JP3687117B2 - Magnetic recording medium and method for manufacturing the same - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for manufacturing a so-called metal magnetic thin film type magnetic recording medium having a ferromagnetic metal thin film as a magnetic layer on a nonmagnetic support.
[0002]
[Prior art]
Conventionally, as a magnetic recording medium, a magnetic powder material such as an oxide magnetic powder or an alloy magnetic powder is placed on a nonmagnetic support in an organic binder such as a vinyl chloride-vinyl acetate strong polymer, a polyester resin, or a urethane resin. A so-called coating-type magnetic recording medium manufactured by applying and drying a dispersed magnetic paint is widely used.
[0003]
On the other hand, with increasing demand for high-density magnetic recording, metallic magnetic materials such as Co—Ni alloy, Co—Cr alloy, and Co—O are plated or vacuum thin film forming means (vacuum deposition method, sputtering method, ion A so-called metal magnetic thin film type magnetic recording medium directly deposited on a nonmagnetic support such as a polyester film, polyamide, or polyimide film by a plating method has been proposed and attracting attention.
[0004]
This metal magnetic thin film type magnetic recording medium is excellent in coercive force, squareness ratio, etc., and the thickness of the magnetic layer can be made extremely thin, so the thickness loss during recording demagnetization and reproduction is extremely small, and electromagnetic conversion characteristics at short wavelengths are achieved. In addition to being excellent, the magnetic layer does not need to be mixed with a binder, which is a nonmagnetic material, and therefore has a number of advantages such as an increased packing density of the magnetic material. For this reason, this metal magnetic thin film type magnetic recording medium is considered to become the mainstream of high-density magnetic recording because of its superior magnetic properties.
[0005]
In such a metal magnetic thin film type magnetic recording medium, in order to further improve the electromagnetic conversion characteristics and obtain a larger output, when forming the magnetic layer of the magnetic recording medium, So-called oblique deposition, in which layers are deposited obliquely, has been proposed and put into practical use.
By the way, in this type of magnetic recording medium, when forming the magnetic layer, oxygen gas is introduced during vapor deposition to improve the magnetic characteristics, ensuring electromagnetic conversion characteristics suitable for high-density magnetic recording, and the surface of the medium. Is intended to improve durability by being covered with metal oxide.
[0006]
Further, as an effective means for improving durability, for example, a method for reducing friction by providing fine irregularities in advance on the magnetic layer, a method for improving the film quality of the medium surface by applying a lubricant, a hard protective film, etc. A method of providing the protective film has been studied, and in particular, formation of a protective film using a diamond-like hard carbon (DLC) film has attracted attention.
[0007]
[Problems to be solved by the invention]
However, when the diamond-like hard carbon film (hereinafter abbreviated as DLC film) is directly formed on a ferromagnetic metal thin film made of Co alone or a Co—Ni alloy as a protective film, the durability obtained is at a practical level. In order to increase the thickness of the DLC film, the thickness of the DLC film must be increased. For this reason, if the wavelength is further shortened along with further higher density recording in the future, a decrease in output due to spacing loss cannot be ignored, which becomes a serious problem.
[0008]
Therefore, the present invention has been proposed in view of such circumstances, and when a DLC film is used as a protective film, sufficient durability is ensured even if the thickness of the DLC film is reduced. An object of the present invention is to provide a method for manufacturing a magnetic recording medium.
[0009]
[Means for Solving the Problems]
As a result of earnest research, the present inventors have partitioned reaction tubes or reaction chambers when forming a DLC film used as a protective film, and each of the partitioned chambers is divided into chambers. Hydrocarbon gas and hydrogen fluoride gas are introduced by continuously changing the gas composition, and the hydrogen and fluorine contents are continuously changed in the thickness direction to form a hydrogen-rich DLC film on the magnetic layer side. The inventors have found that by forming a fluorine-rich DLC film on the surface side, durability is improved and good results can be obtained, and the present invention has been completed.
