JP2001192211A - Method for manufacturing powdery particle of iron- based compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing spindle-shaped target powdery particles which have a moderate axial ratio and from which dissolvable salt is removed as quickly as possible. SOLUTION: A ferrous sulfate aqueous solution is reacted with a mixed alkali aqueous solution, which consists of a ferrous sulfate aqueous solution, an ammonium bicarbonate aqueous solution and an ammonium hydroxide aqueous solution, to obtain a water suspension containing ferrous ions-containing precipitates. The water suspension thus obtained is aged, to which a Co compound containing 10-45 atomic % Co is then added to grow spindle-shaped target seed crystal particles by oxidation reaction so that 30-80% of the whole ferrous ions is oxidized. An oxygen-containing gas is made to pass through the water suspension containing the seed crystal particles to grow target layers on the surface of the seed crystal particles while adding an Al compound containing 5-20 atomic % Al so that the pH of the water suspension is adjusted to 8.0 or lower. The produced spindle-shaped target particles are washed with aqueous ammonia to obtain the objective spindle-shaped target powdery particles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a spindle-shaped alloy magnetic particle powder mainly composed of Fe for magnetic recording, which has an appropriate axial ratio, which is a starting material, and in which soluble salts are removed as much as possible. And a method for producing a spindle-shaped goethite particle powder.

[0002]

2. Description of the Related Art In recent years, devices for magnetic recording / reproducing for audio, video, and computers have been significantly reduced in size and weight, long-time recording, high-density recording, or an increase in storage capacity. Demands for higher performance and higher density recording of magnetic tapes and magnetic disks as magnetic recording media are increasing more and more.

That is, high image quality and high output characteristics of magnetic recording media, particularly, improvement of frequency characteristics, storage characteristics, and durability are required. For that purpose, reduction of noise due to the magnetic recording media, It is required that the coercive force Hc, the coercive force distribution SFD, and 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,
It is used for digital recording type DVC tapes and the like. For computers, it is used for removable disks such as Zip and Super Disk.
-Adopted by FD and is now in the commercialization stage.

[0005] Therefore, there is a strong demand for further improvement of 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 is strongly demanded that they have a large saturation magnetization value, a particle size distribution as narrow as possible, excellent dispersibility, and excellent oxidation stability Δσs. In particular, since the coercive force of the magnetic particle powder is generally generated due to its shape anisotropy, the coercive force tends to increase as the particle axial ratio (average major axis diameter / average minor axis diameter) increases.

In addition, the density of the various magnetic recording media is increased,
In order to improve reliability and durability, it is strongly required that soluble salts be removed as much as possible.

Hereinafter, this fact will be described in detail.

That is, in general, metal magnetic particle powder containing iron as a main component is prepared by reacting an aqueous solution of ferrous salt such as ferrous sulfate with an aqueous solution of alkali such as sodium hydroxide and sodium carbonate. A spindle-shaped goethite particle powder obtained by performing an oxidation reaction by passing an oxygen-containing gas such as air through a water suspension containing a precipitate, a spindle-shaped hematite particle powder obtained by heating and dehydrating the goethite particle powder, or It is obtained by using spindle-shaped particle powder in which a different element other than iron is contained in the particle powder as a starting material, and heating and reducing the starting material in a reducing gas atmosphere.

[0010] As a result of the above-mentioned production method, the spindle-shaped magnetic metal particles contain sodium and sulfate ions and calcium which is unavoidably present in the production method, and contain soluble sodium salts, soluble calcium salts and sulfate ions. In this case, there is a problem that a compound caused by a soluble salt such as a soluble sodium salt and a soluble calcium salt contained when used in a magnetic recording medium is deposited on a magnetic coating film and a magnetic head. . This fact is described in Japanese Unexamined Patent Application Publication No. 9-3
No. 05958, entitled "If the total of the water-soluble ions contained in the magnetic substance, non-magnetic substance, carbon black and filler used in each layer exceeds a certain amount, the friction coefficient is increased when running after storage under high temperature and high humidity conditions. In extreme cases, the phenomenon of sticking occurred and the vehicle stopped running, and in extreme cases, the precipitates resulted in spacing loss, the magnetic tape's reproduction output decreased, and the metal head corroded. It degrades the recording / reproducing characteristics. "

The method for reducing the soluble salt in the metal magnetic particle powder is as follows. 1) Do not use an aqueous alkali solution composed of an alkali metal such as sodium hydroxide as a raw material.
Either method of reducing soluble salts by washing with water has been adopted. The present invention relates to the method 1).

When the soluble salts are reduced by washing with water, it is conceivable to wash each product up to the metal magnetic particle powder with water. However, in the method for producing the metal magnetic particle powder, goethite as a starting material is used. Even if water is washed at the stage of the particle powder and the hematite particle powder, only the water-soluble salt present on the particle surface is removed. It is known that the insoluble impurities move to the particle surface and precipitate as soluble salts. On the other hand, when the metal magnetic particles are washed with water after being made into powder, particularly when the particles have a spindle shape, the magnetic properties such as coercive force tend to decrease, and the dispersibility in the magnetic paint tends to decrease.

