JPH0711310A - Magnetic metallic powder for magnetic recording and its production - Google Patents

Abstract

PURPOSE:To provide the magnetic metallic powder which has the excellent magnetic characteristics suitable for high-density recording and dispersibility at the time of forming a coating material, is improved in the stability in air, is ameliorated in the deterioration of the magnetic characteristics with lapse of time and is extremely suitable for production of high-output and high-density magnetic recording media. CONSTITUTION:Hydrous iron oxide contg. cobalt within the particles is formed by bringing an iron salt and alkali into reaction in the presence of a cobalt compd. The surfaces of this hydrous iron oxide or the iron oxide obtd. by subjecting this hydrous iron oxide to a heat treatment is then coated with a boron compd. and aluminum compd. and if necessary, further a silicon compd. and/or nickel compd. and is then reduced, by which the magnetic metallic powder for magnetic recording is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic metal powder suitable for a magnetic recording material and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, magnetic recording media have been more and more aimed at improving their recording density to make them smaller and have higher performance. Along with this, as magnetic powder for magnetic recording, attention has been paid to iron or iron-based metal magnetic powder (hereinafter referred to as metal magnetic powder), which has higher saturation magnetization and coercive force than iron oxide-based magnetic powder.
Metal magnetic powders are being put to practical use in digital audio tapes and 8mm video tapes, but are expected to be further applied to high-performance recording media such as high-quality video tapes and high-density discs in recent years. There is. When the magnetic metal powder is, for example, acicular particles, a fine powder having a major axis diameter of about 0.5 μm or less, further 0.3 μm or less is usually required, and when this is used as a magnetic paint. It is required to have more excellent dispersibility, oxidation resistance in the coating film, orientation, and filling property.

[0003]

In order to meet the above-mentioned requirements, it has a high coercive force and a large saturation magnetization, and has a dispersibility when used as a magnetic paint, as well as an oxidation resistance and an orientation property in the coating film. It is necessary to obtain a metal magnetic powder having improved filling properties, gloss and the like. In order to obtain such a magnetic metal powder, it is necessary to appropriately select the type of shape-retaining component, the addition method, and the like.

Various measures have been proposed in order to solve these problems. For example, acicular crystal iron hydroxide particles or acicular crystal hematite particles as starting materials are coated with a cobalt compound in advance and then heated. Method of reduction (JP-A-54-
No. 122264, Japanese Patent Publication No. 58-55203), a method in which starting raw material particles are previously coated with a boron compound and a cobalt compound and then heated and reduced (JP-A-2-197).
No. 503), starting material particles are previously coated with a boron compound, a cobalt compound and an aluminum compound and / or a nickel compound, and then heated and reduced (Japanese Patent Application Laid-Open No. HEI 2).
No. 250902) and starting material particles are previously coated with a boron compound, a cobalt compound, a silicon compound, and further an aluminum compound, and then heated and reduced (JP-A-3-12902). It's hard to say that it's enough.

[0005]

As a result of various studies to solve the above-mentioned problems, the present inventors have found that (1) when a cobalt compound is coated in the vicinity of the particle surface of a metal magnetic powder, magnetic properties and oxidation resistance are improved. Property is improved, but when a large amount of cobalt compound is present in the surface layer of the metallic magnetic powder, the dispersibility in a magnetic coating is deteriorated. (2) Compounds such as boron and aluminum are particles of hydrous iron oxide or iron oxide It was found that when the surface is coated more than necessary, it is likely to segregate or peel off from the surface of the metal magnetic powder particles after the reduction treatment.

