JP3144683B2 - 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 (major axis: short) which is optimal as a magnetic particle powder having high output characteristics and a low noise level for high density recording. (Shaft diameter) is large, the particle size is uniform, dendritic particles are not mixed, and the crystallite size is small, the specific surface area is appropriately large, and
The present invention relates to a spindle-shaped iron-based metal magnetic particle powder having a high coercive force and an appropriate saturation magnetization and having excellent oxidation stability.

[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.

In order to increase the residual magnetic flux density Br, it is necessary that the saturation magnetization s of the magnetic particle powder be as large as possible.
It depends on the dispersibility of the magnetic particle powder in the vehicle, the orientation in the coating film, and the filling property.

As described above, iron-based metal magnetic particle powder has a higher saturation magnetization than iron oxide magnetic particle powder, but is a very fine particle of 1 μm or less. It has a very high activity, and after reduction, oxidizes the surface to form an oxide film and then reacts with oxygen in the air to significantly reduce magnetic properties, especially saturation magnetization, even if it is taken out into the air. become. Further, even after this is made into a paint and applied as a magnetic recording medium, the saturation magnetic flux density Bm and the residual magnetic flux density Br of the magnetic recording medium cause deterioration over time. The decrease in the saturation magnetization tends to increase as the metal magnetic particle powder containing iron as a main component becomes finer. Therefore, in recent years where the fineness of the magnetic particle powder is rapidly advancing, it is strongly required that a balance between the magnitude of the saturation magnetization and the oxidative stability is maintained, and a metal containing iron as a main component after reduction is required. A method for oxidizing the surface of magnetic particle powder has become an important issue.

Iron is a metal magnetic particle powder having a main component, generally, goethite particles as a starting material, hematite particles obtained by heating and dehydrating them, or particles containing a different metal other than iron in these 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 direct 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 difficult 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 axis length of the generated particles becomes smaller. 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, JP-A-62-259405 and JP-A-2-51429. However, the spindle-shaped iron-based metal magnetic particle powder obtained by these methods, as shown in FIG. 2 and FIG.
It is hard to say that the particles have a small crystallite size, an appropriate specific surface area and a high coercive force.

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

[Means for solving the problem]

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

That is, the present invention has a major axis diameter of 0.05 to 0.40 μm, a crystallite size of 130 to 170 °, a specific surface area of 30 to 60 m ² / g,
And the coercive force Hc is 1300 to 1700 Oe, and the saturation magnetization s
Is a spindle-shaped iron for magnetic recording containing one or more elements selected from the group consisting of Ni, Al, Si, P, Co, Mg, B, and Zn, which have 100 to 140 emu / g. It is a metal magnetic particle powder as a main component.

[Action]

First, the most important point in the present invention is that the major axis diameter according to the present invention is 0.05 to 0.40 μm, the crystallite size is 130 to 170 °, the specific surface area is 30 to 60 m ² / g, and the coercive force Hc Is 13
Metal magnetic particle powder containing iron as a main component having a saturation magnetization σs of 100 to 140 emu / g and having a large axial ratio (major axis diameter: short axis diameter), a uniform particle size, and a dendritic tree Spindle-shaped, which has no crystal particles, has a small crystallite size, has an appropriate specific surface area, has high coercive force and large saturation magnetization, and has excellent oxidation stability. This is the fact that it is a metal magnetic particle powder containing iron as a main component.

The spindle-shaped iron-based metal magnetic particle powder according to the present invention may be an aqueous alkali carbonate solution or an alkali carbonate.
After aging the suspension containing the FeCO ₃ or Fe-containing precipitate obtained by reacting the aqueous alkali hydroxide solution with the aqueous ferrous salt solution in a non-oxidizing atmosphere, containing the FeCO ₃ or Fe-containing precipitate In generating a spindle-shaped goethite particle powder by aerating and oxidizing an oxygen-containing gas into the suspension, the alkali carbonate aqueous solution, the alkali carbonate / alkali hydroxide aqueous solution, the ferrous salt aqueous solution, and oxygen Before the gas-containing gas is oxidized by passing it through the gas, any of the suspensions containing the FeCO ₃ or Fe-containing precipitate is allowed to have propionic acid or a salt thereof in advance to thereby produce spindle-shaped goethite particles. If necessary, 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, C o, the spindle-shaped goethite particles which have been applied with at least one metal compound selected from the group consisting of Mg, B, and Zn, and then have not been subjected to the application treatment or have been subjected to the application treatment, or these particles. In a non-reducing atmosphere, spindle-shaped hematite particles obtained by performing a heat treatment in a temperature range of 300 to 800 ° C. are heated and reduced in a reducing gas to form a spindle-shaped iron-based metal. After forming the magnetic particles, the spindle-shaped iron-based metal magnetic particles are positively subjected to a surface oxidation treatment in a mixed gas atmosphere of an oxygen-containing gas and a N ₂ gas at a temperature range of 30 to 200 ° C. Can be obtained by

