JPS63245904A - Ferromagnetic powder and manufacture thereof - Google Patents

Abstract

PURPOSE:To increase the quantity of coating of a magnetic metallic layer by forming the magnetic metallic layers containing copper onto the surfaces of oxide magnetic metallic powder particles. CONSTITUTION:Copper is attached onto the surfaces of the oxide magnetic metallic powder of gammaFe2O3, etc., and magnetic metallic layers mainly comprising cobalt, etc., are shaped by reducing and precipitating magnetic metallic ions, thus forming ferromagnetic powder. The efficiency of precipitation is improved remarkably in the presence of copper having high oxidation-reduction potential to the cobalt, etc., thus increasing the quantity of coating of the magnetic metallic layer. Accordingly, ferromagnetic powder having comparatively low coercive force and high saturation magnetization and being adapted for a high- performance magnetic record medium, etc., is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ferromagnetic powder useful as a magnetic recording element in a magnetic recording medium such as a magnetic tape or a magnetic disk, and a method for producing the same.

[Conventional technology]

In recent years, with the improvement in performance such as the output characteristics of magnetic recording media,
Attempts have been made to increase both the coercive force and saturation magnetization of the magnetic powder used as the magnetic recording element.

For example, cobalt-containing iron oxide magnetic powder, such as γ-F8203, which has a cobalt-containing oxide layer formed on the particle surface, has a high retention capacity that can be used for high density by increasing the cobalt content. Magnetic force is obtained.

However, even in such a cobalt-containing iron oxide magnetic powder, the saturation magnetization is at most about 80 emu/g, and higher magnetization has not been obtained, which is insufficient for improving the output of magnetic recording media. .

In addition, Fe, co
Metal magnetic powders made of , Ni, and alloys thereof are known, but these have too high coercive force, so there are major restrictions in terms of use due to erase characteristics (unspecified literature).

On the other hand, the inventors had previously applied for patent application No. 59-141033.
(Japanese Unexamined Patent Publication No. 61-20302) proposes a ferromagnetic powder in which a magnetic metal layer made of metal cobalt, a cobalt-nickel alloy, or the like is formed on the particle surface of an oxide-based magnetic powder.

[Problem that the invention seeks to solve]

However, the ferromagnetic powder according to the above proposal exhibits higher saturation magnetization than the cobalt-containing iron oxide magnetic powder having the oxide layer containing cobalt, but due to its manufacturing method, the amount of the magnetic metal layer deposited is large. There is a limit to the improvement of saturation magnetization due to the fact that it is not possible to improve the saturation magnetization, and it has not always been possible to sufficiently meet the demand for higher output of magnetic recording media in recent years.

Therefore, the present invention provides a ferromagnetic powder that has a relatively low coercive force that is not subject to any restrictions in terms of use and exhibits a larger saturation magnetization than the ferromagnetic powder according to the above proposal, and a method for producing the same, thereby providing a magnetic recording medium. The aim is to contribute to higher performance such as output characteristics.

[Means for solving problems]

As a result of intensive studies to achieve the above object, the inventors found that when a ferromagnetic powder having a magnetic metal layer on the particle surface of an oxide-based magnetic powder contains a specific non-magnetic metal, the above-mentioned It has been discovered that the deposition efficiency when forming a magnetic metal layer by reduction precipitation from magnetic metal ions is significantly improved, the amount of the magnetic metal layer deposited can be increased, and as a result, extremely high saturation magnetization can be achieved. This invention has been made.

That is, the first aspect of the present invention relates to a ferromagnetic powder comprising a magnetic metal layer on the particle surface of an oxide-based magnetic powder and containing copper. The second aspect of the present invention is to form a magnetic metal layer by dispersing an oxide-based magnetic powder in a liquid medium containing magnetic metal ions and a reducing agent, and reducing and depositing a magnetic metal on the particle surface of the powder. By depositing copper on the particle surface of the oxide magnetic powder in advance or by making copper ions exist in the liquid medium, a magnetic metal layer is provided on the particle surface of the oxide magnetic powder and copper is added to the particle surface. It relates to a method for producing ferromagnetic powder characterized by obtaining ferromagnetic powder containing the present invention.