Therefore, in the technique of reducing the soluble salt by washing with water, the soluble salt can be reduced, but it is not easy to reduce the soluble salt to zero and the magnetic properties are lowered, which is not preferable. Therefore, it is required to obtain high-purity goethite particle powder by eliminating the remaining impurities as much as possible by not using an alkaline aqueous solution composed of an alkali metal such as sodium hydroxide as a raw material.

Conventionally, techniques for producing goethite particle powder without using an alkali aqueous solution composed of an alkali metal (JP-A-61-174119, JP-A-10-34)
No. 0805), a technique of obtaining goethite particle powder without using an alkali aqueous solution composed of an alkali metal, and then washing the hematite particle powder and the metal magnetic particle powder after heating and dehydrating the goethite particle powder (Japanese Patent Laid-Open No. 186015, JP-A-9-305958, etc.).

[0015]

The goethite particle powder having an appropriate axial ratio and having as few residual impurities as possible is
Although it is the most demanded at present, a spindle-shaped goethite particle powder which sufficiently satisfies the above-mentioned properties has not yet been provided.

That is, Japanese Patent Application Laid-Open No. 61-174119 describes that goethite particle powder is produced by using an aqueous solution of ferrous sulfate in an aqueous solution of ammonium carbonate. Has an axis ratio of 8 or less, which is not yet sufficient.

The above-mentioned Japanese Patent Application Laid-Open No. 10-83906 discloses that a goethite particle powder is produced from an alkali hydroxide composed of ferrous chloride and an aqueous ammonia solution and an alkali carbonate composed of ammonium carbonate and the like. However, it is not described to wash with ammonia water,
In addition, since the reaction pH at the time of producing goethite particles is high, cobalt ions are eluted as ammine complexes, so that it is difficult to obtain metal magnetic particles having high coercive force.

Also, Japanese Patent Application Laid-Open No. Hei 8-186015 discloses that goethite particle powder is produced using an aqueous solution of ammonium carbonate, but is obtained because only an aqueous solution of ammonium carbonate is used. Since the axial ratio of the metal magnetic particles is not sufficient and an aqueous alkali solution composed of an alkali metal is used for adjusting the pH of the aqueous suspension, the content of soluble sodium salts is high, and the purity of goethite particles is high. Is difficult to say.

Japanese Patent Application Laid-Open No. Hei 9-305958 discloses that goethite particle powder is obtained by using an alkali carbonate containing no alkali metal, and further washed with water to obtain metal magnetic particle powder. Although it is described to reduce the content of water-soluble ions in the solution, since a compound containing an alkali metal is used as an additive, the alkali metal is contained in the goethite particles, and high purity goethite is contained. It is hard to say that particles have been obtained.

Therefore, an object of the present invention is to obtain a spindle-shaped goethite particle powder having an appropriate axial ratio and having as few residual impurities as possible.

[0021]

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

That is, the present invention relates to a ferrous sulfate aqueous solution and a mixed alkali aqueous solution comprising an aqueous solution of ammonium hydrogen carbonate and an aqueous solution of ammonium hydroxide having an equivalent ratio to the aqueous solution of ferrous sulfate of 1.7 to 2.0. After aging the aqueous suspension containing the ferrous-containing precipitate obtained by the reaction in a non-oxidizing atmosphere, an oxygen-containing gas is passed through the aqueous suspension, and the spindle-shaped goethite species is oxidized by an oxidation reaction. Then, an oxygen-containing gas is passed through an aqueous suspension containing the seed particles and the ferrous precipitate to form a goethite layer on the surface of the seed particles by an oxidation reaction. In growing and producing spindle-shaped goethite particles, the aqueous solution of ammonium hydroxide is 55 to 70 mol with respect to the aqueous mixed alkali solution as the aqueous mixed alkali solution.
%, And at the time of the formation of the seed crystal particles, the aqueous suspension containing the ferrous-containing precipitate during aging before the start of the oxidation reaction contains Co with respect to the total Fe.
An oxidation reaction is performed in the range of 30 to 80% of the total Fe ²⁺ by adding a Co compound in an amount of 10 to 45 atomic% in terms of conversion, and during the growth of the goethite layer, the seed crystal particles and the ferrous-containing precipitate And 0.5 to 15 atomic% of Al in terms of Al with respect to all Fe so that the pH of the aqueous suspension containing
A compound is added, and the produced spindle-shaped goethite particles are filtered off, and then washed with aqueous ammonia having a pH of 9.5 to 11.5 to obtain spindle-shaped goethite particles. (The present invention 1).

Further, according to the present invention, the spindle-shaped goethite particles obtained by the production method of the present invention 1 are treated with a sintering inhibitor, and then heat-treated at 400 to 850 ° C. in a non-reducing atmosphere. The present invention relates to a method for producing a compound particle powder containing iron as a main component, characterized by obtaining a powdery hematite particle powder (Invention 2).

