U.S. patent application number 11/985414 was filed with the patent office on 2008-04-03 for magnetic disk drive having a surface coating on a magnetic disk.
This patent application is currently assigned to Fujitsu Limited. Invention is credited to Hiroshi Chiba, Tsukasa Itani, Kazuaki Kurihara, Norikazu Nakamura, Shoichi Suda, Masayuki Takeda, Keiji Watanabe, Eishin Yamakawa.
Application Number | 20080081220 11/985414 |
Document ID | / |
Family ID | 36687061 |
Filed Date | 2008-04-03 |
United States Patent
Application |
20080081220 |
Kind Code |
A1 |
Watanabe; Keiji ; et
al. |
April 3, 2008 |
Magnetic disk drive having a surface coating on a magnetic disk
Abstract
A magnetic disk is produced with improved yield by forming a DLC
protective film by a d.c. magnetron sputtering process conducted in
a sputtering atmosphere containing oxygen. The magnetic disk
carries a lubricating film on the DLC film wherein a fluorocarbon
resin constituting the lubricating film contains photocrosslinking
groups. A lubricating film having non-polar end groups is also
disclosed.
Inventors: |
Watanabe; Keiji; (Kawasaki,
JP) ; Chiba; Hiroshi; (Higashine, JP) ;
Yamakawa; Eishin; (Higashine, JP) ; Itani;
Tsukasa; (Kawasaki, JP) ; Nakamura; Norikazu;
(Kawasaki, JP) ; Suda; Shoichi; (Kawasaki, JP)
; Takeda; Masayuki; (Kawasaki, JP) ; Kurihara;
Kazuaki; (Kawasaki, JP) |
Correspondence
Address: |
GREER, BURNS & CRAIN
300 S WACKER DR
25TH FLOOR
CHICAGO
IL
60606
US
|
Assignee: |
Fujitsu Limited
Kawasaki-shi
JP
|
Family ID: |
36687061 |
Appl. No.: |
11/985414 |
Filed: |
November 15, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11476179 |
Jun 27, 2006 |
|
|
|
11985414 |
Nov 15, 2007 |
|
|
|
09692569 |
Oct 19, 2000 |
7081277 |
|
|
11476179 |
Jun 27, 2006 |
|
|
|
Current U.S.
Class: |
428/814 ;
G9B/5.281 |
Current CPC
Class: |
G11B 5/725 20130101;
G11B 5/8408 20130101; C23C 14/0605 20130101; C23C 14/024 20130101;
Y10T 428/1164 20150115 |
Class at
Publication: |
428/814 |
International
Class: |
G11B 5/725 20060101
G11B005/725 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 22, 1999 |
JP |
11-301349 |
Nov 2, 1999 |
JP |
11-312728 |
Nov 26, 1999 |
JP |
11-336458 |
Claims
1. A magnetic disk drive comprising: a rotary magnetic disk; a
magnetic head scanning a surface of said rotary magnetic disk in a
state that said magnetic head is floated form said surface of said
rotary magnetic disk; an arm carrying said magnetic head; and a
drive mechanism driving said arm, wherein said magnetic disk
carries a lubricating film containing therein a photocrosslinking
functional group, said photocrosslinking functional group causing a
crosslinking in said lubricating film.
2. A magnetic disk drive as claimed in claim 1, wherein said
photocrosslinking functional group is selected from the group
consisting of: an alkenyl group, an alkenyl halide group, an aryl
halide group, an aryl azide group, piperonyl group and epoxy
group.
3. A magnetic disk drive as claimed in claim 1, wherein said
magnetic disk is covered with a carbon film deposited by a CVD
process and wherein said lubricating film is formed on said carbon
film.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This is Divisional of application Ser. No. 11/476,179, filed
Jun. 27, 2006, which is a Divisional of application Ser. No.
09/692,569, filed Oct. 19, 2000, which is based on Japanese
priority applications No. 11-301349, 11-312728 and 11-336458
respectively filed on Oct. 22, 2000, Nov. 2, 2000 and Nov. 26,
2000, the entire contents of which are hereby incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] The present invention generally relates to magnetic
recording of information and more particularly to a magnetic disk
apparatus called hard disk drive and a surface coating provided on
a magnetic disk used in such a hard disk drive.
[0003] Hard disk drives are used extensively in various computers
as a large-capacity, high-speed auxiliary storage device.
[0004] A typical hard disk drive includes a rigid magnetic disk
rotated at a high speed and a magnetic head held on a swing arm so
as to scan the recording surface of the magnetic disk, wherein the
magnetic head scans the recording surface at a high speed generally
in a radial direction of the magnetic disk in response to the
rotational movement of the swing arm. The magnetic disk is usually
rotated at a speed of several thousand r.p.m. and the magnetic head
carries out reading or writing of information in the state that the
magnetic head is floated from the surface of the magnetic disk by a
minute distance.
[0005] A typical hard disk drive includes a plurality of magnetic
disks mounted coaxially on a common drive hub and the swing arm and
the magnetic head are provided for each magnetic disk. The swing
arms corresponding to the magnetic disks are mounted on a common
drive shaft in the form of a unitary body, and the magnetic heads
on the respective swing arms scan the surface of the corresponding
magnetic disk simultaneously in response to the rotation of the
drive shaft.
[0006] FIG. 1 shows the internal structure of a typical hard disk
drive in a plan view, wherein the left side of the broken line
shows the hard disk drive in a state wherein the upper cover is
removed, while the right side of the broken line shows the
construction of a magnetic disk 11 and an arm assembly 12 that
cooperates with the disk 11, wherein the magnetic disk 11 and the
arm assembly 12 form a part of a magnetic disk assembly 10 in which
a plurality of magnetic disks are stacked with each other.
[0007] Referring to FIG. 1, each magnetic disk 11 is mounted upon a
hub 11a that is driven by a motor not illustrated, and the arm
assembly 12 includes a swing arm 12b held on a swing axle 12a and a
magnetic head 12c provided on a free end of the arm 12b. Further, a
coil 12d that forms a part of a voice coil motor 13 is provided on
the arm 12b in correspondence to another free end, opposite to the
first free end on which the magnetic head 12c is provided, wherein
the coil 12d is wound parallel to the scanning surface of the arm
12b.
[0008] Further, magnets 13a and 13b forming another part of the
voice coil motor 13 are disposed above and below the coil 12d.
Thereby, the arm 12 is rotated about the swing axle 12a freely in
response to the energization of the coil 12d. The voice coil motor
13 is subjected to a servo control such that the magnetic head 12c
carried on the arm 12b properly tracks a cylinder or track 11b that
is defined on the magnetic disk 11.
[0009] FIG. 2 is a perspective view showing the internal structure
of the hard disk drive of FIG. 1.
[0010] Referring to FIG. 2, the magnetic disk assembly 10 includes
a plurality of magnetic disks 11.sub.1, 11.sub.2, . . . that are
held commonly on the rotary hub 11a, and the arm assembly 12
includes a plurality of arms corresponding to the plurality of
magnetic disks. Each arm 12b is held on a common rotatable member
12e that in turn is held rotatable about the swing axle 12a, and
all the arms 12b are swung simultaneously in response to the
rotational motion of the member 12e. Of course, the member 12e is
activated in response to the energization of the voice coil motor
13. Further, the entire structure of the hard disk device is
accommodated within a sealed envelope 1.
[0011] FIG. 3 shows the cross-sectional structure of the magnetic
disk 11.
[0012] Referring to FIG. 3, the magnetic disk 11 is formed on a
substrate 11A of Al, and the like, and includes a foundation layer
11B typically of NiP formed on the substrate 11A with a thickness
of about 10 .mu.m, a Cr layer 11C formed on the foundation layer
11B with a thickness of about 300 nm, and a magnetic film 11D of a
Co alloy formed on the Cr foundation layer 11C with a thickness of
about 300 nm, wherein the magnetic film 11D holds written
information in the form of magnetization.
[0013] Further, the surface of the magnetic film 11D thus formed on
the magnetic disk 11 is protected against damages caused by a
physical contact of the magnetic head 12c as in the case of head
crashing event, by providing a hard carbon film 11E on the surface
of the magnetic film 11D, wherein the hard carbon film 11E is
formed with a thickness of about 10 nm and has a diamond-like
structure. Thus, the hard carbon film 11E is called a DLC
(diamond-like carbon) film.
[0014] The hard carbon film 11E thus formed is further covered by a
lubricating film 11F with a thickness of about 2 nm, wherein the
lubricating film 11F is typically formed of a fluorocarbon resin
and is provided so as to reduce the friction between the magnetic
head 12c and the magnetic disk 11. By providing the lubricating
film 11F, damaging of the magnetic film 11D at the time of
contact-start-stop operation of the hard disk drive, and the like,
is minimized.
[0015] In the actual magnetic disk, the layered structure of FIG. 3
is formed not only on the topside of the magnetic disk 11 but also
on the bottom side thereof.
[0016] Conventionally, it is practiced to form the DLC film 11E by
a sputtering process that uses a graphite target. In order to
achieve a high deposition rate at the time of the deposition of the
DLC film 11E, it is commonly practiced to use a high-density d.c.
magnetron sputtering process for the sputter deposition of the DLC
film 11E. In such a conventional d.c. magnetron sputtering process
of the DLC film 11E, it is further practiced to add a gas
containing hydrogen such as H.sub.2 or CH.sub.4 to the sputtering
gas, typically of Ar, so as to terminate the dangling bonds in the
DLC film 11E. By doing so, it is possible to form the DLC film 11E
in the form of an insulating film.
[0017] FIG. 4 shows the construction of a d.c. magnetron sputtering
apparatus 20.
[0018] Referring to FIG. 4, the d.c. magnetron sputtering apparatus
20 includes a processing chamber 21 evacuated at an evacuation port
21A, wherein the processing chamber 21 accommodates therein a
substrate 22 to be processed.
[0019] In the processing chamber 21, there is provided a graphite
target 23A and a graphite target 23B such that the graphite target
23A faces a top surface of the substrate 22 and the graphite target
23B cases a bottom surface of the substrate 22.
[0020] Above the processing chamber 21, there is provided a magnet
25A centrally to the graphite target 23A in the state that the
N-pole of the magnet 25A faces the graphite target 23A. Further, an
annular magnet 26A is provided at the top part of the processing
chamber 21 in the state that the S-pole of the magnetic 26A faces
the graphite target 23A, wherein the magnet 26A is provided so as
to surround the central magnet 25A.
[0021] Similarly, a magnet 25B is provided on the bottom part of
the processing chamber 21 in the state that the N-pole of the
magnet 25B faces the graphite target 23B. Further, an annular
magnet 26B is provided around the central magnet 25B with such an
orientation that the S-pole of the magnet 26B faces the graphite
target 23B.
[0022] The processing chamber 21 is supplied with a mixed gas of Ar
and CH.sub.4 via a mass-flow controller 24A and a line 24B, and a
plasma 28A is formed in the processing chamber 21 adjacent to the
target 23A by supplying a d.c. power from a d.c. power source 27A
to the target 23A. Similarly, a plasma 28B is formed in the
processing chamber 21 adjacent to the target 23B by supplying a
d.c. power from a d.c. power source 27B to the target 23B.
