JPH0461302A - Metal magnetic particle powder mainly made of spindle type iron - Google Patents

Abstract

PURPOSE:To ensure high coercive force and large saturation magnetization and improve stability of oxidation by using a spindle type iron, as the main element, including one or more kinds of elements selected from Ni, Al, Si, P, Co, Mg, B and Zn having the predetermined characteristic. CONSTITUTION:Metal magnetic particle powder mainly made of iron showing long axis diameter of 0.05 to 0.40mum, crystalline size of 110 to 180Angstrom , specific surface area of 30 to 60m<2>/g, coercive force Hc of 1300 to 1700Oe and saturated magnetization sigmas of 100 to 140emu/g has a large axial ratio (long axis diameter: short axis diameter), uniform particle size and does not allow mixture of dendritic particles. Moreover, the main material is a spindle iron having excellent stability of oxidation ensuring small crystalline size, adequate specific area, high coercive force and large saturation magnetization.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is directed to an axial ratio (long axis diameter: short The axial diameter) is large, the particle size is uniform,
It does not contain dendritic particles, has a small crystallite size, has an appropriate specific surface area, has a high coercive force and an appropriate saturation magnetization, and has good oxidation stability. This invention relates to metal magnetic particles whose main component is iron and exhibits an excellent spindle shape.

[Conventional technology]

In recent years, magnetic recording and playback devices for video and audio have become increasingly compact and lightweight. VTRs are being actively developed with the aim of making them smaller and lighter. On the other hand, demands for higher performance and higher recording density for magnetic tape, which is a magnetic recording medium, are increasing.

In other words, magnetic recording media are required to have high image quality, high output characteristics, especially improved frequency characteristics, and lower noise levels. It is necessary to improve the filling properties and the smoothness of the tape surface, and there is a demand for an improvement in the S/N ratio.

These characteristics of magnetic recording media are closely related to the magnetic particles used in magnetic recording media.
In recent years, metal magnetic particles whose main component is iron, which have higher coercive force and larger saturation magnetization than conventional iron oxide magnetic particles, have attracted attention, and have been published in Digital Audiotapes (DAT), 8. It has been put to practical use in magnetic recording media such as video tapes, Hi-8 tapes, and video floppies. However, there is a strong desire to further improve the characteristics of these metal magnetic particles whose main component is iron.

The relationship between the characteristics of the magnetic recording medium and the characteristics of the magnetic particles used will now be detailed as follows.

In order to obtain high image quality as a magnetic recording medium for video,
Nikkei Electronics (1976) May 3rd issue No. 82
~As is clear from the description on page 105, ■Video S/N
Improvements are required in the ratio, (1) chroma S/N ratio, and (2) video frequency characteristics.

In order to improve the video S/N ratio, it is necessary to make the magnetic particles finer, improve their dispersibility in the vehicle, improve their orientation and filling properties in the coating film, and improve the surface of the magnetic recording medium. It is important to improve 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 this purpose, as is clear from the above description, it is necessary to reduce the magnetic particle powder used. It is known that a method of reducing the particle size of is effective.

The value of the specific surface area of the magnetic particles is often used as one way to express the particle size of the magnetic particles, but the noise level caused by the magnetic recording medium tends to decrease as the specific surface area of the magnetic particles used increases. It is also generally known that there are

This phenomenon is shown, for example, in ``Figure 1 j'' of JP-A No. 58-159231. ``Figure 1'' shows the specific surface area of particles and noise in a magnetic tape obtained using metal magnetic particle powder. It is a diagram showing the relationship with the level, and the noise level decreases linearly as the specific surface area of particles increases.

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 particles 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, which increases the dispersibility of the magnetic particles in the vehicle, the orientation and filling properties in the coating film. This makes it difficult to obtain surface smoothness, which causes a decrease in the video S/N ratio.In general, it may not be preferable to increase only the specific surface area of the magnetic particles. Therefore, it is important to select an optimal specific surface area in consideration of the dispersion technology of the magnetic particles in the vehicle.

On the other hand, regarding the noise of metal magnetic particles, it is known that there is a relationship with the crystallite size of the metal magnetic particles.

This phenomenon can be seen, for example, in the first article of ``Comprehensive Collection of Recording Media Responsibilities, Published by Sogo Denshi Research'' (August 15, 1985).
38j etc. on page 23.

"Figure 38" is a diagram showing the correlation between particle crystallite size and noise in a magnetic tape obtained using metal magnetic particle powder containing iron as a main component. The smaller the particle crystallite size, the smaller the noise. It shows what will happen.

