JPS5939728A - 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 alkali medium under heating and pressure and by 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 alkali medium such as NaOH having 0.005- 3mol/l concn. It is treated at 10-105 deg.C under 1.01-10kg/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 such as cobalt acetate, and after adding an alkali soln., the powder is treated in a nonoxidizing atmosphere for 0.1-10hr to deposit Co by 0.5-10wt% of the total amount of Fe in the iron oxide. The resulting powder is optionally subjected to wet heat treatment by heating to 100-250 deg.C in an autoclave, and it is dried.

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 particle for magnetic recording media.

The cobalt-containing magnetic iron oxide powder has a high coercive force, and the magnetic tape obtained using it is suitable for high-density recording, and also has excellent sensitivity in the 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 cobalt-containing magnetic iron oxide has been increasingly desired to improve its performance. Ru.

The magnetic iron oxide substrate particles to which the cobalt compound is deposited are usually produced by a wet process. In the production process of Jin,
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 give gender.

The inventors of the present invention have been busy conducting various studies to improve the performance of the cobalt-containing magnetic iron oxide. (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 the development may vary. In addition, we discovered that the thermal stability of magnetic recording media is easily impaired.We first treated phosphorus-containing magnetic iron oxide in an alkaline medium under pressure at a temperature of 105°C or higher, and then treated it with a cobalt compound. How to apply fiIq 56
-211477 filed a patent application. After further investigation, it was found that even at temperatures below 105°C, the same effects were observed under pressure as at temperatures above 105°C, and the above problem was solved. This completes the present invention.

That is, the present invention provides a cobalt-containing magnetic oxide characterized in that at least a cobalt compound is coated on the edge of magnetic iron oxide powder containing phosphorus treated in an alkaline medium under pressure at a temperature of less than 105°C. This is a method for producing iron powder.

In the method of the present invention, the magnetic iron oxide powder serving as the base particles includes gu Fe* Os e P'e 304 and a bertolide compound (FeOx, 1.33<X<1
．． 55) etc. can be used. These magnetic iron oxides #′i,.

Usually its precursor, acicular hydrated iron oxide (a-0β, 6-
Fe00. ) When producing salmon in I), phosphorus is present in the mother liquor, or acicular hydrated iron oxide or O-f obtained by heating and dehydrating it.
;'etOB 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 treated with an alkaline medium. This treatment is usually advantageously carried out using a closed container, which may be filled with inert gas or air to maintain a predetermined pressure if necessary. As alkaline U liquid,
Hydroxides, carbonates, ammonium compounds of alkali metals, alkaline earth metals, etc.? Specifically, for example, an aqueous medium is used by dissolving an alkali such as sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, or potassium carbonate in a solvent such as water, aqueous alcohol, or aqueous acetone. be able to. The alkali concentration of this aqueous medium is usually 0.005=3 mol/l, preferably 0.01 to 2 mol/l. If this concentration is too high (υ) above the above range, the iron oxide powder may be partially dissolved, and if it is too low, the desired effect may not be obtained. The processing temperature is less than 105°C, usually from 10 to less than 105°C, preferably from 30 to less than 105°C. The inside of the processing system is kept under pressure, but the pressure in that case is usually 1.01~
10kg/Cm2, preferably 1.04-6 kg/c
m''. If the pressure is too high, problems will arise on the packaging, which is undesirable. The treatment time at 6?C is usually 0.5 to 10 hours.

In the present invention, treatment with an acidic medium is also carried out before and/or after the alkaline medium treatment, thereby increasing the processing speed and improving the magnetic properties, particularly the coercive force. In this case, it can be carried out using a dilute aqueous medium of one of various inorganic acids, organic acids or salts thereof. 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 sulfuric acid aluminum. Further, as the organic acid, for example, formic acid, acetic acid, oxalic acid, citric acid, etc. can be used. Treatment with acidic medium is usually 10~
It is preferable to conduct the reaction at 100°C, preferably 20 to 80°C, and in that case, the concentration of the acidic medium is usually 0.01 to 1 mol/l, preferably 0. 0.02 to 0.6 mol/l is suitable.

