JPH0312441B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing magnetic powder for magnetic recording media suitable for high-density magnetic recording.

Magnetic recording usually relies on a method that uses magnetization in the longitudinal direction of the surface of the recording medium. However, with this recording method that uses magnetization in the in-plane longitudinal direction, if an attempt is made to increase the recording density, the demagnetizing field within the recording medium will increase, so the recording density cannot be improved that much.

Therefore, in order to eliminate such inconvenience,
In recent years, perpendicular magnetic recording methods have been proposed that use magnetization in a direction perpendicular to the surface of a recording medium. This perpendicular magnetic recording method can be said to be a recording method essentially suitable for high-density recording, since the demagnetizing field in the recording medium decreases as the recording density increases.

However, in order to employ such a perpendicular magnetic recording method, a magnetic recording medium whose surface has an axis of easy magnetization in the perpendicular direction is required.

Conventionally, as a recording medium that satisfies these demands,
It has been proposed that the recording film is formed from a Co--Cr sputtered film and that the recording film is formed from a coated layer of magnetic fine particles.

By the way, in the case where the recording film is formed of a coating layer of magnetic fine particles, it is conceivable to use hexagonal ferrite such as BaFe ₁₂ O ₁₉ as the magnetic fine particles.

The reason for using hexagonal ferrite is that this ferrite has a flat plate shape and the axis of easy magnetization is perpendicular to the plate surface, so it can be easily vertically aligned by magnetic field alignment treatment or mechanical alignment treatment. It is from. After mixing such magnetic fine particles of hexagonal ferrite and a binder and coating the mixture on the surface of a non-magnetic tape, this coated layer is placed in a magnetic field so that the surface is perpendicular to the direction of the magnetic field. By arranging the easy axis of magnetization of each magnetic fine particle to match the direction of the magnetic field, and then drying the paint, a recording medium suitable for perpendicular magnetic recording can be obtained.

However, when manufacturing a perpendicular magnetic recording medium using the above-mentioned hexagonal ferrite fine particles by a so-called coating method, the following points need to be taken into consideration.

In other words, the above-mentioned hexagonal ferrite has a coercive force
Since the iHc is high and the head is saturated during recording, it is necessary to reduce the coercive force to a value suitable for perpendicular magnetic recording by replacing some of the constituent atoms with atoms of a specific value. be. Further, it is necessary to select the crystal grain size of the hexagonal ferrite in the range of 0.01 to 0.3 μm. The reason is 0.01μm
If it is less than 0.3 μm, it will not exhibit the strong magnetism required for magnetic recording, and if it exceeds 0.3 μm, it will be difficult to advantageously perform perpendicular magnetization recording as high-density recording.

Furthermore, as mentioned above, both coercive force and particle size,
Even if the magnetic powder is controlled, if it does not have the property of being uniformly dispersed in the paint, a good recording medium will not be obtained. It is also necessary not to do so.

As a result of various experimental studies, the present inventors have found that a glass-forming substance is mixed with raw materials containing the basic components and substituted components of the ferrite in a certain ratio,
After melting, the amorphous material obtained by rapidly cooling the melt is subjected to heat treatment to precipitate fine ferrite particles suitable for the purpose, and for this purpose. It has also been found that in order to separate and extract the fine ferrite particles, it is sufficient to wash the glass molding material with a dilute acid such as phosphoric acid or acetic acid, and then wash it with water to remove it.

However, although the ferrite fine particles obtained in this way are isolated and dispersed one by one in the glass material, after acid washing they form secondary aggregates due to magnetic interaction. Each fine particle is not independent. In order to make such secondary aggregates into individual particles, it is necessary to apply an external force to disperse and decompose them. That is, in order to manufacture magnetic recording media, it is necessary to orient the magnetic powder using a magnetic field or mechanical means as described above, and for this purpose, each magnetic powder must be independently dispersed in the paint. Otherwise, sufficient orientation of the magnetic powder will not be obtained. For this reason, the emergence of some kind of dispersion means has been desired.

