JP3011221B2 - Method for producing acicular goethite particle powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a large axis ratio (major axis diameter / short axis diameter-the same applies hereinafter) which is suitable as a starting material for producing magnetic particle powder for magnetic recording, and has a particle size. An object of the present invention is to provide a method for industrially obtaining acicular goethite particle powder that is uniform and does not contain dendritic particles.

[0002]

2. Description of the Related Art In recent years, as the size of a magnetic recording / reproducing apparatus has been reduced, a recording medium such as a magnetic tape or a magnetic disk has been required to have high recording density, high sensitivity characteristics, high output characteristics, and the like.

[0003] The characteristics of magnetic material particles required to satisfy the above requirements for a 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 a magnetic recording medium, it is necessary that the magnetic particle powder has a coercive force as high as possible. "Development of Magnetic Materials and Technology for Highly Dispersing Magnetic Powder" (1982), p. 310, "‥‥ Improvement of magnetic tape performance was due to high sensitivity, high output and low noise. The emphasis was on increasing the coercive force and reducing the particle size of the Fe ₂ O ₃ particles.

To increase the recording density of a magnetic recording medium, the condition for high-density recording on a coating tape is as follows: High output characteristics can be maintained with low noise with respect to the wavelength signal. For this purpose, it is necessary that both the coercive force Hc and the residual magnetization Br are large and the thickness of the coating film is thinner. As described in “‥‥”, it is necessary that the magnetic recording medium has a high coercive force and a large remanent magnetization Br, and for that, 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 residual magnetization Br of a magnetic recording medium depends on the dispersibility of the magnetic particle powder in a vehicle, the orientation in a coating film, and the filling property. It is required that the magnetic particle powder has a large axial ratio, a uniform particle size, and no dendritic particles.

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

At present, magnetic iron oxide particles such as acicular magnetite particles and acicular maghemite particles used as magnetic particles for magnetic recording, or metallic magnetic particles containing iron as a main component are formed into a shape. 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 starting materials 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 forming metal magnetic particles as a main component and heating and oxidizing the magnetite particles in air to form maghemite particles.

As described above, magnetic particle powders having a large axial ratio, uniform particle size, and free of dendritic particles are currently the most demanded, and have such characteristics. In order to obtain magnetic particle powder, it is necessary that goethite particle powder, which is a starting material, has a large axial ratio, has a uniform particle size, and does not contain dendritic particles.

Conventionally, as a method for producing goethite particle powder as a starting material, a suspension containing a ferrous hydroxide colloid obtained by adding an equivalent or more of an aqueous alkali hydroxide solution to an aqueous ferrous salt solution is used. A method of producing needle-like goethite particles by passing an oxygen-containing gas at a temperature of 80 ° C. or lower to carry out an oxidation reaction (Japanese Patent Publication No.
No. 5610), spindle-shaped goethite particles formed by passing an oxygen-containing gas through a suspension containing FeCO ₃ obtained by reacting an aqueous ferrous salt solution and an aqueous alkali carbonate solution to perform an oxidation reaction. (Japanese Unexamined Patent Publication No.
0-80999) and the like.

Further, an oxygen-containing gas is passed through a suspension obtained by adding an equivalent amount or more of an aqueous alkali hydroxide solution to a mixed aqueous solution of an aqueous ferrous salt solution and an aqueous cobalt salt solution to carry out an oxidation reaction. A method for producing acicular goethite particles containing the same (JP-A-48-82395);
In the above method, a method of adding an aluminum compound to the suspension for the purpose of improving the acicularity of the acicular goethite particles to be formed ( Japanese Patent Publication No. 47-30377).
Bulletin, JP-B-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 mixture of dendritic particles, which is currently the most required, is a starting material. In the case of the above-described method for producing goethite particle powder, needle-like goethite particles having a large axial ratio, particularly an axial ratio of 10 or more are generated, but dendritic particles are mixed, and uniform It is hard to say that the particles have a particle size.

In the case of the above-mentioned method, spindle-shaped particles having a uniform particle size and containing no dendritic particles are produced. On the other hand, the axial ratio is at most about 7 and the axial ratio is at most about 7. However, this phenomenon tends to become more pronounced as the major axis diameter of the produced particles decreases.