Based on these findings, as a result of further investigation, a cobalt compound was added during the production reaction process of the iron oxide hydroxide as a starting material to produce iron oxide hydroxide containing cobalt inside the particles. By depositing a boron compound and an aluminum compound, and optionally a silicon compound and / or a nickel compound on the surface of the particles,
Since cobalt is contained inside the particles of the magnetic metal powder, the deterioration of dispersibility can be reduced, and the deposition amount of boron compounds, aluminum compounds, etc. can be reduced. Particle separation or segregation is reduced Fine and has a good particle size distribution, iron oxide hydroxide having a large axial ratio is produced, and the particle surface of iron oxide hydroxide or iron oxide is a boron compound formed during heat treatment. And a glass-like fused film made of aluminum compound, etc.
When a nickel compound is contained on the particle surface of hydrous iron oxide particles or iron oxide particles, during the reduction reaction, the catalytic action of the nickel component allows the reduction reaction to proceed efficiently, and at the same time forms a boron compound, an aluminum compound, etc. Due to the synergistic effect, the reduction reaction can proceed in a state where the shape is not collapsed, and thus the acicularity is good, and the magnetic properties, especially coercive force, squareness ratio, orientation ratio, saturation magnetic flux density (filling property) It has been found that a magnetic metal powder having excellent reversal magnetic field distribution, excellent gloss value and oxidation resistance of the tape, and high output characteristics suitable for high density recording can be obtained.

That is, the present invention provides an iron salt in the presence of cobalt inside the particles, metal magnetic powder for magnetic recording containing boron and aluminum on the surface of particles, and optionally silicon and / or nickel, and a cobalt compound. And an alkali are reacted to produce iron oxide hydroxide containing cobalt inside the particle, and then the iron oxide hydroxide or iron oxide particle surface containing cobalt obtained by heat treatment of the iron oxide hydroxide inside the particle In addition, a boron compound and an aluminum compound, and if necessary, a silicon compound and / or a nickel compound are further deposited, and then reduced.

In the above embodiment of the present invention, (1) iron hydroxide particles containing cobalt inside the particles or iron oxide particles containing cobalt obtained by heat-treating the iron oxide particles on the surface of particles. A method for producing a metal magnetic powder for magnetic recording, wherein the final deposition treatment is a boron compound,
(2) A method for producing a magnetic metal powder for magnetic recording, which comprises heat-treating adhered iron oxide hydroxide or iron oxide particles at 500 to 900 ° C. in a non-reducing atmosphere before reduction, and (3) iron oxide hydroxide. A method for producing a magnetic metal powder for magnetic recording, wherein (4) a method for producing a magnetic metal powder for magnetic recording, in which a cobalt compound is added during the reaction of producing goethite nuclei.
(5) A method for producing a metal magnetic powder for magnetic recording, in which the iron oxide hydroxide containing cobalt inside the particles has a specific surface area of 55 m ² / g or more can be mentioned.

Cobalt, boron, aluminum, silicon and nickel in the magnetic metal powder for magnetic recording are
Presumed to exist in the state of metal or oxide.

In the method of the present invention, first, an iron salt is reacted with an alkali in the presence of a cobalt compound to obtain iron oxide hydroxide containing cobalt inside the particles. By appropriately selecting the iron salt, alkali, reaction conditions, etc., α-FeOO
Although hydrous iron oxide such as H 2, β-FeOOH and γ-FeOOH can be obtained, it is desirable to produce α-FeOOH (goethite) in the present invention. As the iron salt, for example, ferrous sulfate, ferric sulfate, ferrous chloride, ferric chloride, etc. can be used. When using a ferrous salt, it is necessary to neutralize with an alkali and then perform an oxidation reaction. There is. As the alkali, for example, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, aqueous ammonia, ammonia gas or the like can be used.

The cobalt compound may be present by adding the cobalt compound to either the iron salt or alkali before the neutralization reaction to neutralize it, or adding it to a neutralized suspension of the iron salt and alkali. There is a method of adding the cobalt compound to the aqueous solution of the ferrous salt, followed by partial neutralization and oxidation to form a nuclear crystal of hydrous iron oxide. Then, the aqueous solution of the nuclear crystals is neutralized with an alkali and oxidized to grow the nuclear crystals to obtain hydrous iron oxide. This growth reaction has a pH of 2 to 2 on the acidic side.
5. On the alkaline side, the pH is preferably in the range of 10-14. If the pH is in the range of more than 5 and less than 10, the formation of granular magnetite is feared, and if the pH is less than 2, the growth reaction takes a long time. In this reaction,
Obtaining iron oxide hydroxide containing cobalt having a specific surface area of 55 m ² / g or more inside the particles is desirable from the viewpoint of refining the object.

