JPH09320043A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve head touch performance and durability while maintaining output characteristics even in a magnetic recording medium of a shorter minimum recording wavelength, by setting the thickness of a protecting layer in a specific range according to the minimum recording wavelength of the magnetic recording medium. SOLUTION: The magnetic recording medium having a minimum recording wavelength of 0.45μm or smaller has a supporting body, a magnetic layer formed on the supporting body and a protecting layer formed on the magnetic layer. A thickness of the protecting layer is set to be 1/20-1/70 the minimum recording wavelength. More preferably, the protecting layer is formed of a carbon thin film or silicon thin film. Accordingly, even when the magnetic recording medium has the minimum recording wavelength shorter than 0.45μm, head touch performance and durability are improved while output characteristics are maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium excellent in both output characteristics and head touch and durability.

[0002]

2. Description of the Related Art A so-called metal thin film type magnetic recording medium in which a metal is deposited on a support in a vacuum in a vacuum or the like can increase the density of the magnetic material because the magnetic layer contains no binder at all. Is promising for high-density recording.

However, in the magnetic layer of the metal thin film type magnetic recording medium, since the metal is simply attached on the support, the corrosion resistance and durability are poor as they are, and today, higher density recording is required. Therefore, the relative speed between the magnetic recording medium and the head is increasing. In order to deal with such a problem, it has been practiced to apply a carboxylic acid-based or phosphoric acid-based lubricant on the magnetic layer or to provide a nonmagnetic metal protective layer on the magnetic layer. Further, a technique of forming a thin film made of diamond-like carbon as a protective layer on the magnetic layer has attracted attention today. The diamond-like carbon thin film is an amorphous carbon film, and is considered to have a structure in which graphite bonds and diamond bonds are mixed, for example, RF plasma CVD method, ECR plasma CV.
It can be formed by a general-purpose method such as D method or sputtering method. On the other hand, the higher recording density is being advanced today, and the shortest recording wavelength tends to be shortened accordingly.

[0004]

In order to improve the durability and the like, it is desirable to form a thick protective layer, but with this, spacing loss occurs and the output decreases. On the other hand, if the protective layer is formed too thin, the original performance of the protective layer, such as durability and running stability (head touch), deteriorates. As described above, the shortest recording wavelength tends to be shorter to achieve high-density recording today, but even if the shortest recording wavelength is shortened, a protective layer having an appropriate thickness is not formed. Therefore, not only high density recording cannot be achieved, but also the original purpose of improving durability and head touch by forming a protective layer may not be achieved.

Heretofore, the performance of the magnetic recording medium has not been examined by paying attention to the correlation between the thickness of the protective layer and the shortest recording wavelength. Especially, when the recording wavelength is 0.45 μm or less, No measures have been proposed to adjust both of these to improve the output characteristics of the magnetic recording medium and the balance between durability and head touch.

[0006]

The inventors of the present invention have made earnest studies on the shortest recording wavelength of a magnetic recording medium and the thickness of a protective layer in order to solve the above-mentioned problems, and as a result, the shortest recording wavelength is 0.45 μm.
In a magnetic recording medium having a shorter minimum recording wavelength of m or less, a protective layer formed thereon has a thickness of 1/20 to 1/70 of the shortest recording wavelength to maintain sufficient output characteristics. At the same time, they found that good durability and head touch can be obtained, and completed the present invention.

That is, the present invention provides a magnetic recording medium having a support, a magnetic layer formed on the support, and a protective layer formed on the magnetic layer and having a shortest recording wavelength of 0.45 μm or less. The present invention provides a magnetic recording medium characterized in that the thickness of the protective layer is 1/20 to 1/70 of the shortest recording wavelength.

The magnetic recording medium of the present invention has a protective layer on the magnetic layer, and it is particularly preferable to form a protective layer composed of a carbon thin film or a silicon thin film on the metal thin film type magnetic layer. Diamond-like carbon thin film
It can be formed by the known method described above, and the ECR plasma CVD method is often used. In the carbon or diamond-like carbon film, 5 atoms such as hydrogen and nitrogen are contained.
Those containing 0% or less can also be used in the present invention. When forming a carbon thin film by the ECR plasma CVD method, examples of raw material compounds include lower alkanes such as methane and ethane, and aromatic hydrocarbons such as benzene and anthracene. E
The CR plasma CVD method may be carried out according to a known method. For example, the microwave wavelength is 2.45 GH.
z, the output is about 500 W, and the degree of vacuum is 10 ^-1 to 10
^It is preferable that the raw material compound is gasified so that the pressure becomes ^-4 Torr, and is introduced into the plasma excitation chamber. Further, as a method of forming the protective layer with a silicon thin film, for example, a method of sputtering with a target of Si while flowing an oxygen gas can be cited. The silicon thin film formed by such a method is SiO
It is considered to be a substance represented by _x . In addition, oxides, nitrides, carbides such as silicon nitride, carbon nitride, aluminum oxide, boron nitride and the like, and composites thereof are used.

