JPH07129949A - Magnetic disk - Google Patents

Abstract

PURPOSE:To improve the lubricity of a magnetic disk as well as the adsorption of lubricating oil on a protective film by using a protective lubricative film contg. fluorine and carbon and having a graphite structure in combination with fluorine-contg. lubricating oil on a nonmagnetic substrate. CONSTITUTION:A magnetic film 2 is formed on a nonmagnetic substrate 1 to obtain a disk and a graphite film is formed on the disk in 5 to several ten nm thickness by CVD or other method with gaseous hydrocarbon such as methane at 500-1,000 deg.C. Graphite particles are dispersed on the surface of the disk with the formed film and a graphite film is formed by rubbing with a disk or cylinder of ceramics, etc., having a smooth surface and Mohs hardness of 2.5 at 0.2-2.0m/sec sliding rate under 50-500N load. This graphite film is then converted into a fluorinated graphite film by heating in gaseous fluorine. The lubricity of the magnetic disk is improved by using the resulting protective lubricative film contg. fluorine and carbon and having a graphite structure in combination with a film 4 of fluorine-contg. lubricating oil.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk used in an information processing apparatus such as a computer and a workstation, and particularly, a magnetic disk protective film and lubrication suitable for improving the sliding resistance of the magnetic disk. The present invention relates to a film and its lubrication mechanism.

[0002]

2. Description of the Related Art In a conventional magnetic disk device, recording / reproducing has been performed on a magnetic disk rotating at a high speed by using a head slider that floats due to air resistance. Therefore, in order to improve the recording density of the magnetic disk, the flying height of the head slider is reduced and the effective distance from the head slider to the magnetic recording film is reduced by thinning the protective film and the lubricating oil film of the magnetic disk. ing.
However, if the effective distance from the head slider to the magnetic recording film is reduced to the limit, the probability of contact between the head slider and the magnetic disk increases. Since the contact between the head slider and the magnetic disk causes wear of the protective film of the magnetic disk, wear powder present between the head slider and the magnetic disk promotes wear of the protective film and deteriorates or destroys the recording layer. It causes errors and even crashes. For this reason, there has been a demand for a magnetic disk having excellent sliding resistance even when the flying height is reduced.

It is required that the protective film should not be abraded when the head slider is continuously collected at the same time, and should not be damaged by contact with the slider during steady rotation (Tribologist, 36, (1991) 615). for that reason,
The development of a protective film with excellent wear resistance, and the development of a lubricating oil with excellent adsorption and friction and wear resistance to the protective film is in progress.

Recently, magnetic disks using carbon as a protective film material have become mainstream (Tribologist, 3
5 (1990) 157), Japanese Patent Laid-Open No. 01-158622.
It is also known that good durability and environment resistance can be obtained by using a protective film made of a fluorocarbon film as disclosed in Japanese Patent Laid-Open Publication No. 04-44636. Further, as disclosed in JP-A-64-1118, it is possible to improve lubricity by providing a graphite layer having characteristics as a solid lubricant. Furthermore, there is also an invention in which lubricity is improved by using a fluorinated graphite thin film having a graphite structure as a protective layer (Japanese Patent Laid-Open No. 56-1569).
31, JP 56-156932, JP 6
4-30023).

On the other hand, as a lubricating oil, perfluoroalkyl polyether oil, which is chemically inert and has a low vapor pressure, is often used among the fluorine-based synthetic oils (Tribologist, 36, (1991). ) 618). Fluorine-based synthetic oils have low affinity with most substances, and therefore are difficult to adsorb on the protective film. Therefore, in order to solve problems such as scattering due to centrifugal force when the magnetic disk rotates, a fluorine-based synthetic oil having a functional group is often used. It has been reported that the perfluoroalkylalkylpolyether oil film having a functional group strongly adsorbs to a disk medium and exhibits an excellent lubricating effect even under a high speed and high load condition (T.MI.
YAMOTO et al. , STLESP-25 (1
988) 55).

[0006]

Since the above-mentioned fluorine-based synthetic oil has the property of being chemically inert, it exhibits excellent lubricity, but is difficult to adsorb to other materials. Further, the abrasion powder generated by the sliding of the head slider further promotes the abrasion of the protective film.

