JP3141907B2 - Method for producing spindle-shaped iron-based metal magnetic particle powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a spindle-shaped iron-based metal magnetic particle powder having a uniform particle size, free of dendritic particles, and having a high coercive force. It concerns the manufacturing method.

[0002]

2. Description of the Related Art In recent years, VTRs (video tape recorders) have been remarkably popularized. VTRs aiming at long-time recording and miniaturization and lightening have been actively developed, and magnetic recording media used in the VTRs have been developed. Demands for higher performance and higher density recording are also increasing.

[0003] That is, the magnetic recording medium is required to have high image quality, high output characteristics, and especially improvement in frequency characteristics.
It is necessary to improve the residual magnetic flux density Br, increase the coercive force, and improve the smoothness of the tape surface, and the S / N ratio is increasingly required.

As is well known, these characteristics of a magnetic recording medium are closely related to the magnetic particle powder used, and have a higher coercive force and a larger saturation magnetization than conventional iron oxide magnetic particle powder. Metal magnetic particle powder containing iron as a main component is a digital audio tape (DAT), 8 mm
It is used and practically used for magnetic recording media such as video tapes, Hi-8 tapes, and video floppies. However, it is strongly desired to further improve the properties of these metal magnetic particle powders containing iron as a main component.

That is, the relationship between the 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 description of Nikkei Electronics (1976), May 3, page 82-105, that
Improvements in video S / N ratio, chroma S / N ratio, and video frequency characteristics are 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 a vehicle, the orientation and the filling property in a coating film, and It is important to improve the surface smoothness of a magnetic recording medium. Such magnetic particles have a uniform particle size, do not contain dendritic particles, and have an axial ratio (long axis diameter). / Small shaft diameter-the same applies hereinafter) is required to be large.

Next, in order to improve the video frequency characteristics, it is necessary that the coercive force Hc of the magnetic recording medium be high and the residual magnetic flux density Br be large. In order to increase the coercive force Hc of the magnetic recording medium, it is required that the coercive force Hc of the magnetic particle powder be as high as possible, and is currently used for video floppy, DAT, 8 mm video, and Hi-8. The coercive force of the magnetic particles is 1300 Oe to 1
About 800 Oe is required. The coercive force of the magnetic particle powder used for this purpose generally occurs due to its shape anisotropy. Therefore, the coercive force tends to increase as the axial ratio of the particles increases.

The magnetic particle powder containing iron as a main component is generally prepared by reducing goethite particles as a starting material, hematite particles obtained by heating and dehydrating the particles, or particles containing a different metal other than iron in a reducing gas. Medium, obtained by heat reduction.

As described above, magnetic metal particles mainly composed of iron and having a high coercive force and having a uniform particle size and no dendritic particles are presently required at the present time. In order to obtain magnetic metal particle powder containing iron as a main component having such characteristics, the particle size of the goethite particle powder as a starting material is uniform and dendritic particles are not mixed, and , It is required to have a large axial ratio.

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. As described above, a method of generating needle-like goethite particles by passing an oxygen-containing gas at a temperature of 80 ° C. or lower to perform an oxidation reaction (for example, Japanese Patent Publication No. 39-5610), an aqueous ferrous salt solution and an alkali carbonate A method in which an oxygen-containing gas is passed through a suspension containing FeCO ₃ obtained by reacting with an aqueous solution to cause an oxidation reaction, thereby producing spindle-shaped goethite particles (for example, JP-A-50-80999). Is known.

[0012]

SUMMARY OF THE INVENTION Metal magnetic particle powder containing iron as a main component having a uniform particle size, containing no dendritic particles, and having a high coercive force is the most required at present. By the way, according to the above-mentioned method of producing goethite particle powder as a starting material, needle-like goethite particles having a large axial ratio, particularly 10 or more, are generated, but dendritic particles are mixed. Also, in terms of the particle size, it cannot be said that the particles have a uniform 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; There is a disadvantage that particles with a large axial ratio are difficult to generate,
In particular, this phenomenon tends to become more pronounced as the major axis diameter of the produced particles decreases.

