JPH0458653B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a ferromagnetic metal thin film type magnetic recording medium such as a so-called vapor-deposited tape.
More specifically, the present invention relates to an improvement in the method of forming a protective film provided to improve durability and runnability.

[Background technology and its problems]

In the field of magnetic recording, higher recording density and shorter wavelength recording signals are being recorded, and in response to this trend, magnetic recording media with large coercive force Hc and large residual magnetic flux density Br are required.

Conventionally, a thin film of ferromagnetic metal such as a Co-Ni alloy is deposited directly onto a non-magnetic support such as a polyester film using a method such as a vacuum deposition method or a sputtering method. A ferromagnetic metal thin film type magnetic recording medium has been proposed and is attracting attention. This ferromagnetic metal thin film type magnetic recording medium not only has high coercive force Hc and residual magnetic flux density Br, but also has extremely low thickness loss during recording demagnetization and reproduction because the thickness of the magnetic layer can be made extremely thin. It has many advantages in terms of magnetic properties, such as the ability to increase the packing density of ferromagnetic metal materials because there is no need to mix resin binders such as vinyl chloride-vinyl acetate copolymer or polyurethane resin into the layer. ing.

However, the above-mentioned ferromagnetic metal thin film type magnetic recording medium has many drawbacks in terms of durability, runnability, etc., and improvement thereof has become a major issue.

For example, attempts have been made to improve the durability and runnability of the magnetic recording medium by coating the surface of the magnetic layer, that is, the ferromagnetic metal thin film, with a lubricant or the like to form a protective film. However, in this case, the coefficient of friction is initially reduced and running properties are improved, but since the adhesion of the lubricant to the ferromagnetic metal thin film is weak, this lubricant is gradually scraped away by a magnetic head, etc. There are many problems in terms of durability, uniformity, film thickness, etc., such that the effectiveness decreases rapidly due to overheating.

One method has been attempted to form the above-mentioned protective film by plasma polymerization.
As described in No. 88828, it has been reported that an extremely thin polymer film can be obtained by plasma polymerizing carbon fluoride monomer vapor, which is effective in improving the runnability of the above-mentioned magnetic recording medium. has been done.

However, the polymer film obtained by the above plasma polymerization has a problem of insufficient durability due to insufficient crosslinking degree, and it is necessary to further improve this durability in order to put it into practical use. It is requested.

[Purpose of the invention]

Therefore, the present invention has been proposed in response to the above-mentioned needs in the technical field, and provides a plasma polymerization method capable of producing a polymer film with excellent durability, thereby achieving a practical level. It is an object of the present invention to provide a method for manufacturing a magnetic recording medium that can manufacture a ferromagnetic metal thin film type magnetic recording medium having durability of .

[Means for solving problems]

That is, in the method for manufacturing a magnetic recording medium according to the present invention, in forming a protective film by plasma polymerization on the surface of a ferromagnetic metal thin film of a magnetic recording medium in which a ferromagnetic metal thin film is provided on a nonmagnetic support, a monomer gas is The method is characterized in that plasma polymerization is carried out by using fluorocarbon having an unsaturated bond as a carrier gas, using oxygen as a carrier gas, and selecting a monomer gas:carrier gas volume ratio of 75:25 to 85:15. By selecting the type and mixing ratio of monomer gas and carrier gas during polymerization, we can increase the degree of crosslinking of the resulting polymer film and greatly improve its durability. By using this as a protective film, we can create a ferromagnetic metal thin film type. The objective is to improve the durability and running performance of magnetic recording media.

The magnetic recording medium to which the present invention is applied is a so-called ferromagnetic metal thin film type magnetic recording medium in which a ferromagnetic metal material is directly deposited on a nonmagnetic support and a ferromagnetic metal thin film is formed as a magnetic layer. .

Materials for the non-magnetic support include polyesters such as polyethylene terephthalate, polyolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose triacetate, cellulose diacetate, and cellulose acetate butyrate, polyvinyl chloride, polyvinylidene chloride, etc. Examples include plastics such as vinyl resin, polycarbonate, polyimide, and polyamideimide. The nonmagnetic support may be in any form such as a film, tape, sheet, disk, card, or drum.

