JPH02192011A - Magnetic recording medium and production thereof - Google Patents

Abstract

PURPOSE:To improve durability and lubricity even in the case of using a nonmagnetic substrate consisting of a high-polymer film by forming an amorphous carbon film having the specific resistance of a specific value or below on a thin ferromagnetic film. CONSTITUTION:The thin ferromagnetic metallic film 2 consisting of a Co-Ni alloy, etc., is formed on the nonmagnetic substrate 1 consisting of the high- polymer film such as polyethylene terephthalate, polyester, polyimide, polyamide, etc., without contg. fillers and the amorphous carbon film 3 is formed on the thin ferromagnetic metallic film 2. The amorphous carbon film 3 is formed by a vacuum vapor deposition method, etc., which heats and evaporates a carbon source by an electron beam, etc., in a high vacuum. The film quality thereof is essentially the covalent bond in the SP<2> hybride orbit like graphite and the specific resistance thereof is <=0.1OMEGA-cm. The medium protective film having excellent surface lubricity and durability is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a magnetic recording medium having a magnetic layer made of a ferromagnetic metal thin film and a method for manufacturing the same.

(b) Conventional technology In response to the increasing demand for high-density magnetic recording in recent years, metal thin film type magnetism is created by forming a thin film of ferromagnetic metal on a non-magnetic substrate using methods such as vacuum evaporation, ion blating, and sputtering. Development of recording media is underway. Among these metal thin film type media, the one closest to practical use is a Co--Ni based magnetic recording medium formed by vacuum-depositing a Co--Ni based metal on a non-magnetic substrate. In this Co--Ni magnetic recording medium, by introducing oxygen when forming the magnetic layer by vacuum deposition, the magnetic properties are improved and at the same time the film hardness is also improved.

However, as mentioned above, C formed by introducing oxygen
O-Ni magnetic recording media lack lubricity, making stable tape running difficult. Therefore, many magnetic recording media have been proposed in which the above-mentioned drawbacks are solved by applying a liquid lubricant to the surface of the magnetic layer.

Furthermore, recently it has been proposed to take advantage of the lubricating properties of carbon and form an amorphous carbon (α-C) film on the surface of a metal thin film type magnetic recording medium to provide a lubricating effect. The main methods for forming this amorphous carbon film are sputtering and CVD, and the film properties (hardness, lubricity, transparency, specific resistance, etc.) of the amorphous carbon film vary greatly depending on the manufacturing method and thin film formation conditions. Accordingly, the performance as a lubricating protective film for magnetic recording media also differs greatly. For example, when forming an amorphous carbon film by sputtering, using graphite as a target and introducing Ar gas provides excellent lubricity, but the film has low hardness, causing wear on the medium due to friction with the head. Similarly, using a graphite target, A r +H
When sputtering is performed by introducing a mixed gas, a film with high film hardness but low lubricity is formed, and the frictional force increases, so that the medium is likely to be scratched by friction with the head.

For example, Japanese Patent Application Laid-Open No. 62-1.092 eliminates the disadvantages of hard carbon and lubricating carbon as described above.
As shown in Publication No. 20 (G11B5/66), a magnetic recording medium in which lubricating carbon is formed on hard carbon has been proposed. However, in the magnetic recording medium with the above structure, since the amorphous carbon film has a multilayer structure, it is not suitable for mass production.Also, Ar atoms etc. enter the amorphous carbon film, which causes structural defects and reduces durability. decreases.

On the other hand, in the formation of an amorphous carbon film by the CVD method, diamond-like carbon (D L
C') The hardness of the protective film is so high that it is called amorphous diamond, and therefore it is known to have very high durability in scratch tests, etc. However, because the hardness is too high, when applied to flexible media such as vapor-deposited tape Cracks etc. are likely to occur on the surface, and film peeling is likely to occur during tape running. Furthermore, it is difficult to obtain a lubricating amorphous carbon film using the CVD method, and at present it is an amorphous polymer hydrocarbon film (α-C-H polymer film), and although this film has some lubricity, it is inferior in durability. Therefore, like the sputtering method, a two-layer structure combined with hard carbon is used, which poses a problem in mass production.

Also, Japanese Patent Application Laid-Open No. 61-233412 (GlI B
5/66), the specific resistance on the magnetic layer is 102~
A magnetic recording medium is disclosed in which a protective layer made of amorphous carbon of 10' Ω·cm is deposited by sputtering to improve lubricity and wear resistance.

