JPH0950626A - Production of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve durability and corrosion resistance and to provide a magnetic recording medium having high reliability in practical use by solving the problem of microscopic ununiformity of a protective film caused in a process for producing a magnetic recording medium capable of high density magnetic recording and using a ferromagnetic metallic thin film as a magnetic recording layer. SOLUTION: This magnetic recording medium has a magnetic recording layer 2 made of a ferromagnetic metallic thin film on a polymer film 1 and a protective film 3 made of a hard carbon film on the recording layer 2. In this case, a substrate of a magnetic recording medium having >=1×10<8> Ω/sq. surface resistance or <=30nm surface roughness of a face opposite to the protective film forming face is used, adhesiveness to a can is ensured, thermal load on the substrate is relieved and the objective magnetic recording medium with a protective film made of a microscopically homogeneous hard carbon film is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a metal thin film type magnetic recording medium suitable for high density magnetic recording.

[0002]

2. Description of the Related Art In the field of magnetic recording, high performance such as digitalization, miniaturization and long time has been advanced in recent years, and the demand for high density magnetic recording medium has been increased accordingly, and magnetic recording A metal thin film magnetic recording medium having a layer made of a ferromagnetic metal thin film has been actively studied because it is extremely advantageous for short wavelength recording.

[0003]

However, in the magnetic recording medium of the ferromagnetic metal thin film type, since the surface of the magnetic layer has a very good surface property, high-speed contact with the magnetic head during the recording / reproducing process of the magnetic signal is carried out. Due to friction and wear under motion, durability, running property, corrosion resistance, etc. are greatly affected, and their improvement is a major issue.

Therefore, attempts have been made to improve the durability, running property and corrosion resistance by providing a top coat layer on the surface of the magnetic layer. For example, formation of a fatty acid metal salt (Japanese Patent Laid-Open No. 54-113).
303), formation of a sputtered film of a polymer compound having an imide group (Japanese Patent Laid-Open No. 57-116771), sputtered film targeting a polymer compound, carbon, BN, MoS ₂ , SiO ₂ etc. Method, thin film formation by vapor deposition method, formation of diamond-like hard carbon film (materials of the 46th meeting of Japan Society for Applied Magnetics), formation of lubricants such as fatty acids and fatty acid amides (for example, JP-A-56-30609).
No.) and many others have been tried.

However, in the above example, the durability,
Since the running property and the corrosion resistance are not sufficiently satisfied, there is an increasing number of ideas that the respective roles are shared by stacking them. As an example thereof, a fluorocarbon-based lubricant layer is formed on a fatty acid metal salt adsorption layer (JP-A-61-1).
No. 20331), a fluorocarbon lubricant disposed on a hard carbon layer (Japanese Patent Laid-Open No. 61-126627), and a lubricant layer formed on a Si—NO thin film (Japanese Patent Laid-Open No. Sho 61-126627). 61-131231).

However, demands for improving the performance of the magnetic recording medium are strict, and it cannot be said that the above-mentioned constitution has sufficient characteristics, and further improvement in durability and corrosion resistance is desired. The present invention has been made in view of the above circumstances, and provides a method of manufacturing a magnetic recording medium having excellent durability and corrosion resistance and extremely high practical reliability.

[0007]

In order to solve the above problems, the present invention forms a magnetic recording layer made of a ferromagnetic metal thin film on a polymer film, and a protective film layer made of a hard carbon film thereon. In manufacturing a magnetic recording medium, a raw material of a magnetic recording medium having a surface resistance of 1 × 10 ⁸ Ω / □ or more on the surface opposite to the surface on which the protective film is formed is used. A raw material of a magnetic recording medium having a surface roughness of 30 nm or less is used.

[0008]

According to the present invention, in the manufacturing process for forming the protective film, the surface of the surface opposite to the surface on which the protective film is formed has a surface resistance of 1 × 10 ⁸ Ω / □ or more. The surface of the magnetic recording medium that causes charging on the surface or the surface opposite to the surface on which the protective film is formed has a surface roughness of 30 nm or less is used to secure the adhesion to the can and secure the magnetic recording medium. Reduces the heat load received, forms a uniform hard carbon film on a micro level, reduces damage during storage in a high humidity environment, and generates micro cracks during repeated use after storage,
And to prevent peeling of the film.

That is, durability and corrosion resistance are improved by preventing damage to the protective film layer.

[0010]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing the structure of a magnetic tape used in an example of the present invention. In FIG. 1, 1
Is a polymer film, 2 is a magnetic recording layer made of a ferromagnetic metal thin film, 3 is a protective film layer made of a hard carbon film, 4 is a lubricant layer, and 5 is a back coat layer.