As the cobalt compound, various cobalt salts such as cobalt sulfate, cobalt chloride, cobalt acetate and cobalt carbonate, or colloidal cobalt compounds such as cobalt hydroxide and cobalt oxide can be used. Cobalt sulfate and cobalt chloride are particularly preferable. The content of cobalt by the cobalt compound is 0.1 to 10% by weight as Co / Fe with respect to the iron in the hydrous iron oxide produced,
It is preferably 0.3 to 3% by weight. This content is 0.
When it is less than 1% by weight, desired effects such as magnetic properties such as coercive force and saturation magnetization and oxidation resistance cannot be obtained.
On the other hand, if the content is more than 10% by weight, the crystal growth of the hydrous iron oxide is suppressed, the particle size distribution width of the particles is widened, and the axial ratio is lowered. You won't get it.

Next, in the method of the present invention, iron oxide hydroxide containing cobalt obtained as described above inside the particles or iron oxide containing cobalt obtained by heat treatment of the iron oxide hydroxide inside the particles. A boron compound and an aluminum compound, and if necessary, a silicon compound and / or a nickel compound are adhered to the surface of the particles.

The iron oxide containing cobalt inside the particles, which is obtained by heat-treating the iron oxide hydroxide containing cobalt inside the particles, is α-Fe ₂ O ₃ obtained by heating and dehydrating the iron oxide hydroxide. Or γ-Fe ₂ O ₃ or α-Fe ₂ 0 ₃ or γ-Fe ₂ O ₃ obtained by heating and dehydrating the iron oxide hydroxide is further subjected to heat reduction treatment and / or heat oxidation treatment. Fe ₃ O ₄ ,
Iron oxides such as γ-Fe ₂ O ₃ and beltride compounds can be mentioned.

As a method of depositing the boron compound, for example, a method of adding the boron compound to an aqueous suspension of hydrous iron oxide containing cobalt inside the particles and depositing the boron compound in a pH range of 6 to 9 is used. , A method of depositing an organic boron compound on an aqueous suspension of hydrous iron oxide containing cobalt inside particles, adding fine powder of a boron compound to an aqueous suspension of hydrous iron oxide containing cobalt inside particles. A method for depositing, a hydrous iron oxide or iron oxide containing cobalt inside the particles, and an aluminum compound, and optionally a silicon compound and / or a nickel compound, if necessary, to suspend the hydrous iron oxide or iron oxide. Separate the liquid,
A boron compound is added to a wet cake of the iron oxide hydroxide or iron oxide obtained by washing, a repulp slurry or a dried product thereof, and a boron compound is adhered to the surface of the iron oxide hydroxide or iron oxide particles. There are various methods such as Industrially, it is desirable that the boron compound is deposited by the above-mentioned various metal compounds on iron oxide hydroxide or iron oxide containing cobalt inside the particles, and finally by the deposition treatment.

Examples of the boron compound to be deposited include boric acid, boric oxide, borax, sodium borate, aluminum borate, nickel borate, borate salts such as ammonium borate, borate esters, boron alkoxides and the like. Although it can be appropriately selected, boric acid is industrially suitable.

The addition amount of the boron compound is B / Fe
0.1 to 5% by weight, preferably 0.3 to 2% by weight
If this amount is too small, the desired effects of suppressing sintering and oxidation resistance cannot be obtained. Further, when the amount is too large, the saturation magnetization of the metal magnetic powder produced is lowered, and problems such as elution of the boron component when the magnetic tape is formed are not preferable.

As a method of depositing the aluminum compound, for example, the aluminum compound is added to an aqueous suspension of hydrous iron oxide containing cobalt inside the particles, and an alkali or acid is added to adjust the pH to a range of 6-9. Method of neutralizing and depositing aluminum hydrated oxide, adding aluminum organic compound to an aqueous suspension of hydrous iron oxide containing cobalt inside particles, and hydrolyzing to add aluminum hydrated oxide There are various methods, such as a method of depositing the above, a method of adding fine powder of an aluminum compound to an aqueous suspension of iron oxide hydroxide containing cobalt inside the particles, and depositing. Industrially, a method of adding an aqueous solution of an aluminum compound to an aqueous suspension and performing a neutralization treatment is advantageous. In this case, if the neutralization pH is higher than 9, the precipitation rate of the hydrated oxide of aluminum will be lowered and the yield will be poor, and the inclusion of an alkaline component such as sodium will facilitate sintering in the heating in the next step. However, it is not preferable because the effect of the aluminum deposition treatment is impaired.

