JPH088104A - Method of manufacturing acicular magnetic particle powder - Google Patents

Abstract

PURPOSE:To provide a manufacturing method of industrially obtaining a acicular magnetic particle powder in which a grain size is uniform and a dendritic particle is not mixed and also which has a large axial ratio (major axis diameter/ minor axis diameter). CONSTITUTION:An acicular goethite particle is produced by oxidative reaction with an oxygen containing gas made to flow into a suspension containing ferrous hydroxide obtained by making an excessive quantity of the aqueous solution of alkali hydroxide react to the aqueous solution of ferrous salt, and then an acicular goethite particle or an acicular hematite particle obtained by baking an acicular goethite particle by heating is reduced by heating in a reducible gas to obtain an acicular magnetite particle or an acicular metal nagnetic particle containing iron as a main component. Or in a method for manufacturing an acicular magnetic particle powder in which an acicular mghemite particle is obtained by oxidizing an acicular magnetite particle. it is obtained by adding water soluble silicate of 0.05 to 2.0wt.% expressed in terms of Si to total Fe in the aqueous solution of ferrous salt to the reaction solution under oxidative reaction.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention has a uniform particle size suitable as magnetic particle powder for magnetic recording, does not contain dendritic particles, and has a large axial ratio (major axis diameter / minor axis diameter- Hereinafter, it is an object to provide an acicular magnetic particle powder having the same −).

[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. "Development of magnetic materials and high-dispersion technology of magnetic powder" (1982), page 310, "The direction of improving magnetic tape performance was to increase sensitivity and output.
The emphasis was on increasing the coercive force of the acicular γ-Fe ₂ O ₃ particle powder. ".

Further, in order to achieve 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 and to have excellent dispersibility in a vehicle, orientation in a coating film, and filling property.

Although these various characteristics of the magnetic recording medium have a close relationship with the magnetic particle powder used in the magnetic recording medium, in recent years, they have a higher coercive force than the iron oxide magnetic particle powder. Metal magnetic particle powders containing iron as a main component having a large saturation magnetization have attracted attention, and digital audio tape (DAT), 8 mm video tape, Hi-8
It has been put to practical use as a magnetic recording medium such as a tape and a video floppy. However, it is strongly desired to further improve the properties of the metal magnetic particle powder containing iron as a main component.

Now, the relationship between various characteristics of the magnetic recording medium and the characteristics of the magnetic particle powder used will be described in detail below. In order to obtain high image quality as a magnetic recording medium for video, it is clear from the record of Nikkei Electronics (1976) May 3, pp. 82-105 that the video S / N ratio and chroma S / N ratio are , Improvement of video frequency characteristics is required.

In order to improve the video S / N ratio and the chroma S / N ratio, it is necessary to improve the dispersibility of the magnetic particle powder in the vehicle, the orientation and filling property in the coating film, and It is important to improve the surface smoothness of the magnetic recording medium, and such a magnetic particle powder has a uniform particle size, does not contain dendritic particles, and has a large axial ratio. Is required.

Next, in order to improve the video frequency characteristics, it is necessary that the magnetic recording medium has a high coercive force Hc and a large residual magnetic flux density Br. In order to increase the coercive force Hc of the magnetic recording medium, the coercive force Hc of the magnetic particle powder is required to be as high as possible. Since the coercive force of magnetic particle powder is generally caused by its shape anisotropy, the coercive force tends to increase as the particle axial ratio increases.

In order to increase the output of the magnetic recording medium,
Japanese Unexamined Patent Publication No. 63-26821 shows "FIG. 1 is a diagram showing the relationship between the SFD measured on the above-mentioned magnetic disk and the recording / reproducing output. As is clear from Fig. 1, the relationship between the recording and reproducing output is a straight line, which means that the recording and reproducing output can be increased by using a ferromagnetic powder having a small SFD. In order to increase the recording / reproducing output, it is desirable that the SFD is small, and in order to obtain an output higher than usual, it is 0.6
The following S. F. D. is necessary. As stated,
The S. F. D. (Switching F
field distribution, that is, the coercive force distribution needs to be small. For this reason, the coercive force of the magnetic particle powder is as uniform as possible and dendritic particles are not mixed. A small distribution width is required.

At present, magnetic iron oxide particles such as acicular magnetite particles and acicular maghemite particles, which are 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 particles 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. Further, it is obtained by oxidizing the magnetite particles in air to form maghemite particles.

The known Co-modified or Co- and Fe-modified acicular magnetic iron oxide particles are prepared by using acicular magnetite particles or acicular maghemite particles as precursor particles. 0.5 to 15.
The precursor particles are dispersed in an alkaline suspension containing cobalt hydroxide or an alkaline suspension containing cobalt hydroxide / ferrous hydroxide so as to contain 0 atomic% of Co, and the dispersion is heated. It is obtained by processing.

Metal magnetic particle powders containing iron as a main component generally require goethite particles as a starting material, hematite particles obtained by heating and dehydrating these, or particles containing different metals other than iron in these particles. It is obtained by heating and reducing in a reducing gas.

