JP2001262205A - Method for producing spindle-shaped metallic magnetic particle essentially consisting of iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide homogeneous spindle-shaped metallic magnetic particles essentially consisting of iron, having high dispersibility and also high squareness ratio and high orientation properties in a coating film, having an excellent grain size distribution and particularly useful as the one for high recording density, high sensibility and high output. SOLUTION: Specified spindle-shaped hematite particles are formed into a fixed layer with a layer thickness of 3 to 15 cm, the temperature thereof is raised to 400 to 700 deg.C at a temperature rising rate of 10 to 80 deg.C/min in the atmosphere of reducing gas at an empty tower velocity of 40 to 150 cm/s, and reduction is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a spindle-shaped hematite particle having a uniform particle size, a large minor axis diameter, an appropriate axial ratio, and extremely excellent sintering prevention performance. It has good dispersibility (high squareness ratio, high orientation), excellent weather resistance, uniform and excellent coercive force distribution, etc., and especially consumer DAT, 8 mm, Hi-8 tape,
The present invention relates to a method for producing spindle-shaped metal magnetic particles containing iron as a main component, which are suitably used for commercial VTR tapes, computer tapes, disks and the like.

[0002]

2. Description of the Related Art In recent years, consumer DAT, 8 mm, Hi-8
Audio, video, and magnetic recording / reproducing equipment for computers, such as tapes, VTR tapes for business use, computer tapes, and disks, have been intensifying for long-time recording and miniaturization. Recorders) have been remarkably popularized, and the development of VTRs aiming at long-term recording, miniaturization and weight reduction, and transition from analog recording to digital recording has been actively carried out. On the other hand, demands for higher performance, higher density recording, and higher recording reliability of a magnetic tape as a magnetic recording medium are increasing.

[0003] High image quality and high output characteristics of the magnetic recording medium,
In particular, it is required to improve the frequency characteristics. For this 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.
There is a demand for an improvement in the N ratio.

[0004] These characteristics of the magnetic recording medium are closely related to the magnetic particles used in the magnetic recording medium, but in recent years, they have higher coercive force and higher coercive force than conventional iron oxide magnetic particles. Attention has been paid to metal magnetic particles mainly composed of iron having a large saturation magnetization, DAT, 8 mm, Hi-
8 tapes, VTR tapes for business use, computer tapes, and magnetic recording media such as disks have been used. However, there is a strong demand for further improvement in the properties of these metal magnetic particles containing iron as a main component.

The characteristics of the magnetic recording medium will be described in detail below. In order to obtain high image quality as a video magnetic recording medium, it is required to improve the S / N ratio and the video frequency characteristics. For that purpose, to improve the dispersibility of the magnetic particles in the coating, the orientation and the filling in the coating,
It is important to improve the surface smoothness of a magnetic recording medium. In order to improve the video frequency characteristics, it is necessary that the magnetic recording medium has a high coercive force and a high residual magnetic flux density. F.
D. (Switching Field Distri
buttion, that is, the coercive force distribution must be small. Furthermore, it is important to ensure the repetitive running properties and still characteristics of the magnetic recording medium or the reliability of recording when used in a severe environment, in other words, to improve the durability.

It is said that such metal magnetic particles preferably have a large particle size in terms of dispersibility and weather resistance, and have a large axial ratio in terms of the squareness ratio and orientation in a coating film. . On the other hand, from the viewpoint of surface smoothness and noise, the smaller the particle size, the better. However, the smaller the particle size, the more difficult it is to disperse, resulting in a problem in weather resistance. From the viewpoint of saturation magnetization, it is preferable that the particle size is large and the particle size distribution is excellent.However, if the particle size is unnecessarily large, the coercive force tends to decrease. It is necessary to maintain the coercive force by increasing the value.

Generally, metal magnetic particles include goethite particles as a starting material, hematite particles obtained by heating and dehydrating the goethite particles, or particles in which each of the above particles contains a different metal other than iron. It is obtained by performing a heat treatment in a non-reducing atmosphere, if necessary, and then performing a heating reduction in a reducing atmosphere. At this time, the shape and particle size of the goethite particles, which are the starting material, are appropriately controlled.Furthermore, fusion of the particles during heat treatment such as heating and reduction, or deformation of a single particle and shape destruction are prevented. It is necessary that the metal magnetic particles retain and inherit the shape and particle size of the goethite particles.

There are two types of goethite particles as the starting material, namely, acicular goethite particles obtained on the basis of alkali hydroxide and spindle-shaped goethite particles obtained on the basis of alkali carbonate. Acicular goethite particles are generally characterized in that particles having a large axial ratio are easily obtained, but have a problem that the particle size distribution is inferior to spindle-shaped particles and particles having a small particle size are difficult to obtain. Since this particle size distribution is an index of the uniformity of the primary particles, it is closely related to the coercive force distribution of the metal magnetic particles or weather resistance, that is, oxidation stability. Japanese Patent Application Laid-Open No. 5-98321 discloses a technique for obtaining fine, high coercive force and large saturation magnetization of acicular particles having a relatively large axial ratio. Studies have not been made on the heat resistance, heat resistance and weather resistance of the magnetic coating film.

On the other hand, spindle-shaped goethite particles are generally characterized by having an excellent particle size distribution, but it is difficult to obtain particles having a large axial ratio, and when the particle size is increased,
Since the coercive force of metal magnetic particles is lower than that of acicular particles,
Usually, the coercive force is secured by reducing the particle size. As a result, since the particle size is relatively small, the dispersibility in the paint is poor, and also depends on the low axial ratio, etc., the squareness ratio of the coating film, the orientation is low, and it is regarded as a problem. However, it is still not sufficient due to the fact that the particle size is smaller than good particle size distribution. Note that Japanese Patent Laid-Open No.
Japanese Patent No. 2166 discloses a technique for securing coercive force and improving dispersibility with the idea of increasing the axial ratio of spindle-shaped metal magnetic particles. However, the oxidation stability of metal magnetic particles and the weather resistance of a magnetic coating film are disclosed. It is not considered at all.

The heating reduction device used in the heating reduction step includes a fluidized bed reduction device for heating and reducing the starting material while fluidizing the starting material in a powder form. The starting material is granulated into granules to form a fixed bed. There is known a fixed-bed reducing device for reducing by heating and a moving-bed reducing device for moving a layer on which a fixed layer is formed.

As the demand for mass-production technology increases with the increase in the demand for magnetic metal particles, a fixed layer is formed that can be mass-produced without scattering of particles even if the flow rate of a reducing gas such as hydrogen is increased. The apparatus (including the moving bed) is industrially and economically advantageous.

However, when heat reduction is performed in a hydrogen gas atmosphere with a fixed layer formed, the partial pressure of water vapor increases due to rapid reduction occurring in the lower part of the fixed layer, and the particle size of the particles in the upper part of the layer is higher than that in the lower part of the fixed layer. A large amount of shape destruction and short-axis growth occur, and the characteristics of the particles tend to be different between the lower layer and the upper layer, making it difficult to obtain metal magnetic particles having uniform characteristics.

In general, fusion of particles as starting materials, or deformation and shape destruction of single particles are prevented, and the shape and particle size of goethite particles or hematite particles as starting materials are retained and retained by metal magnetic particles. It is necessary to let Shape-broken metal magnetic particles cannot obtain a high coercive force due to a decrease in shape anisotropy, and the particle size distribution is reduced. Further, even in the production of a magnetic recording medium, kneading with a binder resin, an increase in interparticle force in the dispersion process, or an increase in magnetic cohesion, the dispersibility is reduced, and when the magnetic coating film Excellent squareness ratio and excellent S
A magnetic recording medium having FD cannot be obtained.

[0014] Therefore, there is a strong demand for a heat reduction method that prevents the destruction of the particle shape as much as possible and makes the characteristics of the metal magnetic particles uniform in the lower and upper layers where the fixed layer is formed.

Conventionally, as a method for forming a fixed layer to obtain metal magnetic particles containing iron as a main component and having a high coercive force with uniform characteristics of the metal magnetic particles, a method in which a specific steam is introduced at the initial stage of the reduction. A method in which acicular magnetite is obtained by reduction at a temperature of less than 350 ° C. and subsequently reduced in a temperature range of 350 to 550 ° C. (Japanese Patent Laid-Open No. 224609/1992) A method of heating and reducing (Japanese Patent Application Laid-Open No. 54-62915), a method in which an object to be reduced is continuously transferred onto a gas-flowable belt provided in a gas-flow reactor and heated while flowing hydrogen gas in a vertical direction. A method of performing reduction (JP-A-6-93312) and the like are known.

[0016]

SUMMARY OF THE INVENTION In view of the above-mentioned background, spindle-shaped particles have good dispersibility (high squareness ratio, high orientation), excellent weather resistance and excellent coercive force distribution. Combined, preferably coercive force is 103.5-143.2K
A / m (1300-1800 Oe) of metal magnetic particles,
It is required to produce metal magnetic particles having uniform characteristics using an apparatus having a fixed layer.

Conventionally, regarding spindle-shaped goethite and spindle-shaped metal magnetic particles, Japanese Patent Publication No. 1-18961 discloses that an appropriate coercive force can be obtained by appropriately selecting a particle size and an axial ratio thereof to obtain a low specific surface area. Although a technique for reducing the viscosity of a coating material is disclosed, no consideration is given to the oxidation stability of the metal magnetic particles, the squareness of the coating film, the orientation, and the like.

