JPS61252605A - Magnetic powder of iron oxide - Google Patents

Abstract

PURPOSE:To obtain magnetic powder which is magnetically and chemically stable and has excellent anti-magnetic force distribution characteristic by using an intermediate material of magnetite as the core crystal, covering the surface thereof with an oxide including iron of bivalent and/or zinc and moreover covering the surface with a cobalt compound. CONSTITUTION:An intermediate material of magnetite expressed by the general expression, (FeO)x.Fe2O3 (where, 0.1<=x<=0.8) is used as the core crystal, the surface thereof is covered with an oxide including the iron of bivalent or an oxide including the iron of bivalent and zinc, and the surface is then covered with the cobalt compound. An oxide layer including Fe<2+> or an oxide layer including Fe<2+> and Zn can be formed, for example, by dispersing the intermediate material powder of magnetite into the alkali solution and then adding thereto the aqueous solution of ferrous salt or mixed aqueous solution of ferrous salt and zinc salt. The cobalt compound layer is usually formed as the hydroxide of cobalt Co(OH)2 but it may be formed as the oxide, CoOOH, Co3O4, CoO through further heat treatment.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to iron oxide magnetic powder used in coated magnetic recording media such as magnetic tapes and magnetic disks. The present invention relates to an improvement in a cobalt-containing iron oxide magnetic powder having a compound layer.

[Summary of the invention]

The present invention uses a magnetite intermediate as a nucleus crystal in Co-containing iron oxide magnetic powder whose surface is coated with a cobalt compound, and the surface is coated in advance with an oxide containing divalent iron and/or zinc. By further coating the surface with a cobalt compound, it is attempted to obtain a magnetic powder that is magnetically and chemically stable and has excellent coercive force distribution.

[Conventional technology]

Conventionally, y-
Fs, O, particles, especially acicular r-FezOs particles, which have high coercive force due to shape anisotropy, are widely used. These acicular γ-Fet02 particles have advantages such as excellent chemical and magnetic stability and low price.

By the way, in general, in magnetic recording media, the coercive force of magnetic powder is an important factor that affects the recording and reproducing characteristics, and by increasing this coercive force, demagnetization can be suppressed and
It is also known that recording density can be improved. In response to demands for improved performance of video tapes, audio tapes, etc., it is necessary to further increase the coercive force of the magnetic powder.

Therefore, in the past, cobalt compounds were used as T-Fl! ! So-called cobalt-adhered TFeze adsorbed on the surface of 03 particles
It has been proposed to use s particles as magnetic powder.

In this cobalt-coated γ-Fezos particle, the coercive force is increased by concentrating the effect of cobalt ions on the particle surface, and the phenomenon of increase in coercive force over time and the temperature dependence of magnetic properties are improved. is possible. However, in the cobalt-coated γ-FetO particles, although the coercive force increases as the amount of cobalt adsorbed increases, the inventors have found that on the other hand, the saturation magnetization σ per unit weight decreases. This became clear.

If this saturation magnetization σ1 decreases, it will adversely affect electromagnetic characteristics, such as a decrease in recording and reproducing output.

Alternatively, in order to ensure the above-mentioned saturation magnetization σ, it has been considered to use magnetite intermediate particles as nucleus crystals and form a cobalt compound layer on the surface, but in this case, it is also possible to easily increase the coercive force. However, compared to the case of using r-Fe, O, particles, it lacks magnetic stability, tends to increase the change in coercive force over time, and tends to deteriorate the temperature characteristics of magnetic properties. be.

[Problem that the invention seeks to solve]

In this way, in order to ensure saturation magnetization σ8 and obtain high coercive force, if a cobalt compound is adsorbed on the surface of the core magnetite intermediate, Co ions will diffuse into the magnetite intermediate, and the temperature dependence of coercive force will increase. There were problems such as an increase in the magnetism, and changes in the coercive force and saturation magnetization σ over time could not be suppressed.

Therefore, the present invention suppresses the diffusion of Co ions into the magnetite intermediate, and improves the temperature characteristics of coercive force and coercive force.

It improves the temporal change of saturation magnetization σ, and further increases the coercive force He.
The purpose is to provide iron oxide magnetic powder with excellent distribution.

(Means for Solving the Problems) As a result of intensive research to achieve the above-mentioned object, the present inventors have determined that Fe@ The present invention was completed by discovering that by forming an oxide layer containing + or an oxide layer containing Fe1- and Zn, it is possible to effectively suppress the diffusion of Co ions into the magnetite intermediate. The magnetite intermediate represented by -i formula % formula %) is used as a nucleus crystal, and its surface is coated with an oxide containing divalent iron or an oxide containing divalent iron and zinc. It is characterized in that the surface is coated with a cobalt compound.

