JPH06330111A - Production of magnetic metal powder - Google Patents

Abstract

PURPOSE:To provide an industrially advantageous production of a magnetic metal powder which is very appropriately used for the magnetic recording medium. CONSTITUTION:The magnetic metal powder is produced by coating the surface of a needle-like particle of hydrous iron oxide with at least one compound selected from aluminum compounds and zirconium compounds, then heat-treating the coated particle to convert it into hematite, thereafter coating the surface of the resulting hematite particle with an aluminum compound and then heating and reducing the particle.

Description

Detailed Description of the Invention

[0001]

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

[0002]

TECHNICAL BACKGROUND OF THE INVENTION AND PROBLEMS OF THE INVENTION In recent years, magnetic recording media have been more and more aimed at improving their recording density and improving their performance. Along with that, iron or iron-based metal magnetic powders (hereinafter referred to as metal magnetic powders) having higher saturation magnetization and coercive force than needle-shaped magnetite and maghemite as magnetic powders for magnetic recording, and further cobalt-modified magnetic iron oxides thereof. Is in the limelight. Metal magnetic powder is used in digital audio tape, 8mm video tape, etc.
Furthermore, high-definition video tape for high-definition, etc.
There are further expectations for application to high-performance magnetic recording media such as high-density discs.

In recent years, fine magnetic particles having a uniform major axis of 0.3 μm or even 0.2 μm or less and having a uniform particle size without sintering are demanded as metal magnetic powders for high performance magnetic recording media. In addition, it is desired that this material has further excellent dispersibility in a magnetic paint system, orientation in a coating film of the magnetic layer, filling property, smoothness, and the like. In particular, in order to increase the output of the recording medium together with the reduction of particulate noise,
Further, ultrafine particles are desired, and metallic magnetic powders which have small acicular particles and excellent magnetic characteristics and stability over time are becoming more important.

By the way, the metallic magnetic powder is usually obtained by heating and dehydrating acicular hydrous iron oxide such as geethite to obtain iron oxide particles such as hematite, which are heated in a reducing gas atmosphere such as hydrogen. A method of reducing the metal magnetic powder is used. However, in the heat dehydration step, especially in the reduction step, particle sintering and particle shape collapse easily occur, and due to this particle shape collapse and α-Fe crystal particle coarsening,
The magnetic properties of the desired metallic magnetic powder are significantly impaired. And the effect is that the finer the particles of hydrous iron oxide as the starting material, the easier the particle shape collapses to the production of fine metal magnetic powder, and the target of magnetic characteristics and stability over time. It will be difficult to reach the level.

Conventionally, various methods have been proposed to solve the above problems. For example, a method is well known in which the surface of particles of hydrous iron oxide or iron oxide is treated with a so-called shape-retaining agent such as a silicon compound, a boron compound, an aluminum compound, or a zirconium compound, and then dehydrated by heating and then reduced. However, in the above process, for example,
For silicon compounds, boron compounds and phosphorus compounds,
The desired effect for preventing sintering and shape collapse is brought about,
Although it is easy to obtain metal magnetic powder with good magnetic properties, the progress of reduction is likely to be hindered, the dispersibility during the manufacture of magnetic recording media is likely to be impaired, and as a result, the magnetic properties and electromagnetic conversion properties of magnetic recording media deteriorate. Can be seen. Further, in the case of the aluminum compound, it is well compatible with the coating resin and the solvent used at the time of manufacturing the magnetic recording medium, and while having a desirable effect on the dispersibility, it is easily incorporated into the particle matrix during the heat dehydration treatment step, As a result, in the heating reduction treatment process,
It may cause a reduction-suppressing effect, or may be difficult to exert the effect of preventing sintering and maintaining shape. On the other hand, in the case of a zirconium compound, although the above-mentioned effects of preventing sintering and preventing shape collapse can be brought to some extent, in order to optimize it, the deposition amount must be considerably increased, and as a result, the heat reduction treatment step The progress of the reaction in (1) is likely to be hindered, and the magnetic properties such as the saturation magnetization of the obtained metal magnetic powder are likely to be impaired. In any case, there are still few problems to be solved.

