JP3264374B2 - Method for producing spindle-shaped iron-based metal magnetic particle powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an axial ratio (long axis diameter: short axis diameter) which is optimal as magnetic particle powder having high output characteristics and low noise level for high density recording. Is large, the particle size is uniform, dendritic particles are not mixed, and the crystallite size is small, spindle-shaped iron having an appropriate size specific surface area and high coercive force. The present invention relates to a method for producing metal magnetic particle powder as a main component.

[Conventional technology]

In recent years, the long-term recording and the reduction in size and weight of magnetic recording / reproducing devices for video and audio have become intense. In particular, the recent widespread use of VTRs (video tape recorders) has been remarkable. The development of VTRs aiming to reduce the size and weight is being actively pursued. On the one hand,
Demands for higher performance and higher density recording of magnetic tapes, which are magnetic recording media, are increasing.

That is, high image quality of the magnetic recording medium, high output characteristics, especially improvement of frequency characteristics and reduction of noise level are required,
For that purpose, it is necessary to improve the residual magnetic flux density Br, increase the coercive force, and improve the dispersibility, the filling property, and the smoothness of the tape surface, and the S / N ratio is increasingly required.

These various properties of the magnetic recording medium have a close relationship with the magnetic particle powder used in the magnetic recording medium, but in recent years, the high coercive force and the large Attention has been paid to metal magnetic particle powders containing iron having a saturation magnetization as a main component, and they have been used in practical use for magnetic recording media such as digital audio tape (DAT), 8 mm video tape, Hi-8 tape, and video floppy. 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 various 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), May 3, No. 82-
As is clear from the description on page 105, improvements in the video S / N ratio, chroma S / N ratio, and video frequency characteristics are required.

In order to improve the video S / N ratio, it is necessary to reduce the size of the magnetic particle powder and improve the dispersibility in the vehicle, the orientation and the filling property in the coating film, and the surface of the magnetic recording medium. It is important to improve the smoothness.

That is, as one method for improving the video S / N ratio, it is important to reduce the noise level caused by the magnetic recording medium, and for that purpose, the magnetic particle powder used as is clear from the above description It is known that a method of reducing the particle size of the particles is effective.

As one method of expressing the particle size of magnetic particle powder, the value of the specific surface area of the particle powder is often used, but the noise level caused by the magnetic recording medium tends to decrease as the specific surface area of the magnetic particle powder used increases. Is also generally known.

This phenomenon is described in, for example, Japanese Patent Application Laid-Open No. 58-159231.
Figures and the like. FIG. 1 is a diagram showing the relationship between the specific surface area of the particles and the noise level in the magnetic tape obtained using the metal magnetic particle powder. As the specific surface area of the particles increases, the noise level decreases linearly. ing.

Therefore, in order to improve the video S / N ratio and reduce the noise level, it is required that the specific surface area of the magnetic particle powder be as large as possible.

However, if the specific surface area of the magnetic particles becomes too large, the amount of binder per unit surface area of the magnetic particles decreases, and the dispersibility of the magnetic particles in the vehicle, the orientation in the coating film, and the filling property increase. Becomes difficult,
Since the surface smoothness cannot be obtained, this causes a decrease in the video S / N ratio, and it may not be preferable to simply increase the specific surface area of the magnetic particle powder. Therefore, it is important to select an optimum specific surface area in combination with the technique of dispersing the magnetic particle powder in the vehicle.

On the other hand, it is known that the noise of the metal magnetic particle powder is related to the crystallite size of the metal magnetic particle powder.

This phenomenon is described in, for example, “123rd issue of“ Synthetic Electronic Research, “Magnetic Recording Medium Comprehensive Data Collection” (August 15, 1985) ”.
Page, FIG. 38, and the like. FIG. 38 is a diagram showing the correlation between the crystallite size of particles and noise in a magnetic tape obtained using metal magnetic particle powder containing iron as a main component, and the smaller the crystallite size of particles, the smaller the noise. It has become.

Therefore, in order to reduce the noise level caused by the magnetic recording medium, it is also effective to reduce the crystallite size of the metal magnetic particles as much as possible.

As described above, in order to improve the video S / N ratio and reduce the noise level, the crystallite size of the magnetic particle powder is as small as possible, and the specific surface area is appropriately large, especially, 30 to With a particle size of about 60 m ² / g, uniform particle size, and the absence of dendritic particles, dispersibility of the magnetic particle powder in the vehicle, orientation and filling in the coating film are reduced. It is required to be excellent.

Next, in order to improve the chroma S / N, it is important to improve the surface properties and orientation of the magnetic recording medium, and for that purpose, a magnetic particle powder having good dispersibility and orientation is preferred. Such a magnetic particle powder has a large axial ratio (major axis diameter: short axis diameter), a uniform particle size, no dendritic particles, and an appropriate specific surface area. Required to have.

