JPH09259423A - Magnetic recording medium and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a protective film excellent in mechanical strength by plasma- polymerizing Fullerene (spherical carbons) or its deriv. on a magnetic layer. SOLUTION: A magnetic layer, a protective layer and a lubricant layer are successively formed on a nonmagnetic substrate. The protective film has a structure formed by polymerizing Fullerene represented by Cn [where (n) is an integer capable of geometrically forming a spherical compd., e.g. 60, 70, 76 or 84] by addition bonding. This Cn polymerized structure is represented by the molecular formula (Cn+j )x [where (j) is a multiple of both -10 to +10 and 2 and shows the number of carbon atoms fallen form or added to a simple substance of Cn and (x) is a positive integer].

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a magnetic recording medium using spherical carbons called fullerene or a derivative thereof as a raw material for a protective film, and a method for producing the same.

[0002]

2. Description of the Related Art The third after diamond and graphite
It was only in 1990 that the presence of fullerene, which is a spherical carbon compound, was revealed as the crystalline carbon of, and a macroscopic synthesis method was established.

[0003] Fullerenes are a series of spherical carbon compounds consisting only of carbon (Higher Fullerness).
And includes 12 5-membered rings and 12 or more 6-membered rings. That is, 60, 70, 7
A spherical carbon C _n having 6 or 84 carbon atoms (the number of carbon atoms is selected from the number capable of geometrically forming a spherical structure) bonded in a spherical shape to form a cluster,
They are represented as C ₆₀ , C ₇₀ , C _76, C _84, etc., respectively.

For example, C ₆₀ has a polyhedral structure called a "truncated icosahedron" in which all the vertices of a regular icosahedron are cut off to form a regular pentagon. As shown in FIG. It is a cluster in which all the vertices are replaced with carbon atoms C, and has a formal soccer ball-like molecular structure.
Further, C ₇₀ has a so-called rugby ball-like molecular structure as shown in FIG. 6, and C _76, C _{84 and the} like have the same structure.

[0005]

By the way, the above-mentioned fullerenes have been studied in various fields for their uses, and one of the uses is thought to be a raw material for a protective film for a magnetic recording medium. There is.

Generally, in a magnetic recording medium, the surface on the magnetic layer side is slid on the magnetic head at a high speed. Therefore, a protective film is provided on the magnetic layer for the purpose of imparting durability against the sliding.

As the protective film for the magnetic recording medium, one having carbon atoms distributed in an amorphous form has been used so far. This amorphous carbon protective film has an intermediate property between graphite and diamond.

As a method for forming such a carbon protective film, a sputtering method is generally used. In this sputtering method, an inert gas such as Ar is ionized and collided with graphite or a target such as graphite, carbon atoms are released to the outside by the collision energy, and the released carbon atoms are deposited on the surface of the magnetic layer. As a result, a carbon film is formed.

In this sputtering method, since the raw material is composed only of carbon atoms, there are advantages that impurities derived from the raw material are not mixed in the protective film to be formed and the film can be relatively easily formed. However, there is a drawback that the film forming rate is very slow, and there is a problem in terms of productivity.

On the other hand, as a film forming method which has recently received attention because of its high film forming rate, CVD (chemical) is used.
There is a vapor deposition method.

In this CVD method, a mixed gas of a source gas containing a solid product element to be produced (in this case, CH ₄ gas or the like is used to produce carbon) and a carrier gas, A reaction is performed using heat or plasma, and carbon atoms generated by this reaction are deposited on the surface of the magnetic layer to form a carbon protective film.

The CVD method can obtain a film formation rate about 5 to 10 times that of the sputtering method, and is advantageous for increasing productivity. However, this CVD method also has some problems. For example, since the constituent element of the raw material gas is not only carbon, other elements such as hydrogen that have not been decomposed into carbon remain in the protective film, and exhaust gas treatment is difficult.

These two types of film forming methods are currently mainly used as a method for forming a protective film, and each has its advantages and disadvantages.

As a solution to the problems in these film forming methods, the use of fullerenes shown above is promising.

