U.S. patent application number 12/493808 was filed with the patent office on 2010-01-07 for burnishing tape and method of manufacturing the same, and method of burnishing magnetic disk.
This patent application is currently assigned to SHOWA DENKO K.K.. Invention is credited to Kazuya Niwa, Ryuji SAKAGUCHI.
Application Number | 20100003901 12/493808 |
Document ID | / |
Family ID | 41464747 |
Filed Date | 2010-01-07 |
United States Patent
Application |
20100003901 |
Kind Code |
A1 |
SAKAGUCHI; Ryuji ; et
al. |
January 7, 2010 |
Burnishing tape and method of manufacturing the same, and method of
burnishing magnetic disk
Abstract
Disclosed is a burnishing tape, a method of producing the same
and a method of burnishing a magnetic disk with which a surface of
the magnetic disk may be smoothed while contamination of a magnetic
disk caused by crushed abrasive grains is prevented. A burnishing
tape (1) manufactured by the method of manufacturing of the
burnishing tape according to an embodiment of the invention is used
to burnish the magnetic disk. The method includes: kneading and
dispersing abrasive grains (5) and a binder (6) to prepare slurry;
applying the slurry on the support (2) to form a coating layer;
curing the coating layer to form an abrasive grain layer (3); and
forming a liquid lubricant layer (4) on a surface of the abrasive
grain layer (3).
Inventors: |
SAKAGUCHI; Ryuji;
(Chiba-shi, JP) ; Niwa; Kazuya; (Ichihara-shi,
JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
SHOWA DENKO K.K.
Minato-ku
JP
|
Family ID: |
41464747 |
Appl. No.: |
12/493808 |
Filed: |
June 29, 2009 |
Current U.S.
Class: |
451/59 ; 51/295;
51/298 |
Current CPC
Class: |
B24D 11/00 20130101;
B24B 39/06 20130101 |
Class at
Publication: |
451/59 ; 51/298;
51/295 |
International
Class: |
B24B 1/00 20060101
B24B001/00; B24D 11/00 20060101 B24D011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 1, 2008 |
JP |
2008-172598 |
Claims
1. A burnishing tape used to burnish a magnetic disk, the tape
comprising: a support; an abrasive grain layer, which comprises
abrasive grains and is provided on the support; and a liquid
lubricant layer with which a surface of the abrasive grain layer is
coated.
2. The burnishing tape according to claim 1, wherein the thickness
of the liquid lubricant layer is in a range of 0.0001 to 10
micrometers.
3. The burnishing tape according to claim 1, wherein the liquid
lubricant layer comprises a compound which has a perfluoropolyether
structure.
4. The burnishing tape according to claim 2, wherein the liquid
lubricant layer comprises a compound which has a perfluoropolyether
structure.
5. A method of manufacturing of a burnishing tape used to burnish a
magnetic disk, the method comprising: kneading and dispersing
abrasive grains and a binder to prepare a slurry; applying the
slurry on a support to form a coating layer; curing the coating
layer to form an abrasive grain layer; and forming a liquid
lubricant layer on a surface of the abrasive grain layer.
6. The method of manufacturing of the burnishing tape according to
claim 5, wherein the thickness of the liquid lubricant layer is in
a range of 0.0001 to 10 micrometers.
7. The method of manufacturing the burnishing tape according to
claim 5, wherein the liquid lubricant layer comprises a compound
which has a perfluoropolyether structure.
8. The method of manufacturing the burnishing tape according to
claim 6, wherein the liquid lubricant layer comprises a compound
which has a perfluoropolyether structure.
9. A method of burnishing a magnetic disk, which comprises a step
of polishing a surface of a magnetic disk comprising at least an
underlayer, a magnetic layer and a protective layer on a
nonmagnetic substrate, after pressing an abrasive grain surface of
a burnishing tape supplied to the magnetic disk surface, while the
magnetic disk is rotated, wherein the burnishing tape supplied to
the magnetic disk surface is the burnishing tape according to claim
1.
10. A method of burnishing a magnetic disk, which comprises a step
of polishing a surface of a magnetic disk comprising at least an
underlayer, a magnetic layer and a protective layer on a
nonmagnetic substrate, after pressing an abrasive grain surface of
a burnishing tape supplied to the magnetic disk surface, while the
magnetic disk is rotated, wherein the burnishing tape supplied to
the magnetic disk surface is the burnishing tape according to claim
2.
11. A method of burnishing a magnetic disk, which comprises a step
of polishing a surface of a magnetic disk comprising at least an
underlayer, a magnetic layer and a protective layer on a
nonmagnetic substrate, after pressing an abrasive grain surface of
a burnishing tape supplied to the magnetic disk surface, while the
magnetic disk is rotated, wherein the burnishing tape supplied to
the magnetic disk surface is the burnishing tape according to claim
3.
12. A method of burnishing a magnetic disk, which comprises a step
of polishing a surface of a magnetic disk comprising at least an
underlayer, a magnetic layer and a protective layer on a
nonmagnetic substrate, after pressing an abrasive grain surface of
a burnishing tape supplied to the magnetic disk surface, while the
magnetic disk is rotated, wherein: the burnishing tape supplied to
the magnetic disk surface comprises a support and an abrasive grain
layer which contains abrasive grains and is provided on the
support; and a liquid lubricant is supplied between the support and
the abrasive grain layer when the magnetic disk surface is polished
by the burnishing tape.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority of Japanese Patent
Application No. 2008-172598 filed Jul. 1, 2008, the content of
which is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a burnishing tape used for
polishing a surface of a magnetic disk used in, for example, a hard
disk device, a method of manufacturing the same, and a method of
burnishing the magnetic disk.
[0004] 2. Background Art
[0005] Recently, data is recorded on a magnetic disk in a hard disk
device with increasingly higher density. A recording head is spaced
from a magnetic recording surface when moved with respect thereto.
The surface of the magnetic disk should be fairly smooth in order
to reduce the distance between the recording head and the magnetic
recording surface. Accordingly, in the manufacturing process of the
magnetic disk, after a magnetic layer and a protective layer are
formed on a nonmagnetic substrate, a surface of the outermost layer
is burnished with a burnishing tape so as to remove bumps formed or
deposited on the surface.
