U.S. patent application number 11/398653 was filed with the patent office on 2006-10-12 for apparatus for polishing edge surface of glass substrate for magnetic recording media, and process for producing glass substrate.
This patent application is currently assigned to Asahi Glass Company, Limited. Invention is credited to Shohei Chida, Masami Kaneko, Mitsuhiko Komakine.
Application Number | 20060228997 11/398653 |
Document ID | / |
Family ID | 37062679 |
Filed Date | 2006-10-12 |
United States Patent
Application |
20060228997 |
Kind Code |
A1 |
Chida; Shohei ; et
al. |
October 12, 2006 |
Apparatus for polishing edge surface of glass substrate for
magnetic recording media, and process for producing glass
substrate
Abstract
To provide an apparatus for polishing an edge surface of a glass
substrate for magnetic recording media and a process for producing
a glass substrate for magnetic recording media, whereby with
respect to a glass substrate to be used as a substrate for a hard
disk, the quality and productivity can be improved without
requiring extra effort. In a process for practically producing a
hard disk by using a glass substrate 2, the arithmetic average
roughness (Ra) required for the outer edge surface of the glass
substrate is at most 100 nm. With the roughness of this level,
highly productive mechanical polishing by a grindstone is possible.
Further, since such mechanical polishing is possible, the
productivity can be increased by adopting sheet treatment. Further,
by stabilizing the processing margin by employing a grindstone 4
made of resin, variations in the dimensional precision in the
individual glass substrates can be minimized. The grindstone 4 made
of resin is a formed grindstone having a groove 4A formed to
simultaneously polish the outer edge surface 2A of the glass
substrate 2 and chamfers 2B and 2C on both sides thereof. By
employing such a formed grindstone as the grindstone 4 of the
resin, it is possible to simultaneously polish the outer edge
surface 2A of the glass substrate 2 and the chamfers 2B and 2C on
both sides thereof, whereby the productivity and quality can be
further improved.
Inventors: |
Chida; Shohei; (Pranakornsri
Ayutthaya, TH) ; Kaneko; Masami; (Yokohama-shi,
JP) ; Komakine; Mitsuhiko; (Chiyoda-ku, JP) |
Correspondence
Address: |
C. IRVIN MCCLELLAND;OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Asahi Glass Company,
Limited
Chiyoda-ku
JP
|
Family ID: |
37062679 |
Appl. No.: |
11/398653 |
Filed: |
April 6, 2006 |
Current U.S.
Class: |
451/11 ;
451/44 |
Current CPC
Class: |
B24B 9/065 20130101 |
Class at
Publication: |
451/011 ;
451/044 |
International
Class: |
B24B 51/00 20060101
B24B051/00; B24B 1/00 20060101 B24B001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 7, 2005 |
JP |
2005-111104 |
Claims
1. An apparatus for polishing an edge surface of a glass substrate
for magnetic recording media, characterized in that an outer edge
surface and/or an inner edge surface of a glass substrate for
magnetic recording media is polished by pressing said outer edge
surface and/or said inner edge surface against a grindstone made of
resin, prepared by mixing abrasive grains to a resin, so that the
arithmetic average roughness (Ra) of said outer edge surface and/or
said inner edge surface would be at most 100 nm.
2. An apparatus for polishing an edge surface of a glass substrate
for magnetic recording media, which comprises a first station to
carry out mounting and dismounting of the glass substrate, a second
station to carry out grinding of an outer edge surface and/or an
inner edge surface of the glass substrate, a third station to carry
out polishing of the outer edge surface and/or the inner edge
surface of the glass substrate, and a transfer mechanism to
transfer the glass substrate mounted at the first station
sequentially via the second station and the third station to the
first station, wherein at the third station, the outer edge surface
and/or the inner edge surface of the glass substrate is polished by
pressing said outer edge surface and/or said inner edge surface
against a grindstone made of resin, prepared by mixing abrasive
grains to a resin, so that the arithmetic average roughness (Ra) of
said outer edge surface and/or said inner edge surface would be at
most 100 nm.
3. The apparatus for polishing an edge surface of a glass substrate
for magnetic recording media according to claim 1, wherein the
grindstone made of resin is a formed grindstone to simultaneously
polish said outer edge surface and/or said inner edge surface, and
chamfers.
