U.S. patent application number 11/733137 was filed with the patent office on 2007-08-09 for polishing sheet and polishing work method.
This patent application is currently assigned to FUJI SPINNING CO., LTD.. Invention is credited to Takahiro KUME, Hidenori TAKEDA.
Application Number | 20070184757 11/733137 |
Document ID | / |
Family ID | 33487405 |
Filed Date | 2007-08-09 |
United States Patent
Application |
20070184757 |
Kind Code |
A1 |
KUME; Takahiro ; et
al. |
August 9, 2007 |
POLISHING SHEET AND POLISHING WORK METHOD
Abstract
The present invention provides a polishing sheet that can secure
a flatness of a material to be polished and can improve a polishing
efficiency. A polishing pad 1 has a polyurethane sheet 2 made of
polyurethane resin. The polyurethane sheet 2 has large cells 3 with
a generally triangular sectional configuration rounded along a
thickness direction thereof. Polyurethane resin exists in the
polyurethane sheet 2 in a partition wall manner and fine foams 4
are formed in the polyurethane resin. Fine particles 5 added during
manufacture of the polyurethane sheet 2 exist inside some of the
fine foams 4 and the fine particles 5 are separable from the fine
foams. By separating off fine particles positioned at a polishing
face P by dummy polishing or the like, fine foams which evenly
reserve a polishing liquid containing abrasive particles are formed
at the polishing face P.
Inventors: |
KUME; Takahiro; (Touyo-shi,
Ehime, JP) ; TAKEDA; Hidenori; (Imabari-shi, Ehime,
JP) |
Correspondence
Address: |
ROBERTS, MLOTKOWSKI & HOBBES
P. O. BOX 10064
MCLEAN
VA
22102-8064
US
|
Assignee: |
FUJI SPINNING CO., LTD.
18-12, 1-chome, Ningyouchou Nihonbashi, Chuo-ku
Tokyo
JP
|
Family ID: |
33487405 |
Appl. No.: |
11/733137 |
Filed: |
April 9, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10642280 |
Aug 18, 2003 |
7220475 |
|
|
11733137 |
Apr 9, 2007 |
|
|
|
Current U.S.
Class: |
451/28 ;
451/56 |
Current CPC
Class: |
B32B 2266/0278 20130101;
Y10T 428/249953 20150401; Y10T 428/249976 20150401; Y10T 428/24372
20150115; B32B 2264/10 20130101; Y10T 428/249967 20150401; B32B
5/18 20130101; B32B 2307/51 20130101; B24D 3/32 20130101; Y10T
428/24355 20150115; B32B 2266/06 20130101; Y10T 428/249986
20150401; B24B 37/24 20130101; B32B 27/40 20130101 |
Class at
Publication: |
451/028 ;
451/056 |
International
Class: |
B24B 1/00 20060101
B24B001/00; B24B 7/19 20060101 B24B007/19 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 3, 2003 |
JP |
2003-157526 |
Claims
1. A polishing work method for a material to be polished, which
uses a polishing sheet which has an elastic plastic foam sheet in
which fine particles are contained and has a fine foam structure to
be formed at a polishing face thereof by separating off the fine
particles, comprising the steps of; attaching the polishing sheet
to a surface plate of a polishing machine; and after all the fine
particles are substantially separated off from the polishing face,
performing polishing work with the polishing sheet to the material
to be polished by using a polishing liquid containing abrasive
particles.
2. A polishing work method according to claim 1, wherein all the
fine particles are substantially separated off from the polishing
face due to dummy polishing by the polishing machine.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a polishing sheet and a
polishing work method, and in particular relates to a polishing
sheet having an elastic plastic foam sheet in which fine particles
are contained and a polishing work method using the polishing
sheet.
[0003] 2. Description of Related Art
[0004] Conventionally, a polishing sheet is used to perform
flattening work on a material required for flatness at a high
accuracy, such as an optical material such as a lens, a plane
parallel plate, a reflecting mirror or the like, a base plate for a
hard disc, a silicon wafer, a liquid crystal glass or the like. For
example, as a polishing sheet used for accurate flattening work,
e.g. for the silicon wafer or the like, a polishing sheet of a
nonwoven type obtained by drying a nonwoven sheet after the
nonwoven sheet is impregnated with a resin liquid is known (refer
to JP05-8178A publication). However, since the polishing sheet of
this type has flexibility, there are drawbacks in that a polishing
efficiency is low and a roll-off, i.e. peripheral edge portions of
a material to be polished are polished more than a central portion
thereof, occurs easily. In order to improve the polishing
efficiency, there has been disclosed a polishing sheet having an
independent foam structure obtained by hollow fine spherical bodies
or the like in a plastic material with a high hardness (for
example, refer to JP08-500622A publication) . However, because a
polishing sheet of this type has a high hardness, for example, when
the sheet is used in polishing work for an aluminum base plate for
a hard disc, there is a drawback in that defects may occur at a
surface of the aluminum base plate.