Further, 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 large.

In order to increase the coercive force Hc of the magnetic recording medium, it is required that the coercive force Hc of the magnetic particle powder be as high as possible.
Currently, for video floppy, DAT, 8mm video, Hi-
The coercive force of the magnetic particle powder used for 8 etc. is from 1300 Oe
About 1700 Oe is required.

Since the coercive force of the magnetic particle powder is generally generated due to its shape anisotropy, the coercive force tends to increase as the axial ratio (major axis diameter: short axis diameter) of the particles increases. Since the coercive force tends to decrease as the crystallite size decreases, reducing the crystallite size to reduce the noise level for the purpose of improving the video S / N ratio described above,
The coercive force decreases, making it difficult to improve video frequency characteristics. Therefore, there is a strong demand for a magnetic particle powder having a small crystallite size while maintaining the coercive force of the magnetic particle powder as high as possible.

Metal magnetic particle powder containing iron as a main component is generally a goethite particle as a starting material, a hematite particle obtained by heating and dehydrating the same, or a particle containing a dissimilar metal other than iron in a reducing gas, It is obtained by heat reduction.

Conventionally, as a method for producing goethite particle powder as a starting material, a suspension containing ferrous hydroxide obtained by adding an equivalent amount or more of an aqueous alkali hydroxide solution to an aqueous ferrous salt solution at pH 11 or higher is used. A method of producing needle-like goethite particles by performing an oxidation reaction by passing an oxygen-containing gas at a temperature of not more than ℃, and reacting an aqueous ferrous salt solution with an aqueous alkali carbonate solution or an aqueous alkali carbonate / alkali hydroxide solution. A method is known in which an oxygen-containing gas is passed through a suspension containing FeCO ₃ or a Fe-containing precipitate obtained as described above to carry out an oxidation reaction, thereby producing spindle-shaped goethite particles.

[Problems to be solved by the invention]

Large axis ratio (major axis diameter: short axis diameter), uniform particle size, no dendritic particles, small crystallite size, appropriate specific surface area and high coercive force Metal magnetic particle powder containing iron as a main component is currently the most required, but the acicular goethite particles obtained by the former method among the above-mentioned known methods are:
Although the axial ratio (major axis diameter: short axis diameter) is as large as 10 or more, dendritic particles are mixed, and in terms of particle size, it is hard to say that the particles have uniform particle size. Iron-based metal magnetic particle powder obtained by heating and reducing acicular goethite particles has high coercive force due to its large axial ratio (major axis diameter: short axis diameter). Dendritic particles are mixed, and it is hard to say that the particles have a uniform particle size.

Spindle-shaped goethite particles obtained by the latter method out of the above-mentioned known methods are particles having a uniform particle size and containing no dendritic particles, but have an axial ratio (long axis diameter: There is a disadvantage that it is difficult to generate particles having a large (short axis diameter), and in particular, this phenomenon tends to become more pronounced as the long axis diameter of the generated particles decreases. The iron-based metal magnetic particle powder obtained by heating and reducing the spindle-shaped goethite particles has a uniform particle size,
In addition, because the dendritic particles are not mixed, the dispersibility in the vehicle, the orientation in the coating film, and the filling property are excellent, but the axial ratio (long axis diameter: short axis diameter) is small. It has the disadvantage that it is difficult to obtain particles having a high coercive force. Further, studies on the improvement of the axial ratio as described later have made it possible to obtain particles having a relatively high coercive force, but these particles have the disadvantage that their crystallite size is large. A metal mainly composed of iron having a uniform particle size, no dendritic particles, and a high coercive force, a small crystallite size, and an appropriate specific surface area. Magnetic particles have not yet been obtained.

Conventionally, the particle size is uniform, dendritic particles are not mixed, and, furthermore, in order to obtain a spindle-shaped iron-based metal magnetic particle powder having a high coercive force, to obtain spindle-shaped goethite particles Various attempts have been made to increase the axial ratio (major axis diameter: short axis diameter).
JP, JP-A-60-21307, JP-A-60-21819, JP-A-60-36603 and JP-A-2-51429, which are obtained by these methods. The spindle-shaped iron-based metal magnetic particle powder obtained is a particle having a small crystallite size, an appropriate specific surface area and a high coercive force, as shown in FIGS. It is hard to say.

Therefore, the present invention has a large axial ratio (major axis diameter: short axis diameter), uniform particle size, and no mixture of dendritic particles,
Moreover, it is a technical object to obtain spindle-shaped iron-based metal magnetic particle powder having a small crystallite size, an appropriate specific surface area and a high coercive force and having a spindle shape.