The aluminum compound to be deposited is
Aluminum hydrates, hydroxides, oxides or phosphates, aluminum nitrates, aluminum sulfates, aluminum basic salts such as aluminum chloride and aluminum basic salts such as sodium aluminate, aluminum alkoxides, alkyl aluminum compounds, It can be appropriately selected from colloidal aluminum compounds and ultrafine powders of alumina oxide, but among these, hydrated oxides of aluminum are preferable.

The deposition amount of the aluminum compound is 0.1 as Al / Fe with respect to iron in hydrous iron oxide or iron oxide.
-8% by weight, preferably 0.3-5% by weight, and if the amount of deposition is less than 0.1% by weight, desired effects such as suppression of sintering cannot be obtained. Further, if the deposition amount is more than 8% by weight, it takes a long time for the reduction, the aluminum compound is easily segregated or peeled from the particle surface after the reduction treatment, and the saturation magnetization of the obtained metal magnetic powder is lowered, which is desirable. Absent.

As a method of depositing the silicon compound, for example, the silicon compound is added to an aqueous suspension of hydrous iron oxide containing cobalt inside the particles, and the pH is neutralized to a range of 6 to 9 to obtain silicon. Method of depositing compound, method of adding organosilicon compound to aqueous suspension of iron oxide hydroxide containing cobalt inside the particle, method of depositing, aqueous suspension of iron oxide hydroxide containing cobalt inside the particle There are various methods such as a method of adding fine powder of a silicon compound to and depositing.

Examples of the silicon compound to be deposited include silicon dioxide, hydrous silicon dioxide, condensates thereof, sodium orthosilicate, sodium metasilicate, potassium metasilicate, calcium metasilicate, magnesium silicate, and the like, or a silicate thereof. It is appropriately selected from condensates, aqueous silicate solutions such as water glass, silicone oils, silicone resins, chlorosilanes, silanes such as alkoxytenes, siloxanes and the like, and among these, silicates are preferred.

The deposition amount of the silicon compound is 0.1 to 8% by weight, preferably 0.3 to 5% by weight, as Si / Fe, with respect to the iron in the hydrous iron oxide or iron oxide. Is less than 0.1% by weight, desired effects such as suppression of sintering cannot be obtained. On the other hand, if the coating amount is more than 8% by weight, the silicon compound is likely to segregate or peel off from the particle surface after the reduction treatment, and the magnetic properties such as saturation magnetization and coercive force of the obtained metal magnetic powder are deteriorated. Not preferable.

In the present invention, in order to make it industrially more preferable, nickel or copper,
It is desirable to deposit a compound such as silver or calcium on the surface of the iron oxide hydroxide or iron oxide particles. Among the above compounds, the nickel compound is desirable because the produced metal magnetic powder has a good particle shape and magnetic properties are hardly deteriorated. Further, in the present invention in which a nickel compound is used together with a boron compound, an aluminum compound, etc., due to these synergistic effects, acicular metal magnetic powder having a regular particle shape can be obtained, and the acid resistance of the obtained metal magnetic powder can be improved. The chemical conversion is also improved.

As a method of depositing the nickel compound,
For example, a method of adding a nickel compound to an aqueous suspension of iron oxide hydroxide containing cobalt inside the particles, neutralizing the pH to a range of 6 to 9 and depositing the nickel compound, and containing cobalt inside the particles A method of adding an organic nickel compound to an aqueous suspension of hydrous iron oxide and depositing it, adding a fine powder of a nickel compound to an aqueous suspension of hydrous iron oxide containing cobalt inside the particles, and depositing There are ways.

The nickel compound to be deposited can be appropriately selected from nickel salts such as nickel sulfate, nickel chloride and nickel acetate, nickel acetylacetonate, nickel naphthenate and the like. preferable.