4. The apparatus for polishing an edge surface of a glass substrate
for magnetic recording media according to claim 2, wherein the
grindstone made of resin is a formed grindstone to simultaneously
polish said outer edge surface and/or said inner edge surface, and
chamfers.
5. A process for producing a glass substrate for magnetic recording
media, which comprises polishing an outer edge surface and/or an
inner edge surface of a glass substrate for magnetic recording
media by pressing said outer edge surface and/or said inner edge
surface against a grindstone made of resin, prepared by mixing
abrasive grains to a resin, to finish so that the arithmetic
average roughness (Ra) of said outer edge surface and/or said inner
edge surface would be at most 100 nm.
Description
[0001] The present invention relates to an apparatus for polishing
an edge surface of a glass substrate for magnetic recording media
and a process for producing a glass substrate. Particularly, it
relates to an apparatus for polishing an edge surface of a glass
substrate for magnetic recording media and a process for producing
a glass substrate, designed to polish an outer edge surface of a
glass substrate for hard disks made of glass substrate as the base
material.
[0002] As a substrate for hard disks to be mounted for personal
computers, various information recording devices, etc. in recent
years, attention has been drawn to one made of glass excellent in
planalization and substrate strength rather than one made of Al
(aluminum).
[0003] Such a glass substrate for hard disks is processed into a
doughnut-type circular shape, and after such processing into a
circular shape, its outer edge surface is subjected to chamfering
by a grindstone such as an electrodeposited grindstone. However,
the surface roughness of the outer edge surface after such
chamfering is as rough as about 200 nm by arithmetic average
roughness (Ra), and there was a problem such that if it was
attempted to transfer it in such a state to a process step for the
production of hard disks, when the glass substrate was in contact
with a cassette for transportation or with various jigs, particles
were likely to be formed as dusts from the edge surface, etc. of
the glass substrate thus leading to manufacturing defects. Further,
with the rough surface, washing efficiency was poor, and there was
a drawback that dirt or stain on the outer edge surface was hardly
removable thus leading to contamination-type defects.
[0004] Patent Document 1 discloses an apparatus for polishing glass
substrates, wherein at the time of polishing outer peripheral edge
surfaces of glass substrates, a plurality of glass substrates are
laminated and cased by passing a shaft through center holes of the
respective glass substrates, and this substrate case is rotated by
a rotary driving device, and a rotary glass made of nylon is
rotated and pushed against the outer edge surfaces of the plurality
of rotating glass substrates, while an abrasive such as cerium
oxide is supplied, to polish the outer edge surfaces of the glass
substrates. It is thereby possible to polish the outer edge
surfaces of the glass substrates to a level of about 10 nm by
arithmetic average roughness (Ra).
[0005] Patent Document 1: JP-A-12-185927
[0006] However, the polishing apparatus disclosed in Patent
Document 1 had drawbacks such that lamination and separation of the
glass substrates were required to be carried out by manual
operation, and not only extra time and effort were required, but
also scars were likely to result during the handling. Further, in
order to meet the requirement for improvement in precision for
removal of surface defects in recent years, when the glass
substrates were to be laminated, it was necessary to insert a
spacer made of resin between adjacent glass substrates for every
substrate, which also led to a drawback of requiring extra time and
effort. Further, recently, there is a tendency that the dimensional
tolerance of the inner and outer diameters tends to be severe, and
by the polishing apparatus disclosed in Patent Document 1,
variations were observed in the processing margin among the
laminated glass substrates, and to reduce such variations, it was
sometimes necessary to carry out an operation of reversing the
lamination order of laminated substrates in the middle of
processing, which led to a drawback of requiring further time and
effort.
[0007] Furthermore, the depth of damages (scars) due to processing
by an electrodeposited grindstone, forming the roughness, is from
10 to 20 .mu.m from the surface of the glass substrate, and in
order to reduce the surface roughness after processing by such an
electrodeposited grindstone, it is necessary to polish it with a
processing margin of at least the depth of such damages. However,
by a polishing apparatus designed mainly for polishing by free
abrasive grains employing an abrasive such as cerium oxide, like
the polishing apparatus disclosed in Patent Document 1, the
polishing rate tends to be substantially low. Therefore, in order
to secure the productivity, it is necessary to increase the number
of substrates to be treated per batch by laminating a large number
of glass substrates. However, if the number of laminated substrates
is increased, processing margins and variations within the batch
will be large. Accordingly, there was a problem such that as
mentioned above, an extra operation of e.g. reversing the
lamination order of the laminated substrates in the middle of
processing was required.