As described above, the particles have a uniform particle size, no dendritic particles are mixed, and have a large axial ratio, and have a high coercive force and an excellent coercive force distribution. Magnetic particle powders are currently most demanded, and in order to obtain magnetic particle powders having such characteristics, the starting material, goethite particle powders, have a uniform particle size and dendritic particles are mixed. However, it is required to have a large axial ratio.

Conventionally, as a method of 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.
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, in the above-mentioned method, a method of adding a water-soluble silicate 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). JP-A-55-6575, JP-B-55-75, and 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 of the acicular goethite particles produced. 6576
No. gazette) is known.

[0017]

A magnetic particle powder having a large axial ratio, a uniform particle size and no mixed dendritic particles is currently most demanded. In the case of the above-mentioned method for producing goethite particle powder, the needle-shaped goethite particles having a large axial ratio, particularly 10 or more, are produced, but dendritic particles are mixed, and it can be said from the particle size. Therefore, it cannot be said that the particles have a uniform particle size.

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

In the case of the above-mentioned method, acicular goethite particles having a uniform particle size and containing no dendritic particles are produced, but the axial ratio is at most about 9, and the addition amount of the water-soluble silicate is high. As the particle diameter increases, the particle size becomes uniform and dendritic particles do not coexist, but the axial ratio tends to decrease rapidly.

In the case of the above-mentioned method, acicular goethite particles having a large axial ratio are produced, but the addition of water-soluble zinc having the effect of improving the axial ratio causes the particle size to become asymmetric, resulting in dendritic particles. Are easily mixed, and moreover,
There is a problem that it is not industrial or economical because the production efficiency decreases due to the decrease of the production amount per unit time and unit volume.

Therefore, according to the present invention, a needle-shaped goethite particle powder having a uniform particle size and no dendritic particles mixed therein and having a large axial ratio is obtained, and the needle-shaped goethite particle or the needle-shaped goethite is obtained. Needle-like hematite particles obtained by heating and calcining the particles are heated and reduced in a reducing gas to obtain needle-like magnetite particles or needle-like metal magnetic particles containing iron as a main component, or the needle-like magnetite particles. It is a technical subject to obtain acicular maghemite particles by oxidizing.

[0022]

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

That is, the present invention comprises ferrous hydroxide obtained by reacting an aqueous solution of ferrous salt with an aqueous solution of alkali hydroxide having an equivalent amount to Fe ^{2+ in the} aqueous solution of ferrous salt. To the suspension, an oxygen-containing gas is passed through an oxidation reaction to generate acicular goethite particles, and then the acicular goethite particles or acicular hematite particles obtained by heating and firing the acicular goethite particles are obtained. In the method for producing the acicular magnetic particle powder, the acicular magnetite particles are obtained by heating and reducing in a reducing gas, or the acicular magnetite particles are oxidized to obtain acicular maghemite particles. A method for producing acicular magnetic particle powder, which comprises adding 0.05 to 2.0% by weight of water-soluble silicate in terms of Si to all Fe in the aqueous solution of ferrous salt in the liquid. .

The present invention also includes ferrous hydroxide obtained by reacting an aqueous ferrous salt solution with an aqueous alkaline hydroxide solution having an equivalent amount to Fe ^{2+ in the} aqueous ferrous salt solution. To the suspension, an oxygen-containing gas is passed through an oxidation reaction to generate acicular goethite particles, and then the acicular goethite particles or acicular hematite particles obtained by heating and firing the acicular goethite particles are obtained. In the method for producing needle-shaped magnetic particle powder, which is obtained by heating and reducing in a reducing gas to obtain needle-shaped metal magnetic particles containing iron as a main component, in the reaction liquid during the oxidation reaction,
0.0 based on Si for all Fe in the ferrous salt solution
A method for producing acicular magnetic particle powder, which comprises adding 5 to 2.0% by weight of a water-soluble silicate.

Further, according to the present invention, the production of the acicular magnetic particle powder, which comprises adding a water-soluble silicate to a reaction solution in which the degree of oxidation during the oxidation reaction is in the range of 5 to 90%. And a water-soluble silicate to be added to the reaction solution during the oxidation reaction, continuously or intermittently, if necessary.

In the present invention, the acicular magnetite particles or acicular maghemite particles obtained by the above-mentioned manufacturing method are used as precursor particles, and the Fe content of the precursor particles is 0.5.
The precursor particles are dispersed in an alkaline suspension containing cobalt hydroxide or an alkaline suspension containing cobalt hydroxide and ferrous hydroxide so as to contain Co at 15.0 atomic%. A method for producing acicular magnetic iron oxide particles, which comprises obtaining acicular magnetite particles or acicular maghemite particles modified with Co or modified with Co and Fe ²⁺ by heating a suspension. is there.

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.

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

The amount of the aqueous alkaline solution used in the production of the acicular goethite particles of the present invention is determined by the amount of Fe in the aqueous ferrous salt solution.
The amount exceeds the equivalent of ²⁺ . If less than equivalent,
Goethite particles in which the particle sizes are asymmetric and dendritic particles are mixed are generated, or granular magnetite particles are mixed. The upper limit is not particularly limited, but it is not industrially unnecessarily to use an excessive alkaline aqueous solution. In addition, it becomes necessary to discharge excess alkali content. Therefore,
The preferred range is 1.1 to 10.0 equivalents, and more preferably 1.2 to 8.0 equivalents.

