U.S. patent application number 13/209873 was filed with the patent office on 2012-02-23 for method of manufacturing glass substrate for magnetic recording media.
This patent application is currently assigned to SHOWA DENKO K.K.. Invention is credited to Kazuyuki HANEDA.
Application Number | 20120045971 13/209873 |
Document ID | / |
Family ID | 45594437 |
Filed Date | 2012-02-23 |
United States Patent
Application |
20120045971 |
Kind Code |
A1 |
HANEDA; Kazuyuki |
February 23, 2012 |
METHOD OF MANUFACTURING GLASS SUBSTRATE FOR MAGNETIC RECORDING
MEDIA
Abstract
The invention provides a method of manufacturing a glass
substrate for magnetic recording media. And the glass substrate has
high surface smoothness and little waviness. In the primary,
secondary and tertiary lapping process, diamond pads 20A, 20B, and
20C are used, respectively. The diamond pad 20A has an average
diamond grain size of 4 to 12 .mu.m, and a content of diamond
grains of 5 to 70% by volume. The diamond pad 20B has an average
diamond grain size of 1 to 5 .mu.m, and a content of diamond grains
of 5 to 80% by volume. The diamond pad 20C has an average diamond
grain size of 0.2 to 2 .mu.m, and a content of diamond grains of 5
to 80% by volume. In the polishing process, the silicon oxide is
used as abrasive without using cerium oxide.
Inventors: |
HANEDA; Kazuyuki;
(Ichihara-shi, JP) |
Assignee: |
SHOWA DENKO K.K.
Tokyo
JP
|
Family ID: |
45594437 |
Appl. No.: |
13/209873 |
Filed: |
August 15, 2011 |
Current U.S.
Class: |
451/41 |
Current CPC
Class: |
G11B 5/8404
20130101 |
Class at
Publication: |
451/41 |
International
Class: |
B24B 1/00 20060101
B24B001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 17, 2010 |
JP |
2010-182330 |
Claims
1. A method of manufacturing a glass substrate for magnetic
recording media, comprising: a primary lapping process, a secondary
lapping process, a tertiary lapping process, and a polishing
process, for a surface except for an end face of a glass substrate,
in this order; in the primary, secondary and tertiary lapping
process, a diamond pad on which diamond abrasive grain was fixed
using binder was used, and the surface of the diamond pad has a
structure in which plural tile-like projections having a flat top
were provided in line; wherein the diamond pad used in the primary
lapping process has an average diamond grain size of 4 to 12 .mu.m,
and a content of diamond grains in the projection of 5 to 70% by
volume, the diamond pad used in the secondary lapping process has
an average diamond grain size of 1 to 5 .mu.m, and a content of
diamond grains in the projection of 5 to 80% by volume, the diamond
pad used in the tertiary lapping process has an average diamond
grain size of 0.2 to 2 .mu.m, and a content of diamond grains in
the projection of 5 to 80% by volume, and in the polishing process,
silicon oxide is used as abrasive.
2. The method of manufacturing a glass substrate for magnetic
recording media according to claim 1, wherein the size of the
projections of the diamond pad used in primary, secondary and
tertiary lapping process, is 1.5 to 5 mm square with a height 0.2
to 3 mm, and the space between adjacent projections is 0.5 to 3
mm.
3. A method of manufacturing a glass substrate for magnetic
recording media, comprising: a primary lapping process, a secondary
lapping process, and a polishing process, for a surface except end
face of a glass substrate, in this order; in the primary and
secondary lapping process, the diamond pad on which diamond
abrasive grain was fixed using binder is used, and the surface of
the diamond pad has a structure in which plural tile-like
projections having a flat top were provided in line; wherein the
diamond pad used in the primary lapping process has an average
diamond grain size of 3 to 12 and a content of diamond grains in
the projection of 5 to 70% by volume, the diamond pad used in the
secondary lapping process has an average diamond grain size of 0.2
to 5 .mu.m, and a content of diamond grains in the projection of 5
to 80% by volume, and in the polishing process, the silicon oxide
is used as abrasive.
4. The method of manufacturing a glass substrate for magnetic
recording media according to claim 3, wherein the size of the
projections of the diamond pad used in primary, secondary and
tertiary lapping process, is 1.5 to 5 mm square with a height 0.2
to 3 mm, and the space between adjacent projections is 0.5 to 3
mm.
5. The method of manufacturing a glass substrate for magnetic
recording media according to claim 1, wherein in the polishing
process, silicon oxide is used as abrasive without using cerium
oxide.
6. The method of manufacturing a glass substrate for magnetic
recording media according to claim 2, wherein in the polishing
process, silicon oxide is used as abrasive without using cerium
oxide.
7. The method of manufacturing a glass substrate for magnetic
recording media according to claim 3, wherein in the polishing
process, silicon oxide is used as abrasive without using cerium
oxide.
8. The method of manufacturing a glass substrate for magnetic
recording media according to claim 4, wherein in the polishing
process, silicon oxide is used as abrasive without using cerium
oxide.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority of Japanese Patent
Application No. 2010-182330 filed Aug. 17, 2010, 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 is related to a method of
manufacturing a glass substrate for magnetic recording media.
[0004] 2. Background Art
[0005] The magnetic recording media used for a hard disk drive
(HDD) have significantly improved in recording density. Since the
introduction of MR heads and of PRML technology, the areal
recording density has further increased. Moreover, since the
introduction of GMR heads or TMR heads, the areal recording density
has continued to increase at a rate of about 1.5 times a year.
However, in the future a higher lever of areal recording density
will be required.
[0006] In addition, with the improvement in recording density of
such magnetic recording media, there are growing demands for a
substrate used for the magnetic recording media. As a substrate for
magnetic recording media, an aluminum substrate and a glass
substrate are used conventionally. Of these, generally a glass
substrate can be superior to aluminum substrate in hardness,
surface smoothness, rigidity, and impact resistance. Therefore, a
glass substrate has attracted growing attention as a substrate for
magnetic recording media because it is expected to achieve a high
recording density.
[0007] When manufacturing a glass substrate for magnetic recording
media, a disk-shaped glass substrate can be obtained by cutting a
large plate-shaped glass plate to a disk-shaped substrate or by
press-molding molten glass directly on to the disk-shaped glass
substrate using a mold. For surfaces and end faces of the obtained
glass substrate, a lapping (grinding) process and polishing process
are carried out.
[0008] In addition, as a conventional method of manufacturing a
glass substrate for magnetic recording media, a primary lapping
process, secondary lapping process, primary polishing process, and
secondary polishing process of a surface (data side) of a glass
substrate are performed in this order. During these processes, a
lapping process and polishing process on the inner and outer
peripheral end faces of the substrate were performed.
[0009] On the data side of the glass substrate, in the primary
lapping process, a diamond grindstone was used, in the second
lapping process, a diamond grindstone having a smaller grain size
than that used in the primary lapping process was used, in the
primary polishing process, cerium oxide slurry was used, and in the
secondary polishing process, a cerium oxide slurry having a
particle size smaller than that in the primary polishing process
was used.
[0010] In addition, regarding prior art documents relating to the
present invention, for example, in Patent Literature 1, it is
disclosed that when the primary lapping process using diamond
pellets such as resin, metal and vitrified, and then the secondary
lapping process using a diamond pad were performed, a substrate
having surface smoothness and no defects such as scratches or
grinding traces or aspiration traces can be manufactured, and it is
also possible to decrease the process time. [0011] Patent
literature 1: JP Patent No. 4,049,510.