However, even in this magnetic recording medium, the protective layer contains impurity gas such as Ar gas during the sputtering process, so the resistivity of the protective layer is reduced to 1O-2 to 10.
It is very difficult to reduce the resistance to 2Ω·Cm, and manufacturing is difficult. Furthermore, the magnetic recording medium disclosed in the above publication is a hard disk using a nonmagnetic substrate made of an aluminum alloy, and the protective layer made of the above-mentioned amorphous carbon is covered with a polymer film made of polyethylene terephthalate, polyimide, etc. When used in a magnetic tape having a non-magnetic substrate, the effects shown in the above publication were not necessarily obtained.

(c) Problems to be Solved by the Invention The present invention has been made in view of the drawbacks of the above-mentioned conventional examples.
The object of the present invention is to provide a ferromagnetic metal thin film type magnetic recording medium that has excellent durability and lubricity even when a nonmagnetic substrate made of a polymer film is used, and a method for manufacturing the same.

(d) Means for Solving the Problems The magnetic recording medium of the present invention has a ferromagnetic metal thin film formed on a nonmagnetic substrate made of a polymer film containing no filler, and a specific resistance on the ferromagnetic metal thin film. It is characterized by forming an amorphous carbon film of 0.1 Ω-cm or less.

Furthermore, the magnetic recording medium of the present invention is characterized in that the bonding state between carbon atoms of the amorphous carbon film is mainly a covalent bond of an SP2 hybrid orbital.

Furthermore, the magnetic recording medium of the present invention is characterized in that the amorphous carbon film does not contain impurity gas.

Furthermore, the magnetic recording medium of the present invention is characterized in that a protective layer made of a fluorine-based liquid lubricant is coated on the amorphous carbon film.

Further, the method for producing a magnetic recording medium of the present invention includes forming a ferromagnetic metal thin film on a nonmagnetic substrate made of a polymer film containing no filler, and coating carbon atoms on the ferromagnetic metal thin film by vacuum evaporation. It is characterized in that it is deposited to form an amorphous carbon film.

(e) A magnetic recording medium in which an amorphous carbon film is formed on a nonmagnetic substrate that does not contain a functional filler via a ferromagnetic metal thin film has significantly improved durability.

Furthermore, when the amorphous carbon film does not contain an impurity gas, the amorphous carbon film has a small resistivity and improved lubricity.

Furthermore, when a protective layer made of a fluorine-based liquid lubricant is applied and formed on an amorphous carbon film, the liquid lubricant having a polar group enters into the large number of pores existing on the surface of the amorphous carbon film. This prevents oxygen, moisture, etc. from entering the magnetic recording medium, and improves corrosion resistance.

Further, according to the above manufacturing method, an amorphous carbon film containing no impurity gas and mainly composed of covalent bonds of SP' hybrid orbitals is formed.

(-.) Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view of a main part showing the structure of the magnetic tape of this embodiment.

The magnetic tape of this example is made of a Co-Ni alloy (Co
A ferromagnetic metal thin film (2) such as -Cr alloy, FeN) is formed, and an amorphous carbon film (3) is formed on the ferromagnetic metal thin film (2). The amorphous carbon film (3) is formed by a vacuum evaporation method in which a carbon source is heated and evaporated with a main beam in a high vacuum, and its film quality is similar to graphite, with covalent bonds mainly in the SP2 hybrid orbital, and it has a comparatively The resistance is 0.1 Ω-cm or less.

In this example, PET (I) containing no filler was used.
Co-Ni composite (Co-80 wt%, Ni:2
The ferromagnetic metal thin film is formed by forming a ferromagnetic metal thin film with a thickness of 2,000 Ωwt%) and performing electron beam evaporation using a graphite source in a high vacuum of @l×10-' Torr or less, A magnetic tape of Sample 1 was formed by forming an amorphous carbon film with a thickness of 100 mm. The amorphous carbon film is formed at a substrate temperature of 100° C. or less and an electron gun output of 4 KW or more. still,
If the output of the electron gun is less than 4KW, the adhesion force of the amorphous carbon is insufficient.

In addition, as comparative examples, Samples 2 to 5 shown below were created.

