JPH0727808B2 - Plate-shaped Ba ferrite fine particle powder for magnetic recording and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a method for producing a plate-like Ba ferrite fine particle powder, wherein the particle surface has spinel type ferrite (M ²⁺ x
Fe ²⁺ yO · Fe ₂ O ₃ However, 0 <x ≦ 1, 0 ≦ y <1, 0 <x
+ Y ≦ 1, M is a plate-like BaO · nFe ₂ O ₃ (4) modified with Ni, Mn, Zn, Cu, or Mg selected from one or more kinds.
≦ n ≦ 6) Plate-like Ba ferrite fine particle powder for magnetic recording comprising fine particles and a method for producing the same.

[Conventional technology]

In recent years, for example, as described in JP-A-55-86103, it has an appropriate coercive force and a large magnetization value, and
Ferromagnetic non-acicular particles having an appropriate average particle size are being demanded as magnetic materials for recording, particularly as magnetic materials for perpendicular magnetic recording.

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

As one of the conventional methods for producing plate-like Ba ferrite, a method of hydrothermally treating an alkaline suspension containing Ba ions and Fe (III) using an autoclave as a reactor (hereinafter, simply referred to as hydrothermal treatment The law is known).

First, regarding magnetic properties, the coercive force of the plate-like Ba ferrite particle powder for magnetic recording is generally required to be about 300 to 1000 Oe.
In order to reduce the coercive force of the ferrite fine particle powder to obtain an appropriate coercive force, part of Fe (III) in ferrite is Ti (IV)
And Co (II) or Ti (IV), Co (II) and divalent metal ions M (II) other than Co (II) such as Mn and Zn have been proposed.

Also, the magnetization value must be as large as possible,
This fact is described, for example, in "...
・ Saturation magnetization as large as possible for magnetoplumbite ferrite used as magnetic recording medium material ・ ・
Is required. It is as described.

Next, as to the particle size of the plate-like Ba ferrite fine particle powder for magnetic recording, it is required that the particle size is as fine as possible, especially 0.3 μm or less.

This fact is described, for example, in "...
.. It is in the region where the recording wavelength is 1 .mu.m or less that the perpendicular magnetization recording has an advantage over the longitudinal recording.
However, in order to perform sufficient recording / reproducing in this wavelength range, the crystal grain size of the ferrite is preferably about 0.3 μm or less. However, if it becomes about 0.01 μm, it does not exhibit the desired ferromagnetism, so an appropriate crystal grain size is 0.01 to 0.3 μm.
About m is required. Is as described above.

[Problems to be solved by the invention]

Plate-like Ba ferrite particle powder having an appropriate coercive force and a large magnetization value and having an appropriate average particle size is currently most demanded, but in the hydrothermal treatment method as described above, the reaction conditions are By selecting, various Ba ferrite particles will precipitate. The precipitated particles usually have a hexagonal plate shape, and the magnetic properties differ depending on the particle size distribution and average diameter depending on the production conditions.

The present inventor has been involved in research and development of plate-like Ba ferrite particles by a hydrothermal treatment method for many years, and in the process, the average diameter of 0.05 to 0 depending on reaction conditions.
It has been found that plate-like Ba ferrite particles having 3 μm can be obtained.

However, the plate-like B having the above average diameter of 0.05 to 0.3 μm
The a-ferrite particles had a coercive force of 1000 Oe or more when a large magnetization value, especially 40 emug ^-1 or more, was to be obtained.

Therefore, there is a strong demand for establishment of a method for obtaining plate-like Ba ferrite particles having an appropriate coercive force and a large magnetization value and an appropriate average particle size.

[Means for solving problems]

In view of the above, the present inventor has conducted various studies to increase the coercive force of plate-like Ba ferrite particles having an average diameter of 0.05 to 0.3 μm in the hydrothermal treatment method to 300 to 1000 Oe and further increase the magnetization value. As a result, the present invention has been achieved.

