JPH05128504A - Manufacture of magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide the manufacturing method of a magnetic recording medium wherein the problem of its durability and its corrosion-resistant property is solved, a high-cost Freon-based solvent or an organic solvent is not used, its safe and hygienic aspect is excellent and its practical reliability is excellent in the magnetic recording medium wherein a ferromagnetic metal thin film which is most suitable for a high-density magnetic recording operation is used as a magnetic layer. CONSTITUTION:The following are formed sequentially on at least one face of a high-polymer film 1: a magnetic layer 2 composed of a ferromagnetic metal thin film; and a protective film 3 composed of a hard carbon layer. After that, the protective film is coated with a coating liquid in which a fluorine-based lubricant has been dispered in water. The liquid is dried at a temperature of the melting point or higher of said fluorine-based lubricant. Thereby, a fluorine- based lubricant layer 4 is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a metal thin film type magnetic recording medium such as a magnetic tape having a ferromagnetic metal thin film as a magnetic layer, which is most suitable for high density magnetic recording. The present invention relates to a method of manufacturing a magnetic recording medium to be formed.

[0002]

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

However, in the metal thin film type magnetic recording medium, since the magnetic layer has an extremely good surface property, the durability and the durability due to friction and abrasion under high speed sliding with the magnetic head during the recording / reproducing process of signals. Runability and corrosion resistance are greatly affected, and their improvement is a major issue.

Therefore, an attempt has been made to improve 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 Application Laid-Open No. 54-54
No. 113303), formation of a sputtered film of a polymer compound having an imide group (JP-A-57-116771), a sputtered film targeting a polymer compound, carbon, BN, MoS ₂ , SiO _2, etc. Thinning by sputtering or vapor deposition, formation of diamond-like hard carbon film (materials of the 46th meeting of the Japan Society for Applied Magnetics), formation of lubricants such as fatty acids and fatty acid amides (for example, JP-A-56-
No. 30609) and many other attempts have been made.

However, in the above-mentioned examples, durability, running property, corrosion resistance, etc. cannot be sufficiently satisfied, and therefore, there is an increasing number of ideas that the respective roles are shared by stacking layers.

For example, formation of a fluorocarbon type lubricant layer on a fatty acid metal salt adsorption layer (JP-A-61-1203).
31), a hard carbon layer on which a fluorine-based lubricant is disposed (Japanese Patent Laid-Open No. 61-126627), Si-
A lubricant layer formed on an NO thin film (Japanese Patent Laid-Open No. Sho 61-61).
No. 131231).

In particular, in recent years, the combination of a hard carbon layer and a fluorine-based lubricant such as perfluoropolyether, perfluorocarboxylic acid or perfluorocarboxylic acid ester has attracted attention because of its excellent characteristics and has been widely studied. There is.

[0009]

However, the requirements 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. Further, although the above-mentioned fluorine-based lubricant exhibits excellent properties as a lubricant, its solubility is limited, and only a CFC-based solvent or a partial organic solvent can be used. However, it has been pointed out that CFC-based solvents are expensive and cause environmental damage on a global scale, and their use and production will be restricted in the future. Further, even in the case of using an organic solvent, in order to secure an environment in terms of safety and hygiene, it is necessary to deal with expensive manufacturing equipment such as exhaust equipment and explosion-proof structure, which is a problem.

The present invention solves the above-mentioned problems of the prior art by providing a magnetic tape having excellent durability and corrosion resistance and high practical reliability with fluorine-based lubrication without using a CFC-based solvent or an organic solvent. It is an object of the present invention to provide a method for manufacturing a magnetic recording medium that enables formation of an agent layer.

[0011]

To achieve this object, a method of manufacturing a magnetic recording medium according to the present invention comprises a magnetic layer made of a ferromagnetic metal thin film and a hard carbon layer on at least one surface of a non-magnetic substrate. After the protective film layers are sequentially formed, a coating solution in which a fluorinated lubricant is dispersed in water is applied and dried at a temperature equal to or higher than the melting point of the fluorinated lubricant to form a lubricant layer.

[0012]

According to the method of manufacturing a magnetic recording medium of the present invention, the metal thin film magnetic layer having a hard carbon layer is coated with a fluorine-based lubricant in a state of being dispersed in water and dried at a temperature equal to or higher than the melting point of the lubricant. Has become.