Japanese Patent Application Laid-Open No. 9-295814 and Japanese Patent Application Laid-Open No. 10-245233 disclose the idea of increasing the axial ratio similarly to the conventional needle-shaped metal magnetic particles. A technique for obtaining a magnetic force and an excellent coercive force distribution is disclosed, but no consideration is given to oxidation stability. Note that, in the above-mentioned Japanese Patent Application Laid-Open No. 10-245233, the crystallite size D104 of spindle-shaped hematite particles is disclosed.
When the relationship between D110 and D110 is in a specific range, it is also described that the coercive force distribution of the coating film is excellent, but the relationship between the starting material and the crystallite size of goethite particles is not mentioned. It is not sufficient in terms of sintering or shape destruction of the particles in the processing step.

On the other hand, JP-A-7-126704, JP-A-8-165501, and JP-A-8-165117
The publication discloses a technique for obtaining spindle-shaped metal magnetic particles containing Co and Al and having high coercive force in fine particles,
Regarding the oxidation stability of metal magnetic particles, see JP-A-7-12.
No sufficient study has been made in Japanese Patent No. 6704, and the level is not yet satisfactory in Japanese Patent Application Laid-Open No. Hei 8-165501. JP-A-8-165117 discloses that the crystallite sizes D020 and D200 of spindle-shaped goethite particles are different.
Although the ratio of 110 is specified, there is no mention of the growth in the case of forming surface layer particles from seed crystal particles.

Regarding the heat resistance of the metal magnetic particles,
JP-A-59-207024 discloses that a differential thermal curve is 8
Disclosed are metal magnetic particles which do not change up to 0 ° C., and the shape of the particles is not clear, but the one containing 7 atomic% of Al
The one at 0 ° C. is described. Similarly, JP-A-2-191
According to Japanese Patent No. 61, even if the ignition temperature is high, at most 121 ° C.
Therefore, the heat resistance is not sufficient.

Further, Japanese Patent Application Laid-Open No. 10-334455 discloses a magnetic recording medium having excellent head sliding characteristics and good storage properties by setting the amounts of Co, Al and rare earth elements in metal magnetic particles to specific ranges. However, no study has been made on the particle size, shape, particle size distribution, etc. of the starting goethite particles, and sufficient studies have been made on coercive force, weather resistance, and dispersibility. Absent.

In the spindle-shaped goethite particles, while maintaining the feature that the particle size distribution is excellent, the above-mentioned problems, that is, maintaining the coercive force in a state where the particle size is large, include high-angled goethite particles. In order to obtain a high ratio, high orientation, studies have been conducted to increase the axial ratio based on the same concept as the needle-shaped metal magnetic particles, but a sufficient one has not yet been obtained, and individual characteristics It cannot be said that the effects or effects have been sufficiently studied.

In the method described in Japanese Patent Laid-Open No. 224609/1992, the temperature-raising atmosphere is hydrogen, but the temperature-raising rate is not specified, and sufficient studies have been made on the oxidation stability. It is not.

In the method described in the above-mentioned Japanese Patent Application Laid-Open No. 54-62915, the obtained metal magnetic particle powder is likely to be formed by the fact that the temperature rising atmosphere is nitrogen and the superficial velocity of the reducing gas is low. Coercive force is 95.5 KA / m (1200 Oe)
It is hard to say that sufficient studies have been made on the dispersibility in the paint, the squareness ratio in the coating film, the orientation and the like.

In the method described in Japanese Patent Application Laid-Open No. 6-93312, the magnetic particles do not contain Co, and the oxidation stability and dispersibility of the magnetic particles in the paint, the squareness ratio in the paint film, and the orientation It is hard to say that the sex has been sufficiently studied.

Accordingly, the present invention provides a spindle-shaped metal magnetic particle having an excellent particle size distribution, a high dispersibility characteristic of needle-like metal magnetic particles, and a high squareness ratio in a coating film.
Having a high orientation, when obtaining spindle-shaped metal magnetic particles having a further excellent particle size distribution, achieved by a completely different idea from the conventionally thought, furthermore, in the layer in which the fixed layer is formed, It is a technical object to provide further improved metal magnetic particles.

[0027]

The first aspect of the present invention is as follows.
0.5 to less than 10 atomic% of Co with respect to all Fe, Al
And 5 to 10 atomic% of the total Fe and 1 to 5 atomic% of the rare earth element with respect to the total Fe, and the Al / rare earth element ratio is 1.5 to 5 (atomic% relative to Fe). An average major axis length of 0.17 to 0.28 μm, a size distribution (standard deviation / major axis length) of 0.20 or less, an average minor axis length of 0.022 to 0.035 μm, and an average axis ratio of 5 -10,
After the spindle-shaped hematite particles having a crystallite size ratio D110 / D104 of 2.0 to 4.0 are introduced into the reduction device to form a fixed layer having a layer height of 3 to 15 cm, the superficial velocity is 40 to 40. In a reducing gas atmosphere of 150 cm / s, the temperature is raised to 400 to 700 ° C. at a rate of 10 to 80 ° C./min,
A method for producing spindle-shaped metal magnetic particles containing Fe as a main component, characterized in that the spindle-shaped hematite particles are reduced (claim 1).

Further, claim 2 as a preferable embodiment is as follows.
Spindle-shaped hematite particles are used to make Co 0.5% of the total Fe.
Spindle-shaped goethite particles having an average major axis length of 0.18 to 0.30 μm containing at least 8 atomic% and containing 5 to 10 atomic% of Al with respect to all Fe, and having a size distribution (standard deviation / major axis length). Is 0.22 or less, and the average minor axis length is 0.025-0.
The method for producing spindle-shaped metal magnetic particles containing Fe as a main component according to claim 1, which is obtained from spindle-shaped goethite particles having 045 µm and an average axis ratio of 5 to 10.

Further, claim 3 as a preferred embodiment is as follows.
Crystallite size ratio of spindle-shaped goethite particles D020 / D1
10 is 1.8 to 2.4, and the crystallite size ratio D020 / D020 (seed crystal particles) to the seed crystal particles is 1.
3. The process for producing spindle-shaped metal magnetic particles containing Fe as a main component according to claim 2, wherein the ratio of D110 / D110 (seed crystal particles) is 1.02 to 1.10.

In a preferred embodiment, claim 4 is
Spindle-shaped goethite particles are prepared by reacting a mixed alkali aqueous solution of an aqueous solution of an alkali carbonate and an aqueous solution of an alkali hydroxide with an aqueous solution of a ferrous salt. After aging in the above, an oxygen-containing gas is passed through the aqueous suspension to generate spindle-shaped goethite seed crystal particles by an oxidation reaction, and then a water suspension containing the seed crystal particles and a ferrous-containing precipitate is formed. When the oxygen-containing gas is passed through the suspension to grow a goethite layer on the particle surface of the seed crystal particles by an oxidation reaction to generate spindle-shaped goethite particles, an oxidation reaction is performed during the generation of the seed crystal particles. The aqueous suspension containing the ferrous-containing precipitate during the ripening before the start was mixed with the total Fe in a time within 1/2 of the entire ripening period.
The oxidation reaction is carried out in the range of 40 to 50% of the total Fe ²⁺ by adding a Co compound of 0.5 to less than 8 atomic% in terms of o, and 5 to 10 atomic% of the Al compound in terms of Al with respect to all Fe. 4. The method for producing spindle-shaped metal magnetic particles containing Fe as a main component according to claim 2 or 3, which is obtained by adding a metal.

Further, claim 5 as a preferable embodiment is as follows.
The spindle-shaped hematite particles are the spindle-shaped goethite particles according to claim 2, 3 or 4, wherein the ratio of Al / rare earth element is 1.5.
After treatment with a sintering inhibitor composed of a compound of a rare earth element in an amount of 1 to 5 atomic% of the total Fe in terms of the rare earth element so that the crystallite size D104 becomes ５5 (atomic% with respect to Fe). In a non-reducing atmosphere such that D104 / goethite D110 is in the range of 0.9 to 1.1,
The method for producing spindle-shaped metal magnetic particles containing Fe as a main component according to claim 1, which is obtained by performing a heat treatment at 650 to 800 ° C.

In a preferred embodiment, claim 6 is
Spindle-shaped metal magnetic particles containing Fe as a main component,
0.5 to less than 10 atomic% with respect to e, 5 to 10 atomic% of Al with respect to total Fe, and 1 to 5 atomic% of rare earth element with respect to total Fe, and the ratio of Al / rare earth element is The average major axis length of 1.5 to 5 (atomic% relative to Fe) is 0.15 to 0.25 μm, and the size distribution (standard deviation /
Major axis length) is 0.26 or less, average minor axis length is 0.015
0.025 μm, average axis ratio is 5 to 9, ignition temperature is 145 ° C. or more, oxidation stability is 6% or less, and coercive force is 10
3.5 to 143.2 KA / m (1300 to 1800) O
3. The method for producing spindle-shaped metal magnetic particles containing Fe as a main component according to claim 1 which is e.

In a preferred embodiment, claim 7 is
The method for producing spindle-shaped metal magnetic particles containing Fe as a main component according to claim 1 or 6, wherein the spindle-shaped metal magnetic particles containing Fe as a main component are for magnetic recording.

