JPS638222A - Production of magnetic powder for magnetic recording - Google Patents

Abstract

PURPOSE:To produce magnetic powder having high coercive force, high saturation magnetization, uniform coercive force distribution and improved dispersibility, by dispersing needle-like gamma-Fe2O3 particles into water, adding an alkali and treating. CONSTITUTION:Needle-like gamma-Fe2O3 particles as nuclei are dispersed into water. An aqueous solution containing an alkaline earth metallic salt, Co salt and ferrous salt is added to the dispersion and stirred. Successively and alkali is added to the dispersion, which is adjusted to 3.0-6.0mol/l OH<-> ion concentration. Then the dispersion is treated in a nonoxidizing atmosphere at <= the boiling point of the dispersion to form a Co-containing iron oxide layer on the surface of the needle-like gamma-Fe2O3 particles. By this method Co-containing iron oxide magnetic powder 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 magnetic powder, and more specifically,
The present invention relates to a method for producing cobalt-containing iron oxide ferromagnetic powder that enables high recording density.

(Conventional technology and problems to be solved) Conventionally,
Acicular γ-Fe2O3 particles, which have 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-Fe, O: particles have been proposed up to now, but one of the most useful methods is to prepare acicular γ-Fe particles in an alkaline solution. The particles are dispersed, and an alkaline earth metal salt, a cobalt salt, and a ferrous salt are added thereto to form cobalt-containing γ-Fe20. There is a way to make it into particles.

Cobalt-containing QiFe203 obtained by this method
Since the particles have an iron oxide layer containing cobalt formed on the particle surface, the coercive force and saturation magnetization per unit weight increase, but the dispersibility is poor, the coercive force distribution is poor, and the change over time is large. There was a drawback.

An object of the present invention is to provide a method for producing cobalt-containing iron oxide magnetic powder that has high coercive force, high saturation magnetization, uniform coercive force distribution, and little change over time, by eliminating the drawbacks of the above-mentioned conventional techniques. It's about doing.

(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 added with alkaline earth metal salt, cobalt salt, and ferrous salt to form cobalt-containing Q-Fe
By forming an iron oxide layer containing ferrous ions (Fe2+) on the surface of 2O3 particles and concentrating cobalt on the particle surface, an increase in coercive force and a decrease in saturation magnetization per unit weight are suppressed. However, because alkali is added before the step of adding an aqueous solution containing cobalt ions and ferrous ions, it is difficult to obtain the desired high coercive force ferromagnetic powder, and the coercive force distribution is poor. It was found that the change over time becomes large.

Therefore, the present inventor has developed a structure with high coercive force, high saturation magnetization, and
As a result of intensive research to develop magnetic powder with a uniform coercive force distribution and excellent dispersibility, we discovered that after dispersing acicular γ-Fe2O3 particles in water, we obtained a mixture of alkaline earth metal salts, cobalt salts and ferrous salts. was added, and then the OH- ion concentration of this dispersion was 3.
The present invention was made based on the discovery that it is possible to obtain the desired magnetic powder by adding and treating an alkali in an amount of 0 to 6.0 mol/l.

That is, in the present invention, after dispersing acicular γ-Fe2O3 particles in an aqueous solution containing a cobalt salt and a ferrous salt and adding an alkaline earth metal salt, the OH- ion concentration of the dispersion is 3.0. By adding an alkali in an amount of ~6.0 mol/2 and then treating in a non-oxidizing atmosphere at a temperature below the boiling point of the dispersion, iron oxide containing cobalt is formed on the surface of the acicular γ-Fe2O3 particles. The gist of the present invention is a method for producing magnetic powder for magnetic recording, which is characterized by forming a layer.

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

In the present invention, first, the acicular γ-Fe20° particles that serve as the core are dispersed in water, stirred at a temperature below the boiling point (e.g. 90°C) for the required time (e.g. 30 minutes), and then thoroughly dispersed. An aqueous solution containing an alkaline earth metal salt, a cobalt salt, and a ferrous salt is added, and the mixture is further stirred for the required time (eg, 30 minutes). In this case, the alkaline earth metal salts are strontium chloride and barium chloride.

Calcium chloride, etc. can be used, and cobalt salts include cobalt chloride, cobalt sulfate, etc.
As the iron salt, ferrous chloride, ferrous sulfate, etc. can be used.

Subsequently, the OH- ion concentration of this dispersion was increased to 3. ○～6.
Add alkali in an amount to give 0 mol/l.

