JPH0628094B2 - Magnetic recording medium - Google Patents

Description

The present invention relates to a magnetic recording medium in the form of a disk or a tape, for example, and more particularly to a magnetic recording medium suitable for high density recording.

[Conventional technology]

Γ-containing Co as a magnetic material for high density magnetic recording media
Although Fe ₂ O ₃ (coercive force of 600 to 800 oersteds) has been conventionally used, a magnetic recording medium using this magnetic material has a D ₅₀ (described later) of 30 KBPI or less when a magnetic head having a narrow gear length is used. However, there was a problem that only the recording density of

Further, for high density recording, a magnetic recording medium in which metal magnetic powder is dispersed in a binder to form a magnetic layer having a coercive force of 1230 oersteds and a residual magnetic flux density of 1690 gauss on a support (JP-A-58). However, in this magnetic recording medium, since the coercive force and the residual magnetic flux density have the above characteristic values, the D ₅₀ characteristic is 4
Only 8 KBPI was obtained.

[Problems to be solved]

The object of the present invention is to eliminate such drawbacks of the prior art,
It is an object of the present invention to provide a magnetic recording medium capable of high density recording.

[Means for solving problems]

Generally, in order to obtain a magnetic recording medium excellent in high density recording, a magnetic recording medium using metal magnetic powder is recommended, but in the case of achieving high density recording, the thickness of the magnetic layer may change due to the change in the thickness of the magnetic layer. It is believed that the loss will change, and the magnetic layer was considered to be thinned as much as possible (Tohoku University Dentsu Symposium Log Vol. 31, No. 3, pp. 95-104, September 1957). Issue).

However, as a result of various studies by the present inventors, when the coercive force of the magnetic layer is 1400 oersteds or more and the residual magnetic flux density is 1100 gausses or more, preferably 1300 gausses or more, the thickness loss of the magnetic layer is 0. It was found that although it changes in the region of less than 5 μm, it hardly changes in the region of 0.5 μm or more, and it does not deteriorate if the characteristics of D ₅₀ are the same coercive force and residual magnetic flux density of 0.5 μm or more.

By demonstrating that this D ₅₀ characteristic does not depend on the thickness of the magnetic layer, the magnetic layer is designed to be a thick magnetic layer of 0.5 μm or more, rather than being thin, which tends to cause uneven thickness for high density recording. It is possible to form a magnetic layer with a margin above.

Based on the above-mentioned investigation, the present invention has a magnetic layer having a coercive force of 140
0-2000 Elsted, residual magnetic flux density is 1100-
The object was achieved by setting the magnetic layer thickness to 1700 gauss and the magnetic layer thickness to 0.5 μm or more.

In the present invention, as the non-magnetic support, for example, polyester, polyimide, aluminum or the like is used. Further, the magnetic layer formed thereon is a ferromagnetic metal powder such as metallic iron powder, cobalt powder, or iron-nickel alloy powder, and a binder such as vinyl chloride-vinyl acetate-vinyl alcohol copolymer or polyurethane. And a coating material containing, for example, kents, toluene and alcohols are applied on the non-magnetic support and calendered.

When the magnetic recording medium according to the present invention is used as a magnetic disk, it is necessary for the magnetic particles to be oriented in-plane in the random direction or along the circumferential direction of the disk. In particular, by dispersing the magnetic particles in an irregular and non-directional manner, it is possible to obtain one having a low residual magnetic flux density without variation.

〔Example〕

Next, specific examples will be described. A magnetic coating material having the composition described below was applied to both sides of a polyester base film having a thickness of 75 μm, and calendering was performed to form a magnetic layer, which was punched into a disk shape to form a magnetic disk.

In this magnetic recording medium, the above-mentioned ferromagnetic metallic iron powder has a coercive force of 1250 to 1890 Oe and a saturation magnetization of 10
Samples of the magnetic recording medium are used by changing the surface roughness by changing the surface roughness of the magnetic layer (changing the temperature and pressure of the calendar roll in the calendering processing device) in the range of 0 to 300 emu / g. It was created.

