JPS61166110A - Ferromagnetic powder and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve the durability of a magnetic recording medium by a method wherein a magnetic metal layer mainly composed of the metal containing at least a kind of iron, cobalt and nickel is formed on the surface of the non-magnetic semiconductor particles having the specific value or a greater value of hardness. CONSTITUTION:Non-magnetic semiconductor particles are dispersed into the liquid medium containing a reducing agent and magnetic metal ions for the purpose of forming a magnetic metal layer, which is mainly composed of at least a kind of iron, cobalt and nickel on the surface of a non-magnetic semiconductor particles having the Mohs hardness 3. Metal ions are reduced by projecting the light, having the energy laser than that of the band gas of the semiconductor particles, on said dispersed liquid. The abrasive particles such as alpha-Fe2O3, TiO2, Al2O3, Cr2O3 and the like are used as the non-magnetic semiconductor particles, and a sedium hypophosphorous acid, hydrazine, formalin and the like can be used as the reducing agent. The magnetic metal ions are formed by dissolving a metal sulfate, a nitrate, a chloride and the like into a liquid medium. A light is made to irradiate on said dispersion liquid, and an optical catalytic reaction is performed. The magnetic metal layer formed as above is adhered to the surface of the semiconductor particles uniformly and in excellent adhesiveness, thereby enabling to manufacture a magnetic tape which satisfies both durability and electromagnetic conversion characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ferromagnetic powder comprising a magnetic metal layer provided on the surface of non-magnetic semiconductor particles having a Mohs hardness of 3" or more, and a method for producing the same.

[Conventional technology]

In general, magnetic recording media, which have a magnetic layer containing magnetic powder and a binder on a base such as a polyester film, suffer from abrasion of the magnetic layer and deterioration of various magnetic properties due to sliding contact between the magnetic layer and the head. To prevent this, Cr2O3, an abrasive, is added to the magnetic layer.

Aj? 203. TiO2, a! -Fe203 etc. are added.

In order to obtain sufficient durability, it is necessary to add large amounts of these abrasives.

[Problem that the invention seeks to solve]

However, since these abrasives are non-magnetic substances, if they are added in large amounts, the magnetic flux density of the magnetic layer decreases, resulting in sensitivity and
There was a problem that electromagnetic conversion characteristics such as S/N ratio deteriorated.

Therefore, the present invention aims to overcome the above-mentioned conventional problems, that is, to improve the durability of a magnetic recording medium without degrading the electromagnetic conversion characteristics.

[Means for Solving the Problems 1] As a result of repeated studies to achieve the above object, the inventors discovered that Fe, Co and .

By forming a magnetic metal layer that primarily contains at least one metal among Ni, we succeeded in obtaining a completely new magnetic powder that has both the properties of an aggregating agent and the properties of a magnetic powder. did.

That is, since this magnetic powder has properties as an abrasive, there is no need to add the aforementioned abrasive to the magnetic layer as in conventional magnetic recording media, and this magnetic powder can be used alone. As a result, a magnetic recording medium with excellent electromagnetic conversion characteristics and durability can be obtained.

Although such magnetic powder was completely unknown until now, the inventors noted that the conventional abrasive particles have semiconducting properties, and developed a method using this property. It was only by coming up with a method of depositing magnetic metal on the surface of these non-magnetic particles through a photocatalytic reaction, and conducting further extensive studies based on this idea, that we succeeded in obtaining it.

The photocatalytic reaction described above is when semiconductor particles are dispersed in water and irradiated with light having conduction energy from the valence band of the semiconductor particles, generating electrons in the conduction band and holes in the valence band. Here, if a reducing agent is made to coexist with metal ions in the dispersion in advance, the holes generated in the valence band will react with the reducing agent and disappear, and as a result, only electrons will remain in the particles. remain. The semiconductor particles in which only the electrons remain strongly attract the metal ions in the dispersion liquid and are reduced to metal, thereby forming a metal layer with extremely good adhesion on the surface of the semiconductor particles.

Therefore, in the present invention, as the hemispherical particles, particles with a Mohs hardness of 3 or more, such as the abrasive particles mentioned above, are used,
and the novel structure, wherein a uniform magnetic metal layer with good adhesion is formed on the surface of the particles by using, as the metal ion, at least one magnetic metal selected from Fe, NI+゛Co. We succeeded in obtaining magnetic powder. The magnetic properties of this magnetic powder are determined by the magnetic properties of the metal layer on the surface, and the magnetic properties can be controlled arbitrarily by changing the thickness of the metal layer and the type of metal.

This invention was made based on the above findings, and includes iron and iron on the surface of nonmagnetic semiconductor particles with a Mohs hardness of 3 or more.
A first invention relating to a ferromagnetic powder formed by forming a magnetic metal layer containing at least one metal selected from cobalt and nickel as a main component, and an industrially advantageous method for obtaining this ferromagnetic powder using a reducing agent. Non-magnetic semiconductor particles are dispersed in a liquid medium containing magnetic metal ions whose main component is at least one metal selected from iron, cobalt, and nickel, and this dispersion contains particles with a band gap larger than that of the semiconductor particles. A second invention relating to a method for producing ferromagnetic powder, characterized in that the metal ions are reduced on the surface of the semiconductor particles to form a magnetic metal layer by irradiating the semiconductor particles with energetic light. It is.

