JP2000327334A - Spindle-shaped goethite grain, spindle-shaped hematite grain, spindle-shaped metal magnetic grain consisting essentially of iron and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a metallic magnetic grain good in dispersibility and having excellent weather resistance and coercive force distribution by specifying the crystallite size and shape of a goethite grain containing Co and Al in a specific proportion based on the total Fe. SOLUTION: This spindle-shaped goethite grain comprises >=0.5 and <8 atomic% of Co based on the total Fe and 5-10 atomic % of Al and has 0.18-0.30 μm average major axial length, <=0.22 size distribution (standard deviation/major axial length), 0.025-0.045 μm average minor axial length, 5-10 average axial ratio, 1.8-2.4 crystallite size ratio D020/D110, 1.05-1.20 crystallite size ratio D020/D020 (seed crystal grain) for the seed crystal grain and 1.02-1.10 crystallite size ratio D110/D110 (seed crystal grain) for the seed crystal grain. The spindle-shaped goethite grain is produced by mixing an aqueous solution of an alkali carbonate with an aqueous solution of an alkali hydroxide, reacting an aqueous solution of a ferrous salt therewith, aging an aqueous suspension containing the resultant iron(II)-containing precipitate, then aerating the aqueous suspension with an oxygen-containing gas, producing a spindle-shaped goethite seed crystal grain and adding Co and Al thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to spindle-shaped goethite particles, spindle-shaped hematite particles having a uniform particle size, a large short axis diameter, an appropriate axial ratio, and extremely excellent sintering prevention performance. And the dispersibility obtained by using the spindle-shaped hematite particles as a starting material is good (high squareness ratio, high orientation),
Combining excellent weather resistance and excellent coercive force distribution
AT, 8mm, Hi-8 tape, professional VTR tape,
The present invention relates to spindle-shaped metal magnetic particles containing iron as a main component and having a coercive force of 1300 to 1800 Oe suitably used for computer tapes or disks.

[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, the magnetic metal particles include goethite particles as starting materials, hematite particles obtained by heating and dehydrating the goethite particles, or particles in which each of the above-mentioned particles contains a different metal other than iron. And then heat-reduced 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 goethite particle shape and particle size.

There are two types of goethite particles as starting materials, 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.

For the above reasons, consumer DAT, 8
mm, Hi-8 tape, VTR tape for business use, audio and video such as computer tape or disk, metal magnetic particles used for magnetic recording / reproducing equipment media for computers have a large particle size at present.
In addition, metal magnetic particles having a large axial ratio and having a needle-like shape with a coercive force of 1300 to 1800 Oe, which tends to increase the squareness ratio and orientation of the magnetic coating film, are generally used. But,
As described above, the particle size distribution is insufficient, and the improvement has been performed.However, the particle size is relatively large depending on the relatively wide particle size distribution as compared with the spindle-shaped particles. The weather resistance is not sufficient.

[0011]

In view of the background described above, metal magnetic particles having a coercive force of 1300 to 1800 Oe are spindle-shaped particles and have good dispersibility (high squareness ratio and high orientation). There is a demand for metal magnetic particles having both excellent weather resistance and excellent coercive force distribution.

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, and a low specific surface area can be obtained. 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 Nos. 9-295814 and 10-245233 disclose the idea of increasing the axial ratio in the same manner as conventional needle-shaped metal magnetic particles, and have a high spindle-shaped metal magnetic particle. Although a technique for obtaining a magnetic force and an excellent coercive force distribution is disclosed, no consideration is given to oxidation stability at all. Note that, in the above-mentioned Japanese Patent Application Laid-Open No. 10-245233, the crystallite size D10 of spindle-shaped hematite particles is described.
When the relationship between D4 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 insufficient in terms of sintering or shape destruction of particles in the heat treatment 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 characteristic 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-gonal 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.

Accordingly, the present invention provides a spindle-shaped metal magnetic particle having an excellent particle size distribution, and has a high dispersibility and a high squareness ratio in a coating film, which are characteristics of an acicular metal magnetic particle.
In obtaining spindle-shaped metal magnetic particles having high orientation and further excellent particle size distribution, achieving the concept completely different from the conventionally thought, and providing the metal magnetic particles having the above characteristics. This is a technical issue.

[0019]

The first aspect of the present invention is as follows.
0.5 to less than 8 atomic% of Co and Al
Is a spindle-shaped goethite particle having an average major axis length of 0.18 to 0.30 μm containing 5 to 10 atomic% with respect to the total Fe, and a size distribution (standard deviation / major axis length) of 0.22 or less;
Average short axis length 0.025-0.045 μm, average axis ratio 5
Spindle-shaped goethite particles characterized in that they are 10.