The present inventors have conducted various studies on the optimization of the above treatment conditions in order to solve the above problems in the production of metallic magnetic powder, and as a result, as a result, the hydrous iron oxide, which is a substance to be dehydrated by heating, and The presence of a specific shape-retaining agent on the surface of each particle of hematite, which is a heat-reduced product, and the precise control of the amount of each shape-retaining agent and the state of each, make it possible to satisfy both magnetic properties and dispersibility. The present invention has been completed based on the finding that it is extremely important for obtaining powder. That is, the present invention is

(1) The surface of iron hydrated iron oxide particles is first coated with at least one compound selected from aluminum compounds and zirconium compounds, and then heat treated to form hematite. After the second deposition treatment of the aluminum compound on the particle surface, by heat reduction treatment, a method of producing acicular magnetic iron powder,

(2) The method for producing an acicular magnetic iron powder as described in (1) above, wherein the first deposition treatment further includes at least one compound selected from silicon compounds, phosphorus compounds and boron compounds.

(3) When the first deposition treatment is performed with a zirconium compound, a silicon compound is further added to the second deposition treatment.
The method for producing needle-shaped magnetic iron powder according to (1) above, which comprises at least one of a phosphorus compound, a zirconium compound and a boron compound,

(4) When the first deposition treatment is performed only with the zirconium compound, the second deposition treatment further includes at least one of a silicon compound, a phosphorus compound, a zirconium compound and a boron compound. ) The method for producing needle-shaped magnetic iron powder according to

(5) The amount of aluminum (Al) and zirconium (Zr) deposited in the first deposition treatment is in the range of 0.1 to 10% by weight with respect to iron (Fe) of the iron oxide hydroxide particles. There is a method for producing the acicular magnetic iron powder according to (1) above,

(6) In the above (1), the deposition amount of aluminum (Al) in the second deposition treatment is in the range of 0.1 to 10 wt% with respect to the iron (Fe) of the hematite particles. A method for producing needle-shaped magnetic iron powder according to,

(7) In the above (1), the deposition amount of aluminum (Al) in the second deposition treatment is in the range of 0.1 to 8 wt% with respect to the iron (Fe) of the hematite particles. A method for producing needle-shaped magnetic iron powder according to,

(8) The amount of aluminum (Al) deposited on the iron (Fe) of the hematite particles in the second deposition treatment is the amount of all metal elements deposited on the iron oxide hydroxide (iron of the iron oxide hydroxide particles ( (For Fe)) and the total amount of all metallic elements deposited on hematite (for iron (Fe) of hematite particles) in the range of 5 to 95% by weight, the above (1) A method for producing needle-shaped magnetic iron powder according to

(9) The method for producing needle-shaped magnetic iron powder as described in (1) above, wherein the iron oxide hydroxide having been subjected to the first deposition treatment is heat-treated at 350 to 800 ° C. in a non-reducing atmosphere. as well as

(10) The hematite that has been subjected to the adhesion treatment before the heat reduction treatment is heat treated at 300 to 850 ° C.
The method for producing an acicular magnetic iron powder according to (1) above.

A typical iron oxide hydroxide used in the present invention is a metal iron oxide hydroxide mainly composed of iron, such as α-FeOOH (gaesite) and γ-FeOOH.
(Lepidocrocite), β-FeOOH and the like. The acicular oxyhydroxide has a major axis of 0.1 to 0.
It is preferably 6 μm, the axial ratio is 3 to 30, and the specific surface area is preferably 50 to 150 m ² / g. These iron oxide hydroxides are various shape modifier components and reduction accelerator components, etc., if necessary, such as cobalt, nickel, copper,
It may contain compounds such as silver, phosphorus, zinc, manganese, magnesium, boron, aluminum and silicon.

