JPS638224A - Production of ferro magnetic powder for magnetic recording - Google Patents

Abstract

PURPOSE:To produce magnetic powder having high coercive force, high saturation magnetization and small reduction in specific surface area, by dispersing needle-like gamma-Fe2O3 particles into an alkali aqueous solution and successively adding an aqueous solution of sodium citrate and an alkaline earth metallic salt and an aqueous solution of a Co salt and a ferrous salt to the dispersion. CONSTITUTION:Needle-like gamma-Fe2O3 particles as nuclei are dispersed into an aqueous solution of an alkali to give 1.6-3.0mol/l OH<-> ion concentration. To the dispersion is added an aqueous solution containing sodium citrate and an alkaline earth metallic salt. After the temperature of the dispersion is raised, an aqueous solution containing a Co salt and a ferrous salt is added to the dispersion, which is stirred in a nonoxidizing atmosphere at <= the boiling point of the dispersion to form Co-containing iron oxide layer on the surface of the needle-like gamma-Fe2O3 particles. By this method Co-containing iron oxide magnetic powder having improved dispersibility for high-quality magnetic recording can be readily produced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to the production of iron oxide ferromagnetic powder, and more particularly to a method of producing cobalt-containing iron oxide ferromagnetic powder that allows high recording density.

(Conventional technology and problems to be solved) Conventionally,
Acicular γ-Fe203 particles, which have a high coercive force due to shape anisotropy, have been used as magnetic powder for magnetic recording.
In recent years, there has been a demand for magnetic powder for magnetic recording with a high coercive force that enables even higher recording densities, and research on iron oxide magnetic powder containing cobalt is being actively conducted.

By the way, various methods for producing cobalt-containing γ-Fe2O3 particles have been proposed up to now, but one of the most useful methods involves dispersing acicular γ-Fe203 particles in an alkaline solution.

To this, alkaline earth metal salts such as strontium salts, cobalt salts, and ferrous salts are added, and cobalt-containing γ-Fe,
There is a method of using 03 particles.

Cobalt-containing γ-Fe obtained by this method, 03
The particles have cobalt-containing iron oxide dust formed on their surfaces, which increases the coercive force and saturation magnetization per unit weight, but they have poor dispersibility, poor coercive force distribution, and a large specific surface area. The disadvantage was that it decreased.

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned prior art, and to produce acicular γ-Fez○ with high coercive force, high saturation magnetization, and nucleated crystals.
, the specific surface area decreases less than .

The object of the present invention is to provide a method for producing cobalt-containing iron oxide ferromagnetic powder that has a uniform coercive force distribution and excellent dispersibility.

(Means for Solving the Problems) In order to achieve the above object, the present inventor investigated and analyzed the causes of the drawbacks of the conventional method for producing cobalt-containing iron oxide magnetic powder, and found that the conventional method:
Acicular γ-Fe2O3 particles are first dispersed in an alkaline solution, and then an alkaline earth metal salt, a cobalt salt and a first
It is thought that the iron salt was added to form an iron oxide layer containing ferrous ions (F62+) on the surface of the cobalt-containing two-Fe201 particles, thereby suppressing the decrease in saturation magnetization σS per unit weight. However, although increasing the amount of ferrous ions added increases the above σS of cobalt-containing γ-Fe203, the coercive force decreases considerably compared to before addition of ferrous ions, and the specific surface area also decreases compared to the starting material. Fe. It was found that the coercive force was considerably reduced compared to No. 03, and it was difficult to obtain the desired high coercive force ferromagnetic powder.

Therefore, 1. the present inventor has high coercive force, high saturation magnetization, and
The result of intensive research to develop a magnetic powder with less reduction in specific surface area than nucleated acicular γ-Fe, ○, uniform coercive force distribution, and excellent dispersibility.