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

The amount of the water-soluble silicate added is 0.2 to 5.0 atomic% in terms of Si based on the total Fe in the aqueous ferrous salt solution. If the addition amount of the water-soluble silicate is less than 0.2 atomic%, the effect of adding the water-soluble silicate cannot be obtained, and if it exceeds 5.0 atomic%, the water-soluble silicate is added. Is excessive and is released in the reaction solution in an amount exceeding the amount exerted on the formation reaction of acicular goethite particles, which is not preferable. Further, if the amount of water-soluble silicate adsorbed to the acicular goethite particles is too large, the saturation magnetization value may be lowered in the case of acicular magnetic iron oxide particle powder, which is not preferable as a magnetic recording material powder. . The preferred range is 0.3
To 4.0 atom%, more preferably 0.4 to 3.0
It is atomic%.

The water-soluble silicate is added in the reaction solution in which the degree of oxidation during the oxidation reaction is in the range of 5 to 90%. If it is less than 5%, the axial ratio is lowered and the target goethite particles cannot be obtained. If it exceeds 90%, the effect of adding the water-soluble silicate will not be exhibited.
It is preferably 10 to 80%, more preferably 50%
Start to add.

The method of adding the water-soluble silicate is as follows:
The total amount may be added once, but preferably, the effect of adding the water-soluble silicate is greater when added continuously or intermittently. Intermittently means that the water-soluble silicate to be added is divided into several parts and added within the above range.

The reaction temperature in the present invention is in the range of 10 to 55 ° C. in the reaction of acicular goethite particle formation. 10 ° C
If it is less than 55 ° C, fine needle-shaped goethite particles may be generated and the particle size may become asymmetric, and if it exceeds 55 ° C, magnetite may be mixed. The preferred temperature is in the range of 20 to 50 ° C, more preferably 30 to
It is in the range of 45 ° C.

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

In the present invention, the Co compound, Ni compound, Zn compound, Al compound, P, etc., which are usually added to the reaction of goethite particles, are used to improve the characteristics of the magnetic particle powder.
One or more compounds such as compounds may be added,
Also in this case, the acicular goethite particle powder which is the object of the present invention can be obtained. In that case,
It may be at any time in the production reaction of the goethite particles, and in the case of the Al compound and the P compound, the addition amount thereof is preferably 0.5 to 5.0% by weight with respect to the goethite particles, and the Co compound, Ni In the case of a compound and a Zn compound, the magnetization does not decrease or is small, so any amount may be used as long as it is not generated as a foreign substance, and the upper limit of the amount is about 30% by weight.

In the present invention, the acicular goethite particles are coated with a substance having a sintering inhibiting effect, that is, a sintering inhibitor by a well-known method prior to the heat reduction treatment. Sintering between the particles is prevented, the particle shape and the axial ratio of the acicular goethite particles are more easily retained and inherited, and individual independent magnetic particle powders are easily obtained.

As the sintering inhibitor, a well-known Ni compound,
Al compound, Si compound, P compound, Co compound, Mg
One or more compounds selected from compounds, B compounds and Zn compounds can be used. These compounds not only have the effect of preventing sintering, but also have the function of controlling the reduction rate, so they may be used in combination as necessary. In this case, the amount used is 0.3 to 3.0% by weight based on the goethite particle powder because the effect of preventing sintering is not sufficient if the amount is too small, and the saturation magnetization value decreases if the amount is too large.

In the present invention, the obtained acicular goethite particle powder may be heated and fired to obtain acicular hematite particles.

When the needle-shaped goethite particles are heated and fired to obtain the needle-shaped hematite particles, the heating and firing temperature is 250 to 500 ° C. in the case of simply heating and dehydrating in the conventional method. The preferable range is 250 to 300 ° C., and if necessary, heating and firing may be performed in a non-oxidizing atmosphere or an oxidizing atmosphere.

The heating and firing in the non-oxidizing atmosphere or the oxidizing atmosphere is performed by flowing air, oxygen gas or nitrogen gas,
It can be performed in a temperature range of 300 to 800 ° C. It is preferable that the heating and firing temperature is appropriately selected depending on the type of the compound used as the sintering inhibitor and the coating amount. 80
If the temperature exceeds 0 ° C, deformation of particles and sintering between particles and each other are caused. The preferred range is 550
~ 700 ° C.

In the present invention, the obtained needle-shaped goethite particles and needle-shaped hematite particles are used as starting material particles and heated and reduced under a reducing gas (for example, hydrogen gas) flow to obtain needle-shaped magnetite particle powder. The temperature range of the heat reduction is 300 to 550 ° C. When the temperature is lower than 300 ° C, the reduction reaction proceeds slowly and requires a long time. On the other hand, when the temperature exceeds 550 ° C., the reduction reaction rapidly progresses, causing deformation of particles and sintering between particles. A preferred range is 300 to 450 ° C.

In the present invention, the obtained acicular magnetite particle powder can be reoxidized to obtain acicular maghemite particle powder. The temperature range of reoxidation is 200 to 50.
0 ° C. When the temperature is lower than 200 ° C., the progress of the oxidation reaction is slow and it takes a long time. On the other hand, when the temperature exceeds 500 ° C., the oxidation reaction rapidly progresses, causing deformation of particles and sintering between particles. A preferred range is 300 to 450 ° C.