[Means for solving the problem]

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

That is, the present invention provides a suspension containing FeCO ₃ or a Fe-containing precipitate obtained by reacting an aqueous alkali carbonate solution or an aqueous alkali carbonate / alkali hydroxide solution with a ferrous salt aqueous solution under a non-oxidizing atmosphere. After aging, when the oxygen-containing gas is passed through the suspension containing the FeCO ₃ or Fe-containing precipitate to oxidize to produce spindle-shaped goethite particles, the alkali carbonate aqueous solution, the alkali carbonate. The aqueous solution of alkali hydroxide, the aqueous solution of ferrous salt and the oxygen-containing gas are passed through the FeCO ₃ or Fe before oxidation.
In any of the suspensions containing the containing precipitate, propionic acid or a salt thereof is pre-existing to produce spindle-shaped goethite particles, and if necessary, the spindle-shaped goethite particles or the goethite particles. Spindle-shaped hematite particles obtained by heating and dehydrating spindle-shaped goethite particles are coated with at least one metal compound selected from Ni, Al, Si, P, Co, Mg, B and Zn. ,
Next, the spindle-shaped goethite particles which have not been subjected to the deposition treatment or have been subjected to the deposition treatment, or obtained by subjecting these particles to a heat treatment in a temperature range of 300 to 800 ° C. in a non-reducing atmosphere. Spindle-shaped iron-based metal magnetic particles comprising heating the reduced spindle-shaped hematite particles in a reducing gas to obtain spindle-shaped iron-based metal magnetic particles It is a manufacturing method of.

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

As the ferrous salt aqueous solution used in the present invention,
There are aqueous ferrous sulfate and aqueous ferrous chloride.

An aqueous solution of sodium carbonate, potassium carbonate, ammonium carbonate or the like can be used as the aqueous alkali carbonate solution in the present invention, and an aqueous solution of sodium hydroxide, potassium hydroxide or the like can be used as the aqueous alkali hydroxide solution.

The ripening in the present invention is performed under an inert atmosphere by passing an inert gas such as N ₂ gas through the liquid, and is performed while stirring by the passed gas or mechanical operation.

The aging temperature of the suspension containing the FeCO ₃ or Fe-containing precipitate in the present invention is 35 to 60 ° C., and the aging time is 50 to 500 minutes.

When the temperature is lower than 35 ° C., the axial ratio (long axis diameter: short axis diameter) becomes small, and the spindle ratio of the goethite particle powder having a large axial ratio (long axis diameter: short axis diameter) of the present invention is reduced. I can't get it. When the temperature is higher than 60 ° C., a spindle-shaped goethite particle powder having a large axis ratio (long axis diameter: short axis diameter), which is the object of the present invention, can be obtained, but it is necessary to raise the aging temperature more than necessary. Absent.

If the time is less than 50 minutes, a spindle-shaped goethite particle powder having a large axial ratio (long axis diameter: short axis diameter), which is the object of the present invention, cannot be obtained. Even in the case of exceeding 500 minutes, it is possible to obtain a spindle-shaped goethite particle powder having a large spindle ratio (long axis diameter: short axis diameter) aimed at by the present invention,
There is no point in making it longer than necessary.

The pH in the present invention is 7-11. If it is less than 7, or more than 11, no goethite particle powder having a spindle shape can be obtained.

The reaction temperature during oxidation of the goethite formation reaction of the present invention is 35 to 70 ° C. When the temperature is lower than 35 ° C., it is impossible to obtain a spindle-shaped goethite particle powder having a large axial ratio (long axis diameter: short axis diameter), which is the object of the present invention.

When the temperature exceeds 70 ° C., granular hematite particles are mixed in spindle-shaped goethite particles.

The oxidizing means at the time of oxidation of the goethite formation reaction of the present invention is performed by aerating an oxygen-containing gas (for example, air) into the liquid, and is performed while stirring by the aerated gas or mechanical operation.

The propionic acid or a salt thereof according to the present invention is involved in the axial ratio (long axis diameter: short axis diameter) and the short axis diameter of the resulting spindle-shaped goethite particles. Must be present during the reaction at a stage prior to the reaction, and contain an aqueous solution of alkali carbonate, an aqueous solution of alkali carbonate / alkali hydroxide, an aqueous solution of ferrous salt, and an oxygen-containing gas before passing through the oxidation and containing FeCO ₃ or Fe. It can be present at any stage of the suspension containing the precipitate.

As the salt of propionic acid in the present invention, sodium propionate, potassium propionate, calcium propionate, zinc propionate, cobalt propionate, magnesium propionate and the like can be used.

The amount of propionic acid or a salt thereof in the present invention,
It is in the range of 0.1 to 10.0 mol% with respect to Fe.

When the amount is less than 0.1 mol%, a spindle-shaped goethite particle powder having a large axial ratio (long axis diameter: short axis diameter), which is the object of the present invention, cannot be obtained. When it exceeds 10.0 mol%, a goethite particle powder having a spindle shape having a large axial ratio (major axis diameter: short axis diameter), which is the object of the present invention, can be obtained, but there is no point in adding more than necessary. .

