JPH0570146A - Method for producing needle-like goethite particle powder - Google Patents

Abstract

PURPOSE:To industrially produce needle-like goethite particle powder having a uniform particle size and a high axis ratio (major axis diameter/minor axis diameter) free from admixture of dendritic particles. CONSTITUTION:In a method for producing needle-like goethite particle powder by introducing an oxygen-containing gas to a ferrous hydroxide colloid obtained by reacting an aqueous solution of ferrous salt with <equivalent based on Fe<+2> in the solution of an alkali aqueous solution or a reaction solution of a ferrous salt having an iron-containing precipitate colloid to form needle-like goethite nucleus particle from green RAST and then growing the needle-like goethite nucleus particle, before the needle-like goethite nucleus particle are formed, an alkylamine or an oxyalkylamine is added to the solution to give needle-like goethite particle powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a uniform particle size suitable as a starting material for producing magnetic particle powder for magnetic recording, does not contain dendritic particles, and has a large axial ratio (long It is an object of the present invention to provide a new production method whereby an acicular goethite particle powder having an axial diameter / minor axis diameter-the same applies hereinafter) is industrially obtained.

[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 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. This fact is, for example, published by General Technology Center Co., Ltd. "Development of magnetic materials and high-dispersion technology of magnetic powder" (1982), page 310, "... The aim of improving the magnetic tape performance was to improve the sensitivity, increase the output, and reduce the noise. The focus was on high coercive force and fine particle formation of the Fe ₂ O ₃ particle powder.

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 Particles", 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. For that purpose, coercive force Hc and residual magnetization Br are required. As described above, it is necessary for the magnetic recording medium to have a high coercive force and a large residual magnetization Br. It is required that the magnetic particle powder has a high coercive force and is excellent in the dispersibility in the vehicle, the orientation in the coating film and the 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, and 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 known magnetic particle powders are obtained by using goethite particles as a starting material or acicular hematite particles obtained by heat-treating the goethite particles in a reducing gas such as hydrogen to reduce magnetite particles or iron. It is obtained by using metal particles as a main component, or by oxidizing the magnetite particles in air to form 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 particle size of the magnetic particle powder dispersed in is uniform, that dendritic particles are not mixed, and that it have a large axial ratio.

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

Conventionally, various attempts have been made to obtain needle-shaped goethite particles having a uniform particle size and containing no dendritic particles. As a technical means using an organic compound,
JP-B-47-40758 (oxycarboxylic acid or alkali salt thereof), JP-B-53-39880 (aliphatic polyhydric alcohol containing two or more hydroxyl groups),
JP-B-55-4694 (organic phosphonic acid compound), JP-A-53-87998 (aromatic nitro derivative), JP-A-59-78930 (dibasic acid containing a double bond or a salt thereof). ), JP-A-60-21817 (hydroxycarboxylic acid or its salt or its ester), JP-A-60-21818 (hydroxycarboxylic acid or its salt or its ester), JP-A-2-293330 ( Uronic acid, aldonic acid,
Alternatively, lactones thereof or salts thereof and the like can be mentioned.

As a prior art using an alkylamine or an oxyalkylamine, Japanese Patent Laid-Open No. 61-1685 is available.
There are those disclosed in Japanese Patent Laid-Open No. 34-34, Japanese Patent Application Laid-Open No. 62-120310, etc., all of which are technical means for producing plate-shaped goethite particles.

[0012]

As described above, the needle-shaped goethite particle powder having a uniform particle size and no dendritic particles mixed therein and having a large axial ratio is the most demanded at present. There is, however, the above-mentioned Japanese Patent Publication No. 47-407.
58, JP-A-53-87998, JP-A-5
In the technical means disclosed in JP-A No. 9-78930, JP-A No. 60-21817, and JP-A No. 60-21818, the axial ratio is as small as about 10 or less, and Japanese Patent Publication No. 53-39880. Publication, Japanese Patent Publication No. 55-46
In many of the technical means disclosed in Japanese Patent Application Laid-Open No. 94-93, and Japanese Patent Application Laid-Open No. 2-293330, the axial ratio is about 10, and some of them have a larger reaction in the alkaline region where the axial ratio tends to be large, but at most 15 It is a degree.

