JPH06136412A - Production of magnetic metal powder - Google Patents

Abstract

PURPOSE:To produce a magnetic metal powder enhanced in coercive force and sharpened in coercive force distribution by thermally dehydrating alpha-iron oxyhydoxide at a specified temp. in a specified nonreducing steam atmosphere and then thermally reducing the dehydrated material in a reducing atmosphere. CONSTITUTION:alpha-iron oxyhydroxide is thermally dehydrated in a nonreducing atmosphere to form hematite. In this case, an atmosphere contg. 80-100% steam is used as the atmosphere, and the heating temp. is controlled to 350-700 deg.C. Acicular, spindle-shaped or rod-shaped alpha-iron oxyhydroxide having 0.05-1.0mum average major axis is preferably used, and the surface of the grain may be doped with the compd. of >=1 kind of element among Al, Si, B, Co, Ni, Mn, rare-earth elements, Ca, Ba, Sr and Mn. The hematite is thermally reduced in a reducing atmosphere and oxidized and stabilized, as required. Consequently, a magnetic metal powder appropriate for the high-density magnetic recording medium and having a small X-ray particle diameter and with the dispersibility and orientation property improved is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal magnetic material used as a magnetic powder for a high density magnetic recording medium, which has a high coercive force, a sharp coercive force distribution, a small X-ray grain size and excellent dispersibility. The present invention relates to a method for producing powder.

[0002]

2. Description of the Related Art In recent years, metal magnetic powder has been used as a magnetic material for high density magnetic recording media, and has been used as a metal tape for audio.
It is widely used as a metal tape for millimeter VTR, a tape for DAT, and a metal tape for business use. Also, recently
Development is actively carried out aiming at downsizing and weight reduction of magnetic recording devices, long-time recording, high image quality, and high density, and along with this, higher performance is achieved for magnetic tapes, which are magnetic recording media used. High density recording is required. The magnetic metal powder that can meet such requirements is fine,
It must have high coercive force and high saturation magnetization and excellent dispersibility. The metal magnetic powder currently used is produced by heating and reducing acicular α-iron oxyhydroxide or iron oxide in a reducing atmosphere, and then forming an oxide film on the surface of the particles. The magnetic characteristics of the metallic magnetic powder can be controlled by changing the shape of the powder particles and the composition of the alloy, but the coercive force and coercive force distribution are dominated by the particle shape. Regarding the particle shape, alkali hydroxide or alkali carbonate is added to an aqueous solution of ferrous salt for neutralization, and air is blown into the suspension containing the formed precipitate to form needle-shaped α-iron oxyhydroxide. In the process, a shape control agent is added to the suspension to control the acicular ratio (major axis length ÷ minor axis diameter), and the amount of gas blown or the reaction temperature is changed to control the particle size. There is. Here, the coercive force of the metal magnetic powder is determined by the acicular ratio when the particle size is constant, and the coercive force increases as the acicular ratio increases. Therefore, in order to obtain a metal magnetic powder having a large coercive force, long needle-shaped α-iron oxyhydroxide should be used as the starting material. However, recently, there has been a strong demand for higher density magnetic recording media, and from this point of view, there is a demand for metal magnetic powders having shorter particles and higher coercive force than ever before. By the way, in general, on the surface of α-iron oxyhydroxide, in order to prevent sintering of particles during heat reduction, A
1, 1, Si, B, P, Ca, Mg, Ba, Ti, Zr, rare earth elements and the like are deposited as sintering inhibitors, and then heat reduction is performed. As a result, a magnetic metal powder in which the particle shape of the starting material was almost maintained was obtained, but voids caused by water generated during heat reduction or voids due to volume contraction in the sintering inhibitor film were obtained. Etc. may exist, and these vacancies deteriorated the magnetic characteristics. Therefore, in order to improve such a phenomenon, a needle-shaped α-coated with a sintering inhibitor is used.
A method has been proposed and generally adopted in which iron oxyhydroxide is heated and dehydrated in a non-reducing atmosphere to reduce it to hematite before being reduced and then heat-reduced. By adopting this method, it becomes possible to obtain particles with few voids in the particles, and it is becoming possible to obtain short needle-shaped particles having a relatively high coercive force. Even metallic magnetic powders do not meet all the requirements currently required, and there is a current need for further improvement.

