JPH11110753A - Manufacture of magnetic tape - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize the protective layer composed of a carbon thin film and improve the output characteristics, corrosion-resistance and durability of a magnetic tape by a method wherein the plasma emission spectrum intensity IH of an Hα-ray caused by H active species is so controlled as to be larger than the plasma spectrum intensity ICH of a CH-ray caused by CH active species in a plasma CVD method. SOLUTION: A film 3 on which a magnetic layer is formed is made to run on a cooling can roller 2 in a vacuum chamber 1 and raw gas is introduced into the vacuum chamber 1. The plasma of the raw gas is formed by the energy of a microwave A and the ions of the plasma irradiate the film 3 to form a protective film consisting of a carbon thin film. At that time, the plasma emission spectrum intensity ICH of a CH-ray (431±20 nm) caused by CH active species and the plasma emission spectrum intensity IH of an Hα-ray (656±20 nm) caused by Hα active species are so controlled as to be ICH<IH. With this constitution, a magnetic tape which has excellent output characteristics, corrosion-resistance and durability can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic tape manufacturing method for forming a protective layer of a magnetic tape by a plasma CVD method using microwaves.

[0002]

2. Description of the Related Art A so-called metal thin film type magnetic recording medium in which a metal is deposited on a support in a vacuum in a vacuum or the like can increase the density of the magnetic material because the magnetic layer contains no binder at all. Is promising for high-density recording.

However, the magnetic layer of the metal thin-film type magnetic recording medium has poor corrosion resistance and durability as it is because the metal is only deposited on the support. It has been practiced to apply an acid-based or fluorine-based lubricant or to provide a nonmagnetic metal protective layer on the magnetic layer.

Furthermore, today, as a protective layer on a magnetic layer,
Attention has been paid to a technique for forming a thin film composed of a carbon thin film such as diamond-like carbon and graphite. The diamond-like carbon thin film is an amorphous carbon film,
It is considered that graphite and diamond bonds are mixed.

As a method of forming a carbon thin film such as diamond-like carbon, for example, ion beam evaporation, ion beam sputtering, RF sputtering, RF glow discharge, DC-discharge, microwave plasma CVD
Methods, a hot filament CVD method, a hot plasma CVD method and the like are known.
Method D is suitable as a method for forming a protective layer of a magnetic recording medium because film formation can be performed at a relatively low temperature.

[0006] The plasma CVD method using microwaves
Microwave from microwave source (2.45 GHz)
Is guided into a plasma excitation chamber by a waveguide, and a source gas introduced into the plasma excitation chamber is dissociated to deposit a target substance on a base material as an active species.

[0007]

Generally, when a protective film made of a carbon film is formed on a magnetic layer, it is considered desirable to form a harder film for the purpose of improving durability. The media industry has traditionally focused on forming harder carbon thin films. In particular, in the case of a magnetic recording medium using a hard base material such as Al metal or glass as a support such as a hard disk, the hardening of the protective film is aimed at since the base material is not denatured during recording and reproduction.

However, in the case of a magnetic recording tape in which the recording / reproducing head undergoes a denaturation of the base material during recording and reproduction, a protective film that is too hard deteriorates the head touch of the tape, resulting in an insufficient reproduction envelope waveform. Output characteristics cannot be obtained. In addition, magnetic recording tapes tend to be thinner in order to increase their recording capacity,
Providing a protective layer that is too hard causes cupping of the medium due to imbalance in rigidity, which also prevents excellent output characteristics from being obtained. Note that cupping refers to curvature in the width direction of the tape.

Further, as the hardening is pursued, impurities in the film (particularly, in the case of a carbon film, raw materials and substances other than carbon such as hydrogen existing in a vacuum chamber) tend to be removed as much as possible. It is presumed that the material that filled the same gaps as the microcrystals of carbon (called carbon grains) that constitute the carbon thin film is also removed, so that it is considered that the protective film has poor airtightness and is formed underneath. Corrosion resistance of the metal thin film type magnetic layer is deteriorated.