[0014] The iron-based metal magnetic particle powder obtained using the goethite particle powder as a starting material particle is also uniform in particle size, does not contain dendritic particles, and has a large axial ratio. It is hard to say that they do.

On the other hand, by adding an Al compound to the goethite particles, it is possible to prevent the generated goethite particles from being deformed during heat dehydration or heat reduction and to prevent sintering between the particles, and to reduce the magnetic recording medium It is known that the dispersibility, the filling property, and the smoothness of the tape surface can be improved. For example, Japanese Patent Publication No. 43324/1991 is mentioned as the prior art.

However, an aqueous solution containing sodium carbonate and a water-soluble Al compound is mixed with an aqueous solution of ferrous salt, which is a technical means described in the publication, and air is blown to generate α-FeOOH. In a method for producing a metal magnetic powder, the method comprising applying a Si compound and then reducing it in a hydrogen stream at a temperature of 300 to 600 ° C.
The coercive force of the obtained metal magnetic powder is 700 to 1200 Oe.
It is about.

As for the water-soluble Al compound to be added, in the case of alumina sol, only fine particles having an extremely small axial ratio can be obtained. Therefore, the metal magnetic particles obtained by using the goethite particles have a high coercive force. Is difficult to obtain. When only a basic salt compound such as sodium aluminate is added, the resulting goethite particles become coarse and it is difficult to obtain those having a large axial ratio. Further, when only an acidic salt compound such as aluminum chloride or aluminum sulfate is added, it is difficult to obtain a finer one having a large axial ratio.

Accordingly, the present invention provides a goethite particle powder having a uniform particle size, no dendritic particles, and a spindle-like shape containing Al as a starting material. An object of the present invention is to obtain a spindle-shaped iron-based metal magnetic particle powder which is uniform and contains no dendritic particles and has a high coercive force.

[0019]

The above technical object can be achieved by the following method of the present invention. That is, the present invention provides a spindle-shaped goethite having an oxygen-containing gas passed 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. Particles are generated, and the spindle-shaped metal magnetic particles containing iron as a main component are obtained by heating and reducing the goethite particles or the spindle-shaped hematite particles obtained by heating and dehydrating the goethite particles in a reducing gas. In the method for producing a powder, a spindle shape comprising adding an acidic salt compound of Al in the aqueous ferrous salt solution and a basic salt compound of Al in the aqueous alkali carbonate solution in advance is used. This is a method for producing metal magnetic particle powder containing iron as a main component.

In addition, Al added to the ferrous salt aqueous solution
Is an acid salt compound of Al with respect to Fe in the aqueous ferrous salt solution.
It is in the range of 1.0 to 3.0 atomic% in terms of conversion, and the basic salt compound of Al added to the aqueous alkali carbonate solution is 1.0 to 3 in terms of Al with respect to Fe in the aqueous ferrous salt solution. .
It is desirable to be in the range of 0 atomic%.

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

The ferrous salt aqueous solution used in the production reaction of the spindle-shaped goethite particles of the present invention includes:
An aqueous ferrous sulfate solution, an aqueous ferrous chloride solution, an aqueous ferrous nitrate solution, or the like can be used.

As the aqueous alkali carbonate solution used in the present invention, an aqueous sodium carbonate solution, an aqueous potassium carbonate solution, an aqueous ammonium carbonate solution and the like can be used.

As the acidic salt compound of Al used in the present invention by being added to the aqueous ferrous salt solution, aluminum sulfate, aluminum chloride, aluminum nitrate and the like can be used.

The amount of addition in this case is in the range of 1.0 to 3.0 atomic% in terms of Al with respect to Fe in the aqueous ferrous salt solution. Although it may be less than 1.0 atomic%, when the metal magnetic particle powder is used as the magnetic recording medium, the affinity with the binder resin becomes insufficient, so that problems such as dispersibility arise.
If it exceeds 3.0 atomic%, the obtained goethite particles become fine particles, and the desired effect cannot be obtained.

In the present invention, as the basic salt compound of Al to be used by being added to the aqueous alkali carbonate solution, sodium aluminate, potassium aluminate, ammonium aluminate and the like can be used.