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

As mentioned above, in order to improve the video S/N ratio and reduce the noise level, the crystallite size of the magnetic particles should be as small as possible, and the specific surface area should be an appropriate size, especially 30~ 60rrf/g, the particle size is uniform, and dendritic particles are not mixed, so the magnetic particle powder has excellent dispersibility in the vehicle, orientation in the coating film, and filling property. It is required that the

Next, in order to improve chroma S/H, it is important to improve the surface properties and degree of orientation of the magnetic recording medium, and for this purpose, magnetic particle powder with good dispersibility and orientation is recommended. Such magnetic particles must have a large axial ratio (long axis diameter: short axis diameter), uniform particle size, no dendritic particles, and a specific surface area of an appropriate size. You are required to have one.

Furthermore, in order to improve the video frequency characteristics, it is necessary that the magnetic recording medium has a high coercive force Hc and a high residual magnetic flux density Br.

In order to increase the coercive force Hc of a magnetic recording medium, it is required that the coercive force (1c) of magnetic particles is as high as possible. The coercive force of magnetic particles used in such applications is required to be approximately 13,000e to 17,000c.

The coercive force of magnetic particles is generally caused by its shape anisotropy, so the coercive force tends to increase as the axial ratio (major axis diameter: minor axis diameter) of the particles increases. Since the coercive force tends to decrease as the crystallite size decreases,
If the crystallite size is reduced in order to reduce the noise level in order to improve the video S/N ratio as described above, the coercive force decreases, making it difficult to improve the video frequency characteristics. Therefore, there is a strong need for magnetic particles having a small crystallite size while maintaining the coercive force of the magnetic particles as high as possible.

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

As mentioned above, the metal magnetic particle powder whose main component is iron is
It has a larger saturation magnetization than iron oxide magnetic particles, but since it is a very fine particle of less than 1 μm, the surface activity of the particle is very high, and after reduction, the surface oxidizes and forms an oxide film. Even if it is taken out into the air after being formed, it will react with oxygen in the air, resulting in a significant decrease in magnetic properties, especially saturation magnetization. Further, even after this is made into a paint and applied as a magnetic recording medium, the saturation magnetic flux density Bm and residual magnetic flux density Br of the magnetic recording medium deteriorate over time. The decrease in saturation magnetization tends to increase as the metal magnetic particles containing iron as a main component become finer. Therefore, in these days when magnetic particles are rapidly becoming finer, there is a strong demand for a balance between the size of saturation magnetization and oxidation stability. The surface oxidation method of magnetic particles has become an important issue.

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

Conventionally, as a method for producing goethite particle powder, which is a starting material, a suspension containing ferrous hydroxide obtained by adding an equivalent or more aqueous alkali hydroxide solution to a ferrous salt aqueous solution is mixed with p) 111 or more. A method of generating acicular goethite particles by conducting an oxidation reaction by passing an oxygen-containing gas at a temperature of 80° C. or lower, and a method of producing acicular goethite particles using a ferrous salt aqueous solution and an alkali carbonate aqueous solution or an alkali carbonate/alkali hydroxide aqueous solution. A method is known in which spindle-shaped goethite particles are produced by carrying out an oxidation reaction by passing an oxygen-containing gas through a suspension containing FeCO obtained by the reaction or a Fe-containing precipitate. .

[Problem to be solved by the invention]

The axial ratio (long axis diameter: short axis diameter) is large, the particle size is uniform, there are no dendritic particles mixed in, the crystallite size is small, and it has an appropriate specific surface area and high coercive force. At present, metal magnetic particles containing iron as a main component are most in demand, but the acicular goethite particles obtained by the former known method have a low axial ratio (length). Although it has a large axis diameter (short axis diameter) of 10 or more, it contains dendritic particles, and in terms of particle size,
It is difficult to say that the particles have a uniform particle size, and the metal magnetic particles whose main component is iron obtained by thermal reduction of the acicular goethite particles have an axial ratio (major axis diameter: minor axis diameter). Although it has a high coercive force due to its large size, it is difficult to say that it has a uniform particle size because dendritic particles are mixed therein.

The spindle-shaped goethite particles obtained by the latter method among the above-mentioned known methods have uniform particle size, and
Although these particles do not contain dendritic particles, they have the disadvantage that particles with a large axial ratio (major axis diameter: short axis diameter) are difficult to generate. It tends to become more noticeable as it gets smaller. The metal magnetic particles whose main component is iron obtained by heating and reducing these spindle-shaped goethite particles have uniform particle size, and
Although the absence of dendritic particles allows for excellent dispersibility in the vehicle, orientation and filling properties in the coating film, the small axial ratio (major axis diameter: minor axis diameter) results in high retention. It has the disadvantage that it is difficult to obtain particles with magnetic force.

Furthermore, studies on improving the axial ratio as described below have made it possible to obtain particles with a relatively high coercive force, but these particles have the drawback of large crystallite size. A metal whose main component is iron, which has uniform particle size, does not contain dendritic particles, has a high coercive force, has a small crystallite size, and has an appropriate specific surface area. Magnetic particles have not yet been obtained.

