JPH0540934A - Ferromagnetic metal particles for magnetic recording media - Google Patents

Abstract

(57) [Summary] [Object] To provide ferromagnetic metal fine particles for a magnetic recording medium, which prevent deterioration of magnetic properties due to oxidation over time. The present invention relates to a ferromagnetic metal particle used in a coating type magnetic recording medium in which a magnetic layer mainly composed of magnetic powder and a binder is formed on a non-magnetic support, and a metal used in the magnetic layer. It is characterized in that the surface of the fine particles is treated with Rongalit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to ferromagnetic metal fine particles used as magnetic powder for a coating type magnetic recording medium.

[0002]

2. Description of the Related Art Generally, a magnetic recording medium such as a magnetic tape is manufactured by applying a magnetic coating material composed of magnetic powder and a binder resin on a support and drying the coating. In recent years, in the field of magnetic recording, particularly in video tape recorders and the like, higher recording density is required in order to achieve high image quality. Along with this increase in density, iron or a metal material mainly containing iron has been used in place of the iron oxide-based material that has been conventionally used as magnetic powder for magnetic recording media and the like. In recent years, in order to meet such demands, a material having an extremely fine particle shape has been supplied, and by using this as a magnetic powder of a magnetic recording medium, a high recording density and a high recording density can be obtained. Excellent electromagnetic conversion characteristics in the high frequency band are achieved. These iron or ferromagnetic metal fine particles composed of iron are iron oxide, iron oxyhydroxide, Co, Ni, Mn, Cu, Z.
It is produced by reducing iron oxide or iron oxyhydroxide containing a metal other than iron such as n, Ti, and V with hydrogen gas.
These ferromagnetic metal particles have magnetic recording characteristics superior to those of conventional iron oxide-based ferromagnetic fine particles.

However, the above-mentioned ferromagnetic metal fine particles have a high surface activity and have a characteristic that they are easily oxidized in the atmosphere, and they may be ignited in some cases. Such properties tend to become stronger as the magnetic powder becomes finer as the noise of the magnetic recording medium becomes lower. For this reason, when the above-mentioned ferromagnetic metal fine particles are used as the magnetic powder of a magnetic recording medium, during the storage of the ferromagnetic metal fine particles or during the process of forming a coating by a combination with a resin, an organic solvent, etc. After coating on a support such as a film to form a sheet, a predetermined atmosphere and temperature,
During storage under conditions such as humidity, oxidation progresses mainly due to the effects of oxygen, certain gases, and moisture, which leads to deterioration of magnetic properties such as saturation magnetization over time, causing problems with storage stability. It was

To solve this problem, in order to stabilize the surface of the ferromagnetic metal fine particles, an oxide film is generally formed on the surface of the particles by a liquid phase method or a gas phase method to passivate them. The method of making has been taken. Also, a method of covering the ferromagnetic metal fine particles with a certain metal element, a surfactant, or an organic substance such as resin has been used.

[0005]

However, in the method of forming the oxide film passivation and the method of covering with a certain kind of metal element or organic substance, the oxidation of the ferromagnetic metal fine particles is suppressed,
It is not always sufficient to prevent deterioration of magnetic recording characteristics over time. On the contrary, depending on the treatment method, there is a possibility that the surface treatment itself may cause deterioration of the magnetic recording characteristics, or that the dispersibility may be lowered when the coating material is formed.

Therefore, the present invention has been proposed in view of such circumstances, and by treating the surface of the ferromagnetic metal fine particles for a magnetic recording medium, the magnetic recording is excellent in oxidation resistance and less deteriorated with time. It is an object of the present invention to provide ferromagnetic metal fine particles for media.

[0007]

Means for Solving the Problems As a result of intensive research aimed at solving the above-mentioned problems, the inventors of the present invention have achieved remarkable preservation by treating the surface of ferromagnetic metal fine particles for magnetic recording media with Rongalit. The inventors have found that stability is realized and have completed the present invention.