SUMMARY OF THE INVENTION
[0012] However, with the recent development of low magnetic head
flying height, it is required to improve waviness of the glass
substrate of magnetic recording media and surface roughness.
Studies have revealed that although the primary lapping process has
a grinding allowance of 100 .mu.m to 300 .mu.m per-side, the glass
substrate could become damaged in this primary lapping process. As
a result, the surface of the magnetic recording medium in the final
product has a long-term waviness.
[0013] In addition, polishing the glass substrate using cerium
oxide chemical mechanical polishing (CMP) has become a general
technology. However, cerium oxide is expensive; thus a technology
requiring no, or very little, cerium oxide is preferable.
[0014] In view of such conventional circumstances, the object of
the present invention is to provide a method of manufacturing a
glass substrate for magnetic recording media which can produce
glass substrates for magnetic recording media with high
productivity, wherein the manufactured substrate has high surface
smoothness and little waviness.
[0015] The present invention provides the following:
[0016] (1) A method of manufacturing a glass substrate for magnetic
recording media, comprising:
[0017] a primary lapping process,
[0018] a secondary lapping process,
[0019] a tertiary lapping process, and
[0020] a polishing process, for a surface except for an end face of
a glass substrate,
[0021] in this order;
[0022] in the primary, secondary and tertiary lapping process, the
diamond pad on which a diamond abrasive was fixed using a binder,
the surface of the diamond pad has a structure in which plural
tile-like projections having a flat top were provided in line;
[0023] wherein
[0024] the diamond pad used in the primary lapping process has an
average diamond grain size of 4 to 12 .mu.m, and a content of
diamond grains in the projection of 5 to 70% by volume,
[0025] the diamond pad used in the secondary lapping process has an
average diamond grain size of 1 to 5 .mu.m, and a content of
diamond grains in the projection of 5 to 80% by volume,
[0026] the diamond pad used in the tertiary lapping process has an
average diamond grain size of 0.2 to 2 .mu.m, and a content of
diamond grains in the projection of 5 to 80% by volume, and
[0027] in the polishing process, the silicon oxide is used as
abrasive;
[0028] (2) The method of manufacturing a glass substrate for
magnetic recording media according to (1),
[0029] wherein the size of the projections of the diamond pad used
in the primary, secondary and tertiary lapping process, is 1.5 to 5
mm square with a height 0.2 to 3 mm, and the space between adjacent
projections is 0.5 to 3 mm;
[0030] (3) A method of manufacturing a glass substrate for magnetic
recording media, comprising:
[0031] a primary lapping process,
[0032] a secondary lapping process, and
[0033] a polishing process, for a surface except for an end face of
a glass substrate,
[0034] in this order;
[0035] in the primary and secondary lapping process, the diamond
pad on which diamond abrasive grain was fixed using binder is used,
and the surface of the diamond pad has a structure in which plural
tile-like projections having a flat top were provided in line;
[0036] wherein
[0037] the diamond pad used in the primary lapping process has an
average diamond grain size of 3 to 12 .mu.m, and a content of
diamond grains in the projection of 5 to 70% by volume,
[0038] the diamond pad used in the secondary lapping process has an
average diamond grain size of 0.2 to 5 .mu.m, and a content of
diamond grains in the projection of 5 to 80% by volume, and
[0039] in the polishing process, the silicon oxide is used as
abrasive;
[0040] (4) The method of manufacturing a glass substrate for
magnetic recording media according to (3),
[0041] wherein the size of the projections of the diamond pad used
in primary, secondary and tertiary lapping process, is 1.5 to 5 mm
square with a height 0.2 to 3 mm, and the space between adjacent
projections is 0.5 to 3 mm;
[0042] (5) The method of manufacturing a glass substrate for
magnetic recording media according to any one of (1) to (4), in the
polishing process, the silicon oxide is used as abrasive without
using cerium oxide.
[0043] As described above, according to the present invention, a
glass substrates for magnetic recording media, which has high
surface smoothness and little waviness can be manufactured with
high productivity.
BRIEF DESCRIPTION OF DRAWINGS
[0044] FIG. 1 is a perspective view showing lapping operation for
explaining the method of manufacturing a glass substrate for
magnetic recording media according to the present invention.
[0045] FIG. 2A is a plan view showing an enlarged pad surface of
diamond pad used in the lapping process.
[0046] FIG. 2B is a cross-section view showing an enlarged pad
surface of diamond pad used in the lapping process.
[0047] FIG. 3 is a perspective view showing the inner and outer
peripheral lapping process for explaining the method of
manufacturing a glass substrate for magnetic recording media
according to the present invention.
[0048] FIG. 4 is a perspective view showing the inner peripheral
polishing process for explaining the method of manufacturing a
glass substrate for magnetic recording media according to the
present invention.
[0049] FIG. 5 is a perspective view showing the outer peripheral
polishing process for explaining the method of manufacturing a
glass substrate for magnetic recording media according to the
present invention.
[0050] FIG. 6 is a perspective view showing a polishing process for
explaining the method of manufacturing a glass substrate for
magnetic recording media according to the present invention.
[0051] FIG. 7 is a perspective view showing another configuration
example of a lapping or polishing machine used in the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0052] The following method for manufacturing a glass substrate for
magnetic recording media according to the present invention will be
described in detail with reference to the drawings.
[0053] A glass substrate for magnetic recording media manufactured
by the method of the present invention is a disk-shaped glass
substrate having a central aperture. A magnetic recording media is
formed by laminating a magnetic layer, protective layer and
lubricant layer sequentially on the surface of the glass substrate.
In addition, in a magnetic recording and reproducing apparatus (an
HDD), writing or reading of information is performed for magnetic
recording media by attaching a center of the magnetic recording
media to an axis of a spindle motor, and making a magnetic head
float and travel over the surfaces of the magnetic recording media
which is rotated by the spindle motor.
[0054] As for the glass substrate for magnetic recording media, for
example, SiO.sub.2--Al.sub.2O.sub.3--R.sub.2O-based chemical glass
(R represents at least one member selected from alkali metals.),
SiO.sub.2--Al.sub.2O.sub.3--Li.sub.2O-based ceramic glass,
SiO.sub.2--Al.sub.2O.sub.3--MgO--TiO.sub.2-based glass ceramics can
be used. Among them,
SiO.sub.2--Al.sub.2O.sub.3--MgO--CaO--Li.sub.2O--Na.sub.2O--ZrO.sub.2--Y.-
sub.2O.sub.3--TiO.sub.2--As.sub.2O.sub.3-based strengthened
chemical glass,
SiO.sub.2--Al.sub.2O.sub.3--Li.sub.2O--Na.sub.2O--ZrO.sub.2--As.su-
b.2O.sub.3-based strengthened chemical glass,
SiO.sub.2--Al.sub.2O.sub.3--MgO--ZnO--Li.sub.2O--P.sub.2O.sub.5--ZrO.sub.-
2--K.sub.2O--Sb.sub.2O.sub.3-based strengthened chemical glass,
SiO.sub.2--Al.sub.2O.sub.3--MgO--CaO--BaO--TiO.sub.2--P.sub.2O.sub.5--As.-
sub.2O.sub.3-based glass ceramics,
SiO.sub.2--Al.sub.2O.sub.3--MgO--CaO--SrO--BaO--TiO.sub.2--ZrO.sub.2--Bi.-
sub.2O.sub.3--Sb.sub.2O.sub.3-basedglass ceramics can be suitably
used. Further, for example, lithium silicate, SiO.sub.2---based
crystal (quartz, cristobalite, and tridymite), cordierite,
enstatite, aluminum magnesium titanate, spinel-based crystal ([Zn,
and/or Mg] Al.sub.2O.sub.4, [Mg and/or Zn].sub.2TiO.sub.4, as well
as a solid solution between these two crystals), forsterite,
Spodumene, a glass ceramic which includes solid solution crystals
thereof as crystal phase can be suitably used as a glass substrate
for magnetic recording medium.
