JP2740922B2 - Method for producing metal magnetic powder for magnetic recording material - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for producing an iron-based metal magnetic powder suitable for a magnetic recording material.

[Conventional technology]

In recent years, magnetic recording media have been more and more tended to be improved in recording density and to be smaller and have higher performance. Along with this, as a magnetic powder for a magnetic recording material, iron or an iron-based metal magnetic powder (hereinafter, referred to as an iron or iron-based metal powder having a larger saturation magnetization and coercive force than an iron oxide-based magnetic powder.
(Referred to as metal magnetic powder). Metal magnetic powders are being put to practical use in digital audio tapes and 8mm video tapes, but are expected to be applied to high-performance recording media such as high-quality video tapes and high recording density discs in recent years. I have.

When the metal magnetic powder is, for example, acicular particles, usually a long axis diameter of about 0.5μ or less, and further, a fine thing of 0.3μ or less is required, and dispersibility when this is used as a magnetic paint Further, there is a demand for a coating film having better orientation and filling properties.

[Problems to be solved by the invention]

In order to meet the above requirements, it is essential that the iron oxide hydroxide particles, which are the starting materials of the magnetic metal powder, are fine and have a good particle size distribution. Furthermore, while suppressing the particle sintering in the firing step and the reduction step from the hydrous iron oxide to the metal magnetic powder, the dispersibility when the metal magnetic powder is used as a magnetic paint, the orientation in the coating film, the filling property, In order to improve the gloss and the like, it is also necessary to appropriately select the type of the shape maintaining component, the method of addition, and the like.

Various measures have been conventionally proposed to solve these problems. Examples of the shape-retaining component include a silica compound and an aluminum compound, and a method of applying these to the surface of the iron oxide hydroxide particles has been proposed, but it cannot be said that the method is sufficiently satisfactory.

[Means for solving the problem]

The present inventors have conducted various studies in order to solve the above-mentioned problems. As a result, (1) that if a silica compound is present in a large amount in the surface layer of a metal magnetic powder, the dispersibility of a magnetic coating material is deteriorated; 2) It was found that if the hydrated oxide of aluminum was coated on the surface of the iron oxide hydroxide or iron oxide particles more than necessary, segregation or peeling was easy from the surface of the metal magnetic powder particles after the reduction treatment. . As a result of further study based on these findings, it was found that a silicon compound was added during the production reaction process of the iron oxide hydroxide as a starting material to generate silicon-containing iron hydroxide, and then the particle surface was coated with an aluminum compound. Thereby, (1) having a fine and good particle size distribution and producing a high ratio of hydrous iron oxide,
(2) Sintering in the subsequent firing step or reduction step can be reduced, (3) Dispersibility is less deteriorated because silicon is contained in the particles of the metal magnetic powder, (4)
The coating amount of the aluminum compound can be reduced, and the segregation or peeling off from the particle surface of the metal magnetic powder is small, so that the magnetic properties of the metal magnetic powder, especially the coercive force, squareness ratio, orientation ratio, saturation magnetic flux density (filling property) It was found that the switching field distribution was excellent and the gloss value of the tape was high.

That is, the method of the present invention comprises reacting an iron salt with an alkali agent in the presence of a silicon compound to produce silicon-containing iron oxide hydroxide, and then coating the aluminum oxide on the surface of the iron oxide hydroxide or iron oxide particles. A method for producing a metal magnetic powder for a magnetic recording material, comprising reducing.

In the method of the present invention, first, an iron salt is reacted with an alkali agent in the presence of a silicon compound to obtain silicon-containing iron oxide hydroxide. By appropriately selecting an iron salt, an alkali agent, reaction conditions, and the like, α-FeOOH, β-FeOOH, γ-FeOOH and the like can be obtained, and in the present invention, α-FeOOH (goethite) is used. It is desirable to generate it. As iron salts, for example, ferrous sulfate, ferric sulfate,
Ferrous chloride, ferric chloride and the like can be used. When a ferrous salt is used, it is necessary to neutralize with an alkali agent and then perform an oxidation reaction. As the alkaline agent, for example, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, aqueous ammonia, ammonia gas and the like can be used.

