JP3446960B2 - Method for producing magnetic metal powder for magnetic recording using α-iron oxyhydroxide - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a magnetic metal powder for magnetic recording using .alpha.-iron oxyhydroxide, and more particularly to a method of producing a colloidal aluminum-containing powder on the surface. The present invention relates to α-iron oxyhydroxide uniformly coated with ferric hydroxide and a method for producing a magnetic metal powder for magnetic recording which is fine and has excellent magnetic properties with good dispersibility. 2. Description of the Related Art A coating type magnetic recording medium using iron or a magnetic metal powder mainly composed of iron has recently been put to practical use as a magnetic recording medium for the purpose of improving magnetic recording density and reproducing output. ing. [0003] Magnetic metal powder is usually α-FeOOH,
Acicular iron oxyhydroxide (goethite) such as β-FeOOH or γ-FeOOH is dehydrated in an oxidizing gas atmosphere such as air while maintaining its acicularity to make it hematite, and then hydrogenated. It is manufactured by a method of reducing to metallic iron under a reducing gas atmosphere. And magnetic metal powder,
It is widely used as a magnetic recording medium such as a magnetic tape or a magnetic disk after being mixed with a binder resin to form a coating and then applied to a tape or a disk. However, magnetic metal powders obtained by heat treatment such as dehydration, reduction, and oxidation of acicular iron oxyhydroxide generally agglomerate, sinter, or become long between particles in many cases. It has been very difficult to obtain a fine magnetic metal powder without sintering or sintering. [0005] Therefore, when producing magnetic metal powder from acicular iron oxyhydroxide, the acicular iron oxyhydroxide is prepared during or after the preparation of acicular iron oxyhydroxide in order to prevent agglomeration and sintering between particles. Phosphorus compound, silicon compound,
Various methods have been proposed for applying and containing a surfactant and the like. Also, Japanese Patent Application Laid-Open Nos. 56-169706 and 57
Japanese Patent Application Laid-Open Nos. 5804 and 57-116705 propose a method for producing a magnetic metal powder by applying an aluminum compound and a silicon compound during or after the preparation of acicular iron oxyhydroxide. However, these methods are insufficient in their effect. In particular, the smaller the particle size of the acicular iron oxyhydroxide as a raw material, the more easily the particles are likely to aggregate, and the reduction in the dispersibility of the paint by reduction. Difficulty accompanies obtaining a magnetic metal powder with good quality. In Japanese Patent Application Laid-Open No. 63-140005, an aluminum compound and a ferrous salt are added to an aqueous suspension of α-iron oxyhydroxide to carry out an oxidation reaction. A method of coating with a water-soluble carboxylic acid or silicon compound is disclosed. However, the magnetic metal powder obtained by this method has a problem that the effect of aluminum which originally contributes to dispersibility is hindered. Further, since the crystallization condition is pH 8 to 12, a part or most of aluminum is precipitated as a hydroxide, so that it is crystallized at a place other than the particle surface. As a result, aluminum cannot be uniformly dissolved as a solid solution. The effect of improving the dispersibility of the paint is still not seen. Further, there is a problem that the process is very complicated and productivity is poor. SUMMARY OF THE INVENTION It is an object of the present invention to provide a fine magnetic recording magnetic metal having a remarkably improved paint dispersibility and high magnetic properties without causing sintering between particles. An object of the present invention is to provide a method for producing a magnetic metal powder using α-iron oxyhydroxide for obtaining a powder. The above object of the present invention is attained by the following method for producing a magnetic metal powder using α-iron oxyhydroxide. Further, the method for producing a magnetic metal powder for magnetic recording according to the present invention comprises the steps of: (I) adding an aqueous ferrous salt solution and an aqueous aluminum salt solution to an acicular α-iron oxyhydroxide slurry; After adjusting the pH to 2 or less, oxidize with an oxidizing agent, then raise the temperature to 50 ° C. or higher, and further adjust the pH with an alkali.
