JP3092649B2 - Method for producing spindle-shaped metal magnetic particles containing iron as a main component - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a composition having a uniform particle size, free of dendritic particles, and having an appropriate particle shape and axial ratio (major axis diameter / minor axis diameter-the same applies hereinafter). Another object of the present invention is to provide spindle-shaped metal magnetic particles containing iron as a main component and having high coercive force and excellent coercive force distribution.

[0002]

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 intensified. In particular, VTR (video tape recorder) has been remarkably popularized in recent years. 2. Description of the Related Art VTRs aiming at long-term recording and reduction in size and weight have been actively developed.
On the other hand, demands for higher performance and higher density recording of magnetic tapes, which are magnetic recording media, are increasing.

[0003] That is, the magnetic recording medium is required to have high image quality, high output characteristics, and especially improvement in frequency characteristics.
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 increasingly required to be improved.

[0004] These characteristics of the magnetic recording medium have a close relationship with 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 magnetic force and large saturation magnetization, such as digital audio tape (DAT), 8 mm video tape, H
It is used in practical use for magnetic recording media such as i-8 tapes and video floppies. However, it is strongly desired to further improve the properties of these metal magnetic particle powders containing iron as a main component.

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 video magnetic recording medium, the video S / N ratio and the chroma S / N ratio are evident from the recording of Nikkei Electronics (1976), May 3, Issue 82, p. Therefore, it is required to improve video frequency characteristics.

[0006] 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 as such magnetic particle powder, the particle size is uniform, dendritic particles are not mixed, and the appropriate particle shape and axis It is required to be a ratio.

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

In order to increase the output of a magnetic recording medium,
FIG. 1 of JP-A-63-26821 shows the relationship between the SFD measured for the above magnetic disk and the recording / reproducing output. 1, the relationship between the recording and reproduction output becomes a straight line, which indicates that the recording and reproduction 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.
The following S. F. D. is necessary. "
S. of magnetic recording medium F. D. (Switching F
field distribution, that is, it is necessary that the coercive force distribution is small, and for this purpose, the coercive force of the magnetic particles is as uniform as possible and the coercive force is not mixed due to the absence of dendritic particles. A small distribution width is required.

[0009] Metal magnetic particle powder containing iron as a main component generally requires goethite particles as starting materials, hematite particles obtained by heating and dehydrating the particles, or particles containing dissimilar metals other than iron in these particles. , And then heat-reduced in a reducing gas.

As described above, the particles have a uniform particle size, do not contain dendritic particles, have an appropriate particle shape and axial ratio, and have high coercive force and excellent coercive force distribution. Currently, iron-based metal magnetic particle powder is currently the most required, in order to obtain iron-based metal magnetic particle powder having such properties,
The starting material, goethite particle powder, has a uniform particle size without 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 step.

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

Further, an oxygen-containing gas is passed through a ferrous hydroxide colloid or an aqueous ferrous salt solution containing iron carbonate obtained by adding an aqueous solution of an alkali hydroxide or an alkali carbonate in an equivalent amount or less to the aqueous ferrous salt solution. By performing an oxidation reaction to generate needle-like goethite core particles, and then to an aqueous ferrous salt solution containing the needle-like goethite core particles, an equivalent amount or more with respect to the amount of Fe ²⁺ in the aqueous ferrous salt solution. A method of growing the acicular goethite nucleus particles by adding an aqueous alkali hydroxide solution and then passing an oxygen-containing gas therethrough (JP-A-59-48766, JP-A-59-128293, JP-A-59-128293).
128294, JP-A-59-128295, JP-A-60-21818, JP-A-1-115
No. 827) and an aqueous solution of ferrous salt containing acicular core particles obtained in the same manner as above
A method is known in which an aqueous solution of an alkali carbonate is added in an amount equal to or more than the amount of ^2+, and an oxygen-containing gas is passed therethrough to grow the acicular goethite nucleus particles (JP-A-5-33018).

[0013] Further, in a suspension containing ferrous hydroxide having a pH value of 11 or more obtained by reacting an aqueous solution of ferrous salt with an aqueous solution of alkali hydroxide, a spindle is prepared in the presence of a Si compound. Method of adding needle-like goethite particles as core particles and causing the core particles to undergo a growth reaction (JP-A-5-345907) or by reacting an aqueous ferrous salt solution with an aqueous alkali carbonate solution A first-stage reaction in which an oxygen-containing gas is passed through the suspension containing FeCO ₃ to perform an oxidation reaction, and then an oxygen-containing gas is passed through the suspension to continue the oxidation reaction, and a ferrous salt aqueous solution is further added. To produce spindle-shaped goethite particles comprising a second-stage reaction in which the reaction is carried out at a pH in the range of 7 to 11 by the addition of water and an alkali hydroxide or ammonia gas (Japanese Unexamined Patent Publication No.
No. 27945) is also known.

