JPH07331310A - Production of spindle shaped metallic magnetic particle powder consisting essencially of iron - Google Patents

Abstract

PURPOSE:To produce metallic magnetic particle powder having excellent property by passing oxygen-containing gas through a reaction solution of a mixed solution of alkali carbonate with alkali hydroxide with a ferrous salt aq. solution to form a spindle shaped goethite nucleus particle and growing the nucleus particle. CONSTITUTION:A suspension having pH8-10 and containing a FeCO3 precipitate is formed by mixing the aq. solution of ferrous salt such as ferrous sulfate with the mixed aq. solution of alkali carbonate such as Na2CO3 with alkali hydroxide such as NaOH. The fine particle having uniform particle size, absent in dendritic particle, having excellent coercive force and coercive distribution and consisting essentially of Fe is produced by passing the oxidizing gas such as air through the suspension to form the spindle shaped goethite nucleus particle, further adding the mixed solution of the alkali carbonate aq. solution with the alkali hydroxide aq. solution and the ferrous salt aq. solution again to allow it to react with each other, stirring and mixing with the addition of water glass, successively passing the oxidizing gas such as air again to glow the spindle shaped goethite nucleus particle and after that, filtering, separating, drying and pulverizing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a uniform particle size, does not contain dendritic particles, and has an appropriate particle shape and axial ratio (major axis diameter / minor axis diameter-below, the same). In addition, it is an object of the present invention to provide a spindle-shaped metallic magnetic particle powder containing iron as a main component, which has a high coercive force and an excellent coercive force distribution.

[0002]

2. Description of the Related Art In recent years, magnetic recording / reproducing devices for video and audio have become increasingly long-time recording, and have become smaller and lighter. In particular, the spread of VTRs (video tape recorders) has been remarkable recently. The development of VTRs aiming at long-time recording and reduction in size and weight is being actively conducted.
On the other hand, there is an increasing demand for higher performance and higher density recording of magnetic tapes, which are magnetic recording media.

That is, it is required to improve the high image quality, high output characteristics, especially 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, and the S / N ratio is required to be improved more and more.

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

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

In order to improve the video S / N ratio and the chroma S / N ratio, the dispersibility of the magnetic particle powder in the vehicle, the orientation and filling property in the coating film, and It is important to improve the surface smoothness of the magnetic recording medium.As such a magnetic particle powder, the particle size is uniform, dendritic particles are not mixed, and the particle shape and axis are suitable. It is required to be a ratio.

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

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

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

As described above, the particle size is uniform, the dendritic particles are not mixed, the particles have an appropriate particle shape and axial ratio, and also have a high coercive force and an excellent coercive force distribution. The metal magnetic particle powder containing iron as the main component is currently most demanded, and in order to obtain the metal magnetic particle powder containing iron as the main component with such characteristics,
The starting material, goethite particles, has a uniform particle size and does not contain dendritic particles, and has an appropriate particle shape and axial ratio. It is necessary to make it easy to retain and inherit in the processing process.

Conventionally, as a method for producing goethite particle powder as a starting material, a suspension containing ferrous hydroxide colloid obtained by adding an equivalent amount or more of an alkali hydroxide aqueous solution to a ferrous salt aqueous solution has a pH of 11. As described above, a method of forming needle-shaped goethite particles by carrying out an oxidation reaction by passing an oxygen-containing gas at a temperature of 80 ° C. or lower (Japanese Patent Publication No. 39-39
No. 5610) or a suspension containing FeCO ₃ obtained by reacting an aqueous solution of a ferrous salt with an aqueous solution of alkali carbonate, and an oxygen-containing gas is passed through the suspension to carry out an oxidation reaction to obtain spindle-shaped goethite particles. Method for generating the
0-80999) are known.