The present inventors have prepared 1 ferrite particles as described above.
As a result of various studies aimed at providing a method for manufacturing magnetic powder for magnetic recording media that can be made into individual fine particles, it was found that magnetic powder was dispersed one by one in a glass composition material using the above method. After dissolving the glass material to some extent with acid, the magnetic powder is mechanically separated from the glass composition material matrix, and at the same time phosphoric acid ester is attached to the surface of the magnetic powder to form magnetic powder. It has already been discovered that the above objective can be achieved by extracting each individual piece in a form separated by phosphate ester, but later, in addition to phosphate ester, lecithin,
It was found that magnetic powder with good dispersibility could be obtained even when amine-based, ammonium-based compounds, higher fatty acids such as stearic acid and oleic acid, and metal soaps or esters of these fatty acids were used as dispersants, and the present invention was completed. I came to the conclusion. That is, the present invention produces an amorphous body by mixing and melting a basic component of hexagonal ferrite, a substitute component for controlling the coercive force of the ferrite, and a glass-forming substance, followed by rapid cooling. After heat-treating the crystalloid to precipitate fine-particle hexagonal ferrite and removing some of the glass substances it contains, lecithin, amine compounds, ammonium compounds, higher fatty acids such as stearic acid and oleic acid, or these A method for producing magnetic powder for magnetic recording media, which comprises mixing fatty acid metal soap, higher fatty acid ester, alkyl sulfonate, polyoxyethylene ether or ester as a dispersant, and pulverizing and dispersing the mixture using a wet disperser. It is something.

According to the present invention, when separating fine-particle hexagonal ferrite dispersed and precipitated in an amorphous body from the amorphous body, by using a specific dispersant, excellent magnetic field orientation is obtained. A magnetic coating film with good surface properties can be obtained when used as a magnetic recording medium, and the above-mentioned phosphoric acid ester is effective in improving the orientation of magnetic powder, but if drying after application is incomplete, When a coating film is exposed to high temperature and high humidity, phosphate esters are liberated, which may cause problems in the durability of the coating film, but the present invention can compensate for these drawbacks.
The dispersant of the present invention is widely used as a surfactant, and its usefulness lies in its strong penetrating power.
That is, these dispersants penetrate into even the slightest gap between the magnetic powder and the glass composition material and adhere to the surface of the magnetic powder to form a film, which is thought to bring about the above-mentioned excellent effects.

Moreover, since this permeation effect is further promoted by mechanical vibration, it is preferable to apply mechanical vibration during crushing and dispersion.

In the actual process, a dispersant is attached to the surface of the magnetic powder using the following method. That is, a glass composition material and a magnetic powder composition material are mixed and melted, then rapidly cooled to prepare a flake-like amorphous material, and then this flake-like amorphous material is heat-treated at 700 to 900°C to be incorporated into a glass-like material. Fine-grained hexagonal ferrite is precipitated. To extract magnetic powder from this amorphous body,
The flaky material is dissolved using a dilute acid such as acetic acid for a suitable period of time and washed with water. At this time,
The time for dissolving the flaky material with the dilute acid is important. If the time is too long, the magnetic powder will separate from the glass composition and cause secondary aggregation in the solution. On the other hand, if the acid dissolution time is too short, there will be a large amount of remaining glass composition substances, making it difficult to separate the magnetic powder. The acid dissolution time is determined by the ratio of the glass composition material to the magnetic powder composition, the acid concentration, the acid dissolution temperature, etc., and the optimum time must be determined on a case-by-case basis. In this way, under appropriate conditions, the acid-dissolved flakes are mixed with a dispersant solution pre-dissolved in a solvent, and the flakes are crushed using a wet crusher to separate the magnetic powder from the glass component. After sufficiently dispersing the powder, it is filtered through a filter and dried to extract the magnetic powder.

Specifically, the dispersant used in the present invention is lecithin,
Triethanolamine, alkyltrimethylammonium halide, stearic acid, higher fatty acids such as oleic acid, higher fatty acid soaps such as aluminum stearate, higher fatty acid esters such as sorbitan ester, sodium dialkyl sulfosuccinate, sodium alkylbenzene sulfonate, sorbitan fatty acid ester, polyoxyethylene alkyl phenol ether, etc. Among these, lecithin is particularly preferred.