[0014]

The particle size is uniform, dendritic particles are not mixed, the particles have an appropriate particle shape and an axial ratio, and a high coercive force and an excellent coercive force distribution are obtained. Needle-like metal magnetic particles powder mainly composed of iron having
Currently, the most demanded method is to produce goethite particle powder as a starting material by the above-described method. In particular, acicular goethite particles having a large axial ratio, particularly 10 or more, are produced, but dendritic. Particles are mixed, and
In terms of the particle size, it is difficult to say that the particles have a uniform particle size.

In the case of the above-mentioned method, spindle-shaped particles having a uniform particle size and containing no dendritic particles are produced, while the axial ratio is at most about 7, and There is a disadvantage that particles with a large axial ratio are difficult to generate,
In particular, this phenomenon tends to become more pronounced as the major axis diameter of the produced particles decreases. Although various attempts have been made to increase the axial ratio of spindle-shaped goethite particles,
In general, it is difficult to increase the axial ratio while maintaining and inheriting the uniformity of the particle shape and the particle size distribution, and goethite particles satisfying both the uniformity of the particle shape and the particle size distribution and the large axial ratio have not yet been obtained. .

The above-mentioned method includes various properties of the acicular goethite particles obtained by the above-mentioned methods and
That is, although the purpose is to improve the particle size, the axial ratio, the presence or absence of dendritic particles, etc., it cannot be said that both characteristics of the particle shape and the uniformity of the particle size distribution and the axial ratio can be sufficiently satisfied. Was.

Conventionally, iron-based metal magnetic particle powder obtained using goethite particle powder obtained by the above-mentioned known methods as starting material particles is also uniform in particle size and contains dendritic particles. However, it is hard to say that it has a large axial ratio.

The acicular goethite particles obtained by the above-mentioned method have a large axial ratio but cannot be said to have a uniform particle size yet. Moreover, since goethite nucleus particles are generated in the acidic region, the obtained goethite particle powder contains a large amount of acid radicals which are not removed even by washing. Since excessive sintering is caused, the desired metal magnetic particle powder cannot be obtained.

The acicular goethite particle powder obtained by the above-mentioned method has a uniform particle size and a large axial ratio as the goethite particle powder. Coercivity has not yet been obtained.

The spindle-shaped goethite particles obtained by the above-mentioned method can provide goethite particles having a uniform particle size. However, when metal magnetic particles are used, the desired high coercive force is still not obtained. Absent.

Accordingly, the present invention provides a method for producing a high coercive force, excellent coercive force distribution, and having a uniform particle size, no dendritic particles mixed, an appropriate particle shape and an axial ratio. It is a technical object to obtain a spindle-shaped metal magnetic particle powder containing iron as a main component.

[0022]

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

That is, the present invention relates to an iron-containing compound having a pH value in the range of 8.0 to 11.0 obtained by reacting a mixed aqueous alkali solution of an alkali carbonate and an alkali hydroxide with an aqueous ferrous salt solution. An oxygen-containing gas is passed through the suspension containing the precipitate, and the major axis diameter is 0.19 to 0.22 μm.
After performing a spindle-shaped goethite nucleus particle generation reaction for producing spindle-shaped goethite nucleus particles having an axis diameter / short axis diameter of 10 to 13, the mixed alkali is added to a suspension containing the spindle-shaped goethite nucleus particles. By adding and reacting the aqueous solution and the ferrous salt aqueous solution to generate an iron-containing precipitate, or by adding the iron-containing precipitate obtained by reacting the mixed alkali aqueous solution and the ferrous salt aqueous solution. pH value 8.0-
A suspension containing spindle-shaped goethite core particles in the range of 11.0 and an iron-containing precipitate is prepared, and an oxygen-containing gas is passed through the suspension to grow the spindle-shaped goethite core particles. In performing the nuclear particle growth reaction, 0.2 to 5.5 in terms of Si with respect to all Fe in the growth reaction solution.
Long by the presence of 0 atomic% of water soluble silicate
The shaft diameter is 0.20 to 0.23 μm and the shaft ratio (long axis diameter
( Small axis diameter ) of 11 to 13 is generated, and then the spindle-shaped goethite particles are coated with a sintering inhibitor, and then the spindle-shaped goethite particles or the spindle-shaped goethite particles are heated. The spindle-shaped hematite particles obtained by the treatment are heated and reduced in a reducing gas to obtain spindle-shaped metal magnetic particles containing iron as a main component. It is a manufacturing method.

