JPS60263332A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the durability of a protective film to be formed on the surface of a thin ferromagnetic metallic film by selecting the gaseous monomer of fluorocarbon having an unsatd. bond and carrier gas of oxygen at a specified volumetric ratio and executing plasma polymn. CONSTITUTION:A high-frequency coil 4 connected to a frequency oscillator 3 is wound around a reaction chamber 1 for plasma polymn. reaction. An introducing pipe 5 for introducing the gaseous monomer and carrier gas is connected to the chamber 1. A supply chamber 8 which lets off a non-magnetic base 6 on which the thin ferromagnetic metallic film 12 is deposited from a roll 7 and a take-up chamber 10 which takes up the base on a roll 9 are provided on both sides of the chamber 1. The residual air in the chamber 1 is removed and the inside thereof is evacuated; thereafter the fluorocarbon having the unsatd. bond as the gaseous monomer and the oxygen as the carrier gas are selected at 75:25-85:15 volumetric ratio and are introduced into the chamber then the plasma polymn. is executed to form the protective film 13. The protective film which is highly crosslinked and is highly durable is thus formed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] 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, and more specifically to a method for improving durability and runnability. The present invention relates to an improvement in a method for forming a protective film provided for the purpose of

[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, the coercive force H
There is a demand for magnetic recording media with large c and residual magnetic flux density Br.

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 vacuum evaporation or sputtering. 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 has a coercive force HC and a residual magnetic flux density B.
In addition to having a large r, the thickness of the magnetic layer can be made extremely thin, so the thickness loss during recording demagnetization and reproduction is extremely small. The packing density of ferromagnetic metal materials can be increased because there is no need to mix them, etc.
It has a number of advantages in terms of magnetic properties.

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 by coating the surface of the magnetic layer of the magnetic recording medium, that is, the ferromagnetic metal thin film, with a lubricant or the like to form a protective film. 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, the lubricant is gradually scraped off by the magnetic head, etc. There are many problems in terms of durability, uniformity, film thickness, etc., such as a sudden decrease in effectiveness.

On the other hand, attempts have been made to form the above-mentioned protective film by plasma polymerization. It has been reported that a thin polymer film can be obtained and is effective in improving the runnability of the above-mentioned magnetic recording media! I was warned.・Ru.

However, the polymerized film obtained by the plasma polymerization described above has a problem of insufficient durability due to insufficient crosslinking degree, and there is a need to further improve this durability in order to put it into practical use. ing.

[Purpose of the invention]

Therefore, the present invention was 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 3. 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 residue during plasma polymerization, the degree of crosslinking of the resulting polymer film can be increased and durability can be greatly improved, and this can be used as a protective film. This is intended to improve the durability and runnability of ferromagnetic metal thin film type 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, polyvinylitine chloride, etc. Examples include plastics such as vinyl resin, polycarbonate, polyimide, and polyamideimide. In addition, the form of the non-magnetic support 4- is a film, tape, sheet, disk, card,
Any drum or the like may be used.

As the above-mentioned ferromagnetic metal material, iron Fe1 Kobal 1-C
o, metal such as nickel N1 or Co-Ni alloy, F
e-Co alloy, Pe-Ni alloy, Co-N1-Fe-B
Examples include alloys such as alloys.

The means for depositing the ferromagnetic metal material include vacuum evaporation,
Examples include ion blating method and sputtering method.

In the vacuum evaporation method, the ferromagnetic metal material is evaporated by resistance heating, high frequency heating, electron beam heating, etc. under a vacuum of 10 to 1 O-8 Torr, and the evaporated metal (ferromagnetic metal material) is deposited on the nonmagnetic support. It is roughly divided into oblique evaporation method and vertical evaporation method. In the above-mentioned oblique deposition method, 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 vertical vapor deposition method, Bi, TA, and Sb are deposited on a nonmagnetic support in advance in order to improve vapor deposition efficiency and productivity and obtain high coercive force.

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 ion plate ink method is also a type of vacuum evaporation method, in which DC claw discharge, R, F glow discharge is generated in an inert gas atmosphere of 10-4 to IQ-'' Torr, and the above ferromagnetic material is generated during the discharge. The above sputtering method evaporates the metal.
In this method, a claw discharge is caused in an atmosphere mainly composed of argon gas, and the generated atom is used to knock out atoms on the surface of the argon gas. There is a sputtering method, a magnetron sputtering method using macnetron discharge, etc.

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.

In the above plasma polymerization, glow discharge is usually performed in an organic monomer gas alone or in a mixture of the monomer gas and another gas (carrier gas), and a polymer film derived from the excited monomer is placed on a substrate in contact with the discharge area. 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, and 4) it must be uniform. A polymeric film having various properties such as being produced as a protective film 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.
Here, the type and mixing ratio of the monomer gas and carrier gas used are important.

First, as the monomer gas, fluorocarbon (
Carbon fluoride) is used, especially CnF”2n (
A fluorocarbon having an unsaturated bond represented by the general formula (2≦n≦4) is used. 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. be. 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 preferable hexamer gas is tetrafluoroethylene (C
F"2 = CF'2) or hexafluoropyrene (CF2 = CF-CFa).