Sample 2 A magnetic tape was prepared in the same manner as Sample 1 except that a diamond-like carbon film with a thickness of 100 mm was formed instead of the amorphous carbon film. The diamond carbon film is formed using an RF sputtering device using A r+Ht (
1: 1) Gas at 5mT.

rr was introduced and a graphite carbon target was used.

Sample 2 A magnetic tape was prepared in the same manner as Sample 1, except that a 100-layer thick wettable carbon film was formed instead of the amorphous carbon film. The lubricating carbon film was formed by introducing Ar gas at 5 mTorr using an RF sputtering device.
This was done using a graphite carbon target.

Sample 4 A magnetic tape was prepared in the same manner as Sample 1, except that a diamond-like carbon film with a thickness of 50 μm was formed instead of the amorphous carbon film, and a lubricating carbon film with a thickness of 50 μm was formed on the diamond-like carbon film. It was created. The formation of the diamond-like carbon film and the lubricating carbon film was the same as in Sample 2 and Sample 3, respectively.

Sample 5 Ferromagnetic metal thin film instead of amorphous carbon film
Sample 1 except that liquid lubricant was applied to a thickness of about 100 mm.
A magnetic tape was made in the same way.

Next, the friction coefficient, specific resistance, still durability, output fluctuation, and head clogging of the magnetic tapes of Samples 1 to 5 described above were measured, and the results are shown in Table 1 below. In addition, still durability indicates the time until the output suddenly decreases and scratches appear on the medium, and output fluctuation is the maximum and minimum value of the playback output of 7 MH2 when repeated playback is performed 100 times. The value obtained from the difference is shown, and head clogging indicates the number of times the 7 MHz playback output has decreased by 6 dB or more during 100 repeated playbacks.

Table 1 As can be seen from Table 1 above, Sample 2, which had a diamond-like carbon film, had a large friction coefficient, resulting in large output fluctuations, poor output stability, and poor still durability.
In addition, sample 4, which was provided with a diamond-like carbon film and a lubricating carbon film, had a still durability of 180 m1n or more.
It's good, but the output fluctuation is a little bad. In addition, while head clogging occurred in all samples 2 to 5 of the comparative example, it did not occur at all in sample 1 of the example. As described above, the amorphous carbon film of the magnetic tape of this example has excellent surface lubricity and durability, and is very suitable as a medium protective film.

Incidentally, as a result of performing X-ray diffraction on the carbon films of the magnetic tapes of Samples 1 to 3, it was confirmed that all of the carbon films of Samples 1 to 3 had an amorphous structure, with no diffraction peaks observed.

Next, in the same manner as Sample 1, Co was placed on the nonmagnetic film substrate.
After forming a ferromagnetic metal thin film of -Ni alloy, an amorphous carbon film was formed on the ferromagnetic metal thin film using the apparatus shown in FIG.

In Figure 2, (4) is internally 1×10-
``A vacuum chamber maintained at a high vacuum of Torr or less. A type ion source (10) is disposed in the crucible (6).
) contains a graphite source (11) with a purity of 99.9%, which is an evaporation source. (12) is the opening (1
3) and defines the evaporation angle θ1. (14) is coated with Co on a non-magnetic film substrate in the above process.
- A magnetic film on which a ferromagnetic metal thin film of Ni alloy is formed, and the magnetic film (14) is attached to the feed roller (8).
It is sent out from the winding roller (
9). The ion source (10) ionizes Ar gas with a purity of 99.999% from the gas introduction tube (15), and sends Ar ions (16) through the opening (13) of the shielding plate (12) to the magnetic film (14). ). The degree of vacuum in the vacuum chamber (4) during Ar ion irradiation is 8.
X10-'T.

It is rr.

To form an amorphous carbon film using this vacuum evaporation apparatus, first, Ar ions are extracted from the ion source (10) and irradiated toward the magnetic film (14).
The graphite source (11) is sublimated to produce carbon gas (
17) is carried out by depositing carbon atoms onto the ferromagnetic metal thin film of the magnetic film (14) on the cooling roller (7) through the opening (13) of the shielding plate (12).

In this example, in the above manufacturing apparatus, the film formation rate was 200.
person/min, Ar ion voltage is IKV, the ion current density of Ar ions is changed variously, and the thickness is 10.
Samples were prepared by forming an amorphous carbon film, and the specific resistance, still durability, and head clogging of these samples were measured and evaluated. The results are shown in FIG. Note that these measurement and evaluation criteria are the same as those for Samples 1 to 5 described above.