In the present invention, the spindle-shaped hematite particles used as a starting material are preferably those obtained from the spindle-shaped goethite particles described below. The particles constituting the spindle-shaped goethite particles have an average major axis diameter of 0.18 to
0.30 μm, and its size distribution (standard deviation / average major axis diameter) is 0.22 or less. The average minor axis diameter is 0.025 to 0.045 μm. The shape is a spindle shape, and the average axis ratio (major axis diameter / minor axis diameter) is 5 to 10. When the average major axis diameter is less than 0.18 μm, when the metal magnetic particles are used, the coercive force becomes too high, the dispersibility in the paint is poor, and the weather resistance of the coating film tends to deteriorate. on the other hand,
If it exceeds 0.30 μm, it becomes difficult to obtain a desired coercive force in the range of the axial ratio of the present invention. The smaller the size distribution, the better. Therefore, the lower limit is not particularly limited. However, from the viewpoint of industrial productivity, about 0.10 is appropriate. On the other hand, when it exceeds 0.22, oxidation stability and heat resistance deteriorate, and it is difficult to achieve high-density recording. If the average minor axis diameter is less than 0.025 μm, sufficient oxidation stability and heat resistance cannot be obtained, while if it exceeds 0.045 μm, the desired coercive force cannot be obtained. Further, if the average axis ratio is less than 5, the desired coercive force cannot be obtained, while if it exceeds 10, the coercive force becomes too high, or the oxidation stability and heat resistance deteriorate.

The particles constituting the spindle-shaped goethite particles preferably have a BET specific surface area of 100 to 150 m ² / g. If the BET specific surface area is less than 100 m ² / g, the particles are relatively large and the desired coercive force cannot be obtained. On the other hand, if the BET specific surface area exceeds 150 m ² / g, the coercive force becomes unnecessarily high, resulting in oxidation stability and heat resistance. The property is deteriorated.

The particles constituting the spindle-shaped goethite particles are as follows:
It contains 0.5 to less than 8 atomic% of Co with respect to all Fe, and contains 5 to 10 atomic% of Al with respect to all Fe. If the Co content is less than 0.5 atomic%, there is no effect of improving the magnetic properties, and if it is 8 atomic% or more, it becomes difficult to control the particle size. If the Al content is less than 5 at%, the effect of preventing sintering is not obtained, and if it exceeds 10 at%, the saturation magnetization is particularly reduced.

The crystallite size ratio D020 / D110 of the particles constituting the spindle-shaped goethite particles is preferably 1.8 to 2.4. The crystallite size D020 is 200 to 28.
0 ° and D110 are preferably 100 to 140 °, respectively. When D020 / D110 is less than 1.8, the shape retention during heat dehydration or heat reduction becomes insufficient, the dispersibility of the obtained metal magnetic particles in the coating material decreases, and the coercive force distribution tends to deteriorate. is there. Also, D020 / D1
When 10 exceeds 2.4, metal magnetic particles having a target particle size can be obtained, but a target having a desired coercive force tends to be hardly obtained.

The particles constituting the spindle-shaped goethite particles are as follows:
It is formed from a seed crystal part and a surface layer part, and Co is present in the seed crystal part and the surface layer part, and A is present only in the surface layer part.
l exists.

The above-mentioned seed crystal part is a goethite seed crystal particle part formed by oxidation of the added ferrous salt until the Al compound is added. Specifically, it is the portion of the weight ratio of Fe determined by the oxidation rate of Fe ²⁺ , and preferably, the portion is 40 to 50% by weight from the inner center of the seed crystal particles.

The ratio of the crystallite size D020 / D020 (seed crystal particles) of the particles constituting the spindle-shaped goethite particles to the seed crystal particles is preferably 1.05 to 1.20,
D110 (seed crystal particles) is preferably 1.02 to 1.10. When D020 / D020 (seed crystal particles) exceeds 1.20 and D110 / D110 (seed crystal particles) exceeds 1.10, the goethite layer in the surface layer portion becomes too large, and it is difficult to control the shape of goethite particles. D020 / D
020 (seed crystal particles) is less than 1.05, D110 / D11
0 (seed crystal particles) is less than 1.02,
The l-containing goethite layer is reduced, and the effect of preventing sintering during dehydration heating and heat reduction tends to be significantly reduced.

Assuming that the total proportion of Co in the whole particles of the spindle-shaped goethite particles is 100, the proportion of Co contained in the seed crystal portion is preferably 75 to 95, and Preferably it is 80-90.
Further, the abundance ratio of Co contained in the surface layer is preferably 103 to 125, more preferably 106 to 125 with respect to all Co.
~ 120. When the abundance ratio of Co in the seed crystal portion is less than 75 and the abundance ratio of Co in the surface layer portion exceeds 125, Co alloying hardly occurs due to the small amount of Co in the seed crystal portion, and the surface layer becomes Co-rich. Too much, it is difficult to maintain the shape during reduction, and the magnetic properties tend to deteriorate. Further, when the abundance ratio of Co in the seed crystal portion exceeds 95 and the abundance ratio of Co in the surface layer portion is less than 103, Co in the seed crystal portion is likely to be Co-alloyed, but the amount of Co in the surface layer portion is small. In addition, since the amount of Al present at the same time is too large, Co alloying of the surface layer does not work well, and the magnetic properties tend to deteriorate as a whole.

The above-mentioned surface layer portion is defined as Al
It refers to a goethite layer that has grown on the surface of the goethite seed particles after the compound has been added. Specifically, it is a portion of 50 to 60% by weight of Fe from the outermost surface of the particle.
Al is present only in the surface layer, and its content is
5 to 10 atomic% based on e. If the content is less than 5 atomic%, a sufficient sintering preventing effect cannot be obtained during metallization.
On the other hand, if the content exceeds 10 atomic%, the magnetic properties, particularly the saturation magnetization, are reduced, and the crystal growth inside the grains is inhibited, so that the coercive force is hardly developed.

The particles constituting the spindle-shaped goethite particles as described above are obtained by first forming spindle-shaped goethite seed crystal particles and then growing a goethite layer on the surface of the seed crystal particles.

Spindle-shaped goethite seed particles are prepared by reacting an aqueous suspension containing a ferrous-containing precipitate obtained by reacting a mixed alkali aqueous solution of an aqueous alkali carbonate solution and an aqueous alkali hydroxide solution with an aqueous ferrous salt solution. After aging in a non-oxidizing atmosphere, an oxygen-containing gas is passed through the aqueous suspension to generate spindle-shaped goethite seed crystal particles by an oxidation reaction. To the aqueous suspension containing the containing precipitate, a Co compound of not less than 0.5 and less than 8 atomic% in terms of Co with respect to all Fe is added at a time within 1/2 of the entire aging period, and the oxidation reaction is carried out with respect to all Fe ^{2. + In} the range of 50 to 50%. If the addition of the Co compound is performed at a time exceeding 1/2 of the entire aging period, goethite particles having the desired axial ratio and particle size cannot be obtained. Also,
Even when the oxidation reaction is less than 40% or more than 50% of the total Fe ²⁺ , it is difficult to obtain goethite particles having the desired axial ratio and particle size.

The aging is preferably carried out by subjecting the suspension under a non-oxidizing atmosphere to a temperature of usually 40 to 80 ° C. When the temperature is lower than 40 ° C., the axial ratio is small and it is difficult to obtain a sufficient aging effect. When the temperature is higher than 80 ° C., magnetite may be mixed. The aging time is usually 30 to 300 minutes. If the time is less than 30 minutes or more than 300 minutes, it is difficult to obtain the desired axial ratio. In order to obtain a non-oxidizing atmosphere, an inert gas (such as nitrogen gas) or a reducing gas (such as hydrogen gas) may be passed through the reaction vessel of the suspension.

In the formation reaction of the spindle-shaped goethite seed crystal particles, an aqueous ferrous sulfate solution, an aqueous ferrous chloride solution, or the like can be used as the aqueous ferrous salt solution. These may be used alone or as a mixture of two or more as necessary.

The mixed alkali aqueous solution used in the production reaction of the spindle-shaped goethite seed crystal particles is obtained by mixing an alkali carbonate aqueous solution and an alkali hydroxide aqueous solution. In this case, the ratio of the aqueous alkali hydroxide solution is preferably 10 to 40%.
(Specific conversion%), more preferably 15 to 35% (specific conversion%). If it is less than 10%, the desired axial ratio cannot be obtained, and if it exceeds 40%,
Granular magnetite may be mixed.

As the aqueous alkali carbonate solution, an aqueous sodium carbonate solution, an aqueous potassium carbonate solution, an aqueous ammonium carbonate solution and the like can be used, and as the aqueous alkali hydroxide solution, sodium hydroxide, potassium hydroxide and the like can be used. These may be used alone or as a mixture of two or more as needed.

The amount of the mixed alkaline aqueous solution used is preferably 1.3 to 3.5, more preferably 1.5 to 2.5, as the equivalent ratio to the total Fe in the aqueous ferrous salt solution. If it is less than 1.3, magnetite may be mixed, and if it exceeds 3.5, it is not industrially preferable.

The concentration of ferrous iron after mixing the aqueous ferrous salt solution and the mixed aqueous alkali solution is preferably 0.1 to 1.0 mol.
1 / l, more preferably 0.2 to 0.8 mol / l. When the amount is less than 0.1 mol / l, the yield is small,
Not industrial. If it exceeds 1.0 mol / l, the particle size distribution is undesirably large.

The pH value in the formation reaction of the spindle-shaped goethite seed crystal particles is preferably in the range of 8.0 to 11.5, more preferably 8.5 to 11.0. When the pH is less than 8.0, a large amount of acid radicals are contained in the goethite particle powder and cannot be easily removed by washing. In some cases, sintering of the particles may occur. On the other hand, if it exceeds 11.5, it is difficult to obtain the desired high coercive force when the metal magnetic particles are used.