Polyethylene terephthalate is often used as the polymer film used in the magnetic recording medium of the present invention, but other polyester films such as polyethylene naphthalate, cellulose derivatives such as cellulose acetate, and plastic films such as polyamide and polyimide. May be. As the ferromagnetic metal thin film, use iron, cobalt, nickel formed by vacuum deposition, sputtering, or ion plating or an alloy containing them as a main component, or a partial oxide or partial nitride thereof. You can

The protective film made of a hard carbon film can be formed by plasma polymerization of a hydrocarbon gas, a mixed gas of hydrocarbon and argon, or sputtering of carbon or graphite. In the case of forming by plasma polymerization of hydrocarbon gas, hydrocarbon gas or a mixed gas of hydrocarbon gas and an inert gas is introduced into a vacuum vessel, and a pressure of 0.001 to 1 Torr is maintained, By discharging inside the vacuum container, plasma of hydrocarbon gas is generated and a hard carbon film is formed on the surface of the substrate. The discharge method may be either an external electrode method or an internal electrode method, and the discharge frequency can be experimentally determined. Moreover, 0 to -3KV is applied to the electrode on the substrate side.
By applying the voltage of, the hardness of the film and the adhesion can be improved.

As the hydrocarbon gas, methane, ethane,
Propane, butane, pentane, hexane, heptane, octane, benzene and the like can be used. Further, in order to form a hard film, it is desirable to maximize the discharge energy. Further, it is desirable that the temperature of the substrate is as high as possible. On the other hand, sputtering methods include direct current sputtering, alternating current sputtering, high frequency sputtering, magnetron sputtering, and ion beam sputtering, but either method may be used. To form a hard film, the pressure is
0.01 Torr or less is desirable, and the energy density is preferably high. For example, in high frequency magnetron sputtering, 1 W / cm ² or more per target area is preferable, and a voltage of 0 to -3 KV is applied to the electrode holding the substrate. By applying and applying the sputtering, the hardness of the film can be increased and the adhesion can be improved, as in the case of plasma polymerization.

The hard carbon film has a thickness of 50 to 30.
If the range of 0Å is appropriate, and if it is thinner than this, a sufficient protective film effect cannot be obtained, and if it is larger than this,
The output is greatly reduced due to the spacing, and the practicality is reduced. To reduce the heat load generated when the protective film is formed,
As a first method, a charging treatment such as glow discharge is performed to bring the toner into close contact with the can. The surface resistance of the original surface of the magnetic recording medium opposite to the surface on which the protective film is formed is 1 × 10.
^{When 8} Ω / □ or more, a sufficient charging effect can be seen,
If it is lower than this, the electrification tends to be insufficient, the adhesion to the can at the time of forming the protective film is insufficient, and the heat load is locally increased on the magnetic recording medium original fabric to form an inhomogeneous hard carbon film. It is formed. As a second method, a raw material of a magnetic recording medium whose surface roughness on the surface opposite to the protective film forming surface is 30 nm or less is used, and adhesion to a can is performed at the time of forming the protective film. If it is larger than this, the adhesion to the can at the time of forming the protective film is insufficient, the heat load is locally increased on the magnetic recording medium original fabric, and an inhomogeneous hard carbon film is formed. First, second
To achieve the above method, on the surface opposite to the surface on which the protective film is formed,
A raw material of a magnetic recording medium which is a coating layer composed of a mixed filler of carbon black and inorganic particles is used. Alternatively, a raw material of a magnetic recording medium, which is a coating layer containing a polyester resin as a main component, is used on the surface opposite to the protective film forming surface.

Fluorine-based lubricants are effective as the lubricant, and there are perfluorocarboxylic acid and its ester, and perfluoropolyether and its derivative, which can be used alone or in combination. Hereinafter, more specific examples will be shown. (Example 1) Oxygen was deposited on a 6.4-micron-thick polyethylene terephthalate film having wavy projections and granular projections composed of a modified silicone in which silica fine particles having a particle diameter of 180Å are dispersed on a smooth surface and a thickener. While being introduced, continuous oblique vapor deposition was performed by an electron beam method to form a Co—O film having a film thickness of 1500 Å. Then, on the side opposite to the vapor deposition layer,
A coating liquid prepared by dispersing a mixture of carbon black and calcium carbonate in a ratio of 1: 4 by weight in a resin component of aromatic polyester and nitrocellulose in a ratio of 3: 1 by weight was applied by a reverse roll type coating machine, and the temperature of 120 ° C. Dry at temperature 0.5
The back coat layer was formed with a film thickness of micron. When the surface resistance of the back coat layer was measured, it was 3 × 10 ⁸ Ω / □
Met. Furthermore, using the protective film forming device (FIG. 2),
A hard carbon film was formed. The raw material 7 of the magnetic recording medium discharged from the unwinding portion 6 is charged in the discharge processing portion 8 and then adheres to the can 9, and in the nozzle portion 10, a mixed gas of methane and argon (2: 1) is introduced from the gas inlet 12 in the nozzle portion 10. High frequency (10KH
z) By applying a direct current voltage of -1.25 KV to the magnetic tape raw material by using the electrode 11 and the magnetic tape raw material itself as counter electrodes by plasma, discharge is performed to form a hard carbon film of 250 Å film thickness, and then winding. It is wound around the take-up section 13. further,
A mixed lubricant of a fluorine-based carboxylic acid and a fluorine-based carboxylic acid ester was applied thereon with a reverse roll coater under the condition of 10 mg / m ² , and dried at a temperature of 80 ° C to form a lubricant layer. Next, use a slitter to remove the original magnetic tape 8
It was cut to a width of 8 mm to obtain a magnetic tape for 8 mm VTR.