That is, according to the present invention, the surface of the particle is spinel type ferrite (M
²⁺ xFe ²⁺ yO · Fe ₂ O ₃ However, 0 <x ≦ 1, 0 ≦ y <1, 0 <
x + y ≦ 1, M is 1 selected from Ni, Mn, Zn, Cu and Mg
Plate-like BaO ・ nFe ₂ O modified with one or more species
₃ (4 ≦ n ≦ 6) fine particles of plate-like Ba ferrite fine particles for magnetic recording and plate-like BaO · nFe ₂ O ₃ (4 ≦ n ≦ 6)
M ²⁺ (one or more selected from Ni, Mn, Zn, Cu, Mg) or M ^{2 with} respect to the fine particles and all Fe (III) in the plate-like BaO · nFe ₂ O ₃ fine particles ^{+ And} Fe 2 ⁺ is mixed with an alkaline suspension having a pH of 8.0 to 14.0 containing 0.1 to 30.0 atomic% of the mixture, and the mixed solution is heat-treated in a temperature range of 50 to 100 ° C.,
The particle surface of the plate-like BaO · nFe ₂ O ₃ fine particles is spinel-type ferrite (M ²⁺ xFe ²⁺ yO · Fe ₂ O ₃ where 0 <x ≦ 1, 0 ≦
It is a method for producing a tabular Ba ferrite fine particle powder for magnetic recording, which comprises denaturing y <1, 0 <x + y ≦ 1).

[Work]

First, the most important point in the present invention is plate-like BaO · nFe ₂ O.
₃ fine particles and all Fe (III) in the plate-like BaO.nFe ₂ O ₃ fine particles
On the other hand, M ²⁺ (one or more selected from Ni, Mn, Zn, Cu, Mg) or M ²⁺ and Fe ²⁺ in a proportion of 0.1 to 30.0 atomic% pH 8.0 to 14.0 When mixed with an alkaline suspension of, and heat-treating the mixed solution in a temperature range of 50 to 100 ° C.,
The particle surface of the plate-like BaO · nFe ₂ O ₃ fine particles is spinel-type ferrite (M ²⁺ xFe ²⁺ yO · Fe ₂ O ₃ where 0 <x ≦ 1, 0 ≦
y <1, 0 <x + y ≦ 1), and as a result, the coercive force of the plate-like BaO.nFe ₂ O ₃ fine particles is 300 to 1000 O.
The point is that it can be set to e and the magnetization value can be increased.

In the present invention, the conversion rate of spinel type ferrite is mainly influenced by excess NaOH concentration and heating temperature, and the magnetic properties and conductivity of the BaO.nFe ₂ O ₃ fine particles modified by the spinel type ferrite produced are composition and spinel. Depends on the rate of transformation by type ferrite.

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

Plate BaO · nFe ₂ O ₃ fine particles in the present invention may be used as it is a plate-like BaO · nFe ₂ O ₃ particles produced from an aqueous solution, also 500 a plate-like BaO · nFe ₂ O ₃ fine particles Plate-like BaO.nFe ₂ O ₃ fine particles whose magnetization value is increased by heat treatment in the temperature range of 900 ° C. may be used, and the same effect can be obtained in any case.

The amount of M ²⁺ or M ²⁺ and Fe ²⁺ in the present invention is a plate-like BaOn.
It is 0.1 to 30.0 atomic% with respect to the total Fe (III) in the Fe ₂ O ₃ fine particles.

If it is less than 0.1 atomic%, the transformation by spinel type ferrite is not sufficient.

If it exceeds 30.0 atom%, the coercive force will drop extremely,
It is not preferable as a magnetic material for magnetic recording.

Plate-like BaFe ₁₂ O ₁₉ fine particles and M ²⁺ or M ²⁺ and F in the present invention
The order of mixing with the alkaline suspension containing e ²⁺ may be either first or simultaneously.