The reaction for producing spindle-shaped goethite seed particles is as follows.
This is performed by an oxidation reaction in which an oxygen-containing gas (for example, air) is passed through the liquid. The superficial velocity of the oxygen-containing gas is preferably 0.5 to 3.5 cm / s, more preferably 1.0 to 3.0 cm / s.
0 cm / s. If it is less than 0.5 cm / s, the oxidation rate is too slow, so that particulate magnetite particles are apt to be mixed. On the other hand, if it is more than 3.5 cm / s, the oxidation rate is too fast, and it is possible to control the particle size to the target. It becomes difficult. The superficial velocity is the amount of oxygen-containing gas per unit cross-sectional area (the bottom cross-sectional area of the column reactor, the hole diameter of the nest plate, and the number of holes are not taken into account), and the unit is cm / sec. is there.

The temperature in the reaction for producing the spindle-shaped goethite seed crystal particles may be generally at a temperature of 80 ° C. or less at which goethite particles are produced. When the temperature exceeds 80 ° C., magnetite may be mixed in the spindle-shaped goethite particles. Preferably it is in the range of 45 to 55 ° C.

In the formation reaction of the spindle-shaped goethite seed crystal particles, as the Co compound, cobalt sulfate, cobalt chloride, cobalt nitrate or the like can be used. These may be used alone or as a mixture of two or more as necessary. C
The o-compound is added to the suspension containing the ferrous-containing precipitate that has been aged before the oxidation reaction is performed.

The amount of the Co compound added was 0.5 atomic% based on the total Fe in the spindle-shaped goethite particles as the final product.
And less than 8 atomic%. When the content is less than 0.5 atomic%, there is no effect of improving the magnetic properties of the metal magnetic particles, and when the content is 8 atomic% or more, it is possible to reduce the size and obtain the desired axial ratio and size. Absent.

The pH value in the growth reaction of the goethite layer is usually from 8.0 to 11.5, preferably from 8.5 to 11.5.
It is in the range of 1.0. When the pH is less than 8.0, a large amount of acid radicals are contained in the goethite particle powder and cannot be easily removed by washing. May cause. If it exceeds 11.5, the desired particle size distribution may not be obtained when metal magnetic particles are used.

The growth reaction of the goethite layer is performed by an oxidation reaction in which an oxygen-containing gas (for example, air) is passed through the liquid. The superficial velocity of the oxygen-containing gas is preferably higher than that during the seed crystal particle formation reaction. If not increased, the viscosity of the water suspension increases when Al is added,
Growth in the short axis direction is further promoted, the axial ratio is reduced, and a desired axial ratio may not be obtained. However, this does not apply when the superficial velocity at the time of the seed crystal particle formation reaction is 2.0 cm / s or more.

The temperature in the growth reaction of the goethite layer is as follows:
Usually, it may be performed at a temperature of 80 ° C. or less at which goethite particles are generated. When the temperature exceeds 80 ° C., magnetite may be mixed in the spindle-shaped goethite particles. Preferably, it is in the range of 45 to 55 ° C.

In the growth reaction of the goethite layer, as the Al compound, aluminum sulfate, aluminum chloride,
Acid salts such as aluminum nitrate, sodium aluminate,
Aluminates such as potassium aluminate and ammonium aluminate can be used. These may be used alone or as a mixture of two or more as necessary.

The addition of the Al compound can be carried out at the same time as the aeration while the superficial velocity of the oxygen-containing gas is preferably increased during the seed crystal particle production reaction. When the addition of Al takes a long time, the addition can be performed by switching to a nitrogen-containing gas in a sense that the oxidation reaction does not proceed. still,
If the Al compound is dividedly added or continuously or intermittently added while the oxygen-containing gas is passed, the sufficient effect of the present invention cannot be obtained.

The amount of addition of the Al compound is 5 to 10 with respect to the total Fe in the spindle-shaped goethite particles as the final product.
Atomic%. If the content is less than 5 atomic%, a sufficient sintering preventing effect cannot be obtained at the time of metallization, and if it exceeds 10 atomic%, the formation of particles other than goethite is also induced, and the magnetic properties, particularly the saturation magnetization, are reduced. As a result, the coercive force is hardly developed because the crystal growth inside the grains is inhibited.

As described above, spindle-shaped hematite particles used as a starting material of the present invention are obtained. The particles constituting the spindle-shaped hematite particles used in the present invention have an average major axis diameter of 0.17 to 0.28 μm and a size distribution (standard deviation / average major axis diameter) of 0.20 or less. The average minor axis diameter is 0.022 to 0.035 μm.
The shape is a spindle shape, and the axial ratio (major axis diameter / minor axis diameter) is 5 to 10. When the average major axis diameter is less than 0.17 μm, when the metal magnetic particles are used, the coercive force becomes too high, the dispersibility in the paint is poor, and the weather resistance of the coating film tends to deteriorate. On the other hand, if it exceeds 0.28 μm, it becomes difficult to obtain the target coercive force in the range of the axial ratio of the present invention. The smaller the size distribution, the better. Therefore, the lower limit is not particularly limited. However, from the viewpoint of industrial productivity, about 0.10 is appropriate. On the other hand, when it exceeds 0.20, the oxidation stability and heat resistance deteriorate, and it is difficult to achieve high-density recording. If the average minor axis diameter is less than 0.022 μm, sufficient oxidation stability and heat resistance cannot be obtained, while if it exceeds 0.035 μm, the desired coercive force cannot be obtained. Further, if the axial ratio is less than 5, the desired coercive force cannot be obtained, while if it exceeds 10, the coercive force becomes too high, or the oxidation stability and heat resistance deteriorate.

The spindle-shaped hematite particles preferably have a BET specific surface area of 30 to 70 m ² / g, more preferably 35 to 70 m ² / g.
６５65 m ² / g. BET specific surface area is 30m ² / g
When the particle size is less than the above, sintering has already occurred in the heat treatment step with the particle size of the present invention, the size distribution is deteriorated, the size distribution of the metal magnetic particles is also deteriorated, and the SFD of the coating film is also deteriorated. On the other hand, when it exceeds 70 m ² / g, prevention of sintering in the heat reduction step becomes insufficient, and the size distribution of the metal magnetic particles deteriorates.
The SFD of the coating also deteriorates.

The particles constituting the spindle-shaped hematite particles are as follows:
Co contains at least 0.5 atomic% and less than 10 atomic% with respect to all Fe, Al contains 5 to 10 atomic% with respect to all Fe,
Further, the content of the rare earth element is 1 to 5 atomic% with respect to the total Fe, and the ratio of Al / the rare earth element (each atomic% with respect to Fe) is 1.5 to 5.

The particles constituting the spindle-shaped hematite particles have a crystallite size ratio D110 / D104 of 2.0 to 4.0. The crystallite size D104 is 100 to 150 °,
D110 is 200 to 300 °. D110 / D10
If 4 is less than 2.0, the particle growth during dehydration heating has occurred excessively, and the particle size distribution deteriorates along with the growth in the short axis direction, and the coercive force of the obtained metal magnetic particles is low, and The properties also deteriorate. When D110 / D104 is more than 4.0, crystal growth by dehydration heating is insufficient, and a shape retaining effect at the time of heat reduction cannot be expected, coercive force decreases, and particle size distribution further deteriorates.

The particles constituting the spindle-shaped hematite particles are as follows:
A seed crystal portion, an intermediate layer portion, and an outermost layer portion, wherein Co is present in the seed crystal portion and the intermediate layer portion, Al is present only in the intermediate layer portion, and in the outermost layer portion. Only rare earth elements are present. In the outermost layer, other elements such as Al, Si, B, Ca, Mg, Ba, and S may be supplemented as necessary to improve the sintering prevention effect and adjust the magnetic properties.
One, two or more compounds of elements selected from r, Co, Ni and the like may be used. These compounds not only have the effect of preventing sintering but also have the function of controlling the reduction rate, and thus may be used in combination as necessary. However, if the amount is too large, the saturation magnetization decreases when metal magnetic particles are used. Therefore, the optimum amount may be appropriately selected depending on the type of combination.

The above-mentioned seed crystal part is the one in which the seed crystal part of the goethite particles is changed as it is.
The weight ratio of Fe from the inner center of the seed crystal particles is 40 to 50% by weight. Further, the intermediate layer portion is a surface layer portion of the goethite particles that has been changed as it is. Preferably, the weight ratio of Fe from the outermost surface when the outermost layer made of a rare earth element compound on the particle surface is removed is 50%. 〜60% by weight.

Assuming that the total proportion of Co in the whole particles of the spindle-shaped hematite particles is 100, the proportion of Co contained in the seed crystal portion is preferably 75 to 95, more preferably Preferably it is 80-90.
Further, the content ratio of Co contained in the intermediate layer portion is preferably 103 to 125, more preferably 10
6 to 120. If the abundance ratio of Co in the seed portion is less than 75 and the abundance ratio of Co in the intermediate layer portion exceeds 125, Co alloying is unlikely to occur due to the small amount of Co in the seed portion. Since it becomes Co-rich too much, it tends to be difficult to maintain the shape at the time of reduction and to deteriorate magnetic properties. Further, when the abundance ratio of Co in the seed crystal part exceeds 95 and the abundance ratio of Co in the intermediate layer part is less than 103, the Co in the seed crystal part is likely to be Co-alloyed, but the Co amount in the intermediate layer is reduced. On the other hand, since the amount of Al present at the same time is too large, the alloying of the surface layer portion with Co is not successful, and the magnetic properties tend to deteriorate as a whole. If Co is present in the outermost layer as required, the effect is different, and it is considered that it acts on the control of the overall reduction rate or the oxidation stability of the outermost surface. On the other hand, Co is considered to be important in that it is present simultaneously with the Fe element inside the grains and directly involved in alloying with Fe mainly present in each layer.