(Structure and operation of the invention) As described above, the ferromagnetic powder of the present invention is characterized by having a magnetic metal layer on the particle surface of the oxide-based magnetic powder and containing copper, which is a non-magnetic metal, inside. For example, when γ-Feto* powder is used as the oxide-based magnetic powder, the saturation magnetization is about 86 emu/g in the copper-free ferromagnetic powder of the comparative example described below.
The ferromagnetic powders of Examples 1.2.3.4 of the present invention, which will be described later, all have an extremely high saturation magnetization of 90 emu/g or more, which makes it possible to increase the output of magnetic recording media using the same. On the other hand, the coercive force exhibits the characteristics of the core oxide-based magnetic powder and exhibits a relatively low value that is not subject to any restrictions in terms of use.

The reason why the ferromagnetic powder of the present invention exhibits extremely high saturation magnetization as described above is presumed to be as follows. In other words, the above-mentioned magnetic metal layer is generally formed by reduction precipitation of magnetic metal ions, but due to the presence of copper, which has a high redox potential compared to magnetic metals such as cobalt, nickel, and iron during this precipitation, It is considered that the precipitation efficiency of the magnetic metal is significantly improved, and as a result, the amount of the magnetic metal layer deposited on the surface of each particle increases, and a high saturation magnetization is achieved accordingly.

In this way, copper can be incorporated into the ferromagnetic powder by depositing copper on the particle surface of the oxide-based magnetic powder to be used in advance by an appropriate means, or by depositing copper in the liquid medium used for reductive precipitation of the magnetic metal layer. It is sufficient to employ a method in which copper ions are present in the magnetic metal and the magnetic metal is reduced and precipitated at the same time, and the former method is particularly effective in improving the precipitation efficiency of the magnetic metal.

As the copper content in the ferromagnetic powder increases, the precipitation efficiency of magnetic metal increases, but if it increases too much, the proportion of non-magnetic components in the ferromagnetic powder as a whole increases, and the saturation magnetization decreases. If the amount is too small, the effect will not be fully exhibited, so it is best to set it in a range that accounts for 0.1 to 10% by weight of the entire ferromagnetic powder, and 1.0 to 8.0% by weight is particularly optimal. It is.

The constituent metals of the magnetic metal layer include cobalt, nickel,
Although various magnetic metals such as iron and alloys thereof can be used, a magnetic metal mainly composed of cobalt, that is, cobalt alone or an alloy mainly composed of cobalt and containing another magnetic metal such as nickel, is particularly suitable. The amount of this magnetic metal layer deposited is 5% of the total ferromagnetic powder having this layer.
~50 weight%, particularly preferably 10~40ffi amount%
It is best to set the range to cover . If the amount of this coating is too small, sufficient magnetic properties, especially improvement in saturation magnetization, will be observed.
On the other hand, if the amount is too large, the shape of the magnetic powder will change significantly, and when used in a magnetic recording medium, the dispersibility and orientation of the magnetic layer in the binder will deteriorate.

As the oxide-based magnetic powder forming the magnetic metal layer, any of various oxide-based powders conventionally known as magnetic recording elements of magnetic recording media can be used, but 7F is particularly suitable.
Iron oxide magnetic powders such as ez 03 , F ex Os , intermediate oxides thereof, Co-containing r-Fe! Ox
Cobalt-containing iron oxide magnetic powder, barium ferrite magnetic powder, chromium oxide magnetic powder, etc., which have a cobalt-containing oxide layer on the particle surface, such as Co-containing Fe, O, etc., are suitable.

In order to form the magnetic metal layer, the above oxide-based magnetic powder may be dispersed in a liquid medium containing magnetic metal ions and a reducing agent, and the magnetic metal may be reduced and precipitated on the particle surface of the powder. In the method of the present invention, as mentioned above, when carrying out the above-mentioned reduction precipitation, oxide-based magnetic powder that has been coated with copper on the particle surface in advance is used, or copper is deposited in the liquid medium. The presence of ions makes it possible to significantly improve the efficiency of magnetic metal deposition and increase the amount of magnetic metal deposited.

Here, as a specific means for reducing and precipitating the magnetic metal as described above, any general method for forming a metal layer such as electroless plating can be adopted, but in particular, Japanese Patent Application No. 59-141033 The most suitable method is one that utilizes a photocatalytic reaction, as detailed in the above issue. That is, according to the photocatalytic reaction, a very uniform magnetic metal layer can be formed on the particle surface of the oxide-based magnetic powder without damaging the particle shape, so that a ferromagnetic powder with particularly desirable magnetic properties can be obtained.

