JPH0317774B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention is characterized in that the particle surface is composed of magnetite ( FeO _y・
Plate-shaped metamorphosed with Fe ₂ O ₃ , but O<y≦1)
A plate-shaped Ba ferrite fine particle powder for magnetic recording consisting of BaFe ₁₂ O ₁₉ fine particles and a method for producing the same.

In recent years, appropriate coercive force (Hc) and large magnetization (M)
There is an increasing demand for ferromagnetic non-acicular particles having a high dispersibility and good dispersibility as magnetic materials for recording, particularly magnetic materials for perpendicular magnetic recording.

Generally, Ba ferrite particles are well known as ferromagnetic non-acicular particles.

However, Ba ferrite particles obtained by dry method usually have low coercive force.
It has a value of 30,000e or more, which is so high that it is not preferable as a magnetic material for magnetic recording. In other words, as a magnetic material for magnetic recording, 300
~10000e is requested.

Therefore, as a method to reduce the coercive force of Ba ferrite particles, for example, Fe in Ba ferrite can be
() with other metal ions (e.g. Co())
Attempts have already been made to reduce Hc while minimizing the change in saturation magnetization by substituting Ti() with Ti().

Next, regarding the average diameter, conventional Ba ferrite particle powder becomes polycrystalline with an average diameter of several μm due to sintering, and even when crushed, it becomes polycrystalline with an average diameter of several μm.
Since it is about 1 μm, it has poor dispersibility when made into a paint, and is not preferred as a magnetic material for magnetic recording.

That is, magnetic materials for magnetic recording are required to be as fine as possible, especially with an average diameter of about 0.05 to 0.3 μm. This fact is true, for example, in JP-A-53-
For example, the statement in Japanese Patent Application Laid-open No. 125219 (1982) that "...there is a difficulty in uniformly coating a magnetic recording material with a thickness exceeding 0.5μ...", and the statement in Japanese Patent Application Laid-open No. 125219-1982 "...perpendicular magnetization recording is in-plane recording. However, its significance becomes clear in the region where the recording wavelength is 1 μm or less.

However, in order to perform sufficient recording and reproduction in this wavelength range, the crystal grain size of the above ferrite must be approximately
Desirably 0.3μm or less. However, if it is about 0.01 μm, it will not exhibit the desired ferromagnetism, so a suitable crystal grain size is required to be about 0.01 to 0.3 μm. For example, the average particle size of the barium ferrite magnetic powder is preferably 0.3 μm or less, and fine particles with an average particle size of 0.03 to 0.3 μm are particularly suitable. The reason is that the average particle size
If it is less than 0.03 μm, it will not exhibit sufficient ferromagnetism required for magnetic recording, and if it exceeds 0.3 μm, it will be difficult to carry out magnetic recording advantageously as high-density recording. ” is as stated.

Furthermore, as for the magnetization value, it is necessary to have it as large as possible, and this fact has been demonstrated, for example, by
As stated in Japanese Patent No. 56-149328, "... magnetoplumbite ferrite used as a magnetic recording medium material is required to have as large a saturation magnetization as possible."

On the other hand, one of the conventional methods for producing Ba ferrite is a method in which an alkaline suspension containing Ba ions and Fe() is subjected to hydrothermal treatment using an autoclave as a reaction device (hereinafter referred to simply as hydrothermal treatment). According to this hydrothermal treatment method, Ba ferrite particles can be precipitated by selecting reaction conditions.

The present inventor has been involved in the research and development of plate-shaped Ba ferrite particles using a hydrothermal treatment method for many years. We have obtained the knowledge that ferrite particles can be obtained.

However, in order to obtain a large magnetization value, especially 40 emug ^-1 or more, plate-shaped Ba ferrite particles having an average diameter of 0.05 to 0.3 μm have a coercive force of 10,000 e.
All I could get was more than that.

In view of the above, the present inventor set the coercive force of plate-shaped Ba ferrite particles having an average diameter of 0.05 to 0.3 μm to 300 to 10,000 e in a hydrothermal treatment method, and
The present invention was achieved as a result of various studies aimed at further increasing the magnetization value.