The content of the Co compound is at least 0.5 atomic% and less than 10 atomic% based on the total Fe. 0.5 atomic%
If less than 10%, the effect of improving magnetic properties is not obtained when metal magnetic particles are used.
Control of the reduction rate becomes difficult, and shape destruction is likely to occur.
Al is present only in the intermediate layer portion and accounts for 5 to 10 atomic% of the total Fe. If the content is less than 5 atomic%, a sufficient sintering preventing effect cannot be obtained during metallization. On the other hand, when the content exceeds 10 atomic%, the magnetic properties, particularly the saturation magnetization, are reduced, and the crystal growth inside the grains is inhibited, so that the coercive force is hardly developed.

The outermost layer portion is made of a rare earth compound. The content of rare earth elements contained in the outermost layer is
It is 1 to 5 atomic% with respect to e. If the content is less than 1 atomic%, the effect of preventing sintering is not sufficient, and when metal magnetic particles are used, the size distribution deteriorates, and the SFD of the coating film also deteriorates. If it exceeds 5 atomic%, a significant decrease in saturation magnetization occurs.

The ratio between the Al element and the rare earth element is
It is 1.5 to 5 as Al / rare earth element. When it is smaller than 1.5, sufficient oxidation stability is hardly obtained when metal magnetic particles are used, and when it is more than 5, sufficient heat resistance cannot be obtained, and the ignition temperature tends to be low.

The spindle-shaped hematite particles as described above are prepared by coating the spindle-shaped goethite particles with a sintering inhibitor on the surface of the spindle-shaped goethite particles with a sintering inhibitor to prevent sintering prior to heat dehydration. It is obtained by performing a heat treatment in a reducing atmosphere.

As the sintering inhibitor, a compound of a rare earth element is used. As the rare earth element compound, one or more compounds such as scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, and samarium are preferable, and the rare earth element chloride, sulfate,
Nitrates and the like can be used. The treatment method may be either a dry method or a wet method, preferably a wet coating treatment.
The amount used is preferably 1 to 5 atomic% based on the total Fe.
It is. When the content is less than 1 atomic%, the effect of preventing sintering is not sufficient, and when metal magnetic particles are used, the size distribution deteriorates, and the SFD of the coating film further deteriorates. If it exceeds 5 atomic%, the saturation magnetization value will be extremely low.

In the present invention, a rare earth element compound is added so that the ratio of Al / rare earth element contained in the spindle-shaped goethite is 1.5 to 5 (the ratio of the atomic ratio of each element to the total Fe). I do. If the ratio is less than 1.5, sufficient oxidation stability cannot be obtained when the metal magnetic particles are used. On the other hand, when it exceeds 5, not only the sufficient heat resistance cannot be obtained but also the rare earth element having the effect of preventing sintering becomes too small, and the shape retaining effect at the time of metallization becomes insufficient.

In order to improve the sintering prevention effect and adjust the magnetic field, if necessary, other elements such as Al and S
One or more compounds of elements selected from i, B, Ca, Mg, Ba, Sr, Co, Ni, and the like may be used. These compounds not only have the effect of preventing sintering but also have the function of controlling the reduction rate, and thus may be used in combination as necessary. However, if the amount is too large, the saturation magnetization decreases when metal magnetic particles are used. Therefore, the optimum amount may be appropriately selected depending on the type of combination.

By coating in advance with the sintering inhibitor and the like, sintering between particles and particles is prevented,
Spindle-shaped hematite particles that further retain and inherit the particle shape and axis ratio of the spindle-shaped goethite particles can be obtained, thereby retaining and inheriting the above-described shape and the like, and individually independent spindle-shaped metal mainly composed of iron. Magnetic particles are easily obtained.

The spindle-shaped goethite particles coated with the sintering inhibitor are subjected to 650 to 80 under a non-reducing atmosphere.
When the heat treatment is performed within the range of 0 ° C., the crystallite size D104 of the spindle-shaped hematite particles is D104 / D110.
Heat treatment is performed so as to be in the range of 0.9 to 1.1 (goethite). If the heat treatment temperature is lower than 650 ° C., the ratio tends to be less than 0.9, while if it exceeds 800 ° C., the ratio tends to exceed 1.1. In addition, D104 / D
When 110 (goethite) is less than 0.9, when metal magnetic particles are used, the particle size distribution is widened and the SFD of the coating film is deteriorated. When D104 / D110 (goethite) exceeds 1.1, shape destruction and sintering in hematite occurs, and even when metallic magnetic particles are used, the particle size distribution is wide and the particle size distribution is wide.
There is also a sintered body, and when it is made into a coating film, the squareness ratio, SF of the coating film
Both D deteriorate.

The hematite particles after the heat treatment may be washed to remove impurity salts such as Na ₂ SO ₄ . In this case, it is preferable to remove unnecessary impurities by performing washing under conditions where the coated sintering inhibitor does not elute. Specifically, the pH can be increased to remove the cationic impurities, and the pH can be reduced to remove the anionic impurities, whereby the washing can be performed more efficiently.

Next, the spindle-shaped hematite particles as described above were used as a starting material, introduced into a reducing device to form a fixed layer, and reduced by heating to obtain spindle-shaped metal magnetic particles containing iron as a main component. obtain. In the present invention, in forming the fixed layer of spindle-shaped hematite particles, it is preferable that the hematite particles are granulated by an ordinary method and used as granules having an average diameter of 1 to 5 mm.

As the reduction device having a fixed layer formed thereon in the present invention, a mobile reduction device (continuous type) for forming a fixed layer on a belt or tray and reducing while transferring the belt or tray is preferable.

The layer height of the starting material in the present invention is 3 to 1
5 cm, preferably 4 to 14 cm. If it exceeds 15 cm, problems such as a decrease in the coercive force of the upper portion of the fixed layer due to an increase in the partial pressure of water vapor due to rapid reduction of the lower portion of the fixed layer occur, and the overall characteristics deteriorate. 3cm
If it is less than the above, it depends on the gas superficial velocity, but the granulated material may be scattered, which is not preferable. In consideration of industrial productivity, 3 to 14 cm is preferable.

In the present invention, the atmosphere during which the temperature is raised to the reduction temperature of 400 to 700 ° C. is a reducing gas atmosphere.
Hydrogen is suitable as the reducing gas. In an atmosphere other than the reducing gas, particularly in an inert gas atmosphere such as nitrogen, when switching to the reducing gas in the reduction step after the temperature rise as shown in the comparative example described below, rapid reduction occurs and uniform particle growth occurs. It is difficult to obtain a high coercive force because it is difficult.

The superficial velocity of the reducing gas in the heating step in the present invention is 40 to 150 cm / s, preferably 40 to 1 cm / s.
40 cm / s. When the superficial velocity is less than 40 cm / s, the speed at which the water vapor generated by the reduction of the hematite particles is carried out of the system becomes extremely slow, so that the coercive force at the upper part of the layer and the SFD of the coating film are reduced, and the whole is high. No coercive force is obtained. When it exceeds 150 cm / s, the target spindle-shaped alloy magnetic particles can be obtained, but the reduction temperature requires a high temperature,
Problems such as scattering and breakage of granules are likely to occur, which is not preferable.

The heating rate according to the present invention is 10 to 80 ° C./m
in, preferably 20 to 70 ° C./min. When the rate of temperature rise is less than 10 ° C./min, the reduction proceeds very slowly from the lower part of the layer in the low temperature region, so that the obtained metal magnetic particles having a very small crystallite size are likely to be generated, and the generated water vapor Is very slow, the coercive force in the upper part of the layer, the SFD of the coating film are reduced, and the crystallinity of the lower layer is deteriorated, so that a high coercive force cannot be obtained as a whole. On the other hand, when the temperature exceeds 80 ° C./min, the behavior becomes close to the behavior when the temperature is raised in nitrogen, rapid reduction occurs, and the transition to α-Fe occurs under the condition of a relatively high water vapor partial pressure. The resulting metal magnetic particles also have a large crystallite size, a low coercive force, and a poor SFD of the coating film.

The atmosphere in the heating and reducing step in the present invention is a reducing gas, and hydrogen is preferably used as the reducing gas.

The heat reduction temperature in the heat reduction step in the present invention is 400 to 700 ° C., preferably 400 to 650 ° C.
More preferably, it is 400 to 600 ° C. The reduction temperature is
It is preferable to appropriately select from the above temperature range according to the type and amount of the compound used for coating the starting material. When the heat-reduction temperature is lower than 400 ° C., the progress of the reduction is very slow and not industrial, and the obtained spindle-shaped alloy magnetic particles have a low saturation magnetization value. If it exceeds 700 ° C,
The reduction reaction proceeds abruptly, causing shape destruction of the particles and sintering between the particles, and the coercive force is reduced.

The spindle-shaped metal magnetic particles containing iron as a main component after heat reduction can be obtained by a known method, for example, immersion in an organic solvent such as toluene, or the like. After once replacing the atmosphere of the particles with an inert gas,
It can be taken out into the air by a method of finally producing air while gradually increasing the oxygen content in the inert gas, or a method of gradually oxidizing using a gas obtained by mixing oxygen and water vapor.

