JPH06333230A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the durability of a magnetic recording medium with a ferromagnetic metallic thin film capable of high density magnetic recording as the magnetic recording layer after storage over a long period of time especially in an environment at high temp. and humidity and to obtain a magnetic recording medium having very high practical reliability. CONSTITUTION:A magnetic layer made of a ferromagnetic metallic thin film 2 is formed on a nonmagnetic substrate 1, a protective layer made of a hard carbon film 4 is formed on the thin film 2 with a layer 3 of fluoride of a ferromagnetic metal in-between and a lubricant layer 5 of a fluorine-contg. lubricant is further formed on the surface of the carbon film 4. By this structure, strain existing in the hard carbon film 4 is absorbed and the objective magnetic recording medium excellent in durability after storage over a long period of time especially in an environment at high temp. and humidity is stably obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal thin film type magnetic recording medium suitable for high density magnetic recording, more specifically a magnetic tape,
The present invention relates to a magnetic recording medium such as a magnetic disk.

[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.

A conventional magnetic recording medium will be described below. FIG. 2 is an enlarged cross-sectional view of a conventional magnetic recording medium. In FIG. 2, reference numeral 1 is a substrate made of a polymer film such as a polyester film or a polyimide film or a non-magnetic metal thin film such as an aluminum thin film. Reference numeral 2 is a magnetic recording layer made of a ferromagnetic metal thin film, and cobalt, nickel, iron or an alloy containing them as a main component is deposited on the substrate 1 by a vacuum vapor deposition method such as an electron beam vapor deposition method, a sputtering method or an ion plating method. Has been formed.
Reference numeral 5 denotes a lubricant layer, which is formed on the magnetic recording layer 2 by an organic compound by a conventional coating method or a vacuum deposition method.

In the magnetic recording medium having the above-mentioned structure, for example, in the case of a magnetic tape, the surface of the magnetic layer has a very good surface property in order to achieve high density magnetic recording. Therefore, the running durability is greatly affected by friction and wear under high speed sliding with the magnetic head during the recording / reproducing process of the magnetic signal, and its improvement is a major issue.

Therefore, a fluorine-based lubricant having excellent lubricating properties has been developed and studied. For example, a polar group such as a carboxyl group, an amino group, a phosphoric acid group, a hydroxyl group or a mercapto group and a fluoroalkyl group are attached to the molecular end to improve the adhesion to a ferromagnetic metal thin film and to exert excellent lubricity Fluorine-based lubricant having at least one group and at least one aliphatic alkyl group (JP-A-61-10)
7529, JP-A-62-92225, JP-A-62-92226, JP-A-62-92227, JP-A-61-107527, JP-A-61-
Japanese Patent Laid-Open No. 107528 and Japanese Patent Laid-Open No. 60-229221).

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. That is, as shown in FIG. 3, a lubricant layer is formed on a protective film, for example, a lubricant layer is formed on a Si—N—O type thin film (Japanese Patent Laid-Open No. 61-131231), hard carbon. One in which a fluorine-based lubricant is disposed on the layer (Japanese Patent Laid-Open No. 61-126627, Japanese Patent Laid-Open No. 62-2).
No. 19314) is proposed.

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.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances and is excellent in durability after long-term storage, particularly after long-term storage under the influence of high temperature and multiple chambers, and is extremely high in practical use. It is intended to provide a reliable magnetic recording medium.

[0009]

In order to solve the above problems, in the magnetic recording medium of the present invention, a ferromagnetic metal thin film layer is formed on a nonmagnetic substrate, and a ferromagnetic metal thin film layer is formed thereon. Compound layer, and a hard carbon layer is sequentially formed thereon.

[0010]

[Function] The structure in which the hard carbon film layer is formed on the surface of the ferromagnetic metal thin film via the ferromagnetic metal fluoride layer absorbs the internal strain at the time of forming the hard carbon film, and after long-term storage at high temperature and high humidity Also in the above, it is possible to prevent the generation of microscopic defects due to the strain inherent in the hard carbon film, and improve the durability and the corrosion resistance due to the excellent protective effect inherent in the hard carbon film.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 embodiment of the present invention. In FIG. 1, is a substrate made of a polymer film, 2 is a magnetic recording layer made of a ferromagnetic metal thin film, 3 is a metal fluoride layer, 4 is a hard carbon film, 5 is a lubricant layer, and 6 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 are used. May be.

As the ferromagnetic metal thin film, iron, cobalt, nickel or an alloy containing them as a main component formed by a vacuum deposition method, a sputtering method or an ion plating method, or a partial oxide or a partial nitride thereof is used. Can be used.

The ferromagnetic metal fluoride is obtained by treating the ferromagnetic metal thin film with plasma of a non-polymerizable fluorine compound such as tetrafluoromethane.

When performing the plasma treatment of a fluorine compound, a fluorine compound gas or a mixed gas of a fluorine compound gas and an inert gas is introduced into a vacuum container, and then 0.0
While maintaining the pressure of 01 to 1 Torr, the interior of the vacuum vessel is discharged to generate plasma of a fluorine compound gas to form a metal fluoride layer on the surface of the ferromagnetic metal thin film. The discharge method may be either an external electrode method or an internal electrode method, and the discharge frequency can be experimentally determined.

The protective film made of a hard carbon film can be formed by plasma polymerization of a hydrocarbon gas, a mixed gas of carbon hydrogen and argon, or sputtering of carbon or graphite.