That is, in the present invention, the particle surface is composed of magnetite ( FeO
Magnetic recording plate made of plate-shaped BaFe ₁₂ O ₁₉ fine particles metamorphosed with _y・Fe ₂ O ₃ (O<y≦1)
Ba ferrite fine particles powder, plate-shaped BaFe ₁₂ O ₁₉ particles, and total Fe in the plate-shaped BaFe ₁₂ O ₁₉ particles ()
PH containing less than 50 atomic % of Fe()
Mix with 8.0~14.0 Fe(OH) ₂ alkaline suspension;
By heat-treating the mixture in a non-oxidizing atmosphere at a temperature range of 50 to 100°C, the above-mentioned plate-like
This is a method for producing plate-shaped Ba ferrite fine particles for magnetic recording by modifying the particle surface of BaFe ₁₂ O ₁₉ fine particles with magnetite ( FeO _y ·Fe ₂ O ₃ , where O<y≦1).

Next, the configuration of the present invention will be described.

The present inventor has obtained an average diameter obtained by a hydrothermal treatment method.
In order to set the coercive force of the plate-shaped Ba ferrite particles having a size of 0.05 to 0.3 μm to 300 to 10,000 e, and to further increase the magnetization value, various studies were conducted to develop plate-shaped BaFe ₁₂ O _{19 fine} particles and the plate-shaped BaFe ₁₂ O ₁₉ fine particles. PH8.0~ Contains less than 50 atomic% of Fe() relative to the total Fe() in
14.0 of Fe(OH) ₂ alkali suspension and heat-treating the mixture in a non-oxidizing atmosphere at a temperature range of 50 to 100°C, the plate-like BaFe ₁₂ O ₁₉ fine particles The particle surface is coated with magnetite ( FeO _y・Fe ₂ O ₃ ,
However, it can be metamorphosed at O<y≦1), and as a result, the coercive force of plate-like BaFe ₁₂ O ₁₉ fine particles is
It was found that it is possible to increase the magnetization value to 10,000e and increase the magnetization value.

And the metamorphism rate of magnetite is mainly due to excess
Depends on NaOH concentration and heating temperature,
We obtained the knowledge that the magnetism and electrical conductivity of BaFe ₁₂ O ₁₉ fine particles metamorphosed with magnetite are influenced by the composition and magnetite metamorphosis rate.

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

The amount of Fe(OH) ₂ in the present invention is
BaFe ₁₂ O ₁₉ It is less than 50 atomic % of the total Fe () in the fine particles.

If it exceeds 50 atomic %, Fe(OH) ₂ that does not contribute to magnetite metamorphosis remains or is mixed as an oxide.

If it is less than 0.1 atomic %, metamorphosis by magnetite is not sufficient.

Platy BaFe ₁₂ O ₁₉ fine particles and Fe in the present invention
The order of mixing with the (OH) ₂ alkali suspension may be either first or simultaneously.

The pH in the present invention is 8.0 to 14.0. PH is 8.0
If it is less than that, it is difficult for Fe(OH) ₂ to exist stably. In addition, if it is strongly alkaline, Fe(OH) ₂ will exist stably, and at the same time Fe(OH) ₂ will cause plate-like Ba
Since a modification reaction of ferrite particles also occurs, the object of the present invention can be fully achieved with a pH of 14.0 or less, considering industrial effects.

The heating temperature in the present invention is 50 to 100°C.
If the temperature is less than 50°C, Fe in the present invention
The metamorphism reaction of plate-like Ba ferrite particles by (OH) ₂ becomes difficult to occur. Further, although the modification reaction occurs even when the temperature exceeds 100°C, considering that it is carried out in an aqueous solution, the object of the present invention can be sufficiently achieved at a temperature of 100°C or lower.

The present invention configured as described above has the following effects.

That is, according to the present invention, the magnetization M value in a magnetic field of 10 KOe is 40 emu/g or more, and the coercive force Hc
is 300 to 10,000e, and the particle surface is modified with magnetite and has an average diameter of 0.05 to 0.3 μm.
Since BaFe ₁₂ O ₁₉ fine particles can be obtained, it is suitable as a magnetic material for magnetic recording, especially a magnetic material for perpendicular magnetic recording.

In addition, since the plate-shaped Ba ferrite fine particles obtained by the present invention have the particle surface modified with magnetite, the particle surface itself is modified and the electrical resistance is lowered.

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 and Comparative Examples is a value measured using an electron micrograph.

In addition, the magnetization value was measured in a powder state in a magnetic field of 10KOe, and the coercive force was measured at a filling degree of 1.6.
It is expressed as a value measured in g/cm ³ .