As described above, under the specific reduction conditions, the reduction proceeds uniformly in the entire fixed layer, and the difference in magnetic properties between the upper and lower portions of the fixed layer becomes small. As a result, the obtained spindle-shaped metal magnetic particles are dispersed even in a low magnetic field. It has even better properties (high squareness ratio, high orientation), and has both excellent weather resistance and excellent magnetic force distribution. Specifically, regarding the magnetic property difference between the upper and lower fixed layers,
The coercive force is 3.2 KA / m (40 Oe) or less, preferably 2.4 KA / m (30 Oe) or less, and the saturation magnetization is 4 Am ²
/ Kg (4 emu / g) or less, preferably 3 Am ² / k
g (3 emu / g) or less, and the squareness ratio (σr / σs)
003, preferably 0.002 or less, and a crystallite size D110 of 8 ° or less, preferably 6 ° or less.

As described above, for example, particles constituting spindle-shaped metal magnetic particles containing iron as a main component and having the following preferable characteristics can be obtained. That is, the average major axis diameter is 0.15 to 0.25 μm, and the size distribution (standard deviation / average major axis diameter) is 0.26 or less. The average minor axis diameter is 0.015 to 0.025 μm.
The shape is a spindle shape, and the axial ratio (major axis diameter / minor axis diameter) is 5 to 9. If the average major axis diameter is less than 0.15 μm, the coercive force becomes too high, the dispersibility in the paint is poor, and the weather resistance of the coating film tends to deteriorate. On the other hand, if it exceeds 0.25 μm, it becomes difficult to obtain the target coercive force within the range of the axial ratio of the present invention. The smaller the size distribution, the better. Therefore, the lower limit is not particularly limited. However, from the viewpoint of industrial productivity, about 0.10 is appropriate. On the other hand, 0.26
May be exceeded, but the oxidation stability, heat resistance and SFD of the coating film
No further improved characteristics can be obtained. If the average minor axis diameter is less than 0.015 μm, sufficient oxidation stability and heat resistance cannot be obtained, while if it exceeds 0.025 μm, the desired coercive force cannot be obtained. Further, if the axial ratio is less than 5, the desired coercive force cannot be obtained, and both the squareness ratio and the orientation ratio of the coating film deteriorate. On the other hand, if it exceeds 9, the coercive force becomes too high, or the oxidation stability and heat resistance deteriorate.

The spindle-shaped metal magnetic particles mainly composed of iron preferably have a specific surface area of 30 to 60 m ² / g, more preferably 35 to 55 m ² / g. Specific surface area is 30
If it is less than m ² / g, sintering has already occurred in the heat reduction step, and it is difficult to improve the squareness ratio of the coating film, whereas if it exceeds 60 m ² / g, the viscosity in the paint becomes too high and it is difficult to disperse. Is not preferred.

The particles constituting the spindle-shaped metal magnetic particles containing iron as a main component contain 0.5 to less than 10 atomic% of Co with respect to the total Fe. Further, Al is contained in an amount of 5 to 10 atomic% with respect to all Fe. Further, it contains 1 to 5 atomic% of the rare earth element with respect to the total Fe, and the ratio of Al / the rare earth element is 1.5 to 5. The reason for each limitation is the same as in the case of spindle-shaped hematite particles.

Further, the particles constituting the spindle-shaped metal magnetic particles containing iron as a main component are stable in oxidation of saturation magnetization (σs) one week after the accelerated aging test in an environment of a temperature of 60 ° C. and a relative humidity of 90%. The property (Δσs) is 6% or less in absolute value, and the ignition temperature is 145 ° C. or more. Also, the coercive force Hc
Is 103.5 to 143.2 KA / m (1300 to 180
0 Oe), preferably 107.4 to 139.3 KA / m.
(1350-1750 Oe) and the saturation magnetization s is 110
^{~160Am 2 / kg (110~160emu / g} ),
The squareness ratio (σr / σs) is 0.50 or more. Further, the crystallite size D110 is 130-180 °, preferably 1
40-170 °.

The spindle-shaped metal magnetic particles containing iron as a main component preferably have a squareness ratio (Br / Bm) in the coating film characteristics of 397.9 KA / m (5 kOe) in a magnetic field orientation of preferably 0.
85 or more, more preferably 0.86 or more, the orientation (O
R) is preferably 3.1 or more, more preferably 3.2 or more, and the coercive force distribution (SFD) is preferably 0.51 or less,
More preferably, it is 0.50 or less. 238.7
The squareness ratio (Br / Bm) in the coating properties at a magnetic field orientation of KA / m (3 kOe) is preferably 0.84 or more, more preferably 0.85 or more, and the orientation (OR) is preferably 3.0 or more, It is more preferably at least 3.1, and the coercive force distribution (SFD) is preferably at most 0.52, more preferably at most 0.51. Further, the weather resistance (ΔBm) in the coating film characteristics is 5% or less for a coating film having a magnetic field orientation of 397.9 KA / m (5 kOe).

[0094]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical embodiment of the present invention is as follows. The average major axis diameter, minor axis diameter, and axis ratio of each particle were all shown as average values of numerical values measured from electron micrographs. The standard deviation was also determined at the same time, and the value obtained by dividing the standard deviation by the average major axis diameter was shown as a size distribution.

The specific surface area of the particles is "Monosorb MS-1".
1 "(manufactured by Cantachrome Co., Ltd.) and the value measured by the BET method.

The crystallite size of each particle indicates the size of the crystal particle measured by the X-ray diffraction method, and indicates the thickness of the crystal particle in a direction perpendicular to each crystal plane of each particle. It is shown by a value calculated from the diffraction peak curve for each crystal plane using the following Scherrer equation.

Crystallite size = Kλ / βcos θ where β = half-width of the true diffraction peak corrected for the machine width due to the apparatus (in radians) K = Scherrer constant (= 0.9) λ = wavelength of X-ray (Cu Kα ray 0.1542 nm) θ = diffraction angle (corresponding to the diffraction peak of each crystal plane)

The magnetic properties of the metal magnetic particles containing iron as a main component were measured using an external magnetic field of 795.8 KA / m (1) using a “vibrating sample magnetometer VSM-3S-15” (manufactured by Toei Industry Co., Ltd.).
0 kOe).

The amounts of Co, Al, and rare earth elements of the spindle-shaped goethite particles and the spindle-shaped metal magnetic particles containing iron as a main component are described in "Inductively Coupled Plasma Emission Spectrometer SPS400."
0 "(manufactured by Seiko Denshi Kogyo KK).

The magnetic coating film was prepared by adding the following components to a 100 cc polybin at the following ratio and mixing and dispersing for 8 hours with a paint shaker (manufactured by Red Devil Co.) to obtain a 25 μm thick polyethylene. It was obtained by coating on a terephthalate film with an applicator to a thickness of 50 μm, and then drying in a two-level magnetic field of 238.7 KA / m (3 kOe) and 397.9 KA / m (5 kOe). . 3 mmφ steel ball 800 parts by weight Spindle-shaped metal magnetic particles mainly composed of iron 100 parts by weight Polyurethane resin having sodium sulfonate group 20 parts by weight Cyclohexanone 83.3 parts by weight Methyl ethyl ketone 83.3 parts by weight Toluene 83.3 parts by weight The magnetic properties of the obtained magnetic coating film were measured.

The oxidation stability (Δσs) of the saturation magnetization value (σs) of the powder and the oxidation stability (ΔBm) of the saturation magnetic flux density (Bm) of the magnetic coating film are determined in a thermostatic chamber at a temperature of 60 ° C. and a relative humidity of 90%. After the accelerated aging test in which the powder or the magnetic coating film is allowed to stand for one week, the saturation magnetization value of the powder and the saturation magnetic flux density of the magnetic coating film were measured, respectively. The value obtained by dividing the difference (absolute value) between σs ′ and Bm ′ after one week by σs and Bm before the start of the test, that is, Δσs, Δ
Bm was calculated for each.

The ignition temperature of the powder was measured using a “TG / DTA measuring device SSC5100TG / DTA22” (manufactured by Seiko Instruments Inc.).

Spindle-shaped goethite particles, spindle-shaped hematite particles and spindle-shaped metal magnetic particles were produced by the following methods, and various properties and physical properties were measured or calculated by the methods described above. (Production of spindle-shaped goethite particles) Sodium carbonate 25m
ol and 19 mol of an aqueous sodium hydroxide solution (sodium hydroxide is 27.5 m in terms of a prescribed conversion with respect to the mixed alkali)
ol%. ) Containing 30 L of mixed alkaline aqueous solution
Into a bubble column, and nitrogen gas is introduced at a superficial velocity of 2.20 c.
Adjust to 47 ° C. while venting at m / s. Then Fe ²⁺
20 L of an aqueous solution of ferrous sulfate containing 20 mol (a mixed alkali aqueous solution with respect to ferrous sulfate is 1.72 in a standard conversion)
This corresponds to 5 equivalents. ) Was put into a bubble column and aged for 30 minutes. Then, 4 L of an aqueous solution of cobalt sulfate containing 1.0 mol of Co ²⁺ (corresponding to 5 atom% in terms of Co with respect to all Fe) was added, and further 4 hours. After aging for 30 minutes (10% of the total aging time of the Co addition time), air was passed at a superficial velocity of 1.50 cm / s, and the oxidation rate of Fe ²⁺ was 4%.
The oxidation reaction was performed to 0% to generate goethite seed crystal particles. An aqueous suspension containing goethite seed particles oxidized to an oxidation rate of Fe ²⁺ of 40% was fractionated, and the goethite seed particles obtained by quickly washing, filtering, and washing with a dilute acetic acid aqueous solution were obtained. The composition analysis of
Was 54.00% by weight and Co was 2.45% by weight.
The crystallite size D020 (seed crystal particles) is 245 °,
D110 (seed crystal particles) was 125 °.

