JP2999446B2 - Magnetic recording medium and magnetic recording / reproducing system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording / reproducing system using a high frequency and a magnetic recording medium suitable for the system.

[0002]

2. Description of the Related Art As a magnetic recording medium, a so-called metal thin film type magnetic recording medium in which a magnetic layer composed of a ferromagnetic metal thin film formed on a support by a vacuum deposition method or the like is known. This type of magnetic recording medium is considered to be promising for high-density recording because the magnetic layer contains no binder and therefore has a large amount of magnetic substance per unit volume (that is, the density of the magnetic material is high). . Magnetic materials for forming such a metal thin film include Co-based, Co-Ni-based, and Co-based.
-A ferromagnetic metal (alloy) such as Cr is used.

[0003] The high-precision television system (so-called high-vision system), which is being studied today, has a much higher image quality than the conventional system. Although required, a vapor deposition type magnetic recording medium is considered to be promising for high-density recording corresponding to a high-vision system.

[0004]

In order to achieve high-density recording, it is necessary to achieve a high C / N by using a high frequency, for example, a frequency of 20 MHz or more. Has dealt with it by making the magnetic layer multilayer. However, there is a problem that such a method does not provide sufficiently satisfactory performance, increases the consumption of expensive magnetic metal, and lowers the yield. In addition, vapor deposition type magnetic recording media capable of coping with high-frequency recording have been studied from various viewpoints such as the thickness of a magnetic material and the thickness of a magnetic layer, but no satisfactory magnetic recording medium has been found yet.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in view of the above situation, and as a result, have found that the SFD (switching field distortion) indicating the degree of variation of the coercive force in the magnetic layer.
(distribution) value has a great influence on the C / N characteristics, and it has been found that more desirable C / N characteristics can be obtained when the SFD value in the longitudinal direction of the medium among the SFD values is equal to or less than a specific value. Was completed.

That is, the present invention relates to a magnetic recording medium having a support and a metal thin-film type magnetic layer formed on the support by a vacuum film forming method, wherein the SFD (switc
(hingfield distribution) value is 0.8 or less, and said magnetic recording medium and 20 MHz
An object of the present invention is to provide a magnetic recording / reproducing system using the above recording frequencies.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The magnetic recording medium of the present invention has a longitudinal SFD value of 0.8 or less, preferably 0.7 or less. This SFD value is equal to the magnetic hysteresis B as shown in FIG.
In the H loop, the half value width ΔH of the differential curve divided by the magnetic field (Hp) at the peak of the differential curve (SFD = Δ
H / Hp).

The reason why a high C / N is obtained when the SFD value in the longitudinal direction is 0.8 or less as in the present invention is not clear, but is considered as follows. That is, when the SFD value in the longitudinal direction is 0.8 or less, the variation in coercive force is small, the noise is reduced, and the factor that hinders the output is reduced, so that the output is increased. As a result, the C / N is increased. Because it became.

In the magnetic recording medium of the present invention, the SFD value in the vertical direction is 2.5 or less, particularly 2.3 or less, and the SFD value in the longitudinal direction (a) and the SFD value in the vertical direction (b)
When the ratio (a) / (b) is 0.25 or more, particularly 0.3 or more, a magnetic recording / reproducing method using a recording frequency exceeding 20 MHz and further using a reproducing head having a head gap length of less than 0.2 μm. Better C / N characteristics can be obtained in the reproduction system. The longitudinal direction and the perpendicular direction of the medium are shown in FIG. 2 using a magnetic tape as an example.

The SFD value can be easily calculated from the magnetic hysteresis BH loop (longitudinal or vertical) of the target magnetic recording medium. In the present invention, various methods can be used to adjust the SFD value to the above range. Some examples are as follows. 1. In vacuum evaporation, control to prevent disturbance of metal vapor flow. In the sputtering method, the film (substrate) is largely inclined to control the amount of adhesion. At present, the SFD values of vapor-deposited magnetic tapes such as a vapor deposition tape for Hi-8, a vapor deposition tape for DVC, and a vapor deposition tape for data stretching are 0.95 or more in the longitudinal direction and 2.7 or more in the vertical direction. Since these values are not proper values, a high C / N in a high frequency band is not obtained.