The reason why the axial ratio is likely to be large in the reaction in the alkaline region is that in the above-mentioned Japanese Patent Laid-Open No. 2-293330, "... Generally, the acidic method has an advantage that uniform particles having a narrow particle size distribution can be obtained. On the other hand, it has the drawback that particles with a high axial ratio are difficult to obtain and the shape retention in post-treatments such as heat dehydration treatment is poor.On the other hand, the alkali method gives particles with a high axial ratio and heat dehydration treatment etc. Although it has the advantage of excellent shape retention in the post-treatment, it has the drawback of widening the particle size distribution range.

When the alkali method is used,
Since an alkaline aqueous solution of about 2 equivalents or more is used with respect to Fe ²⁺ in the ferrous salt aqueous solution, it becomes expensive and the pollution treatment cost is considerably high when the waste alkaline water solution used is treated excessively. Become.

Therefore, the present invention is technically an industrial method for producing acicular goethite particle powder having a uniform particle size and no dendritic particles mixed therein by the acidic method and having a large axial ratio. This is an issue.

[0016]

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

That is, the present invention is selected from an aqueous solution of a ferrous salt and an aqueous solution of an alkali hydroxide which is less than an equivalent amount to Fe ²⁺ in the aqueous solution of the ferrous salt, an aqueous solution of an alkali carbonate, or an aqueous solution of a mixed alkali hydroxide and an alkali carbonate. The ferrous hydroxide colloid or the iron-containing precipitate obtained by reacting the ferrous hydroxide colloid or the iron-containing precipitate colloid obtained by reacting with an aqueous alkali solution is passed through an oxygen-containing gas. In the method of producing acicular goethite core particles by oxidizing acetic acid colloids via green rust, and then growing the goethite nucleus particles, the acicular goethite core particles Of acicular goethite particles consisting of allowing alkylamine or oxyalkylamine to exist in the liquid before the formation of It is a concrete method.

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

As the aqueous ferrous salt solution used in the present invention, an aqueous ferrous sulfate solution, an aqueous ferrous chloride solution or the like can be used.

As the alkali hydroxide aqueous solution used in the present invention, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution or the like may be used, and as the alkali carbonate aqueous solution, sodium carbonate aqueous solution, potassium carbonate aqueous solution, ammonium carbonate aqueous solution or the like may be used. It is also possible to use a mixed aqueous solution of these.

The amount of the alkali hydroxide aqueous solution, the alkali carbonate aqueous solution, or the alkali hydroxide / alkali carbonate mixed aqueous solution used is less than the equivalent amount to Fe ²⁺ in the ferrous salt aqueous solution. If the amount is more than the equivalent, needle-shaped goethite particles having a uniform particle size and containing no dendritic particles cannot be obtained. Also, magnetite particles may be mixed.

The amount of acicular goethite core particles in the present invention is preferably 10 mol% or more based on the produced goethite particles. When it is less than 10 mol%, it becomes difficult for the growth reaction to occur while maintaining the morphology of the generated acicular goethite core particles, and the acicular goethite particles intended by the present invention cannot be obtained.

Since the alkylamine or oxyalkylamine in the present invention affects the particle size of the acicular goethite particles to be formed, the presence or absence of dendritic particles, the axial ratio, and the like, acicular goethite core particles are generated. It is necessary to keep it in the previous liquid, and the ferrous salt solution,
Any of an alkali hydroxide aqueous solution, an alkali carbonate aqueous solution or an alkali hydroxide / alkali carbonate mixed aqueous solution, a ferrous salt reaction solution containing a ferrous hydroxide colloid or an iron-containing precipitate colloid, and a reaction solution at the time of forming green rust You may add in a liquid.

As the alkylamine, methylamine,
Aliphatic primary amines such as ethylamine and propylamine,
Aliphatic secondary amines such as dimethylamine, diethylamine and dipropylamine, and aliphatic tertiary amines such as trimethylamine, triethylamine and tripropylamine, etc., and water-soluble ones thereof can be used.

As the oxyalkylamine, there are monomethanolamine, dimethanolamine, trimethanolamine, monoethanolamine, diethanolamine, triethanolamine and the like, and water-soluble ones thereof can be used.