First, since fullerene is composed of only carbon atoms, elements other than carbon are rarely mixed in the protective film to be formed.

Further, since only the van der Waals force acts between the fullerene spherical molecules, it can be sublimated at a relatively low temperature of about 550 ° C. unlike graphite or graphite.

Therefore, if fullerene is formed by vapor deposition using a sublimation source, it is possible to form a high-purity carbon protective film at a high film formation rate.

However, only the van der Waals force acts between the fullerene molecules as described above. For this reason, the mechanical strength of the film formed as a vapor deposition film is weak, and peeling and film abrasion are likely to occur. This is a fatal defect as a protective film.

Therefore, the present invention has been proposed in view of such conventional circumstances, and a protective film having high purity and excellent mechanical strength is formed at a high film forming rate, and good running property, An object of the present invention is to provide a magnetic recording medium which is durable and has excellent productivity, and a method for manufacturing the same.

[0020]

The present inventors have made intensive studies from various angles with the object of achieving the above object. As a result, when spherical carbons represented by the molecular formula C _n or a derivative thereof is vapor-deposited in an inert gas plasma, the spherical carbons are polymerized with each other to obtain a plasma polymerized film having excellent mechanical strength. Came to obtain the knowledge of.

The present invention has been completed based on these findings.

That is, the magnetic recording medium of the present invention comprises a magnetic layer, a protective film and a lubricant layer formed in this order on a non-magnetic support, and the protective film is made of C _n (where n is a geometrical value). It is an integer capable of forming a spherical compound.), Or a spherical carbon or derivative thereof having a structure polymerized by an addition bond.

Further, in the method for producing a magnetic recording medium of the present invention, after forming a magnetic layer on a non-magnetic support, C _n (where n is an integer capable of geometrically forming a spherical compound). ) A spherical carbon or a derivative thereof represented by the formula (4) is used for plasma polymerization using a sublimation source to form a protective film, and then a lubricant is applied.

In the plasma polymerization of spherical carbons or their derivatives, a film formation rate equal to or higher than that of the CVD method can be obtained. On the other hand, unlike the CVD method, elements other than carbon are mixed in the protective film or exhaust gas treatment is performed. There is no problem. Moreover, the formed film is superior in mechanical strength to the vapor-deposited film formed by vacuum vapor deposition because the molecules are addition-polymerized with each other.

Therefore, a magnetic recording medium in which a protective film is formed by plasma polymerization of spherical carbons or derivatives thereof and a lubricant layer is formed on this protective film can obtain good running properties and durability. Also, high productivity can be obtained.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

In the magnetic recording medium according to this embodiment, a magnetic layer, a protective film and a lubricant layer are sequentially formed on a non-magnetic support, and in particular, the protective film is C _n (where n is 6
It is an integer capable of forming a geometrically spherical compound selected from 0, 70, 76, 84 and the like. ) Has a structure in which spherical carbons represented by () are polymerized by an addition bond.

This C _n polymer structure has a structure of (C _{n + j} ) _x (provided that
n is an integer that can form a geometrically spherical compound selected from 60, 70, 76, 84 and the like, and j is -10 to 10
X is a positive integer. ). Here, the value of j represents the number of carbons missing or added from the C _n simple substance. That is, C ₅₈ , C _56, ..., C _62, etc. are obtained by the lack or addition of carbon from C _n , and these are polymerized. Therefore, this C _n polymerized structure does not necessarily have an integer multiple of C _n It is not always the skeleton of.

Such a C _n polymerized structure can take various forms. For example, in the case of a C ₆₀ dimer, in addition to the C ₁₂₀ structure shown in FIG. There is a C ₁₁₈ structure as shown in FIG. 2 or a C ₁₁₆ structure as shown in FIG. Those having a higher degree of polymerization are considered to have a mixture of these bond forms.

This protective film may be formed only by these C _n polymerized structures, but in this case, it is presumed that the C _n polymerized structures are spread over the whole in a network form by covalent bonds. Further, if it has a C _n polymerized structure partially, the C _n polymerized structure distributed in amorphous, the portion not polymerized is presumed that are bound together by van der Waals forces . In addition, in this protective film, together with the above C _n polymerization structure,
C _n simple molecule such as C _{60 as a} raw material may be mixed.