Conventionally, spindle-shaped goethite particles were used to obtain spindle-shaped gold Ili magnetic particles whose main component was iron, which had uniform particle size, no dendritic particles, and high coercive force. Various methods have been attempted to increase the axial ratio (long axis diameter: short axis diameter) of
32922, JP 60-21307, JP 60-21819, JP 60-36603
There are methods described in Japanese Patent Application Laid-open No. 2-51429 and spindle-shaped metal magnetic particles mainly composed of iron obtained by these methods as shown in FIGS. 2 and 3 below.
As shown in the figure, the crystallite size is small, and it is difficult to say that the particles have an appropriate specific surface area and a high coercive force.

Therefore, the present invention has a large axial ratio (long axis diameter: short axis diameter),
It has a uniform grain size and no dendritic particles, a small crystallite size, an appropriate specific surface area, a high coercive force and a large saturation magnetization, and is oxidation stable. The technical problem is to obtain spindle-shaped metal magnetic particles mainly composed of iron, which have excellent properties.

[Means for Solving the Problems] The above technical problems can be achieved by the present invention as follows.

That is, the present invention has a major axis diameter of 0.05 to 0.40μ, a crystallite size of 110 to 180, and a specific surface area of 30 to 30.
60rrr/g, and coercive force Hc is 1300~
17000e, and the saturation magnetization σs is 100 to 140
emu/g Ni, ^1, Si, P, Co
, Mg, B, and Zn, and is spindle-shaped metal magnetic particle powder mainly composed of iron.

[For production]

First, the most important point in the present invention is that the major axis diameter of the present invention is 0.05 to 0.40 μm and the crystallite size is 110 to 1
80 people, the specific surface area is 30 to 60 volts, and the coercive force l (C is 1300 to 17000e,
Metal magnetic particle powder mainly composed of iron with a saturation magnetization σS of 100 to 140 e+wu/g has a large axial ratio (long axis diameter: short axis diameter), uniform particle size, and contains dendritic particles. It mainly consists of spindle-shaped iron, which has a small crystallite size, an appropriate specific surface area, high coercive force, large saturation magnetization, and excellent oxidation stability. The fact is that it is a metal magnetic particle powder as a component.

The spindle-shaped metal magnetic particle powder containing iron as a main component according to the present invention is obtained by reacting an aqueous alkali carbonate solution or an alkali carbonate/alkali hydroxide solution with an aqueous ferrous salt solution, such as PeCO5 or a Pe-containing precipitate. After aging the suspension containing FeCO2 or P in a non-oxidizing atmosphere,
In producing spindle-shaped goethite particle powder by passing an oxygen-containing gas into the suspension containing the e-containing precipitate for oxidation, the alkali carbonate aqueous solution, the alkali carbonate/alkali hydroxide aqueous solution, the alkali carbonate/alkali hydroxide aqueous solution, the - the pe before being oxidized by passing through an aqueous iron salt solution and an oxygen-containing gas;
either to a suspension containing cOs or a Fe-containing precipitate;
Goethite particles exhibiting a spindle shape are produced by pre-existing propionic acid or a salt thereof, and if necessary, the goethite particles exhibiting the spindle shape or the spindle shape obtained by heating and dehydrating the goethite particles exhibiting the spindle shape. Hematite particles exhibiting Ni, ^I, St, P
, Co, Mg, B, and Zn, and then the spindle-shaped goethite particles or The spindle-shaped hematite particles obtained by heat-treating these particles at a temperature range of 300 to 800°C in a non-reducing atmosphere are heated and reduced in a reducing gas to produce mainly spindle-shaped iron. After forming the metal magnetic particles as a component, the spindle-shaped metal magnetic particles mainly composed of iron are actively surface-treated in a mixed gas atmosphere of oxygen-containing gas and N2 gas in a temperature range of 30 to 200°C. It can be obtained by oxidation treatment.

In the present invention, the reason why spindle-shaped goethite particles with a large axial ratio (major axis diameter: minor axis diameter) are obtained is that the present inventors explained that propionic acid or its salt is present as shown in the comparative example below. Goethite particles exhibiting a spindle shape with a large axial ratio (major axis diameter: minor axis diameter) in both cases, when only ripening is performed without ripening, and when propionic acid or its salt is present without ripening. This is thought to be due to the synergistic effect of the aging process and propionic acid or its salt.

In the present invention, the reason why iron-based magnetic metal particles having an appropriate specific surface area and high coercive force despite having a small crystallite size can be obtained is as follows. thinking.

Conventionally, after obtaining a suspension containing PeCO2 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,
When the spindle-shaped goethite particles obtained by oxidizing the FeCO5 or Fe-containing precipitate-containing suspension by passing an oxygen-containing gas through the suspension, careful observation with an electron microscope reveals that elongated primary particles form straw. The crystals grow in a bundled manner, and as the number of primary particles increases, the width direction of the goethite particles grows larger, resulting in a spindle shape with a small axial ratio (major axis diameter: minor axis diameter). Goethite particles are easily obtained.