The amount of the nickel compound deposited is 0.1 to 8 as Ni / Fe relative to iron in the hydrous iron oxide or iron oxide.
%, Preferably 0.3 to 5% by weight, and if the amount of deposition is less than 0.1% by weight, the desired effects such as reduction promotion cannot be obtained. On the other hand, if the coating amount is more than 8% by weight, the magnetic properties such as the saturation magnetization, the coercive force and the reversal magnetic field distribution of the obtained metal magnetic powder are deteriorated, which is not preferable.

In the present invention, a suitable dispersant is added to an iron oxide hydroxide containing cobalt on the particle surface or an aqueous iron oxide suspension containing cobalt obtained by heat-treating the iron oxide hydroxide on the particle surface. , For example, adding phosphate, polyphosphate, polyacrylate, carboxylate, etc.,
It is possible to improve the dispersibility of the iron oxide hydroxide or iron oxide, and then carry out a deposition treatment of an aluminum compound and, if necessary, a silicon compound and / or a nickel compound.

The order of depositing the boron compound, the aluminum compound, the silicon compound and the nickel compound is not particularly limited, but in order to obtain the target product having more excellent magnetic properties, the iron oxide hydroxide containing cobalt inside the particles is used. Alternatively, it is desirable that the iron oxide containing cobalt inside the particles obtained by heating the iron oxide hydroxide is heat-treated with an aluminum compound, a silicon compound and a nickel compound, and finally with a boron compound.

In order to make the method of the present invention industrially more preferable, P, Cr, Mn, Cd, P are further added.
Compounds such as d, Ca, Mg, Sr, Zn, Sn, W and Zr may be appropriately used in combination for the deposition treatment. The above-mentioned adhesion treatment and the adhesion treatment in the present invention include a treatment of simply adhering to the particle surface and a case of uniformly coating the particle surface, but in the present invention, the particle surface is uniformly coated. Is preferable.

As described above, iron oxide hydroxide containing cobalt inside the particles is produced, and then the iron oxide hydroxide or the iron oxide containing iron oxide containing cobalt obtained by heat treatment of the iron oxide hydroxide is added. On the surface of the particles, a boron compound and an aluminum compound, and if necessary, a silicon compound and / or a nickel compound is applied to the surface of the particles,
Then, the metal magnetic powder of the present invention is manufactured by reduction.

Before the reduction, if necessary, the iron oxide hydroxide or iron oxide particles that have been subjected to the deposition treatment are subjected to a non-reducing atmosphere such as air or nitrogen gas at 500 to 900 ° C., preferably 600 to 800. You may heat-process at ℃. By this heat treatment, the entire particles are burned and become dense, and it is possible to further suppress the sintering at the time of reduction and the collapse of the particle shape. If the heat treatment temperature is too high, acicularity is deteriorated or coarsened due to intra-particle and inter-particle sintering at the iron oxide stage, which is not preferable. On the other hand, if the heat treatment temperature is too low, many pores remain in the particles and the particles themselves are not dense crystals, so that the shape deterioration in the subsequent reduction step is large and the desired effect cannot be obtained.

For the reduction to the metallic magnetic powder, various known methods can be adopted. Usually, hydrogen is used as a reducing gas, for example, and hydrogenated iron oxide or iron oxide can be substantially all reduced to a metal by treating at 350 to 600 ° C.

The metal magnetic powder of the present invention obtained by reduction ignites when exposed to the atmosphere and rapidly changes into iron oxide, and therefore, when taken out into the atmosphere, it is stabilized by various known methods. . For example, a method of slowly evaporating and stabilizing toluene after immersion in an organic solvent such as toluene, a method of passing an oxygen-containing gas through a liquid phase or a gas phase of toluene such as stabilization, and further oxidation by various compounds. There is a method of using the suppression film forming treatment and the above method in combination.

The thus obtained metal magnetic powder for magnetic recording of the present invention has magnetic properties such as coercive force, squareness ratio, orientation, saturation magnetic flux density (filling property) and reversal magnetic field distribution, and oxidation resistance. Is good, and when used in a magnetic tape, high output characteristics are obtained, and an excellent magnetic medium having a high recording density is obtained.