The carbon number n of the spherical carbons C _n used as a raw material is preferably 60 from the viewpoint of easy availability of the raw material and strength of the film. The polymer film can be formed by using other spherical carbons, but the carbon number n is 7
The polymer film formed by high-order spherical carbons such as 0, 76, 84 has inferior mechanical strength as compared with the polymer film formed by C ₆₀ . In addition, spherical carbons other than C ₆₀ have a large decrease in production yield and are not very useful industrially. Hydrocarbons, halogens, hydroxyl groups, carboxyl groups or the like may be added to the spherical carbons C _n . However, if the number of these additions is large, it becomes disadvantageous in the polymerization of spherical carbons. From the viewpoint of the mechanical strength of the protective film, it is preferable that the number of additions is small.

Such a protective film is formed by plasma polymerization using spherical carbon C _n or its derivative as a sublimation source (sublimates a C _n raw material in a gas phase and applies plasma,
Polymerize C _n molecules. Can be used to form a film.

The greatest advantage of the spherical carbons C _n or its derivative is that only the van der Waals force acts between the molecules, which is different from graphite or graphite at a relatively low temperature of about 550 ° C. It can be sublimated. Therefore, a strong film can be formed in a short time by plasma polymerization using the spherical carbons C _n or its derivative as a sublimation source.

Various types of known plasma discharge such as direct current discharge, low frequency discharge, high frequency discharge, microwave discharge, etc. can be adopted as the plasma generation discharge method, and the types of electrodes and the discharge generation method are the internal electrode method, An external electrode system, a waveguide system, a capacitive coupling type, an inductive coupling type, an electrodeless oscillation type, etc. can be selected.

From the standpoint of improving the uniformity and stability of plasma, it is desirable that the plasma polymerization be carried out in a mixed atmosphere of spherical carbons as a raw material and carrier gas together with a carrier gas. As the carrier gas, any of those commonly used in plasma polymerization can be used,
Examples include argon, nitrogen and helium.

As for the discharge conditions, there is no problem in polymerization if the direct current discharge is within a range where the Paschen's law, which shows the relationship between the gas pressure, the electrode distance, and the voltage, is satisfied, and the alternating current discharge is within the dischargeable range. Gas pressure is preferably 13 Pascal (100 mT)
It is as follows.

The magnetic recording medium of the present invention is provided with the protective film as described above, and the lubricant layer is further formed on the protective film. In order to improve the running property and durability of the magnetic recording medium, it is not enough to form the protective film, and it is necessary to use the lubricant layer together.

Examples of the lubricant include RA (where R is a hydrophobic group and A is a hydrophilic group) or R ¹ -A-R ² (where R ¹ and R ² are hydrophobic groups). And A is a hydrophilic group) is used.

In this compound, the hydrophobic groups R, R
¹ and R ² are CH ₃ (CH ₂ ) _m −, CH ₃ (CH ₂ ) _{m
-C 6 H 4 - (CH 2} ) n -, CF 3 (CF 2) m - (CH 2)
_n − (where m and n are integers of 1 or more) and the like are introduced.

The hydrophilic group A is -S in RA.
i (OR ³ ) ₃ (provided that R ³ is CH ₃ , C ₂ H ₅ ), −
^{_{SiCl 3, -Ti (OR 3)}} 3 ( where, R ³ is CH _3, C ₂
H ₅ a is), - COOH, -OH, -NH 2 or the like is introduced, the ^{R 1 -A-R 2 -COO -} , - CONH- , etc. is introduced.

As the other material constituting the magnetic recording medium, for example, the material of the non-magnetic support or the magnetic layer, any of those usually used can be used.

For example, as the non-magnetic support, polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polyethylene and polypropylene, cellulose triacetate,
From cellulose derivatives such as cellulose diacetate and cellulose triacetate butyrate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polymer materials such as polycarbonates and polyamideimides, aluminum alloys, titanium alloys, etc. Become a metal plate,
Examples of the support include a support formed of alumina glass, ceramics, and the like. The form is not limited at all, and may be any form such as a tape form, a sheet form, and a drum form.