[0008] The present invention has been made under these
circumstances, and it is an object of the present invention to
provide an apparatus for polishing an edge surface of a glass
substrate for magnetic recording media, whereby formation of scars
due to handling can be prevented, and the productivity can be
improved without requiring extra effort.
[0009] To accomplish the above object, the present invention
provides the following:
[0010] 1. An apparatus for polishing an edge surface of a glass
substrate for magnetic recording media, characterized in that an
outer edge surface and/or an inner edge surface of a glass
substrate for magnetic recording media is polished by pressing said
outer edge surface and/or said inner edge surface against a
grindstone made of resin, prepared by mixing abrasive grains to a
resin, so that the arithmetic average roughness (Ra) of said outer
edge surface and/or said inner edge surface would be at most 100
nm.
[0011] 2. An apparatus for polishing an edge surface of a glass
substrate for magnetic recording media, which comprises a first
station to carry out mounting and dismounting of the glass
substrate, a second station to carry out grinding of an outer edge
surface and/or an inner edge surface of the glass substrate, a
third station to carry out polishing of the outer edge surface
and/or the inner edge surface of the glass substrate, and a
transfer mechanism to transfer the glass substrate mounted at the
first station sequentially via the second station and the third
station to the first station, wherein at the third station, the
outer edge surface and/or the inner edge surface of the glass
substrate is polished by pressing said outer edge surface and/or
said inner edge surface against a grindstone made of resin,
prepared by mixing abrasive grains to a resin, so that the
arithmetic average roughness (Ra) of said outer edge surface and/or
said inner edge surface would be at most 100 nm.
[0012] 3. The apparatus for polishing an edge surface of a glass
substrate for magnetic recording media according to the above 1 or
2, wherein the grindstone made of resin is a formed grindstone to
simultaneously polish said outer edge surface and/or said inner
edge surface, and chamfers.
[0013] 4. A process for producing a glass substrate for magnetic
recording media, which comprises polishing an outer edge surface
and/or an inner edge surface of a glass substrate for magnetic
recording media by pressing said outer edge surface and/or said
inner edge surface against a grindstone made of resin, prepared by
mixing abrasive grains to a resin, to finish so that the arithmetic
average roughness (Ra) of said outer edge surface and/or said inner
edge surface would be at most 100 nm.
[0014] The invention as defined in the above 1, 2 and 3, has been
made on such a basis that in the polishing apparatus disclosed in
Patent Document 1, the cause to hinder improvement of the
productivity resides in the adoption of a free abrasive grain type
polishing apparatus employing an abrasive for carrying out high
precision polishing, and the cause for incapability of readily
absorbing variations in the processing margins of glass substrates,
resides in the adoption of batch treatment.
[0015] Firstly, in Patent Document 1, the outer edge surface is
polished with high precision at a level of 10 nm by arithmetic
average roughness (Ra). However, it has been found that the
practical arithmetic average roughness (Ra) required for the
production of hard disks may be at a level of at most 100 nm
without any problem such as formation of dust, and at this level,
mechanical polishing with high productivity is feasible by
employing a grindstone made of resin (such as urea resin) having a
hardness lower than the glass substrate, and that by suitably
selecting the abrasive material (such as diamond) for the
grindstone of resin, the abrasive grain size, the abrasive grain
density, the abrasive hardness, the specification of the resin,
etc., polishing can be accomplished so that the arithmetic average
roughness (Ra) after the processing would be from 30 nm to 100 nm.
Further, as such mechanical polishing is feasible, it has been
found possible to adopt sheet treatment to increase the
productivity and to eliminate variations in processing margins of
the glass substrates caused by lamination polishing, and further,
to absorb variations in dimensional precision of individual glass
substrates.