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 ferrous salt solution with an aqueous alkali hydroxide solution. Since the viscosity of the alkaline suspension containing the compound becomes high and the reaction time becomes long, the particle size of the acicular goethite particles formed is uneven, and dendritic particles are mixed.

According to the above method, 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 the amount is large, magnetite is mixed with goethite, which causes a problem.

In addition, when the above method is combined with the above, there arises 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.

Accordingly, the present invention provides acicular goethite particles containing Co and Al, which have a large axial ratio, are more uniform in particle size, do not contain dendritic particles, and do not contain magnetite. Generating it is a technical task.

[0019]

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

That is, according to the present invention, an oxygen-containing gas is passed through an alkaline suspension having a pH of 11 or more and containing ferrous hydroxide obtained by reacting an aqueous ferrous salt solution with an aqueous alkali hydroxide solution to oxidize. In the method for producing needle-like goethite particles, a water-soluble cobalt salt is previously added to the aqueous ferrous salt solution in an amount of 0.1 to 1 in terms of Co with respect to Fe.
0.0 atomic% is added, and a water-soluble aluminum salt is added to either one of the ferrous salt aqueous solution and the alkali hydroxide aqueous solution in terms of Al to 0.5 to 5.
0 atomic% is added, and the aqueous ferrous salt solution is reacted with the aqueous alkali hydroxide solution to form p-containing ferrous hydroxide.
An alkaline suspension of H11 or more is obtained. Then, while oxidizing by passing an oxygen-containing gas through the suspension, Co and Al are further contained by adding a water-soluble aluminum salt aqueous solution. A method for producing acicular goethite particle powder, which comprises producing acicular goethite particles.

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

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

As the aqueous alkali hydroxide 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 and the like can be used.

The addition amount of the water-soluble cobalt salt is 0.1 to 10.0 atomic% in terms of Co with respect to Fe in the aqueous ferrous salt solution. If the content is less than 0.1 atomic%, the effect of obtaining a large axial ratio is insufficient, and if it is more than 10.0 atomic%, the excess cobalt salt becomes independent other than the acicular goethite particles. It is not preferable because a cobalt compound may be formed or magnetite or the like may be mixed.

The water-soluble cobalt salt in the present invention is involved in the morphology of the needle-like goethite particles to be formed, such as the particle size and the axial ratio. It is necessary to add and dissolve in the solution of ferrous salt aqueous solution,
Alternatively, an aqueous solution in which a water-soluble cobalt salt is dissolved in water is added and mixed.

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

In the present invention, the water-soluble aluminum salt added to either the aqueous ferrous salt solution or the aqueous alkali hydroxide solution before the production of ferrous hydroxide is used to grow the ferrous hydroxide particles to be produced. It is involved in the morphology of the needle-like goethite particles generated by the oxidation reaction, such as the particle size and the axial ratio, and is added and dissolved in advance in one of the aqueous ferrous salt solution and the aqueous alkali hydroxide solution. Alternatively, an aqueous solution obtained by dissolving a water-soluble aluminum salt in water is added to and mixed with one of the above.
In addition, use aluminum sulfate, aluminum chloride, etc.
In this case, add and dissolve in the ferrous salt aqueous solution.
Is preferable, when sodium aluminate or the like is used.
Must be added and dissolved in an aqueous alkali hydroxide solution.
Is preferred.

In this case, the addition amount of the water-soluble aluminum salt is 0.5 to 5.0 atomic% in terms of Al with respect to Fe in the aqueous ferrous salt solution. When the content is less than 0.5 atomic%, the effect of suppressing the growth of the generated ferrous hydroxide particles, which is the object of the present invention, cannot be obtained, and the effect is not more than 5.0 atomic%.
If the ratio exceeds 1, 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 ferrous hydroxide to increase the reaction rate in the oxidation reaction. Because it is involved, it is preferable to dissolve the water-soluble aluminum salt in water and add it to the suspension as an aqueous solution in order to quickly disperse and uniformly act in the liquid.

In this case, the amount of the water-soluble aluminum salt aqueous solution added is such that Al
It is 0.5 to 5.0 atomic% in conversion. When the content is less than 0.5 at%, the effect of lowering the viscosity of the suspension is not sufficient, and when it exceeds 5.0 at%, magnetite may be mixed.

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

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 becomes high and the reaction time becomes long, and it is not economical to use an excess alkali hydroxide aqueous solution unnecessarily. 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.
It is. If the temperature is lower than 30 ° C., fine needle-like goethite may be formed and the particle size may be uneven. If the temperature is higher than 45 ° C., magnetite may be mixed, which is not preferable.