Next, the air flow rate was adjusted to the superficial velocity of 2.30.
After increasing to ³ cm / s, 1 L of an aluminum sulfate aqueous solution containing 1.6 mol of Al ³⁺ (8% in terms of Al with respect to all Fe)
It corresponds to atomic%. ) Was added at a rate of 3 ml / sec or less to carry out an oxidation reaction, followed by water washing with a filter press to an electric conductivity of 60 μS / cm to obtain a press cake.

The goethite particles obtained by drying and pulverizing a part of the cake by a conventional method have a spindle shape, a BET specific surface area of 135.4 m ² / g,
Average major axis diameter is 0.275 μm, σ (standard deviation) is 0.0
459 μm, size distribution (standard deviation / major axis diameter) is 0.1
67, the average minor axis diameter was 0.0393 μm, the axial ratio was 7.0, and no dendritic particles were present. The crystallite size D020 of the whole particles was 262 °, and D110 was 131.
Å, and the ratio D020 / D110 was 2.0. Further, the relationship with the crystallite size of the seed crystal particles is D02
0 / D020 (seed crystal particles) was 1.07, and D110 /
D110 (seed crystal particles) was 1.05. Also, Fe
Is 51.5% by weight, Co is 2.72% by weight, and Al is 1.
By comparison with the analysis value of the goethite seed crystal particles, the Co content of the seed crystal part was 4.30 atomic% with respect to Fe of the seed crystal part, and the existence ratio of Co in the seed crystal part was 99% by weight. Is 86.0, when the existing ratio of all Co to all Fe in the whole particles is 100, and the existing ratio of Co in the surface layer is 109.3 by calculation.
The Co content of the whole particles was 5 atomic% based on the total Fe, and the Al content was 8 atomic% based on the total Fe.
Al was present only in the surface layer.

Next, a press cake containing 1000 g of spindle-shaped goethite particles (9.22 mol as Fe) was sufficiently dispersed in 40 L of water.
2 L of a neodymium nitrate aqueous solution containing 1.2 g of neodymium nitrate hexahydrate (corresponding to 3 at% as Nd based on the total Fe in the goethite particles) was added thereto, followed by stirring, and then a 25.0 wt% concentration of neodymium nitrate. After adjusting the pH to 9.5 by adding an aqueous solution of sodium carbonate as a precipitant, the mixture was washed with a filter press, and the obtained press cake was extruded on a molding plate having a hole diameter of 4 mm using a compression molding machine and dried at 120 ° C. Thus, a molded article of goethite particles coated with an Nd compound was obtained. The content of Co in the goethite particles obtained by pulverizing the molded particles was 5 atomic% with respect to the total Fe, the content of Al was 8 atomic% with respect to the total Fe, and the content of Nd was the total Fe. And the ratio of Al to Nd is Al / Nd
(Atomic% based on total Fe) was 2.67. Al was present only in the intermediate layer portion, and Nd was present only in the outermost layer portion.

(Production of Spindle-Shaped Hematite Particles)
Spindle-shaped goethite particles coated with the compound
For the size of 110, D104 of the obtained spindle-shaped hematite particles is D104 / D110 (goethite particles).
73 in the air so as to fall within the range of 0.9 to 1.1.
The resultant was dehydrated by heating at 0 ° C. to obtain spindle-shaped hematite particles composed of spindle-shaped hematite particles having an outermost layer composed of an Nd compound.

The obtained spindle-shaped hematite particles had an average major axis diameter of 0.241 μm and a (standard deviation) of 0.0434 μm.
m, size distribution (standard deviation / average major axis diameter) is 0.18
0, average short axis diameter is 0.0309 μm, axis ratio is 7.8, B
The ET specific surface area is 48.5 m ² / g, and the content of Co in the particles is 5 atomic% with respect to all Fe, the content of Al is 8 atomic% with respect to all Fe, and the content of Nd is The amount is all Fe
Was 3 atomic%, and Al / Nd was 2.67. Further, the crystallite size D104 is 130 °, and the ratio of goethite particles to D110 is D104 / D1.
It was 0.99 as 10 (goethite particles). D110 is 285 °, and the ratio D110 / D
104 was 2.19.

(Production of spindle-shaped metal magnetic particles)
Layered spindle-shaped hematite particles having an outermost layer
480 cm
H at a gas superficial velocity of 70 cm / s at ℃ _TwoVent the gas,
The temperature is raised to 480 ° C at a reduction rate of 0 ° C / min.
And then heat-reduce. Then switch to nitrogen gas
And cooled to 70 ° C,
Gradually increase the oxygen partial pressure to achieve the same ratio as air particles
A stable oxide film was formed on the surface.

From the obtained spindle-shaped metal magnetic particles, a part was extracted from the lower part (part having a layer height of 2 cm or less) and part from the upper part (part having a height of 5 cm or more), and magnetic properties and crystallites were separated separately from the remaining particles. The size was measured.

The obtained iron-containing metal magnetic particles containing Co, Al and Nd have an average major axis diameter of 0.18.
0 μm, σ (standard deviation) 0.0422 μm, size distribution (standard deviation / major axis diameter) 0.234, average minor axis diameter 0.0230 μm, axial ratio 7.8, BET specific surface area 4
The particles consisted of 3.4 m ² / g, particles having an X-ray crystal particle diameter D110 of 155 °, and had a spindle shape, uniform particle size and few dendritic particles. Also, the content of Co in the particles is
e is 5 atomic%, and the content of Al is 8
The content of atomic% and Nd was 3 atomic% with respect to the total Fe, and the ratio of Al / Nd was 2.67. The magnetic properties of the spindle-shaped metal magnetic particles are as follows.
3.5 KA / m (1552 Oe), and the saturation magnetization s
Is 130.0 Am ^{2 /} kg (130.0 emu / g),
The squareness ratio (σr / σs) is 0.502, and the oxidation stability Δσs of the saturation magnetization is 4.5% as an absolute value (actual measurement value -4.5).
%) And the ignition temperature was 156 ° C. When the orientation magnetic field is 397.9 KA / m (5 kOe), the sheet characteristics are such that the sheet Hc is 118.3 KA / m (1486 Oe).
e), sheet squareness ratio (Br / Bm) 0.875, sheet OR 3.45, sheet SFD 0.470, ΔBm
Was 3.0% (measured value -3.0%). When the orientation magnetic field is 238.7 KA / m (3 kOe), the sheet Hc is 117.8 KA / m (1480 Oe), the sheet squareness ratio (Br / Bm) is 0.866, and the sheet OR is 3.3.
4. Sheet SFD was 0.485 and ΔBm was 2.8% (actually measured value -2.8%).

The spindle-shaped metal magnetic particles extracted from the lower layer portion have a coercive force Hc of 124.2 KA / m (1561 O / m).
e), the saturation magnetization σs is 129.6 Am ² / kg (12
9.6 emu / g), squareness ratio (σr / σs) is 0.50
3. The X-ray particle size D110 was 153A. On the other hand, the spindle-shaped metal magnetic particles extracted from the upper layer portion have a coercive force H
c is 122.9 KA / m (1545 Oe), saturation magnetization σ
s is 130.8 Am ^{2 /} kg (130.8 emu /
g), the squareness ratio (σr / σs) was 0.501, and the X-ray particle size D110 was 156 °.

[0113]

According to the present invention, specific spindle-shaped hematite particles are used as a starting material, and specific reduction conditions, that is, the thickness of the layer is made thinner as a whole, so that there is no delay in local temperature increase in the layer, By using a reactive gas and specifying the gas superficial velocity and the heating rate, reduction proceeds uniformly in the entire layer, and as a result, there is little difference in quality between the top and bottom of the layer, and the metal magnetism shows excellent quality as a whole. It has been found that particles can be obtained.

The effect of using specific hematite particles as a starting material and the effect of using hematite particles composed of specific goethite particles as a starting material are considered as follows. Conventionally, various metal salts have been added to improve the shape and the like of spindle-shaped goethite particles as a starting material for metal magnetic particles containing iron as a main component. Among them, it is known that Co forms a solid solution with iron when formed into metal magnetic particles, has a function of increasing magnetization, and increasing its coercive force Hc.

On the other hand, the action of these elements in the formation reaction of spindle-shaped goethite particles is due to the fact that, when Co is dissolved, fine particles are obtained and the particle diameter in the minor axis direction is small. It is known that goethite particles having an appropriately large axial ratio can be obtained.

The present inventors have examined in detail the function of Co in the spindle-like goethite formation reaction. As a result, when Co is added during the ripening period, the time of the addition is changed to within 1/2 of the total aging time. By adding and properly controlling the superficial superficial velocity, it is possible to increase the minor axis diameter of the particles and to relatively decrease the axial ratio. It was found that when a coating film was used, the squareness ratio and orientation were dramatically improved.

Despite the fact that the spindle-shaped goethite particles, which are the starting materials, have a large short axis diameter and a relatively small axial ratio, the reason why the squareness and orientation of the coating film made of metal magnetic particles are excellent is as follows. The growth of each crystal plane (D020, D110) of the seed crystal particles of the spindle-shaped goethite particles is different from the growth of each crystal plane after the surface layer particles are formed.
In addition to the fact that 020 / D110 is 1.8 to 2.4, the short axis diameter is large and the axis ratio is relatively small. It is thought that the sintering prevention property was very excellent and the shape destruction was effectively suppressed.