The needle-shaped magnetite particles and the needle-shaped magnetite particles, which are intermediate oxides of the needle-shaped maghemite particles, may be used, and the needle-shaped magnetite particles may be further heated in the temperature range of 250 to 500 ° C. By adjusting the amount of ferrous iron that is oxidized to form needle-shaped beltride compound particles, or the needle-shaped maghemite particles are heated and reduced again in a temperature range of 300 to 550 ° C. under a reducing gas flow. It is also possible to adjust the amount of ferrous iron to be produced to form the beltride compound particles.

In the present invention, the temperature range of heat reduction when obtaining the metal magnetic particle powder containing iron as a main component is 300 to 300.
550 ° C is preferred. When the temperature is lower than 300 ° C, the reduction reaction proceeds slowly and requires a long time. Also, 550 ° C
If it exceeds, the reduction reaction will rapidly proceed, causing deformation of the particles and sintering between the particles and each other.

The acicular metal magnetic particle powder containing iron as a main component after reduction by heating in the present invention is a known method, for example, a method of immersing in an organic solvent such as toluene or a needle containing iron after reduction as a main component. After once replacing the atmosphere of the powdery metallic magnetic particles with an inert gas, gradually increasing the oxygen content of the inert gas and finally turning it into air to take out into the air by a method such as gradual oxidation. You can

The Co modification of the acicular magnetite particle powder or acicular maghemite particle powder in the present invention can be carried out by a conventional method, for example, Japanese Patent Publication No. 52-24237, Japanese Patent Publication No. 52-24238, and Japanese Patent Publication No. 52-3
As described in Japanese Patent No. 6751 and Japanese Patent Publication No. 52-36863, precursor particles are dispersed in an alkaline suspension containing cobalt hydroxide or cobalt hydroxide / ferrous hydroxide, It is performed by heating the dispersion liquid.

The cobalt hydroxide in the present invention can be obtained by using a water-soluble cobalt salt such as cobalt sulfate or cobalt chloride and an aqueous alkali hydroxide solution such as sodium hydroxide or potassium hydroxide.

The ferrous hydroxide in the present invention is obtained by using a water-soluble ferrous salt such as ferrous sulfate and ferrous chloride and an aqueous alkali hydroxide solution such as sodium hydroxide and potassium hydroxide. .

In transforming Co, the heat treatment is preferably carried out in a temperature range of 50 to 100 ° C. in a non-oxidizing atmosphere.

The temperature of the Co transformation is related to the treatment time. If the temperature is set to 50 ° C. or lower, the magnetite particles or the maghemite particles transformed with Co or with Fe and Fe ²⁺ are formed. It is difficult and requires extremely long processing even if it is generated.

The amount of the water-soluble cobalt salt modified in the present invention is determined by the amount of Fe in the magnetite particles or the maghemite particles.
On the other hand, it is 0.5 to 15.0 atomic% in terms of Co. 0.
If it is less than 5 atomic%, the effect of improving the coercive force of the obtained acicular magnetite particles or maghemite particles cannot be sufficiently achieved. 15.0 atom%
If it exceeds, the effect of reducing the coercive force distribution of the obtained acicular magnetite particles or maghemite particles is not sufficient. When considering the coercive force and coercive force distribution of needle-shaped magnetite particles or maghemite particles, 2.0
˜13.0 atomic% is preferred.

Almost all of the added water-soluble cobalt salt is used for the transformation of the magnetic iron oxide particles on the particle surface.

The amount of metamorphism of the ferrous salt aqueous solution is 1.0 to 20.0 atom% in terms of Fe with respect to Fe in the magnetite particles or the maghemite particles. When it is less than 1.0 atom%, a sufficient coercive force cannot be obtained, and when it exceeds 20.0 atom%, the squareness ratio and the degree of orientation are lowered, which is not preferable.

The amount of the alkaline aqueous solution used is in the range of 0.5 to 2.0 mol / l as the suspension concentration.
When it is less than 0.5 mol / l, a sufficient coercive force cannot be obtained, and when it exceeds 2.0 mol / l, it may not be more than necessary, and it is unnecessary after the reaction. It is not industrial even from the cleaning efficiency of removing salts.

[0057]

The operation of the method of the present invention having the above-mentioned structure is as follows.

The effect of adding the water-soluble silicate during the ordinary goethite particle formation reaction is as follows.
The axial ratio can be shortened as described in Japanese Patent Publication No. 13941. That is, the function of suppressing the growth of goethite crystal particles suppresses the growth of the particles in the long axis direction and shortens the axial ratio. In this case, an aqueous solution of alkali carbonate is used, but it has been confirmed that the growth in the major axis direction is suppressed even in the reaction in the strongly alkaline region using the aqueous solution of alkali hydroxide as in the present invention.

However, when the water-soluble silicate is added during the oxidation reaction in the present invention, not only the effect of suppressing the growth in the long axis direction due to the water-soluble silicate can be canceled out, but also Since it is possible to suppress the generation of new fine goethite particles in the production reaction solution, it is possible to obtain goethite particles having a uniform particle size and a good axial ratio.

