JPH0575807B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing metal magnetic particles having an isotropic shape and having iron as a main component. The present invention relates to a method for producing metal magnetic particles containing iron as a main component, which have an isotropic shape with a uniform particle size and have σs.

The main uses of the iron-based metal magnetic particles having an isotropic shape produced by the present invention are as material powder for magnetic toner for electrostatic copying and as magnetic particle powder for magnetic recording. .

[Conventional technology]

The spread of electrostatic copying machines has been remarkable in recent years.
Along with this, research and development of magnetic toner, which is a developer, is active, and improvements in its properties are required.

Magnetic toner is generally produced by dispersing isotropically shaped magnetic particles in a synthetic resin, but in order to improve its properties, the material powder, the magnetic particles, must have a high coercive force. It is necessary to have Hc and a large saturation magnetization σs, and the grain size must be uniform.

This phenomenon is explained, for example, in Japanese Patent Publication No. 57-60765, "...In order to improve conveyance, it is necessary that the strength of magnetization of magnetic toner particles, that is, the residual magnetic flux Br, be high. In order to obtain magnetic toner particles with such characteristics, it is necessary that the granular magnetic particle powder, which is the raw material for the magnetic tonneau, has as large a saturation magnetization σs as possible and a high coercive force Hc.
and the description in Japanese Patent Publication No. 53-21656, ``...By uniformly dispersing iron oxide throughout the developer particles, the magnetic susceptibility necessary for visualizing the electrostatic latent image is obtained...''
This is as described.

On the other hand, magnetically isotropic magnetic recording media, especially floppy disks, are widely used as magnetic recording media for inputting and outputting information with the spread of office computers, word processors, and the like.
A floppy disk is generally a disk in which one or both sides of a sonosheet-like polyester base is coated with isotropically shaped magnetic particles.

In recent years, as magnetic recording and reproducing equipment has become smaller and lighter, there has been an increasing need for higher performance in floppy disks, which are magnetic recording media.
That is, high recording density characteristics and high output characteristics are required.

The characteristics of magnetic particles with an isotropic shape suitable for satisfying the above requirements for magnetic recording media are as follows:
It has a high coercive force Hc and a large saturation magnetization σs, and the grain size is uniform. This phenomenon is explained, for example, in Japanese Patent Publication No. 61-31057, which states that ``...high recording density characteristics and high output characteristics are required.'' In order to satisfy the above requirements for floppy disks, suitable magnetic recording The characteristics of magnetic particles are as follows: "They have a high coercive force Hc and a large saturation magnetization σs..." and "Development of Magnetic Materials and Highly Dispersed Magnetic Powder Technology" published by Sogo Technological Center Co., Ltd. (1982) ), page 74, ``...The major challenges in the design of magnetic coating layers to overcome the factors for high-density recording are (1) uniform dispersion of magnetic particles... ” as stated.

As mentioned above, magnetic particles with an isotropic shape are used in various fields, but the characteristics commonly required for magnetic particles in all fields are high coercive force Hc and large It has a saturation magnetization σs and a uniform grain size.

Generally, acidic iron oxide particles such as magnetite particles and maghemite particles are widely used as magnetic particles exhibiting an isotropic shape.
As the performance of magnetic toners and magnetic recording media improves, metal magnetic particles whose main component is iron and which exhibit an isotropic shape and have a higher coercive force Hc and a larger saturation magnetization σs than these magnetic iron oxide particles. are attracting attention, and there is a strong demand for improving the properties of these particles.

Conventionally, the method for producing isotropically shaped metal magnetic particles containing iron as a main component involves reacting a reaction aqueous solution containing ferrous hydroxide obtained by reacting an aqueous ferrous salt solution with an alkali. A method is known in which magnetite particles are generated from an aqueous solution by passing an oxygen-containing gas through the solution, and the magnetite particles are reduced by heating in a reducing gas.

[Problem that the invention seeks to solve]

It has a high coercive force Hc and a large saturation magnetization σs,
Moreover, metal magnetic particles mainly composed of iron having an isotropic shape with uniform particle size are currently in high demand, but the isotropic shape obtained by the known method as described above is The magnetic properties of metal magnetic particles mainly composed of iron exhibiting a coercive force Hc of about 240 Oe and a saturation magnetization σs of about 240 Oe at most.
The amount is about 150 emu/g, which is still far from being sufficient.

In addition, in the case of using a known method, the particle size of the magnetite particles produced from an aqueous solution is asymmetric, and the metal magnetic particles whose main component is iron obtained by thermally reducing the magnetite particles are naturally also asymmetric. It becomes symmetrical.

Therefore, there is a strong need for a technical means to obtain iron-based magnetic metal particles having a high coercive force Hc and a large saturation magnetization σs, and exhibiting an isotropic shape with uniform particle size. There is.

