JPS6246432A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To permit high density recording and easy production by specifying the thickness of a magnetic layer of a magnetic recording medium to <=20 times the average grain size (plate size) of the ultrafine particle magnetic powder coated thereon. CONSTITUTION:The magnetic recording medium is constituted of a substrate and the magnetic layer which is formed thereon and consists of the ultrafine particle magnetic powder, binder, additive, etc. Ba ferrite, Sr ferrite, Ca ferrite, Pb ferrite and the substituent and solid soln. thereof can be used for the ultrafine particle magnetic powder to be used. The adequate average grain size (plate size) of the magnetic powders is in a 0.01-0.2mum, more preferably 0.02-0.1mum range. The magnetic recording medium of which the magnetic layer obtd. in the above-mentioned has the thickness of <=20 times the average grain size of the magnetic powder is perpendicularly oriented with the magnetic powder and exhibits the electromagnetic conversion characteristic excellent for high density recording.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a magnetic recording medium using hexagonal ferrite ultrafine particle magnetic powder.

[Technical background of the invention and its problems]

Conventionally, magnetic recording media such as magnetic tapes and magnetic disks have been widely used, in which acicular magnetic powder such as T-Fe203 or Co-7Fe203 is coated on a substrate together with a binder. By the way, magnetic recording media using these acicular magnetic powders have the property that the acicular particles lie in the plane of the medium and are magnetized in the in-plane direction of the magnetic recording medium, so a method of magnetic recording in the in-plane longitudinal direction is adopted. ing. However, recently there has been a demand for high-density recording in order to record large amounts of information, and to achieve this, perpendicular magnetic recording has been proposed in place of the conventional in-plane longitudinal recording. This perpendicular magnetic recording method is a method of recording using residual magnetization in a direction perpendicular to the surface of a magnetic recording medium, and has the property that the recording state becomes more stable as the recording density increases. As a magnetic powder suitable for such perpendicular magnetic recording, an ultrafine powder of a hexagonal ferrite substitute such as Ba ferrite has been developed (Japanese Patent Laid-Open Publication No. 55-86103, et al.).

Hexagonal ferrite or a substitute thereof is an ultrafine magnetic powder having a hexagonal plate shape or a shape similar to this, and the axis of easy magnetization is perpendicular to the plate surface. Therefore, a magnetic recording medium using this hexagonal ferrite magnetic powder is
By applying the magnetic powder to the substrate surface with the plate surface oriented parallel to the surface of the magnetic recording medium, residual magnetization in the direction perpendicular to the substrate surface can be easily obtained.

As described above, methods for arranging the plate surfaces of magnetic particles parallel to the medium surface in hexagonal ferrite coated media, that is, methods for perpendicularly aligning the easy magnetization axes of magnetic particles, have been proposed in Japanese Patent Application Laid-Open No. 55-163633, A magnetic field orientation method such as that disclosed in Publication No. 57-58243, etc., and Japanese Patent Application Laid-open No. 57-5
A mechanical alignment method has been developed as shown in Japanese Patent No. 8240. The magnetic field orientation method requires complicated processes such as controlling the viscosity of the coating film when it enters the magnetic field and controlling the increase in viscosity during drying in the magnetic field, so a simpler orientation method is desired. ing. Also, in the mechanical orientation method,
Since orientation is achieved simply by applying shear stress to the paint film, it has the advantage of a simple orientation process, but this method requires the use of highly viscous paint, which limits its range of application. There was a problem.

[Purpose of the invention]

The present invention was made in order to solve the problems in the manufacturing process of the macrogonal ferrite ultrafine particle coated medium described above, and it is a perpendicular magnetic recording medium for high-density recording that can be easily manufactured without using the complicated processes described above. The purpose is to provide a medium.

[Summary of the invention]

That is, the present invention provides a magnetic recording medium in which a magnetic layer is formed by applying ultrafine magnetic powder having a plate-like particle shape and an axis of easy magnetization in a direction perpendicular to the plate surface onto a substrate. By setting the thickness of the magnetic layer to 20 times or less the average particle diameter (plate diameter) of the ultrafine magnetic powder, high-density recording is made possible and manufacturing thereof is facilitated.

The magnetic recording medium of the present invention is composed of a substrate and a magnetic layer formed thereon, which is made of ultrafine magnetic powder, a binder, additives, and the like.

The substrate used in the present invention may be a flexible substrate such as a film made of polyethylene terephthalate or polyolefin sulfide, or a rigid substrate such as a surface-finished aluminum disk.

As the ultrafine magnetic powder used in the present invention, Ba ferrite, Sr ferrite, Qa mitsuerite, Pb ferrite, and their substituted products and solid solutions can be used (JP-A-55-86103, JP-A-56-611).
Publication No. 01, etc.). The average particle size (plate diameter) of these magnetic powders is 0.01 to 0.2 μm - preferably 0.02 to 0.1
A range of μm is suitable. Further, the ratio of the average particle diameter (plate diameter) to the thickness (plate thickness) of the ultrafine magnetic powder is greater than 1, preferably greater than 2. Such ultrafine magnetic powder particles can be produced by, for example, the glass crystallization method disclosed in Japanese Patent Application Laid-Open No. 54-143859.

The binder used in the present invention includes polyvinyl chloride,
Typical products such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, polynylidene chloride, acrylic resin, cellulose derivatives such as nitrocellulose, polyester resin, polyurethane resin, epoxy resin, etc. A resin used as a binder for magnetic recording media is used. Note that it is desirable to add a curing agent such as isocyanate to cure the coating film.