As can be seen from Figure 3, the ion current density is OmA/
cm'', that is, a sample with a resistivity of 011Ω-cm or less, in which an amorphous carbon film of Co-Ni alloy was formed only by electron beam evaporation without Ar ion irradiation, does not cause head clogging and has the best still durability. It is.

FIG. 4 is a diagram showing the specific resistance value of each amorphous carbon film.

As can be seen from FIG. 4, the higher the connectivity of the SP2 hybrid orbital, the lower the specific resistance. The specific resistance of the amorphous carbon film formed by the vacuum evaporation method of the present invention is 10-1 to 1
It is within the range of 0-Ω-cm.

Next, Sample 6.7 shown below was prepared as a comparative example.

Sample 6 Made of PET containing filler made of silicon oxide with an average particle size of 1000 particles at a density of 20000 particles/cm', thickness 9 μm, maximum surface roughness 250 particles, average surface roughness 14
The above example (sample 1) was deposited on a 0A nonmagnetic film substrate.
A magnetic tape of sample 6 was prepared by forming a ferromagnetic metal thin film of Co--N1 alloy and an amorphous magnetic film in the same manner as described above.

Sample 7 A magnetic tape was prepared in the same manner as Sample 6, except that instead of the amorphous carbon film, a protective layer made of a fluorine-based liquid lubricant and having a thickness of approximately 100 mm was coated on a ferromagnetic metal thin film.

Next, when the above-mentioned sample 1.5.6.7 magnetic tape was still reproduced, changes in the reproduction output depending on the still reproduction time were measured, and the results are shown in FIGS. 5 to 8, respectively. The combinations of the nonmagnetic substrate and the protective layer of Sample 1.5.6.7 are as shown in Table 2 below.

As can be seen from Table 2, Figures 5 to 8, the playback output of sample 1 did not decrease even after the still playback time of 180 minutes passed, whereas the playback output of sample 5 remained around 110 minutes and that of sample 7 after 120 minutes. The playback output was almost 0 before and after. In addition, in sample 6, the reproduction output almost reached O when the still reproduction time was about 4 minutes.

In other words, from the above results, the amorphous carbon film improves the still durability when a non-magnetic substrate that does not contain filler is used, but it actually worsens the still durability when a substrate containing filler is used. It turns out that it does.

Next, in this example (sample 1), the film thickness of the amorphous carbon film was changed to 150 mm (sample A) and 250 mm (sample B).
), 350 people (sample C) were used to form three types of magnetic tapes, and the change in the still playback output of each magnetic tape depending on the still time and the maximum playback output at recording frequencies of 7 MHz and 10 MHz were measured. In addition, as a comparative example, a ferromagnetic metal thin film made of a Co-Ni alloy with a thickness of about 200 OA was deposited on a PET substrate containing filler.
Furthermore, on top of that is a layer of approximately 30 mm thick made of fluorine-based liquid lubricant.
A magnetic tape (sample 1) was prepared by coating a protective layer on the magnetic tape, and the change in the still playback appearance of the magnetic tape depending on the still time and the maximum playback output at recording frequencies of 7 MHz and 10 MHz were measured. The above measurement results are shown in Table 3 below. In addition, the above still playback is performed at a temperature of 25℃ and a temperature of 6.
It is defined under an environmental condition of 5%, and the value is the rate of decrease with respect to the initial output. Further, the above maximum reproduction output is a value based on a comparative example (sample D).

Table 3 As can be seen from Table 3 above, when an amorphous carbon film is formed, the low power of the still reproduction output can be suppressed regardless of the film thickness. Furthermore, if the thickness of the amorphous carbon film is as thin as 15OA, the maximum reproduction output in the short wavelength region of 10MI-(2) will be significantly improved to 3.6dB. As the thickness increases, the maximum playback output decreases.

Next, a magnetic tape according to another embodiment of the present invention will be described.

In another example, a C0N1 alloy (Co:
A ferromagnetic metal thin film with a thickness of 1,500 to 2,000 layers was formed, and the vacuum was then reduced to lXl0-''T.