The object of the present invention is to have excellent lubricating properties,
In addition, it is possible to improve the anti-sliding property of the magnetic disk by using a protective lubrication film that has a good lubricating oil adsorption property and that has a lubrication mechanism that prevents the abrasion powder from promoting wear of the protective film. is there.

[0008]

As shown in FIG. 1, a magnetic disk has a structure in which a magnetic film 2, a protective lubricating film 3 and a lubricating oil film 4 are laminated on a non-magnetic substrate 1. The non-magnetic substrate 1 and the magnetic film 2 are made of a material that does not demagnetize even at high temperatures. For example, in addition to Al / Al alloy / carbon, glass, ceramics (ZrO ₂ , T
iC, Si ₃ N _4, etc.) can be used. Magnetic film 2
As the alloy, a Co—Cr based alloy, a Co—Zr based alloy, or the like can be used. The protective lubricating film 3 is a protective film having a graphite structure containing fluorine and carbon represented by the composition formula (CF) n and having a lubricating property. Further, the lubricating oil film 4 uses a fluorine-based synthetic oil.

The protective lubricating film 3, which is a feature of the present invention, can be formed by the following method.

First, a graphite film 5 is formed on a disk having a magnetic film 2 formed on a non-magnetic substrate 1 at 500 to 1000 ° C. by using a hydrocarbon gas such as methane by a CVD method.
A film of several tens nm is formed. Alternatively, graphite is sputtered at 500 to 1000 ° C. to 5 to several 10 nm.
Form a film. Alternatively, graphite particles can be used to form a graphite film having a film thickness of 5 to several tens of nm by rubbing in the following manner. Graphite particles having a particle diameter of 5 to several tens nm are dispersed on the surface of the disk on which the magnetic film 2 has been formed. Then, 50 to 50 on a disk or cylinder having a smooth surface and a Mohs hardness of 2.5 or more, such as ceramics.
Slip velocity 0.2-2.0m / s with 0N load
Rub at ec to form a graphite film.

A disk on which a graphite film was formed by the above method was placed in a fluorine gas (fluorine partial pressure: 0.3 × 10 ⁵ to
It can be made into a fluorinated graphite by heating at 0.8 × 10 ⁵ Pa) at 300 to 600 ° C. for 1 hour. At this time, the fluorine content in the protective lubricating film 3 is 40 to 6
It is preferably 0 atomic%.

The lubricating oil film 4 has an average molecular weight of 150.
It is desirable to use 0-6000 perfluoroalkyl ether oil.

Another example of the magnetic disk structure utilizing the present invention is shown in FIG. A magnetic film 6, a protective film 7, and a protective lubricating film 8 are laminated on the non-magnetic film 5. Since the non-magnetic substrate 5 and the magnetic film 6 are not subjected to high-temperature heat treatment in the magnetic disk manufacturing process, the materials are not limited by heat resistance.
The protective film 7 is a carbon thin film or ceramics (Ti
It may be a solid thin film such as C, Si ₃ N ₄ , ZrO ₂ or the like. The protective lubricating film 8 is a film obtained by mixing and applying fluorinated graphite powder and fluorine-based synthetic oil.

The protective film 7 shown in FIG. 2 may have a film thickness of 10 nm or less.

The protective lubricating film 8 which is a feature of the present invention
Can be formed on the protective film 7 by the following method.

Particles of fluorinated graphite are dispersed in a fluorine-based synthetic oil such as perfluoroalkyl ether oil by stirring. Bubbles mixed by bubbling are removed from this grease-like liquid. By coating this on the protective film 7, the protective lubricating film 8 having a grease effect can be formed. The protective lubricating film 8 has a thickness of 5 to 100 n.
m is suitable.

For the protective lubricating film 8, it is preferable to use a perfluoroalkyl ether oil having an average molecular weight of 1500 to 6000 as the fluorine-based synthetic oil and a particle diameter of 2 to 60 nm as the fluorinated graphite particles. Further, it is possible to substitute a fluororesin such as polytetrafluoroethylene having a particle diameter equivalent to that of fluorinated graphite.

In the magnetic disk having the structure shown in FIG. 2, the protective lubricating film 8 can be directly formed on the magnetic film 6 without forming the protective film 7, but in that case, 10
A film thickness of nm or more is suitable.