[0036]

【Example】

Example 1 (1) Formation reaction of goethite nuclei crystals 1.50 mol in a reaction vessel equipped with an air blowing tube and a stirrer.
20 liters of ferrous sulfate aqueous solution / l and 10 as Co
Add 2250 ml of g / l cobalt sulfate aqueous solution,
The temperature was raised to 0 ° C., and while maintaining this temperature, 1075 ml of a 10 mol / l sodium hydroxide aqueous solution was added with stirring,
Air is blown into this at a rate of 10 liters / minute for 100
The reaction was carried out for about 200 minutes to obtain a goethite nucleus crystal.

(2) Growth reaction of nuclei crystal In order to grow to a desired particle size, 1615 ml of 10N aqueous sodium hydroxide solution was added at a rate of 8 ml / min while maintaining the above-mentioned nuclei crystal slurry at 50 to 55 ° C. Then, air was introduced at a rate of 5 l / min for neutralization and oxidation reaction. The growth rate is 2.5 times the weight ratio to the nuclei. The goethite containing cobalt inside the particles obtained by this growth reaction was filtered and washed. The specific surface area (BET method) of this product was 76 m ² / g.

(3) Adhesion treatment of aluminum compound 120 g of goethite obtained as described above was treated with 15 parts of water.
The suspension was suspended in 00 ml and the liquid temperature was kept at 30 ° C. and the pH was kept at 5. To this slurry, 250 ml of 15 g / l aluminum sulfate aqueous solution as Al was added for 30 minutes, aged for 30 minutes, and then 4N ammonia water was added to adjust the slurry pH to 7.5 in about 2 hours. Then hold for 1 hour and filter,
It was washed with water and dried.

(4) Deposition Treatment of Boron Compound Next, 100 g of the dried product was placed in a mortar, 5.7 g of boric acid powder was added, and the mixture was crushed and mixed for 10 minutes.

(5) Reduction to Metallic Magnetic Powder After that, 100 g of the adhered material of the boron compound was heat-treated in a muffle furnace at 740 ° C. for 2 hours in the atmosphere to obtain α-Fe ₂ O ₃ . Then, 50 g of α-Fe ₂ O ₃ was added to a vertical fixed bed stainless steel reduction reactor (inner diameter: 43 mmφ, height: 500 m).
m) and under a hydrogen stream with a linear velocity of about 10 cm / sec, 42
Reduction was performed at 5 ° C until the dew point of the exhaust gas reached -20 ° C.
The time required for the reduction was 185 minutes. The obtained reduced product was cooled in a nitrogen stream, immersed in toluene, and then toluene was gradually evaporated at room temperature to obtain a metal magnetic powder (Sample A) of the present invention.

Example 2 In the same manner as in Example 1, except that the (3) aluminum compound deposition treatment was replaced with the following (3) aluminum compound and silicon compound deposition treatment. After processing, a metal magnetic powder of the present invention (Sample B) was obtained.

(3) Deposition treatment of aluminum compound and silicon compound Deposition treatment of silicon compound 120 g of goethite thus obtained was treated with 15 parts of water.
The mixture was suspended in 00 ml, and the liquid temperature was kept at 30 ° C. and pH was maintained at 9 with ammonia water. 15 g / l as Si in this slurry
100 ml of the sodium silicate aqueous solution was added in 30 minutes and aged for 30 minutes, then a 3N sulfuric acid aqueous solution was added and the slurry pH was adjusted to 7.0 in about 1 hour.

150 ml of 15 g / l aqueous solution of aluminum sulfate as Al was added to the slurry for the aluminum compound deposition treatment in 30 minutes, aged for 30 minutes, and 4N ammonia water was added to the slurry for about 1 hour to adjust the slurry pH to 7. It was set to 5.

Example 3 In Example 1, after the aluminum compound deposition treatment, 30 g of nickel sulfate aqueous solution of 10 g / l was added as Ni.
Minutes, and after aging for 30 minutes, 1N Ammore water was added to adjust the slurry pH to 7.5. Then, the pH is maintained at 7.5 while stirring for 1 hour, and then treated in the same manner as in the case of the same example except that filtration, washing with water and drying are performed,
A metal magnetic powder (Sample C) of the present invention was obtained.