The above-mentioned ferromagnetic metal materials include metals such as iron Fe, cobalt Co, and nickel Ni, Co-Ni alloy, Fe-Co alloy, Fe-Ni alloy, Co-Ni-Fe-
Examples include alloys such as B alloy.

Examples of the means for depositing the ferromagnetic metal material include a vacuum deposition method, an ion plating method, and a sputtering method. The above vacuum evaporation method is 10 ^-4 to 10 ^-8
Resistance heating of the above ferromagnetic metal material under Torr vacuum,
Evaporate metal (ferromagnetic metal material) onto the above non-magnetic support by evaporating it by high frequency heating, electron beam heating, etc.
It is roughly divided into oblique evaporation method and vertical evaporation method. The above-mentioned oblique deposition method is a method in which the ferromagnetic metal material is obliquely deposited on a non-magnetic support in order to obtain a high coercive force. It also includes things that are done. In the above-mentioned vertical deposition method, Bi, Tl, Sb,
A base metal layer such as Ga or Ge is formed in advance, and the ferromagnetic metal material is vertically deposited on the base metal layer. The above-mentioned ion plating method is also a type ^of vacuum evaporation method, and ^the
DC glow discharge and RF glow discharge are caused in an inert gas atmosphere, and the ferromagnetic metal is evaporated during the discharge. The above spatuta method is
A glow discharge is caused in an atmosphere mainly composed of argon gas at 10 ^-3 to ^{10 -1} Torr, and the generated argon ions are used to knock out atoms on the target surface.
There are the polar sputter method, the high frequency sputter method, and the magnetron sputter method using magnetron discharge.

In the present invention, a protective film is formed on the surface of the ferromagnetic metal thin film of the above-mentioned magnetic recording medium by plasma polymerization.

The above plasma polymerization usually involves performing glow discharge in an organic monomer gas alone or in a mixture of the monomer gas and another gas (carrier gas), and depositing a polymer film derived from the excited monomer on a substrate in contact with the discharge region. For example, 1. It must have high adhesion to the ferromagnetic metal thin film that is the substrate. 2. It must have high density. 3. It must be heat resistant. 4. It must be produced as a uniform film. A polymeric film having various properties such as these is formed as a protective film.

In the present invention, a polymer film is formed by glow discharge in a mixed gas of monomer gas and carrier gas, and the type and mixing ratio of the monomer gas and carrier gas used are important here.

First, as the monomer gas, a fluorocarbon (carbon fluoride) is used, especially a fluorocarbon having an unsaturated bond represented by the general formula CnF _2o (2≦n≦4). The number of carbon atoms in the fluorocarbon having unsaturated bonds is preferably 4 or less; if the number of carbon atoms exceeds 4, the degree of crosslinking may be insufficient and a polymer film with sufficient durability may not be obtained. Similarly, the above-mentioned fluorocarbon must have an unsaturated bond, and if it does not have this unsaturated bond, not only will the degree of crosslinking of the resulting polymer film be insufficient, but the formation of the film will be extremely slow. In some cases, there is a possibility that a polymer film may not be obtained. Particularly preferred monomer gases include tetrafluoroethylene ( _CF2 = _CF2 ) and hexafluoropyrene ( _CF2 =CF- _CF3 ).

On the other hand, oxygen is used as the carrier gas. This oxygen is presumed to have the effect of promoting the cleavage of unsaturated bonds in monomers and transfer to radicals during plasma polymerization, and also has the effect of eliminating unnecessary radicals, resulting in the quality of the resulting polymer film. It is useful for improving the

The monomer gas and carrier gas must be mixed at a predetermined ratio before use.
According to experiments conducted by the present inventors, it has been found that by setting the monomer gas:carrier gas volume ratio within the range of 75:25 to 85:15, a polymer film with extremely excellent durability can be produced. That is, if the proportion of the carrier gas is less than 15% by volume or exceeds 25% by volume, a polymeric film with sufficient durability cannot be obtained, and therefore a ferromagnetic metal thin film type magnetic recording medium cannot be obtained. It is difficult to raise the durability of to a practical level.

Plasma polymerization is carried out using the above-mentioned monomer gas and carrier gas. Next, an example of a reaction apparatus used for carrying out plasma polymerization in the present invention will be described.

FIG. 1 is a schematic diagram showing the configuration of a reaction apparatus actually used in the present invention.

