JPH05262528A - Production of nheedlelike goethite grain powder - Google Patents

Abstract

PURPOSE:To improve the quality by adding specific amounts of a water-soluble silicate and a water-soluble Al salt to an aqueous solution of an alkali or its reactional solution with an aqueous solution of a ferrous salt, then aerating the solution with an O2-containing gas and carrying out the oxidizing reaction. CONSTITUTION:A water-soluble silicate such as Na2SiO3 is added to an alkaline aqueous solution such as NaOH to prepare a mixture solution. A water-soluble Al salt such as Al2(SO4)3 is added to an aqueous solution of a ferrous salt such as FeCl2 and the obtained mixture solution is then added and mixed with the prepared mixture solution so as to afford 0.1-0.7 atomic% of Si/Fe and 0.1-3.0 atomic% of Al/Fe. The resultant solution is then warmed at a prescribed temperature and pH is regulated to >=11. Thereby, a suspension containing Fe(OH)2 and Al(OH)3 is obtained and then aerated with an oxygen-containing gas such as air in a prescribed quantity to carry out the oxidizing reaction. As a result, the objective needlelike goethite grain powder having a high axial ratio (major axis diameter/minor axis diameter) and a uniform grain size without containing dendritic grains mixed therein is obtained.

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) suitable as a starting material for producing magnetic particle powder for magnetic recording, and has a more uniform particle size. It is an object of the present invention to provide a needle-shaped goethite particle powder in which dendritic particles are not mixed, by increasing production efficiency, industrially and economically.

[0002]

2. Description of the Related Art In recent years, with the progress of miniaturization and weight reduction of magnetic recording / reproducing devices, there is an increasing need for higher performance of recording media such as magnetic tapes and magnetic disks. That is, high recording density, high sensitivity characteristics and high output characteristics 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 for the magnetic particle powder to have a coercive force as high as possible. "Development of magnetic materials and high-dispersion technology for magnetic powder" (1982), page 310, "The direction of improving magnetic tape performance was to improve sensitivity and output.
The focus was on increasing the coercive force of the acicular γ-Fe ₂ O ₃ particle powder. It is clear from the description.

Further, in order to achieve a high recording density of the magnetic recording medium, the above-mentioned "Development of Magnetic Materials and Highly Dispersion Technology of Magnetic Powder", No. 3,
The condition for high-density recording on the coated tape on page 12 is that it can maintain high output characteristics with low noise for short-wavelength signals. Therefore, coercive force Hc and residual magnetization Br are both As described above, it is necessary that the magnetic recording medium has a high coercive force and a large remanent magnetization Br. It is required to have a high coercive force, excellent dispersibility in a vehicle, orientation in a coating film, and filling property.

As is well known, the magnitude of 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 currently used as magnetic particles for magnetic recording, or metallic magnetic particles containing iron as a main component, have the same shape. A relatively high coercive force is obtained by utilizing the anisotropy derived from, that is, by increasing the axial ratio (major axis diameter / minor axis diameter).

In these known magnetic particle powders, the starting material, goethite particles, is added in a reducing gas such as hydrogen in an amount of 300-4.
It is obtained by reducing at 00 ° C. to magnetite particles or metal particles containing iron as a main component, or subsequently oxidizing the magnetite particles at 200 to 300 ° C. in air to give maghemite particles.

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. It is required that the magnetic particle powder to be dispersed in has a large axial ratio (major axis diameter / minor axis diameter), has a uniform particle size, and does not contain dendritic particles.

As described above, the magnetic particle powder having a large axial ratio (major axis diameter / minor axis diameter), a uniform particle size and no mixed dendritic particles is currently most demanded. In order to obtain magnetic particle powder having such characteristics, the starting material, goethite particle powder, has a large axial ratio (major axis diameter / minor axis diameter), and the particle size is uniform. However, it is necessary that 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 generating 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.

In the above method, a water-soluble silicate is added during the reaction in order to improve the particle size of the acicular goethite particles formed (Japanese Patent Publication No. 55-8461 and Japanese Patent Publication No. 55-32652). Japanese Patent Publication No. JP-A-2003-242242), a method of adding a water-soluble silicate and a water-soluble zinc salt during the reaction in order to improve the particle size and axial ratio (major axis diameter / minor axis diameter) of the acicular goethite particles produced (JP-B-55) No. 6575, Japanese Patent Publication No. 55-6576) and the like are known.

