JPH061618A - Production of acicular goethite powdery particle - Google Patents

Abstract

PURPOSE:To restrain resinous particles by adding Al salt water solution to alkaline suspension obtained from Co salt, Al salt added ferrous salt aqueous solution and alkali hydroxide aqueous solution of the specified quantities while passing oxygen contg. gas through it. CONSTITUTION:Water soluble Co salt, such as CoSO4 and water soluble Al salt, such as Al2(SO4)3 are added to and dissolved in aqueous solution of ferrous salt, such as FeSO4 so that Co/Fe and Al/Fe may be 0.1-10.0 atomic % and 0.5-5.0 atomic % respectively. Aqueous solution of alkali salt, such as NaOH is added to and mixed in the ferrous salt aqueous solution by the specified quantity to prepare alkaline suspension of >=pH11 including Fe(OH)2, CO(OH)2 and Al(OH)3. Oxygen contg. gas is passed through the alkaline suspension at 30-45 deg.C to oxidize it while water soluble Al salt aqueous solution is added to accelerate reaction and after the formed particles are filtered out, washed with water and dried, they are pulverized to obtain acicular goethite particles contg. Co and Al.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention has a large axial ratio (major axis diameter / minor axis diameter--the same applies hereinafter) suitable as a starting material for producing magnetic particle powder for magnetic recording, and It is an object of the present invention to provide a method for producing acicular goethite particle powder that is uniform and does not contain dendritic particles in an industrial manner.

[0002]

2. Description of the Related Art In recent years, with the progress of downsizing and weight reduction of magnetic recording / reproducing equipment, high recording density, high sensitivity characteristics, high output characteristics, etc. for recording media such as magnetic tapes and magnetic disks are required.

The characteristics of the magnetic material particle powder required to satisfy the above requirements for the magnetic recording medium are as follows:
It has high coercive force and excellent dispersibility.

That is, in order to increase the sensitivity and output of the magnetic recording medium, it is necessary that the magnetic particle powder have a coercive force as high as possible. "Development of magnetic materials and high-dispersion technology of magnetic powder" (1982), page 310, "... The aim of improving magnetic tape performance was to improve sensitivity, output, and noise. The focus was on high coercive force and fine particle formation of the Fe ₂ O ₃ particle powder.

In order to increase the recording density of the magnetic recording medium, the condition for high density recording in the coating tape on page 312 of "Development of Magnetic Material and High Dispersion Technology of Magnetic Powder" is short. It is possible to maintain high output characteristics with low noise with respect to a wavelength signal. For that purpose, it is necessary that both the coercive force Hc and the residual magnetization Br are large and the coating film is thinner. As described above, it is necessary for the magnetic recording medium to have a high coercive force and a large remanent magnetization Br. Therefore, the magnetic particle powder has a high coercive force,
It is required that the dispersibility in the vehicle, the orientation in the coating film and the filling property are excellent.

The remanent magnetization Br of the magnetic recording medium depends on the dispersibility of the magnetic particle powder in the vehicle, the orientation in the coating film, and the filling property. To improve these properties, the remanent magnetization Br is dispersed in the vehicle. It is required that the magnetic particle powder to be produced has a large axial ratio, that the particle size is uniform, and that dendritic particles are not mixed.

As is well known, the magnitude of the coercive force of magnetic particle powder depends on any of shape anisotropy, crystal anisotropy, strain anisotropy and exchange anisotropy, or their interaction. There is.

At present, magnetic iron oxide particles such as acicular magnetite particles and acicular maghemite particles, which are used as magnetic particles for magnetic recording, or metallic magnetic particles containing iron as a main component, have different shapes. A relatively high coercive force is obtained by utilizing the derived anisotropy, that is, by increasing the axial ratio.

These magnetic particle powders are obtained by heating and reducing goethite particles as a starting material or needle-like hematite particles obtained by heat-treating the goethite particles in a reducing gas such as hydrogen to obtain magnetite particles or iron. It is obtained by using metal magnetic particles as a main component, and heating and oxidizing the magnetite particles in air to obtain maghemite particles.