The shortest recording wavelength of the magnetic recording medium of the present invention is 0.45 μm or less, and the thickness of the protective layer formed as described above is determined by the shortest recording wavelength of the obtained magnetic recording medium. . That is, the thickness of the protective layer is formed to be 1/20 to 1/70 of the shortest recording wavelength. If the thickness of the protective layer is thicker than 1/20 of the shortest recording wavelength, the output is lowered, and conversely, if it is thinner than 1/70, durability and head touch are lowered. Especially the shortest recording wavelength is 0.35 μm
In the following cases, the thickness of the protective layer is 1/40 of the shortest recording wavelength.
It is preferably 1/70.

In the present invention, the shortest recording wavelength is 0.45 μ.
In a magnetic recording medium of m or less, the thickness of the protective layer is adjusted according to the shortest recording wavelength in order to solve the problem of balance between output and durability (head touch) when the protective layer is formed. Specifically, it has been found that it is optimum that the protective layer has a thickness of 1/20 to 1/70 of the shortest recording wavelength. The shortest recording wavelength is 0.45
In the case of a magnetic recording medium having a thickness larger than μm, even if the protective layer is somewhat thick, the effect on output is small, and the problem of output decrease is not so concerned.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The magnetic recording medium of the present invention is characterized in that the thickness of the protective layer is adjusted in accordance with the shortest recording wavelength as described above. Although it may be a mold, it is particularly effective in the case of a metal thin film type.

The metal thin film is formed by a usual method such as vapor deposition or sputtering. Examples of the magnetic material forming the metal thin film type magnetic layer include ferromagnetic metal materials used in the production of ordinary metal thin film type magnetic recording media.
Ferromagnetic metals such as o, Ni, Fe, Fe-Co, F
e-Ni, Co-Ni, Fe-Co-Ni, Fe-C
u, Co-Cu, Co-Au, Co-Y, Co-La,
Co-Pr, Co-Gd, Co-Sm, Co-Pt, N
i-Cu, Mn-Bi, Mn-Sb, Mn-Al, Fe
-Cr, Co-Cr, Ni-Cr, Fe-Co-Cr,
Examples include ferromagnetic alloys such as Ni-Co-Cr. As the magnetic layer, a thin film of iron or cobalt or a thin film of a ferromagnetic alloy mainly containing iron or cobalt is preferable. Further, at least one selected from ferromagnetic alloys mainly containing iron, cobalt and nickel and their nitrides or carbides is also preferable.

Further, Fe-C and Fe-C, which are formed by a so-called ion-assisted deposition method of supplying ions such as nitrogen ions, oxygen ions and carbon ions during the deposition of iron.
System, Fe-NO system, Fe-CO system, Fe-NC-
It may be an O-based magnetic layer.

For high density recording, the magnetic layer of the magnetic recording medium is preferably formed on a substrate by oblique evaporation. 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 a degree. The magnetic layer formed by vapor deposition may have either a single-layer structure or a multi-layer structure, and in particular, the durability can be improved by introducing an oxidizing gas to form an oxide on the surface of the magnetic layer. The thickness of the metal thin film type magnetic layer is not limited, but is preferably 500 to 5000 Å, and particularly 800 to 3
000Å is preferable. Further, the metal thin film type magnetic layer may have a single layer structure or a multilayer structure.

When the magnetic layer is of a coating type, the magnetic powder usually used in this field and a magnetic coating material containing various additives usually used, such as a dispersant, an abrasive and a lubricant, are appropriately added. The magnetic layer may be formed. Particularly preferable magnetic powders include acicular metal powders containing iron as a main component (metal powders), acicular cobalt-coated iron oxides and hexagonal ferromagnetic powders.