When the hydrocarbon gas is formed by plasma polymerization, the hydrocarbon gas or a mixed gas of the hydrocarbon gas and the inert gas is introduced into a vacuum container, and 0.00
While maintaining a pressure of 1 to 1 Torr, discharge inside the vacuum container to generate plasma of hydrocarbon gas,
A hard carbon film is formed on the surface of the substrate. As the discharge type,
Either the external electrode method or the internal electrode method may be used, and the discharge frequency can be experimentally determined. Also,
By applying a voltage of 0 to -3 KV to the electrode on the substrate side, 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 increase the discharge energy as much as possible. Further, it is desirable that the temperature of the substrate be as high as possible.

On the other hand, the sputtering method includes DC sputtering, AC sputtering, high frequency sputtering, magnetron sputtering,
There are ion beam sputtering and the like, but either method may be used. To form a hard film, the pressure is 0.01 Torr
r 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. On the other hand, by sputtering, the hardness of the film can be increased and the adhesion can be improved, as in the case of plasma polymerization.

The thickness of the hard carbon film is 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.

The lubricant used in the present invention is not particularly limited, but polar groups such as carboxyl group, amino group, phosphoric acid group, hydroxyl group and mercapto group, and fluoroalkyl group or perfluoropolyether. Fluorine-based lubricants having at least one base and at least one base are effective. For forming the lubricant layer in the present invention, a conventional coating method such as a bar coating method, a reverse roll coating method or a die coating method can be applied.

A more specific embodiment will be described below. (Example 1) Oxygen was introduced onto a 7-micron-thick polyethylene terephthalate film having wavy projections and granular projections composed of a modified silicone in which silica fine particles having a particle size of 120Å were dispersed on a smooth flat surface and a thickener. While performing continuous oblique vapor deposition by the electron beam method, Co with a film thickness of 1800Å
An -O film was formed.

Next, a coating solution prepared by dispersing a mixture of carbon black and calcium carbonate in a ratio of 3: 2 by weight in a resin component in a ratio of 3: 2 by weight of polyurethane and nitrocellulose on the side opposite to the vapor-deposited layer was applied in a reverse roll system. It was applied by a coater and dried at a temperature of 110 ° C. to form a back coat layer with a film thickness of 0.5 μm.

Further, a mixed gas of tetrafluoromethane is introduced on the vapor-deposited layer in the vacuum chamber to obtain a vacuum degree of 0.1T.
A high frequency (10 KHz) plasma was generated at orr to form a ferromagnetic metal fluoride layer. 10 or 2
It was run at 0,40 m / min, and three types of original fabrics having metal fluoride layer thicknesses of 8, 4, 2Å were prepared. Then, by using high frequency (10 KHz) plasma of a mixed gas of methane and argon, the electrode and the magnetic tape raw material itself are used as opposite electrodes.
A direct current voltage of -1.5 KV was applied to the original magnetic tape to discharge it to form a hard carbon film having a thickness of 250 Å.

Further, a lubricant containing a fluorine-containing carboxylic acid is applied on the treated layer by a reverse roll coater, and 75
It was dried at a temperature of ° C to form a lubricant layer. Then, the raw magnetic tape was cut into a width of 8 mm with a slitter to obtain 8 mm VTR magnetic tapes (magnetic tapes made from metal fluoride layer thicknesses of 8, 4 and 2Å are magnetic tapes 1, 2 and 3, respectively).

Further, as a comparative example, a magnetic tape 4 was prepared in the same manner as in the example except that the metal fluoride layer was not provided.

The formation of the metal fluoride was confirmed by the photoelectron spectroscopy analysis from the 1s peak of fluorine newly appearing at the binding energy of 685 eV.

After storing these magnetic tapes in an environment of 40 ° C. and 80% for 3 months, a still 8 mm VTR (EV-S900, manufactured by Sony) modified commercially available was used for the durability against repeated running and the repeated running. ,It was measured. The results (Table 1)
Shown in.

[0031]

[Table 1]

The still durability was measured 5 times with 2 samples in an environment of 5 ° C. and 80% RH, and the time from the initial output to a decrease of 6 dB was measured, and the average value was taken as the still life of the tape.

The durability during repeated running was measured at 5 ° C. 8
After repeatedly running for 200 passes in an environment of 0% RH, the output reduction from the initial stage was measured.

As is clear from (Table 1), each of the magnetic tapes 1 to 3 of the present invention has a still life of 30 minutes or more and a low output reduction after repeated running. However, in the magnetic tape 4 having no metal fluoride layer, a significant decrease in still life and output reduction after repeated running was observed, and the magnetic tape 3 was used in an environment of 40 ° C. and 80%.
When the tape surface after storage for one month was observed with an optical microscope, discoloration due to the generation of corrosion products was observed.

[0035]

As described above, according to the present invention, by forming a hard carbon film on a ferromagnetic metal thin film via a metal fluoride, long-term storage, especially in a hot and humid environment, is achieved. It is possible to improve durability after storage for a period of time.
It is possible to provide a magnetic recording medium of extremely high practical reliability, 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 enlarged sectional view of a conventional magnetic recording medium.

FIG. 3 is a schematic enlarged sectional view of a conventional magnetic recording medium.

[Explanation of symbols]

 1 Substrate 2 Magnetic Recording Layer 3 Metal Fluoride Layer 4 Hard Carbon Film Layer 5 Lubricant Layer 6 Backcoat Layer

Claims (1)

[Claims] 1. A ferromagnetic metal thin film formed on a non-magnetic substrate, a metal fluoride layer formed on the ferromagnetic metal thin film, and a hard carbon film layer formed on the metal fluoride layer. Magnetic recording medium.