JP2000203847A - Cobalt-containing fusiform hematite particulate powder for fusiform magnetic alloy particulate powder predominant in iron and cobalt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject hematite particulate powder prevented from shape degradation to a minimum when reduced under heating for producing fusiform magnetic alloy particulate powder, therefore suitable as a raw material for such magnetic powder consisting mainly of Fe and Co, having high coercive force, high saturated magnetization level and high oxidation stability and affording excellent SFD of the magnetic coating film therefrom. SOLUTION: This Co-contg. fusiform hematite particulate powder has the following characteristics: average major axis is 0.05-0.14 μm, axis ratio (average major axis/average minor axis) is 4-8, crystallite size D101 is 50-80 Å, saturated magnetization level σs is 0.5-2 Am2/kg, and containing>20 atom.% but <=45 atom.% of cobalt, 5-15 atom.% of aluminum, and 5-15 atom.%, on a rare earth element basis, of rare earth element compound(s), based on the total Fe, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention can prevent shape destruction in the heating and reducing step for obtaining spindle-shaped alloy magnetic particles as much as possible, so that it has a high coercive force, a large saturation magnetization, and excellent oxidation. Stability and excellent S in magnetic coating
The present invention relates to a Co-containing spindle-shaped hematite particle powder having FD and suitable as a material for a spindle-shaped alloy magnetic particle powder containing Fe and Co as main components.

[0002]

2. Description of the Related Art In recent years, magnetic recording / reproducing devices for audio, video, and computers have become increasingly compact and lightweight, long-time recording, high-density recording, or increased storage capacity. Demands for higher performance and higher density recording of magnetic tapes and magnetic disks as recording media are increasing more and more.

That is, high image quality and high output characteristics of a magnetic recording medium, particularly, improvement of frequency characteristics and improvement of storage characteristics and durability are required. For this purpose, a high coercive force Hc and a coercive force distribution SFD are required. It is required that the weather resistance ΔBm be excellent.

[0004] These characteristics of the magnetic recording medium are closely related to the magnetic particle powder used in the magnetic recording medium, and in recent years, the coercive force is higher than that of the conventional iron oxide magnetic particle powder. And magnetic metal particles containing iron as a main component and having a large saturation magnetization σs are attracting attention, such as digital audio tape (DAT), 8 mm video tape, Hi-
8 tapes, and W-VHS tapes for HDTV,
Used for digital recording type DVC tapes and the like. For computers, it is used for removable disks such as Zip and Super Disk. Recently, large capacity Hi-FD is used.
And is currently in the commercialization stage.

[0005] Therefore, it is strongly desired to further improve the characteristics of the magnetic metal particles containing iron as a main component.

That is, in order to obtain a magnetic recording medium having a higher coercive force, an excellent coercive force distribution SFD, and an excellent weather resistance ΔBm, the magnetic metal particles containing iron as a main component require a higher coercive force. It has a large saturation magnetization and
It is strongly required that the distribution of the particle size be as narrow as possible, the dispersibility be excellent, and the oxidation stability Δσs be excellent.

However, it is difficult to obtain metal magnetic particle powders satisfying all of these properties due to the production method.

[0008] That is, generally, the magnetic metal particles containing iron as a main component are passed through an aqueous solution containing an iron-containing precipitate obtained by reacting an aqueous ferrous salt solution and an aqueous alkaline solution with an oxygen-containing gas such as air. Spindle-like hematite particle powder obtained by heating and dehydrating the spindle-like goethite particle powder obtained by performing the oxidation reaction, or spindle-like hematite particle powder obtained by adding a different element other than iron to the spindle-like hematite particle powder. Is used as a starting material particle powder, and the starting material particle powder can be obtained by heat reduction under a reducing gas atmosphere.

Since the conditions such as the atmosphere and the temperature in the heating and reducing step are very severe, the spindle-shaped hematite particles tend to cause sintering between the particles and the particles. In particular, in order to obtain a large saturation magnetization value, which is an advantage of metal magnetic particle powder, it is necessary to increase the heating reduction temperature as much as possible and to promote reduction sufficiently, but when the heating reduction temperature is increased, On the contrary, the spindle-shaped hematite particle powder tends to cause shape breakage.

In recent years, in order to obtain metal magnetic particle powder having a high coercive force, the particle size has been increasingly reduced, and spindle-shaped hematite particles have also been reduced. In particular, 0.14 μm
When the following fine particles are obtained, destruction of the particle shape in the heat reduction step tends to be more remarkable. The metal magnetic particle powder whose shape has been destroyed in this manner cannot obtain a high coercive force due to a decrease in shape anisotropy, and the particle size distribution decreases. And even in the production of magnetic recording media, dispersibility is reduced due to kneading with a binder in a vehicle, an increase in interparticle force in a dispersion process, or an increase in magnetic cohesion, and the magnetic coating film In this case, the squareness ratio of the magnetic recording medium decreases, and a magnetic recording medium having an excellent SFD cannot be obtained.

