JPS6253444B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing hexagonal plate-shaped or plate-shaped magnetoplumbite-type ferrite fine particles with reduced coercive force, and the purpose thereof is to make them suitable as magnetic powder for perpendicular magnetic recording. The object of the present invention is to provide an economical and stable method for producing fine magnetoplumbite-type ferrite particles.

In recent years, in response to the demand for higher density magnetic recording, a perpendicular magnetic recording method that is capable of recording at a density several times higher than that of the conventional method (longitudinal recording method) has been proposed and is being put into practical use.

The magnetic recording medium used in this perpendicular magnetic recording method, unlike the conventional method, must have an axis of easy magnetization perpendicular to the surface of the magnetic tape or magnetic disk. is broadly divided into the following two series.

(1) Spatter, vapor deposited film (Co-Cr system) (2) Coated film (Ba ferrite) Among these, the coated film using Ba ferrite, which is a typical example of magnetoplumbite ferrite, is easy to mass produce and is stable. It is said that Ba ferrite powder for perpendicular magnetic recording has the following characteristics: (1) It must be as fine as possible without becoming superparamagnetic.

(2) Particles with good dispersibility, narrow particle size distribution, and easy orientation.

(3) The particle size is small and the coercive force is appropriately low.

The present invention is a wet method for producing fine hexagonal plate-like or plate-like magnetoplumbite-type ferrite fine particles with appropriately reduced coercive force suitable for such a coated perpendicular magnetic recording medium.

Generally, magnetoplumbite-type ferrite, represented by Ba ferrite, is characterized by a high coercive force, and its value tends to increase as the grain size decreases. For example, particles with a particle size of 0.1 to 0.3 μm
In Ba ferrite, the coercive force (iHc) is 3000~
Powder with a high coercive force of 5000 (Oe) can be obtained relatively easily. When magnetoplumbite-type ferrite fine particles, which inherently have a high coercive force, are used as a magnetic recording material, it is necessary to reduce the coercive force of the fine particles to a value suitable for magnetic recording.

The value of coercive force suitable for this magnetic recording varies depending on the head material used (ferrite type, alloy type, amorphous, etc.), but is usually said to be in the range of 300 to 2000 (Oe).

Generally, the following methods can be considered as methods for reducing the coercive force of the magnetoplumbite type ferrite particles. Namely, (1) a method of replacing some of the iron atoms constituting magnetoplumbite ferrite with other elements; (For example, 2Fe ³⁺ →M ²⁺ +
M ⁴⁺ , 3Fe ³⁺ →2M ²⁺ +M ⁵⁺ ) (2) A method of forming particles with a thin thickness (3) A method of forming particles with a large amount of mechanical strain.

The method for reducing coercive force of the present invention basically belongs to the method (1), but the effect of the method (2) is partially added.

The present inventors previously proposed a method for producing magnetoplumbite-type ferrite fine particles using Fe ₃ O ₄ ,
(FeO)x・Fe ₂ O ₃ (0<x<1) or γ-
Iron oxides such as Fe ₂ O ₃ are used as the iron source, and this and Ba,
We have discovered and filed an application for a new manufacturing method characterized by hydrothermally treating a compound containing at least one element among Sr and Pb together with an oxidizing agent in an alkaline aqueous solution (Japanese Patent Laid-Open No. 58-69727). Furthermore, as a method for producing finer magnetoplumbite-type ferrite particles, the present inventors used fine iron oxide with a particle size of 500 Å or less as the raw material iron oxide in the above-mentioned hydrothermal treatment method, and used sodium oleate during the hydrothermal treatment. We have discovered and filed an application for a method for producing finer magnetoplumbite-type ferrite particles, which is characterized by the addition of a surfactant such as. (Patent application 58-136812).

The present inventors continued to develop a method for reducing the coercive force in a method for producing magnetoplumbite ferrite by hydrothermal treatment using iron oxide as a raw material ^. We investigated the method of replacing iron oxide with other metals, but it is generally known to be effective in reducing coercive force in dry methods (including flux methods and crystallized glass methods). No good results were obtained even when applied to a hydrothermal treatment method using the raw material.

It is presumed that this is because the substitutable components are different due to the difference in the manufacturing method (reaction temperature, reaction mechanism, etc.) between the wet method and the dry method.

By replacing part of the Fe ³⁺ that makes up magnetoplumbite ferrite with a different element of the M ²⁺ -Sn ⁴⁺ system (M ²⁺ is a divalent element), most of the other properties are lost. It is possible to reduce only the coercive force according to the degree of substitution, and furthermore, this M ²⁺
-Sn ⁴⁺ type (M ²⁺ is a divalent element) Different elements are added during hydrothermal treatment or Fe ₃ O ₄ , (FeO) _x・Fe ₂ O ₃
The present invention was completed based on the discovery that iron oxides such as (0<x<1) and γ-Fe ₂ O ₃ can be added during production. That is, the present invention provides (1) magnetite (Fe ₃ O ₄ ) _or (FeO)
Fe ₂ O ₃ (0<x<1) or γ-iron oxide (γ
―Fe ₂ O ₃ ) and a compound containing at least one element among Ba, Sr, and Pb are hydrothermally treated together with an oxidizing agent in an alkaline aqueous solution to reduce the coercive force when producing magnetoplumbite-type ferrite fine particles. A wet manufacturing method for magnetoplumbite-type ferrite fine particles, which is characterized by adding a compound containing a substituent element for.