By adding sodium citrate and alkaline earth metal salt to the acicular γ-Fe2O3 particles, and then adding cobalt salt and ferrous salt, the decrease in coercive force and specific surface area due to the addition of ferrous ions can be suppressed. The present invention was made based on the discovery that it is possible to obtain the desired magnetic powder.

That is, the present invention provides acicular γ-Fe2O3 particles with OH-
``Dispersed in an aqueous solution containing an amount of alkali such that the ion concentration is 166 to 3.0 mol/l, added with sodium citrate and an alkaline earth metal salt, then cobalt salt and ferrous iron. By adding an aqueous solution containing a salt and treating it at a temperature below the boiling point of the dispersion in a non-oxidizing atmosphere, iron oxide dust containing cobalt is formed on the surface of the acicular γ-Fe, 03 particles. The gist of this paper is a method for producing ferromagnetic powder for magnetic recording.

The present invention will be explained in detail below based on examples.

As mentioned above, in short, the greatest feature of the present invention is that by adding sodium citrate and alkaline earth metal salt, the reduction in coercive force and specific surface area is suppressed.
This makes it possible to obtain a cobalt-containing iron oxide magnetic powder with particularly high coercive force even with a smaller amount of cobalt added than in conventional methods.

These treatments are performed at a temperature below the boiling point, but as the treatment temperature becomes lower, a longer treatment time becomes necessary, so it is preferable to perform the treatment at a temperature as high as possible near the boiling point.

In the present invention, first, the acicular γ-Fe20° particles that serve as the nucleus are sufficiently dispersed in an aqueous solution containing an alkali, and at that time, the amount of alkali is such that the OH-ion concentration is 1.6 to 3.0.
It is necessary to add the amount such that the amount becomes mol/l. As the alkali, sodium hydroxide, potassium hydroxide, lithium hydroxide, etc. can be used. If the amount of alkali added is outside the above range, it will be difficult to expect the above effects.

Next, after heating the above dispersion to an appropriate temperature (e.g., 80°C), sodium citrate was added, and the temperature was further raised (e.g., 90°C).
℃), add an aqueous solution containing an alkaline earth metal salt, further raise the temperature (e.g., 100°C), add an aqueous solution containing a cobalt salt, and stir thoroughly for the required time (e.g., 7 hours). In addition to strontium chloride, barium chloride, calcium chloride, etc. can be used as alkaline earth metal salts.
Further, as the cobalt salt, cobalt chloride, cobalt sulfate, etc. can be used.

Then, an aqueous solution containing ferrous salt is added and the required time (e.g.
Stir for 1 hour). Note that as the ferrous salt, ferrous chloride, ferrous sulfate, etc. can be used.

Note that these treatments, especially before and after adding the ferrous salt, are performed in a non-oxidizing atmosphere because it is necessary to prevent air from entering.

According to such a process, acicular γ-Fe20. An iron oxide layer containing cobalt is formed on the surface of the core crystals, has high saturation magnetization, high coercive force, and uniform coercive force distribution.
Moreover, a cobalt-containing iron oxide magnetic powder with less decrease in specific surface area and excellent monodispersity can be obtained.

Next, one embodiment of the present invention will be described. It goes without saying that the present invention is not limited to this embodiment.

(Example) 4000 g of acicular γ-Fe203 powder (Kani 36008, saturation magnetization: 74 emu/g, specific surface area: 34 m"/g) produced by a conventional method was added to 24 Q water at 320 g.
After adding 0g of NaOH to a caustic soda aqueous solution and thoroughly dispersing it, the temperature of this dispersion was raised to 80°C, 100g of sodium citrate was added, and the temperature was further raised to 90°C. Add 660 mQ of an aqueous solution containing 60.8 g of strontium chloride, add 2Q of an aqueous solution containing 333 g of cobalt chloride at 100"C, continue stirring at this temperature while preventing air incorporation as much as possible, and after 1 hour. , about 30m after 3 hours, 5 hours and 7 hours, respectively.
A sample of Q was taken. After 7 hours of sample collection, the first chloride
An aqueous solution containing 569 g of iron at 2° C. was added and stirred for 1 hour to complete the reaction. Each sample collected and the slurry after the reaction were thoroughly washed with water, dehydrated, and dried. The magnetic properties of the obtained sample were measured using a vibrating sample magnetometer (Model VSM-3S, manufactured by Toei Kogyo) in an external magnetic field of 10 KOe, and the magnetic properties were measured using an automatic specific surface area measuring device (Model 2200, manufactured by Micromeritics). Surface area was measured. The results are shown in Tables 1 and 2.
It is shown in the table, FIGS. 1 and 2.