The following table shows D ₅₀ and head output when the coercive force, the residual magnetic flux density, the surface roughness and the characteristic layer thickness of each of these samples were variously changed. Note that D ₅₀ represents the recording density at which the output becomes 50% of the long-wavelength recording / reproducing output, and this numerical value is a standard for the maximum recording density that can be realized by the device. Therefore, if D ₅₀ is ₅₀ KBPI or more, it is evaluated as a magnetic recording medium for high density recording. The head output is
It is desirable that the voltage is 70 μV or more in relation to the amplifier noise.

The coercive force and residual magnetic flux density in the table are measured with a sample vibrating magnetometer, the magnetic layer thickness is measured with a stylus surface roughness meter, and the surface roughness is a stylus diameter of 2 μm and a stylus load of 23 m
g, cutoff 0.08 mm, scanning speed 0.03 mm / sec. In addition, the electromagnetic conversion characteristics are a magnetic head using a magnetic core made of iron-nickel alloy (Sendust), and a gear length of 0.3 μm.
m, a track width of 30 μm, and a relative velocity with the magnetic recording medium of 3.1 m / sec.

〔The invention's effect〕

As is clear from this table, as in Comparative Example 1, the residual magnetic flux density is as large as 1730 gauss and the surface roughness is 0.019.
Even if it is as low as μm, if the coercive force is only 1250 oersteds, both the value of D ₅₀ and the head output are small.

Further, as in Comparative Example 2, even if the coercive force of the magnetic layer is appropriate, if the residual magnetic flux density is too high, the head output is large, but D
₅₀ Poor characteristics.

On the other hand, as in Examples 1 to 8, the coercive force of the magnetic layer is 1400 oersteds or more and the residual magnetic flux density is 1 or more.
For 100 to 1700 gauss, D ₅₀ is 56 KBP
It exhibits high characteristics of I or higher.

When the coercive force of the magnetic layer exceeds 2,000 ersted, the core of the magnetic head may be magnetically saturated. Therefore, the coercive force of the magnetic layer must be restricted to the range of 1400 to 2,000 ersted. If the residual magnetic flux density is less than 1100 gauss, a sufficient head output cannot be obtained due to the amplifier noise.

Here, when the thickness of the magnetic layer is 0.5 μm or more, D
_{In order to more specifically} show the assertion that the ₅₀ characteristics hardly depend on the thickness, and that when the thickness of the magnetic layer is less than 0.5 μm, coating unevenness is likely to occur, which is not preferable in mass production, the following Example 9 will be given. Will be explained.

Example 9 A magnetic disk was prepared in the same manner as in Example 1 except that the thickness of the magnetic layer was changed to 0.4, 0.5, 4.0 and 5.5 μm. The following table shows the results of measuring the D ₅₀ characteristics and coating unevenness of these magnetic disks.

As is clear from this result, the thickness of the magnetic layer is 0.5.
When the thickness is more than μm, the D ₅₀ characteristic hardly changes, and the small module size indicates that it is suitable for mass production in which uneven coating is less likely to occur.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Akira Miyake 1-1-88, Tora, Ibaraki-shi, Osaka Inside Hitachi Maxell Co., Ltd. (56) References JP-A-53-70397 (JP, A) JP-A-SHO 54-30002 (JP, A) JP-A-57-154618 (JP, A) JP-A-59-142742 (JP, A)

Claims (3)

[Claims] 1. A magnetic recording medium comprising a non-magnetic support and a magnetic layer comprising ferromagnetic fine powder dispersed in a non-magnetic binder, wherein the magnetic layer has a high coercive force of 1400 to 2000 oersteds. A magnetic recording medium characterized by being regulated to a magnetic force range, a residual magnetic flux density being regulated to a low residual magnetic flux density range of 1100 to 1700 gauss, and a magnetic layer thickness being regulated to 0.5 μm or more. . 2. The coercive force of the magnetic layer is restricted to a high coercive force range of 1400 to 1890 oersteds, and the residual magnetic flux density is restricted to a low residual magnetic flux density range of 1300 to 1700 gauss, and the ferromagnetic particles are ferromagnetic. The magnetic recording medium according to claim (1), which is a metal powder. 3. The magnetic recording medium is a magnetic disk, and the ferromagnetic fine powder is dispersed in a plane of the magnetic layer in a random and non-oriented manner. Alternatively, the magnetic recording medium according to the item (2).