[0003]

As described above, as the performance of the magnetic recording / reproducing apparatus has increased in recent years, there has been a strong demand for higher output and lower noise in the magnetic recording medium used together. There is. Therefore, metal magnetic powders used for magnetic recording media are also required to be fine, have high coercive force, have a sharp coercive force distribution, have a small X-ray particle size, and have excellent dispersibility. However, with the above-mentioned conventional techniques, metal powders satisfying all the above items have not been obtained. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a metal magnetic powder having excellent characteristics that cannot be obtained by the above-mentioned conventional method.

[0004]

Means for Solving the Problems The present invention which achieves the above-mentioned object is to heat-dehydrate α-iron oxyhydroxide in a non-reducing atmosphere to hematite, and then heat-reduce it in a reducing atmosphere to reduce metal. In the method for obtaining magnetic powder, the atmosphere during the heat dehydration treatment is a steam atmosphere of 80 to 100%, and the heating temperature is 350 to 700 ° C.

The α-iron oxyhydroxide used in the present invention is produced by a general method, that is, a ferrous salt is neutralized with an aqueous alkali hydroxide solution, and air is blown into a suspension containing the produced green last. The needle-shaped α-iron oxyhydroxide or ferrous salt produced in step 1 is neutralized with an aqueous solution of alkali carbonate,
The spindle-shaped α-iron oxyhydroxide and ferric salt produced by blowing air into the suspension containing the produced iron carbonate are neutralized with an aqueous alkali hydroxide solution, and heated under high alkaline conditions to produce the product. Needle-like or rod-like α-iron oxyhydroxide is preferred. In the α-iron oxyhydroxide particles, Co,
Ni, Cr, Mn, Zn, Cu, Ca, Mg, Ba, S
r, rare earth element (La, Ce, Pr, Nd, Sm, G
A metal compound such as d, Dy or Y) may be doped as a particle shape control agent, a magnetic property control agent, or a sintering inhibitor. As a raw material of the short needle-shaped magnetic powder for the high-density magnetic recording medium used in the present invention,
Α-Iron oxyhydroxide having an average major axis length in the range of 0.05 to 1.0 μm is preferred. If the particle size is less than 0.05 μm, a metallic magnetic powder with practical magnetic properties cannot be obtained.
The above is too large to be suitable for magnetic powder for high density magnetic recording media.

Next, Al, Si, B, Co, Ni, Mn, a rare earth element, and C are formed near the surface of α-iron oxyhydroxide.
The compound of one or more elements selected from a, Ba, Sr, and Mg is contained. As a method of containing, a water-soluble salt of the element to be contained is dispersed in α-iron oxyhydroxide. A method of adding fine crystals of hydroxide formed by neutralizing with an acid or an alkali to a particle surface while stirring, or a reaction for producing α-iron oxyhydroxide In the latter stage, there is a method in which an aqueous solution salt of an element to be contained is added alone or a mixture with a ferrous salt is added, and doping is performed by an oxidation reaction. As described above, the purpose of containing these elements is to control the magnetic characteristics and prevent sintering of particles, and the addition amount and combination of these elements can be empirically determined. For example, when the amount of the non-reducing element added as a sintering inhibitor is expressed as oxide (eg Al ₂ O ₃ , SiO ₂ ), 10
When it is set to 0, the weight ratio is preferably 2.0 to 20.0. If it is less than 2.0, the effect of preventing sintering is insufficient, and even if the method of the present invention is adopted, a metal magnetic powder having excellent characteristics cannot be obtained. On the other hand, if it exceeds 20.0, the content of the oxide having no magnetic property increases, and the saturation magnetization becomes small, which is not preferable. Further, the amounts of Co and Ni added as magnetic property control agents are Co = 0.5 to 40 and Ni = 0.
5 to 20 is a preferable range.

Next, the above-mentioned surface-treated α-iron oxyhydroxide is thoroughly washed, dried, and then 80 to 100%.
Heat treatment is performed at a temperature of 350 to 700 ° C in a steam atmosphere.
In this heat treatment, the lower the partial pressure of water vapor, the smaller the effect of the present invention, and the lower the characteristics of the magnetic metal powder. Therefore, it is desirable to perform the heat treatment in a water vapor atmosphere as close to 100% as possible. Further, in controlling the steam atmosphere, a method of effectively utilizing steam generated by heating of α-iron oxyhydroxide can be considered, but with this method, it is difficult to control the steam partial pressure to a constant value. A more reliable method is to introduce heated steam and non-reducing gas into the heat treatment chamber. Further, when the heat treatment is carried out in a 100% steam atmosphere, it is only necessary to feed heated steam, so that the control is easy. A fixed bed, a rotary kiln, or the like can be used as the device for the heat dehydration treatment. The dehydration temperature is preferably 350 to 700 ° C, more preferably 400 to 650 ° C.
If the dehydration treatment temperature is less than 350 ° C, there is no effect of baking up the particles, and if it exceeds 700 ° C, the hematite produced by heating dehydration has already progressed to sintering, and the coercive force of metal magnetic powder is low. When it is used as a medium, it causes an increase in the X-ray particle size of the metal magnetic powder, which is not preferable because of its noise. The above treatment temperature is a tentative guide, and the optimum treatment temperature is appropriately determined because it varies depending on the size of particles, the type and amount of the sintering inhibitor.