In addition, the magnetic recording medium of the present invention contains additives such as higher fatty acids, higher fatty acid esters, lubricants such as silicone oil and fluorine oil, abrasives such as aluminum oxide, chromium oxide, and silicon carbide, and charging agents such as carbon black. Inhibitors can be added if necessary.

As a coating method for producing the magnetic recording medium of the present invention, any method such as a doctor blade method, gravure method, reverse roll method, or slot die method can be used when coating a flexible substrate. At this time, in order to roughly improve the uniformity and smoothness of the coating film, a smoother may be brought into contact immediately after coating by the above method.

Further, when coating a rigid substrate, a dipping method, a spin code method, etc. can be used.

For those coated on flexible substrates, surface smoothing treatment can also be performed using a supercalender device. Also. Due to the surface finish by burnishing treatment,
The magnetic recording medium obtained in this way, which has a magnetic layer thickness of 20 times or less than the average particle size of the magnetic powder, has a vertically oriented magnetic powder, and has a high density. Shows excellent electromagnetic conversion characteristics in records.

Although the mechanism for this improvement in properties has not yet been clarified, it is believed that particle shape effects are effective during drying shrinkage when a magnetic coating is applied to a substrate and a magnetic layer is formed, or during the calendering process for flexible substrates. This is thought to be due to the particle orientation effect caused by the action of In addition,
- A medium consisting of a magnetic layer that is much thinner than conventional media is highly desirable from the viewpoint of resource conservation.

[Embodiments of the invention]

The present invention will be specifically described below based on Examples.

Example 1 Ba ferrite Co-Ti substituted ultrafine particle magnetic powder particle size 0
．． 09, czmx thickness 0.025μm (average) 10
0 parts by weight Vinyl acetate copolymer (VAGH) 12 parts by weight Polyurethane (N-2304) 4 parts by weight Abrasive (chromium oxide) 3 parts by weight Lubricant (higher fatty acids, higher fatty acid esters) 1.2 parts by weight Solvent (methyl ethyl ketone) / toluene / cyclohexanone = 2/2/1) After stirring and mixing the above composition, perform a high dispersion treatment using a dispersion machine, then add and mix 4 parts of isocyanate, and filter this to obtain a magnetic paint, It was coated onto a polyethylene terephthalate sheet having a thickness of 75 μm using a gravure coater, smoothed to be uniform, and dried. This coating film was subjected to a surface smoothing treatment using a super calender to obtain an original recording medium. A disk-shaped sample of this film was punched and processed into a 3.5-inch flexible disk. Note that when applying the magnetic paint, the coating conditions were changed to obtain samples No. 1 to No. 4 with different thicknesses of the magnetic layer.

Comparative Example 1 A flexinor disk was produced in the same manner as in Example 1, except that the thickness of the magnetic layer was more than 20 times the average particle diameter of the ultrafine magnetic powder used. In addition, when applying the magnetic paint, the application conditions were changed to obtain comparative sample No. 015.6 in which the thickness of the magnetic layer was different.

Example 2 The average particle size of the ultrafine magnetic powder used was 0.06 μm,
A flexible disk was produced in the same manner as in Example 1 except that a disk having an average thickness of 0.02 μm was used.

When applying the magnetic paint, one sample of Nos. 017 to 10 with different coating thickness was obtained by changing the coating conditions.

Comparative Example 2 A flexible disk was produced in the same manner as in Example 2, except that the thickness was more than 20 times the average particle diameter of the ultrafine magnetic powder used. In addition, when applying magnetic paint,
Comparative samples Nos. 11 and 12 having different thicknesses of magnetic layers were obtained by changing the coating conditions.

For these samples, the magnetic layer thickness, the squareness ratio after demagnetizing field correction of the magnetization curve perpendicular to the surface of the magnetic recording medium, and the linear recording density D50 at which the reproduction output is halved were measured. The measurement results are shown in the table below. In the measurement of D5°, a magnetic head with a gap of 0.23 μm was used.

(The following is a blank space) It can be seen from the above table that in the examples of the present invention, an improvement in the perpendicular squareness ratio and an improvement in high-density recording characteristics were obtained.

In addition, in the above embodiment, an example using a flexible substrate was explained, but the present invention is not limited to such an embodiment, and it is also possible to use a hard disk.

[Effects of the Invention] As is clear from the above examples, the magnetic recording medium of the present invention has I! The plate-shaped magnetic powder is oriented parallel to the plane without the need for special orientation means during manufacturing, and it also exhibits excellent electromagnetic conversion characteristics in high-density recording, and the magnetic layer can be formed thinly. This is also highly desirable from the viewpoint of resource conservation.

Claims (5)

[Claims] (1) In a magnetic recording medium in which a magnetic layer is formed by applying ultrafine magnetic powder having a plate-like particle shape and an axis of easy magnetization in a direction perpendicular to the plate surface on a substrate, the magnetic layer A magnetic recording medium characterized in that the thickness of the ultrafine magnetic powder is 20 times or less the average particle diameter (plate diameter) of the ultrafine magnetic powder. (2) The magnetic recording medium according to claim 1, wherein the thickness of the magnetic layer is 10 times or less the average particle diameter (plate diameter) of the ultrafine magnetic powder. (3) A magnetic recording medium characterized in that the ultrafine magnetic powder is hexagonal ferrite. (4) The average particle diameter (plate diameter) of ultrafine magnetic powder is 0.01
The magnetic recording medium according to any one of claims 1 to 3, wherein the magnetic recording medium has a thickness of 0.2 μm. (5) The magnetic recording according to any one of claims 1 to 4, wherein the ratio of the average particle diameter (plate diameter) to the thickness (plate thickness) of the ultrafine magnetic powder is greater than 1. Medium.