Further, the present invention is characterized in that the ratio of the alkali hydroxide in the mixed alkali aqueous solution is 5 to 35 mol%, and the pH value of the reaction solution during the spindle-like goethite nucleus particle generation reaction and the spindle A method for producing spindle-shaped metal magnetic particles containing iron as a main component, wherein the pH value of the reaction solution during the growth reaction of the core goethite core particles is within ± 0.5.

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

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

As the aqueous alkali solution used in the present invention, an aqueous sodium carbonate solution, an aqueous potassium carbonate solution, an aqueous ammonium carbonate solution or the like as an aqueous alkali carbonate solution, or an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution or the like as an aqueous alkali hydroxide mixed with the alkali carbonate may be used. Can be mentioned.

The mixed alkali aqueous solution used during the goethite nucleus particle generation reaction and the goethite nucleus particle growth reaction of the present invention is obtained by mixing alkali carbonate and alkali hydroxide, and the ratio of alkali hydroxide in the mixed alkali aqueous solution is reduced. 5
~ 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. Preferably it is 10-25 mol%, More preferably, it is 15-2.
0 mol%.

The amount of the mixed aqueous alkali solution used is such that the alkali equivalent ratio to the total Fe in the aqueous ferrous salt solution is 1.3 to 1.3%.
3.5. If the ratio is less than 1.3, magnetite may be mixed, and if it exceeds 3.5, it is not industrially preferable. The preferred range is 1.5 to 2.5.

In the present invention, the pH value at the time of the goethite nucleus particle generation reaction and the pH value at the time of the goethite nucleus particle growth reaction are:
It is in the range of 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 by washing. It will cause the result. If it exceeds 11.0,
The desired high coercive force cannot be obtained when metal magnetic particles are used. Preferably it is in the range of 8.5 to 10.0.

The difference between the pH value of the reaction solution during the reaction for producing goethite nucleus particles and the pH value of the reaction solution during the reaction for growing goethite nuclei particles is within a range of ± 0.5 in each reaction solution. If the difference in pH value exceeds ± 0.5, the coercive force of the metal magnetic particle powder is still insufficient. Preferably it is ± 0.3, more preferably ± 0.1. Preferably, the conditions are the same as much as possible. In this case, it is preferable that the ratio of the alkali hydroxide in the mixed aqueous alkali solution and the alkali equivalent ratio to the total Fe in the aqueous ferrous salt solution be 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 at the time of the goethite nucleus particle formation reaction and the temperature at the time of the goethite nucleus particle growth reaction may be generally set to a temperature of 80 ° C. or less at which goethite particles are formed.
When the temperature exceeds 80 ° C., magnetite may be mixed in the spindle-shaped goethite particles. Preferably 45-5
It is in the range of 5 ° C.

In the present invention, the amount of goethite nucleus particles present during the growth reaction of goethite nucleus particles is from 30 to 70% by weight based on the resulting acicular goethite particle powder. If the content is less than 30% by weight, dendritic particles are generated by generating new nuclei of goethite particles, and the particle size of the generated goethite particles becomes uneven. 7
If the content 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 particles cannot be obtained. Preferably it is 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. May be present in any suspension containing the spindle-shaped goethite core particles and the iron-containing precipitate.

In this case, the spindle-shaped goethite core particles are FeCO 2 obtained by reacting a mixed alkali aqueous solution of an alkali carbonate and an alkali hydroxide with a ferrous salt aqueous solution.
Spindle-shaped goethite particles obtained by oxidizing an aqueous solution containing ₃ by passing an oxygen-containing gas into the aqueous solution can also be used as core particles in the growth reaction solution of the present invention as core particles.

In both cases of the goethite nucleus particle formation reaction and 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 this case, the aging is preferably carried out in a temperature range of usually from 40 to 80 ° C. for the suspension under a non-oxidizing atmosphere. If the temperature is lower than 40 ° C., it is difficult to obtain a sufficient ripening effect due to a small axial ratio.
Magnetite may be mixed.