Moreover, when the spindle-shaped goethite particles are subjected to sintering prevention treatment and heated in a reducing gas to obtain metal magnetic particles, the spindle-shaped goethite particles become elongated like bundles of straw. Because crystal growth between primary particles progresses,
The crystallite size of the obtained metal magnetic particle powder was Fe (
Only crystallite sizes larger than those of metal magnetic particles using acicular goethite obtained by the oxidation reaction of OH) t as a starting material have been obtained.

On the other hand, the goethite particles exhibiting a spindle shape in the present invention have an axial ratio (major axis diameter: short axis diameter) due to the synergistic effect of the aging process and propionic acid or its salt. 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, resulting in a smaller crystallite size. Considering this, some of the many experimental examples conducted by the present inventor will be extracted and explained as follows.

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

That is, sodium propionate is 0 to 10.
Example 1 and Example 5 described below except that 0 mol% was present.
The graph shows the relationship between the axial ratio (long axis diameter: short axis diameter) of spindle-shaped goethite particles obtained in the same manner as in each example of Example 7 and the amount of sodium propionate present.

In FIG. 1, curves A, B, and C each have a major axis diameter of 0.3 to
0.5 μm, major axis diameter approximately 0.2 μm, and major axis diameter 0.5 μm.
It is a goethite particle powder exhibiting a spindle shape of about 1 μm.

As is clear from FIG. 1, as the amount of sodium propionate increases, the axial ratio (long axis diameter: short axis diameter) of the resulting spindle-shaped goethite particles increases, which is around 1.

Conventionally, in a method of producing spindle-shaped goethite particle powder by passing an oxygen-containing gas through a suspension containing FeCO5 obtained by reacting an aqueous alkali carbonate solution and an aqueous ferrous salt solution to oxidize the suspension. There is a method disclosed in JP-A-50-80999 in which carboxylic acids such as citric acid, tartaric acid, and their salts are present, but in this case, "a rotating spherical body with a shape ranging from a spindle shape to a shape close to a sphere" is used. Goethite particles with a small axial ratio (major axis diameter: minor axis diameter) are obtained, which is completely different from the action and effect of propionic acid or its salt in the present invention. It is.

FIG. 2 shows the relationship between the BET specific surface area and the crystallite size of spindle-shaped metal magnetic particles whose main component is iron.

In FIG. 2, the marks Δ and × are spindle-shaped metal magnetic particle powders containing iron as a main component obtained by the conventional method, respectively. This is a metal magnetic particle powder containing iron as a main component obtained by the method described in JP-A-2-51429.

In addition, the symbol ◯ indicates the spindle-shaped metal magnetic particle powder containing iron as a main component according to the present invention.

Although the spindle-shaped star metal magnetic particle powder of the present invention is mainly composed of iron, the crystallite size is smaller than that of the spindle-shaped metal magnetic particle powder mainly composed of iron obtained by conventional methods. First, it has a specific surface area of an appropriate size.

FIG. 3 shows the relationship between the coercive force and the crystallite size of spindle-shaped metal magnetic particles whose main component is iron.

In FIG. 3, marks △ and This is a metal magnetic particle powder containing iron as a main component obtained by the method described in JP-A-2-51429.

Further, the symbol O indicates a spindle-shaped metal magnetic particle powder containing iron as a main component according to the present invention.

The spindle-shaped metal magnetic particles according to the present invention have a higher coercive force despite having a smaller crystallite size than the spindle-shaped metal particles mainly composed of iron obtained by conventional methods. It is something.

In general, the values of crystallite size, specific surface area, etc. change depending on the reduction conditions, particle size of the starting material, etc., but as can be seen from Figures 2 and 3, the values obtained by the conventional method When spindle-shaped goethite particles are used as a starting material, it is found that it is difficult to maintain a balance depending on reduction conditions and the like.

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

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

Examples of the aqueous alkali carbonate solution in the present invention include aqueous solutions of sodium carbonate, potassium carbonate, ammonium carbonate, etc.; examples of the aqueous alkali hydroxide solution include sodium hydroxide,
Aqueous solutions such as potassium hydroxide can be used.

Aging in the present invention is carried out in an inert atmosphere by passing an inert gas such as N gas into the liquid, and is carried out while stirring using the aeration gas or mechanical operation.

In the present invention, the aging temperature of the suspension containing FeCO3 or Pe-containing precipitate is 35 to 60°C, and the aging time is 50 to 50°C.
00 minutes.