Further, an oxygen-containing gas is passed through a ferrous hydroxide colloid obtained by adding an equivalent amount or less of an aqueous alkali hydroxide solution or an aqueous alkali carbonate solution to the aqueous ferrous salt solution or an aqueous ferrous salt solution containing iron carbonate. To produce acicular goethite core particles by performing an oxidation reaction, and then, in an aqueous ferrous salt solution containing the acicular goethite core particles, an equivalent amount or more based on the amount of Fe ^{2+ in} the ferrous salt aqueous solution. A method of growing the acicular goethite nucleus particles by adding an aqueous solution of alkali hydroxide and then aerating an oxygen-containing gas (JP-A-59-48766, JP-A-59-128293, and JP-A-59-128).
128294, JP-A-59-128295, JP-A-60-21818, and JP-A-1-115.
No. 827) or a ferrous salt aqueous solution containing needle-shaped nucleus particles obtained in the same manner as described above, Fe in the ferrous salt aqueous solution is added.
There is known a method (Japanese Patent Laid-Open No. 5-33018) in which an acetic acid aqueous solution of an amount equal to or more than the amount of ²⁺ is added and then an oxygen-containing gas is aerated to grow the acicular goethite nucleus particles.

Further, in a suspension containing ferrous hydroxide having a pH value of 11 or more obtained by reacting an aqueous solution of ferrous salt and an aqueous solution of alkali hydroxide, in the presence of a Si compound, the spindle -Like goethite particles are added as core particles, and acicular goethite particles are generated by growing and reacting the core particles (JP-A-5-345907), or an aqueous solution of ferrous salt is reacted with an aqueous solution of alkali carbonate. A first-stage reaction in which an oxygen-containing gas is passed through the suspension containing FeCO ₃ thus obtained to carry out an oxidation reaction, and then an oxygen-containing gas is passed through the reaction to continue the oxidation reaction and further ferrous salt aqueous solution. And alkali hydroxide or ammonia gas are added to produce spindle-shaped goethite particles comprising a second-step reaction in which the reaction is carried out in a pH range of 7 to 11 (JP-A-6-1).
No. 27945) is also known.

[0014]

[Problems to be Solved by the Invention] The particle size is uniform, the dendritic particles are not mixed, and the particles have an appropriate particle shape and axial ratio. Moreover, a high coercive force and an excellent coercive force distribution are obtained. The acicular metal magnetic particle powder containing iron as a main component has
Although the most demanded at present, the above-described method for producing the goethite particle powder as the starting material produces acicular goethite particles having a large axial ratio, particularly 10 or more, but dendritic particles. Particles are mixed, and also
In terms of particle size, it cannot be said that the particles have a uniform particle size.

In the case of the above-mentioned method, particles having a uniform particle size and spindle-shaped particles in which dendritic particles are not mixed are produced, while the axial ratio is at most about 7. There is a drawback that particles with a large axial ratio are difficult to generate,
In particular, this phenomenon tends to become more remarkable as the major axis diameter of the produced particles becomes smaller. Although various methods of increasing the axial ratio of the spindle-shaped goethite particles have been tried,
Generally, it is difficult to increase the axial ratio while maintaining and maintaining the uniformity of particle shape and particle size distribution, and goethite particles that satisfy both the uniformity of particle shape and particle size distribution and a large axial ratio have not yet been obtained. .

The above-mentioned method includes various characteristics of needle-shaped goethite particles obtained by the above-mentioned method and
That is, the purpose is to improve the particle size, the axial ratio, the presence or absence of dendritic particles, etc., but it is hard to say that both characteristics of particle shape and particle size distribution uniformity and axial ratio can be sufficiently satisfied. It was

Conventionally, the metal magnetic particle powder containing iron as a main component, which is obtained by using the goethite particle powder obtained by any of the above-mentioned methods as the starting material particles, also has a uniform particle size and dendritic particles are mixed. However, it is hard to say that it has a large axial ratio.

Further, the acicular goethite particle powder obtained by the above-mentioned method has a large axial ratio, but cannot be said to have a uniform particle size. Moreover, since the goethite nucleus particles are generated in the acidic region, the obtained goethite particle powder contains a large amount of acid radicals that are not removed even by washing, and when the metal magnetic particle powder is used, Since it causes excessive sintering, the intended metal magnetic particle powder cannot be obtained.

The needle-shaped goethite particle powder obtained by the above-mentioned method has a uniform particle size as the goethite particle powder and a large axial ratio. The coercive force cannot be obtained yet.