The aging time is 30 to 300 minutes. If the time is less than 30 minutes, the axial ratio cannot be sufficiently increased. Although it may be longer than 300 minutes, it does not mean that the time is longer than necessary.

To obtain 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.

The water-soluble silicate used in the present invention includes water glass, sodium silicate, sodium metasilicate, potassium silicate and the like.

The water-soluble silicate is added to the suspension containing spindle-shaped goethite core particles during the goethite core particle growth reaction.
A water-soluble silicate of 0.2 to 5.0 atomic% in terms of Si with respect to all Fe is present. If the content is less than 0.2 atomic%, the effect of adding the water-soluble silicate cannot be obtained, and a high coercive force cannot be obtained when the metal magnetic particles are used.
If the content exceeds 5.0 atomic%, the saturation magnetization value decreases when the metal magnetic particles are used. Preferably 0.5 to
2.0 atomic%, more preferably 0.8 to 1.5 atomic%.

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 passing the ferrous salt aqueous solution, the alkaline aqueous solution, and the oxygen-containing gas 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 dividedly added or added continuously or 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, a P compound which are usually added during the reaction for forming goethite particles in order to improve various properties of the spindle-shaped metal magnetic particles containing iron as a main component. , Si compounds, etc. or 2
The seed or more may be added during the production reaction of the core particles or during the growth reaction of the core particles, and in this case, the intended spindle-shaped goethite particle powder can be obtained.

In the present invention, the spindle-shaped goethite particles are coated with a substance having an effect of preventing sintering, ie, a sintering inhibitor, by a well-known method prior to the heat reduction treatment, whereby the particles and Sintering between the particles is prevented, the particle shape and the axial ratio of the spindle-shaped goethite particles are more easily maintained and inherited, and spindle-like metal magnetic particles mainly containing iron as independent components are easily obtained.

As a well-known sintering inhibitor, 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, and thus may be used in combination as necessary. In this case, the use amount is small, the sintering prevention effect is not sufficient, and if it is too large, the saturation magnetization value is reduced.
3.0% by weight.

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

The heat treatment in the non-reducing gas atmosphere is performed under the flow of air, oxygen gas, and nitrogen gas at 300 to 800
The heating temperature can be appropriately selected according to the type of the compound used for the coating treatment of the spindle-shaped goethite particles. When the temperature exceeds 800 ° C., deformation of the particles and sintering between the particles and the particles are caused.

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

The spindle-shaped metal magnetic particles containing iron as the main component after the heat reduction in the present invention can be obtained by a known method, for example, by immersing the particles in an organic solvent such as toluene, or by reducing the spindle containing iron as the main component. After the atmosphere of the metallic magnetic particles is once replaced with an inert gas, the oxygen content in the inert gas is gradually increased while the air is finally converted to air to be gradually oxidized to be taken out into the air. Can be.

[0060]

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

As described above, usually, spindle-shaped goethite particles do not contain dendritic particles and have a uniform particle size, but it is difficult to obtain a large axial ratio. Many attempts have been made to obtain spindle-shaped goethite particles having a large axial ratio, but it is hard to say that sufficient results have been obtained. Therefore, when the metal magnetic particle powder is formed using spindle-shaped goethite particles, a satisfactory coercive force is not obtained.

The reaction for growing spindle-shaped goethite nucleus particles by the presence of a water-soluble silicate in a suspension containing ferrous hydroxide having a pH value of 11 or more in the method described above has a good axial ratio. Although goethite particles having high crystallinity have been obtained, in this case, growth in the short axis direction is suppressed. That is, the axial ratio is improved by the effect of reducing the short axis, not for the growth in the long axis direction.
For this reason, it is difficult to say that a high coercive force is still obtained when using metal magnetic particles.

The present inventors have conducted intensive studies and 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 and an aqueous ferrous salt solution with iron-containing precipitates. Of the present invention for growing spindle-shaped goethite nucleus particles in a suspension containing an aqueous solution and in the presence of a water-soluble silicate.

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

In addition, since the pH value of the reaction solution during the spindle-like goethite nucleus particle formation reaction and the pH value of the reaction solution during the spindle-like goethite nucleus particle growth reaction are within ± 0.5, the dendritic particles are formed. Of water-soluble silicate to be produced in the growth reaction solution, having the advantage of being able to produce spindle-shaped goethite particles having a uniform particle size and an appropriate particle shape and an axial ratio without any mixture of Accordingly, an effect that the sintering prevention efficiency is higher than that of a normal sintering prevention process is obtained.