[0055] In the process of producing glass substrates for this
magnetic recording media, firstly, a disk-shaped glass substrate
which has a central aperture is obtained by cutting a glass
substrate from a big glass plate, or directly pressing a glass
substrate from melting glass by using a mold.
[0056] Then, lapping (grinding) process and polishing process are
carried out for surfaces and end faces of the resulting glass
substrate. In addition, between these processes, the method may
further include a lapping process and polishing process for an
inner and outer peripheral end face of the glass substrates.
[0057] As the method of manufacturing a glass substrate for
magnetic recording media according to the present invention, when
the lapping process is carried out for surfaces except end face of
a glass substrate, a diamond pad to which diamond abrasive grain
was fixed with binder is used. The diamond pad is described below.
Therefore, according to the present invention, with no use or less
use of expensive cerium oxide slurry used in conventional polishing
process, a polishing surface having little waviness and high
surface smoothness can be obtained.
[0058] In other words, the polishing process using conventional
cerium oxide slurry becomes unnecessary, and, as a result the
two-step conventional polishing process can be changed to a
one-step polishing process with use of silicon oxide slurry.
Therefore, the method of the present invention reduces cost for
polishing a glass substrate for magnetic recording media, and
obtains high productivity.
[0059] The method of manufacturing a glass substrate for magnetic
recording media according to the present invention is described in
detail as following, referring to examples of the first and the
second embodiments.
Example of First Embodiment
[0060] As example of a first embodiment, primary lapping process,
inner and outer peripheral lapping process, inner peripheral
polishing process, second lapping process, tertiary lapping
process, outer peripheral polishing process and primary polishing
process are performed in this order.
[0061] As the primary lapping process, a lapping machine 10 as
shown in FIG. 1 is used, and a primary lapping process is carried
out for surfaces except end face of the glass substrate W. In other
words, this lapping machine 10 includes a pair of upper and lower
faceplates 11 and 12, and several sheets of glass substrates are
sandwiched between the faceplates 11 and 12 which are rotating in
directions opposite to each other, and then both sides of the glass
substrates W are lapped by grinding pads installed in the
faceplates 11 and 12.
[0062] The grinding pad used for the primary lapping process is a
diamond pad 20A to which diamond abrasive grain was fixed with
binder (bond) as shown in FIGS. 2A and 2B. In addition, the lapping
surface 20a has plural tile-like projections having a flat top
which are installed in line.
[0063] It is preferable that the size S of the projections 21 of
the diamond pad 20A used in primary lapping process be 1.5 to 5 mm
square with a height T 0.2 to 3 mm, and the space G between
adjacent projections be 0.5 to 3 mm. According to the present
invention, by using the diamond pad 20A satisfying the above range,
liquid coolant or lapping fluid can reach everywhere equally, and
grinding dust can be discharged smoothly from a space interval of
the projection 21 of the lap surface 20a.
[0064] In addition, it is preferable that the diamond pad 20A used
in the primary lapping process have an average diamond grain size
of 4 to 12 .mu.m, and a content of diamond grains in the projection
21 of 5 to 70% by volume. It is more preferable that the diamond
pad 20A have a content of diamond grains of 20 to 30% by volume.
This increases cost due to an increase in the process time when the
diamond abrasive grain size and content are less than the above
range. On the other hand, it becomes more difficult to obtain
desired surface roughness when the diamond abrasive grain size and
the content exceed the above range. In addition, as a binder of
diamond pad 20A, for example, polyurethane resin, phenol-based
resin, melamine-based resin, etc. can be used.
[0065] As the inner and outer peripheral lapping process, lapping
machine 30 as shown in FIG. 3 is used, and lapping process is
carried out for inner peripheral end surface of a central aperture
of glass substrate W and outer peripheral end face of the glass
substrate W. The lapping machine 30 includes inner peripheral
grindstone 31 and outer peripheral grindstone 32. The laminated
substrates X is obtained by laminating plural pieces of glass
substrates W in the state that the central apertures is matched
each other wherein spacers (not shown) are sandwiched. While
rotating the laminated substrates X around axis, and inserting an
inner peripheral grindstone 31 into a central aperture of glass
substrates and putting glass substrates W in a radial direction
between outer peripheral grindstone 32 which is placed on the
periphery of each glass substrate W, the inner peripheral
grindstone 31 and outer peripheral grindstone 32 are rotated in the
direction opposite to that of laminated substrates X. And at the
same time as lapping the inner peripheral end face of the glass
substrates W by the inner peripheral grindstone 31, outer
peripheral end face of the glass substrates W is lapped by the
peripheral grindstone 32.
[0066] In addition, since there are waveforms having projection and
recess lines alternately in an axial direction on the surface of
the inner peripheral grindstone 31 and the outer peripheral
grindstone 32, in addition to grinding the inner peripheral end
face and the outer peripheral end face of glass substrates W, it is
possible to chamfer the edge portion between the two principal
surfaces and inner and outer peripheral end face of glass
substrates W.
[0067] As the inner peripheral polishing process, a polishing
machine 40 as shown in FIG. 4 is used, and the polishing process is
carried out for the inner peripheral end face of a central aperture
of glass substrate W. That is, the polishing machine 40 has an
inner peripheral polishing brush 41, while rotating laminated
substrates X around the axis, and the inner peripheral polishing
brush 41 inserted in a central aperture of each glass substrate W
is rotated in the direction opposite to that of the glass
substrates W and moved vertically. At this time, polishing fluid is
dropped to the inner peripheral polishing brush 41. And then, the
inner peripheral end face of glass substrates W is polished by the
inner peripheral polishing brush 41. At the same time, the edge
portion of the inner and outer peripheral end face, which was
chamfered in the inner and outer peripheral lapping process, is
polished. In addition, as the polishing fluid, for example, the
slurried fluid obtained by dispersing silicon oxide (colloidal
silica) or cerium oxide abrasive grain into water can be used.
[0068] As the secondary lapping process, like the primary lapping
process, a lapping machine 10 as shown in FIG. 1 is used, and, the
secondary lapping process is carried out for surfaces except end
face of glass substrate W. That is, while sandwiching plural pieces
of glass substrates W between a pair of upper and lower faceplates
11 and 12, which are rotating in directions opposite to each other,
both sides of these glass substrate W are lapped by a grinding pad
installed in the faceplate 11, 12.