Further, in forming either a coating type or a metal thin film type magnetic layer, a back coat layer can be further formed on the surface of the support opposite to the surface on which the magnetic layer is formed. The back coat layer is made of a coating material in which carbon black and / or ceramic fine particles and a binder are dispersed.
It may be formed by coating so as to have a thickness of about 0 μm (after drying), or may be formed by attaching a metal or semimetal to a support by vapor deposition or the like. There are various conceivable metals to be attached as the back coat layer, but Al, C
u, Zn, Sn, Ni, Ag and the like and alloys thereof are used, and Cu-Al alloy is preferable. Furthermore, by performing oxidation, carbonization and nitridation at the time of vapor deposition, an oxide film,
Ceramics such as a carbonized film, a nitrided film and a composite thereof are particularly suitable. Further, as the semimetal forming the back coat layer, Si, Ge, As, S
c, Sb, etc. are used, and Si is preferable. The thickness of the metal thin film type back coat layer is about 0.05 to 1.0 μm.

Further, in the present invention, a lubricant layer made of a suitable lubricant may be formed on the protective layer. The lubricant layer may be formed by applying a solution obtained by dissolving a lubricant in an appropriate solvent, or may be formed by spraying the lubricant in a vacuum. When the lubricant is formed by spraying, it is preferable to spray the lubricant onto the magnetic layer formed on the support with a sprayer equipped with an ultrasonic oscillator (hereinafter, referred to as an ultrasonic sprayer).
As the lubricant, in either case of coating or spraying, a fluorine-based lubricant such as perfluoropolyether is preferable,
Specifically, as the perfluoropolyether, those having a molecular weight of 2,000 to 5,000 are suitable.
OMBLIN Z DIAC "[carboxyl group modified,
Montecatini Co., Ltd.], “FOMBLIN ZD
OL "[alcohol modified, Montecatini Co., Ltd.]
Commercially available products such as "Demnum SA" (manufactured by Daikin Industries) can be used. The amount of lubricant sprayed may be appropriately determined in consideration of the use of the magnetic recording medium, the type of lubricant, etc., but the thickness of the formed lubricant layer is 5 to 100.
It is about Å.

The support used in the magnetic recording medium of the present invention includes polyesters such as polyethylene terephthalate and polyethylene naphthalate; polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate; polycarbonates; Polyvinyl chloride; polyimide; plastics such as aromatic polyamide are used. The thickness of these supports is about 2.5 to 50 μm.

[0019]

Embodiments of the present invention will be described below. However, the invention is not limited to these examples.

Example 1 Two magnetic layers having a thickness of 1000 Å were laminated on a PET film having a thickness of 6.3 μm to form a two-layer magnetic layer. Here, the magnetic layers were formed one by one by the vapor deposition apparatus shown in FIG. In FIG. 1, 1 is a film, 2 is an unwind roll, 3 is a can roll, 4 is a take-up roll, 5 is a bombarding means, 6 and 6'is an expander roll,
Reference numeral 7 is an oxygen gas introduction tube, 8 is a shielding plate for restricting a metal vapor region, 9 is an electron gun, and 10 is a crucible. These are arranged in a vacuum vessel (not shown), and the inside of the vacuum vessel is maintained at a degree of vacuum of about 1 × 10 ^-4 to 1 × 10 ^-6 Torr. The film 1 is conveyed from the unwinding roll 2 through the can roll 3 to the winding roll 4 (traveling speed of the film is 1.0 m / min). An electron beam was irradiated from the electron gun 9 onto Co contained in the crucible 10 to vaporize Co, and a magnetic layer made of Co was formed on the film 1 conveyed on the can roll 3. Further, oxygen gas was introduced (40 SCCM) from the oxygen gas introduction pipe 7 into the vapor deposition region to oxidize the Co surface. This operation was repeated twice to form a two-layer magnetic layer.

Next, an ECR plasma C is formed on the magnetic layer.
A protective layer composed of a diamond-like carbon thin film having a thickness of 100 ° was formed by the VD method. Further, on this protective layer, a perfluoropolyether having a -OH group which is a polar group (Demnum SA: manufactured by Daikin Industries) is formed to a thickness of 20 mm.
To form a lubricant layer. A back coat layer was formed on the surface of this film opposite to the surface on which the magnetic layer was formed. The back coat layer has a thickness of 0.2 after drying a binder containing carbon having a diameter of 20 to 30 nm.
It was applied to a film so as to have a thickness of 5 μm and dried to form a film. The film obtained above, on which the magnetic layer, the diamond-like carbon protective layer, the fluorine-based lubricating layer and the back coat layer were formed, was cut into a width of 8 mm and loaded into a cassette case to obtain an 8 mm video tape.