Further, the spindle-shaped goethite particle powder obtained by the above-mentioned method gives goethite particles having a uniform particle size, but when the powder is made of metal magnetic particles, the desired high coercive force is not yet obtained. Absent.

Therefore, according to the present invention, the particle size is uniform, the dendritic particles are not mixed, the particle shape and the axial ratio are appropriate, and the high coercive force and the excellent coercive force distribution are obtained. A technical problem is to obtain a spindle-shaped metal magnetic particle powder containing iron as a main component.

[0022]

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

That is, according to the present invention, the pH value obtained by reacting the mixed alkali aqueous solution of alkali carbonate and alkali hydroxide with the ferrous salt aqueous solution is in the range of 8.0 to 11.0. In the suspension containing the precipitate, after performing a spindle-shaped goethite nucleus particle generation reaction for generating spindle-shaped goethite nucleus particles by aerating an oxygen-containing gas, in a suspension containing the spindle-shaped goethite nucleus particles, The mixed alkaline aqueous solution and the ferrous salt aqueous solution are added and reacted to generate an iron-containing precipitate, or the iron-containing precipitate obtained by reacting the mixed alkaline aqueous solution and the ferrous salt aqueous solution is added. To prepare a suspension containing spindle-shaped goethite core particles having a pH value in the range of 8.0 to 11.0 and an iron-containing precipitate, and oxygen-containing gas was passed through the liquid to prepare the suspension. Grow goethite core particles In performing spindle-shaped goethite nucleus particle growth reaction, Si relative to the total Fe in the growth reaction
Spindle-shaped goethite particles are produced by the presence of 0.2 to 5.0 atom% of water-soluble silicate, and then the spindle-shaped goethite particles are coated with a sintering inhibitor. Goethite particles or the spindle-shaped hematite particles obtained by heat-treating the spindle-shaped goethite particles are heated to reduce in a reducing gas to obtain spindle-shaped metallic magnetic particles containing iron as a main component. This is a method for producing a spindle-shaped metallic magnetic particle powder as a main component.

Further, the present invention is characterized in that the proportion of the alkali hydroxide in the mixed alkaline aqueous solution is 5 to 35 mol%, and further the pH value of the reaction solution and the spindle during the spindle-shaped goethite nucleus particle formation reaction. The method for producing a spindle-shaped metallic magnetic particle powder containing iron as a main component, wherein the pH value of the reaction solution during the reaction of growing goethite nucleus particles is within ± 0.5.

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

Examples of the ferrous salt aqueous solution used in the present invention include ferrous sulfate aqueous solution and ferrous chloride aqueous solution.

Examples of the alkaline aqueous solution used in the present invention include sodium carbonate aqueous solution, potassium carbonate aqueous solution and ammonium carbonate aqueous solution as the alkaline carbonate aqueous solution, and sodium hydroxide, potassium hydroxide etc. as the alkaline hydroxide aqueous solution mixed with the alkaline carbonate. Can be mentioned.

The mixed alkali aqueous solution used in the goethite nucleus particle formation reaction and the goethite nucleus particle growth reaction of the present invention is a mixture of alkali carbonate and alkali hydroxide, and the proportion of alkali hydroxide in the mixed alkali aqueous solution is 5
Is about 35 mol%. If it is less than 5 mol%, a sufficient axial ratio cannot be obtained, and if it exceeds 35 mol%,
Granular magnetite may be mixed. It is preferably 10 to 25 mol%, more preferably 15 to 2
It is 0 mol%.

The amount of the mixed alkali aqueous solution used is such that the alkali equivalent ratio to the total Fe in the ferrous salt aqueous solution is 1.3 to.
It is 3.5. If it is less than 1.3, magnetite may coexist, and if it exceeds 3.5, it is industrially undesirable. The preferable range is 1.5 to 2.5.

In the present invention, the pH value during the goethite nucleus particle formation reaction and the pH value during the goethite nucleus particle growth reaction are
The range is 8.0 to 11.0. If the pH is less than 8.0, a large amount of acid radicals will be contained in the goethite particle powder and cannot be easily removed even by washing. Therefore, when the metal magnetic particle powder is used, the particles are burned together. It causes a conclusion. If it exceeds 11.0,
The intended high coercive force cannot be obtained when the metal magnetic particle powder is used. It is preferably in the range of 8.5 to 10.0.