In the present invention, various well-known methods are applied to the deposition treatment of at least one compound selected from the group consisting of aluminum compounds and zirconium compounds on the surface of the particles of hydrous iron oxide as the base particles. You can
For example, in an aqueous suspension of hydrous iron oxide, aluminum sulfate, aluminum chloride, aluminum acetate, sodium aluminate, aluminum alkoxide, alkylaluminum compound, zirconium oxycarbonate, ammonium zirconium carbonate, zirconium oxychloride, zirconium oxysulfate, zirconium acetate. , A solution of zirconium stearate, zirconium tetra-n-butoxide, zirconium acetylacetate, etc. is added, and an oxide such as aluminum or zirconium or a hydrous oxide is added to the surface of the hydrous iron oxide particles by neutralization or hydrolysis. It can also be carried out by precipitation, or by adding alumina sol or the like and mixing and adhering. In the deposition treatment, an aluminum compound,
The amount of the zirconium compound deposited is 0.1 to 10% by weight, preferably 0.5 to 8% by weight, as Al / Fe, with respect to iron in the hydrous iron oxide as the base particles.
As 0.05 to 10% by weight, preferably 0.1 to 5
% By weight. If the deposition amount is less than the above range, the desired effect cannot be obtained, and if the deposition amount is more than the above range, it takes a long time to reduce to the target substance, or the saturation magnetization of the target substance. Or, as described above, these compounds taken into the particle matrix during the heat dehydration treatment step are separated during the reduction treatment step and the resulting densification of the magnetic metal powder particles is likely to be impaired. In some cases, deterioration of magnetic properties is unavoidable.

In order to further improve the shape retention during heat treatment, a silicon compound, a phosphorus compound or a boron compound may be used in combination during the adhesion treatment on the iron oxide hydroxide. The treatment amount of each compound in this case is 0.05 to 10 as M / Fe, where M is the total weight of Al, Zr, Si, P, and B with respect to iron in the hydrous iron oxide as the base particles. %, Preferably 0.1 to 5% by weight.

As the silicon compound, for example, sodium orthosilicate, sodium metasilicate, water glass or the like can be used. As the phosphorus compound, for example, phosphoric acids such as orthophosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, and hexametaphosphoric acid, and salts of these acids such as sodium, potassium, ammonia, calcium, and magnesium can be used. Industrially, it is preferable to use phosphoric acid, monobasic sodium phosphate, dibasic sodium phosphate, monobasic ammonium phosphate, and dibasic ammonium phosphate. As the boron compound, for example, boric acid compounds such as boric acid, boric oxide, sodium borate (borax), ammonium borate, magnesium borate, manganese borate, zinc borate, and aluminum borate may be used. I can. Industrially, boric acid and sodium borate (borax) are preferably used.

In addition, in the coating treatment on the iron oxide hydroxide, if necessary, a reduction accelerator component, for example, a compound such as cobalt, nickel, copper or silver may also be coated.

In the present invention, the particles of the hydrous iron oxide particles that have been adhered to the surface as described above are separated from the suspension and then 300 to 850 ° C., preferably 350 to 800 ° C.
More preferably, it is heat-treated at 450 to 750 ° C. in a non-reducing atmosphere, for example, in air or in an inert gas atmosphere for dehydration and conversion to hematite (α-Fe ₂ O ₃ ). If the heat treatment temperature deviates from the above range, the remarkable effect on the sintering of the target product or the collapse of the particle shape may be impaired, and further, the target particles may not be sufficiently densified.