The difference between the presence of the water-soluble silicate during the growth reaction in the present invention and the effect of preventing sintering with the water-soluble silicate added after the well-known reaction is not yet clear. The inventors have found that the difference between the case where a Si compound is simply adsorbed on the particle surface by a known method and the Si compound which is adsorbed and reacted with a stronger bonding force on the particle surface by the growth reaction in the present invention. Therefore, the water-soluble silicate present at the time of the growth reaction in the present invention can more effectively exert the effect of preventing sintering at the time of heat reduction when forming metal magnetic particle powder containing iron as a main component. I think it's done.

On the other hand, in the method described above, it is difficult to make the alkali equivalent ratio to the total Fe in the aqueous ferrous salt solution the same in the spindle-shaped goethite nucleus particle formation reaction and the spindle-shaped goethite nucleus particle growth reaction. Also, it is considered that metal magnetic particles having high coercive force could not be obtained because the composition of the alkali used was different.

That is, in the spindle-like goethite nucleus particle formation reaction and the spindle-like goethite nucleus particle growth reaction according to the present invention, the alkali equivalent ratio to the total Fe in the ferrous salt aqueous solution is set to the same condition. By making the ratio of the alkali hydroxide equal, when the metal magnetic particles are powdered, a material having a particularly high coercive force can be obtained.Furthermore, in the spindle-shaped goethite core particle growth reaction, water-soluble silicate is used. It is considered that the sintering prevention effect can be further improved if present, and a higher coercive force can be obtained.

[0069]

Next, the present invention will be described with reference to examples and comparative examples. The major axis diameter of the particles in Examples and Comparative Examples,
The axial ratio was shown by the average value of the values measured from the electron micrographs, and the specific surface area of the particles was shown by the value measured by the BET method.

The magnetic properties of the metal magnetic particles containing iron as a main component were measured using an “oscillating sample magnetometer VSM-3S-15” (manufactured by Toei Kogyo Co., Ltd.) under an external magnetic field of 10 kOe.

<Production of Spindle-Shaped Goethite Particle Powder> Examples 1-4, Comparative Examples 1-4;

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

A part of the spindle-shaped goethite core particles is extracted,
The needle-like goethite core particles obtained by filtration, washing and drying have a major axis of 0.19 μm and an axial ratio of 10, as shown in the electron micrograph (× 30000) of FIG. And the particle size was uniform.

Then, in a suspension containing spindle-shaped goethite core particles in which the reactor was made non-oxidizing atmosphere by passing N ₂ gas, 3.95 l of a 6.5N aqueous solution of Na ₂ CO _{3 was} added.
1.6 L of 0N NaOH aqueous solution (N against mixed alkali
aOH corresponds to 15 mol%. 5.) and an aqueous solution of ferrous sulfate containing 1.5 mol / l of Fe ²⁺ 6.
7 l (the amount of an aqueous alkali solution corresponds to 1.5 equivalents to ferrous sulfate), and the temperature was raised to 50 ° C. and maintained for 20 minutes. ₂ 2
After adding 21.05 g (8.5% by weight of the total Fe, corresponding to 0.5 atomic% in terms of Si) with stirring and mixing, a pH value of 9.6 (pH at the time of the reaction for forming goethite core particles) was obtained.
The difference from the value is 0.1. ), At a temperature of 50 ° C, 150 l of air per minute was passed for 2.0 hours to carry out the growth reaction of the spindle-shaped goethite core particles.

The resulting particles were filtered, washed with water, dried and pulverized in a conventional manner to obtain acicular goethite particles.
As shown in the electron micrograph (× 30000), the particles were spindle-shaped and had a major axis of 0.22 μm, an axial ratio of 13,
The BET specific surface area was 97 m ² / g, no dendritic particles were present 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 formation reaction, the type, concentration and amount of the aqueous alkali carbonate, the type of the aqueous alkali hydroxide, Concentration, amount used and ratio in mixed alkaline aqueous solution, type of ferrous salt aqueous solution, alkali equivalent to total Fe in ferrous salt aqueous solution, ripening temperature and ripening 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 in the reactor, the type, concentration and amount of the aqueous alkali carbonate solution, the type of the aqueous alkali hydroxide solution,
Concentration, amount used and ratio in mixed alkaline aqueous solution, type and amount of ferrous 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 particles were obtained in the same manner as in Example 1, except that the type, amount and timing of addition of, and the reaction temperature and reaction pH were variously changed.