If the temperature is lower than 35°C, the axial ratio (long axis diameter: short axis diameter) will be small, and it will not be possible to obtain spindle-shaped goethite particles with the desired axial ratio (long axis diameter - short axis diameter). . 60℃
Even when exceeding the target axial ratio (major axis diameter: short axis diameter)
Although it is possible to obtain goethite particles having a large spindle shape, there is no point in raising the ripening temperature more than necessary.

If the time is less than 50 minutes, spindle-shaped goethite particles with a large desired axial ratio (long axis diameter: short axis diameter) cannot be obtained; if the time exceeds 500 minutes, the desired axial ratio cannot be obtained. Although it is possible to obtain goethite particle powder exhibiting a spindle shape with a large (major axis diameter: minor axis diameter), there is no point in making the process longer than necessary.

The pH in the present invention is 7-11. less than 7 or 1
If it exceeds 1, it is impossible to obtain spindle-shaped goethite particles.

The reaction temperature during oxidation of the goethite production reaction of the present invention is 35 to 70°C. If the temperature is less than 35° C., goethite particles having a spindle shape with a desired axial ratio (long axis diameter: short axis diameter) cannot be obtained.

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

The oxidation means during the oxidation of the goethite production reaction of the present invention is carried out by aerating an oxygen-containing gas (for example, air) into the liquid, and is carried out while stirring by the aerating gas or mechanical operation.

In the present invention, propionic acid or its salt has an axial ratio (long axis diameter: short axis diameter) of spindle-shaped goethite particles to be produced.
Since it is involved in the short axis diameter and short axis diameter, it is necessary to make it present in the reaction at a stage before oxidation by aerating oxygen-containing gas. It can be present at any stage in the suspension containing the FeC0 or Pe-containing precipitate before oxidation by passing an aqueous iron salt solution and an oxygen-containing gas through it.

Salts of propionic acid in the present invention include sodium propionate, potassium propionate, calcium propionate, zinc propionate, cobalt propionate,
Magnesium propionate L and the like can be used.

The amount of propionic acid or its salt in the present invention is F
It is in the range of 0.1 to 10.0 mol% with respect to e.

If the amount is less than 0.1 mol%, it is impossible to obtain goethite particles having a spindle shape with a large axial ratio (major axis diameter: minor axis diameter).If it exceeds io, o mol%, Although it is also possible to obtain spindle-shaped goethite particles with a desired axial ratio (major axis diameter: minor axis diameter), 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 thermal reduction, the starting material is made of Ni in advance.
, Al, Si, , P , , Co, Jig, , B, and Zn. These metal compounds not only have a sintering prevention effect but also , also has the function of controlling the reduction rate, so it is preferable to use them in combination as necessary.

The starting material coated with the above metal compound can be reduced as it is to obtain the desired metal magnetic particle powder whose main component is iron, but it is possible to control the magnetic properties and powder properties, and to control the shape. For control purposes, it is preferable to perform heat treatment in advance in a non-reducing gas atmosphere by a conventional method prior to reduction.

The heat treatment in the non-reducing gas atmosphere includes air,
It can be carried out under a flow of oxygen gas or nitrogen gas at a temperature in the range of 300 to 800°C, and the heat treatment temperature can be appropriately selected depending on the requirements of the metal compound used for the deposition treatment of the starting material particles. preferable.

If the temperature exceeds 800''C, deformation of the particles and sintering of the particles and each other will occur.

The temperature range of thermal reduction in the present invention is 300 to 550
°C is preferred.

If the temperature exceeds 550° C., the reduction reaction rapidly progresses, causing deformation of the particles and sintering of the particles and each other.

If the temperature is less than 300°C, the reduction reaction progresses slowly and takes a long time.

In the present invention, the metal magnetic particles mainly composed of iron after thermal reduction are stabilized by surface oxidation treatment at a temperature range of 30 to 200°C in a mixed gas atmosphere of oxygen-containing gas and N2 gas. be done.

The ratio of mixed gas is air:N2 gas ratio 1=100
A range of 0 to 120 is preferable, and an appropriate mixing ratio may be selected in consideration of the processing temperature. Mixing ratio is 1:10
Although the treatment may be performed with a low air amount of less than 0.00, the oxidation reaction will take a long time to proceed.

There is no problem if the processing temperature is less than 30"C, but
This is not preferable because the oxidation reaction progresses slowly and the treatment time becomes long. If the temperature exceeds 200"C, the oxidation reaction proceeds excessively in the case of the above-mentioned mixed gas ratio, resulting in a decrease in magnetic properties, particularly saturation magnetization σS, which is not preferable.

In the surface oxidation treatment method of the present invention, as shown in the examples below, after the heat generated by the oxidation reaction by the gas at the above-mentioned mixing ratio reaches its peak, the oxidation treatment is repeated by increasing the ratio of the oxygen-containing gas one after another. It is desirable to carry out the method in multiple steps.