The present invention will be explained in detail below with reference to Examples.

For example, a magnetoplumbite-type Ba ferrite is selected as the desired magnetic crystal, and in order to obtain the coercive force (iHc) required for magnetic powder for magnetic recording media, some of the Fe ³⁺ ions in the Ba ferrite are
Substituted with Co ²⁺ −Ti ⁴⁺ ions to BaFe _10.4 Co _0.8 Ti _0.8
It was O ₁₉ . B ₂ O ₃ 13.4 (wt
%), BaO38.6 (wt%) as magnetic powder forming substance,
Fe ₂ O ₃ 41.8 (wt%), TiO ₂ 3.2 (wt%), CoO30 (wt
%) to make the composition BaCO ₃ , H ₃ BO ₃ , Fe ₂ O ₃ ,
TiO ₂ and CoCO ₃ were weighed and thoroughly mixed using a mixer. This mixture was placed in a platinum crucible and heated to 1350℃ using a high-frequency heater to melt it, and then
The above molten mixture was spouted onto a roll at a rotation speed of 200 mm and rapidly cooled to obtain a flaky amorphous material. This amorphous body is heated to 800℃ in an electric furnace,
This temperature was maintained for 4 hours to precipitate magnetic powder.
The flakes were placed in a 20wt% acetic acid solution heated to 80°C for 4 hours to etch the glass composition. At this time, the flakes were observed by SEM, and it was confirmed that the glass composition material was only slightly interposed between the magnetic powders.

To 100 parts by weight of this flaky material, 100 parts by weight of cyclohexanone and 10 parts by weight of lecithin as a dispersant were added, and the mixture was ground and dispersed in a sand grinder for about 2 hours. The solution thus obtained was filtered using a filter and dried using a spray dryer.

The magnetic powder obtained by the above method was analyzed using a transmission electron microscope.
When observed by SEM, it was confirmed that each magnetic powder existed independently.

A coating film was formed on a polyester film using the magnetic medium obtained by the above method to prepare a magnetic recording tape. The coated surface was calendered to a surface roughness of 0.1 μm. When we measured the electromagnetic conversion characteristics of the magnetic recording tape obtained in this way, we found that
A recording wavelength of 0.6 μm and a modulation noise of -42b _B were obtained. On the other hand, for comparison, a magnetic tape was made in the same way using magnetic powder without dispersion treatment, and the electromagnetic conversion characteristics were measured, and the output decreased sharply at recording wavelengths of 1.0 μm or less, and the modulation noise was -30 dB. It was.

In the above example, a grind mill was used as the wet grinding and mixing machine, but the same effect can be obtained with other wet grinding mixers by adjusting the rotation speed, operating time, and the poles or rods inserted at the same time. It was done.

Furthermore, when a magnetic recording tape was manufactured using aluminum stearate in place of lecithin as a dispersant and in the same process as the above method, a tape with a modulation noise level almost equivalent to that of lecithin was obtained.

As detailed above, according to the present invention, it is possible to provide a method for producing magnetic powder for magnetic recording media, which can efficiently produce magnetic powder that exhibits sufficient characteristics for use in magnetic media capable of high-density recording. can.

Claims (1)

[Claims] 1. A basic component of hexagonal ferrite, a substitute component for controlling the coercive force of the ferrite, and a glass-forming substance are mixed and melted, and then rapidly cooled to create an amorphous body. After heat treatment to precipitate fine particulate hexagonal ferrite and remove some of the glass substances contained, lecithin amine compounds, ammonium compounds, higher fatty acids, metal soaps of higher fatty acids, higher fatty acid esters, alkyl sulfones are produced. 1. A method for producing magnetic powder for magnetic recording media, which comprises mixing a dispersing agent selected from acid salts and polyoxyethylene ethers or esters, and pulverizing and dispersing the mixture using a wet pulverizer.