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

In the present invention, in order to improve the properties of the magnetic particles and the like, it is possible to add different elements such as Ni, Zn, P, and Si which are usually added during the reaction for producing goethite particles.

The filtration, washing and drying for obtaining acicular goethite particles may be carried out according to a conventional method.

[0038]

An oxygen-containing gas is added to an alkaline suspension containing ferrous hydroxide obtained by adding a water-soluble cobalt salt to the aqueous solution of ferrous salt and reacting the aqueous solution with an alkali hydroxide. In order to obtain needle-like goethite particles having a large axial ratio by oxidizing by aeration, simply adding a water-soluble cobalt salt will increase the reaction time, and the resulting needle-like goethite particles will be uneven in particle size. And dendritic particles are also mixed.

Therefore, a water-soluble aluminum salt is added to the alkaline suspension to lower the viscosity of the suspension,
It is conceivable to promptly promote the oxidation reaction to shorten the reaction time. However, if a 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 Application Laid-Open No. 54-20998).
However, when a water-soluble silicate is added, the viscosity may decrease, but the axial ratio may decrease, and insoluble alkali metal salts may precipitate, so metal magnetic particle powder containing iron as a main component Is not preferred.

From the above, in the present invention, before the ferrous hydroxide is formed, the water-soluble cobalt salt is added to the aqueous ferrous salt solution in advance, and A water-soluble aluminum salt in an amount of 0.5 to 5.0 atomic% in terms of Al with respect to Fe in an aqueous iron salt solution is formed when one of the aqueous ferrous salt solution and the aqueous alkali hydroxide solution is added thereto. It has been 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. FIG.
It shows the particle structure of ferrous hydroxide generated by adding a water-soluble aluminum salt to the aqueous solution of ferrous salt, and it can be confirmed that the particle size is uniform with fine particles, No. 2 shows the particle morphology of ferrous hydroxide when no water-soluble aluminum salt is added, and it can be confirmed that the particles are large and uneven in particle size.

From the above results, the present inventor concludes that the aluminum compound formed from the added water-soluble aluminum salt is adsorbed on the surface of the generated ferrous hydroxide fine particles to suppress the growth. thinking. Further, it was confirmed that magnetite did not precipitate within the range of the above addition amount.

The ferrous hydroxide particles are large and uneven, so that in the process of forming needle-like goethite particles, dendritic particles are formed and the particle size of the goethite particles is also uneven. It is considered to be.

However, when the obtained alkaline suspension containing fine ferrous hydroxide is oxidized by passing an oxygen-containing gas to oxidize it, needle-like goethite particles are preliminarily prepared. It has been found that as the oxidation reaction proceeds with only the water-soluble aluminum salt added before the formation, the effect is lost, the viscosity of the suspension increases, and the reaction time also increases.

The inventor of the present invention has proposed that in order to maintain the large axial ratio of the acicular goethite particles produced by utilizing the fine ferrous hydroxide particles and to shorten the reaction time, the reaction time of the ferrous hydroxide may be reduced. In addition to the addition of the water-soluble aluminum salt to either one before the formation of iron, the viscosity of the suspension is reduced by appropriately adding the water-soluble aluminum salt during the oxidation reaction to reduce the reaction. It has been found that time can be shortened.

Therefore, in the present invention, fine ferrous hydroxide particles can be obtained, and in the oxidation reaction, the minor axis diameter of the acicular goethite particles can be reduced and the axial ratio can be increased. Thus, acicular goethite particles containing Co and Al having a large axial ratio, a more uniform particle size, and free of dendritic particles are obtained.

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 reduced by heating in a reducing gas such as hydrogen. The magnetite particles or metal magnetic particles containing iron as a main component, and also, when the magnetite particles are magnetic particles obtained by heating and oxidizing in air to form maghemite particles, excellent. Needle-like property can be maintained,
Even when a magnetic paint is kneaded with a binder resin for use in a magnetic recording medium, the dispersibility of the magnetic paint is excellent because of good compatibility with the binder resin.

