JPH03275520A - Production of hexagonal plate-like barium ferrite - Google Patents

Abstract

PURPOSE:To obtain a hexagonal plate-like barium ferrite of super-fine, monodisperse system which is suitable as the magnetic powder for magnetic recording based on a coprecipitation method without using an autoclave, by adding a specified compd. to a coprecipitate solid material produced from iron salt and Ba salt as the main components, and the calcining the material in the presence of a flux or the by-product salt produced in the process of coprecipitation. CONSTITUTION:Silica sol (e.g. silica sol produced from alkylsilicate) is added to a coprecipitate solid material produced from iron salt and Ba salt as the main components (e.g. an aq. soln. of FeCl2, BaCl2, CoCl2, and TiCl4 is dropped to an aq. soln. of NaOH and NaCO3 to obtain a coprecipitate). Then this mixture is calcined in the presence of a flux (e.g. NaCl) or by-product salt produced in the process of coprecipitation.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing hexagonal plate-shaped barium ferrite, in which the axis of easy magnetization of the hexagonal plate-shaped barium ferrite is perpendicular to the plate-shaped crystal grains. , is useful as a magnetic material for high-density recording.

[Prior Art 1] In the field of magnetic recording, as video, digital audio, etc. appear, the demand for high recording density is increasing. In the current mainstream method of in-plane magnetic recording, if an attempt is made to increase the recording density, the demagnetizing field within the magnetic layer increases, resulting in a decrease in the reproduction output, and there is a limit to the improvement in the recording density. Therefore, perpendicular magnetic recording, which magnetizes in a direction perpendicular to the recording surface of a recording medium, has been proposed and is seen as a promising method suitable for high-density recording.

How to make a magnetic layer with an axis of easy magnetization in the perpendicular direction is as follows:
There are two methods: one method is to apply a thin film of Co--Cr or the like on the substrate by sputtering or vapor deposition, and the other method is to apply powder such as barium ferrite together with a binder. Thin films have an advantage in terms of recording density, but they have problems with durability and are expensive because they require a vacuum process to manufacture. Since coating is currently the mainstream technology and is better established, the coating type is closer to practical application.

Hexagonal root-shaped barium ferrite particles are well known as magnetic powder for coated perpendicular magnetic recording. &fi air recording hexagonal plate-shaped barium ferrite particles have a particle size of 0.02
The basic condition for powder properties is to be monodispersed with ~0.2μ intestine, and for magnetic properties, saturation magnetization must be as high as possible and coercive force must be freely controlled between 200 and 20,000e. . There are three methods for producing hexagonal plate-shaped barium ferrite particles for magnetic recording that meet this condition:
is known.

(1) A coprecipitate of ferric hydroxide and barium carbonate is obtained by mixing an alkali and an alkali carbonate with stirring into an aqueous solution containing a ferric salt and a barium salt to adjust the pH to 10 or more. After passing this coprecipitate through the mouth, completely washing with water, and drying,
A method of obtaining barium ferrite particles by heat treatment at a temperature of around 00°C (co-precipitation-firing method: Japanese Patent Application Laid-open No. 56-60002).

(2) A barium ferrite precursor (crystalline, A method of obtaining barium ferrite particles by reaction-generating barium ferrite (with incomplete magnetic properties), followed by washing, drying, and firing (usually at temperatures above 0°C) (hydrothermal synthesis method: e.g., M, Niyama, Bul
l, Chew, Soc, Jpn,, 49(19
7G), 1855 and Japanese Patent Publication No. 60-12973).

(3) Components that make up barium ferrite, such as barium oxide and iron oxide, and components that form glass, such as boron oxide, are mixed, the molten mixture is rapidly solidified to form an amorphous body, and this is heat-treated. After precipitating barium ferrite in a glass substance, the resulting fine powder is treated with a dilute acid such as acetic acid to dissolve and remove the glass-forming component that is the matrix, and the barium ferrite particles are extracted, washed with water, and dried. Methods (glass crystallization method: e.g. Kenjo.

Ido, Nikkei New Materials, April 28, 1986 issue, p. 52, and JP-A-56-67904).

In addition, as an improvement to the above method (1), after forming a coprecipitate of ferric hydroxide and barium salt in an alkaline aqueous solution, it is neutralized with an acid until the pH becomes 6 to 8, and the solid substance to be 11 is removed. A method of drying and firing at 700 to 1100°C to obtain hexagonal plate-shaped barium ferrite particles (Japanese Patent Application Laid-Open No. 60-8102
Publication No. 7) has been proposed.

