JP3337046B2 - Spindle-shaped metal magnetic particles containing cobalt and iron as main components and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle-shaped metal magnetic powder containing cobalt and iron as a main component, which is most suitable as a magnetic material powder for a high-density magnetic recording medium, and a method for producing the same.

The spindle-shaped metal magnetic particles comprising cobalt and iron as main components according to the present invention are fine particles, have a uniform particle size, do not include dendritic particles, and have a high coercive force. Spindle-shaped metal magnetic particles containing cobalt and iron as main components, having an excellent coercive force distribution and a large saturation magnetization, and also having excellent oxidation stability.

Further, the spindle-shaped metal magnetic particles according to the present invention, which contain cobalt and iron as main components, have excellent dispersibility and filling properties when used as a magnetic recording medium.

[0004]

2. Description of the Related Art In recent years, long-time recording, miniaturization and lightening of magnetic recording / reproducing devices for video and audio have been promoted. In particular, VTRs (video tape recorders) have been remarkably popularized recently. 2. Description of the Related Art VTRs aiming at time recording and reduction in size and weight have been actively developed.
On the other hand, there is a demand for higher performance and higher density recording of a magnetic tape as a magnetic recording medium.

[0005] That is, it is required to improve the high image quality, high output characteristics, and especially the frequency characteristics of the magnetic recording medium.
Improvement of residual magnetic flux density Br, high coercive force and dispersibility,
It is necessary to improve the filling property and the smoothness of the tape surface.
An improvement in the N ratio is required.

[0006] These characteristics of the magnetic recording medium are closely related to the magnetic particle powder used in the magnetic recording medium, but in recent years, these properties are higher than those of the conventional iron oxide magnetic particle powder. Attention has been paid to metal magnetic particle powder mainly composed of iron having a magnetic force and a large saturation magnetization, and has been put to practical use in magnetic recording media such as digital audio tape (DAT), 8 mm video tape, and Hi-8 tape. . However, it is strongly desired to further improve the characteristics of these metal magnetic particles.

Now, the relationship between the characteristics of the magnetic recording medium and the characteristics of the magnetic particle powder used will be described in detail as follows.

In order to obtain high image quality as a magnetic recording medium for video, "Nikkei Electronics" (1976)
As is clear from the record of No. 133, pp. 82-105,
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 the magnetic recording medium, and such magnetic particles are fine particles, and have a uniform particle size, do not contain dendritic particles, and It is required to have an appropriate axial ratio (major axis diameter / short axis diameter, hereinafter simply referred to as “axial ratio”).

Next, in order to improve the video frequency characteristics, it is necessary that the magnetic recording medium has a high coercive force and a high residual magnetic flux density Br. In order to increase the coercive force of a magnetic recording medium, it is required that the magnetic particles have as high a coercive force as possible.

Since the coercive force of the magnetic particle powder is generally caused by its shape anisotropy, a high coercive force can be obtained by making the particles as fine as possible or by increasing the axial ratio of the particles. . For example, Japanese Patent Publication No. 1-18961 states that “‥‥ coercive force increases as the axial ratio increases, while coercive force is affected by the particle size, and is larger than the particle size at which superparamagnetism appears. Therefore, the target coercive force is
It can be obtained by appropriately selecting the particle size and its axial ratio. ‥‥ ”.

Furthermore, the coercive force distribution (SFD: Swi)
tching Field Distribution
n) is required to be excellent.

This fact is described in Japanese Patent Laid-Open Publication No. Sho 63-26821, "‥‥ FIG. 1 is a diagram showing the relationship between the SFD measured for the above magnetic disk and the recording / reproducing output. The relationship between the SFD and the recording / reproducing output is a straight line as is clear from FIG.
F. D. It can be seen that the recording / reproducing output is increased by using a ferromagnetic powder having a small particle size. That is, in order to increase the recording / reproducing output, S.P. F. D. Is preferably small, and in order to obtain an output higher than usual, an S.D. F. D. is necessary. ‥‥ ”.

The requirements for these metal magnetic particle powders are not limited, and the fine particles described above are required to have a large coercive force and a large saturation magnetization value.
For example, in Japanese Patent Application Laid-Open No. 5-98321, "‥‥ In order to achieve high density of a magnetic recording medium, the metal magnetic powder used is a fine particle, has a high coercive force, a large saturation magnetic flux density, It is also necessary to have excellent dispersibility and excellent oxidation stability. ‥‥ Saturation magnetic flux density varies depending on the composition of metal magnetic powder, particle size, and thickness of oxide film. In the case of an alloy having a reduced size, the addition of cobalt is effective.
‥ Naturally, the saturation magnetic flux density also increases. ‥‥ However, since the axial ratio greatly affects the coercive force, it cannot be made extremely small. ‥‥ ”.

That is, the magnetic material powder for a high-density magnetic recording medium is fine particles, has a uniform particle size, does not contain dendritic particles, and has a high coercive force, an excellent coercive force distribution and a large saturation magnetization. And have excellent oxidation stability.

In general, the metal magnetic particle powder is obtained by subjecting goethite particles as a starting material, hematite particles obtained by heating and dehydrating the particles, or particles containing a different metal other than iron to these particles, if necessary, In reducing gas,
It is obtained by heat reduction.

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 amount or more of an alkali hydroxide aqueous solution to a ferrous salt aqueous solution is used. A method of producing acicular goethite particles by conducting an oxidation reaction by passing an oxygen-containing gas at a temperature of 80 ° C. or lower (Japanese Patent Publication No. 39-5)
No. 610, etc., hereinafter referred to as “iron hydroxide-based goethite particles”
That. -), A method of producing spindle-shaped goethite particles 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 carry out an oxidation reaction (particularly, Japanese Patent Application Laid-Open No. 50-80999, hereinafter referred to as "iron carbonate-based goethite particles".
And an oxygen-containing gas is passed through a suspension containing FeCO ₃ or an iron-containing precipitate obtained by reacting an aqueous solution of ferrous salt with a mixed aqueous solution of an alkali carbonate and an alkali hydroxide to carry out an oxidation reaction to thereby form a spindle. There are known methods for producing goethite particles (for example, JP-A-2-51429, hereinafter referred to as "alkaline combined goethite particles").

As a prior art for obtaining metal magnetic particle powders using goethite particles such as iron hydroxide-based goethite particles, iron carbonate-based goethite particles, and alkali-based goethite particles as starting material particles, Japanese Patent Publication No. 55-29577
Japanese Patent Publication No. 1-18961, Japanese Patent Publication No. 2-57
No. 122, Japanese Patent Publication No. 3-43323, Japanese Unexamined Patent Publication No.
JP-A-3-222404, JP-A-3-49026, JP-A-4-63210, JP-A-5-6216
6, JP-A-5-98321, JP-A-6-2
5702, JP-A-6-36265, JP-A-6-139553, JP-A-6-140222 and JP-A-6-215360.

[0019]

The iron hydroxide-based goethite particles have a large axial ratio, in particular, acicular goethite particles of 10 or more, but contain dendritic particles.
Also, the particle size cannot be said to be uniform. For example, the above-mentioned Japanese Patent Application Laid-Open No. 5-62166 discloses a method in which "‥‥ is produced by air oxidation of a hydrolyzate of ferrous salt with an alkali hydroxide. According to this method, goethite particles are miniaturized. To do this, for example, add a water-soluble silicate to the reaction system. ‥‥ Branches easily occur in the particles. ‥‥ Expand the particle size distribution of the metal magnetic powder. ‥‥ Make the goethite particles extremely small. Moreover, the above-mentioned alkali hydroxide method has a limit in trying to equalize the particle size distribution. "
It is as described. In addition, when metal magnetic particles are used, high coercive force is easily obtained, but it is difficult to reduce the particle size, and excellent coercive force distribution is also caused due to difficulty in obtaining uniform particle size. It is hard to obtain.