The amount of alkylamine or oxyalkylamine added is 5 to 30 mol% with respect to Fe ²⁺ . 5
If it is less than mol%, the target particle size of the present invention is uniform, dendritic particles are not mixed, and acicular goethite particles having a large axial ratio cannot be obtained. Thirty
When it exceeds mol%, the major axis diameter of the acicular goethite particles produced becomes small, and as a result, the axial ratio also becomes small, and the acicular goethite particles aimed at by the present invention cannot be obtained.

The growth reaction of the acicular goethite nucleus particles in the present invention is carried out by adding ferrous salt to the reaction solution containing the acicular goethite nucleus particles, if necessary, and then adding oxygen to the reaction solution while maintaining the pH at 3 to 6. A method of aerating a containing gas, if necessary for the ferrous salt reaction solution containing the acicular goethite nucleus particles,
After adding the ferrous salt, an aqueous solution of alkali carbonate or a mixed solution of alkali carbonate and alkali hydroxide is added to adjust the pH to 8 to
A method of ventilating an oxygen-containing gas in the range of 10 and a ferrous salt reaction solution containing the acicular goethite core particles, if necessary, after adding a ferrous salt, and then adding an aqueous alkali hydroxide solution to a pH of 11 or more. Any method of ventilating the oxygen-containing gas may be used.

The reaction temperature in the present invention is usually 80 ° C. or lower at which goethite particles are formed. 8
When the temperature exceeds 0 ° C, granular magnetite particles are mixed in the acicular goethite particles.

The oxidizing means in the present invention is carried out by aerating an oxygen-containing gas (for example, air) in the liquid, and may be accompanied by agitation by mechanical operation if necessary.

In the present invention, not only the reaction for producing goethite nucleus particles and the reaction for growing goethite nucleus particles can be carried out in the same reaction tower, but also in the case where separate reaction towers are used. The target goethite particles are obtained.

Further, in the present invention, in order to improve the characteristics of the magnetic particle powder and the like, heterogeneous elements other than Fe such as Co, Ni, Zn, P, Al and Si, which are usually added during the formation reaction of goethite particles, are used. It can be added, and the same effect can be obtained in this case as well.

[0032]

In the present invention, a ferrous hydroxide colloid or an iron-containing precipitate colloid obtained by reacting an aqueous ferrous salt solution with an aqueous alkali solution having an equivalent amount to Fe ²⁺ in the liquid is included. The ferrous salt reaction solution was ventilated with an oxygen-containing gas for oxidation to generate needle-shaped goethite core particles via Greenlast, and then the needle-shaped goethite particles were grown by growing the goethite core particles. In the method of producing, when the alkylamine or oxyalkylamine is present in the liquid before the acicular goethite core particles are produced, the particle size is uniform and dendritic particles are not mixed, Moreover, needle-shaped goethite particles having a large axial ratio, in particular, an axial ratio of 10 or more are obtained.

As a method for producing acicular goethite particle powder, there are an acid method and an alkali method. The acid method is inferior in shape retention, and the alkali method is excellent in shape retention. Japanese Patent Laid-Open No. 2-2933.
It is stated in JP-A-30.

Therefore, the present inventor uses the acidic method, which can be manufactured at a low cost, has a uniform particle size having a shape-retaining property similar to that of the alkaline method and does not contain dendritic particles.
Regarding the method by which the acicular goethite particle powder having a large axial ratio can be obtained, the difference was examined by measuring the X-ray particle size of each goethite particle obtained by the acidic method and the alkaline method.

As a result, as shown in FIG. 1, the ratio of the (100) plane X-ray grain size to the (010) plane X-ray grain size of the goethite particles (hereinafter referred to as D010 / D100) is different. I found out that The goethite particles A obtained by the acidic method have D010 / D100 of 1.0 to
In contrast to 1.4, Goethite particles B obtained by the alkali method had D010 / D100 of 1.6 to 2.3.