This method of utilizing photocatalytic reaction is a method of reducing and depositing a desired metal on the surface of the oxide-based magnetic powder by utilizing this semiconductor property since it has semiconductor properties. Specifically, first, a suitable reducing agent such as sodium hypophosphite, hydrazine, formalin, ethanol, formic acid, sodium formate, etc. is dissolved in water or other liquid medium in which a magnetic metal salt is dissolved, and then a suitable reducing agent is dissolved in water or other liquid medium in which a magnetic metal salt is dissolved. Disperse oxide magnetic powder.

Next, when this dispersion is irradiated with light having an energy greater than the energy of the band gap from the valence band to the conduction band of the magnetic powder, electrons are generated in the conductor and holes are generated in the valence band. The holes immediately diffuse within the particles and reach the particle surface, but the holes react with the reducing agent in the dispersion and disappear, leaving only electrons to accumulate.

Then, the oxide-based magnetic powder, which is negatively charged by the accumulated electrons, strongly attracts the positively charged magnetic metal ions, and the attracted metal ions obtain electrons on the particle surface of the magnetic powder and are reduced to the metal. Precipitates on particle surfaces.

Here, the above precipitation efficiency is due to the fact that copper is deposited on the particle surface of the oxide-based magnetic powder as described above, or the copper ions present in the dispersion are first reduced and precipitated on the particle surface. By doing so, it will improve dramatically. In addition, in the photocatalytic reaction, by appropriately setting the amount of magnetic metal salt relative to the oxide-based magnetic powder, the temperature of the reaction dispersion, the time of light irradiation, etc., it is possible to coat the particle surface of the magnetic powder with magnetic metal or the like. A metal layer containing copper is formed very uniformly.

The temperature of the dispersion liquid is 90°C or less, particularly preferably 1
It is desirable to set it as 0-60 degreeC. The light irradiation time varies depending on the type and composition of the magnetic metal layer, but is generally 0.5 to 50
It takes about an hour. In addition, in addition to the oxide magnetic powder, metal salt, and reducing agent, the dispersion liquid may contain a complexing agent such as sodium citrate or sodium tartrate to assist in stable precipitation of the metal. , and pH of boric acid, ammonium sulfate, sodium hydroxide, potassium hydroxide, ammonia, etc. to adjust the pH of the dispersion to an appropriate value.
A regulating agent may also be included. The pH of the dispersion is 6.0 to 1). 0, preferably in the range of 7°0 to 10.0.

The light for carrying out the photocatalytic reaction has energy greater than the energy of the band gap of the oxide-based magnetic powder, and generally light having a wavelength of 20θ to 800 nm is suitable.

Further, the irradiation light does not need to be monochromatic light, and polychromatic light using a xenon lamp or a mercury lamp as a light source can be applied.

In addition, in the method of this invention, when depositing copper on the particle surface of the oxide-based magnetic powder in advance, the deposition means is not particularly limited, and general metal layer forming means such as electroless plating method may be employed. However, most preferably, a method using a photocatalytic reaction similar to that described above is recommended. The conditions for the photocatalytic reaction in this case are the same as those for forming the magnetic metal layer described above.

〔Effect of the invention〕

The ferromagnetic powder of the present invention has a magnetic metal layer on the particle surface of the oxide-based magnetic powder and contains copper, so it has a relatively low coercive force, which is a characteristic of the oxide-based magnetic powder. Moreover, it exhibits extremely high saturation magnetization, is not subject to the limitations of use as with metal magnetic powders, and provides excellent electromagnetic conversion characteristics, particularly high output characteristics, to magnetic recording media using it as a magnetic recording element. Further, according to the method of the present invention, the excellent ferromagnetic powder described above can be obtained easily and reliably.

〔Example〕

Hereinafter, the present invention will be specifically explained based on embodiments.

Example 1 1 (l) of water was mixed with 20 g of copper sulfate, 80 g of ethylene diamine tetraacetyl acid (EDTA) and 100 ml of formalin, and an appropriate amount of sodium hydroxide was added to adjust the pH of the liquid to 12. ) has a coercive force of 32
3 oersted, saturation magnetization? 2.3 emu/g,
γ-Fe consisting of acicular particles having a square shape of 0.44 mm, an average major axis diameter of 0.3 μm, and an average axial ratio of 8.