Example 4 In Example 2, after the aluminum compound deposition treatment, 30 g of a 10 g / l nickel sulfate aqueous solution was added as Ni.
Minutes, and after aging for 30 minutes, 1N Ammore water was added to adjust the slurry pH to 7.5. Then, the pH is maintained at 7.5 while stirring for 1 hour, and then treated in the same manner as in the case of the same example except that filtration, washing with water and drying are performed,
A metal magnetic powder (Sample D) of the present invention was obtained.

Example 5 Goethite (120 g) prepared in Example 1 by adding an aqueous cobalt sulfate solution during the reaction for producing goethite nuclei.
On the other hand, 75 ml of a 10 g / l boric acid aqueous solution as B was used instead of the deposition treatment of (3) and (4) of Example 1 above.
Was added, and then 150 ml of a 15 g / l sodium silicate aqueous solution was added as Si, and further 15 g was added as Al.
250 ml of 1 / l aluminum sulfate aqueous solution is added,
A metal magnetic powder (Sample E) of the present invention was obtained by the same treatment as in the same example except that the boron compound, aluminum compound and silicon compound were applied.

Comparative Example 1 Metal magnetic powder containing no cobalt was treated in the same manner as in Example 1 except that the goethite was prepared without adding the aqueous solution of cobalt sulfate in the reaction for producing goethite nuclei. (Sample F) was obtained.

Comparative Example 2 Metal magnetic powder containing no cobalt was treated in the same manner as in Example 2 except that the goethite was prepared without adding the aqueous solution of cobalt sulfate in the reaction for producing goethite nuclei in Example 2. (Sample G) was obtained.

Comparative Example 3 Goethite 120 prepared in Example 1 without adding the aqueous solution of cobalt sulfate during the reaction for producing goethite nucleus crystals.
For g, instead of the deposition treatment of (3) of Example 1, 15 g / l aluminum sulfate aqueous solution 2 as Al was used.
After adding 50 ml to form a film of an aluminum compound, 10 g / l of cobalt sulfate aqueous solution as Co 7
A metal magnetic powder (Sample H) was obtained by the same treatment as in the same example except that 5 ml was added for 30 minutes and the mixture was aged for 30 minutes.

Comparative Example 4 Goethite 120 prepared in Example 1 without adding the aqueous cobalt sulfate solution during the reaction for producing goethite nuclei.
For g, instead of the deposition treatment of (3) of Example 2, an aqueous solution of sodium silicate of 15 g / l as Si 1
00 ml was added, and then 100 ml of 15 g / l aluminum sulfate aqueous solution was added as Al to form a film of an aluminum compound, and then Co was added at 10 g / l.
75 ml of aqueous solution of cobalt sulfate in
A magnetic metal powder (Sample I) was obtained by the same treatment as in the same example except that the aging was performed for 0 minutes.

Comparative Example 5 Goethite 120 prepared in Example 1 without adding the aqueous cobalt sulfate solution during the reaction for producing goethite nuclei.
Instead of the deposition treatment of (3) and (4) in Example 1, 250 g of aluminum sulfate aqueous solution of 15 g / l as Al was added to g, and further 10 g of boron was added.
After adding 75 ml of an aqueous solution of boric acid of 1 / l to form a coating film of an aluminum compound and a boron compound, 225 ml of an aqueous solution of cobalt sulfate of 10 g / l as Co was added to 30 ml.
A magnetic metal powder (Sample J) was obtained by the same treatment as in the same example except that the addition was carried out for 30 minutes and the mixture was aged for 30 minutes.

Comparative Example 6 Goethite 120 prepared in Example 1 without adding the aqueous cobalt sulfate solution during the reaction for producing goethite nuclei.
Instead of the deposition treatment of (3) and (4) of Example 2, 150 g of a 15 g / l sodium silicate aqueous solution of Si was added to g, and then 15 g / l of Al was added.
1 of aluminum sulfate aqueous solution (250 ml) was further added, and further, 10 g / l of boric acid aqueous solution (75 ml) was added as boron to form a film of an aluminum compound, a silicon compound and a boron compound, and then Co was added at 10 g / l.
225 ml of cobalt sulfate aqueous solution of
A magnetic metal powder (Sample K) was obtained by the same treatment as in the case of the same example except that it was aged for 30 minutes.

