JPH04230004A - Manufacture of magnetic recording needle ferroalloy magnetic particle powder - Google Patents

Abstract

PURPOSE:To provide the step of industrially manufacturing the title magnetic recording needle ferroalloy magnetic particle powder in the long axial diameter of 0.05-0.2mum having high coersive force and large saturated magnetic susceptibility further in excellent S.F.D and lower decline ratio of coersive force. CONSTITUTION:An oxide film is formed on the surface of said ferroalloy magnetic particles by processing the needle ferroalloy magnetic particles in the long axial diameter of 0/05-0.2mum produced by thermal-reducing wet needle ferric oxide particles or needle hematite particles in the mixed gas atmosphere of an inert gas containing steam of 10-50g/cm<3> with oxygen containing gas.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention has a high coercive force and a larger saturation magnetization, and has an S. F. D. The present invention relates to a method for producing acicular iron alloy magnetic particles for magnetic recording having an excellent long axis diameter of 0.05 μm or more and less than 0.2 μm, which has excellent properties and a low rate of decrease in coercive force due to the formation of an oxide film.

0002

[Background Art] In recent years, magnetic recording and reproducing equipment for video and audio has become increasingly long-lasting, compact and lightweight.In particular, the spread of VTRs (video tape recorders) has been remarkable. 2. Description of the Related Art VTRs are being actively developed with the aim of recording for long periods of time and being smaller and lighter. On the other hand, there is an increasing demand for higher performance of magnetic tape, which is a magnetic recording medium, that is, higher recording density and improved output characteristics.

These characteristics of magnetic recording media are closely related to the magnetic particles used in magnetic recording media, and in recent years, magnetic particles with higher coercivity and higher coercive force than conventional iron oxide magnetic particles have been developed. Acicular iron alloy magnetic particles with large saturation magnetization have attracted attention, and have been used in digital audio tapes (D
It has been put to practical use in magnetic recording media such as AT), 8mm video tape, Hi-8 tape, and video floppy.

However, the demand for improving the characteristics of these acicular iron alloy magnetic particles continues, and from the standpoint of improving the noise level and output characteristics of magnetic recording media, acicular iron alloy magnetic particles are becoming fine particles. , has a larger saturation magnetization, and has a larger saturation magnetization. F. D. It is required that the rate of decrease in coercive force due to the formation of an oxide film is small.

It is known that the noise level of a magnetic recording medium is closely related to the particle size of the acicular iron alloy magnetic particles used, and that the smaller the particle size, the lower the noise level tends to be. Recently, especially,
Fine acicular iron alloy magnetic particle powder of less than 0.2 μm is required.

In order to improve the output characteristics of a magnetic recording medium, in addition to the above-mentioned high coercive force and large saturation magnetization,
S. F. D. (Switching Field Di
It is required that the distribution is excellent.

This fact is explained in Japanese Unexamined Patent Publication No. 63-26821: "Figure 1 is a diagram showing the relationship between the S.F.D. measured for the above-mentioned magnetic disk and the recording/reproducing output." The relationship between S.F.D. and recording/reproduction output is a straight line as is clear from Figure 1.
．． It can be seen that recording and reproducing output increases by using ferromagnetic powder with a small . That is, in order to increase the recording/reproducing output, S. F. D. It is preferable that the S.I. F. D. is necessary. ” as stated.

Generally speaking, as the acicular iron alloy magnetic particles become finer, especially less than 0.2 μm, the coercive force increases and the noise level of the magnetic recording medium tends to be improved. Since the surface activity of the particles becomes extremely large, when taking out the acicular iron alloy magnetic particles obtained by heating reduction under a hydrogen gas flow into the air, an inert gas with a gradually increased oxygen content is used. When an oxide film is produced by a well-known method such as by flowing oxide, the oxide film is rough and unnecessary oxide film is formed in some parts, making the film non-uniform. Therefore, a distribution of coercive force occurs and S. F. D. deterioration, and the rate of decrease in coercive force due to the formation of an oxide film also increases. Furthermore, it is difficult to obtain acicular iron alloy magnetic particles having large saturation magnetization. These phenomena are
There is a tendency that the finer the particle size, the more likely it is to occur.

