JPH0991689A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve corrosion resistance and running stability and to suppress cupping by using a large amt. of a fluorescence generating substrate in diamondlike carbon forming a protective layer. SOLUTION: This magnetic recording medium has a substrate, a magnetic layer formed on the substrate and a protective layer formed on the magnetic layer and made of a thin diamondlike carbon film contg. a fluorescene generating substance. The ratio (C2 ,000 /C1 ,000 ) of the intensity C2 ,000 of the diamondlike carbon film at 2,000cm<-1> by Raman spectroscopy to the intensity C1 ,000 at 1,000cm<-1> has been regulated to >=1.8. In the case of C2 ,000 /C1 ,000 >=1.8, various molecules such as molecules each consisting of a limited number of bonded carbon atoms and double bonds exist at random and bonding property to a lubricant is improved, therefore superior corrosion resistance and durability are ensured.

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 specifically to a magnetic recording medium having a protective layer formed of a diamond-like carbon thin film formed on a magnetic layer, which is excellent in corrosion resistance, running stability, and reduction of cupping. Recording medium

[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 by vacuum evaporation or the like can increase the density of the magnetic material because the magnetic layer contains no binder. It is said to be promising for high density recording. However, the magnetic layer of the metal thin film type magnetic recording medium is inferior in corrosion resistance and durability as it is because the metal is simply attached to the support, and in order to improve this, a fluorine-based material such as perfluoropolyether is used. The above-mentioned lubricants, hydrocarbon-based lubricants or lubricants using these in combination have been applied, or a protective layer of a non-magnetic material has been provided on the magnetic layer. Further, today, attention is focused on a method of forming a thin film made of diamond-like carbon as a protective layer on a magnetic layer. The diamond-like carbon thin film is considered to have a structure in which graphite bonds and diamond bonds are mixed. As a method for forming a diamond-like carbon thin film on the magnetic layer, RF (Ra
dio Frequency: Plasma CVD (Chemical Vapor)
Deposition: Chemical vapor deposition method or ECR (Electron Cyc
rotoron Resonance: Electron cyclotron resonance) Plasma
A method such as CVD is used. Of these, ECR plasma
The CVD is a method of applying a microwave to a raw material gas in a high vacuum to turn the gas into plasma and form a thin film on an object (on a magnetic layer), and is generally used for forming a diamond-like carbon thin film.

[0003]

Conventionally, in order to further improve durability, a thin film closer to diamond has been formed. However, although diamond-like carbon close to the composition of diamond is certainly excellent in durability, it does not have a stable binding coefficient with a lubricant and a stable friction coefficient cannot be obtained, or its corrosion resistance is poor, or the diamond-like carbon itself There is a problem that cupping is remarkable due to the large tension.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that the diamond-like carbon forming a protective layer contains a large amount of fluorescent substances, thereby exhibiting excellent corrosion resistance and stability. It was found that the above friction coefficient can be obtained and the occurrence of cupping can be reduced, and the present invention has been completed.

That is, the present invention has a support, a magnetic layer formed on the support, and a protective layer formed on the magnetic layer and comprising a diamond-like carbon thin film containing a substance emitting a fluorescence. In the magnetic recording medium characterized in that the intensity at 1000 cm ^-1 by Raman spectroscopy of the diamond-like carbon thin film (C ₁₀₀₀ ) and 2000 cm
The ratio to the strength (C ₂₀₀₀ ) at ^-1 is C ₂₀₀₀ / C ₁₀₀₀ ≧ 1.
The present invention provides a magnetic recording medium characterized in that

The magnetic recording medium of the present invention has a protective layer made of a diamond-like carbon thin film formed on a magnetic layer formed on a support by a method such as vapor deposition. In the present invention, however, Raman is particularly preferable. Intensity at 1000 cm ^-1 (C ₁₀₀₀ ) and 2000 cm ^{-1 in} the spectroscopic chart
A diamond-like carbon thin film whose ratio with (C ₂₀₀₀ ) is C ₂₀₀₀ / C ₁₀₀₀ ≧ 1.8 is used. Raman spectroscopic analysis is an index for knowing the number of unsaturated bonds in a diamond-like carbon thin film. In the case where the above two intensities in Raman spectroscopic analysis satisfy the above relation, various molecules such as finite number of carbon-bonded molecules and double bonds are randomly present to improve the bondability with the lubricant. Therefore, it has excellent corrosion resistance and durability.