The iron carbonate-based goethite particles described above have a uniform particle size, and spindle-shaped particles containing no dendritic particles are formed. On the other hand, the axial ratio is at most about 7, and the axial ratio is at most about 7. Large particles are difficult to generate. For example, Japanese Patent Laid-Open Publication No.
No. 2166, "{spindle-type goethite particles obtained by hydrolyzing ferrous salt with alkali carbonate and then oxidizing with air are refined and uniform in particle size distribution.} It is considered that the ratio is small and it is difficult to increase the coercive force due to shape anisotropy. " In addition, when the metal magnetic particles are used, there is a problem that it is difficult to obtain a high coercive force.

The goethite particles combined with the alkali described above can produce spindle-shaped particles having a uniform particle size and a large axial ratio. For example, "‥" in Japanese Patent Laid-Open Publication No.
Spindle-shaped goethite particles having a large axial ratio (major axis diameter / short axis diameter) can be obtained. ‥‥ ”. In addition, metal magnetic particles having a higher coercive force are easily obtained as compared with iron carbonate-based goethite particles.

Therefore, first, the above-mentioned prior arts in the case of obtaining metal magnetic particles using iron hydroxide-based goethite particles and iron carbonate-based goethite as starting material particles were studied.

Japanese Patent Publication No. 55-29577, Japanese Patent Publication No. 1-18961, Japanese Patent Publication No. 2-5712.
No. 2, JP-B-3-43323, JP-A-3-49026, JP-A-5-62166, JP-A-5-98321, and JP-A-6-36265. In the technical means described in the gazette,
In each case, the coercive force Hc of the obtained metal magnetic particles was 18
It is 50 Oe or less.

According to the technical means described in the above-mentioned JP-A-6-139553, the coercive force H
An example in which c exceeds 1850 Oe is also shown, but since the axial ratio is increased to increase the coercive force, the particle size is also reduced to 0.
The size is larger than 2 μm.

In the technical means described in JP-A-63-222404 and JP-A-6-215360, since no specific method is described, which method is used to generate goethite particles is not considered. Unknown. However, when iron carbonate-based goethite particles are used as a starting material as described in the above-mentioned publications, metal magnetic particles having a coercive force Hc of more than 1850 Oe are not obtained from the fine particles. It can be estimated that the coercive force Hc of 1850 Oe or more is obtained by using the systemic goethite particles.

Next, the above-described prior arts were examined for obtaining metal magnetic particle powders using alkali-combined goethite particles as starting material particles.

According to the technique described in JP-A-4-63210, an iron-containing precipitate obtained by reacting an aqueous solution of ferrous salt with an aqueous solution of an alkali carbonate and an aqueous solution of an alkali hydroxide in combination as an aqueous alkali solution. In the case where a zinc compound is present in a suspension containing, a spindle ratio can be further improved. In particular, spindle-shaped goethite particles having an axis ratio of 15 or more (applicant's note: iron carbonate-based goethite Particles can be generated, and the coercive force of the obtained metal magnetic particle powder can be increased.
Those exceeding 0 Oe have not been obtained.

The combination of an aqueous alkali carbonate solution and an aqueous alkali hydroxide solution is disclosed in JP-A-6-2570, supra.
No. 9 in the technical means described in Japanese Patent Application Laid-Open No. 6-140222 and Examples 6 and 7 in the technical means described in Japanese Patent Application Laid-Open No. 6-140222 described above.
In Example 9 of Japanese Patent Publication No. 2 and Example 7 of Japanese Patent Application Laid-Open No. 6-140222, although the axial ratio is not described, it is not clear. Since spindle-shaped goethite particles having a relatively large axial ratio are easily obtained, the use of spindle-shaped goethite particles having a large axial ratio does not mean that metal magnetic powder of about 1800 to 1850 Oe is obtained. It can be estimated.

From these results, when the metal magnetic particles were obtained using the conventional goethite particles as starting material particles, the particles were fine particles, the particle size was uniform, and no dendritic particles were present. The metal magnetic particles having an appropriate axial ratio, and having a high coercive force, an excellent coercive force distribution and a large saturation magnetization value, and having excellent oxidative stability and balanced properties. Absent.

Therefore, the present invention uses the alkali-combined goethite particles as a starting material,
In particular, the average major axis diameter is 0.05 to 0.12 μm,
Moreover, it is a technical object to obtain spindle-shaped metal magnetic particles having a coercive force Hc of 1850 to 2500 Oe and a saturation magnetization of 135 emu / g or more.

[0031]

The above technical objects can be achieved by the present invention as described below.

That is, according to the present invention, cobalt is contained in an amount of 8 to 50 atomic% in terms of Co with respect to the total Fe in the spindle-shaped metal magnetic particles, has an average major axis diameter of 0.05 to 0.12 μm, and an average short axis. The shaft diameter is 0.01 to 0.02 μm, the axial ratio is 4 to 7, the X-ray particle diameter (D ₁₁₀ ) is in the range of the following formula 1, and the coercive force Hc is 1850 to 2500 Oe, and the saturation is Spindle-shaped metal magnetic particles having a magnetization value of 135 emu / g or more and containing cobalt and iron as main components.

[Equation 1] [(L × 500) +100] Å-[(L × 50
0) +120]} where L is the average major axis diameter (μm).

[0033] The present invention also provides a suspension containing an iron-containing precipitate obtained by reacting an aqueous solution of ferrous salt by using an aqueous solution of an alkali carbonate and an aqueous solution of an alkali hydroxide in a non-oxidizing atmosphere. After maintaining and stirring and aging, an oxygen-containing gas is passed through the suspension to perform an oxidation reaction to generate spindle-shaped goethite particles, and the spindle-shaped goethite particles or the spindle-shaped goethite particles are heated and dehydrated. Spindle-shaped hematite particles obtained by coating with a sintering inhibitor, and heating and reducing in a reducing gas to obtain spindle-shaped metal magnetic particles. Spindle-shaped metal magnetic particles containing cobalt and iron as main components. In the powder production method, the addition of the alkali hydroxide aqueous solution
The alkali carbonate aqueous solution and the iron before aging
The suspension containing any precipitate containing
Addition amount of the alkali carbonate aqueous solution to the alkali carbonate aqueous solution
By setting the molar ratio to 0.2 to 1.2, the total amount of the aqueous alkali carbonate solution and the aqueous alkali hydroxide solution becomes 1.3 to 2.5 equivalents relative to all Fe in the ferrous salt aqueous solution, Further, in one of the ferrous salt aqueous solution, the alkali carbonate aqueous solution, the alkali hydroxide aqueous solution and the suspension containing the iron-containing precipitate before the aging, S
One, two or more compounds selected from the elements i, Nd, Y, La, Ce, Pr, and Tb are used in an amount of 0.1 to 1.0 in terms of element with respect to all Fe in the ferrous salt aqueous solution. At the same time as the ferrous salt aqueous solution, the suspension containing the iron-containing precipitate before the aging, and the suspension during the aging. Is 8 to 50 atomic% in terms of Co with respect to all Fe in the ferrous salt aqueous solution.
And the oxidation rate of Fe ²⁺ in the oxidation reaction solution is in the range of 20 to 50% with respect to the total Fe in the ferrous salt aqueous solution. Under the same conditions, Al, Si, Nd, Y, La, Ce, P
One or two or more compounds selected from the elements of r and Tb are added in the range of 0.1 to 10.0 atomic% in terms of element with respect to all Fe in the ferrous salt aqueous solution. This is a method for producing spindle-shaped metal magnetic particle powder containing cobalt and iron as main components.