[0013]

SUMMARY OF THE INVENTION Large axial ratio (major axis diameter /
A magnetic particle powder having a (minor axis diameter), a uniform particle size and no mixed dendritic particles is currently most demanded, but it produces a goethite particle powder as a starting material. In the case of the above-mentioned method, acicular goethite particles having a large axial ratio (major axis diameter / minor axis diameter), especially 10 or more, are generated, but dendritic particles are mixed and the particle size is Therefore, it cannot be said that the particles have a uniform particle size.

In the case of the above-mentioned method, particles having a uniform particle size and having a spindle shape in which dendritic particles are not mixed are produced, while the axial ratio (major axis diameter / minor axis) is used. Diameter)
Is about 7 at most, and there is a drawback that particles with a large axial ratio (major axis diameter / minor axis diameter) are difficult to be generated. In particular, this phenomenon becomes more remarkable as the major axis diameter of generated particles becomes smaller. There is a tendency.

In the case of the above-mentioned method, needle-shaped goethite particles having a uniform particle size and containing no dendritic particles are produced, but the axial ratio (major axis diameter / minor axis diameter) is about 9 at most. As the amount of water-soluble silicate added increases, the particle size becomes uniform and dendritic particles do not coexist, but the axial ratio (major axis diameter / minor axis diameter) tends to decrease rapidly. is there.

In the case of the above-mentioned method, acicular goethite particles having a large axial ratio (major axis diameter / minor axis diameter) are produced, but the effect of improving the axial ratio (major axis diameter / minor axis diameter) is obtained. With the addition of water-soluble zinc having a particle size, the particle size becomes asymmetric, and dendritic particles are likely to be mixed.
Since the production amount per unit volume (hereinafter referred to as the production amount) is reduced, the production efficiency is reduced, which is not industrially or economically problematic.

Therefore, in the present invention, a large axial ratio (major axis diameter /
(Minor axis diameter), with more uniform particle size and no dendritic particles mixed in, acicular goethite particles can be produced in an industrially and economically advantageous manner by increasing the production amount and increasing production efficiency. Is a technical issue.

[0018]

The above technical problems can be achieved by the present invention as follows.

That is, according to the present invention, p containing ferrous hydroxide obtained by reacting a ferrous salt aqueous solution with an alkaline aqueous solution.
In the method for producing acicular goethite particles by passing an oxygen-containing gas through a suspension of H11 or more to oxidize the suspension, the suspension before the oxidizing reaction is performed by passing the alkaline aqueous solution and the oxygen-containing gas. Water-soluble silicate in any one of the liquids of 0.1 to 0.
A water-soluble aluminum salt is added in an amount of 7 atomic% and is added to any one of the suspensions before the oxidation reaction is performed by passing the ferrous salt aqueous solution, the alkaline aqueous solution and the oxygen-containing gas. Is 0.1 to 3 in terms of Al with respect to Fe.
This is a method for producing acicular goethite particle powder, which comprises producing acicular goethite particles containing Si and Al by adding 0 atomic%.

[0020]

First, the most important point in the present invention is to ventilate an oxygen-containing gas into a suspension having a pH of 11 or more containing ferrous hydroxide obtained by reacting an aqueous ferrous salt solution with an aqueous alkaline solution. In the method for producing acicular goethite particles by oxidizing the water-soluble silicate in the liquid of any of the suspensions before the oxidation reaction by aeration of the alkaline aqueous solution and oxygen-containing gas. The suspension before adding 0.1 to 0.7 atom% in terms of Si in terms of Si and aerating the aqueous solution of ferrous salt, the aqueous alkaline solution and an oxygen-containing gas to cause an oxidation reaction. When a water-soluble aluminum salt is added to any one of the liquids in an amount of 0.1 to 3.0 atom% in terms of Al with respect to Fe, a large axial ratio (major axis diameter / minor axis diameter) is obtained. Having dendritic grains with a more uniform grain size There is a fact that can be mixed acicular goethite particles not more increased production by efficiently generated.

In the present invention, the reason why needle-shaped goethite particles having a large axial ratio (major axis diameter / minor axis diameter), a more uniform particle size and no mixed dendritic particles can be efficiently produced. As described in Comparative Examples below, the present inventor has an object in any method in which each of water-soluble silicate or water-soluble aluminum salt is added alone in the reaction for producing goethite particles. Since acicular goethite particles cannot be efficiently generated, it is considered to be due to the synergistic effect of the water-soluble silicate and the water-soluble aluminum salt.

