JPS5864222A - Manufacture of magnetic iron oxide powder containing cobalt - Google Patents

Abstract

PURPOSE:To considerably increase the coercive force of magnetic iron oxide powder contg. a phosphorus component in the surface by depositing a cobalt compound on the powder after treating the powder with an aqueous medium. CONSTITUTION:Magnetic iron oxide powder contg. a phosphorus component in the surface is treated with an acidic or alkaline liq. medium contg. water, alcohol, aqueous acetone or the like as a solvent to liberate and remove the P component as a soluble salt. The acid or alkali concn. of the medium is adjusted to about 0.05-1N, and >= about 35wt% as P of the phosphorous component is removed. The treated particles are dispersed in an aqueous cobalt compound soln., and by adding an aqueous alkali soln. to the dispersion, the cobalt compound is deposited on the particles. Cobalt sulfate, cobalt acetate or the like is used as the cobalt compound, and in case of the cobalt compound alone, the cobalt compound is deposited by about 0.5-10% as Co basing on the total amount of Fe in the particles.

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 excellent fidelity in the high frequency range, and has recently been widely used in the tubes of magnetic recording media such as video tapes.

Various methods are known for incorporating cobalt into magnetic iron oxide powder, but usually a cobalt-containing compound is deposited on the particle surface of magnetic iron oxide powder, and the deposit is further grown into crystals. The magnetic iron oxide powder used as the substrate on which the cobalt compound is applied is usually obtained by heat-treating acicular hydrated iron oxide obtained by a wet method, and then dehydrating it.
．． Terre-FezQs and then reduce and'es
04. It is further oxidized to r-FezOs, or a bertolide compound (FeOx 1.s
a<x<1.55') is used. In order to suppress the generation of branched particles due to sintering between particles, the formation of bulky pores, and the growth of coarse particles during the heat treatment process, these materials are usually used as materials in the preceding stage of heat treatment 6. Phosphorous compounds are added to certain acicular hydrated iron oxides and α-Felon. Therefore, the particle surface of the magnetic iron oxide powder obtained by adding these phosphorus compounds and then heat-treating the particles usually contains 0.1 to 0.8 F of phosphorus on a P-equivalent weight basis.

On the other hand, in recent years there has been a significant demand for higher densities in magnetic recording media, and in conjunction with this, there has been an even stronger demand for improved performance of cobalt-containing magnetic iron oxides. As a result of various studies on improving the performance of cobalt-containing magnetic iron oxide, the present inventors found that when a cobalt compound is attached to magnetic iron oxide particles (hereinafter referred to as precursor) containing phosphorus on the surface (:

The precursor is previously treated with an aqueous medium to liberate the phosphorus present on the particle surface of the precursor as a soluble salt,
It is known that when a part or all of the cobalt compound is removed and then a cobalt compound is applied, the improvement in magnetic properties such as coercive force due to the adhesion of the cobalt compound is significantly large.
This completes the present invention. That is, the present invention has 1
This is a method for producing cobalt-containing magnetic iron oxide powder, which comprises treating magnetic iron oxide particles containing phosphorus on the particle surface with an aqueous medium and then depositing a cobalt compound on the particle surface.

In the present invention, when cobalt is deposited as a precursor of magnetic iron oxide particles containing phosphorus, comparison! By pre-treating the precursor with an aqueous medium in a simple and simple operation, magnetic oxidation with excellent magnetic properties such as coercive force can be achieved without impairing the thermal and mechanical stability of magnetic iron oxide-based magnetic recording media. It is a method that can produce iron powder, and is a very industrially difficult method. Although the reason for the improvement of the present invention is not clear, a film of a phosphorus compound is formed on the surface of the precursor particle, and this film is removed from the surface of the particle by leaching with an aqueous medium. The cobalt compound is more easily adhered to the base particles evenly and firmly, and the magnetic iron oxide particles of the base and their particle surfaces are released as It is speculated that this is because the synergistic effect of the magnetic properties with the cobalt adhesion layer is more effectively brought about.

The magnetic iron oxide particles used as a precursor for depositing cobalt compounds in the method of the present invention include acicular hydrated iron oxides (α, β, r -FeOOH) or α-Fetus, which is heated and dehydrated, coated with a phosphorus compound and then heated and reduced to res Oa, or further heated and oxidized.

r-Ve! om, or the intermediate oxide hel & todride PeOx (1,88(X < 1
．． 56) etc.

In the method of the present invention, the precursor can be treated with an aqueous medium by various methods, but 11)
For example, using water, aqueous alcohol, acetone, etc. as a solvent,
They can be treated with acidic or alkaline media. Note that the treatment with these media can be carried out in multiple stages by combining them, but in the case of treatment with an alkaline medium, it is preferable to perform the treatment with an acidic medium next. (
2) The concentration of acid or alkali in the aqueous medium is 1 usually 0.0
If the concentration is too low than the above range, the desired effect cannot be obtained, and if it is too high, it is not economically advantageous and the magnetic iron oxide grains are □The particles may be partially dissolved and the particle shape may be impaired.