[0005] On the other hand, a polishing sheet obtained by pasting a
film with a high hardness or the like to an elastic plastic foam of
a suede type with a foam structure produced by wet film forming
process has been disclosed (for example, refer to JP10-249709A
publication) . An elastic plastic foam is generally produced by the
wet film forming process, and relatively large cells extending in a
direction approximately perpendicular to a polishing face are
formed in the interior of the elastic plastic foam. Further,
elastic plastic exists between adjacent cells in a manner of a
partition wall, and relatively small fine foams whose sizes have
not been controlled are formed in the partition wall.
[0006] Further, a polishing sheet for a silicon wafer where fine
particles of barium carbonate are contained in an elastic plastic
foam as abrasive particles has been disclosed (for example, refer
to JP2001-1270A publication).
[0007] However, since the polishing sheet disclosed in the
JP10-249709A publication has an elastic plastic foam sheet as a
base sheet, there are problems about the polishing efficiency and
the roll-off like that in the JP05-8178A publication. Further, when
the polishing sheet of the JP2001-1270 publication is used in
polishing work for an aluminum base plate, there is such a problem
that defects may occur at a surface of the aluminum base plate by
the fine particles contained in the polishing sheet. Accordingly,
there is a need for development of a polishing sheet which can
secure flatness of a material to be polished and has a high
polishing efficiency, and which does not cause defects at a surface
of the material to be polished, such as an aluminum base plate or
the like.
SUMMARY OF THE INVENTION
[0008] In view of the above circumstances, an object of the present
invention is to provide a polishing sheet which has an elastic
plastic foam sheet as a polishing sheet and which can secure
flatness of a material to be polished and can improve a polishing
efficiency, and a polishing work method using the polishing
sheet.
[0009] In order to achieve the above object, a first aspect of the
present invention is directed to a polishing sheet having an
elastic plastic foam sheet containing fine particles, wherein the
elastic plastic foam sheet has a fine foam structure to be formed
at a polishing face thereof by separating off the fine
particles.
[0010] In the first aspect, since the elastic plastic foam sheet
has a fine foam structure to be formed at a polishing face thereof
by separating off the fine particles, fine foams which can reserve
a polishing liquid containing abrasive particles are formed at the
polishing face by separating off the fine particles from the
polishing face. Therefore, the abrasive particles contained in the
polishing liquid are always supplied to the fine forms formed at
the polishing face during polishing, so that a polishing efficiency
can be improved and a flatness of a material to be polished can be
secured.
[0011] In the first aspect, a continuously foamed body of
polyurethane may be used for the elastic plastic foam sheet.
Further, fine particles may be contained in the polishing face of
the elastic plastic foam sheet to be separable therefrom. In this
case, it is preferable that the particle diameter of the fine
particles is in the range of from 0.6 .mu.m to 5 .mu.m, since, when
the diameter is less than 0.6 .mu.m, sizes of the fine foams are
too small to allow the abrasive particles to be reserved in the
fine foams, and when the diameter exceeds 5 .mu.m, the strength of
the elastic plastic foam sheet becomes lowered. If the fine
particles are abrasive particles of at least one kind selected from
ceric oxide, zirconia, alumina-zirconia, aluminum oxide, alumina
ceramics, silicon dioxide, silicon carbide, diamond, ferric oxide,
titanium oxide, manganese dioxide, calcium carbonate, and chromium
oxide, the fine particles can be easily separated off from the
polishing face because these particles have no coupling or bonding
property with the elastic plastic foam. In this case, as a second
aspect of the present invention, the elastic plastic foam sheet may
have first fine foamed cells to be formed by separating off the
fine particles and second fine foamed cells that do not contain the
fine particles at the polishing face.
[0012] Furthermore, a third aspect of the present invention is
directed to a polishing work method for a material to be polished,
which uses a polishing sheet which has an elastic plastic foam
sheet in which fine particles are contained and has a fine foam
structure to be formed at a polishing face thereof by separating
off the fine particles, comprising the steps of; attaching the
polishing sheet to a surface plate of a polishing machine; and
after all the fine particles are substantially separated off from
the polishing face, performing polishing work with the polishing
sheet to the material to be polished by using a polishing liquid
containing abrasive particles.
[0013] According to the third aspect of the present invention,
since all the fine particles are substantially separated off from
the polishing face prior to the polishing work, the same function
and effects as the first aspect can be achieved, and since the fine
particles do not exist at the polishing face of the material to be
polished when the polishing work is performed, occurrence of
defects at the polishing face of the material to be polished due to
the fine particles can be prevented. At this time, the polishing
machine for separating off all the fine particles substantially
from the polishing face may be differed from a polishing machine
for conducting the polishing work, and dummy polishing may be
performed by the same polishing machine for separating off all the
fine particles substantially from the polishing face.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] An embodiment where a polishing sheet according to the
present invention is applied to a polishing pad polishing for an
aluminum base plate used for a hard disc will be explained with
reference to the following drawings.