Therefore, there is a strong demand for spindle-shaped hematite particle powder capable of preventing the destruction of the particle shape as much as possible in the heat reduction step.

On the other hand, fine particles, in particular, having a major axis diameter of 0.14 μm
The following iron-based metal magnetic particle powder, when taken out into the air after the heat-reduction step, undergoes an oxidizing reaction rapidly due to oxygen in the air, resulting in a significant decrease in magnetic properties, especially saturation. Due to the decrease in the magnetization value, it was not possible to obtain metal magnetic particle powder having the intended large saturation magnetization value,
Furthermore, it is inferior in weather resistance ΔBm when used as a magnetic coating film. Therefore, there is a strong demand that the metal magnetic particles have a large saturation magnetization immediately after reduction and have excellent oxidation stability.

Conventionally, as a method for obtaining metal magnetic particle powder mainly composed of iron having a high coercive force, a method of reducing the particle diameter of metal magnetic particle powder mainly composed of iron (Japanese Patent Application Laid-open No. JP-A-135436) is known. Further, in order to improve oxidation stability, Co is contained in a large amount exceeding 20 atomic% as a different element other than Fe (JP-A-3-174704, JP-A-3-2704).
93703, JP-A-5-101917, JP-A-6-176912, JP-A-8-165501
JP, JP-A-9-22522, JP-A-9-22
No. 523) is widely known.

[0014]

The Co-containing spindle-shaped hematite particle powder capable of preventing the shape destruction in the heating and reducing step as much as possible is the most required at present, but satisfies these characteristics. Starting material particle powder has not yet been provided.

That is, in the case of the method of reducing the particle size of the metal magnetic particle powder containing iron as a main component, as described above, since the spindle-shaped hematite particle powder is a fine particle, the particles are not reduced when heated and reduced. Sintering between them easily occurs, and shape destruction easily occurs. Therefore, it is difficult for the obtained metal magnetic particle powder to obtain a desired high coercive force, and only a coercive force of at most 159.2 kA / m (2000 Oe) is obtained. Further, the dispersibility is reduced due to the shape destruction of the particles due to the heat reduction of the fine particles, which is inferior to the SFD when a magnetic coating film is formed.

When a large amount of the above-mentioned known cobalt is contained, a metal magnetic particle powder having improved oxidation stability can be obtained, but excessive particle growth is liable to occur during heat treatment, and shape destruction is induced. Therefore, the obtained metal magnetic particle powder cannot obtain a high coercive force due to the reduced shape anisotropy, and has a reduced size distribution and reduced dispersibility. As a result, only about 0.40 metal magnetic particle powder was obtained.

Therefore, according to the present invention, since the shape destruction in the heat reduction step can be prevented as much as possible, a higher coercive force, in particular, 159.2 kA / m (2000O
e) Above coercivity, large saturation magnetization, especially 130 Am
² / kg (130 emu / g) or more, excellent in oxidative stability, and excellent SFD in magnetic coating film, in particular, 0.
It is a technical object of the present invention to provide a Co-containing spindle-shaped hematite particle powder suitable as a material for a spindle-shaped alloy magnetic particle powder containing Fe and Co as main components and having both of less than 40.

[0018]

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

That is, according to the present invention, the average major axis diameter is 0.05 to
0.14 μm, axial ratio (average major axis diameter / average minor axis diameter) of 4 to
8, a crystallite size _{D 104} is 50～80A, saturation magnetization value σs is 0.5~2Am ² / kg, and,
Co containing more than 20 atomic% and less than 45 atomic% of Co in terms of Co, 5 to 15 atomic% of aluminum in terms of Al, and 5 to 15 atomic% of rare earth compounds in terms of rare earth elements with respect to all Fe. The present invention is a Co-containing spindle-shaped hematite particle powder for a spindle-shaped alloy magnetic particle powder containing Fe and Co as a main component, comprising a spindle-containing spindle-shaped hematite particle powder.

The structure of the present invention will be described in more detail as follows.

The particle shape of the hematite particles according to the present invention is spindle-shaped. Spindle-shaped hematite particle powder can be obtained by subjecting spindle-shaped goethite particles to a heat dehydration treatment.

As is well known, the spindle-shaped hematite particle powder inherits the particle shape of the spindle-shaped goethite particle powder.
The particle powder has a shape in which the central part is thick and gradually tapered from the central part toward both ends, the dendritic particles are not mixed, and the particle size distribution is excellent. .

In the spindle-shaped hematite particles according to the present invention, the content of cobalt is more than 20 at% and not more than 45 at%, preferably 21 to 40 at% in terms of Co with respect to the total Fe.
More preferably, it contains 21 to 35 at%, aluminum contains 5 to 15 at%, preferably 6 to 14 at% in terms of Al with respect to the total Fe, and the rare earth element contains
5 to 15 at.%, Preferably 5 to 12 at.% In terms of rare earth element.