In the above-mentioned Japanese Patent Application Laid-Open No. 64-33019, for example, the method of adding an aluminum compound to a suspension of ferrous hydroxide is described as “(1) while supplying an oxygen-containing gas. It may be performed continuously or intermittently, or various methods such as adding only the first half or only the latter half may be adopted. However, in this case, it is added to the suspension after the production of ferrous hydroxide, and there is no description about the effect of the addition before the production of ferrous hydroxide.

[0050]

EXAMPLES Next, examples and comparative examples illustrate the present invention.

Incidentally, the major axis diameter and the axial ratio 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 was represented by a geometric standard deviation (σg) obtained by the following method. That is, the major axis diameter of 350 particles shown in a 120,000-fold electron micrograph was measured, and the logarithmic normal was calculated from the actual major axis diameter and the number of particles calculated from the measured value according to a statistical method. On the probability paper, the horizontal axis represents the major axis diameter of the particles, and the vertical axis represents the cumulative number of particles belonging to each of the major axis diameter sections at equal intervals in percentage. Then, the value of the major axis diameter corresponding to 50% and 84.13% of the number of particles is read from this graph, and the geometric standard deviation (σg) = the major axis diameter (μm) / 50% number of particles / μm / Long axis diameter when the number is 84.13% (μm)
It was shown by the value calculated according to.

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

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

At a temperature of 45 ° C., 1 minute
0.5 mol / l after 60 minutes after aeration of 50 l of air
Aluminum sulfate aqueous solution 200ml (Fe to Al
This corresponds to 1.0 atomic% in conversion. ) Was added. This operation was repeated once more after 60 minutes. Subsequently, at a temperature of 45 ° C., 150 liters of air per minute was passed for 80 minutes to produce acicular goethite particles. The produced particles were washed with water, separated by filtration, dried and pulverized by a conventional method. The acicular goethite particles contain 2.5 atomic% of Co / Fe, Al / F
e was 1.77 atomic%.

The electron micrograph (× 30) shown in FIG.
000), it is clear that the major axis is 0.34 on average.
The average particle size was 15 μm, the axial ratio was 15, and the standard deviation was 0.73. The particles 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, amount and timing of water-soluble aluminum salt, type and amount of aqueous solution of water-soluble aluminum salt during oxidation Example 1 was repeated except that the addition method and the reaction temperature were variously changed.
In the same manner as in the above, acicular goethite particles were produced.

Tables 1 and 2 show the main manufacturing conditions and various characteristics at this time.

[0059]

[Table 1]

[0060]

[Table 2]

The needle-like 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 acicular goethite particles obtained in Comparative Example 2 were asymmetric particles, and the electron micrograph (× 3
0000), the axial ratio was small.

[0062]

According to the method for producing acicular goethite particle powder according to the present invention, as shown in the above examples, it has a large axial ratio, a uniform particle size, and a mixture of dendritic particles. Needleless goethite particles can be obtained.

The acicular goethite particle powder thus obtained is used as a starting material, and the acicular magnetite particle powder obtained by heating and reducing, or the acicular metal magnetic particle powder containing iron as a main component, Needle-like maghemite particles obtained by heating and oxidizing magnetite particles in air also have a large axial ratio, are more uniform in particle size, and do not contain dendritic particles. It is suitable as a magnetic particle powder for high recording density, high sensitivity, and high output.

[Brief description of the drawings]

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

FIG. 2 is an electron micrograph (× 30000) showing the 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 the acicular goethite particles obtained in Example 1.

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

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

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

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

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

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C01G 49/00-49/16 H01F 1/11

Claims (1)

(57) [Claims] An oxygen-containing gas is passed through an alkaline suspension having a pH of 11 or more and containing ferrous hydroxide obtained by reacting an aqueous ferrous salt solution with an aqueous alkali hydroxide solution to oxidize the needle. In the method for producing the goethite particles, a water-soluble cobalt salt is added in advance to the aqueous solution of 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. A water-soluble aluminum salt is added to either one of the aqueous solution and the alkali hydroxide aqueous solution in an amount of 0.5 to 5.0 atomic% in terms of Al with respect to Fe, and the ferrous salt aqueous solution and the alkali hydroxide aqueous solution are added. To obtain an alkaline suspension containing ferrous hydroxide having a pH of 11 or more. Then, during the oxidation by passing an oxygen-containing gas through the suspension, a water-soluble aluminum salt aqueous solution is further added. A method for producing acicular goethite particle powder, which comprises producing acicular goethite particles containing Co and Al by adding.