In a preferred embodiment, the spindle-shaped goethite particles have a crystallite size ratio D020 / D110 of 1.
And the crystallite size ratio D020 / D020 (seed crystal particles) with respect to the seed crystal particles is 1.05 to 1.
20, D110 / D110 (seed crystal particles)
1.10.

A second aspect of the present invention is that Co is contained in an amount of 0.5 to less than 10 atomic% with respect to all Fe, and Al is contained in an amount of 5 to 10% with respect to all Fe.
10 atomic% and a rare earth element in an amount of 1 to 5 atomic% based on the total Fe, and an Al / rare earth element ratio of 1.5 to 5
(The average long axis length is 0.17, each being an atomic% with respect to Fe)
Spindle-shaped hematite particles having a size distribution (standard deviation / long axis length) of 0.20 or less, an average short axis length of 0.022 to 0.035 μm, an average axis ratio of 5 to 10, and a crystallite. Spindle-shaped hematite particles characterized in that the size ratio D110 / D104 is 2.0 to 4.0.

A third aspect of the present invention is that Co is contained in an amount of 0.5 to less than 10 atomic% with respect to all Fe, and Al is contained in an amount of 5 to 10% with respect to all Fe.
10 atomic% and a rare earth element in an amount of 1 to 5 atomic% based on the total Fe, and an Al / rare earth element ratio of 1.5 to 5
(Atom% to Fe) 0.15
０．２0.25 μm, size distribution (standard deviation / long axis length) is 0.30 or less, average short axis length 0.015 to 0.025 μm
m, average axis ratio is 5 to 9, ignition temperature is 135 ° C. or more, oxidation stability is 10% or less, and coercive force is 1300 to 18
The content is spindle-shaped metal magnetic particles mainly composed of iron, which is characterized by being 00 Oe.

A fourth aspect of the present invention is to provide 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 an oxidizing atmosphere,
An oxygen-containing gas is passed through the aqueous suspension to produce spindle-shaped goethite seed crystal particles by an oxidation reaction, and then an oxygen-containing gas suspension is added to the aqueous suspension containing the seed crystal particles and the ferrous-containing precipitate. In growing a goethite layer on the particle surface of the seed crystal particles by oxidizing reaction by passing a gas to produce spindle-shaped goethite particles, at the time of generation of the seed crystal particles, during ripening before the start of the oxidation reaction, To the aqueous suspension containing the ferrous-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 ripening period to carry out an oxidation reaction. A method for producing spindle-shaped goethite particles, which is performed in the range of 40 to 50% of the total Fe ²⁺ , and which comprises adding 5 to 10 atomic% of an Al compound in terms of Al to the total Fe ²⁺ .

A fifth aspect of the present invention is that the spindle-shaped goethite particles are converted to a total of Fe in terms of rare earth element so that the ratio of Al / rare earth element is 1.5 to 5 (atomic% with respect to Fe).
After treatment with a sintering inhibitor consisting of a compound of a rare earth element in an amount of 1 to 5 at.
A process for producing spindle-shaped hematite particles is characterized in that heat treatment is performed at 650 to 800 ° C. in a non-reducing atmosphere so that the ratio becomes 104 / goethite D110 in the range of 0.9 to 1.1.

A sixth aspect of the present invention is to produce spindle-shaped metal magnetic particles containing iron as a main component, wherein the spindle-shaped hematite particles are heat-reduced in a reducing atmosphere at a temperature of 400 to 700 ° C. The content of the law.

First, the spindle-shaped goethite particles according to the present invention will be described. The particles constituting the spindle-shaped goethite particles according to the present invention 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 short 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 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, 0.2
If it exceeds 2, the oxidative 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.
If it exceeds 045 μm, the desired coercive force cannot be obtained.
Furthermore, if the average 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
Alternatively, the oxidation stability and heat resistance deteriorate.

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

The particles constituting the spindle-shaped goethite particles according to the present invention contain 0.5 to 8 atomic% of Co with respect to all Fe.
And less than 5 at% of Al with respect to the total 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 according to the present invention is 1.8.
-2.4 is preferred. The crystallite size D020 is preferably 200 to 280 °, and the D110 is preferably 100 to 140 °. 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, D
When 020 / D110 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 according to the present invention are formed of a seed crystal portion and a surface layer portion, wherein Co is present in the seed crystal portion and the surface layer portion, and Al is present only in the surface layer portion. Exists.

The seed crystal portion refers to a goethite seed crystal particle portion 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 crystallite size ratio of the particles constituting the spindle-shaped goethite particles according to the present invention to the seed crystal particles D020 /
D020 (seed crystal particles) is preferably from 1.05 to 1.20, and D110 / D110 (seed crystal particles) is preferably from 1.02 to 1.10.
10 is preferred. 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 / D020 (seed crystal particles) is less than 1.05;
When 110 / D110 (seed crystal particles) is less than 1.02, the amount of the Al-containing goethite layer in the surface layer decreases, 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 particles constituting the spindle-shaped goethite particles according to the present invention is 100, the proportion of Co in the seed crystal portion is all Co.
Is preferably from 75 to 95, more preferably from 80 to
90. The proportion of Co contained in the surface layer is preferably 103 to 125, more preferably 106 to 120, based on the total Co. 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 refers to Al in the growth reaction.
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.