In the present invention, the spindle-shaped goethite particles obtained by the present invention 1 are treated with a sintering inhibitor, and then heat-reduced at 400 to 700 ° C. in a reducing atmosphere to contain iron as a main component. A method for producing compound particle powder containing iron as a main component, characterized by obtaining spindle-shaped alloy magnetic particle powder.

The present invention also relates to a method for preparing the spindle-shaped hematite particles obtained according to the present invention 2 in a reducing atmosphere under a reducing atmosphere.
This is a method for producing compound particle powder containing iron as a main component, which is obtained by heating and reducing at ~ 700 ° C to obtain spindle-shaped alloy magnetic particles containing iron as a main component.

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

The particles constituting the spindle-shaped goethite particles in the present invention are obtained by first producing spindle-shaped goethite seed crystal particles and then performing a growth reaction for growing a goethite layer on the surface of the seed crystal particles.

The spindle-shaped goethite seed particles are formed in an aqueous suspension containing a ferrous-containing precipitate obtained by reacting an aqueous ferrous sulfate solution with an aqueous mixed alkali solution comprising an aqueous ammonium hydrogen carbonate solution and an aqueous ammonium hydroxide solution. After aging the liquid in a non-oxidizing atmosphere, an oxygen-containing gas is passed through the aqueous suspension to generate spindle-shaped goethite seed crystal particles. In the aqueous suspension containing the precipitate, 10 to 10% of Co
It is obtained by adding 35 atomic% of a Co compound.

In the production reaction of the spindle-shaped goethite seed crystal particles, it is not preferable to use an aqueous ferrous sulfate solution other than an aqueous ferrous sulfate solution, for example, an aqueous ferrous chloride solution contains chlorine. Ferrous concentration after mixing the aqueous ferrous sulfate solution and the mixed alkaline aqueous solution,
0.1-1.0 mol / l, preferably 0.2-0.8
mol / l. If less than 0.1 mol / l,
Low yield and not industrial. If it exceeds 1.0 mol / l, the particle size distribution is undesirably large.

In the present invention, an aqueous solution of ammonium hydrogen carbonate (NH ₄ HCO ₃ ) and an aqueous solution of ammonium hydroxide (NH ₄ OH) are used. When an alkaline aqueous solution composed of an alkali metal is used, the spindle-shaped goethite particle powder intended in the present invention cannot be obtained because the alkali metal remains in the particles. The mixing ratio of the aqueous solution of ammonium hydrogen carbonate and the aqueous solution of ammonium hydroxide is such that the aqueous solution of ammonium hydroxide is
0 mol%, preferably 57 to 65 mol%. When the amount of ammonium hydrogen carbonate is large, the axial ratio of the obtained goethite particles becomes small. On the other hand, if the amount of ammonium hydroxide is too large, magnetite is likely to be generated, and cobalt is easily eluted.

The total amount of the aqueous ammonium bicarbonate solution and the aqueous ammonium hydroxide solution used is 1.7 to 2.0, preferably 1.75 to 1.95, as an equivalent ratio to the total Fe in the aqueous ferrous sulfate solution. is there. If it is less than 1.7, magnetite tends to be mixed, and if it exceeds 2.0, it is not industrially preferable.

The pH of the aqueous suspension containing the ferrous precipitate in the present invention is preferably 7.5 to 8.5, more preferably 8.0 to 8.4. If the pH is less than 7.5, magnetite is mixed, which is not preferable. pH is 8.
If it exceeds 5, undesirably, the elution of cobalt becomes remarkable.

The ripening reaction of the spindle-shaped goethite seed particles is carried out with stirring in a non-oxidizing atmosphere. In the non-oxidizing atmosphere, an inert gas (such as nitrogen gas) or a reducing gas (such as hydrogen gas) is passed through the liquid. Preferably, it is nitrogen gas.

The ripening reaction of the spindle-shaped goethite seed particles is preferably carried out at a temperature of 40 to 80 ° C. for the aqueous suspension under a non-oxidizing atmosphere. 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 30
~ 300 minutes. If the time is less than 30 minutes, the axial ratio cannot be sufficiently increased. If the time exceeds 300 minutes, it is difficult to obtain a sufficient aging effect because ammonia evaporates.

The oxidizing means in the production reaction of the spindle-shaped goethite seed crystal particles is performed by passing an oxygen-containing gas (for example, air) through the liquid.

The temperature in the formation reaction of the spindle-shaped goethite seed crystal particles is usually set at 80 ° C. to generate goethite particles.
It may be performed at a temperature of not more than ℃. If 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, a Co compound such as cobalt sulfate or cobalt nitrate is added to an aqueous suspension containing an aged ferrous precipitate before performing an oxidation reaction. I do. The amount of the Co compound added depends on the total amount of Fe in the spindle-shaped goethite particles as the final product.
10 to 45 at%, preferably 20 to 35 at%. If it is less than 10 atomic%, there is no effect of improving the magnetic properties of the metal magnetic particle powder, and if it exceeds 45 atomic%, the axial ratio decreases due to miniaturization.