[0023] The plasma 28A thus formed acts upon the surface of the
graphite target 23A and the sputtered C atoms are deposited on the
top surface of the substrate 22 to form a DLC film corresponding to
the DLC film 11E. Similarly, the plasma 28B acts upon the surface
of the graphite target 23B and the sputtered C atoms are deposited
on the bottom surface of the substrate 22 to form a DLC film
corresponding to the DLC film 11E.
[0024] In such a d.c. magnetron sputtering apparatus, it is
possible to form a ring-shaped plasma region of high plasma density
in the plasma 28A by disposing the magnet 26A around the magnet
25A, wherein the sputtering process is promoted in such a
high-density plasma region and the deposition of the DLC film on
the top surface of the substrate 11E is facilitated. Similarly, it
is possible to form a ring-shaped plasma region of high plasma
density in the plasma 28B by disposing the magnet 26B around the
magnet 25B, and the deposition of the DLC film on the bottom
surface of the substrate 22 is facilitated.
[0025] On the other hand, the inventor of the present invention has
discovered a problem in such a d.c. magnetron sputtering process of
the DLC film that uses a ring-shaped high-density plasma in that
deposition of a DLC film or a similar structure occurs not on the
substrate 22 but on the graphite target 23A or 23B in the central
part where the plasma density is low. It is believed that such a
DLC film covers uniformly on the surface of the target 23A or 23B
at the beginning but is removed as a result of sputtering in the
ring-shaped region where the plasma density is high. Thus, in such
a ring-shaped region of the target 23A or 23B, exposure of the
fresh target surface is maintained.
[0026] It should be noted that the DLC film thus deposited on the
central part of the target 23A or 23B is an insulating film and
easily causes charge-up as a result of contact with the plasma 28A
or 28B. Thereby, the DLC film tends to cause scattering in the
processing chamber 21 and forms exotic fragments on the surface of
the substrate 22. Thereby, the yield of the DLC film on the
substrate 22 is reduced.
[0027] In the magnetic disk 11 of FIG. 3, the lubricating film 11F
performs an important function of reducing friction between the
magnetic disk surface and the slider surface of the magnetic head
as noted before. It should be noted that the slider surface of the
magnetic head makes a direct contact with the magnetic disk 11 in
the contact-start-stop operation of the magnetic disk drive. In
view of the fact that the magnetic disk drive is used in various
environmental conditions, it is required that the lubricating film
11F functions as an effective lubrication layer over a wide range
of temperature and/or moisture condition. The importance of the
lubricating film 11F is increasing further in recent magnetic disk
drives having increased recording density characterized by a very
narrow gap between the magnetic disk surface and the magnetic head.
With is regard to the lubricating film 11F, reference should be
made to the U.S. Pat. No. 3,778,308, U.S. Pat. No. 4,267,238 and
the U.S. Pat. No. 4,268,556.
[0028] Conventionally, a perfluoro resin compound having a highly
polar group such as OH group or COOH group as the endcap group has
been used for the lubricating film 11F. In such a lubricating film
11F of perfluoro resin compound, the polar end group of the
perfluoro-resin compound functions to cause adherence or bonding of
the lubricating layer 11F on the underlying surface of the hard
carbon film 11E.
[0029] On the other hand, such a conventional lubricating film 11F
using conventional perfluoro resin compound encounters a problem in
that, while the bottom part of the lubricating film 11F is thus
bonded firmly upon the surface of the underlying hard carbon film
11E, the upper part of the lubrication film 11F is not bonded and
forms a mobile component that can move freely over the surface of
the hard carbon film 11E and hence the surface of the magnetic disk
11.
[0030] Thus, there is a tendency that the mobile component of the
lubricating film 11F is displaced in the radial direction of the
magnetic disk 11 toward the peripheral edge thereof as a result of
the centrifugal force caused by the high-speed rotation of the
magnetic disk. The mobile component thus displaced is accumulated
at the peripheral part of the magnetic disk and increases the disk
thickness of the peripheral part at the magnetic disk 11.
[0031] Thus, the existence of such a mobile component causes a
serious problem particularly in recent high-recording-density
magnetic disk drives in which the air gap formed between the
magnetic disk surface and the magnetic head is reduced and the
rotational speed of the magnetic disk is increased.
[0032] In order to reduce the proportion of the mobile component,
it is necessary increase the proportion of the bonded component in
the lubricating film 11F, and it has been proposed to form the
lubricating film 11F immediately after the formation of the hard
carbon film 11E such that the lubricating film 11F causes a
reaction with the reactive surface of the hard carbon film 11E.
However, the reactive surface of the hard carbon film 11E adsorbs a
large amount of impurities in the air within a short time after
formation of the hard carbon film 11E. Thus, such a process has
been not effective for reducing the mobile component.
[0033] Further, it has been proposed to activate the surface of the
hard carbon film 11E by a plasma process as disclosed in the
Japanese Laid-Open Patent Publications 62-150226 and 63-2117, or by
irradiating ozone ultraviolet radiation as taught in the Japanese
Laid Open Publications 4-6624 and 6-301970. However, there still
remains difficulty to increase the proportion of the bonded layer
in the lubricating film 11F in the magnetic disk of FIG. 3.
[0034] Further, it has been proposed in the Japanese Laid-Open
Patent Publication 7-262555 and 8-124142 to induce a reaction in
the lubricating film 11F to cause a bonding with the underlying
hard carbon film 11E by applying optical radiation to the
lubricating film 11F after deposition on the hard carbon film 11E
such that optically excited electrons form radicals that
facilitates the bonding reaction of the lubricating film 11F upon
the hard carbon film 11E.
[0035] However, such a process is effective only after optical
exposure conducted for a long period of time and the throughput of
production of the magnetic disk drive is deteriorated
substantially. Further, there is a risk in such an optical
radiation process in that the surface of the lubricating film 11F
may be oxidized as a prolonged optical exposure. When such
oxidation is caused, the friction at the surface of the lubricating
film 11F may be increased. Further, such optical processing is
conducted in the air and the chance that impurities in the air
contaminate the lubricating film 11F. When such contamination is
caused, there is a possibility that the impurities on the
lubricating film 11F may act as nuclei of water drop condensation
and the water drops act to collect further impurities in the form
of condensates. Thereby, the condensates may cause the problem of
increased drive torque of the magnetic disk due to increased
friction and further various problems such as contamination of the
magnetic head, deterioration of floating of the magnetic head,
corrosion of the magnetic head, and the like.
SUMMARY OF THE INVENTION
[0036] Accordingly, it is a general object of the present invention
to provide a novel and useful magnetic disk and a magnetic disk
drive wherein the foregoing problems are eliminated.
[0037] Another and more specific object of the present invention is
to provide a magnetic disk protected by a high-quality DLC film and
a magnetic disk drive using such a magnetic disk.
[0038] Another object of the present invention is to provide method
of producing a magnetic disk having an improved high-quality DLC
protective film.
[0039] Another object of the present invention is to provide a
magnetic disk drive, comprising:
[0040] a magnetic disk carrying a magnetic film, said magnetic disk
being rotatable about a rotational axis;
[0041] a motor causing said magnetic disk to rotate about said
rotational axis;
[0042] a swing arm pivoted on a pivot axis so as to scan a surface
of said magnetic disk generally in a radial direction thereof;
and
[0043] a magnetic head provided on said swing arm,
[0044] said magnetic disk carrying thereon a carbon film so as to
cover said magnetic film,
[0045] wherein said carbon film contains therein oxygen atoms such
that said oxygen atoms form any of an ether bonding or a carbonyl
bonding with carbon atoms constituting said carbon film.
[0046] Another object of the present invention is to provide a
magnetic disk drive, comprising:
[0047] a magnetic disk carrying a magnetic film, said magnetic disk
being rotatable about a rotational axis;
[0048] a motor causing said magnetic disk to rotate about said
rotational axis;
[0049] a swing arm pivoted on a pivot axis so as to scan a surface
of said magnetic disk generally in a radial direction thereof;
and
[0050] a magnetic head provided on said swing arm,
[0051] said magnetic disk carrying thereon a carbon film so as to
cover said magnetic film,
[0052] wherein said carbon film contains therein oxygen atoms and
nitrogen atoms.
[0053] Another object of the present invention is to provide a
magnetic disk comprising:
[0054] a substrate;
[0055] a magnetic film formed on said substrate; and
[0056] a carbon film covering said magnetic film,
[0057] said carbon film containing therein oxygen atoms such that
said oxygen atoms form any of an ether bonding or carbonyl bonding
with carbon atoms constituting said carbon film.
[0058] Another object of the present invention is to provide a
magnetic disk, comprising:
[0059] a substrate;
[0060] a magnetic film formed on said substrate; and
[0061] a carbon film covering said magnetic film,
[0062] said carbon film containing therein oxygen atoms and
nitrogen atoms.
[0063] Another object of the present invention is to provide a
method of making a magnetic disk, comprising the steps of:
[0064] depositing a magnetic film on a substrate; and
[0065] depositing a carbon film on said magnetic film,
[0066] said step of depositing said carbon film is conducted in a
plasma atmosphere containing an inert gas and oxygen.
[0067] According to the present invention, any insulating carbon
film formed on the surface of a carbon sputter target during a
sputtering process of the carbon film on the magnetic disk is
effectively removed by admixing oxygen into the plasma atmosphere.
As a result, the problem of the carbon film on the sputter target
surface causing a scattering to the magnetic disk surface as a
result of charge-up during the sputtering process is eliminated and
the yield of production of the magnetic disk is improved
substantially. The carbon film thus formed on the magnetic disk is
a DLC film and has a characteristic feature of containing oxygen
atoms in the form of either ether bonding or carbonyl bonding with
the carbon atoms that constitute the carbon film. In the case the
sputtering atmosphere contains oxygen and nitrogen, the DLC film
thus formed contains oxygen atoms and nitrogen atoms. In order to
prevent excessive decrease of the deposition rate of the carbon
film on the magnetic disk, it is preferable to control the oxygen
concentration in the sputtering atmosphere such that the carbon
film contains oxygen atoms in the range of 0.1-7%.
[0068] Another object of the present invention is to provide a
magnetic disk having an improved lubricating film and a magnetic
disk drive using such a magnetic disk.
[0069] Another object of the present invention is to provide a
method of producing an improved lubricating film of a magnetic
disk.
[0070] Another object of the present invention is to provide a
magnetic disk drive comprising:
[0071] a rotary magnetic disk;
[0072] a magnetic head scanning a surface of said rotary magnetic
disk in a state that said magnetic head is floated form said
surface of said rotary magnetic disk;
[0073] an arm carrying said magnetic head; and
[0074] a drive mechanism driving said arm,
[0075] wherein said magnetic disk carries a lubricating film
containing therein a photocrosslinking functional group, said
photocrosslinking functional group causing a crosslinking in said
lubricating film.