The structure of the present invention will be described in detail as follows.

First, a spindle-shaped metal magnetic particle powder containing iron and cobalt and iron according to the present invention (hereinafter, referred to as a powder).
It is simply referred to as “spindle-shaped metal magnetic particle powder”. ).

The spindle-shaped metal magnetic particles according to the present invention have an average major axis diameter of 0.05 to 0.12 μm. 0.05μ
If it is less than m, the particle diameter becomes too small and approaches the superparamagnetic region, so that the saturation magnetization value decreases and the coercive force also decreases. When it exceeds 0.12 μm, a large saturation magnetization value is easily obtained, but it is difficult to obtain a high coercive force in the range of the axial ratio in the present invention. The preferred range is 0.05 to
0.10 μm.

The average minor axis diameter is 0.01 to 0.02 μm. If it is less than 0.01 μm, it becomes close to the superparamagnetic region, so that it is difficult to obtain a large saturation magnetization value, and the coercive force also decreases. If it exceeds 0.02 μm, it becomes difficult to obtain a high coercive force in the range of the axial ratio in the present invention. A preferred range is 0.01 to 0.018 μm.

The axial ratio is between 4 and 7. If less than 4,
It becomes difficult to obtain a high coercive force. When it exceeds 7, a high coercive force is easily obtained, but a large saturation magnetization value is hardly obtained.

X of the spindle-shaped metal magnetic particles according to the present invention
Sentsubu径(D ₁₁₀₎ is 125～180A. 125Å
If it is less than 1, it is difficult to obtain a large saturation magnetization value. 18
If it exceeds 0 °, a large saturation magnetization value can be obtained, but the coercive force Hc decreases due to the shape. The preferred range is 130-160 °.

The relationship between the average average major axis diameter and the X-ray particle diameter of the spindle-shaped metal magnetic particles according to the present invention is expressed by the following equation (1).

[Equation 1] [(L × 500) +100] Å-[(L × 50
0) +120]} where L is the average major axis diameter (μm). This relationship is shown in FIG.
Shown in The region in FIG. 1 is the target range of the present invention. In the case of the region in FIG. 1, it is difficult to obtain a high saturation magnetization value. In the region in FIG. 1, it is difficult to obtain a high coercive force, and the coercive force distribution is deteriorated. In addition, it is difficult to obtain excellent dispersibility when used as a magnetic recording medium.

The spindle metal magnetic particles according to the present invention have a coercive force Hc of 1850 to 2500 Oe. 1850O
Although it may be less than e, improvement in frequency characteristics when a magnetic recording medium is used cannot be expected. Although it may exceed 2500 Oe, it is not increased more than necessary due to the relationship between the recording and reproducing heads. The preferred range is 1900-2400O
e, a more preferred range is 2000-2300 Oe
It is.

The saturation magnetization value of the spindle-shaped metal magnetic particles according to the present invention is 135 emu / g or more. 135 emu
If it is less than / g, it is difficult to obtain a magnetic recording medium having a large saturation magnetic flux density, which is not preferable as a high-density recording material powder.

The content of cobalt in the spindle-shaped metal magnetic particles according to the present invention depends on the total Fe content of the spindle-shaped metal magnetic particles.
Is in the range of 8 to 50 atomic% in terms of element. If it is less than 8 atomic%, it is difficult to obtain a large saturation magnetization value and excellent oxidation stability. If it exceeds 50 atomic%, the saturation magnetization value will decrease. The preferred range is 9-4
3 atomic%. More preferably, it is in the range of 9 to 36 atomic%.

Next, the production of the spindle-shaped goethite particles which are the starting material particles of the spindle-shaped metal magnetic particles according to the present invention will be described.

The aqueous ferrous salt solution used in the present invention includes an aqueous ferrous sulfate solution and an aqueous ferrous chloride solution.

Examples of the aqueous alkali carbonate solution used in the present invention include an aqueous sodium carbonate solution, an aqueous potassium carbonate solution, and an aqueous ammonium carbonate solution.

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

In the present invention, an aqueous alkali carbonate solution and an aqueous alkali hydroxide solution are used in combination. When the aqueous alkali carbonate solution is used alone, it is difficult to obtain metal magnetic particles having a large coercive force Hc. When an aqueous alkali hydroxide solution is used alone, it is difficult to obtain goethite particles having a uniform particle size and fine particles, and dendritic particles may be present in some cases. Powder is difficult to obtain.

For the aqueous alkali hydroxide solution, an aqueous alkali hydroxide solution having a molar ratio of 0.2 to 1.2 with respect to the aqueous alkali carbonate solution is added. If it is less than 0.2 , it is difficult to obtain metal magnetic particles having a large coercive force Hc, as in the case where the aqueous alkali carbonate solution is used alone. When it exceeds 1.2, it is difficult to obtain goethite particles having a uniform particle size as in the case of using the aqueous alkali hydroxide solution alone, and dendritic particles may be mixed, In some cases, granular particles may be present. Therefore, it is difficult to obtain fine metal magnetic particles having a uniform particle size. The preferred range is 0.3 to 1.0 .

The total amount of the aqueous alkali carbonate solution and the aqueous alkali hydroxide solution is 1 to the total amount of Fe in the aqueous ferrous salt solution.
When the amount is 3 to 2.5 equivalents and the amount is less than 1.3 equivalents, granular particles may be mixed. If it exceeds 2.5 equivalents, it is difficult to obtain fine particles of goethite particles having a uniform particle size. A preferred range is from 1.4 to 2.4 equivalents.

Therefore, the pH value of the reaction solution is 7.0 to 1 in the same manner as in the usual reaction for producing iron carbonate-based goethite particles.
1.0, and a more preferred pH value is 8.0-1.
0.0.

In the present invention, the aqueous alkali hydroxide solution is added in any of a suspension containing an aqueous alkali carbonate solution and an iron-containing precipitate before aging. Particularly, it is preferable to add the compound to an aqueous alkali carbonate solution.

In the aging in the present invention, the stirring is maintained under a non-oxidizing atmosphere for 2.0 to 7.0 hours.
When the aging time is less than 2.0 hours, it is difficult to obtain fine goethite particles. Even when the aging time exceeds 7.0 hours,
The goethite particles intended for the present invention are obtained, but there is no point in making them longer than necessary. The preferred range is 3-5 hours.

In this case, the aging temperature is in the range of 40 to 60 ° C. If the temperature is lower than 40 ° C., the size of the goethite particles will be small, but it is difficult to obtain those having an appropriate axial ratio. When the temperature is higher than 60 ° C., it is difficult to obtain goethite particles having a small particle size. The preferred range is 45-55 ° C.

The non-oxidizing atmosphere can be formed by passing an inert gas (such as N ₂ gas) through the reaction vessel of the suspension.

In the present invention, Si, Nd, and the like are contained in any one of an aqueous ferrous salt solution, an aqueous alkali carbonate solution, an aqueous alkali hydroxide solution, and a suspension containing the iron-containing precipitate before the aging. One or more compounds selected from the elements of Y, La, Ce, Pr, and Tb are added. The reason why the timing of addition is as described above is because the grain shape and the growth property of the crystal plane of the present invention are taken into consideration. Specifically, the axial ratio is 4 to 8, and the X-ray particle size ratio (D ₀₂₀ / D ₁₁₀₎
Is to obtain goethite particles of 2.0 to 3.5.