The magnetic layer of the magnetic recording medium of the present invention is of a ferromagnetic metal thin film type, and is formed by a normal vacuum film forming method such as vapor deposition or sputtering, so that the SFD value falls within the range of the present invention. It is necessary to adjust the film forming conditions. Examples of the magnetic material for forming the metal thin film type magnetic layer include ferromagnetic metal materials used in the manufacture of ordinary metal thin film type magnetic recording media, for example, ferromagnetic metals such as Co, Ni, and Fe, Fe-Co, Fe-Ni, Co-Ni, Fe-Co
-Ni, Fe-Cu, Co-Cu, Co-Au, Co-
Y, Co-La, Co-Pr, Co-Gd, Co-S
m, Co-Pt, Ni-Cu, Mn-Bi, Mn-S
b, Mn-Al, Fe-Cr, Co-Cr, Ni-C
and ferromagnetic alloys such as r-Fe-Co-Cr and Ni-Co-Cr. Oxide, nitrogen, and carbide magnetic films are formed by a so-called ion-assisted deposition method in which a gas such as oxygen, nitrogen, or carbon dioxide or a mixed gas thereof is ionized and irradiated during deposition. Is also good.

For high-density recording, the magnetic layer is preferably formed on a support by oblique evaporation or sputtering. The method for oblique deposition is not particularly limited, and follows a conventionally known method. The degree of vacuum at the time of vapor deposition is 10 ^-4 to 10 ^-7 Torr
It is about. The degree of vacuum when using the sputtering method is about 10 ⁻² to 10 ⁻⁵ Torr. The magnetic layer formed by vapor deposition may have either a single layer structure or a multilayer structure. In particular, by introducing an oxidizing gas such as oxygen to form an oxide on the surface of the magnetic layer, the durability can be improved. The thickness of the magnetic layer is not limited, but is preferably from 50 to 500 nm, particularly preferably from 80 to 300 nm. The magnetic layer may have a single layer or a multilayer structure.

A protective film having a thickness of 1 to 50 nm is provided on the magnetic layer. Examples of the material constituting the protective film include carbon-based thin films, oxides, nitrides, and carbides of metals such as Al, as well as SiC and compounds containing the same. In particular, a protective film made of diamond-like carbon is preferable.

On the surface of the magnetic layer or the protective film, there is provided a lubricating layer having a thickness of 0.5 to 5 nm made of a lubricating agent, particularly a fluorine-based lubricating agent such as perfluoropolyether.
Examples of the lubricant include carboxyl group-modified perfluoropolyether and alcohol-modified perfluoropolyether, and those having a molecular weight of 500 to 50,000 are preferable. More specifically, FOMBLIN Z DIAC or FOMBLIN Z trade name of Montecatini Co., Ltd.
DOL, Daikin Industries' trade name Demnum SA, and the like. Further, compounds having a fluorinated alkyl group and an alkyl group or an alkenyl group can also be used. The support constituting the magnetic recording medium of the present invention may be either magnetic or non-magnetic. Generally, it is non-magnetic. As the support, polyethylene terephthalate (PET),
Polyesters such as polyethylene naphthalate (PEN), olefinic resins such as polyamide, polyimide, polysulfone, polycarbonate, and polypropylene;
An organic material (resin) such as a cellulose resin and a vinyl chloride resin is used. The thickness of the support is 1 to 30
0 μm, particularly preferably 1 to 10 μm. Incidentally, an undercoat layer for improving the adhesion to the magnetic layer is appropriately provided on the surface of the support.

On the other surface (back surface) of the support, a back coat film is provided. For example, the back coat film is provided by a plating method such as a vapor deposition method, a DC sputtering method, an AC sputtering method, a high-frequency sputtering method, a DC magnetron sputtering method, a high-frequency magnetron sputtering method, and an ion beam sputtering method. Further, a back coat film can be provided by applying a paint containing carbon black and a binder.

[0016]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1 (1) Production of magnetic tape Using a target of Co-Pt-Ni-Cr-B (82: 5: 5: 3, atomic ratio), using an RF magnetron sputtering apparatus, argon and nitrogen ( 90:10, volume ratio), at a degree of vacuum of 5 × 10 ⁻³ Torr and a thickness of 4.3.
A magnetic layer having a thickness of 0.15 μm was continuously formed on a μm polyamide film. The running speed of the film is 2.5
m / min, the sputter output was 4 kW, and the film was inclined by 23 ° with respect to the target with respect to the running direction.

Next, ECR plasma CVD is performed on the magnetic layer.
A protective layer made of a diamond-like carbon thin film having a thickness of 0.01 μm was formed by the method. Further, a perfluoropolyether [trade name: Demnum SA:
(Manufactured by Daikin Industries, Ltd.) to a thickness of 0.002 μm to form a lubricating layer. A coating containing carbon black and a binder was applied on the surface of the film opposite to the surface on which the magnetic layer was formed to a thickness of 0.5 μm (dry thickness) to form a back coat layer.

The film obtained above on which the magnetic layer, protective layer, lubricating layer and back coat layer are formed is 8 mm thick.
Cut to width, load into cassette case and Hi-8
A videotape of the type was obtained.