In this case, the amount of addition is in the range of 1.0 to 3.0 atomic% in terms of Al with respect to Fe in the aqueous ferrous salt solution. Although it may be less than 1.0 atomic%, when the metal magnetic particle powder is used as the magnetic recording medium, the affinity with the binder resin becomes insufficient, so that problems such as dispersibility arise.
If the content exceeds 3.0 atomic%, the desired effect cannot be obtained because the obtained goethite particles are coarse.

In the present invention, the total addition amount of the respective Al compounds is at least 1.3 atomic% in terms of Al with respect to Fe.
And preferably in the range of 2.0 to 6.0 atomic%.
You. If less than 1.3 atomic%, the metal magnetic particles
However, when used as a magnetic recording medium, it does not
May be sufficient, causing problems in dispersibility, etc.
Therefore, the content is preferably 2.0 atomic% or more. Even if it is added in excess of 6.0 atomic%, the amount of Al added in excess of 6.0 atomic%
The compound is meaningless because it is not contained in the resulting goethite particles.

The atomic ratio between the acidic salt compound and the basic salt compound of Al is in the range of 1: 2 to 2: 1. 1: 2
If it is less than 1, the obtained goethite particles become coarse, and the desired effect cannot be obtained. If the ratio exceeds 2: 1, the obtained goethite particles become fine particles, and the desired effect cannot be obtained.

In the present invention, each Al compound is added in a ferrous salt aqueous solution or an alkali carbonate aqueous solution before neutralization into a suspension containing FeCO ₃ . May be added and stirred or dissolved, or an aqueous solution in which each is separately dissolved may be added and mixed.

When both the acidic salt compound of Al and the basic salt compound of Al are directly mixed and added at the time of neutralization, an Al colloid is formed, and each Al compound is defined in the present invention. Conversely, when added to each of the aqueous solutions,
The desired effect cannot be obtained due to the formation of Al colloid.

The pH value of the suspension containing FeCO ₃ in the present invention is 8 to 10 as in the conventional method. pH
If it is less than 8, or if the pH exceeds 10, no spindle-shaped goethite particles having a uniform particle size can be obtained.

In the present invention, the suspension containing FeCO ₃ is preferably aged in a non-oxidizing atmosphere. Aging is performed by subjecting the suspension under a non-oxidizing atmosphere to usually 40 to
It is preferable to carry out in a temperature range of 80 ° C. If the temperature is lower than 40 ° C., the axial ratio becomes small and it is difficult to obtain a sufficient aging effect. If the temperature is higher than 80 ° C., particulate magnetite may be mixed.

The aging time is 30 to 300 minutes. If the time is less than 30 minutes, the axial ratio cannot be sufficiently increased. It can be over 300 minutes,
There is no point in taking longer than necessary.

In order to form a non-oxidizing atmosphere, an inert gas (such as N ₂ gas) or a reducing gas (such as H ₂ gas) may be passed through the reaction vessel of the suspension.

The temperature at the time of the oxidation reaction in the present invention may be usually at a temperature of 80 ° C. or less at which goethite particles are formed. When the temperature exceeds 80 ° C., particulate magnetite particles are mixed in spindle-shaped goethite particles.

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

In the present invention, in order to prevent the deformation of the particle shape and the sintering between the particles during the heat reduction, the starting materials are made of Ni compound, Al compound, Si compound, P compound, Co compound, Mg compound, B compound in advance. It is preferable to apply a coating treatment with one or more metal compounds selected from compounds and Zn compounds. Since these metal compounds have not only a sintering preventing effect but also a function of controlling a reduction rate, It is preferable to use them in combination as needed.

The starting material coated with the above metal compound can be reduced as it is to obtain the desired metal magnetic particle powder containing iron as a main component. In order to control the shape, it is preferable to perform a heat treatment in a non-reducing gas atmosphere in advance before the reduction by a conventional method.

The heat treatment in the non-reducing gas atmosphere is performed under a flow of air, oxygen gas, and nitrogen gas at 300 to 800.
C., and the heat treatment temperature is more preferably selected as appropriate according to the type of the metal compound used for coating the starting material particles. When the temperature exceeds 800 ° C., deformation of the particles and sintering between the particles and the particles are caused.

