JPS5939729A - Manufacture of magnetic iron oxide powder containing cobalt - Google Patents

Abstract

PURPOSE:To manufacture magnetic iron oxide powder contg. Co and having superior coercive force and thermal characteristics, by treating magnetic iron oxide powder contg. P in a soln. of an acid medium, treating it in a soln. of an alkali medium under heating and pressure, and depositing a Co compound on the powder. CONSTITUTION:Magnetic iron oxide powder such as gamma-Fe2O3 contg. 0.1-1wt% P is suspended in a soln. of an acid medium such as sulfuric acid having 0.01- 1mol/l concn. It is treated at 10-100 deg.C, separated by filtration, and washed. The powder is then suspended in a soln. of an alkali medium such as NaOH having 0.005-3mol/l concn. It is treated at 105-200 deg.C under 2.2-20kg/cm<2> pressure for 0.5-10hr, separated by filtration, and washed. This magnetic iron oxide powder is dispersed in an aqueous soln. of an inorg. or org. acid salt of Co, and after adding an alkali soln., the powder is treated at a temp. below the b.p. in a nonoxidizing atmosphere for 0.1-10hr to deposit the Co compound by 0.5-10wt% of the total amount of Fe in the iron oxide when expressed in terms of Co.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing cobalt-containing magnetic iron oxide powder useful as a magnetic material for magnetic recording media.

Cobalt-containing magnetic iron oxide powder has a high coercive force, and a magnetic tape obtained using it is suitable for high-density recording and has excellent sensitivity in a high frequency range. For this reason, it is widely used in the field of magnetic recording media such as audio and video, but in recent years there has been a significant demand for higher densities in magnetic recording media, and there is an even greater desire for improved performance of cobalt-containing magnetic iron oxide. .

The magnetic iron oxide substrate particles to which the cobalt compound is deposited are usually produced by a wet process. In this manufacturing process,
Phosphorous compounds are added during the generation of acicular hydrated iron oxide and during the subsequent heat treatment for dehydration, reduction, and oxidation to suppress particle shape deformation, sintering, and coarsening of particles caused by heat treatment, resulting in a highly acicular shape. It is common practice to use sex as sexual power.

In the process of conducting various studies on improving the performance of the above-mentioned cobalt-containing magnetic iron oxide, the present inventors discovered that (1) the improvement in magnetic properties due to the adhesion of a cobalt compound significantly affects the properties of the substrate particles to which it is adhered; (2) In particular, when magnetic iron oxide containing phosphorus is used as the base particle, it is difficult to sufficiently develop magnetic properties such as coercive force due to adhesion, and there are still many variations in the development. Moreover, they discovered that the thermal stability of magnetic recording media was easily impaired, and first treated phosphorus-containing magnetic iron oxide in an alkaline medium under pressure at a temperature of 105°C or higher, and then coated it with a cobalt compound. Patent application 1984-21 for how to wear
A patent application was filed as No. 1477. After further investigation, it was found that the magnetic properties were further improved by treatment with an acidic medium prior to treatment with an alkaline medium, and the above problems were found to be resolved. This completes the present invention.

That is, in the present invention, a magnetic iron oxide powder containing phosphorus is treated in an acidic medium, then treated in an alkaline medium under pressure at a temperature of 105° C. or higher, and then coated with a cobalt compound. This is a method for producing cobalt-containing magnetic iron oxide powder.

In the method of the present invention, the magnetic iron oxide powder serving as the base particles includes r-Fe, 03, Fe504, and bertolide compound (FeOx, 1.33<X<1.55).
etc. can be used. These magnetic iron oxides are
Usually its precursor, acicular hydrated iron oxide (α, β, γ-F
e00H) in which phosphorus was present in the mother liquor during production,
Acicular hydrated iron oxide or α-petos obtained by heating and dehydrating it
The iron oxide is coated with phosphorus, and usually contains 0.1 to 1% by weight of phosphorus in terms of P based on the weight of iron oxide.

In the present invention, the magnetic iron oxide powder containing phosphorus is first treated with an acid medium.

This treatment can be carried out in dilute aqueous media of various inorganic acids, organic acids or their salts. Examples of the inorganic acids that can be used include hydrochloric acid, sulfuric acid, hydrofluoric acid, and nitric acid, and examples of their salts include ferrous chloride and aluminum sulfate. Further, as the organic acid, for example, formic acid, acetic acid, oxalic acid, citric acid, etc. can be used. The treatment with the acidic medium is usually carried out preferably at a temperature of 10 to 100°C, preferably 20 to 80°C, and in that case, it may be carried out at atmospheric pressure or under increased pressure.

The concentration of the acidic medium is usually 0.01 to 1 mol/l, preferably 0.02 to 0.6 mol/l.