[0019]

As described above, according to the present invention, the magnetic disk is used in combination with the protective lubricating film having a graphite structure containing fluorine and carbon and the fluorine-based lubricating oil to improve the adsorption of the lubricating oil to the protective film. At the same time, since the protective film functions as a solid lubricant, it has the effect of improving the lubricity of the magnetic disk. Further, the abrasion powder generated by sliding is mixed with the lubricating oil to play the role of grease, which has the effect of preventing the progress of abrasion.

Since graphite has a layered structure, it has a characteristic of exhibiting anisotropy. That is, carbon atoms are connected by covalent bonds within the same plane, and van between parallel planes.
Because they are connected by the der waals force, the distance is 3.4 Å, which is rather long. Therefore, shearing is likely to occur in the direction perpendicular to the C axis (parallel to the reference plane). Therefore, it is used as a solid lubricant. Since graphite has a large interlayer distance, a chemically active substance such as a halogen, an acid, or an alkali metal is introduced to form an intercalation compound.

[0021] Graphite has a high temperature (300 to 600).
When fluorine gas is reacted at (° C.), carbon of the fluorinated graphite and fluorine are covalently bonded, and the atomic arrangement of carbon changes from sp ² to sp ³ hybrid orbital. The hexagonal net-like planar structure of graphite changes to a zigzag structure (Fig. 3), and the electrical conductivity peculiar to graphite is lost, resulting in an electrically insulating intercalation compound fluorinated graphite (CF) n.
To generate. As shown in FIG. 3, in the fluorinated graphite, fluorine atoms face each other in the layer, and due to the repulsive force, the interlayer distance is 7.3Å (5.68 to 8.5 depending on the condition).
Å) and the sliding on this side is good. Fluorinated graphite becomes a mixture of C and (CF) n when the content of F is small,
When the F content is high, a large amount of —CF ₂ — bonds and —CF ₃ groups are included. That is, if the content of F is too small or too large, the molecular structure of the fluorinated graphite shown in FIG. 3 has an irregular arrangement, and the performance as a solid lubricant is reduced.

Further, in fluorinated graphite, since carbon and fluorine are strongly bound to each other, the intermolecular attractive force is reduced, and the surface energy is reduced. For example, when measuring the contact angle with water at 30 ° C, it is 27 ° for glass and 1 for Teflon.
While it is 09 °, fluorinated graphite shows a large value of 143 °. Further, it does not have a specific melting point, and the decomposition temperature is 320 to 420 ° C., which is stable to heat. Therefore, it is used as a solid lubricant. Unlike solid lubricants such as graphite and molybdenum disulfide, it exhibits excellent lubrication performance in vacuum and in all atmospheres, especially at high pressures and high speeds.

In the present invention, the graphite carbon film formed on the magnetic film is fluorinated at a high temperature (300 ° C. to 600 ° C.) by utilizing the above-mentioned excellent lubricating property of fluorinated graphite.
The protective film has a graphite structure containing carbon and fluorine. As described above, this film shows good lubricity as a solid lubricant because of good slippage between layers and low surface energy.

On the other hand, the fluorine-based synthetic oil used as the lubricating oil has a C—F bond energy in the molecule of 116 kc.
Since it is large as al / mole, van der waa
It has a small Is force and is difficult to adsorb to other substances. Therefore, although it exhibits excellent lubricity, it is difficult to adsorb to the friction surface, so that there is a problem that it scatters when the disk rotates.

However, since the fluorine compounds tend to have an affinity with each other, the use of fluorinated graphite as the protective lubricating film can enhance the adsorption force of the lubricating oil.

As the lubricating oil, it is desirable to use a chemically inert perfluoroalkyl ether oil having a low vapor pressure among the fluorine-based synthetic oils. Furthermore, if the average molecular weight of the perfluoroalkyl polyether oil is too small, it will scatter when the magnetic disk rotates,
If the average molecular weight is too large, the kinematic viscosity is high and the fluidity is poor, and oil starvation easily occurs. Therefore, by using a perfluoroalkylpolyether oil having an appropriate average molecular weight, it becomes possible to use the lubricating oil more effectively.