This reactor uses an electrodeless system because there is no contamination of the electrodes and good discharge stability, and an inductively coupled system, and the plasma oscillation frequency is 13.56MHz. The reaction apparatus is equipped with a reaction chamber 1 for plasma polymerization reaction, and a matching circuit network 2 is provided around the reaction chamber 1.
A high frequency coil 4 connected to a frequency oscillator 3 via a high frequency coil 4 is wound thereon. In addition, an introduction pipe 5 for introducing monomer gas and carrier gas is connected to the reaction chamber 1, and the monomer gas and carrier gas, whose flow rates have been adjusted in advance by, for example, a mass flow controller, are mixed so as to have the above-mentioned mixing ratio. and then introduced into the reaction chamber 1. Further, on both sides of the reaction chamber 1, there are supply chambers 8 for feeding out from a roll 7 a non-magnetic support 6 on which a non-magnetic metal thin film is deposited and a ferromagnetic metal thin film is deposited on the surface; After passing the magnetic support 6 into the reaction chamber 1, the winding chamber 10 is connected to a winding chamber 10 for winding the magnetic support 6 onto a roll 9. Plasma polymerization is carried out while the non-magnetic support 6 is continuously driven via a guide roller 11. Configured to deposit a reactive polymeric film. The supply chamber 8 and the winding chamber 10 are each connected to a vacuum pump, so that the entire chamber including the reaction chamber 1 is maintained at a high vacuum.

Using the reactor configured as described above, first remove the residual air in the reaction chamber 1 to a temperature of 10 ^-2 Torr.
After that, while introducing a mixed gas of monomer gas and carrier gas having a predetermined mixing ratio into the reaction chamber 1 at a predetermined flow rate, the oscillator 3
, and apply RF power to the coil 4 to discharge it. The above plasma polymerization reaction is generally desirably carried out in a vacuum state ^of 10 ^-3 to 3 Torr in order to cause good discharge;
Torr level is adopted.

As a result, a plasma polymerized film is grown on the surface of the ferromagnetic metal thin film deposited on the non-magnetic support 6 as a protective film. That is, as shown in FIG. 2, the obtained magnetic recording medium has a ferromagnetic metal thin film 12 laminated on a non-magnetic support 6, and a polymerized metal film obtained by the above plasma polymerization on the surface of this ferromagnetic metal thin film 12. The protective film 13 is formed by stacking the films as a protective film 13.

Protective film 1 obtained by the above plasma polymerization reaction
The film thickness of No. 3 is preferably in the range of 50 to 500 Å, and more preferably in the range of 50 to 150 Å. If the film thickness is less than 50 Å, the lubricity imparting effect and durability will be insufficient, and if it exceeds 500 Å, for example, spacing loss (thickness loss) will increase when the tape is made to slide on the surface of a magnetic head. .

As mentioned above, in the present invention, a fluorocarbon having an unsaturated bond is used as a monomer gas, oxygen is used as a carrier gas, and the ratio of the monomer gas to the carrier gas is set at a predetermined ratio, so that a high degree of crosslinking is achieved. A highly durable polymeric film can be formed by plasma polymerization reaction, and a magnetic recording medium with excellent durability can be manufactured by depositing this polymeric film as a protective film 13 on a ferromagnetic metal thin film 12. becomes possible.

Next, specific examples of the present invention will be described, but it goes without saying that the present invention is not limited to these examples.

〔Example〕

Example 1 A Co-Ni alloy film (Co content: 80% by weight, Ni content: 20% by weight) having a thickness of 1000 Å was formed by vapor deposition on a polyethylene terephthalate film by oblique vapor deposition.

Next, tetrafluoroethylene (C ₂ F ₄ ) is used as a monomer gas and oxygen (O ₂ ) is used as a carrier gas, and the ratio of these monomer gases to the carrier gas is C ₂ F ₄ :O ₂ of 75:25 by volume. Set as follows, total flow rate 100ml/min, pressure 6.0
×10 ^-2 Torr, high frequency output (frequency 13.56MHz)
The plasma polymerization reaction was carried out under the conditions of 400W, and the above
A sample tape was prepared by forming a plasma polymerized film with a thickness of 280 Å on a Co-Ni alloy film.