As described above, the magnetic particle powder having a large axial ratio, a uniform particle size and no mixed dendritic particles is currently most demanded, and has such characteristics. In order to obtain the magnetic particle powder, it is necessary that the starting material, goethite particle powder, has a large axial ratio, the particle size is uniform, and the dendritic particles are not mixed.

Conventionally, as a method for producing goethite particle powder as a starting material, a suspension containing ferrous hydroxide colloid obtained by adding an equivalent amount or more of an alkali hydroxide aqueous solution to a ferrous salt aqueous solution has a pH of 11. As described above, a method of forming needle-shaped goethite particles by carrying out an oxidation reaction by passing an oxygen-containing gas at a temperature of 80 ° C. or lower (Japanese Patent Publication No. 39-39
5610 gazette), spindle-shaped goethite particles obtained by aerating an oxygen-containing gas through a suspension containing FeCO ₃ obtained by reacting a ferrous salt aqueous solution with an alkali carbonate aqueous solution to carry out an oxidation reaction. Method for generating the
0-80999) and the like are known.

Further, an oxygen-containing gas is passed through a suspension obtained by adding an equivalent amount or more of an alkali hydroxide aqueous solution to a mixed aqueous solution of a ferrous salt aqueous solution and a cobalt salt aqueous solution to carry out an oxidation reaction. A method of forming needle-shaped goethite particles containing the particles (Japanese Patent Laid-Open No. 48-82395),
In the method described above, a method of adding an aluminum compound to the suspension for the purpose of improving the acicularity of the acicular goethite particles produced (Japanese Patent Publication No. 47-41760 and Japanese Patent Publication No. 59-17161). And JP-A-64-3
No. 3019) is also known.

[0013]

A magnetic particle powder having a large axial ratio, a uniform particle size, and no mixed dendritic particles is the starting material, which is most demanded at present. In the case of the above-mentioned method for producing goethite particle powder, needle-shaped goethite particles having a large axial ratio, in particular, an axial ratio of 10 or more are produced, but dendritic particles are mixed and are even. It is hard to say that the particles have a particle size.

In the case of the above-mentioned method, the particles have a uniform particle size, and spindle-shaped particles in which dendritic particles are not mixed are produced. On the other hand, the axial ratio is at most about 7, and the axial ratio is at most 7. Has a drawback that it is difficult to generate large particles, and in particular, this phenomenon tends to become more remarkable as the major axis diameter of the generated particles becomes smaller.

According to the method described above, acicular goethite particles having a large axial ratio can be produced, but ferrous hydroxide obtained by reacting an aqueous solution of ferrous salt with an aqueous solution of alkali hydroxide. Since the viscosity of the alkaline suspension containing C becomes high and the reaction time becomes long, the particle size of the acicular goethite particles produced is asymmetric and dendritic particles are mixed.

According to the method described above, acicular goethite particles having excellent acicularity can be produced,
If the amount of the aluminum compound added to the reaction solution is small, the effect cannot be obtained, and if it is large, there is a problem that magnetite is mixed with goethite.

Further, when the above and the above are combined, there is a problem that magnetite is more likely to be mixed because the aqueous solution of the cobalt salt and the aluminum compound are used in combination.

Therefore, the present invention provides needle-like goethite particles containing Co and Al, which have a large axial ratio without mixing magnetite, have a more uniform particle size, and do not contain dendritic particles. It is a technical issue to generate it.

[0019]

The above technical problems can be achieved by the following method of the present invention.