The spindle-like goethite seed crystal forming reaction is carried out in the range of 30 to 80% of the total Fe ²⁺ . If it is less than 30%, the axial ratio becomes too small, and it is difficult to obtain a high coercive force when the metal magnetic particles are used. On the other hand, if it exceeds 80%, the formation of goethite particles is almost completed and the added Al
The effect of the compound is not sufficiently obtained, and the coercive force decreases.

An oxygen-containing gas is passed through the aqueous suspension containing the spindle-shaped goethite seed particles to grow a goethite layer on the surface of the spindle-shaped goethite seed particles. By adding an Al compound to the mixture, spindle-shaped goethite particles can be obtained.

As the Al compound, aluminum sulfate,
Acid salts such as aluminum nitrate and aluminates such as ammonium aluminate can be used. The addition time of the Al compound may be either an aqueous suspension containing spindle-shaped goethite seed crystal particles and a ferrous-containing precipitate before passing the oxygen-containing gas in the growth reaction, or an aqueous suspension during the growth reaction. May be present. In particular, it is preferable before starting the growth reaction of the goethite layer. Further, the effects of the present invention are not changed even if the Al compound is dividedly added or added continuously or intermittently, but rather can be improved.

The amount of the Al compound added is 0.5 to 0.5 with respect to the total Fe in the spindle-shaped goethite particles as the final product.
It is 15 atomic%, preferably 1.0 to 12 atomic%.
If it is less than 0.5 atomic%, there is no sintering prevention effect, and 1
If it exceeds 5 atomic%, the axial ratio decreases.

PH in the growth reaction of the goethite layer
The value is less than 8.0, and preferably ranges from 7.0 to 7.8. When the pH exceeds 8.0, the elution of cobalt tends to occur, and the desired high coercive force cannot be obtained when the metal magnetic particles are used. When the pH value is less than 7.0, magnetite is undesirably mixed.

The oxidizing means in the growth reaction of the goethite layer is performed by passing an oxygen-containing gas (for example, air) through the liquid.

The temperature for the growth reaction of the goethite layer may be generally at a temperature of 80 ° C. or less at which goethite particles are formed. 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.

The obtained spindle-shaped goethite particles were adjusted to pH
Wash with ammonia water of 9.5 to 11.5. Sulfate ions can be removed by washing with ammonia water. If the pH of the aqueous ammonia is outside the above range, the sulfate ions cannot be sufficiently removed. The temperature range of the aqueous ammonia is preferably 30 to 50C. 30 ° C
If the temperature is less than 50 ° C., the washing efficiency is lowered.

After washing with ammonia water, it is preferable to further wash with water. As the washing water, ion exchange water is preferable.

The spindle-shaped goethite particles obtained by the present invention have an average major axis diameter of 0.08 to 0.30 μm, an axial ratio of 8 to 12, preferably 9 to 12, and a BET specific surface area of 100. ~ 250 m ² / g, Co content is all Fe
Is 10 to 45 atomic% in terms of Co, and the Al content is 0.5 to 15 atomic% in terms of Al with respect to all Fe.

Next, in the present invention, the spindle-shaped goethite particle powder obtained by the production method of the present invention is subjected to a sintering preventing treatment with a sintering inhibitor and a heat treatment in a non-reducing atmosphere. Spindle-shaped hematite particles can be obtained.

As the sintering inhibitor, a compound of a rare earth element is used. As the compound of the rare earth element, one or more compounds such as scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, and samarium are suitable. As the rare earth element compound, it is preferable to use a rare earth element chloride or nitrate.
The treatment method may be either a dry method or a wet method, preferably a wet coating treatment. The amount used is preferably 0.5 to 15 atomic%, more preferably 1.0 to 12 atomic%, based on the total Fe in terms of rare earth elements. 0.5
When the number is less than the atom, the effect of preventing sintering is not sufficient, and the SFD (coercive force distribution) deteriorates when the metal magnetic particles are used. If it exceeds 15 atomic%, the saturation magnetization value will be low.

It is preferable that the Co compound also coats the particle surface of the goethite particle powder in order to prevent sintering and control the reduction rate. As the cobalt compound, cobalt acetate and cobalt nitrate are preferable. The amount of the Co compound added depends on the total amount of Co in addition to the amount of Co present inside the goethite particles.
It is added to e in a range not exceeding 50 atomic% in terms of Co.

In order to improve the sintering prevention effect, one or more of compounds of elements selected from Si, B, Mg, Ba, Sr and the like may be used as necessary. 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. In this case, the total amount used is preferably 1 to 15 atomic% as a total amount of the total iron of the spindle-shaped goethite particle powder and the rare earth element compound used as the sintering inhibitor. If the amount is small, the effect of preventing sintering is not sufficient, and if the amount is too large, the saturation magnetization decreases when the metal magnetic particles are used. Therefore, the optimum amount may be appropriately selected depending on the type of combination.

By coating in advance with the sintering inhibitor or the like, sintering between the particles and the particles is prevented, and spindle-shaped hematite particles that further retain and inherit the particle shape and axis ratio of the spindle-shaped goethite particles. A powder can be obtained, whereby it becomes easy to obtain spindle-shaped alloy magnetic particle powder mainly containing iron, which retains and inherits the above-mentioned shape and the like.

