JPS63255817A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To permit high-density perpendicular magnetic recording by specifying the coercive force of hexagonal ferrite powder to 200-600 oersted and specifying the ratio of the amt. of residual magnetization of a perpendicular component and the amt. of residual magnetization of an intra-surface component to >=2.0. CONSTITUTION:The hexagonal ferrite powder 13 having a large ratio of grain size and thickness and low coercive force and a coating type medium consisting of an org. binder and having good perpendicular orientational property are used. The ratio of the residual magnetic flux density of the perpendicular component of the magnetization curve of the hexagonal ferrite powder and the residual magnetic flux density of the intra-surface component is >=2.0; the grain size is 0.05-0.3mum; the ratio of the grain size and the thickness is 15-25; and the coercive force is 200-600 oersted. The relatively small coercive force and the high-density recording with the medium having the good perpendicular orientational are thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a magnetic recording medium that enables high-density perpendicular magnetic recording.

BACKGROUND OF THE INVENTION In recent years, magnetic recording has been moving toward higher density and digitalization. Conventionally, the main magnetic recording method has been a magnetic recording method using so-called in-plane magnetization, which has an easy axis of magnetization within the plane of the magnetic recording medium. However, in this method, as the recording density is increased, the magnetization directions within the magnetic recording medium are arranged so as to repel each other, making it difficult to achieve high density. Recently, a new method of magnetic recording, called perpendicular magnetization, in which the axis of easy magnetization is perpendicular to the inner surface of the magnetic recording medium, has been developed, making it possible to dramatically increase the recording density. became. (For example, Iwasaki: High-density magnetic recording using perpendicular magnetization: Nikkei Electronics August 7, 1978
Day number. P100-111) In such a perpendicular magnetic recording system, the magnetic powder used must have an axis of easy magnetization in a direction perpendicular to the surface of the recording medium.

At present, there are some in which a cobalt-chromium (Co-Cr) alloy film is formed on the surface of a supporting base by sputtering. (For example, Iwasaki, Yamazaki: On Go - Cr sputtered films with perpendicular magnetic anisotropy: 7th Academic Conference of the Japan Society of Applied Magnetics, 4PA-7, 1975) Also, Co -
In addition to Cr, coated perpendicular magnetic recording media made of barium ferrite are also being developed. (For example, JP-A-60-69
(No. 822 Publication) Problems to be Solved by the Invention However, although these magnetic recording media have good perpendicular alignment, the Co--Cr alloy film has problems when the Co--Cr and the magnetic head slide. There are disadvantages in that both the recording medium and the magnetic head are subject to severe wear, the recording medium itself has poor flexibility, and the head does not run smoothly.

Also, conventionally known hard magnetic materials such as Ba
Fe, □01. Hexagonal ferrite such as (barium ferrite) has a hexagonal flat plate shape, and the axis of easy magnetization is perpendicular to the plane of the flat plate, so this macrogonal ferrite can be used as magnetic powder for recording media. If this is possible, it will be possible to form a recording medium layer by a coating method, and it is thought that a product with good head wear and head runnability, as in the case of a Co--Cr sputtered film, will be obtained.

However, the macrogonal ferrite of the conventional example has a high coercive force Hc and a plate ratio (ratio D/l of the maximum diagonal length D of a hexagonal plate shape to the thickness t) of 15 or less. Practical M that is inexpensive and has excellent wear resistance and running performance.
In the n-Zn type head (manganese-zinc ferrite head), not only is it not possible to perform sufficient recording and reproduction, but due to the high coercive force and high platelet ratio, particles tend to aggregate with each other during the film formation process using the coating method. Therefore, it has been impossible to obtain a perpendicular magnetic recording medium that has poor perpendicular alignment and is capable of high recording density. That is, in the magnetization curve, the residual magnetic flux density of the vertical component (on Br) and the residual magnetic flux density of the in-plane component (on Br
The ratio CBr/3r') was less than 2, which had the disadvantage that it was difficult to form a perpendicularly magnetized film.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention uses a hexagonal medium that has a large grain size to thickness ratio and a low coercive force, instead of using a continuous alloy film-like medium obtained by conventional sputtering methods. It has been found that an excellent high-density recording medium can be obtained by using a coated medium with good vertical alignment made of crystalline ferrite powder and an organic binder system.

The inventors have discovered that a hexagonal ferrite coated medium with a relatively small coercive force and excellent vertical alignment can be an excellent high-density recording medium. In other words, the magnetic recording medium of the present invention has a small coercive force and excellent vertical alignment (the ratio of the residual magnetic flux density of the perpendicular component to the residual magnetic flux density of the in-plane component of the magnetization curve is large), so it can be used in high-density recording areas ( Excellent recording and reproducing characteristics in the short wavelength region). This is because in conventional longitudinal recording (in-plane recording), in order to achieve high-density recording, a medium with a high coercive force is required to resist a large demagnetizing field, and a thin medium with low magnetization is required to reduce the demagnetizing field. for,
This is because in perpendicular recording, the magnetic field is small at high recording densities (short wavelength recording), so the coercive force can be lowered and there is no need to make the medium thinner.