The ferromagnetic metal fine particles for a magnetic recording medium in the present invention include ferromagnetic metal materials such as Fe, Co and Ni, Fe-Co, Fe-Ni, Fe-Co-Ni and C.
o-Ni, Fe-Mn-Zn, Fe-Ni-Zn, Fe
-Co-Ni-Cr, Fe-Co-Ni-P, Fe-C
F such as o-B, Fe-Co-Cr-B, Fe-Co-V
Ferromagnetic metal fine particles composed of various ferromagnetic alloy materials containing e, Co, and Ni as main components, and further Al, Si, Ti, Cr, Mn, and C for the purpose of improving various characteristics.
It may be one to which an element such as u, Zn, Mg or P is added. Although the specific surface area of these ferromagnetic metal fine particles is arbitrary, it is highly effective when applied to a specific surface area of 25 m ² / g or more, particularly 30 m ² / g or more.

In the present invention, the fine metal particles for the coating type magnetic recording medium containing the above-mentioned fine ferromagnetic metal particles contain Rongalit. The ferromagnetic metal particles are
Treatment is carried out in water or an organic solvent containing this compound.
Further, these compounds may be used alone or in combination of different kinds of compounds.

Rongalit has the general formula HOCH ₂ SO ₂ N
Represented by a.2H ₂ O, its water-soluble, aqueous solution is obtained from the reaction of formalin with sodium dithionite in an alkaline solvent, which is a typical sulfoxylate salt. Rongalit is reductive and its reducing power is stronger than sulfite, but not as strong as lithium aluminum hydroxide. Lithium aluminum hydride dissolved in the dehydrated organic solvent reduces to the oxide film on the surface of the metal fine particles, but Rongalit does not have a reducing ability enough to reduce the oxide film.

As a method of surface-treating the ferromagnetic metal fine particles with the Rongalit, for example, a method of immersing the ferromagnetic metal fine particles in a treatment liquid dissolved in an aqueous solvent can be mentioned. In this case, the solvent for the Rongalit is not particularly limited, but any of water, alcohol solvents such as ethanol, ketone solvents such as acetone, and aromatic solvents such as toluene can be used. However, the solubility in an organic solvent is extremely low, and an organic solvent having a high relative dielectric constant is required to improve the solubility. The amount of the compound used is 0.03 to 30 parts by weight, preferably 0.1 to 10 parts by weight, based on 100 parts by weight of the magnetic metal particles. When the amount is out of the above range, a small amount cannot be obtained, and when the amount is out of the above range, the effect is not changed, and the excess amount is wasted. May adversely affect the physical properties of. Rongalit may be used alone or as a mixture.

[0012]

[Function] By treating the surface of the ferromagnetic metal fine particles with the solution of Rongalit, it is possible to enhance the strength during the storage of the ferromagnetic metal fine particles, the preparation of the magnetic coating material containing the ferromagnetic metal fine particles, and the storage of the magnetic recording medium. The oxidation reaction on the surface of the magnetic metal fine particles is prevented. It is considered that this is because the reducing property of Rongalit effectively functions and the shape of the oxide lattice on the surface of the metal fine particles, that is, the oxidation is effectively suppressed. Also, Rongalit has a deoxidizing effect, and by blocking the pores (micropores) existing in the oxide film on the surface of the ferromagnetic metal fine particles, the Rongalit prevents oxygen atoms from penetrating into the oxide film. It seems that effective oxidation resistance is developed.

In the present invention, the treatment can be most effectively performed when water is used as the treatment solvent. However, as shown in the examples, the ferromagnetic metal fine particles are not affected by the water solvent. Not only does it have no adverse effect on the magnetic properties, but conversely, the results of accelerated tests of changes over time show that the magnetic properties are better retained than untreated metal fine particles. In particular, although the value of the coercive force immediately after the treatment decreased, the decrease of the coercive force during the accelerated test of aging change was remarkably improved. The surface of the ferromagnetic metal fine particles has a thin oxide film for the purpose of stabilization. In the process of forming this oxide film, the volume of the ferromagnetic metal fine particles expands, and micropores are generated in the oxide film due to structural irregularity. It is considered that the oxidation of the metal fine particles preferentially occurs from the active point due to such structural irregularity. Treatment with water causes a temporary reaction between such active sites and water or dissolved oxygen, causing a decrease in saturation magnetization and coercive force, but this in turn deactivates the active sites. But also. This is considered to be the reason why the magnetic properties are better than those of untreated metal after the accelerated test of aging.