[0006] Burnishing is conducted using, for example, a burnishing
tape having an alumina coating material applied thereto. The
burnishing tape is pressed against a medium surface by a rubber
contact roll so that the medium surface is polished lightly. Since
any abnormal bumps on the medium surface may be removed during the
burnishing process, the distance between the recording head and the
magnetic recording surface may be reduced in a hard disk device
(see, for example JP-A-11-277339).
[0007] An exemplary burnishing tape (i.e., a burnishing tape) used
in the burnishing process may typically be a tape which includes a
polyester base film having an abrasive layer formed thereon. The
abrasive layer is made to contact and slide against the surface of
the magnetic disk at the side of the magnetic layer. With this
process, fine dust adhering to the surface of the magnetic disk is
removed and the surface is polished to remove the abnormal bumps on
the surface. In this manner, the surface is smoothed. Examples of
the abrasive may include particles having an average particle
diameter of about 0.05 to 50 micrometers. Namely, the abrasive may
be particles of chromic oxide, .alpha.-alumina, silicon carbide,
nonmagnetic iron oxide, diamond, .gamma.-alumina,
.alpha.,.gamma.-alumina, fused alumina, corundum and synthetic
diamond (see, for example, JP-A-09-054943).
[0008] JP-A-2001-079774 discloses, regarding a polishing film for
burnishing a hard disk protective layer, covering the surfaces of
abrasive particles with a coating agent in order to prevent
transfer of ionic impurities from a polishing film to a surface of
the hard disk protective layer. JP-A-9-85628 discloses increasing
the polishing force of a burnishing tape and preventing scratching
generated on a polishing surface by providing a ceramic coating
layer on a surface of the burnishing tape.
SUMMARY OF THE INVENTION
[0009] Burnishing of a magnetic disk is typically a process of
polishing a surface of a magnetic disk using a burnishing tape. In
particular, an abrasive grain surface of the burnishing tape is
pressed against a surface of the magnetic disk at the side of a
magnetic layer while the magnetic disk is being rotated. In this
manner, the magnetic disk surface is polished to remove bumps and
thus the magnetic disk surface may be smoothed.
[0010] The burnishing tape is extended between a feed reel and a
take-up reel. The burnishing tape is sequentially supplied from the
feed reel and is taken up by the take-up reel. In the course of the
burnishing tape being moved from the feed reel to the take-up reel,
a surface of the burnishing tape opposite to the abrasive grain
surface (i.e., a back surface) may be pressed by, for example, a
rubber backing roll or a felt piece such that the polishing surface
of the burnishing tape may be pressed against the surface of the
magnetic disk. The burnishing tape is supplied from the reel. The
used burnishing tape is taken up and collected by another reel.
[0011] Recently, data is recorded on a magnetic disk with
increasingly high density. To increase the recording density, the
distance between the magnetic head and the magnetic disk is
reduced. Now, contamination of the magnetic disk surface during the
burnishing process has become a problem.
[0012] According to the study of the present inventors, it has been
found that contaminant of the magnetic disk surface contains
alumina particles, which are produced during the burnishing
process. In particular, abrasive grains are separated from the
burnishing tape or crushed to produce the alumina particles
contained in the contaminant. More particularly, it has been found
that, when the magnetic disk surface is polished to remove the
bumps formed thereon during the burnishing process, the abrasive
grains adhering to the burnishing tape are separated or the
surfaces of the abrasive grains are crushed (i.e., split) slightly
and the separated grains or the abrasive grain powder produced by
the crushing may adhere to the magnetic disk surface, thereby
contaminating the magnetic disk surface.
[0013] Recently, the abrasive grains used for the burnishing tape
are often deposited particles (i.e., crystal growth particles)
instead of crushed grains. This is because higher processing
accuracy has been demanded in the burnishing process. In
particular, variation in the particle diameter and the shape of the
abrasive grains is small in the deposited particles, which may
prevent production of slight scratches on the surface to be
burnished. However, since the deposited particles have smooth and
spherical surfaces as compared to the crushed grains, it is
difficult to stably keep the deposited particles on a support of
the burnishing tape. It is therefore considered that the abrasive
grains are easily separated from the burnishing tape during
burnishing of the magnetic disk surface.
[0014] The invention has been made in view of the aforementioned
and an object thereof is to provide a burnishing tape, a method of
producing the same and a method of burnishing a magnetic disk with
which contamination of a surface of the magnetic disk may be
prevented during a burnishing process of the magnetic disk.
[0015] The present inventors have intensively studied to solve the
problem and found that separation or crushing of the abrasive
grains may be prevented by a novel burnishing tape for burnishing
the magnetic disk and thus contamination of the magnetic disk
surface caused by the burnishing tape may be reduced. In
particular, a surface of an abrasive grain layer on the support may
be coated with a liquid lubricant layer having the thickness of
0.0001 to 10 micrometers to stabilize the shearing force (i.e., the
coefficient of dynamic friction) applied to the burnishing tape.
The invention has the following aspects.
[0016] (1) A first aspect of the invention is a burnishing tape
used to burnish a magnetic disk, the tape including: a support; an
abrasive grain layer provided on the support, the abrasive grain
layer containing abrasive grains; and a liquid lubricant layer with
which a surface of the abrasive grain layer is coated.
[0017] (2) In a second aspect of the invention, the thickness of
the liquid lubricant layer may be in a range of 0.0001 to 10
micrometers.
[0018] (3) In a third aspect of the invention, the liquid lubricant
layer may include a compound which has a perfluoropolyether
structure.
[0019] (4) A fourth aspect of the invention is a method of
manufacturing a burnishing tape used to burnish a magnetic disk,
the method including: kneading and dispersing abrasive grains and a
binder to prepare slurry; applying the slurry on a support to form
a coating layer; curing the coating layer to form an abrasive grain
layer; and forming a liquid lubricant layer on a surface of the
abrasive grain layer.
[0020] (5) In a fifth aspect of the invention, the thickness of the
liquid lubricant layer may be in a range of 0.0001 to 10
micrometers.
[0021] (6) In a sixth aspect of the invention, the liquid lubricant
layer may include a compound which has a perfluoropolyether
structure.