In this case, examples of the Si compound include sodium silicate, potassium silicate, water glass and the like.

As the elements of Nd, Y, La, Ce, Pr and Tb, water-soluble salts such as sulfates, chlorides and nitrates of the respective elements can be used.

Si, Nd, Y, La, Ce, Pr, Tb
The addition amount of one or more compounds selected from the elements is in the range of 0.1 to 1.0 atomic% based on the total Fe in the aqueous ferrous salt solution. When the content is less than 0.1 atomic%, it is difficult to obtain a high coercive force and a large saturation magnetization value which are the objects of the present invention. If the content exceeds 1.0 atomic%, the axial ratio becomes too small, and it is difficult to obtain metal magnetic particles having a high coercive force. The preferred range of the Si compound is 0.1 to 0.5 at%, more preferably 0.1 to 0.3 at%. Also, N
A preferred range of the compound selected from the elements d, Y, La, Ce, Pr, and Tb is 0.1 to 0.5 atomic%.

In addition, when adding each of the above-mentioned compounds, if they are added with an aqueous solution dissolved in water, they are rapidly stirred and added to the solution.
It is preferable because it can be dispersed.

Examples of the Co compound used in the present invention include cobalt sulfate, cobalt acetate, cobalt chloride, and cobalt nitrate.

The amount of the Co compound is in the range of 8 to 50 atomic% in terms of Co with respect to the total Fe in the aqueous ferrous salt solution. If the content is less than 8 atomic%, it is difficult to form fine particles, and it is difficult to obtain metal magnetic particle powder having high coercive force, high saturation magnetization, and excellent oxidation stability. If it exceeds 50 atomic%, the saturation magnetization value will decrease. A preferred range is from 9 to 43 atomic%. More preferably 9 to 3
The range is 6 atomic%.

The Co compound is added in any of the aqueous ferrous salt solution, the suspension containing the iron-containing precipitate before ripening, and the suspension during ripening. If it is added after the oxidation reaction is started, fine goethite particles cannot be obtained. A preferred range is from immediately after the start of ripening to 120 minutes after the start of ripening.

When the Co compound is added, it is preferable to add the Co compound in an aqueous solution dissolved in water, because the Co compound can be rapidly stirred and dispersed in the solution.

In the present invention, the temperature range of the oxidation reaction is 40.
６０60 ° C. When the temperature is lower than 40 ° C., fine goethite particles can be obtained, but the axial ratio is smaller than the object of the present invention. When the temperature is higher than 60 ° C., goethite fine particles as the object of the present invention can be obtained, but granular particles may be present in some cases. A preferred range is 45-55 ° C.

In the present invention, one or more compounds selected from the elements of Al, Si, Nd, Y, La, Ce, Pr, and Tb are added to the liquid in the course of the oxidation reaction. In this case, the time of addition is such that the oxidation rate of Fe ²⁺ in the oxidation reaction solution is 20% of the total Fe in the aqueous ferrous salt solution.
It is in the liquid during the oxidation reaction in the range of ５０50%. If the oxidation rate is less than 20%, the axial ratio is lower than the target axial ratio of the present invention, and it is difficult to obtain high coercive force metal magnetic particles. If it exceeds 50%, it becomes impossible to obtain metal magnetic particle powder satisfying the high coercive force and large saturation magnetization value aimed at by the present invention. A preferred range is 30 to 5
The range is 0%.

As the Al compound, aluminum sulfate,
Examples thereof include aluminum chloride, aluminum nitrate, sodium aluminate, potassium aluminate, and ammonium aluminate.

Further, Si, Nd, Y, La, Ce, P
One or more compounds selected from the elements of r and Tb are the same as those described above.

Al, Si, Nd, Y, La, Ce, P
The addition amount of one or more compounds selected from the elements r and Tb is 0.1 to 10.0 atomic% based on the total Fe in the aqueous ferrous salt solution. When the content is less than 0.1 atomic%, it is difficult to obtain the effect of preventing sintering in the heat treatment step. If it exceeds 10.0 atomic%, the axial ratio becomes smaller than the object of the present invention, and it becomes impossible to obtain metal magnetic particles having a high coercive force. In addition, when the number of compounds not involved in magnetization is increased, the saturation magnetization value also decreases. A preferred range is 0.5 to 6.0 atomic%.

The preferable addition amount of the Al compound is 0.1
To 3.0 atomic%, and a preferable addition amount of the Si compound is 0.5 to 2.0 atomic%. Also, N
1 selected from the elements d, Y, La, Ce, Pr, and Tb
The preferred addition amount of the seed or two or more compounds is 1.0 to
The range is 2.0 atomic%.

When these compounds are added in combination, the total amount of the compounds to be added is 0.1 to 10.0 atomic% in terms of each element with respect to all Fe in the aqueous ferrous salt solution.
Can be added in such an amount. 0.1
If it is less than atomic%, the sintering prevention effect is not sufficient,
The oxidation stability and coercive force of metal magnetic particles containing iron as a main component are insufficiently improved. If it exceeds 10.0 atomic%, the axial ratio becomes smaller than the object of the present invention, and it becomes impossible to obtain metal magnetic particles having a high coercive force. In addition, when the number of compounds not involved in magnetization is increased, the saturation magnetization value also decreases. In addition, the reduction time may be long. A preferred range is 0.5 to 6.0 atomic%.

It is preferable that the Al compound is solid-solved on the surface of the goethite particles, which is excellent in shape retention and oxidation stability when metal magnetic particles containing iron as a main component are used. Not only that, when a magnetic recording medium is used, the compatibility with the binder resin is improved, and the dispersibility and durability are also excellent. Therefore, A
It is preferable to use a combination of the l compound and the above compound other than the Al compound.

When the Si element is used, the effect of preventing sintering is particularly excellent, and when a compound of a rare earth element such as Nd is used, the effect of preventing sintering can be exhibited, Used for magnetic recording media because it is a volatile substance
COOM, -SO ₃ M (M is a metal) can be improved conformability also good dispersibility with the binder resin having an acidic functional group, such as.

Accordingly, it is preferable to add the above-mentioned compounds by appropriately combining the combination of the above-mentioned compounds and the amount of addition depending on the purpose, provided that the oxidation rate of the oxidation reaction is in the range of 20 to 50%.

In addition, it is preferable to add each of the above compounds with an aqueous solution dissolved in water, since the compounds can be rapidly stirred and dispersed in the solution.

The oxidizing means in the present invention is carried out by passing an oxygen-containing gas (for example, air) through the liquid, and may also be used in combination with mechanical stirring.

The spindle-shaped goethite particles produced in the present invention are filtered, washed with water and dried by a conventional method to obtain a particle powder.

Next, the spindle-shaped goethite particles according to the present invention, which are the starting material particles, will be described.

The spindle-shaped goethite particles according to the present invention have an average major axis diameter of 0.05 to 0.15 μm, an average minor axis diameter of 0.010 to 0.025 μm, and an axial ratio (major axis diameter / minor axis diameter). ) Is 4 to 8, and the X-ray particle size ratio (D ₀₂₀ / D
₁₁₀ ) is in the range of 2.0 to 3.5.
Is a spindle-shaped goethite particle powder.

The average major axis diameter is 0.05 to 0.15 μm. If it is less than 0.05 μm, the particle diameter of the metal magnetic particle powder becomes small, and becomes close to the superparamagnetic region, so that the saturation magnetization value and the coercive force decrease. 0.
If it exceeds 15 μm, a large saturation magnetization value is easily obtained, but it is difficult to obtain a high coercive force in the range of the axial ratio in the present invention. The preferred range is 0.05-0.1
The range is 2 μm.