03 powder was added and well dispersed. continue,
While stirring this dispersion, the liquid temperature was maintained at 40°C and a xenon lamp (manufactured by Nakatashi Denki) with an output of LKW was used to
After irradiation with light for a period of time, filter.

By washing with water, magnetic powder was obtained in which copper was uniformly adhered to the particle surface of γ-Fet02.

Next, add this magnetic powder to 1 liter of water (25 liters of cobalt sulfate).
0 g, sodium hypophosphite 200 g.

450 g of trisodium citrate and 250 g of boric acid were mixed and well dispersed in a solution (solution B) prepared by adding an appropriate amount of sodium hydroxide to adjust the pH to 9.0. and,
While stirring the dispersion, the temperature of the dispersion was maintained at 50° C., and the dispersion was irradiated with light for 5 hours using a xenon lamp (described above) with an output of 1 KW, and then washed with water.

By filtering and drying, a ferromagnetic powder having a magnetic metal layer made of cobalt on the particle surface was obtained.

Example 2 A ferromagnetic powder was obtained in the same manner as in Example 1, except that the copper sulfate in solution A was changed to 40 g, the ethylenediamine tetraacetic acid was changed to 120 g, and the formalin was changed to 200 ml.

Example 3 A ferromagnetic powder having a magnetic metal layer made of an alloy of cobalt and nickel on the particle surface was prepared in the same manner as in Example 1, except that the cobalt sulfate in liquid B was changed to 200 g and 50 g of nickel sulfate was added. Obtained.

Example 4 No copper adhesion treatment with liquid A, and 1 part of copper sulfate was added to liquid B.
A ferromagnetic powder was obtained in the same manner as in Example 1 except that 0 g was added.

Comparative Example A ferromagnetic powder was obtained in the same manner as in Example 1, except that the copper deposition treatment using liquid A was not performed.

Example 5 100 g of barium ferrite powder consisting of hexagonal plate-shaped particles with a coercive force of 530 oersted, saturation magnetization of 53.5 emu/g, square shape of 0.44, and average particle size of 0.08 μm was used in place of γ-Fe, O, and powder. A ferromagnetic powder was obtained in the same manner as in Example 1 except for the following.

The saturation magnetization and coercive force of the ferromagnetic powders of the above Examples and Comparative Examples were measured. The results are shown in the table below along with the amounts of copper and magnetic metal (Co + N L only in Example 3, Co in the others) of each magnetic powder. Note that this amount of adhesion was measured by analysis using a fluorescent X-ray device.

*; C0 = 31.5% by weight, N i = 2.0% by weight
From the above table, ferromagnetic powders (Examples 1 to 5) according to the present invention
All of them have a large amount of magnetic metal deposited and exhibit extremely high saturation magnetization, for example, the core oxide magnetic powder is γ-p.
Saturation magnetization when e2o3 is 90 emu/g or more,
In particular, it is clear that in the case of the above oxide-based magnetic powder coated with copper in advance (Examples 1 to 3), it is 92 emu/g or more.

On the other hand, the ferromagnetic powder (comparative example) in which copper was not deposited had a higher deposit than the ferromagnetic powder of the present invention (examples 1 and 2) under the same conditions for forming the magnetic metal layer. It can be seen that the amount is small and the saturation magnetization is greatly inferior.

Claims (5)

[Claims] (1) A ferromagnetic powder comprising a magnetic metal layer on the particle surface of an oxide-based magnetic powder and containing copper. (2) The ferromagnetic powder according to claim (1), wherein the copper content is in a range of 0.1 to 10% by weight of the entire ferromagnetic powder. (3) The ferromagnetic powder according to claim (1) or (2), wherein the magnetic metal layer is mainly composed of cobalt. (4) In forming a magnetic metal layer by dispersing an oxide-based magnetic powder in a liquid medium containing magnetic metal ions and a reducing agent and reducing and depositing a magnetic metal on the particle surface of the powder, the oxide-based magnetic By using a powder with copper already deposited on the particle surface or by making copper ions exist in the liquid medium, the particle surface of the oxide-based magnetic powder is provided with a magnetic metal layer and contains copper. A method for producing ferromagnetic powder, characterized by obtaining ferromagnetic powder. (5) A dispersion of oxide-based magnetic powder is irradiated with light having a larger energy than the band gap from the valence band to the conduction band of the powder to reduce and precipitate the magnetic metal. ) The method for producing the ferromagnetic powder described in item 2.