(2) Substitution element components for reducing coercive force have already been replaced with magnetite (Fe ₃ O ₄ ) or (FeO) _x・Fe ₂ O ₃
(0<x<1) or γ-iron oxide (γ-
An iron compound containing a substituent element component for reducing coercive force, such as Fe ₂ O ₃ ), and a compound containing at least one element among Ba, Sr, and Pb are hydrothermally treated with an oxidizing agent in an alkaline aqueous solution. A wet manufacturing method for magnetoplumbite type ferrite fine particles. and (1) and (2) above.
The substitution element for reducing the coercive force is Sn ⁴⁺ or
The present invention provides a method for producing magnetoplumbite-type ferrite fine particles characterized by being M2 ⁺ -Sn4 ⁺ -based (M2 ⁺ is a divalent element).

By implementing the present invention, the coercive force of magnetoplumbite-type ferrite can generally be reduced, but its main purpose is to reduce the coercive force of fine magnetoplumbite-type ferrite particles to a value suitable for magnetic recording. There is a particular thing. Therefore, it is preferable to carry out the present invention under the manufacturing conditions of finer magnetoplumbite-type ferrite particles as previously proposed by the present inventors. Alternatively, plate-shaped magnetoplumbite type ferrite fine particles can be produced.

As iron oxide which is the main raw material of the method of the present invention
_{Fe 3} O _{4 , ( FeO )} Can be used regardless of the shape of the In order to improve reactivity and produce fine particles, fine iron oxide particles with a small particle size of 500 Å or less are preferable.

Barium, strontium, and iron compounds as auxiliary raw materials can generally be used as long as they exhibit a certain level of solubility under the reaction conditions. For this purpose, chlorides, nitrates, hydroxides, etc. are usually used. Carbonates and sulfates are generally poorly soluble and are not preferred.

In this way, it is generally possible to select Ba, Sr, and Pb ferrites as the skeleton of substituted magnetoplumbite ferrite, but from the viewpoint of ease of manufacture and the purpose of reducing coercive force,
Ba ferrite is used.

In addition, as a replacement element component to reduce coercive force,
Sodium stannate or tin tetrachloride can be used as a tetravalent tin compound or as a divalent substitution compound.
Divalent compounds such as Fe, Cu, Zn, Co, Ni, Mn, Mg, etc., whose ionic radius is basically similar to Fe ³⁺ are used, and preferably bivalent compounds such as Fe, Cu, Zn, etc. are used.

The ratio of these iron oxides to barium, strontium, lead compounds, and substitution components for reducing coercive force is AO・n(Fe ₂ −2 ^X /6M ²⁺ 〓Sn ⁴⁺ 〓O
₃ ) In the display (where A = at least one of Ba, Sr, Pb)
seed. M ²⁺ = at least one divalent metal such as Fe, Cu, Zn, Co, Ni, Mn, Mg, etc.) n = 4 to 6, preferably in the range of 5 to 6, X = in the range of 0.3 to 0.9 .
Furthermore, in order to produce fine magnetoplumbite-type ferrite particles, it is effective to add a surfactant such as sodium oleate or sodium linoleate during the hydrothermal treatment.

As the alkali used in the reaction, caustic alkalis such as sodium hydroxide and potassium hydroxide are usually used. When using sodium hydroxide, the alkali concentration is calculated as the free alkali concentration after neutralization.
0.01-10N, preferably 0.05-2N. Hydrothermal treatment temperature is 80℃~360℃, preferably 220℃~280℃
is within the range of

As the oxidizing agent, common oxidizing agents such as nitrates, nitrites, chlorates, perchlorates, hydrogen peroxide, and oxygen can be used. Also, as iron oxide, γ-
When using Fe ₂ O ₃ , an oxidizing agent is not essentially necessary, but it is recommended to add a small amount of oxidizing agent to prevent the generation of a reducing atmosphere from the container material under alkaline reaction conditions. be done.

The present invention will be explained below with reference to Examples, but it goes without saying that the Examples are only examples of the present invention and do not limit the present invention in any way.

Example 1 A ferrous chloride aqueous solution containing 0.12 mol, a ferric chloride aqueous solution containing 0.24 mol, and an aqueous solution containing 2.4 g of sodium stannate were thoroughly mixed (for T-Fe).
The atomic ratio of Sn was 0.3/12), and a caustic soda aqueous solution was added dropwise thereto, and the mixture was reacted for 2 hours at a pH of 12 and a reaction temperature of 45°C, to obtain black tin-containing magnetite.