As a method of allowing the silicon compound to be present, a method in which the silicon compound is neutralized by putting it in one liquid before the neutralization reaction between the iron salt and the alkali agent, or added to a neutralized suspension of the iron salt and the alkali agent There are a method and a method of adding during the reaction of the neutralized suspension, and a method of adding during the reaction of the neutralized suspension is preferable. A particularly desirable method is to partially neutralize and oxidize an aqueous ferrous salt solution to generate goethite nuclei, and then oxidize while neutralizing with an alkali agent to grow nuclei to obtain goethite, thereby growing goethite. That is, the silicon compound is continuously added little by little during the reaction. This growth reaction is pH2 ~
5. On the alkaline side, the pH is preferably in the range of 10 to 14. If the pH is more than 5 and less than 10, the generation of particulate magnetite is feared, and if the pH is less than 2, the growth reaction takes a long time.

More preferably, the specific surface area is 55 m ² from the viewpoint of miniaturization.
/ g or more of silicon-containing iron oxide hydroxide.

As the silicon compound, various silicates such as sodium orthosilicate, potassium orthosilicate, sodium metasilicate, potassium metasilicate, water glass or other silicon compounds such as colloidal silica can be used. Particularly, water glass is one of the preferable ones.
The content of silicon by the silicon compound is 0.1 to 5% by weight as Si / Fe with respect to the iron in the produced hydrous iron oxide, preferably
0.3 to 3% by weight. When the content is less than 0.1% by weight, effects such as improvement of the particle size distribution of the produced iron oxide hydroxide particles and suppression of the desired sintering cannot be obtained. On the other hand, when the content is more than 5% by weight, the crystal growth of the hydrous iron oxide is suppressed, the particle size distribution width of the particles is widened, the axial ratio is lowered, and a long time is required for the reduction, and the saturation magnetization of the metal magnetic material is lowered.

Next, in the method of the present invention, the surface of the silicon-containing hydrated iron oxide particles is coated with an aluminum compound. There are various methods for coating the aluminum compound. For example, a solution of an acidic salt of aluminum such as aluminum nitrate, aluminum sulfate, or aluminum chloride or a basic salt of aluminum such as sodium aluminate is added to an aqueous suspension of silicon-containing hydrous iron oxide, and an alkali or acid is added to adjust the pH. A method of coating a hydrated oxide of aluminum by neutralizing to a range of 6 to 9, a solution of an organic aluminum compound such as an aluminum alkoxide, an alkyl aluminum compound or the like in an aqueous suspension of a silicon-containing hydrous iron oxide aqueous suspension To form a hydrated oxide of aluminum outside the system of an aqueous suspension of silicon-containing iron oxide hydroxide and hydrolyze it to form a hydrated oxide of aluminum. A method of adding and coating. Industrially,
A method in which an aqueous solution of an aluminum compound is added to an aqueous suspension and subjected to a neutralization treatment is advantageous. In this case, if the neutralization pH is higher than 9, the precipitation rate of hydrated oxides of aluminum decreases and the yield deteriorates. In addition, sintering becomes extremely easy due to the incorporation of alkali components such as sodium. It is not preferable because the effect is lost.

In the present invention, α-Fe ₂ O ₃ obtained by calcining silicon-containing hydrated iron oxide at 550 to 900 ° C., preferably 600 to 800 ° C. or Fe ₃ O obtained by reducing the same ₄ , γ-Fe ₂ O
_{3. An} aluminum compound may be coated on the surface of iron oxide particles such as a beltride compound.

Examples of the aluminum compound to be coated include hydrated oxides, hydroxides, oxides and phosphates of aluminum, and among them, hydrated oxides are preferred.

The coating amount of the aluminum compound is 0.1 to 8% by weight, preferably 0.3 to 5% by weight as Al / Fe with respect to the iron in the hydrous iron oxide or iron oxide, and it is desirable that the coating amount is less than 0.1% by weight. No effect such as suppression of sintering is provided.
On the other hand, if the content is more than 8% by weight, the reduction takes a long time, the aluminum compound tends to segregate or peel off from the particle surface after the reduction treatment, and the saturation magnetization of the metal magnetic material also decreases.

In the present invention, a suitable dispersing agent such as phosphate, polyphosphate, polyacrylate, carboxylate, etc. is added to an aqueous suspension of silicon-containing hydrated iron oxide or iron oxide to prepare the hydrated iron oxide or oxide. The coating treatment of the aluminum compound can be performed after improving the dispersion of iron.

In order to make the method of the present invention more industrially preferable, a compound such as nickel, copper, cobalt, silver, calcium or the like which acts as a reduction accelerator in the subsequent reduction step is coated on the surface of the iron oxide hydroxide or iron oxide particles. May be
In addition, P, Cr, Mn, B, Cd, Pb, Ca, Mg, Sr, Zn, Sn, W, Zr, Co
Such a compound may be used in combination for coating treatment.