When the content of cobalt is 20 atomic% or less based on the total Fe, the obtained spindle-shaped alloy magnetic particles containing Fe and Co as main components can sufficiently improve the oxidation stability. In addition, it is difficult to obtain a large saturation magnetization value. If the content exceeds 45 atomic%, it becomes very difficult to control the reduction rate, and shape destruction and sintering occur between the particles during heating and reduction, making it difficult to obtain a high coercive force.

When the content of aluminum is 5
When the content is less than atomic%, it is difficult to control the reduction rate, and shape destruction occurs in the reduction step, and the obtained spindle-shaped alloy magnetic particles containing Fe and Co as a main component are not adsorbed by a binder having a functional group. It is weak and it is difficult to obtain a high squareness ratio. If the content exceeds 15 atomic%, the reduction itself does not easily proceed, and a large saturation magnetization value is hardly obtained because the ratio of the nonmagnetic component increases.

When the content of the rare earth element is less than 5 atomic% based on the total Fe, it is very difficult to control the reduction rate, and it is difficult to obtain a high coercive force due to shape destruction. In addition, the effect of preventing sintering is not sufficient, and the SFD on the magnetic coating film deteriorates. If the content exceeds 15 atomic%, the reduction itself does not easily proceed, and a large saturation magnetization value is hardly obtained because the ratio of the nonmagnetic component increases.

As the rare earth element, scandium,
Yttrium, lanthanum, cerium, praseodymium,
One or more of neodymium, samarium, and the like are suitable. Particularly, yttrium and neodymium are preferable.

The average major axis diameter of the spindle-shaped hematite particles according to the present invention is 0.05 to 0.14 μm. When the average major axis diameter is less than 0.05 μm, the obtained spindle-shaped alloy magnetic particles become superparamagnetic, so that a large saturation magnetization cannot be obtained, and at the same time, it is difficult to obtain a high coercive force. Conversely 0.1
If it exceeds 4 μm, the desired high coercive force cannot be obtained.

The spindle ratio of the spindle-shaped hematite particles according to the present invention is 4 to 8. When the axial ratio is less than 4, a high coercive force cannot be obtained because the shape anisotropy of the obtained spindle-shaped alloy magnetic particles is reduced. If it exceeds 8, although it depends on the major axis diameter, a relatively high coercive force can be obtained, but it is difficult to obtain a large saturation magnetization value.

[0030] The present invention crystallite size _{D 104} of hematite particles into spindle-shaped according to is 50～80A. When the crystallite size D ₁₀₄ is less than 50 °, the crystal growth of the spindle-shaped hematite particles is small, the control of the reduction rate becomes insufficient, and it becomes difficult to obtain a desired high coercive force due to shape destruction. If it exceeds 80 °, excessive crystal growth in the spindle-shaped hematite particles promotes growth in the short axis direction, lowers the shape anisotropy, and makes it difficult to obtain a high coercive force.

The spindle-shaped hematite particles according to the present invention
The saturation magnetization value s is 0.5 to 2 Am ²/ Kg (0.5 ~
2 emu / g). σs is 0.5 Am²/ Kg
(0.5 emu / g), spindle-shaped hematite grains
Fine powder distribution is good, but spindle-shaped alloy magnetic particle powder
In this case, the dispersibility is poor. σs is 2 Am²/ K
g (2 emu / g), contains cobalt
The spinel compound during dehydration heating due to
In large amounts, short-axis growth occurs, and if excessive,
Spindle-shaped hematite particles cause shape destruction,
It is difficult to obtain spindle-shaped alloy magnetic particles having coercive force.

The average minor axis diameter of the spindle-shaped hematite particles according to the present invention is preferably 0.010 to 0.022 μm. When the average minor axis diameter is less than 0.010 μm, the obtained spindle-shaped alloy magnetic particles become superparamagnetic, so that a large saturation magnetization cannot be obtained, and at the same time, it is difficult to obtain a high coercive force. If it exceeds 0.022 μm, the desired high coercive force cannot be obtained.

The size distribution (standard deviation / average major axis diameter) of the spindle-shaped hematite particles according to the present invention is preferably 0.20 or less. When the size distribution exceeds 0.20, the obtained spindle-shaped alloy magnetic particle powder naturally has a poor size distribution, so that the SFD in the magnetic coating film is inferior. It is difficult to make it.

Spindle-shaped hematite particles according to the present invention
Has a BET specific surface area of 30 to 150 m ²/ G, especially 5
0-120m²/ G is preferred.

Next, a spindle-shaped alloy magnetic particle powder mainly composed of Fe and Co obtained by using the spindle-shaped hematite particle powder according to the present invention will be described.

The spindle-shaped alloy magnetic particles containing Fe and Co as main components in the present invention contain Co in an amount of 2 to the total Fe.
More than 0 atomic% and 45 atomic% or less, preferably 21 to 4
0 at%, more preferably 21 to 35 at%. Al is contained in an amount of 5 to 15 at%, preferably 6 to 14 at%, based on the total Fe. Further, the rare earth element is contained in an amount of 5 to 15 at%, preferably 5 to 12 at% based on the total amount of Fe.