[0016] According to the above 2, the polishing time by the
grindstone made of resin at the third station is substantially
equal to the grinding time at the second station in the previous
step, and sheet processing is feasible, whereby mounting and
dismounting of the glass substrate are carried out at the first
station, the glass substrate is transferred from the first station
to the second station by the transfer mechanism and then grinding
is carried out; and then, the substrate is transferred from the
second station to the third station, followed by polishing. At that
time, the second glass substrate is subjected to grinding at the
second station. The glass substrate after completion of polishing
at the third station, is transferred by the transfer mechanism to
the first station, then dismounted here and transferred to the next
step. Accordingly, by the polishing apparatus as defined in the
above 2, grinding and polishing by a grindstone made of resin can
be carried out by a single polishing apparatus. Thus, as compared
with the polishing apparatus disclosed in Patent Document 1, labor
saving and space saving will be possible.
[0017] As disclosed in the above 3, in the polishing apparatus
according to the above 1 or 2, the grindstone made of resin is
preferably a formed grindstone to simultaneously polish the outer
edge surface and/or the inner edge surface and chamfers of the
glass substrate for magnetic recording media.
[0018] By employing a formed grindstone as the grindstone made of
resin, the outer edge surface and/or the inner edge surface of the
glass substrate, and the chamfers can simultaneously be polished,
whereby the productivity will be further improved. Further, the
groove of the formed grindstone may readily be formed into a shape
whereby the entire edge surface and chamfers can uniformly be
processed, by e.g. a method wherein a glass substrate to be
processed is pressed against the grindstone made of resin, formed
into a rod shape, with a force higher than the pressing force
during the polishing, so that a concave recess is formed
(transferred) on the surface of the rod shape grindstone made of
resin. Whereas, in the polishing apparatus disclosed in the Patent
Document 1, polishing is carried out by a brush, whereby the tip of
the brush is hardly pressed against chamfers, and the chamfers
cannot be polished with good precision.
[0019] As described above, by the apparatus for polishing an edge
surface of a glass substrate for magnetic recording media and the
process for producing a glass substrate according to the present
invention, an outer edge surface and/or an inner edge surface of
the glass substrate is polished by pressing the outer edge surface
and/or the inner edge surface of the glass substrate against a
grindstone made of resin, prepared by mixing abrasive grains to a
resin, so that the arithmetic average roughness (Ra) of the outer
edge surface and/or inner edge surface of the glass substrate would
be at most 100 nm, whereby the productivity can be improved without
formation of scars due to handling or without requiring extra
effort.
[0020] In the accompanying drawings,
[0021] FIG. 1 is a view illustrating the construction of an
embodiment of the apparatus for polishing a glass substrate.
[0022] FIG. 2 is a view illustrating an embodiment of
grinding/polishing to be carried out by the polishing apparatus
shown in FIG. 1.
[0023] FIG. 3 is a view illustrating a formed grindstone prepared
from a grindstone made of resin, to polish the outer periphery of a
glass substrate.
[0024] FIG. 4 is a view illustrating a stick-form grindstone
prepared from a grindstone made of resin, to polish the outer
periphery of the glass substrate.
[0025] In the FIGS., reference numeral 1 represents a turn table, 2
a glass substrate, 3 a grindstone for grinding the outer edge
surface, 4 a grindstone made of resin, 5 a grindstone for grinding
an inner edge surface, 6 a grindstone for polishing an inner edge
surface, 7 a holder, 10 an apparatus for polishing an edge surface
of a glass substrate, 30 a stick-form grindstone, A a first
station, B a second station and C a third station.
[0026] Now, preferred embodiments of the apparatus for polishing an
edge surface of a glass substrate for magnetic recording media and
the process for producing a glass substrate, according to the
present invention, will be described in detail with reference to
the accompanying drawings.