In the present invention, in order to prevent deformation of the particle shape and sintering between particles during heat reduction, the starting material is
It is preferable to perform the deposition treatment with at least one metal compound selected from i, Al, Si, P, Co, Mg, B and Zn. Since these metal compounds not only have a sintering preventing effect but also have a function of controlling the reduction rate, they are preferably used in combination as needed.

The starting material that has been subjected to the deposition treatment with the metal compound can be used as it is to obtain a metal magnetic particle powder containing iron as a main component even if it is reduced as it is. For control, it is preferable to perform a heat treatment in a non-reducing gas atmosphere in advance by a conventional method prior to reduction.

The heat treatment in the non-reducing gas atmosphere can be performed in a temperature range of 300 to 800 ° C. under the flow of air, oxygen gas, and nitrogen gas, and the heat treatment temperature is used for the deposition treatment of the starting material particles. It is more preferable to appropriately select according to the type of the metal compound.

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 preferably from 300 to 550 ° C.

If the temperature is lower than 300 ° C., the progress of the reduction reaction is slow,
It takes a long time.

On the other hand, when the temperature exceeds 550 ° C., the reduction reaction proceeds rapidly, causing deformation of the particles and sintering between the particles.

The iron-based metal magnetic particle powder after the heat reduction in the present invention may be obtained by a known method, for example, a method of immersing in an organic solvent such as toluene and the atmosphere of the reduced iron-based metal magnetic particle powder. After once replacing with inert gas,
It can be taken out into the air by a method such as gradually oxidizing the air by finally increasing the oxygen content in the inert gas while gradually increasing the oxygen content.

In the present invention, conventionally, in order to improve various properties of the metal magnetic particle powder containing iron as a main component, when generating goethite particles as a starting material, Co, Ni, and C are usually added.
Dissimilar metals other than Fe, such as r, Zn, Al and Mn, can be added. In this case, too, the axial ratio (long axis diameter: short axis diameter) aimed at by the present invention is large, and It is possible to obtain a goethite particle powder having a small size, an appropriate specific surface area and a high coercive force.

[Action]

First, the most important point in the present invention is that a suspension containing FeCO ₃ or a Fe-containing precipitate obtained by reacting an aqueous alkali carbonate solution or an aqueous alkali carbonate / alkali hydroxide solution with an aqueous ferrous salt solution is used. After ripening in an oxidizing atmosphere, an oxygen-containing gas is passed through the suspension containing the FeCO ₃ or Fe-containing precipitate to oxidize the suspension, thereby producing spindle-shaped goethite particle powder. The aqueous solution of the alkali carbonate and alkali hydroxide, the aqueous solution of ferrous salt and the oxygen-containing gas before oxidation and oxidation of the FeCO ₃ or the suspension containing the Fe-containing precipitate, in advance, propionic acid or Spindle-shaped goethite particles are generated by the presence of the salt, and the spindle-shaped goethite particles or the spindle-shaped goethite particles are heated. When spindle-shaped hematite particles obtained by water are reduced by heating in a reducing gas, the axial ratio (major axis diameter: short axis diameter) is large, the particle size is uniform, and dendritic particles are mixed. In addition, it is possible to obtain spindle-shaped iron-based metal magnetic particle powder having a small crystallite size, an appropriate size specific surface area, and a high coercive force. It is a fact.

Further, in the present invention, the resulting spindle-shaped goethite particles are subjected to a coating treatment with at least one metal compound selected from Ni, Al, Si, P, Co, Mg, B and Zn. Alternatively, the particles are placed in a non-reducing atmosphere at 300 to 8
Even when the spindle-shaped hematite particles obtained by performing the heat treatment in the temperature range of 00 ° C. are heat-reduced in a reducing gas, the metal magnetic particle powder containing iron as a main component of the present invention is used. The shape and axis ratio (long axis diameter: short axis diameter) of the spindle-shaped goethite particles can be further improved by preventing the deformation of particles and the sintering between particles during heating and reduction. Can be effectively retained and inherited.

In the present invention, the reason why goethite particles having a spindle shape with a large axial ratio (major axis diameter: short axis diameter) can be obtained is as follows.
The present inventors, as shown in the comparative examples below, when only ripening without the presence of propionic acid or a salt thereof, in any case where propionic acid or a salt thereof is present without ripening In addition, since the effects of the present invention cannot be obtained, it is considered that this is due to a synergistic effect between the aging step and propionic acid or a salt thereof.

Conventionally, after obtaining a suspension containing FeCO ₃ or a Fe-containing precipitate obtained by reacting an aqueous alkali carbonate solution or an aqueous alkali carbonate / alkali hydroxide solution with an aqueous ferrous salt solution, the FeC
Spindle-shaped goethite particles obtained by oxidizing a suspension containing an O ₃ or Fe-containing precipitate by passing an oxygen-containing gas into the suspension, are carefully observed with an electron microscope. The crystal grows like a bundle,
Axial ratio (major axis diameter: short axis diameter) in order to increase the width direction of one goethite particle by increasing the number of secondary particles.
Spindle-shaped goethite particles having a small particle size are easily obtained.