[0076] Another object of the present invention is to provide a
method of producing a magnetic disk, comprising the steps of:
[0077] coating a disk surface with a lubricating layer comprising
molecules having a photocrosslinking functional group;
[0078] causing a photocrosslinking in said molecules by applying an
optical radiation to said lubricating layer.
[0079] Another object of the present invention is to provide an
apparatus for producing a magnetic disk, comprising:
[0080] a disk holder adapted to hold a magnetic disk coated with a
lubricating film;
[0081] a processing chamber accommodating said disk holder, said
processing chamber applying a processing to said magnetic disk held
on said disk holder;
[0082] a far-ultraviolet optical radiation source provided in said
processing chamber so as to irradiate said lubricating film on said
magnetic disk with an optical radiation in the state that said
magnetic disk is held in said disk holder; and
[0083] a heat source provided in said processing chamber so as to
heat said magnetic disk in the state that said magnetic disk is
held in said disk holder,
[0084] wherein said far-ultraviolet source produces a monochromatic
ultraviolet radiation characterized by a half-width height of 15 nm
or less.
[0085] According to the present invention, it becomes possible to
reduce the proportion of the mobile components in the lubricating
film on the surface of the magnetic disk by using a lubricating
material containing a photocrosslinking functional group and
causing the lubricating material to form a gel, after applying the
lubricating material on the surface of the magnetic disk to form
the lubricating film, such that a photocrosslinking reaction takes
place in the molecules of the lubricating film. Such a crosslinking
reaction is caused as a result of exposure of the lubricating film
to the optical radiation having a wavelength corresponding to the
absorption wavelength of the photocrosslinking functional group. As
a result of the photocrosslinking reaction, the proportion of the
freely moving mobile component is reduced in the lubrication film,
and the problem of the mobile component moving toward the
peripheral part of the rotating magnetic disk to build up a thick
lubrication layer in such a peripheral part of the disk is
effectively eliminated. Thereby, the problem of head crashing is
eliminated even in such a case the air gap between the magnetic
disk surface and the magnetic head is reduced for high-density
recording of information.
[0086] Another object of the present invention is to provide a
fluorocarbon resin composition having, as an endcap group, a
tri-organosiylyl group not causing hydrolysis or dehydration
condensation, represented by a general formula ##STR1## wherein
R.sup.1, R.sup.2, R.sup.3 represent independently or commonly any
of an alkyl group, an aryl group and an aralkyl group, including
those substituted with halogen or nitrogen.
[0087] Another object of the present invention is to provide a
method of forming a fluorocarbon resin having an endcap group
represented by a formula ##STR2## (R.sup.1, R.sup.2, R.sup.3
represent independently or commonly any of an alkyl group, an aryl
group and an aralkyl group, including those substituted with
halogen or nitrogen),
[0088] said method comprising the step of:
[0089] silylzing a fluorocarbon resin having OH at an end gap group
by any of chlorosilane, silylamine and silylamide.
[0090] Another object of the present invention is to provide a
fluorocarbon resin having an endcap group represented by a formula
##STR3## wherein R.sup.4, R.sup.5 and R.sup.6 represent commonly or
independently a hydrogen atom or an organic group, at least one of
said groups R.sup.4-R.sup.6 being an organic group),
[0091] said endcap group having eight or more electrons.
[0092] According to the present invention, a lubricating film
having a high bonding rate to an underlying magnetic disk surface
is obtained by using a fluorocarbon resin without using polar
endcap groups in the lubricating film. Because of elimination of
the use of polar endcap groups, the problem of coagulation, which
tends to occur in the conventional lubricating film that uses polar
endcap groups in the resin, is effectively eliminated. In order to
achieve a strong adherence to the underlying disk surface, the
present invention uses non-polar endcap groups such that the endcap
groups contain .pi. electrons. Preferably, the non-polar endcap
group contains at least eight .pi. electrons. Because of the
improved bonding rate, the lubricating film remains on the surface
of the magnetic disk without lateral displacement, even in such a
case the magnetic disk is rotated at a high speed. Further, the
lubricating film thus formed effectively reduces the friction of
the surface of the magnetic disk.
[0093] Other objects and further features of the present invention
will become apparent from the following detailed description when
read in conjunction with the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0094] FIG. 1 is a diagram showing the construction of a magnetic
disk drive according to a related art;
[0095] FIG. 2 is another diagram showing the construction of the
magnetic disk drive of FIG. 1;
[0096] FIG. 3 is a diagram showing the cross-sectional view of a
magnetic disk according to a related art;
[0097] FIG. 4 is a diagram showing the construction of a sputtering
apparatus used for producing a magnetic disk according to a related
art;
[0098] FIG. 5 is a diagram showing the construction of a sputtering
apparatus used for producing a magnetic disk according to a first
embodiment of the present invention;
[0099] FIGS. 6A and 6B are diagrams showing the construction of a
magnetic disk according to the first embodiment of the present
invention;
[0100] FIGS. 7A-7D are diagrams showing the occurrence of arc
events with time during the sputtering process to form a DLC film
according to the first embodiment of the present invention;
[0101] FIGS. 8A-8C are further diagrams showing the occurrence of
arc events with time during the sputtering process to form a DLC
film according to the first embodiment of the present
invention;
[0102] FIG. 9 is a diagram showing the relationship between the
deposition rate of a DLC film and oxygen concentration in the
sputtering atmosphere according to the first embodiment of the
present invention;
[0103] FIG. 10 is another diagram showing the relationship between
the deposition rate of a DLC film and oxygen concentration in the
sputtering atmosphere according to the first embodiment of the
present invention;
[0104] FIG. 11 is a diagram showing the relationship between the
magnetization of a magnetic film and oxygen concentration in the
sputtering atmosphere used for forming a DLC film according to the
first embodiment of the present invention;
[0105] FIG. 12 is a diagram showing the relationship between the
magnetization of a magnetic film and oxygen concentration in the
sputtering atmosphere used for forming a DLC film according to the
first embodiment of the present invention;
[0106] FIG. 13 is a diagram showing the relationship between the
oxygen concentration level in a DLC film and the oxygen content in
the sputtering atmosphere used for forming the DLC film according
to the first embodiment of the present invention;
[0107] FIG. 14 is a diagram showing the construction of a magnetic
disk drive according to a second embodiment of the present
invention in an oblique view;
[0108] FIG. 15 is a diagram showing the construction of a magnetic
disk used in the magnetic disk drive of FIG. 14 according to the
second embodiment of the present invention in a cross-sectional
view;
[0109] FIGS. 16A-16C are diagrams showing the construction of an
apparatus used for causing a photocrosslinking reaction in a
lubricating film provided on a magnetic disk according to the
second embodiment of the present invention; and
[0110] FIG. 17 is a diagram showing the construction of a magnetic
disk according to a third embodiment of the present invention in a
cross-sectional view.
DETAILED DESCRIPTION OF THE INVENTION
First Embodiment
[0111] FIG. 5 shows the construction of a d.c. magnetron sputtering
apparatus 30 used for forming a DLC film in a first embodiment of
the present invention, wherein those parts corresponding to the
parts described previously are designated by the same reference
numerals.
[0112] Referring to FIG. 5, the sputtering apparatus 30 has a
construction similar to the sputtering apparatus 20 of FIG. 4
except that the sputtering apparatus 30 includes additional
mass-flow controller 24C and a line 24D for supplying oxygen into
the processing chamber 21.
[0113] Thus, by using the sputtering apparatus 30 of FIG. 5, it
becomes possible to carry out a sputtering process in a plasma
atmosphere containing oxygen radical, wherein the oxygen radical
thus formed in the processing chamber 21 immediately reacts with
and removes any DLC film or DLC particles that are formed on the
surface of the graphite target 23A or 23B in correspondence to the
central region thereof where the plasma density is low.
[0114] Thus, the problem of charged-up particles causing scattering
and contaminating the surface of the substrate 22, on which
deposition of a DLC film is to be made, is eliminated, and the
yield of production of the magnetic disk is improved.
[0115] FIG. 6A shows the cross-sectional structure of a magnetic
disk 31 formed by the d.c. magnetron sputtering apparatus 30 of
FIG. 5, wherein those parts of FIG. 6A explained already with
reference to preceding drawings are designated by the same
reference numerals and the description thereof will be omitted.
[0116] Referring to FIG. 6A, the illustrated structure is obtained
when the d.c. sputtering apparatus of FIG. 5 is operated under the
condition that the internal pressure of the processing chamber 21
is set to 0.665 Pa (5 mTorr) wherein an Ar gas mixture containing
10% of CH.sub.4 is supplied to the processing chamber 21 from the
line 24B via the mass-flow controller 24A with a flow-rate of 99
SCCM simultaneously with an oxygen gas, which is supplied from the
line 24D via the mass-flow controller 24C with a flow-rate of 1
SCCM. The flow-rate ratio of the gas supplied from the line 24B to
the gas supplied from the line 24D can be changed variously within
a preferable range.
[0117] Referring to FIG. 6A, the magnetic disk 31 has a
cross-sectional structure similar to the one of the magnetic disk
11 explained with reference to FIG. 3 except that a DLC film 31E
having a structure as represented in FIG. 6B is formed in place of
the DLC film 11E of FIG. 3. As represented in FIG. 6B, oxygen atoms
form an ether bonding or carbonyl bonding with respect to the C
atoms in the DLC film 31E.
[0118] FIGS. 7A-7D represent the number of arc events per minute
during the deposition process of the DLC film 31E in the processing
chamber 21 for various gas-flow-rate ratios of the Ar/CH.sub.4
mixed gas to the oxygen gas supplied respectively via the lines 24B
and 24D. It should be noted that such arc is caused as a result of
charge-up of the insulating DLC film formed on the graphite target
23A or 23B and is interpreted as representing the number of DLC
particles deposited on the target. Thus, it is interpreted that
increase of the arc events indicates an increase of the DLC
particles deposited on the target.
Experiment 1 (Comparative Experiment)
[0119] FIG. 7A shows the observed arc events in the sputtering
apparatus 30 of FIG. 5 for the case in which the line 24D is
closed. Thus, the experiment of FIG. 7A represents a comparative
experiments corresponding to the conventional deposition process of
the DLC film 11E conducted by using the sputtering apparatus 20 of
FIG. 4. In the experiment of FIG. 7A, the internal pressure of the
processing chamber 21 was set to 0.665 Pa as noted before and the
deposition was made under the d.c. electric power to 1.5 kW while
flowing the Ar/CH.sub.4 mixed gas with a flow-rate of 100 SCCM. The
deposition was conducted continuously for 36 hours. Under such
condition, a deposition rate of 1.99 nm/second was obtained.
[0120] Referring to FIG. 7A, it can be seen that occurrence of the
arc event is observed already only after 3 hours from the start of
the deposition and the number of the arc events per minute
increases thereafter with time. The result of FIG. 7A indicates
that it is necessary to conduct a cleaning process of the target
every two or three hours when the DLC film 11E is to be formed
according to the conventional process. Such a frequent cleaning
process naturally causes a decrease in the throughput of production
of the magnetic disk.