[Structure and operation of the invention] Non-magnetic semiconductor particles having a Mohs hardness of 3 or more used in the present invention include Q4-Fe203, TiO3, A
In addition to conventional general-purpose abrasive particles such as l2O3 and Cr2O3, various particles with a Mohs hardness of 3 or more, such as S
iC, GaP, Si, GaAs, CdS, 5rT
i03, I nP, Cd Se, Ba SO2, C
Various particles such as aCO3 and ZnO are included. The average particle diameter of these particles is usually 1. It is desirable that it be about ooX to 2-. In addition, as for the characteristics of these semiconductors, the energy of the band gap from the valence band to the conduction band is generally 0.5 to 6. It is preferable that the energy level of the conduction band is about OeV and has a negative potential with respect to the standard hydrogen electrode potential.

The magnetic metal layer formed on the surface of this semiconductor particle is made of iron,
The main component is at least one of cobal l- and nickel, but the magnetic metal may also contain a small amount of nonmagnetic metal or nonmetal. The thickness of this metal layer is 5 parts by weight based on 100 parts by weight of the semiconductor particles.
0~], 000 parts by weight, preferably 100~500
It is preferable that the amount be in parts by weight. If this amount is too small, a sufficient amount of saturation magnetization cannot be obtained, and if this amount is too large, the inner layer may become non-uniform and stable magnetic properties may not be expected, so both are undesirable.

The ferromagnetic powder according to the present invention comprising such constituent elements can also be obtained essentially by forming the magnetic metal layer on the surface of the semiconductor particles by a technique such as electroless plating. However, in order to obtain more stable magnetic properties, the method of forming a magnetic metal layer using the photocatalytic reaction described above is the most recommended method.

In this photocatalytic reaction, first a reducing agent and iron are used.

A dispersion liquid is prepared in which non-magnetic semiconductor particles are dispersed in a liquid medium containing magnetic metal ions whose main component is at least one of cobalt and nickel. As the reducing agent, any reducing agent used in electroless plating, such as sodium hypophosphite, hydrazine, formalin, ethanol, formic acid, and thorium formate, can be used. ” Magnetic metal ions are usually sulfates of the corresponding metals,
It is produced as a salt such as nitrate or chloride by dissolving it in a liquid medium.

Water is usually used as the liquid medium, but various solvents outside water can be used as long as they can dissolve the magnetic metal salt and do not interfere with the photocatalytic reaction.

When the liquid medium is water, the concentrations of each component in the dispersion are generally 1 to 2009 y/l water for the reducing agent, 1 to 200 y/l water for the magnetic metal salt, and 1 to 200 y/l water for the nonmagnetic semiconductor particles.
What is necessary is just to make it y/l water.

In addition, when the liquid medium is water, an appropriate complexing agent and P
It is preferable to include an H regulator in the dispersion). As the complexing agent, sodium citrate and sodium tartrate are generally used, and as the pH adjusting agent, boric acid, ammonium sulfate, caustic soda, caustic potash, ammonia, etc. are used, and the pH of the liquid is 60 to 110, preferably 7
Adjust so that it is in the range of 0 to 100.

The temperature of the dispersion liquid is adjusted to uniformly precipitate the magnetic metal.
The temperature is preferably set at a temperature at which the reducing agent does not decompose thermally, usually 80°C or less, preferably 10 to 60°C.

Such a dispersion liquid is then irradiated with light to cause the aforementioned photocatalytic reaction to occur. The light may be any light having energy greater than the bandgap of the semiconductor particles, and light having a wavelength of 200 to 800 nm is usually used.

Of course, this light does not need to be monochromatic, so
Polychromatic light from a xenon lamp or mercury lamp as a light source may be applied. The irradiation time varies greatly depending on the amount of magnetic metal to be deposited, the liquid temperature, etc., but is generally about 1 to 10 hours.

The magnetic metal layer formed in this way is adhered to the surface of the semiconductor particle with good adhesion and uniformity, which contributes to stabilizing the magnetic properties and provides magnetic performance that can replace conventional magnetic powder. Provides excellent ferromagnetic powder.

``Effects of the Invention'' As described in 2 below, according to the present invention, it is possible to provide a ferromagnetic powder that has both properties as an abrasive and as a magnetic powder, and by using this magnetic powder as a magnetic recording element. It becomes possible to manufacture magnetic tapes and other magnetic recording media that satisfy both durability and electromagnetic conversion characteristics.

〔Example〕

EXAMPLES Below, examples of the present invention will be described in more detail.