[0027] FIG. 1 is a view illustrating the construction of an
embodiment of the apparatus 10 for polishing an edge surface of a
glass substrate for magnetic recording media. The processing system
by this apparatus 10 for polishing an edge surface is a system
designed to simultaneously carry out, at different sites, at least
a step to carry out mounting and dismounting of the glass
substrate, a step to carry out rough grinding of inner and outer
edge surfaces of the glass substrate and a step to carry out
polishing of the inner and outer edge surfaces of the glass
substrate, and to realize such a design, the system comprises a
plurality of stations including at least a first station A to carry
out mounting and dismounting of the glass substrate, a second
station B to carry out rough grinding of the inner and outer edge
surfaces of the glass substrate, and a third station C to carry out
polishing of the inner and outer edge surfaces of the glass
substrate, and a transfer mechanism to transfer the glass substrate
mounted at the first station A sequentially via the above mentioned
respective stations. Further, this processing system is designed so
that the grinding and polishing of the edge surfaces of one glass
substrate will be finished every time in a duration of the time for
polishing which requires the longest operation time among the above
three steps plus the time for one transportation between the
stations.
[0028] One shown in FIG. 1 is the simplest three station type
polishing apparatus 10. A first station A to carry out mounting and
dismounting of a glass substrate, a second station B to carry out
grinding of inner and outer edge surfaces of the glass substrate
and a third station C to carry out polishing of inner and outer
edge surfaces of the glass substrate, are arranged at equal
intervals (360.degree./n where n is the number of stations,
120.degree. in this case) on a turn table 1.
[0029] Glass substrates to be processed are rotatably supported by
three glass substrate holders 7 disposed at the positions of
120.degree. on this turn table 1. This turn table 1 is provided
with a rotation driving mechanism, and the three glass substrate
holders 7, 7 and 7 will be stepwise driven to correspond to the
positions of the first station A, second station B and third
station C, respectively. The timing of the stepwise driving is the
above-mentioned time for polishing plus the time for one transfer
between stations. Firstly, at the first station A, dismounting of a
polished glass substrate and mounting of a non-polished glass
substrate are carried out; at the second station B, grinding of
inner and outer edge surfaces of the glass substrate is carried
out, and at the third station C, polishing of inner and outer edge
surfaces of the glass substrate is carried out, simultaneously in a
parallel fashion. Grinding and polishing are carried out at
different stations, and grinding stones are separately prepared as
shown in FIG. 2, i.e. a grinding stone 3 for grinding the outer
edge surface, a grinding stone 4 for polishing the outer edge
surface, a grinding stone for grinding the inner edge surface, and
a grinding stone 6 for polishing the inner edge surface. In the
embodiment, the grinding stone 4 for grinding the outer edge
surface and the grinding stone 6 for polishing the inner edge
surface are grinding stones made of resin of the present invention,
and accordingly, the grinding stone 4 for polishing the outer edge
surface will be referred to the grinding stone 4 made of resin, and
the grinding stone 6 for polishing the inner edge surface will be
referred to as the grinding stone 6 made of resin. As such a
grinding stone made of resin, one prepared by mixing diamond
abrasive grains to a urethane resin or urea resin may, for example,
be preferably used.
[0030] The glass substrate 2 is rotatably supported via the disk
holder 7 on the turn table 1 and transferred sequentially in the
order of stations A, B and C. And, at the second station B and the
third station C, the inner edge surface and the outer edge surface
of the glass substrate 2 are subjected to grinding and polishing in
contact with the grinding stone for the respective grinding, and
the grinding stone for the respective polishing, as shown in FIG.
2. The grindstone 3 for grinding the outer edge surface and the
grindstone 4 made of resin are provided at the stations B and C,
respectively, movable in the radial direction of the turn table 1
so that at the time of rotational movement of the table 1, they are
retreated outwardly to be out of contact with the glass substrates
2 and at the time of processing, they are moved inwardly to be in
contact with the glass substrates 2. As the mechanism for movement
of the respective grindstones 3 and 4, servo motor air cylinders
are respectively applied, so that in the grinding, the moving rate
of the grindstone is freely adjusted, and in the polishing,
constant pressure processing is realized by a constant air pressure
by the air cylinder.