[0015] FIG. 1 is a sectional view illustratively showing a
polishing pad of an embodiment to which the present invention is
applicable;
[0016] FIG. 2 is a sectional view illustratively showing a state of
the polishing pad according to the embodiment where fine particles
at a polishing face have been separated by dummy polishing;
[0017] FIG. 3 is a process diagram showing manufacturing process of
a polishing pad;
[0018] FIG. 4 is a sectional view illustratively showing a
polyurethane sheet before conducting buffing process;
[0019] FIG. 5 is a sectional view illustratively showing the
polyurethane sheet after conducting the buffing process;
[0020] FIG. 6 is a process diagram showing an outline of polishing
work process;
[0021] FIG. 7 is a front view showing a schematic constitution of a
polishing machine;
[0022] FIG. 8 is a sectional view illustratively showing polishing
work process for an aluminum base plate;
[0023] FIG. 9 shows an electron microscopic photograph in the
vicinity of a polishing face of a polishing pad of a comparative
example 1 before conducting dummy polishing;
[0024] FIG. 10 shows an electron microscopic photograph in the
vicinity of a polishing face of a polishing pad of a example 1
before conducting dummy polishing; and
[0025] FIG. 11 shows an electron microscopic photograph in the
vicinity of a polishing face of a polishing pad of a example 1
after conducting dummy polishing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Polishing Pad
[0026] As shown in FIG. 1, a polishing pad 1 (a polishing sheet)
has a polyurethane sheet 2 which is formed from polyurethane resin
as an elastic (soft) plastic foam sheet whose one face is formed
like nap. The polyurethane sheet 2 is formed with large cells
(pores) 3 with a generally triangular section, which are rounded
along a direction of a thickness thereof. The cell 3 is formed such
that a size of a portion of the cell positioned at the side of a
polishing face P opposed to a face of a material to be polished is
made smaller than that of a portion of the cell positioned at the
side of an attaching face of the polishing pad to a polishing
machine. Polyurethane resin exists in a manner of a partition wall
between adjacent cells 3, and fine foams 4 dispersed generally
evenly are formed in the polyurethane resin. These fine foams 4
mutually connect 3-dimensionally in a network manner through fine
communication holes (not shown). Therefore, the polyurethane sheet
2 is constituted as a continuously foamed body of polyurethane.
[0027] Fine particles 5 added at a time of manufacturing the
polyurethane sheet 2 are contained in some of the fine foams 4. The
particle diameter of the fine particle 5 is set to a range of from
0.6 to 5 .mu.m, and the fine foam 4 is set such that the size
thereof is larger than the particle diameter of the fine particle
5. The fine foam 4 containing the fine particle 5 generally has a
space larger than the fine foam 4 which does not contain the fine
particle 5. Further, the fine particles 5 which are positioned at
the polishing face P of the polyurethane sheet 2 and positioned in
the vicinity of an inner wall face of the cell 3 exist in fine
foams 4 which can be separated from the polishing face P and the
inner wall face of the cell 3. Therefore, the fine particles 5 are
contained in the polyurethane sheet 2 and the polyurethane sheet 2
has a fine foam structure to be formed at the side of the polishing
face P by separating off fine particles 5. Incidentally, the cells
3 and some of the fine foams 4 are opened at the polishing face P
of the polyurethane sheet 2.
[0028] Further, the polishing pad 1 is provided, at an opposing
face side (a lower face side) to the polishing face P of the
polyurethane sheet 2, with a film layer 7 made of polyethylene
terephthalate (PET) which is utilized as a base material at a time
of manufacturing the polyurethane sheet 2. A double adhesive tape 8
for attaching the polishing pad 1 to a polishing machine, which has
a peeling paper (release paper) 9 on one face side (a lowermost
face side) thereof is adhered to a lower face side of the film
layer 7.
Manufacturing Method of Polishing Pad
[0029] As shown in FIG. 3, in order to manufacture a polishing pad
1, first, polyurethane resin, fine particles 5 and additives are
blended in blending process. Polyurethane resin such as polyester
base resin, polyether base resin or the like is used as the resin,
and polyurethane resin is dissolved in N,N-dimethyl-formaldehyde
(hereinafter, abbreviated as DMF) of a solvent such that it
occupies 30% in solution, so that polyurethane resin solution is
obtained. As additives, pigment such as carbon black or the like,
hydrophilic activator for accelerating foaming, hydrophobic
activator of film-forming stabilizer and the like can be used in
order to control the size or amount (number) of the fine foams
4.