When the still characteristics of the obtained sample tape were measured, it was found that the still time was 90 minutes and the durability was significantly improved compared to that without the plasma polymerized film (Comparative Example 1) described below. In addition,
The above still characteristics indicate the still time until the playback output attenuates to 50% after recording a 4.2MHz video signal on a sample tape, and serves as an indicator of the durability of the magnetic tape. .

Comparative Example 1 A Co-Ni alloy film (Co content: 80% by weight, Ni content: 20% by weight) with a film thickness of 1000 Å was deposited on a polyethylene terephthalate film by oblique evaporation, and the still characteristics were measured as a sample tape. As a result, the still time was 30 minutes.

Example 2 A Co-Ni alloy film (Co content: 80% by weight, Ni content: 20% by weight) having a thickness of 1000 Å was formed by vapor deposition on a polyethylene terephthalate film by oblique vapor deposition.

Next, hexafluoropropylene (C ₃ F ₆ ) was used as the monomer gas, oxygen (O ₂ ) was used as the carrier gas, and the ratio of these monomer gases to the carrier gas, C ₃ F ₆ :O ₂ , was 80:20 by volume.
Set the total flow rate to 100ml/min, pressure
5.0×10 ^-2 Torr, high frequency output (frequency 13.56MHz)
The plasma polymerization reaction was performed under the conditions of 500W, and the above
A sample tape was prepared by forming a plasma polymerized film with a thickness of 300 Å on a Co-Ni alloy film.

When the still characteristics of the sample tape obtained were measured, it was found that the still time was 100 minutes, and the durability was significantly improved compared to each comparative example.

Comparative Example 2 In the previous Example 1, the volume ratio of C ₃ F ₆ :O ₂ was
A sample tape was prepared by forming a plasma polymerized film with a thickness of 280 Å on a Co-Ni alloy film in the same manner as in Example 1 except that the ratio was set to 95:5.

When the still characteristics of the obtained sample tape were measured, the still time was 5 minutes.

Comparative Example 3 In the previous Example 1, the volume ratio of C ₃ F ₆ :O ₂ was
A sample tape was prepared by forming a plasma polymerized film with a thickness of 300 Å on a Co-Ni alloy film in the same manner as in Example 1 except that the ratio was set to 90:10.

When the still characteristics of the obtained sample tape were measured, the still time was 5 minutes.

Comparative Example 4 In Example 1 above, the volume ratio of C ₃ F ₆ :O ₂ was
A sample tape was prepared by forming a plasma polymerized film with a thickness of 250 Å on a Co-Ni alloy film in the same manner as in Example 1 except for setting the ratio to be 70:30.

When the still characteristics of the obtained sample tape were measured, the still time was 25 minutes.

Comparative Example 5 In the previous Example 1, the volume ratio of C ₃ F ₆ :O ₂ was
A sample tape was prepared by forming a plasma polymerized film with a thickness of 200 Å on a Co-Ni alloy film in the same manner as in Example 1 except for setting the ratio to be 60:40.

When the still characteristics of the obtained sample tape were measured, the still time was 30 minutes.

Comparative Example 6 In Example 1 above, the volume ratio of C ₃ F ₆ :O ₂ was
A sample tape was prepared by forming a plasma polymerized film with a thickness of 220 Å on a Co-Ni alloy film in the same manner as in Example 1 except for setting the ratio to be 50:50.

When the still characteristics of the obtained sample tape were measured, the still time was 25 minutes.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to produce a plasma polymerized film that is highly crosslinked and has excellent durability, and therefore it is possible to produce a magnetic recording medium with excellent durability. be.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a plasma reaction apparatus used in the present invention, and FIG. 2 is an enlarged sectional view of a main part showing the structure of a magnetic recording medium obtained by the present invention. 6...Nonmagnetic support, 12...Ferromagnetic metal thin film, 13...Protective film.

Claims (1)

[Claims] 1. When forming a protective film by plasma polymerization on the surface of the ferromagnetic metal thin film of a magnetic recording medium comprising a ferromagnetic metal thin film provided on a non-magnetic support, a fluorocarbon having an unsaturated bond is used as a monomer gas, and a carrier gas is used. A method for producing a magnetic recording medium, characterized in that plasma polymerization is carried out using oxygen and selecting a monomer gas:carrier gas at a volume ratio of 75:25 to 85:15.