[0069] The grinding pad used for the secondary lapping process,
like the diamond pad 20A as shown in FIGS. 2A and 2B, is a diamond
pad 20B to which diamond abrasive grain was fixed with binder
(bond). In addition, the lapping surface 20a has plural tile-like
projections having a flat top which are installed in line.
[0070] As the same as the diamond pad 20A shown in FIGS. 2A and 2B,
it is preferable that the size S of the projections 21 of the
diamond pad 20B used in secondary lapping process be 1.5 to 5 mm
square with a height T 0.2 to 3 mm, and the space G between
adjacent projections be 0.5 to 3 mm. According to the present
invention, by using the diamond pad 20B to satisfy the above range,
liquid coolant or lapping fluid can reach everywhere equally, and
grinding dust can be discharged smoothly from an interval of the
projection 21 of the lap surface 20a.
[0071] In addition, it is preferable that the diamond pad 20B used
in the secondary lapping process have an average diamond grain size
of 1 to 5 .mu.m, and a content of diamond grains in the projection
21 of 5 to 80% by volume. It is more preferable that the content of
diamond grains be 50 to 70% by volume. This increases cost due to
an increase in the process time when the diamond abrasive grain
size and content are less than the above range. On the other hand,
it becomes more difficult to obtain desired surface roughness when
the diamond abrasive grain size and content exceed the above range.
In addition, as a binder of diamond pad 20B, for example,
polyurethane resin, phenol-based resin, melamine-based resin, etc.
can be used.
[0072] As the tertiary lapping process, like the primary and
secondary lapping processes, the lapping machine 10 as shown in
FIG. 1 is used, and the tertiary lapping process is carried out for
surfaces except for the end face of the glass substrate W. In other
words, this lapping machine 10 includes a pair of upper and lower
faceplates 11 and 12, several sheets of glass substrates sandwiched
between the faceplates 11 and 12 which are rotating in directions
opposite to each other, and both sides of the glass substrates W
are lapped by grinding pads installed in the faceplates 11 and
12.
[0073] The same as the diamond pad 20A as shown in FIGS. 2A and 2B,
the grinding pad used for the tertiary lapping process is a diamond
pad 20C to which diamond abrasive grain was fixed with binder
(bond). In addition, the lapping surface 20a has plural tile-like
projections having a flat top which are installed in line.
[0074] The same as the diamond pad 20A shown in FIGS. 2A and 2B, it
is preferable that the size S of the projections 21 of the diamond
pad 20A used in tertiary lapping process be 1.5 to 5 mm square with
a height T 0.2 to 3 mm, and the space G between adjacent
projections be 0.5 to 3 mm. According to the present invention, by
using the diamond pad 20C to satisfy the above range, liquid
coolant or lapping fluid can reach everywhere equally, and grinding
dust can be discharged smoothly from an interval of the projection
21 of the lap surface 20a.
[0075] In addition, it is preferable that the diamond pad 20A used
in the tertiary lapping process have an average diamond grain size
of 0.2 to 2 .mu.m, and a content of diamond grains in the
projection 21 of 5 to 80% by volume. It is more preferable that it
have a content of diamond grains of 50 to 80% by volume. This
increases cost due to increase the process time when diamond
abrasive grain size and content are less than the above range. On
the other hand, it becomes more difficult to obtain desired surface
roughness when the diamond abrasive grain size and content exceed
the above range. In addition, as a binder of diamond pad 20C, for
example, polyurethane resin, phenol-based resin, melamine-based
resin, etc. can be used.
[0076] As the outer peripheral polishing process, a polishing
machine 50 as shown in FIG. 5 is used, and the polishing process is
carried out for the outer peripheral end face of the glass
substrate W. The polishing machine 50 has a rotating shaft 51 and
outer peripheral polishing brush 52. The laminated substrates X is
obtained by laminating plural pieces of glass substrates W in the
state that the central apertures match each other wherein spacers
(not shown) are sandwiched. While rotating laminated substrates X
around the axis by the rotating shaft 51 inserted in a central
aperture of each glass substrate W, the outer peripheral polishing
brush 52 in contact with the surface of the outer peripheral end
face of the glass substrates, is rotated in the direction opposite
to that of the glass substrates W and moved vertically. At this
time, polishing fluid is dropped to the outer peripheral polishing
brush 51. And then, the outer peripheral end face of glass
substrates W is polished by the outer peripheral polishing brush
51. At the same time, the edge portion of the inner and outer
peripheral end face, which was chamfered in the inner and outer
peripheral lapping process, is polished. In addition, as the
polishing fluid, for example, the slurried fluid obtained by
dispersing silicon oxide (colloidal silica) or cerium oxide
abrasive grain into water can be used.
[0077] As primary polishing process, polishing machine 60 as shown
in FIG. 6 is used, and primary polishing process is carried out for
surfaces except for the end face of the glass substrate W. That is,
while sandwiching plural pieces of glass substrates W between a
pair of upper and lower faceplates 61 and 62, which are rotating in
directions opposite to each other, both sides of these glass
substrates W are polished by the grinding pad installed in the
faceplates 61 and 62.
[0078] The grinding pad used for the primary polishing process is a
hard polishing cloth made of urethane, for example. When the
polishing process is carried out for surfaces except for the end
face of glass substrate W, polishing fluid is dropped to the glass
substrates W. As the polishing fluid, for example, the slurried
fluid obtained by dispersing silicon oxide (colloidal silica)
abrasive grain into water can be used.
[0079] In addition, the glass substrate W subjected to the lapping
and polishing process is fed to the cleaning process and final
inspection process. And in the final cleaning process, for example,
a chemical cleaning method using cleaner (chemical) combined with
an ultrasonic method is used to clean the glass substrate W and
remove the abrasive, for example, used in the above step. In
addition, with the inspection process, by using laser optical
inspection equipment, for example, examination of the presence or
absence of distortion or scratches on the surface of the glass
substrate W can be performed.
[0080] As the method of manufacturing a glass substrate for
magnetic recording media according to the present invention,
diamond pads 20A, 20B, 20C to which diamond abrasive grains as
shown in FIGS. 2A and 2B were fixed to with binder in the primary,
secondary and tertiary lapping process are used. In addition, the
lapping surface 20a of the diamond pads 20A, 20B, 20C has plural
tile-like projections having a flat top which are installed in
line.
[0081] According to the present invention, by using such diamond
pads 20A, 20B, 20C, it is possible that while grinding dust is
discharged smoothly from an interval of projection 21 of lapping
surface 20a, the surfaces except for the end face of the glass
substrate W can be polished to smoothness. In addition, since a
two-step conventional polishing process (primary and secondary
polishing processes) can be changed to a one-step polishing
process, the application of expensive cerium oxide abrasive grain
can be reduced. In addition, since the polishing process has a long
process time in comparison with a lapping process, process time can
be reduced. Thus, according to the present invention, it is
possible to manufacture the glass substrate for magnetic recording
media, wherein the substrate has a high surface smoothness and
little waviness with high productivity.
Example of the Second Embodiment
[0082] As an example of a second embodiment, primary lapping
process, inner and outer peripheral lapping process, inner
peripheral polishing process, second lapping process, outer
peripheral polishing process and primary polishing process are
performed in this order.
[0083] As the primary lapping process, the lapping machine 10 as
shown in FIG. 1 is used, and a primary lapping process is carried
out for surfaces except for the end face of the glass substrate W.