As alkalis, sodium hydroxide, potassium hydroxide,
Lithium hydroxide or the like can be used. If the amount of alkali added is outside the above range, problems will arise in any of the characteristics and properties of the resulting cobalt-containing iron oxide magnetic powder, making it impossible to achieve the object of the present invention. Specifically, when the OH- ion concentration is 3.0 mol/l or less, the effect of increasing the coercive force is small, and when the OH- ion concentration is 6.0 mol/l or more, the increase in the coercive force is about the same.

Industrially, it is also disadvantageous because it becomes very highly alkaline.

After adding the alkali, the mixture is stirred at a temperature below the boiling point (eg, 100° C.) for a required period of time. This treatment is performed in a non-oxidizing atmosphere because it is necessary to prevent air from entering.

Through this process, a cobalt-containing iron oxide layer is formed on the surface of the acicular γ-Fe2O3 nucleus crystal, which has high saturation magnetization, high coercive force, and a uniform coercive force distribution that does not change over time. A cobalt-containing iron oxide magnetic powder with a small amount of cobalt and excellent dispersibility can be obtained.

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

(Example) Acicular γ-Fe20 produced by a conventional method. Powder (retention crab 3500e, saturation magnetization: 73 emu/g) 3000
After dispersing g in 20 fl of water, the temperature was raised to 90° C., stirred for 30 minutes, and 500 mΩ of an aqueous solution in which 45.63 g of strontium chloride was dissolved was added. The temperature was further raised to 100°C, 1.52 g of an aqueous solution containing 422 g of cobalt sulfate and 834 g of ferrous sulfate was added, and after stirring for 30 minutes,
Add aqueous solution 82 in which 6000 g of sodium hydroxide was dissolved, continue stirring while maintaining this temperature while preventing air from entering as much as possible, and after 1 hour, 3 hours, 5 hours, and 7 hours. Samples of about 3QmQ each were taken and reacted for 8 hours. Each sample collected and the slurry after the reaction were thoroughly washed with water, then filtered and dried. The magnetic properties of each of the obtained samples were measured using a vibrating sample magnetometer (model VSM-3S manufactured by Toei Kogyo) with an external magnetic field of 10 KOe. The results are shown in Table 1 and Figure 1.

The cobalt-containing iron oxide magnetic powder obtained after 8 hours of reaction treatment has a coercive force He of 6870e and a saturation magnetization σ
s was 76.5 emu/g.

(Comparative example) As a comparative example, cobalt-containing oxidized 'ljc magnetic powder was prepared in the same manner as in the above example except that strontium salt, cobalt salt and ferrous salt were added after adding alkali in the addition step in the above example. Manufactured. Then, the magnetic properties of each sample obtained by sampling in the same manner were measured. The results are shown in Table 1 and Figure 1.

In this comparative example, the cobalt-containing iron oxide magnetic powder obtained after 8 hours of reaction treatment had a coercive force He of 6750e, a saturation magnetization ffs of 76, and 3 emu/g.

Table 1 Coercive force He (○e) 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 approximately 48
Knead the magnetic paint in a ball mill for an hour! I made 4 adjustments.

Cobalt-containing iron oxide magnetic powder...75 parts by weight Vinyl chloride-vinyl acetate copolymer...19 Dioctyl phthalate...4j lecithin
... 2 Toluene
...100 〃Methyl isobutyl ketone ・
...10 o This magnetic paint was coated on a polyester film having a thickness of 12 μm so that the dry thickness was approximately 6 μm, and was dried under magnetic field orientation to produce a magnetic tape. The squareness ratio (Br/8m) and switching field distribution (SFD) of each of the obtained magnetic tapes were measured, and the results shown in Table 2 were obtained.

Table 2 As is clear from Table 2, 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. It was confirmed that the coercive force distribution was uniform and the dispersibility was excellent, and it was also confirmed through experiments that there was little change over time.

(Effects of the Invention) As detailed above, according to the present invention, cobalt-containing iron oxide magnetic powder that has high coercive force, high saturation magnetization, uniform coercive force distribution, and excellent dispersibility can be easily produced. This makes it possible to manufacture high-quality magnetic recording media.

[Brief explanation of drawings]

FIG. 1 is a characteristic diagram showing the relationship between coercive force Hc of cobalt-containing iron oxide magnetic powder and reaction treatment time.

Claims (1)

[Claims] After dispersing the acicular γ-Fe_2O_3 particles in an aqueous solution containing a cobalt salt and a ferrous salt and adding an alkaline earth metal salt, the OH^- ion concentration of the dispersion was 3.0.
By adding an alkali in an amount of ~6.0 mol/l and then treating in a non-oxidizing atmosphere at a temperature below the boiling point of the dispersion, iron oxide containing cobalt was formed on the surface of the acicular γ-Fe_2O_3 particles. A method for producing magnetic powder for magnetic recording, which comprises forming a layer.