The temperature range of the heat reduction in the present invention is 3
00-550 degreeC is preferable. When the temperature is lower than 300 ° C., the progress of the reduction reaction is slow and a long time is required. Also, 5
If the temperature exceeds 50 ° C., the reduction reaction proceeds rapidly, causing deformation of the particles and sintering between the particles.

The iron-based metal magnetic particles powder after heat reduction in the present invention can be prepared by a known method, for example, immersion in an organic solvent such as toluene, or reduced iron-based metal magnetic particles. After the atmosphere of the powder is once replaced with an inert gas, it can be taken out into the air by a method such as gradually oxidizing by gradually increasing the oxygen content in the inert gas into air while gradually increasing the oxygen content.

In the present invention, in order to improve the various characteristics of the metal magnetic particle powder containing iron as a main component, a Co compound, a Ni compound usually added together with an Al compound when producing goethite particles as a starting material have been conventionally used. Compound, Cr compound, Zn compound, Mn compound, P compound, Si compound,
One or two or more compounds selected from the B compounds can be added, and also in this case, the target particle size of the present invention is uniform, dendritic particles are not mixed, and Spindle-shaped goethite particles having high coercive force can be obtained.

[0044]

The operation of the present invention having the above-described configuration is as follows.

In order to obtain metal magnetic particle powder having a uniform particle size, no dendritic particles, and a high coercive force, the axial ratio is determined by the above method. Although large needle-like goethite particles are generated, dendritic particles are mixed, and it is difficult to say that the particles have a uniform particle size. By improving spindle-shaped goethite particles in which particles are not mixed, it is possible to obtain metal magnetic particle powder having a uniform particle size, no dendritic particles mixed, and high coercive force. Worked.

On the other hand, it is known that the use of an Al compound in the metal magnetic particle powder can improve the dispersibility, filling property, and smoothness of the tape surface when used as a magnetic recording medium. The magnetic particle powder is evaluated based on the familiarity with the binder resin, and the evaluation method can be measured by the solid acid amount and base amount described later. In general, it is said that the larger the amount of the solid base, the better the compatibility with the binder resin which is generally used at present (for example, a polyurethane resin is added to a vinyl chloride-vinyl acetate copolymer).

In the method of using an Al compound in the metal magnetic particle powder, (A) a method of adding at the time of a reaction for forming goethite particles (for example, Japanese Patent Publication No. 3-43324, cited above), and (B) a goethite particle before heat treatment Alternatively, a method of coating the surface of the hematite particles after heating and dehydrating the goethite particles with an Al compound (see, for example,
No. 134858) and (C) a method of coating the particle surface of the obtained metal magnetic particle powder with an Al compound (for example,
JP-A-58-161709).

However, regarding the method (B),
The magnetic properties, especially the coercive force, decrease. The method (C) is not industrial because it requires wet pulverization and peptization of the magnetic metal particles. In the method (A), as described above, it is difficult to obtain a high coercive force.

However, as a result of various studies by the present inventors,
In the method of (A), it was found that the characteristics were different depending on the timing of adding the Al compound in the process of forming goethite particles. The addition timing is as follows: (a) neutralization and FeC
A method of adding to each raw material aqueous solution before forming a suspension containing O ₃ , (b) a method of adding after the formation of the suspension, (c)
There are a method of adding a suspension containing FeCO ₃ during or after ripening, a method (d) of adding during the oxidation reaction after aging, and a method (e) of adding after the oxidation reaction.

Of these, when added at the times of (b) and (c), the resulting goethite particles become extremely fine, so that they are very difficult to handle and have low coercive force. When added at the time of (d), the particles become coarse and the axial ratio is not sufficient, and when added at the time of (e), the result is the same as that of the method (B) described above. Was.