In the present invention, after the treatment with the aqueous medium, the magnetic iron oxide obtained is usually subjected to V filtration and water washing, and the resulting magnetic iron oxide is coated with at least a cobalt compound. The cobalt compounds to be used include inorganic or organic acid salts of cobalt, specifically cobalt sulfate, cobalt chloride, cobalt acetate, etc. In addition, compounds such as ferrous iron, manganese, zinc, chromium, and nickel can be deposited in combination with cobalt compounds.Specifically, for example, ferrous sulfate, ferrous chloride, manganous sulfate, etc. , manganous chloride, nickel chloride, zinc chloride, and the like can be used.

Various methods can be used to deposit the cobalt compound or other metal compounds. 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 mixture of a metal salt aqueous solution and an alkali solution; (3) A method of dispersing magnetic iron oxide in a mixture of a metal salt aqueous solution and an alkali solution; (4) A method of dispersing magnetic iron oxide in an aqueous metal salt solution and dropping this dispersion into an alkali solution; (5) A method of dispersing magnetic iron oxide in an aqueous metal salt solution and adding it to an aqueous alkali solution; There are methods such as dispersing iron in an alkali-13 aqueous solution and adding a metal salt aqueous solution thereto, and these methods can be adopted as appropriate. Further, at this time, the cobalt compound and other metal compounds can be applied simultaneously or sequentially as appropriate. Further, the alkaline solution is added to the metal salt in the dispersion in the same amount or in an equivalent amount or more to neutralize the metal salt and deposit the reaction products 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. This treatment time is usually about 0.1 to 10 hours.

In the case of a cobalt compound alone, the amount of the metal compound deposited is usually C compared to the total weight (weight basis) K of iron oxide.
0.5 to 10% as O, and for example, when depositing a combination of a cobalt compound and a ferrous compound, the former is
0.5 to 10% as O, 1 to 2% excluding the latter as Fe+
It is appropriate to set it to 0%. In addition, when a cobalt compound and a ferrous compound are treated together, the treatment effect of the alkaline medium can be made even more desirable.

The magnetic iron oxide slurry l- that has been subjected to the above-mentioned adhesion treatment can be further subjected to heat treatment as required. This heat treatment can be carried out by various methods, for example (
1) Heat the slurry in an autoclave at 100-250°C.
(2) A method in which the nuclear 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) The above-mentioned ( 2) Moist cake 60-25
There are methods such as heat treatment at 0℃ in the presence of water vapor, and (4) method of dry heat treatment at 100 to 300℃ after drying the wet cake of (2) above. This can be done by It is desirable to perform this heat treatment in a non-oxidizing atmosphere. However, when the heat treatment in the presence of water vapor as described in (3) above is performed, the treatment effect with the alkaline medium is even more desirable. be able to.

The cobalt-containing magnetic iron oxide obtained by the present method 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 coercive force and excellent thermal properties. It has excellent squareness ratio, orientation, saturation magnetic flux density, etc. Although the reason for the above-mentioned improvement in the present invention is not clear, the particle surface of the magnetic iron oxide powder before being coated with the cobalt compound is activated by treatment with an alkaline medium, and the cobalt compound is activated. It is surmised that it becomes easier to adhere more uniformly and firmly, and as a result, the above-mentioned magnetic properties are improved.

Example 1 A predetermined percentage of birophosphoric acid (α-1i'e
00H nucleus crystal precipitate (■) equivalent addition 1 = 02 Jugetsu Gradually add a sodium hydroxide aqueous solution containing a fixed amount (addition amount of P/a- to α-Fe00H precipitate: 20.2 times 19) and react with gas oxidation to approximately double the number of nuclei crystals. Made it grow.

After filtering and washing the reaction solution of the upper Si- with water, a predetermined amount of ol/(17-phosphoric acid (added amount in terms of P relative to t-Fe00H:
(1,3'5 M M,' N ) (L - Fe0
It was deposited on 0H. This material is dehydrated by the usual method (
650℃ in air), reduction (in hydrogen containing water vapor, 420℃)
℃) and reoxidation (in air at 280℃) to obtain γ-pe.
, O, (coercive force Qlc): 4100e, axial ratio (L/W
): 9, major axis length: 0.4~o, 5p, 1-Fe20
P content in ppm relative to SK, i: 0.73% by weight)
I got it.