[0030] As the fine particles 5, fine particles which have neither
compatibility with polyurethane resin solution nor bonding property
with a polyurethane resin and, for example, in case of fine
particles for abrasive particles, fine particles of one kind or
mixture of at least two kinds selected from a group of ceric oxide,
zirconia, alumina-zirconia, aluminum oxide, alumina ceramics,
silicon dioxide, silicon carbide, diamond, ferric oxide, titanium
oxide, manganese dioxide, calcium carbonate, and chromium oxide can
be used. When the amount of addition of the fine particles 5 to the
polyurethane resin is less than 1% by weight, change of the fine
foam 4 is reduced (the size of the fine foam 4 is small) so that it
becomes hard to exhibit effects in polishing. On the contrary, when
the amount of addition is more than 100% by weight, because the
polishing pad 1 itself is reduced in strength and separating-off
property (from the polishing face P and the inner wall face of the
cell 3) of the fine particles 5 is deteriorated, the amount is not
preferable. The amount of addition of the fine particles 5 is
preferably in a range of from 1 to 100% by weight, more preferably
in a range of from 10 to 50% by weight.
[0031] Fine particles 5, additives such as pigment and the like,
and DMF which is a solvent are added in prepared polyurethane resin
solution to be stirred and mixed sufficiently. After aggregated
masses or the like are removed by filtration, resin emulsion
including fine particles 5 added and mixed is prepared by carrying
out defoaming under vacuum.
[0032] In the next film forming process, the prepared resin
emulsion is continuously applied on a base member (the film layer
7) made of PET such that its thickness becomes substantially
uniform by using a reverse coater, and the polyurethane resin is
re-solidified by dipping the base member in water to remove the
DMF. When the DMF is removed from the resin emulsion in water,
relatively large cells 3 are formed. At this time, since the DMF is
removed from the surface side of the resin emulsion applied rather
than the base member side due to that the base member hinders water
from permeating thereinto, portions of the cells 3 positioned at
the side of the base member are formed so as to become larger than
portions thereof at the surface side. Further, when the DMF is
separated into water, fine foams 4 are formed in the polyurethane
resin in a continuous foaming manner. Incidentally, the fine foams
4 are formed in a partition wall of the polyurethane sheet 2 so as
to be distributed generally evenly.
[0033] Next, in buffing process, buffing (surface sanding) is
performed to a surface of the polishing face P side of the
sheet-like polyurethane resin obtained, thereby removing a surface
layer (so-called a skin layer) of the polyurethane resin. FIG. 4
and FIG. 5 illustratively show a polyurethane sheet 2 before buffed
and a polyurethane sheet 2 after buffed, respectively. By the
buffing process, some of the cells 3 and the fine foams 4 are
opened to the polishing face P, so that the polishing face P of the
polyurethane sheet 2 obtains a nap property. At this time, the fine
particles 5 positioned in the vicinity of the polishing face P of
the polyurethane sheet 2 are contained in the fine foams 4 such
that they may be separated therefrom. Incidentally, the film layer
7 is omitted in FIGS. 4 and 5.
[0034] Here, the cells 3 are formed to be aligned in the obtained
sheet-like polyurethane resin in a thickness direction thereof and
the polyurethane resin exists in a partition wall shape for
partitioning the cells 3. In the above-described film forming
process, if control is carried out such that the sizes of the fine
foams 4 are made large without changing the shape, the size of the
cells 3 formed in the polyurethane sheet 2 and the used amount of
the polyurethane resin, the thickness of the partition wall becomes
large so that the area of the polishing face P (refer to FIG. 1) of
the polyurethane sheet 2 becomes large. Accordingly, in the film
forming process, by polishing efficiency during polishing work into
consideration, control is carried out so as to secure the thickness
of the partition walls to become large, i.e., the area of the
polishing face P of the polyurethane sheet 2 to become large.
[0035] Next, in laminating process, one face of a double adhesive
tape 8 with a peeling paper 9 attached to the other face thereof is
adhered to a face opposite to the polishing face P of the base
member (the film layer 7), and in the next cutting process, dies
cutting is performed so as to obtain a desired shape, for example,
a circle with a diameter of 640 mm. Subsequently, in inspecting
process, an inspection is made for confirming that there is neither
stain nor adhesion of scraps, such as buffs or the like, on a
product, so that a polishing pad 1 is finished.
Polishing Work
[0036] Next, a polishing work method where polishing pads 1 are
attached or mounted to a polishing machine for both surface
polishing serving as a polishing machine and polishing work is
conducted to an aluminum base plate serving as a material to be
polished will be explained.