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 inventor, as shown in a comparative example below, when ripening alone is performed without propionic acid or a salt thereof, and when propyne acid or a salt thereof is present without ripening. Since no spindle-shaped goethite particles having a large axial ratio (major axis diameter: short axis diameter) can be obtained, it is considered that this is due to a synergistic effect between the aging step and propionic acid or a salt thereof.

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 present inventor thinks as follows.

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.

On the other hand, the goethite particles having a spindle shape in the present invention 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, and thereby have an axial ratio (long axis diameter: short axis). Shaft diameter) is improved, and by controlling the growth of goethite particles in the width direction during the particle growth process, the growth of the primary particles in the width direction during reduction is suppressed,
As a result, it is considered that the crystallite size was reduced.

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.

Generally, the crystallite size, specific surface area, and the like vary depending on the reduction conditions, the particle size of the starting material, and the like, but as can be seen from FIGS. 2 and 3, the values are obtained by the conventional method. It can be seen that when goethite particles having a spindle shape are used as a starting material, it is difficult to balance them by reducing conditions and the like.

Next, conditions for implementing 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.

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

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.

If the temperature is lower than 35 ° C., the axial ratio (major axis diameter: short axis diameter) becomes small, and a spindle-shaped goethite particle powder having a large desired axial ratio (long axis diameter: short axis diameter) cannot be obtained. . Even when the temperature exceeds 60 ° C., spindle-shaped goethite particles having a large desired axial ratio (major axis diameter: short axis diameter) can be obtained, but there is no point in raising the aging temperature more than necessary.

When the time is less than 50 minutes, a spindle-shaped goethite particle powder having a large desired axial ratio (major axis diameter: short axis diameter) cannot be obtained. When the time exceeds 500 minutes, a spindle-shaped goethite particle powder having a large desired axial ratio (major axis diameter: short axis diameter) can be obtained, but there is no point in setting the time 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 spindle-shaped goethite particles having a large desired axial ratio (major axis diameter: short axis diameter).

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 performing agitation by the aerated gas, mechanical operation, or the like.

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.

If it is less than 0.1 mol%, it is not possible to obtain a spindle-shaped goethite particle powder having a large desired axial ratio (major axis diameter: short axis diameter). When it exceeds 10.0 mol%, a goethite particle powder having a spindle shape having a large desired axial ratio (major axis diameter: short axis diameter) can be obtained, but there is no point in adding more than necessary.

In the present invention, in order to prevent the deformation of the particle shape during heating and reduction and the crystallization between the particles, the starting material is previously N
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.

When the temperature exceeds 550 ° C., the reduction reaction proceeds rapidly, causing deformation of the particles and sintering between the particles.

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

Magnetic metal particles to the iron after the heat reduction at the present invention as a main component, by applying a surface oxidation treatment with a mixed temperature range of 30 to 200 ° C. in a gas atmosphere of oxygen-containing gas and N ₂ gas, stabilized Is done.

Ratio of the mixed gas is air: the ratio of N ₂ gas 1: 1000 0
Is preferable, and an appropriate mixing ratio may be selected in consideration of the processing temperature. Although the treatment may be carried out with a low proportion of air having a mixing ratio of less than 1: 1000, the progress of the oxidation reaction is prolonged.

Although there is no problem even if the treatment temperature is lower than 30 ° C., it is not preferable because the progress of the oxidation reaction is slow and the treatment time is long. If the temperature exceeds 200 ° C., the mixed gas ratio is not preferable because the oxidation reaction proceeds excessively and the magnetic properties, especially the saturation magnetization σs, decrease.

As the surface oxidation treatment method in the present invention, as shown in the following examples, after the heat generated by the oxidation reaction reaches a peak by the gas of the mixing ratio, the oxidation treatment is further repeated by sequentially increasing the ratio of the oxygen-containing gas. It is desirable to carry out the method in multiple stages.

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 metal magnetic particle powder having a small size, an appropriate specific surface area and a high coercive force.