In the method of the present invention, after treatment with the acidic medium, the material is usually filtered and washed with water, and then treated with an alkaline medium. It is usually advantageous to carry out this process using a closed container;
If necessary, it may be filled with inert gas or air to maintain a predetermined pressure. Examples of the alkaline medium include hydroxides, carbonates, and ammonium compounds of alkali metals, alkaline earth metals, etc. (specifically, hydroxides), potassium hydroxide, calcium hydroxide, sodium carbonate, An aqueous medium obtained by dissolving an alkali such as potassium carbonate in a solvent such as water, aqueous alcohol, or aqueous acetone can be used. The alkaline concentration of this aqueous medium is usually from 0.00 to 3 mol/l, preferably from 0.01 to 2 mol/l.

If this concentration is too high, the iron oxide powder may be partially dissolved, and if it is too low, the desired effect may not be obtained.

The treatment temperature is 105°C or higher, usually 105-200°C, preferably 110-150°C. The inside of the processing system is kept under pressure, and the pressure in that case is usually 2.2 to 20 kg/
crn", preferably from 2.4 to 111 cg/w. If the pressure is too high, problems will occur on the equipment, which is undesirable. The treatment time is usually from 0.5 to 10 hours.

In the present invention, after the alkaline medium treatment, the magnetic iron oxide obtained is usually filtered and washed with water, and the resulting magnetic iron oxide is coated with at least a cobalt compound. Examples of the cobalt compound used include inorganic and organic acid salts of cobalt, and specific examples include cobalt sulfate, cobalt chloride, and cobalt acetate. Further, in addition to the cobalt compound, compounds such as ferrous iron, manganese, zinc, chromium, and nickel can be deposited in combination with the cobalt compound. Specifically, for example, ferrous sulfate, ferrous chloride, manganous sulfate, manganous chloride, ff1-nickel chloride, zinc chloride, etc. can be used.

Cobalt compounds and other metal compounds can be deposited by various methods. For example, (1) a metal salt aqueous solution of a compound to which magnetic iron oxide is adhered (
(2) A method of dispersing magnetic iron oxide in a mixed solution of a metal salt aqueous solution and an alkaline solution; (3) A method of dispersing magnetic iron oxide in a mixed solution of a metal salt aqueous solution and an alkaline solution; (4) A method of dispersing magnetic iron oxide in a metal salt aqueous solution and dropping this dispersion into an alkaline solution; (5) There are methods such as dispersing magnetic iron oxide in an alkaline aqueous solution and adding a metal salt aqueous solution to this.
These can be adopted as appropriate. Further, in this case, the cobalt compound and other metal compounds can be applied simultaneously or sequentially as appropriate. Further, the alkaline solution is added in an equivalent amount or more than an equivalent amount to the metal salt in the dispersion to neutralize the metal salt, and the reaction products thereof are deposited on the surface of the magnetic iron oxide particles. This deposition treatment is preferably carried out in a non-oxidizing atmosphere at a temperature below the boiling point. The treatment time is usually about 0.1 to 10 hours, and the amount of the metal compound deposited is usually 0.5 to 10 as C0 when a cobalt compound is used alone with respect to the total Fe amount (M amount basis) of iron oxide. %, or for example, when depositing a combination of a cobalt compound and a ferrous compound, the former is
6 and 0.5 to 10%, and the latter as Fe, 1 to 10%.
2° (1. The treatment effect of the medium can be made even more desirable.

The magnetic iron oxide slurry that has been subjected to the adhesion treatment can be further subjected to heat treatment as necessary. This heat treatment can be carried out by various methods, for example fl
) The slurry was heated at 100-250'C in an autoclave.
(2) A method in which the slurry is filtered and washed with water, and the resulting wet cake is dispersed in water again, and a slurry is wet-heat-treated at 100 to 250 °C in an autoclave; (3) a method in which the above-mentioned ( 2) moist cake 60~2
A method of heat treatment in the presence of steam at 50°C! There are other methods, such as drying the damp cake and then dry heating it at 100 to 100 °C, and these methods can be used alone or in combination. This heat treatment is preferably carried out under a non-oxidizing +i: atmosphere +214 atmosphere.

In addition, when performing the heat treatment in the presence of water vapor in the above (3), the treatment effect by the acidic medium and the alkaline medium can be -I-desired 4''L,v.

The cobalt-containing magnetic iron oxide obtained by the method of the present invention has excellent coercive force and thermal properties, as is clear from the examples below, and the magnetic recording medium obtained using this material also has excellent coercive force and squareness ratio. , excellent orientation, saturation magnetic flux density, etc.

In the present invention, although the reason for the improvement is not clear, the particle surface of the magnetic iron oxide powder before being coated with a cobalt compound is activated by treatment with an acidic medium and an alkaline medium, and the cobalt The compound is -)f
4. It is believed that this makes it easier to adhere uniformly and firmly, and as a result, the above-mentioned magnetic properties are improved.