The difference between the pH value of the reaction solution during the goethite nucleus particle formation reaction and the pH value of the reaction solution during the goethite nucleus particle growth reaction is within ± 0.5. When the pH value difference exceeds ± 0.5, the coercive force of the metal magnetic particle powder is still insufficient. It is preferably ± 0.3, more preferably ± 0.1. It is preferable to use the same conditions as much as possible, and in that case, it is preferable that the ratio of alkali hydroxide in the mixed alkaline aqueous solution and the alkali equivalent ratio to all Fe in the ferrous salt aqueous solution are the same.

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

In the present invention, the temperature during the goethite nucleus particle forming reaction and the goethite nucleus particle growing reaction may be usually 80 ° C. or lower at which goethite particles are formed.
If it exceeds 80 ° C., magnetite may be mixed in the spindle-shaped goethite particles. Preferably 45-5
It is in the range of 5 ° C.

The amount of goethite nucleus particles present during the goethite nucleus particle growth reaction in the present invention is 30 to 70% by weight based on the acicular goethite particle powder produced. When the amount is less than 30% by weight, new nuclei of goethite particles are generated to generate dendritic particles, and the particle size of the generated goethite particles becomes asymmetric. 7
If it exceeds 0% by weight, the growth reaction of the spindle-shaped particles as the core particles does not sufficiently occur, and the desired spindle-shaped goethite particle powder cannot be obtained. It is preferably 40 to 60% by weight.

In the present invention, the goethite nucleus particles may be present before the start of the goethite nucleus particle growth reaction, and before the ferrous salt aqueous solution, the alkaline aqueous solution, and the oxygen-containing gas are aerated in the growth reaction. It may be present in any of the suspensions containing the spindle-shaped goethite core particles and the iron-containing precipitate.

The spindle-shaped goethite core particles in that case are FeCO obtained by reacting a mixed alkali aqueous solution of alkali carbonate and alkali hydroxide with a ferrous salt aqueous solution.
_The spindle-shaped goethite particles obtained by aerating an aqueous solution containing ₃ with an oxygen-containing gas to oxidize it can also be used by adding it to the growth reaction solution as core particles in the growth reaction of the present invention.

Further, in both the case of the goethite nucleus particle formation reaction and the case of the goethite nucleus particle growth reaction, the suspension containing the iron-containing precipitate may be aged by maintaining and stirring under a non-oxidizing atmosphere. In that case, it is preferable that the aging is carried out in the temperature range of 40 to 80 ° C. for the suspension under a non-oxidizing atmosphere. When the temperature is lower than 40 ° C, it is difficult to obtain a sufficient aging effect due to the small axial ratio, and when the temperature exceeds 80 ° C,
Magnetite may be mixed.

The aging time is 30 to 300 minutes. If it is less than 30 minutes, the axial ratio cannot be sufficiently increased. It may exceed 300 minutes, but there is no point in making it longer than necessary.

To create a non-acidic atmosphere, an inert gas (such as nitrogen gas) or a reducing gas (such as hydrogen gas) may be passed through the reaction vessel of the suspension.

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

The water-soluble silicate is contained in the suspension containing the spindle-shaped goethite nucleus particles during the goethite nucleus particle growth reaction.
0.2 to 5.0 atomic% of water-soluble silicate in terms of Si is present with respect to all Fe. If it is less than 0.2 atomic%, the effect of adding the water-soluble silicate cannot be obtained, and high coercive force cannot be obtained when the metal magnetic particle powder is used.
When it exceeds 5.0 atomic%, the saturation magnetization value is lowered when the powder is made of metal magnetic particles. Preferably 0.5-
It is 2.0 atom%, and more preferably 0.8 to 1.5 atom%.

The water-soluble silicic acid solution may be added before the start of the goethite nucleus particle growth reaction, and the spindle-shaped goethite before the ferrous salt aqueous solution, the alkaline aqueous solution, and the oxygen-containing gas are aerated in the growth reaction. It may be present in any of the suspensions containing the core particles and the iron-containing precipitate. Further, even if the water-soluble silicate is added in a divided manner, or continuously and intermittently, the effect of the present invention is not changed but can be improved.