[Problem to be Solved by the Invention 1] When using barium ferrite powder as magnetic powder for magnetic recording, it is particularly important that the particle size is 0. It is an ultra-fine powder of 0.2 μm in diameter and has a particle size distribution of ζ-noyap and is monodisperse. The glass crystallization method (3) described in the conventional technology can overcome this condition relatively easily, but it requires a high temperature to melt the raw materials and another heat treatment is required. , has the disadvantage of high cost.

The above-mentioned (1) coprecipitation/heating method has a simple process;
The cost is much lower than other methods, but it is extremely difficult to achieve monodispersity. In addition, the coprecipitate has very poor oral permeability, and it is necessary to improve the washing of the coprecipitate.

In addition, the hydrothermal synthesis method mentioned in (2) above removes the drawbacks of the coprecipitation/heating method by hydrothermally treating the coprecipitate in an autoclave, but the use of an autoclave increases the scale. Then, there is a problem that the cost becomes high.

In the above-mentioned improved method in which a neutralization reaction is incorporated after coprecipitation in the coprecipitation/heating method, the coprecipitate is not washed, so that the time and effort required for washing can be significantly reduced.

However, since the particle size of ferric hydroxide cannot be controlled, 0.2
It is difficult to obtain hexagonal plate-shaped barium ferrite with a size smaller than μ.

0.0 by coprecipitation and heating method without using an autoclave. O1~0
．． An extremely inexpensive method for producing monodispersed hexagonal plate-shaped barium ferrite powder with a particle size of 2 μm is to co-precipitate ferrous hydroxide and barium salt in an alkaline aqueous solution, and then blow an oxygen-containing gas such as air onto this. oxidation to produce a coprecipitate of iron oxyoxide lFe0011) and barium salt, and plating the alkaline suspension of the obtained coprecipitate with acid.
A step of neutralizing until the H value falls within the range of 7 to 12 and recovering the solid matter, and firing the solid matter to produce hexagonal plate-shaped barium ferrite, which is then washed to remove unnecessary materials. A method for manufacturing hexagonal plate-shaped barium ferrite has been proposed (Japanese Patent Laid-Open No. 63-225
534).

However, as the density of magnetic recording progresses, the demand for smoothness of the coated If surface becomes higher and higher, and it has become necessary to further improve the dispersibility of the magnetic powder.

Furthermore, even with methods for producing barium ferrite based on coprecipitation, the dispersibility of the powder is still insufficient, and there is a strong desire to improve the dispersibility.

[Means for Solving the Problems] In order to solve the various problems mentioned above, the inventors of the present invention have made various studies and have added silica sol to a co-precipitated solid material mainly composed of iron salts and barium salts. Then, they discovered a method for producing hexagonal root-shaped barium ferrite, which is characterized by firing in the presence of a by-product salt or a flux during coprecipitation.

A general method for producing barium ferrite particles by a coprecipitation-calcination method is well known.
In 0002, an aqueous solution containing a ferric salt and a barium salt,
A mixed solution containing an alkali and an alkali carbonate is brought into contact and the pH is adjusted to 10 or more to obtain a coprecipitate, which is filtered, washed, dried, and calcined at around 900°C to produce barium ferrite particles. ing.

In addition, in JP-A No. 64-5914, a coprecipitate was obtained using ferric salt and barium salt as raw materials, and the resulting alkaline slurry was neutralized to a pH value in the range of 8 to 1O, and then washed. The barium ferrite particles are made by passing through the mouth and drying the barium ferrite particles, and then firing the solid material.

In addition, in the above-mentioned Japanese Patent Application Laid-Open No. 63-225534, ferrous hydroxide and barium salt are co-precipitated in an alkaline aqueous solution, which is oxidized by contacting with an oxygen-containing gas, etc., and iron oxyoxide and barium salt are co-precipitated. A precipitate is produced, and the alkaline suspension of the coprecipitate is neutralized with acid to a pH of 7 to 12 to recover the solid matter. This solid material is fired at 650 to 900°C for 1 to 20 hours to produce barium ferrite particles.

The coprecipitated solids used in the present invention are those produced by these methods.

However, in the present invention, since the coprecipitate-containing slurry is fired in the presence of by-product salt or flux during coprecipitate formation, the pH value of the coprecipitate-containing slurry is 7 to 1.
It is difficult to obtain barium ferrite particles with good characteristics unless the co-precipitated solid material is neutralized to zero and recovered by one-port filtration.

Si reduces the saturation magnetization when it enters barium ferrite, so it is an element that is not often used as an additive element in compounds.
-265827, Si is added to make barium ferrite particles uniform in particle size and improve dispersibility. In both applications, Si is added as a silicate, the former is washed with water after addition, the latter is washed with water at the same time as addition, and in both applications, the coprecipitate is washed with water, then heat treated and fired, and the coprecipitate is Firing is not performed in the presence of by-product salts or fluxes during the reaction.