In other words, this lapping machine 10 includes a pair of upper
and lower faceplates 11 and 12, several sheets of glass substrates
sandwiched between the faceplates 11 and 12 which are rotating in
directions opposite to each other, both sides of the glass
substrates W are lapped by grinding pads installed in the
faceplates 11 and 12.
[0084] The grinding pad used for the primary lapping process, the
same as the diamond pad 20A as shown in FIGS. 2A and 2B, is a
diamond pad 20D to which diamond abrasive grain was fixed with
binder (bond). In addition, the lapping surface 20a has plural
tile-like projections having a flat top which are installed in
line.
[0085] It is preferable that the size S of the projections 21 of
the diamond pad 20D used in primary lapping process be 1.5 to 5 mm
square with a height T 0.2 to 3 mm, and the space G between
adjacent projections be 0.5 to 3 mm. According to the present
invention, by using the diamond pad 20D to satisfy the above range,
liquid coolant or lapping fluid can reach everywhere equally, and
grinding dust can be discharged smoothly from an interval of the
projection 21 of the lap surface 20a.
[0086] In addition, it is preferable that the diamond pad 20D used
in the primary lapping process have an average diamond grain size
of 3 to 10 .mu.m, and a content of diamond grains in the projection
21 of 5 to 70% by volume. It is more preferable that it have a
content of diamond grains of 20 to 30% by volume. This increases
cost due to increase the process time when diamond abrasive grain
size and content are less than the above range. On the other hand,
it becomes more difficult to obtain desired surface roughness when
the diamond abrasive grain size and content exceed the above range.
In addition, as a binder of diamond pad 20D, for example,
polyurethane resin, phenol-based resin, melamine-based resin, etc.
can be used.
[0087] As the inner and outer peripheral lapping process, lapping
machine 30 as shown in FIG. 3 is used, and lapping process is
carried out for inner peripheral end surface of a central aperture
of glass substrate W and outer peripheral end face of the glass
substrate W. The lapping machine 30 includes the inner peripheral
grindstone 31 and outer peripheral grindstone 32. The laminated
substrates X is obtained by laminating plural pieces of glass
substrates W in the state that the central apertures match each
other wherein spacers (not shown) is sandwiched. While rotating the
laminated substrates X around axis, and inserting the inner
peripheral grindstone 31 into a central aperture of glass
substrates and putting glass substrates W in a radial direction
between the outer peripheral grindstone 32 which is placed on the
periphery of each glass substrate W, the inner peripheral
grindstone 31 and outer peripheral grindstone 32 are rotated in the
direction opposite to that of laminated substrates X. And at the
same time as grinding the inner peripheral end face of the glass
substrates W by the inner peripheral grindstone 31, the outer
peripheral end face of the glass substrates W is lapped by
peripheral grindstone 32.
[0088] In addition, since there are waveforms having a projection
and recess line alternately in an axial direction on the surface of
the inner peripheral grindstone 31 and the outer peripheral
grindstone 32, in addition to grinding inner peripheral end face
and the outer peripheral end face of glass substrates W, it is
possible to chamfer the edge portion between the two principal
surfaces and inner and outer peripheral end face of glass
substrates W.
[0089] As the inner peripheral polishing process, using the
polishing machine 40 as shown in FIG. 4, and polishing process is
carried out for the inner peripheral end face of a central aperture
of the glass substrate W. That is, the polishing machine 40 has an
inner peripheral polishing brush 41, while rotating laminated
substrates X around axis, and the inner peripheral polishing brush
41 inserted in a central aperture of each glass substrate W is
rotated in the direction opposite to that of the glass substrates W
and moved vertically. At this time, polishing fluid is dropped to
inner peripheral polishing brush 41. And then, the inner peripheral
end face of glass substrates W is polished by the inner peripheral
polishing brush 41. At the same time, the edge portion of the inner
and outer peripheral end face, which was chamfered in the inner and
outer peripheral lapping process, is polished. In addition, as the
polishing fluid, for example, the slurried fluid obtained by
dispersing silicon oxide (colloidal silica) or cerium oxide
abrasive grain into water can be used.
[0090] As the secondary lapping process, like the primary lapping
process, the lapping machine 10 as shown in FIG. 1 is used, and,
the secondary lapping process is carried out for surfaces except
end face of glass substrate W. That is, while sandwiching plural
pieces of glass substrates W between a pair of upper and lower
faceplates 11 and 12, which are rotating in directions opposite to
each other, both sides of these glass substrate W are lapped by
grinding pad installed in the faceplate 11, 12.
[0091] The grinding pad used for the secondary lapping process,
like the diamond pad 20A as shown in FIGS. 2A and 2B, is a diamond
pad 20E to which diamond abrasive grain was fixed with binder
(bond). In addition, the lapping surface 20a has plural tile-like
projections having a flat top which are installed in line.
[0092] The same as the diamond pad 20A as shown in FIGS. 2A and 2B,
it is preferable that the size S of the projections 21 of the
diamond pad 20E used in the secondary lapping process be 1.5 to 5
mm square with a height T 0.2 to 3 mm, and the space G between
adjacent projections be 0.5 to 3 mm. According to the present
invention, by using the diamond pad 20E to satisfy the above range,
liquid coolant or lapping fluid can reach everywhere equally, and
grinding dust can be discharged smoothly from an interval of
projection 21 of lap surface 20a.
[0093] In addition, it is preferable that the diamond pad 20E used
in the secondary lapping process have an average diamond grain size
of 0.2 to 2 .mu.m, and a content of diamond grains in the
projection 21 of 5 to 80% by volume. It is more preferable that it
have a content of diamond grains of 50 to 70% by volume. This
increases cost due to an increase in the process time when diamond
abrasive grain size and content are less than the above range. On
the other hand, it becomes more difficult to obtain desired surface
roughness when the diamond abrasive grain size and content exceed
the above range. In addition, as a binder of diamond pad 20E, for
example, polyurethane resin, phenol-based resin, melamine-based
resin, etc. can be used.
[0094] As the outer peripheral polishing process, using the
polishing machine 50 as shown in FIG. 5, the polishing process is
carried out for outer peripheral end face of glass substrate W. The
polishing machine 50 has a rotating shaft 51 and outer peripheral
polishing brush 52. The laminated substrates X is obtained by
laminating plural pieces of glass substrates W in the state that
the central apertures match each other wherein spacers (not shown)
are sandwiched. While rotating laminated substrates X around the
axis by the rotating shaft 51 inserted in a central aperture of
each glass substrate W, the outer peripheral polishing brush 52 in
contact with the surface of the outer peripheral end face of the
glass substrates, is rotated in the direction opposite to that of
the glass substrates W and moved vertically. At this time,
polishing fluid is dropped to outer peripheral polishing brush 51.
And then, the outer peripheral end face of glass substrates W is
polished by the outer peripheral polishing brush 51. At the same
time, the edge portion of the inner and outer peripheral end face,
which was chamfered in the inner and outer peripheral lapping
process, is polished. In addition, as the polishing fluid, for
example, the slurried fluid obtained by dispersing silicon oxide
(colloidal silica) or cerium oxide abrasive grain into water can be
used.