[0008] Next, the α-iron oxyhydroxide that has been subjected to the above heat dehydration treatment is heated and reduced in a reducing atmosphere according to a conventional method, and after cooling, the surface of the particles is stabilized by oxidation according to a conventional method. To obtain metallic magnetic powder of.

[0009]

[Operation and effect] The method for producing the metallic magnetic powder of the present invention is
Since the heat dehydration treatment of α-iron oxyhydroxide is performed in the steam atmosphere of 80 to 100% and the heating is performed in the temperature range of 350 to 700 ° C, the characteristics of the metal magnetic powder obtained by the reduction can be obtained by the conventional method. It has a higher coercive force, a sharper coercive force distribution, a smaller X-ray grain size related to noise when used as a medium, and an excellent dispersibility. Since the method for producing the metallic magnetic powder of the present invention heat-treats in a high-concentration water vapor atmosphere, the shape of the particles when made into hematite has an empty space as compared with that in a conventional non-reducing atmosphere. There are few pores and the particle surface is smooth. Therefore, it is presumed that when this is used as the metal magnetic powder, the acicularity is good, there are few defects inside the particles, the surface is smooth, and the magnetic properties are good.

[0010]

EXAMPLES The present invention will be specifically described below with reference to examples. (1) Production of α-iron oxyhydroxide (Sample A) In a reaction vessel equipped with a stirrer and an air blowing nozzle,
Nitrogen gas is flowed out to drive out the oxidizing gas, and 8.0 mol of ferrous chloride, 0.3 mol of nickel chloride dissolved in 4 liters of distilled water, and 20 liters of a 1.5 mol / liter sodium hydroxide aqueous solution are mixed. The mixed suspension was kept at 40 ° C., air of 10 liter / min was blown for 2 hours, and the needle-shaped α
-Iron ferric oxyhydroxide is obtained. The α-iron oxyhydroxide particles had an average major axis length of 0.4 μm and a specific surface area of 73 m ² / g. Next, the obtained α-iron oxyhydroxide was collected by filtration, washed with water and dispersed in 40 liters of distilled water, and 0.38 mol of cobalt chloride was dissolved in 2 liters of distilled water. After adding the aqueous solution and stirring well,
Gradually add an aqueous solution of sodium hydroxide to the pH of the aqueous solution.
Was adjusted to 8 and stirred for 30 minutes. Then, in terms of SiO ₂ ,
152 ml of 100 g / liter water glass aqueous solution was added to the suspension and stirred for 30 minutes, then 2 liters of 0.5 mol / liter aluminum chloride aqueous solution was gradually added dropwise, and also sodium hydroxide aqueous solution was added dropwise. The pH of the suspension was adjusted to 8 and stirred for 30 minutes. The surface treated α
-Iron oxyhydroxide was collected by filtration, washed with water and dried in a drier at 120 ° C to obtain sample A. The amounts of the elements added by the surface treatment are as follows in terms of weight ratio when iron is 100.