Next, the iron oxide hydroxide or iron oxide coated as described above is separated from the suspension, washed, dried, and then reduced to produce a metal magnetic powder. In this case, if necessary, calcination may be performed at 550 to 900 ° C, preferably 650 to 850 ° C, before reduction. By this calcination, the whole particles are baked to be dense, and sintering during reduction and collapse of the particle shape can be further suppressed. If the sintering temperature is too high, it is not preferable because acicularity is deteriorated or coarsened due to sintering within and between particles at the stage of iron oxide. On the other hand, if the firing temperature is too low, many pores remain in the particles, and the particles themselves are not dense crystals, so that the shape is greatly deteriorated in the subsequent reduction step, and the desired effect cannot be obtained.

Various known methods can be used for the reduction to the metal magnetic powder. Usually, hydrogen is used as a reducing gas, for example.
By treating at 0 to 600 ° C., substantially all of the iron oxide hydroxide or iron oxide can be reduced to the metal. The metal magnetic powder obtained by such reduction is ignited when it comes into contact with the atmosphere and rapidly changes to iron oxide. Therefore, when it is taken out to the atmosphere, it is usually stabilized using various known methods. For example, a method of stabilizing by evaporating toluene slowly after being immersed in an organic solvent such as toluene, a method of stabilizing by passing an oxygen-containing gas through a liquid or gaseous phase such as toluene, and a method of oxidizing with various compounds. There is a method in which the suppression film forming treatment and the above method are used in combination.

The magnetic metal powder for a magnetic recording material of the present invention thus obtained has magnetic properties such as coercive force, squareness ratio, orientation, saturation magnetic flux density (filling property), switching magnetic field distribution, and gloss value of the tape. It is excellent.

〔Example〕

Example 1 (1) Formation reaction of goethite nucleus crystal A reaction vessel equipped with an air blowing tube and a stirrer was charged at 1.50 mol /
Ferrous sulfate aqueous solution 20 was added, and the temperature was raised to 50 ° C. While maintaining this temperature, a 10 mol / aqueous sodium hydroxide aqueous solution 1.07 was added with stirring (precipitated Fe 15 g /).
Air was blown in at a rate of 10 / min to react for 100 to 200 minutes to obtain goethite nuclei.

(2) Growth reaction of nucleus crystal In order to grow to a desired particle diameter, while maintaining the above nucleus slurry at 50 to 55 ° C, 1.61 of 10N aqueous sodium hydroxide solution was added at a rate of 8 ml / min, and air was added. Was fed at a rate of 5 / min to carry out neutralization and oxidation reactions. The growth magnification is 2.5 times the weight ratio to the nucleus crystal.

In this growth reaction, a 0.5 mol / sodium orthosilicate aqueous solution was continuously added in parallel with the sodium hydroxide aqueous solution. The pH during the growth reaction was maintained at 3-5. The amount of sodium orthosilicate added was 1.0% by weight as Si / Fe with respect to the iron in the resulting goethite.

The silicon-containing goethite thus obtained was filtered and washed. The specific surface area (BET method) was 75 m ² / g.

(3) Coating treatment of aluminum compound 120 g of this goethite was suspended in 1.5 of water,
C and the pH was kept at 5. The slurry for about 2 hours the slurry of aluminum chloride (AlCl ₃ · 6H ₂ O) solution was added at 30 minutes, it was added aqueous ammonia 4N After aging for 30 minutes
The pH was adjusted to 7.5. The amount of aluminum chloride to be added was set to 5.0 as Al / Fe with respect to iron in goethite.
% By weight.

Subsequently, nickel chloride (NiCl ₂ · 6H ₂
O) An aqueous solution was added for 30 minutes, and after aging for 30 minutes, 1N ammonia water was added to adjust the slurry pH to 7.5, and the surface of the goethite was coated with a nickel compound. The amount of nickel chloride added was determined by changing the amount of nickel
/ Fe as 1.0% by weight. Thereafter, the mixture was kept for 1 hour, filtered, washed with water and dried.