Moreover, when the spindle-shaped goethite particles are subjected to a sintering prevention treatment and a heat treatment in a reducing gas to obtain metal magnetic particle powders by a usual method, the straw-like elongated bundle is obtained. Since the crystal growth between the primary particles proceeds, the crystallite size of the obtained metal magnetic particle powder is Fe
Only those having a larger value than the crystallite size of the metal magnetic particle powder obtained from acicular goethite obtained by the oxidation reaction of (OH) ₂ as a starting material were obtained.

In the present invention, the reason why a metal magnetic particle powder containing iron as a main component having an appropriate specific surface area and a high coercive force despite a small crystallite size is obtained,
The inventor of the present invention has concluded that the spindle-shaped goethite particles of the present invention have an axial ratio (long axis) which can be narrowed in the width direction of the particles due to a synergistic effect of the aging step and propionic acid or a salt thereof. It is considered that the growth of the primary particles in the width direction during reduction is suppressed by controlling the growth of the goethite particles in the width direction during the particle growth process.

Now, a description will be given of a part of many experimental examples conducted by the inventor as described below.

FIG. 1 shows the relationship between the abundance of sodium propionate and the axial ratio of spindle-shaped goethite particles (major axis diameter: short axis diameter).

That is, a spindle-shaped goethite obtained in the same manner as in Examples 1, 5 and 7, except that sodium propionate was present in an amount of 0 to 10.0 mol% based on Fe. It shows the relationship between the axial ratio of particles (major axis diameter: short axis diameter) and the amount of sodium propionate.

In FIG. 1, curves A, B, and C each have a major axis diameter of 0.3 to
Spindle-shaped goethite particle powder of about 0.5 μm, major axis diameter of about 0.2 μm, and major axis diameter of about 0.1 μm.

As is clear from FIG. 1, the axial ratio (major axis diameter: short axis diameter) of the spindle-shaped goethite particles obtained tends to increase as the amount of sodium propionate increases.

Conventionally, a method of producing spindle-shaped goethite particle powder by oxidizing a suspension containing FeCO ₃ obtained by reacting an aqueous alkali carbonate solution and an aqueous ferrous salt solution by passing an oxygen-containing gas through the suspension. In Japanese Patent Application Laid-Open No. 50-80999, there is a method in which a carboxylic acid such as citric acid and tartaric acid and a salt thereof are present. Are obtained. Goethite particles having a small axial ratio (major axis diameter: short axis diameter) are obtained, which is completely different from the action and effect of propionic acid or a salt thereof in the present invention. Things.

FIG. 2 shows the relationship between the BET specific surface area and the crystallite size of a spindle-shaped iron-based metal magnetic particle powder.

In FIG. 2, the symbols Δ and X are spindle-shaped iron-based metal magnetic particle powders obtained by the conventional method, which are disclosed in JP-A-60-36603 and JP-A-60-36603, respectively. It is a metal magnetic particle powder containing iron as a main component obtained by the method described in Japanese Patent Application Laid-Open No. 2-51429.

The circles indicate the spindle-shaped iron-based metal magnetic particle powder according to the present invention.

The spindle-shaped iron-based metal magnetic particle powder according to the present invention has a smaller crystallite size compared to the spindle-shaped iron-based metal magnetic particle powder obtained by a conventional method. It has an appropriate specific surface area.

FIG. 3 shows the relationship between the coercive force and the crystallite size of the spindle-shaped iron-based metal magnetic particle powder.

In FIG. 3, the symbols Δ and X are spindle-shaped iron-based metal magnetic particle powders obtained by the conventional method, which are obtained by the conventional method. It is a metal magnetic particle powder containing iron as a main component obtained by the method described in Japanese Patent Application Laid-Open No. 2-51429.

The circles indicate the spindle-shaped iron-based metal magnetic particle powder according to the present invention.

The spindle-shaped metal magnetic particle powder according to the present invention has a high coercive force despite the small crystallite size, as compared with the spindle-shaped iron-based metal particle powder obtained by the conventional method. Things.

[Examples] Next, the present invention will be described with reference to Examples and Comparative Examples.

In addition, the major axis diameter and the axial ratio (major axis diameter: minor axis diameter) of the particles in the following Examples and Comparative Examples are values indicated by average values of values measured from electron micrographs,
The specific surface area was expressed by the value measured from the N ₂ gas adsorption according to the BET method.

The crystallite size refers to the size of a crystal particle measured by an X-ray diffraction method as a diameter of the crystal particle in a direction perpendicular to the (110) crystal plane. The measurement is based on a crystallinity measurement method. The values were calculated using the following Scherrer equation.