[0010]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that when a protective layer of a magnetic tape is formed by a plasma CVD method using microwaves, the hardness and the hardness are improved by adopting a specific method. It has been found that the airtightness is optimized, and that a magnetic tape having excellent corrosion resistance and output characteristics can be obtained, thereby completing the present invention.

That is, the present invention provides a method for producing a magnetic tape, comprising the step of forming a protective layer made of a carbon thin film on a metal thin film type magnetic layer formed on a support by a plasma CVD method using microwaves. In the above, the plasma C
In the VD method, CH lines (431 ±
A plasma emission spectral intensity I _CH of 20 nm), that the plasma emission spectral intensity I _H of Hα-rays due to H active species (656 ± 20 nm) is, towards the I _H is controlled to be greater than I _CH It is intended to provide a method for producing a magnetic tape, which is a feature of the present invention.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a magnetic tape according to the present invention is characterized in that a carbon thin film is formed on a metal thin film type magnetic layer formed on a support by vapor deposition or the like by a plasma CVD method using microwaves. The protective layer is formed of

The ECR plasma CVD method is performed by, for example, an apparatus as shown in FIG. In FIG. 1, 1 is a vacuum container, 2 is a cooling can roll, 3 is a film, and 4 is an ECR.
Electromagnet for use, 5 for plasma excitation chamber, 6 for rectangular waveguide, 7 for microwave power supply, 8 for quartz window, 9 for power monitor,
10 is an isolator, 11 is a matching device (three stub tuner), 12 is a gas flow controller, 13 is a turbo molecular pump, 14 is a mechanical booster pump,
Reference numeral 15 denotes a rotary pump, and A denotes a microwave.

The apparatus shown in FIG. 1 is an example of an apparatus for forming a carbon thin film as a protective layer of a vapor-deposited magnetic tape, and a film 3 on which a magnetic layer running on a cooling can roll 2 in a vacuum vessel 1 is formed. A carbon thin film is formed on the magnetic layer.
In FIG. 1, a diverging magnetic field is formed by the ECR electromagnet (coil) 4 from the plasma excitation chamber 5 toward the vacuum vessel 1. 2.45 GHz microwave guided by rectangular waveguide 6 connected to plasma excitation chamber 5 (A in the figure)
Is introduced into the plasma excitation chamber 5 through the quartz window 8. The raw material gas introduced into the plasma excitation chamber 5 absorbs microwave energy to generate high density, highly active plasma. Due to the divergent magnetic field generated by the coil 4, ions in the plasma are extracted toward the vacuum vessel 1 and irradiated toward the film 3 in the vacuum vessel 1, and adhere to the magnetic layer surface of the film 3 to form a thin film. You.

In the apparatus shown in FIG. 1, the raw material gas is converted into plasma by microwave energy. In the present invention, the plasma emission spectrum intensity I _{CH of} the CH line (431 ± 20 nm) caused by the CH active species at that time, In contrast to the plasma emission spectrum intensity I _{H of} the Hα ray (656 ± 20 nm) caused by the H active species, I _H is controlled to be greater than I _CH , that is, I _CH <I _H. And Preferably, I _CH <I _H <3I _CH , and more preferably, 1.5 I _CH <I _H <3I _CH .