[0121] After the experiment of FIG. 7A, the surface resistivity was
measured for the targets 23A and 23B and it was indicated that the
targets 23A and 23B have a resistivity of
0.7.times.10.sup.-2-1.0.times.10.sup.-2 .OMEGA.cm in the eroded
region thereof. Outside the eroded region, a resistivity exceeding
the upper detectable limit value of 2.0.times.10.sup.5 .OMEGA.cm
was observed. This result clearly indicates the existence of an
insulating film on the surface of the target.
[0122] As a result of the XPS analysis conducted on the DLC film
thus formed on the substrate 22, it was confirmed that the DLC film
contains oxygen atoms with a ratio of less than 0.0005 with respect
to the number of the carbon atoms contained in the DLC film. This
result of the XPS analysis indicates that the content of oxygen in
the sputtering atmosphere is substantially zero in the experiment
of FIG. 7A.
Experiment 2
[0123] FIG. 7B shows the observed arc events per minute for the
experiment in which the deposition of the DLC film 31E is conducted
on the substrate 22 under a condition similar to the case of the
experiment of FIG. 7A, except that an oxygen gas is supplied to the
processing chamber 21 from the line 24D with a flow-rate of 1 SCCM
in addition to the mixed gas of Ar/CH.sub.4 supplied with a
flow-rate of 99 SCCM from the line 24B. Thus, in the experiment of
FIG. 7B, the sputtering atmosphere contains 1 of oxygen in terms of
flow-rate, and a deposition rate of 1.96 nm/second was obtained for
the DLC film 31E on the substrate 22.
[0124] Referring to FIG. 7B, it can be seen that occurrence of the
arc event is successfully and effectively suppressed as a result of
addition of oxygen to the sputtering atmosphere. While a few arc
events are recognized after ten hours from the start of the
deposition, no appreciable increase of the arc events is observed
until 25 hours from the start of the deposition.
[0125] The result of FIG. 7B clearly indicates that addition of a
small amount of oxygen to the sputtering gas can effectively
suppress the formation of insulating deposits, primarily formed of
DLC, on the surface of the target 23A or 23B, and the yield of the
DLC film 31E on the substrate 22 is improved together with the
quality. In the experiment of FIG. 7B, it should be noted that the
number of the arc events after 36 hours is only 6 times per
minute.
[0126] After the experiment of FIG. 7B, the surface resistivity was
measured for the targets 23A and 23B and a value of
2.5.times.10.sup.-2-2.7.times.10 .OMEGA.cm was observed for the
entire surface region thereof. Further, the XPS analysis of the DLC
film 31E on the substrate 22 revealed the existence the oxygen
atoms with an atomic ratio of 0.001 with regard to the carbon atoms
in the DLC film 31E.
Experiment 3
[0127] FIG. 7C shows the observed arc events per minute for the
experiment in which the deposition of the DLC film 31E is conducted
on the substrate 22 under a condition similar to the case of the
experiment of FIG. 7A or FIG. 7B, except that an oxygen gas is
supplied to the processing chamber 21 from the line 24D with a
flow-rate of 10 SCCM in addition to the mixed gas of Ar/CH.sub.4
supplied with a flow-rate of 90 SCCM from the line 24B. Thus, in
the experiment of FIG. 7C, the sputtering atmosphere contains 10%
of oxygen in terms of flow-rate, and a deposition rate of 1.76
nm/second was obtained for the DLC film 31E on the substrate
22.
[0128] Referring to FIG. 7C, it can be seen that occurrence of the
arc event is successfully and effectively suppressed as a result of
addition of oxygen to the sputtering atmosphere. While a few arc
events are recognized after 36 hours from the start of the
deposition, no arc event was observed at all until 30 hours from
the start of the deposition.
[0129] The result of FIG. 7C clearly indicates that addition of a
small amount of oxygen to the sputtering gas can effectively
suppress the formation of insulating deposits, primarily formed of
DLC, on the surface of the target 23A or 23B, and the yield of the
DLC film 31E on the substrate 22 is improved, together with the
quality. In the experiment of FIG. 7C, it should be noted that the
number of the arc events after 36 hours is only 0.5 times per
minute.
[0130] After the experiment of FIG. 7C, the surface resistivity was
measured for the targets 23A and 23B and a value of
8.times.10.sup.-3-2.5.times.10.sup.-2 .OMEGA.cm was observed for
the entire surface region thereof. Further, the XPS analysis of the
DLC film 31E on the substrate 22 revealed the existence the oxygen
atoms with an atomic ratio of 0.014 with regard to the carbon atoms
in the DLC film 31E.
Experiment 4
[0131] FIG. 7D shows the observed arc events per minute for the
experiment in which the deposition of the DLC film 31E is conducted
on the substrate 22 under a condition similar to the case of the
experiment of FIG. 7A-FIG. 7C, except that an oxygen gas is
supplied to the processing chamber 21 from the line 24D with a
flow-rate of 50 SCCM in addition to the mixed gas of Ar/CH.sub.4
supplied with a flow-rate of 50 SCCM from the line 24B. Thus, in
the experiment of FIG. 7D, the sputtering atmosphere contains 50%
of oxygen in terms of flow-rate, and a deposition rate of 1.76
nm/second was obtained for the DLC film 31E on the substrate
22.
[0132] Referring to FIG. 7D, it can be seen that occurrence of the
arc event is successfully and effectively suppressed as a result of
addition of oxygen to the sputtering atmosphere, and no arc event
was observed at all even after 35 hours from the start of the
deposition.
[0133] The result of FIG. 7D clearly indicates that addition of
oxygen to the sputtering gas up to the proportion of 50% can
effectively suppress the formation of insulating deposits,
primarily formed of DLC, on the surface of the target 23A or 23B,
and the yield of the DLC film 31E on the substrate 22 is improved,
together with the quality. In the experiment of FIG. 7D, it should
be noted that the number of the arc events after 36 hours is only
0.05 times per minute.
[0134] After the experiment of FIG. 7D, the surface resistivity was
measured for the targets 23A and 23B and a value of
8.times.10.sup.-3 .OMEGA.cm was observed for the entire surface
region thereof. Further, the XPS analysis of the DLC film 31E on
the substrate 22 revealed the existence the oxygen atoms with an
atomic ratio of 0.07 with regard to the carbon atoms in the DLC
film 31E.
Experiment 5 (Comparative Experiment)
[0135] FIG. 8A shows the observed arc events in the sputtering
apparatus 30 of FIG. 5 for the case in which the line 24D is
closed. Thus, the experiment of FIG. 8A represents a comparative
experiments corresponding to the conventional deposition process of
the DLC film 11E conducted by using the sputtering apparatus 20 of
FIG. 4, similarly to the experiment of FIG. 7A. In the experiment
of FIG. 8A, the internal pressure of the processing chamber 21 was
set to 0.665 Pa as noted before and the deposition was made under
the d.c. electric power to 1.5 kW while flowing a mixed gas of
Ar/H.sub.2 in place of the Ar/CH.sub.4 mixed gas such that the
Ar/H.sub.2 mixed gas contains H.sub.2 with a proportion of 20%. The
flow rate of the Ar/H.sub.2 mixed gas was set to 100 SCCM and the
deposition was conducted continuously for 36 hours.
[0136] Referring to FIG. 8A, it can be seen that arc events are
observed already after only 2 hours from the start of the
deposition and that the number of the arc events per minute
increases thereafter with time. The result of FIG. 8A indicates
that it is necessary to conduct a cleaning process of the target
every two or three hours when the DLC film 11E is to be formed
according to the process of FIG. 8A. Such a frequent cleaning
process naturally causes a decrease in the throughput of the
production of the magnetic disk.
[0137] After the experiment of FIG. 8A, the surface resistivity was
measured for the targets 23A and 23B and it was indicated that the
targets 23A and 23B have a resistivity of
0.7.times.10.sup.-3-1.3.times.10.sup.-2 .OMEGA.cm in the eroded
region thereof. Outside the eroded region, a resistivity exceeding
the upper detectable limit of 2.0.times.10.sup.5 .OMEGA.cm was
observed. This result indicates the existence of insulating film on
the surface of the target.
Experiment 6
[0138] FIG. 8B shows the observed arc events per minute for the
experiment in which the deposition of the DLC film 31E is conducted
on the substrate 22 under a condition similar to the case of the
experiment of FIG. 8A, except that an oxygen gas is supplied to the
processing chamber 21 from the line 24D with a flow-rate of 10 SCCM
in addition to the mixed gas of Ar/H.sub.2 supplied with a
flow-rate of 90 SCCM from the line 24B. Thus, in the experiment of
FIG. 8B, the sputtering atmosphere contains 10% of oxygen in terms
of flow-rate.
[0139] Referring to FIG. 8B, it can be seen that occurrence of the
arc event is successfully and effectively suppressed as a result of
addition of oxygen to the sputtering atmosphere, and the occurrence
of the arc event is only about 0.2 times/minute after 35 hours from
the start of the deposition.
[0140] The result of FIG. 8B clearly indicates that addition of a
small amount of oxygen to the sputtering gas can effectively
suppress the formation of insulating deposits, primarily formed of
DLC, on the surface of the target 23A or 23B, and the yield of the
DLC film 31E on the substrate 22 is improved together with the
quality.
[0141] After the experiment of FIG. 8B, the surface resistivity was
measured for the targets 23A and 23B and a value of
6.times.10.sup.-3-1.6.times.10.sup.-2 .OMEGA.cm was observed for
the entire surface region thereof. Further, the XPS analysis of the
DLC film 31E on the substrate 22 revealed the existence the oxygen
atoms with an atomic ratio of 0.01 with regard to the carbon atoms
in the DLC film 31E.
Experiment 7
[0142] FIG. 8C shows the observed arc events per minute for the
experiment in which the deposition of the DLC film 31E is conducted
on the substrate 22 under a condition similar to the case of the
experiment of FIGS. 8A and 8B, except that an oxygen gas is
supplied to the processing chamber 21 from the line 24D with a
flow-rate of 50 SCCM in addition to the mixed gas of Ar/H.sub.2
supplied with a flow-rate of 50 SCCM from the line 24B. Thus, in
the experiment of FIG. 8C, the sputtering atmosphere contains 50%
of oxygen in terms of flow-rate.
[0143] Referring to FIG. 8C, it can be seen that occurrence of the
arc event is successfully and effectively suppressed as a result of
addition of oxygen to the sputtering atmosphere, and the occurrence
of the arc event is only about 0.09 times/minute after 36 hours
from the start of the deposition.
[0144] The result of FIG. 8C clearly indicates that addition of a
small amount of oxygen to the sputtering gas can effectively
suppress the formation of insulating deposits, primarily formed of
DLC, on the surface of the target 23A or 23B, and the yield of the
DLC film 31E on the substrate 22 is improved together with the
quality.