With respect to the metal magnetic powder sample thus obtained, the powder magnetic characteristics were measured by a conventional method. Also,
In order to evaluate the oxidative stability, the sample powder was allowed to stand for 1 week in an environment of a temperature of 60 ° C. and a relative humidity of 80%, the accelerated aging change of σs was measured, and the deterioration rate Δσs (%) of the saturation magnetization was measured as follows. It was calculated by the formula.

[0054] (Where σs₀Is σs before aging, and σs₁Is σ after aging
s)

Further, a magnetic coating material having the following composition was prepared by using the above-mentioned sample powder, which was then coated so that the dry film thickness was 10 μm, and after the orientation treatment, the magnetic tape was prepared by drying by a conventional method. The properties were measured. Metal magnetic powder 5 parts by weight Dispersant 0.25 〃 Polyurethane resin 2.96 〃 Mixed solvent 13.4 〃 (Toluene / MEK / Cyclohexanone (4.5 / 4.
5/1))

These magnetic characteristics, that is, the coercive force (H
c: Oe), saturation magnetization (σs: emu / g), saturation magnetic flux density (Bm: Gauss), squareness ratio (Rs, SQ), orientation ratio (OR) and switching field distribution (SFD), and further The 60 ° -60 ° gloss was measured with a gloss meter. The results are shown in Tables 1 and 2.

[0057]

[Table 1]

[0058]

[Table 2]

[0059]

Industrial Applicability The magnetic metal powder obtained by the present invention has excellent magnetic properties suitable for high-density recording and excellent dispersibility at the time of coating, and also has improved stability in air. Therefore, the deterioration of the magnetic characteristics with time is improved, and it is extremely suitable for manufacturing a high-output, high-recording-density magnetic medium. Further, the present invention is capable of economically and advantageously producing the above-mentioned magnetic powder having excellent performance by a relatively simple means, and is of great industrial significance.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location H01F 1/06 (72) Inventor Haruki Ichinose 1 Ishihara-cho, Yokkaichi-shi, Mie Ishihara Industrial Co., Ltd. Yokkaichi In the office

Claims (9)

[Claims] 1. A magnetic metal powder for magnetic recording, which contains cobalt inside the particles and also contains boron and aluminum on the surface of the particles. 2. The magnetic metal powder for magnetic recording according to claim 1, further comprising silicon and / or nickel on the surface of the particles. 3. An iron hydroxide is obtained by reacting an iron salt with an alkali in the presence of a cobalt compound to produce iron oxide hydroxide containing cobalt inside the particles, and then heat-treating the iron oxide hydroxide or iron oxide hydroxide. The method for producing a metal magnetic powder for magnetic recording, comprising: applying a boron compound and an aluminum compound to the surface of an iron oxide particle containing the obtained cobalt inside the particle, and then reducing the particle. 4. The method for producing a magnetic metal powder for magnetic recording according to claim 3, wherein a boron compound, an aluminum compound, a silicon compound and / or a nickel compound is deposited on the surface of the particles and then reduced. 5. The method for producing a metal magnetic powder for magnetic recording according to claim 3, wherein a material to be finally deposited on the surface of the particles is a boron compound. 6. The metal magnetic powder for magnetic recording according to claim 3, wherein the iron oxide hydroxide or iron oxide particles after the deposition treatment are heat-treated at 500 to 900 ° C. in a non-reducing atmosphere before reduction. Manufacturing method. 7. The hydrous iron oxide is goethite.
7. A method for producing the magnetic metal powder for magnetic recording according to any one of 6 to 6. 8. The method for producing a magnetic metal powder for magnetic recording according to claim 3, wherein a cobalt compound is added during the reaction of producing goethite nuclei. 9. The method for producing a metal magnetic powder for magnetic recording according to claim 3, wherein the hydrous iron oxide containing cobalt inside the particles has a specific surface area of 55 m ² / g or more.