 80 ° C. for 1 week, and accelerated aging changes of σs, Bm, Rs, and Hc were measured, and the deterioration rate Δσs ( %) And ΔBm (%) were calculated by the following equations. These results are shown in Table 1.
And shown in Table 2.

(In the formula, σs is σs before aging and σs ′ is σs after aging) (In the formula, Bm is Bm before aging and Bm ′ is Bm after aging) [Effects of the Invention] The metal magnetic powder according to the method of the present invention has remarkably improved oxidative stability, can retain excellent magnetic properties for a long time, and is excellent in storage stability itself in handling and handling. , It is very preferable for process control,
Further, it has a good dispersibility in the medium and is extremely suitable for producing a high-output high-density magnetic recording medium.

In addition, the method of the present invention is capable of imparting highly stable oxidation resistance of stable quality to the metal magnetic powder by so-called gradual oxidation treatment with steam, which is easy to operate under low steam concentration and is extremely efficient. It is very useful.

Front Page Continuation (56) References JP-A-56-55503 (JP, A) JP-A-56-203 (JP, A) JP-A-63-239802 (JP, A)

Claims (2)

[Claims] 1. Metal magnetic powder mainly composed of iron is mixed with water vapor and hydrogen gas in an inert gas so that the water vapor partial pressure is 0.1 to 30 mmHg and the water vapor partial pressure / hydrogen partial pressure is 0.6 to 15. A method for producing a metal magnetic powder for magnetic recording, which comprises heat-treating at a temperature of 100 to 500 ° C. in a gas atmosphere obtained by. 2. Metal magnetic powder mainly composed of iron is mixed with water vapor and hydrogen gas in an inert gas so that the water vapor partial pressure is 0.1 to 30 mmHg and the water vapor partial pressure / hydrogen partial pressure is 0.6 to 15. A method for producing a metal magnetic powder for magnetic recording, which comprises heat-treating at a temperature of 100 to 500 ° C. in the gas atmosphere and then oxidizing with an oxygen-containing gas.