Here, β = half-width of the true diffraction peak obtained by subtracting the mechanical width by the apparatus K = Scherrer constant (0.9) λ = wavelength of characteristic X-ray θ = diffraction angle <Production of spindle-shaped goethite particle powder>
Example 1 1945 g of sodium propionate (5.0 mol% based on Fe) was introduced into a reaction vessel maintained in a non-oxidizing atmosphere by flowing N ₂ gas at a rate of 3.4 cm per second. After adding 1.35 mol / Na ₂ CO ₃ aqueous solution 600 containing
Aqueous ferrous sulfate 300 containing ²⁺ 1.35 mol / was added and mixed to produce FeCO ₃ at a temperature of 50 ° C.

In the suspension containing FeCO ₃ above, N ₂ gas is continuously supplied every second.
After blowing at a speed of 3.4 cm and holding at a temperature of 50 ° C. for 300 minutes, air was passed through the suspension containing FeCO ₃ at a temperature of 50 ° C. at a speed of 2.8 cm / sec for 5.5 hours to cause yellow-brown precipitate particles. Was generated. The pH during air ventilation is 8.5 to
It was 9.5.

The yellow-brown precipitate particles were separately washed with water, dried and pulverized by a conventional method.

The obtained tan particle powder was goethite as a result of X-ray diffraction. As is clear from the electron micrograph (× 30000) shown in FIG. 4, the average value of the major axis diameter was 0.31 μm and the axial ratio (major axis diameter). : Short axis diameter) The particles consisted of spindle-shaped particles having a ratio of 15.8: 1, and had a uniform particle size without dendritic particles.

Examples 2 to 7, Comparative Examples 1 to _{3 In} the formation reaction of FeCO ₃ or Fe-containing precipitate, the type, concentration and amount of the aqueous alkali carbonate solution, the presence or absence of the use of the aqueous alkali hydroxide solution, the type of propionic acid or a salt thereof, Except for changing the amount and the existence time, the type, concentration and amount of the ferrous salt aqueous solution, the temperature, the temperature and the time in the aging step and the temperature and the reaction time in the oxidation step,
Spindle-shaped goethite particle powder was obtained in the same manner as in Example 1.

Tables 1 and 2 show the main production conditions and various characteristics at this time.

The spindle-shaped goethite particles obtained in Examples 2 to 7 were all uniform in particle size and free of dendritic particles.

An electron micrograph (× 30000) of the spindle-shaped goethite particles obtained in Example 5 is shown in FIG.

The spindle-shaped goethite particle powder obtained in Comparative Example 1 has a large short axis diameter and an axial ratio (long axis diameter: short axis diameter) as shown in the electron micrograph (× 30000) in FIG. It was small.

Example 8 2.0 mol / of CoSO ₄ · 7H ₂ O aqueous solution 9.1, to produce a precipitate of Co (OH) ₂ was added to 10.0 mol / NaOH solution 3.65 with stirring. After discharging the supernatant of the Co (OH) ₂ precipitate as much as possible, a cobalt propionate solution having a total volume of 25 by adding 36.5 mol of propionic acid is prepared.

1.35 mol / Na ₂ C in a reaction vessel maintained in a non-oxidizing atmosphere by flowing N ₂ gas at a rate of 3.4 cm per second
After the O ₃ aqueous solution 600 was added, the ferrous sulfate aqueous solution 300 containing 1.35 mol / Fe ²⁺ was added and mixed, and FeCO ₃ was generated at a temperature of 48 ° C.

In the suspension containing FeCO ₃ , the previously prepared cobalt propionate solution is added.

The suspension containing FeCO ₃ obtained subsequently while blowing N ₂ gas at a rate per second 3.4cm, it was held for 300 minutes at a temperature 48 ° C., the suspension containing the FeCO _3, the temperature 48 Air was bubbled in at 2.8 cm per second at 5.1 ° C. for 5.1 hours to produce tan precipitated particles.

The pH during air ventilation was 8.4 to 9.5.

The yellow-brown precipitate particles are separated, washed with water, dried,
Crushed.

As a result of X-ray diffraction, the obtained yellow-brown particle powder was goethite, and the average value of the major axis diameter was 0.27 μm, and the axial ratio (major axis diameter:
The particles consisted of spindle-shaped particles (short axis diameter) of 14.8: 1, and had uniform particle sizes without dendritic particles.

Example 9 A spindle-shaped goethite particle powder was obtained in the same manner as in Example 8, except that 3.0 mol / of zinc propionate was used instead of 4.5 mol / of cobalt propionate.

Tables 1 and 2 show the main production conditions and various characteristics at this time.

The spindle-shaped goethite particles obtained in Example 9 had a uniform particle size and did not contain dendritic particles.