For example, looking at the relationship between the particle size and saturation magnetization of acicular iron alloy magnetic particles, it is difficult to obtain a saturation magnetization of 120 emu/g or more with fine particles of about 0.1 μm.

Various methods have been tried in the past to form an oxide film when the acicular iron alloy magnetic particles obtained by thermal reduction are taken out into the air. As a method using a mixed gas of a gas and an oxygen-containing gas, JP-A-56-55503 and JP-A-56-69301 are known.

[0011]

Problem to be Solved by the Invention: It has a high coercive force and a larger saturation magnetization, and moreover, an S. F. D. Acicular iron alloy magnetic particles with excellent properties and a low rate of decrease in coercive force due to oxide film formation are currently in high demand. Acicular iron alloy magnetic particles that fully satisfy these requirements have not yet been obtained.

In particular, when an oxide film is formed by the above-mentioned known method on fine acicular iron alloy magnetic particles of less than 0.2 μm, the surface activity of the acicular iron alloy magnetic particles increases. is very large, and as a result, a dense and uniform oxide film cannot be formed.

Therefore, the technical object of the present invention is to form a dense and uniform oxide film on the surface of fine acicular iron alloy magnetic fine particles of less than 0.2 μm.

[0014]

[Means for Solving the Problems] The above technical problems can be achieved by the present invention as follows.

That is, the present invention provides acicular iron alloy magnetic particles having a major axis diameter of 0.05 μm or more and less than 0.2 μm obtained by thermally reducing acicular hydrated ferric oxide particles or acicular hematite particles. By processing at a temperature below 50°C in a mixed gas of an inert gas and an oxygen-containing gas containing ~50 g/m3 of water vapor, or if necessary,
Treated at a temperature below 50°C in a mixed gas of an inert gas and an oxygen-containing gas containing 0 g/m3 of water vapor,
Then, the above treatment is carried out in an inert gas containing 10 to 50 g/m3 of water vapor at a temperature of 150°C or lower, or, if necessary, in a mixed gas of an inert gas containing water vapor and an oxygen-containing gas. Acicular iron alloy magnetic particle powder for magnetic recording, which comprises forming an oxide film on the particle surface of the acicular iron alloy magnetic particles by further repeating the treatment and the treatment in an inert gas containing water vapor. This is the manufacturing method.

Next, various conditions for implementing the present invention will be described.

[0017] In the present invention, the major axis diameter is 0.05 μm or more.
．． Acicular iron alloy magnetic particles of less than 2 μm are obtained by heating and dehydrating the acicular hydrated ferric oxide particles and the acicular hydrated ferric oxide particles at a temperature of 250° C. or higher and lower than 300° C. using a conventional method. Highly densified acicular hematite particles obtained by heat-treating acicular hematite particles and the acicular hydrated ferric oxide particles in a non-reducing atmosphere at a temperature range of 300 to 850°C are used as starting materials. The starting material is heated and reduced in a temperature range of 350 to 450° C. under a flow of hydrogen gas. Here, needle-like means axial ratio (long axis diameter/short axis diameter)
is 4 or more, and includes not only needle-shaped particles but also spindle-shaped, rice grain-shaped, and strip-shaped particles. In addition, the starting material contains different elements other than Fe, such as Al, Ni, Co, B, Zn, P, and Si, which are usually used to improve the properties of acicular iron alloy magnetic particles. The particles may be coated or coated on the surface of the particles.

The formation of the oxide film in the present invention involves heating the acicular iron alloy magnetic particles at 50°C in a mixed gas of an inert gas containing 10 to 50 g/m3 of water vapor and an oxygen-containing gas.
This is done by processing at temperatures below. If the water vapor contained in the mixed gas is less than 10 g/m3, the control of the oxidation treatment is insufficient, making it difficult to form a dense and uniform oxide film, which makes it difficult to form a dense and uniform oxide film. Magnetic particle powder cannot be obtained. Even if it exceeds 50 g/m3, the acicular iron alloy magnetic particle powder which is the object of the present invention can be obtained.
There is no point in adding more than necessary.

The amount of oxygen in the mixed gas may be such that rapid oxidation does not occur during the formation of the oxide film, and preferably the content starts from about 0.02 to 0.1% by volume.
The amount of air can be increased step by step until the atmospheric composition is reached in the final stage.