(2) Performance evaluation The SFD value, C / C
The N characteristics were evaluated by the following method. Table 1 shows the results.
Shown in

Measurement method of SFD value The SFD value in the longitudinal direction and the vertical direction of the video tape was measured using a sample vibration type magnetometer [model BH manufactured by Riken Denshi Co., Ltd.
V-50 (VSM-MH measurement system, with differential calculation function)]. The maximum external magnetic field was measured by applying 10 kOe.

C / N measurement method A sine wave signal from a transmitter is input as shown in Table 1 from a transmitter using an evaluator modified from a commercially available Hi8 VTR drive as shown in Table 1, and then a spectrum analyzer is used to input a sine wave signal as shown in Table 1. The output at the time of reproducing with the reproducing head of each head gap length shown in FIG. Then
With respect to the measured output C, a noise level at a frequency lower by 1 MHz is measured, and this is set to N. C / N is this ratio. Table 1 shows relative values based on C / N of Comparative Example 1 as a reference (0 dB).

Example 2 In Example 1, the sputter output was 2.8 kW, the degree of vacuum was 9 × 10 ⁻³ Torr, and the film was inclined by 13 ° with respect to the target with respect to the running direction. Otherwise, a video tape was produced in the same manner as in Example 1, and the same evaluation as in Example 1 was performed. Table 1 shows the results.

Comparative Example 1 In Example 1, the film was cooled to -40 ° C., the sputter output was set to 1.6 kW, the degree of vacuum was set to 3 × 10 ⁻² Torr, and the film was moved with respect to the target based on the running direction. , 4 °. Otherwise, a video tape was produced in the same manner as in Example 1, and the same evaluation as in Example 1 was performed. Table 1 shows the results.

Example 3 A ferromagnetic metal thin film type magnetic layer having a thickness of 150 nm was formed on a PET film having a thickness of 6.3 μm by a vacuum evaporation method. The deposition sources at this time were Co, Cr, and Si, and vapor deposition was performed at a deposition rate of 450 nm / min while oxygen was passed using three electron guns. Also, when forming the film,
Cooled to 3 ° C. When the composition of the magnetic layer was measured by Auger electron spectroscopy, the ratio of Co, Cr, Si, and O was
They were 60 at%, 16 at%, 3 at%, and 11 at%, respectively. Next, a protective layer, a lubricating layer, and a back coat layer were formed in the same manner as in Example 1, a video tape was obtained, and the same evaluation as in Example 1 was performed. The results are shown in Table 1, and the evaluation was shown as a relative value using Comparative Example 2 as a reference (0 dB).

Comparative Example 2 A video tape was obtained in the same manner as in Example 3 except that the cooling temperature of the film was -35 ° C., and the same evaluation as in Example 1 was performed. Table 1 shows the results.

[0027]

[Table 1]

[0028]

According to the present invention, it is possible to obtain a metal thin film type magnetic recording medium exhibiting excellent C / N characteristics particularly in a magnetic recording / reproducing system using a recording frequency exceeding 20 MHz.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a method for measuring an SFD value.

FIG. 2 is a schematic view showing a longitudinal direction and a vertical direction of a magnetic tape.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeshi Miyamura 2606 Kabane-cho, Akaga-cho, Haga-gun, Tochigi Prefecture Inside Kao Co., Ltd. References JP-A-8-171716 (JP, A) JP-A-9-97413 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 5/66

Claims (6)

(57) [Claims] 1. A magnetic recording medium comprising a support and a metal thin-film type magnetic layer formed on the support by a vacuum film forming method, wherein the magnetic recording medium has a longitudinal switching field distance (SFD).
Ibution) value Ri der 0.8, SFD value in the vertical direction
2.5 The magnetic recording medium according to der Rukoto features below. 2. A support and a vacuum film forming method on the support.
Recording medium having a thin metal film type magnetic layer formed
The body and the longitudinal SFD (switching field distr
ibution) value is 0.8 or less, SFD value in the longitudinal direction
Ratio (a) / (b) between (a) and SFD value (b) in the vertical direction
Is 0.25 or more . 3. A support and a vacuum film forming method on the support.
Recording medium having a thin metal film type magnetic layer formed
The body and the longitudinal SFD (switching field distr
ibution) value is 0.8 or less and the vertical SFD value is
2.5 or less, the SFD value (a) in the longitudinal direction and the vertical direction
The ratio (a) / (b) of the SFD value (b) is 0.25 or more
A magnetic recording medium according to claim 1. 4. The method according to claim 1, wherein the vacuum film forming method is a vacuum evaporation method.
The magnetic recording medium according to any one of claims 1 to 3, wherein 5. A magnetic recording / reproducing system using the magnetic recording medium according to claim 1 and a recording frequency of 20 MHz or more. 6. The magnetic recording / reproducing system according to claim 5, wherein the head gap length of the reproducing head of the system is less than 0.2 μm.