JPH08236326A - Metal powder for magnetic recording and production thereof - Google Patents

Abstract

PURPOSE: To provide a metal powder having superior magnetic characteristics for magnetic recording and producing method thereof. CONSTITUTION: A metal powder for magnetic recording contains Co, rare earth element, Al and Fe. The Co content is 10-50wt.%, rare earth element content is 5-20wt.%, Al content is 0-0.1wt.%, and Fe content is 29.9-80wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal powder for magnetic recording suitable for increasing the output of a coating type magnetic recording medium such as a magnetic tape and a magnetic disk, and a method for producing the same.

[0002]

2. Description of the Related Art As a magnetic recording medium, γ-
Ferric oxide, chromium dioxide, cobalt-doped γ-ferric oxide, cobalt-coated γ-ferric oxide, metal iron powder, ferrite powder and the like are appropriately selected and used according to the intended use. In particular, metal iron powder is suitable when high density recording is required and is widely used.

In recent years, with the increasing density of magnetic recording, it has been required to make the magnetic recording powder, which is a material of the recording medium, into fine particles. However, the magnetic energy of the magnetic recording powder tends to decrease as it becomes finer. For this reason, the demand has been met by improving the particle shape, improving the particle size distribution, firing at the time of production, controlling the temperature of reduction, the atmosphere, etc., but this has also reached the limit.

Therefore, a technique for increasing the magnetic energy inside the metal powder has been studied in order to promote the formation of fine particles. The magnetic properties of alloys are known as the Slater-Pauling curve. Conventionally, when the content of cobalt is 30 atomic% (29% by weight) and iron is 70 atomic% (71% by weight), the maximum transition metal It is known to have a magnetic moment of

A technique for applying this cobalt-iron alloy system to a metal powder for magnetic recording composed of fine particles has been studied, but a large amount of cobalt is not sufficiently incorporated into the particles, resulting in insufficient alloying of the powder. However, there are drawbacks such as deterioration of shape when heated at high temperature and reduction, acicularity, independence of particles cannot be maintained, and desired coercive force and saturation magnetization cannot be obtained. It was

[0006]

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide a magnetic recording metal powder having excellent magnetic properties and a method for producing the same.

[0007]

SUMMARY OF THE INVENTION The gist of the present invention is that a magnetic recording metal powder is composed of cobalt, a rare earth element, aluminum and iron as a metal, and the content of the cobalt is 10 to 50% by weight. %, The content of the rare earth element is 5 to 20% by weight, the content of the aluminum is 0 to 0.1% by weight, and the content of the iron is 29.
It is about 9 to 80% by weight. The present invention is described in detail below.

In the magnetic recording metal powder of the present invention, the content of cobalt is 10 to 50% by weight. When it is less than 10% by weight, the effect of increasing the magnetic energy inside the magnetic powder for magnetic recording is small, and when it exceeds 50% by weight,
The iron and the cobalt cannot be present uniformly, and the coercive force,
Since the saturation magnetization and the like decrease, the range is limited.

The content of the rare earth element is 5 to 20% by weight. If it is less than 5% by weight, the shape-retaining effect is small, and if it exceeds 20% by weight, the iron and the rare earth element cannot exist uniformly, and the saturation magnetization is lowered as an impurity. To be done. The rare earth element is not particularly limited, and examples thereof include lanthanum, neodymium, cerium, praseodymium, and the like.

The aluminum content is 0 to 0.1.
% By weight. When it exceeds 0.1% by weight, flame-retardant cobalt-aluminum-iron spinel is generated to prevent alloying of the above cobalt and iron, and it remains in the particles even after the reduction process during production. Since it remains and hinders the improvement of the magnetic energy, it is limited to the above range.

The metal powder for magnetic recording of the present invention has a particle size of 0.03 to 0.13 μm in major axis and 0.003 to minor axis.
It is preferably 0.05 μm. If it deviates from the above range, it becomes difficult to reduce the thickness of the coating film. The magnetic powder for magnetic recording preferably has a coercive force of 1900 Oe or more. When the coercive force is less than 1900 Oe, self-demagnetization is large and only a medium with low output can be obtained, and the object of the present invention cannot be achieved. The magnetic recording metal powder has a temperature of 6
The rate of change in saturation magnetization after standing for 7 days at 0 ° C. and 90% relative humidity is preferably within 15%. If it exceeds 15%, the medium itself also has poor stability over time, and the residual magnetization is reduced by storage, and the output of the recording signal is lowered and deteriorated. If necessary, the metal powder for magnetic recording may contain another metal in an amount of 0 to 1% by weight. The other metal is not particularly limited, and examples thereof include silicon, titanium, calcium and the like.