That is, according to the present invention, oxygen-containing gas is passed through an alkaline suspension having a pH of 11 or more containing ferrous hydroxide obtained by reacting an aqueous solution of ferrous salt and an aqueous solution of alkali hydroxide to oxidize the suspension. In the method for producing needle-shaped goethite particles by carrying out, the water-soluble cobalt salt in the ferrous salt aqueous solution is 0.1 to 1 in terms of Co with respect to Fe in advance.
0.0 atomic% was added, and a water-soluble aluminum salt was added to either one of the ferrous iron salt aqueous solution and the alkali hydroxide aqueous solution with respect to Fe in an amount of 0.5 to 5.
0 atom% is added, and the ferrous hydroxide aqueous solution is reacted with the alkali hydroxide aqueous solution to obtain p containing ferrous hydroxide.
An alkaline suspension of H11 or more is obtained, and then Co and Al are added by adding an aqueous solution of a water-soluble aluminum salt during the oxidation by passing an oxygen-containing gas into the suspension. A method for producing a needle-shaped goethite particle powder, characterized in that acicular goethite particles are produced.

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

The ferrous salt aqueous solution in the present invention includes:
An aqueous solution of ferrous sulfate, ferrous chloride or the like can be used.

As the alkali hydroxide aqueous solution in the present invention, an aqueous solution of sodium hydroxide, potassium hydroxide or the like can be used.

As the water-soluble cobalt salt in the present invention, cobalt sulfate, cobalt chloride or the like can be used.

The amount of the water-soluble cobalt salt added is 0.1 to 10.0 atom% in terms of Co with respect to Fe in the aqueous ferrous salt solution. If it is less than 0.1 atom%, the effect for obtaining a large axial ratio is insufficient, and if it exceeds 10.0 atom%, excess cobalt salt becomes independent other than acicular goethite particles. Cobalt compounds may be generated, and magnetite and the like may be mixed, which is not preferable.

Since the water-soluble cobalt salt in the present invention is involved in the shape of the acicular goethite particles to be formed, such as the particle size and the axial ratio, at the time of its addition, an oxygen-containing gas is passed through to carry out an oxidation reaction. It is necessary to add or dissolve it in the solution of the ferrous iron salt aqueous solution before
Alternatively, an aqueous solution in which a water-soluble cobalt salt is dissolved is added and mixed separately.

As the water-soluble aluminum salt in the present invention, aluminum sulfate, aluminum chloride, sodium aluminate, etc. can be used.

In the present invention, the water-soluble aluminum salt added to either the aqueous ferrous salt solution before the production of ferrous hydroxide or the aqueous alkali hydroxide solution is the growth of ferrous hydroxide particles produced. It is related to the shape of the needle-shaped goethite particles produced by the oxidation reaction, such as the particle size and the axial ratio, and therefore is added and dissolved in advance in either the ferrous salt aqueous solution or the alkali hydroxide aqueous solution. Or an aqueous solution in which a water-soluble aluminum salt is dissolved in water is added and mixed to either one of the above.

In this case, the amount of the water-soluble aluminum salt added is 0.5 to 5.0 atom% in terms of Al with respect to Fe in the ferrous iron salt aqueous solution. If it is less than 0.5 atom%, the effect of suppressing the growth of particles of the produced ferrous hydroxide, which is the object of the present invention, cannot be obtained, and 5.0 atom%
If it exceeds, magnetite may be mixed.

The water-soluble aluminum salt added during the oxidation of the suspension in the present invention reduces the viscosity of the alkaline suspension containing the ferrous hydroxide and accelerates the reaction rate in the oxidation reaction. Since it is involved, it is preferable to dissolve the water-soluble aluminum salt in water and add it as an aqueous solution to the suspension in order to quickly disperse in the liquid and make it act uniformly.

In this case, the amount of the water-soluble aluminum salt aqueous solution added is such that Al in relation to Fe in the ferrous iron salt aqueous solution.
It is 0.5 to 5.0 atom% in terms of conversion. If it is less than 0.5 atom%, the effect of lowering the viscosity of the suspension is not sufficient, and if it exceeds 5.0 atom%, magnetite may be mixed.

During the oxidation, it may be added in several times within the range of the above addition amount, and the amount of the water-soluble aluminum salt added before the production of the ferrous hydroxide is added. Is 1.0 to 10.0 atomic% in terms of Al with respect to Fe in the ferrous salt aqueous solution. If the total amount of addition exceeds 10.0 atom%, the risk of magnetite being mixed in the goethite particles as the final product becomes high.