This is different from the present invention in that the present invention performs firing in the presence of a by-product salt during the coprecipitation reaction or an additional flux.

By-product salt during coprecipitation is a neutral salt that is produced as a by-product when producing a coprecipitate solid mainly composed of barium salt and iron salt, or a salt that precipitates when drying the coprecipitate. and sodium chloride is the most desirable. In addition, the flux may be any substance that is used in a normal flux method.
Examples include halides such as chlorides of Na, K, Li, and Ca, krt salts, and the like. These may be used alone or in a mixture of two or more, but sodium chloride is most preferred.

Since the by-product salt or flux is precipitated on the coprecipitate drying stage, it is not uniformly distributed and its size is much larger than the coprecipitate particles. Co-precipitate particles that are not in contact with by-product salts, etc. have a slower barium ferrite production reaction than those that are in contact with them.

The present invention aims at uniformly promoting the reaction for producing barium ferrite such as sodium chloride described in - by adding silica sol.

Historically, after barium ferrite is formed, by-product salts and the like work to prevent barium ferrite from sintering.

By-product salts such as sodium chloride or fluxes are very different from silica sol (they dissolve well, so if silica sol covers the coprecipitate particles that have gathered together, sodium chloride will easily spread over the surface of the coprecipitate, resulting in barium ferrite) This is because the production reaction proceeds uniformly.

Therefore, it is important that the silica sol added in the present invention uniformly covers the coprecipitate.

The silica sol used in the present invention can be made from inorganic compounds as raw materials, but silica sol made from alkyl silicate is superior in terms of purity. Furthermore, intermediate products and silica sol precursors obtained when silica sol is produced by hydrolyzing alkyl silicate can also be used in the present invention.

Since the process of producing a coprecipitated solid mainly composed of iron salt and barium salt is generally carried out in an aqueous solution, the silica sol to be added and its intermediate products and precursors as mentioned above are mixed with water,
It is preferable to add it in a state where it is dispersed or dissolved in a water-soluble organic solvent.

In the present invention, as described above, in the case of a silica sol dispersed in water or a water-soluble solvent, a suspension containing a coprecipitated solid generally produced as described above is used. It can be added to the suspension, or it can be added and mixed after the coprecipitated solids have been collected by filtration or centrifugation, or they can be added after the coprecipitated solids have been dried and mixed thoroughly. It's okay.

In addition, when adding intermediate products or precursors of silica sol, it is preferable to thoroughly dry the coprecipitated solids before adding them, as they still have reactivity. .

If the coprecipitated solid is sufficiently dried, it is also possible to add an organosol of silica dissolved in a polar solvent or an aromatic organic solvent, or a solution of an intermediate product or precursor thereof.

If the silica sol is not sufficiently dried, it can be dispersed in water or an intermediate to low alcohol that mixes well with water, or a ketone such as acetone, or a dissolved silica sol or its intermediate or precursor solution can be co-precipitated into a solid. It is preferable to add it to the product in order to mix it uniformly.

In this way, a solution such as silica sol is added to the suspension containing the coprecipitated solid or its dry powder, mixed, and then dried to remove the solvent and the like.

The amount added to barium ferrite such as silica sol is 5
In terms of iOa, 3 x 10-" to 0.75 wt% is desirable. If the amount added exceeds 0.75 wt%, the amount of Si that enters the barium ferrite after firing increases, reducing the saturation magnetization of the barium ferrite. However, if the content is less than 3 x In-''wt%, it will be less effective in obtaining monodispersed barium ferrite particles with excellent dispersibility.

What is important in the present invention is to perform firing in the presence of a flux or a by-product salt in order to lower the barium ferrite production reaction temperature, prevent agglomeration, and obtain barium ferrite particles with good dispersibility. That is, the flux generally used in the production method of barium ferrite by the flux method,
In particular, alkali metal or alkaline earth metal halides and water-soluble fluxes stable at temperatures above 800°C (e.g. N
The present invention is characterized in that the firing is carried out in the presence of azSOa, etc.) or in the presence of a by-product salt such as sodium chloride produced during the coprecipitation reaction.

After adding a solution such as silica sol and thoroughly mixing, the solvent of the solution is evaporated, and if there is no by-product salt as mentioned above, a flux is added, and then heated at 650 to 900°C for 1 to 20 hours. Fire.

When the firing temperature is lower than 650℃, barium ferrite /
[If the acid reaction does not proceed well and the firing temperature is higher than 90 υ°C, it is difficult to maintain a 10-dispersion state.