[0037] As shown in FIG. 7, a polishing machine 20 used for
polishing work is provided with a base stand 23 in which a power
source section, a control section, a motor for driving the
polishing machine 20 and the like. A lower surface plate 22 for
polishing a lower face of an aluminum base plate that is a material
to be polished is disposed above the base stand 23. An upper
surface plate 21 for polishing an upper face of the aluminum base
plate, which has a center axis on an extension of a center axis of
the lower surface plate 22, is disposed above the lower surface
plate 22. Polishing pads 1 are respectively attached to an upper
face of the lower surface plate 22 and a lower face of the upper
surface plate 21. The upper surface plate 21 and the lower surface
plate 22 are supported so as to be respectively rotatable in
opposite directions (arrows in FIG. 7), and a rotational driving
force for the upper surface plate 21 is conveyed from the motor
inside the base stand 23 via a vertical transmission shaft (not
shown) housed in a post 30, a horizontal support shaft 31 and a
drive shaft 24, while a rotational driving force for the lower
surface plate 22 is conveyed from the motor via gears (not shown)
and the like. Further, a surface plate vertical moving cylinder 25
which can move the upper surface plate 21 vertically is fixed to
the horizontal support shaft 31. Furthermore, the drive shaft 24
extends through a supply disc 26 which has a plurality of polishing
liquid supplying tubes 38 to supply the polishing liquid to the
upper surface plate 21 to be fixed to the upper surface plate 21. A
working pressure adjusting cylinder 27 for adjusting a pressure
which pressurizes the upper surface plate 21 toward the lower
surface plate 22 during polishing work is disposed on the supply
disc 26.
[0038] Further, one end of a liquid feeding pipe 37 for feeding the
polishing liquid is connected to the supply disc 26, and another
end thereof is connected to a liquid feeding pump 36 for feeding
the polishing liquid. The liquid feeding pump 36 is connected to a
polishing liquid tank (not shown) which reserves the polishing
liquid.
Polishing Pad Attaching Process
[0039] As shown in FIG. 6, in attaching process, first, the
polishing pads 2 are attached to the polishing machine 20. That is,
the upper surface plate 21 is moved upwardly by the surface plate
vertical moving cylinder 21 to be separated from the lower surface
plate 22, so that the peeling paper 9 are peeled off from the
polishing pads 1 and the polishing pads 1 are pasted to the lower
face of the upper surface plate 21 and the upper face of the lower
surface plate 22. Incidentally, in this state, fine particles 5 are
contained in the polishing faces P of the two polishing pads 1 to
be separable therefrom.
Dummy Polishing Process
[0040] In the next dummy polishing process, the upper surface plate
21 is moved downward by the surface plate vertical moving cylinder
25, a dummy material to be polished which is equivalent to an
aluminum base plate (an aluminum base plate different from a
subject aluminum base plate for polishing work) is sandwiched
between the two upper and lower polishing pads 1, and then a dummy
polishing for separating off fine particles existing at the
polishing faces P of the polishing pads 1 and existing in the
vicinity of inner wall faces of the cells 3 is conducted under the
conditions such that a rotational speed of a motor, an applied
pressure and the like are substantially equal to those in case of
actual polishing of an aluminum base plate. As shown in FIG. 2, in
the dummy polishing process, all the fine particles positioned at
the polishing faces P of the two upper and lower polishing pads 1
and in the vicinity of the inner wall faces of the cells 3 are
separated off from the fine foams 4 by pressing force from the
working pressure adjusting cylinder 27 and deformation of the
partition walls due to rotations of the upper surface plate 21 and
the lower surface plate 22, and new fine openings of the fine foams
4 which can reserve and allow the polishing liquid to move are
formed in addition of the openings of the fine foams 4 formed in
the buffing process. As described above, in the film forming
process for the polishing pad 1, since the fine foams 4 are formed
so as to be distributed uniformly in the partition walls of the
polyurethane sheet 2, a state that the fine foams 4 are generally
uniformly distributed at the polishing face P can be obtained in
this dummy polishing process.
Polishing Work Process
[0041] Next, in polishing work process, the dummy material to be
polished is replaced by a subject aluminum base plate for polishing
work, and then both surfaces of the aluminum base plate are
subjected to polishing work. That is, as shown in FIG. 8, an
aluminum base plate 40 is sandwiched by two polishing pads 1
rotated together with the upper surface plate 21 and the lower
surface plate 22 due to pressure from the working pressure
adjusting cylinder 27, and a slurry-like polishing liquid 35
including abrasive particles is supplied between the polishing pads
1 and the aluminum base plate 40. The abrasive particles contained
in the polishing liquid 35 enter into a space between the polishing
pads 1 and the aluminum base plate 40 so that both the surfaces
(surfaces to be polished) of the aluminum base plate 40 are
subjected to polishing work.