The spindle-shaped alloy magnetic particles containing Fe and Co as the main components in the present invention have an average major axis diameter of 0.05 to 0.05.
0.14 μm, preferably 0.05-0.13 μm, the axial ratio is 4-8, and the crystallite size D of the particles
₁₁₀ is 120 to 170 degrees. The size distribution is 0.18 or less, and the average minor axis diameter is 0.010 to 0.0.
20 μm.

The spindle-shaped alloy magnetic particles containing Fe and Co as the main components in the present invention have a BET specific surface area of 35 to 35.
65 m ² / g, preferably of 40 to 60 ² / g.

The spindle-shaped alloy magnetic particles containing Fe and Co as main components according to the present invention have a coercive force of 159.2 to 1
98.9 kA / m (2000 to 2500 Oe).
Further, the saturation magnetization value is 130 to 160 Am ² / kg (13
0-160 emu / g), preferably 135-160 A
m ² / kg (135-160 emu / g).

In the present invention, the spindle-shaped alloy magnetic particles containing Fe and Co as main components have a temperature of 60 ° C. and a relative humidity of 9%.
The aging degradation Δσs (oxidation stability) of the saturation magnetization value σs one week after the accelerated aging test in an environment of 0% is 10% or less as an absolute value, and preferably 8% or less.

The characteristics of the magnetic coating film using the spindle-shaped alloy magnetic particles containing Fe and Co as main components in the present invention are as follows.
The squareness ratio (Br / Bm) is at least 0.85, preferably at least 0.5.
86 or more, and the SFD is less than 0.40, preferably 0.39 or less.

The characteristics of the magnetic coating film using the spindle-shaped alloy magnetic particles containing Fe and Co as main components in the present invention are as follows.
Degradation of saturated magnetic flux density Bm with time after one week of accelerated aging test in an environment of a temperature of 60 ° C. and a relative humidity of 90% Δ
Bm (weather resistance) is 8% or less in absolute value, preferably 6% or less.

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

The spindle-shaped hematite particles according to the present invention are prepared by, for example, heating and dehydrating spindle-shaped goethite particles at 350 ° C. or less in an oxidizing atmosphere,
It can be obtained by performing heat treatment in a temperature range of more than 50 ° C and less than 700 ° C.

The spindle-shaped goethite particles as the starting material particles have an average major axis diameter of 0.05 to 0.17 μm, preferably 0.05 to 0.15 μm, and a size distribution of 0.24 or less. . Moreover, the average short axis diameter is 0.010 to
0.025 μm, preferably 0.010-0.023 μm
m. The axial ratio is 4-8.

The spindle-shaped goethite particles, which are the starting material particles, are obtained by converting cobalt into Co in terms of Co with respect to all Fe.
It contains not less than 45 at% and more than 45 at%, and contains 5 to 15 at% of aluminum in terms of Al with respect to all Fe.

The spindle-shaped goethite particles as the starting material particles have a BET specific surface area of 100 to 250 m ² /
g, preferably 120 to 230 m ² / g.

The spindle-shaped goethite particle powder as the starting material particle powder is 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 obtained spindle-shaped goethite particle powder is coated with a compound of Co element, a compound of Al element and a sintering inhibitor in order to prevent sintering prior to the heat dehydration treatment. Keep it.

The rare earth element compound is used as the sintering inhibitor.

In order to improve the effect of preventing sintering, or if necessary, other elements such as Si, B, Ca, M
One, two or more compounds of elements selected from g, Ba, Sr 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.

By coating in advance with the sintering inhibitor, sintering between the particles and the particles is prevented, and spindle-shaped hematite particle powder that retains and inherits the particle shape and axis ratio of the spindle-shaped goethite particles is obtained. As a result, it becomes easier to obtain spindle-shaped alloy magnetic particle powders that retain the above-mentioned shape and the like and independently contain Fe and Co as main components.

The atmosphere for the heating dehydration treatment and the heating treatment of the spindle-shaped goethite particles is an oxidizing gas atmosphere. When the reaction is carried out in an inert gas atmosphere, it is difficult to control the dehydration reaction and the particle growth, causing a reduction in the axial ratio and a deterioration in the distribution due to the particle deformation, and the coercive force of the obtained spindle-shaped alloy magnetic particles is also easily reduced.

When the heat dehydration temperature exceeds 350 ° C.,
The dehydration reaction occurs rapidly, causing a reduction in the axial ratio and a deterioration in the distribution due to the deformation of the particles.

When the heating temperature is 450 ° C. or lower, sufficient grain growth does not occur, the control of the reduction rate during the heat reduction becomes insufficient, and the desired high coercive force cannot be obtained due to shape destruction and the like. On the other hand, when the heating temperature is 700 ° C. or higher, excessive crystal growth occurs, particularly growth in the short axis direction is promoted, and phenomena such as a high coercive force cannot be obtained with the spindle-shaped alloy magnetic particles.