[0011]
In the present invention, a magnetic layer made of a ferromagnetic thin film is formed on a nonmagnetic support by a vacuum thin film forming technique, and a diamond-like hard carbon film as a protective film is formed on the magnetic layer by a vacuum thin film forming technique. In the method for manufacturing a magnetic recording medium, a part of the interior of a reaction tube or reaction chamber is divided into two chambers by a partition plate, while introducing a hydrocarbon gas into one chamber and introducing a fluorocarbon gas into the other chamber The diamond-like hard carbon film is formed on the magnetic layer by running a non-magnetic support on which the magnetic layer is formed from the one chamber side toward the other chamber side. A diamond-like hard carbon film containing a large amount of hydrogen is formed on the side, and a diamond-like hard carbon film containing a large amount of fluorine is formed on the surface side .
[0012]
In the present invention, a diamond-like hard carbon film is provided as a protective film on a ferromagnetic metal thin film formed as a magnetic layer on a nonmagnetic support.
In the Raman spectrum of carbon, a peak derived from sp ₃ bond and a peak derived from sp ₂ bond are observed, but the diamond-like hard carbon film mentioned here is a mixture of sp ₃ bond and sp ₂ bond. This means that there is a broad peak derived from doing this.
[0013]
As a method for forming this diamond-like hard carbon film, for example, a sputtering method, a CVD method or the like can be used.
In the present invention, when the diamond-like hard carbon film is formed, a part of the reaction tube or the reaction chamber is partitioned into two or more chambers, and hydrocarbon gas and fluorocarbon gas are introduced into the partitioned chambers, respectively. To do. Here, as the hydrocarbon gas, methane, ethane, toluene, propane, acetylene, butane, or the like can be used. As the fluorocarbon gas, fluorinated ethylene, fluorinated ethane, octafluorocyclobutane, Freon 23, or the like. Can be used.
[0014]
As a result, a DLC film containing a large amount of hydrogen is formed on the ferromagnetic metal thin film side, and a DLC film containing a large amount of fluorine is formed near the surface. Thus, durability is improved by controlling the hydrogen and fluorine contents in the DLC film obtained by changing the composition of the introduced gas.
Here, it is preferable that the contents of hydrogen and fluorine change continuously in the thickness direction of the protective film. Thereby, the strength of the film itself is improved, and sufficient durability can be ensured even if the film thickness is thin.
[0015]
In forming this diamond-like hard carbon film, for example, an organic silicon compound (silicone) gas such as hexamethyldisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, or an organic silicon fluoride gas may be introduced. . Thereby, silicon is taken into the obtained diamond-like hard carbon film, and a more remarkable effect can be expected.
[0016]
The magnetic recording medium to which the present invention is applied includes a so-called metal magnetic thin film type magnetic recording medium in which a ferromagnetic metal thin film is formed as a magnetic layer on a nonmagnetic support by a vacuum thin film forming technique.
In the metal magnetic thin film type magnetic recording medium, any of the nonmagnetic supports and the metal magnetic materials constituting the ferromagnetic metal thin film conventionally used in this type of magnetic recording medium can be used. There is no particular limitation.
[0017]
Specifically, examples of the metal magnetic material include ferromagnetic metals such as Fe, Co, Ni, Fe—Co, Co—O, Fe—Co—Ni, Fe—Cu, Co—Cu, Co—Au, Ferromagnetic alloys such as Co-Pt, Mn-Bi, Mn-Al, Fe-Cr, Co-Cr, Ni-Cr, Fe-Co-Cr, Co-Ni-Cr, Fe-Co-Ni-Cr, etc. Can be mentioned.
[0018]
These single-layer films may be used, or multilayer films may be used.
In the case of the nonmagnetic support and the ferromagnetic metal thin film, or a multilayer film, an underlayer or an intermediate layer is provided to improve the adhesion between the layers and control the coercive force. Also good. Further, for example, the vicinity of the surface of the magnetic layer may be an oxide for improving the corrosion resistance.