In the present invention, various known methods can be applied to carry out the deposition treatment of the aluminum compound using the hematite obtained as described above as the base particles. For example, to an aqueous suspension of hematite, acidic salts such as aluminum sulfate and aluminum chloride, sodium aluminate, a solution such as basic salts of aluminum such as aluminum acetate, and neutralize by adding an alkali or an acid, Alternatively, it can be carried out by hydrolyzing a solution of an organic aluminum compound such as an aluminum alkoxide or an alkylaluminum compound to precipitate aluminum hydrous oxide on the surface of hematite particles, or by adding and adhering alumina sol or the like. it can. In the deposition treatment, the deposition amount of aluminum was A with respect to the iron in the hematite as the base particles.
The 1 / Fe content is 0.05 to 10% by weight, preferably 0.1 to 10% by weight, and more preferably 0.1 to 5% by weight.

The amount of aluminum (Al) deposited on the iron (Fe) of the hematite particles in the second deposition treatment is
Between the total amount of metallic elements deposited on the hydrous iron oxide (for iron (Fe) in the iron oxide hydroxide particles) and the total amount of metallic elements deposited for hematite (for iron (Fe) in the hematite particles) It is 5 to 95% by weight, preferably 10 to 90% by weight, based on the total amount. If the deposition amount is less than the above range, the desired effect is not provided, and if the deposition amount is more than the above range, it takes a long time to reduce to the target, or the saturation magnetization of the target is It drops.

When the aluminum compound is adhered to the hematite of the base particles, before or after the treatment, for example, a silicon compound, a phosphorus compound,
In some cases, an additional deposition treatment with a zirconium compound or a boron compound may give more desirable results. In this case, the processing amount of each compound is Si, P, Z
Total amount of deposition M as r or B and A to hematite
The ratio of the total amount (1 + deposited amount) and the total amount (Al + M) to Fe is 0.05 to 10% by weight, preferably 0.1 to 5% by weight.

For the silicon compound, phosphorus compound and zirconium compound, the compounds described in the first deposition can be used in the same manner.

In addition, in the above-mentioned adhesion treatment to hematite, if necessary, reduction accelerator components, for example, compounds such as cobalt, nickel, copper, silver and the like may also be subjected to the adhesion treatment.

Hematite coated with an aluminum compound or the like is separated from the suspension, washed, dried, and, if necessary, granulated before and after drying, and then heat-reduced to obtain the object of the present invention. To be

Prior to the heat reduction treatment, a non-reducing atmosphere, for example, in air or in an inert gas atmosphere, 30
The heat treatment at 0 to 850 ° C., preferably 450 to 750 ° C. may produce more desirable results. This is presumed to be because the film formed by the deposition treatment of the aluminum compound or the like becomes uniform and dense by this heat treatment, and as a result, the desired effect is easily exhibited. If the temperature range of the heat treatment is higher than the above range, sintering and shape collapse of the hematite particles are likely to occur, and if the temperature range is lower than the above range, the homogenization and densification of the target are incomplete. Therefore, it is difficult to obtain the desired effect.

In the present invention, the reduction treatment for converting the deposited hematite particles into a magnetic metal powder can be carried out by various well-known methods. Usually, a reducing gas such as hydrogen gas is used. Using 350
Treatment at ˜600 ° C. can reduce substantially all of the iron oxide to metallic iron. The metal magnetic powder obtained by such reduction is generally subjected to a stabilization treatment by various known methods when taken out into the atmosphere. For example, after soaking in an organic solvent such as toluene, slowly evaporate and stabilize toluene or the like, or stabilize by aerating an oxygen-containing gas in a liquid phase or gas phase such as toluene. It is possible to use the method described above in combination with a coating treatment for inhibiting oxidation by various compounds.

The thus obtained metal magnetic powder according to the present invention is excellent in magnetic properties such as coercive force, squareness ratio, orientation, saturation magnetic flux density (filling property) and reversal magnetic field distribution, and gloss value of tape. It is a thing.

As described above, according to the method of the present invention, it is possible to obtain hematite having a good shape and minimizing the incorporation of the aluminum compound into the particle matrix, and as a result, aluminum in the reduction process is obtained. Separation of the compound is reduced, the obtained magnetic metal powder becomes dense and has a good shape, and by treating the aluminum compound with hematite, an aluminum compound suitable for dispersion during the production of the magnetic medium is produced on the particle surface. It is presumed that a dense coating layer with a large number of distributions can be easily obtained, and higher dispersibility and higher magnetic properties can be achieved.