[0020] As the inert gas, nitrogen gas, argon gas, etc. can be used.

[0021] If the temperature is 50°C or higher, the oxidation treatment is insufficiently controlled, making it difficult to form a dense and uniform oxide film. is not obtained.

[0022] The formation of the oxide film in the present invention can be further carried out at a temperature of 150°C or lower in an inert gas containing 10 to 50 g/m3 of water vapor, if necessary. can produce a uniform film. When the temperature is 150° C. or higher, the rate of decrease in coercive force of the obtained acicular iron alloy magnetic particles increases. Considering the rate of decrease in coercive force, the temperature is preferably 0 to 100°C, more preferably 0 to 50°C.

[0023] The water vapor contained in the inert gas is 10g/
If it is less than m3, it is difficult to form a more uniform and dense oxide film. Even if the amount exceeds 50 g/m3, it is possible to form a more uniform and dense oxide film, but there is no point in adding more than necessary.

The formation of the oxide film in the present invention can be carried out by repeating the treatment in a mixed gas of an inert gas containing water vapor and an oxygen-containing gas and the treatment in an inert gas containing water vapor, if necessary. This makes it possible to form a more dense and uniform coating.

[0025]

[Function] First, the most important point in the present invention is that acicular iron having a major axis diameter of 0.05 μm or more and less than 0.2 μm is obtained by heating and reducing acicular hydrated ferric oxide particles or acicular hematite particles. The alloy magnetic particles are placed in a mixed gas of an inert gas containing 10 to 50 g/m3 of water vapor and an oxygen-containing gas,
When treated at a temperature below 50°C, a dense and uniform oxide film can be formed on the particle surface of the acicular iron alloy magnetic particles, resulting in high coercive force and larger saturation magnetization. Moreover, S. F. D. is excellent,
Another fact is that acicular iron alloy magnetic particles having a major axis diameter of 0.05 μm or more and less than 0.2 μm can be obtained, and the rate of decrease in coercive force due to the formation of an oxide film is small.

[0026] In the present invention, if necessary, further 50
When treated in an inert gas containing 10 to 50 g/m3 of water vapor at a temperature below °C, the formation of an unnecessary oxide film is partially prevented, so the particle surface of the acicular iron alloy magnetic particles is A dense and uniform oxide coating is formed by
As a result, the magnitude of saturation magnetization, S. F. D. Acicular iron alloy magnetic particles having a major axis diameter of 0.05 μm or more and less than 0.2 μm, which have better properties such as the rate of decrease in coercive force due to the formation of an oxide film, can be obtained.

[0027] In the present invention, if necessary, the treatment in a mixed gas of an inert gas containing water vapor and an oxygen-containing gas and the treatment in an inert gas containing water vapor are repeated, thereby making the product even more dense and uniform. As a result, acicular iron alloy magnetic fine particles having a major axis diameter of 0.05 μm or more and less than 0.2 μm, which have even better properties as described above, are obtained.

[0028] As to the reason why a dense and uniform coating is produced in the present invention, the present inventor has discovered that the combination of an inert gas containing 10 to 50 g/m3 of water vapor and an oxygen-containing gas as shown in the comparative example below. When treated at a temperature of 50°C or higher in a mixed gas, less than 10g/m3 or 50g/m3
Acicular iron alloy magnetic material which has the various properties targeted by the present invention in any case when treated at a temperature below 50°C in a mixed gas of an inert gas and an oxygen-containing gas containing water vapor exceeding 3 m3. Since no particle powder was obtained, it is believed that this is due to a synergistic effect between the water vapor content and temperature in the mixed gas of an inert gas containing water vapor and an oxygen-containing gas.

[0029]

[Examples] Next, the present invention will be explained with reference to Examples and Comparative Examples.

The long axes and axial ratios (long axis diameter/short axis diameter) of the particles in the following Examples and Comparative Examples are shown as average values of values measured from electron micrographs. The magnetic properties of the acicular iron alloy magnetic particles were determined using the "Vibrating Sample Magnetometer VSM-3S-
15" (manufactured by Toei Kogyo Co., Ltd.) and an external magnetic field of 10K.
The measurement was performed up to Oe.