[0031] Further, the grinding stone 5 for grinding the inner edge
surface and the grinding stone 6 made of resin are provided at the
stations B and C, respectively, movably in a perpendicular
direction to the plane of the turn table 1, so that at the time of
movement of the turn table 1, they are retreated to positions not
to hinder the rotation of the turn table 1, and in a state where
the turn table 1 is stopped, the grinding stone 5 for grinding the
inner edge surface and the grindstone 6 made of resin are driven so
that they are located in the circular holes of the glass substrates
2 supported by the glass substrate holders 7. And, at the time of
processing, they are moved in the radial direction of the turn
table 1 so that they will be in contact with the inner edge
surfaces of the glass substrates 2. The state shown in FIG. 2 is
the state where the processing is being carried out, and the
grinding stone 3 or 4 for processing the outer edge surface is
moved in the direction shown by arrow X from the position retreated
during the rotational driving of the turn table 1 and brought in
contact with the outer edge surface of the glass substrate 2, and
the grinding stone 5 or 6 for processing the inner edge surface is
firstly moved in the direction shown by arrow Z to be located in
the circular hole of the glass substrate 2 and then moved in the
direction shown by arrow X to be in contact with the inner edge
surface of the glass substrate 2. The grinding stone 3 or 4 for
processing the outer edge surface and the grinding stone 5 or 6 for
processing the inner edge surface both rotated at a high speed to
grind or polish the outer edge surface and the inner edge surface
of the glass substrate 2 in contact. The glass substrate 2 is
rotationally driven at a low speed by a rotational driving
mechanism of the glass substrate holder 7 at the station B or C, so
that processing carried out over the entire edge surface of
360.degree.. Such outer edge surface processing and inner edge
surface processing are simultaneously carried out in a parallel
fashion at the stations B and C, respectively.
[0032] The stations B and C are different in that the grinding
stone to be used are for grinding and for polishing, respectively,
but with respect to the mechanism, they are provided with similar
driving mechanisms. Further, dismounting of a processed glass
substrate 2 and mounting a non-processed glass substrate 2 to be
carried out at the first station A, may be carried out by manual
operation, but from the viewpoint of automatic efficiency, in this
embodiment, a robot is provided.
[0033] In the above construction, at the first station A, a
processed glass substrate 2 is dismounted by a robot mechanism, and
instead, a non-processed glass substrate 2 is transported to the
glass substrate holder 7. This glass substrate holder 7 is provided
with a vacuum suction mechanism, and the non-processed glass
substrate 2 is securely held by the operation of the vacuum suction
mechanism. Here, the glass substrate 2 thus held is required to be
located accurately at the concentric position to the rotational
axis of the glass substrate holder 7 throughout the grinding and
polishing at the stations B and C. This is required so that the
inner and outer edge surfaces are accurately concentrically
processed in the grinding and polishing at the stations B and C.
For this purpose, precision in the transport positioning of a
non-processed glass substrate 2 on the glass substrate holder 7 by
the above-mentioned robot, and to carry out grinding by maintaining
the concentric position obtained by the grinding by eliminating a
change of the glass substrate holder during the transportation
between the stations B and C, become important.
[0034] At the second station B, when the glass substrate held by
the glass substrate holder 7 is brought by the rotation of the turn
table 1, a coupling relation is taken between the rotation
mechanism (not shown) to rotate the glass substrate 2 at a low
speed and the glass substrate holder 7. This can be carried out by
a clutch mechanism (not shown), so that during the rotation of the
turn table 1, the coupling is released, and when the turn table
stops at the station position, the coupling is effected to make
rotation of the glass substrate 2 by the above rotation mechanism
possible. The above clutch mechanism is provided in the same manner
also at the third station C, to make rotation of the glass
substrate 2 by the rotation mechanism via the clutch mechanism
possible.
[0035] In the above embodiment, a turn table 1 is shown as the
transfer mechanism to sequentially transfer the glass substrate 2
via the respective stations A, B and C. However, the transfer
mechanism is not limited thereto so long as it is a mechanism
wherein the means for transfer between the respective stations A, B
and C are driven simultaneously with one another and the glass
substrate 2 to be transferred will return to the initial mounting
position. A suitable conveyer may be employed.
[0036] In the polishing apparatus 10 of the embodiment, a
mechanical polishing method by means of the grinding stones 4 and 6
made of resin is employed in the steps for polishing the outer and
inner edge surfaces of the glass substrate 2. This is based on the
following viewpoint.
[0037] In the polishing apparatus disclosed in Patent Document 1,
the cause to hinder improvement of the productivity resides in that
a chemical polishing apparatus employing an abrasive for high
precision polishing is employed, and the cause for being incapable
of readily absorbing variations in the processing margins of the
glass substrates, resides in that batch treatment is adopted.