The spindle-shaped 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 removal of cationic impurities is carried out by raising the pH, and the removal of anionic impurities is carried out by lowering the pH, so that the sintering inhibitor is not eluted.
More efficient cleaning.

Next, a method for producing spindle-shaped alloy magnetic particles containing Fe and Co as main components in the present invention will be described.

In the present invention, the spindle-shaped hematite particles according to the present invention are heated and reduced in a reducing gas atmosphere to obtain spindle-shaped alloy magnetic particles containing Fe and Co as main components.

The temperature range of the heat reduction in the present invention is 4
It is preferable to carry out in a temperature range of 00 to 700 ° C. The heat reduction temperature is more preferably selected as appropriate according to the type of the compound used in the coating treatment of the spindle-shaped goethite particles. When the temperature is lower than 400 ° C., the progress of the reduction reaction is slow and a long time is required. When the temperature exceeds 700 ° C., the reduction reaction proceeds rapidly, causing deformation of the particles and sintering between the particles and the particles.

In the present invention, Fe and Co after heat reduction are used.
Spindle-shaped alloy magnetic particles powder containing as a main component a known method, for example, a method of immersing in an organic solvent such as toluene,
A method in which the atmosphere of the spindle-shaped alloy magnetic particles containing Fe and Co as a main component after the reduction is once replaced with an inert gas, and then the air is finally formed while gradually increasing the oxygen content in the inert gas. It can be taken out into the air by a method of gradually oxidizing using a mixed gas of oxygen and water vapor.

[0062]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical embodiment of the present invention is as follows.

The average major axis diameter and average minor axis diameter of the spindle-shaped goethite particle powder, the spindle-shaped hematite particle powder, and the spindle-shaped alloy magnetic particle powder containing Fe and Co as main components in the present invention are all electron micrographs. The average value of the numerical values measured from is shown. In addition, the axial ratio was determined as average major axis diameter / average minor axis diameter.

The content of Co, Al, rare earth element and other metal elements in the spindle-shaped goethite particle powder, spindle-shaped hematite particle powder and spindle-shaped alloy magnetic particle powder containing Fe and Co as main components in the present invention. The amount was measured using “Inductively Coupled Plasma Emission Spectroscopy Analyzer SPS4000” (manufactured by Seiko Instruments Inc.).

The specific surface area of the particle powder is “Monosorb MS”
-11 "(manufactured by Cantachrome Co., Ltd.) and the value measured by the BET method.

[0066] The crystallite size _{D 104} and spindle-shaped alloy magnetic particle crystallite size _{D 110} of hematite particles, "X-ray diffraction apparatus" (manufactured by Rigaku) (measurement conditions: Target Cu, tube voltage 40 kV, tube current 40 mA) The Use X
The size of the crystal particles measured by the X-ray diffraction method was determined by comparing the (104) crystal plane of the hematite particles and the (11)
0) It represents the thickness of a crystal grain in a direction perpendicular to each of the crystal planes, and is a value calculated from the diffraction peak curve of each crystal plane using the following Scherrer's formula. .

D ₁₀₄ or D ₁₁₀ = Kλ / βcos θ, where β = half-width (in radians) of a true diffraction peak corrected for the mechanical width caused by the apparatus. K = Scherrer constant (= 0.9), λ = wavelength of X-ray (Cu Kα-ray 0.1542 nm), θ = diffraction angle (corresponding to diffraction peak of (104) plane or (110) plane)

The X-ray diffraction measurement of the spindle-shaped hematite particles was carried out using the X-ray diffractometer described above, and the diffraction angle 2θ was 10-6.
Measured at 0 °. The smaller the amount of spinel-type iron oxide produced in the X-ray chart, the lower the saturation magnetization value s of the spindle-shaped hematite particles.

The magnetic properties of the spindle-shaped alloy magnetic particles containing Fe and Co as main components are described in "Vibration sample magnetometer VSM-3".
S-15 "(manufactured by Toei Industry Co., Ltd.)
It was measured at 95.8 kA / m (10 kOe).

The magnetic properties of the magnetic coating film piece were as follows:
A magnetic paint prepared by putting the mixture in a 00 ml polybin at the following ratio and mixing and dispersing for 8 hours with a paint shaker (manufactured by Red Devil Co.) was applied to a 25 μm-thick polyethylene terephthalate film with a thickness of 50 μm using an applicator. To a thickness of 500 mT (5 kG
auss) was dried in a magnetic field to measure the magnetic properties of the magnetic coating pieces obtained. 800 parts by weight of 3 mmφ steel ball, 100 parts by weight of spindle-shaped alloy magnetic particles mainly composed of Fe and Co, 20 parts by weight of a polyurethane resin having a sodium sulfonate group, 83.3 parts by weight of cyclohexanone, 83.3 parts by weight of methyl ethyl ketone 83.3 parts by weight of toluene.