The coating liquid in which the fluorine-based lubricant is dispersed in water dries while aggregating in the evaporation process after coating, but at that time, it easily collects on the minute defects on the surface, and at a temperature higher than the melting point. Since it is dried, it melts, then solidifies, and adheres firmly to the surface. That is, it has a function of strongly and firmly adhering the lubricant to the minute defects existing on the surface of the protective film.
It can prevent and reduce damage in the process of recording and reproducing signals, and also prevents moisture from entering into defective parts during storage and prevents rust, which improves durability and corrosion resistance. Is to have.

Further, since it is not necessary to dissolve the fluorine-based lubricant, an expensive CFC-based solvent and an organic solvent which poses a safety and health problem are not used, and neither exhaust equipment nor expensive manufacturing equipment having an explosion-proof structure is required. Therefore, both the economic effect and the improvement of the characteristics can be secured without exposing the worker to the vapor of the organic solvent.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is an enlarged sectional view showing the structure of a magnetic tape used in one embodiment of the present invention. In FIG. 1, 1
Is a polymer film, 2 is a magnetic layer made of a ferromagnetic metal thin film, 3 is a protective film layer made of a hard carbon layer, 4 is a fluorine-based lubricant layer, and 5 is a back coat layer.

The polymer film 1 used in the magnetic recording medium of the present embodiment is a polymer film of polyethylene terephthalate, polyethylene naphthalate, polyphenylene sulfide, aromatic polyamide, polyimide or the like, and has a fine particle coating layer on the surface thereof. A shape-controlled one is suitable.

The ferromagnetic metal thin film of the magnetic layer 2 is a magnetic film formed by an ion plating method, a sputtering method, an electron beam evaporation method or the like, and is made of Co, Co-Ni, Co-O or C.
o-Cr, Co-Ti, Co-W, Co-Mo, Co-
It is appropriately selected from Ni-O, Co-Pt-BO, and the like.

The protective layer 3 composed of a hard carbon layer can be formed by plasma polymerization of a hydrocarbon gas or a mixed gas of hydrocarbon 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 to form 0.001.
To 1 Torr is maintained, and the inside of the vacuum vessel is discharged to generate plasma of hydrocarbon gas to form a hard carbon layer. The discharge method may be either the external electrode method or the internal electrode method, and the discharge frequency can be experimentally determined. Further, 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. Also, it is desirable to raise the temperature of the substrate 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 any method may be used. To form a hard film, the pressure is 0.01 Torr
The following is desirable, and the energy density should be high,
For example, in high frequency magnetron sputtering, 1 W / cm ² or more per target area is preferable, and by applying a voltage of 0 to -3 kV to the electrode on the side holding the substrate, sputtering is performed, similar to the case of plasma polymerization. In addition, the hardness of the film can be increased and the adhesion can be improved.

The thickness of the hard carbon layer is preferably in the range of 50 to 300 A, and when it is thinner than this,
If a sufficient protective film effect cannot be obtained and is larger than this, spaging between the magnetic head and the magnetic layer increases,
It causes deterioration of electromagnetic conversion characteristics.

As the fluorine-based lubricant, a carboxylic acid group,
Those having a polar group such as an ester group are effective, and perfluoroalkylcarboxylic acid and its ester are suitable, and they can be used alone or in combination.

The coating amount of the fluorine-based lubricant is 1 mg /
The range of m ² to 30 mg / m ² is preferable, and if it is lower than 1 mg / m ² , it does not show sufficient durability and corrosion resistance,
If it is more than m ² , the spacing between the magnetic head and the magnetic layer increases, causing deterioration of electromagnetic conversion characteristics.

To prepare the dispersion of the fluorine-based lubricant,
It can be obtained by carrying out dispersion treatment by applying mechanical energy with a high-speed stirrer, or by dissolving a lubricant in a small amount of solvent and adding it to a large amount of water with high-speed stirring. It is desirable that the high-speed stirring be continuously performed until just before the coating even after the coating liquid is adjusted.

Hereinafter, the magnetic recording medium of the present invention will be described more specifically in comparison with a comparative example.