[0014]

The present invention will be described below with reference to examples.
Needless to say, what is limited by the embodiments of the present invention
is not. -Example-The concentration of Rongalit used in the examples shown in Table 1 below,
The sample used for the comparative example is shown. The ferromagnetic metal particles used are
Relatively small specific surface area (SSA: 53m ²/ G)
Is.

[0015]

[Table 1] To each 50 ml of this aqueous solution, 2.0 g of ferromagnetic metal fine particles were added and left for 2 hours. Then, filtration was performed using a membrane filter, and the obtained ferromagnetic metal fine particles were vacuum dried for 8 hours while being kept at 30 ° C. to obtain a treated powder.

The coercive force H _C and the saturation magnetization σs of the obtained treated powder were measured immediately after drying. 90% humidity thereafter,
After leaving it in a thermo-hygrostat kept at 60 ℃ for 2 weeks,
The same measurement was performed again to evaluate the amount of decrease over time. As a comparative example, fine metal particles that have been treated by immersion in water only,
With respect to the ferromagnetic metal fine particles that were dried without the surface treatment, the change with time of the magnetic characteristics was examined by the above method. Here, Δσs and ΔHc are used as indexes showing the decrease in saturation magnetization and coercive force during the storage period of 2 weeks. Here, all of these values are evaluated in the unit of% by the following formula. The results are shown in Table 2. Δσs = [− (σs treated powder initial value−σs treated powder 2 weeks later value) / σs treated powder initial value × 100 ΔHc = [− (Hc treated powder initial value−Hc treated powder 2 weeks later value) / Hc treated powder Initial value] × 100 In the table, sample 1 is metal fine particles stored for 2 weeks and sample 2 for 3 weeks together with nitrous oxide, and comparative example 1 is untreated.

[0017]

[Table 2] -Examples-Metallic fine particles having a large specific surface area (SSA: 57 m ² / g)
Was used and treated and tested in the same manner as in the example. Table 3 below shows the concentration of Rongalit used in Examples and the samples used in Comparative Examples.

[0018]

[Table 3] To each 50 ml of this aqueous solution, 2.0 g of ferromagnetic metal fine particles were added and left for 2 hours. Then, filtration was performed using a membrane filter, and the obtained ferromagnetic metal fine particles were vacuum dried for 8 hours while being kept at 30 ° C. to obtain a treated powder.

The coercive force H _C and the saturation magnetization σs of the treated powder thus obtained were measured immediately after drying. 90% humidity thereafter,
After leaving it in a thermo-hygrostat kept at 60 ℃ for 2 weeks,
The same measurement was performed again to evaluate the amount of decrease over time. In addition, as a comparative example, metal fine particles subjected to a treatment soaked only in water,
With respect to the ferromagnetic metal fine particles that were dried without the surface treatment, the change with time of the magnetic characteristics was also examined by the method described above. Hereinafter, evaluation was performed in the same manner as in Examples, and the results are shown in Table 4.

[0020]

[Table 4]

[0021]

As is apparent from the examples, as compared with the untreated magnetic powder, by performing the aqueous solution treatment including the case of only water, a remarkable decrease in the saturation magnetization with time was observed, and the same retention was observed. The magnetic force is also kept stable. In addition, when Rongalit is obviously used, its effect is remarkable. Further, not only the negative effect of using the aqueous solution as the treatment solvent is not found, but also a remarkable improvement can be seen by only treating with water as compared with the case of no treatment. Therefore, according to the present invention, the ferromagnetic metal powder for a magnetic recording medium is remarkably improved in the temporal stability of the magnetic properties and the storage stability.

Claims (1)

[Claims] 1. Ferromagnetic metal fine particles for a magnetic recording medium, the surface of which is treated with Rongalit.