Δσs, which is an evaluation of the oxidation stability of the saturation magnetization value of the powder, and ΔBm, which is an evaluation of the weather resistance of the saturation magnetic flux density Bm of the magnetic coating film, are obtained by placing the powder in a thermostat at a temperature of 60 ° C. and a relative humidity of 90%. After the accelerated aging test in which the body or the magnetic coating film piece 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 are measured, respectively, and σs and Bm before the test start and the accelerated aging test for one week The difference (absolute value) between the subsequent σs ′ and Bm ′ is divided by σs and Bm before the start of the test, respectively, to obtain Δσs,
It was calculated as ΔBm. The closer the Δσs and ΔBm are to 0%, the better the oxidation stability.

<Production of Spindle-Shaped Goethite Particle Powder> 25 mol of sodium carbonate and an aqueous sodium hydroxide solution
30 l of a mixed alkali aqueous solution containing 0 mol (sodium hydroxide corresponds to 28.6 mol% in terms of a prescribed conversion with respect to the mixed alkali) is charged into the bubble column, and nitrogen gas is passed at a superficial velocity of 2.21 cm / s. While adjusting to 47 ° C. Then, 20 l of an aqueous ferrous sulfate solution containing 20 mol as Fe ²⁺ (a mixed alkali aqueous solution with respect to ferrous sulfate corresponds to 1.75 equivalents in terms of a prescribed conversion) was charged into a bubble column and aged for 20 minutes. 4 l of an aqueous solution of cobalt sulfate containing 4.2 mol of Co ²⁺ (2
It corresponds to 1 atomic%. ) Was added and the mixture was further aged for 4 hours and 40 minutes, and then air was passed at a superficial velocity of 1.32 cm / s to carry out an oxidation reaction until the oxidation rate of Fe ²⁺ was 40%, thereby producing goethite seed crystal particles.

Next, the air flow rate was adjusted to a superficial velocity of 3.31.
After increasing the concentration to 1 cm / s, 1 l of an aqueous solution of aluminum sulfate containing 2.4 mol of Al ³⁺ (corresponding to 12 atom% in terms of Al with respect to the total Fe) was added at a rate of 3 ml / sec or less to carry out the oxidation reaction. After that, water was washed with a filter press to an electric conductivity of 60 μS to obtain a press cake.

A spindle-shaped goethite particle powder obtained by drying and pulverizing a part of the cake by a conventional method has a spindle shape as shown in the transmission electron micrograph of FIG. Has a BET specific surface area of 179.2 m ² /
g, average major axis diameter is 0.131 μm, σ (standard deviation) is 0.0250 μm, size distribution (standard deviation / major axis diameter) is 0.191, average minor axis diameter is 0.0175 μm, and axis ratio is 7. 5. No dendritic particles are present at all,
The Co content of the whole particles was 21 atomic% based on the total Fe, and the Al content was 12 atomic% based on the total Fe.

<Production of Spindle-Shaped Hematite Particle Powder> Then, 1000 g of the spindle-shaped goethite particle powder thus obtained was obtained.
After sufficiently dispersing the press cake containing (7.8 mol as Fe) in 40 l of water, 2 l of an yttrium nitrate aqueous solution containing 243 g of yttrium nitrate hexahydrate (as Y with respect to all Fe in the spindle-shaped goethite particles powder) 2 liters of a cobalt sulfate solution containing 197 g of cobalt sulfate heptahydrate (corresponding to 9 atomic% as Co with respect to the total Fe in the spindle-shaped goethite particles) and stirred. Then, an aqueous solution of sodium carbonate having a concentration of 25.0% by weight was added as a precipitant to adjust the pH to 9.5, and then washed with a filter press, and the obtained press cake was molded using a compression molding machine to form a molded plate having a pore size of 3 mm. And dried at 120 ° C. to obtain spindle-shaped goethite particles powder coated with Y and Co compounds. The content of Co in the obtained spindle-shaped goethite particles was 30 atom% with respect to all Fe, the content of Al was 12 atom% with respect to all Fe, and the content of Y was 8 atom with respect to all Fe. %Met.

The spindle-shaped goethite particles coated with the Y and Co compounds are dehydrated in air at 300 ° C.
Heat dehydration was performed at 600 ° C. in the same atmosphere to obtain spindle-shaped hematite particles.

As shown in the transmission electron micrograph of FIG. 2, the obtained spindle-shaped hematite particles had an average major axis diameter of 0.122 μm and a σ (standard deviation) of 0.0218 μm.
m, size distribution: 0.179, average minor axis diameter: 0.016
8 μm, axial ratio 7.3, BET specific surface area 95.7 m ²
/ G, the content of Co in the particles is 30 atomic% based on the total Fe, the content of Al is 12 atomic% based on the total Fe, and the content of Y is 8 atomic% based on the total Fe. Met. The crystallite size D ₁₀₄ is 76 °, and the saturation magnetization value is 1.
0Am was ^{2 /kg(1.0emu/g).}