[0042] As described above, in the polishing pad 1 of this
embodiment, the fine foams 4 are approximately uniformly
distributed at the polishing face P, and the polishing liquid
containing the abrasive particles is reserved inside the fine foams
4 and the cells 3, and it is movable through the communication
holes formed in the network manner. The spaces (pores) of the fine
foams 4 obtained by separating off the fine particles 5 in the
dummy polishing process are larger than those of the fine foams 4
in which no fine particles exist originally. Accordingly, the
former allows the abrasive particles to move in a higher degree of
freedom than the latter, and the number of the spaces of the fine
foam 4 can be controlled to increase by adjusting the addition
amount of the fine particles 5 in the blending process. For this
reason, in the polishing process, the polishing work is conducted
to the aluminum base plate 40 such that the abrasive particles
contained in the polishing liquid can move between the fine foams 4
and the cells 3 through the communication holes and that they can
be generally uniformly and sufficiently supplied to the faces to be
polished of the aluminum base plate 40. Therefore, the polishing
work can be conducted without causing polishing unevenness while
flatness is being secured to the surface of the aluminum base plate
40, and the polishing work is conducted approximately evenly to
both a peripheral portion and a central portion of the aluminum
base plate 40, thereby inferior work due to the roll-off can be
reduced.
[0043] Further, in the polishing pad 1 of the present embodiment,
it is possible to secure the area of the polishing face P of the
polyurethane sheet 2 to be larger by controlling the thickness of
the partition walls to become large. Therefore, since a contacting
area of the polishing face P and the aluminum base plate 40 is
increased by thus increasing the area of the polishing face P of
the polishing pad 1, it is made possible to improve polishing
efficiency.
[0044] Further, in the polishing work using the polishing pad 1 of
this embodiment, since all the fine particles 5 are substantially
removed (separated off) from the polishing face P in the dummy
polishing process, no fine particles 5 exist at the polishing face
P in the polishing work process. Accordingly, occurrence of the
defects due to the polishing work to the surface of the aluminum
base plate 40 can be prevented.
[0045] In general, for polishing work to the aluminum base plate
40, a particle diameter of abrasive particles used is in a range of
from 0.1 to 1 .mu.m or so in primary polishing and it is in a range
of from 0.001 to 0.1 .mu.m or so in secondary polishing. In this
embodiment, since the fine foam 4 is formed such that its size is
larger than the particle diameter of the fine particle 5, the fine
foam 4 having a desired size can be easily realized by changing the
particle diameter of the fine particles 5 that are added when
manufacturing the fine form 4. If the diameter of the particle size
5 is smaller than 0.6 .mu.m, the size of the fine foam 4 becomes
too small to reserve the abrasive particles, so that it becomes
difficult to enhance the polishing efficiency. On the contrary, if
the particle diameter is larger than 5 .mu.m, the strength of the
polishing pad 1 and the separating-off property of the fine
particles 5 are influenced because the thickness of the partition
walls of the polyurethane resin is in a range of from 5 to 10 .mu.m
or like at thin portions thereof. Due to these reasons, for
polishing, the particle diameter of the fine particle 5 is
preferably from 0.6 .mu.m to 5 .mu.m, and more preferably from 1
.mu.m to 3 .mu.m. By controlling the sizes of the fine foams 4 and
the communication holes in the film forming process, the movement
of the polishing liquid including the abrasive particles is made
easy inside the polishing pad 1, between the cells 3 and between
the fine foams 4. Therefore, not only in the secondary polishing
but also in the primary polishing, the polishing efficiency can be
improved in cooperation with supplying of the polishing liquid from
the inside of the polishing pad 1 and the cells 3 to the fine foams
4.
[0046] Incidentally, in this embodiment, the polyurethane resin
sheet has been exemplified as the elastic plastic foam sheet, but
this invention is not limited to this example. For example, resin
which forms continuous foams such as polyester resin may be used.
When the polyester resin is used, continuous foams may be easily
formed according to the wet film forming process. Further, in this
embodiment, the wet film forming process has been exemplified as
the process for manufacturing the polyurethane sheet, dry film
forming process maybe used. At this time, for example, hydrophilic
activator or the like for promoting foaming may be added to form
continuous foam body.
[0047] Further, in this embodiment, the coating of the resin
emulsion to the PET-made base material by the reverse coater has
been exemplified, however, for example, a roll coater or a knife
coater may be used. Any coater may be used as long as it can allow
uniform coating to the base material. Further, for example, a
nonwoven sheet, a woven sheet or the like may be listed as a usable
base material other than the PET.
[0048] Furthermore, in this embodiment, the example that the
polyurethane sheet 2 is formed on the base material made of the PET
has been shown, but it is possible to obtain only the polyurethane
sheet 2 by peeling off the base material that is solidified in a
wet type manner after applying the resin emulsion to the PET, and
the polyurethane sheet 2 may be directly attached to the surface
plate of the polishing machine. In this case, other base material
may be adhered to the polyurethane sheet 2, and a nonwoven sheet or
a woven sheet made of synthetic fibers may be used as the base
material other than the film made of the PET.