The fusiform goethite particles coated with the sintering inhibitor are treated under a non-reducing atmosphere at 400-85.
Heat treatment is performed within the range of 0 ° C. to obtain spindle-shaped hematite particles. The non-reducing atmosphere can be one or more gas flows selected from air, oxygen gas, nitrogen gas and the like. On the other hand, when the temperature is lower than 400 ° C., a long time is required for the heat treatment. On the other hand, when the temperature is higher than 850 ° C., deformation of particles and sintering between particles and particles are caused.

The particles constituting the spindle-shaped hematite particles according to the present invention have an average major axis diameter of 0.05 to 0.3 μm.
m, preferably 0.05 to 0.2 μm, and an axial ratio of 8
-12, preferably 8.5-12, and the BET specific surface area value is 30-140 m ² / g.

The cobalt content of the spindle-shaped hematite particles is 10 to 50 atomic% based on the total Fe in terms of Co, and the Al content is 0.5 to 1 atomic% based on the total Fe in terms of Al.
5 atomic%, and the content of the rare earth element is 0.5 to 15 atomic% based on the total Fe in terms of the rare earth element.

Next, in the present invention, the spindle-shaped goethite particle powder obtained by the production method of the present invention is subjected to a sintering preventing treatment with the sintering inhibitor and directly heated and reduced, or The spindle-shaped alloy magnetic particle powder containing iron as a main component can be obtained by any of the methods of heating and reducing the spindle-shaped hematite particle powder obtained by the production method of the above.

Further, after the spindle-shaped goethite particles obtained by the production method of the present invention are subjected to the sintering preventing treatment with the sintering inhibitor, heat treatment in a non-reducing atmosphere and heat reduction in a reducing atmosphere are carried out. Can be obtained continuously to obtain spindle-shaped alloy magnetic particles containing iron as a main component.

The spindle-shaped goethite particle powder coated with the above-mentioned sintering inhibitor can be directly reduced to obtain a desired spindle-shaped alloy magnetic particle powder containing iron as a main component. In order to control the powder characteristics and control the powder shape, it is preferable to perform a heat treatment in a non-reducing gas atmosphere in advance by a conventional method before the reduction.

The non-reducing atmosphere can be one or more gas flows selected from air, oxygen gas, nitrogen gas and the like. The heat treatment temperature can be in the range of 400 to 850 ° C., and it is more preferable that the heat treatment temperature is appropriately selected according to the type of the compound used for the coating treatment of the spindle-shaped goethite particles. If the temperature is lower than 400 ° C., a long time is required for the heat treatment, and if the temperature is higher than 850 ° C., deformation of the particles and sintering between the particles and the particles are caused.

The temperature range of the heat reduction in the present invention is 4
00-700 degreeC is preferable. When the temperature is lower than 400 ° C., the progress of the reduction reaction is slow, and a long time is required. Also, 7
If the temperature exceeds 00 ° C., the reduction reaction proceeds rapidly, causing deformation of the particles and sintering between the particles and the particles.

The spindle-shaped alloy magnetic particles after heat reduction according to the present invention may be prepared by a known method, for example, immersion in an organic solvent such as toluene, or by inertizing the atmosphere of the reduced spindle-shaped alloy magnetic particles once. After replacing with gas, take it out into the air by gradually increasing the oxygen content in the inert gas and finally converting it into air, or by gradually oxidizing using a mixed gas of oxygen and water vapor. Can be.

Spindle-shaped alloy magnetic particles obtained by the present invention
The powder has an average major axis diameter of 0.05 to 0.20 μm.
And the axial ratio is 7 or more, preferably 7 to 9,
Is D ₁₁₀Is preferably 120 to 170 °, more preferably
Or 130-160 °. Also, the size distribution is
0.20 or less is preferable, and the BET specific surface area value is 40 to 7
0m²/ G. Also contains cobalt
The amount is 10 to 50 atomic% in terms of Co with respect to the total Fe, preferably
Or 20 to 40 atomic%, and the Al content is
Is 0.5 to 15 atomic% with respect to all Fe,
The content of the class element is 0.1 in terms of rare earth element relative to all Fe.
5 to 15 atomic%. The soluble sodium salt is 1
0 ppm or less, soluble calcium salt is 100 ppm or less
Below, the residual sulfur content is 50 ppm or less.

The spindle-shaped alloy magnetic particles obtained according to the present invention have a coercive force Hc of 159.2 to 198.9 kA /
m (2000 to 2500 Oe) is preferred, and more preferably 167.1 to 198.9 kA / m (2100 to 25 Oe).
00 Oe), and the saturation magnetization value s is 120 to 160
^{Am 2 / kg (120~160emu / g} ) , more preferably 130~160Am ² / kg (13
0-160 emu / g). The squareness ratio (σr / σs) is 0.
52 to 0.55, the oxidation stability Δσs of the saturation magnetization is 10
% Or less is preferable.