When added at the time of (a),
As described above, in the case of a water-soluble Al compound to be added, particularly, in the case of alumina sol, only goethite particles having a fine and extremely small axial ratio are obtained, and in the case of sodium aluminate, the particles are coarsened. It was found that those having a large axial ratio were difficult to obtain, and in the case of aluminum chloride and aluminum sulfate, there were problems that it was difficult to obtain a large axial ratio.

For this reason, the present inventors have found that in the case of alumina sol, the alumina sol is a solid, and when added at the time of neutralization, it becomes a nucleus of goethite particles to be formed, and only fine particles having a very small axial ratio can be obtained. Absent. Further, aluminum has both a function as a coagulant and a function as a crystal growth controlling agent. When an acid salt of Al is used alone, only an effect of controlling crystal growth is exerted, and a material having a large axial ratio is obtained. However, it is considered that when the basic salt compound of Al is used alone, only the aggregation effect is exerted and the particles are coarsened. Although the reason for this is not yet clear, it is believed that the aluminum is neutralized to form a solid, which is attributed to the manner of adsorption when adsorbed to the neutralized iron and the structure of the aluminum compound itself.

Therefore, the present inventor studied variously whether spindle-shaped goethite particles containing a large amount of an Al compound, which can improve the compatibility with the binder resin, can be obtained when the metal magnetic particles are used as the powder. As a result, before neutralizing the aqueous ferrous salt solution and the aqueous alkali carbonate solution into a suspension containing FeCO ₃ , an acidic salt compound of Al was added to the aqueous ferrous salt solution, respectively. Further, a basic salt compound of Al is added to the aqueous alkali carbonate solution and then a neutralization reaction is performed to form a suspension containing FeCO ₃ , and then an oxygen-containing gas is passed to perform an oxidation reaction. It has been found that by performing this, it is possible to produce spindle-shaped goethite particles having a uniform particle size, no dendritic particles being mixed, and having a large amount of Al.

The reason for this is that the acid salt compound of Al is added to an aqueous solution of ferrous salt having the same acidity, and the basic salt compound of Al is added to an aqueous solution of alkali carbonate having the same alkalinity. Is carried out smoothly, each Al compound is taken into FeCO ₃ , and further, it is thought that in the process of forming spindle-shaped goethite particles, a large amount of Al compounds could be successfully contained. It is considered that the agglomeration effect and the crystal growth control effect described above advantageously acted on shape control.

As a result, the spindle-shaped goethite particles or the spindle-shaped hematite particles obtained by heating and dehydrating the goethite particles are heated and reduced in a reducing gas, so that the particle sizes are uniform. As a result, a spindle-shaped iron-based metal magnetic particle powder containing no dendritic particles and having a high coercive force was obtained.

[0056]

Next, the present invention will be described with reference to examples and comparative examples. In the following Examples and Comparative Examples, the average diameter and the axial ratio of the particles were all the average values of the values measured from the electron micrographs.

The magnetic properties and coating properties of the metal magnetic particles containing iron as a main component are described in "Vibration sample magnetometer VSM-3S-
15 "(manufactured by Toei Industry Co., Ltd.) and an external magnetic field of 10K
It was measured over Oe.

Regarding the compatibility of the metal magnetic particle powder containing iron as a main component with the binder resin, n-butylamine (basic substance) is adsorbed on the magnetic powder, and the concentration of the non-adsorbed n-butylamine is adjusted to 0.1. The amount of solid acid measured by titration with a 1N HClO ₄ / acetic acid solution or the amount of myristic acid (acidic substance) adsorbed on magnetic powder and the concentration of myristic acid not adsorbed are measured by “ion chromatography HIC-6A” (Shimadzu Corporation) From the amount of the solid base measured by the method described in (1).

<Production of Spindle-Shaped Goethite Particle Powder> Examples 1 to 3 and Comparative Examples 1 to 5;

Example 1 In a reaction vessel maintained in a non-oxidizing atmosphere by flowing N ₂ gas at a rate of 50 l / min, 51.3 g of aluminum sulfate (relative to Fe ²⁺ in an aqueous ferrous sulfate solution) was added. 1.5
It corresponds to atomic%. ) Dissolved Fe ²⁺ 0.8mol
/ L and 1.6 mol of 24.6 g of sodium aluminate (corresponding to 1.5 atomic% based on Fe ²⁺ in the aqueous ferrous sulfate solution).
/ L of an aqueous solution of Na ₂ CO ₃ (corresponding to 2.0 equivalents to Fe ²⁺ in an aqueous solution of ferrous sulfate).
A suspension containing FeCO ₃ was formed at a pH of 9.4 and a temperature of 56 ° C.