Then, the D010 / D100 is prepared by the acid method.
As a result of investigating a method in which the oxygen content is about 2, the oxygen-containing gas is passed through the ferrous salt reaction solution containing the ferrous hydroxide colloid or the iron-containing precipitate colloid to oxidize, and the goethite nucleus is passed through the green last. D010 / D of needle-shaped goethite particles obtained by allowing alkylamine or oxyalkylamine to exist in the liquid before the particles are formed.
We have found that 100 is close to 2.

The value of D010 / D100 is determined from the half-value width of the diffraction line measured using an "X-ray diffractometer RAD-IIA type" (manufactured by Rigaku Denki Co., Ltd.).
The X-ray particle size was measured and determined by the equation (Rer).

As the growth reaction of the acicular goethite nucleus particles in the present invention, the oxygen-containing gas is aerated while the pH of the ferrous salt reaction solution containing acicular goethite nucleus particles is maintained at 3 to 6, as described above. To the ferrous salt reaction solution containing the acicular goethite core particles, an aqueous solution of alkali carbonate or a mixed solution of alkali carbonate and alkali hydroxide is added to adjust the pH to 8
Any of a method of ventilating an oxygen-containing gas in the range of 10 to 10 and a method of ventilating the oxygen-containing gas at a pH of 11 or more by adding an aqueous alkali hydroxide solution to the ferrous salt reaction solution containing the acicular goethite nucleus particles. But it's okay.

Among them, the preferred method is to carry out the growth reaction in the alkaline range of pH 8 to 10 or pH 11 or more. In this case, impurities such as sulfur and chlorine do not remain on the surface of the particles. Since sintering does not occur during heating and reduction and the particle shape does not collapse, acicular goethite particle powder having a uniform particle size and a large axial ratio, particularly an axial ratio of 15 or more can be obtained.

The most preferable method is to add an aqueous solution of an alkali carbonate to a ferrous salt reaction solution containing needle-shaped goethite core particles, and aerate an oxygen-containing gas in a pH range of 8 to 10 to carry out an oxidation reaction. In this case, FeCO ₃ produced by the reaction of Fe ²⁺ and alkali carbonate remaining in the ferrous salt reaction solution produces needle-shaped crystals of goethite nucleus particles produced from Greenlast. Since the crystal habit can be taken over and the axial ratio can be further increased, acicular goethite particle powder having a uniform particle size and a large axial ratio, particularly an axial ratio of 20 or more can be obtained.

[0041]

EXAMPLES Next, the method of the present invention will be described with reference to Examples and Comparative Examples. The major axis diameter and the axial ratio 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 value of D010 / D100 is determined from the half-value width of the diffraction line measured using an "X-ray diffractometer RAD-IIA type" (manufactured by Rigaku Denki Co., Ltd.).
The X-ray particle size was measured and determined by the equation of r).

Example 1 Aqueous ferrous sulfate solution 25 containing 1.0 mol / l of Fe ²⁺
1 and 20 l of a 1.25N NaOH aqueous solution (corresponding to 0.5 equivalent to Fe ²⁺ in the ferrous sulfate aqueous solution) were mixed, and Fe (O 2) was added at pH 7.4 and a temperature of 38 ° C.
A ferrous sulfate aqueous solution containing H) ₂ was produced.

5 l of an aqueous solution containing 152.8 g of monoethanolamine in the aqueous ferrous sulfate solution containing Fe (OH) ₂ (monoethanolamine is 10 m with respect to Fe ²⁺ ).
Corresponds to ol%. ) Was added, 50 l of air per minute was aerated for 3 hours at a temperature of 40 ° C. to generate goethite particles. FIG. 2 shows an electron micrograph (× 30000) of the particle powder obtained by extracting a part of the reaction solution, filtering, washing with water and drying by a conventional method.

The obtained acicular goethite particle powder is shown in FIG.
As shown in, the acicular particles had a major axis diameter of 0.17 μm and an axial ratio of 12. Moreover, the particle size was uniform and dendritic particles were not mixed.

The above-mentioned goethite particles are used as acicular goethite core particles, and an aqueous ferrous sulfate solution containing the acicular goethite core particles (the amount of goethite core particles present is 50 mol% with respect to the produced goethite particles). Add 10 l of 5.0 N Na ₂ CO ₃ aqueous solution (corresponding to 2.0 equivalents to Fe ²⁺ in the residual ferrous sulfate aqueous solution) and add pH.
9.4, 100 liters of air per minute at a temperature of 40 ° C
Aerated for a period of time to produce a goethite particle powder. The produced goethite particles were filtered, washed with water and dried by a conventional method.