That is, when the water-soluble silicate is added during the oxidation reaction, the water-soluble silicate has an action of lowering the viscosity of the reaction solution, and as described above, new fine goethite particles are generated. This is probably because the grain size was suppressed and the uniform grain size could be maintained, and the original crystal habit of goethite could be utilized to exert growth in the long axis direction. The original crystal habit of goethite means that the goethite crystal has the highest continuity and is easy to grow in the dense long axis direction of the crystal.

Further, in the present invention, it is effective to add the entire amount of the water-soluble silicate at one time, but the effect can be further enhanced by the continuous or intermittent addition. That is, according to the method of continuously or intermittently adding the water-soluble silicate to the reaction solution in which the degree of oxidation during the oxidation reaction is in the range of 5 to 90%, the particle size is more uniform and dendritic. Needle-like goethite particles having no larger particles and a larger axial ratio are obtained.

The degree of oxidation during the oxidation reaction is 50%.
A larger effect can be obtained by starting the first addition by the time. This is because if the oxidation is added after the degree of oxidation exceeds 50%, the viscosity of the reaction solution cannot be lowered so much that the effect of adding the water-soluble silicate cannot be sufficiently exerted. Is.

When the water-soluble silicate is added during the oxidation reaction, the obtained goethite particles are used as starting material particles and various heat treatments are performed to obtain magnetic particles, which is more effective in preventing sintering. It was confirmed to be effective. The reason is that during the oxidation reaction, the water-soluble silicate added continuously or intermittently is gradually and properly adsorbed and reacted in the goethite formed on the surface of the goethite particles. It is considered that the reason for this is that a good coating layer is formed because it is included in the film.

As a result, when the obtained goethite particles are used as the starting material particles, the obtained acicular magnetic particle powder is more uniform in particle size and does not contain dendritic particles. Since it has a large axial ratio, it was possible to obtain good results that it was excellent in the squareness ratio and the degree of orientation when used as a magnetic recording medium, as shown in Examples below. Further, the same effect is obtained with the acicular metal magnetic particle powder containing iron as a main component.

[0065]

The present invention will be described below with reference to Examples and Comparative Examples.

The degree of oxidation is a value, expressed as a percentage, of the proportion of Fe ³⁺ content in the total Fe content measured by the redox titration method.

The major axis diameter and the axial ratio of the particles are shown by the average of the numerical values measured from electron micrographs.

The magnetic properties and coating properties of the magnetic iron oxide particles were measured by using a vibrating sample magnetometer VSM-3S-15 (manufactured by Toei Industry Co., Ltd.), and needle magnetite particles and needle maghemite were used. The particle powder was measured with an external magnetic field of 5 KOe, the Co-modified magnetic iron oxide particle powder and the metallic magnetic particle powder containing iron as a main component were measured up to an external magnetic field of 10 KOe.

The squareness ratio, the degree of orientation and the S. F. D. Was measured using the sheet sample piece obtained by the method of Example 19 described later. Also, S. F. D. Was obtained by obtaining the differential curve of the demagnetization curve of the magnetic hysteresis curve using the differential circuit of the magnetometer, measuring the half width of this curve, and dividing this value by the coercive force.

<Method for Producing Acicular Goethite Particle Powder> Examples 1 to 3 and Comparative Examples 1 to 4;

Example 1 Fe containing 103 g of anhydrous aluminum sulfate (corresponding to 2 mol% with respect to Fe ²⁺ in the aqueous ferrous sulfate solution)
²⁺ 1.5 mol / l ferrous sulfate aqueous solution 20 l and 5.3
Mixing with 30 mol of 3 mol / l NaOH aqueous solution (corresponding to 5.33 equivalent to Fe ^{2+ in} ferrous sulfate aqueous solution), a suspension containing Fe (OH) ₂ is formed at a temperature of 40 ° C. I went. The suspension containing Fe (OH) ₂ was bubbled with 150 l / min of air at a temperature of 40 ° C. for 75 minutes.

A part of the reaction solution during the oxidation reaction was withdrawn, and the degree of oxidation was 20%.
20.8 g of 28.9% No. 3 water glass in terms of SiO ₂
And 210 minutes later (the degree of oxidation was 50%), 20.8 g of the No. 3 water glass was added, and 42
After 0 minutes (the degree of oxidation was 85%), 20.8 g of the above-mentioned No. 3 water glass (the total amount of Si added in three divided portions was calculated as Fe ²⁺ in the ferrous sulfate aqueous solution ^). Was 1.0 atom% in terms of Si), and the reaction was terminated. The time required for the reaction was 8.2 hours.

The produced goethite particles were filtered, washed with water and dried by a conventional method.

As a result of electron microscopic observation, the obtained goethite particle powder was needle-like particles having a major axis of 0.34 μm and an axial ratio of 14. Moreover, the particle size was uniform and dendritic particles were not mixed.

Examples 2 to 3, Comparative Examples 1 to 4 Type and concentration of aqueous ferrous salt solution, type and concentration and equivalent amount of alkaline aqueous solution, reaction temperature, air aeration rate and type and addition amount of water-soluble silicate. Needle-shaped goethite particles were produced in the same manner as in Example 1 except that the degree of oxidation and the addition method were changed.