The present invention will be further described below with reference to examples and comparative examples.

【Example】

Example 1 Needle-like geesite (specific surface area = 80 m ² / g, major axis =
200 g (0.25 μm, minor axis = 0.01 μm) was suspended in 6 liters of water and kept at 30 ° C. 62.9 ml of a nickel chloride aqueous solution (20 g / liter as Ni) was added, and the pH was adjusted to 8 with ammonia water for 1 hour. After that, 189 ml of an aqueous solution of sodium aluminate (20 g / liter as Al) was added, and then hydrochloric acid was added to adjust the pH to 8 in 1 hour, and after that, the mixture was kept for 1 hour, and after the first stage adhesion treatment, washed with filtered water. And dried. After dehydration and calcination at 600 ° C in the air to make hematite, it is dispersed in water with a mixer to prepare a suspension, and then a sodium aluminate aqueous solution (20 g / liter as Al)
After adding 126 ml, pH was adjusted to 8 with hydrochloric acid for 1 hour.
And then hold for 1 hour to carry out the second stage deposition treatment, then wash with water and dry, and put 50 g of this into a vertical reduction container,
Reduction was carried out at 400 ° C. in a hydrogen flow of 10 liters / minute. The target metal magnetic powder thus obtained is immersed in toluene,
It was air-dried in the air and taken out into the air.

Example 2 In Example 1, after nickel hydroxide was applied to the iron oxide hydroxide, an aqueous solution of sodium aluminate (20% as Al) was used.
(g / liter) 31.5 ml was added, and then hydrochloric acid was added to adjust the pH to 8 for 1 hour, and then the mixture was kept for 1 hour to carry out the first-stage deposition treatment, followed by washing with filtered water and drying. After dehydration and calcination at 600 ° C in the air to make hematite, it is dispersed in water with a mixer to prepare a suspension, and then a sodium aluminate aqueous solution (20 g / liter as Al)
After adding 283 ml, pH was adjusted to 8 with hydrochloric acid for 1 hour.
And then held for 1 hour to carry out the second stage deposition treatment. Thereafter, the same treatment as in the case of the same example was carried out to obtain the intended metal magnetic powder.

Example 3 Needle-like geesite (specific surface area = 100 m ² / g, major axis =
200 g (0.20 μm, minor axis = 0.008 μm) was suspended in 6 liters of water and kept at 30 ° C. Nickel chloride aqueous solution (20 g / liter as Ni) 62.9 ml
Was added and the pH was adjusted to 8 with ammonia water in 1 hour. Thereafter, 189 ml of an aqueous solution of sodium aluminate (20 g / liter as Al) and 126 ml of sodium orthosilicate (10 g / liter as Si) were added, and then hydrochloric acid was added to adjust the pH to 8 in 1 hour, and then hold for 1 hour. After the first stage deposition treatment, it was filtered, washed with water and dried. After dehydration and calcination at 600 ° C in the air to make hematite, it is dispersed in water with a mixer to prepare a suspension, and then an aqueous solution of sodium aluminate (as Al 2
(0 g / liter) 126 ml was added, and then pH was adjusted to 8 with hydrochloric acid in 1 hour, and then the mixture was kept for 1 hour and then the second
After the deposition treatment of the first step, it is washed with water and dried, 50 g of which is placed in a vertical reduction container and 10 liters / minute at 400 ° C in a hydrogen stream.
I reduced it with. The target metal magnetic powder thus obtained was immersed in toluene, air-dried in the air, and taken out into the air.