Next, a method for producing spindle-shaped goethite particles according to the present invention will be described. The particles constituting the spindle-shaped goethite particles according to the present invention 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.

The spindle-shaped goethite seed crystal 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 in a non-oxidizing atmosphere, usually at a temperature of 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-acidic atmosphere, an inert gas (such as nitrogen gas) or a reducing gas (such as hydrogen gas) may be passed through the reaction vessel of the suspension.

In the production reaction of the spindle-shaped goethite seed particles, as the ferrous salt aqueous solution, an aqueous ferrous sulfate solution, an aqueous ferrous chloride solution, or the like can be used. 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. 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 alkali aqueous solution used is 1.3 to 3. equivalent ratio to the total Fe in the ferrous salt aqueous solution.
5, preferably 1.5 to 2.5. 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, so that the target particle size can be controlled. 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 usually 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 8.0-11.5, preferably 8.5-1.
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 by increasing the superficial velocity of the oxygen-containing gas during the reaction for generating seed crystal particles. 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 addition amount 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.

Next, the spindle-shaped hematite particles according to the present invention will be described. The particles constituting the spindle-shaped hematite particles according to the present invention have an average major axis diameter of 0.17 to 0.28 μm.
And the size distribution (standard deviation / average major axis diameter) is 0.2
0 or less. In addition, the average minor axis diameter is 0.022 to 0.0
35 μm. The shape is a spindle shape, and the axial ratio (major axis diameter / minor axis diameter) is 5 to 10. Average major axis diameter is 0.1
If the particle size is less than 7 μm, the coercive force becomes too high when metal magnetic particles are used, 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 0.035 μm
If it exceeds, 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 300, the coercive force becomes too high or the oxidation stability and heat resistance deteriorate.

The spindle-shaped hematite particles according to the present invention are
The ET specific surface area is preferably from 30 to 70 m ² / g, more preferably from 35 to 65 m ² / g. When the BET specific surface area is less than 30 m ² / g, sintering has already occurred in the heat treatment step with the particle size of the present invention, and the size distribution deteriorates.
The size distribution of the metal magnetic particles also deteriorates, and the SFD of the coating film also deteriorates. On the other hand, if it exceeds 70 m ² / g, the prevention of sintering in the heat reduction step becomes insufficient, the size distribution of the metal magnetic particles deteriorates, and the SFD of the coating film also deteriorates.

In the particles constituting the spindle-shaped hematite particles according to the present invention, Co is 0.5 at.
Less than 0 atomic%, Al contains 5 to 10 atomic% with respect to the total Fe, and the content of the rare earth element is 1 to 5 atomic% with respect to the total Fe, and the content of Al / the rare earth element is The ratio (atomic% relative to Fe) is 1.5 to 5.

The crystallite size ratio D110 / D104 of the particles constituting the spindle-shaped hematite particles according to the present invention is 2.0.
４4.0. The crystallite size D104 is 100
Å150 ° and D110 is 200２００300 °. D1
When 10 / D104 is less than 2.0, the particle growth during dehydration heating is excessive, and the particle size distribution is deteriorated along with the growth in the short axis direction, and the coercive force of the obtained metal magnetic particles is low. , Dispersibility also deteriorates. 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 according to the present invention are formed of a seed crystal part, an intermediate layer part and an outermost layer part, wherein Co is present in the seed crystal part and the intermediate layer part, Al exists only in the intermediate layer portion, and rare earth elements exist only in the outermost layer portion. In the outermost layer, other elements such as Al, Si, B, Ca, and M are supplemented as necessary to improve the sintering prevention effect and adjust the magnetic field.
One or more of compounds of elements selected from g, 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.

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 entirety of the particles constituting the spindle-shaped hematite particles according to the present invention is 100, the proportion of Co in the seed crystal portion is all Co.
Is preferably from 75 to 95, more preferably from 80 to
90. The proportion of Co contained in the intermediate layer is preferably 103 to 125, more preferably 106 to 120, based on the total Co. 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. In addition, the seed crystal Co
When the abundance ratio of Co exceeds 95 and the abundance ratio of Co in the intermediate layer portion is less than 103, Co in the seed crystal portion is large and it is easy to form a Co alloy. , The surface layer portion is not easily alloyed with Co, and the magnetic properties as a whole tend to be deteriorated.
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 0.5 atomic% or more and less than 10 atomic% with respect to all 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.