[0019]
As a means for forming the ferromagnetic metal thin film, a vacuum vapor deposition method in which the above-described metal magnetic material is heated and evaporated under vacuum and deposited on the nonmagnetic support, or evaporation of the metal magnetic material is performed during discharge. Any of the so-called PVD techniques, such as an ion plating method, a sputtering method in which atoms on the target surface are knocked out with argon ions generated by glow discharge in an atmosphere containing argon as a main component, can be used.
[0020]
Of course, the configuration of the magnetic recording medium to which the present invention is applied is not limited to this, but can be changed without departing from the gist of the present invention, for example, if necessary, a backcoat layer is formed, It is possible to form an undercoat layer on the nonmagnetic support or to form various layers such as a lubricant layer. In this case, any conventionally known materials can be used as the nonmagnetic pigment, the resin binder, the material contained in the lubricant layer, and the like contained in the backcoat layer.
[0021]
[Action]
When forming a DLC film as a protective film on a magnetic layer made of a ferromagnetic metal thin film formed by a vacuum thin film forming technique on a nonmagnetic support, a part of the reaction tube or reaction chamber is partitioned into two or more chambers. Then, hydrocarbon gas and fluorocarbon gas are respectively introduced into the partitioned chambers. As a result, the protective film obtained has a structure containing a large amount of hydrogen on the magnetic layer side and a large amount of fluorine near the surface. As a result, the hydrogen-rich DLC film adheres firmly to the magnetic layer made of the ferromagnetic metal thin film, while excellent lubricity is obtained near the surface due to the effect of fluorine, and the friction coefficient is reduced. Therefore, sufficient durability can be obtained.
[0022]
【Example】
Hereinafter, the present invention will be described with reference to specific examples, but it goes without saying that the present invention is not limited to these examples.
First, the structure of the plasma CVD continuous film forming apparatus used in the protective film forming process when manufacturing the magnetic tape of this example will be described.
[0023]
As shown in FIG. 1, this plasma CVD continuous film forming apparatus uses a Co or Co—Ni film or the like in a vacuum chamber 11 whose interior is maintained at a predetermined degree of vacuum by an exhaust system 12 attached to the head. A tape-like non-magnetic support (object to be processed) 1 having a magnetic layer formed by vapor deposition or the like is fixed in a counterclockwise direction from a feed roll 4 that rotates at a constant speed in the counterclockwise direction in FIG. It is made to run sequentially toward the winding roll 5 that rotates at high speed.
[0024]
In the middle of the non-magnetic support 1 traveling from the feed roll 4 side to the take-up roll 5 side, the non-magnetic support 1 is provided so as to be drawn downward in FIG. , 5 is provided so as to rotate at a constant speed in the clockwise direction in FIG.
Further, guide rolls 2a and 2b are disposed between the feed roll 4 and the rotation support 3 and between the rotation support 3 and the take-up roll 5, respectively. The nonmagnetic support 1 traveling between the rotary support 3 and the take-up roll 5 is applied with an appropriate tension so that smooth travel is performed.
[0025]
The feed roll 4, the take-up roll 5, and the rotary support 3 have a cylindrical shape having a length substantially the same as the width of the nonmagnetic support 1.
Therefore, in this plasma CVD continuous film forming apparatus, the nonmagnetic support 1 is sequentially fed from the feed roll 4, passes along the outer peripheral surface of the rotary support 3, and further to the take-up roll 5. It is made to wind up.
[0026]
On the other hand, in the vacuum chamber 11, a reaction tube 6 is provided below the rotary support 3, and when passing between the rotary support 3 and the reaction tube 6, the non-tube having a magnetic layer on the surface is provided. A protective film is formed on the magnetic support 1.
As the reaction tube 6, for example, quartz tube Pyrex glass, plastic, or the like can be used.
[0027]
Inside the reaction tube 6, an acceleration electrode 10 for generating plasma is incorporated.
The accelerating electrode 10 is preferably made of a material that is easy to permeate gas and that can apply a uniform electric field and is rich in flexibility. For example, a metal mesh such as a wire mesh is suitable. As a constituent material of such an accelerating electrode 10, for example, copper is representative, but from the viewpoint of conductivity, for example, gold or the like can also be used.