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 above-mentioned monomer gas and carrier gas must be mixed at a predetermined ratio before use, and according to the inventor's experiments, the volume ratio of monomer gas to carrier gas is 7.
By setting within the range of 5:25 to 85:15,
It was found that a polymer film with extremely high durability was produced. That is, when the proportion of the carrier residue is less than 15 volume parts or exceeds 25 volume parts,
A polymeric film having sufficient durability cannot be obtained, and therefore it is difficult to raise the durability of a ferromagnetic metal thin film type magnetic recording medium 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 it is an inductively coupled system, and the plasma oscillation frequency is 13.56.
It is MHz. The reaction apparatus is equipped with a reaction chamber 1 for plasma polymerization reaction, and a high-frequency coil 4 connected to a frequency oscillator 3 via a matching network 2 is wound around the reaction chamber 1. has been done. Further, an introduction pipe 5 for introducing a monomer gas and a carrier gas is connected to the reaction chamber 1, and the monomer gas and the carrier gas, whose flow rates have been adjusted in advance by, for example, a mass flow controller, are mixed at the above-mentioned mixing ratio. The components are mixed together and 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. It is configured to attach a polymer film formed by a polymerization reaction. 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 reaction apparatus configured as described above, first, the residual air in the reaction chamber 1 is sufficiently removed to reduce the pressure to about 1Q-2 Torr, and then monomer gas and carrier gas are mixed at a predetermined mixing ratio. The oscillator 3 is operated while gas is introduced into the reaction chamber 1 at a predetermined flow rate, and RF' power is applied to the coil 4 to release it. In addition, in the above plasma polymerization reaction, in order to cause a good discharge, lθ is generally
It is desirable to carry out the process in a vacuum state of ~3 Torr, and usually about 10-2 Torr is employed.

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, the obtained magnetic recording medium is
As shown in the figure, a ferromagnetic metal thin film 1 is placed on a non-magnetic support 6.
2 are laminated, and a polymeric film obtained by the plasma polymerization described above is further laminated as a protective film 13 on the surface of this ferromagnetic metal thin film 12.

The thickness of the protective film 13 obtained by the plasma polymerization reaction is preferably in the range of 50 to 500 Å, more preferably in the range of 50 to 150 Å. If the film thickness is less than 50A, the lubricating effect and durability will be insufficient, and if it exceeds 500λ, the spacing loss (thickness loss) will increase when the tape is made to slide on the surface of a magnetic head, for example. .

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

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 =12- A Co--Ni alloy film (Co content: 8 µm) having a thickness of 1000 Å was deposited on an ethylene terephthalate film using an oblique evaporation method.

Next, tetrafluoroethylene (
C2F4) and oxygen (0
2), the ratio C2F4:02 of these monomer gas and carrier gas was set to be 75:25 by volume, and the total flow rate IQQm//mi, pressure (i.Q
I Q-” Torr, high frequency output (frequency 13.5
A plasma polymerization reaction was carried out under the conditions of 6MH2) 400 W to form a plasma polymerized film with a thickness of 280A on the Co-Ni alloy film to prepare a sample tape.

When the still characteristics of the obtained sample tape were measured, the still time was 90 minutes, and it was found that the durability was significantly improved compared to that without the plasma polymerized film (Comparative Example 1) described below. Note that the above still characteristics are based on 4. It shows the still time until the playback output attenuates to 50% after recording a 2 MHz video signal, and serves as a measure of the durability of the magnetic tape.

Comparative Example 1 A Co-Ni alloy film (with a CO content of 8 mm) having a film thickness of 1000 A was formed by vapor deposition on a polyethylene terephthalate film by oblique vapor deposition, and the still characteristics were measured as a raw sample tape. Methyl time was 30 minutes.

Example 2 A Co--Ni alloy film (cobalt content: 8 mm) was deposited on a polyethylene terephthalate film to a thickness of 1000 Å by oblique deposition.

Next, hexafluoropropylene (CaFa) was used as the monomer gas, and oxygen (02
), the ratio of these monomer gas and carrier gas CaFe:02 was set to be 80:20f by volume, the total flow rate was 100 ml/min, the pressure was 5,
(l X I Q-2 Torr, high frequency output (frequency 1
3.5 A plasma polymerization reaction was performed under the conditions of 6 MI (Z) 500 W, and a film thickness of 300 A was formed on the above Co-Ni alloy film.
A sample tape was prepared by forming a plasma polymerized film.

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

Comparative Example 2 In Example 1 above, CgFe:02 had a volume ratio of 9
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 5:5.

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

Comparative Example 3 In Example 1 above, C3P6:02 had a volume ratio of 9
A sample tape was prepared by forming a plasma polymerized film with a thickness of 300 A on a Co-Ni alloy film in the same manner as in Example 1, except that the ratio was set to 0:10.

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

Comparative Example 4 In Example 1 above, C3F6:02 had a volume ratio of 7
A sample tape was prepared by forming a plasma polymerized film with a film thickness of 25ON on a Co-Ni alloy film in the same manner as in Example 1 except that the ratio was set to 0:30.

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

Comparative Example 5 In Example 1 above, C3F6:02 was 60 in volume ratio.
:40, and a sample tape was prepared by forming a plasma polymerized film with a thickness of 200A on a Co-Ni alloy film in the same manner as in Example 1 except for the following.

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

Comparative Example 6 In Example 1 above, C3F6:02 had a volume ratio of 1
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 that the ratio was set to 6-50:50.

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 that is excellent in durability.

[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] In 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 nonmagnetic support, a fluorocarbon having an unsaturated bond is used as a monomer gas and as a carrier gas. 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 volume ratio of 75:25 to 85:15.