[0095] As the primary polishing process, the polishing machine 60
as shown in FIG. 6 is used, and the primary polishing process is
carried out for surfaces except end face of glass substrate W. That
is, while sandwiching plural pieces of glass substrates W between a
pair of upper and lower faceplates 61, 62, which are rotating in
directions opposite to each other, both sides of these glass
substrate W are polished by the grinding pad installed in the
faceplates 61, 62.
[0096] The grinding pad used for the primary polishing process is a
hard polishing cloth made of urethane, for example. When the
polishing process is carried out for surfaces except for the end
face of glass substrate W, polishing fluid is dropped to the glass
substrates W. As the polishing fluid, for example, the slurried
fluid obtained by dispersing silicon oxide (colloidal silica)
abrasive grain into water can be used.
[0097] In addition, the glass substrate W subjected to the lapping
and polishing process is fed to the cleaning process and final
inspection process. And in the final cleaning process, for example,
a chemical cleaning method using cleaner (chemical) combined with
an ultrasonic method is used to clean the glass substrate W and
remove the abrasive, for example, used in the above step. In
addition, the inspection process, by using laser optical inspection
equipment, for example, examination of the presence or absence of
distortion or scratches on the surface of the glass substrate
W.
[0098] As the method of manufacturing a glass substrate for
magnetic recording media according to the present invention,
diamond pads 20D, 20E to which diamond abrasive grain as shown in
FIGS. 2A and 2B were fixed to with binder in the primary and
secondary lapping process are used. In addition, the lapping
surface 20a of the diamond pads 20D, 20E has plural tile-like
projections having a flat top which are installed in line.
[0099] According to the present invention, by using such diamond
pads 20D, 20E, it is possible that while grinding dust is
discharged smoothly from an interval of projection 21 of lap
surface 20a, the surfaces except of end face of the glass substrate
W can be polished to smoothness. In addition, since two-steps
conventional polishing process (primary and secondary polishing
processes) can be changed to one-step polishing process, the
application of expensive cerium oxide abrasive grain can be
reduced. In addition, since the polishing process has a long
process time in comparison with a lapping process, the process time
can be reduced. Thus, according to the present invention, it is
possible to manufacture the glass substrate for magnetic recording
media, wherein the substrate has a high surface smoothness and
little waviness with high productivity.
[0100] According to the present invention, as a lapping fluid used
in each lapping process of the first and second embodiments, a
commercial source can be used. Lapping fluid, by classifying
roughly, includes water-based lapping fluid and oil-based lapping
fluid. The water-based lapping fluid contains pure water and a
suitable amount of alcohol with addition of polyethylene glycol as
a viscosity modifier, amine, and surfactant etc. On the other hand,
the oil-based lapping fluid contains oil with addition of an
appropriate amount of stearic acid as an extreme pressure additive.
For example, as commercial lapping fluid, water-based Sabrelube
9016 (manufactured by Chemetall) can be used.
[0101] In addition, according to the present invention, polishing
auxiliaries and anticorrosive may be added to the lapping fluids
used in each lapping process and polishing fluids used in polishing
process in the first and the second embodiments.
[0102] Specifically, polishing auxiliaries include an organic
polymer having sulfonate group or carboxylic acid group at least.
And an organic polymers containing sodium sulphonate or sodium
carboxylate, having average molecular weight of 4000-10000, is
preferable. Thus, it is possible to smooth surfaces of the glass
substrate W in the above processes.
[0103] As an organic polymer containing a carboxylic acid or sodium
sulfonate, for example, GEROPON SC/213 (Product Name/Rhodia),
GEROPON T/36 (Product Name/Rhodia), GEROPON TA/10 (Product
Name/Rhodia), GEROPON TA/72 (Product Name/Rhodia), New Karugen WG-5
(Product Name/Takemoto Oil & Fat Corporation), Agurizoru G-200
(Product Name/Kao Corporation), Demoru EP Powder (Product Name/Kao
Corporation), Demoru RNL (Product Name/Kao Corporation), Isoban
600-SF35 (Product name/Kuraray Ltd.), Polystar OM (Product Name/NOF
Corporation), Sokalan CP9 (Product Name/BASF Japan (Ltd.)), Sokalan
PA-15 (Product Name/BA SF Japan Ltd.), Tokisanon GR-31A (Product
Name/Sanyo Chemical Industries, Corporation), 7248 Sorpol (Product
Name/Toho Chemical Industries, Ltd.), Sharoru AN-103P (Product
Name/Dai-ichi Kogyo Seiyaku Co., Ltd. Corporation), Aron T-40
(Product Name/Toagosei Chemical Industry Co., Ltd.), Panakayaku CP
(product Name/Nippon Kayaku Inc.), roll disk H12C (Product
Name/Nippon Nyukazai Co., Ltd.) can be used. As the polishing
auxiliaries, Demoru RNL (Product Name/Kao Corporation) and Polystar
OM (Product Name/NOF Corporation) is preferably used.
[0104] In addition, the magnetic recording media manufactured using
the glass substrate W generally includes corrosion-prone material
such as Co, Ni and Fe in magnetic layer. Thus, by adding a
corrosion inhibitor in the lapping and polishing solution described
above, it is possible to prevent the magnetic layer from corrosion
and to obtain a magnetic recording medium excellent in
electromagnetic conversion characteristics.
[0105] As a corrosion inhibitor, it is preferable to use
benzotriazole or a derivative thereof. As derivatives of
benzotriazole, for example, the compound obtained by substituting
one, two or more hydrogen atoms of benzotriazole by a carboxyl
group, methyl group, amino group, hydroxyl group. In addition, as
derivatives of benzotriazole, 4-carboxy benzotriazole or a salt
thereof, 7-carboxymethyl benzotriazole or a salt thereof,
benzotriazole butyl ester, 1-hydroxymethyl benzotriazole,
1-hydroxybenzotriazole etc. can be used. As the addition amount of
corrosion inhibitor, the total amount of diamond slurry during use,
it is preferable to use less than 1% by mass concerning to the
total amount of diamond slurry during using, and 0.001% to 0.1% by
mass is more preferable.
[0106] In addition, the present invention is not intended to be
limited to those of the embodiments. It is possible to make changes
in various ways without departing from the spirit of the
invention.
[0107] For example, regarding the lapping machine used in each
lapping process and polishing machine used in polishing process of
the first and second embodiments, it is possible that the polishing
or lapping machine include a pair of lower faceplate 71 and upper
faceplate 72 and plural carriers 73 which, for example, were placed
at the surface of lower faceplate 71 which is opposed to the
faceplate 72 as shown in FIG. 7. Glass substrates (not shown) are
placed into a plural number of opening 74 (for example, 35 in the
present embodiment) installed in each carrier 73, and then the
glass substrates are lapped by lapping pad or polished by polishing
pad which are installed in the lower faceplate 71 and upper
faceplate 72.
[0108] Specifically, the lower faceplate 71 and upper faceplate 72
can be rotated at the same central axis and in directions opposite
to each other with the rotation movement of the rotation shafts 71a
and 72a which are rotated by drive motor (not shown), wherein the
rotation shafts 71a and 72a are placed at the center of the lower
faceplate 71 and upper faceplate 72. Also, a recess 75 for placing
the plurality carriers 73 (for example, five in this embodiment) is
provide on the surface of lower faceplate 71 wherein the surface is
facing upper faceplate 72.