The main production conditions and the characteristics of the particle powder at this time are shown in Tables 1 and 2.

[0077]

[Table 1]

[0078]

[Table 2]

<Production of Needle-like Magnetite Particle Powder> Examples 4 to 6 and Comparative Examples 5 to 8;

Example 4 5.3 kg of a paste of needle-shaped goethite particles obtained in Example 1 and filtered and washed with water (about 1.6 K of needle-shaped goethite particles)
Equivalent to g. ) Was suspended in 40 l of water. The pH at this time was 8.9. Then, 100 ml of an aqueous solution containing 5.9 g of sodium phosphate (corresponding to 0.37 wt% as P with respect to needle-shaped goethite particles) was added to the above suspension and stirred for 10 minutes, and then sodium silicate was further added. After adding 100 ml of an aqueous solution containing 24 g (corresponding to 1.5 wt% as Si with respect to the needle-shaped goethite particles) and stirring for 10 minutes, it was filtered and dried to be coated with a P compound and a Si compound. A needle-shaped goethite particle powder was obtained.

The needle-shaped goethite particle powder whose surface was covered with a P compound and a Si compound was treated with 30 parts in air.
Heat treatment was performed at 0 ° C., and then heat treatment was performed at 650 ° C. for 15 minutes in air to obtain a needle-like hematite particle powder coated with a P compound and a Si compound.

Next, 500 g of acicular hematite particle powder whose particle surface is coated with a P compound and a Si compound is put into a retort reduction container, and H _{2 is} rotated while being driven and rotated.
Gas was aerated at a rate of 2 l / min and reduced at a reduction temperature of 340 ° C. to obtain acicular magnetite particle powder coated with a P compound and a Si compound.

As a result of electron microscopic observation, the obtained acicular magnetite particle powder coated with the P compound and the Si compound had an average value of 0.32 μm in the major axis and an axial ratio of 9, and the particles had a uniform particle size. However, the dendritic particles were not mixed. As a result of magnetic measurement, the coercive force Hc is 435.
Oe and saturation magnetization s were 83.4 emu / g.

Examples 5 to 6 and Comparative Examples 5 to 8 Example 4 except that the types of starting materials, the types and addition amounts of metal compounds to be coated, the dehydration temperature, the heating temperature in air, and the reduction temperature were variously changed. In the same manner as described above, a needle-shaped magnetite particle powder was obtained.

Table 3 shows the main production conditions and the characteristics of the particle powder at this time.

[0086]

[Table 3]

<Production of acicular maghemite particle powder> Examples 7 to 9 and Comparative examples 9 to 12;

Example 7 500 g of acicular magnetite particle powder having the particle surface coated with a P compound and a Si compound obtained in Example 4 was oxidized in air at 320 ° C. for 90 minutes to convert the particle surface into a P compound. A maghemite particle powder coated with the Si compound was obtained.

The acicular maghemite particle powder obtained by coating the surface of the particles with a P compound and a Si compound had a long axis of 0.33 μm and an axial ratio of 9 as a result of electron microscope observation.
The particles were uniform in particle size and did not contain dendritic particles. Moreover, as a result of the magnetic measurement, the coercive force Hc is 382.
Oe and saturation magnetization s were 75.8 emu / g.

Examples 8 to 9 and Comparative Examples 9 to 12 Needle-shaped maghemite particle powders were obtained in the same manner as in Example 7 except that the type of needle-shaped magnetite particles and the oxidation temperature were variously changed.

Table 4 shows the main production conditions and the characteristics of the particle powder at this time.

[0092]

[Table 4]

<Production of Needle-like Magnetite Particle Powder Modified with Co> Examples 10 to 12 and Comparative Examples 13 to 16;

Example 10 100 g of needle-shaped magnetite particle powder having the particle surface coated with a P compound and a Si compound obtained in Example 4 was mixed with cobalt sulfate and sulfuric acid first while preventing air from entering as much as possible. Cobalt using ferrous iron 2.8 mol% and ferrous iron 6.5
It is poured into 1.0 l of water in which mol% is dissolved and dispersed until it becomes a fine slurry, and then 18-
102 ml of a NaOH aqueous solution of N was added, and water was further added to make the total volume 1.3 l to prepare a dispersion liquid having an OH group concentration of 1.0 mol / l. The temperature of the dispersion was raised to 95 ° C., and after stirring for 5 hours, the slurry was taken out, washed with water, filtered, and dried at 60 ° C. to obtain acicular magnetite particle powder modified with Co. It was

The obtained particles were observed by an electron microscope.
The shape and particle size of the magnetite particles in which the surface of the precursor particle is covered with a P compound and a Si compound are inherited, the major axis is 0.32 m, the axial ratio is 8, and the particle size is uniform. . Moreover, as a result of the magnetic measurement, the coercive force Hc is 720
Oe and saturation magnetization s were 86.1 emu / g.

Examples 11 to 12 and Comparative Examples 13 to 16 The amount of precursor magnetite particles was 100 g and the total volume of the treatment liquid was 1.3 l, the type of precursor, the amount of Co added, and the addition of ferrous iron. Example 1 except that the amount was variously changed
In the same manner as in 0, needle-like magnetite particles modified with Co or modified with Co and Fe ²⁺ were obtained.