In the present invention, a Co compound, a Ni compound, an Al compound and a P compound, which are usually added during the formation reaction of goethite particles, are used in order to improve various characteristics of the spindle-shaped metal magnetic particle powder containing iron as a main component. , Si compounds, etc., or 2
One or more seeds may be added during the reaction for producing the nuclear particles or during the reaction for growing the nuclear particles, and in this case, the desired spindle-shaped goethite particle powder can be obtained.

In the present invention, the spindle-shaped goethite particles are coated with a substance having a sintering-preventing effect, that is, a sintering-preventing agent, by a known method prior to the heat reduction treatment. Sintering between the particles is prevented, the particle shape and axial ratio of the spindle-shaped goethite particles are more easily retained and inherited, and individually independent spindle-shaped metallic magnetic particles containing iron as a main component are easily obtained.

As the sintering inhibitor, as is well known, one or more compounds selected from Ni compounds, Al compounds, Si compounds, P compounds, Co compounds, Mg compounds, B compounds and Zn compounds are used. can do.
These compounds not only have the effect of preventing sintering, but also have the function of controlling the reduction rate, so they may be used in combination as necessary. If the amount used in this case is small, the effect of preventing sintering is not sufficient, and if it is too large, the saturation magnetization value decreases.
It is 3.0% by weight.

The spindle-shaped goethite particle powder coated with the above compound can be directly reduced to obtain the desired spindle-shaped metallic magnetic particle powder containing iron as a main component. In order to control the characteristics and the shape, it is preferable to perform a heat treatment in a non-reducing gas atmosphere in advance by a conventional method prior to the reduction.

The heat treatment in the non-reducing gas atmosphere is carried out under the flow of air, oxygen gas and nitrogen gas at 300 to 800.
It can be carried out in a temperature range of 0 ° C, and it is more preferable that the heat treatment temperature is appropriately selected according to the kind of the compound used for the coating treatment of the spindle-shaped goethite particles. If it exceeds 800 ° C., deformation of particles and sintering between particles and each other are caused.

The temperature range of heat reduction in the present invention is 3
The temperature is preferably 00 to 550 ° C. When the temperature is lower than 300 ° C, the reduction reaction proceeds slowly and requires a long time. Also, 5
If the temperature exceeds 50 ° C., the reduction reaction will rapidly proceed, causing deformation of the particles and sintering between the particles and each other.

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

[0060]

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

As described above, the spindle-shaped goethite particles usually have no dendritic particles and have a uniform particle size, but it is difficult to obtain a large axial ratio. Many attempts have been made so far to obtain spindle-shaped goethite particles having a large axial ratio, but it cannot be said that sufficient results have been obtained. Therefore, when the spindle-shaped goethite particles are used to form the metal magnetic particle powder, a satisfactory coercive force is not obtained.

The reaction of growing the spindle-shaped goethite core particles in the presence of a water-soluble silicate in a suspension containing ferrous hydroxide having a pH value of 11 or more in the above-mentioned method has a good axial ratio. Although goethite particles having dense crystallinity are obtained, in this case, growth in the minor axis direction is suppressed. That is, the axial ratio is improved by the effect of reducing the minor axis, and not the growth in the major axis direction.
Therefore, it cannot be said that a high coercive force is still obtained when the metal magnetic particle powder is used.

As a result of diligent research, the present inventor has found that spindle-shaped goethite core particles having a pH value of 8.0 to 11.0 obtained by reacting a mixed alkali aqueous solution with a ferrous iron salt aqueous solution and an iron-containing precipitate. The present invention has conceived a method of the present invention for growing spindle-shaped goethite core particles in a suspension containing a substance and in the presence of a water-soluble silicate.

According to the present invention, the pH value is 8.0 to 11.0.
In a suspension containing the spindle-shaped goethite core particles and the iron-containing precipitate, the spindle-shaped shape of the goethite particles is maintained in order to carry out the growth reaction of the spindle-shaped goethite core particles, which is higher than that of the above method. Although the density is not high, it is possible to obtain higher coercive force because the low bulk density makes it easier to release the water during reduction to the outside of the system and prevents sintering. I believe.