Further, it is difficult to completely prevent generation of abrasion powder due to sliding of the magnetic disk and the slider.
When the conventional carbon protective film is used, the abrasion powder acts as an abrasive and further promotes abrasion. However, when fluorinated graphite is used for the protective film, the generated abrasion powder also becomes fine particles of fluorinated graphite. This fluorinated graphite powder has excellent affinity with the fluorinated synthetic oil, and the mixture of the fluorinated synthetic oil and the fluorinated graphite particles has a grease effect. Therefore, it is possible to prevent the acceleration of wear.

[0028]

EXAMPLES Next, examples of the present invention will be described.

[Example 1] A chromium underlayer film was formed on a φ5.25 "glass substrate, and a cobalt-nickel magnetic film was formed on the surface thereof.
After forming a 60 nm carbon protective film at 0 ° C., 350
Fluorine gas was flown at 0 ° C. to form a fluorinated graphite protective lubricating film having a film thickness of 60 nm. It was confirmed by X-ray diffraction measurement that this protective lubricating film had a graphite structure. Further, a 5 nm lubricating oil film made of perfluoroalkyl polyether was formed to complete the magnetic disk. A ferrite alloy was used for the head slider.

[0030]

[Table 1]

Table 1 shows the results of a CSS test conducted 1000 k times with the magnetic disk and head slider subjected to a load of 100 × 10 to ³ N on the head slider. There was no crash that caused the head slider to damage the magnetic film.

[Comparative Example 1] Similar to the magnetic disk in the above-mentioned Example 1, a lubricating oil film made of perfluoroalkyl polyether was directly applied to a magnetic disk having a carbon protective film having a thickness of 60 nm formed at 300 ° C. by a sputtering method. The formed magnetic disk was manufactured. Ferrite alloy is used for the head slider, and the load is 100 × 10 ~ ³
Table 1 shows the results of performing a CSS test in the same manner as in the examples by applying N. A crash occurred after 650 passes.

From Example 1 and Comparative Example 1, it was found that the magnetic disk of the present invention exhibits effective lubricity in the CSS system.

[Embodiment 2] FIG. 4 shows the results of the same sliding test as in Embodiment 1 except that the fluorine content of the magnetic disk protective film of Embodiment 1 was changed to 20 to 80 atomic%.

Fluorine content 40, 50, 60 atomi
The maximum friction coefficient of c% was 0.08 or less,
Those of 20, 25, and 75 atomic% exceeded 0.15. When the coefficient of friction exceeds 0.1, the vibration of the head slider becomes large, and noise occurs during read / write.

By Raman measurement, the fluorine content was 2
The 0,25 atomic% protective film has a large amount of unbound C, and
The protective film of 5 atomic% contained a large amount of —CF ₂ — and —CF ₃ . Therefore, it is considered that the function of the solid lubricant was reduced or the adsorption force of the lubricating oil was not appropriate because the graphite structure of the protective film was irregular.

Therefore, the content of fluorine in the protective film is 40
-60 atomic% is suitable.

[Example 3] The same sliding test as in Example 1 was conducted using perfluoroalkyl ether oil having an average molecular weight of 800 to 10,000 for the lubricating oil film of the magnetic disk of Example 1.

A magnetic disk using a perfluoroalkyl polyether oil having an average molecular weight of 1500 to 6000 is
Even if the sliding test was conducted 1000 times for the number of passes, it did not crash, but the others crashed. It is considered that the low molecular weight perfluoroalkyl ether oil had a high volatility and the high molecular weight perfluoroalkyl ether oil had a high kinematic viscosity, so that the fluidity was poor and a crash occurred. Therefore, a perfluoroalkyl ether oil having an average molecular weight of 1500 to 6000 is suitable.

[Example 4] A carbon film having a thickness of 10 nm was formed on the magnetic film of Example 1 by sputtering, and 20 wt% of fluorinated graphite particles having different particle diameters were formed thereon.
Example 1 was carried out using a magnetic disk coated with a lubricant mixed with perfluoroalkyl polyether oil to a thickness of 100 nm.
The result of the sliding test similar to that shown in FIG.

When a lubricant film mixed with fluorinated graphite having a particle diameter of 2 to 60 nm is used, the maximum friction coefficient is 0.
Although it was 1 or less, the maximum friction coefficient exceeded 0.1 when fluorinated graphite particles smaller or larger than this particle size range were used. This is because, when the particle size is too small, it was found from the X-ray diffraction measurement that the graphite structure of the fluorinated graphite particles was irregularly arranged. From this, it is considered that it did not function as a solid lubricant. Further, it is considered that when the particle diameter is large, the fluorinated graphite particles prevent the perfluoroalkyl ether oil from entering between the head slider and the lubricant film or the protective film.

