JPH0573698B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing magnetic iron oxide particles having an isotropic shape, and more specifically, a method for producing magnetic iron oxide particles having a uniform particle size and independent particles. Moreover, high coercive force
The present invention relates to a method for producing magnetic iron oxide particles having an isotropic shape with Hc and large saturation magnetization σs.

The isotropically shaped magnetic iron oxide particles produced by the present invention are mainly used as pigment powder for paints, magnetic particles for magnetic recording, and material powder for magnetic toner for electrostatic copying. .

[Conventional technology]

Conventionally, magnetite particles have been widely used as black pigments and magnetite particles as brown pigments, and from the viewpoint of improving work efficiency and improving coating film properties in the energy-saving era,
In the production of paints, there is an increasing demand for improvement in the dispersibility of magnetic iron oxide particles exhibiting an isotropic shape, such as magnetite particles and maghemite particles, in a vehicle.

For a magnetic iron oxide particle powder exhibiting an isotropic shape with excellent dispersibility, it is necessary that the particle size is uniform and that each particle is independent.

Furthermore, in recent years, electrostatic copying machines have become widespread, and 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 iron oxide particles in a synthetic resin. It is necessary that the particle size is uniform and the individual particles are independent, resulting in excellent dispersibility, and that it also has a high coercive force Hc and a large saturation magnetization σs.

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

Next, 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.

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 properties of magnetic particles suitable for satisfying the above requirements for magnetic recording media include excellent dispersibility due to uniform particle size and independent particles, and high coercive force. Hc and large saturation magnetization σs. This phenomenon is
For example, ``Development of magnetic materials and high dispersion technology of magnetic particles'' (1982) published by Sogo Gijutsu Center Co., Ltd.
On page 74, there is a statement that says, "...The major challenges in designing magnetic coating layers to overcome the factors for high-density recording are (1) uniform dispersion of magnetic particles..." and “…” of Special Publication No. 61-31057.
...High recording density characteristics and high output characteristics are required. The characteristics of magnetic particles suitable for magnetic recording to satisfy the above requirements for floppy disks are high coercive force Hc and large saturation magnetization σs...
It is as stated in the following statement:

As mentioned above, isotropically shaped magnetic iron oxide particles such as magnetite particles and maghemite particles are used in various fields, but magnetic iron oxide particles are commonly required in all fields. The characteristics of the powder are that the particle size is uniform and the individual particles are independent, resulting in excellent dispersibility, and furthermore, it has a high coercive force Hc and a large saturation magnetization σs.

Conventionally, as a method for producing magnetic iron oxide particles exhibiting an isotropic shape, an oxygen-containing gas is passed through a reaction aqueous solution containing ferrous hydroxide obtained by reacting an aqueous ferrous salt solution with an alkali. A known method is to generate magnetite particles from an aqueous solution, and then, if necessary, heat and oxidize the magnetite particles in air to obtain maghemite particles.

[Problem that the invention seeks to solve]

Magnetic iron oxide particles exhibit excellent dispersibility due to uniform particle size and independent particles, and exhibit an isotropic shape with high coercive force Hc and large saturation magnetization σs. Although this is currently the most requested method, when using the known method as described above, the particle size of magnetite particles produced from an aqueous solution is asymmetric, and it is difficult to say that the individual particles are independent. The particle size of the maghemite particles obtained by heating and oxidizing the magnetite particles is naturally asymmetric, and it is difficult to say that the individual particles are independent.

In addition, the magnetic properties of magnetite particle powder generated from an aqueous solution have a coercive force Hc of about 120 Oe at most,
The saturation magnetization σs is as low as about 86 mu/g at most, and the magnetic properties of the maghemite particles obtained by heating and oxidizing the above-mentioned magnetite particles have a coercive force Hc of about 100 Oe at most and a saturation magnetization σs.
was as low as 75 mu/g at most.

Therefore, magnetic iron oxide particles exhibit excellent dispersibility due to uniform particle size and independent particles, and exhibit an isotropic shape with high coercive force Hc and large saturation magnetization σs. There is a strong need to establish technical means to obtain powder.

[Means for solving the problem] The present inventor has discovered that the particle size is uniform and the individual particles are independent, resulting in excellent dispersibility.
Furthermore, the present invention was achieved as a result of various studies aimed at obtaining isotropically shaped magnetic iron oxide particles having a high coercive force Hc and a large saturation magnetization σs.

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. Generate hematite particles with a uniform isotropic shape, heat and reduce the hematite particles in a reducing gas to produce magnetite particles with a uniform isotropic shape, or further oxidize. This is a method for producing magnetic iron oxide particles having an isotropic shape, by forming maghemite particles having an isotropic shape with uniform particle size.

[Effect]

First, the most important point in the present invention is that β-FeOOH particles with a specific surface area of 150 m ² /g or more are used.
Acidic suspension containing less than 0.1mol/100~
When hydrothermally treated in a temperature range of 130°C, it is possible to produce hematite particles with a uniform particle size and an isotropic shape in which each individual particle is independent. The magnetite particles produced and the maghemite particles obtained by further heating and oxidation, if necessary, also maintain and inherit the particle shape of the hematite particles that are the starting material, so the particle size is uniform and each particle is independent. This is the fact that the particles have an isotropic shape.