[0109] As a plural carrier 73, for example, it can be obtained by
forming a disk made from epoxy resin which is strengthened by
mixing aramid fiber and fiberglass. And these plural carriers 73
are placed around the axis 71a in the inner wall of recess 75. In
addition, a planet gears part 76 is installed in the periphery of
each carrier 73 over the entire circumference. Meanwhile, in the
inner periphery of the recess 75, a sun gear portion 77 which
rotates with the rotation shaft 71a while being intermeshed with
the planetary gear carrier 76 of each 73 is provided. In the
periphery of the recess 75, the fixed gear portion 78 which is
intermeshed with planetary gear 76 of each carrier 73 is
provided.
[0110] When the sun gear portion 77 rotates with the rotating shaft
71a, since sun gear portion 77 and fixed gear portion 78 are
intermeshed with the planetary gear 76, these plural carriers 73
move (revolution) in the same direction as that of rotation shaft
71a around the periphery of the rotation shaft 71a in a recess 75.
At the same time, each of these plural carriers 73 rotates
(rotation) in the direction opposite to that of rotation shaft 71a
around each central axis. The above motion is so-called planetary
motion.
[0111] Therefore, when the above configuration is adopted by the
lapping machine used in each lapping process, the plural glass
substrates held at the opening 75 of each carrier 73 can be lapped
by the lapping pad or polished by the polishing pad placed at the
lower faceplate 71 and upper faceplate 72 while being moved as
planetary motion. In the case of this configuration, the glass
substrate can be lapped or polished not only more accurately, but
also quickly.
EXAMPLE
[0112] The effects of the present invention become clear by the
following Examples. It is apparent that the present invention is
not limited to the Examples, but may be modified and changed
without departing from the scope and spirit of the invention.
Example 1
[0113] In Example 1, firstly, a glass substrate (manufactured by
Ohara, TS-10SX) having an outside diameter of 48 mm, center hole of
12 mm, thickness of 0.560 mm was used.
[0114] And, for the glass substrate, primary lapping process, inner
and outer peripheral lapping process, inner peripheral polishing
process, secondary lapping process, the tertiary lapping process,
outer peripheral polishing process and primary polishing process
were performed in this order.
[0115] In detail, the primary lapping process is carried out by
using a lapping machine including a pair of upper and lower
faceplates. While several sheets of glass substrates are sandwiched
between the faceplates which are rotating in directions opposite to
each other, both sides of the glass substrates are lapped by
lapping pads installed in the faceplates. At this time, Toraizakuto
(Product Name/Manufactured by Sumitomo 3M) was used as the lapping
pad of the primary lapping process. The size of the projections of
the lapping pad is 2.6 mm square with a height 2 mm, and the space
between adjacent projections is 1 mm, the average particle size of
the diamond grains is 9 .mu.m, a content of diamond grains in the
projection of 20%. As the lapping machine, the four-way
double-sided lapping machine (16B, manufactured by Hamai Co., Ltd)
was used. The lapping process is carried out for 15 minutes, under
the condition that rotational speed of the faceplate is 25 rpm, the
processing pressure is 120 g/cm.sup.2. As a lapping fluid,
Sabrelube 9016 (Manufactured by Chmetall) is used after diluted
1:10 in water, lapping amount per one side of the glass substrate
was about 100 .mu.m.
[0116] In the inner and outer peripheral lapping process, lapping
machine including inner peripheral grindstone and outer peripheral
grindstone was used. The laminated substrates are obtained by
laminating plural pieces of glass substrates in the state that the
central apertures match each other wherein spacers are sandwiched.
While rotating the laminated substrates around the axis, and
inserting inner peripheral grindstone into a central aperture of
glass substrates and putting glass substrates in a radial direction
between outer peripheral grindstones which is placed on the
periphery of each glass substrate, the inner peripheral grindstone
and outer peripheral grindstone are rotated in the direction
opposite to that of laminated substrates. And at the same time as
grinding inner peripheral end face of the glass substrates by inner
peripheral grindstone, outer peripheral end face of the glass
substrates is lapped by peripheral grindstone. The inner peripheral
grindstone and outer peripheral grindstone use diamond grains with
the average particle size of 10 .mu.m. The rotation speed of the
inner peripheral grindstone and outer peripheral grindstone is 1200
rpm and 600 rpm, respectively, and processing was carried out for
30 seconds.
[0117] As the inner peripheral polishing process, using a polishing
machine having an inner peripheral polishing brush, while laminated
substrates are rotated around the axis, and the inner peripheral
polishing brush inserted in a central aperture of each glass
substrate is rotated in the direction opposite to that of the glass
substrates and moved vertically, at the same time polishing fluid
is dropped to inner peripheral polishing brush, the inner
peripheral end face of glass substrates is polished by the inner
peripheral polishing brush. In this case, a nylon brush was used as
the inner peripheral polishing brush. The rotation speed of inner
peripheral polishing brush is 300 rpm, and processing was carried
out for 10 minutes
[0118] The secondary lapping process is carried out by using a
lapping machine including a pair of upper and lower faceplates.
While several sheets of glass substrates is sandwiched between the
faceplates which are rotating in directions opposite to each other,
both sides of the glass substrates are lapped by lapping pads
installed in the faceplates. At this time, Toraizakuto (Product
Name) manufactured by Sumitomo 3M was used as the lapping pad of
the secondary lapping process. The size of the projections 21 of
the lapping pad is 2.6 mm square with a height 2 mm, and the space
between adjacent projections is 1 mm, the average particle size of
the diamond grains is 3 .mu.m, a content of diamond grains in the
projection of 50%. As the lapping machine, the four-way
double-sided lapping machine (16B, manufactured by Hamai Co., Ltd)
was used. Lapping process is carried out for 10 minutes, under the
condition that rotational speed of the faceplate is 25 rpm, the
processing pressure is 120 g/cm.sup.2. As a lapping fluid,
Sabrelube 9016 (Manufactured by Chmetall) is used after diluted
1:10 in water, lapping amount per one side of the glass substrate
was about 30 .mu.m.
[0119] The tertiary lapping process is carried out by using a
lapping machine including a pair of upper and lower faceplates.
While several sheets of glass substrates is sandwiched between the
faceplates which are rotating in directions opposite to each other,
both sides of the glass substrates are lapped by lapping pads
installed in the faceplates. At this time, Toraizakuto (Product
Name) manufactured by Sumitomo 3M was used as the lapping pad of
the primary lapping process. The size of the projections 21 of the
lapping pad is 2.6 mm square with a height 2 mm, and the space
between adjacent projections is 1 mm, the average particle size of
the diamond grains is 0.5 .mu.m, a content of diamond grains in the
projection of 60%. As the lapping machine, the four-way
double-sided lapping machine (16B, manufactured by Hamai Co., Ltd)
was used. Lapping process is carried out for 10 minutes, under the
condition that rotational speed of the faceplate is 25 rpm, the
processing pressure is 120 g/cm.sup.2. As a lapping fluid,
Sabrelube 9016 (Manufactured by Chmetall) is used after diluted
1:10 in water, lapping amount per one side of the glass substrate
was about 10 .mu.m.