(4) Production of metal magnetic powder Next, 100 g of the dried cake was placed in a muffle furnace in air.
Calcination was performed at 0 ° C. for 2 hours to obtain α-Fe ₂ O ₃ . Then, α-Fe
50 g of ₂ O ₃ is fed into a stainless steel vertical fixed-bed reduction reactor (inner diameter: 4
3 mmφ, height: 500 mm) and reduced under a hydrogen stream at a linear velocity of about 10 cm / sec at 425 ° C until the dew point of the exhaust gas became -20 ° C. The time required for the reduction was 185 minutes. The obtained reduced product was cooled in a nitrogen stream and then immersed in toluene, and then the toluene was gradually evaporated at room temperature to obtain a metal magnetic powder (Sample A) of the present invention.

Example 2 A metal magnetic powder of the present invention (sample B) was obtained in the same manner as in Example 1, except that the amount of sodium orthosilicate was changed to 2.0% by weight.

Example 3 In Example 1, the addition amount of sodium orthosilicate was 3.0% by weight, and the addition amount of aluminum chloride was
The same treatment was carried out except that the content was changed to 3.0% by weight to obtain a metal magnetic powder (sample C) of the present invention.

Comparative Example 1 In Example 1, sodium orthosilicate was not added during the growth reaction of the goethite nucleus crystal, and after coating the aluminum hydrated oxide, an aqueous sodium orthosilicate solution was added.
Minutes, aging for 30 minutes, then adding 1N diluted sulfuric acid to adjust the slurry pH to 7.5 in about 2 hours, and then adding an aqueous nickel chloride solution to prepare silicon-coated goethite, A metal magnetic powder (sample D) was obtained.

Comparative Example 2 In Example 2, sodium orthosilicate was not added during the growth reaction of the goethite nucleus crystal, and after coating the aluminum hydrated oxide, an aqueous solution of sodium orthosilicate was added.
Minutes, aging for 30 minutes, then adding 1N diluted sulfuric acid to adjust the slurry pH to 7.5 in about 2 hours, and then adding an aqueous nickel chloride solution to prepare silicon-coated goethite, A metal magnetic powder (sample E) was obtained.

Comparative Example 3 In Example 3, sodium orthosilicate was not added during the growth reaction of the goethite nucleus crystal, and after coating the aluminum hydrated oxide, an aqueous solution of sodium orthosilicate was added.
Minutes, aging for 30 minutes, then adding 1N diluted sulfuric acid to adjust the slurry pH to 7.5 in about 2 hours, and then adding an aqueous nickel chloride solution to prepare silicon-coated goethite, A metal magnetic powder (sample F) was obtained.

The magnetic properties of the thus obtained metal magnetic powder sample were measured by a conventional method. Further, in order to evaluate the oxidation stability, the sample powder was left for 1 week in an environment of a temperature of 60 ° C. and a relative humidity of 80%, and the change with time of the accelerated σs was measured, and the deterioration rate of the saturation magnetization Δσs (%) Was determined by the following equation.

(Where σs ⁰ is σs before aging, σs ¹ is σs after aging
Further, using the sample powder, a magnetic paint having the following composition was prepared, and then applied so as to have a dry film thickness of 10 μm, followed by orientation treatment and drying. It was measured by an ordinary method.

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 properties, that is, coercive force (Hc: Oe), saturation magnetization ( s: emu / g), saturation magnetic flux density (Bm: Gauss), squareness ratio (Rs, SQ), orientation ratio (OR), and switching field distribution (SF)
D) was measured, and further, 60-60 ° gloss was measured with a gloss meter. The results are shown in the table.

[Effects of the Invention] The metal magnetic powder obtained by the method of the present invention has excellent magnetic properties, is also improved in stability in air, and the deterioration with time of the magnetic properties is improved. By this method, it is also possible to obtain ultrafine metal magnetic powder having a major axis diameter of 0.2 μm or less and a specific surface area of 50 m ² / g or more.

Continuation of the front page (72) Inventor Tetsuji Fujioka 1 Ishiharacho, Yokkaichi-shi, Mie Pref. 59-41453 (JP, A) JP-B 61-14202 (JP, B2)

Claims (2)

(57) [Claims] 1. A reaction for obtaining goethite by partially neutralizing and oxidizing an aqueous ferrous salt solution to form goethite nuclei, and then oxidizing the solution while neutralizing the solution with an alkali agent to grow the nuclei. A method of producing a metal magnetic powder for a magnetic recording material, wherein the growth reaction of the nucleus crystal is carried out in the presence of a silicon compound, and then the surface of the goethite particles is coated with an aluminum compound and then reduced. 2. The method for producing a metal magnetic powder for a magnetic recording material according to claim 1, wherein said goethite is baked before or after coating with an aluminum compound.