[0145] After the experiment of FIG. 8C, the surface resistivity was
measured for the targets 23A and 23B and a value of
6.times.10.sup.-3-1.0.times.10.sup.-2 .OMEGA.cm was observed for
the entire surface region thereof. Further, the XPS analysis of the
DLC film 31E on the substrate 22 revealed the existence the oxygen
atoms with an atomic ratio of 0.04 with regard to the carbon atoms
in the DLC film 31E.
[0146] The result of the experiments 1-4 explained before also
indicates a decrease of the deposition rate of the DLC film 11E or
31E formed on the substrate 22 with increasing oxygen content in
the sputtering atmosphere. It is believed that this tendency is
caused as a result of the oxidation of the DLC film formed on the
substrate 22. A similar tendency was confirmed also in the
experiments 5-7.
[0147] FIG. 9 shows the relationship between the rate of the DLC
film on the substrate 22 and the oxygen concentration of the
sputtering gas, wherein the experiment of FIG. 9 was conducted
under a condition slightly different from the condition of the
experiments 1-4.
[0148] Referring to FIG. 9, it can be seen that the deposition rate
of the DLC film decreases generally linearly with the oxygen
concentration in the sputtering gas from the initial value of about
1.6 nm/second to the value of 1.3 nm/second or less in the case the
sputtering gas contains oxygen with a proportion of 50%. From the
relationship of FIG. 9, it is concluded that the preferable oxygen
concentration in the sputtering gas does not exceed 50% in the case
a gas mixture of Ar/CH.sub.4 is used for the sputtering gas.
[0149] FIG. 10 shows the relationship between the deposition rate
and the oxygen concentration in the sputtering gas corresponding to
the experiments 5-7 explained before, wherein the experiment of
FIG. 10 is conducted under a condition slightly difference from the
condition of the experiments 5-7.
[0150] Referring to FIG. 10, it can be seen that the deposition
rate of the DLC film decreases generally linearly with the oxygen
concentration in the sputtering gas from the initial value of about
1.7 nm/second to the value of about 1.2 nm/second in the case the
sputtering gas contains oxygen with a proportion of 50%. From the
relationship of FIG. 10, it is concluded that the preferable oxygen
concentration in the sputtering gas does not exceed 50% also in the
case a gas mixture of Ar/H.sub.2 is used for the sputtering
gas.
[0151] On the other hand, the requirement to guarantee no arc
occurrence during the process of growing a DLC film to have a
thickness of 20 nm, in other words the requirement to guarantee
that the frequency of occurrence of the arc event is less than once
in ten seconds during the sputtering process of the DLC film,
imposes a condition that the oxygen concentration in the sputtering
gas should be at least equal to or larger than 1% in any of the
Ar/CH.sub.4 mixture or Ar/H.sub.2 mixture.
[0152] Meanwhile, the process of forming the DLC film 31E by a
sputtering process conducted in an atmosphere containing oxygen as
proposed in the present invention involves a step of causing the
magnetic film on the magnetic disk to make a contact with the
sputtering gas containing oxygen. Thus, there arises a concern that
the performance of the magnetic film of the magnetic disk may be
degraded as a result of such an exposure of the magnetic film to
the sputtering gas containing oxygen. Thus, the inventor of the
present invention has conducted an investigation with regard to the
effect of oxygen in the sputtering gas on the magnetization of the
magnetic film 11D on the magnetic disk 11.
[0153] FIG. 11 shows the magnetization of the magnetic film 11D for
the case in which the DLC film 31E of FIG. 6A is formed in the
sputtering gas of the Ar/CH.sub.4 mixture added with various
amounts of oxygen (O.sub.2).
[0154] Referring to FIG. 11, it can be seen that the magnetization
of the magnetic film 11E underneath the DLC film 31E is
substantially constant irrespective of the oxygen concentration in
the sputtering gas and takes a value of about 2600 Oe (205400 A/m)
as long as the oxygen concentration is in the range between 0% and
50%.
[0155] FIG. 12 shows the magnetization of the magnetic film 11D in
the case the DLC film 31E is formed in a sputtering gas of the
Ar/H.sub.2 gas mixture containing various amounts of oxygen.
[0156] Again, FIG. 12 shows that no substantial change of
magnetization occurs even when the oxygen concentration in the
sputtering gas is changed variously within the range of 0-50%.
[0157] FIG. 13 shows the relationship between the oxygen
concentration in the sputtering atmosphere and the oxygen
concentration in the DLC film 31E thus formed as a result of the
sputtering, wherein the oxygen concentration in the DLC film 31E is
represented in terms of the ratio of the oxygen atoms to the carbon
atoms constituting the DLC film 31E.
[0158] Referring to FIG. 13, it can be seen that the oxygen
concentration in the DLC film 31E increases generally linearly with
increasing oxygen concentration in the DLC film 31E, although there
is a slight difference in the rate of increase between the case the
oxygen gas is added to the Ar/CH.sub.4 gas mixture and the case the
oxygen gas is added to the Ar/H.sub.2 mixture. As noted previously,
the DLC film 31E contains oxygen atom with a concentration of 0.1
atomic percent in the case the oxygen concentration in the
Ar/CH.sub.4 sputtering gas is about 1%. In the case the oxygen
concentration in the Ar/CH.sub.4 mixed sputtering gas is 50%, the
DLC film 31E contains oxygen atoms with a concentration of about 7
atomic percent.
[0159] In the case the Ar/H.sub.2 mixed gas is used for the
sputtering gas, the DLC film 31E contains about 0.1 atomic percent
of oxygen atoms when the DLC film 31E is formed in the sputtering
gas atmosphere containing 1% of oxygen, while the DLC film 31E
contains oxygen with a concentration of about 4 atomic percent when
the DLC film 31E is formed in the sputtering gas atmosphere
containing 50% of oxygen.
[0160] In the present embodiment, it is also possible to use other
oxygen source such as NO or NO.sub.2 in place of the O.sub.2 gas
for supplying oxygen to the sputtering atmosphere. When such a gas
containing nitrogen in addition to oxygen is used, the DLC film 31E
thus formed contains nitrogen atoms in addition to the oxygen
atoms.
[0161] By using the magnetic disk 31 of FIG. 6A in the magnetic
disk drive of FIG. 1, it becomes possible to produce the magnetic
disk drive with reduced cost and improved yield.
Second Embodiment
[0162] FIG. 14 shows the construction of a magnetic disk drive 50
according to a second embodiment of the present invention.
[0163] Referring to FIG. 14, the magnetic disk drive 50 is a
so-called hard disk drive and includes a magnetic disk 40 rotated
by a rotary hub 40A and an arm 52A provided adjacent to the
magnetic disk 40, wherein the arm 52A is driven by a voice coil
motor 52 about a rotary shaft 52B and scans the surface of the
magnetic disk 40 generally in the radial direction thereof. The
swing arm 52A carries a slider 53 at a tip end part thereof and the
slider 53 carries a magnetic head 51 thereon. The magnetic disk
drive 50 having such a construction is accommodated in a closed
enclosure. In the illustrated example, a number of the magnetic
disks 40 are mounted on the hub 40A coaxially.
[0164] FIG. 15 shows the cross-sectional structure of the magnetic
disk 40.
[0165] Referring to FIG. 15, the magnetic disk 40 has a
construction similar to that of the magnetic disk 31 of FIG. 6A and
includes a disk substrate 41A typically of Al, a foundation layer
41B of NiP formed on the disk substrate 41A, a magnetic film 41C
formed on the foundation layer 41B and a hard carbon protective
film 41D formed on the magnetic film 41C for protecting the
magnetic film 41C, wherein the DLC film 31E explained before with
reference to the previous embodiment may be used for the hard
carbon film 41D. Alternately, the hard carbon film 41D may be
formed of a DLC film deposited by a CVD process typically with a
thickness of less than 8 nm.
[0166] In the magnetic disk 40 of FIG. 15, it should be noted that
the hard carbon protective film 41D is further covered by a
lubricating film 41E, wherein the lubricating film 41E is formed of
a fluorocarbon resin preferably containing a polar group such as
OH.
[0167] In the present embodiment, it should be noted that the
lubricating film 41E is formed of a fluorocarbon resin having an
photocrosslinking functional group containing 2-30 carbon atoms
such as alkenyl group, alkyl halide group, aryl halide group, aryl
azide group, piperonyl group, epoxy group, and the like, as the
endcap group at the end or side chain of the resin skeleton.
[0168] The molecules constituting the lubricating film and
containing such a functional group are crosslinked as a result of
irradiation of optical radiation (far-ultraviolet radiation) having
a wavelength corresponding to the absorption wavelength of the
functional group. As a result of such an photocrosslinking
reaction, the proportion of the non-crosslinked molecules, which
form the mobile layer in the lubricating film 41E, is reduced and
the problem of the lubricating film 41E increases the thickness at
the peripheral part of the magnetic disk is eliminated.
[0169] It is preferable that the resin constituting the lubricating
film 41E has a fluorocarbon skeleton, particularly a
perfluoro-polyether skeleton, and the foregoing photocrosslinking
functional group is introduced to the end or side chain of the
skeleton. Thereby, it is preferable that the resin constituting the
lubricating film 41E has an average molecular weight, represented
in terms of the molecular weight of polymethyl methacrylate in
gel-permeation chromatography, of 1200 or more, preferably 2000 or
more.
[0170] The wavelength of the optical radiation used for causing the
desired crosslinking changes depending on the functional group
used. In the case a chloromethylphenylethyl group is used for the
photocrosslinking functional group, an ArF excimer radiation of the
wavelength of 193 nm can be used for causing the photocrosslinking.
In the event a piperonyl group is used, a Xe.sub.2 excimer
radiation having a wavelength of 172 nm can be used. Further, a
F.sub.2 excimer radiation having a wavelength of 157 nm can be used
when a vinyl group is used for the photocrosslinking functional
group.
[0171] It should be noted that these excimer radiation has a very
sharp spectrum characterized by a half-height width of 15 nm or
less, and the desired photocrosslinking reaction can be induced
efficiently.
[0172] Generally, it is possible to use any of KrF, ArF, XeCl,
KrCl, Xe.sub.2, F.sub.2, Kr and Ar excimer radiation depending on
the optical absorption wavelength or photochemical reaction
mechanism of the photocrosslinking functional group.
[0173] It should be noted that the foregoing promotion of the
crosslinking reaction in the lubricating film 41E can be achieved
not only by the irradiation of the far-ultraviolet radiation but
also by irradiation of electron beam or X-ray. In this case, it is
possible to use alkenyl group or aryl halide group for the
photocrosslinking functional group.
[0174] As will be explained with reference to other embodiment, the
crosslinking reaction can be promoted by applying a heat treatment
at the temperature of 30-300.degree. C., preferably 80-150.degree.
C., at the time of the photocrosslinking reaction. When the
photocrosslinking reaction is conducted at the temperature lower
than the foregoing temperature range, the effect of crosslinking
becomes insufficient, while the magnetic performance of the
magnetic film 41C may be deteriorated when the crosslinking
reaction is conducted at the temperature higher than the foregoing
preferable range.