[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 is a value obtained by expressing the size of a crystal particle measured by an X-ray diffraction method in the direction perpendicular to the (110) crystal plane.
The value was calculated from the line profile of the diffraction line of the surface using the following Scherrer equation.

Here, β = half value 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 Oxidation stability is the rate of change of saturation magnetization with time (%) ,
The saturation magnetization reduction rate (%) after standing for 4 days in an atmosphere at a temperature of 40 ° C. and a relative humidity of 70% was shown.

<Production of Spindle-Shaped Goethite Particle Powder> Example 1
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 The type, concentration and amount of an aqueous alkali carbonate solution in the reaction for producing FeCO ₃ or a Fe-containing precipitate, whether or not an aqueous alkali hydroxide solution was used, 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.

The cobalt propionate solution prepared in advance is added to the suspension containing FeCO ₃ .

The suspension containing FeCO ₃ obtained subsequently while blowing N ₂ gas at a rate per second 3.4c, after holding 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 Example 8 except that 30 mol / zinc propionate was used instead of 4.5 mol / cobalt propionate.
In the same manner as in the above, spindle-shaped goethite particles were obtained.

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

The spindle-shaped goethite particles obtained in Example 9 were all uniform and did not contain dendritic particles.

<Production of spindle-shaped hematite particles> Examples 10 to 1
1; Examples 10 to 11 Spindle-shaped hematite particles obtained by dehydrating the spindle-shaped goethite particles obtained in Examples 2 and 5 in air at 300 ° C were obtained.

Obtained hematite particles, as a result of electron microscopic observation,
The average long axis diameter is 0.36 μm, the axial ratio (long axis diameter: short axis diameter) is 15.0: 1, and the long axis diameter is 0.18 μm.
(Short axis diameter) was 11.0: 1.

<Adhering Treatment of Spindle-Shaped Goethite Particle Powder with Metal Compound> Examples 12 to 20, Comparative Examples 4 to 6; Example 12 Separately, the water-soluble spindle-shaped goethite particles obtained in Example 1 and having a weight of 10 kg were obtained. Was suspended in 200 of water. At this time, the pH of the suspension was 9.2.

Next, 1.3 kg of Al (NO ₃ ) ₃ .9H ₂ O was added to the above suspension so as to be 13.0% by weight with respect to goethite, and further Co (CH ₃ COO) was added so as to be 23.2% by weight with respect to goethite. ) ₂
The · 4H ₂ O2.32Kg, and stirred for 15 min after addition. At this time, the pH of the suspension was 4.70.

Next, NaOH was added to the above suspension to adjust the pH to 9.8, and then 150 g of oleic acid was added to 1.5 wt% with respect to goethite, followed by sufficient washing with hot water at 60 ° C. using a rotary filter. 15
1.5 kg of H ₃ BO ₃ was added to the mixture so as to obtain a weight%, and the mixture was stirred for 20 minutes.

Furthermore, it separates with a filter press, and is dried, Al, Co,
Goethite to which the B compound was applied was obtained. The contents of Al, Co, and B in the obtained goethite are each 0.1 as Al.
89 wt%, Co was 5.32 wt%, and B was 0.68 wt%.

Examples 13 to 20, Comparative Examples 4 to 6 Types of particles to be treated, Al, Si, P, Ni, Mg, Co, B and
Example 12 by variously changing the kind and the addition amount of the Zn compound.
Spindle-shaped goethite particles coated with a metal compound were obtained in the same manner as in the above.

 Table 3 shows the main processing conditions at this time.

<Manufacture of spindle-shaped iron-based metal magnetic particle powder> Examples 12 to 30, Comparative Examples 7 to 9; Example 21 The Al, Co, and B compounds obtained in Example 12 were applied. 5.0 Kg of the spindle-shaped goethite particle powder was heated in air at 400 ° C. to obtain a spindle-shaped hematite particle powder having Al, Co, and B compounds adhered thereto.

The above-mentioned Al, Co, and B compounds were charged into a fluidized bed heating reduction furnace with 2000 g of spindle-shaped hematite particle powder having a spindle shape attached thereto.
₂ Gas is introduced at a rate of 180 per minute, and a reduction temperature of 390
Time reduced.