The magnetic coating film obtained by using the spindle-shaped alloy magnetic particles obtained by the present invention has a coercive force Hc
Is 159.2 to 198.9 kA / m (2000 to 250
0 Oe), the squareness ratio (Br / Bm) is 0.82 or more, the SFD is 0.45 or less, and the oxidation stability ΔBm is less than 8%.

[0065]

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

In the present invention, the average major axis diameter, average minor axis diameter, and axial ratio of the spindle-shaped goethite particles, the spindle-shaped hematite particles, and the spindle-shaped alloy magnetic particles are all numerical values measured from electron micrographs. The average value was shown.

The amount of Co, the amount of Al, the amount of a rare earth element, the amount of sodium of the spindle-shaped goethite particle powder, the spindle-shaped hematite particle powder, and the spindle-shaped alloy magnetic particle powder in the present invention,
The calcium content and the content of other metal elements were measured using "Inductively Coupled Plasma Emission Spectroscopy Analyzer SPS4000" (manufactured by Seiko Instruments Inc.).

The residual sulfur content of the spindle-shaped alloy magnetic particles was measured using a “carbon / sulfur measurement device” (manufactured by Horiba).

The BET specific surface area value of the particle powder was indicated by a value measured by a BET method using “Monosorb MS-11” (manufactured by Cantachrome Co., Ltd.).

The crystallite size D ₁₁₀ (the X-ray crystal particle diameter of the spindle-shaped alloy magnetic particles) was measured using an “X-ray diffractometer” (Rigak
u) (Measurement conditions: target Cu, tube voltage 40 kV,
Using a tube current of 40 mA), the size of the crystal particles measured by the X-ray diffraction method was determined using the (110)
It represents the thickness of a crystal grain in a direction perpendicular to each of the crystal planes, and is represented by a value calculated from the diffraction peak curve for each crystal plane using the following Scherrer equation.

D ₁₁₀ = Kλ / βcosθ

Here, 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 the diffraction peak of (110) plane).

The magnetic properties of the spindle-shaped alloy magnetic particles and the magnetic coating pieces were measured using a vibration sample magnetometer VSM-3S-15.
Using an external magnetic field 795.8
It was measured at 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.

3 mmφ steel ball: 800 parts by weight, spindle-shaped alloy magnetic particle powder: 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.

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 was 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, and σs and Bm measured before the test was started.
Δs and ΔBm were calculated by dividing the difference (absolute value) between σs ′ and Bm ′ one week after the accelerated aging test by σs and Bm before the start of the test, respectively. Δσs and ΔBm are 0
% Indicates that the oxidation stability is excellent.

<Production of Spindle-Shaped Goethite Particle Powder> 30 mol of ammonium bicarbonate and 45 m
ol (aqueous ammonium hydroxide solution corresponds to 60 mol% in terms of a prescribed conversion with respect to the mixed alkali) was charged into a reaction tower equipped with a stirrer equipped with bubble dispersion blades at a rate of 400 rpm. While rotating the stirrer at a speed, the temperature is adjusted to 50 ° C. while passing nitrogen gas at a flow rate of 60 l / min. Then, 16 l of an aqueous ferrous sulfate solution containing 20 mol as Fe2 + (a mixed alkaline aqueous solution with respect to ferrous sulfate corresponds to 1.875 equivalents in terms of a prescribed conversion) was charged into a bubble column, and aged for 25 minutes.
4 l of an aqueous solution of cobalt sulfate containing 2 + 4.0 mol (total F
This corresponds to 20 atomic% in terms of Co with respect to e. ) Was added and the mixture was aged for an additional 2 hours and 35 minutes. Then, the reaction was carried out while passing air at a flow rate of 2 l / min until 40% of the total Fe2 + was oxidized.

Then, 1 liter of an aqueous solution of aluminum sulfate containing 3 + 1.6 mol of Al (corresponding to 8 atomic% in terms of Al with respect to all Fe) was added, and an oxidation reaction was further performed until the reaction was completed. The pH at the end of the reaction was 7.65.

The obtained goethite particle-containing slurry was separated by filtration using a press filter, washed with ammonia water adjusted to pH = 10.5 using ammonia, and then further washed with ion-exchanged water. And made it into a press cake. From the filtrate after filtration, 59 ppm of Co2 +
Was detected.

A spindle-shaped goethite particle powder obtained by drying and pulverizing a part of the cake by a conventional method has an average major axis diameter of 0.173 μm and an average minor axis diameter of 0.0162 μm.
m, the axial ratio is 10.7, the size distribution (standard deviation / average major axis diameter) is 0.182, and the BET specific surface area value is 175.7 m ^2.
/ G, the Co content of the particles as a whole is 1
The content was 9.8 atomic% and the Al content was 8 atomic% with respect to all Fe. Adsorption rate of Co (residual amount of Co / added amount of Co)
Was 98.8%.