The pH of the suspension containing ferrous hydroxide in the present invention is 11 or more. If the pH is less than 11,
Magnetite may be mixed in, and when the pH exceeds 14, the viscosity is high and the reaction time is long, and it is not economical to use an excessive amount of alkali hydroxide aqueous solution. Therefore, it is preferable that the pH is in the range of more than 12 and less than 14.

The reaction temperature in the present invention is 30 to 45 ° C.
Is. If the temperature is lower than 30 ° C, fine needle-shaped goethite may be formed and the particle size may become asymmetric, and if it exceeds 45 ° C, magnetite may be mixed, which is not preferable.

The oxidizing means in the present invention is performed by passing an oxygen-containing gas (for example, air) through the liquid.

Further, in the present invention, in order to improve the characteristics of the magnetic particle powder and the like, it is possible to add a different element such as Ni, Zn, P or Si, which is usually added, during the production reaction of goethite particles.

The filtration, washing with water and drying for obtaining the acicular goethite particle powder may be carried out according to a conventional method.

[0038]

[Function] An oxygen-containing gas is added to an alkaline suspension containing ferrous hydroxide obtained by reacting an aqueous ferrous salt solution with a water-soluble cobalt salt in the solution and reacting with an aqueous alkali hydroxide solution. To obtain acicular goethite particles with a large axial ratio by aeration and oxidation, simply adding a water-soluble cobalt salt will increase the reaction time, and the acicular goethite particles obtained will have an asymmetric particle size. And dendritic particles are also mixed.

Therefore, a water-soluble aluminum salt is added to the alkaline suspension to reduce the viscosity of the suspension,
It is considered to promote the oxidation reaction promptly to shorten the reaction time. However, if the water-soluble aluminum salt is simply added, magnetite may be mixed in the acicular goethite particles.

A method of adding a water-soluble silicate to the alkaline suspension (Japanese Patent Laid-Open No. 54-20998).
However, when a water-soluble silicate is added, the viscosity may decrease, but the axial ratio may also decrease, and insoluble alkali metal salts may precipitate, so metal magnetic particle powder containing iron as the main component. Is not preferable.

From the above, in the present invention, before the production of ferrous hydroxide, the water-soluble cobalt salt is added to the liquid of the aqueous solution of the ferrous salt in advance, and A water-soluble aluminum salt of 0.5 to 5.0 atom% in terms of Al with respect to Fe in the iron salt aqueous solution is formed by adding it to one of the ferrous salt aqueous solution and the alkali hydroxide aqueous solution. It was found that there is an effect of suppressing the growth of ferrous hydroxide fine particles.

The results are shown by electron micrographs (× 30000) of ferrous hydroxide in FIGS. 1 and 2. Figure 1
It shows the particle structure of ferrous hydroxide produced by adding a water-soluble aluminum salt to the solution of an aqueous solution of ferrous salt, and it can be confirmed that the particle size is fine and the particle size is uniform. No. 2 shows the particle morphological structure of ferrous hydroxide when the water-soluble aluminum salt is not added, and it can be confirmed that the particles are large and the particle size is also asymmetric.

From the above results, the present inventors have determined that the aluminum compound produced from the added water-soluble aluminum salt is adsorbed on the surface of the produced ferrous hydroxide fine particles to suppress the growth. thinking. It was also confirmed that magnetite did not precipitate within the above range of addition amount.

Since the ferrous hydroxide particles are large and asymmetric, dendritic particles are generated in the process of forming acicular goethite particles, and the size of the goethite particles is also asymmetric. It is supposed to be.

However, when acicular goethite particles are formed by an oxidation reaction in which an oxygen-containing gas is passed through the obtained alkaline suspension containing fine ferrous hydroxide to oxidize it, ferrous hydroxide is It was found that the water-soluble aluminum salt added before the formation of the reaction alone loses its effect, increases the viscosity of the suspension, and prolongs the reaction time as the oxidation reaction progresses.