The minor axis diameter is 0.010 to 0.025 μm. If it is less than 0.010 μm, the particle diameter of the metal magnetic particle powder becomes small and close to the superparamagnetic region, so that the saturation magnetization value decreases and the coercive force also decreases.
If it exceeds 0.025 μm, it becomes difficult to obtain a high coercive force in the range of the axial ratio in the present invention. A preferred range is from 0.010 to 0.020 μm.

The axial ratio ranges from 4 to 8. If it is less than 4, it becomes difficult to obtain metal magnetic particles having a high coercive force. When it exceeds 8, a high coercive force is easily obtained, but a large saturation magnetization value is hardly obtained.

The X-ray particle size (D ₀₂₀ ) is from 160 to 300 °. If the angle is less than 160 °, it is difficult to obtain metal magnetic particles having a high coercive force. If it exceeds 300 °, the short axis diameter becomes too large, the axial ratio decreases, and it becomes difficult to obtain metal magnetic particles having a high coercive force. The preferred range is 18
0-280 °.

The X-ray particle size (D ₁₁₀ ) is 70 to 200 °. If it is less than 70 °, it is difficult to obtain metal magnetic particles having a high coercive force. If it exceeds 200 °, the short axis diameter becomes too large, the axial ratio decreases, and it becomes difficult to obtain metal magnetic particles having a high coercive force. The preferred range is 80-1.
50 °.

X-ray particle size ratio (D ₀₂₀ / D ₁₁₀ )
It is simply referred to as “(D ₀₂₀ / D ₁₁₀ )”. -) Is 2.0 ~
3.5. If it is less than 2.0, the effect for obtaining metal magnetic particles having a high coercive force is not sufficient. 3.
If it exceeds 5, the short axis diameter becomes too large and the axial ratio decreases, and it becomes difficult to obtain metal magnetic particle powder having a high coercive force. A preferred range is 2.1 to 3.1.

The content of cobalt in the spindle-shaped goethite particles according to the present invention is in the range of 8 to 50 atomic% in terms of element with respect to the total Fe in the spindle-shaped goethite particles. The preferred range is 9 to 43 atomic%. More preferably, it is in the range of 9 to 36 atomic%.

Further, Al, Si, Nd, Y, La, Ce, P contained in the spindle-shaped goethite particles according to the present invention.
The content of one or more compounds selected from the elements r and Tb is 10.0 atomic% or less in terms of the element with respect to the spindle-shaped goethite particles.

Next, the production of the spindle-shaped metal magnetic particles according to the present invention using the spindle-shaped goethite particles according to the present invention as starting material particles will be described.

As starting material particles, if necessary, spindle-shaped hematite particles obtained by heating and dehydrating spindle-shaped goethite particles can also be used. This heat dehydration may be performed by a commonly used method.
50-500 ° C.

In a suspension prepared by suspending the spindle-shaped goethite particles or the spindle-shaped hematite particles in water, the semi-synthetic starch or the semi-synthetic cellulose soluble in water or hot water is mixed with the spindle-shaped goethite particles or cellulose. After adding and stirring 0.1 to 5.0% by weight with respect to the spindle-shaped hematite particles, a cake obtained by compression dehydration can be granulated and formed, and used in a non-reducing gas atmosphere. Heat treatment such as heat treatment or reduction treatment is preferable because handling becomes easy.

Further, in order to improve the magnetic properties of the obtained spindle-shaped metal magnetic particles, prevent deformation of the particles during heat reduction and prevent sintering between the particles, the spindle-shaped goethite particles or the spindle-shaped hematite particles are used in advance. Powder of Ni, A
1, Si, P, Co, Ca, Mg, Ba, Sr, Bi,
One or more metal compounds selected from the elements of B, Zn, Nd, Y, La, Ce, Pr, and Tb can be coated by a conventional method. Since these metal compounds not only have the effect of preventing sintering but also have the function of controlling the reduction rate, it is preferable to use them in combination as needed. The powder or spindle-shaped hematite particles can be coated in combination in an element conversion range of 1 to 50% by weight.

The content of each compound added at the time of producing the spindle-shaped goethite particle powder and each compound coated by the coating treatment in the obtained spindle-shaped metal magnetic particle powder was Co.
Except for the compound, the total amount of each compound in terms of element is 20 atomic% or less, preferably 15 atomic% or less, more preferably 10 atomic% or less, based on all Fe.

In the case where a Co compound is further coated to improve the magnetic properties, the total amount of the spindle-shaped goethite particles and the amount added in the formation reaction is the total Fe of the obtained spindle-shaped metal magnetic particles. 50 atomic% or less,
The coverage is preferably 50% or less of the total amount of Co contained in the spindle-shaped metal magnetic particle powder. If it exceeds 50%, a large amount of Co will be present on the surface of the metal magnetic particles, so that it will be difficult to form a solid solution inside the particles during heat reduction, and it will be difficult to obtain a large saturation magnetization value. Preferably it is 30% or less.

The target metal magnetic particle powder can be obtained by directly reducing the particle powder coated with the above-mentioned metal compound. However, in order to control the magnetic properties and the shape, it is necessary to reduce the particle powder. Prior to this, it is preferable to perform a heat treatment in a non-reducing gas atmosphere in advance.

The heat treatment in the non-reducing gas atmosphere is carried out under a flow of air, oxygen gas and nitrogen gas at 300 to 800
Annealing can be performed in a temperature range of ° C., and it is more preferable that the heat treatment temperature is appropriately selected according to the type of the metal compound used for the coating treatment of the particle powder. 800 ° C
In the case where it exceeds 3, 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 30.
0-550 ° C. When the temperature is lower than 300 ° C., the progress of the reduction reaction is slow, and a long time is required. If the temperature exceeds 550 ° C., the reduction reaction proceeds rapidly, causing deformation of the particles and sintering between the particles.

The spindle-shaped metal magnetic particles after heat reduction in the present invention may be prepared by a known method, for example, immersion in an organic solvent such as toluene, or by replacing the atmosphere of the reduced metal magnetic particles with an inert gas. After that, the oxygen content in the inert gas is gradually increased while the oxygen content is gradually increased, whereby the inert gas can be taken out into the air by a method of gradually oxidizing.

[0098]

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

Conventionally, to obtain metal magnetic particle powder having a high coercive force, as described above, the coercive force of the magnetic particle powder is generated due to its shape anisotropy. Or increasing the axial ratio of the particles.

In other words, when iron hydroxide-based goethite particles are used as a starting material, a metal particle having a high coercive force exceeding 1850 Oe and containing iron as a main component can be obtained by utilizing a large axial ratio which is a characteristic of the particles. Is obtained,
When iron carbonate-based goethite particles are used as a starting material, it is difficult to obtain metal magnetic particles having high coercive force exceeding 1850 Oe as fine particles.

Therefore, the present inventor used the alkali-based goethite particles as a starting material and prepared the above-mentioned balanced properties, particularly, an average major axis diameter of 0.05 to 0.12 μm and a coercive force. We worked on obtaining spindle-shaped metal magnetic particles having an Hc of 1850 to 2500 Oe and a saturation magnetization of 135 emu / g or more.

The above-mentioned Japanese Patent Publication No. 1-18961, “１−
The coercive force increases as the axial ratio increases. On the other hand, the coercive force is affected by the particle size. When the coercive force is larger than the particle size at which superparamagnetism appears, the coercive force increases as the particle size decreases. Therefore, the desired coercive force can be obtained by appropriately selecting the particle size and its axial ratio. ‥‥ ”was considered.