The metal magnetic thin film can be formed as a continuous film by a PVD (physical vapor deposition) method such as plating, sputtering, or vacuum vapor deposition. As the metal magnetic thin film, Fe, Co, Ni, Co-Ni based alloy, C
o-Pt-based alloy, Co-Pt-Ni-based alloy, Fe-Co
Alloys, Fe-Ni alloys, Fe-Co-Ni alloys,
Fe-Ni-B type alloy, Fe-Co-B type alloy, Fe-
An example is a magnetic metal thin film made of a Co-Ni-B alloy or the like. In this case, the thickness of the metal magnetic thin film is 50 nm to 2
It is preferably about 00 nm.

[0044]

EXAMPLES Examples to which the present invention is applied will be described below in detail with reference to specific experimental data.

Plasma Polymerization Device In the present invention, various plasma polymerization devices can be used for forming the protective film. Here, the configuration of the parallel plate electrode type capacitively coupled plasma device used in this embodiment will be described. To do.

FIG. 4 shows a parallel plate electrode type capacitively coupled plasma polymerization apparatus used in this embodiment.

This plasma polymerization apparatus comprises a reactor 1 having a capacity of about 20 liters, and the reactor 1 is provided with gas supply pipes 2 and 3. Also, at the bottom of the reactor 1,
An exhaust port 9 connected to a vacuum exhaust system including an oil diffusion pump 4, rotary pumps 5 and 6, liquid nitrogen traps 7 and 8 is provided.

In the reactor 1, plasma generating electrodes 10 and 11 are arranged in parallel at an interval of 10 cm,
One electrode 10 is connected to a plasma power supply 13 via an impedance matching device 12. Also, the upper electrode 1
Carrier gas in the form of a shower from 0
It is designed to be introduced between 0 and 11. Here, Ar gas or He gas was used as the carrier gas.

Further, a molybdenum boat 14 and a sample 15 for sublimation of fullerene are placed between the electrodes 10 and 11.
The molybdenum boat 14 is connected to the molybdenum boat 14 with a direct current power supply 16 connected to each other with a space of 0 cm therebetween.

The output of the plasma power supply 13 is AC 13.5.
It is a radio wave of MHz. Here, this output is 10W
To 100 W, plasma was generated in a carrier gas constant flow rate system set to 13.5 Pascal, and fullerene contained in the molybdenum boat 14 was sublimated in the plasma to perform plasma polymerization. The film thickness during the polymerization was continuously monitored by the sensor 17.

Fullerene, which is a raw material, was obtained from the soot produced at that time by generating a DC arc discharge using a carbon graphite rod as an electrode in a He atmosphere. The conditions for producing soot are an applied voltage of 60 V, a discharge current of 200 A, and a He gas pressure of 100 Torr.

[0052] From soot generated in this manner, C _n by extraction with an organic solvent such as benzene or toluene
Is obtained. The mixture of C _n was applied to a silica gel column using benzene or toluene as a developing solvent to separate C ₆₀ or C ₇₀ . Then, each separated extract was dried to obtain a raw material for plasma polymerization.

Example 1 A Co-Ni-based alloy was deposited on a polyethylene terephthalate film having a thickness of 10 μm by an oblique vapor deposition method to give a film thickness of 1
A metal magnetic thin film of 00 nm is formed, length 20 cm, width 8
It was cut into mm.

A plasma-polymerized film (protective film) having a thickness of 10 nm was formed on the surface of the metal magnetic thin film by using C ₆₀ fullerene alone as a sublimation source and using the plasma polymerization apparatus described above.
The plasma was Ar gas plasma and was generated at an output of 10W.

Next, a toluene solution of heptyl stearate was applied on the protective film so that the amount of heptyl stearate applied was 5 mg / m ² , to form a lubricant layer, and a sample tape was prepared.

Examples 2 to 6 Sample tapes were prepared in the same manner as in Example 1 except that the output of the plasma power source was changed as shown in Table 1 when forming the plasma polymerized film.