<Production of Spindle-Shaped Hematite Particle Powder> After the obtained press cake of the spindle-shaped goethite particle powder was sufficiently dispersed in water, an aqueous yttrium nitrate solution (total Fe
And an aqueous solution of cobalt acetate (12 at.% Based on the total Fe), and the mixture was sufficiently stirred. Then, while stirring, an aqueous solution of ammonium bicarbonate was added to adjust the pH of the aqueous solution to 7.2, and then filtered and washed with a filter press to obtain a press cake. The obtained press cake was extruded and molded with a molding plate having a hole diameter of 3 mm using an extrusion molding machine, and was then dried at 120 ° C.
To obtain a granulated product of spindle-shaped goethite particles coated with 8 atomic% of a Y compound in terms of Y and 12 atomic% of a Co compound in terms of Co with respect to all Fe. The content of Co in the obtained spindle-shaped goethite particles was 32 atom% based on the total Fe, the content of Al was 12 atom% based on the total Fe, and the content of Y was 8 atom based on the total Fe. %Met

The granules of the spindle-shaped goethite particles coated with the Y and Co compounds are dehydrated in air at 300 ° C.
Thereafter, the mixture was heated and dehydrated at 600 ° C. in the same atmosphere to obtain a granulated product of spindle-shaped hematite particles.

<Production of Spindle-Shaped Alloy Magnetic Particle Powder> 100 g of granulated granules of the spindle-shaped hematite particle powder obtained here
(Average diameter: 2.6 mm) was placed in a batch-type fixed bed reduction device having an inner diameter of 72 mm, and the bed height was set to 5.5 cm.
The temperature was raised to 500 ° C. while passing a nitrogen gas at a gas superficial velocity of 50 cm / s at a temperature of 600 ° C., and then switched to hydrogen gas, and the temperature was raised to 600 ° C. while passing a hydrogen gas at a gas superficial velocity of 50 cm / s. Heat reduction was carried out until the exhaust gas dew point reached -30 ° C to obtain a granulated product of spindle-shaped alloy magnetic particles.

Thereafter, the gas was switched again to nitrogen gas and
Until the product temperature is maintained at 60 ° C. and then mixed with air to gradually increase the oxygen concentration to 0.35 vol% until the product temperature becomes [retention temperature + 1] ° C. (maximum product temperature 100
(C, treatment time: 2 hours) A surface oxidation treatment was performed to form a surface oxide layer on the surface of the particles to obtain granules of spindle-shaped alloy magnetic particles.

The spindle-shaped alloy magnetic powder obtained here was prepared from particles having an average major axis diameter of 0.131 μm, an axial ratio of 8.0, a BET specific surface area of 47 m ² / g, and a crystallite size D ₁₁₀ of 148 °. In other words, it had a spindle shape, a uniform particle size, and no dendritic particles. Also, the Co content in the particles is
And the Al content was 8 atomic% and the Y content was 8 atomic% with respect to the total Fe.

Further, soluble Na was 2 ppm and soluble Ca was 2 ppm.
Was 80 ppm and the residual sulfur content was 51 ppm. Soluble Fe was not detected from the spindle-shaped alloy magnetic particle powder.

The magnetic properties of the spindle-shaped alloy magnetic particles are as follows. The coercive force Hc is 181.0 kA / m (2270O
e), the saturation magnetization value σs is 145.3 Am ² / kg (14
5.3 emu / g) and squareness ratio (σr / σs) of 0.54
3. The oxidation stability Δσs of the saturation magnetization value is 7.
7% (actual value-7.7%).

The characteristics of the magnetic coating film are as follows.
81.0 kA / m (2275 Oe), squareness ratio (Br / B
m) is 0.842, SFD is 0.384, oxidation stability Δ
Bm was 5.3% (actually determined value-5.3%) as an absolute value.

[0089]

The most important point in the present invention is that a spindle-shaped goethite particle powder is obtained without using an alkali aqueous solution composed of an alkali metal, and the goethite particle powder is washed with ammonia water to have a proper axis ratio. Further, it is a fact that a goethite particle powder having high purity can be obtained.

In the present invention, an aqueous solution of ammonium hydrogen carbonate and an aqueous solution of ammonium hydroxide are used in order not to leave alkali metals. Conventionally, when an ammonium compound is used as an aqueous alkaline solution, Fe-containing precipitates are formed due to elution of cobalt due to formation of an ammine complex ([M (NH ₃ ) _a ] ^{n +} , where M is an n-valent metal ion). The pH of the aqueous suspension contained could not be increased.
In addition, when the pH is lowered, magnetite is mixed and the axis ratio of goethite particles is reduced. In the present invention, the pH of the aqueous suspension was determined to be a region in which magnetite was not mixed and the axial ratio was not reduced, and a reaction for forming goethite particles was performed.

On the other hand, by specifying the pH of the aqueous suspension containing the ferrous-containing precipitate in the range of 7.5 to 8.5, since the alkali metal does not exist, the goethite particles easily adsorb anions. As a result, goethite particles containing a large amount of sulfate ions could not be sufficiently removed by washing with ordinary water. In the present invention, it is possible to remove sulfate ions by washing with ammonia water having a pH of 9.5 to 11.5.