First, efforts were made to improve spindle-shaped goethite particles, which are the starting material particles of the spindle-shaped metal magnetic particles, and as a result, spindle-shaped goethite particles, which were the starting material particles according to the present invention, were obtained.

As described above, the average major axis diameter is 0.1 mm.
05-0.15 μm, average short axis diameter is 0.010-0.0
25 μm, the axial ratio is 4 to 8, and the X-ray particle size ratio (D
₀₂₀ / D ₁₁₀₎ is a spindle-shaped goethite particles consisting of in the range of 2.0 to 3.5.

The spindle-shaped goethite particles having an axial ratio of 4 to 8 are not much different from the conventional spindle-shaped goethite particles, but have the same (D ₀₂₀ / D) when the conventional axial ratio is _{almost the} same.
₁₁₀ ) is 1.5 to 1.9, which makes it difficult to obtain metal magnetic particles having a high coercive force. However, the spindle-shaped goethite particles according to the present invention have an average major axis diameter of 0.05 to 0.1.
Even when the axial ratio is 4 to 8 at 5 μm, (D ₀₂₀ / D ₁₁₀ ) is 2.0 to 3.5, which is a great difference.

This difference of (D ₀₂₀ / D ₁₁₀ ) is due to the fact that the crystal planes were generated with different degrees of growth. The degree of growth of the crystal plane could be related to any one of a ferrous salt aqueous solution, an alkali carbonate aqueous solution, an alkali hydroxide aqueous solution and a suspension containing an iron-containing precipitate before aging. Si, Nd, Y, La, Ce, P
It has been found that it is the effect of one or more compounds selected from the elements r and Tb.

The contribution to the degree of growth of the crystal plane depends on the effect of increasing the axial ratio by using an alkali carbonate and an alkali hydroxide in combination, and the effects of Si, Nd,
The addition of one or more compounds selected from the elements of Y, La, Ce, Pr, and Tb suppresses an increase in the axial ratio due to the addition of the compound, and a Co compound is added. It is considered that this acts in the direction of micronization, and that seed crystals of the spindle-shaped goethite particles are generated by a long-term aging reaction.

Then, the seed crystal particles are placed in an oxidizing reaction solution having an oxidation degree in the oxidation reaction in the range of 20 to 50% by Al, Si, Nd, Y, La, Ce, Pr, T, and T.
By adding one or more compounds selected from the elements b, the effect of promoting the growth in the short axis direction rather than the long axis direction is superimposed, and the axial ratio according to the present invention is 4 to 4. 8, and (D ₀₂₀ / D ₁₁₀ ) is 2.0 to 3.5.
It is thought that spindle-shaped goethite particles were generated.

In the case of alkali hydroxide-based goethite particles and alkali carbonate-based goethite particles, the axial ratio of the present invention and (D
₀₂₀ / D ₁₁₀₎ relationship and the average major axis diameter and (D ₀₂₀ / D
₁₁₀ ), the spindle-shaped goethite particles according to the present invention cannot be obtained when the type of the compound to be added is changed or when the timing of addition is changed. is there.

When the spindle-shaped goethite particles according to the present invention thus obtained are used as starting material particles and spindle-shaped metal magnetic particles are obtained by a conventional method, the degree of growth of the crystal faces of the spindle-shaped goethite particles is lower than that of the conventional reaction. And one or more compounds selected from the added elements of Al, Si, Nd, Y, La, Ce, Pr, and Tb were dissolved in goethite particles to be formed. It is considered that a high coercive force was obtained despite the small axial ratio of the obtained metal magnetic particles of 4 to 7.

In addition, the degree of growth of the crystal face of the spindle-shaped goethite particles is different from that of the conventional reaction, and the fact that Co is contained makes it possible to reduce the primary particles in the particles in the heat reduction treatment in the case of forming metal magnetic particles. It is considered that a large saturation magnetization was obtained because the growth could be performed easily and uniformly.

The method of introducing Co includes a method of adding and adding the spindle-shaped goethite particles during the production reaction, and a method of coating the obtained spindle-shaped goethite particles. The former method is larger. Saturation magnetization value is easily obtained, and in the latter case, the solid solution and diffusion into the inside of the particles are insufficient due to the heat treatment by heat dehydration or heat reduction of Co coated and adsorbed on the surface compared to the former. In addition, it is considered that it is difficult to obtain a large saturation magnetization value.

Further, although the reason is not clear, it is considered that the growth degree of the crystal face of the spindle-shaped goethite particles is a metal magnetic particle powder having an excellent coercive force distribution as shown in Examples described later. I have.

This is in agreement with the results of the present inventor's numerous experiments. The spindle-shaped metal magnetic particles according to the present invention have an average major axis diameter of 0.05 to 0.12 μm and are composed of fine particles. Even when the ratio is 4 to 7, it has a high coercive force, an excellent coercive force distribution, a large saturation magnetization value, and excellent oxidation stability. This is demonstrated by examples.

That is, in the spindle-shaped metal magnetic particles according to the present invention, the axial ratio when the coercive force Hc is maximized is:
They found that it was not necessary to have a large axial ratio.

When the relationship between the average major axis diameter of the spindle-shaped metal magnetic particles and the X-ray particle diameter is in the range shown in FIG. 1, a high coercive force of 1850 to 2500 Oe and an excellent coercive force distribution are obtained. And 135 emu / g
It has been found that the above-mentioned large saturation magnetization can be obtained.

In terms of the relationship between the average major axis diameter and (D ₁₁₀ ), the technical means described in each of the above publications, in particular, those described in Example 9 of the above-mentioned Japanese Patent Application Laid-Open No. 6-25702. Figure 1
And the above-mentioned JP-A-6-140222.
Each of Examples 6 and 7 of the publication is in the region of FIG. 1 and is different from the spindle-shaped metal magnetic particles according to the present invention in the region of FIG. In the area of
In a region where a higher saturation magnetization value cannot be obtained, it is difficult to obtain a high coercive force, and the coercive force distribution is deteriorated. In the region of the present invention, the fine particles of the present invention have a high coercive force and an excellent coercive force distribution, and a large saturation magnetization value and oxidation stability can be obtained in a well-balanced manner. They have found that the dispersibility and the filling properties are also excellent.

[0118]

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

In the following Examples and Comparative Examples, the major axis diameter, the minor axis diameter and the axial ratio of the particles are all shown by the average of numerical values measured from electron micrographs, and the specific surface area of the particles is BE.
It is shown by the value measured by the T method.

The X-ray particle size is determined by measuring the size of the crystal particles measured by the X-ray diffraction method in the goethite particle powder as (02
The crystal planes of (0) and (110) represent the diameters of crystal grains in a direction perpendicular to the crystal plane of (110) in the case of the metal magnetic particle powder.
The values were calculated from the line profiles of the diffraction lines on the (020) and (110) planes of the crystal using the following Scherrer equation.

D (X-ray particle size) = Kλ / βcos θ where β = half-value width of a true diffraction peak obtained by subtracting the mechanical width of the apparatus K = Scherrer constant (0.9) λ = wavelength of characteristic X-ray θ = Diffraction angle

The content of each of the elements such as Co, Al, Si, Nd, Y, and Ce is determined by using a “high-frequency plasma emission spectrometer ICAP-575” (Nippon Jarrell Ash Co., Ltd.).
Manufactured by the Company).

The degree of oxidation was shown by a value determined by redox titration after replacing the reaction solution with an inert gas and heating and dissolving with a mixed acid of sulfuric acid and phosphoric acid while passing the gas through.