[0038] In Patent Document 1, the outer edge surface is polished to
a high level of precision of about 10 nm by arithmetic average
roughness (Ra). However, it has been found that when hard disks are
produced by using glass substrates, if the arithmetic average
roughness (Ra) of the inner and outer peripheral edge surfaces of
the glass substrates is at a level of at most 100 nm, there will be
practically no problem such as formation of dust. And, it has been
found that at this level, mechanical polishing with high
productivity is feasible by using a grindstone made of a resin
(such as a urea resin or a urethane resin) having a hardness lower
than the glass substrate and that by properly selecting the
abrasive grain material (such as diamond abrasive grains) for the
grindstone of resin, the abrasive grain size, the abrasive grain
density, the abrasive grain hardness, the specification of the
resin, etc., it is possible to accomplish polishing so that the
arithmetic average roughness (Ra) after the processing would be
from 30 nm to 100 nm.
[0039] Furthermore, it has been found that since the mechanical
polishing is feasible, sheet treatment can be adopted to increase
the productivity and at the same time to eliminate variations in
the processing margins of the glass substrates caused by lamination
polishing, and with respect to variations in the dimensional
precision of individual glass substrates, so that such variations
can be absorbed, the grindstone is made to be a grindstone 4 made
of a resin (such as a urea resin or a urethane resin) having a
hardness lower than the glass substrate 2. By properly selecting
the abrasive grain material (such as diamond abrasive grains) for
the grindstone 4 made of resin, the abrasive grain size, the
abrasive grain density, the abrasive grain hardness, the
specification of the resin etc., it is possible to accomplish
polishing so that the arithmetic average roughness (Ra) after the
processing would be from 30 nm to 100 nm.
[0040] And, the grindstone 4 made of resin is preferably a formed
grindstone having a groove 4A formed to simultaneously polish the
outer edge surface 2A of the glass substrate 2 and chamfers 2B and
2C on both sides thereof, as shown in FIG. 3(A). By adopting such a
formed grindstone as the grindstone 4 made of resin, it is possible
to simultaneously polish all of the outer edge surface 2A and the
chambers 2B and 2C on both sides thereof, of the glass substrate 2,
whereby the productivity and uniformity in processing will further
be improved.
[0041] Further, the shape (the grindstone shape) of the groove 4A
of the formed grindstone can easily be formed by pressing the
peripheral edge portion of the glass substrate 2 to be processed to
a grindstone 4 made of resin formed into a rod shape wherein a
groove 4A is not yet formed, with a force higher than the pressing
force during the polishing, as shown in FIG. 3(B), whereby the
surface of the grindstone 4 made of resin in a rod shape will be
recessed in a concave shape (transferred) to readily form a groove
4A in conformity with the peripheral edge shape of the glass
substrate 2.
[0042] The grindstone 4 made of resin is not limited to a formed
grindstone, and a stick-form grindstone 30 as shown in FIG. 4 may
also be employed. In such a case, as shown in FIG. 4(A), the
surface of the stick-form grindstone 30 is pressed against the
outer edge surface 2A of the glass substrate 2 and the stick-form
grindstone 30 is reciprocated along its axial direction, to polish
the outer edge surface 2A of the glass substrate 2. Then, as shown
in FIG. 4(B), the stick-form grindstone 30 is inclined so that the
surface of the stick-form grindstone 30 is pressed against a
chamfer 2B of the glass substrate 2 and the stick-form grindstone
30 is reciprocated along its axial direction, to polish the chamfer
2B of the glass substrate 2. Then, as shown in FIG. 4(C), the
stick-form grindstone 30 is inclined in the opposite side so that
the surface of the stick-form grindstone 30 is pressed against a
chamfer 2C of the glass substrate 2 and the stick-form grindstone
30 is reciprocated in its axial direction to polish the chamfer 2C
of the glass substrate 2. Thus, the polishing step of the glass
substrate 2 is completed.
[0043] The entire disclosure of Japanese Patent Application No.
2005-111104 filed on Apr. 7, 2005 including specification, claims,
drawings and summary are incorporated herein by reference in its
entirety.
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