Example 4 In Example 3, after the iron oxide hydroxide was coated with nickel, 31.5 ml of an aqueous solution of sodium phosphate (20 g / liter as P) and 189 ml of an aqueous solution of sodium aluminate (20 g / liter as Al) were used. Was added, and then hydrochloric acid was added to adjust the pH to 8 in 1 hour, and then the mixture was kept for 1 hour to perform the first-stage deposition treatment. Thereafter, the same treatment as in the case of the same example was carried out to obtain the intended metal magnetic powder.

Example 5 In Example 1, after nickel was coated on the hydrous iron oxide, 189 ml of an aqueous zirconyl ammonium carbonate solution (20 g / liter as Zr) was added instead of the aqueous sodium aluminate solution, and then hydrochloric acid was added. Add 1
The pH was adjusted to 8 for a certain period of time, and then the temperature was maintained for 1 hour to perform the deposition treatment of the first step, followed by washing with filter water and drying. Atmosphere, 600
After dehydration and calcination at ℃ to make hematite, it was dispersed in water with a mixer to prepare a suspension, and 126 ml of an aqueous solution of sodium aluminate (20 g / liter as Al) was added, and then hydrochloric acid was used for 1 hour. Then, the pH was adjusted to 8 and the temperature was maintained for 1 hour to carry out the second stage deposition treatment. Thereafter, the same treatment as in the case of the same example was carried out to obtain the intended metal magnetic powder.

Example 6 In Example 1, after nickel was coated on the hydrous iron oxide hydroxide, 189 ml of an aqueous zirconyl ammonium carbonate solution (20 g / liter as Zr) and 63 ml of an aqueous sodium aluminate solution (20 g / liter as Al) were used. After the addition, hydrochloric acid was added to adjust the pH to 8 in 1 hour, and then the mixture was kept for 1 hour to carry out the first-stage adhesion treatment, followed by washing with filter water and drying. After dehydration and calcination at 600 ° C. in the air to make hematite, it was dispersed in water with a mixer to prepare a suspension, and 126 ml of an aqueous solution of sodium aluminate (20 g / liter as Al) was added, and then hydrochloric acid was added. Use it for 1 hour to adjust the pH to 8 and then hold for 1 hour before
The deposition process of the first step was performed. Thereafter, the same treatment as in the case of the same example was carried out to obtain the intended metal magnetic powder.

Example 7 In Example 5, iron hydroxide was coated with a nickel compound and a zirconium compound, and 31.5 ml of an aqueous sodium silicate solution (20 g / liter as Si) was added.
Was added, and then hydrochloric acid was added to adjust the pH to 8 in 1 hour, and then the mixture was kept for 1 hour to carry out a coating treatment on hydrous iron oxide. Thereafter, the same treatment as in the case of the same example was carried out to obtain the intended metal magnetic powder.

Example 8 In Example 5, a nickel compound and a zirconium compound were deposited on hydrous iron oxide, 31.5 ml of an aqueous sodium phosphate solution (20 g / liter as P) was added, and then hydrochloric acid was added. Then, the pH was adjusted to 8 in 1 hour, and then the temperature was maintained for 1 hour to perform the adhesion treatment on the hydrous iron oxide. Thereafter, the same treatment as in the case of the same example was carried out to obtain the intended metal magnetic powder.

Example 9 In Example 5, a nickel compound and a zirconium compound were deposited on hydrous iron oxide, 31.5 ml of an aqueous sodium borate solution (20 g / liter as B) was added, and then hydrochloric acid was added. Then, the pH was adjusted to 8 in 1 hour, and then the temperature was maintained for 1 hour to perform the adhesion treatment on the hydrous iron oxide. Thereafter, the same treatment as in the case of the same example was carried out to obtain the intended metal magnetic powder.

Example 10 In Example 5, 63 ml of sodium aluminate (20 g / liter as Al) and 63 ml of sodium orthosilicate (20 g / liter as Si) were added at the time of depositing an aluminum compound on hematite. Other than the above, the same treatment as in the case of the same example was carried out to obtain the target metal magnetic powder.