In the magnetic recording metal powder of the present invention, goethite is heated and dehydrated at 250 to 600 ° C. to obtain α-ferric oxide, and then the α-ferric oxide is heated at 200 to 500 ° C.
In the method for producing a metal powder for magnetic recording, the goethite is obtained by coprecipitating cobalt and a rare earth element, and the particle size is 0.03 to 0.15 μm in the major axis. Yes, 0 to 0.1 in terms of metal
It is obtained by the method for producing a metal powder for magnetic recording containing aluminum by weight.

The above-mentioned goethite is obtained by coprecipitating cobalt and rare earth elements. The method for obtaining the above-mentioned goethite is not particularly limited, for example, a solution containing a ferrous salt and a solution containing a solution containing cobalt and a rare earth element are neutralized by adding an excess alkali, and then, Examples thereof include a method of oxidizing using air.

Examples of the ferrous salt include ferrous chloride, ferrous sulfate, ferrous nitrate and the like.
As the alkali, hydroxide of alkali metal, carbonate of alkali metal, ammonia or the like can be used, but sodium carbonate is more preferable. When sodium carbonate is used, fine and uniform particles are easily obtained.

The solution containing cobalt and the rare earth element may be added in the process of neutralizing by adding an excess alkali to the solution containing the ferrous salt and then performing air oxidation. If a solution containing a large amount of the above cobalt and rare earth element is added to the initial stage of the preparation of goethite, the nuclear control of goethite will be hindered and the particle distribution, acicularity and the like will be impaired. When the solution containing the cobalt and the rare earth element is added in the latter stage of the above-mentioned goethite preparation, the diffusion of cobalt into the particles becomes insufficient, and the desired cobalt-iron alloy cannot be obtained, and the necessary magnetic properties are expressed. do not do.

The goethite has a particle size of 0.03 to 0.15 μm in major axis. If it is less than 0.03 μm, it is difficult to maintain the acicularity of the particles, and the contribution of the surface to the volume of the obtained metal powder for magnetic recording becomes large. 15
If it exceeds μm, desired fine particles cannot be obtained, which is unsuitable for use as a metal powder for high-density magnetic recording.
It is limited to the above range.

The above-mentioned goethite is 0 to 0.1 in terms of metal.
It contains aluminum by weight. The aluminum has a great effect on heat dehydration at high temperature, shape retention during reduction, and prevention of interparticle fusion, but when a large amount of cobalt is contained, the aluminum contains a non-reducible cobalt-aluminum-iron spinel. Since it is generated, it is limited to the above range.

The goethite is heated and dehydrated at 250 to 600 ° C. If the temperature is lower than 250 ° C., it takes a long time to dehydrate the above-mentioned goethite, which is not industrial and many pores remain inside the particles of the dehydrated product. Melts and the shape collapses. Further, since the above-mentioned goethite has a high cobalt content, spinel formation which seems to be cobalt-ferrite confirmed by X-ray diffraction at the time of heat dehydration at a high temperature causes spinel formation compared to conventional goethite having a low cobalt content. Since the melt at high temperature is remarkable and it cannot withstand the heat dehydration at 600 ° C. or higher, it is limited to the above range.

The above goethite is reduced at 200 to 500 ° C. If the temperature is lower than 200 ° C., it takes a long time for reduction, which is not industrial, and if the temperature exceeds 500 ° C., deterioration of dispersibility due to fusion between particles and the like occur. The above-mentioned goethite has a cobalt content of 10
The reduction temperature is more preferably less than 400 ° C., since the reduction is sufficiently large at about 50% by weight and the reduction proceeds sufficiently even at a relatively low temperature.

As a method for obtaining the metal powder for magnetic recording of the present invention from the above-mentioned goethite, there can be mentioned, for example, a conventionally used method.
Heat dehydration at 00-600 ° C for 0.5-10 hours, 200
After reduction in a hydrogen stream at ˜500 ° C., the metal powder for magnetic recording of the present invention is obtained by gradually contacting with air at less than 200 ° C.

In the production method of the present invention, after the reduction is completed and the cobalt-iron alloying is completed, this may be dispersed in a solvent to coat the surface with aluminum. In this manufacturing method, cobalt-aluminum-iron spinel is not generated and the magnetic properties are not deteriorated. Further, in this case, the effect of improving familiarity between the magnetic recording metal powder of the present invention and the resin can be expected.