<Production of Spindle-Shaped Alloy Magnetic Particle Powder> Next, 100 g of the obtained spindle-shaped hematite particle powder was put into a fixed-bed reducing device having an inner diameter of 72 mm, and 35 l of H 2 / min.
After passing ₂ gases and reducing by heating at a reduction temperature of 600 ° C,
After switching to nitrogen gas and cooling to 80 ° 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 spindle-shaped alloy magnetic particles thus obtained are shown in FIG.
As shown in the transmission electron micrograph, the average major axis diameter was 0.105 μm and σ (standard deviation) was 0.0163 μm.
m, size distribution (standard deviation / major axis diameter) is 0.155, average minor axis diameter is 0.0154 μm, axis ratio is 6.8, BET specific surface area is 50.1 m ² / g, and crystallite size D ₁₁₀ is 1
It consisted of 52 ° particles, had a spindle shape, uniform particle size, and had few dendritic particles. The content of Co in the particles was 30 atomic% based on the total Fe, and the content of Al was
e is 12 atomic%, and the content of Y is 8
Atomic%.

The magnetic properties of the spindle-shaped alloy magnetic particles containing Fe and Co as main components have a coercive force of 188.
0 kA / m (2362 Oe) and a saturation magnetization of 140.5 Am ² / kg (140.5 emu /
g), the squareness ratio (σr / σs) is 0.543, and the oxidation stability Δσs of the saturation magnetization value is 7.0% as an absolute value (actual value−
7.0%). The properties of the magnetic coating film are as follows.
Is 191.9 kA / m (2411 Oe), the saturation magnetic flux density Bm is 389.5 mT (3895 G), and the squareness ratio (Br /
Bm) was 0.873, SFD was 0.382, and ΔBm was 5.1% (actual measurement value-5.1%).

[0081]

The most important points in the present invention are that the average major axis diameter is 0.05 to 0.14 μm, the axial ratio is 4 to 8, the crystallite size D ₁₀₄ is 50 to 80 °, and the saturation magnetization value is 0. .5
２2 Am ^{2 /} kg (0.5 to ² emu / g), and more than 20 atomic% in terms of Co with respect to all Fe
The Co-containing spindle-shaped hematite particle powder containing at most atomic% of cobalt, 5 to 15 atomic% of aluminum in terms of Al, and 5 to 15 atomic% of a rare earth compound in terms of a rare earth element has a shape destruction in the heat reduction step. It can be prevented as much as possible.

The reason why the shape destruction can be prevented as much as possible is not yet clear, but the present inventor has suppressed the formation of spinel-type iron oxide in the spindle-shaped hematite particle powder and has an appropriate crystallite size. Further, it is considered that the synergistic effect of the fact that the spindle-shaped hematite particles contain a specific amount of aluminum and a specific amount of a rare earth element is included.

Further, the spindle-shaped hematite particle powder according to the present invention is obtained by subjecting the spindle-shaped goethite particle powder to a heat dehydration treatment at 350 ° C. or less in an oxidizing atmosphere, and further, to a temperature of 450 to 700 ° C. in an oxidizing gas atmosphere. By performing the heat treatment in the temperature range described above, the generation of spinel-type iron oxide can be suppressed, so that the shape breakage of the particles can be prevented as much as possible, having an appropriate crystallite size, and a good size distribution. The present inventor believes that a spindle-shaped hematite particle powder can be obtained.

Further, by using the spindle-shaped hematite particle powder according to the present invention, it is possible to prevent shape destruction at the time of heat reduction, prevent a decrease in coercive force, and obtain Fe and Co having excellent dispersibility. Spindle-shaped alloy magnetic particles as a main component are obtained.

Further, Co is contained in an amount of more than 20 at% and not more than 45 at% with respect to the total Fe, so that the oxidation stability can be improved in composition, and the sintering prevention property is improved as described above. Is further improved, the shape distribution during various heat treatments is further improved, the distribution becomes narrower, and spindle-shaped alloy magnetic particles having synergistically improved oxidation stability are obtained.

When the spindle-shaped alloy magnetic particle powder containing Fe and Co as a main component is manufactured using the spindle-shaped hematite particle powder according to the present invention as a starting material, the spindle-shaped alloy magnetic particle powder has a high coercive force and a large saturation. It has a magnetization value, excellent oxidation stability, and good dispersibility in a binder resin, so that it has a high coercive force even in a magnetic coating film, and has a squareness ratio (Br / Bm), SFD Fe and Co with good weather resistance
Can be obtained.

[0087]

Next, examples, comparative examples and reference examples will be described.

Goethite particle powders 1-4: Spindle-shaped goethite particles having the properties shown in Table 1 were prepared as starting material particle powders.

[0089]

[Table 1]

Examples 1-4, Comparative Examples 1-4: The type of starting material particles, the type of coating used for sintering prevention treatment, the composition ratio, the dehydration temperature during hematite formation, the heating temperature, and the atmosphere were varied. Other than the above, spindle-shaped hematite particles were obtained in the same manner as in the embodiment of the invention.