This T-FexOs was suspended in a 1 mol/l aqueous sodium hydroxide solution to form a slurry of 100 g/73, and the slurry was placed in an autoclave. Fill this with crab gas and maintain the pressure at 4.8 kg/am2.
It was treated at ℃ for 3 hours. Thereafter, the slurry was filtered and washed with water to obtain M-Fe+Os. P content of this material (P conversion)
was 0.56 weight ♀1%, and the powder pickup truck was 100X.

1-Fe obtained as above C! On 100g
was dispersed in 1 liter of water to make a slurry, and while blowing KN into the liquid, 70 d of a 0.85 mol/l 'fAtWt copanototo aqueous solution and 125 d of a 1 mol/l sulfuric acid 8i' (-iron aqueous solution) were added, and then While stirring, 175 ml of a 10 mol/l sodium hydroxide aqueous solution was added, and the mixture was further stirred at a temperature of 30°C for 5 hours.Then, the slurry was washed with FA and water, and the resulting wet cake was placed in a separate container. After putting water into an autoclave, the system was replaced with N2 gas, sealed, and dried at 60°C for 15 hours in the atmosphere at 130°C to obtain the desired cobalt-containing magnetic iron oxide powder (A). Obtained.

Example 2゜The desired results were obtained in the same manner as in Example 1, except that the treatment with an alkaline medium in an autoclave was carried out at 50°C for 3 hours while maintaining the pressure at 5.5 kg/cm2. A cobalt-containing magnetic iron oxide powder (B) was obtained.

Example 3 In Example 1, the treatment with an alkaline medium in an autoclave was carried out for 3 hours while maintaining the pressure at 4.0 kgAm'.
The desired cobalt-containing magnetic iron oxide powder (C) was obtained in the same manner as in Example 1 except that the heating was carried out at 0° C. for 3 hours.

Example 4 The same procedure as in Example 1 was carried out except that the treatment with an alkaline medium in an autoclave was carried out at 100'C for 3 hours (the pressure at this time was 5.51 cg/cmt), Target cobalt-containing magnetic iron oxide powder CD
) was obtained.

Example 5 In Example 1, -Fe, O was added prior to treatment with an alkaline medium in an autoclave.

was suspended in a 0.08 mol/l sulfuric acid aqueous solution to give 100
The desired cobalt-containing magnetic iron oxide powder (E) was prepared in the same manner as in Example 1, except that the slurry was made into a slurry of 1.5 g /
I got it.

Example 6 - Filter the slurry after treatment with alkaline medium in the autoclave as in Example 1.

The product obtained by washing with water - F6. Os further 0.08
The desired cobalt-containing magnetic oxide was prepared in the same manner as in Example 1, except that it was suspended in a mol/l sulfuric acid aqueous solution to form a 100 g/J slurry, and immersed at 40°C under atmospheric pressure for 3 hours. Iron powder CF) was obtained.

Comparative Example In Example I, a magnetic iron oxide powder (G) containing balt was obtained in the same manner as in Example 1 except that the treatment with the alkaline medium was not performed.

The coercive forces of the above samples (A) to (G) were measured by a conventional method, and the results are shown in Table 1 below.

Further, for Samples (A) to (G)K, compositions were prepared according to the following proportions and kneaded in a ball mill to produce magnetic paints.

(1) Cobalt-containing magnetic iron oxide 10
0 parts by weight (2) Soybean lecithin
1 (3) Surfactant
4 “(4) Vinyl chloride vinyl acetate copolymer resin
15〃(5) Diocticif 4 rate
5 (6) Methyl ethyl ketone
111 〃(ka toluene
122 In the next step (A), each magnetic coating was applied to a polyester film using a conventional method, oriented and dried to produce a magnetic tape having a magnetic coating film of about 9μ. For each tape, the coercive force (H, c), squareness ratio (Br/Brn)
, orientation (OR), and saturation magnetic flux density (Bm). The results are shown in Table 1 below.

@Rice This value was determined by chemical analysis and is expressed as weight percent in terms of P.

As is clear from the results in Table 1 above, 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] Production of a cobalt-containing magnetic iron oxide powder, characterized in that the magnetic iron oxide powder containing phosphorus is treated in an alkaline medium under pressure at a temperature below 105°C, and then coated with at least a cobalt compound. Method.