[0175] During such an photocrosslinking reaction conducted in the
elevated temperature environment, it is preferable to suppress the
oxygen content in the atmosphere to be less than about 10 ppm,
preferably less than about 1 ppm, in order to suppress the effect
of ozone oxidation and to promote pure crosslinking reaction.
[0176] By controlling the atmosphere of the photocrosslinking
reaction, a hydrophobic surface characterized by a contact angle of
100.degree. or more with respect to water is obtained for the
lubricating film 41E. When the contact angle is smaller than
100.degree., there appears a tendency that the a large water
droplet is formed on the surface of the lubricating film 41E when
the magnetic disk drive is used in a high temperature and high
humidity environment, while such a large water droplet causes the
problem of contamination or corrosion of the magnetic head.
[0177] FIGS. 16A-16C show the construction of an apparatus 60 used
in the present invention for carrying out the photocrosslinking
reaction of the lubricating film 41E, wherein FIG. 16A shows an
oblique view, FIG. 16B shows a side view and FIG. 16C shows a front
view.
[0178] Referring to FIG. 16A, the reaction apparatus includes a
reaction chamber 61 in which the photocrosslinking reaction is
carried out and a transport system 62 transporting the magnetic
disks 40 of FIG. 15 to and away from the reaction chamber 61. The
transport system 62 includes a cassette 62A accommodating the
magnetic disks 40 to be processed, wherein the cassette 62A
transports the magnetic disks 40 in the direction represented in
FIG. 16A by an arrow A in the state that the magnetic disks 40 are
accommodated in the cassette 62A.
[0179] Further, it should be noted that the transport system 62
includes a number of arms 62B adapted to hold the magnetic disks 40
in the cassette 62A in such a manner that each arm 62B is movable
in the direction represented by an arrow B. Thereby, the magnetic
disk 40 held on the arm 62B is inserted into the reaction chamber
61 as the arm 62B is moved toward the reaction chamber 61 in the
direction B. Thus, the magnetic disks 40 held in the cassette 62
are inserted into the reaction chamber 61 one by one by the arm 62B
as the cassette 62 is moved in the direction A.
[0180] It should be noted that the reaction chamber 61 has a
laterally elongated shape and thus, the reaction chamber 61 can
process a plurality of magnetic disks 40 in parallel. The reaction
chamber 61 is equipped with an optical source 61A of the
far-ultraviolet radiation used to cause the photocrosslinking
reaction in the lubricating film 41E formed on the surface of the
magnetic disk 40 and an infrared optical source 61B for
facilitating the photocrosslinking reaction. Each of the
far-ultraviolet optical source 61A and the infrared optical source
61B extends laterally in the elongating direction of the reaction
chamber 61.
[0181] In operation, the reaction chamber 61 is supplied with a
nitrogen gas from an inlet line 61C having a temperature regulator
for controlling the temperature of the nitrogen gas to be supplied
to the reaction chamber 61. The nitrogen gas thus introduced via
the line 61C fills the reaction chamber 61 and is exhausted from an
outlet line 62B, wherein the atmosphere in the reaction chamber 61
is controlled as a result of filling of the reaction chamber 61 by
the nitrogen gas such that the oxygen concentration in the reaction
chamber 61 is below about 10 ppm.
[0182] Referring to FIGS. 16B and 16C, the cassette 62A is moved in
the direction A by a belt-conveyer mechanism 62C and the arm 62B is
inserted into the cassette 62A from the lower side of the
belt-conveyer mechanism in the upward direction. As the arm 62B is
lifted in the upward direction, the arm 62B holds a magnetic disk
40 in the cassette 62A and lifts the disk 40 further in the upward
direction into the reaction chamber 61.
[0183] In the reaction chamber 61, it should be noted that the
far-ultraviolet radiation source 61A includes a far-ultraviolet
lamp 61a such as an excimer lamp and a cooperating reflector 61b,
while the infrared radiation source 61B includes an infrared lamp
61c and a cooperating reflector 61d. In the construction of FIGS.
16A-16C, the infrared radiation source 61B is disposed underneath
the far-ultraviolet radiation source 61A and heats the magnetic
disk 40 held by the arm 62B to a desired temperature prior to the
crosslinking processing conducted by the far-ultraviolet radiation
source 61A.
[0184] As can be seen from the side view of FIG. 16B, the
far-ultraviolet radiation source 61A and the infrared radiation
source 61B are provided in the processing chamber 41 so as to
irradiate the topside and bottom side of the magnetic disk 40 by
the far-ultraviolet radiation and the infrared radiation. A
commercially available excimer lamp such as model UER-200-172
supplied by Ushio Electric Co., Ltd. can be used for the
far-ultraviolet radiation source 61A, wherein the foregoing excimer
lamp can emit a far-ultraviolet radiation of the wavelength of 172
nm with a half-height width of 14 nm. In the illustrated example,
the far-ultraviolet radiation source 61A is disposed with a
separation of about 5 mm from the surface of the magnetic disk 40.
By using the far-ultraviolet radiation source 61A, it becomes
possible to conduct irradiation of the far-ultraviolet radiation to
the surface of the magnetic disk 40 within a variation of 15% in
the case the magnetic disk 40 is a 3.5-inch magnetic disk.
[0185] Next, experiments of the photocrosslinking reaction
conducted by the apparatus of FIGS. 16A-16C will be explained
below.
Experiment 8
[0186] In this experiment, the magnetic disk 40 having a structure
as represented in FIG. 15 is formed by using an Al disk as the
substrate 41A, wherein the substrate 41A is covered with the
foundation layer 41B of NiP by conducting a plating process. The
surface of the NiP film 41B thus formed is then subjected to a
polishing process such that the NiP film 41B has a surface
roughness Ra of about 6.5 nm. Further, the magnetic film 41C is
formed by depositing a Cr film or a CoCrTa film on the NiP film 41B
by a d.c. magnetron sputtering process conducted in an Ar
atmosphere, and a DLC film is deposited on the magnetic film 41C by
a CVD process as the hard carbon protective layer 41D with a
thickness of about 8 nm.
[0187] After the magnetic disk 40 is thus prepared, the lubricating
film 41E is formed on the protective film 41D by coating a
perfluoro polyether film having a piperonyl group at the end of the
resin skeleton, wherein the magnetic disk 40 thus formed with the
lubricating film 41E is introduced into the reaction chamber 61 of
the processing apparatus of FIGS. 16A-16C for photocrosslinking
reaction of the lubricating film 41E.
[0188] In the reaction chamber 41, there is formed a nitrogen
atmosphere controlled such that the oxygen content in the nitrogen
atmosphere is less than about 10 ppm, and the magnetic disk 40 is
exposed to the far-ultraviolet radiation of the wavelength of 172
nm produced by a Xe.sub.2 excimer lamp, which is used for the
far-ultraviolet radiation source 61a, at room temperature with a
dose of 800 mJ/cm.sup.2 for a duration of about 100 seconds.
[0189] After the foregoing photocrosslinking reaction, the
thickness of the lubricating film 41E was measured, and the
magnetic disk 40 thus processed was further immersed into a solvent
(FC-77 of 3M) so as to dissolve the unreacted mobile layer into the
solvent. After the foregoing treatment in the solvent, the
thickness of the lubricating film 41E was again measured.
[0190] As a result of the measurement conducted after the treatment
in the solvent, it was found that the initial thickness of 1.4 nm
of the lubricating film 41E is decreased slightly to 1.38 nm,
indicating that the bonding ratio, defined as a ratio of thickness
of the lubricating film before and after the solvent treatment, is
98.5% for the lubricating form of the present experiment. The
foregoing bonding ratio corresponds to the gel ratio of the
lubricating film 41E.
Experiment 9
[0191] In this experiment, a magnetic disk carrying a perfluoro
polyether lubricating film having the piperonyl group at the end of
the resin skeleton similar to the one used in the previous
experiment is used for the magnetic disk 40 and the
photocrosslinking reaction is conducted in the reaction chamber 41
by using a nitrogen atmosphere containing oxygen with a
concentration of 10 ppm or less.
[0192] In the experiment, the infrared radiation source 62B is
activated so that the temperature of the magnetic disk 40 is
elevated to 120.degree. C., and the photocrosslinking reaction was
conducted by exposing the lubricating film 41E of the magnetic disk
40 to the far-ultraviolet radiation of the wavelength of 172 nm
from the far-ultraviolet radiation source 62A for a duration of 20
seconds with a dose of 160 mJ/cm.sup.2.
[0193] The lubricating film 41E of the magnetic disk 40 thus
processed showed the bond ratio of 99.2%.
Experiment 10
[0194] In this experiment, the magnetic disk 40 having a structure
as represented in FIG. 15 is formed by using an Al disk as the
substrate 41A, wherein the substrate 41A is covered with the
foundation layer 41B of NiP by conducting a plating process. The
surface of the NiP film 41B thus formed is then subjected to a
polishing process such that the NiP film 41B has a surface
roughness Ra of about 6.5 nm. Further, the magnetic film 41C is
formed by depositing a Cr film and a CoCrTa film consecutively on
the NiP film 41B by a d.c. magnetron sputtering process conducted
in an Ar atmosphere with respective thicknesses of 50 nm and 40 nm,
and a DLC film is deposited on the magnetic film 41C by a CVD
process as the hard carbon protective layer 41D with a thickness of
about 8 nm.
[0195] After the magnetic disk 40 is thus prepared, the lubricating
film 41E is formed on the protective film 41D by coating a
perfluoro polyether film having a chloromethylphenyl group at the
end of the resin skeleton by a spin coating process with a
thickness of about 2.5 nm, wherein the magnetic disk 40 thus formed
with the lubricating film 41E is introduced into the reaction
chamber 61 of the processing apparatus of FIGS. 16A-16C for
photocrosslinking reaction of the lubricating film 41E.
[0196] In the reaction chamber 41, there is formed a nitrogen
atmosphere controlled such that the oxygen content in the nitrogen
atmosphere is less than about 10 ppm, and the magnetic disk 40 is
exposed to the far-ultraviolet radiation of the wavelength of 193
nm produced by an ArF excimer lamp, which is used for the
far-ultraviolet radiation source 61a, at room temperature with a
dose of 100 mJ/cm.sup.2 for a duration of about 100 seconds.
[0197] After the foregoing photocrosslinking reaction, the
thickness of the lubricating film 41E was measured, and the
magnetic disk 40 thus processed is immersed into a solvent (FC-77
of 3M) so as to dissolve the unreacted mobile layer into the
solvent. After the foregoing treatment in the solvent, the
thickness of the lubricating film 41E was again measured.
[0198] As a result of the measurement conducted after the treatment
in the solvent, it was observed that the bonding ratio is 97.1% for
the lubricating form of the present experiment.
Experiment 11 (Comparative Experiment)
[0199] In this comparative experiment, the process of exposure to
the far-ultraviolet radiation was omitted in the Experiment 8. It
turned out that the bond ratio of the lubricating film 41E thus
obtained as a result of the comparative experiment is only 38%,
indicating that more than half of the lubricating film 41E is a
mobile layer.