In order to achieve this high-density recording, a medium with excellent vertical alignment is required, and it can be said that the medium of the present invention with low coercive force and high vertical alignment is most suitable for high-density recording. In particular, the particle size of the hexagonal crystal particles obtained by the coprecipitation method is 0.
Powder having a diameter of 0.05 to 0.3 μm and a ratio of particle size to thickness of 15 to 25 can be said to be an excellent magnetic powder that is easily vertically aligned when applied.

EXAMPLE Hereinafter, an example of the present invention will be described based on the drawings. The figure shows a schematic diagram of a perpendicular magnetic recording medium in an embodiment of the present invention.

In the figure, 11 is a support substrate, 12 is a magnetic layer, 13 is hexagonal ferrite particles, and 14 is an organic binder.

First, the average particle diameter was 0.1 μm and the thickness of plate-like particles was 0.05 μm (plate ratio 2
100 parts by weight of the barium ferrite powder of 0), 10 parts by weight of vinyl chloride vinyl acetate copolymer, 10 parts by weight of polyurethane resin, 1.5 parts by weight of polyisocyanate, 1 part by weight of lecithin, and 0.0 parts by weight of stearic acid as a binder. 5 parts by weight,
A magnetic paint was prepared by mixing and dispersing a composition consisting of 125 parts by weight of methyl ethyl ketone and 120 parts by weight in a ball mill for about 80 hours. This magnetic paint was applied onto a 13 μm thick polyester film to a dry thickness of 4 μm, dried, surface treated, and then cut into a predetermined width to produce a magnetic tape.

The magnetic properties (degree of vertical orientation) of this tape were measured using a VST (vibrating sample magnetometer) using a magnetization curve in a direction perpendicular to the medium surface and a magnetization curve in a direction parallel to the medium surface. The results are shown in Table 1.
Shown in sample number 1. Next, this tape was subjected to recording and playback tests. However, the media/head relative speed is 37.5 m/
The sec recording/reproducing head is a Mn-Zn ferrite head with a gap length of 0.28 m, a trunk width of 35 μm, a number of turns of 20 turns, and a recording frequency of 7.5 MHz. The results are also shown in Table 1, sample number 1.

Sample numbers 2 to 27 in Table 1 show what happens to the reproduction output when the coercive force, particle size to particle size to thickness ratio, and vertical orientation of the magnetic powder are changed in the same manner. Also sample number 2
8 to 32 are comparative examples other than the present invention.

Here, the vertical orientation is determined by calculating both the in-plane and perpendicular hysteresis curves (B-H curves) of the medium using VSM, and the residual magnetization CBr (JL) in the perpendicular direction of the medium and the in-plane (horizontal)
Find the residual magnetization (Br (“)) in the direction and calculate the ratio (B
The value of r(JL)/Br('')) was taken.

* However, test numbers 28 to 32 are comparative examples [the larger the residual magnetization in the vertical direction is compared to the residual magnetization in the horizontal direction, the better the perpendicularly magnetized film, Br (1) /
Br (“)〉2] In the claims, the reason why the coercive force of the hexagonal ferrite is limited to 200 to 6000e is because if it is less than 2000e, the coercive force is too low and recording demagnetization occurs. This is because if it is 6000e or more, the coercive force is too high and sufficient recording cannot be performed with the Mz-Zn ferrite head.

Further, the average particle size of the hexagonal ferrite powder is 0.05 to 0.
The reason why the grain size and thickness ratio was limited to 3 μm and 15 to 25 was because if the average grain size is 0.05 μm or less, the saturation magnetization is not large enough and it is difficult to obtain high reproduction output.
This is because if it exceeds m, noise will increase during recording and reproduction, which is undesirable. Also, if the ratio of grain size to thickness is less than 15, the particles tend to be vertically oriented (which makes it difficult to obtain sufficient reproduction output), and if the ratio is more than 25, noise will increase during recording and reproduction, which is undesirable. It is.

Effects of the Invention As described above, the present invention is extremely useful for achieving high-density recording in a medium in which the hexagonal ferrite has a relatively small coercive force and has good vertical alignment. .

[Brief explanation of the drawing]

The figure is a schematic diagram of a hexagonal ferrite coated perpendicular magnetic recording medium according to an embodiment of the present invention. 11...Supporting base, 12...Magnetic layer,
13... Hexagonal ferrite particles, 14...
...Organic binder. Name of agent: Patent attorney Toshio Nakao Haka 1 person 11--Ichimasho base 12-Ichimi 1

Claims (2)

[Claims] (1) A magnetic recording medium consisting of a supporting substrate, magnetic powder coated on the surface thereof, and an organic binder layer, in which the magnetic powder consists of hexagonal ferrite powder, and its coercive force is 200 to 200
600 Oersted, and the ratio of the amount of residual magnetization of the perpendicular component to the amount of residual magnetization of the in-plane component is 2.0 or more. (2) Particle size of hexagonal ferrite powder is 0.05 to 0.3μ
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a particle diameter of m and a ratio of particle size to thickness of 15 to 25.