Neutralization and aging at 3.5 or more, (II) washing, drying, and sintering the slurry of α-iron oxyhydroxide having the aluminum-containing colloidal ferric hydroxide uniformly coated on the obtained surface And then reducing in a reducing gas to form an oxide film on the surface. Hereinafter, the production method of the present invention will be described in more detail. In the present invention, acicular α-iron oxyhydroxide is used as a raw material. The properties, production method, and the like of the acicular α-iron oxyhydroxide are not particularly limited, but the preferred average major axis diameter is 0.1 to 0.25 μm. In addition, it is preferable that at least one selected from nickel, manganese, aluminum, silicon, phosphorus, zinc, calcium, and magnesium besides iron. In the present invention, an aqueous ferrous salt solution and an aqueous aluminum salt solution are added to the acicular α-iron oxyhydroxide slurry, and the mixture is thoroughly mixed and stirred. Examples of the ferrous salt used here include sulfates and chlorides, and sulfates are preferably used in consideration of economic efficiency and reaction stability. As the aluminum salt, sulfate,
Nitrate, chloride and the like are exemplified. Also in this case, sulfate is preferred from an industrial point of view. The preferred range of the ferrous salt is 10/100 to 100/100 in terms of the atomic ratio of iron in the ferrous salt with respect to the iron in the iron oxyhydroxide being 100. The preferred range of the aluminum salt is as follows.
The atomic ratio of aluminum in the ferrous salt when it is set to 00 is 6/100 to 30/100. In this way, iron and aluminum are deposited on the iron oxyhydroxide surface. In the present invention, it is necessary that the pH of the iron oxyhydroxide slurry sufficiently mixed and stirred as described above is adjusted to 2 or less. For this purpose, an acid may be added before or after the addition of the aqueous ferrous salt solution and the aqueous aluminum salt solution. In any case, it is necessary that the pH of the iron oxyhydroxide slurry be adjusted to pH 2 or less before oxidation. is there. When the pH exceeds 2, the ferrous salt in the slurry does not contain an aluminum salt, and newly forms α-iron oxyhydroxide and magnetite. Next, the iron oxyhydroxide is oxidized by an oxidizing agent. The oxidizing agent used here is not particularly limited, and may be any of air, oxygen, peroxides such as ozone and hydrogen peroxide. Particularly, peroxides such as hydrogen peroxide are preferred.
The reason for this is that the use of a strong peroxide results in an α-iron oxyhydroxide with a particularly finely divided aluminum-containing colloidal ferric hydroxide. Next, the temperature of the slurry is raised to 50 ° C. or higher, preferably 70 ° C. or higher. If the temperature is lower than 50 ° C., fine aluminum-containing colloidal ferric hydroxide is not uniformly deposited on the surface, and as a result, the properties and characteristics of the final magnetic metal powder are inferior. Then, the slurry is adjusted to pH 3.5 or more, preferably pH 3.5 to 9.0 with alkali, and then subjected to neutralization heat treatment. The alkali used here is not particularly limited, but a carbonate such as sodium carbonate is generally used. Here, if the pH is less than 3.5, aluminum is not contained in fine ferric hydroxide particles, and the properties and properties of the final magnetic metal powder are inferior. The α-iron oxyhydroxide in this slurry is
Fine aluminum-containing colloidal ferric hydroxide is uniformly applied on the surface. The slurry of α-iron oxyhydroxide thus obtained is washed, dried and calcined. This drying is 1
The calcination is performed at 00 to 200 ° C. for about 12 hours, and the calcination is performed in the air or in a nitrogen atmosphere at 300 to 800 ° C., preferably 400 to 700 ° C. Next, it is reduced in a reducing gas to form an oxide film on the surface. This reduction is performed in a reducing gas such as hydrogen gas or carbon monoxide gas.