The rate of decrease in coercive force is determined by immersing a portion of the acicular iron alloy magnetic particles immediately after reduction in toluene, taking it out into the air, and evaporating the toluene. The difference between the coercive force value of the alloy magnetic particles and the coercive force value of stable acicular iron alloy magnetic particles obtained by generating a sufficient oxide film by various methods is calculated as the coercive force value of the acicular iron alloy magnetic particles after air drying. The value divided by the magnetic force value is expressed as a percentage (%).

[0032]S. F. D. The measurement involves using a sheet sample obtained by the following method, using the differential circuit of the magnetic measuring instrument to obtain a differential curve of the demagnetization curve of the magnetic hysteresis curve, and measuring the half-width of this curve. It was calculated by dividing this value by the coercive force.

[0033] The sheet-like sample piece was prepared by placing iron alloy magnetic particles, resin, and solvent in a 100 cc polybottle in the proportions shown below, and then mixing and dispersing the mixture in a paint conditioner for 6 hours. of polyethylene terephthalate film using an applicator to a thickness of 50 μm, and then 3K Gauss
Obtained by drying in a magnetic field of s.

3mmφ steel ball
800 parts by weight Iron alloy magnetic particle powder
100 parts by weight Polyurethane resin having sodium sulfonate group 20 parts by weight Cyclohexanone

83.3 parts by weight Methyl ethyl ketone
83.3 parts by weight toluene

83.3 parts by weight

0035
Example 1 Goethite particle powder exhibiting a spindle shape with a major axis of 0.16 μm and an axial ratio (major axis diameter/minor axis diameter) of 10, the particle surface of which was coated with an Al compound, a Co compound, a Ni compound, and a B compound ( Al/Fe=3.1 at%, Co/Fe=6.
0 at%, Ni/Fe=0.5 at%, B/Fe=4.
3 at. A spindle-shaped hematite particle powder with a diameter of 8.5 was obtained.

[0036] 140 g of the above hematite particle powder was added to a volume of 3
The hydrogen gas was poured into a retort container with a capacity of 37 liters, and hydrogen gas was aerated at a rate of 20 liters per minute while rotating.
It was reduced at 0°C to obtain acicular iron alloy magnetic particles.

Next, hydrogen gas was switched to nitrogen gas, and cooling was continued while nitrogen gas was flowing.
After holding for 0.5 hours in a mixed gas of 0.1% by volume oxygen and nitrogen gas containing water vapor, the amount of oxygen was reduced to 0.2% by volume.
% by volume and treated at a reaction temperature of 40° C. for 7 hours while passing a mixed gas of oxygen and nitrogen gas containing water vapor to form an oxide film on the particle surface of the acicular iron alloy magnetic particles. After the above operation was completed, the acicular iron alloy magnetic particles having an oxide film formed on their surfaces were taken out from the retort into the air.

As a result of electron microscopic observation, the obtained acicular iron alloy magnetic particles had a long axis of 0.11 μm and an axial ratio (long axis diameter/
The short axis diameter) was 7. In addition, the magnetic properties have a coercive force of 15
30 Oe, saturation magnetization is 132 emu/g, coercive force reduction rate is 2.9%, coating film properties are 0.84 square, S.
F. D. was 0.45.

Example 2, Comparative Examples 1 to 4 Various types of starting materials, thermal reduction temperature, amount of water vapor, amount of O2, temperature and time in the treatment step with a mixed gas of an inert gas containing water vapor and an oxygen-containing gas were varied. Acicular iron alloy magnetic particles were obtained in the same manner as in Example 1 except for the following changes. The main manufacturing conditions at this time are shown in Table 1, and the various properties of the acicular iron alloy magnetic particles are shown in Table 2.

Example 3 A densified material coated with Al compound, Co compound, Ni compound and B compound (heat treatment temperature 40
0°C), major axis 0.15 μm, axial ratio (major axis diameter/minor axis diameter) 9
．． 140 g of spindle-shaped hematite particles (Al/Fe = 2.0 at%, Co/Fe = 5.0 at%, Ni/Fe = 0.5 at%, B/Fe = 4.0 at%) in volume 3
The mixture was placed in a 1-liter retort container, and while being driven and rotated, hydrogen gas was passed through at a rate of 20 liters per minute, and the mixture was reduced at a reduction temperature of 400° C. to obtain acicular iron alloy magnetic particles.