In order to shorten the reaction time by maintaining a large axial ratio of the acicular goethite particles produced by utilizing the fine particles of ferrous hydroxide, the present inventors have proposed In addition to adding the water-soluble aluminum salt to either one of the above before iron is formed, the viscosity of the suspension is lowered by adding the water-soluble aluminum salt during the oxidation reaction. We have found that the time can be shortened.

Therefore, in the present invention, fine particles of ferrous hydroxide can be obtained, and the minor axis diameter of the acicular goethite particles can be reduced in the oxidation reaction to increase the axial ratio. Thus, needle-shaped goethite particles containing Co and Al having a large axial ratio, a more uniform particle size, and no mixed dendritic particles can be obtained.

Further, in the present invention, since a large amount of Al can be contained, the acicular hematite particles obtained by heat-treating the acicular goethite particles are heated and reduced in a reducing gas such as hydrogen. And magnetite particles or metal magnetic particles containing iron as a main component, and even when the magnetite particles are heated and oxidized in air to form maghemite particles, the magnetic particle powder is excellent. Can retain needle-like properties, and
Even when it is kneaded with a binder resin for a magnetic recording medium to form a magnetic coating material, it is well compatible with the binder resin, and therefore it has excellent dispersibility in the case of a magnetic coating material.

In the above-mentioned Japanese Patent Laid-Open No. 64-33019, for example, a method of adding an aluminum compound to a suspension of ferrous hydroxide is described in "... While supplying an oxygen-containing gas. , May be carried out continuously or intermittently, or various methods such as adding only in the first half or only in the second half, etc. may be employed. However, in this case, it is added to the suspension after ferrous hydroxide is produced, and there is no description about the effect of addition before the production of ferrous hydroxide.

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

The major axis diameters and axial ratios of the particles in the following examples and comparative examples are all shown by the average of the numerical values measured from electron micrographs.

The particle size distribution of the particles is shown by the geometric standard deviation value (σg) obtained by the following method. That is, the major axis diameter of 350 particles shown in an electron micrograph at 120,000 times is measured, and the logarithmic normal is calculated from the actual major axis diameter and the number of particles calculated from the measured values according to a statistical method. On the probability paper, the major axis diameter of the particles is plotted on the horizontal axis, and the cumulative number of particles belonging to each major axis diameter section equally spaced on the vertical axis is plotted as a percentage. Then, the values of the major axis diameters corresponding to the numbers of particles of 50% and 84.13% are read from this graph, and the geometric standard deviation value (σg) = the major axis diameter when the number of particles is 50% (μm) / Long axis diameter (μm) when the number is 84.13%
The value calculated according to

The amounts of Co and Al contained in the acicular goethite particles were measured by fluorescent X-ray analysis.

EXAMPLE 1 168.5 g of cobalt sulfate (corresponding to 3.0 atom% in terms of Co in terms of Fe) and 34 g of aluminum sulfate (in relation to Fe) were added to 20 l of a 1.0 mol / l ferrous sulfate aqueous solution. (Corresponding to 1.0 atom% in terms of Al) and added and dissolved, 3.33 mol / l NaOH aqueous solution 30
1 was added, and at pH 13.5 and a temperature of 45 ° C, Fe (O
A suspension containing H) ₂ , Co (OH) ₂ and Al (OH) ₃ was obtained.

1 minute per minute was added to the above suspension at a temperature of 45.degree.
0.5 mol / l after 60 minutes of aeration with 50 l of air
Aluminum sulfate aqueous solution of 200 ml (Al for Fe
It corresponds to 1.0 atom% in conversion. ) Was added. After 60 minutes, this operation was repeated once again. Subsequently, at a temperature of 45 ° C., 150 l / min of air was aerated for 80 minutes to generate acicular goethite particles. The produced particles were washed with water, separated by filtration, dried and pulverized by a conventional method. The needle-shaped goethite particles have a Co / Fe content of 2.5 atomic% and an Al / F content.
e was 1.77 atomic%.