In the present invention, in order to improve various properties of metal magnetic particles whose main component is iron, Co and Ni, which are usually added when producing goethite particles as a starting material, are used.
, Cr, ZnSAl, PIn, and other metals other than Fe can be added, and in this case as well, the axial ratio (long axis diameter: short axis diameter) targeted by the present invention is large, and the crystallite size is small. It is possible to obtain goethite particles having a small surface area, an appropriate specific surface area, and a high coercive force.

〔Example] Next, the present invention will be explained with reference to Examples and Comparative Examples.

In addition, the long sleeve diameter of particles in the following examples and comparative examples,
The axial ratio (long axis diameter: short axis diameter) is the average value of values measured from electron micrographs, and the specific surface area is the value measured from the amount of N2 gas adsorbed by the BET method. Ta.

Crystallite size is the size of crystal grains measured by X-ray diffraction method expressed as the diameter of crystal grains in the direction perpendicular to the (110) crystal plane;
) from the line profile of the diffraction line of the plane using the following Scherrer equation.

β cos θ However, β = half-width of the true diffraction peak after subtracting the mechanical width due to the device - Scherrer constant (0,9) λ = wavelength of characteristic X-ray θ = diffraction angle Oxidation stability is the change in saturation magnetization over time It is expressed as a rate of change (%), and it is expressed as a rate of decrease in saturation magnetization (%) after being left for 4 days in an atmosphere with a temperature of 40'C1 and a relative humidity of 70%.

<Production of spindle-shaped goethite particle powder Example 1
-9, Comparative Examples 1-3; Example 1 Into a reaction vessel maintained in a non-oxidizing atmosphere by flowing N, gas at a rate of 3.4 cm/sec, 1945 g of sodium propionate (5.5 cm/sec for Fe) was added. 1.35 mol/l of Na, C
After adding O3 aqueous solution 6001, Fe! '1.35s
Ferrous sulfate aqueous solution containing +ol/Q 3007! were added and mixed to generate PeCO, at a temperature of 50'C.

The suspension containing FeC0z was kept at a temperature of 50°C for 300 minutes while continuously blowing Nt gas at a rate of 3.40-per second, and then the suspension containing FeC0z was kept at a temperature of 50°C. Air was bubbled through the tube at a rate of 2.80 mm per second for 5.5 hours to form a tan precipitate.

Note that the pH during air ventilation was 8.5 to 9.5.

The yellow-brown precipitated particles are separated by furnace, washed with water, dried, and
Shattered.

As a result of X-ray diffraction, the obtained yellow-brown particles were found to be goethite, and the electron micrograph shown in FIG. 4 (X 30,000
), it consists of spindle-shaped particles with an average major axis diameter of 0.31 μm and an axial ratio (major axis diameter: minor axis diameter > 15.8:1), the particle size is uniform, and dendritic particles are mixed. It was something I wouldn't do.

Examples 2 to 7, Comparative Examples 1 to 3 Type, concentration, and amount of alkali carbonate aqueous solution used in reaction for producing PeC03 or Be-containing precipitate, presence or absence of use of alkali hydroxide aqueous solution, type of propionic acid or its salt, lid The spindle shape was prepared in the same manner as in Example I, except that the presence period, the type, concentration and amount of the ferrous salt aqueous solution, temperature, temperature and time in the ripening step, and temperature and reaction time in the oxidation step were varied. Goethite particle powder with the following properties was obtained.

The main manufacturing conditions and characteristics at this time are shown in Tables 1 and 2.

The spindle-shaped goethite particles obtained in Examples 2 to 7 all had uniform particle sizes and did not contain dendritic particles.

An electron micrograph (x 30,000) of the spindle-shaped goethite particles obtained in Example 5 is shown in FIG.

In addition, as shown in the electron micrograph (x 30000) of FIG. 6, the spindle-shaped goethite particles obtained in Comparative Example 1 have a large short axis diameter and an axial ratio (long axis diameter: short axis diameter).
was small.

Example 8 2. Co50a H7nlo aqueous solution of Omol/e9.
1 ffi, stirring 10. Owol/N of l
3.65 ml of aOH solution was added to form a Co(OH) precipitate. After draining as much of the supernatant liquid of this Co(OH)z precipitate as possible, a cobalt propionate solution is prepared by adding 36.5*ol of propionic acid to make the total volume 251.

1,35 mol into a reaction vessel maintained in a non-oxidizing atmosphere by flowing 6 gases at a rate of 3.4 cm per second.
/j! After adding NagCO=aqueous solution 6001 of F
Ferrous sulfate aqueous solution containing 1.35 layers o1/R 30
0 f was added and mixed, and FeC0t was added at a temperature of 48°C.
was generated.

The cobalt propionate solution prepared in advance is added to the suspension containing FeCO5.