[0022] (7) A seventh aspect of the invention is a method of
burnishing a magnetic disk in which an abrasive grain surface of a
burnishing tape supplied to a magnetic disk surface is pressed
against and polishes the magnetic disk surface while a magnetic
disk is being rotated, the disk including, on a nonmagnetic
substrate, at least an underlayer, a magnetic layer and a
protective layer, wherein the burnishing tape supplied to the
magnetic disk surface is the burnishing tape according to any one
of above (1) to (3).
[0023] (8) A eighth aspect of the invention is a method of
burnishing a magnetic disk in which an abrasive grain surface of a
burnishing tape supplied to a magnetic disk surface is pressed
against and polishes the magnetic disk surface while a magnetic
disk is being rotated, the disk including, on a nonmagnetic
substrate, at least an underlayer, a magnetic layer and a
protective layer, wherein: the burnishing tape supplied to the
magnetic disk surface includes a support and an abrasive grain
layer which contains abrasive grains and is provided on the
support; and a liquid lubricant is supplied between the support and
the abrasive grain layer when the magnetic disk surface is polished
by the burnishing tape.
[0024] According to the burnishing tape of an aspect of the
invention, the liquid lubricant layer may prevent crushing of the
abrasive grains included in the abrasive grain layer or removal of
the crushed grains during burnishing of the magnetic disk. Thus,
contamination of the magnetic disk surface caused by the crushed
abrasive grains may be prevented. With this configuration, a
surface-smoothed magnetic disk, which is sufficiently clean, may be
provided.
[0025] According to the method of manufacturing a burnishing tape
of an aspect of the invention, an excellent burnishing tape may be
provided easily and reliably.
[0026] According to the method of burnishing according to an aspect
of the invention, the liquid lubricant layer may prevent crushing
of the abrasive grains included in the abrasive grain layer of the
burnishing tape or removal of the crushed grains. Thus,
contamination of the magnetic disk surface caused by the crushed
abrasive grains may be prevented. With this configuration, a
surface-smoothed magnetic disk, which is sufficiently clean, may be
provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a longitudinal cross-sectional view of an
exemplary burnishing tape according to an embodiment of the
invention.
[0028] FIG. 2A is a schematic diagram showing an exemplary
burnisher in which the burnishing tape shown in FIG. 1 is
incorporated.
[0029] FIG. 2B is a schematic diagram showing an exemplary
burnisher in which the burnishing tape shown in FIG. 1 is
incorporated.
[0030] FIG. 3 is a longitudinal cross-sectional view of an
exemplary magnetic disk to be burnished in the burnisher shown in
FIGS. 2A and 2B.
[0031] FIG. 4A is a cross-sectional view of a burnishing tape in
which a very thin binder layer is formed on an abrasive grain
layer.
[0032] FIG. 4B is a cross-sectional view of a related art
burnishing tape in which abrasive grains are separated or abrasive
grains are chipped.
[0033] FIG. 4C is a cross-sectional view of an exemplary burnishing
tape according to an embodiment of the invention.
[0034] FIG. 5 is a schematic configuration diagram showing an
exemplary magnetic recording and reproducing device in which the
magnetic disk shown in FIG. 3 is incorporated.
DETAILED DESCRIPTION OF THE INVENTION
[0035] Hereinafter, a burnishing tape, a method of manufacturing
the same and a method of burnishing according to embodiments of the
invention will be described.
Burnishing Tape
[0036] First, a burnishing tape according to an embodiment of the
invention will be described.
[0037] FIG. 1 is a longitudinal cross-sectional view of a
burnishing tape according to an embodiment of the invention.
[0038] A burnishing tape 1 according to the present embodiment
smoothes a surface of a magnetic disk 10 in the following manner: a
surface of the burnishing tape 1 is made to slide against a surface
of the magnetic disk 10 shown in FIGS. 2A and 2B to polish the
surface of the magnetic disk 10 and remove abnormal bumps formed
thereon.
[0039] The burnishing tape 1 includes a support 2, an abrasive
grain layer 3 provided on the support 2 and a liquid lubricant
layer 4 with which a surface of the abrasive grain layer 3 is
coated.
[0040] The material of the support 2 is not particularly limited
and may be various resin materials, such as polyethylene
terephthalate.
[0041] The abrasive grain layer 3 includes abrasive grains 5 and a
binder 6. The surface of the abrasive grain layer 3 has bumps that
reflect the shape of the abrasive grains 5.
[0042] Examples of the abrasive grains 5 may include particles of
chromic oxide, .alpha.-alumina, silicon carbide, nonmagnetic iron
oxide, diamond, .gamma.-alumina, .alpha.,.gamma.-alumina, fused
alumina, corundum and synthetic diamond. These substances may be
used alone or in combination thereof.
[0043] The binder 6 is able to bond the abrasive grains 5 and the
support 2 or bond the abrasive grains 5 together. The material of
the binder is not particularly limited and may be a thermosetting
resin, thermoplastic resin and photosensitive resin.
[0044] Examples of the thermosetting resin may include urea resin,
melamine resin, phenol resin, epoxy resin, unsaturated polyester
resin, alkyd resin and urethane resin.
[0045] Examples of the thermoplastic resin may include
acrylonitrile styrene butadiene rubber (ABS) resin, styrene
butadiene rubber resin, polybutadiene resin and acrylic
rubber-based MBS resin.
[0046] Examples of the photosensitive resin may include methacrylic
resin, phenol resin, urea resin, melamine resin, polystyrene resin,
polyacetal resin, polycarbonate resin and epoxy resin.
[0047] These resin materials may be used alone or in combination
thereof.
[0048] The burnishing tape 1 according to the present embodiment of
the invention is characterized in that the surface of the abrasive
grain layer 3 is coated with the liquid lubricant layer 4.
[0049] The thickness of the liquid lubricant layer 4 may preferably
be in a range of 0.0001 to 10 micrometers, and more preferably in a
range of 0.1 to 3 micrometers. With the liquid lubricant layer 4
having the thickness in this range, separation or crushing of the
abrasive grains may be prevented. Even if separation or crushing of
the abrasive grains occurs, scattering of the abrasive grain powder
may be prevented. With this configuration, adhesion of contaminant
that may inhibit the magnetic head from moving in a manner spaced
from the magnetic disk in a hard disk device incorporating the
magnetic disk may be prevented.