Table 2 shows the conditions for the sintering prevention treatment and the conditions for hematite formation, and Table 3 shows the properties of the obtained spindle-shaped hematite particles.

Reference Examples 1-2: Spindle-shaped hematite particles were obtained by changing the type of starting material particles and subjecting them to heat treatment in one step without dehydration.

Table 2 shows the treatment conditions and Table 3 shows the characteristics of the spindle-shaped hematite particles.

[0094]

[Table 2]

[0095]

[Table 3]

Use Examples 1-4, Reference Use Examples 1 and 2, and Comparative Use Examples 1-4: Each spindle-shaped hematite particle powder shown in Table 3 was heated and reduced at 600 ° C. to obtain a spindle-shaped alloy magnetic particle powder. I got

Tables 4 and 5 show various characteristics of the spindle-shaped alloy magnetic particles at this time.

[0098]

[Table 4]

[0099]

[Table 5]

Using the spindle-shaped alloy magnetic particle powders shown in Tables 4 and 5, magnetic coating pieces were obtained in the same manner as in the embodiment of the present invention.

Table 6 shows the properties of the obtained magnetic coating film pieces.

[0102]

[Table 6]

[0103]

The spindle-shaped hematite particles according to the present invention have a spinel-type iron oxide within a specific range and have an appropriate crystallite size, so that shape destruction during heat reduction can be achieved. Therefore, it is suitable as a starting material for spindle-shaped alloy magnetic particles containing Fe and Co as main components.

The spindle-shaped alloy magnetic particles containing Fe and Co as the main components produced using the spindle-shaped hematite particles according to the present invention are fine particles having a good size distribution and dendritic particles. , High coercive force, large saturation magnetization, excellent oxidation stability, and good dispersibility in the binder resin. It is suitable as a spindle-shaped alloy magnetic particle powder mainly containing Fe and Co for a recording medium.

The magnetic recording medium of the present invention using the spindle-shaped alloy magnetic particles containing Fe and Co as main components has high coercive force, excellent SFD, and excellent weather resistance.

[Brief description of the drawings]

FIG. 1 is a transmission electron micrograph (30) showing the particle shape of spindle-shaped goethite particles obtained in an embodiment of the present invention.
000 times)

FIG. 2 is a transmission electron micrograph (30) showing the particle shape of the spindle-shaped hematite particles obtained in the embodiment of the invention.
000 times)

FIG. 3 is a transmission electron micrograph (300) showing the particle shape of the spindle-shaped alloy magnetic particles obtained in the embodiment of the invention.
00)

FIG. 4 is a transmission electron micrograph (× 30000) showing the particle shape of spindle-shaped goethite particle powder 1 in Example.

FIG. 5 is a transmission electron micrograph (× 30000) showing the particle shape of spindle-shaped goethite particle powder 2 in Example.

FIG. 6 is a transmission electron micrograph (× 30000) showing the particle shape of spindle-shaped goethite particle powder 3 in Example.

FIG. 7 is a transmission electron micrograph (30000) showing the particle shape of the spindle-shaped hematite particles obtained in Example 3.
Times)

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

FIG. 9 is a transmission electron micrograph (30000) showing the particle shape of the spindle-shaped hematite particles obtained in Comparative Example 1.
Times)

FIG. 10 is a transmission electron micrograph (30000) showing the particle shape of the spindle-shaped hematite particles obtained in Comparative Example 3.
Times)

FIG. 11 is a transmission electron micrograph (30000) showing the particle shape of the spindle-shaped alloy magnetic particle powder obtained in Use Example 3 using the spindle-shaped hematite particle powder obtained in Example 3.
Times)

FIG. 12 is a transmission electron micrograph (× 30000) showing the particle shape of the spindle-shaped alloy magnetic particles obtained in Use Example 4 using the spindle-shaped hematite particle powder obtained in Example 4.

FIG. 13 is an X-ray diffraction pattern of a spindle-shaped hematite particle powder obtained in the embodiment of the invention (：: hematite, Δ:
Spinel-type iron oxide).

FIG. 14 is an X-ray diffraction pattern (○: hematite, Δ: spinel-type iron oxide) of the spindle-shaped hematite particles obtained in Comparative Example 1.

FIG. 15 is an X-ray diffraction pattern (○: hematite) of the spindle-shaped hematite particle powder obtained in Comparative Example 2.

Claims (1)

[Claims] An average major axis diameter of 0.05 to 0.14 μm,
The axial ratio (average major axis diameter / average minor axis diameter) is 4 to 8, the crystallite size D ₁₀₄ is 50 to 80 °, the saturation magnetization value s is 0.5 to ² Am ² / kg, and Co containing Fe in excess of 20 at% and up to 45 at% in terms of Co, aluminum in 5 to 15 at% in terms of Al, and 5 to 15 at% in terms of rare earth element with respect to Fe A spindle-shaped hematite particle powder for a spindle-shaped alloy magnetic particle powder containing Fe and Co as a main component, comprising a spindle-shaped hematite particle powder.