Example 11 In Example 5, 63 ml of sodium aluminate (20 g / liter as Al) and sodium phosphate (P) were used in the treatment of depositing the aluminum compound on hematite.
Was added in the same manner as in the case of the same example except that 20 g / liter) of 63 ml was added.

Example 12 In Example 5, 63 ml of sodium aluminate (20 g / liter as Al) and sodium borate (B
Was added in the same manner as in the case of the same example except that 20 g / liter) of 63 ml was added.

Example 13 In Example 5, the same as in the case of Example 5 except that the hematite having been subjected to the deposition treatment was subjected to the heat treatment at 600 ° C. for 2 hours in a nitrogen atmosphere before the heat reduction. Then, the desired metallic magnetic powder was obtained.

Example 14 Similar to Example 7, except that the heat-treated hematite was heat-treated at 600 ° C. for 2 hours in a nitrogen atmosphere before the heat reduction. Then, the desired metallic magnetic powder was obtained.

Example 15 In Example 10, the same as in the case of Example 10 except that the hematite having been subjected to the deposition treatment was subjected to the heat treatment at 600 ° C. for 2 hours in the nitrogen atmosphere before the heat reduction. Then, the desired metallic magnetic powder was obtained.

Comparative Example 1 In Example 1, except that the addition amount of the aqueous solution of sodium aluminate in the first-stage deposition treatment was changed to 315 ml and that the second-stage deposition treatment was not performed. The same treatment as in the case of the same example was performed to obtain a metal magnetic powder as a comparative sample.

Comparative Example 2 In Example 1, the aluminum compound was not deposited in the first stage deposition treatment, and the addition amount of the sodium aluminate aqueous solution was 315 ml in the second stage deposition treatment.
A metal magnetic powder as a comparative sample was obtained by the same procedure as in the above example except that

Comparative Example 3 In Example 1, instead of the dehydration and calcination treatment after the first-stage deposition treatment, magnetite was obtained by reduction at 400 ° C. in a hydrogen stream. A comparative sample was obtained by treating in the same manner as in the example except that the treatment was performed.

Comparative Example 4 In Example 3, the deposition treatment with the silicon compound in the deposition treatment of the first step was not performed, and the deposition treatment of the second step was replaced with the sodium aluminate aqueous solution, and A comparative sample was obtained by treating in the same manner as in the same example except that 251 ml of an aqueous sodium acid solution (10 g / liter as Si) was used.

Comparative Example 5 In Example 5, 126 ml of an aqueous solution of sodium aluminate (20 g / liter as Al) was added instead of the first deposition treatment of the zirconium compound on the hydrous iron oxide.
Further, instead of depositing the aluminum compound on the hematite, a zirconium oxychloride aqueous solution (Zr is 2
(0 g / liter) was added and neutralized with caustic soda, and treated in the same manner as in the same example to obtain a metal magnetic powder as a comparative sample.

Comparative Example 6 In Example 5, in the first deposition treatment of the zirconium compound on the iron oxide hydroxide, 189 ml of an aqueous zirconium oxychloride solution (20 g / liter as Zr) and an aqueous sodium aluminate solution (20 g / liter as Al) were used. A metal magnetic powder of a comparative sample was obtained in the same manner as in the same example except that 126 ml was added and the second deposition of the aluminum compound on the hematite was not performed.

Comparative Example 7 In Example 5, the first deposition of the zirconium compound on the hydrous iron oxide was not carried out, and the sodium aluminate aqueous solution (20 g as Al was used in the deposition of the aluminum compound on the hematite). / Liter) 126
A metal magnetic powder of a comparative sample was obtained by performing the same treatment as in the same example except that 189 ml of an aqueous zirconium oxychloride solution (20 g / liter as Zr) was simultaneously added in parallel.

The magnetic characteristics of each of the metallic magnetic powder samples obtained in the above Examples and Comparative Examples were measured by a conventional method. Moreover, a magnetic tape was prepared by a conventional method using these samples. The magnetic paint was prepared by mixing and dispersing the following compounding compositions, and the dry film thickness was adjusted to 10 μm. The magnetic characteristics of the prepared magnetic tape were also measured by a conventional method.