[0028]
A DC power source 13 disposed outside the vacuum chamber 11 is connected to the acceleration electrode 10, and a voltage higher than the substrate potential is supplied from the DC power source 13. The voltage applied to the acceleration electrode 10 is preferably + 500V to 2000V.
Further, a partition plate 7 is disposed in the reaction tube 6, and the interior thereof is partitioned into two chambers 6 a and 6 b by the partition plate 7.
[0029]
A hydrocarbon gas inlet 8 and a fluorocarbon gas inlet 9 are respectively formed in the partitioned two chambers 6a and 6b. The hydrocarbon gas inlet 8 and the fluorocarbon gas inlet 9 are provided through the bottom of the vacuum tank 11, and the hydrocarbon gas inlet 8 and the fluorocarbon gas inlet 9 are interposed therebetween. A hydrocarbon gas and a fluorocarbon gas are respectively introduced into the partitioned two chambers 6a and 6b so as to be controlled to a predetermined atmosphere.
[0030]
Thereby, when performing a plasma CVD by applying a predetermined voltage to the accelerating electrode 10 to form a protective film, the accelerating electrode 10 is fed from the feed roll 4 and travels along the outer peripheral surface of the rotary support 3. When the nonmagnetic support 1 passes between the rotary support 3 and the partitioned chamber 6a, a DLC film containing a large amount of hydrogen is formed on the magnetic layer on the nonmagnetic support 1, and the rotary support 3 and the partitioned chamber 6b, a DLC film containing a large amount of fluorine is formed on the DLC film containing a large amount of hydrogen. As a result, the magnetic layer and the DLC film containing a large amount of hydrogen adhere firmly, while the DLC film containing a large amount of fluorine formed near the surface provides excellent lubricity and reduces the friction coefficient. Is planned. Therefore, good durability can be ensured.
[0031]
Therefore, using the plasma CVD continuous film forming apparatus having such a configuration, a magnetic tape was manufactured as follows.
First, after applying an undercoat layer by coating silica fine particles having a diameter of 120 angstroms on a nonmagnetic support made of polyethylene terephthalate having a thickness of 10 μm at a rate of 12 particles / μm ^2, Co is deposited on the undercoat layer by vacuum deposition. A magnetic metal layer made of a single-layer film was provided by forming a ferromagnetic metal thin film made of 1 to a thickness of 0.15 μm.
[0032]
Subsequently, the above-mentioned ferromagnetic metal thin film is formed by using the plasma CVD continuous film forming apparatus shown in FIG. 1 (the diameter of the rotating support is 60 cm and the reaction tube is a 20 × 10 cm rectangular parallelepiped). After mounting the nonmagnetic support on the feed roll, plasma CVD was performed under predetermined conditions to form a diamond-like carbon film having a thickness of 50 mm on the ferromagnetic metal thin film.
[0033]
When performing this plasma CVD, toluene was introduced from the above-mentioned hydrocarbon gas inlet and ethylene fluoride was introduced from the fluorocarbon gas inlet to a ratio of 4: 1. The reaction pressure was 0.1 Torr, a gold mesh was used as the acceleration electrode, and a DC voltage of 1.5 kV was applied to the acceleration electrode. Then, toluene and ethylene fluoride were decomposed by such glow discharge, and a DLC film containing fluorine was formed on the surface of the ferromagnetic metal thin film.
[0034]
Thereafter, fluorinated phosphazine (manufactured by Dow Chemical Co., Ltd.) was applied and formed on the DLC film as a lubricant layer so as to have a film thickness of 20 angstroms, and further cut into 8 mm width to obtain a sample tape.
Sample tape 1 produced as described above, and comparative tape 1 produced in the same manner as in the above example, except that toluene alone was introduced only from the hydrocarbon gas inlet in the plasma CVD apparatus described above as a comparative example, A mixed gas of toluene and ethylene fluoride (a ratio of 4: 1) was introduced only from the carbon hydrogen gas inlet, and the rest of the comparative tape 2 produced in the same manner as in the above example was a commercially available 8 mm video deck ( Recording was performed using a Sendust head having a track width of 20 μm so that the shortest recording wavelength was 0.5 μm.