[0050] If the thickness of the liquid lubricant layer 4 is smaller
than 0.0001 micrometers, an effect of preventing the occurrence of
the crushed powder may be impaired. If the thickness of the liquid
lubricant layer 4 is larger than 10 micrometers, the occurrence of
the crushed powder may be decreased but the liquid lubricant may
easily be transferred to the material to be polished. As a result,
the likelihood of occurrence of contamination of the surface of the
material to be polished may be increased.
[0051] In the present embodiment, the liquid lubricant layer may
preferably include a compound having a perfluoropolyether
structure. If the liquid lubricant layer is provided on the surface
of the abrasive grain layer, the liquid lubricant may be
transferred to the magnetic disk during the burnishing process as
described above. Since the compound having a perfluoropolyether
structure is generally used as a lubricant to be applied onto a
magnetic disk surface, the likelihood of causing problems is
reduced even if the liquid lubricant of the magnetic tape is
transferred to the magnetic disk.
[0052] The liquid lubricant layer 4 provided on the surface of the
abrasive grain layer 3 may protect the abrasive grains 5 included
in the abrasive grain layer 3. The liquid lubricant layer 4 may
prevent crushing, or removal of the crushed grains during
burnishing of the magnetic disk 10 using the burnishing tape 1 may
be prevented. The surface of the magnetic disk 10 may be smoothed
while preventing contamination of the magnetic disk 10 caused by
the crushed grains of the abrasive grains 5.
[0053] With the liquid lubricant layer 4 having the thickness in
the above-described range provided on the abrasive grain layer 3,
slight scattering of the crushed grains produced by the crushing of
the abrasive grains 5 during burnishing of the magnetic disk 10 may
be reliably prevented. As a result, it is possible to reliably
prevent contaminant (i.e., crushed abrasive grains), which may
inhibit the magnetic head from moving in a manner spaced from the
magnetic disk, from adhering onto the surface of the magnetic disk
10.
[0054] If the thickness of the liquid lubricant layer 4 is smaller
than 0.0001 micrometers, an effect of preventing the occurrence of
the crushing of abrasive grains 5 or removal of the crushed grains
may become insufficient. If the thickness of the coating layer 4 is
larger than 10 micrometers, the occurrence of crushing of the
abrasive grains 5 or removal of the crushed grains may be reliably
prevented. However, the thickness of the lubricant layer 4 covering
the surface of abrasive grains 5 may be excessively large, and thus
the function as the burnishing tape may become poor.
Method of Manufacturing Burnishing Tape
[0055] Next, a method of manufacturing the burnishing tape
according to an embodiment of the invention will be described. The
method of manufacturing the burnishing tape according to an
embodiment of the invention may include: (1) kneading and
dispersing the abrasive grains and the binder to prepare a slurry;
(2) applying the slurry onto the support to form a coating layer;
(3) making the coating layer cured to form the abrasive grain layer
3; and (4) forming the liquid lubricant layer 4 on the surface of
the abrasive grain layer 3. Hereinafter, each process will be
described.
(1) Preparation of Slurry
[0056] First, the abrasive grains 5 and the binder 6 are kneaded
and dispersed to prepare a slurry.
[0057] If the above-described resin is used as the binder 6, the
resin material may be kneaded and dispersed with the abrasive
grains in the form of a precursor thereof. The precursor of the
resin may be a monomer or an oligomer which reacts in various
processes in the manufacturing process to yield a target resin.
[0058] The slurry may contain a solvent, which helps adjust the
viscosity of the slurry suitable for application which will be
described later.
[0059] The solvent is not particularly limited, but may be a
ketone-based solvent, ester-based solvent, aromatic hydrocarbon
solvent, alcohol-based solvent and ether-based solvent.
[0060] The content of the abrasive grains 5 in the slurry is
preferably in a range of 100 to 400 parts by mass and more
preferably 200 to 400 parts by weight with respect to the content
of the binder 6 or its precursor. If the content of the abrasive
grains 5 is larger than 400 parts by mass, the likelihood of the
removal of the abrasive grains 5 in the obtained abrasive grain
layer 3 may be increased. If the content of the abrasive grains 5
is smaller than 100 parts by mass, the abrasive grains 5 may be
buried into the binder 6, and it will become difficult to form
bumps that reflect the shape of the abrasive grains 5 on the
surface of the abrasive grain layer 3.
[0061] Any kneader may be used so long as it is usually employed in
the method of manufacturing this kind of burnishing tape.
(2) Formation of Coating Layer
[0062] Next, the slurry is applied onto the support 2 to form a
coating layer.
[0063] The slurry may be coated by any method usually employed in
the method of manufacturing this kind of burnishing tape. For
example, the slurry may be coated through roll coating or
applying.
(3) Curing of Coating Layer
[0064] Next, the coating layer formed on the support 2 is made to
cure and form the abrasive grain layer 3.
[0065] The method of curing may be selected according to the types
of the binder included in the coating layer and may include
heat-treatment or ultraviolet irradiation.
[0066] In this process, the abrasive grain layer 3 having bumps
that reflect the shape of the abrasive grains 5 may be formed on
the surface.
(4) Formation of Lubricant Layer
[0067] Next, the liquid lubricant layer 4 is formed on the abrasive
grain layer 3.
[0068] The liquid lubricant layer 4 may be formed on the abrasive
grain layer 3 by applying a liquid lubricant or a lubricant
solution in which a lubricant is dissolved in a solvent.
[0069] The liquid lubricant layer 4 may be applied by the same
methods described in the process (2).
[0070] Conventional burnishing tapes are usually manufactured in
the processes (1) to (3) among the described processes (1) to (4).
In this method of manufacturing, the abrasive grains are kneaded
with the binder in the process of (1) so that the surface of the
abrasive grain is covered with the binder. If the abrasive grain is
made to cure as an abrasive grain layer on the support, the surface
of the abrasive grain layer is slightly coated with a solid binder.
The thickness of the coating layer of the binder, however, is very
small and may be as thin as less than 0.01 micrometers according to
analysis of the present inventors. This is because the binder
covering an upper surface of the abrasive grains 5 as shown in FIG.
4A will gather on the support 2 due to self-weight at the time of
curing, and the thickness of the binder 6 on the surface 5c of the
abrasive grains 5 becomes very thin.