There is a method described in JP-A-64-33019 for adding a silicon compound and an aluminum compound in the reaction for forming acicular goethite particles. This method is to supply an oxygen-containing gas to a suspension containing ferrous hydroxide while adding a silicon compound and an aluminum compound, and increase the production amount of acicular goethite particles by a high-concentration reaction. The more the particle size becomes asymmetric and the dendritic particles increase, the more the effect and effect of the present invention are completely different.

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

Examples of the ferrous salt used in the present invention include ferrous sulfate aqueous solution and ferrous chloride aqueous solution.

Examples of the alkaline aqueous solution used in the present invention include sodium hydroxide aqueous solution and potassium hydroxide aqueous solution.

Examples of the water-soluble silicate used in the present invention include sodium silicate and potassium silicate.

The amount of the water-soluble silicate added is 0.1 to 0.7 atom% in terms of Si with respect to Fe. 0.1 atom%
If it is less than the above range, it is difficult to produce a needle-shaped goethite particle powder in which the particle size targeted by the present invention is more uniform and dendritic particles are not mixed. 0.7 atom%
If it exceeds, the acicular goethite particles having a large axial ratio (major axis diameter / minor axis diameter) cannot be obtained.

The water-soluble silicate in the present invention is involved in the particle size of the acicular goethite particles produced and the morphology of dendritic particles and the like. It needs to be performed before the addition, and can be added to any of the solutions in the suspension containing the alkaline aqueous solution and ferrous hydroxide.

The water-soluble aluminum salt used in the present invention includes aluminum sulfate, sodium aluminate, aluminum chloride and the like.

The amount of the water-soluble aluminum salt added is Fe
On the other hand, it is 0.1 to 3.0 atom% in terms of Al. 0.1
When the content is less than atomic%, it is difficult to produce the acicular goethite particle powder which is more uniform in particle size and does not contain dendritic particles, which is the object of the present invention. 3.0
When the content exceeds the atomic%, the effect of the present invention can be obtained, but the saturation magnetization of the acicular magnetic iron oxide particle powder obtained by using the acicular goethite particles produced is lowered.

The water-soluble aluminum salt in the present invention is involved in the axial ratio (major axis diameter / minor axis diameter) of the acicular goethite particles produced, particle size, morphology of dendritic particles and the like, and therefore its addition. It is necessary that the time is before the oxygen-containing gas is ventilated to carry out the oxidation reaction, and in any solution of the ferrous salt aqueous solution, the alkaline aqueous solution and the suspension containing ferrous hydroxide. It can be added.

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

Next, the present invention will be described with reference to examples and comparative examples.

The major axis diameter and the axial ratio (major axis diameter / minor axis diameter) of the particles in the following Examples and Comparative Examples are all shown as the average value 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 Si and Al contained in the acicular goethite particles were measured by fluorescent X-ray analysis.

Example 1 Ferrous sulfate 1.5 mol / l obtained by adding aluminum sulfate so as to contain 1.0 atom% in terms of Al / Fe.
Sodium silicate (No. 3) (SiO ₂ 28.55 wt%) 37.8 was added so that 24 l of the aqueous solution contained 0.50 atomic% in terms of Si / Fe prepared in advance in the reactor.
6.7-N NaOH aqueous solution obtained by adding g (corresponding to 0.50 atomic% in terms of Si / Fe) 26
In addition to 1, Fe (O
An aqueous solution containing H) ₂ and Al (OH) ₃ was obtained.

Needle-like goethite particles were produced by bubbling 100 l / min of air at a temperature of 50 ° C. for 9 hours through the aqueous solution containing Fe (OH) ₂ and Al (OH) ₃ . The production amount was 7.1 g / l / hour. The end point of the oxidation reaction is
It was judged by the presence or absence of blue color reaction of Fe ²⁺ using a 1% hydrochloric acid acidic red blood salt solution. The produced particles were washed with water, filtered, dried and pulverized by a conventional method. The acicular goethite particles are made of Si
/ Fe was 0.61 atomic%, and Al / Fe was 1.0 atomic%.

Further, the electron micrograph (× 30
000), it is clear that the long axis is 0.46 on average.
The average particle size was 25 μm, the axial ratio (major axis diameter / minor axis diameter) was 25, the standard deviation value was 0.78, and the particle size was uniform, and dendritic particles were not mixed.