Further, the pH value of the reaction solution during the spindle-shaped goethite nucleus particle formation reaction and the pH value of the reaction solution during the spindle-shaped goethite nucleus particle growth reaction are within the range of ± 0.5. Has the advantage that spindle-shaped goethite particles having a uniform particle size and an appropriate particle shape and axial ratio can be produced, and that the water-soluble silicate to be present in the growth reaction solution is present. Thus, the effect of higher sintering prevention efficiency can be obtained as compared with the usual sintering prevention treatment.

The difference in the effect of preventing the sintering between the presence of the water-soluble silicate during the growth reaction and the known water-soluble silicate added after the completion of the reaction in the present invention is not yet clear, but The inventors have found that there is a difference in the relationship between the case where a Si compound is simply adsorbed on the particle surface by a well-known method and the Si compound which is adsorbed / reacted with a stronger binding force on the particle surface by the growth reaction in the present invention. Therefore, the water-soluble silicate that was present during the growth reaction in the present invention can more effectively exhibit the effect of preventing sintering during heating and reduction when the powder is made of metal magnetic particles containing iron as a main component. I think it was made.

On the other hand, in the above-mentioned method, it is difficult to make the alkali equivalent ratio to the total Fe in the aqueous solution of ferrous salt in the spindle-shaped goethite nucleus particle formation reaction and the spindle-shaped goethite nucleus particle growth reaction the same conditions. Moreover, it is considered that the metal magnetic particle powder having a high coercive force could not be obtained because the compositions of the alkalis used were different.

That is, in the spindle-shaped goethite nucleus particle forming reaction and the spindle-shaped goethite nucleus particle growth reaction in the present invention, the same alkali equivalent ratio to the total Fe in the ferrous salt aqueous solution is set to the same condition, and in the mixed alkaline aqueous solution. By making the proportions of the alkali hydroxides equal, it is possible to obtain those with a particularly high coercive force in the case of powdered metal magnetic particles, and further to add water-soluble silicate in the spindle-shaped goethite nucleus particle growth reaction. It is considered that the presence of these elements makes it possible to further improve the effect of preventing sintering and obtain a higher coercive force.

[0069]

The present invention will be described below with reference to Examples and Comparative Examples. Major axis diameter of particles in Examples and Comparative Examples,
The axial ratios are shown as the average of the numerical values measured from electron micrographs, and the specific surface area of the particles is shown as the value measured by the BET method.

The magnetic properties of the metallic magnetic particle powder containing iron as a main component were measured with an external magnetic field of 10 kOe using a "vibrating sample magnetometer VSM-3S-15" (manufactured by Toei Industry Co., Ltd.).

<Production of spindle-shaped goethite particle powder> Examples 1 to 4, Comparative Examples 1 to 4;

Example 1 0.3 N was added to 3.9 l of a 6.5 N Na ₂ CO ₃ aqueous solution in a reactor under a non-oxidizing atmosphere by passing N ₂ gas.
NaOH aqueous solution of 32.8 l (Na against mixed alkali
OH corresponds to 15 mol%. ) Is added to form a mixed solution, and then 13.3 l of a ferrous sulfate aqueous solution containing Fe ²⁺ 1.5 mol / l (the alkaline aqueous solution corresponds to 1.5 equivalents to ferrous sulfate) is added. 9 up to 50 ℃
After maintaining and maintaining for 0 minutes, 150 l of air per minute was aerated for 2.0 hours at pH 9.5 and a temperature of 50 ° C. to generate spindle-shaped goethite core particles.

A part of the spindle-shaped goethite core particles was extracted,
The needle-shaped goethite core particles obtained by filtration, washing with water, and drying had a major axis of 0.19 μm and an axial ratio of 10 as shown in the electron micrograph (× 30000) of FIG. 1, and had dendritic particles at all. No, the particle size was uniform.