The magnetic properties of the magnetite particles obtained in the present invention are high, with a coercive force Hc of 200 Oe or more and a saturation magnetization σs of 88 emu/g or more.
The magnetic properties of maghemite particle powder are coercive force Hc
is 130 Oe or more, and the saturation magnetization σs is high, 76 emu/g or more.

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 and oxidation treatment in a reducing gas in the present invention can be performed by conventional methods.

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. magnetic iron oxide particles can be obtained.

〔Example〕

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

In addition, the average diameter of the particles in the following examples is the average of numerical values measured from electron micrographs, and the specific surface area is the 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, with a specific surface area of 190
m ² /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 were hematite as shown in the X-ray diffraction shown in Figure 2, and the electron micrograph (×20000) shown in Figure 3
As is clear from the above, the particles have an isotropic shape with an average particle diameter 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 1, and H ₂ gas was passed through the container at a rate of 1 minute per minute while driving and rotating the container, and the container was reduced at a reduction temperature of 350° C. to obtain magnetite particle powder. As is clear from the electron micrograph (×20000) shown in Figure 4, the obtained magnetite particles have a uniform particle size and an average diameter in which each particle is independent.
The particles had an isotropic shape of 0.6 μm. Further, as a result of magnetic measurement, the coercive force Hc was 261 Oe, and the saturation magnetization σs was 92 emu/g.

70g of the above magnetite particle powder in air at 300℃
was oxidized for 60 minutes to obtain maghemite particle powder.

As is clear from the electron micrograph (×20000) shown in FIG. 5, the obtained maghemite particle powder has the following characteristics:
The particles were uniform in particle size and had an isotropic shape with an average diameter of 0.6 μm in which each particle was independent. ,
Further, as a result of magnetic measurement, the coercive force Hc was 152 Oe, and the saturation magnetization σs was 78.5 emu/g.

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
Place the acidic suspension of 1.4 in a closed container and heat it at 105℃ for 12
Hydrothermal treatment for 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 by X-ray diffraction, and were particles with an isotropic shape with an average particle diameter of 0.15 μm as a result of electron micrograph observation. The particle size was uniform, and each particle was an independent particle.

70 g of the above-mentioned hematite particle powder was put into a retort reduction container 1, and H ₂ gas was passed through the container at a rate of 1 minute per minute while driving and rotating the container, and the container was reduced at a reduction temperature of 350° C. to obtain magnetite particle powder.

As a result of electron microscopic observation, the obtained magnetite particles were found to be isotropic particles with a uniform particle size and an average diameter of 0.15 μm in which individual particles were independent. In addition, as a result of magnetic measurement, the coercive force
Hc was 270 Oe, and saturation magnetization σs was 90 emu/g.

70g of the above magnetite particle powder in air at 300℃
was oxidized for 60 minutes to obtain maghemite particle powder.
As a result of electron microscopic observation, the obtained maghemite particles were found to be isotropic particles with uniform particle size and an average diameter of 0.15 μm in which individual particles were independent. In addition, as a result of magnetic measurement, the coercive force
Hc was 184 Oe, and saturation magnetization σs was 77.9 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. 7, the obtained magnetite particle powder has the following properties:
The particle size was asymmetric, and the particles had an average diameter of 0.2 μm, making it difficult to say that each particle was independent. Further, as a result of magnetic measurement, the coercive force Hc was 116 Oe, and the saturation magnetization σs was 84.5 emu/g.

The maghemite particles obtained by oxidizing the above magnetite particles in the same manner as in Example 1 are shown in FIG.
As is clear from the electron micrograph (x20,000) shown in Figure 2, the particles were asymmetric in particle size and had an average diameter of 0.2 μm, making it difficult to say that the individual particles were independent. In addition, as a result of magnetic measurement, the coercive force Hc is 98Oe,
The saturation magnetization σs was 72.0 emu/g.

〔Effect of the invention〕

According to the method for producing magnetic iron oxide particles exhibiting an isotropic shape according to the present invention, as shown in the above examples and comparative examples, the particle size is uniform and the individual particles are independent. Therefore, it has excellent dispersibility, as well as high coercive force Hc and large saturation magnetization σs.
Since it is possible to obtain magnetic iron oxide particles having an isotropic shape having .

[Brief explanation of the drawing]

1, 3 to 8 are all electron micrographs, and FIG. 1 is the β-FeOOH particle powder used as a starting material when producing hematite in Example 1, and FIGS. 3 and 6 are Hematite particles obtained in Example 1 and Example 2, respectively; FIGS. 4 and 7 show magnetite particles obtained in Example 1 and Comparative Example 1, respectively; FIGS. 5 and 8
are maghemite particles obtained in Example 1 and Comparative Example 1, respectively. 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 exhibiting an isotropic shape with uniform particle size are generated, and the hematite particles are is thermally reduced in a reducing gas to produce magnetite particles with a uniform particle size and an isotropic shape, or further oxidized to produce maghemite particles with a uniform particle size and an isotropic shape. A method for producing magnetic iron oxide particles exhibiting a characteristic isotropic shape.