Example 1 120 plate-shaped BaFe ₁₂ O ₁₉ particles with an average diameter of 0.2 to 0.3 μm
g (specific surface area S value 31m ² /g, magnetization M value 36emug ^-1 ,
Coercive force Hc1050Oe) mixed with 0.17 mol Fe(OH) ₂ alkaline suspension (Fe() to Fe() 13.1
Corresponds to atomic percent. ), then add water to bring the total volume to 1.5 (PH12.3), heat the mixture to 90°C, and heat it at this temperature while preventing air from entering as much as possible. Stir the solution for 1 hour.

The produced dark brown particles were separately washed with water, treated with acetone, and then dried at room temperature.

As a result of electron microscopic observation, no significant difference in particle shape or size was found before and after the reaction.

The obtained dark brown particle powder has a specific surface area S value of 28
m ² /g, coercive force Hc690Oe, magnetization M value
It was 45 emug ^-1 .

FIG. 1 is an X-ray diffraction diagram of the obtained dark brown particles. In FIG. 1, peak A indicates a Ba ferrite peak, and peak B indicates a magnetite peak, indicating a two-phase structure.

Example 2 Platy BaFe ₁₂ O ₁₉ particles with an average diameter of 0.15 to 0.25 μm
120g (specific surface area S value 31m ² /g, magnetization M value
36emug ^-1 , coercivity Hc1050Oe) and 0.21mol Fe
(OH) ₂ mixed with alkaline suspension (for Fe()
Fe() corresponds to 16.2 atomic%. ), then add water to bring the total volume to 1.5 (PH12.4), and then heat the mixture to 90°C,
1 at this temperature while preventing air intrusion as much as possible.
Stir the solution for an hour.

The produced dark brown particles were separately washed with water, treated with acetone, and then dried at room temperature.

As a result of electron microscopic observation, no significant difference in particle shape or size was found before and after the reaction.

The obtained dark brown particle powder has a specific surface area S value of 27
m ² /g, coercive force Hc520Oe, magnetization M value
It was 49 emug ^-1 .

In addition, as a result of X-ray diffraction, the obtained dark brown particles showed peaks of magnetite and Ba ferrite, indicating that it had a two-phase structure.

Example 3 Platy BaFe ₁₂ O ₁₉ particles with an average diameter of 0.2 to 0.3 μm
120g (specific surface area S value 28m ² /g, magnetization M value
39emug ^-1 , coercivity Hc1120Oe) and 0.31mol Fe
(OH) ₂ mixed with alkaline suspension (for Fe()
Fe() corresponds to 23.9 atomic%. ), then add water to bring the total volume to 1.5 (PH12.5), and then heat the mixture to 70°C,
1 at this temperature while preventing air intrusion as much as possible.
Stir the solution for an hour.

The produced dark brown particles were separately washed with water, treated with acetone, and then dried at room temperature.

As a result of electron microscopic observation, no significant difference in particle shape or size was found before and after the reaction.

The obtained dark brown particle powder has a specific surface area S value of 24
m ² /g, coercive force Hc620Oe, magnetization M value
It was 52 emug ^-1 .

In addition, as a result of X-ray diffraction, the obtained dark brown particles showed peaks of magnetite and Ba ferrite, indicating that it had a two-phase structure.

[Brief explanation of the drawing]

FIG. 1 is an X-ray diffraction diagram of the dark brown particles obtained in Example 1. In FIG. 1, peak A indicates the peak of Ba ferrite, and peak B indicates the peak of magnetite.

Claims (1)

[Claims] 1. The particle surface is magnetite ( FeO _y・Fe ₂ O ₃ ,
However, plate-shaped metamorphosed with 0<y≦1)
Plate-shaped Ba ferrite fine particle powder for magnetic recording consisting of BaFe ₁₂ O ₁₉ fine particles. 2 Plate-shaped BaFe ₁₂ O ₁₉ fine particles and the plate-shaped BaFe ₁₂ O ₁₉
Fe(OH)2 is mixed with an alkaline suspension of Fe(OH) ₂ with a pH of 8.0 to 14.0 containing 50 atomic % or less of Fe() based on the total Fe() in the fine particles, and the mixed solution is placed in a non-oxidizing atmosphere. By heating in a temperature range of 50 to 100°C, the particle surface of the plate-shaped BaFe ₁₂ O ₁₉ fine particles becomes magnetite ( FeO _y・Fe ₂ O ₃ , where O<y≦1).
A magnetic recording plate characterized by being metamorphosed by
Manufacturing method of Ba ferrite fine particle powder.