Next, a method for producing spindle-shaped hematite particles according to the present invention will be described. In the present invention, the spindle-shaped goethite particles obtained as described above are coated on the surface of the spindle-shaped goethite particles with a sintering inhibitor to prevent sintering prior to the heat dehydration treatment.

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 the powder coercive force distribution (SFDr) is deteriorated when metal magnetic particles are used. 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 effect of preventing sintering and adjust the magnetic properties, 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 the sintering inhibitor or the like in advance, sintering between the particles and the 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.
A sintered body also exists, and when it is used as a coating film, both the squareness ratio and the SFD 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 metal magnetic particles mainly composed of iron according to the present invention will be described. The particles constituting the spindle-shaped metal magnetic particles containing iron as a main component according to the present invention have an average major axis diameter of 0.15 to 0.25 μm and a size distribution (standard deviation / average major axis diameter) of 0. 30 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 5-9.
It is. 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, when it exceeds 0.30, oxidation stability and heat resistance deteriorate, and SFD of the coating film also deteriorates, making it difficult to achieve high-density recording. 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 according to the present invention preferably have a specific surface area of 30 to 60 m ² / m ² .
g, more preferably 35 to 55 m ² / g. If the specific surface area is less than 30 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.
If it exceeds ² / g, the viscosity in the coating composition becomes too high and dispersion becomes difficult, which is not preferred.

The particles constituting the spindle-shaped metal magnetic particles containing iron as a main component according to the present invention are such that Co is contained in an amount of 0.
5 to less than 10 atomic%. 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.

The particles constituting the spindle-shaped metal magnetic particles containing iron as a main component according to the present invention have a temperature of 60 ° C. and a relative humidity of 90 °.
%, The oxidation stability (.DELTA..sigma.s) of the saturation magnetization (.sigma.s) after one week of the accelerated aging test is 10% or less, preferably 8% or less in absolute value, and the ignition temperature is 1%.
The temperature is 35 ° C. or higher, preferably 140 ° C. or higher.

The spindle-shaped metal magnetic particles mainly composed of iron according to the present invention have a coercive force Hc of 1300 to 1800 Oe, preferably 1350 to 1750 Oe. The saturation magnetization s is 110 to 160 emu / g.

The crystallite size D110 of the particles constituting the spindle-shaped metal magnetic particles mainly composed of iron according to the present invention is 13
0 to 180 °, preferably 140 to 170 °.

The spindle-shaped metal magnetic particles containing iron as a main component according to the present invention preferably have a squareness ratio (Br / Bm) of 0.84 or more, more preferably 0.85 or more, in the characteristics of the coating film at a magnetic field orientation of 5 kOe. As described above, the orientation (OR) is preferably 2.8 or more, more preferably 2.9 or more, and the coercive force distribution (SFD) is preferably 0.53 or less, more preferably 0.52 or less. Further, the squareness ratio (Br / Bm) in the properties of the coating film in a 3 kOe magnetic field orientation is preferably 0.8.
2 or more, more preferably 0.83 or more, orientation (OR)
Is preferably 2.6 or more, more preferably 2.7 or more,
The coercive force distribution (SFD) is preferably 0.54 or less, more preferably 0.53 or less.

The spindle-shaped metal magnetic particles containing iron as a main component according to the present invention have a weather resistance (ΔBm) in coating film properties of 5%.
It is 8% or less, preferably 6% or less in a coating film having a kOe magnetic field orientation.

Next, a method for producing spindle-shaped metal magnetic particles containing iron as a main component according to the present invention will be described. In the present invention, spindle-shaped metal magnetic particles containing iron as a main component can be obtained by heating and reducing the spindle-shaped hematite particles according to the present invention. The temperature range of heat reduction is 400
~ 700 ° C is preferred. If the temperature is lower than 400 ° C.,
The reduction reaction progresses slowly and takes a long time. Also, 700
If the temperature exceeds ℃, the reduction reaction may proceed rapidly to cause deformation of the particles and sintering between the particles.

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. The method of once replacing the atmosphere with an inert gas, then gradually increasing the oxygen content in the inert gas to finally produce air, and gradually oxidizing using a mixed gas of oxygen and water vapor It can be taken out into the air by the above method.

[0081]

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 represents the size of a crystal particle measured by an X-ray diffraction method and 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 / βcosθ 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 a “vibrating sample magnetometer VSM-3S-15” (manufactured by Toei Kogyo Co., Ltd.) under an external magnetic field of 10 kOe.

The amount of Co, the amount of Al, and the amount of rare earth elements of the spindle-shaped goethite particles and the spindle-shaped metal magnetic particles containing iron as a main component were determined by the inductively coupled plasma emission spectrometer SPS400.
0 "(manufactured by Seiko Denshi Kogyo KK).