Further, the electron micrograph (× 30
000), it is clear that the long axis is 0.34 on average.
The particles had an average particle size of .mu.m, an axial ratio of 15, and a standard deviation value of 0.73 and were uniform in particle size, and did not contain dendritic particles.

Examples 2 to 5 and Comparative Examples 1 to 4 Type and amount of water-soluble cobalt salt, type of water-soluble aluminum salt, amount and timing of addition, type and amount of aqueous solution of water-soluble aluminum salt during oxidation And Example 1 except that the addition method and the reaction temperature were variously changed.
Needle-shaped goethite particles were produced in the same manner as in.

The main manufacturing conditions and various characteristics at this time are shown in Tables 1 and 2.

[0059]

[Table 1]

[0060]

[Table 2]

The needle-shaped goethite particles obtained in Comparative Examples 1 and 3 contained dendritic particles as shown in the electron micrographs (× 30000) shown in FIGS. 6 and 8, respectively. The needle-shaped goethite particles obtained in Comparative Example 2 were asymmetric particles, and the electron micrograph (× 3) shown in FIG.
0000), the axial ratio was small.

[0062]

EFFECTS OF THE INVENTION According to the method for producing acicular goethite particles according to the present invention, as shown in the above examples, the particles have a large axial ratio, the particle sizes are uniform, and dendritic particles are mixed. It is possible to obtain non-acicular goethite particles powder.

The acicular goethite particle powder thus obtained is used as a starting material, and the acicular magnetite particle powder is obtained by heating and reducing, or the acicular metal magnetic particle powder containing iron as a main component. Needle-shaped maghemite particle powder obtained by heating and oxidizing magnetite particle powder in air also has a large axial ratio, is more uniform in particle size, and is a particle in which dendritic particles are not mixed, and thus is currently most demanded. Suitable as high recording density, high sensitivity, high output magnetic particle powder.

[Brief description of drawings]

FIG. 1 is an electron micrograph (× 30000) showing a particle structure of particles obtained from a suspension containing ferrous hydroxide obtained in Example 1.

FIG. 2 is an electron micrograph (× 30000) showing a particle structure of particles obtained from the suspension containing ferrous hydroxide obtained in Comparative Example 1.

FIG. 3 is an electron micrograph (× 30000) showing the particle structure of needle-shaped goethite particles obtained in Example 1.

FIG. 4 is an electron micrograph (× 30000) showing the particle structure of needle-shaped goethite particles obtained in Example 2.

5 is an electron micrograph (× 30000) showing the particle structure of needle-shaped goethite particles obtained in Example 3. FIG.

6 is an electron micrograph (× 30000) showing the particle structure of needle-shaped goethite particles obtained in Comparative Example 1. FIG.

7 is an electron micrograph (× 30000) showing the particle structure of needle-shaped goethite particles obtained in Comparative Example 2. FIG.

8 is an electron micrograph (× 30000) showing the particle structure of needle-shaped goethite particles obtained in Comparative Example 3. FIG.

Claims (1)

[Claims] 1. A needle obtained by reacting an aqueous solution of a ferrous salt with an aqueous solution of an alkali hydroxide to obtain an alkaline suspension having a pH of 11 or more and containing ferrous hydroxide, which is ventilated with an oxygen-containing gas to oxidize the needle. In the method for producing granular goethite particles, a water-soluble cobalt salt is previously added to the aqueous solution of the ferrous salt in an amount of 0.1 to 10.0 atomic% in terms of Co with respect to Fe, and the ferrous salt is added. In one of the aqueous solution and the aqueous solution of alkali hydroxide, a water-soluble aluminum salt is added to Fe in an amount of 0.5 to 5.0 atomic% in terms of Al, and the aqueous solution of ferrous salt and the aqueous solution of alkali hydroxide are added. To obtain an alkaline suspension having a pH of 11 or more containing ferrous hydroxide, and then, while oxygen is passed through the suspension to oxidize, a water-soluble aluminum salt aqueous solution is further added. A method for producing acicular goethite particle powder, characterized in that acicular goethite particles containing Co and Al are generated by addition.