[Means for solving problems]

The present inventor has conducted various studies in order to obtain iron-based magnetic metal particles having a high coercive force Hc and a large saturation magnetization σs, and exhibiting an isotropic shape with uniform particle size. As a result, the present invention was achieved.

That is, the present invention reduces the particle size by hydrothermally treating an acidic suspension containing β-FeOOH particles with a specific surface area of 150 m ² /g or more at a concentration of less than 0.1 mol/g in a temperature range of 100 to 130°C. Hematite particles with a uniform isotropic shape are generated, and the hematite particles are heated and reduced in a reducing gas to produce metal magnetic particle powder mainly composed of iron, which has an isotropic shape with a uniform particle size. [Operation] First, the most important point in the present invention is that the specific surface area is 150 m ² /g or more. A certain β-FeOOH particle
Acidic suspension containing less than 0.1mol/100~
Hydrothermal treatment in a temperature range of 130°C produces hematite particles with uniform particle size, and when the hematite particles are heated and reduced in a reducing gas, they have a high coercive force Hc, especially 250 Oe or more. death,
Another fact is that it is possible to obtain iron-based metal magnetic particles having an isotropic shape and having a large saturation magnetization σs, in particular, 170 emu/g or more.

In the present invention, since it is possible to generate hematite particles with uniform particle size from an aqueous solution, it is possible to produce iron-based metals with an isotropic shape obtained by heating and reducing the hematite particles. The magnetic particle powder is also uniform in particle size.

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

The β-FeOOH particles in the present invention need to have a specific surface area of 150 m ² /g or more.
When it is less than 150 m ² /g, it is difficult to obtain hematite particles with uniform particle size, and the reaction for producing hematite particles takes a long time. 150
β-FeOOH particles having a particle size of m ² /g or more can be obtained by a method of hydrolyzing a ferric chloride aqueous solution by heating it in a temperature range of 70 to 90°C.

The suspension containing β-FeOOH in the present invention is
It must be acidic, and if it is not acidic,
In the temperature range of 100 to 130°C, β-FeOOH is generated stably, so hematite particles are not generated.

The concentration of the acidic suspension containing β-FeOOH particles in the present invention is less than 0.1 mol/. 0.1mol/
If it is above, hematite particles will not be generated.

The reaction temperature in the present invention is 100 to 130°C. If the temperature is less than 100°C, the dissolution of β-FeOOH does not proceed sufficiently, so that hematite particles are not generated. Although hematite particles are generated when the temperature exceeds 130°C, it is not industrially or economically viable because special equipment such as a high-pressure container is required.

The heating reduction treatment in a reducing gas in the present invention can be carried out by a conventional method.

In addition, the hematite particles, which are the starting material, can be coated with a substance that has a sintering prevention effect, such as Si, Al, or P compounds, which is usually carried out prior to heat treatment, so that they have better dispersibility. It is possible to obtain metal magnetic particles having an isotropic shape and containing iron as a main component.

In the present invention, the heat-reduced metal magnetic particle powder containing iron as the main component can be obtained by a well-known method, for example, by immersing it in an organic solvent such as toluene, or by immersing the reduced iron-based magnetic particle powder in an atmosphere. After the gas is once replaced with an inert gas, it can be taken out into the air by a method of gradual oxidation by gradually increasing the oxygen content in the inert gas and finally turning it into air.

〔Example〕

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

In addition, the average diameter of particles in the following examples is the average value of numerical values measured from electron micrographs,
The specific surface area is a value measured by the BET method.

Example 1 500 ml of FeCl ₃ aqueous solution containing 0.05 mol of Fe ³⁺ was added to 80
Heating at 0C for 30 minutes produced yellow-brown precipitated particles. The pH of the suspension at this time was 1.3. Electron micrograph (×50000) of yellowish brown particles obtained by extracting a portion of the reaction solution, washing with water, filtering, and drying.
is shown in Figure 1. As a result of X-ray diffraction, this yellowish brown particle powder was found to be β-FeOOH, and the specific surface area was 190 m ² /
It was hot at g.

PH containing the above 0.05 mol/β-FeOOH particles
Place the acidic suspension of 1.3 in a closed container and heat it at 125℃ for 15 minutes.
Hydrothermal treatment for hours produced a reddish-brown precipitate. The particles obtained by washing the reddish brown precipitate with water, filtering, and drying are hematite as shown in the X-ray diffraction shown in Figure 2, and the average particle size is clear from the electron micrograph (x20000) shown in Figure 3. The particles have an isotropic shape of 0.6 μm, the particle size is uniform, and
Each particle was an independent particle.