In the iron oxide magnetic powder of the present invention, the surface of the magnetite intermediate which is the nucleus crystal is an oxide layer containing Fe" or
These oxide layers are coated with an oxide layer containing, for example, magnetophyte intermediate particles in an alkaline solution and then an aqueous solution of a ferrous salt or a combination of a ferrous salt and a zinc salt. Formed by adding a mixed aqueous solution.

Here, the ferrous salts used include ferrous chloride,
Examples include ferrous ii-acid, and zinc salts include zinc chloride,
Examples include zinc sulfate. Further, as the alkali, sodium hydroxide, potassium hydroxide, lithium heptahydroxide, etc. are used.

On the other hand, the magnetite intermediate coated with the above oxide layer is further coated with a cobalt compound, and this cobalt compound is also obtained by adding an aqueous solution of a cobalt salt such as cobalt chloride, cobalt a, cobalt sulfate, etc. to an alkaline solution. It is formed by

The cobalt compound layer is usually made of cobalt hydroxide C.
o (OH)! Co OOH, Co 304. C.

It may also be an oxide such as O. Alternatively, in an alkaline solution of a metal salt containing a ferrous salt and a cobalt salt, an oxidation reaction is carried out by blowing in an oxidizing gas such as air or adding an oxidizing agent such as HyO□. The iron layer may be epitaxially grown.

The cobalt compound layer is formed by adding the ferrous salt or an aqueous solution containing the ferrous salt and zinc salt, stirring at a temperature below the boiling point for 30 minutes or more, and then adding an aqueous solution of the cobalt salt. It is preferable to do so. If the cobalt salt is added too soon, not only will the desired effect not be obtained, but the coercive force Hc distribution will widen and magnetic stability will also be lost.

[Effect]

In this way, by first forming an oxide layer containing ferrous iron or ferrous iron and zinc on the surface of the magnetite intermediate, and then forming a cobalt compound layer containing cobalt atoms, CO ions can be absorbed into the magnetite intermediate. Diffusion into the body is suppressed, and the temperature characteristics of coercive force HC and changes over time in coercive force Hc and saturation magnetization σ8 are improved.

〔Example〕

Hereinafter, specific examples of the present invention will be described, but the present invention is not limited to these examples.

Example 1゜Coercive force Hc420 (Oe) x saturation magnetization σ* 79 em
u/g magnetite intermediate (F e”/F e”=0
．． After dispersing 100 g of ferrous sulfate (25%) in 860 ml of an aqueous solution containing 115.2 g of sodium hydroxide,
Add 100 ml of an aqueous solution containing 7.41 g and incubate at 70°C for 3
After stirring for 0 minutes, the temperature was raised, and the mixture was stirred at 100° C. for 30 minutes.

Then an aqueous solution 1 containing 10.43 g of cobal chloride
00nl! was added and stirred for 6 hours, followed by dehydration and drying.

When the magnetic properties of the magnetic powder thus obtained were measured, the coercive force Hc was 650 (Oe) x saturation magnetization σ,
is 80. It was Oemu/g.

Also, when a magnetic tape was made using this magnetic powder, the coercive force He of this magnetic tape was 680 (Oe) x 59 dB for transfer and 59 dB for erasing. It was 2.5du.

Example 2 Magnetite intermediate 1 similar to that used in Example 1 above
00g to an aqueous solution containing 115.2g of sodium hydroxide 8
100 mj of an aqueous solution containing 17.41 g of ferrous sulfate and 2.15 g of zinc sulfate after being dispersed in 60 ml! was added, stirred at 70°C for 30 minutes, then raised to temperature, and heated to 100°C for 30 minutes.
Stirred for 0 minutes.

Then, 100 g of an aqueous solution containing 10.43 g of cobal chloride
mj! was added and stirred for 7 hours, followed by dehydration and drying.

When the magnetic properties of the magnetic powder thus obtained were measured, the coercive force He was 653 (Oe) x saturation magnetization σ1
was 81.2 emu/g.

Further, when a magnetic tape was produced using this magnetic powder, the coercive force Hc of this magnetic tape was 685 (Oe) x 59.5 dB for transfer and 73 dB for erasure.

Example 3 Magnetite intermediate 1 similar to that used in Example 1 above
Aqueous solution containing 15.2 g of sodium hydroxide 8
After dispersing in 60 ml, 100 ml of an aqueous solution containing 17.41 g of ferrous sulfate was added.

Then immediately 100 mj of an aqueous solution containing 10.43 g of cobal chloride)! was added, stirred at 100°C for 3 hours, and then dehydrated and dried.