For the magnetic coating film, the following components were put into a 100 cc polybin at the following ratio, and mixed and dispersed for 8 hours using a paint shaker (manufactured by Red Devil Co., Ltd.) to prepare a magnetic coating material having a thickness of 25 μm. It was obtained by coating on a terephthalate film using an applicator to a thickness of 50 μm, and then drying in a two-level magnetic field of 3 kOe and 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.).

A spindle-shaped goethite particle powder, a spindle-shaped hematite particle powder, and a spindle-shaped metal magnetic particle powder were produced by the following methods, and various properties and physical properties were measured or calculated by the methods described above. 30 L of a mixed alkali aqueous solution containing 25 mol of sodium carbonate and 19 mol of an aqueous sodium hydroxide solution (sodium hydroxide corresponds to 27.5 mol% in terms of a prescribed conversion with respect to the mixed alkali) is charged into a bubble column, and nitrogen gas is introduced. The temperature is adjusted to 47 ° C. while aerating at a superficial velocity of 2.20 cm / s. Next, 20 mo as Fe ²⁺
20 L of an aqueous solution of ferrous sulfate (a mixed alkali aqueous solution with respect to ferrous sulfate corresponds to 1.725 equivalents in terms of a specified conversion) in a bubble column and aged for 30 minutes.
4L of cobalt sulfate aqueous solution containing 1.0 mol of ²⁺ (total Fe
Corresponds to 5 atomic% in terms of Co. ) Was added and the mixture was aged for 4 hours and 30 minutes (10% of the total aging time of the Co addition time).
An oxidation reaction was performed until the oxidation rate of Fe ²⁺ reached 40% by passing air at m / s to produce goethite seed crystal particles. In addition, Fe ²⁺
A water suspension containing the goethite seed particles oxidized to an oxidation rate of 40% is fractionated, and the goethite seed particles obtained by quickly washing, filtering, and washing with a dilute acetic acid aqueous solution are subjected to composition analysis. As a result, Fe was 54.00% by weight and Co was 2.45% by weight. The crystallite size D020 (seed crystal particles) was 245 °, and 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 as shown in the transmission electron micrograph of FIG. 1, and have a BET specific surface area. 135.4 m ² / g, average major axis diameter 0.275 μm, σ (standard deviation) 0.0459 μm
m, the size distribution (standard deviation / major axis diameter) is 0.167, the average minor axis diameter is 0.0393 μm, the axial ratio is 7.0, and no dendritic particles are present. The child size D020 was 262 ° and D110 was 131 °, and the ratio D020 / D110 was 2.0. Further, the relationship with the crystallite size of the seed crystal particles is D020 / D
020 (seed particles): 1.07, D110 / D110
(Seed crystal particles) was 1.05. Further, when Fe is 51.
5% by weight, 2.72% by weight of Co, and 1.99% by weight of Al. By comparison with the analysis values of the goethite seed crystal particles, the Co content of the seed crystal part was higher than the Fe content of the seed crystal part. 4.30 atomic%, and the Co abundance ratio in the seed crystal portion is 1% of the total Co abundance with respect to the total Fe in the entire grain
00, it is 86.0, and C in the surface layer portion is
The existence ratio of o was 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) obtained here 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 was added. 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.

The spindle-shaped goethite particles coated with the above-mentioned Nd compound were prepared such that D104 of the obtained spindle-shaped hematite particles was D104 / D11 with respect to the size of D110 of the particles.
By heating and dehydrating in air at 730 ° C. so as to be 0 (goethite particles) in the range of 0.9 to 1.1, spindle-shaped hematite particles composed of spindle-shaped hematite particles having an outermost layer composed of an Nd compound were obtained. .

The obtained spindle-shaped hematite particles had an average major axis diameter of 0.1 as shown in the transmission electron micrograph of FIG.
241 μm, σ (standard deviation) 0.0434 μm, size distribution (standard deviation / average major axis diameter) 0.180, average minor axis diameter 0.0309 μm, axial ratio 7.8, BET specific surface area 48.5 m ² / G, and the content of Co in the particles is 5 atomic% with respect to the total Fe, the content of Al is 8 atomic% with respect to the total Fe, and the content of Nd is 3 atomic% with respect to the total Fe. Atomic%, and Al / Nd was 2.67. Further, the crystallite size D104 was 130 °, and the ratio of goethite particles to D110 was 0.99 as D104 / D110 (goethite particles). D110 is 2
85 ° and the ratio D110 / D104 is 2.19.
Met.

[0096] After the Nd spindle-shaped hematite particles 100g having an outermost layer made of a compound was placed in a fixed bed reduction apparatus having an inner diameter of 72 mm, bubbled with H ₂ gas per minute 35L, and thermally reduced in a reducing temperature 480 ° C., After switching to nitrogen gas and cooling to 70 ° C., the oxygen partial pressure was gradually increased while passing water vapor to form a stable oxide film on the particle surface at the same ratio as air.