Table 5 shows the main production conditions and characteristics at this time.

[0098]

[Table 5]

<Production of acicular maghemite particle powder modified with Co> Examples 13 to 15 and Comparative Examples 17 to 20;

Example 13 100 g of needle-shaped maghemite particle powder having the particle surface coated with a P compound and a Si compound obtained in Example 7 was mixed with cobalt sulfate and sulfuric acid first while preventing air from entering as much as possible. Cobalt using ferrous iron 2.8 mol% and ferrous iron 6.5
Pour into 1.0 l of water in which mol% is dissolved, disperse until a fine slurry is formed, then add 18 to the dispersion.
102 ml of -N NaOH solution was added, and water was further added to make the total volume 1.3 l to prepare a dispersion liquid having an OH group concentration of 1.0 mol / l. The temperature of the dispersion was raised to 90 ° C., and after stirring for 4.5 hours, the slurry was taken out, washed with water, separated by filtration, dried at 60 ° C., and needle-shaped maghemite particles modified with Co were obtained. Obtained.

The obtained particles were observed by an electron microscope.
The shape and particle size of the acicular maghemite particles in which the particle surface of the precursor is covered with P compound and Si compound are inherited, and the major axis is 0.32 μm, the axial ratio is 9, and the particle size is uniform. there were. As a result of magnetic measurement, the coercive force Hc was 712 Oe, and the saturation magnetization σs was 84.3 emu / g.

Examples 14 to 15 and Comparative Examples 17 to 20 The amount of precursor acicular maghemite particles is 100 g, and the total volume of the treatment liquid is 1.3 l. The type of precursor, the amount of Co added, and ferrous iron. Needle-shaped maghemite particles modified with Co or Co and Fe ²⁺ were obtained in the same manner as in Example 13 except that the addition amount of was changed variously.

Table 6 shows the main manufacturing conditions and characteristics at this time.

[0104]

[Table 6]

<Production of Metallic Magnetic Particle Powder Containing Iron as Main Component> Examples 16 to 18 and Comparative Examples 21 to 24;

Example 16 An amount of press cake corresponding to 1000 g of needle-shaped goethite particles obtained by filtering and washing with water obtained in Example 1 was suspended in 30 l of water. The pH of the suspension at this time was 8.9. Then, Al (NO ₃₎ in the suspension ₃ · 9H ₂ O
120 g (corresponding to 12% by weight with respect to goethite particles) was added and stirred for 10 minutes, and then Co (CH ₃ CO 2
O) 2 a ₂ · 4H ₂ O to 210g (goethite particles
This corresponds to 1% by weight. ) Was added and stirred for 10 minutes. Further, 120 g of H ₃ BO ₃ (corresponding to 12% by weight with respect to goethite particles) was added and stirred for 10 minutes. The pH of the suspension at this time was 4.8.

Then, ammonia water was added to adjust the pH to 9.5, and the mixture was filtered by a filter press and dried to obtain goethite particle powder coated with Al compound, Co compound and B compound. The content of Al in the obtained goethite particle powder was 0.8 wt% as Al, the content of Co was 4.6 wt% as Co, and the content of B was 0.8 wt% as B.

800 g of acicular goethite particle powder coated with the above Al compound, Co compound and B compound was heat treated in air at 300 ° C. to obtain Al compound, Co compound and B compound.
A needle-like hematite particle powder coated with the compound was obtained.

Next, the obtained acicular hematite particle powder 10 coated with the Al compound, the Co compound and the B compound was obtained.
0 g was put into a fixed bed reduction device with an inner diameter of 72 mm, and 6 g / min
A reduction of 415 ° C. was carried out by bubbling with 0 1 H ₂ gas.

The metal magnetic particle powder containing Al, Co and B and containing iron as a main component, which was obtained by reduction, was immersed in a toluene solution so as not to cause rapid oxidation when taken out into the air. I took it out. A part was taken out and a stable oxide film was formed on the surface while evaporating toluene.

As a result of electron microscope observation, the metal magnetic particle powder containing iron as a main component containing Al, Co and B was
The average major axis was 0.29 μm and the axial ratio was 8, and the particle size was uniform and the number of dendritic particles was small. Further, the magnetic characteristics are such that the coercive force Hc is as high as 1740 Oe, and the saturation magnetization σ
s was 141.3 emu / g.

Examples 17 to 18 and Comparative Examples 21 to 24 By varying the types of particles to be treated, the types and addition amounts of coatings, the heating temperature and the reduction temperature in the heating reduction step,
By the same method as in Example 16, metal magnetic particle powder containing iron as a main component was obtained.

Table 7 shows the main manufacturing conditions and characteristics at this time.

[0114]

[Table 7]

<Production of Magnetic Tape> Examples 19 to 33, Comparative Examples 25 to 44;

Example 19 A needle-shaped magnetite particle powder having the particle surface obtained in Example 4 coated with a P compound and a Si compound, a resin and a solvent were placed in a 140 cc glass bottle in the following proportions and then painted. The magnetic coating material prepared by mixing and dispersing with a conditioner for 2 hours was applied on a polyethylene terephthalate film having a thickness of 25 μm to a thickness of 40 μm using an applicator, and then 1450 Gaus.
It was obtained by orienting in a magnetic field of s and then drying.