The cobalt-containing iron oxide magnetic powder obtained after 8 hours of reaction treatment has a coercive force He of 6670 s and a saturation magnetization σ
The S content was 78 emu/g and the specific surface area was 32 m 2 /g.

(Comparative Example) As a comparative example, a cobalt-containing iron oxide magnetic powder was produced in exactly the same manner as in the above example except that the treatment was performed without adding the sodium citrate used in the above example, and the powder was obtained by sampling in the same manner. The magnetic properties and specific surface area of each sample were measured. The results are also shown in Table 1, Table 2, and Figures 1 and 2.

The cobalt-containing iron oxide magnetic powder obtained after 8 hours of reaction treatment as in 2 has a coercive force He of 6530e and a saturation magnetism σ
The S content was 77 emu/g and the specific surface area was 29 m27 g.

Using the cobalt-containing iron oxide magnetic powder obtained in the above Examples and Comparative Examples, the components of the following composition were added to it, and approximately 48
The magnetic paint was prepared by kneading it in a ball mill for an hour.

Cobalt-containing iron oxide magnetic powder...75 parts by weight Vinyl chloride-vinyl acetate copolymer...19rr Dioctyl phthalate...4 Lecithin
... 2 Toluene
...100++ Methyl isobutyl ketone
...100 This magnetic paint was coated on a polyester film with a thickness of 12 μm so that the dry thickness was about 6 μm, and dried while applying magnetic field orientation to produce a magnetic tape. The squareness ratio (Br/8m) and reversal magnetic field distribution (S F D) of each of the obtained magnetic tapes were measured, and the results shown in Table 3 were obtained.

Table 3 As is clear from Table 3, the magnetic tape manufactured using the cobalt-containing iron oxide magnetic powder obtained by the method of the present invention has lower squareness ratio and reversal magnetic field distribution than the comparative example. Are better. It can also be seen that the coercive force distribution is uniform, the dispersibility is excellent, and the specific surface area decreases little.

(Effects of the Invention) As detailed above, according to the present invention, acicular γ-Fe20. A cobalt-containing iron oxide magnetic powder with less decrease in specific surface area, uniform coercive force distribution, and excellent dispersibility can be easily and economically produced with a small amount of cobalt added. Therefore, it is possible to manufacture high quality magnetic recording media.

[Brief explanation of drawings]

FIG. 1 is a characteristic diagram showing the relationship between the coercive force He of the cobalt-containing iron oxide magnetic powder and the reaction treatment time, and FIG. 2 is a characteristic diagram showing the relationship between the specific surface area of the magnetic powder and the reaction treatment time. Figure 1 Reaction treatment time (hr)

Claims (1)

[Claims] Acicular γ-Fe_2O_3 particles with an OH^- ion concentration of 1
．． Dispersed in an aqueous solution containing an alkali in an amount of 6 to 3.0 mol/l, to which sodium citrate and an alkaline earth metal salt are added, and then a cobalt salt and a ferrous salt are added. By adding an aqueous solution and treating in a non-oxidizing atmosphere at a temperature below the boiling point of the dispersion, the acicular γ
- A method for producing a ferromagnetic powder for magnetic recording, comprising forming an iron oxide layer containing cobalt on the surface of Fe_2O_3 particles.