Then, in a suspension containing spindle-shaped goethite core particles in which N ₂ gas was ventilated to make the reactor a non-oxidizing atmosphere, 1.95 l of a 6.5 N Na ₂ CO ₃ aqueous solution was added to 3.
1.6 liter of 0N NaOH aqueous solution (N for mixed alkali
aOH corresponds to 15 mol%. 5.) and a mixed solution containing Fe ^{2+ and} 1.5 mol / l Fe ²⁺ ferrous sulfate aqueous solution
7 liters (alkali aqueous solution corresponds to 1.5 equivalents to ferrous sulfate) was added and the temperature was raised to 50 ° C. and maintained for 20 minutes. _Two two
8.55 wt%) 21.05 g (corresponding to 0.5 atom% in terms of Si based on total Fe) was added and mixed with stirring, and then a pH value of 9.6 (pH at the time of goethite nucleus particle formation reaction)
The difference from the value is 0.1. ), 150 l of air per minute was aerated for 2.0 hours at a temperature of 50 ° C. to carry out the growth reaction of the spindle-shaped goethite nucleus particles.

The produced particles are separated by filtration, washed with water, dried and pulverized by a conventional method, and the acicular goethite particle powder obtained is shown in FIG.
As shown in the electron micrograph (× 30000), the particles were spindle-shaped and had a major axis of 0.22 μm and an axial ratio of 13,
The BET specific surface area was 97 m ² / g, the dendritic particles were not mixed at all, and the particle size was uniform.

Examples 2 to 4, Comparative Examples 1 to 4 Atmosphere before the start of the oxidation reaction of the reactor in the spindle-shaped goethite nucleus particle forming reaction, the kind, concentration and amount of the alkali carbonate aqueous solution, the kind of the alkali hydroxide aqueous solution, Concentration, amount used and ratio in mixed alkaline aqueous solution, type of ferrous salt aqueous solution, alkaline equivalent to total Fe of ferrous salt aqueous solution, aging temperature and aging time, reaction temperature, reaction pH and spindle-shaped goethite core particle growth The amount of nuclear particles present in the reaction, the atmosphere before the start of the oxidation reaction of the reactor, the type of alkali carbonate aqueous solution, the concentration and amount used, the type of alkali hydroxide aqueous solution,
Concentration, usage amount and ratio in mixed alkaline aqueous solution, type and usage amount of ferrous iron salt aqueous solution, alkali equivalent to total Fe of ferrous salt aqueous solution, presence or absence of aging, aging temperature and aging time, water-soluble silicic acid solution Spindle-shaped goethite particle powder was obtained in the same manner as in Example 1 except that the type, the addition amount and the addition timing, the reaction temperature, and the reaction pH were variously changed.

The main manufacturing conditions at this time are shown in Tables 1 to 3,
The properties of the resulting goethite particles are shown in Table 4. In Comparative Example 2, N in the spindle-shaped goethite nucleus particle formation reaction
A water-soluble silicate is added to an aOH aqueous solution.

[0078]

[Table 1]

[0079]

[Table 2]

[0080]

[Table 3]

[0081]

[Table 4]

<Production of Metallic Magnetic Particle Powder Containing Iron as Main Component> Examples 5-8, Comparative Examples 5-8;

Example 5 An amount of press cake corresponding to 1000 g of the spindle-shaped goethite particles obtained by filtering and washing with water obtained in Example 1 was suspended in 30 liters of water. The pH of the suspension at this time was 9.2. Then, Al (NO ₃₎ in the suspension ₃ · 9H ₂ O
120 g (corresponding to 12% by weight with respect to goethite particles) was added and stirred for 10 minutes, and then Co (CH ₃ CO 2
O) 2 a ₂ · 4H ₂ O to 210g (goethite particles
This corresponds to 1% by weight. ) Was added and stirred for 10 minutes. Further, 120 g of H ₃ BO ₃ (corresponding to 12% by weight with respect to goethite particles) was added and stirred for 10 minutes. The pH of the suspension at this time was 4.8.

Next, ammonia water was added to adjust the pH to 9.5, the mixture was filtered by a filter press and dried to obtain goethite particles powder coated with Al compound, Co compound and B compound. The Al content in the obtained goethite particle powder was 0.8 wt% as Al, the Co content was 4.5 wt% as Co, and the B content was 0.8 wt% as B.