<Coating of Spindle-Shaped Goethite Particle Powder with Metal Compound> Examples 10 to 18, Comparative Examples 4 to 6; Example 10 Pressing of separately washed and washed spindle-shaped goethite particles obtained in Example 1 4000 g of the cake (corresponding to 1000 g of goethite particles having a spindle shape) was suspended in 30 pieces of water. At this time, the pH of the suspension was 9.1.

Next, 120 g of Al (NO ₃ ) ₃ .9H ₂ O was added to the above suspension so as to be 12.0% by weight based on goethite, and the mixture was stirred for 10 minutes.

Next, 211 g of Co (CH ₃ COO) ₂ .4H ₂ O was added to the above suspension so as to be 21.1% by weight with respect to goethite, followed by stirring for 10 minutes. At this time, the pH of the suspension was 5.03.

Further, after adjusting the pH to 9.5 by adding NaOH, washing with warm water, the suspension was added to goethite in 18.0.
A solution in which 180 g of H ₃ BO ₃ was dissolved so as to obtain a weight% was slowly added, followed by stirring for 15 minutes. Next, this suspension was separated by filtration with a filter press and dried to obtain goethite to which Al, Co, and B compounds had been applied.

The contents of Al, Co, and B in the obtained goethite were 0.71 wt% as Al, 4.24 wt% as Co, and 0.74 wt% as B, respectively.
%Met.

Examples 11 to 18, Comparative Examples 4 to 6 Types of particles to be treated, Al, Si, P, Ni, Mg, Co, B and
Example 10 with various changes in the type and amount of the Zn compound
Spindle-shaped goethite particles coated with a metal compound were obtained in the same manner as described above.

 Table 3 shows the main processing conditions at this time.

<Production of Spindle-Shaped Hematite Particle Powder> Example 19 The spindle-shaped goethite particles obtained in Example 11 were dehydrated in air at 300 ° C. to obtain spindle-shaped hematite particles.

Obtained hematite particles, as a result of electron microscopic observation,
Average long axis diameter 0.36μm, axial ratio (long axis diameter: short axis diameter) 1
5.0: 1.

<Production of spindle-shaped iron-based metal magnetic particle powder> Examples 20 to 29, Comparative Examples 7 to 9; Example 20 The Al, Co, and B compounds obtained in Example 10 were applied. 700 g of the spindle-shaped goethite particle powder was heated in air at 410 ° C. to obtain a spindle-shaped hematite particle powder on which Al, Co, and B compounds were adhered.

100 g of the spindle-shaped hematite particle powder having the spindle shape to which the Al, Co, and B compounds are adhered are charged into a rotary retort reduction vessel having a volume of about 10, and the H ₂ gas is supplied at a speed of 40 rpm while being rotated.
And reduced at a reduction temperature of 400 ° C.

The metal magnetic particle powder containing Al, Co, and B as a main component and obtained by reduction was immersed in a toluene solution and taken out so as not to cause rapid oxidation when taken out into the air. .

A part was taken out and a stable oxide film was formed on the surface while evaporating toluene.

The metal magnetic particle powder mainly composed of iron containing Al, Co and B is an electron micrograph (× 30000) shown in FIG.
As is clear from FIG. 2, the average major axis is 0.27 μm, the axial ratio (major axis diameter:
14.8: 1, specific surface area 49.8 m ² / g and crystallite size 16
The particle size was 0 °, and the particle size was uniform and fine without dendritic particles.

The magnetic characteristics are as follows: coercive force Hc1550Oe, saturation magnetization ss15
It was 6.9 emu / g.

Example 21-29, Comparative Examples 7-9 kinds of the starting material, coloration of the spindle in the same manner except that the heat treatment temperature and the type and reduction temperature, and H ₂ flow rate of non-reducing atmosphere was varied from Example 20 Thus, metal magnetic particle powder containing iron as a main component was obtained. Table 4 shows the main manufacturing conditions and various characteristics at this time.

The spindle-shaped iron-based metal magnetic particle powders obtained in Examples 20 to 29 were all uniform in particle size and free of dendritic particles.

FIG. 8 shows an electron micrograph (× 30000) of the metal magnetic particle powder containing iron as a main component obtained in Example 24.

[Effects of the Invention] According to the method for producing a spindle-shaped iron-based metal magnetic particle powder according to the present invention, the axial ratio (major axis diameter: short axis diameter) is obtained as described in the preceding embodiment. Is mainly composed of spindle-shaped iron that has a uniform grain size, no dendritic particles, a small crystallite size, an appropriate specific surface area and a high coercive force. Since metal magnetic particle powder as a component can be obtained, it is suitable as magnetic particle powder for high density recording and low noise level.

Further, in the production of a magnetic paint, when the metal magnetic particle powder containing iron as a main component according to the present invention is used, the dispersion in the vehicle is good, the filling property is extremely excellent, and the S / N
A preferable magnetic recording medium having a large ratio can be obtained.