[0022]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Example 1 About 1.2 L of pure water was added to 190 g of sodium carbonate to dissolve it, and nitrogen gas was blown thereinto to expel oxygen in the system, and then Fe ²⁺
500 ml of a ferrous sulfate solution having a concentration of 80 g / L was added and mixed with stirring. This suspension is stirred at 300 ml / mi
After 30 minutes, 10% misch metal (cerium about 50%, lanthanum about 30%, neodymium about 15%, praseodymium about 4%, other alloys) hydrochloric acid solution 44 g, cobalt chloride solution ( 80 g of 50% cobalt hexachloride as a hexahydrate was added, and the mixture was subjected to an oxidation reaction for a total of 4 hours and then filtered. Obtained.

Further, this cake was heat-treated in air at 550 ° C. for 2 hours, then reduced in a hydrogen stream at 400 ° C., cooled to room temperature, and then gradually introduced air in nitrogen gas to stabilize. Chemical treatment to obtain a metal magnetic powder. After lightly pulverizing the metal powder in a mortar, the VSM magnetometer was used to measure the magnetic characteristics under a sweeping magnetic field of 10 kOe and X-ray diffraction for copper-K.
It was measured at α, 40 kV and 30 mA. Table 1 shows the magnetic characteristics. In Table 1, "saturation magnetization change rate" is the temperature 60
The change rate after standing still for 7 days at 90 ° C. and 90% relative humidity is shown.

The particle shape and distribution were photographed with a transmission electron microscope at 80 kV. FIG. 1 shows an X-ray diffraction chart of the heat dehydrated product. FIG. 2 shows an X-ray diffraction chart of the metal powder. An electron micrograph of the metal powder is shown in FIG.

Example 2 The procedure of Example 1 was repeated, except that the heat treatment condition in air was 600 ° C. Example 3 The procedure of Example 1 was repeated except that the total amount of a solution prepared by dissolving 9.6 g of lanthanum chloride heptahydrate (reagent) in about 100 ml of pure water was added instead of adding the misch metal solution. Example 4 Example 1 was repeated except that the total amount of a solution prepared by dissolving 8.9 g of neodymium chloride hexahydrate (reagent) in about 100 ml of pure water was added instead of adding the misch metal solution.

Comparative Example 1 Example 1 was repeated except that the misch metal solution was not added. An electron micrograph of the obtained metal powder is shown in FIG. As you can see in the picture, the melt is intense,
The particles became almost spherical.

COMPARATIVE EXAMPLE 2 Without adding the misch metal solution, 47.8 g of aluminum sulfate (aluminum sulfate 14-18 hydrate, reagent, aluminum content 9.2% by weight) was replaced by about 100 m.
It was carried out in the same manner as in Example 2 except that one dissolved in 1 l of water was added. The X-ray diffraction chart of the heat dehydration product is shown in FIG. FIG. 6 shows the X-ray diffraction chart of the metal powder. In the chart of the heat dehydration product, a spinel peak was observed in addition to the α-ferric oxide peak, and this peak was also observed in the chart of the metal powder, indicating that spinel remained in the metal powder. . Considering the position of the peak, it was considered that cobalt-aluminum-iron spinel, which is difficult to reduce, was generated during heat dehydration (heat treatment), and this inhibited cobalt-iron alloying. As a result, a sample with low coercive force and saturation magnetization was obtained.

Comparative Example 3 The amount of cobalt chloride solution added and the amount of misch metal solution were reduced to 12 g and 28 g, respectively, and aluminum sulfate (aluminum sulfate 14-18 hydrate, reagent, aluminum content 9.2% by weight) was added. ) 17.4g about 100
Add the one dissolved in ml of water and heat dehydration to 6
The same procedure as in Example 2 was carried out except that the procedure was performed at 50 ° C. The magnetic powder of Comparative Example 3 is of the conventional type (cobalt content 4
%), And the effect of the present invention can be understood by comparing with the examples. That is, the magnetic powders of Examples had high magnetic energy (high coercive force, high saturation magnetization) and were excellent in oxidative stability.

Comparative Example 4 The procedure of Comparative Example 3 was repeated, except that the amount of cobalt chloride solution was increased to 80 g, which was the same as in Example, and that heat dehydration was performed at 600 ° C. This magnetic powder is a sample example when only the amount of cobalt is simply increased by the conventional method. With the increase of cobalt, almost no increase in magnetic energy was observed, and the shape collapsed, so that the coercive force decreased.