In order to form an oxide film on the surface, the magnetic metal powder is obtained by gradually increasing the oxygen concentration in a mixed gas of an inert gas and an oxygen gas, and finally obtaining an atmospheric concentration. It is better to take out. The shape of the magnetic metal powder for magnetic recording obtained by the production method of the present invention is acicular, and the preferable average major axis diameter is 0.05 to 0.25 μm and the specific surface area is 4 μm.
0 to 55 m ² / g. A preferred composition is that iron is 1
6 to 15 atomic% of aluminum in atomic ratio assuming 00
It contains. The present invention will be specifically described below based on examples and the like. Example 1 100 g of acicular α-iron oxyhydroxide having a comparative area of 85 m ² / g and an average major axis diameter of 0.25 μm was well separated and suspended in 2000 ml of water. To this suspension, ferrous sulfate 0.25 mol / l
Then, 560 ml of a mixed aqueous solution composed of 0.19 mol / l of aluminum sulfate was added, and the mixture was thoroughly mixed and stirred to disperse each component, and then adjusted to pH 1.7 at room temperature. The slurry contains 0.1 g of divalent iron ions.
/ L or less and oxidized by adding aqueous hydrogen peroxide. 1
After dispersing for an hour, the temperature was raised to 80 ° C., and the pH was maintained at 3.5 with an aqueous solution of sodium carbonate, followed by heating for 1 hour. Further pH
7 and heat-formed for 1 hour, then cooled and washed. The α-iron oxyhydroxide thus obtained was observed by a TEM photograph shown in FIG.
-It was found that very fine colloidal ferric hydroxide was uniformly deposited on the surface of the iron oxyhydroxide. As a result of chemical analysis, it was found that the added aluminum was 100% deposited. That is, the deposition amount of aluminum is α
-The atomic ratio was 10% when Fe in iron oxyhydroxide was defined as 100. The amount of the ferric salt deposited was 1 in atomic ratio when Fe in α-iron oxyhydroxide was 100.
2.4%. The α-iron oxyhydroxide thus obtained has a specific surface area of 65 m ² / g, and an average major axis diameter of 0.3.
It was 25 μm. Table 1 also shows these starting materials and production conditions. The α-iron oxyhydroxide slurry was caked with a filter press, and dried at 100 to 120 ° C. overnight. Then, after baking at 400 ° C. in air, reduction was performed at 500 ° C. in hydrogen gas to obtain acicular magnetic metal powder. Finally, a stable oxide film was formed on the reduced needle-shaped magnetic metal powder, and then taken out into the atmosphere to obtain a magnetic metal powder for magnetic recording. The properties thereof were, as shown in Table 2, a specific surface area of 55 m ² / g and an average major axis diameter of 0.15 μm. Here, the specific surface area was measured using a Micromeritics Model 2200 manufactured by Shimadzu Corporation, and the average major axis diameter was 100 particles recognized as a single particle on a TEM photograph.
The major axis diameters were measured, and the average value was determined. The magnetic properties and dispersibility of the magnetic metal powder were evaluated. The magnetic properties were measured for coercive force (Hc) and saturation magnetization (σs).
The measurement was performed using an SM with an external magnetic field of 10 KOe and a packing ratio of 0.85. On the other hand, the dispersibility was evaluated by preparing a sheet according to the following method and evaluating the gloss of the sheet. Table 2 also shows these results. <Preparation of sheet> a) Coating composition (parts by weight) Pigment 100 Polyurethane resin having sodium sulfonate group 10 Vinyl chloride resin 10 Toluene 150 MEK 150 Cyclohexanone 40 Lubricant 1 The material was dispersed in a sand grinder at 1500 rpm for 3 hours to prepare a paint. C) Sheet preparation conditions The above-mentioned paint is applied on a base film and, after orientation, at 100 ° C.
And dried. <Measurement conditions> a) Glossiness JIS was measured using a gloss meter manufactured by Nippon Denshoku Industries Co., Ltd.