[0049] Further, in this embodiment, the polishing machine 20 which
polishes both surfaces of the material to be polished has been
exemplified as the polishing machine, but the present invention
may, of course, be applied to a polishing machine which polishes
one surface of a material, and a polishing machine which polishes a
resin-made lens, a spherical glass or the like. Furthermore, in
this embodiment, the example that the polishing pads 1 are attached
to the polishing machine 20, and the fine particles at the
polishing face are separated off by the dummy polishing has been
shown, but the polishing pad 1 may be attached to the polishing
machine 20 after the fine particles 5 of the polishing pad 1 have
been separated off in advance by using an exclusive polishing
machine for dummy polishing, an exclusive machine for separating
off fine particles (for example, which may be a machine for
carrying out the separating-off by utilizing vibrations) or the
like. By employing such an exclusive machine, the fine particles 5
are almost entirely prevented from entering into the polishing
machine 20. In the above-described embodiment, the example that
fine particles are separated off from the polishing face P of the
polishing pad 1 under the same conditions as those in the case that
the aluminum base plate is polished has been shown, however, it is
unnecessary to make the conditions in the dummy polishing process
equal to those in the polishing work process since it is sufficient
in this invention that once the fine particles are separated off
from the polishing face P of the polishing pad 1.
[0050] Next, examples of the polishing pad 1 manufactured according
to the above embodiment will be explained. Incidentally,
comparative examples manufactured for comparison will also be
described.
EXAMPLE 1
[0051] As shown in the following Table 1, in Example 1, white fused
alumina particles having an average particle diameter of 2.0 .mu.m
were used as the fine particles 5, and polyester-diphenylmethane
diisocyanate (MDI) base polyurethane resin was uses as the
polyurethane resin. Resin emulsion was prepared by adding and
blending white fused alumina of 40 weight parts, a DMF dispersing
liquid of 40 weight parts including carbon black of 30% as pigment,
and hydrophilic activator of 2 weight parts, hydrophobic activator
of 2 weight parts and DMF of 52 weight parts, to DMF solution of
100 weight parts including polyurethane resin of 30%. The polishing
pad 1 was manufactured by using this resin emulsion. TABLE-US-00001
TABLE 1 ADDITION AMOUNT (WEIGHT PART) TO DMF SOLUTION OF 100
PARTICLE WEIGHT PARTS INCLUDING DIAMETER POLYURETHANE RESIN OF
(.mu.m) 30% EXAMPLE 1 2.0 10 EXAMPLE 2 0.6 10 EXAMPLE 3 5.0 10
EXAMPLE 4 2.0 3 EXAMPLE 5 2.0 10 EXAMPLE 6 2.0 15 COMPARATTVE NON-
0 EXAMPLE 1 ADDITION COMPARATIVE 2.0 30 EXAMPLE 2
EXAMPLE 2 To EXAMPLE 3
[0052] As shown in Table 1, in Examples 2 and 3, the same
conditions as those in Example 1 were employed except for a
difference in a particle diameter of the white fused alumina
particles. In Example 2, the particle diameter was 0.6 .mu.m and in
Example 3, it was 5.0 .mu.m.
EXAMPLE 4 To EXAMPLE 6
[0053] As shown in Table 1, in Examples 4 to 6, the same conditions
as those in Example 1 were employed except for a difference in an
addition amount of the white fused alumina. In Example 4, the
addition amount of the white fused alumina was 3 weight parts, in
Example 5, it was 10 weight parts, and in Example 6, it was 15
weight parts.
COMPARATIVE EXAMPLE 1
[0054] As shown in Table 1, in Comparative Example 1, the same
conditions as those in Example 1 were employed except for
non-addition (0 weight parts) of the white fused alumina.
COMPARATIVE EXAMPLE 2
[0055] As shown in Table 1, in Comparative Example 2, the same
conditions as those in Example 1 were employed except for an
addition amount of the white fused alumina of 30 weight parts.
However, a polishing pad could not be manufactured because film
forming was not achieved.
Dummy Polishing And Polishing Work
[0056] By using the polishing pads of Examples and Comparative
Examples, dummy polishing and polishing work were conducted under
the following conditions:
[0057] Used Polishing Machine: 9B-5P POLISHING MACHINE manufactured
by SPEED FIRM INC.
[0058] Polishing Speed (rpm): 25r/m
[0059] Working Pressure: 100 g/cm.sup.2
[0060] Slurry (Polishing Liquid): DL3471 produced by FIJIMI
CORPORATED (average particle diameter: 0.8 .mu.m; Mixed liquid of
DL3471:water=1:3 was used.)
[0061] Slurry Supplying Amount: 100 cc/min
[0062] Kind of Material to be Polished: aluminum base plate for 95
mm.phi. hard disc
[0063] Polishing Time: one minute; three minutes
Evaluation
[0064] Next, the polishing pads of Examples and Comparative
Examples were evaluated on the basis of improvement degree in
waviness calculated from a polishing rate to an aluminum base plate
and waviness thereof. Further, regarding polished aluminum base
plates, appearance evaluation about presence/absence of defect
occurrence to surfaces of the aluminum base plates was made
according to visual inspection. Furthermore, section structures of
the polyurethane sheets of Examples and Comparative Examples in the
vicinity of the polishing faces P thereof were confirmed by
microscopic photographs.
Polishing Rate
[0065] The polishing rate is one of numerical values indicating a
polishing efficiency and it represents a polishing amount per one
minute with a thickness. Weight reduction of the aluminum base
plate was calculated from measured weight before the polishing work
and measured weight after the polishing work, and then the
polishing rate was calculated from the polished area and the
specific gravity of the aluminum base plate.
Improvement Degree In Waviness
[0066] Waviness is one of measurement items for evaluating a
surface accuracy (flatness) to a disc base plate, a silicon wafer
or the like, it is expressed with angstrom unit (A) to a waviness
amount (Wa) per unit area of a surface image which is observed by
an optical non-contacting surface roughness tester. Evaluation was
made by using the "Optiflat" as a test and evaluation machine. In
particular, in a disc base plate used for a fixed magnetic disc (a
hard disc) device used in combination with a floating type magnetic
head, since floating property of the magnetic head deteriorates
according to an increase of this waviness, it is important to
suppress the waviness as small as possible during the polishing
work. As the measured numerical value becomes lower, the waviness
becomes small, accordingly, which means that a more flat face is
realized. An improvement degree in waviness is a difference in a
waviness amount (Wa) between the aluminum base plate before and
after the polishing work, and an increase in the improvement degree
means a reduction in the waviness amount, which indicates that a
flatness of the aluminum base plate is secured.
[0067] Regarding the polishing pads 1 of Example 1 to Example 3 and
the polishing pad of Comparative Example 1, the results obtained by
conducting the polishing work tests about a polishing time of one
minute and evaluating the polishing rates, the improvement degrees
in waviness and the appearances of these polishing pads are shown
in Table 2. Further, regarding the polishing pads 1 of Example 1 to
Example 6 and the polishing pad of Comparative Example 1, the
results obtained by conducting polishing work tests about a
polishing time of three minutes and evaluating the polishing rates,
the improvement degrees in waviness and the appearances of these
polishing pads are shown in Table 3. TABLE-US-00002 TABLE 2
POLISHING IMPROVEMENT RATE DEGREE IN (.mu./min) WAVINESS(.ANG.)
DEFECTS EXAMPLE 1 0.8 2.21 Non EXAMPLE 2 0.8 1.90 Non EXAMPLE 3 0.9
2.04 Non COMPARATIVE 0.8 1.85 Non EXAMPLE 1
[0068] As shown in Table 2, regarding the polishing rate, all of
the polishing pads 1 of Example 1 to Example 3 where the white
fused alumina was added and the polishing pad of Comparative
Example 1 where no white fused alumina was added were stable and
there was found no difference among them. Further, regarding the
appearance, no defects were found at the surfaces of the polished
aluminum base plates. The polishing pads 1 of Example 1 to Example
3 were improved largely regarding the waviness as compared with the
polishing pad of Comparative Example 1. It was confirmed that the
improvement degree of Example 1 where the white fused alumina
particles with the particle diameter of 2.0 .mu.m were added was
high among them.
[0069] As shown in Table 3, the improvement degree in waviness is
improved by extending the polishing time. However, the polishing
pads of Examples are higher in improvement degree than the
polishing pad of Comparative Example 1 even if the polishing time
is extended. Furthermore, regarding the addition amount of the
white fused alumina, it was confirmed that the improvement degree
in waviness of Example 5 including the white fused alumina of 10%
by weight was high. TABLE-US-00003 TABLE 3 POLISHING IMPROVEMENT
RATE DEGREE IN (.mu./min) WAVINESS(.ANG.) DEFECTS EXAMPLE 1 0.7
3.75 Non EXAMPLE 2 0.7 3.05 Non EXAMPLE 3 0.8 3.33 Non EXAMPLE 4
0.7 3.20 Non EXAMPLE 5 0.7 3.75 Non EXAMPLE 6 0.6 3.35 Non
COMPARATIVE 0.7 2.90 Non EXAMPLE 1 COMPARATIVE (Film Forming
Impossible) EXAMPLE 2
[0070] FIGS. 9 and 10 show electron microscopic photographs of
portions in the vicinity of the polishing faces of the polishing
pads of Comparative Example 1 and Example 1 before the dummy
polishing is conducted. As apparent from FIG. 10, it is found that
the alumina particles with the particle diameter of 2 .mu.m are
dispersed evenly in the polishing pad of Example 1. Further, FIG.
11 shows an electron microscopic photograph of a portion in the
vicinity of a polishing face of the polishing pad 1 of Example 1
after the dummy polishing was conducted. Almost all the alumina
particles at the polishing face and the inner wall faces of the
cells were separated and only a slight amount of the particles
confined in the partition walls remain in the polishing pad. Thus,
it is possible to change the sizes and the number of fine foams in
the partition walls by addition of the alumina particles.
* * * * *