[0071] If the conventional burnishing tape including the abrasive
grain layer 3 is used to burnish the magnetic disk, as shown in
FIG. 4B, the abrasive grains 5 contained in the burnishing tape may
be separated to produce traces 8 of separation or produce crushed
abrasive grains 7. Abrasive grains separated or crushed are removed
from the burnishing tape and contaminate the magnetic disk surface
during burnishing.
[0072] In order to prevent the occurrence of such a phenomenon, as
shown in FIG. 4C, the invention includes the liquid lubricant layer
4 provided on the surface of the abrasive grain layer 3 of the
conventional burnishing tape prepared in the processes of (1) to
(3). With this configuration, the shearing force applied to the
burnishing tape 1 of an embodiment of the invention during
burnishing may be stabilized. Thus, the separation or crushing of
the abrasive grains 5 which constitute the abrasive grain layer 3
of the burnishing tape may be prevented. As a result, contamination
of the magnetic disk surface during burnishing may be
prevented.
Burnishing
[0073] Next, a method of burnishing according to an embodiment of
the invention will be described.
[0074] FIGS. 2A and 2B are schematic diagrams of an exemplary
burnisher used in a burnishing process of the invention. FIG. 3 is
a longitudinal cross-sectional view of an exemplary magnetic disk
to be burnished according to an embodiment of the invention.
[0075] In the burnishing of the invention, the polishing surface S
(i.e., the surface of the liquid lubricant layer) is pressed
against a surface of the magnetic disk 10 to make them slide
against each other to polish the surface of magnetic disk 10 and
remove the abnormal bumps on the surface.
[0076] First, an exemplary magnetic disk to which the burnishing of
the invention is applied will be described with reference to FIG.
3.
[0077] The magnetic disk 10 shown in FIG. 3 schematically includes
an underlayer 12, an intermediate layer 13, a magnetic layer 14 and
a protective layer 15 laminated successively on both main surfaces
of a nonmagnetic substrate 11. A lubricant layer 16 is provided on
top of these layers.
[0078] The material of the nonmagnetic substrate 11 is not
particularly limited and may include a nonmagnetic aluminum alloy
material and glass material usually employed as a material for the
magnetic disk 10. Examples of the glass material may include usual
soda glass, alumino silicate-based glass and amorphous glass.
Examples of the aluminum alloy material may include an Al--Mg alloy
consisting mainly of Al. Alternatively, the nonmagnetic substrate
11 may be formed of any nonmagnetic substances, such as silicon,
titanium and ceramic, and various resin materials.
[0079] The nonmagnetic substrate 11 may contain an substrate of
aluminum or glass and a surface layer in which one or more layers
consisting of NiP, NiP alloy or another alloy are formed on the
substrate of aluminum or glass by plating, sputtering or other
processes.
[0080] The underlayer 12 may be formed of Cr or a Cr alloy
consisting of Cr and one or more of Ti, Mo, Al, Ta, W, Ni, B, Si,
Mn and V.
[0081] When the underlayer 12 is formed as a multilayered
nonmagnetic underlayer, at least one of layers constituting the
nonmagnetic underlayer may be formed of Cr or the above-described
Cr alloy.
[0082] The nonmagnetic underlayer may consist of a NiAl-based
alloy, a RuAl-based alloy or a Cr alloy (an alloy which consists of
Cr and one or more of Ti, Mo, Al, Ta, W, Ni, B, Si and V).
[0083] If a multilayered nonmagnetic underlayer is used, at least
one of the layers constituting the nonmagnetic underlayer may
consist of a NiAl-based alloy, RuAl-based alloy or the
above-described Cr alloy.
[0084] The intermediate layer 13 preferably uses a nonmagnetic
material formed of a Co alloy consisting mainly of Co and having an
hcp structure from a viewpoint of promoting epitaxial growth of the
Co alloy. Examples of the Co alloy may include a Co--Cr-based
alloy, Co--Cr--Ru-based alloy, Co--Cr--Ta-based alloy and
Co--Cr--Zr-based alloy. The intermediate layer 13 may preferably
include one or more of these Co-based alloys.
[0085] The magnetic layer 14 preferably uses a material formed of a
Co alloy consisting mainly of Co and having an hcp structure.
Examples of the Co alloy may include a Co--Cr--Ta-based alloy,
Co--Cr--Pt-based alloy, Co--Cr--Pt--Ta-based alloy,
Co--Cr--Pt--B-based and Co--Cr--Pt--B--Cu-based alloy. The magnetic
layer 14 may preferably include one or more of these Co-based
alloys. The magnetic disk according to the present embodiment may
also have a layered structure consisting or two or more magnetic
layers.
[0086] The protective layer 15 may be formed of a carbon-based
material, such as CVD carbon, amorphous carbon, hydrogen-containing
carbon, nitrogen-containing carbon and fluorine-containing carbon,
which are formed by plasma CVD, and ceramic-based materials, such
as silica and zirconia. Among these, hard and fine CVD carbon is
suitably used from the viewpoint of economical efficiency and
productivity. The thickness of the protective layer 15 may
preferably be 0 to 150 angstroms (1 to 15 nm), and more preferably
be 20 to 60 angstroms (2 to 6 nm). If the protective layer 15 is
too thin, durability may become insufficient. If the protective
layer 15 is too thick, loss during recording and reproduction may
become large.
[0087] The lubricant layer 16 which is the top layer may be formed
of a material containing a polymer of polymerized unsaturated
group-containing perfluoropolyether compound. The polymerized
unsaturated group-containing perfluoropolyether compound may be a
compound which includes an organic group having a polymerizable
unsaturated bonding at least one end of perfluoropolyether, which
is a main chain.
[0088] The magnetic disk to be burnished by the method according to
the invention may be an in-plane magnetic disk or a perpendicular
magnetic disk.
[0089] Next, an exemplary burnisher used to burnish in the
invention will be described with reference to FIGS. 2A and 2B.
[0090] A burnisher 20 shown in FIGS. 2A and 2B includes a magnetic
disk rotary drive mechanism 21, burnishing tapes 1a and 1b, a
burnishing tape running system 22 and a burnishing tape pressing
device 23.
[0091] The magnetic disk rotary drive mechanism 21 includes a
spindle 24 which is driven to rotate by an unillustrated spindle
motor, and a magnetic disk holding mechanism 25 attached to the
center of the spindle 24. The central portion of the magnetic disk
10 is secured to the magnetic disk holding mechanism 25, which
holds the magnetic disk 10. When the spindle 24 is driven to rotate
with the magnetic disk 10 held by the magnetic disk holding
mechanism 25, the magnetic disk 10 is rotated according to the
rotational direction and the rotational rate of the spindle 24.