Measured at 45 ° according to Z8741. Examples 2 to 11 Properties of acicular α-iron oxyhydroxide as starting material, pH during oxidation, type of aluminum salt, amount of aluminum salt added, type of ferrous salt, ferrous salt Amount added, pH during aging
And the temperature at the time of ripening was changed as shown in Table 1, except that α-oxyhydroxide having a very fine colloidal ferric hydroxide uniformly deposited on the surface was used in the same manner as in Example 1. An iron slurry was obtained. The specific surface area and average major axis diameter of the α-iron oxyhydroxide thus obtained were as follows. A) Example 2: Specific surface area 65 m ² / g, average major axis diameter 0.
25 μm. B) Example 3: Specific surface area 55 m ² / g, average major axis diameter 0.
27 μm. C) Example 4: specific surface area 64 m ² / g, average major axis diameter 0.
25 μm. D) Example 5: Specific surface area 61 m ² / g, average major axis diameter 0.
24 μm. E) Example 6: specific surface area 65 m ² / g, average major axis diameter 0.
25 μm. F) Example 7: specific surface area 67 m ² / g, average major axis diameter 0.
24 μm. G) Example 8: Specific surface area 68 m ² / g, average major axis diameter 0.
25 μm. H) Example 9: specific surface area 69 m ² / g, average major axis diameter 0.
25 μm. I) Example 10: specific surface area 60 m ² / g, average major axis diameter 0.15 μm. J) Example 11: Specific surface area 65 m ² / g, average major axis diameter 0.26 μm. These α-iron oxyhydroxides were caked, dried, calcined and reduced in accordance with Example 1 to obtain acicular magnetic metal powder. Finally, a stable oxide film was formed on the reduced needle-shaped magnetic metal powder, and then taken out into the atmosphere to obtain a magnetic metal powder for magnetic recording. The properties, magnetic properties and dispersibility of the magnetic metal powder were evaluated in the same manner as in Example 1, and the results are shown in Table 2. Comparative Example 1 As shown in Table 1, a slurry of α-iron oxyhydroxide was obtained in exactly the same manner as in Example 1 except that no oxidizing agent was used and no ferrous salt was added. FIG. 2 shows a TEM photograph of the α-iron oxyhydroxide. Α obtained in this way
- specific surface area of the iron oxyhydroxide 75 m ² / g, an average major axis diameter 0.25 [mu] m. The α-iron oxyhydroxide was formed into a cake, dried, calcined and reduced in accordance with Example 1 to obtain a needle-shaped magnetic metal powder. Finally, a stable oxide film was formed on the reduced needle-shaped magnetic metal powder, and then taken out into the atmosphere to obtain a magnetic metal powder for magnetic recording. The properties, magnetic properties and dispersibility of the magnetic metal powder were evaluated in the same manner as in Example 1, and the results are shown in Table 2. Comparative Example 2 As shown in Table 1, a slurry of α-iron oxyhydroxide was obtained in exactly the same manner as in Example 1 except that no aluminum salt was added. The α-iron oxyhydroxide thus obtained has a specific surface area of 65 m ² / g and an average major axis diameter of 0.25 μm.
m. The α-iron oxyhydroxide was formed into a cake, dried, calcined, and reduced according to Example 1, to obtain a needle-shaped magnetic metal powder. Finally, a stable oxide film was formed on the reduced needle-shaped magnetic metal powder, and then taken out into the atmosphere to obtain a magnetic metal powder for magnetic recording. The properties, magnetic properties and dispersibility of the magnetic metal powder were evaluated in the same manner as in Example 1, and the results are shown in Table 2. Comparative Example 3 As shown in Table 1, except that the pH at the start of oxidation was set to 3.