The obtained goethite particle powder had a major axis diameter of 0. 0 as shown in the electron micrograph (× 30000) of FIG.
The particles were acicular particles having a particle size of 30 μm and an axial ratio of 20. Also, D01
0 / D100 was 1.85, and the particle size was uniform and dendritic particles were not mixed.

Examples 2 to 5, Comparative Examples 1 and 2 Type and amount of ferrous salt aqueous solution, type and concentration and amount of alkaline aqueous solution, alkylamine or oxyalkylamine when acicular goethite core particles are formed. Type, amount and time of addition, type of different element, amount and time of addition, reaction temperature at the time of formation and aeration rate of air, amount of goethite nucleus particles present during growth reaction of acicular goethite nucleus particles, type of alkaline aqueous solution Needle-shaped goethite particles were produced in the same manner as in Example 1 except that the concentration, the amount used, the pH during the reaction, the reaction temperature, and the air aeration amount were variously changed.

The main production conditions and various characteristics of the acicular goethite particles produced at this time are shown in Tables 1 and 2.

The needle-shaped goethite particles obtained in Examples 1 to 5 were observed by an electron microscope and found to have a uniform particle size and no dendritic particles mixed therein, a large axial ratio, and D0.
10 / D100 was also close to 2.

The needle-shaped goethite particles obtained in Comparative Example 1 were asymmetric in particle size and contained dendritic particles. Further, the axial ratio was small, and D010 / D100 was about 1.

In Comparative Example 2, the needle-shaped goethite particles are directly generated by passing an oxygen-containing gas at a pH of 11 or more without generating the needle-shaped goethite core particles via green last.

[0053]

[Table 1]

[0054]

[Table 2]

[0055]

According to the method for producing needle-shaped goethite particle powder according to the present invention, as shown in the above-mentioned Examples, the particle size is uniform, dendritic particles are not mixed, and the large axis is large. An acicular goethite particle powder having a ratio can be obtained.

The needle-shaped magnetite particle powder obtained by heating and reducing the needle-shaped goethite particle powder according to the present invention as a starting material, and the needle-shaped maghemite particle powder obtained by heat-reducing and then oxidizing the particles also have particle sizes. Is uniform, does not contain dendritic particles, and has a large axial ratio, and is suitable as a magnetic particle powder for high recording density, high sensitivity, and high output.

[Brief description of drawings]

FIG. 1 X-ray grain size (D100) and D01 of (100) plane.
FIG. 3 is a diagram showing the relationship between 0 / D100 and the relationship between goethite particles A obtained by the acidic method and goethite particles B obtained by the alkaline method.

FIG. 2 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite core particle powder obtained in Example 1.

3 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite particle powder obtained in Example 1. FIG.

FIG. 4 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite core particle powder obtained in Example 4.

FIG. 5 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite particle powder obtained in Example 4.

6 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite core particle powder obtained in Comparative Example 1. FIG.

FIG. 7 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite particle powder obtained in Comparative Example 1.

FIG. 8 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite particle powder obtained in Comparative Example 2.

Claims (1)

[Claims] 1. An aqueous ferrous salt solution and an aqueous alkali hydroxide solution or an aqueous alkaline carbonate solution selected from an aqueous solution of an alkaline carbonate or an alkaline hydroxide / alkali carbonate mixed solution which is less than equivalent to Fe ²⁺ in the aqueous ferrous salt solution. Oxygen-containing gas is passed through a ferrous salt reaction solution containing ferrous hydroxide colloid or iron-containing precipitate colloid obtained by reacting the above to oxidize the ferrous hydroxide colloid or iron-containing precipitate colloid. By generating needle-shaped goethite core particles via green last, then in a method of generating needle-shaped goethite particles by growing the goethite core particles, before the needle-shaped goethite core particles are generated. A method for producing acicular goethite particle powder, characterized in that an alkylamine or an oxyalkylamine is present in the liquid.