After the reduction, after once replaced with N ₂ gas and H ₂ gas was cooled N ₂ gas to 50 ° C. while supplying 160 N / min. Then
0 air into N ₂ gas 160 N / min while maintaining the furnace temperature to 50 ° C..
A mixed gas of air and N ₂ gas mixed at a rate of 2 N / min was aerated. After the exothermic peak due to the oxidation reaction at the mixed gas ratio was observed, the air amount was increased to 0.4 N / min, and the air mixed ratio in the mixed gas was increased. In this way, after an exothermic peak due to an oxidation reaction at the mixed gas ratio is observed, the air mixing ratio is increased stepwise by a method of increasing the air ratio in the mixed gas, and finally air 1.2 N / mi
The oxidation treatment was continued with a mixed gas of n and N ₂ gas at a rate of 160 N / min, and the oxidation treatment was performed until the heat generated by the oxidation disappeared and the temperature of the product reached approximately 50 ° C., which was almost the same as the furnace temperature. During this time, the temperature of the article reached a maximum of 75 ° C.

Subsequently, while maintaining the furnace temperature at 50 ° C. and the N ₂ gas amount at 160 N / min, gradually increase the air mixing ratio, and finally reduce the air amount.
20 N / min. No exotherm was observed during this time.

Further, the mixture was cooled to room temperature while passing a mixed gas of 40 N / min of air and 140 N / min of N ₂ gas.

Once the air flow rate was set to 0 / min and the atmosphere was replaced with N ₂ gas, the gas was obtained in this manner. Spindle-shaped iron-based metal particle powder having an oxide film formed on the surface was recovered.

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 0.28 μm, the axial ratio (major axis diameter:
15.0: 1, specific surface area 49.2 m ² / g and crystallite size 15
The particle size was 5 mm, and the particle size was uniform and fine without dendritic particles.

The magnetic characteristics are as follows: coercive force Hc1530Oe, saturation magnetization σs13
5.4 emu / g and Δσs / σs were −4.2%.

Examples 22 to 30, Comparative Examples 7 to 9 The same as Example 21 except that the type of the starting material, the type of the heat treatment temperature and the type of the non-reducing atmosphere, and the reduction temperature, the H ₂ flow rate, and the surface oxidation treatment conditions were variously changed. Thus, a spindle-shaped iron-based metal magnetic particle powder was obtained.

 Table 4 shows the main manufacturing conditions and various characteristics at this time.

Each of the spindle-shaped iron-based metal magnetic particle powders obtained in Examples 22 to 30 had a uniform particle size and did not contain dendritic particles.

FIG. 8 shows an electron micrograph (× 30000) of the metal magnetic particle powder containing iron as a main component obtained in Example 26.

The reduced iron-based metal magnetic particle powder in each of Comparative Examples 7 to 9 was immersed in a toluene solution so as not to cause rapid oxidation when taken out into the air. Was. For the measurement, a part was taken out and a stable oxide film was formed on the surface while evaporating toluene. Japanese Patent Application Laid-Open No. 62-259405 discloses a method of obtaining a spindle-shaped iron-based metal magnetic particle powder having a uniform particle size, containing no dendritic particles, and having a high coercive force.
Examples 1 and 2 and Comparative Example 1 described in Japanese Patent Application Laid-Open Publication No. H10-26095 were additionally tested, and the results of measuring the crystallite size of the obtained metal magnetic particle powder are shown in Comparative Examples 10 to 12 below.

Comparative Example 10 The reaction vessel of 15 was supplied with a concentration of 1 mol /
Of ammonium carbonate aqueous solution 5 is stirred.

To this solution, a 0.4 mol / concentration aqueous ferrous sulfate solution 5 at a temperature of 40 ° C. is slowly dropped.

Next, the resulting suspension of ferrous carbonate was kept at 40 ° C. for 30 minutes, and then air was blown at 40 ° C. at a rate of 15 / min to obtain goethite. The oxidation reaction was for 2 hours and 40 minutes.

The resulting goethite was spindle-shaped, uniform particles having a major axis diameter of 0.15 μm and an axial ratio (major axis diameter: minor axis diameter) of 6.

After thoroughly washing 100 g of this goethite, add 2 pH 3 water
Disperse with.

To this dispersion, 127 ml of an aqueous solution of nickel chloride having a concentration of 0.2 mol / was added, and the pH was gradually adjusted to 11 with stirring. Further, 400 ml of an aqueous solution of water glass having a concentration of 0.2 mol / was added, and the mixture was sufficiently stirred and adjusted to pH9.

Next, washing, filtration and drying were performed to obtain goethite having nickel / silicon adhesion amounts of 2.1 atomic% and a Si / Fe ratio of 5 atomic%, respectively.