Example A predetermined amount of birophosphoric acid (α-Fe00
) Addition amount in terms of P based on the i-nuclear crystal precipitate: 20.2% by weight
An aqueous solution of hydroxide (containing di) was added, followed by air oxidation to obtain α-Fe00) i nucleus crystals, and a predetermined amount of orthophosphoric acid (added in terms of P to the α-Fe00H precipitate frl: : 0. Gradually add a sodium hydroxide aqueous solution containing 2% by weight, react with air oxidation,
Nucleic crystals were grown approximately twice as much.

After the above reaction solution was filtered and washed with water, a predetermined amount of orthophosphoric acid (amount added in terms of P relative to α-Fe00H: 0.35
% by weight) was deposited on cf-Fe00H. This material was dehydrated (in air + 4-1650"C), reduced (in hydrogen containing water vapor, 420Y;), and reoxidized (in air at 280"C) using the usual methods to obtain r -Fetus (coercive force (Hc ): 4100 e-.

Axial ratio (L/W): 9, major axis length: 0.4-0.5μ, r
−Fe2O, P ￟ chest, P containing j vs. 20, 7
3% by weight).

This γ-Fe20S was suspended in a 0.08 mol/l sulfuric acid aqueous solution to make a 100 g/l slurry, which was immersed at 40°C for 3 hours under atmospheric pressure, filtered through p-filtration, and washed with water. -Fe20s was suspended in a 0.5 mol/l aqueous sodium hydroxide solution to form a 100 g slurry, and the slurry was placed in an autoclave. While filling this with elemental gas and maintaining the pressure at 2.4 kg/tyn2,
It was treated at 10°C for 2 hours. After this, Sura IJ-'t 7j
After filtering and washing with water, γ-Fe2O3 was obtained. The P-containing -Ml (P-exchanged rIi) of this product was 0.44 kg, and the powder yield was 98%.

100 g of r-Fe203 obtained as above was dispersed in water 11 to make a slurry, and N gas was blown into the liquid to form a slurry of 70 tnl of 0.85 mol/lCv sulfurized cobalt aqueous solution and 1 mol/l of starch acid. Ferrous aqueous solution 125ml
and then 10 mol/l hydroxide with stirring)
Add 175 ml of IJum water bath, and then add 175 ml of IJum water bath and
The slurry was then filtered through D' and washed with water, and the resulting wet cake was placed in an autoclave together with water in a separate container.
After exchanging the inside of the system with N2 gas, it was sealed and heat treated at 13°C for 6 hours in the presence of steam. 60 in the atmosphere after treatment
It was dried at ℃ for 15 hours to obtain the desired cobalt-containing magnetic iron oxide powder (5).

Comparative Example 1 Cobalt-containing magnetic iron oxide powder (I3) was prepared at 14J in the same manner as in the above Example except that the treatment with the acidic medium was not performed.

Comparative Example 2 Cobalt-containing magnetic iron oxide powder (C1 was replaced by I4I) in the same manner as in the example except that the treatment with the acidic medium and the alkaline medium was not performed.

The coercive forces of Samples (4) to (C) were measured using a conventional method, and the results are shown in Table 1 below.

Further, for Samples (4) to (C), mixtures were prepared according to the formulation ratios shown below and kneaded in a ball mill to produce magnetic paints.

(1) Cobalt-containing magnetic iron oxide 100 parts by weight (
2) Soy lecithin II (3) Surfactant 4 (4) Salt pea vinyl acetate copolymer resin 15 (5) Dioctyl phthalate 5 (6) Methyl ethyl ketone 1
11〃(ka toluene 1
22 Next, each magnetic paint was applied to a polyester film using a conventional method, and the oriented edges were dried to a thickness of about 9 μm.
A magnetic tape with a magnetic coating film was prepared. For each tape, coercive force (He), squareness ratio (Br/Bm), orientation (OR), and saturation magnetic flux density (Bm) were measured using conventional methods. The results are shown in Table 1.

Table 1 Examples of sushi (note) - * - This value was determined by chemical analysis and is expressed in P conversion n lightning quantity chi.

As is clear from the results in Table 1 above, it can be seen that the cobalt-containing magnetic iron oxide powder obtained by the method of the present invention has improved magnetic properties, particularly coercive force.

Patent applicant: Ishihara Sangyo Co., Ltd.

Claims (1)

[Claims] Cobalt, characterized in that magnetic iron oxide powder containing phosphorus is treated in an acidic medium, then treated in an alkaline medium under pressure at a temperature of 105° C. or higher, and then coated with at least a cobalt compound. A method for producing magnetic iron oxide powder.