Further, the present inventors have conducted intensive studies on heat treatment before heat reduction from the viewpoint of sintering prevention performance.
The relationship between the surface and the crystallite size of the D104 surface of the obtained spindle-shaped hematite particles is D104 / D110 (goethite).
It was found that only when the ratio was within the range of 0.9 to 1.1, when the coating film was formed as spindle-shaped metal magnetic particles, a high squareness ratio, a high orientation, and a low coercive force distribution were exhibited.

By defining the growth ratio of specific crystal planes from spindle-shaped goethite particles to spindle-shaped hematite particles, the reason for exhibiting a high squareness ratio, high orientation, and low coercive force distribution in the coating film is as follows. That the obtained spindle-shaped hematite particles have a specific crystal size ratio (D110 /
D104 is 2.0 to 4.0), and in addition, the crystal growth of the spindle-shaped hematite particles in the heat treatment is a crystallite size capable of appropriately controlling the reduction rate, and effectively prevents sintering during reduction. At the same time, it is considered that the sintering and shape destruction by the heat treatment are extremely reduced because it is in the range where the growth is not excessively larger than necessary beyond the shaped body particles.

Further, the present inventors have studied the ratio of Al to the rare earth element. As a result, when the ratio of Al / the rare earth element is in the range of 1.5 to 5, the metal magnetic particles have excellent oxidation stability. In addition, it has been found that the ignition temperature is very good.
Although the reason is not clear, it is considered that these elements mainly form the outermost layer of the metal magnetic particles as oxides.Although Al has a higher antioxidant effect due to aging as an oxide film than rare earth elements, However, it is considered that a rare earth element, which is also very stable as an oxide against heat, is considered to be strong, and it is presumed that the rare earth element has an optimal composition that makes use of both advantages.

As described above, even in the spindle shape, the short axis diameter is made large, the axis ratio is relatively low, and the sintering prevention effect is maximized in each heat treatment step, based on a concept completely different from the conventional concept. By exhibiting, while maintaining coercive force, excellent particle size distribution, dendritic particles are not mixed, and
And a rare earth element in a specific ratio, it is possible to obtain spindle-shaped metal magnetic particles mainly composed of iron having excellent oxidation stability and ignition temperature, and the obtained metal magnetic particles and sulfonic acid can be obtained. When a paint is formed with a binder resin having sodium as a functional group, the squareness ratio and orientation, which are the properties of the coating film, are improved even in a low magnetic field, and the coercive force distribution is excellent, and in addition, the weather resistance is improved. Have been found to be satisfactory, and the present invention has been completed.

[0122]

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, which do not limit the scope of the present invention.

Examples 1 to 6, Comparative Examples 1 to 5 (1) Production of spindle-shaped goethite particles Spindle-shaped goethite particles 1 and 2 were obtained as shown in Table 1 according to the embodiment of the present invention. Table 1 shows various properties of the obtained spindle-shaped goethite particles.

[0124]

[Table 1]

(2) Production of Spindle-Shaped Hematite Particles Spindle-shaped hematite particles 1 and 2 were obtained as shown in Table 2 according to the embodiment of the present invention. That is, the spindle-shaped goethite particles 1 and 2 obtained in the above (1) were used, and the kind and amount of the coating used for the sintering prevention treatment, the heating dehydration temperature, and the temperature of the subsequent heating treatment were variously changed. In the same manner as in the embodiment, spindle-shaped hematite particles were obtained. The production conditions are shown in Table 2, and various properties of the obtained spindle-shaped hematite particles are shown in Table 3.

[0126]

[Table 2]

[0127]

[Table 3]

(3) Production of Metallic Magnetic Particles Containing Iron as Main Component The spindle-shaped hematite particles obtained in the above (2) are used as particles to be treated, and the layer height, the temperature-raising gas type, and the gas vacancy in the heat reduction step are reduced. Metal magnetic particles containing iron as a main component were obtained in the same manner as in the embodiment of the present invention except that the tower speed, the heating rate, and the reduction temperature were variously changed. Table 4 shows the reduction conditions at this time.
Table 5 shows the properties of the obtained metal magnetic particles containing iron as a main component, Table 6 shows the properties of the metal magnetic particles above and below the layer, and Table 7 shows the properties of a magnetic coating film.

[0129]

[Table 4]

[0130]

[Table 5]

[0131]

[Table 6]

[0132]

[Table 7]

[0133]

As described above, according to the present invention, a specific spindle-shaped hematite particle is used as a starting material, and a reducing gas having a specific layer height and a specific gas superficial velocity at a temperature rise is used. Further, by specifying the heating rate, the reduction proceeds uniformly in the entire layer, and as a result, the difference in characteristics between the upper and lower layers is small, and the spindle-shaped metal magnetic particles containing iron as a main component are the same as those in the above examples. As shown, the particle size is uniform, the dendritic particles are not mixed, and the dispersibility is better even in a low magnetic field (high squareness ratio,
(Highly oriented), which has more excellent weather resistance and excellent coercive force distribution, and is particularly useful as a magnetic particle for high recording density, high sensitivity, and high output.

Claims (7)

[Claims] 1. An alloy containing 0.5 to less than 10 atomic% of Co with respect to total Fe, 5 to 10 atomic% of Al with respect to total Fe, and 1 to 5 atomic% of a rare earth element with respect to total Fe. And an average major axis length of 0.17 to 0.28 μm with an Al / rare earth element ratio of 1.5 to 5 (atomic% relative to Fe) and a size distribution (standard deviation / major axis length) of 0 .20 or less, spindle-shaped hematite particles having an average minor axis length of 0.022 to 0.035 μm, an average axis ratio of 5 to 10, and a crystallite size ratio D110 / D104 of 2.0 to 4.0 are placed in a reducing device. To form a fixed layer having a layer height of 3 to 15 cm, and then, in a reducing gas atmosphere having a superficial tower speed of 40 to 150 cm / s, a heating rate of 10 to 80 ° C./min and 400 to 7
A method for producing spindle-shaped metal magnetic particles containing Fe as a main component, wherein the temperature is raised to 00 ° C. to reduce the spindle-shaped hematite particles. 2. The spindle-shaped hematite particles convert Co to all Fe
0.5 to less than 8 at% and Al having an average major axis length of 0.18 to
Spindle-shaped goethite particles having a size of 0.30 μm, a size distribution (standard deviation / long axis length) of 0.22 or less, an average short axis length of 0.025 to 0.045 μm, and an average axis ratio of 5 to 10. The method for producing spindle-shaped metal magnetic particles containing Fe as a main component according to claim 1, which is obtained from spindle-shaped goethite particles. 3. The spindle-shaped goethite particles have a crystallite size ratio D020 / D110 of 1.8 to 2.4 and a crystallite size ratio D020 / D020 (seed crystal particles) with respect to the seed crystal particles of 1.05. ~ 1.20, D110 / D110
The method for producing spindle-shaped metal magnetic particles containing Fe as a main component according to claim 2, wherein (seed crystal particles) is 1.02 to 1.10. 4. An aqueous suspension containing a ferrous-containing precipitate obtained by reacting a spindle-shaped goethite particle with a mixed alkali aqueous solution of an aqueous alkali carbonate solution and an aqueous alkali hydroxide solution and an aqueous ferrous salt solution. After aging in a non-oxidizing atmosphere, an oxygen-containing gas is passed through the aqueous suspension to produce spindle-shaped goethite seed particles by an oxidation reaction, and then the seed particles and the ferrous precipitate When an oxygen-containing gas is passed through the aqueous suspension containing the solution, a goethite layer is grown on the surface of the seed crystal particles by an oxidation reaction to produce spindle-shaped goethite particles. In the aqueous suspension containing the ferrous-containing precipitate during aging prior to the start of the oxidation reaction, 0.5 to 8 atomic% in terms of Co with respect to all Fe, Less than Co
The compound is obtained by adding a compound, performing an oxidation reaction in the range of 40 to 50% of the total Fe ²⁺ , and adding an Al compound of 5 to 10 atomic% in terms of Al with respect to the total Fe. 4. The method for producing spindle-shaped metal magnetic particles containing Fe as a main component according to 2 or 3. 5. The spindle-shaped hematite particles according to claim 2,
Or 1 to 5 atomic% with respect to all Fe in terms of a rare earth element so that the spindle-shaped goethite particles according to 4 are in a ratio of 1.5 to 5 (atomic% with respect to each Fe) of Al / rare earth element.
650-800 ° C. in a non-reducing atmosphere such that after treatment with a sintering inhibitor comprising a rare earth element compound of The method for producing spindle-shaped metal magnetic particles containing Fe as a main component according to claim 1, which is obtained by performing a heat treatment in (1). 6. A spindle-shaped metal magnetic particle containing Fe as a main component, wherein Co is contained in an amount of 0.5 to less than 10 atomic% of the total Fe.
Al contains 5 to 10 atomic% with respect to the total Fe and 1 to 5 atomic% of the rare earth element with respect to the total Fe, and the Al / rare earth element ratio is 1.5 to 5 (atomic% with respect to Fe, respectively). An average major axis length is 0.15 to 0.25 μm, a size distribution (standard deviation / major axis length) is 0.26 or less, an average minor axis length is 0.015 to 0.025 μm, and an average axis ratio is 5 to 9 The ignition temperature is 145 ° C. or higher, the oxidation stability is 6% or lower,
The coercive force is 103.5 to 143.2 KA / m (1300 to KA / m).
The method for producing spindle-shaped metal magnetic particles containing Fe as a main component according to claim 1, which is 1800 Oe). 7. The method for producing spindle-shaped metal magnetic particles containing Fe as a main component according to claim 1, wherein the spindle-shaped metal magnetic particles containing Fe as a main component are used for magnetic recording.