Ni = 3.0 Co = 5.0 SiO ₂ = 3.4 Al ₂ O ₃ = 6.0 Example 1 Sample A was set in a stationary heating furnace having a structure in which gas flows, and 100% steam heated to 500 ° C. was flowed. Then, after the temperature in the furnace reached 500 ° C., the temperature was maintained for 3 hours. Next, after cooling this product, it was reduced under a steam flow at 490 ° C. for 3 hours, then cooled to room temperature, and then nitrogen gas was caused to flow, and air was gradually fed into this nitrogen gas flow to stabilize the metal magnetic powder. Got When the hematite particles obtained by heating and dehydrating the metal magnetic powder in this manner are observed with an electron microscope, the particles have few pores and have a smooth particle surface as shown in FIG. It was The obtained metal magnetic powder was fine particles having an average major axis length of 0.18 μm, and its magnetic characteristics were measured. As a result, Hc = 1695 Oe,
σs = 132 emu / g, squareness ratio (Rs) = 0.505, specific surface area (BET) = 58.0 m ² / g, X-ray particle size (Lc) = 149 Å. Also, by observation with an electron microscope,
It was confirmed that the particles were a metal magnetic powder with few pores and a smooth particle surface. The results showing the relationship between the magnetic properties of the metal magnetic powder and the heat dehydration treatment conditions are shown in Table 1.
Table 2 shows the magnetic properties of the obtained metal magnetic powder when used as a tape, and the SFD value of the tape showing the coercive force distribution.

Example 2 The same evaluation was carried out on the metal magnetic powder obtained by treating under the same conditions as in Example 1, except that the atmosphere of the heat dehydration treatment was 15% nitrogen gas and 85% steam. went. The results are shown in Tables 1 and 2.

Comparative Example 1 Sample A was placed in a reaction furnace using the same apparatus as in Example 1.
Nitrogen gas at 600 ° C. was flowed to treat at a target temperature for 3 hours, and then reduction / stabilization treatment was carried out in the same manner as in Example 1 to obtain metal magnetic powder. The treatment temperature was selected such that the metal magnetic powder with the best magnetic properties was obtained when the treatment was carried out in a nitrogen atmosphere. Further, when the hematite particles obtained by subjecting the metal magnetic powder to a heat dehydration treatment were observed with an electron microscope, more voids were confirmed in the particles as compared with the hematite particles of Example 1. An electron micrograph is shown in FIG. The obtained metal magnetic powder was evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

Comparative Example 2 Sample A was placed in a reactor using the same apparatus as in Example 1.
Air was passed at 650 ° C. to treat at a target temperature for 3 hours, and then reduction / stabilization treatment was carried out in the same manner as in Example 1 to obtain a magnetic metal powder. The treatment temperature was selected such that the metal magnetic powder having the best magnetic properties can be obtained when the treatment is performed in an air atmosphere. Further, when the hematite particles obtained by subjecting the metal magnetic powder to a heat dehydration treatment were observed with an electron microscope, as with the hematite particles of FIG. 2 (Comparative Example 1), the hematite particles contained in the particles were larger than those of the hematite particles of Example 1. Many holes were confirmed. An electron micrograph is shown in FIG. The obtained metal magnetic powder was evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

Comparative Example 3 The same treatment as in Example 1 was carried out except that the nitrogen gas concentration was 50% and the water vapor concentration was 50%. The obtained metal magnetic powder was evaluated in the same manner as in Example 1, and the results are shown in Table 1. A decrease in coercive force, which is thought to be due to a decrease in water vapor concentration, was observed.

(Measurement Method of X-ray Particle Size) The X-ray particle size in the above-mentioned Examples and Comparative Examples is Fe obtained by an X-ray diffractometer.
_{The full} width at half maximum of the diffraction peak of ₍₁₁₀₎ was calculated from the 2θ value by the following formula. D ₍₁₁₀₎ = Kλ / β cos θ K: Scherrer constant (0.9) λ: wavelength of irradiated X-ray β: half width of diffraction peak (corrected to true value) θ: diffraction angle (tape forming method) In Examples and Comparative Examples, the magnetic metal powder was formed into a tape as follows. Mixed solution of metal magnetic powder 100 g, polyurethane resin 11 g, vinyl chloride-vinyl acetate copolymer 7.75 g, toluene / methyl ethyl ketone / cyclohexanone = 1/1/1
g was mixed and dispersed with a sand grinder for 5 hours to prepare a magnetic paint. Next, 2.5 g of Coronate L as a cross-linking agent was added to this paint, which was then coated on a polyester film and dried at 100 ° C. by applying a magnetic field of 3000 gauss. Then, calendering is performed at 80 ° C and linear pressure of 200 kg / cm, and after aging at 60 ° C for 24 hours, cut and cut into VSM.
The magnetic characteristics were measured with a maximum applied magnetic field of 5 kOe using a magnetometer.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

The metal magnetic powder obtained by the method of the present invention has a higher coercive force than the metal magnetic powder by the conventional method, as is clear from the comparison between the above-mentioned Examples of the present invention and Comparative Examples. The coercive force distribution indicated by the SFD value when formed into a tape is also sharp. Further, when formed into a tape, the X-ray particle size of the metal magnetic powder, which is related to the noise of the tape, is small, and the squareness ratio of the tape exhibiting dispersion and orientation is good, which makes it extremely suitable for making high-density magnetic recording media. A metallic magnetic powder is obtained.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing the particle structure of hematite obtained by the method of Example 1.