[0092] The magnetic disk rotary drive mechanism 21 is configured to
rotate the magnetic disk 10 in a rotational direction (the
direction of arrow r in FIGS. 2A and 2B) such that the scanning
direction of a track of the magnetic disk 10 which is rotated is
opposite to the running direction of a first burnishing tape 1a
which is moved between a first guide roll 26 and a second guide
roll 27 (i.e., the direction of arrow Ra in FIGS. 2A and 2B), which
will be described later, and is opposite to the running direction
of a second burnishing tape 1b which is moved between a fifth guide
roll 30 and a sixth guide roll 31 (i.e., the arrow Rb direction in
FIGS. 2A and 2B).
[0093] The burnishing tapes 1a and 1b are elongated tapes
fabricated in the method of manufacturing of the burnishing tape
described above.
[0094] A burnisher 20 includes a first burnishing tape 1a and a
second burnishing tape 1b. The first burnishing tape 1a is moved
such that a polishing surface S thereof is moved opposing a first
main surface 10a of the magnetic disk 10. The second burnishing
tape 1b is moved such that a polishing surface S thereof is moved
opposing a second main surface 10b of the magnetic disk 10.
[0095] The burnishing tape running system 22 has a first burnishing
tape running system 22a and a second burnishing tape running system
22b, and the magnetic disk 10 is disposed between the burnishing
tape running system 22a and the second burnishing tape running
system 22b. The first burnishing tape running system 22a includes
an unillustrated supply roll, a take-up roll and first to fourth
guide rolls 26 to 29 disposed below the supply roll and the take-up
roll.
[0096] The first to fourth guide rolls 26 to 29 are disposed such
that each rotation axis thereof is substantially parallel to a
first main surface 10a of the magnetic disk 10 and rotation axes
thereof are mutually substantially parallel to each other. The
first and second guide rolls 26 and 27 are disposed such that their
distances from the first main surface 10a of the magnetic disk 10
are substantially equal to each other. The third and fourth guide
rolls 28 and 29 are disposed such that their distances from the
first main surface 10a of the magnetic disk 10 are substantially
equal to each other at a position further apart from the magnetic
disk 10 than the first and second guide rolls 26 and 27
[0097] In the thus-configured first burnishing tape running system
22a, the elongated first burnishing tape 1a is sequentially fed out
from the supply roll. The first burnishing tape 1a fed from the
supply roll is moved along a substantially U-shaped running route
while being guided by the first to fourth guide rolls 26 to 29, and
then taken up by the take-up roll. Here, the polishing surface S of
the first burnishing tape 1a opposes the first main surface 10a of
the magnetic disk 10 when moving between the first and second guide
rolls 26 and 27.
[0098] The second burnishing tape running system 22b includes an
unillustrated supply roll, a take-up roll and fifth to eighth guide
rolls 30 to 33. The fifth to eighth guide rolls 30 to 33 are
disposed symmetrically with the first to fourth guide rolls 26 to
29 at both sides of the magnetic disk 10.
[0099] In the thus-configured second burnishing tape running system
22b, an elongated second burnishing tape 1b is sequentially fed
from the supply roll. The second burnishing tape 1b fed from the
supply roll is moved along a substantially U-shaped running route
while being guided by the fifth to eighth guide rolls 30 to 33 and
then taken up by the take-up roll. Here, the polishing surface S of
the second burnishing tape 1b opposes the second main surface 10b
of the magnetic disk 10 when moving between the fifth and sixth
guide rolls 30 and 31.
[0100] The burnishing tape pressing device 23 includes a first
burnishing tape pressing device 23a and a second burnishing tape
pressing device 23b. The first burnishing tape pressing device 23a
presses the first burnishing tape 1a which is moved between the
first and second guide rolls 26 and 27 to bring into contact with
(i.e., dab against) the first main surface 10a of the magnetic disk
10. The second burnishing tape pressing device 23b presses the
second burnishing tape 1b which is moved between the fifth and
sixth guide rolls 30 and 31 to bring into contact with (i.e., dab
against) the second main surface 10b of the magnetic disk 10.
[0101] In a state in which the magnetic disk 10 is driven to rotate
in the direction of arrow r shown in FIGS. 2A and 2B by the
magnetic disk rotary drive mechanism 21, if the first burnishing
tape 1a moving between the first and second guide rolls 26 and 27
is pressed against the first main surface 10a of the magnetic disk
10 by the first burnishing tape pressing device 23a, and the second
burnishing tape 1b moving between the fifth and sixth guide rolls
30 and 31 is pressed against the second main surface 10b of the
magnetic disk 10 by the second burnishing tape pressing device 23b,
the polishing surface S of the first burnishing tape 1a is made to
slide against the first main surface 10a and the polishing surface
S of the second burnishing tape 1a is made to slide against the
second main surface 10b. In this manner, both main the surfaces 10a
and 10b of the magnetic disk 10 are polished by the burnishing
tapes 1a and 1b so that bumps on both the main surfaces 10a and 10b
are removed to provide smooth main surfaces. Here, in the burnisher
20 of the present embodiment, since unused burnishing tapes 1a and
1b are sequentially fed from the supply roll, used for polishing
and then taken up to the take-up roll, unused burnishing tapes 1a
and 1b are always supplied to each main surface of the magnetic
disk 10. Thus, each main surface 10a and 10b of the magnetic disk
10 may be polished efficiently.
[0102] The first and second burnishing tape pressing devices 23a
and 23b are preferably formed of a material having flexibility at
an area to be in contact with the burnishing tapes 1a and 1b. With
this configuration, the polishing surfaces S of the burnishing
tapes 1a and 1b may be pressed against the surfaces of the magnetic
disk 10 sufficiently close to each other so as to efficiently
polish the surface of the magnetic disk 10. Exemplary first and
second burnishing tape pressing devices 23a and 23b may be, for
example, a pad consisting of resin or textile or a device having a
pressing member, such as a rubber roller, which will be made to
abut a back surface of the burnishing tape so as to press the
burnishing tapes 1a and 1b against the magnetic disk 10.
