JPH0520677A - Ferromagnetic metal fine particle - Google Patents

Abstract

PURPOSE:To obtain a ferromagnetic metal fine particles for magnetic recording medium excellent in oxidization resistance showing little secular deterioration for a long term by treating the surface of the particles with aq. soln. of boric acid or borate. CONSTITUTION:The surface of ferromagnetic metal particles is treated with an aq. soln. of boric acid or borate. As for the ferromagnetic metal fine particles, ferromagnetic metal material such as Fe, Co, Ni, etc., or ferromagnetic alloy material essentially comprising these elements are used. The boric acid ion in an borate aq. soln. used includes orthoboric acid ion, diboric acid ion, tetraboric acid ion and other polyboric acid ion. With this surface treatment, long-term stability and holding stability of magnetic characteristics can be significantly improved.

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
It is manufactured by applying a magnetic coating material composed of magnetic powder and binder resin on a support and drying. In recent years, in the field of magnetic recording, particularly in video tape recorders and the like, higher recording density is required 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 magnetic conversion characteristics in the frequency band are achieved. These iron or ferromagnetic metal fine particles composed of iron are iron oxide, iron oxyhydroxide, Co, Ni, Mn, Cu, Zn, T.
It is manufactured by reducing iron oxide, iron oxyhydroxide, etc. containing metals other than iron such as i and V with hydrogen gas and has magnetic recording characteristics superior to those of conventional iron oxide-based ferromagnetic fine particles. ing.

However, the ferromagnetic metal fine particles have a high surface activity and are easily oxidized in the atmosphere, and may be ignited in some cases. Such a property
As the magnetic powder becomes finer with the decrease in the number of nozzles in the magnetic recording medium, it tends to become stronger and stronger. Therefore, when it is used as a magnetic powder for a magnetic recording medium, it is stored on the support such as a polyester film during the storage of the ferromagnetic metal fine particles, the process of coating with a combination with a resin or an organic solvent, and the like. After applying and forming into a sheet,
During storage under conditions of temperature, humidity, etc., oxidation progresses mainly due to the influence of oxygen, certain gases, or water, which leads to deterioration of storage characteristics such as saturation magnetization over time. There was a problem. For this problem,
Generally, a liquid layer method or a vapor layer method is used to stabilize the metal fine particles by forming an oxide film on the surface to passivate them, or the ferromagnetic metal fine particles are treated with a certain metal element, a surfactant, This is dealt with by covering with an organic substance such as resin.

[0004]

However, the above-mentioned method of forming an oxide film to passivate or covering with a certain kind of metal element or organic substance surely suppresses the oxidation of the ferromagnetic metal particles, and It is hard to say that it is sufficient to prevent deterioration of recording characteristics over time. On the contrary, depending on the treatment method, when the surface treatment itself causes deterioration of the magnetic properties, there is a risk that the dispersibility at the time of forming a coating material may be reduced.

Therefore, the present invention has been made in view of such a situation, and by devising the surface treatment of the metal fine particles, the present invention is particularly excellent in oxidation resistance and has a strong strength for magnetic recording media with little deterioration over time. It is an object to provide magnetic metal fine particles.

[0006]

The inventors of the present invention have conducted extensive studies to achieve the above-mentioned object, and as a result, by treating the surface of ferromagnetic metal fine particles with an aqueous solution of boric acid or borate. The inventors have found that excellent storage stability can be realized, and have completed the present invention. here,
The ferromagnetic metal fine particles of the present invention include Fe, Co, Ni.
Ferromagnetic metal materials such as Fe-Co, Fe-Ni, Fe-
Co-Ni, Co-Ni, Fe-Mn-Zn, Fe-N
i-Zn, Fe-Co-Ni-Cr, Fe-Co-N
i-P, Fe-Co-B, Fe-Co-Cr-B, Fe
Various ferromagnetic alloy materials containing Fe, Co, and Ni as main components, such as —Co—V, can be cited. For the purpose of imparting or improving various properties to these, Al, Si, T
It also includes those to which elements such as i, Cr, Mn, Mg, and P are added. The specific surface area of these ferromagnetic metal fine particles is arbitrary, but is preferably 25 m ² / g or more, particularly 30 m ²
It was confirmed that when it is applied to a resin having a viscosity of 1 g / g or more, its effectiveness is high and it is effective for deterioration with time. The present invention resides in that the surface of the ferromagnetic metal fine particles is treated with an aqueous solution of boric acid or borate. Here, in borate aqueous solution,
Examples of borate ions include orthoborate ion, diborate ion, tetraborate ion, and other polyborate ions. As the cation that constitutes the borate,
In addition to monovalent cations such as NH ₄ ⁺ , Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ , and Cs ⁺ , divalent or trivalent metal ions are contained, and even a hydrogen salt coexisting with a proton may be used. Good. These may be used alone or in some cases, may be a mixed solution of two or more kinds.

[Action]

The surface of the ferromagnetic metal fine particles of the present invention is treated with an aqueous solution of boric acid or borate, and then the solvent is immediately removed. The surface of the ferromagnetic metal fine particles, which are generally called metal magnetic powder, forms a thin oxide film for the purpose of storage stability. This oxide film has an extremely irregular structure due to the expansion of volume associated with oxidation, and has a large specific surface area. Treating the surface with an aqueous solution of boric acid or borate as in the present invention closes the structural irregularity generated in the above-mentioned oxidation process, that is, micropolis, and prevents oxygen, water, certain corrosive gases, etc. from this site. It is considered that the effect of suppressing intrusion can be added. This is also suggested by the fact that the magnetism is maintained high when treated with boric acid or borate. Generally, chemically adsorbed water is present on the surface of the oxide film of such ferromagnetic metal fine particles, and among them, the hydroxyl group of the chemically adsorbed water bound to the hexacoordinated iron ion is basic. However, boric acid is an acid, and by the neutralization reaction with the basic hydroxyl group of surface chemically adsorbed water,
It is presumed that it dehydrates and forms a chemically stable film on the surface. This is, for example, 3690 cm in the infrared reflection absorption spectrum of a diluted sample of ferromagnetic metal fine particles.
It is also clear from the fact that the absorption band derived from the OH stretching vibration of the hydroxyl group in the chemically adsorbed water of ^-1 disappears by the treatment with boric acid.

[0008]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention should not be construed as being limited thereto. Example 1 Needle-shaped iron particles were used as the ferromagnetic metal particles for the magnetic recording medium. The particles have a specific surface area of 53.9 m ² / g,
Coercive force Hc = 1590 (Oe), saturation magnetization σs = 120
emu / g, average major axis length 0.3 μm, acicular ratio 8 to 1
It is 0. Boric oxide B ₂ O ₃ was used as boric acid. This was dissolved in water to prepare a 0.05 mol / 50 ml aqueous solution. As the treatment method, the particles were placed on a filter paper in a scattered state, and the aqueous solution was poured into the particles. The needle-like particles were almost completely filtered, washed repeatedly with ethanol, and then vacuum dried. The obtained ferromagnetic metal fine particles after the treatment were stored for 1 week under the conditions of a temperature of 60 ° C. and a humidity of 90%, and the deterioration with time of magnetic properties was examined by comparison with the initial value before the storage. The results are shown in Table 1. In addition, as a comparative example, untreated needle-shaped iron particles (Comparative Example 1) and needle-shaped iron particles simply immersed in water (Comparative Example 2) were stored under the same conditions as those of the above-mentioned Examples to prevent deterioration with time. It was measured. The effect is also shown in the table.

[Equation 1]

Example 2 In Example 2, the same acicular iron particles as in the previous example were used as the metal fine particles, but orthoboric acid H ₃ BO ₃ was used as the boric acid. Dissolve this orthoboric acid in water to give 0.05 mol /
It was adjusted to a 50 ml aqueous solution. As the treatment method, the particles were placed on a filter paper in a scattered state, and the aqueous solution was poured into the particles. The acicular iron particles were almost completely filtered, washed with ethanol repeatedly, and then vacuum dried. The obtained ferromagnetic metal fine particles after the treatment were stored for 1 week under the conditions of a temperature of 60 ° C. and a humidity of 90%, and the deterioration with time of magnetic properties was examined by comparison with the initial value before the storage. The results are shown in Table 2. As comparative examples, untreated iron particles (Comparative Example 1) and iron particles simply immersed in water (Comparative Example 2) were stored under the same conditions, and the deterioration with time was measured. The effect is also shown in the table.

[Equation 2]

Example 3 In Example 3, the same needle-shaped iron particles as in the previous example were used as the metal fine particles, but ammonium borate (N
Using H _{4) 3} BO _3. This ammonium borate was dissolved in water to prepare a 0.05 mol / 50 ml aqueous solution.
As the treatment method, the particles were placed on a filter paper in a scattered state, and the aqueous solution was poured into the particles. The acicular iron particles were almost completely filtered, washed with ethanol repeatedly, and then vacuum dried. The obtained ferromagnetic metal fine particles after the treatment were stored for 1 week under the conditions of a temperature of 60 ° C. and a humidity of 90%, and the deterioration with time of magnetic properties was examined by comparison with the initial value before the storage. The results are shown in Table 3. As comparative examples, untreated iron particles (Comparative Example 1) and iron particles simply immersed in water (Comparative Example 2) were stored under the same conditions, and the deterioration with time was measured. The effect is also shown in the table.

[Equation 3]

Based on the results of Tables 1 to 3 above, the effect of the surface treatment of the present invention is evaluated. Here, σs (Initial Dmage) and Hc (Initial Dma) are used as indices showing the initial saturation magnetization and the decrease in coercive force due to the surface treatment.
ge) As an index showing the loss of these values after 2 weeks △
σs and ΔHc are used. All of these values are evaluated by the following formula in units of%. σs = [-(σs treated powder initial value-σs untreated powder initial value) /
σs initial value of untreated powder] × 100 Hc = [− (initial value of Hc treated powder−initial value of Hc untreated powder) /
Hc untreated powder initial value] × 100 Δσs = [− (σs treated powder initial value−σs treated powder two weeks later) / σs untreated powder initial value] × 100 ΔHc = [− (Hc treated powder initial value Value-value after 2 weeks of Hc-treated powder) / initial value of Hc-untreated powder] × 100 The evaluation results obtained are listed in Table 4.

[Equation 4]

From Table 4, the following points become clear. (1) When water is used as the solvent, the decrease of the initial value in the saturation magnetization is as small as σs of 0.36%. Therefore, the use of water as the treatment solvent is not a problem. (2) Deterioration of saturation magnetization when stored for 2 weeks under conditions of temperature of 60 ° C and humidity of 90% is much smaller when boric acid is treated than when treated only with water, and the oxidation resistance is high. Remarkably observed. In the untreated case, Δσs is 17.63% under the same conditions. (3) The present invention also significantly suppresses the decrease in the holding power when stored for 2 weeks under the conditions of a temperature of 60 ° C. and a humidity of 90%. In the case of untreated one, ΔHc is −9.48% under the same conditions. Therefore, considering that ΔHc when treated with only water is −1.69%, the metal magnetic powder oxide film can be considerably suppressed only by treating with water. (4) The initial value of the coercive force becomes a positive value by the B ₂ O ₃ treatment, and this value is maintained even after 2 weeks, which means that the treatment effectively blocks the structural irregularity of the surface of the metal fine particles. Suggests that.

[0013]

As is clear from the above examples, by performing the treatment of the present invention as compared with the untreated one, a remarkable decrease in the saturation magnetization with time is observed, and at the same time, the coercive force is stably maintained. Be drunk Also, the use of an aqueous solvent with this treatment does not affect the magnetic properties of the metallic magnetic particles. Therefore, the present invention can remarkably improve the temporal stability and the retention stability of the magnetic properties.

Claims (1)

1. A ferromagnetic metal fine particle for a magnetic recording medium, wherein the metal fine particle is surface-treated with an aqueous solution of boric acid or borate.