2 is an electron micrograph showing the particle structure of hematite obtained by the method of Comparative Example 1. FIG.

FIG. 3 is an electron micrograph showing the particle structure of hematite obtained by the method of Comparative Example 2.

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[Procedure amendment]

[Submission date] December 15, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

Ni = 3.0 Co = 5.0 SiO ₂ = 3.4 Al ₂ O ₃ = 6.0 Example 1 Sample A was set in a stationary heating furnace having a structure in which gas flows, and 100% steam heated to 500 ° C. was flowed. Then, after the temperature in the furnace reached 500 ° C., the temperature was maintained for 3 hours. Next, after cooling this product, it was reduced under a hydrogen stream at 490 ° C. for 3 hours, then cooled to room temperature, and then nitrogen gas was made to flow, and air was gradually introduced into this nitrogen gas flow to stabilize the metal magnetic properties. A powder was obtained. When hematite particles obtained by subjecting sample A of iron oxyhydroxide to heat dehydration treatment were observed with an electron microscope, as shown in FIG. 1, there were few voids in the particles and the particle surface was smooth. The obtained metal magnetic powder was fine particles having an average major axis length of 0.18 μm, and its magnetic characteristics were measured. As a result, Hc = 1695 Oe, σs = 13
2emu / g, squareness ratio (Rs) = 0.505, specific surface area (BE
T) = 58.0 m ² / g, X-ray particle size (Lc) = 149 Å. Further, it was confirmed by observation with an electron microscope that the particles were a metal magnetic powder having few pores and a smooth particle surface. The results showing the relationship between the magnetic properties of the metal magnetic powder with respect to the heat dehydration treatment condition are shown in Table 1, and the magnetic properties when the obtained metal magnetic powder is used as a tape and the SFD value of the tape showing the coercive force distribution are shown. The results are shown in Table 2.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction content]

Comparative Example 1 Sample A was placed in a reaction furnace using the same apparatus as in Example 1.
Nitrogen gas at 600 ° C. was flowed to treat at a target temperature for 3 hours, and then reduction / stabilization treatment was carried out in the same manner as in Example 1 to obtain metal magnetic powder. The treatment temperature was selected such that the metal magnetic powder with the best magnetic properties was obtained when the treatment was carried out in a nitrogen atmosphere. When the hematite particles obtained by subjecting the iron oxyhydroxide of Sample A to heat dehydration were observed with an electron microscope, a large number of voids were confirmed in the particles as compared with the hematite particles of Example 1. An electron micrograph is shown in FIG. The obtained metal magnetic powder was evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

Comparative Example 2 Sample A was placed in a reactor using the same apparatus as in Example 1.
Air was passed at 650 ° C. to treat at a target temperature for 3 hours, and then reduction / stabilization treatment was carried out in the same manner as in Example 1 to obtain a magnetic metal powder. The treatment temperature was selected such that the metal magnetic powder having the best magnetic properties can be obtained when the treatment is performed in an air atmosphere. Observation of the hematite particles obtained by subjecting the iron oxyhydroxide of Sample A to a heat dehydration treatment under an electron microscope revealed that, as with the hematite of FIG. 2 (Comparative Example 1), the hematite particles contained in the particles were larger than those of Example 1. Many vacancies were confirmed. An electron micrograph is shown in FIG. The obtained metal magnetic powder was evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

[0017]

[Table 1]

Claims (2)

[Claims] 1. A method for obtaining a metal magnetic powder by heat dehydration treatment of α-iron oxyhydroxide in a non-reducing atmosphere to hematite, and then heat reduction in a reducing atmosphere.
A method for producing a metal magnetic powder, characterized in that an atmosphere during the heat dehydration treatment is a steam atmosphere of 80 to 100% and a heating temperature is 350 to 700 ° C. 2. The average major axis length of α-iron oxyhydroxide is 0.
05-0.1 μm, Al, Si, B,
2. The method for producing a metal magnetic powder according to claim 1, which contains a compound of one or more elements selected from Co, Ni, Mn, rare earth elements, Ca, Ba, Sr, and Mg.