While continuing to blow N2 gas into the resulting suspension containing FeCO3 at a rate of 3.4 cm/sec, the temperature was increased to 48 cm.
After being held at 0.degree. C. for 300 minutes, air was bubbled through the FeCO.sub.5-containing suspension at a temperature of 48.degree. C. at a rate of 2.8 centimeters per second for 5.1 hours to form yellow-brown precipitated particles.

Note that the pH during air ventilation was 8.4 to 9.5.

The yellow-brown precipitated particles were separated in a furnace, washed with water, dried, and pulverized by a conventional method.

As a result of x1 diffraction, the obtained yellow-brown particles were found to be goethite, exhibiting a spindle shape with an average major axis diameter of 0.27μ and an axial ratio (major axis diameter: minor axis diameter) of 14.8:I. It consisted of particles, the particle size was uniform, and dendritic particles were not mixed.

Example 9 Instead of using cobalt propionate 4°5mol/N, zinc propionate 3. Goethite particles having a spindle shape were obtained in the same manner as in Example 8, except that 01/l was used.

The main manufacturing conditions and characteristics at this time are shown in Tables 1 and 2.

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

<Production of spindle-shaped hematite particles> Example 1O~
11: Examples 10 to 11 The spindle-shaped goethite particles obtained in Examples 2 and 5 were dehydrated in air at 300"C to obtain spindle-shaped hematite particles.

As a result of electron microscopic observation, the obtained hematite particles had an average major axis diameter of 0.36 pm, an axial ratio (major axis diameter: minor axis diameter) of 15.0:l, and a major axis diameter of 0.18 μ. ■,
The axial ratio (long axis diameter: short axis diameter) was 11.0:l.

<Adhesion treatment of spindle-shaped goethite particles with a metal compound> Examples 12 to 20, Comparative Examples 4 to 6; Example 12 10 kg of spindle-shaped goethite particles obtained in Example 1, separated by furnace and washed with water. 200 pieces of pressed cake! suspended in water. The pH of the suspension at this time was 9.2.

Next, 13.0% by weight of goethite was added to the suspension.
1.3Kg of AI (N(h)s・9H20 so that
Co(CHzCOO)z 4) 1202.32 was added so that the amount was 23.2% by weight based on the goethite.
Kg was added and stirred for 15 minutes. The p)I of the suspension at this time was 4.70.

Then, NaOH was added to the above suspension to adjust the pH to 9.8.
After adjusting to 150g of oleic acid to make it 1.5% by weight based on goethite, after thoroughly washing with warm water at 60°C using a rotary filter, the content becomes 15% by weight based on goethite. ) IJOy 1
．． 5 kg was added and stirred for 20 minutes.

Furthermore, it is separated in a furnace using a filter press and dried to obtain A1, Co
, Goethite coated with B compound was obtained.

The contents of A1, Co, and B in the obtained goethite are as follows:
Each 8l is 0.89wtχ, co is 5.32w
tχ, B was 70.6+3wtχ.

Examples 13-20, Comparative Examples 4-6 Types of particles to be treated: Al, Si, P, Ni,
Mg, Co.

By varying the types and amounts of B and Zn compounds,
Spindle-shaped goethite particles coated with a metal compound were obtained in the same manner as in Example 12.

Table 3 shows the main processing conditions at this time.

<Production of spindle-shaped metal magnetic particles mainly composed of iron> Examples 21 to 30, Comparative Examples 7 to 9; Example 21 The ^1, Co, and B compounds obtained in Example 12 were deposited. 5.0 kg of spindle-shaped goethite particles were heat-treated in air at 400°C to obtain spindle-shaped hematite particles coated with Al, Co, and B compounds.

2000 g of spindle-shaped hematite particles coated with the Al, Co, and B compounds were placed in a fluidized bed heating reduction furnace, H2 gas was passed through at a rate of 1801/min, and the reduction temperature was 390°C for 15 hours. The time was shining.

After the reduction,■! After replacing the gas with N2 gas, N
Then, the gas was cooled to 50° C. at a flow rate of 16 ON 1 /win.

Next, while keeping the furnace temperature at 50°C, turn on N□ gas for 16 hours.
A mixed gas of air kyt gas mixed with air at a ratio of 0.2Nl/win was vented. After an exothermic peak due to the oxidation reaction at that mixed gas ratio was observed, the air amount was increased to 0.4 Nl/win to increase the air mixing ratio in the mixed gas. In this way,
After the exothermic peak due to the oxidation reaction was observed at that mixed gas ratio, the air mixing ratio was gradually increased by increasing the air ratio in the mixed gas, and finally the air was 1.2N.
The oxidation treatment was continued with a mixed gas at a ratio of 1/win, N, and gas at a ratio of 16ON/win, and the oxidation treatment was performed until the heat generation due to oxidation disappeared and the temperature of the item reached approximately 50°C, which is almost the same as the furnace temperature. . During this time, the temperature of the item will be up to 75
It reached °C.