Here, the plasma emission spectrum intensity is measured by the following method. Using an emission spectrum monitor for plasma process (PCM401) manufactured by SC Technology Co., Ltd., an optical fiber detector is set in a view port (not shown) of the vacuum vessel 1 of the apparatus shown in FIG. 1 for measurement. This is shown in FIG. FIG. 2 is a partially enlarged view of the apparatus of FIG. 1, and the detector 21 has a position L / 2 at the height of the center of the plasma excitation chamber 5, that is, half the height L of the plasma excitation chamber 5.
And the horizontal distance x from the can roll is 3 cm
It is set to a position within. Measurement conditions are 250-8
Data is obtained in a 50 nm wavelength region by integrating 0.1 sec × 100 times. FIG. 5 shows an example of the emission spectrum obtained by the measurement. Figure 5 is a C ₂ H ₄ and H ₂ in the apparatus of FIG. 1 H ₂
Are mixed and supplied so that the mixing ratio becomes 40%, and the plasma CVD method is performed under the conditions of a vacuum degree of the plasma excitation chamber of 4.0 × 10 ⁻⁴ Torr, a microwave output of 600 w, and a distance of 70 mm between the ECR point and the support. Is an emission spectrum in the case of performing the above. In FIG. 5, a spectrum of 656 ± 20 nm is an emission spectrum by hydrogen plasma (called Hα ray).
And the spectrum observed at the position of 431 ± 20 nm is the emission spectrum of CH plasma. In the present invention, the two emission spectrum intensities are controlled so that the plasma emission spectrum intensity I _H of the Hα line is larger than the plasma emission spectrum intensity I _{CH of the} CH line (I _CH <I _H ).

In order for I _CH and I _H to _satisfy I _CH <I _H ,
It can be achieved by setting the kind of hydrocarbon gas, the mixing ratio with hydrogen gas, the degree of vacuum in the plasma excitation chamber, the microwave output, and the distance between the ECR point and the support when performing the plasma CVD method as follows. Kinds of hydrocarbon gas As the hydrocarbon gas, the peak of the Hα ray tends to increase as the ratio of hydrogen in the molecule increases. For this reason,
In the present invention, a hydrocarbon represented by a composition formula of C _n H _m and satisfying a relationship of m / n ≧ 2 is preferable. Specific examples of the hydrocarbons satisfying the above conditions include saturated hydrocarbons such as methane and ethane, and unsaturated hydrocarbons such as ethylene.

Mixing ratio of hydrocarbon gas and hydrogen gas The hydrocarbon gas is used by mixing with hydrogen gas. At that time, the ratio of the hydrogen gas is preferably 10 to 60% (volume ratio), and more preferably 30 to 50% (volume ratio).
By mixing hydrogen gas in the above range, hydrogen plasma is appropriately generated and reacts with carbon plasma generated from hydrocarbon gas to become hydrocarbon, filling gaps between carbon grains in the film and acting as a buffer. It is thought that a carbon protective film having appropriate softness is obtained by the function. The mixing amount of hydrocarbon gas and hydrogen gas is measured by mass flow meter,
That is, it is determined by the volume ratio.

The degree of vacuum in the plasma excitation chamber is 10 ⁻² to 10 ⁻⁵ Torr.
r, particularly preferably 10 ^-3 to 10 ^-4 Torr. In a low-vacuum system, the mean free path of gas particles is short, and hydrogen ions once dissociated from molecules collide with other particles, lose energy, and re-molecularize. As a result, the peak of the Hα line tends to decrease. On the other hand, in a high vacuum system, the peak of the Hα line increases for the opposite reason. In a high-vacuum system, electrons are sufficiently accelerated and collide with molecules, so that they are easily dissociated. This also tends to increase the peak of the Hα ray.

Microwave output The microwave preferably has a range of 300 to 900 watts. If the microwave output is too low, the source gas becomes difficult to be dissociated due to energy shortage, and the peak of the Hα ray tends to decrease. Conversely, if the microwave output is too high, the film will have adverse effects such as burning.

The distance between the ECR point and the support The plasma CVD method is preferably an ECR plasma CVD method. In particular, the ECR point (a region where electrons efficiently absorb microwave energy by an electron cyclotron resonance phenomenon) and the support are preferably used. Is preferably 5 to 150 mm. E
Once the CR point moves away from the support, the ions once dissociated are EC
Energy is lost during transfer from the R point onto the film, and it is likely to re-molecularize. Therefore, in this case, the peak of the Hα ray tends to be smaller. By setting the distance between the ECR point and the support within the above range, the plasma density near the support is improved, and a carbon thin film having good film quality can be formed efficiently.