[0103] In the burnisher 20 of the present embodiment, the first and
second burnishing tape pressing devices 23a and 23b each include
metal blocks 34 and 35, pads 36 and 37 attached to one side surface
of the metal blocks 34 and 35 and a driving means (not shown) which
makes the metal blocks 34 and 35 reciprocate in a horizontal
direction (i.e., a direction perpendicular to each main surface of
the magnetic disk, indicated by arrows F1 and F2 in FIGS. 2A and
2B).
[0104] In such burnishing tape pressing devices 23a and 23b, as
shown in FIG. 2A, when the driving means makes the metal blocks 34
and 35 move in the direction of arrow F1 with the pads 36 and 37
being spaced apart from the burnishing tapes 1a and 1b (i.e., a
stand-by state), the pads 36 and 37 abut the back surface of the
burnishing tapes 1a and 1b and press the burnishing tapes 1a and 1b
against the magnetic disk 10. As a result, as shown in FIG. 2B, the
polishing surfaces S of the burnishing tapes 1a and 1b are brought
into contact with the main surfaces of the magnetic disk 10. In
this state, when the driving means makes the metal blocks 34 and 35
move in the direction indicated by the arrow F2, the burnishing
tapes 1a and 1b move apart from the magnetic disk 10, and further,
the pads 36 and 37 move apart from the burnishing tapes 1a and 1b,
and the driving means returns to its stand-by state.
[0105] Next, an operation of the burnisher 20 will be
described.
[0106] The first burnishing tape 1a is placed on the first
burnishing tape running system 22a and the second burnishing tape
1b is placed on the second burnishing tape running system 22b.
[0107] The magnetic disk holding mechanism 25 is mounted on and
held by the magnetic disk 10.
[0108] As shown in FIG. 2A, in the initial state of the burnisher
20, each of the pads 36 and 37 of the first and second burnishing
tape pressing devices 23a and 23b is spaced apart from the
burnishing tapes 1a and 1b (i.e., stand-by state).
[0109] Next, when operation of each part is turned on, the magnetic
disk rotating drive mechanism 21 drives the magnetic disk 10 to
rotate in the direction of arrow r shown in FIG. 4A. Each supply
roll sequentially feeds the first and second burnishing tapes 1a
and 1b. The fed first burnishing tape 1a is moved along the
substantially U-shaped running route while being guided by the
first to fourth guide rolls 26 to 29, and then taken up by the
take-up roll. The fed second burnishing tape 1b is moved along the
substantially U-shaped running route while being guided by the
fifth to eighth guide rolls 30 to 33, and then taken up by the
take-up roll.
[0110] The polishing surface S of the first burnishing tape 1a
which is moved between first and second guide rolls 26 and 27
opposes the first main surface 10a of the magnetic disk 10 and is
moved in a direction opposite the scanning direction of the track
of the magnetic disk 10.
[0111] The polishing surface S of the second burnishing tape 1b
which is moved between the fifth guide roll 30 and the sixth guide
roll 31 opposes the second main surface 10b of the magnetic disk 10
and is moved in a direction opposite the scanning direction of the
track of the magnetic disk 10.
[0112] Next, the first burnishing tape pressing device 23a presses
the first burnishing tape 1a moving between the first and second
guide rolls 26 and 27 against the first main surface 10a of the
magnetic disk 10 and brings the polishing surface S of the
burnishing tape 1a in contact with (i.e., dab against) the first
main surface 10a. The second burnishing tape pressing device 23b
presses the second burnishing tape 1a which is moved between the
fifth and sixth guide rolls 26 and 27 against the second main
surface 10b of the magnetic disk 10 and brings the polishing
surface S of the burnishing tape 1b in contact with (i.e., dab
against) the second main surface 10b.
[0113] When the polishing surface S of the moving first burnishing
tape 1a is pressed against the first main surface 10a of the
magnetic disk 10 while the magnetic disk 10 being driven to rotate
in the direction of arrow r in FIGS. 2A and 2B and the polishing
surface S of the moving second burnishing tape 1b is pressed
against the second main surface 10b of the magnetic disk 10, the
polishing surface S of the first burnishing tape 1a is made to
slide against the first main surface 10a and the polishing surface
S of the second burnishing tape 1a is made to slide against the
second main surface 10b. In this manner, both the main surfaces 10a
and 10b of the magnetic disk 10 are polished by the burnishing
tapes 1a and 1b so that bumps on both the main surfaces 10a and 10b
are removed to provide smooth main surfaces.
[0114] Since the lubricant layer 4 having the above-described
structure is provided in the burnishing tape 1, the occurrence of
crushing of the abrasive grains 5 included in the abrasive grain
layer 3 or removal of the crushed grains may be prevented. In this
manner, the surface of the magnetic disk 10 may be smoothed while
contamination of the magnetic disk 10 caused by the crushed grains
is prevented. Even if the thus-processed magnetic disk 10 is
incorporated in a magnetic recording and reproducing device (i.e.,
a hard disk device) in which the distance between the magnetic head
and the magnetic disk 10 is very small, collision between the
magnetic head and the magnetic disk 10 may be prevented to provide
desired operating characteristics.
[0115] The burnishing tape 1 used in the present embodiment
includes the abrasive grain layer 3 on the support 2 and the
surface of the abrasive grain layer 3 is covered by the liquid
lubricant layer 4 having the thickness of 0.01 to 10 micrometers.
In another embodiment, however, a burnishing tape having no liquid
lubricant layer may alternatively be supplied to the burnisher as a
burnishing tape 1 and a liquid lubricant may be dropped onto the
burnishing surface from above the burnishing tape during
burnishing. The dropping amount of the liquid lubricant should be
carefully determined. If the dropping amount of the liquid
lubricant is too large, the surface of the magnetic disk may be
contaminated with the liquid lubricant.
[0116] The burnished magnetic disk according to the invention is
then processed at a final inspection process (i.e., a tester) and
is incorporated in the magnetic recording and reproducing device
(i.e., the hard disk device).