Experiment 12 (Comparative Experiment)
[0200] In this comparative experiment, the piperonyl endcap group
terminating the perfluoro polyether resin skeleton in the
Experiment 8 is replaced with a CF.sub.3 group. It turned out that
the bond ratio of the lubricating film 41E thus obtained is only
65% even in the case exposure to the far-ultraviolet radiation of
172 nm wavelength is conducted.
Experiment 13 (Comparative Experiment)
[0201] In this experiment, the photocrosslinking reaction of the
Experiment 8 is conducted by using a low-pressure mercury lamp for
the far-ultraviolet radiation source 62A in place of the excimer
lamp. In this case, a bonding ratio of only 60% was attained.
Experiment 14 (Comparative Experiment)
[0202] In this experiment, the photocrosslinking reaction of the
Experiment 9 is conducted by using a deuterium lamp having a
central wavelength of 160 nm and a half-height width of 30 nm for
the far-ultraviolet radiation source 62A in place of the excimer
lamp. In this case, a bonding ratio of only 80% was attained.
Further, it was necessary to carry out the exposure over a duration
four times as large as in the case of the Experiment 8 for
achieving the foregoing bonding ratio.
Experiment 15
[0203] In this experiment, the exposure dose of the far-ultraviolet
radiation and the atmosphere of the photocrosslinking reaction are
changed variously and the contact angle to water and the friction
coefficient were obtained. The result of this experiment is
summarized in TABLE I. TABLE-US-00001 TABLE I exp. dose bonding
wetting friction (mJ/cm2) atmosphere ratio(%) angle coeff(.mu.s)
100 N.sub.2 78.2 114 0.9 300 N.sub.2 85.5 116 0.7 800 N.sub.2 98.5
116 0.5 100 air 75.2 48 3.2 300 air 92.3 21 3.6 800 air 90.0 4 3.9
none 40.0 90 2.0
[0204] In the foregoing experiment, the friction coefficient of the
lubricating film 41E was obtained with regard to a thin-film
magnetic head having a slider of a sintered body of alumina and TiC
for the state in which the magnetic disk is activated from a
stationary stat to a rotational speed of 1 r.p.m. under the
condition that the magnetic head is applied with a load of 1.5 gf
(0.0147N). The friction coefficient was thereby measured by using a
disk abrasion tester.
[0205] As can be seen from TABLE I, there occurs a decrease of the
bonding ratio with decreasing exposure dose of the far-ultraviolet
radiation, while it can also be seen that a bonding ratio exceeding
98% can be realized by employing an exposure dose of 800 mJ/cm2 or
more in the nitrogen atmosphere. The lubricating film 41E thus
formed has additional advantageous features of large contact angle
to water and very small friction coefficient of 0.5.
[0206] In the case the foregoing photocrosslinking reaction is
conducted in the air, on the other hand, it can be seen that the
water contact angle becomes very small, indicating that the
lubricating film 41E has a hydrophilic surface. Further, the
friction coefficient is increased substantially.
Experiment 16
[0207] Next, examination was made with regard to the
contact-start-stop cycles for various magnetic disks produced
according to the process of the Experiment 8 but with various
exposure doses of the far-ultraviolet radiation in the
photocrosslinking process conducted in the nitrogen atmosphere.
[0208] In the experiment, the same thin-film magnetic head used in
the Experiment 15 was used, and the contact-start-stop experiment
was made by repeatedly driving the magnetic disk 40 in the magnetic
disk drive 50 of FIG. 14 at the rotational speed of 3600 r.p.m. for
15 seconds and by stopping the magnetic disk 40 for 15 seconds.
During the driving phase the magnetic disk 40, the magnetic head
was floated from the surface of the lubricating film 41E of the
magnetic disk 40 by a distance of 0.1 .mu.m. In the experiment, the
number of the contact-start-stop cycles until the friction
coefficient reaches 0.6 was obtained. TABLE II below summarizes the
result of the experiments. TABLE-US-00002 TABLE II exp. dose number
of CSS cycles when (mJ/cm2) atmosphere friction coeff. reached 0.6
100 N2 20,000 300 N2 25,000 1000 N2 30,000 none -- 7,000
[0209] The result of TABLE II indicates that the friction
coefficient of 0.6 is reached within 7000 cycles when no
photocrosslinking of the lubricating film 41E was made and that
contact-start-stop cycles of 30,000 is possible when the
photocrosslinking reaction was conducted in the N.sub.2 atmosphere
under the exposure dose of 1000 mJ/cm.sup.2.
Third Embodiment
[0210] Next, a third embodiment of the present invention will be
described.
[0211] In an investigation that constitutes a foundation of the
present invention, the inventor has discovered that the adhesion of
the lubricating film to the surface of the magnetic disk is
improved substantially when a non-polar group is introduced as an
end cap group rather than using conventional polar groups such as
oxoacid group, hydroxyl group, ester group, ether group, carboxyl
group or formyl group for the end gap group, and that the .pi.
electrons of the non-polar group contributes to the improvement of
the lubricating film substantially.
[0212] A typical example of the non-polar end cap group of the
present embodiment is a triorganosilyl group. In view of the
general tendency that the long-term stability of the resin becomes
deteriorated when the triorganosilyl group undergoes hydrolysis or
dehydration condensation due to the existence of alkoxyl group in
the triorganosilyl group, it is required that the triorganosilyl
group constituting the endcap group in the fluorocarbon resin of
the present embodiment has to be chosen from those that do not
cause hydrolysis or dehydration condensation.
[0213] The triorganosilyl group of the present embodiment has a
general formula represented as ##STR4## independently any of an
alkyl groups, an alkenyl group, an aryl group, an alkenyl group,
including those substituted with halogen or nitrogen.
[0214] For the alkyl group, those having 1-20 carbon atoms, such as
methyl group, ethyl group, propyl group, butyl group, hexyl group,
octyl group, dodecyl group, and the like can be used. For the
alkenyl group, those having 2-20 carbon atoms, such as vinyl group,
allyl group, isopropenyl group, butenyl group, and the like. For
the aryl group, those having 6-30 carbon atoms such as phenyl
group, naphtyl group, anthryl group, and the like. For the aralkyl
group, those having 7-30 carbon atoms such as benzyl group,
diphenylmethyl group, phenylethyl group, and the like can be
used.
[0215] As noted previously, the inventor of the present invention
has discovered that .pi. electrons in the endcap group of the
fluorocarbon resin skeleton perform important contribution to the
adherence of the lubricating film to the underlying magnetic disk
surface. Thus, it is preferable that at least one of the foregoing
substitution groups R.sup.1, R.sup.2 and R.sup.3 has .pi.
electrons. Larger than the number of the .pi. electrons, stronger
the adherence of the lubricating film to the underlying surface. In
view of availability of the material, it is preferable to use
phenyl group or benzyl group for the foregoing groups R.sup.1,
R.sup.2 and R.sup.3
[0216] In the event an alkyl group free from the .pi. electrons is
used for the substitution groups R.sup.1, R.sup.2 and R.sup.3, it
is possible to improve the adherence by applying heat or radiation
to the lubrication film formed on the magnetic disk surface.
[0217] Another typical example of the non-polar endcap group used
in the present embodiment has eight or more .pi. electrons and
represented by a general formula ##STR5##
[0218] wherein R.sup.4, R.sup.5 and R.sup.6 represent commonly or
independently a hydrogen atom or an organic group, and wherein at
least one of the groups R.sup.4, R.sup.5 and R.sup.6 represent an
organic group. The organic group may be selected from any of an
alkyl group, an alkenyl group, an aryl group, and an aralkyl group,
including those substituted with halogen or nitrogen, and at least
one of the organic group has a .pi. electron. Thereby, the total
number of the .pi. electrons in the endcap groups is 8 or more,
preferably 14 or more. For the alkyl group, it is possible to use
those having 1-20 carbon atoms such as methyl group, ethyl group,
propyl group, butyl group, hexyl group, octyl group, dodecyl group,
and the like. For the alkenyl group, it is possible to use those
having 2-20 carbon atoms such as vinyl group, allyl group,
isopropenyl group, butenyl group, and the like. For the aryl group,
it is possible to use those having 6-30 carbon atoms such as phenyl
group, naphtyl group, anthryl group, and the like. For the alkyl
group, it is possible to use those having 7-30 carbon atoms such as
benzyl group, diphenylmethyl group, phenylethyl group, and the
like. Larger the number of the .pi. electrons in the endcap group,
stronger the adherence of the lubricating film to the magnetic disk
surface. Thus, it is preferable to use phenyl group, benzyl group,
naphtyl group or anthryl group for the substitute groups R4, R5 and
R6, provided that the total number of the .pi. electrons in the
endcap groups is eight or more.
[0219] Thus, the lubricating film of the present invention uses
non-polar endcap groups contrary to conventional lubricating film
that uses polar endcap groups such as oxoacid group, hydroxyl
group, ester group, ether group, carboxyl group, formyl group, and
the like. In view of absence of polarity in the endcap group, the
lubricating film of the present invention can successfully avoid
the problem of coagulation of the fluorocarbon resin, which is
caused as a result of the action of the polar endcap group.
Further, it should be noted that, in the lubricating film of the
present invention, the .pi. electrons in the endcap group improves
adherence of the lubricating film to an underlying hard carbon
protective film, particularly a DLC film, without introducing the
polar group.
[0220] Although not limited, it is preferable that the fluorocarbon
resin has a skeleton formed of carbon atoms or a skeleton formed of
carbon atoms and containing oxygen atoms, wherein fluorine atoms
are bonded to the carbon skeleton in such a fluorocarbon resin.
[0221] While the fluorocarbon resin may contain other various atoms
such as hydrogen atoms, chlorine atoms, alkyl groups having 1-5
carbon atoms, and the like bonded to the resin skeleton, it is
preferable that the proportion of the fluorine atoms in the atoms
bonded to the carbon skeleton is equal to or larger than 50%. In
the present invention, it is preferable to use a fluorine resin
having a perfluoro skeleton or a perfluoroether skeleton, wherein
the resin having a perfluoroether skeleton is most preferable.
While the skeleton of a fluorocarbon resin, including the resin
used in the present invention, generally makes a bonding with an
endcap group via an oxygen atom, the present invention also
includes a fluorocarbon resin that makes bonding with an endcap
group directly, without intervening an oxygen atom.
[0222] Thus, the fluorocarbon resin of the present invention can be
generally represented as E-O-A-O-E (6) or E-A-E (7) wherein E
represents the endcap group while A represents the resin skeleton.
O represents the oxygen atom.
[0223] Further, the present invention can also use a resin having
the endcap group at only one end of the resin skeleton or a resin
having the endcap group at a branched end.
[0224] In order to avoid loss of film thickness caused as a result
of evaporation, and further in view of avoiding the wear of the
film, the resin forming the lubricating film of the present
invention should have a molecular weight falling in a range between
500-10,000, preferably 1,000-5,000, more preferably
2,000-3,000.