800 g of the spindle-shaped goethite particle powder coated with the Al compound, the Co compound and the B compound was heat-treated in air at 350 ° C. to obtain a spindle-shaped hematite particle powder coated with the Al compound, the Co compound and the B compound. Obtained. 100 g of the spindle-shaped hematite particle powder coated with the Al compound, the Co compound, and the B compound was used and the inner diameter was 72 mm.
Was charged into the fixed-bed reducing apparatus of No. _{2, and} 60 l / min of H ₂ gas was aerated, and reduction was performed at a reduction temperature of 400 ° C.

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

As shown in the electron micrograph (× 30000) of FIG. 7, the powder of metallic magnetic particles containing iron, Al, Co and B as a main component had an average major axis of 0.16 μm,
The axial ratio was 8, the particle size was uniform, and the number of dendritic particles was small. Further, the magnetic characteristics are that the coercive force Hc is 1930 Oe.
And the saturation magnetization σs is 141.2 emu /
It was g.

Examples 6 to 8 and Comparative Examples 5 to 8 By changing the kind of particles to be treated, the kind and amount of coating material, the heating temperature, and the reduction temperature in the heating reduction step,
By the same method as in Example 5, metal magnetic particle powder containing iron as a main component was obtained.

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

[0090]

[Table 5]

[0091]

According to the method for producing a spindle-shaped metallic magnetic particle powder containing iron as a main component according to the present invention, as shown in the above-mentioned Examples, the particle size is uniform and dendritic particles are mixed. The main component is iron, which has an appropriate particle shape and axial ratio, and has a high coercive force and an excellent coercive force distribution, as well as more excellent residual magnetic flux density and squareness. Since it is possible to obtain the spindle-shaped metallic magnetic particle powder, it is suitable as a magnetic particle powder for high recording density, high sensitivity and high output.

[Brief description of drawings]

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

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

FIG. 3 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped goethite particle powder obtained in Example 2.

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

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

FIG. 6 is an electron micrograph (× 30000) showing the particle structure of the goethite particle powder obtained in Comparative Example 4.

7 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped metallic magnetic particle powder obtained in Example 5. FIG.

Claims (3)

[Claims] 1. An iron-containing precipitate having a pH value in the range of 8.0 to 11.0, which is obtained by reacting a mixed alkali aqueous solution of alkali carbonate and alkali hydroxide with a ferrous iron salt aqueous solution. After carrying out a spindle-shaped goethite nucleus particle forming reaction in which oxygen-containing gas is passed through the suspension to generate spindle-shaped goethite nucleus particles, the mixed alkaline aqueous solution is added to the suspension containing the spindle-shaped goethite nucleus particles. And an aqueous ferrous salt solution are added and reacted to produce an iron-containing precipitate, or an iron-containing precipitate obtained by reacting the mixed alkaline aqueous solution with an aqueous ferrous salt solution is added to produce a pH. A suspension containing spindle-shaped goethite nucleus particles having a value in the range of 8.0 to 11.0 and an iron-containing precipitate is prepared, and an oxygen-containing gas is passed through the solution to form the spindle-shaped goethite nucleus particles. Grow spindle spindle In carrying out the nuclear particle growth reaction, spindle-shaped goethite particles are generated by allowing water-soluble silicate of 0.2 to 5.0 atomic% in terms of Si to exist in the growth reaction solution to exist in terms of Si. Then, after coating the spindle-shaped goethite particles with a sintering inhibitor, the spindle-shaped goethite particles or the spindle-shaped hematite particles obtained by heat-treating the spindle-shaped goethite particles are heated in a reducing gas. A method for producing a spindle-shaped metallic magnetic particle powder containing iron as a main component, which comprises reducing to obtain a spindle-shaped metallic magnetic particle containing iron as a main component. 2. The method for producing a spindle-shaped metallic magnetic particle powder containing iron as a main component according to claim 1, wherein the proportion of the alkali hydroxide in the mixed alkaline aqueous solution is 5 to 35 mol%. 3. The pH value of the reaction solution during the spindle-shaped goethite nucleus particle formation reaction and the pH value of the reaction solution during the spindle-shaped goethite nucleus particle growth reaction are within a range of ± 0.5. The method for producing a spindle-shaped metallic magnetic particle powder containing iron as a main component according to claim 1.