After continuously ripening the suspension at a temperature of 56 ° C. for 2 hours while flowing 50 l of N ₂ gas per minute, the N ₂ gas was stopped and the temperature of the suspension was lowered. 55 ° C. and 150 liters of air per minute into the suspension
Vent for a period of time to produce tan precipitated particles. The yellow-brown precipitate particles were separated by filtration, washed with water, dried and pulverized by a conventional method.

As a result of X-ray diffraction, the obtained tan particle powder was goethite.
As is clear from (30000), the Al compound contained 0.76 wt% in terms of Al and had a major axis diameter of 0.19 μm as an average value.
The particles consisted of spindle-shaped particles having a m and an axial ratio of 10 and had uniform particle sizes and did not contain dendritic particles.

Examples 2 and 3, Comparative Examples 1 to 5 Types of ferrous salt aqueous solution in producing goethite particles,
Kind of alkali carbonate aqueous solution, kind of Al acidic salt compound or Al basic salt compound added / dissolved in ferrous salt aqueous solution or alkali carbonate aqueous solution and amount used for Fe ²⁺ , Compound of each of the above Al Goitite particles having a spindle shape were obtained in the same manner as in Example 1 except that the addition solution and the timing of, the flow rate of the aerated gas in the aging step, the temperature and the time, and the reaction temperature were variously changed.

Tables 1 and 2 show the main production conditions and various properties of the goethite particles at this time. In Comparative Example 2, as is clear from the electron micrograph (× 30000) shown in FIG. 5, the measurement of the major axis diameter and the axial ratio was omitted because the particles were fine irregular particles.

[0065]

[Table 1]

[0066]

[Table 2]

<Production of Spindle-Shaped Hematite Particle Powder> Examples 4 to 6, Comparative Examples 6 to 9;

Example 4 A considerable amount of press cake was added to 1500 g of spindle-shaped goethite particles obtained in Example 1 after filtration and washing with water.
Suspended in 0 l of water. The pH of the suspension at this time was 8.
Nine. Then, 315 of cobalt acetate was added to the above suspension.
g (corresponding to 21 wt% of cobalt acetate with respect to goethite) was added, and the mixture was stirred and dispersed for 10 minutes. Then, 180 g of boric acid was added to the suspension.
(Corresponding to 12 wt% of boric acid with respect to goethite) and stirred for 10 minutes. Next, an aqueous ammonia solution having a concentration of 15% was added so that the pH of the suspension became 7.3, and the resulting mixture was separated by filtration to remove unnecessary salts. The goethite press cake separated by filtration was dried to obtain goethite particles coated with a Co compound and a B compound. The content of Co and B in the obtained goethite was 3.7 atomic% in terms of Co for the Co compound, and 0.71% in terms of B for the B compound.
Atomic%.

Next, the goethite particles were placed in air for 40 minutes.
After heating and dehydration at 0 ° C. for 30 minutes, spindle-shaped hematite particles were obtained.

Examples 5 and 6, Comparative Examples 6 to 9 Spindle-shaped hematite particles were obtained in the same manner as in Example 4, except that the type of particles to be treated was changed. Table 3 shows the main production conditions and various characteristics at this time. In Comparative Example 6, in addition to the Co compound and the B compound, an Al compound (20 wt% as aluminum nitrate with respect to goethite) was used.
Corresponds to. ) Was coated.

[0071]

[Table 3]

<Production of spindle-shaped iron-based metal magnetic particle powder> Examples 7 to 9, Comparative Examples 10 to 13;

Example 7 100 g of the spindle-shaped hematite particle powder obtained in Example 4 was charged into a rotary retort reduction vessel having a volume of about 10 l, and H ₂ gas was supplied at a rate of 20 l / min while being driven to rotate. It was aerated and reduced at a reduction temperature of 400 ° C.