Example 1 Water 101 Cobalt sulfate 950y Sodium hypophosphite 675y Sodium citrate 1,850y Ho
Acid: 975 g Mix the above ingredients, add an appropriate amount of caustic soda to the solution, and adjust the P of the liquid.
H was adjusted to 90, and titanium oxide CT i02 ) particles 50y- with a particle size of about 500X were added to this liquid and well dispersed. Next, while stirring this dispersion, output 1
Light was irradiated for 8 hours using a xenon lamp. Thereafter, the dispersed particles were taken out, washed with water, and dried to obtain a ferromagnetic powder in which a metallic cobalt layer was formed on the surface of the TlO2 particles.

Example 2 As non-magnetic semiconductor particles, titanium oxide particles were replaced with particles having an average particle diameter of 1. , oooX silicon carbide (SiC) particles 50
A ferromagnetic powder in which a metal cobal I layer was formed on the surface of SiC particles was obtained in the same manner as in Example 1 except that y was used.

Example 3 α-F was produced in the same manner as in Example 1, except that alpha hematite (α-Fez03) particles 50P with an average particle diameter of 500
A ferromagnetic powder was obtained in which a metallic cobalt layer was formed on the surface of e203 particles.

Example 4 A metallic cobalt layer was formed on the surface of Al2O3 particles in the same manner as in Example 1, except that alumina (A1203) particles 50y with an average particle diameter of 1,000 were used instead of titanium oxide as nonmagnetic semiconductor particles. ferromagnetic powder was obtained.

Example 5 A ferromagnetic powder in which a metallic cobalt layer was formed on the surface of T103 particles was obtained in the same manner as in Example 1, except that the amount of cobalt sulfate added was changed from 950y to 7507y.

Example 6 Ferrous sulfate 150 instead of copal sulfate l-950p
A ferromagnetic powder in which an iron-cobalt alloy layer was formed on the surface of TlO2 particles was obtained in the same manner as in Example 1 except that y and cobalt sulfate I-800y were used.

Example 7 1 Kobal) Instead of 950y, 150y of nickel sulfate
A ferromagnetic powder in which a nickel-cobalt alloy layer was formed on the surface of Tie particles was obtained in the same manner as in Example 1, except that Tie and cobalt sulfate 800y were used.

Comparative Example 1 In Example 3, 1y of PdC was added to IA' water to the mixed solution without adding titanium oxide particles.

After adding 20 CC of a Pd solution in which Pd was dissolved, a heating reaction was carried out at 80°C for 1 hour without irradiation with light to obtain spherical metal cobalt particles.

Magnetic paints were prepared by mixing and dispersing the magnetic powders obtained in the above Examples and Comparative Examples in a ball mill for 48 hours according to the following composition.

Ferromagnetic powder 800 parts by weight Polyurethane 70 parts by weight Polyisocyanate 20 parts by weight Methyl isobutyl ketone 500 parts by weight Toluene
Next, add 500 parts by weight of the above magnetic paint to a thickness of 12/2.
17n polyester base film with a dry thickness of 4. After coating and drying to obtain Irm, a magnetic tape was produced by cutting into a predetermined width. Table 1 shows the magnetic properties of the magnetic powders obtained in the Examples and Comparative Examples, as well as the prrn, p saturation magnetic flux density, and residual magnetic flux density of the magnetic tapes, as well as the rotation of the VTR at the same point on each tape. The results are shown in which the head was brought into sliding contact for one hour and the change in the output signal before and after the sliding contact was measured.

In addition, in Comparative Example 2- in Table 1, the magnetic powder of Comparative Example 1 was used, and 48 parts by weight of titanium oxide particles with an average particle diameter of 1) tyn were added to the magnetic paint, and the same procedure as described in 2. This figure shows the results of the produced magnetic tape. In addition, the output before and after each sliding contact is based on the output before sliding contact of Comparative Example 1 (OdB
) and is expressed as a relative value.

As is clear from Table 1, the magnetic tape with no abrasive added (Comparative Example 1) has a high magnetic flux density, but its durability is poor and the head becomes clogged, making it unplayable. The magnetic tape containing the additive (Comparative Example 2) has improved durability, but only low output can be obtained. In contrast, those according to this invention (Examples 1 to 7)
has a high magnetic flux density, a large output, and excellent durability.

Claims (3)

[Claims] (1) A ferromagnetic powder obtained by forming a magnetic metal layer containing at least one metal selected from iron, cobalt, and nickel as a main component on the surface of nonmagnetic semiconductor particles having a Mohs hardness of 3 or more. (2) The amount of the magnetic metal layer is 50 to 1,000 parts by weight based on 100 parts by weight of the non-magnetic semiconductor particles.
1) Ferromagnetic powder described in section 1). (3) Non-magnetic semiconductor particles are dispersed in a liquid medium containing a reducing agent and magnetic metal ions whose main component is at least one of iron, cobalt, and nickel, and the above-mentioned semiconductor particles are added to the dispersion. A method for producing a ferromagnetic powder, comprising reducing the metal ions on the surface of the semiconductor particle to form a magnetic metal layer by irradiating the semiconductor particle with light having an energy greater than the band gap of the particle.