Example 7 At the time of forming a plasma polymerized film, H at an output of 40 W was used.
A sample tape was prepared in the same manner as in Example 1 except that e-gas plasma was generated.

Examples 8 and 9 Sample tapes were produced in the same manner as in Example 7 except that the output of the plasma power source was changed as shown in Table 1 when forming the plasma polymerized film.

Example 10 When forming a plasma polymerized film, C ₆₀ and C ₇₀ were set to 5:
A sample tape was prepared in the same manner as in Example 1 except that a mixture (C ₆₀ / C ₇₀ fullerene) mixed at a ratio of 5 (molar ratio) was used as a sublimation source and Ar gas plasma was generated at an output of 60 W. It was made.

Example 11 A sample tape was prepared in the same manner as in Example 1 except that C ₇₀ fullerene was used alone as a sublimation source to form a plasma polymerized film, and Ar gas plasma was generated at an output of 60 W. It was made.

Example 12 C ₆₀ and C ₇₆ were mixed in a ratio of 5: 5 when forming a plasm polymer film.
A sample tape was produced in the same manner as in Example 1 except that a mixture (C ₆₀ / C ₇₆ fullerene) mixed at a ratio (molar ratio) was used as a sublimation source and Ar gas plasma was generated at an output of 60 W. did.

Example 13 When forming a plas-polymerized film, C ₆₀ : C ₈₄ was changed to 5: 5.
A sample tape was produced in the same manner as in Example 1 except that a mixture (C ₆₀ / C ₈₄ fullerene) mixed at a ratio (molar ratio) was used as a sublimation source and Ar gas plasma was generated at an output of 60 W. did.

[0063]

[Table 1]

Comparative Example 1 Instead of forming a plasma-polymerized film, vapor deposition was performed under a vacuum of 10 ⁻³ Pascal using C ₆₀ fullerene alone as a sublimation source, and the protective film was formed. A sample tape was produced in the same manner.

Comparative Example 2 Instead of forming a plasma polymerized film, a carbon protective film was formed by a sputtering method.

Comparative Example 3 Instead of forming a plasma polymerized film, a carbon protective film was formed by a CVD method.

Comparative Example 4 A sample tape was prepared in the same manner as in Example 1 except that the lubricant was not applied on the plasma polymerized film.

With respect to the sample tape manufactured as described above, the friction coefficient, still characteristics and scratch strength were measured. Table 2 shows the results. In addition, these measuring methods are as follows.

Friction coefficient: This is the coefficient of friction of the sample tape with respect to the stainless steel guide pin, and is 20 when the shuttle travels.
It shows the coefficient of friction at the 200th time when it is performed 0 times. The smaller the value, the lower the friction and the better the running performance.

Still characteristics: An 8 mm video deck modified for a durability test was used. The video deck for durability test has a rotating drum and a recording / reproducing system, and the output change of only the same portion of the sample tape is monitored. Using this deck, the time (minutes) required for the output to reach half the value of the first reproduction was measured. The larger the value, the better the durability. The measurement was performed for a maximum of 120 minutes.

Scratch strength: A protective film was formed on a glass plate under the same conditions as when forming a film on each sample tape. Then, the protective film was rubbed with tweezers, and the state of scratches on the protective film at that time was visually observed. ◎: When scars are scarcely recognized, ○: Slight scratches are recognized but almost no problem, △: When scratches are slightly recognized,
X shows the case where many scratches are seen and becomes a problem in terms of durability.

[0072]

[Table 2]

As is clear from the results of Table 2, Examples 1 to 1 in which a plasma-polymerized film of fullerene was formed as a protective film
The sample tape of Example 13 has a protective film having higher strength than the sample tape of Comparative Example 1 in which a vapor deposition film of fullerene is formed as a protective film, and is excellent in durability. This is because in a fullerene vapor deposited film, only van der Waals force acts between fullerene molecules, whereas in the case of a fullerene plasma polymerized film, addition polymerization occurs between fullerene molecules and a strong film is formed. It is because it forms.