[0225] The fluorocarbon resin of the present invention can be
produced easily by causing a fluorocarbon resin having a reactive
group, such as hydroxyl (OH) group, at the end of the resin
skeleton to react with a substance having a desired group to be
used for the endcap group. For example, a fluorocarbon resin having
a triorganosilyl endcap group represented by Eq. (1) or (4) can be
produced by causing a silylization reaction in the fluorocarbon
resin having a hydroxyl end group by a compound that has the
desired group to be used for the endcap group, such as
chlorosilanes, silylamines, silylamides, and the like. In this
case, a solvent having one or both of a CH bond and a CCl bond and
further a CF bond is used to dissolve the fluorocarbon resin having
a hydroxyl endcap group and an amine catalyst to cause a desired
silylization together with the tri-organo chlorosilane. The solvent
used for such a purpose may be a mixture of
1,1-dichloro-2,2,3,3,3-pentafluoropropane and
1,1,2,2,3-pentafluoroether. Alternatively, a compound supplied from
3M under the trade name of HFE (hydrofluoroether) or a compound
supplied from Japan Zeon under the tradename of Zeorora. For the
amine catalyst, it is possible to use triethylamine, pyridine, and
the like. Further, the fluorocarbon resin having the formula of Eq.
(5) can be produced also easily by carrying out a dehydrating
condensation reaction of the fluorocarbon resin having a hydroxyl
endcap group with a material having the desired organic group for
the endcap group under existence of an acid catalyst.
[0226] The lubricating film of the present embodiment thus produced
is applied upon the surface of the magnetic disk in the form
dissolved in a suitable solvent together with necessary additives
or surfactants. The application of the lubricating film may be
achieved by various processes such as dip-coating process or
spin-coating process. It is preferable that the surface of the
magnetic disk, on which the lubricating film of the present
embodiment is applied, is covered with a DLC film, including the
one described in the preceding embodiment.
[0227] In a high-density magnetic disk drive, a DLC film may be
formed by a CVD process with a thickness of 8 nm or less for
reducing the distance between a magnetic film formed underneath the
DLC film and a magnetic head scanning the surface of the magnetic
disk. By using a CVD process, it is possible to reduce the
thickness of the DLC film, while the magnetic disk having such an
extremely thin DLC film shows the tendency of metal migration of
the magnetic material forming the magnetic film. The lubricating
film of the present embodiment shows a particularly strong
adherence when formed on such a very thin DLC film and covers the
surface of the DLC film uniformly. Thus, the lubricating film
effectively insulates the magnetic disk from various contaminants
originating from moisture coagulation and the reliability and
resistance against corrosion of the magnetic disk drive is improved
substantially.
[0228] In the as-formed state, the lubricating film formed on the
DLC film contains a substantial amount of mobile layer not bonded
to the surface of the DLC film. As noted previously, such a mobile
layer tends to cause a problem of lateral displacement and
accumulation at the peripheral part of the magnetic disk with
high-speed rotation of the magnetic disk. In the lubricating film
of the present embodiment, the proportion of such a mobile layer
can be reduced substantially by applying radiation and/or heat so
as to facilitate crosslinking in the fluorocarbon resin
constituting the lubricating film. Such a crosslinking process
induced by optical radiation or heating is particularly effective
for reducing the mobile component in the lubricating film of the
present embodiment.
[0229] Hereinafter, experiments conducted by the inventor of the
present invention with regard to the lubricating film of the
present embodiment will be explained with reference to FIG. 17
showing a magnetic disk 70.
[0230] Referring to FIG. 17, the magnetic disk 70 is constructed on
a disk substrate 71A of Al or a glass, wherein the substrate 71A
carries thereon a foundation layer 71B of NiP or NiAl. The
foundation layer 71B is subjected to a texture processing and has a
surface roughness Ra of about 5 nm, and a magnetic film 71C of Co,
Co or a CoCr alloy is formed on the foundation layer 71B thus
processed. Further, a protective film 71D of DLC or SiO.sub.2 is
formed on the magnetic film 71C, and a lubricating film 71E of the
present embodiment is formed on the protective film 71D. In view of
description with regard to the structure of the magnetic disk
provided previously with preceding embodiments, further description
thereof will be omitted.
Experiment 17
[0231] In this experiment, the fluorocarbon resin used for the
lubricating film of 71E of the present invention was produced.
[0232] In this experiment, a four-neck flask fitted with a
condenser, a tube for N.sub.2 bubbling, a stirring rod and an
addition funnel, was charged with perfluoro polyether having a
hydroxyl endcap group, together with an equivalent-weight mixed
solution of 1,1-dichloro-2,2,3,3,3-pentafluoro propane and
1,3-dichloro-1,1,2,2,3-pentafluoro propane (AK-225 of Asahi Glass,
and anhydrous pyridine was added further with an amount triple
times in moles with respect to the endcap hydroxyl group. The
mixture thus formed was then stirred at 50.degree. C. in the flask
while bubbling N.sub.2, and triphenyl chlorosilane (Tph) diluted
with the AK-225 solution of twice the amount of Tph, was added from
the addition funnel such that the amount of Tph becomes triple
times the amount of the endcap hydroxyl group in the flask. After
the addition of Tph, a silylization reaction was caused in the
flask by continuing stirring for four hours at 70.degree. C.
[0233] After the silylization process, rinsing was conducted in
water until the solution becomes neutral. Further, the solution was
rinsed twice by butyl acetate, and the solvent was removed by
evaporation in a rotary evaporator. Further, filtration was made by
using a 0.1 .mu.m membrane filter and the sample thus obtained was
subjected to an NMR analysis. As a result of the NMR analysis, it
was indicated that 98% of the hydroxyl group of the perfluoro
polyether was silylized.
Experiment 18
[0234] A fluorocarbon resin was produced similarly to the
Experiment 17, except that triphenyl chlorosilane (TPh) was
replaced with tribenzyl chlorosilane (TBz), allyldimethyl
chlorosilane (ADM), dimethylvinyl chlorosilane (DMV), trivinyl
chlorosilane (TVn), diphenylvinyl chlorosilane (DPV), and triethyl
chlorosilane (TEt). As a result of the NMR analysis, it was
indicated that more than 95% of the hydroxyl group was silylized
for all of these resins.
Experiment 19
[0235] In order to evaluate the high-temperature resistance of the
fluorocarbon resin of the present embodiment, a thermogravimetric
analysis was conducted for each of the seven resins obtained in the
Experiments 17 and 18 explained before. The experiment was made in
a nitrogen atmosphere while increasing the temperature at the rate
of 20.degree. C./min. TABLE III below summarizes the observed
weight loss for each of the resin specimens, wherein the resin
specimens are identified in TABLE III by the endcap group such as
TPh, TBz, . . . . TABLE-US-00003 TABLE III temperature of resin 5%
weight loss (.degree. C.) TPh 390 TBz 360 DPv 365 ADM 330 DMV 320
TVn 332 TEt 331 compar. expt. OH 300
Experiment 20
[0236] In this experiment, the seven fluorocarbon resins produced
by the Experiments 17 and 18 are applied to the magnetic disk 70 of
FIG. 17 in the form of the lubricating film 71E.
[0237] More specifically, the lubricating film 71E is formed by
dipping the magnetic disk 70 of FIG. 17 into a solution of the
fluorocarbon resin in which the fluorocarbon resin is dissolved in
a solution (FC-77 solution of Simitomo 3M Co, Ltd.) in the state
that the magnetic disk 70 lacks the lubricating film 71E.
[0238] For the sake of comparison, a similar magnetic disk coated
with a fluorocarbon resin having the hydroxyl group as the endcap
group was also prepared.
[0239] In the experiment, the thickness of the lubricating film 71E
was measured by an infrared absorption spectroscopy for the
as-formed state, and the magnetic disk thus formed with the
lubricating film 71E was dipped in the foregoing FC-77 solvent so
as to dissolve any mobile layer not bonded to the magnetic disk
70.
[0240] After the dipping process, the magnetic disk was pulled up
from the solvent and the thickness of the lubricating film 71E was
again measured by the infrared absorption spectroscopy. By dividing
the thickness of the lubricating film 71E after the dipping process
into the solvent by the initial thickness, the bonding ratio was
obtained.
[0241] Further, a similar measurement was conducted also for the
bonding ratio with regard to the magnetic disk 70 for the case the
lubricating film 71E is subjected to an exposure process to an
optical radiation produced by a low-pressure mercury lamp for 5
seconds before the magnetic disk is dipped into the solvent for
removal of the mobile layer.
[0242] TABLE IV below summarizes the bonding ratio thus obtained
for the various magnetic disk specimens having various fluorocarbon
resins for the lubricating film 71E. Similarly to TABLE III, TABLE
IV identifies the fluorocarbon resin in terms of the endcap group.
Further, TABLE IV also indicates the number of .pi. electrons
included in the endcap group. TABLE-US-00004 TABLE IV bond ratio
bond ratio rein (no exposure) (with exposure) .pi. electrons TPh
57% 60% 18 TBz 58% 65% 18 DPV 45% 55% 14 ADM 37% 48% 2 DMV 40% 48%
2 TMn 34% 48% 6 TEt 30% 52% 0 OH 35% 42% 0
Experiment 21
[0243] In the present experiment, a contact-start-stop operation
test was made for a magnetic disk drive that uses the magnetic disk
70 of FIG. 17 for the case the lubricating film 41E is formed of
TPh. The magnetic disk 70 was prepared similarly to the Experiment
20 except that the magnetic film 41C was formed in the form of
consecutive stacking of a Cr film and a CoCrTa film with respective
thicknesses of 50 nm and 40 nm.
[0244] In the contact-start-stop experiment, the magnetic disk thus
prepared and carrying the fluorocarbon lubricating film 41E with a
thickness of 2.5 nm was mounted on a magnetic disk drive, and the
surface of the lubricating film 41E was scanned by a magnetic head
having a slider of a sintered body of alumina and TiC. During the
high-speed rotation phase of the magnetic disk, the magnetic head
was floated over the magnetic disk with a separation of 0.1 .mu.m
between the top surface of the lubricating film 41E and the slider
surface. The contact-start-stop experiment was conducted by
repeating the stationary phase of the magnetic disk in which the
magnetic disk is stationary and the high-speed rotation phase in
which the magnetic disk is rotating at the speed of 3600 r.p.m.,
wherein the stationary phase and the high-speed rotation phase were
repeated alternately, each with 15 seconds. In the experiment, the
number of the contact-start-stop cycles was evaluated
[0245] TABLE V summarizes the result of the contact-start-stop
experiments noted above, wherein TABLE V represents the number of
the cycles the until the friction coefficient reaches the value of
0.6. For the sake of comparison, TABLE V also represents the number
of the contact-start-stop experiments for the case the fluorocarbon
lubricating film 71E contains OH as the endcap group.
[0246] From TABLE V, it can be seen that the number of the
contact-start-stop cycles is increased substantially by using the
lubricating film 71E of the present embodiment.
[0247] Further, the present invention is not limited to the
embodiments described heretofore, but various variations and
modifications may be made without departing from the scope of the
invention.
* * * * *