Magnetic powder 5.00 parts by weight Dispersant 0.25 parts by weight Polyurethane resin 2.96 parts by weight Mixed solvent ^* 13.40 parts by weight ^* Toluene / MEK / cyclohexane (4.5 / 4.5
/ 1)

Measured magnetic characteristics, coercive force (Hc: O
e), saturation magnetization (σs: emu / g), squareness ratio (Rs,
SQ), orientation ratio (OR), switching field distribution (SFD) and 60 ° -60 ° gloss measured with a gloss meter are shown in Tables 1 and 2.

[0058]

[Table 1]

[0059]

[Table 2]

[0060]

EFFECTS OF THE INVENTION According to the method of the present invention, particle sintering and particle shape collapse can be suppressed without causing problems in the heat dehydration treatment and heat reduction treatment as seen in the conventional deposition treatment of the shape-retaining agent. In addition, the dispersibility in the magnetic recording medium is good, and the fine metal magnetic powder suitable for high density recording can be efficiently produced, which is a very industrially advantageous method.

Front page continued (72) Inventor Masaaki Moriyama 1 Ishihara-cho, Yokkaichi-shi, Mie Ishihara Industrial Co., Ltd. Yokkaichi Operations

Claims (10)

[Claims] 1. Hematite particles obtained by first applying at least one compound selected from an aluminum compound and a zirconium compound to the surface of iron oxide hydroxide particles, and then heat-treating to form hematite. A method for producing acicular magnetic iron powder by subjecting a surface to a second deposition treatment of an aluminum compound and then subjecting it to a heat reduction treatment. 2. The method for producing an acicular magnetic iron powder according to claim 1, wherein the first deposition treatment further includes at least one compound selected from silicon compounds, phosphorus compounds and boron compounds. 3. The method according to claim 1, wherein when the first deposition treatment is performed with a zirconium compound, the second deposition treatment further includes at least one of a silicon compound, a phosphorus compound, a zirconium compound and a boron compound. Method for producing needle-shaped magnetic iron powder of. 4. When the first deposition treatment is performed only with a zirconium compound, the second deposition treatment further includes a silicon compound,
The method for producing acicular magnetic iron powder according to claim 2, wherein at least one of a phosphorus compound, a zirconium compound, and a boron compound is included. 5. With respect to iron (Fe) of the iron oxide hydroxide particles,
The method for producing acicular magnetic iron powder according to claim 1, wherein the amounts of aluminum (Al) and zirconium (Zr) deposited in the first deposition treatment are in the range of 0.1 to 10% by weight. 6. With respect to iron (Fe) of hematite particles,
The method for producing acicular magnetic iron powder according to claim 1, wherein the amount of aluminum (Al) deposited in the second deposition treatment is in the range of 0.1 to 10% by weight. 7. The iron (Fe) of the hematite particles,
The method for producing acicular magnetic iron powder according to claim 1, wherein the amount of aluminum (Al) deposited in the second deposition treatment is in the range of 0.1 to 8% by weight. 8. The deposition amount of aluminum (Al) on the iron (Fe) of the hematite particles in the second deposition treatment is such that the deposition amount of all metal elements on the hydrous iron oxide (iron (Fe of hydrous iron oxide particles) And the total amount of all metallic elements deposited on hematite (based on iron (Fe) in hematite particles), the range of 5 to 95% by weight. Method for producing needle-shaped magnetic iron powder of. 9. The method for producing an acicular magnetic iron powder according to claim 1, wherein the first iron oxide hydroxide treated is heat-treated at 350 to 800 ° C. in a non-reducing atmosphere. 10. The method for producing an acicular magnetic iron powder according to claim 1, wherein the adhered hematite is heat-treated at 300 to 850 ° C. before the heat reduction treatment.