70 g of the above-mentioned hematite particle powder was put into a retort reduction container (No. 1), and H ₂ gas was passed through the container at a rate of 10 per minute while driving and rotating the container, and the container was reduced at a reduction temperature of 420°C.

The metal magnetic particle powder, which is mainly composed of iron and exhibits an isotropic shape obtained by reduction, is once immersed in a toluene solution to prevent rapid oxidation when taken out into the air. By evaporating this, a stable oxide film was formed on the particle surface.

As a result of electron microscopy observation, the metal magnetic particle powder whose main component is iron obtained in this way has an average diameter of
The particles had an isotropic shape of 0.6 μm and were uniform in particle size. Also, as a result of magnetic measurement, the coercive force Hc is 263 Oe, and the saturation magnetization σs is 187 emu/g.
It was hot.

Example 2 FeCl ₃ concentration when producing β-FeOOH
β-FeOOH with a specific surface area of 240 m ² /g was obtained in the same manner as in Example 1 except that the amount was 0.01 mol/g.

PH containing the above 0.01mol/β-FeOOH particles
Put the acidic suspension of 1.4 into a closed container and heat it at 105℃.
Hydrothermal treatment for 12 hours produced a reddish brown precipitate. The particles obtained by washing the reddish-brown precipitate with water, filtering, and drying were found to be hematite as a result of X-ray diffraction, and as is clear from the electron micrograph (×20000) shown in Figure 4, the particles had an average particle diameter of 0.15 μm. The particles had a square shape, were symmetrical, and each particle was independent.

70 g of the above-mentioned hematite particles were put into a retort reduction container (No. 1), and H ₂ gas was passed through the container at a rate of 10 per minute while the container was driven and rotated, thereby being reduced at a reduction temperature of 400°C.

The metal magnetic particle powder, which is mainly composed of iron and exhibits an isotropic shape obtained by reduction, is once immersed in a toluene solution to prevent rapid oxidation when taken out into the air. By evaporating this, a stable oxide film was formed on the particle surface.

As a result of electron microscopy observation, the metal magnetic particle powder whose main component is iron obtained in this way has an average diameter of
The particles had an isotropic shape of 0.15 μm and were uniform in particle size. In addition, as a result of magnetic measurement,
Coercive force Hc is 280Oe, saturation magnetization σs is
It was 177.5 emu/g.

Comparative example 1 Ferrous sulfate aqueous solution containing 1.5 mol/Fe ²⁺ 20
3.45-N prepared in advance in the reactor
In addition to NaOH aqueous solution 20 (corresponds to 1.15 equivalents to Fe ²⁺ ), Fe
An aqueous ferrous salt solution containing (OH) ₂ was produced.

The above ferrous salt aqueous solution containing Fe(OH) ₂ was heated to a temperature of 90°C.
Magnetite particle powder was produced by bubbling air at 100 °C per minute for 220 minutes.

As is clear from the electron micrograph (×20000) shown in FIG. 5, the obtained magnetite particle powder has the following properties:
The particles had an isotropic shape with an average diameter of 0.2 μm.

The above magnetite particles were heated and reduced in the same manner as in Example 1, and a stable oxide film was further formed on the particle surface.

As a result of electron microscopy observation, the metal magnetic particle powder whose main component is iron obtained in this way has an average diameter of
The particles had an isotropic shape of 0.2 μm, and the particle size was asymmetric. In addition, as a result of magnetic measurement,
The coercive force Hc was 236 Oe, and the saturation magnetization σs was 147 emu/g.

〔Effect of the invention〕

According to the method for producing iron-based metal magnetic particles exhibiting an isotropic shape according to the present invention, as shown in the above-mentioned Examples and Comparative Examples, a high coercive force is obtained.
It is a metal magnetic particle powder mainly composed of iron, which has Hc and a large saturation magnetization σs, and has an isotropic shape with a uniform particle size. It is suitable as a magnetic particle powder for magnetic recording.

[Brief explanation of drawings]

1, 3 to 5 are electron micrographs, and FIG. 1 is the β-FeOOH particle powder used in producing hematite in Example 1, and FIGS. 3 and 4 are respectively 1 and Example 2, and FIG. 5 shows the magnetite particles obtained in Comparative Example 1. FIG. 2 is an X-ray diffraction diagram of the hematite particles obtained in Example 1.

Claims (1)

[Claims] 1 β- with a specific surface area of 150 m ² /g or more
By hydrothermally treating an acidic suspension containing FeOOH particles at a concentration of less than 0.1 mol/in at a temperature range of 100 to 130°C, hematite particles having an isotropic shape with uniform particle size are generated, and the hematite particles are is heated and reduced in a reducing gas to produce iron-based magnetic particles with an isotropic shape with uniform particle size. Method for producing metal magnetic particle powder.