1.5 mmφ glass beads 100 g Needle-like magnetite particle powder 15 g Toluene 5.6 g Phosphate ester (GAFACRE-610 Toho Chemical Co., Ltd.) 0.6 g Lecithin 0.6 g Vinyl chloride vinyl acetate copolymer resin (Vinyllite VAGH Union) Carbite (manufactured) 3.75 g Butadiene acrylonitrile rubber (Hycar 1432J Nippon Zeon (manufactured)) 0.75 g Methyl isobutyl ketone: methyl ethyl ketone: toluene = 3: 1: 1 mixed solution 40.5 g

The S. F. D. Is 0.4
7, the coercive force Hc is 427 Oe, and the squareness ratio Br / Bm is 0.
The degree of orientation was 84 and the degree of orientation was 2.7.

Examples 20 to 33, Comparative Examples 25 to 44 Example 19 except that the type of magnetic particle powder was variously changed.
A magnetic tape was manufactured in the same manner as in. The needle-shaped magnetite particle powder and the needle-shaped maghemite particle powder were 1450.
The Gauss, Co modified magnetic iron oxide particle powder and the metal magnetic particle powder containing iron as a main component were oriented in a magnetic field of 1900 Gauss.

Various characteristics of the magnetic tape are shown in Tables 8 to 12.

[0121]

[Table 8]

[0122]

[Table 9]

[0123]

[Table 10]

[0124]

[Table 11]

[0125]

[Table 12]

[0126]

According to the method for producing the acicular magnetic particle powder of the present invention, the acicular goethite particle powder has the uniform particle size and the dendritic particles are mixed, as shown in the above-mentioned Examples. In addition, needle-shaped goethite particle powder having a large axial ratio can be obtained.

The needle-shaped goethite particle powder according to the present invention is used as a starting material, and the needle-shaped magnetite particle powder obtained by heating and reducing, or the needle-shaped metal magnetic particle powder containing iron as a main component, and then heat-reduced The acicular maghemite particle powder obtained in this manner also has a uniform particle size and does not contain dendritic particles, and since it has a large axial ratio, the acicular magnetic particle powder according to the present invention is As shown in the above Examples, the particle size is uniform and dendritic particles are not mixed,
Moreover, since it has a large axial ratio, it is possible to obtain a needle-shaped magnetic particle powder that is excellent in the squareness ratio and the degree of orientation when used as a magnetic recording medium. It is suitable as a magnetic particle powder for high output.

Claims (5)

[Claims] 1. A suspension containing ferrous hydroxide obtained by reacting an aqueous solution of ferrous salt and an aqueous alkali hydroxide solution in which Fe ^{2+ in the} aqueous solution of ferrous salt exceeds an equivalent amount. , Acicular goethite particles are produced by performing an oxidation reaction by passing an oxygen-containing gas, and then the acicular goethite particles or acicular hematite particles obtained by heating and firing the acicular goethite particles in a reducing gas. Or to obtain needle-shaped magnetite particles by heat reduction with, or in the method for producing needle-shaped magnetic particle powder to obtain needle-shaped maghemite particles by oxidizing the needle-shaped magnetite particles, in the reaction solution during the oxidation reaction, A method for producing acicular magnetic particle powder, characterized in that 0.05 to 2.0% by weight of water-soluble silicate in terms of Si is added to all Fe in the ferrous salt aqueous solution. 2. A suspension containing ferrous hydroxide obtained by reacting an aqueous solution of ferrous salt and an aqueous alkali hydroxide solution in which Fe ^{2+ in the} aqueous solution of ferrous salt exceeds the equivalent amount. , Acicular goethite particles are produced by performing an oxidation reaction by passing an oxygen-containing gas, and then the acicular goethite particles or acicular hematite particles obtained by heating and firing the acicular goethite particles in a reducing gas. In the method for producing needle-shaped magnetic particle powder, which is obtained by heating and reducing with acicular metal magnetic particles containing iron as a main component, in the reaction liquid during the oxidation reaction, with respect to all Fe in the ferrous salt aqueous solution. A method for producing acicular magnetic particle powder, which comprises adding 0.05 to 2.0% by weight of water-soluble silicate in terms of Si. 3. The degree of oxidation during the oxidation reaction is 5 to 90%.
The method for producing acicular magnetic particle powder according to claim 1 or 2, wherein a water-soluble silicate is added to the reaction solution having the range of. 4. The acicular magnetic particle powder according to claim 1, wherein the water-soluble silicate added to the reaction solution during the oxidation reaction is added continuously or intermittently. Manufacturing method. 5. The acicular magnetite particles or acicular maghemite particles obtained by the manufacturing method according to claim 1, claim 3 or claim 4 is used as a precursor particle, and Fe of the precursor particle is 0. The precursor particles are dispersed in an alkaline suspension containing cobalt hydroxide or an alkaline suspension containing cobalt hydroxide and ferrous hydroxide so as to contain 5 to 15.0 atomic% of Co, A process for producing needle-shaped magnetic particle powder, characterized in that needle-shaped magnetite particles or needle-shaped maghemite particles modified with Co or modified with Co and Fe ²⁺ are obtained by heating the suspension. .