The pH in the present invention is 8.0 to 14.0. When the pH is less than 8.0, it is difficult to stably exist M ²⁺ or M ²⁺ and Fe ²⁺ hydroxide. If it is strongly alkaline, M ²⁺ or M ²⁺ and
The hydroxide of Fe ²⁺ exists stably, and at the same time, M ²⁺ or M ²⁺
Also, since a conversion reaction of plate-like Ba ferrite particles due to Fe ²⁺ hydroxide also occurs, the pH of 14.0 or less is sufficient to achieve the object of the present invention in view of industrial effects.

The heating temperature in the present invention is 50 to 100 ° C.

When the temperature is lower than 50 ° C., the conversion reaction of the plate-like Ba ferrite particles due to M ²⁺ or hydroxides of M ²⁺ and Fe ²⁺ in the present invention is difficult to occur. Further, the metamorphism reaction occurs at a temperature exceeding 100 ° C., but 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.

〔Example〕

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

In addition, the average diameter of the particles in the following Examples and Comparative Examples is a value measured by an electron micrograph.

The magnetization value is measured in a powder state in a magnetic field of 10 KOe, and the coercive force is a value measured at a filling degree of 1.6 g / cm ³ .

Example 1 A plate-like Ba ferrite particle powder produced by a hydrothermal treatment method was used.
The average diameter obtained by heat treatment at 700 ℃ is 0.2 ~
150 μg of 0.3 μm tabular BaFe ₁₂ O ₁₉ particles (specific surface area S value 23 m ² /
g, magnetization M value 45emug ^-1 , coercive force Hc2000 Oe) and 0.10mol F
e (OH) ₂ and an alkaline suspension containing 0.01 mol of Mn (OH) ₂ are mixed (M ²⁺ and Fe ²⁺ correspond to 6.8 atom% with ^respect to Fe (III)), and then By adding water,
After adjusting the total volume to 1.5 (pH 12.3), the temperature of the mixed solution was heated to 90 ° C., and the solution was stirred at this temperature for 1 hour.

The black-brown particle powder thus produced was separately washed with water, treated with acetone, and then dried at room temperature.

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

The obtained blackish brown particle powder had a specific surface area S value of 26 m ² / g, a coercive force Hc900 Oe, and a magnetization M value of 50 emug ^-1 .

As a result of the X-ray diffraction pattern and the fluorescent X-ray analysis shown in FIG. 1, the obtained black-brown particle powder shows peaks of Ba ferrite and Mn ferrite, and it can be seen that the powder has a two-phase structure. In FIG. 1, peak A indicates the peak of Ba ferrite,
Peak B is the peak of Mn ferrite.

Example 2 A plate-like Ba ferrite particle powder produced by a hydrothermal treatment method was used.
The average diameter obtained by heat treatment at 800 ℃ is 0.15
〜0.25μm plate-like BaFe ₁₂ O ₁₉ particles 150g (specific surface area S value 28m
² / g, magnetization M value 47emug ^-1 , coercive force Hc3700 Oe) and 0.21mol
Of Fe (OH) ₂ and 0.01 mol of Cu (OH) ₂ in an alkaline suspension (for Fe (III), Mn ²⁺ and Fe ²⁺ are ^equal to 13.
This corresponds to 6 atom%. ), And then water was added to bring the total volume to 1.5 (pH 12.4), and then the temperature of the mixed liquid was heated to 90 ° C., and the liquid was stirred for 1 hour at this temperature.

The black-brown particle powder thus produced was separately washed with water, treated with acetone, and then dried at room temperature.

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

The obtained blackish brown particle powder had a specific surface area S value of 29 m ² / g, a coercive force Hc 800 Oe, and a magnetization M value of 55 emug ^-1 .

Further, the obtained blackish brown particle powder is subjected to X-ray diffraction and fluorescence X.
As a result of the line analysis, the peaks of Cu ferrite and Ba ferrite are shown, and it can be seen that the two-phase structure is shown.