The magnetic properties and the coating properties of the metal magnetic particles were measured using a “vibrating sample magnetometer VSM-3S-15” (manufactured by Toei Kogyo Co., Ltd.) under an external magnetic field of 10 KOe.

Oxidation stability was determined by the decrease rate (Δσ) of the saturation magnetization after being left for one week in an atmosphere at 60 ° C. and a relative humidity of 90%.
s).

The square shape of the coating film and S.I. F. D. The measurement of
This was performed using a sheet sample obtained by the method of Reference Example 1 described later. In addition, S.I. F. D. Is to obtain a differential curve of a demagnetization curve of a magnetic hysteresis curve using a differentiation circuit of the magnetometer, measure a half width of the curve, and divide this value by a coercive force of a peak value of the curve. Determined by

<Production of Goethite Particle Powder>
15, Comparative Examples 1 to 6;

Example 1 Na ₂ CO ₃ was introduced into a reactor kept in a non-oxidizing atmosphere by flowing N ₂ gas at a rate of 50 l / min.
20 l of an aqueous solution containing 5 mol and 10 l of an aqueous solution containing 18 mol of NaOH (corresponding to a molar ratio of 0.72 with respect to Na ₂ CO ₃ : the total amount of Na ₂ CO ₃ and NaOH corresponds to 1.70 equivalents to the total Fe) ) And No. 3 water glass so as to contain 0.25 atomic% in terms of Si with respect to all Fe, and then 20 l of an aqueous ferrous sulfate solution containing 20 mol of all Fe was added and mixed (total Fe concentration was 20%). 0.4 mol /
This corresponds to 1. ) To form an iron-containing precipitate at a temperature of 47 ° C.

While the N ₂ gas was continuously blown into the suspension containing the iron-containing precipitate at a rate of 50 l / min, the temperature was maintained at 47 ° C. for 60 minutes.
After an aqueous solution of cobalt sulfate was added so as to contain 18 atomic% in terms of conversion, it was kept for another 4 hours and aged.

When the oxidizing rate of the oxidation reaction became 40% by passing 90 l of air per minute at a temperature of 47 ° C. into the liquid of the suspension containing the iron-containing precipitate after aging, the total Fe was removed. No. 3 water glass solution was added so as to contain 1.75 atomic% in terms of Si, and 100% under the same oxidation reaction conditions as above.
The oxidation reaction was continued for a further minute to produce tan precipitated particles.
In addition, pH during air ventilation is 8.0-9.5,
The oxidation reaction time was 220 minutes .

The yellow-brown precipitate particles were separated by filtration, washed with water, dried and pulverized in a conventional manner to obtain about 2 kg of yellow-brown particle powder.

The obtained tan precipitate particles were goethite, and as shown in the electron micrograph (× 30000) in FIG. 2, the major axis diameter was 0.108 μm and the minor axis diameter was 0.016 μm.
m, the axial ratio was 6.8, and (D ₀₂₀ / D ₁₁₀ ) was 2.26. Dendritic particles were not mixed at all, and the particle size was uniform. The spindle-shaped particles had a Co content of 17.94 at% and a Si content of 1.93 at%.

Examples 2 to 15 and Comparative Examples 1 to 6 The amount of the aqueous alkali carbonate solution, the amount of the aqueous alkali hydroxide solution used, the timing of addition and the alkali ratio (NaOH / Na ₂ ) in the formation reaction of the FeCO ₃ or iron-containing precipitate. C
O ₃ : molar ratio), the presence / absence of the compound to be added before aging, the type, amount and time of addition, the temperature and time in the aging step, the amount and time and time of addition of the Co compound, the temperature in the oxidation step, the oxidation Goethite particles were produced in the same manner as in Example 1 except that the type, amount and timing of addition (oxidation rate) of the compound added during the process were variously changed.

The main manufacturing conditions at this time are shown in Tables 1 to 4.
The properties of the resulting goethite particles are shown in Tables 3 and 4.

[0135]

[Table 1]

[0136]

[Table 2]

[0137]

[Table 3]

[0138]

[Table 4]

<Production of Hematite Particle Powder> Example 16
To 30, Comparative Examples 7 to 12;

Example 16 An amount of press cake corresponding to 800 g of the spindle-shaped goethite particles obtained in Example 1 was suspended in 15 l of water.
At this time, the pH of the suspension was 8.5.

Next, aluminum nitrate 9 hydrate was added to the above suspension so that the weight of the solution was 10% by weight based on the goethite particles.
Neodymium nitrate hexahydrate and 10 wt.
% By weight of cobalt acetate tetrahydrate,
Further, boric acid was added so as to be 15% by weight based on the goethite particles, and the mixture was stirred for 10 minutes. P of the suspension at this time
H was 4.5.

Further, the pH was adjusted to 9.5 by adding an aqueous ammonia solution, followed by filtration with a filter press, washing with water, and
After drying, goethite particles coated with Al, Nd, Co, and B compounds were obtained.

The goethite particles coated with the Al, Nd, Co, and B compounds were heat-treated at 400 ° C. in air to obtain spindle-shaped hematite particles.

Examples 17 to 30, Comparative Examples 7 to 12 Example 16 except that the type of particles to be treated, the type and amount of the compound containing the coating element, the heating dehydration temperature, the presence / absence of annealing, and the temperature were variously changed. A coated hematite particle powder was obtained in the same manner as described above.

In Example 22, aluminum nitrate 9-hydrate and 10% by weight of cobalt acetate tetrahydrate were added to the suspension in an amount of 4% by weight based on the goethite particles. Then, after adjusting the pH to 9.0 by adding an aqueous NaOH solution, No. 3 water glass was added so as to be 8% by weight, and the mixture was filtered off with a filter press, washed with water and dried.

The main processing conditions at this time are shown in Tables 5 and 6.

[0147]

[Table 5]

[0148]

[Table 6]

<Production of Metal Magnetic Particle Powder>
45, Comparative Examples 13 to 18;

Example 31 100 g of spindle-shaped hematite particle powder coated with the Al, Nd, Co, and B compounds obtained in Example 16 was charged into a fixed-bed reducing device having an inner diameter of 72 mm, and H ₂ gas was supplied. Ventilation was performed at a rate of 35 l / min, and the reduction was terminated when the exhaust gas dew point reached -30 ° C at a reduction temperature of 420 ° C. The reduction time at this time was 370 minutes.

[0151] After the reduction, once substituted with N ₂ gas, N ₂ gas 50 l / min while flowing 40 ° C. The H ₂ gas
Cooled down. Next, while maintaining the furnace temperature at 40 ° C.,
₂ gas 50l / min Air in gas 0.2l / mi
A mixed gas of air and N ₂ gas mixed at a ratio of n was ventilated. After an exothermic peak was observed by the oxidation reaction at the mixed gas ratio, the air amount was increased to 0.4 l / min, and the air ratio in the mixed gas was increased. In this way, after an exothermic peak due to the oxidation reaction at the mixed gas ratio is observed, the air mixing ratio is increased stepwise by a method of increasing the air ratio in the mixed gas, and finally, the air is mixed with 0.6 l of air. /
The oxidation treatment was continued with a mixed gas of 50 l / min of N ₂ gas and N ₂ gas, and the oxidation treatment was performed until the heat of the oxidation disappeared and the temperature of the product reached approximately 40 ° C. which was almost the same as the furnace temperature. During this time, the temperature of the article reached a maximum of 75 ° C.

Subsequently, the furnace temperature was set to 40 ° C. and the N ₂ gas flow rate was set to 50.
While maintaining 1 / min, the mixing ratio of air was gradually increased, and the air amount was finally set to 10 1 / min. During this time,
No fever was observed. Further, the mixture was cooled to room temperature while passing a mixed gas of N ₂ gas and air under the same conditions.