[0120] In the outer peripheral polishing process, a polishing
machine having an outer peripheral polishing brush was used. The
laminated substrates were obtained by laminating plural pieces of
glass substrates in the state that the central apertures match each
other wherein spacers are sandwiched. While rotating laminated
substrates around the axis by the rotating shaft inserted in a
central aperture of each glass substrate, the outer peripheral
polishing brush in contact with the surface of the outer peripheral
end face of the glass substrates, is rotated in the direction
opposite to that of the glass substrates and moved vertically. At
the same time polishing fluid is dropped to outer peripheral
polishing brush, outer peripheral end face of glass substrates was
polished by the outer peripheral polishing brush. In the case, a
nylon brush was used as the outer peripheral polishing brush. The
rotation speed of outer peripheral polishing brush is 300 rpm, and
processing was carried out for 10 minutes
[0121] In the primary polishing process, the polishing machine
including a pair of upper and lower faceplates is used. While
sandwiching plural pieces of glass substrates between a pair of
upper and lower faceplates, which are rotating in directions
opposite to each other, both sides of these glass substrate are
polished by a polishing pad installed in the faceplates.
[0122] In this case, as the primary polishing pad, Smoke Aid type
(manufactured by Filwel) was used. The polishing fluid is polishing
slurry having silica content is 0.5 wt % by adding water to a
silica abrasive polishing fluid having 40 wt % silica as solids
content (0.08 .mu.m average particle size, Compol, manufactured by
Fujimi). As the polishing machine, the four-way double-sided
polishing machine (16B, manufactured by Hamai Co., Ltd) was used.
Polishing process is carried out for 30 minutes, under the
condition that rotational speed of the faceplate is 25 rpm, the
processing pressure is 110 g/cm.sup.2, while the polishing liquid
is supplied in a rate of 7 L/minutes. Polishing amount per one side
of the glass substrate was about 2 .mu.m.
[0123] And the glass substrates obtained after the above processes
were treated using chemical cleaning by the anionic surfactant
combined with ultrasound treatment. As a result, the glass
substrates for magnetic recording media of Example 1 were
obtained.
Example 2
[0124] In Example 2, the lapping processes of the glass substrates
in Example 1 were changed to two-steps. As the lapping pad used in
the primary lapping process, lap of glass substrate, Toraizakuto
(Product Name, Manufactured by Sumitomo 3M) was used. The size of
the projections of the lapping pad is 2.6 mm square with a height 2
mm, and the space between adjacent projections is 1 mm, the average
particle size of the diamond grains is 4 .mu.m, a content of
diamond grains in the projection of 50%. As the lapping machine,
the four-way double-sided lapping machine (16B, manufactured by
Hamai Co., Ltd) was used. Lapping process is carried out for 10
minutes, under the condition that rotational speed of the faceplate
is 25 rpm, the processing pressure is 120 g/cm.sup.2. As a lapping
fluid, Sabrelube 9016 (Manufactured by Chmetall) is used after
diluted 1:10 in water, lapping amount per one side of the glass
substrate was about 30 .mu.m.
[0125] The secondary lapping process, the primary polishing
process, and others were carried out as the same as in Example
1.
Comparative Example 1
[0126] In Comparative Example 1, the lapping process of glass
substrates in Example 1 is changed to two-steps, and the polishing
process was changed to two-steps. In detail, the tertiary lapping
process in Comparative Example 1 was not carried out, and two-step
polishing processes were carried out under the following
conditions
[0127] In the primary polishing process, the polishing machine
including a pair of upper and lower faceplates is used. While
sandwiching plural pieces of glass substrates between a pair of
upper and lower faceplates, which are rotating in directions
opposite to each other, both sides of these glass substrate are
polished by polishing pad installed in the faceplates.
[0128] In this case, the primary polishing pad, Smoke Aid type
(manufactured Filwel) was used. The polishing fluid is polishing
slurry having ceria content of 0.6 wt % obtained by adding water to
ceria abrasive polishing fluid (SHOROX Tohoku Metal Chemical Co.,
Ltd., particle size 1.0 microns). As the polishing machine, the
four-way double-sided polishing machine (16B, manufactured by Hamai
Co., Ltd) was used. Polishing process is carried out for 40
minutes, under the condition that rotational speed of the faceplate
is 30 rpm, the processing pressure is 110 g/cm.sup.2, while the
polishing liquid is supplied in a rate of 8 L/minutes. Polishing
amount per one side of the glass substrate was about 15 .mu.m.
[0129] In the secondary polishing process, the polishing machine
including a pair of upper and lower faceplates is used. While
sandwiching plural pieces of glass substrates between a pair of
upper and lower faceplates, which are rotating in directions
opposite to each other, both sides of these glass substrate are
polished by polishing pad installed in the faceplates.
[0130] In this case, the primary polishing pad, Smoke Aid type
(manufactured Filwel) was used. The polishing fluid is polishing
slurry having ceria content of 0.6 wt % obtained by adding water to
a commercially available ceria abrasive polishing fluid having
ceria content of 12 wt % (SHOROX Tohoku Metal Chemical Co., Ltd.,
particle size 1.0 microns). As the polishing machine, the four-way
double-sided polishing machine (16B, manufactured by Hamai Co.,
Ltd) was used. Polishing process is carried out for 30 minutes,
under the condition that rotational speed of the faceplate is 25
rpm, the processing pressure is 110 g/cm.sup.2, while the polishing
liquid is supplied in a rate of 8 L/minutes. Polishing amount per
one side of the glass substrate was about 2
[0131] Then, surface roughness Ra and little waviness of the glass
substrate obtained in Examples 1 and 2, and Comparative Example 1
were measured. As the measurement of surface roughness Ra and
little waviness, Atomic Force Microscope (D3000 Manufactured by
Digital Instruments) was used.
[0132] As a result, surface roughness Ra of glass substrates for
magnetic recording medium of Example 1 was 0.3 nm, micro-waviness
Wa is 0.2 nm, surface roughness Ra of glass substrates for magnetic
recording medium of Example 2 is 0.3 nm, micro-waviness Wa is 0.25
nm, surface roughness Ra of glass substrates for magnetic recording
medium of Comparative Example 1 is 0.5 nm, micro-waviness Wa was
0.3 nm. Therefore, in Examples 1 and 2, a glass substrate (glass
substrate for magnetic recording media) having high surface
smoothness and little swell can be manufactured, in comparison with
Comparative Example 1.
DENOTATION OF REFERENCE NUMERALS
[0133] 10 . . . lapping machine [0134] 11,12 . . . faceplate [0135]
20A, 20B . . . diamond pad [0136] 20a . . . lap surface [0137] 21 .
. . projection [0138] 30 . . . lapping machine [0139] 31 . . .
inner peripheral grindstone [0140] 32 . . . outer peripheral
grindstone [0141] 40 . . . polishing machine [0142] 41 . . . inner
peripheral polishing brush [0143] 50 . . . polishing machine [0144]
51 . . . rotating shaft [0145] 52 . . . outer peripheral polishing
brush [0146] 60 . . . polishing machine [0147] 61,62 . . .
faceplate [0148] 71 . . . bottom faceplate [0149] 72 . . . upper
faceplate [0150] 73 . . . carrier [0151] 74 . . . opening [0152] 75
. . . recess [0153] 76 . . . planet gears part [0154] 77 . . . sun
gears part [0155] 78 . . . fixed gear part [0156] W . . . glass
substrate [0157] X . . . laminated substrates
* * * * *