Next, the furnace temperature was set to 50°C, and the Hz gas flow rate was set to 16ON.
The air mixing ratio was gradually increased while maintaining the temperature at t/s+in, and the air amount was finally set to 2ON17sin. No fever was observed during this time.

Furthermore, air 40Nl/sin, Hz gas 14ON
The mixture was cooled to room temperature while passing a mixed gas of 1/sin.

-Dan, change the air flow rate! , /-1n, and after replacing with h gas, the thus obtained spindle-shaped metal particle powder mainly composed of iron with an oxide film formed on the surface was collected.

This ^1, metal magnetic particle powder mainly composed of iron containing Co and B can be seen in the electron micrograph (X 30
000), the average major axis is 0.28 μm, the axial ratio (major axis diameter: minor axis diameter) is 15.0; l, and the specific surface area is 49.2
rd/g and crystallite size of 155, the particle size was uniform and fine without any citrus-like particles.

In addition, the magnetic properties are as follows: coercive force Hc 15300e, saturation magnetization σs 135.4 emu/g, ΔσS/σs -
It was 4.2%.

Examples 22 to 30, Comparative Examples 7 to 9 Same as Example 21 except that the type of starting material, heat treatment temperature, type of non-reducing atmosphere, reduction temperature, H2 flow rate, and surface oxidation treatment conditions were variously changed. A spindle-shaped metal magnetic particle powder mainly composed of iron was obtained.

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

The spindle-shaped gold rl mainly composed of iron obtained in Examples 22 to 30! All of the magnetic particles had a uniform particle size and did not contain dendritic particles.

FIG. 8 shows an electron micrograph (x30000) of the metal magnetic particle powder containing iron as a main component obtained in Example 26.

In addition, in each of Comparative Examples 7 to 9, the reduced metal magnetic particles containing iron as a main component were immersed in a toluene solution to prevent them from being violently oxidized when taken out into the air. I took it out. For measurement, the - portion was taken out and a stable oxide film was formed on the surface while toluene was evaporated.

Table [Effects of the Invention] As shown in the above-mentioned examples, the spindle-shaped metal magnetic particles powder mainly composed of iron according to the present invention have an axial ratio (major axis diameter:
It has a large short axis diameter), a uniform particle size, no dendritic particles mixed in, a small crystallite size, an appropriate specific surface area, and a high coercive force. It is a spindle-shaped metal magnetic particle powder mainly composed of iron, which has a saturation magnetization of a large size and excellent oxidation stability, so it is suitable as a magnetic particle powder for high-density recording and low noise level. It is.

Furthermore, when the metal magnetic particle powder containing iron as a main component according to the present invention is used in the production of magnetic paint, it is well dispersed in the vehicle, has extremely excellent filling properties, and has a low S/N ratio.
A preferable magnetic recording medium with a large ratio can be obtained.

[Brief explanation of drawings]

FIG. 1 shows the relationship between the amount of sodium propionate present and the axial ratio (major axis diameter: minor axis diameter) of spindle-shaped goethite particles. In FIG. 1, curves A, B, and C each have a major axis diameter of 03
It is a goethite particle powder exhibiting a spindle shape with a diameter of about 0.5 .mu.m, a long axis diameter of about 0.2 .mu.m, and a long axis diameter of about 0.1 .mu.m. FIG. 2 shows the relationship between the BET specific surface area and the crystallite size of spindle-shaped metal magnetic particles whose main component is iron. In FIG. 2, △ and
This is a metal magnetic particle powder containing iron as a main component in the present invention. FIG. 3 shows the relationship between coercive force and crystallite size of spindle-shaped metal magnetic particles whose main component is iron. In FIG. 3, marks Δ and X are spindle-shaped metal magnetic particle powders mainly composed of iron obtained by the conventional method, and marks 0 are
This is a metal magnetic particle powder containing iron as a main component in the present invention. 4 to 6 are electron micrographs (x 30,000) showing the particle structure of spindle-shaped geltite particles obtained in Example 1, Example 5, and Comparative Example 1, respectively. FIGS. 7 and 8 are electron micrographs (x30 (100)) showing the particle structure of the spindle-shaped metal magnetic particles mainly composed of iron obtained in Example 21 and Example 26.

Claims (1)

[Claims] (1) Major axis diameter 0.05 to 0.40 μm, crystallite size 1
10 to 180 Å and a specific surface area of 30 to 60 m^2
/g, and the coercive force Hc is 1300 to 1700O
e, and the saturation magnetization σs is 100 to 140 emu/g
Ni, Al, Si, P, Co, Mg, B and Zn
A spindle-shaped metal magnetic particle powder whose main component is iron and which contains one or more elements selected from the following.