By properly selecting the above conditions,
The plasma emission spectrum intensities I _CH and I _H can be set to satisfy I _CH <I _H , but in the present invention, it is particularly preferable to satisfy all of the above conditions. As a result, the hydrocarbon gas obtains sufficient energy and is dissociated into carbon plasma and hydrogen plasma, and the carbon plasma generates hard carbon microcrystals. At the same time, it is thought that hydrogen plasma is generated appropriately by the dissociation of hydrocarbon gas and the added hydrogen gas, reacts with carbon plasma to become hydrocarbon, and fills the gaps of carbon grains in the film and acts as a buffer. As a result, a carbon protective film having appropriate softness is obtained. As a result, the head touch of the tape is improved, the reproduction envelope waveform is improved, and the reproduction output characteristics are improved. Further, by filling the gaps of carbon grains in the film, the airtightness of the carbon thin film is also improved, and the corrosion resistance of the metal thin film type magnetic layer formed below the protective layer is improved.

Further, in the present invention, in addition to the above, in addition to the above, the temperature of the support when performing the plasma CVD method is -20
The temperature is preferably set to 80 ° C. In this temperature range, a more desirable carbon thin film can be obtained. Specifically, the temperature of the can roll 2 of the apparatus shown in FIG.

In FIG. 1, a metal thin film type magnetic layer is formed on a film 3 serving as a magnetic tape. The magnetic layer is made of a ferromagnetic metal such as cobalt, iron, nickel or an alloy containing these. It may be a single layer or a multilayer. The thickness of the metal thin film type magnetic layer is about 100 to 200 nm.

As a material for the support, a normal non-magnetic support can be used, and polyethylene terephthalate (P
ET), polyesters such as polyethylene naphthalate (PEN); polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate; polycarbonates;
Plastics such as polyvinyl chloride; polyimide; and aromatic polyamide are used. The thickness of these films is about 3 to 20 μm. In particular, the method of the present invention has a thickness of 3 to
Even when a thin support having a thickness of 10 μm is used, the method can be carried out without damaging the support.

The thickness of the carbon thin film formed on the magnetic layer is 5 to
ECR plasma C
It is desirable to select the conditions of the VD method, raw material compounds, running speed, and the like. Except for the step of forming a thin film by the ECR plasma CVD method, the method conforms to a normal magnetic tape manufacturing method.

[0027]

Embodiments of the present invention will be described below. However, the invention is not limited to these examples.

Examples 1 to 8 and Comparative Examples 1 to 6 A PET film (thickness: 6 μm) on which a Co magnetic layer having a thickness of 180 nm was formed by an oblique deposition apparatus was set in the apparatus shown in FIG. On top, ECR plasma CV
A protective layer made of a carbon thin film and having a thickness of 15 nm was formed by Method D. At this time, the film forming speed was 10 m / min, and the type and flow rate of the source gas were as shown in Table 1. The degree of vacuum, microwave output, distance between the ECR point and the film, and film temperature in the plasma excitation chamber were as shown in Table 1. CH line (431 ± 2) for ECR plasma CVD
0 nm) plasma emission spectrum intensity I _CH and plasma emission spectrum intensity I of Hα ray (656 ± 20 nm)
_H was measured by the method described above, and the intensity ratio was calculated. Table 1 also shows the results.

Next, a 0.5 μm-thick back coat layer containing carbon black and a binder as main components was formed on the surface of the film opposite to the surface on which the magnetic layer was formed. Further, on the protective layer, a fluorine-based lubricant [trade name: A
M2001 (manufactured by Daikin Industries, Ltd.)]
The lubricant was applied to a thickness of nm to form a lubricant layer.

The thus obtained film on which the magnetic layer, the protective layer, the lubricating layer and the back coat layer are formed is 8 mm thick.
It was cut into a width and loaded into a case for an 8 mm video cassette to obtain an 8 mm video tape.