[0092]

Next, examples and comparative examples will be described.

Examples 1 to 6 and Comparative Examples 1 to 10 Spindle-shaped goethite particles were obtained in the same manner as in the embodiment of the invention except that the production conditions of the spindle-shaped goethite particles were variously changed. The production conditions at this time are shown in Tables 1 and 2, and various properties of the obtained spindle-shaped goethite particles are shown in Table 3.

A in Table 3 indicates that magnetite particles were mixed in the goethite particles.

[0095]

[Table 1]

[0096]

[Table 2]

[0097]

[Table 3]

Using spindle-shaped goethite particles having the characteristics shown in Table 3, spindle-shaped hematite particles were obtained in the same manner as in the embodiment of the present invention. The production conditions at this time are shown in Table 4, and various characteristics of the obtained spindle-shaped hematite particles are shown in Table 5. In Example 5, the heat treatment was not performed after the treatment with the sintering inhibitor. Comparative Example 11 is a hematite particle powder obtained by heating and dehydrating the goethite particle powder described in the embodiment without washing with ammonia water. Comparative Example 12 is the hematite particle powder obtained by washing the goethite particle powder described in the embodiment with ammonia water having a pH of 9.0 and heating and dehydrating.

[0099]

[Table 4]

[0100]

[Table 5]

Using spindle-shaped hematite particles having the properties shown in Table 5, spindle-shaped alloy magnetic particles were obtained in the same manner as in the embodiment of the present invention. Tables 6 and 7 show the production conditions at this time and various characteristics of the obtained spindle-shaped alloy magnetic particle powder. In Example 5, after the sintering prevention treatment shown in Table 4 was performed, the heat reduction treatment was performed without hematite formation.

[0102]

[Table 6]

[0103]

[Table 7]

[0104]

According to the manufacturing method of the present invention, the magnetic recording F
Spindle-shaped goethite particles having a suitable axial ratio as a starting material of the spindle-shaped alloy magnetic particles containing e as a main component and from which soluble salts have been removed as much as possible can be obtained.

The spindle-shaped metal magnetic particles obtained according to the present invention are high-purity particles, and thus are suitable as a magnetic recording medium having high density recording, high output, high reliability and improved weather resistance. It is.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G002 AA05 AA06 AA10 AB03 AB05 AD03 AE03 5D006 BA04 BA05 BA08 5E040 AA11 AA19 AB02 AB09 CA06 HB08 HB09 HB17 NN01 NN02 NN17 NN18

Claims (4)

[Claims] 1. An aqueous ferrous sulfate solution obtained by reacting a mixed alkali aqueous solution comprising an aqueous solution of ammonium hydrogen carbonate and an aqueous solution of ammonium hydroxide having an equivalent ratio to the aqueous solution of ferrous sulfate of 1.7 to 2.0. After aging the aqueous suspension containing the ferrous precipitate obtained in a non-oxidizing atmosphere, an oxygen-containing gas is passed through the aqueous suspension to produce spindle-shaped goethite seed crystal particles by an oxidation reaction. Then, an oxygen-containing gas is passed through an aqueous suspension containing the seed crystal particles and the ferrous-containing precipitate to grow a goethite layer on the particle surfaces of the seed crystal particles by an oxidation reaction. In producing the goethite particles, the aqueous solution of ammonium hydroxide is 55 to 70 m
ol%
At the time of formation of the seed crystal particles, a Co compound of 10 to 45 atomic% in terms of Co with respect to the total Fe is added to an aqueous suspension containing a ferrous-containing precipitate during aging before the oxidation reaction starts. The oxidation reaction is performed in the range of 30 to 80% of the total Fe ^{2+. During} the growth of the goethite layer, the pH of an aqueous suspension containing the seed crystal particles and the ferrous-containing precipitate is less than 8.0. After adding 0.5 to 15 atomic% of an Al compound in terms of Al with respect to all Fe, the formed spindle-shaped goethite particles are filtered off, and then p
A method for producing compound particle powder containing iron as a main component, wherein spindle-type goethite particle powder is obtained by washing with ammonia water having a H of 9.5 to 11.5. 2. After treating the spindle-shaped goethite particle powder obtained by the production method according to claim 1 with a sintering inhibitor,
A method for producing compound particle powder containing iron as a main component, wherein a heat treatment is performed at 400 to 850 ° C. in a non-reducing atmosphere to obtain spindle-shaped hematite particle powder. 3. After treating the spindle-shaped goethite particle powder obtained by the production method according to claim 1 with a sintering inhibitor,
A method for producing a compound particle powder containing iron as a main component, wherein a spindle-shaped alloy magnetic particle powder containing iron as a main component is obtained by heating and reducing at 400 to 700 ° C. in a reducing atmosphere. 4. The spindle-shaped hematite particle powder obtained by the production method according to claim 2 is reduced to 400 to
A process for producing compound particle powder containing iron as a main component, wherein the compound is heated and reduced at 700 ° C. to obtain spindle-shaped alloy magnetic particles containing iron as a main component.