■Acids that can be used include various inorganic acids, organic acids, and their salts.11 Usually, for example, hydrochloric acid, sulfur #II,
Hydrofluoric acid, nitric acid, ferrous chloride, aluminum sulfate, and the like can be used alone or in combination. Examples of the alkali include hydroxides, carbonates, and ammonium compounds of alkali metals such as cypress, alkaline earth metals, and usually, for example, hydroxide.

Potassium hydroxide, calcium hydroxide, sodium carbonate,
Potassium carbonate and the like can be used alone or in combination.

141 This treatment can be carried out by forming a fixed bed or fluidized bed of the precursor powder and passing the aqueous medium through it, even if the magnetic iron oxide powder as a precursor is stirred and immersed in an aqueous medium. You may. In any case, it is necessary to liberate the phosphorus compound present on the surface of the precursor particles from the surface as a soluble salt, and remove some or all of it from the aqueous medium system. After the aqueous dispersion has been thoroughly leached with a medium, it is filtered and preferably washed with water so that the phosphorus content present on the surface of the precursor is at least 85%, preferably at least 50%, particularly preferably at least 60%. It is preferable that the particles have been removed from the surface of the particles.

In the method of the present invention, a cobalt compound is deposited on the magnetic iron oxide base particles (hereinafter referred to as base particles) that have been treated with the aqueous medium (2).This can be done by various methods.

For example, (1) a method in which base particles are dispersed in an aqueous cobalt compound solution and an aqueous alkali solution is added thereto.

■ A method of dispersing the base particles in a mixed solution of a cobalt compound and alkaline water SO, ■ A method of dispersing the base particles in water and then adding a nicobalt aqueous solution and an aqueous alkali solution, (4) A method of dispersing the base particles in an alkaline aqueous solution. There are methods such as dispersing the +51 base particles in an aqueous cobalt compound solution and adding a cobalt compound aqueous solution thereto, and dispersing the +51 base particles in a cobalt compound aqueous solution and dropping this dispersion into an alkaline aqueous solution. can be applied simultaneously with the cobalt compound or sequentially as appropriate. In any case, an equivalent amount or more than an equivalent amount of the alkali-added metal compound such as cobalt is added to neutralize the compound, and the reaction product thereof is deposited on the surface of the base particle. After the reaction is complete, the deposited slurry is filtered, washed, dried and, if necessary, subjected to a conventional heat treatment such as 150-800℃ under a non-oxidizing atmosphere or an oxidizing atmosphere.
Heated at 0°C.

The cobalt compounds used in the method of the present invention include:
Cobalt inorganic or organic salts include cobalt sulfate, cobalt chloride, cobalt acetate, and the like. When a metal compound other than cobalt is deposited in combination with a cobalt compound, for example, ferrous sulfate, ferrous chloride, ferrous manganese sulfate, ferrous manganese chloride, etc. can be used in combination. What are the amounts of these compounds added?

Usually, when a cobalt compound is used alone, the amount of Co is 0.5 to 10% based on the total amount of Fa in the base particles, and when a combination of a cobalt compound and a ferrous compound is used, the former Co 05~lOs, the latter as I? It is appropriate to set e to 1 to 20.

Next, the present invention will be explained with reference to Examples and Comparative Examples.

-1, Preparation of precursor +1) Add a sodium hydroxide aqueous solution to a 1 mol/l sulfuric acid first needle aqueous solution and air oxidize the solution at a temperature of 88°C to obtain acicular hydrated ferric oxide particles from the reaction mother liquor with a pH of 7. (α−
Fe00H) was generated. After filtering and washing with water, a predetermined amount of (or)9-acid (P for α-Fe00H)
(Fesσ
I got 0. (Sample A: 0.85% based on P equivalent weight)■
) Sample A was heat treated in air at 2.50℃ for 2 hours.
- Reoxidized to Fa x Os. (Sample B; 0.8z better on P conversion weight basis) +31 A-Fe00H of (1) above was heated to 2
After heating and dehydrating for a period of time to obtain α-Fe00H, a predetermined amount of orthophosphoric acid (P for α-Fe and Os) was added to the aqueous slurry.
0.27% on a converted weight basis), α-Fe*Os
Particles were given #Ik1 0 and then 41 in a hydrogen gas atmosphere.
It was heat-treated at 0°C for 2 hours to reduce, and then heat-treated at 250°C for 3 hours in air to reoxidize to obtain γ-Fat (Js. (Sample C: 0.27% based on P equivalent weight) )4)
To α-Fe00H of the above (υ), add orthophosphoric acid equivalent to O, S* on a P-equivalent weight basis to make the phosphorus content a
-re Adsorbed onto OOH particles. Is this one mentioned above? In the same manner as in the case of
esOs powder was obtained. (Sample D: P conversion weight standard 0.6
7qb) 151 The α-Pests of (1) above were reduced at 850°C for 2 hours in a hydrogen gas atmosphere without adding orthophosphoric acid, and further 1: Oxidized in air at 250°C for 2 hours to form 1-F.
Got @gos. (Sample E: 0.(1
) 2. Cobalt deposition method (1) Magnetic iron oxide powder (precursor) of samples A-H was
The wet cake that has been immersed in a predetermined aqueous medium for a predetermined time, filtered and washed with water is made into an aqueous slurry of l 0011/I,
A 1 mol/l cobalt sulfate aqueous solution 60- and a 1 mol/l ferrous sulfate aqueous solution 185- are added to the slurry, and then a 5 mol/l 9ium hydroxide aqueous solution 8Q Oli is added.
The reaction was carried out at 25°C in an inert gas atmosphere by adding t, and the reaction solution was then aged in that state for 10 hours.
It was filtered, washed with water, and then dried at 110°C for 10 hours.