After the air flow was once stopped and the atmosphere was replaced with N ₂ gas, the spindle-shaped metal magnetic particles containing iron as a main component and having an oxide film formed on the surface thus obtained were recovered.

The spindle-shaped metal magnetic particles had an average major axis diameter of 0.085 μm, an average minor axis diameter of 0.013 μm, and an axial ratio of 6.5 as shown in the electron micrograph (× 30000) of FIG. , (D ₁₁₀ ) was 148 °, the particle size was uniform and the number of dendritic particles was small. The magnetic properties are
Coercive force Hc is 2032 Oe, saturation magnetization s is 138 em
u / g, squareness ratio r / s is 0.518, Δσs is -15%
And the Co content was 20.23 atomic% (the amount of coated Co based on the total Co was 11.0%), and Si was 1.93.
Atomic%, Al was 2.91 atomic%, Nd was 1.53 atomic%, and B was 1.28 atomic%.

Examples 32 to 45, Comparative Examples 13 to 18 Metals containing iron as a main component in the same manner as in Example 31 except that the type of the particles to be treated and the reduction temperature in the reduction heating step were variously changed. Magnetic particle powder was obtained.

Tables 7 and 8 show the main production conditions and various characteristics at this time.

[0157]

[Table 7]

[0158]

[Table 8]

<Production of Coated Film> Reference Examples 1 to 21;

Reference Example 1 100 parts by weight of spindle-shaped metal magnetic particles obtained in Example 31 and a vinyl chloride copolymer resin MR-110 having a strong polar functional group in a 30 atom% solution of cyclohexanone were used.
50 parts by weight (manufactured by Zeon Corporation) were kneaded for 50 minutes using an 88 cc plastmill to obtain a kneaded product.

The kneaded material was placed in a 140 cc glass bottle at the following ratio and mixed and dispersed for 6 hours, and a magnetic coating prepared by coating was applied on a 25 μm thick polyethylene terephthalate film to a thickness of 50 μm using an applicator. Next, the sample was dried in a magnetic field of 8 K Gauss to produce a coating film, thereby preparing a sheet sample.

Kneaded material 100 parts by weight 1 mmφ glass beads 530 parts by weight Cyclohexanone 50 parts by weight Methyl ethyl ketone 57 parts by weight Toluene 57 parts by weight

The coercive force Hc of the coating film obtained from this sheet sample piece was 2114 Oe, the degree of orientation SQ was 0.882, and
F. D. Was 0.391.

Reference Examples 2 to 21 Coating films were produced in the same manner as in Reference Example 1, except that the types of metal magnetic particles were changed in various ways. Tables 9 and 10 show various properties of the coating film.

[0165]

[Table 9]

[0166]

[Table 10]

[0167]

The spindle-shaped metal magnetic particles according to the present invention have an average major axis diameter of 0.05 to 0.05 as shown in the above-mentioned Examples.
0.12 μm, fine particles, uniform particle size, no dendritic particles mixed, axial ratio of 4 to 7, and high coercive force of 1850 to 2500 Oe, excellent coercive force distribution and 135 emu / G, which has a large saturation magnetization value of at least / g, and has excellent oxidative stability and good balance of properties. Therefore, it is suitable for high recording density, high sensitivity, and high output magnetic recording media. It is suitable as a magnetic material powder.

Further, the spindle-shaped metal magnetic particles according to the present invention have a good dispersibility in a vehicle in the production of a magnetic coating material, and a magnetic recording medium having extremely excellent filling properties can be obtained.

[Brief description of the drawings]

FIG. 1 is a view showing a relationship between an average major axis diameter (μm) and an X-ray particle diameter (D ₁₁₀ ) of a spindle-shaped metal magnetic particle powder according to the present invention.

FIG. 2 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped goethite particles obtained in Example 1.

FIG. 3 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped goethite particles obtained in Example 10.

FIG. 4 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped goethite particles obtained in Example 14.

FIG. 5 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped goethite particles obtained in Comparative Example 1.

FIG. 6 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped goethite particles obtained in Comparative Example 5.

FIG. 7 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped metal magnetic particles obtained in Example 31.

8 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped metal magnetic particles obtained in Example 40. FIG.

9 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped metal magnetic particles obtained in Example 44. FIG.

FIG. 10 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped metal magnetic particles obtained in Comparative Example 13.

FIG. 11 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped metal magnetic particles obtained in Comparative Example 17.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI H01F 1/06 H01F 1/06 A

Claims (2)

(57) [Claims] 1. Cobalt contains 8 to 50 atomic% of cobalt in terms of Co with respect to the total Fe in the spindle-shaped metal magnetic particles, has an average major axis diameter of 0.05 to 0.12 μm, and an average minor axis diameter of 0. .0
1 to 0.02 μm, the axial ratio (major axis diameter / minor axis diameter) is 4 to 7, the X-ray particle size (D ₁₁₀ ) is in the range of the following formula 1, and the coercive force Hc is 1850. Spindle-shaped metal magnetic particles containing cobalt and iron as main components, characterized by having a saturation magnetization of 135 emu / g or more. [Equation 1] [(L × 500) +100] Å-[(L × 50
0) +120]} where L is the average major axis diameter (μm). 2. A suspension containing an iron-containing precipitate obtained by reacting an aqueous solution of ferrous salt by using an aqueous solution of an alkali carbonate and an aqueous solution of an alkali hydroxide in combination is maintained and stirred under a non-oxidizing atmosphere. After aging, an oxygen-containing gas is passed through the suspension to perform an oxidation reaction to produce spindle-shaped goethite particles, which are obtained by heating and dehydrating the spindle-shaped goethite particles or the spindle-shaped goethite particles. Spindle-shaped hematite particles are coated with a sintering inhibitor and heated and reduced in a reducing gas to obtain spindle-shaped metal magnetic particles. A method for producing spindle-shaped metal magnetic particles containing cobalt and iron as main components. The addition time of the aqueous alkali hydroxide solution
Aqueous solution and suspension containing the iron-containing precipitate before aging
In any of the solutions, and add
The addition amount was 0.2 in molar ratio with respect to the aqueous alkali carbonate solution.
To 1.2 so that the total amount of the aqueous alkali carbonate solution and the aqueous alkali hydroxide solution is 1.3 to 2.5 equivalents to the total Fe in the aqueous ferrous salt solution. Si, in one of the suspension containing the aqueous alkali carbonate solution, the aqueous alkali hydroxide solution and the iron-containing precipitate before the aging,
One or two or more compounds selected from the elements of Nd, Y, La, Ce, Pr, and Tb are added in an amount of 0.1 to 1.0 atomic% in terms of element with respect to all Fe in the ferrous salt aqueous solution. The Co compound is added to any of the ferrous salt aqueous solution, the suspension containing the iron-containing precipitate before the ripening, and the suspension during the ripening. Total Fe in aqueous ferrous salt solution
In the range of 8 to 50 atomic% in terms of Co, and wherein the oxidation rate of Fe ²⁺ in the oxidation reaction solution is in the range of 20 to 50% with respect to all Fe in the aqueous ferrous salt solution. In the developing solution, under the same conditions as the oxidation reaction, A
One, two or more compounds selected from the elements of l, Si, Nd, Y, La, Ce, Pr, and Tb are added in an amount of 0.1 to 10 in terms of element with respect to all Fe in the ferrous salt aqueous solution. A method for producing spindle-shaped metal magnetic particles containing cobalt and iron as main components, which is added in a range of 0.0 at%.