When fired, the hexagonal root-shaped barium ferrite powder is mixed with by-product salt such as sodium chloride or a flux, so the salt is removed by washing. This cleaning operation is extremely easy compared to the operation of cleaning alkali from a coprecipitate containing iron hydroxide or hydrated iron oxide.

In addition, components for controlling the magnetic properties such as coercive force of hexagonal plate barium ferrite, such as titanium and cobalt, may be added as necessary at an appropriate stage, usually during coprecipitation or before neutralization. It's okay.

【Example] The present invention will be explained in detail by examples.

Example 1 FeC1,il+□0 0.2G+mol and CoC
Ia・6Ha0 0. (12 mol and TiC140,
02mol and BaCl2・2H,00,0261a+o
An aqueous solution of N
a0111.2 mol and Na2COz O,052
Fe (011
12 and Co (0 old 2, Tt (0) 1) 4, mouth ac
A slurry of coprecipitate of t3 was prepared. Fe(
0141, was oxidized to give Fe0011. At this time C
o, Ti is a solid solution in Fe00.

Then, neutralize with INHcI until pH 9.48,
After passing the slurry through the mouth, the cake was dried at 120° C. for one day and night. X dry powder! When analyzed by single diffraction, a −F
e001(, BaCO3, NaCl peaks were observed.

This dry powder was added to a silica sol made from alkyl silicate (manufactured by Colcoat ■ [Cerazol J, SiO□ equivalent: 35
% ethanol solution sol) to dry powder 0.2wt
% (0.07 wt% in terms of S102) and mixed in a ball mill for 1 hour. After mixing, evaporate the ethanol and add 82
Calcinate in air at 0°C for 2 hours, then wash with water,
Barium ferrite powder was obtained by drying at 120° C. for 1 day and night.

Table 1 shows the results of shape observation of the powder by SEM and magnetic properties by VSM.

Comparative Example 1 A dry powder of a coprecipitated solid was obtained in the same manner as in Example 1. After that, without adding silica sol, the dry powder was used as it was at 82
Baked in air at 0°C for 2 hours, then washed with water,
Barium ferrite powder was obtained by drying at 120° C. for 1 day and night.

Table 1 shows the properties of the powder obtained in the same manner as in Example 1.

Comparative example 2 FeC1,・4H,00,26 mol and CoC1,・
6H, 00,02mol and TiCl4 0.02mol
l and BaCl,-2H, 00,0261 mol
An aqueous solution of 750 e of distilled water was prepared as Na01
11.2 sol and NazCOx O, 0522 garden o
1 was added dropwise to an alkaline solution dissolved in 750 mff of distilled water at 15°C with stirring, and
and Go (OHI *, Ti (all), , B
A coprecipitate slurry was prepared at aC0°. 15 while stirring
Fe was reacted with air at a flow rate of 4β/■in for 2 hours at °C.
10HI 2 was oxidized to Fe0011. At this time, Co and Ti are in solid solution with Fe00. After thoroughly washing the slurry, it was passed through the mouth, and the cake was heated to 120°C.
Dry day and night. When the dry powder was analyzed by X-ray diffraction, a
-Fe00H and BaCO3 peaks were observed. Add alkyl silicate silica sol (Colcoat ■) to this dry powder.
0.2 wL% (0.07 wt% in terms of Sin□) of Celazol J (Sin, 35% ethanol solution sol in terms of W) was added to the dry powder, and the mixture was mixed in a ball mill for 1 hour. After mixing, the ethanol was removed, and the mixture was calcined in air at 820°C for 2 hours, washed with condensed water, and dried at 120°C day and night to obtain barium ferrite powder.

The characteristics of this powder are shown in Table 1 and were not desirable because it was not fired in the presence of by-product salt or flux during coprecipitation.

(Leaving space below) Table l Powder properties Next, for the powders of Example 1 and Comparative Example 1.2, binder resin and solvent were mixed in a paint conditioner for 4 hours at the following mixing ratio, and the obtained academic materials were appropriately mixed. The mixture was diluted to a certain viscosity and formed into a film using an applicator, and the gloss was measured using a simple gloss meter manufactured by Horiba (IG-310).

Barium ferrite magnetic powder 100 parts by weight Modified PVC 10 parts by weight Methyl ethyl ketone 30 parts by weight Toluene
30 parts by weight of cyclohexanone and 15 parts by weight can be provided.

The obtained characteristic values are shown in the table. It was as follows.

Claims (1)

[Claims] A hexagonal plate-shaped barium ferrite characterized by adding silica sol to a co-precipitated solid material mainly composed of iron salt and barium salt, and then firing it in the presence of a by-product salt or a flux during co-precipitation formation. manufacturing method.