Next, hydrogen gas was switched to nitrogen gas, and cooling was performed while flowing nitrogen gas, and then 12 g/m3
After holding for 0.5 hours in a mixed gas of 0.1 volume % oxygen and nitrogen gas containing water vapor, the oxygen content was switched to 0.3 volume %, and the inert gas containing water vapor and oxygen containing While aerating the mixed gas with the gas, the reaction temperature was 4.
An oxide film was formed on the particle surface of the acicular iron alloy magnetic particles by treating at 5°C for 5.0 hours, and then passing nitrogen gas containing 12 g/m3 of water vapor for 0.5 hours at a reaction temperature of 40°C. Ta.

After the above operation was completed, the acicular iron alloy magnetic particles having an oxide film formed on their surfaces were taken out of the retort into the air. The main manufacturing conditions at this time are shown in Table 1, and the various properties of the acicular iron alloy magnetic particles are shown in Table 2.

Examples 4 to 6 Types of starting materials, thermal reduction temperature, amount of water vapor, O2 amount, temperature and time in the treatment step with a mixed gas of inert gas containing water vapor and oxygen-containing gas, and inert gas containing water vapor Except for varying the amount of water vapor, temperature, time, and number of times a series of treatments were performed in the gas treatment process,
Acicular iron alloy magnetic particles were obtained in the same manner as in Example 3. The main manufacturing conditions at this time are shown in Table 1, and the various properties of the acicular iron alloy magnetic particles are shown in Table 2.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

Effects of the Invention According to the method for producing acicular iron alloy magnetic particles according to the present invention, as shown in the above embodiments, the powder has a high coercive force and a larger saturation magnetization. F. D.
Acicular iron alloy magnetic particles with a major axis diameter of 0.05 μm or more and less than 0.2 μm can be obtained, which have excellent magnetic properties and a low rate of decrease in coercive force due to oxide film formation, resulting in high recording density, high output, and low coercive force. Suitable as magnetic particle powder for noise level.

Claims (3)

[Claims] Claim 1: Long axis diameter 0.05 μm obtained by thermal reduction of acicular hydrated ferric oxide particles or acicular hematite particles
10 to 5 acicular iron alloy magnetic particles with a diameter of less than 0.2 μm
Forming an oxide film on the particle surface of the acicular iron alloy magnetic particles by treating at a temperature of less than 50° C. in a mixed gas of an inert gas and an oxygen-containing gas containing 0 g/m3 of water vapor. A method for producing acicular iron alloy magnetic particles for magnetic recording. Claim 2: Long axis diameter of 0.05 μm obtained by thermal reduction of acicular hydrated ferric oxide particles or acicular hematite particles.
10 to 5 acicular iron alloy magnetic particles with a diameter of less than 0.2 μm
Treated at a temperature below 50°C in a mixed gas of an inert gas and an oxygen-containing gas containing 0 g/m3 of water vapor,
Next, the acicular iron alloy magnetic particles are treated in an inert gas containing 10 to 50 g/m3 of water vapor at a temperature of 150°C or lower to form an oxide film on the particle surface of the acicular iron alloy magnetic particles. A method for producing acicular iron alloy magnetic particles for recording purposes. 3. Long axis diameter 0.05 μm obtained by thermal reduction of acicular hydrated ferric oxide particles or acicular hematite particles
10 to 5 acicular iron alloy magnetic particles with a diameter of less than 0.2 μm
Treated at a temperature below 50°C in a mixed gas of an inert gas and an oxygen-containing gas containing 0 g/m3 of water vapor,
Next, after treatment in an inert gas containing 10 to 50 g/m3 of water vapor at a temperature of 150°C or lower, the above treatment and water vapor are further carried out in a mixed gas of an inert gas containing water vapor and an oxygen-containing gas. A method for producing acicular iron alloy magnetic particles for magnetic recording, characterized in that an oxide film is formed on the particle surface of the acicular iron alloy magnetic particles by repeatedly performing the above-mentioned treatment in an inert gas containing the acicular iron alloy magnetic particles.