■ In the above B-111, 1 mol/! in place of the ferrous sulfate aqueous solution. The same treatment was carried out except that 851 Lt of 111 manganese sulfate water solution was added.

Example 1 Magnetic iron oxide powder (precursor) of Sample B was suspended in a 0.5N slurry in an aqueous hydrochloric acid solution with a constant concentration of 1001/l/l, and immersed at 2.5°C for 5 hours with stirring. After that, the slurry is filtered, washed with water, and then the above! -(A deposition treatment was performed according to method 11 to obtain the desired magnetic iron oxide powder.

Example (1) The desired cobalt-containing magnetic iron oxide powder was obtained in the same manner as in Example 1, except for using a sulfuric acid aqueous solution.

Example 8 The desired cobalt-containing magnetic iron oxide powder was obtained in the same manner as in Example 1, except that a 0.5 normal concentration hydrofluoric acid aqueous solution was used as the aqueous medium. .

EXAMPLE The desired cobalt-containing magnetic iron oxide powder was obtained in the same manner as in Example 1, except that a 0.5N aqueous sodium hydroxide solution was used as the aqueous medium.

Example 5 Example 1 except that an aqueous solution of dichloride having a concentration of 0.5N was used as the aqueous liquid medium in Example 1 (:
The desired magnetic iron oxide powder was obtained in the same manner as in the case of .

Example 6 In Example 1, the sample was immersed in an aqueous sodium hydroxide solution with a normal concentration of O2 for 5 hours, and then treated with an aqueous medium.
．． The desired magnetic iron oxide powder was obtained by carrying out C2 in the same manner as in Example 1, except that it was immersed in a 1N sulfuric acid aqueous solution for 10 hours.

Example? In Example 1, sample man (P
The desired cobalt-containing magnetic iron oxide powder was obtained in the same manner as in Example 1 except that est4) was used.

Example 8 Sample C (γ
The desired cobalt-containing magnetic iron oxide powder was obtained in the same manner as in Example 1, except that -FewOs) was used.

Example 9 Sample D (
The desired cobalt-containing magnetic iron oxide powder was obtained in the same manner as in Example 1 except that y-Peso was used.

Example 10 The desired cobalt-containing magnetic iron oxide powder was obtained in the same manner as in Example 1, except that the deposition treatment was carried out in accordance with the deposition method 2-111.

Comparative Example 1 The cobalt deposition method 2-(
A cobalt-containing magnetic iron oxide powder was obtained by the deposition treatment according to B.

Comparative Example 2 Sample B as a magnetic iron oxide precursor was coated according to the cobalt deposition method 2-1 above without being treated with an aqueous medium to obtain a cobalt-containing magnetic iron oxide powder.

The coercive force (Hc) and thermal properties (Tp) of the magnetic iron oxide powders obtained in the above Examples and Comparative Examples were determined by conventional methods.
were measured, and a magnetic paint was prepared using a proprietary composition.

Magnetic iron oxide powder 100 parts by weight Vinegar-vinyl chloride copolymer-fat 10.5# Soybean resin
1.6# Diocdelphthalate 4
1 Surfactant 4 #Methyl ether ketone 84 l toluene
Each of the 98 # magnetic paints was coated on a polyethylene film using a conventional method and subjected to orientation treatment to obtain a magnetic recording medium having a film thickness of 8 μm. The coercive force (Hc) of these magnetic recordings is determined by the usual method.

The squareness ratio (Br/Bm) and orientation ratio (0 liters) were adjusted, and the dephosphorization rate (the content of P before and after treatment with an aqueous medium) was determined by chemical analysis. These results are shown in Table 1.Thermal characteristics refer to the temperature dependence of coercive force, and the value expressed as (coercive force at 125°C) + (coercive force at room temperature) x 100 (
work).

As is clear from the results in Table 1, according to the method of the present invention,
It is possible to increase the coercive force f of magnetic iron oxide powder by adhering the conorct compound without impairing its thermal properties, and the magnetic tape's rectangular piece and orientation ratio are also excellent. I understand that there is something.

Patent applicant: Ishihara Sangyo Co., Ltd.

Claims (1)

[Claims] A method for producing cobalt-containing magnetic iron oxide powder, which comprises treating magnetic iron oxide particles containing phosphorus on the surface of the particles with an aqueous medium and then depositing a cobalt compound thereon.