In the present invention, "fluoresce" means to fluoresce when irradiated with laser light under the following conditions. Laser light wavelength: 488 nm Power: 300 mW Irradiation time: 600 seconds This condition is also the condition for Raman spectroscopic analysis in the present invention.

A diamond-like carbon thin film containing a substance emitting fluorescence as described above and having a specific Raman intensity ratio can be formed on a magnetic layer by a usual ECR plasma CVD method. It is preferable to use a carbon source consisting of, preferably benzene. ECR
The plasma CVD method may be performed according to a known method. Normally, the microwave frequency is 2.45 GHz, the output is about 500 W, and the carbon source is set to a vacuum degree of 10 ^-1 to 10 ^-4 Torr. Flowing benzene gas. In the magnetic recording medium of the present invention, the thickness of the protective layer made of a diamond-like carbon thin film is preferably 50 to 200Å.

In the magnetic recording medium of the present invention, the magnetic layer may be a coating type, but is preferably a metal thin film type magnetic layer formed by vapor deposition or the like. 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, for example, Co, Ni, ferromagnetic metals such as 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-Sm, Co
-Pt, Ni-Cu, Mn-Bi, Mn-Sb, Mn-Al, Fe-Cr, Co-
Examples include ferromagnetic alloys such as Cr, Ni-Cr, Fe-Co-Cr, and Ni-Co-Cr. The magnetic layer is preferably at least one selected from ferromagnetic alloys mainly containing iron, cobalt and nickel and their nitrides or carbides. For high density recording, the magnetic layer of the magnetic recording medium is preferably formed on the substrate by oblique vapor deposition. The method of oblique vapor deposition is not particularly limited and is based on a conventionally known method. The degree of vacuum during vapor deposition is about 10 ⁻⁴ to 10 ⁻⁷ Torr. The magnetic layer formed by vapor deposition may have either a single-layer structure or a multi-layer structure. In particular, by introducing an oxidizing gas to form an oxide on the surface of the magnetic layer,
The durability can be improved. In the present invention, the magnetic layer may be a single layer or multiple layers,
When forming a multilayer magnetic layer by vapor deposition, the thickness of the magnetic layer is
In the case of two layers, the thickness of the lower magnetic layer is preferably 100 to 2000Å, the thickness of the upper magnetic layer is preferably 50 to 1000Å, and in the case of three layers,
The thickness of the lower magnetic layer is preferably 100 to 2000Å, the thickness of the intermediate magnetic layer is 100 to 1000Å, and the thickness of the upper magnetic layer is preferably 50 to 1000Å. Although the number of magnetic layers may be large, two to five layers are considered to be suitable as a practical range.

In the magnetic recording medium of the present invention, the support includes polyesters such as polyethylene terephthalate and polyethylene naphthalate; polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate;
Polycarbonate; polyvinyl chloride; polyimide; plastics such as aromatic polyamide are used. The thickness of these supports is about 3 to 50 μm.

Further, in the magnetic recording medium of the present invention,
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 a paint in which carbon black or the like and a binder are dispersed.
It may be formed by coating so as to have a thickness (after drying) of about 0 μm, or may be formed by depositing a metal or a semimetal on a support by vapor deposition or the like. There are various possible metal deposits for the backcoat layer, including Al, Cu, Z.
n, Sn, Ni, Ag, etc. and their alloys are used, Cu-A
l alloys are preferred. In addition, Si, Ge, As, Sc, Sb, etc. are used as the semi-metal forming the back coat layer,
Si is preferred. The thickness of the metal thin film type back coat layer is about 0.05 to 1.0 μm.

Further, in the magnetic recording medium of the present invention,
A top coat layer made of a suitable lubricant may be further formed on the protective layer made of the diamond-like carbon thin film as described above. The top coat layer may be formed by coating a lubricant dissolved in a suitable 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 on the magnetic layer formed on the support by using a sprayer equipped with an ultrasonic oscillator (hereinafter referred to as an ultrasonic sprayer). As the lubricant, in any case of coating or spraying, a fluorine-based lubricant such as perfluoropolyether is preferable, and specifically, the perfluoropolyether has a molecular weight of 2000 to
5000 is suitable, for example "FOMBLIN Z DIAC"
[Carboxyl group-modified, Montecatini Co., Ltd.],
"FOMBLIN Z DOL" [Alcohol modified, Montecatini
The product sold under the trade name of] can be used. The amount of lubricant sprayed may be appropriately determined in consideration of the application of the magnetic recording medium, the type of lubricant, etc., but the thickness of the formed top coat layer is about 10 to 200Å.