Further, the backcoat agent carbon black (trade name Monarch 280 and Vulcan XC72R manufactured by Cabot Corporation, USA) and calcium carbonate (trade name Homocal D manufactured by Shiraishi Industry Co., Ltd.) are mixed (magnetic tape 2; 1 :).
3, magnetic tape 3; 1: 2, magnetic tape 4; 2: 3, magnetic tape 5; 1: 1)
Magnetic tapes were prepared (magnetic tapes 1 to 5). Further, as a comparative example, a magnetic tape 6 was produced in the same manner as in the example, except that a back coat layer was formed with a coating liquid containing urethane resin as a main component and carbon black dispersed therein.

(Example 2) Particle size of 180Å on a smooth surface
Using a polyethylene terephthalate film having a thickness of 6.3 μm, which has wavy projections and granular projections composed of a modified silicone in which silica fine particles are dispersed and a thickener, and has different roughness on the side opposite to the magnetic layer forming surface, Others are Example 1
A magnetic tape was prepared in the same manner as (magnetic tape 7-
12). The surface roughness was measured by using an atomic force microscope (SAF300 manufactured by Seiko Denshi KK) to calculate the average surface roughness SRa.

Using these magnetic tapes 1 to 12, the still durability and storage characteristics were measured by using a commercially available remodeling machine of 8 mm VTR (EV-S900, manufactured by Sony Corporation). The still durability was measured 5 times with 2 samples in an environment of 5 ° C. and 80% RH, and the time until the initial output decreased by 6 dB was measured.
The average value was defined as the still life of the tape.

The storage characteristics are 1 in an environment of 40 ° C. and 80% RH.
After leaving for a month, the surface was observed with an optical microscope at a magnification of 100 times and the dropout was measured. Then 10
A 0-pass repeated running test was performed to measure the change in output. Dropout recorded and played for 10 minutes with 2 samples,
For 3 μsec, the number of signal defects with an output decrease of 10 dB or more was measured, the average value for 1 minute was calculated, and the value before storage was 1.
The rate of increase was calculated as 0.

[0020]

[Table 1]

And

[0022]

[Table 2]

The tape trial conditions and evaluation results are summarized in
You. As is clear from (Table 1) and (Table 2), surface resistance
Is 1 × 10⁸Magnetic tape with a back surface of Ω / □ or more 1
~ 3 and the surface roughness of the base film running surface is 30 nm
Magnetic tapes 7-9 manufactured using
There is little increase in dropout after storage, and
Output reduction after return running is small and corrosion resistance is reduced
No deterioration of the still durability was observed, while the surface resistance was
Anti 1 × 10 ⁸Magnetic tapes less than Ω / □ 4-6 and tape
If the surface roughness of the running film is 30 nm or more
The magnetic tapes 10-11 produced by using them are still durable.
Of the dropout, and the increase in dropout after storage is also large.
The corrosion resistance is low.

Further, when the surface of the magnetic tape after storage was observed with an optical microscope at a magnification of 100 times, the magnetic tape 1
No corrosion products were observed in Nos. 3 and 7 to 9, but in the magnetic tapes 4 to 6 and 10 to 11, partial discoloration was observed, indicating that corrosion had started.

[0025]

As described above, according to the present invention, by reducing the heat load in the manufacturing process of the protective film, it is possible to form a protective film that is also microscopically uniform and improves the still durability.
The storability can be improved, and there is an excellent effect of improving the practical characteristics of the metal thin film type magnetic recording medium.

[Brief description of drawings]

FIG. 1 is a schematic enlarged sectional view showing the configuration of a magnetic tape used in a first embodiment of the present invention.

FIG. 2 is a schematic view of a protective film forming apparatus used in the first and second embodiments of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Polymer film 2 Magnetic recording layer 3 Protective film layer 4 Lubricant layer 5 Back coat layer 6 Unwinding part 7 Magnetic recording medium original material 8 Discharge processing part 9 Can 10 Nozzle 11 Electrode 12 Gas introduction part 13 Winding part 14 Power supply Part 15 Vacuum pump 16 Vacuum chamber

Claims (2)

[Claims] 1. A surface opposite to a surface on which a protective film is formed in a manufacturing process of forming a magnetic recording layer made of a ferromagnetic metal thin film on a polymer film and a protective film layer made of a hard carbon film on the ferromagnetic metal thin film. A method for manufacturing a magnetic recording medium, characterized in that a raw material of the magnetic recording medium having a surface resistance of 1 × 10 ⁸ Ω / □ or more is used. 2. A surface opposite to a surface on which a protective film is formed in a manufacturing process of forming a magnetic recording layer made of a ferromagnetic metal thin film on a polymer film and a protective film layer made of a hard carbon film on the ferromagnetic metal thin film. A method of manufacturing a magnetic recording medium, comprising using a raw material of a magnetic recording medium having a surface roughness of 30 nm or less.