An amorphous carbon film with a thickness of 80 to 100 A is formed on the ferromagnetic metal thin film by performing electron beam evaporation (applying power: 4 KW) using a graphite source under the conditions of RR, and further perfluorocarbon film is formed on the ferromagnetic metal thin film. A magnetic tape of Sample 8 was prepared by dipping a fluorine-based liquid lubricant made of alkyl carboxylic acid into a protective layer by dipping 5×10 mg/C+11 j4.

In addition, as a comparative example, Co
A fluorine-based liquid lubricant made of perfluoroalkylcarboxylic acid is directly applied to the Ni alloy ferromagnetic metal thin film by the dipping method without forming an amorphous carbon film.
．． A magnetic tape of Sample 9 was prepared by applying 5×10-” mg/Cm2 to form a protective layer.

Next, the still durability, coefficient of dynamic friction, and corrosion resistance of the magnetic tape of Sample 8.9 and the magnetic tape of Sample 1 of the above-mentioned Example were investigated, and the results are shown in Table 4 below. Regarding still durability, the time required for the reproduction output to decrease by 3 dB from the initial value after still reproduction of a magnetic tape is measured, and the coefficient of dynamic friction is an index for evaluating running stability. Corrosion resistance is measured by the tension of the magnetic tape at the front and back.
After the magnetic tape was left for 20 days at a temperature of 90% humidity, the state of corrosion on the surface of the magnetic tape was observed using an optical microscope.

Table 4 As can be seen from Table 4 above, the magnetic tape of Sample 8 had an amorphous carbon film formed on the ferromagnetic metal thin film J2, and a protective layer made of a fluorine-based liquid lubricant formed thereon. Excellent still durability and running properties, as well as excellent corrosion resistance. On the other hand, the magnetic tape of Sample 1 in which only the amorphous carbon film was formed on the ferromagnetic metal thin film -L improved in still durability and running performance, but did not improve in corrosion resistance. The reason why the corrosion resistance of Sample 1 is not improved is considered to be that a large number of pores are formed on the surface of the amorphous carbon film.

On the other hand, the reason why the corrosion resistance of Sample 8 improved is that the fluorine-based liquid lubricant having polar groups entered the pores on the surface of the amorphous carbon film.
This is thought to be due to the prevention of oxygen, moisture, etc. from entering the magnetic tape.

In the above examples, perfluoroalkylcarboxylic acid was used as the fluorine liquid lubricant, but it also has a molecular weight of 500 to 20,000 and polar groups -OH, -COOH in the molecule.

0COC)i, -NH2, etc. may be used.

(1.) Effects of the Invention According to the present invention, a ferromagnetic metal thin film type magnetic recording medium having excellent durability and lubricity can be provided.

Furthermore, according to the present invention, it is possible to provide a magnetic recording medium with improved corrosion resistance.

Further, according to the invention, it is possible to provide a method for manufacturing a metal thin film type magnetic recording medium, which allows the above-mentioned magnetic recording medium to be manufactured with good mass productivity.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the main part showing the structure of the magnetic tape of the present invention;
Figure 2 is a schematic cross-sectional view showing a magnetic tape manufacturing device;
Figure 4 shows the characteristics of the magnetic tape, Figure 4 shows the resistance value of the amorphous carbon film, and Figures 5, 6, 7, and 8 show the changes in the still playback output depending on the still time. FIG. (1)...Nonmagnetic substrate, (2)...Ferromagnetic metal thin film, (3)...Amorphous carbon film.

Claims (5)

[Claims] (1) A ferromagnetic metal thin film is formed on a nonmagnetic substrate made of a polymer film containing no filler, and an amorphous carbon film with a specific resistance of 0.1 Ω-cm or less is formed on the ferromagnetic thin film. magnetic recording media. (2) The magnetic recording medium according to claim 1, wherein the bonding state between carbon atoms of the amorphous carbon film is mainly a covalent bond of an SP^2 hybrid orbital. (3) The magnetic recording medium according to claim (1) or (2), wherein the amorphous carbon film does not contain impurity gas. (4) The magnetic recording medium according to claim (1), (2) or (3), wherein a protective layer made of a fluorine-based liquid lubricant is coated on the amorphous carbon film. (5) A ferromagnetic metal thin film is formed on a non-magnetic substrate made of a polymer film containing no filler, and carbon atoms are deposited on the ferromagnetic metal thin film by vacuum evaporation to form an amorphous carbon film. A method for manufacturing a magnetic recording medium.