This goethite was reduced at 420 ° C. in a hydrogen stream to obtain magnetic iron powder.

As a result of observation with an electron microscope, this magnetic iron powder had inherited the spindle shape of goethite. Its characteristics are major axis diameter 0.12μm,
Axial ratio 5.5, coercive force [Hc] 1516 Oe, saturation magnetization [σs] 144 em
u / g, the specific surface area [SSA] was 55.1 m ² / g, and the crystallite size was 210 °.

Comparative Example 11 100 g of goethite produced in the same manner as in Comparative Example 10 was sufficiently washed with water, and then dispersed in water 2 at pH 3.

Into this dispersion, 127 ml of a 0.2 mol / concentration aqueous nickel chloride solution and a 0.2 mol / concentration aqueous aluminum chloride solution
216 ml of the mixture was gradually adjusted to pH 11 with sufficient stirring, and 240 ml of a 0.2 mol / water solution of water glass was added.

Next, washing, filtration, and drying were performed, and the adhesion amounts of nickel, aluminum, and silicon were 2.0 atomic% in a Ni / Fe ratio,
A goethite having a 2.7 atomic% / Fe ratio and a 2.9 atomic% Si / Fe ratio was obtained.

This goethite was reduced at 400 ° C. in a hydrogen stream to obtain magnetic iron powder.

As a result of observation with an electron microscope, this magnetic iron powder had inherited the spindle shape of goethite. Its characteristic is that the major axis diameter is 0.12μ
m, axial ratio 5.5, Hc1520Oe, σs137emu / g, specific surface area 59.1m ²
/ g, and the crystallite size was 202 °.

Comparative Example 12 Comparative Example except that sodium carbonate was used instead of ammonium carbonate
A game site was obtained in the same manner as 10.

The obtained goethite was uniform particles having a major axis diameter of 0.2 and an axial ratio of 8.

This goethite was treated in the same manner as in Comparative Example 10 so that the amounts of nickel and silicon deposited were 2.0 atomic% in a Ni / Fe ratio and 2.0% in Si / F, respectively.
A game site with an e ratio of 4.9 atomic% was obtained.

This goethite was reduced at 420 ° C. in a hydrogen stream to obtain magnetic iron powder. As a result of observation with an electron microscope, this magnetic iron powder had inherited the spindle shape of goethite.

Its characteristics are major axis diameter 0.16μm, axial ratio 7.3, Hc1560Oe,
s143emu / g, specific surface area 52.2 m ² / g, and crystallite size was 208 °.

[Effects of the Invention] The spindle-shaped iron-based metal magnetic particle powder according to the present invention has a large axial ratio (long axis diameter: short axis diameter) and a uniform particle size, as described in the above Examples. And dendritic particles are not mixed, and the crystallite size is small, the specific surface area of an appropriate size, and has a high coercive force and a saturation magnetization of an appropriate size, Since it is a spindle-shaped iron-based metal magnetic particle powder having excellent oxidation stability, it is suitable as a 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. FIGS. 7 and 8 are electron micrographs (× 30000) showing the particle structure of the spindle-shaped iron-based metal magnetic particles obtained in Examples 21 and 26.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kenji Okinaka 4-1-2, Funariminami, Naka-ku, Hiroshima-shi, Hiroshima Inside Toda Industries Co., Ltd. Creative Center (72) Koji Mori Funairi, Naka-ku, Hiroshima-shi, Hiroshima 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 Referee Masato Hariya Referee Hideo Taguchi Referee Kazuyuki Shimotano Referee Kazuyuki Shimono (56) References JP 62-259405 (JP) JP-A-53-76957 (JP, A) JP-A-59-232922 (JP, A) JP-A-2-156001 (JP, A) JP-A-50-80999 (JP, A) Patent 2 640817 (JP, B1) JP-B-60-11446 (JP, B2) Published by General Electronic Research, "Magnetic Recording Media General Materials" (Showa 60) p123

Claims (1)

(57) [Claims] 1. A major axis diameter of 0.05 to 0.40 μm and a crystallite size of 130
Å170 °, the specific surface area is 30-60 m ² / g, and the coercive force Hc is 1300-1700 Oe, and the saturation magnetization s is
Ni, Al, Si, P, Co, Mg, B and Z at 100-140 emu / g
2. Spindle-shaped iron-based metallic magnetic particle powder for magnetic recording, containing one or more of the elements selected from n.