Example 1 A particle size of 180Å on a smooth surface
On a polyethylene terephthalate film having a thickness of 10.3 microns having wavy projections and granular projections composed of a modified silicone in which silica fine particles are dispersed and a thickener, continuous oblique vapor deposition is performed by an electron beam method while introducing oxygen, A Co-Ni-O film having a film thickness of 2000 Å was formed. Then,
On the side opposite to the vapor-deposited layer, a coating liquid prepared by dispersing a mixture of carbon black and calcium carbonate in a ratio of 1: 1 by weight in a resin component of polyurethane and nitrocellulose in a ratio of 1: 1 by weight is applied by a reverse roll type coating machine. , And dried to form a back coat layer with a film thickness of 0.7 micron. Furthermore, a high frequency (10
(kHz) plasma, a DC voltage of -1.5 kV was applied to the magnetic tape raw material using the electrode and the magnetic tape raw material as the counter electrodes, and discharge was performed to form a hard carbon layer of 250 A film thickness. Furthermore, a perfluoroalkylcarboxylic acid (melting point: 59 ° C.) or a perfluoroalkylcarboxylic acid ester (melting point: 58 ° C.) is dispersed in water to form a coating solution of 7 mg / m ² in a reverse roll system. It was applied with a coater and dried at a temperature of 90 ° C to 70 ° C to form a lubricant layer. Then, the magnetic tape stock is cut into 8 mm width and 8 mm
It was used as a magnetic tape for VTR (Samples 1 to 6).

As comparative examples, those prepared in the same manner as in the examples except that the drying temperature was set to 50 ° C. (samples 7 and 8), and those prepared in the same manner as in the examples except that the hard carbon layer was not formed (sample 9) ), A sample (Sample 10) formed in the same manner as in the example except that toluene was used as the coating solvent.

A commercially available 8 mm VTR was used for these magnetic tapes.
(EV-S900, manufactured by Sony Corporation) was modified and the still durability and storage characteristics were measured.

For the still durability, the time from the initial output to a decrease of 6 dB was measured for three samples, and the average was taken as the still life of the tape.

The storage characteristics are 1 in an environment of 30 ° C. and 80% RH.
After leaving for a month, the dropout was measured.

The dropout was recorded and reproduced for 10 minutes with two samples, the number of signal defects in which the output decreased by 15 μsec, 16 dB or more was measured, the average value for 1 minute was calculated, and the value before storage was set to 1.0. , The rate of increase was calculated.

Table 1 shows manufacturing conditions and measurement results.

[0036]

[Table 1]

As is clear from (Table 1), the magnetic tapes 7 and 8 dried at a temperature lower than the melting point and the magnetic tape 9 without the hard carbon layer show low still durability, and after storage in a high humidity environment. The increase in dropout is also large, indicating a decrease in corrosion resistance. Further, the magnetic tape 10 coated with an organic solvent shows an improvement tendency in still durability and corrosion resistance as compared with the magnetic tapes 7 to 9, but shows insufficient characteristics.

As described above, according to the present invention, without using an expensive CFC-based solvent or an organic solvent,
It enables the formation of a fluorine-based lubricant layer, can improve the still life, and can prevent the increase of dropout after storage in a high-humidity environment. It is excellent in improving the practical properties of metal thin film magnetic recording media. There is an effect.

[0039]

As described above, according to the present invention, after a magnetic layer made of a ferromagnetic metal thin film and a protective film layer made of a hard carbon layer are sequentially formed on at least one surface of a non-magnetic substrate, a fluorine-based lubricant is applied. By applying a coating liquid dispersed in water, by drying at a temperature of the melting point of the fluorine-based lubricant or higher,
Provided is a magnetic recording medium manufacturing method capable of forming a fluorine-based lubricant layer without using a fluorocarbon solvent or an organic solvent for a magnetic tape having excellent durability and corrosion resistance and high practical reliability. It is a thing.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view of a magnetic recording medium according to an embodiment of the present invention.

[Explanation of symbols]

 1 polymer film 2 magnetic layer 3 protective film layer 4 fluorine-based lubricant layer 5 back coat layer

Claims (1)

[Claims] 1. A non-magnetic substrate, on which a magnetic layer made of a ferromagnetic metal thin film and a protective film layer made of a hard carbon layer are sequentially formed on at least one surface of the non-magnetic substrate, and then a coating solution in which a fluorine-based lubricant is dispersed in water is applied. A method for producing a magnetic recording medium, which comprises applying and drying at a temperature equal to or higher than the melting point of the fluorine-based lubricant to form a fluorine-based lubricant layer.