[0035]
The sample tape 1 and the comparative tapes 1 and 2 were recorded 100 times in an environment of a temperature of 20 ° C. and a relative humidity of 60%, and then reproduced, and the amount of deterioration of the output value after 100 times with respect to the initial output value was determined. Examined.
As a result, in this example, the amount of deterioration after repeated recording stopped within 1 dB. On the other hand, the comparative tape 1 deteriorated by 4 to 5 dB, and the comparative tape 2 deteriorated by 2 to 3 dB.
[0036]
Further, when still reproduction was performed under the same environment, the time until the reproduction output decreased by 3 dB was stable for 2 hours or more at any 20 points in this example, whereas 5 for Comparative Tape 1 The variation was large with ~ 20 minutes, and the time was short. Moreover, with comparative tape 2, it was 30 to 60 minutes, and in any case did not reach this example.
[0037]
Further, when the friction coefficient of each tape was measured, it was 0.20 for sample tape 1, 0.30 for comparative tape 1, and 0.25 for comparative tape 2, and it was found that sample tape 1 was still superior. .
For this reason, the durability is insufficient only by forming the DLC film as a protective film, and sufficient runnability and durability cannot be ensured even with a DLC film containing only fluorine, but the magnetic layer side does not absorb hydrogen. It was found that good durability can be obtained even with a thin film thickness of about 5 nm by using a DLC film containing a large amount and a DLC film containing a large amount of fluorine only in the vicinity of the surface.
[0038]
Next, a sample tape 2 was prepared using hexamethyldisiloxane instead of fluorinated ethylene under the same conditions as in the previous sample tape 1.
The amount of deterioration of the sample tape 2 after repeated recording is within 1 dB, the time until the reproduction output decreases by 3 dB in still reproduction is 2 hours or more, and the friction coefficient is 0.18, which is a further improvement over the previous sample tape 1. Admitted.
[0040]
【The invention's effect】
As is clear from the above description, in the present invention, when a DLC film is formed as a protective film on a nonmagnetic support having a magnetic layer made of a ferromagnetic metal thin film, a part of the reaction tube or reaction chamber is formed. A partition is formed, and a hydrocarbon film and a fluorocarbon gas are respectively introduced into these partitioned chambers, and a protective film is formed on a nonmagnetic support having a traveling magnetic layer. The structure is hydrogen-rich on the magnetic layer side and fluorine-rich near the surface. For this reason, the protective film which is hard and excellent in self-lubricating property can be obtained, the adhesive force to the magnetic layer can be strengthened, and the durability can be improved.
[0041]
Therefore, according to the present invention, it is possible to provide a magnetic recording medium having good durability without impairing high-density recording characteristics.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a configuration of a plasma CVD apparatus used for forming a diamond-like carbon film when a magnetic tape is manufactured by applying the present invention.
[Explanation of symbols]
1 Nonmagnetic support (object to be treated)
3 Rotating Support 4 Feed Roll 5 Take-up Roll 6 Reaction Tube 7 Partition Plate 8 Hydrocarbon Gas Inlet 9 Fluorocarbon Gas Inlet 10 Accelerating Electrode 11 Vacuum Tank 12 Exhaust System

Claims (1)

A magnetic recording medium in which a magnetic layer made of a ferromagnetic thin film is formed on a nonmagnetic support by a vacuum thin film forming technique, and a diamond-like hard carbon film as a protective film is formed on the magnetic layer by a vacuum thin film forming technique . In the manufacturing method,
A part of the inside of the reaction tube or the reaction chamber is divided into two chambers by a partition plate, the hydrocarbon gas is introduced into one chamber, and the fluorocarbon gas is introduced into the other chamber. The diamond-like hard carbon film is formed on the magnetic layer by running a non-magnetic support on which the magnetic layer is formed toward the other chamber side,
A method for producing a magnetic recording medium, comprising: forming a diamond-like hard carbon film containing a large amount of hydrogen on the magnetic layer side; and forming a diamond-like hard carbon film containing a large amount of fluorine on the surface side. .

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