[0013]

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

Examples 1 and 2 and Comparative Example 1 First, cobalt was vapor-deposited on a PET film having a thickness of 6.5 μm to form a magnetic layer having a thickness of 2000 Å. Then the normal
A protective layer consisting of a diamond-like carbon thin film was formed on the magnetic layer by an ECR plasma CVD device. Conditions at this time and the thickness of the protective layer and Raman spectroscopic analysis method 1000 cm
Strength at ^-1 (C ₁₀₀₀ ) and strength at 2000 cm ^-1
The ratio with (C ₂₀₀₀ ) is shown in Table 1.

[0015]

[Table 1]

As described above, a back coat layer containing carbon black as a main component and having a thickness of 0.5 μm is formed by a gravure coating method on the surface of the PET film on which the magnetic layer and the diamond-like carbon layer are formed, which is opposite to the magnetic layer surface. Then
Further, a lubricating layer made of a fluorine-based lubricant [FOMBLIN Z DIAC, modified by carboxyl group, manufactured by Montecatini Co.] was formed on the diamond-like carbon layer by a gravure coating method. The obtained film was slit into a width of 8 mm and placed in an 8 mm VTR cassette to manufacture an 8 mm video tape. The results of Raman spectroscopic analysis of each diamond-like carbon thin film are shown in FIG.

<Performance Evaluation> 8 mm manufactured by the above
The video tape was evaluated for corrosion resistance, change in friction coefficient, and occurrence of cupping by the following methods. The results are shown in Table 2. Corrosion resistance The reduction rate ΔBs (%) of the saturation magnetic flux density was measured after the 8 mm video tape was stored under the conditions of 60 ° C. and 90% RH for 1 week. Friction body (diameter 5m) under the condition of friction coefficient 20 ℃ / 50% (temperature / humidity)
m, made of stainless steel, surface roughness 0.2 s) 1
At a speed of 4.3 mm / sec, make a wrap angle of 115 °, and
The value when a tension of 0 g was applied to the tape was measured by a friction coefficient measuring machine. The friction coefficient (μ) is 1 pass, 10
The measurement was performed after 0 passes and 1000 passes. Occurrence of cupping The amount of cupping was determined as follows: -a (μ)
m) and the cupping generated on the back coat layer side [Fig. 2
(B)] was defined as + b (μm).

[0018]

[Table 2]

The Raman intensity ratio (C ₂₀₀₀ / C ₁₀₀₀ ) is shown in FIG.
Shows the correlation between corrosion resistance and friction coefficient. The conditions that the friction coefficient is 0.3 or less and the corrosion resistance is 10% or less are the Raman intensity ratio (C
It can be seen that ₂₀₀₀ / C ₁₀₀₀ ) is required to be 1.8 or more.

[0020]

As described above, according to the present invention, it is possible to obtain a magnetic recording medium which has excellent corrosion resistance, stability of friction coefficient, and less cupping.

[Brief description of drawings]

FIG. 1 is a chart showing the results of Raman spectroscopic analysis of protective layers of magnetic recording media obtained in Example 1 and Comparative Example 1.

FIG. 2 is a schematic diagram showing a cupping measurement method in an example.

FIG. 3 is a graph showing the correlation between the Raman intensity ratio (C ₂₀₀₀ / C ₁₀₀₀ ) and the corrosion resistance and friction coefficient.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junko Ishikawa 2606 Akabane, Kaigamachi, Haga-gun, Tochigi Prefecture Kao Corporation Research Institute

Claims (1)

[Claims] 1. A support, a magnetic layer formed on the support, and a protective layer formed on the magnetic layer and made of a diamond-like carbon thin film containing a substance that emits fluorescence. In the magnetic recording medium, the Raman spectroscopy of the diamond-like carbon thin film is used.
Strength at 1000 cm ^-1 (C ₁₀₀₀ ) and strength at 2000 cm ^-1
A magnetic recording medium characterized in that the ratio with (C ₂₀₀₀ ) is C ₂₀₀₀ / C ₁₀₀₀ ≧ 1.8.