Examples 2 to 4 Various changes of ferrous salt aqueous solution type, Fe ²⁺ concentration, NaOH aqueous solution concentration, type of water-soluble aluminum salt, addition amount and timing, addition amount of water-soluble silicate Needle-shaped goethite particles were produced in the same manner as in Example 1 except that the above-mentioned procedure was performed. The main manufacturing conditions at this time are shown in Table 1, and various characteristics are shown in Table 2. The needle-shaped goethite particle powders obtained in Examples 2 to 4 all have a large axial ratio (major axis diameter / minor axis diameter) as a result of electron microscope observation, and do not contain dendritic particles.
The particles having a geometric standard deviation value of 0.70 or more were uniform. Also, the production amount is preferably 6.3 g / l / hour,
It was 6.5 g / l / hour or more, and the production efficiency was excellent.

Comparative Example 1 A needle-shaped goethite particle powder was produced in the same manner as in Example 4 except that the water-soluble aluminum salt and the water-soluble silicate were not added. The main manufacturing conditions at this time are shown in Table 1, and various characteristics are shown in Table 2. The obtained acicular goethite particle powder is an electron micrograph (× 30000) shown in FIG.
As shown in (1), dendritic particles were mixed, and the geometric standard deviation value was 0.52, and the particles were asymmetrical.

Comparative Example 2 Without adding aluminum sulfate, sodium silicate (No. 3)
Needle-shaped goethite particle powder was produced in the same manner as in Example 4 except that (SiO ₂ 28.55 wt%) was changed to 0.50 atom% in terms of Si / Fe. The main manufacturing conditions at this time are shown in Table 1, and various characteristics are shown in Table 2. The obtained acicular goethite particle powder is an electron micrograph (× 300) shown in FIG.
As shown in (00), the particles had a small axial ratio (major axis diameter / minor axis diameter).

Comparative Example 3 A needle-shaped material was prepared in the same manner as in Example 4 except that the water-soluble silicate was not added and the addition amount of aluminum sulfate was changed to 1.0 atom% in terms of Al / Fe to change the addition timing. A goethite particle powder was produced. The main manufacturing conditions at this time are shown in Table 1, and various characteristics are shown in Table 2. The obtained acicular goethite particle powder is as shown in the electron micrograph (× 30000) shown in FIG.
Dendritic particles were mixed, and the geometric standard deviation was 0.52, and the particles were asymmetric in particle size.

Comparative Example 4 A production reaction was carried out in the same manner as in Example 1 except that the method of adding the water-soluble aluminum salt and the water-soluble silicate was changed. The main manufacturing conditions at this time are shown in Table 1, and various characteristics are shown in Table 2. The particle powder obtained in Comparative Example 4 was an asymmetric particle with a geometric standard deviation of 0.57. Moreover, the production amount was 3.6 g / l / hour, and the production efficiency was extremely poor.

[0045]

EFFECTS OF THE INVENTION According to the method for producing acicular goethite particles according to the present invention, as shown in the above-mentioned examples, a large axial ratio (major axis diameter / minor axis diameter) and a uniform particle size are obtained. However, the needle-shaped goethite particle powder in which the resinous particles are not mixed can be obtained industrially and economically by increasing the production amount and increasing the production efficiency.

The needle-shaped goethite particle powder thus obtained is used as a starting material, and the needle-shaped magnetite particle powder obtained by heating and reducing, or the needle-shaped maghemite particles obtained by further oxidizing after heating and reducing. In addition, since the particles have a large axial ratio (major axis diameter / minor axis diameter), and the particle size is more uniform and dendritic particles are not mixed, the high recording density currently required most, It is suitable as a magnetic particle powder for high sensitivity and high output.

[0047]

[Brief description of drawings]

1 to 5 show "Example 1" and "Comparative Example 1", respectively.
8 to 10 are electron micrographs (× 30000) showing the particle structure of the acicular goethite particles obtained in “Comparative Example 4”.

[Table 1]

[Table 2]

Claims (1)

[Claims] 1. Needle-shaped goethite particles obtained by reacting a ferrous salt aqueous solution with an alkaline aqueous solution, which is obtained by reacting a ferrous hydroxide aqueous solution, with a suspension having a pH of 11 or more and passing an oxygen-containing gas to oxidize the suspension. In the method for producing, a water-soluble silicate is added to Fe in an amount of 0.1 in terms of Si in the liquid of any one of the suspensions before the oxidation reaction is performed by passing the alkaline aqueous solution and the oxygen-containing gas. To 0.7 atomic% of water, and water is added to any one of the suspensions before the oxidation reaction is performed by aerating the ferrous salt aqueous solution, the alkaline aqueous solution, and the oxygen-containing gas. A needle-shaped goethite particle powder characterized by producing acicular goethite particles containing Si and Al by adding a soluble aluminum salt to Fe in an amount of 0.1 to 3.0 atom% in terms of Al. Manufacturing method.