The obtained metal magnetic particles containing iron as a main component containing Co, Al and Nd had an average major axis diameter of 0.178 μm and a σ of σ, as shown in the transmission electron micrograph of FIG.
(Standard deviation) 0.0456 μm, size distribution (standard deviation / major axis diameter) 0.256, average minor axis diameter 0.0234 μm
m, axial ratio 7.6, BET specific surface area 42.1 m ₂ / g,
The particles consisted of particles having an X-ray crystal grain size of D110 of 158 °, and had a spindle shape, uniform particle size, and few dendritic particles.
Further, the content of Co in the particles is 5 atomic% based on the total Fe, the content of Al is 8 atomic% based on the total Fe, and the content of Nd is 3 atomic% based on the total Fe. The Al / Nd ratio was 2.67. The magnetic properties of the spindle-shaped metal magnetic particles are as follows. The coercive force Hc is 1540 Oe, the saturation magnetization s is 128.8 emu / g, and the squareness ratio (σr / σ
s) was 0.498, the oxidation stability Δσs of the saturation magnetization was 4.9% (measured value -4.9%) in absolute value, and the ignition temperature was 153 ° C. When the orientation magnetic field is 5 kOe, the sheet characteristics are such that the sheet Hc is 1470 Oe, and the sheet squareness ratio (Br / Bm, Bm is 3527 G) is 0.1.
872, sheet OR 3.39, sheet SFD 0.4
76, ΔBm was 3.4% (actually-measured value -3.4%). When the orientation magnetic field is 3 kOe, the sheet Hc is 1
462 Oe, sheet squareness ratio (Br / Bm, Bm is 3438G) 0.863, sheet OR 3.27, sheet SFD 0.493, ΔBm 3.5% (actual value−
3.5%).

[0098]

Conventionally, various metal salts have been added to improve the shape and the like of spindle-shaped goethite particles as a starting material of 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 caused by the fact that, when Co is dissolved, fine particles are obtained and the particles are small in the minor axis direction. It is known that goethite particles having an appropriately large axial ratio can be obtained.

Thus, the present inventors have examined in detail the function of Co in the spindle-shaped goethite formation reaction. As a result, when Co is added at the ripening time, the addition time is changed to within 1/2 of the total ripening 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.

Although the spindle-shaped goethite particles, which are the starting materials, have a large minor axis diameter and a relatively small axial ratio, the reason why the squareness ratio 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 the heat treatment before the heat reduction from the viewpoint of the 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 examined the ratio of Al to the rare earth element. As a result, it was found that when Al / rare earth element is in the range of 1.5 to 5, the oxidation stability of the metal magnetic particles is excellent. 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 made relatively low, and the sintering prevention effect is maximized in each heat treatment step. 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.

[0106]

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 5 and Comparative Examples 1 to 3 <Production of Spindle-Like Goethite Particle Powder> Table 1 shows the conditions for forming spindle-like goethite particles, ie, the conditions for the reaction for forming goethite seed crystal particles and the conditions for the growth reaction. Spindle-shaped goethite particles were obtained in the same manner as in the embodiment of the present invention except that various changes were made as shown in Table 2. Table 3 shows properties of the obtained spindle-shaped goethite particles. FIG. 4 shows an electron micrograph showing the particle morphology of the spindle-shaped goethite particles obtained in Example 5.

Comparative Example 1 Table 3 shows various properties of goethite particles obtained by the method described in Example 2 of JP-A-10-245233. The obtained goethite particles are shown in the transmission electron micrograph of FIG. The axis ratio of the obtained goethite particles was as large as over 13 and the size distribution was poor. In addition, the growth of the surface goethite layer on the seed crystal particles is also different,
The crystallite size ratio of D020 / D110 was also less than 1.8.

Comparative Example 2 The reaction for producing goethite particles was carried out in the same manner as in the embodiment of the invention, except that the time of Co addition was set to １ ／ or more of the total ripening time and the air flow velocity was changed. . The obtained goethite particles had an axial ratio of less than 5, resulting in poor size distribution.

Comparative Example 3 In the reaction for producing goethite particles, the Al content was adjusted to 12 atomic%.
The procedure was performed in the same manner as in the embodiment of the invention except that the addition was performed so that The obtained goethite particles have a specific surface area of 1
It exceeded 60 m ² / g.

[0111]

[Table 1]

[0112]

[Table 2]

[0113]

[Table 3]

Examples 6 to 10 and Comparative Examples 4 to 10 <Production of Spindle-Shaped Hematite Particles> The spindle-shaped goethite particles obtained in Examples 1 to 5 and Comparative Examples 1 to 3 were subjected to a sintering prevention treatment. Spindle-shaped hematite particles were obtained in the same manner as in the embodiment, except that the kind and amount of the coating used for the above, the heating dehydration temperature, and the temperature of the subsequent heat treatment were variously changed. The production conditions are shown in Table 4, and various properties of the obtained spindle-shaped hematite particles are shown in Table 5. FIG. 5 shows a transmission electron micrograph showing the morphology of the spindle-shaped hematite particles obtained in Example 10.