[Brief description of the drawings]

FIG. 1 shows the relationship between the abundance of sodium propionate and the axial ratio (major axis diameter: short axis diameter) of spindle-shaped goethite particles. In FIG. 1, curves A, B, and C respectively have a major axis diameter of 0.3 to
Spindle-shaped goethite particles having a length of about 0.5 μm, a major axis of about 0.2 μm, and a major axis of about 0.1 μm. FIG. 2 shows the relationship between the BET specific surface area and the crystallite size of a spindle-shaped iron-based metal magnetic particle powder. In FIG. 2, the marks Δ and X are spindle-shaped iron-based metal magnetic particle powders obtained by the conventional method,
It is a metal magnetic particle powder containing iron as a main component in the present invention. FIG. 3 shows the relationship between the coercive force and the crystallite size of the spindle-shaped iron-based metal magnetic particle powder. In FIG. 3, symbols Δ and X indicate spindle-shaped iron-based metal magnetic particle powder obtained by the conventional method,
It is a metal magnetic particle powder containing iron as a main component in the present invention. FIGS. 4 to 6 are electron micrographs (× 30000) showing the particle structure of the spindle-shaped goethite particles obtained in Example 1, Example 5, and Comparative Example 1, respectively. 7 and 8 are electron micrographs (× 30000) showing the particle structure of the spindle-shaped iron-based metal magnetic particles obtained in Examples 20 and 24.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kenji Okinaka 4-1-2, Funariminami, Naka-ku, Hiroshima-shi, Hiroshima Inside Toda Kogyo Co., Ltd. 4-1-2 Minami Toda Kogyo Co., Ltd. Creative Center (72) Inventor Hiroshi Kawasaki 4-1-2 Funairi Minami, Naka-ku, Hiroshima-shi, Hiroshima Toda Kogyo Co., Ltd. Creative Center (72) Inventor Norimichi Nagai 4-1-2, Funairi Minami, Naka-ku, Hiroshima-shi, Hiroshima Pref. Toda Kogyo Co., Ltd. Creation Center Referee Chief Judge Shuichi Kageyama Judge Asayuki Nakamura Judge Judge Koji Amemiya (56) References Patent 2704537 (JP, B2) (58) ) Surveyed field (Int.Cl. ⁷ , DB name) B22F 9/22 H01F 1/06 C01G 49/08

Claims (2)

(57) [Claims] 1. A suspension containing a FeCO ₃ or Fe-containing precipitate obtained by reacting an aqueous alkali carbonate solution or an aqueous alkali carbonate / alkali hydroxide solution with an aqueous ferrous salt solution is aged in a non-oxidizing atmosphere. After that, when the oxygen-containing gas is passed through the suspension containing the FeCO ₃ or Fe-containing precipitate and oxidized to produce spindle-shaped goethite particles, the alkali carbonate aqueous solution and the alkali carbonate.
Propionic acid or a salt thereof is pre-existing in any of the suspensions containing the FeCO ₃ or Fe-containing precipitate before oxidizing by passing the aqueous alkali hydroxide solution, the ferrous salt aqueous solution and the oxygen-containing gas, and oxidizing them. By doing so, spindle-shaped goethite particles are generated, and the spindle-shaped goethite particles or the spindle-shaped hematite particles obtained by heating and dehydrating the spindle-shaped goethite particles in a reducing gas. A method for producing spindle-shaped iron-based metal magnetic particle powder, characterized by obtaining a spindle-shaped iron-based metal magnetic particle by heat reduction. 2. A suspension containing an FeCO ₃ or Fe-containing precipitate obtained by reacting an aqueous alkali carbonate solution or an aqueous alkali carbonate / alkali hydroxide solution with an aqueous ferrous salt solution is aged in a non-oxidizing atmosphere. After that, when the oxygen-containing gas is passed through the suspension containing the FeCO ₃ or Fe-containing precipitate and oxidized to produce spindle-shaped goethite particles, the alkali carbonate aqueous solution and the alkali carbonate.
Propionic acid or a salt thereof is pre-existing in any of the suspensions containing the FeCO ₃ or Fe-containing precipitate before oxidizing by passing the aqueous alkali hydroxide solution, the ferrous salt aqueous solution and the oxygen-containing gas, and oxidizing them. Spindle-shaped goethite particles are generated by keeping the spindle-shaped goethite particles or the spindle-shaped goethite particles obtained by heating and dehydrating the spindle-shaped goethite particles.Ni,
Al, Si, P, Co, Mg, coated with at least one metal compound selected from B and Zn, and then the particles or the particles in a non-reducing atmosphere at a temperature range of 300 to 800 ° C. Spindle-shaped iron obtained by heating and reducing spindle-shaped hematite particles obtained by a heat treatment in a reducing gas to obtain spindle-shaped iron-based metal magnetic particles; A method for producing metal magnetic particle powder containing as a main component.