The spindle-shaped iron-based metal magnetic particle powder obtained by reduction is immersed in a toluene solution and taken out so as not to cause rapid oxidation when taken out into the air. . A part was taken out and a stable oxide film was formed on the surface while evaporating toluene.

As a result of observation with an electron microscope, this spindle-shaped iron-based metal magnetic particle powder was found to have an average major axis of 0.1 mm.
The particle size was 13 μm, the axial ratio was 7.5, the particle size was uniform, and there were few dendritic particles. The Al compound was 1.10 wt% in terms of Al with respect to Fe, and the magnetic properties were a coercive force Hc1655Oe and a saturation magnetization ss149 emu / g. The amount of solid acid is 0.235 mg / m ² ,
The solid base amount was 0.858 mg / m ² .

Examples 8 and 9 and Comparative Examples 10 to 13 Spindle-shaped iron-based metal magnetic particles mainly composed of iron in the same manner as in Example 7 except that the kind of particles to be treated and the reduction temperature were variously changed. A powder was obtained. Table 4 shows the main manufacturing conditions and various characteristics at this time.

[0077]

[Table 4]

[0078]

According to the method for producing spindle-shaped iron-based metal magnetic particles according to the present invention, as shown in the preceding embodiment, the particle size is uniform and dendritic particles are formed. Suitable for high recording density, high sensitivity, and high output magnetic particle powder, because it is possible to obtain a spindle-shaped iron-based metal magnetic particle powder having a high coercive force without being mixed. It is.

[Brief description of the drawings]

FIG. 1 is an electron micrograph (× 3000) showing the particle structure of the spindle-shaped goethite particle powder obtained in Example 1.
0).

FIG. 2 is an electron micrograph (× 3000) showing the particle structure of spindle-shaped goethite particles obtained in Example 2.
0).

FIG. 3 is an electron micrograph (× 3000) showing the particle structure of spindle-shaped goethite particles obtained in Example 3.
0).

FIG. 4 is an electron micrograph (× 3000) showing the particle structure of the spindle-shaped goethite particles obtained in Comparative Example 1.
0).

FIG. 5 is an electron micrograph (× 3000) showing the particle structure of the spindle-shaped goethite particles obtained in Comparative Example 2.
0).

FIG. 6 is an electron micrograph (× 3000) showing the particle structure of the spindle-shaped goethite particles obtained in Comparative Example 3.
0).

FIG. 7 is an electron micrograph (× 3000) showing the particle structure of the spindle-shaped goethite particle powder obtained in Comparative Example 4.
0).

FIG. 8 is an electron micrograph (× 3000) showing the particle structure of the spindle-shaped goethite particles obtained in Comparative Example 5.
0).

Claims (2)

(57) [Claims] 1. A goethite particles exhibited fusiform by performing an oxidation reaction by bubbling an oxygen-containing gas into the suspension containing FeCO ₃ obtained by reacting a ferrous salt aqueous solution and aqueous alkali carbonate solution To produce the spindle-shaped iron-based metal magnetic particle powder obtained by heating and reducing the goethite particles or the spindle-shaped hematite particles obtained by heating and dehydrating the goethite particles in a reducing gas. The method of producing a spindle-shaped fiber, wherein an acidic salt compound of Al is added in advance to the aqueous solution of ferrous salt, and a basic salt compound of Al is added to the aqueous solution of alkali carbonate. Of producing metal magnetic particle powder containing iron as a main component and exhibiting the following. 2. The method according to claim 1, wherein the acidic salt compound of Al added to the aqueous ferrous salt solution is in the range of 1.0 to 3.0 at% in terms of Al with respect to Fe in the aqueous ferrous salt solution. 2. The spindle-shaped iron according to claim 1, wherein the basic salt compound of Al added to the aqueous solution is in a range of 1.0 to 3.0 atomic% in terms of Al with respect to Fe in the aqueous ferrous salt solution. 3. A method for producing metal magnetic particle powder comprising as a main component.