FIG. 3 shows the plasma emission spectrum of Example 1 and FIG. 4 shows the plasma emission spectrum of Comparative Example 2.

(2) Evaluation of Performance The 8 mm video tape obtained above was evaluated for corrosion resistance, surface properties on the magnetic layer side, output characteristics and still durability by the following methods. Table 2 shows the results. Corrosion resistance The 8 mm video tape obtained above was stored for one month in an environment of a temperature of 65 ° C. and a humidity of 85% RH. From the saturation magnetic flux density Bs ₀ before storage and the saturation magnetic flux density Bs ₁ after storage, B
The retention of the saturation magnetic flux density was calculated from s ₁ / Bs ₀ × 100 (%), and the corrosion resistance was evaluated. Surface properties Optical surface roughness meter (Zymo, Model Maxim / 3
D5700), a 40-fold Fizeau lens was used, and five points were measured without a filter, and the average value was taken as the surface roughness (Ra). Output The luminance output and the color output were measured using a modified deck of an 8 mm VTR. Here, the output is 8 mm of Comparative Example 1.
Relative evaluation using a video tape as a reference (0 dB) was performed. Still Durability A luminance signal was recorded by the above-mentioned deck, and the time until the reproduction output decreased by 3 dB from the initial value was measured during still reproduction.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

By optimizing the protective layer made of a carbon thin film as in the present invention, a magnetic tape having excellent output characteristics, corrosion resistance and durability can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a thin film forming apparatus used in the present invention.

FIG. 2 is a schematic diagram showing a measurement position of a plasma emission spectrum intensity.

FIG. 3 shows a plasma emission spectrum in the plasma CVD method of Example 1.

FIG. 4 is a plasma emission spectrum in the plasma CVD method of Comparative Example 2.

FIG. 5 is a plasma emission spectrum in a plasma CVD method according to the method of the present invention.

[Explanation of symbols]

 1: vacuum container 2: cooling can roll 3: film 4: electromagnet for ECR 5: plasma excitation chamber 6: rectangular waveguide 7: microwave power supply 11: matching device (three stub tuner) A: microwave

Continued on the front page (72) Inventor Hirohide Mizunoya 2606 Akabane, Kakaicho, Haga-gun, Tochigi Pref.

Claims (8)

[Claims] 1. A method for manufacturing a magnetic tape, comprising: forming a protective layer made of a carbon thin film on a metal thin film type magnetic layer formed on a support by a plasma CVD method using microwaves. C caused by CH active species in plasma CVD
H line and the plasma emission spectral intensity I _CH of (431 ± 20nm), Hα line due to H active species (656 ± 20n
m) A method of manufacturing a magnetic tape, wherein the plasma emission spectrum intensity I _H is controlled so that I _H is higher than I _CH . 2. A plasma emission spectrum intensity I of a CH line.
_CH and Hα-ray plasma emission spectrum intensity I _H is less than I _CH <
2. The method according to claim 1, wherein a relationship of I _H <3I _CH is satisfied. 3. A gas mixture of a hydrogen gas and a hydrocarbon gas, wherein the ratio of the hydrogen gas is 10 to 60% (volume ratio) as a source gas for the plasma CVD method. 2. The production method according to 2. 4. The method according to claim 1, wherein the plasma CVD is performed at -20 to 80.degree.
The production method according to any one of claims 1 to 3, wherein the production is performed at a temperature of the support. 5. The method according to claim 1, wherein the plasma CVD method is performed at 10 ⁻² to 10 ^−5.
The method according to claim 1, wherein the method is performed at a degree of vacuum of Torr. 6. The manufacturing method according to claim 1, wherein said plasma CVD method is an ECR plasma CVD method. 7. The distance between the ECR point and the support is 5 to 150.
The production method according to any one of claims 1 to 6, which is mm. 8. The method according to claim 1, wherein the thickness of the support is 3 to 10 μm.