These plasma-polymerized films have the same strength and durability as the sputter carbon film formed in Comparative Example 2 or the CVD carbon film formed in Comparative Example 3.

Here, the sputtering method has a low film formation rate, and the CVD method has a problem of low film purity and exhaust gas treatment. On the other hand, in plasma polymerization of fullerene, C
A film formation rate equivalent to that of the VD method can be obtained, a high-purity polymer film can be formed in a short time, and the formed thin film has excellent strength and durability. That is, it can be said that the fullerene plasma-polymerized film is excellent in both mechanical properties and productivity.

However, the sample tape of Comparative Example 4 in which the lubricant was not applied on the plasma polymerized film had a high friction coefficient and poor still durability. From this, it can be seen that the use of the lubricant is indispensable for using the plasma polymerized film as the protective film of the magnetic recording medium.

Looking at the experimental data in more detail,
It can be seen that particularly the polymer films formed with high plasma power as in Examples 4 to 6 or Examples 8 and 9 have more excellent strength and durability. Further, as in Examples 7 to 9, even when He gas is used for plasma, the same characteristics as when Ar gas is used are obtained.

In Examples 10 to 13, a mixture of C ₆₀ and higher fullerenes such as C ₇₀ or C ₇₆ , or these higher fullerenes were used alone as a sublimation source. These plasma-polymerized films also have higher strength than the fullerene vapor-deposited film of Comparative Example 1, but are still inferior in still characteristics or scratch strength to the plasma-polymerized film formed by using C ₆₀ alone. . This has been confirmed by experiments, but it is difficult for higher-order fullerenes such as C ₇₀ or C ₇₆ to polymerize fullerene molecules with each other as compared with C ₆₀ . Further, higher fullerenes such as C ₇₀ have a very low production yield, which is disadvantageous from an industrial viewpoint. Therefore, it is desirable to use C ₆₀ as sublimation source from properties and industrial point of view.

[0079]

As is apparent from the above description, in the present invention, a protective film is formed on the magnetic layer of the magnetic recording medium by plasma polymerization of spherical carbons or their derivatives, and this protective film is further formed. Since the lubricant layer is formed on the film, a protective film excellent in mechanical strength can be formed at a film formation rate equal to or higher than that of the CVD method. Also, in this plasma polymerization, unlike the CVD method, impurities originating from the raw material are not mixed into the protective film and no problem of exhaust gas treatment occurs.

Therefore, the magnetic recording medium having such a protective film formed thereon can have good running properties and durability, high productivity, and is industrially very advantageous.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the structure of C ₁₂₀ .

FIG. 2 is a schematic diagram showing the structure of C ₁₁₈ .

FIG. 3 is a schematic diagram showing the structure of C ₁₁₆ .

FIG. 4 is a schematic cross-sectional view showing one structural example of a plasma polymerization apparatus.

FIG. 5 is a schematic diagram showing the structure of C ₆₀ fullerene.

FIG. 6 is a schematic diagram showing the structure of C ₇₀ fullerene.

Claims (4)

[Claims] 1. A magnetic layer, a protective film, and a lubricant layer are sequentially formed on a non-magnetic support, and the protective film is C _n (where n can form a geometrically spherical compound). A magnetic recording medium characterized in that the spherical carbons represented by the formula (1) or a derivative thereof has a structure polymerized by an addition bond. 2. The protective film comprises (C _{n + j} ) _x (where n is an integer capable of geometrically forming a spherical compound, and j is −).
X is a positive integer that is a multiple of 2 of 10 to 10. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is composed of a polymer represented by the following formula or a derivative thereof, and the polymer or derivative thereof is amorphous. 3. After forming a magnetic layer on a non-magnetic support,
After forming a protective film by plasma polymerization using spherical carbons represented by C _n (where n is an integer capable of geometrically forming a spherical compound) or a derivative thereof as a sublimation source. A method for manufacturing a magnetic recording medium, which comprises applying a lubricant. 4. The method for producing a magnetic recording medium according to claim 3, wherein different spherical carbons are mixed and used as a sublimation source.