At this time, the particle size of the tin-containing magnetite (spinel structure) produced was confirmed in another experiment under the same conditions to be an average particle size of 120 Å (calculated from the half-width of X-ray diffraction). After adding each aqueous solution containing 14 g of sodium oleate, 6 g of caustic soda, 12 g of barium nitrate, and 6 g of sodium nitrate to this slurry solution, this was charged into an autoclave with an internal volume of 2 equipped with a stirrer (the same applies hereinafter),
The reaction was carried out at 265°C for 5 hours. The product was washed and dried, and subjected to X-ray diffraction, electron microscopy, and magnetization measurements. The product is Fe ₂ ⁺ -Sn ⁴⁺ substituted Ba ferrite, which has a hexagonal plate shape or plate shape with an average particle size of 0.20 μm and a plate ratio of 10 to 20, and a coercive force (iHc) of 1950.
(Oe) and saturation magnetization (σs) of 47 (emu/g).

Furthermore, the amount of tin added was increased to 0.5/12 and 0.7/12 as the atomic ratio of Sn to T-Fe.
The reaction was carried out under almost the same conditions as above to obtain Fe ²⁺ -Sn ⁴⁺ substituted Ba ferrites with different degrees of substitution. The average particle size and shape were almost the same as above.
FIG. 1 also shows the relationship between the magnetic properties and the amount of substitution of these magnetic powders obtained, as well as the case where different metal substitution is not performed (reference example).

As is clear from this figure, it can be seen that the coercive force can be reduced depending on the amount of substitution.

Example 2 The amount of sodium stannate added was 4.8 g, and when adding this sodium stannate, an aqueous solution containing 3.1 g of cupric chloride was added (atomic ratio of Sn and Cu to T-Fe). The experiment was carried out under the same conditions as in Example 1, except that the average particle size was 0.22 μm and the plate ratio was 10 to 20. Cu ²⁺ - Sn ⁴⁺ substituted Ba ferrite was obtained.

The results of measuring the magnetic properties of this Cu ²⁺ -Sn ⁴⁺ substituted Ba ferrite are also shown in Figure 1.

As is clear from this figure, the rate of reduction in coercive force due to the amount of substitution is greater than that of the Fe ²⁺ -Sn ⁴⁺ substitution type in Example 1.
The trend is consistent with that of Ba ferrite.

Example 3 A ferrous chloride aqueous solution containing 0.12 mol and a ferric chloride aqueous solution containing 0.24 mol were mixed well, a caustic soda aqueous solution was added dropwise thereto, and the mixture was reacted for 2 hours at a pH of 11 and a reaction temperature of 45°C, resulting in a black color. obtained magnetite.
After adding each aqueous solution containing 4 g of sodium stannate (atomic ratio of Sn to T-Fe 0.5/12), 14 g of sodium oleate, 6 g of caustic soda, 12 g of barium nitrate, and 6 g of sodium nitrate to this magnetite slurry solution, the mixture was placed in an autoclave. Prepared at 265℃
The mixture was reacted for 6 hours to obtain Fe ²⁺ -Sn ⁴⁺ substituted Ba ferrite.

This material has a hexagonal plate shape or plate shape with an average particle size of 0.20 μm and a plate ratio of 10 to 20, and has a coercive force (iHc) of
is 1220 (Oe), and the saturation magnetization (σs) is 47 (emu/
g) particles.

[Brief explanation of the drawing]

FIG. 1 shows the relationship between the magnetic properties and the amount of substitution.

Claims (1)

[Claims] 1. Magnetite (Fe ₃ O ₄ ) or (FeO) _x .
Fe ₂ O ₃ (0<x<1) or γ-iron oxide (γ-
When manufacturing magnetoplumbite type ferrite fine particles by hydrothermally treating an iron compound called Fe ₂ O ₃ ) and a compound containing at least one element among Ba, Sr, and Pb together with an oxidizing agent in an alkaline aqueous solution, Sn ⁴⁺
or M ²⁺ −Sn ⁴⁺ type compounds (M ²⁺ is a divalent element)
A wet manufacturing method for magnetoplumbite-type ferrite fine particles characterized by adding. 2 Sn ⁴⁺ or M ²⁺ −Sn ⁴⁺ type compound (M ²⁺ is a divalent element) has already been converted into magnetite (Fe ₃ O ₄ ) or (FeO) _x・Fe ₂ O ₃ (0<x<1) Or an iron compound containing a substituent element component for reducing coercive force contained in an iron compound such as γ-iron oxide (γ-Fe ₂ O ₃ ) and Ba,
A wet method for producing magnetoplumbite-type ferrite fine particles, which comprises hydrothermally treating a compound containing at least one element among Sr and Pb together with an oxidizing agent in an alkaline aqueous solution.