Comparative Example 5 Heat dehydration (heat treatment) was performed at 55 without adding a cobalt chloride solution.
The same procedure as in Comparative Example 2 was performed except that the procedure was performed at 0 ° C. FIG. 7 shows an X-ray diffraction chart of the heat dehydrated product. FIG. 8 shows an X-ray diffraction chart of the metal powder. Unlike the system containing a large amount of cobalt (comparison, see FIGS. 1 and 2), spinel peaks are not observed in the heat dehydrated product, but spinel peaks are observed in the metal powder after reduction. This is because there is no cobalt, aluminum by heat dehydration is a solid solution is the same crystal form of alumina α- ferric oxide, the first time the bivalent iron ions produced during reduction FeAl ₂
It gave rise to an aluminum spinel of O ₄ , which is clearly different from the system with cobalt.

Comparative Example 6 Example 1 except that no cobalt chloride solution was added.
I went in the same way. FIG. 9 shows a transmission type electric photograph of metal powder. Although not as high as in Comparative Example 1, it can be seen that the melt of the particles is severe and the acicular ratio is remarkably lowered. Considering together with the examples, the effect of adding the rare earth is more exerted when cobalt is present, and it can be said that it is particularly useful in a system rich in cobalt.

As described above, when a large amount of cobalt is introduced into the particles, by removing aluminum,
It has become possible to prevent the formation of a difficult-to-reduce cobalt-aluminum-iron spinel at the time of heat dehydration and to sufficiently advance the cobalt-iron alloying in the subsequent reduction.

Further, by doping the rare earth element together with cobalt into the particles, it was possible to suppress the deterioration of the particle shape during the heat dehydration reduction. By such a method, it was possible to obtain metal powder having a high magnetic energy which has never been obtained.

[0035]

[Table 1]

[0036]

Since the metal powder for magnetic recording and the method for producing the same according to the present invention have the above-mentioned structure, no deterioration in magnetic properties due to the finer particles found in the conventional metal powder for magnetic recording is observed. It can be suitably used for increasing the output of coating type magnetic recording media such as magnetic tapes and magnetic disks.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction chart of the heat dehydrated product of Example 1.

FIG. 2 is an X-ray diffraction chart of the metal powder of Example 1.

FIG. 3 is an electron micrograph showing the particle shape and particle distribution of the metal powder of Example 1.

FIG. 4 is an electron micrograph showing the particle shape and particle distribution of the metal powder of Comparative Example 1.

FIG. 5 is an X-ray diffraction chart of the heat dehydrated product of Comparative Example 2.

FIG. 6 is an X-ray diffraction chart of the metal powder of Comparative Example 2.

FIG. 7 is an X-ray diffraction chart of the heat dehydrated product of Comparative Example 5.

FIG. 8 is an X-ray diffraction chart of the metal powder of Comparative Example 5.

FIG. 9 is an electron micrograph showing the particle shape and particle distribution of the metal powder of Comparative Example 6.

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display area H01F 1/06 H01F 1/06 N

Claims (4)

[Claims] 1. A metal powder for magnetic recording comprising cobalt, a rare earth element, aluminum and iron as a metal, wherein the content of cobalt is 10 to 50% by weight.
And the content of the rare earth element is 5 to 20% by weight, and the content of the aluminum is 0 to 0.1% by weight.
And the iron content is 29.9 to 80% by weight, the magnetic recording metal powder. 2. The particle size has a major axis of 0.03 to 0.13.
The metal powder for magnetic recording according to claim 1, which has a short diameter of 0.003 to 0.05 μm and a coercive force of 1900 Oe or more. 3. The metal powder for magnetic recording according to claim 2, wherein the rate of change in saturation magnetization after standing for 7 days at a temperature of 60 ° C. and a relative humidity of 90% is within 15%. 4. When manufacturing the metal powder for magnetic recording according to claim 1, 2 or 3, the goethite is 250 to 6 pieces.
A method for producing a metal powder for magnetic recording, comprising heating and dehydrating at 00 ° C to give α-ferric oxide, and then reducing the α-ferric oxide at 200 to 500 ° C. The site is obtained by coprecipitating cobalt and a rare earth element, and the particle size is 0.03 to 0.1 in the major axis.
A method for producing a metal powder for magnetic recording, which has a thickness of 5 μm and contains 0 to 0.1% by weight of aluminum in terms of metal.