[0117] In the other embodiment, as a method of burnishing a
magnetic disk, which includes a step of polishing a surface of a
magnetic disk comprising at least an underlayer, a magnetic layer
and a protective layer on a nonmagnetic substrate, after pressing
an abrasive grain surface of a burnishing tapes 1a and 1b supplied
to the magnetic disk surface, while the magnetic disk is rotated,
the burnishing tapes 1a and 1b supplied to the magnetic disk
surface includes a support 2 and an abrasive grain layer 3 which
contains abrasive grains and is provided on the support 2; and the
method of burnishing a magnetic disk further includes a step of
supplying a liquid lubricant between the support 1 and the abrasive
grain layer when the magnetic disk surface is polished by the
burnishing tape 1.
[0118] When implementing this method, since viscosity of a 100%
lubricant is excessively high, the lubricant may preferably be
diluted with a solvent. The concentration of the lubricant may
preferably be 0.01% by volume and thus the dripping amount of the
diluted solution may preferably be about 0.01 to 1 cc per second. A
fluorine-based solvent may be used as the solvent.
[0119] As described above, contamination of the magnetic disk
surface may be prevented, which has the same effect as the
burnishing process in which a lubricant is supplied before the
burnishing process and the resulting burnishing tape 1 having the
lubricant layer 4 is used during the burnishing, as described
previously.
Magnetic Recording and Reproducing Device
[0120] Next, an example of a magnetic recording and reproducing
device in which the magnetic disk processed by the burnishing
process of the invention is incorporated will be described.
[0121] FIG. 5 is a schematic configuration diagram of an exemplary
magnetic recording and reproducing device.
[0122] The magnetic recording and reproducing device 80 includes a
burnished magnetic disk 10 according to the embodiment of the
invention, a medium driving section 81 which drives to rotate the
magnetic disk 10, a magnetic head 82 which records information in
the magnetic disk 10 and reproduces the recorded information, a
head driving section 83 which drives a magnetic head 27 to move
relatively with the magnetic disk 10 and a recording and
reproducing signal processing system 84. The recording and
reproducing signal processing system 84 is configured to process
input data, transmit obtained recording signals to the magnetic
head 82, process reproducing signals from the magnetic head 82 and
output obtained data.
[0123] The surface of the magnetic disk 10 of the magnetic
recording and reproducing device 80 is fairly smooth due to the
burnishing process of the invention and is thus very clean.
Accordingly, even if the distance between the magnetic head 82 and
the magnetic disk 10 is very small, collision between the magnetic
head 82 and the magnetic disk 10 may be prevented to provide high
recording density and reliability.
Example
[0124] An Example for demonstrating the invention will be given
below for illustrative purposes only. The invention is not limited
to the Example.
Fabrication of Magnetic Disk
[0125] A washed glass substrate (manufactured by HOYA Corporation,
2.5 inches in outer diameter) is placed in a film forming chamber
of a DC magnetron sputtering apparatus (C-3010 manufactured by
Canon ANELVA Corporation). A vacuum is formed in film forming
chamber so that the ultimate vacuum becomes 1.times.10.sup.-5 Pa.
On this glass substrate, a target of 89Co-4Zr-7Nb (Co content 89 at
%, Zr content 4 at % and Nb content 7 at %) is used to form a
100-nm-thick underlayer by sputtering at the substrate temperature
of 100.degree. C. or less.
[0126] The glass substrate is then heated to 200.degree. C., and a
5-nm-thick intermediate layer is formed on the underlayer using a
65Co-30Cr-5B target. Then, a 25-nm-thick magnetic layer is formed
using a 61Co-20Cr-17Pt-2B target. In this sputtering process, a
layer is formed using argon as the process gas with the pressure
inside the film forming chamber being 0.5 Pa.
[0127] A 5-nm-thick protective film layer is formed on the magnetic
layer by the plasma CVD.
[0128] A lubricant layer consisting of perfluoropolyether is formed
by dipping. In this manner, a magnetic disk having various layers
formed on the glass substrate is obtained.
[0129] Each of the thus-obtained 1000 magnetic disks is placed in a
tape burnisher 20 as shown in FIGS. 2A and 2B to polish the surface
thereof.
[0130] A burnishing tape is fabricated in the following manner.
Alumina particles (i.e., crystal growth particles) having an
average particle diameter of 0.5 micrometers are made to adhere to
a polyethylene terephthalate film by epoxy resin in a single
particle layer. Then, a perfluoropolyether liquid lubricant layer
is applied to the alumina particle surface to the thickness of
about 1 micrometer.
[0131] The thickness of the layer formed by using the epoxy resin
is about 0.3 micrometers from the surface of the film. The
thickness of the epoxy resin layer is about 0.2 micrometers from
the upper surfaces of the alumina particles. The burnishing tape is
pressed against the magnetic disk surface at the pressure of 98 mN.
The magnetic disk is driven to rotate at 300 rpm. The burnishing
tape is fed at the rate of 10 mm per second. In this manner, the
burnishing is continued for 5 seconds.
Evaluation of Burnishing Tape
[0132] Each of the thus-obtained 1000 magnetic disks is placed in a
tester (i.e., a surface test device) and the disk surface of each
magnetic disk is examined. As a result, separated alumina grains
are observed to adhere into the surfaces of three magnetic
disks.
Comparative Example
[0133] Each of 1000 magnetic disks are fabricated and subject to a
tape burnishing process both under the same condition as that in
the Example. In this example, the burnishing tape, which is the
same as that used in the Example except that no liquid lubricant
layer is provided, is used.
[0134] Each of the thus-fabricated 1000 magnetic disks is examined
under the same condition as that of the Example, and the separated
alumina particles are observed to adhere into the surfaces of 55
disks.
[0135] According to the comparison result, it is found that the
method of Example of the invention has significant effects. In
particular, the number of the alumina particles adhering into the
surface of the magnetic disks is only three out of 1000 after
burnishing the magnetic disks, while the number of the alumina
particles adhering into the surface of the magnetic disks is as
many as 55 out of 1000 in the Comparative Example in which no
liquid lubricant layer is provided.
[0136] The burnishing tape according to an embodiment of the
invention may smooth the surface of the magnetic disk while
magnetic disk contamination caused by crushed abrasive grains is
prevented. Thus, the burnishing tape is suited to burnish the
magnetic disk which is to be applied to a hard disk device in which
the distance between the magnetic head and the magnetic disk is
very small.
[0137] It is apparent that the present invention is not limited to
the above Example, but may be modified and changed without
departing from the scope and spirit of the invention.
* * * * *