In Comparative Example 4, the method described in Example 2 of JP-A-10-245233 was used. The obtained hematite particles have an axis ratio of 12 or more, have a poor size distribution, and have a ratio of D104 to D110 of goethite of more than 1.1 and a crystallite size ratio of D110 / D104 of 2.0. Was less than. FIG. 8 shows a transmission electron micrograph showing the particle morphology of the obtained hematite particles.

Comparative Example 5 was performed in the same manner as in the embodiment of the present invention. The obtained hematite particles had an axial ratio of less than 5, and had poor size distribution. Also, D110 / D1
04 had a crystallite size ratio of less than 2.0.

Comparative Example 6 was performed in the same manner as in the embodiment of the present invention. The obtained hematite particles have a specific surface area of 70 m ^2.
/ G larger than D110 / g and D110 / D10
4 had a crystallite size ratio of less than 2.0.

Comparative Example 7 was carried out in the same manner as in Example 6 except that the goethite particles obtained in Example 1 of the present invention were used and the Nd content was added so as to be 6.0 atomic%.
The ratio of Al / rare earth in the obtained hematite particles is 1.5.
Was less than.

Comparative Example 8 was carried out in the same manner as in Example 7 except that the goethite particles obtained in Example 2 of the present invention were used and the Y content was added to 1.5 atomic%. The ratio of Al / rare earth in the obtained hematite particles exceeded 5.0.

Comparative Example 9 was performed using the goethite particles obtained in Example 4 of the present invention, adding Nd and Co in the same manner as in Example 9, and changing the heating and dehydrating temperature. The obtained hematite particles have a very large specific surface area and the ratio of D104 to D110 of goethite is less than 0.9;
The crystallite size ratio of 110 / D104 also exceeded 4.0.

Comparative Example 10 uses the goethite particles obtained in Example 4 of the present invention.
Co was added, and the heating and dehydration temperature was changed. The obtained hematite particles have a poor size distribution, the ratio of D104 to D110 of goethite exceeds 1.1,
The crystallite size ratio of D110 / D104 was also less than 2.0.

[0122]

[Table 4]

[0123]

[Table 5]

Examples 11 to 15 and Comparative Examples 11 to 17:
Production of Metal Magnetic Particles Containing Iron as Main Component> The spindle-shaped hematite particles obtained in Examples 6 to 10 and Comparative Examples 4 to 10 are used as particles to be treated, 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 addition amount, the heating temperature, and the reduction temperature in the heat reduction step were variously changed. Table 6 shows the reducing conditions at this time and various properties of the obtained metal magnetic particles containing iron as a main component, and Table 7 shows various properties when a magnetic coating film was used. FIG. 6 shows a transmission electron micrograph showing the particle morphology of the spindle-shaped metal magnetic particles containing iron as a main component and obtained in Example 15. FIG. 9 shows Comparative Example 11
A transmission electron micrograph showing the particle morphology of the metal magnetic particles containing iron as a main component obtained in the above was shown.

In Comparative Example 11, the method described in Example 2 of JP-A-10-245233 was used.

[0126]

[Table 6]

[0127]

[Table 7]

[0128]

The spindle-shaped goethite particles and spindle-shaped hematite particles according to the present invention have a uniform particle size, do not contain dendritic particles, have a large minor axis diameter, and have an appropriate axial ratio. In addition, the seed crystal part and the surface layer part are composed of particles having different crystal growth properties, and in addition, the spindle-shaped hematite particles have a specific crystallite size ratio and a growth ratio with respect to the crystallite size of the goethite particles to a specific value, Shape breakage in both the heat treatment and heat reduction steps is effectively suppressed, and the particles having a specified Al / rare earth ratio allow the spindle-shaped goethite particles or the spindle-shaped hematite particles to be used as a starting material. The obtained spindle-shaped metal magnetic particles containing iron as a main component have a uniform particle size, do not contain dendritic particles, and have good dispersibility even in a low magnetic field (high-angle shape). , A high orientation), high density recording because it combines an excellent coercive force distribution and excellent weather resistance, high sensitivity, is suitable as a high-power magnetic particles.

[Brief description of the drawings]

FIG. 1 is a transmission electron micrograph (3000) showing the particle shape of spindle-shaped goethite particles obtained in an embodiment of the invention.
0 times).

FIG. 2 is a transmission electron micrograph (3000) showing the particle shape of spindle-shaped hematite particles obtained in the embodiment of the invention.
0 times).