When the magnetic properties of the magnetic powder thus obtained were measured, the coercive force Hc was 640 (Oe) x km and the sum magnetization σ was 81.2 emu/g.

Further, when a magnetic tape was produced using this magnetic powder, the coercive force He of this magnetic tape was 678 (Oe) x 57.5 dB for transfer and 63.5 aB for erasure.

Comparative Example 1 Magnetite intermediate 1 similar to that used in Example 1 above
00g to an aqueous solution containing 115.2g of sodium hydroxide 18
After dispersing in 60 m#, 100 n1 of an aqueous solution containing 8.94 g of cobalt chloride was added, stirred at 100° C. for 6 hours, and then dehydrated and dried.

When the magnetic properties of the magnetic powder thus obtained were measured, the coercive force He was 650 (Oe) x saturation magnetization σ1
was 79.5 emu/g.

Further, when a magnetic tape was produced using this magnetic powder, the coercive force Hc of this magnetic tape was 680 (Oe) x 58 dB for transfer and 66 dB for erasure.

Comparative Example 2 Magnetite Intermediate 1 similar to that used in Example 1 above
After dispersing 00g in 860mi of an aqueous solution containing 1.15.2g of sodium hydroxide, 10.43ml of cobalt chloride
100 mj of aqueous solution containing g! was added and stirred at 100°C for 6 hours.

Next, 100 ml of an aqueous solution containing 17.41 g of ferrous sulfate
[ was added, stirred for 1 hour, and dehydrated and dried.

When the magnetic properties of the magnetic powder thus obtained were measured, the coercive force Hc was 655 (Oe) x saturation magnetization σ1
was 82.3 emu7g.

Further, when a magnetic tape was produced using this magnetic powder, the coercive force Hc of this magnetic tape was 682 (Oe) x 54.1 dB for transfer and 64.5 dB for erasure.

Example 1 above. Example 2. Comparative example 1. For each magnetic powder obtained in Comparative Example 2, the temperature characteristics of coercive force Ha were investigated. The results are shown in Figure 1. In addition, in this Figure 1,
Curve a shows the temperature characteristics of the magnetic powder obtained in Example 1 and Example 2, Curve A shows the temperature characteristics of the magnetic powder obtained in Comparative Example 1, Curve C shows the temperature characteristic of the magnetic powder obtained in Comparative Example 2. The temperature characteristics of each are shown below.

From FIG. 1, it is clear that the magnetic powders obtained in the Examples according to the present invention all had improved temperature characteristics compared to the Comparative Examples.

Furthermore, the time-dependent change ΔHe in the coercive force Hc and the time-dependent change Δσ in the saturation magnetization σ of each of these samples at 100° C. in air were investigated. The results are shown in Figures 2 and 3, respectively. In these Figures 2 and 3, curve A
Curve B represents Example 12, Curve C represents Comparative Example 11, and Comparative Example 2.

From these FIGS. 2 and 3, it can be seen that in the examples of the present invention, improvements were seen in both the coercive force Hc and the saturation magnetization σ1, and the effect was particularly large in Example 2.

〔Effect of the invention〕

As is clear from the above description, in the iron oxide magnetic powder of the present invention, the magnetite intermediate is used as a nucleus crystal, and the surface thereof is coated in advance with an oxide layer containing ferrous iron or ferrous iron and zinc. Furthermore, since it is coated with a cobalt compound, the temperature characteristics of the coercive force He, the coercive force Ha, and the saturation magnetization σ, which occur when the magnetite intermediate is coated with Co to increase the coercive force He, change over time. The deterioration of iron oxide can be improved, and an iron oxide magnetic powder with high coercive force Hc and excellent magnetic stability can be obtained.

Furthermore, since a magnetite intermediate is used as the nucleus crystal, a high saturation magnetization σ can be achieved.

Furthermore, according to the present invention, an iron oxide magnetic powder having excellent coercive force Hc distribution and good transfer and erasing properties can be obtained.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram showing the temperature characteristics of coercive force Hc in each magnetic powder of Examples and Comparative Examples of the present invention, Figure 2 is a characteristic diagram showing changes in coercive force Hc over time, and Figure 3 is a characteristic diagram showing the change in coercive force Hc over time. FIG. 3 is a characteristic diagram showing changes in magnetization σ over time.

Claims (1)

[Claims] General formula (FeO)_x-Fe_2O_3 (however, 0.1
≦x≦0.8) is used as a nucleus crystal, its surface is coated with an oxide containing divalent iron or an oxide containing divalent iron and zinc, and the surface is further coated with an oxide containing divalent iron or oxide containing divalent iron and zinc. Iron oxide magnetic powder coated with a cobalt compound.