Further, from the relationship between the Sommerfeld number and the friction coefficient, in the region where the friction coefficient is 0.1 or less, it is not sure that the solid lubrication between the solids, that is, the head slider and the carbon film are in direct contact with each other. Recognize.

Therefore, since the friction coefficient was 0.1 or less, the fluorinated graphite particles used for the lubricant film were 2 to 60.
A particle size of nm is desirable.

[Embodiment 5] The magnetic disk of Embodiment 1 is
A friction test (load 200 × 10 to ³ N) was performed using a ferrite alloy ball (φ10 mm).

The results of the friction test are shown in FIG. 20 passes
The friction coefficient remains stable after the 00th friction test, and SE
As a result of observing the friction surface with M, no damage to the magnetic film was confirmed.

Comparative Example 2 The magnetic disk of Comparative Example 1 was
Example 5 using a ferrite alloy ball (φ10 mm)
The same friction test was performed.

The results of the friction test are shown in FIG. 70 passes
The friction coefficient began to be disturbed after 0 times, and the friction coefficient sharply increased in the vicinity of 1400 passes. When the friction surface of the magnetic disk after the friction test was observed by SEM, the carbon film was worn and the magnetic film was partially exposed.

From Example 5 and Comparative Example 1, it is considered that, in the contact recording type magnetic disk device, the magnetic disk of the present invention exhibits excellent lubricity.

[0049]

INDUSTRIAL APPLICABILITY The present invention, in addition to a magnetic disk device for recording / reproducing by the CSS system, a contact recording system for recording / reproducing while sliding a head slider and a magnetic disk, or a magnetic disk device having an extremely small flying height. Is also applicable.

[Brief description of drawings]

FIG. 1 is a structural diagram of a magnetic disk of the present invention.

FIG. 2 is a structural diagram of a magnetic disk of the present invention.

FIG. 3 is a structural diagram of fluorinated graphite used for a protective lubricating film in the present invention.

FIG. 4 is a diagram showing the relationship between the fluorine content and the maximum friction coefficient of the magnetic disk protective film of the present invention in Example 2.

FIG. 5 is a diagram showing the relationship between the particle size of fluorinated graphite in the lubricating film of the magnetic disk of the present invention in Example 4 and the maximum friction coefficient.

FIG. 6 is a diagram showing a friction test result of a magnetic disk of the present invention in Example 5.

FIG. 7 is a diagram showing the results of a friction test of a magnetic disk in Comparative Example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Nonmagnetic substrate, 2 ... Magnetic film, 3 ... Protective lubricating film, 4 ... Lubricating oil film, 5 ... Nonmagnetic substrate, 6 ... Magnetic film, 7 ... Protective film, 8 ... Protective lubricating film.

Claims (8)

[Claims] 1. A magnetic disk comprising a magnetic recording film, a protective lubricating film having a graphite structure containing fluorine and carbon, and a fluorine-based synthetic oil used as a lubricating oil film. 2. The fluorine content in the protective lubricating film is 40
2. The method according to claim 1, wherein the content is -60 atomic%.
The magnetic disk described. 3. The magnetic disk according to claim 1, wherein the protective lubricating film has a fluorinated graphite structure represented by a composition formula of (CF) n. 4. The lubricating oil film has an average molecular weight of 150.
The magnetic disk according to claim 1, wherein a perfluoroalkyl ether oil having a viscosity of 0 to 6000 is used. 5. A carbon protective film is provided on the magnetic recording film,
Furthermore, a magnetic disk characterized by using a mixture of fluorinated graphite particles and a fluorinated lubricating oil as a lubricating protective film. 6. The magnetic disk according to claim 5, wherein the particle diameter of fluorinated graphite is 2 to 60 nm in the magnetic disk. 7. A magnetic disk device according to the CSS system, characterized in that the magnetic disk according to claim 1 or 5 is used. 8. A magnetic disk drive using a contact recording method, wherein the magnetic disk according to claim 1 or 5 is used.