The main manufacturing conditions at this time are shown in Tables 1 to 3.
Table 4 shows the properties of the resulting goethite particles. In Comparative Example 2, the N-type at the time of the spindle-like goethite nucleus particle generation 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 to 8, Comparative Examples 5 to 8;

Example 5 An amount of press cake equivalent to 1000 g of spindle-shaped goethite particles obtained in Example 1 and separated by filtration and washed with water was suspended in 30 l of water. At this time, the pH of the suspension was 9.2. Next, Al (NO ₃ ) ₃ .9H ₂ O was added to the above suspension.
(Which corresponds to 12 wt% based goethite particles.) 120 g was stirred in for 10 minutes, Co (CH ₃ CO
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 based on the goethite particles) was added, and the mixture was stirred for 10 minutes. At this time, the pH of the suspension was 4.8.

Then, the pH was adjusted to 9.5 by adding aqueous ammonia, followed by filtration with a filter press and drying to obtain goethite particle powder coated with an Al compound, a Co compound and a B compound. The content of Al in the obtained goethite particle powder was 0.8 wt% as Al, the content of Co was 4.5 wt% as Co, and the content of B 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 is heated in air at 350 ° C. to obtain the 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 is 72 mm in inner diameter.
And fixed at a reduction temperature of 400 ° C. while passing H ₂ gas at 60 l / min.

The iron-based metal magnetic particle powder containing Al, Co and B obtained by reduction is 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 metal magnetic particles containing Al, Co and B and containing iron as the main component have an average major axis of 0.16 μm,
The axial ratio was 8, the particle size was uniform, and there were few dendritic particles. The magnetic properties are as follows: coercive force Hc is 1930 Oe
And the saturation magnetization σs is 141.2 emu /
g.

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

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

[0090]

[Table 5]

[0091]

According to the method for producing spindle-shaped metal magnetic particles containing iron as a main component according to the present invention, as shown in the preceding embodiment, 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 high coercive force and excellent coercive force distribution, and also has better residual magnetic flux density and squareness. Thus, it is suitable as a magnetic particle powder for high recording density, high sensitivity, and high output.

[Brief description of the drawings]

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

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 2.

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

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

Claims (3)

(57) [Claims] 1. An iron-containing precipitate having a pH value in the range of 8.0 to 11.0 obtained by reacting a mixed alkali aqueous solution of an alkali carbonate and an alkali hydroxide with an aqueous ferrous salt solution. An oxygen-containing gas is passed through the suspension so that the major axis diameter is equal to 0.
19 to 0.22 μm, axial ratio (major axis diameter / short axis diameter)
After performing a spindle-like goethite nucleus particle generation reaction for producing spindle-like goethite nucleus particles having a particle size of 10 to 13, the suspension containing the spindle-like goethite nucleus particles contains the mixed alkali aqueous solution and the ferrous salt aqueous solution. Is added and reacted to form an iron-containing precipitate, or by adding an iron-containing precipitate obtained by reacting the mixed aqueous alkali solution with an aqueous ferrous salt solution to adjust the pH value to 8.0 to 8.0. A suspension containing spindle-shaped goethite core particles in the range of 11.0 and an iron-containing precipitate is prepared, and an oxygen-containing gas is passed through the suspension to grow the spindle-shaped goethite core particles. In carrying out the nuclear particle growth reaction, the presence of a water-soluble silicate of 0.2 to 5.0 atomic% in terms of Si with respect to the total Fe in the growth reaction solution results in a major axis diameter of 0.20 to 0.20.
0.23 μm, and the axial ratio (major axis diameter / minor axis diameter) is 11
To produce spindle-shaped goethite particles is -13, then the spindle-shaped goethite after the particles were coated with the anti-sintering agent, spindle obtained by heat treating the spindle-shaped goethite particles or該紡spindle-shaped goethite particles A method for producing spindle-shaped metal magnetic particles containing iron as a main component, comprising heating and reducing the hematite particles in a reducing gas to obtain spindle-shaped metal magnetic particles containing iron as a main component. 2. The method according to claim 1, wherein the ratio of the alkali hydroxide in the mixed aqueous alkali solution is 5 to 35 mol%. 3. The method according to claim 1, wherein the pH value of the reaction solution during the spindle-shaped goethite nucleus particle generation reaction and the pH value of the reaction solution during the spindle-shaped goethite nucleus particle growth reaction are within ± 0.5. A method for producing a spindle-shaped metal magnetic particle powder containing iron as a main component according to claim 1.