(2) Performance evaluation Output of the 8 mm video tape obtained above
The envelope was evaluated by the following method as an index of durability and head touch. Table 1 shows the results. Output The output was measured by modifying a commercially available 8 mm VTR. Hi-
Head gap 10 μm instead of 8 VTR head
By using the above head and changing the relative speed between the head and the tape, it is possible to make a relative evaluation assuming an arbitrary shortest recording wavelength of 0.45 μm or less. Example 1
Then, the shortest recording wavelength was set to 0.38 μm. The output was a relative evaluation using Comparative Example 1 as a reference (0 dB). Durability Durability was evaluated by measuring the reduction in output after setting the above 8 mm tape on a commercially available 8 mm VTR and reproducing in still mode for 5 hours with respect to the output before the test. Envelope The envelope was measured using an advantest TR4171 type spectrum analyzer, RBW = 10 kHz, VB
The output waveform (envelope) obtained under the condition of W = 30 kHz, frequency span = 0 MHz, sleep time = 40 ms, mileage = 16 times was measured, and as shown in FIG. 2, the maximum value B and the minimum value A of the output waveform were measured. Then, the amount of chipping was calculated as follows. Chipping amount (dB) = 20 log (A / B) The smaller the chipping amount, the better the head touch.

Example 2 In the same manner as in Example 1, except that the thickness of the diamond-like carbon protective layer was changed to 45 Å, 8 m was obtained.
An m-biteo tape was produced and the same test as in Example 1 was performed. However, in the second embodiment, the output was evaluated assuming that the shortest recording wavelength is 0.28 μm. Table 1 shows the results.

Example 3 In Example 1, instead of the diamond-like carbon protective layer, a protective layer of SiO _x thin film having a thickness of 80 Å was formed. Here, the SiO _x thin film was formed by sputtering with a target of Si and an oxygen gas flow at an output of 2.5 kW. Otherwise, the same as in Example 1, 8 mm
A video tape was produced and the same test as in Example 1 was performed. However, in the third embodiment, the output was evaluated assuming that the shortest recording wavelength is 0.32 μm. Table 1 shows the results.

Example 4 In Example 3, sputtering was carried out in which a nitrogen gas was aerated instead of the oxygen gas and Si was used as a target in a nitrogen atmosphere. As a result, the thickness of silicon nitride is 55Å
Was formed. Otherwise, an 8 mm video tape was produced in the same manner as in Example 1, and the same test as in Example 1 was performed. Also in Example 4, the output was evaluated assuming that the shortest recording wavelength was 0.32 μm. Table 1 shows the results.

Comparative Example 1 8 was carried out in the same manner as in Example 1 except that the thickness of the diamond-like carbon protective layer was 220 Å.
A mm video tape was produced and the same test as in Example 1 was performed. Table 1 shows the results.

Comparative Example 2 8 m was prepared in the same manner as in Example 1 except that the diamond-like carbon protective layer had a thickness of 40 Å.
An m-biteo tape was produced and the same test as in Example 1 was performed. Table 1 shows the results.

[0028]

[Table 1]

[0029]

As described above, according to the present invention, it is possible to improve the head touch and the durability while maintaining the output characteristics even in the magnetic recording medium having the shorter shortest recording wavelength.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a vapor deposition apparatus for manufacturing a magnetic recording medium of the present invention.

FIG. 2 is a model diagram showing maximum and minimum values of an envelope waveform.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Film 3 Can roll 9 Electron beam gun 10 Crucible

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hirohide Mizutani 2606 Akabane Kai, Haga-gun, Tochigi Prefecture Kao Stock Company Research Institute (72) Inventor Katsumi Endo 2606 Akabane Kai, Haga-gun, Tochigi Kao Stock Company Research Institute

Claims (3)

[Claims] 1. A magnetic recording medium having a support, a magnetic layer formed on the support, and a protective layer formed on the magnetic layer and having a shortest recording wavelength of 0.45 μm or less. The layer thickness is 1/20 to 1/7 of the shortest recording wavelength.
A magnetic recording medium characterized by being 0. 2. The protective layer comprises a carbon thin film.
The magnetic recording medium described. 3. The shortest recording wavelength is 0.35 μm or less, and the thickness of the protective layer is 1/100 of the shortest recording wavelength.
The magnetic recording medium according to claim 1 or 2, which has a thickness of 40 to 1/70.