FIG. 3 is a transmission electron micrograph (× 30000) showing the particle shape of spindle-shaped metal magnetic particles containing iron as a main component and obtained in an embodiment of the invention.

FIG. 4 is a transmission electron micrograph (× 30000) showing the particle shape of spindle-shaped goethite particles obtained in Example 5.

FIG. 5 is a transmission electron micrograph (× 30000) showing the particle shape of spindle-shaped hematite particles obtained in Example 10.
It is.

FIG. 6 is a transmission electron micrograph (× 30000) showing the particle shape of spindle-shaped metal magnetic particles containing iron as a main component and obtained in Example 15.

FIG. 7 is a transmission electron micrograph (× 30000) showing the particle shape of spindle-shaped goethite particles obtained in Comparative Example 1.

FIG. 8 is a transmission electron micrograph (× 30000) showing the particle shape of spindle-shaped hematite particles obtained in Comparative Example 4.

FIG. 9 is a transmission electron micrograph (× 30000) showing the particle shape of spindle-shaped metal magnetic particles containing iron as a main component and obtained in Comparative Example 11.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G002 AA03 AA05 AA09 AA10 AB04 AD03 AE03 5E040 AA11 AA19 AB02 AB09 HB08 HB09 HB11 HB17 NN00 NN01 NN02 NN06 NN12 NN17 NN18

Claims (7)

[Claims] 1. Spindle-shaped goethite having an average major axis length of 0.18 to 0.30 μm containing 0.5 to less than 8 atomic% of Co with respect to total Fe and 5 to 10 atomic% of Al with respect to total Fe. Particles having a size distribution (standard deviation / major axis length) of 0.22 or less and an average minor axis length of 0.025 to 0.045 μm
And spindle-shaped goethite particles having an average axis ratio of 5 to 10. 2. 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) to the seed crystal particles of 1.05. ~ 1.20, D110 / D110
The spindle-shaped goethite particles according to claim 1, wherein (seed crystal particles) are 1.02 to 1.10. 3. The composition contains 0.5 to less than 10 atomic% of Co with respect to all Fe, 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 spindle-shaped hematite particles having an average major axis length of 0.17 to 0.28 μm and a ratio of Al / rare earth element of 1.5 to 5 (atomic% with respect to Fe), and having a size distribution (standard deviation / length). Axis length) is 0.20 or less, average short axis length is 0.022 to
0.035 μm, average axis ratio 5-10, crystallite size ratio D
Spindle-shaped hematite particles, wherein 110 / D104 is 2.0 to 4.0. 4. 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 A
The average major axis length is 0.15 to 0.25 μm, where the ratio of l / rare earth element is 1.5 to 5 (atomic% relative to Fe), the size distribution (standard deviation / major axis length) is 0.30 or less, the average Iron having a short axis length of 0.015 to 0.025 μm, an average axis ratio of 5 to 9, an ignition temperature of 135 ° C. or more, an oxidation stability of 10% or less, and a coercive force of 1300 to 1800 Oe. Spindle-shaped metal magnetic particles containing as a main component. 5. 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 under a non-oxidizing atmosphere. After aging, an oxygen-containing gas is passed through the aqueous suspension to generate spindle-shaped goethite seed crystal particles by an oxidation reaction, and then an aqueous suspension containing the seed crystal particles and a ferrous-containing precipitate is formed. When an oxygen-containing gas is passed through the liquid and a goethite layer is grown on the particle surface of the seed crystal particles by an oxidation reaction to generate spindle-shaped goethite particles, the oxidation reaction starts when the seed crystal particles are generated. To the aqueous suspension containing the ferrous sediment during the previous aging, a Co compound of 0.5 to less than 8 atomic% in terms of Co with respect to all Fe is added to the aqueous suspension within 1/2 of the total aging period. And oxidation reaction of all Fe ²⁺ A process for producing spindle-shaped goethite particles, wherein the process is performed in a range of 50%, and an Al compound is added in an amount of 5 to 10 atomic% in terms of Al with respect to all Fe. 6. The spindle-shaped goethite particles according to claim 1 or 2, wherein the ratio of Al / rare earth element is 1.5 to 5 (each Fe
% Of the total F in terms of rare earth elements
e is treated with a sintering inhibitor comprising a compound of a rare earth element in an amount of 1 to 5 atomic% with respect to e, and the crystallite size D104 is determined as D104 / goethite D110 in the range of 0.9 to 1.1. 650-800 ° C in a reducing atmosphere
A method for producing spindle-shaped hematite particles, wherein a heat treatment is performed. 7. A method for producing spindle-shaped metal magnetic particles containing iron as a main component, wherein the spindle-shaped hematite particles according to claim 3 are reduced by heating at 400 to 700 ° C. in a reducing atmosphere.