Example 3 150 g of plate-shaped BaFe ₁₂ O ₁₉ particles having an average diameter of 0.2 to 0.3 μm (specific surface area S value 32 m ² / g, magnetization M value 38 emug ⁻¹ , coercive force Hc1200 O
e) and an alkaline suspension containing 0.31 mol of Fe (OH) ₂ and 0.04 mol of Ni (OH) ₂ (Fe (III) vs. Fe (I
I) and Ni (II) correspond to 21.6 atomic%. ), And then water was added to bring the total volume to 1.5 (pH 12.5), and then the temperature of the mixed solution was brought to 70 ° C. by heating, and the solution was stirred at this temperature for 1 hour.

The black-brown particle powder thus produced was separately washed with water, treated with acetone, and then dried at room temperature.

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

The obtained blackish brown particle powder had a specific surface area S value of 31 m ² / g, a coercive force Hc550 Oe, and a magnetization M value of 52 emug ^-1 .

Further, the obtained blackish brown particle powder is subjected to X-ray diffraction and fluorescence X.
As a result of the line diffraction analysis, the peaks of Ni ferrite and Ba ferrite are shown, and it can be seen that the two-phase structure is shown.

[Effect]

The plate-like Ba ferrite particle powder according to the present invention has a magnetization M value of 40 emu / g in a magnetic field of 10 KOe, as shown in the above-mentioned Examples.
It is above, the coercive force Hc is 300 ~ 1000 Oe, the average diameter of the particle surface is modified by spinel type ferrite 0.05 ~ 0.
Since BaO.nFe ₂ O ₃ fine particles having 3 μm can be obtained, it is suitable as a magnetic material for magnetic recording, particularly as a magnetic material for perpendicular magnetic recording.

Further, in the tabular Ba ferrite fine particles obtained by the present invention, since the particle surface is modified with spinel type ferrite, the entire particle surface is modified and the electric resistance becomes low.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction diagram of the blackish brown particle powder obtained in Example 1. In Figure 1, peak A shows the peak of Ba ferrite and peak B shows Mn.
Shows the peak of ferrite.

 ─────────────────────────────────────────────────── ─── Continued Front Page Examiner Yoshizo Hiratsuka

Claims (2)

[Claims] 1. The particle surface is spinel type ferrite (M ²⁺ xFe
²⁺ yO · Fe ₂ O ₃ However, 0 <x ≦ 1, 0 ≦ y <1, 0 <x +
y ≦ 1, M is a plate-like BaO · nFe ₂ O ₃ (4 ≦) modified with one or more selected from Ni, Mn, Zn, Cu and Mg).
n ≦ 6) Plate-like Ba ferrite fine particle powder for magnetic recording comprising fine particles. 2. A plate-shaped _{BaO · nFe 2 O 3 (4} ≦ n ≦ 6) particulate, plate-like _{BaO · nFe 2 O 3 (4} ≦ n ≦ 6) the total Fe in the microparticles
0.1 to 30.0 atom% of M ²⁺ (one or more selected from Ni, Mn, Zn, Cu, Mg) or M ²⁺ and Fe ²⁺ with respect to (III)
Of the plate-like BaO.nFe ₂ O ₃ (4 ≦ n) by mixing with an alkaline suspension having a pH of 8.0 to 14.0 at a ratio of 10 to 100 ° C. and heat-treating the mixed solution at a temperature range of 50 to 100 ° C. ≤6) Spinel type ferrite (M ²⁺ xFe ²⁺ yO ・ Fe ₂ O
₃ However, 0 <x ≦ 1, 0 ≦ y <1, 0 <x + y ≦ 1, M
Is one or more selected from Ni, Mn, Zn, Cu, and Mg), and a method for producing plate-like Ba ferrite fine particle powder for magnetic recording, comprising: