JPS5854485B2 - Metal magnetic powder and processing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a metal magnetic powder useful as a recording element of a magnetic recording medium and a processing method, and its purpose is to provide a metal magnetic powder with excellent oxidation resistance and dispersibility. It is in the point of doing.

Metal magnetic powders such as metal iron powders are generally manufactured by heating and reducing metal oxide powders, and have very high coercive force (He) compared to oxide-based magnetic powders. Due to its excellent magnetic performance, its future potential is expected.

However, metal magnetic powders are easily oxidized in the air, and as the oxidation progresses, magnetic properties such as saturation magnetization (σS) deteriorate over time, which is a problem in terms of storage stability, and there is a high risk of ignition, which is a safety concern. Furthermore, when preparing magnetic paint for use in magnetic recording media such as magnetic tapes, particles tend to aggregate and cannot be uniformly dispersed in the binder, resulting in poor sensitivity characteristics and S/N ratio. There are disadvantages such as insufficient

For this reason, conventionally, metal magnetic powder immediately after thermal reduction is immersed in an organic solvent such as toluene or xylene, filtered, and air-dried to gradually oxidize the particle surface to form oxides. Attempts have been made to form a film to improve oxidation resistance, or to coat the particle surface with various substances to improve oxidation resistance and dispersibility.

However, at present, even with these methods, sufficiently satisfactory oxidation resistance and dispersibility have not been achieved.

The inventors have conducted various studies to improve the drawbacks inherent in metal magnetic powder as described above, and have found that if the particle surface of metal magnetic powder is coated with a lanolin fatty acid salt, it will have excellent acid resistance. The inventors have discovered that this invention provides excellent magnetic powder filling properties and paint fluidity when preparing a magnetic paint for use in magnetic recording media. .

Lanolin fatty acids refer to fatty acids made from wool fat.
Although it contains various fatty acid components like beef tallow fatty acid, its salt has a characteristic that it has good solubility in organic solvents such as toluene.

Therefore, in order to coat the particle surface of metal magnetic powder, a simple operation of immersing the metal magnetic powder in an organic solvent in which a salt of lanolin fatty acid is dissolved is sufficient, and the coating on the particle surface that is formed is It becomes very uniform and dense.

Other common fatty acid salts, such as alkali metal salts and ammonium salts of simple fatty acids with about 6 to 26 carbon atoms, have low solubility in water, but have little or no solubility in organic solvents such as toluene. does not indicate.

Metal magnetic powders are unsuitable for treatment in an aqueous medium, so coating with these fatty acid salts is carried out using a suspension of fatty acid salt powder dispersed in an organic solvent. In this case, a film lacking in density and uniformity is formed in which the fatty acid salt powder is merely adhered, and as a result, sufficient oxidation resistance and dispersibility as in the present invention are not imparted.

The metal magnetic powder that is the object of this invention is preferably a powder containing iron as a main ingredient and optionally containing elements such as cobalt, chromium, or nickel. An alloy powder consisting of two or more of , cobalt, and nickel may also be used.

Calcium salts are the best salts of lanolin fatty acids.

In addition, the amount of coating is 0.7 to 5 w with respect to the metal magnetic powder.
t% is preferable; if it is less, the effect of improving oxidation resistance and dispersibility will be insufficient; if it is too much, a magnetic coating is prepared and applied to the substrate to form a magnetic layer. This may cause bleed-out or the paint film may become viscous.

Toluene is the most preferred organic solvent.

Coating treatment with salts of lanolin fatty acids can also be carried out by dissolving the above salts in the organic solvent, since ordinary metal magnetic powder is immersed in an organic solvent such as toluene after being generated by thermal reduction. It can also be carried out by immersing a metal magnetic powder, either untreated or subjected to various other treatments such as air drying, into an organic solvent in which the above-mentioned salts are dissolved.

Hereinafter, this invention will be explained in detail with reference to Examples.

Example 1 0.1 per 100 parts (by weight, same below) of toluene
5 parts of lanolin fatty acid calcium was dissolved under heating at 90°C, 10 parts of metal iron magnetic powder (average major axis 0.4 μrrL) was added to this solution, and stirred and mixed for 5 hours.
When vacuum drying was performed, a metal iron magnetic powder whose particle surface was coated with about 1.5 wt% calcium lanolin fatty acid was obtained.

Example 2 The amount of lanolin fatty acid calcium in Example 1 was varied to produce various metal iron magnetic powders with different amounts of calcium salt coating.

Comparative Example 1 The same treatment as in Example 1 was carried out using a suspension prepared by dispersing 1.5 parts of sodium stearate powder in 100 parts of toluene instead of the toluene solution of calcium lanolin fatty acid in Example 1. I did it.

For each of the metal iron magnetic powder obtained in Example 1 and Comparative Example 1, and the conventional general metal iron magnetic powder (Comparative Example 2) immersed in toluene and air-dried, 60
FIG. 1 shows the change over time in the saturation magnetization (σS) when placed in a corrosive atmosphere at 90% RH.

In the figure, curve A shows the change in the saturation magnetization amount of Example 1, curve B shows the change in Comparative Example 1, and curve C shows the change in Comparative Example 2.

Using the crushed metal iron magnetic powders of Example 1 and Comparative Examples 1 and 2, magnetic paints having the following compositions were prepared.

Metallic iron magnetic powder (example or comparative example)...7
0 copies.

Binder: 20 parts of VAGH (manufactured by UCC, USA, vinyl chloride, vinegar, vinyl alcohol prepolymer), 2'
7 parts of Tupol N1432J (manufactured by Nippon Zeon Co., Ltd., acrylonitrile-butadiene copolymer), 3 parts of Coronate L (manufactured by Nippon Polyurethane Co., Ltd., trifunctional polyisocyanate).

Additives: 1.4 parts of carbon black and 0.5 parts of liquid paraffin.

Solvent: 100 parts of methyl isobutyl ketone and 100 parts of toluene.

Each of these magnetic paints was coated with a thickness of 11μ according to the usual method.
A magnetic tape was manufactured by applying the film to a polyester film of 4 μm to a dry coating thickness of 4 μm, and the squareness ratio (Br/Bs) and maximum magnetic flux density (Bs
) are shown in the table below.

As is well known, the dispersibility of magnetic powder is expressed as the squareness ratio, and the filling property and fluidity (viscosity) of the paint are expressed as changes in maximum magnetic flux density.

On the other hand, the maximum magnetic flux density and squareness ratio were measured when magnetic tapes were manufactured in the same manner as above for each of the various metal magnetic powders with different coating amounts of lanolin fatty acid calcium obtained in Example 2. did.

The results are shown in FIG. 2 in comparison with the amount of lanolin fatty acid calcium coating.

Curve means the squareness ratio of the magnetic tape.

From the above results, the metal magnetic powder according to the present invention has excellent oxidation resistance and storage stability because the particle surface is coated with lanolin fatty acid salt, and it can be used to create magnetic It can be seen that the dispersibility and filling properties of the magnetic powder when the coating material is prepared and the fluidity of the coating material are improved, making it possible to provide a magnetic recording medium with excellent magnetic properties.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram showing the change over time in the saturation magnetization of the metallic iron magnetic powders of Examples and Comparative Examples, and Figure 2 is a graph showing the variation in the amount of lanolin fatty acid calcium coating, the maximum magnetic flux density, and the squareness ratio of the magnetic tape. FIG. A: Saturation magnetization change curve of magnetic powder of Example 1, B: Comparative example 1, C: Comparative example 2, D: ...The maximum magnetic flux density of the magnetic tape, E...The curves of changes in the squareness ratio of the magnetic tape.

Claims (1)

[Scope of Claims] 1. A metal magnetic powder characterized in that the particle surface is coated with a film containing a lanolin fatty acid salt. 2. The metal magnetic powder according to claim 1, wherein the lanolin fatty acid salt is a calcium salt. 3. A method for treating metal magnetic powder, which comprises dissolving a salt of lanolin fatty acid in an organic solvent, and mixing the metal magnetic powder by immersing it in this solution. 4. The method for processing metal magnetic powder according to claim 3, wherein the metal magnetic powder is a magnetic powder mainly composed of metal iron. 5. The method for treating metal magnetic powder according to claim 3 or 4, wherein the lanolin fatty acid salt is a calcium salt. 6 Claim 3, in which the organic solvent is toluene,
The method for treating metal magnetic powder according to item 4 or 5.