A slurry of α-iron oxyhydroxide was obtained in exactly the same manner as in Example 1. The specific surface area of the α-iron oxyhydroxide thus obtained was 35 m ² / g, and magnetite was mixed in the slurry, so that it could not be used as a magnetic metal powder for magnetic recording. Comparative Example 4 As shown in Table 1, a slurry of α-iron oxyhydroxide was obtained in exactly the same manner as in Example 1 except that the pH during aging was set to 3. The specific surface area of the α-iron oxyhydroxide thus obtained was 65 m ² / g, and the average major axis diameter was 0.25 μm. This α-iron oxyhydroxide was formed into a cake, dried, calcined and reduced in accordance with Example 1 to obtain a needle-shaped magnetic metal powder. Finally, a stable oxide film was formed on the reduced needle-shaped magnetic metal powder, and then taken out into the atmosphere to obtain a magnetic metal powder for magnetic recording. The properties, magnetic properties and dispersibility of the magnetic metal powder were evaluated in the same manner as in Example 1, and the results are shown in Table 2. Comparative Example 5 As shown in Table 1, except that the aging temperature was 30 ° C.
A slurry of α-iron oxyhydroxide was obtained in exactly the same manner as in Example 1. The specific surface area of the α-iron oxyhydroxide thus obtained was 65 m ² / g, and the average major axis diameter was 0.25 μm. This α-iron iron oxyhydroxide was formed into a cake, dried, calcined and reduced according to Example 1 to obtain a needle-shaped magnetic metal powder. Finally, a stable oxide film was formed on the reduced needle-shaped magnetic metal powder, and then taken out into the atmosphere to obtain a magnetic metal powder for magnetic recording. The properties, magnetic properties and dispersibility of the magnetic metal powder were evaluated in the same manner as in Example 1, and the results are shown in Table 2. Comparative Example 6 As shown in Table 1, the pH at the time of oxidation was 10, the air was used as an oxidizing agent, the pH at the time of aging was 9.5, the temperature at the time of aging was 90.degree. In the same manner as in Example 1, a slurry of α-iron oxyhydroxide was obtained. The specific surface area of the α-iron oxyhydroxide thus obtained is 65 m ² /
g, average major axis diameter was 0.35 μm. This α-iron oxyhydroxide was formed into a cake, dried, calcined and reduced in the same manner as in Example 1 to obtain an acicular magnetic metal powder. Finally, a stable oxide film was formed on the reduced needle-shaped magnetic metal powder, and then taken out into the atmosphere to obtain a magnetic metal powder for magnetic recording. The properties, magnetic properties and dispersibility of the magnetic metal powder were evaluated in the same manner as in Example 1, and the results are shown in Table 2. [Table 1] [Table 2] As apparent from the results in Table 2, Example 1
Nos. 11 to 11 are excellent in magnetic properties because of their higher coercive force and saturation magnetization as compared with Comparative Examples 1 to 2 and 4 to 6. Further, in Examples 1 to 11, the gloss value after 3 hours was higher than those in Comparative Examples, so that the paint dispersibility was excellent. Comparative Example 3 was not compared because magnetite was generated. According to the present invention described above, a fine magnetic metal powder for magnetic recording having remarkably improved paint dispersibility and high magnetic properties can be obtained without causing sintering between particles. .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a TEM photograph (× 300000) showing the particle state of α-iron oxyhydroxide obtained in Example 1. FIG. 2 is a TEM photograph (× 300,000) showing the particle state of α-iron oxyhydroxide obtained in Comparative Example 1.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Toshige Ito 53-8 Uematsu, Nadazaki-cho, Kojima-gun, Okayama Prefecture (56) References JP-A-59-45931 (JP, A) A) JP-A-3-293703 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01G 49/02 H01F 1/06

Claims (1)

(I) A ferrous salt aqueous solution and an aluminum salt aqueous solution are added to a needle-like α-iron oxyhydroxide slurry,
After mixing and stirring sufficiently to adjust the pH to 2 or less, oxidizing with an oxidizing agent, then raising the temperature to 50 ° C. or more, and further neutralizing and ripening with an alkali at pH 3.5 or more, (II) the obtained surface After washing the slurry of α-iron oxyhydroxide uniformly coated with aluminum-containing colloidal ferric hydroxide, drying and firing, and then reducing in a reducing gas to form an oxide film on the surface A method for producing a magnetic powder for magnetic recording, comprising: