U.S. patent application number 10/798305 was filed with the patent office on 2005-05-26 for polishing sheet and manufacturing method of elastic plastic foam sheet.
This patent application is currently assigned to Fuji Spinning Co., Ltd.. Invention is credited to Iwao, Tomohiro, Kume, Takahiro.
Application Number | 20050112354 10/798305 |
Document ID | / |
Family ID | 34587560 |
Filed Date | 2005-05-26 |
United States Patent
Application |
20050112354 |
Kind Code |
A1 |
Kume, Takahiro ; et
al. |
May 26, 2005 |
Polishing sheet and manufacturing method of elastic plastic foam
sheet
Abstract
A polishing sheet which can improve waviness at a face of a
material to be polished and which has a long life is provided. The
polishing pad 1 has a polyurethane sheet 2 made of polyurethane
resin. The polyurethane sheet 2 has a polishing layer which is
disposed inside a surface layer and which is allowed to wear away
by polishing and whose thickness is larger than a thickness of the
surface layer. The polishing layer has an approximately uniform
foam structure in a direction of the thickness of the polishing
sheet 2 by being formed foams whose space volume is larger than
that of foams formed at the surface layer and which are
communicated so as to form a network by continuous holes whose
diameter is smaller than that of the space volume of the foams
formed at the polishing layer.
Inventors: |
Kume, Takahiro; (Touyo-shi,
JP) ; Iwao, Tomohiro; (Touyo-shi, JP) |
Correspondence
Address: |
NIXON PEABODY, LLP
401 9TH STREET, NW
SUITE 900
WASHINGTON
DC
20004-2128
US
|
Assignee: |
Fuji Spinning Co., Ltd.
Tokyo
JP
|
Family ID: |
34587560 |
Appl. No.: |
10/798305 |
Filed: |
March 12, 2004 |
Current U.S.
Class: |
428/304.4 ;
427/331; 428/318.4; 451/66 |
Current CPC
Class: |
B32B 25/14 20130101;
B32B 5/18 20130101; B32B 38/0004 20130101; B32B 5/32 20130101; Y10T
428/249987 20150401; B32B 27/40 20130101; B24D 3/32 20130101; Y10T
428/249953 20150401; B32B 2038/0016 20130101; B24D 11/001 20130101;
B32B 5/245 20130101; B32B 5/02 20130101 |
Class at
Publication: |
428/304.4 ;
451/066; 428/318.4; 427/331 |
International
Class: |
B24B 007/00; B24B
009/00; B24B 005/00; B24B 029/00; B32B 003/26; B32B 009/00; B05D
001/40; B05D 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 25, 2003 |
JP |
2003-393700 |
Claims
What is claimed is:
1. A polishing sheet having an elastic plastic foam sheet, wherein
the elastic plastic foam sheet has a polishing layer which is
disposed inside a surface layer and which is allowed to wear away
by polishing and whose thickness is larger than a thickness of the
surface layer, and wherein the polishing layer has an approximately
uniform foam structure in a direction of the thickness of the
elastic plastic foam sheet by being formed foams whose space volume
is larger than that of foams formed at the surface layer and which
are communicated so as to form a network by continuous holes whose
diameter is smaller than that of the space volume of the foams
formed at the polishing layer.
2. A polishing sheet according to claim 1, wherein a thickness of
the polishing layer is not less than 50 .mu.m.
3. A polishing sheet according to claim 1, wherein the elastic
plastic foam sheet is made of polyurethane.
4. A polishing sheet according to claim 1, wherein the elastic
plastic foam sheet is integrally formed by the surface layer, the
polishing layer, and an elastic layer which gives elasticity to the
polishing layer.
5. A polishing sheet according to claim 4, wherein foams, whose
space volume is larger than that of the foams formed at the
polishing layer and which are long in the direction of the
thickness of the elastic plastic foam sheet, are formed at the
elastic layer.
6. A polishing sheet according to claim 1, wherein the polishing
sheet further has a supporting layer which is made of at least one
selected from a flexible film, a nonwoven fabric and a woven fabric
and which is disposed at one side of the elastic plastic foam sheet
to support the elastic plastic foam sheet.
7. A polishing sheet according to claim 6, wherein the polishing
sheet further has an elastic layer which gives elasticity to the
polishing layer and which is disposed between the elastic plastic
foam sheet and the supporting layer.
8. A polishing sheet according to claim 7, wherein the polishing
sheet further has a flexible film between the elastic plastic foam
sheet and the elastic layer.
9. A polishing sheet according to claim 1, wherein a groove for
accommodating and discharging shavings occurred from a material to
be polished is formed at the surface layer and the polishing
layer.
10. A polishing sheet according to claim 1, wherein the surface
layer is removed from the elastic plastic foam sheet.
11. A polishing sheet according to claim 10, wherein a thickness of
the polishing layer is not less than 50 .mu.m.
12. A polishing sheet according to claim 10, wherein the elastic
plastic foam sheet is integrally formed by the polishing layer and
an elastic layer which gives elasticity to the polishing layer.
13. A polishing sheet according to claim 10, wherein the polishing
sheet further has a supporting layer which is made of at least one
selected from a flexible film, a nonwoven fabric and a woven fabric
and which is disposed at one side of the elastic plastic foam sheet
to support the elastic plastic foam sheet.
14. A polishing sheet according to claim 10, wherein a groove for
accommodating and discharging shavings occurred from a material to
be polished is formed at the polishing layer.
15. A manufacturing method of an elastic plastic foam sheet for a
polishing sheet, comprising the steps of; coating approximately
uniformly a polyurethane resin emulsion, which includes a
polyurethane resin, a first organic solvent that the polyurethane
resin can be dissolved, and a second organic solvent whose
solubility to water is smaller than that of the first organic
solvent and which controls coagulation of the polyurethane resin,
to a base material; and soaking the base material coated by the
polyurethane resin emulsion into a coagulation liquid whose main
component is water, and wherein the elastic plastic foam sheet has
a polishing layer which is disposed inside a surface layer and
which is allowed to wear away by polishing and whose thickness is
larger than a thickness of the surface layer, and the polishing
layer has an approximately uniform foam structure in a direction of
the thickness of the elastic plastic foam sheet by being formed
foams whose space volume is larger than that of foams formed at the
surface layer and which are communicated so as to form a network by
continuous holes whose diameter is smaller than that of the space
volume of the foams formed at the polishing layer.
16. A manufacturing method according to claim 15, wherein the
second organic solvent is ethyl acetate, and the polyurethane resin
emulsion is prepared by adding the second organic solvent of a
range of from 20 parts to 45 parts to a polyurethane resin
solution, that the polyurethane resin is dissolved into the first
organic solvent, of 100 parts.
17. A manufacturing method according to claim 15, wherein the
method further comprising a step of removing the surface layer from
the elastic plastic foam sheet.
18. A manufacturing method of an elastic plastic foam sheet for a
polishing sheet, comprising the steps of; coating approximately
uniformly a polyurethane resin emulsion, which includes a
polyurethane resin and a third organic solvent that the
polyurethane resin can be dissolved, to a base material; and
soaking the base material coated by the polyurethane resin emulsion
into a coagulation liquid including a fourth organic solvent and
water, and wherein the elastic plastic foam sheet has a polishing
layer which is disposed inside a surface layer and which is allowed
to wear away by polishing and whose thickness is larger than a
thickness of the surface layer, and the polishing layer has an
approximately uniform foam structure in a direction of the
thickness of the elastic plastic foam sheet by being formed foams
whose space volume is larger than that of foams formed at the
surface layer and which are communicated so as to form a network by
continuous holes whose diameter is smaller than that of the space
volume of the foams formed at the polishing layer.
19. A manufacturing method according to claim 18, wherein a density
of the fourth organic solvent in the coagulation liquid is ranged
of from 20 weight percent to 50 weight percent.
20. A manufacturing method according to claim 18, wherein the
method further comprising a step of removing the surface layer from
the elastic plastic foam sheet.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a polishing sheet and a
manufacturing method of an elastic plastic foam sheet for the
polishing sheet, and in particular relates to a polishing sheet
having an elastic plastic foam sheet which is of use to precision
polishing work and a manufacturing method of an elastic plastic
foam sheet for 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 coagulating a nonwoven fabric after the
nonwoven sheet is impregnated with a resin solution 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 corresponding to
W094/04599). However, because the 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 sheet is generally produced
by the wet film forming process, and relatively large cells
extending in a direction approximately perpendicular to a surface
of the polishing sheet are formed in an interior of the elastic
plastic foam sheet. A foaming surface layer (a skin layer), whose
thickness is approximately several micro meters and whose surface
is flat, is formed at the surface of the polishing sheet. The skin
layer is removed by conducting buffing treatment in order to
improve flatness of the surface of the polishing sheet, and such a
polishing sheet has a honeycomb shaped cell structure that
relatively large cells are opened at a surface of a polishing
layer. The surface for contacting a material to be polished of the
polishing sheet having such a honeycomb shaped cell structure is
formed uneven. A polishing liquid is reserved by the opened
relatively large cells, and the material to be polished is polished
by pressing the reserved polishing liquid at a time of polishing
the material. Since foreign substances such as sludge (polishing
shavings) and the like are accommodated inside the large cells,
scratches (polishing defects) and the like which occur at the
surface of the material to be polished can be prevented.
[0006] Further, a method for polishing the surface of the material
to be polished by a non-buffing type polishing sheet which retains
the flat skin layer and which do not have the opened relatively
large cells, by giving no buffing treatment to the surface of the
above-stated elastic plastic foam sheet, has been disclosed. This
method can improve waviness which is one of measurement items for
evaluating flatness to the surface of the material to be polished
(for example, refer to JP2001-62704A publication corresponding to
U.S. Pat. No. 6,439,965). At present, the method for polishing the
surface of the material to be polished by this non-buffing type
polishing sheet is mainly used in secondary polishing for the
aluminum base plate for the hard disc.
[0007] Thus, the method disclosed in the JP2001-62704A publication
is a method for polishing the material to be polished by retaining
a flat face (flatness) of the surface of the skin layer, and which
can improve the waviness of the material to be polished. However,
since a diameter of the opened relatively large cells changes due
to abrasion at the surface of the polishing sheet and polishing
performance (waviness of the surface, polishing rate) is gradually
lowered, it has a disadvantage in a life span of the polishing
sheet. Especially, in polishing for the aluminum base plate or the
like for the hard disc having a large capacity, since lowering in
the waviness at the surface causes performance dropping in the hard
disc, it is required to improve both the waviness at the surface of
the aluminum base plate or the like and the life span of the
polishing sheet.
SUMMARY OF THE INVENTION
[0008] In view of the above circumstances, an object of the present
invention is to provide a polishing sheet which can improve
waviness at a face of a material to be polished and which has a
long life and a manufacturing method of an elastic plastic foam
sheet for a polishing sheet thereof.
[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, wherein the elastic plastic foam sheet
has a polishing layer which is disposed inside a surface layer and
which is allowed to wear away by polishing and whose thickness is
larger than a thickness of the surface layer, and wherein the
polishing layer has an approximately uniform foam structure in a
direction of the thickness of the elastic plastic foam sheet by
being formed foams whose space volume is larger than that of foams
formed at the surface layer and which are communicated so as to
form a network by continuous holes whose diameter is smaller than
that of the space volume of the foams formed at the polishing
layer.
[0010] In the first aspect, the elastic plastic foam sheet has a
polishing layer which is disposed inside the surface layer. Since a
surface of the elastic plastic foam sheet is approximately flat due
to the surface layer, the polishing sheet can polish a material to
be polished with the flat surface layer, and after the surface
layer is worn away, the polishing sheet can continue to polish the
material to be polished with the polishing layer. Since the
polishing layer has the approximately uniform foam structure in the
direction of the thickness of the elastic plastic foam sheet by
being formed foams whose space volume is larger than that of foams
formed at the surface layer and which are communicated so as to
form the network by continuous holes whose diameter is smaller than
that of the space volume of the foams formed at the polishing
layer, a polishing liquid containing abrasive particles is reserved
by the foams which are uniformly formed at the polishing layer and
is supplied to a polishing face of the material to be polished
through the continuous holes at a time of polishing the material to
be polished. Accordingly, the face of the material to be polished
is polished uniformly and waviness to the face of the material to
be polished can be improved. Further, since the polishing layer is
allowed to wear away by polishing and its thickness is larger than
that of the surface layer, even if the polishing layer is worn away
partially by polishing, the polishing sheet can polish the material
to be polished continuously due to the thickness of the polishing
layer. Accordingly, a polishing sheet having a long life can be
obtained.
[0011] In the first aspect, in order to improve a life of the
polishing sheet, it is preferable that a thickness of the polishing
layer is not less than 50 .mu.m and that the elastic plastic foam
sheet is made of polyurethane. The polishing sheet may further have
a supporting layer which is made of at least one selected from a
flexible film, a nonwoven fabric and a woven fabric and which is
disposed at one side of the elastic plastic foam sheet to support
the elastic plastic foam sheet. In such a polishing sheet, since
the elastic plastic foam sheet is supported by the supporting
layer, the polishing sheet can be attached flatly and easily to a
polishing machine. Further, if a groove for accommodating and
discharging shavings (sludge) occurred from the material to be
polished is formed at the surface layer and the polishing layer,
occurrence of defects (scratches) at a polishing face of the
material to be polished can be prevented since the shavings are
removed from the face via the groove.
[0012] As one embodiment of the polishing sheet, the elastic
plastic foam sheet may be integrally formed by the surface layer,
the polishing layer, and an elastic layer which gives elasticity to
the polishing layer. At this time, foams, whose space volume is
larger than that of the foams formed at the polishing layer and
which are long in the direction of the thickness of the elastic
plastic foam sheet, may be formed at the elastic layer. Such a
polishing sheet can contact the material to be polished
approximately equally since the elastic layer deforms elastically
at a time of polishing the material to be polished.
[0013] As another embodiment of the polishing sheet, the polishing
sheet may have an elastic layer which gives elasticity to the
polishing layer and which is disposed between the elastic plastic
foam sheet and the supporting layer. In such an embodiment, if the
polishing sheet further has a flexible film between the elastic
plastic foam sheet and the elastic layer, the surface of the
polishing sheet (elastic plastic foam sheet) is not generally
influenced by a shape of the material to be polished at a time of
contacting the material to be polished.
[0014] Further, in the first aspect, the surface layer may be
removed from the elastic plastic foam sheet. In such an embodiment,
since the polishing layer is exposed at the surface of the elastic
plastic foam sheet, the polishing liquid can be reserved on the
surface of the polishing layer by the foams formed at the polishing
layer. It is desirable that the surface of the polishing layer is
flat. At this time, it is preferable that a thickness of the
polishing layer is not less than 50 .mu.m. The elastic plastic foam
sheet may be integrally formed by the polishing layer and an
elastic layer which gives elasticity to the polishing layer.
Further, the polishing sheet may have a supporting layer which is
made of at least one selected from a flexible film, a nonwoven
fabric and a woven fabric and which is disposed at one side of the
elastic plastic foam sheet to support the elastic plastic foam
sheet. A groove for accommodating and discharging shavings occurred
from the material to be polished may be formed at the polishing
layer.
[0015] A second aspect of the present invention is directed to a
manufacturing method of an elastic plastic foam sheet for a
polishing sheet, comprising the steps of; coating approximately
uniformly a polyurethane resin emulsion, which includes a
polyurethane resin, a first organic solvent that the polyurethane
resin can be dissolved, and a second organic solvent whose
solubility to water is smaller than that of the first organic
solvent and which controls coagulation of the polyurethane resin,
to a base material; and soaking the base material coated by the
polyurethane resin emulsion into a coagulation liquid whose main
component is water, and wherein the elastic plastic foam sheet has
a polishing layer which is disposed inside a surface layer and
which is allowed to wear away by polishing and whose thickness is
larger than a thickness of the surface layer, and the polishing
layer has an approximately uniform foam structure in a direction of
the thickness of the elastic plastic foam sheet by being formed
foams whose space volume is larger than that of foams formed at the
surface layer and which are communicated so as to form a network by
continuous holes whose diameter is smaller than that of the space
volume of the foams formed at the polishing layer.
[0016] In the second aspect of the present invention, since the
second organic solvent is restricted to elute into the coagulation
liquid whose main component is water due to that the second organic
solvent included in the polyurethane resin emulsion is smaller in
solubility to water than the first organic solvent, a speed of
substitution between the second organic solvent and the coagulation
liquid is delayed so that coagulation of polyurethane resin
progresses approximately uniformly. Accordingly, the polishing
sheet, where the polishing layer is disposed inside a surface layer
and the polishing layer has an approximately uniform foam structure
in a direction of the thickness of the elastic plastic foam sheet
by being formed foams whose space volume is larger than that of
foams formed at the surface layer and which are communicated so as
to form a network by continuous holes whose diameter is smaller
than that of the space volume of the foams formed at the polishing
layer, can be obtained.
[0017] In the second aspect, it is preferable that the second
organic solvent is ethyl acetate, and the polyurethane resin
emulsion is prepared by adding the second organic solvent of a
range of from 20 parts to 45 parts to a polyurethane resin
solution, that the polyurethane resin is dissolved into the first
organic solvent, of 100 parts. The manufacturing method may further
comprise a step of removing the surface layer from the elastic
plastic foam sheet.
[0018] Further, a third aspect of the present invention is directed
to a manufacturing method of an elastic plastic foam sheet for a
polishing sheet, comprising the steps of; coating approximately
uniformly a polyurethane resin emulsion, which includes a
polyurethane resin and a third organic solvent that the
polyurethane resin can be dissolved, to a base material; and
soaking the base material coated by the polyurethane resin emulsion
into a coagulation liquid including a fourth organic solvent and
water, and wherein the elastic plastic foam sheet has a polishing
layer which is disposed inside a surface layer and which is allowed
to wear away by polishing and whose thickness is larger than a
thickness of the surface layer, and the polishing layer has an
approximately uniform foam structure in a direction of the
thickness of the elastic plastic foam sheet by being formed foams
whose space volume is larger than that of foams formed at the
surface layer and which are communicated so as to form a network by
continuous holes whose diameter is smaller than that of the space
volume of the foams formed at the polishing layer.
[0019] In the third aspect of the present invention, the
polyurethane resin emulsion, which includes the polyurethane resin
and the third organic solvent that the polyurethane resin can be
dissolved, is coated approximately uniformly to the base material,
and the base material coated by the polyurethane resin emulsion is
soaked into the coagulation liquid including the fourth organic
solvent and water. According to the third aspect, the same effects
as the above second aspect can be obtained. At this time, it is
preferable that a density of the fourth organic solvent in the
coagulation liquid is ranged of from 20 weight percent to 50 weight
percent. The manufacturing method may further comprise a step of
removing the surface layer from the elastic plastic foam sheet.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a sectional view illustratively showing a
polishing pad of an embodiment to which the present invention is
applicable;
[0021] FIG. 2 is a process diagram showing manufacturing process of
the polishing pad;
[0022] FIG. 3 is a front view showing a schematic constitution of a
film forming apparatus;
[0023] FIG. 4 is a sectional view illustratively showing polishing
pads of other embodiments to which the present invention is
applicable, FIG. 4A showing a polishing pad having an elastic layer
in which large cells whose size (length) is as large as a half of a
thickness of a polyurethane sheet are formed and which are
positioned at a side of a supporting member, and FIG. 4B showing a
polishing pad having a polyurethane sheet that large cells are
formed between the polyurethane sheet and a supporting member;
[0024] FIG. 5 is a sectional view illustratively showing foaming
structures of polishing pads, FIG. 5A showing the foaming structure
of the polishing pads used for Examples 1, 4, 5 and 6, FIG. 5B
showing the foaming structure of the polishing pad used for Example
3, FIG. 5C showing the foaming structure of the polishing pads used
for Examples 2 and 7, FIG. 5D showing the foaming structure of the
polishing pad used for Example 8, and FIG. 5E showing the foaming
structure of the polishing pad used for Comparative Example 1;
[0025] FIG. 6 shows an electron microscopic photograph of a
sectional view of the polishing pad used for Example 6;
[0026] FIG. 7 shows an electron microscopic photograph of a
sectional view of the polishing pad used for Example 7; and
[0027] FIG. 8 shows an electron microscopic photograph of a
sectional view of the polishing pad used for Example 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
(First Embodiment)
[0028] A first 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 drawings.
[0029] <Polishing Pad>
[0030] As shown in FIG. 1, a polishing pad 1 has a polyurethane
sheet 2 which is formed by a polyurethane resin and which serves as
an elastic plastic foam sheet. A surface layer (skin layer, See
numeral 9 in FIG. 6.), at which small foams are formed, is removed
from the polishing pad 1. Thus, in this embodiment, the
polyurethane sheet 2 constitutes a polishing layer, and the
polishing layer once positioned inside the surface layer is exposed
at a surface of the polyurethane sheet 2. In the polyurethane sheet
2, foams 3 which are approximately uniformly dispersed in the
polyurethane resin. A space volume of the foams 3 is larger than
that of the foams formed at the surface layer. These foams 3 are
communicated so as to form a network by unillustrated continuous
holes whose diameter is smaller than that of the space volume of
the foams 3. Further, the polyurethane sheet 2 (polishing layer)
has an approximately uniform foam structure in a direction of its
thickness. The foams 3 positioned at a vicinity of a polishing face
P are opened at the polishing face P so as to form open portions
4.
[0031] The polishing pad 1 has a supporting member 7 (supporting
layer), which functions as a base material at a time of
manufacturing the polyurethane sheet 2, at an opposite face side (a
lower face side) of the polishing face P of the polyurethane sheet
2. Such a base material, for example, is made of at least one
selected from a flexible film such as a film made of polyethylene
terephthalate (hereinafter abbreviated as "PET"), a nonwoven
fabric, and a woven fabric. A double adhesive tape 8 for attaching
the polishing pad 1 to a polishing machine, which has a peeling
paper (a release paper) on one face side (a lowermost face side)
thereof, is adhered to a lower face side of the supporting member
7.
[0032] <Manufacturing Process of Polishing Pad>
[0033] The polishing pad 1 according to this embodiment is
manufactured by carrying out each manufacturing process shown in
FIG. 2. First, a polyurethane resin, N, N-dimethyl-formaldehyde
(hereinafter abbreviated as "DMF") serving as a first organic
solvent, a control organic solvent serving as a second organic
solvent, and additives are blended in blending process. The
polyurethane resin is selected from a polyester resin, a polyether
resin, a polycarbonate resin or the like. A polyurethane resin
solution is obtained by dissolving the polyurethane resin into the
DMF such that it occupies 30% in the solution. A predetermined
amount of the control organic solvent is added in order to control
viscosity of the obtained polyurethane resin solution and to
control (delay) a speed of substitution between the DMF and water
in film forming process as explained below. A solvent that
solubility to water is smaller than that of the DMF and that can be
uniformly blended with or dispersed to the polyurethane resin
solution without re-solidifying (gelatinizing) the polyurethane
resin dissolved in the DMF is used for the control organic solvent.
As concrete examples for such a solvent, ethyl acetate, isopropyl
alcohol, and the like can be listed. It is preferable that an
adding amount or dosage of the control organic solvent is ranged of
from 20 to 45 parts to the polyurethane resin solution of 100 parts
and that additives such as pigment and the like are added to the
polyurethane resin solution to be stirred and mixed sufficiently.
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 foams 3. After
aggregated masses or the like are removed by filtration, a
polyurethane resin emulsion (hereinafter referred to "resin
emulsion") is obtained by carrying out defoaming under vacuum.
[0034] In film forming process, the resin emulsion prepared in the
blending process is continuously applied on the base material such
that its thickness becomes substantially uniform by using a knife
coater, and the polyurethane resin is re-solidified (reproduced and
coagulated) by soaking the applied base material into a coagulation
liquid to remove the DMF and the control organic solvent.
[0035] The film forming process is carried out, for example, by a
film forming apparatus as shown in FIG. 3. The film forming
apparatus is equipped in series with a pretreatment bath 10 which
is filled with a pretreatment liquid 15 such as water, DMF water
solution (a mixed liquid of the DMF and water) or the like and in
which the base material such as the woven fabric, the woven fabric
or the like is soaked, a coagulation bath 20 which re-solidifies
the polyurethane resin and which is filled with a coagulation
liquid 25 whose main component is water that is a poor solvent to
the polyurethane resin, and a washing bath 30 which is filled with
washing 35 such as water or the like for washing the coagulated
polyurethane resin, and a cylinder type drying machine 50 for
drying the polyurethane resin.
[0036] A base material supplying roller 41 for supplying a base
material 43 is disposed at an upstream side of the pretreatment
bath 10. The pretreatment bath 10 has a pair of guide rollers 13 at
a lower portion thereof and an approximately central portion in a
direction of conveying the base material 43. Over a liquid level of
the pretreatment liquid 15, guide rollers 11 and 12 are disposed at
a side of the base material supplying roller 41, and a pair of
pressure rollers 18 for dehydrating a superabundant pretreatment
liquid on the pretreated base material 43 is disposed at a side of
the coagulation bath 20. A knife coater 46 (a doctor knife) for
coating the resin emulsion 45 approximately uniformly onto one side
of the base material 43 is disposed at a downstream of the pair of
pressure rollers 18. The coagulation bath 20 has a guide roller 23
at a lower portion thereof and at a side of the washing bath 30.
Over a liquid level of the coagulation liquid 25, a guide roller 21
is disposed at a side of the pretreatment bath 10, and a pair of
pressure rollers 28 for dehydrating the coagulation liquid 25 on
the re-solidified polyurethane resin is disposed at a side of the
washing bath 30. The washing bath 30 has four guide rollers 33 at
an upper portion thereof and five guide rollers 33 at a lower
portion thereof in a direction of conveying the base material 43
such that the base material 43 is conveyed up and down by the guide
rollers 33 alternatively. Over a liquid level of the washing liquid
35, a guide roller 31 is disposed at a side of the coagulation bath
20, and a pair of pressure rollers 38 for dehydrating the washing
liquid 35 on the washed polyurethane resin is disposed at a side of
the cylinder type drying machine 50. In the cylinder type drying
machine 50, four cylinders each having a heat source are disposed
vertically such that the cylinders form four stages. A winding
roller 42 for winding the dried polyurethane resin is disposed at a
downstream side of the cylinder type drying machine 50.
Incidentally, the pressure rollers 18, 28, 38, the cylinder type
drying machine 50, and the winding roller 42 are driven by rotation
force transmitted from an unillustrated rotation driving motor so
that the base material 43 is conveyed from the base material
supplying roller 41 to the winding roller 42 with the rotation
force.
[0037] In a case that the base material 43 is the nonwoven fabric
or the woven fabric, the base material 43 is drawn out from the
base material supplying roller 41 and introduced (soaked)
continuously into the pretreatment liquid 15 via the guide rollers
11 and 12. By conducting the pretreatment to the base material 43
with the pretreatment liquid 15 in order to close opened portions
in the fabric, infiltration of the resin emulsion 45 into an
interior of the base material 43 is restricted at the time of
coating the resin emulsion 45. The base material 43, after pulling
up from the pretreatment liquid 45, is squeezed to remove and drop
the superabundant pretreatment liquid 15 by the pair of pressure
rollers 18. The pretreated base material 43 is conveyed to a side
of the coagulation bath 20 to apply the resin emulsion 45 which is
prepared in the blending process approximately uniformly by the
knife coater 46. Incidentally, since the pretreatment is not
essential in a case that the base material 43 is a film made of the
PET or the like, the base material 43 may be conveyed directly from
the guide roller 12 to the pair of pressure rollers 18, or, the
pretreatment liquid 15 may not be poured to the pretreatment bath
10.
[0038] The base material 43 which is coated by the resin emulsion
45 is introduced to the coagulation liquid 25 via the guide roller
21. In the coagulation liquid 25, the skin layer with a thickness
of several micron meters (.mu.m) is formed at a surface of the
coated resin emulsion 45. Thereafter, the polyurethane resin is
re-solidified by a progress of substitution between the DMF in the
resin emulsion 45 plus the control organic solvent and the
coagulation liquid 25. At a time of deliquoring the DMF and the
control organic solvent, the foams 3 are formed inside the
polyurethane resin such that a continuously foamed body is formed.
The re-solidified polyurethane resin is pulled up from the
coagulation liquid 25 and introduced to the washing liquid 35 via
the guide roller 31 after removing and dropping the superabundant
coagulation liquid 25 by the pair of pressure rollers 28.
[0039] The polyurethane resin is washed by passing through the
guide rollers 33 up and down alternatively in the washing liquid
35. The polyurethane resin is pulled up from the washing liquid 35
after washing, and it is squeezed to remove and drop the
superabundant washing liquid 35 by the pair of pressure rollers 38.
Then, the polyurethane resin is passed through alternatively along
each circumference of the four cylinders of the cylinder type
drying machine 50 (See arrows in FIG. 3.), so that the polyurethane
resin is dried. The dried polyurethane resin is wound by the
winding roller 42.
[0040] By the way, the foams 3 are dispersed approximately
uniformly in a direction along a thickness of the obtained
sheet-shaped polyurethane resin, and the foams 3 are communicated
so as to form the network by the continuous holes. By adding the
control organic solvent to the polyurethane resin solution in the
blending process, the progress of the substitution between the DMF
in the resin emulsion 45 plus the control organic solvent and the
coagulation liquid 25 is delayed at a time of soaking into the
coagulation liquid 25 in the film forming process. Accordingly, the
polishing layer, which is disposed inside the skin layer that is
formed at the surface of the polyurethane resin, has a thickness of
not less than 50 .mu.m and has an approximately uniform foam
structure in a direction of a thickness thereof.
[0041] As shown in FIG. 2, in buffing process, buffing (surface
sanding) treatment is conducted to a surface at a side of the
polishing face P of the obtained sheet-shaped polyurethane resin to
remove the skin layer formed at the surface of the polyurethane
resin. Thus, a part of the foams 3 is opened at the polishing face
P to form the open portions 4.
[0042] In laminating process, one face of the double adhesive tape
8 with a peeling paper attached to another face thereof is adhered
to a face opposite to the polishing face P of the base material 43
(supporting member 7), and in cutting process, dies cutting is
performed so as to obtain a desired shape such as, for example, a
circle or the like. In product inspection process, inspection is
made for confirming that there is neither stain nor adhesion of
scraps, such as buffs or the like, on the product (polishing pad
1), so that the manufacturing of the polishing pad 1 is
finished.
[0043] <Effects of Polishing Pad>
[0044] In the conventional wet film forming process, a resin
emulsion that the polyurethane resin is dissolved into the DMF and
additives are mixed thereto is coated to the base material, and the
coated base material is soaked into a coagulation liquid of which
main component is water. Since the DMF is a solvent used generally
for dissolving the polyurethane resin and it can be blended to
water at an optional rate, first, substitution (re-solidification
of the polyurethane resin) at a surface of the resin emulsion
between the DMF and the coagulation liquid occurs, so that a skin
layer is formed. Then, because the coagulation liquid enters into
an interior of the resin emulsion from portions where the
coagulation liquid is easy to enter at the skin layer, portions
where the substitution between the DMF and the coagulation liquid
progresses rapidly and portions where the substitution thereof
delays occur. As a result of this, relatively large cells are
formed at the re-solidified polyurethane resin. In a case that a
film made of the PET, etc. that prevents infiltration of water is
used for the base material, the large cells are shaped like a
trigonal pyramid having a largely rounded configuration at a side
of the base material because the DMF elutes only from the coating
side of the resin emulsion.
[0045] In such a polishing pad using the conventional polyurethane
resin, a polishing rate thereof or the like changes due to that a
diameter of the large cells that are opened at the polishing face
changes when the polyurethane resin is worn away according to
polishing. Therefore, in primary polishing, since such a polishing
pad can only utilize one fourth of a thickness thereof, a life of
the polishing pad becomes short. In secondary polishing, a
non-buffing type polishing pad without removing the skin layer is
mainly used, but a life of such a polishing pad becomes short in
the same manner.
[0046] Inventors realized that the large cells are formed at the
re-solidified polyurethane resin due to differences in the speed of
the substitution between the DMF and water, and based on this
realization, Inventors had an idea that it is possible to eliminate
or control the formation of the large cells by making the speed of
the substitution late to re-solidify the polyurethane resin slowly.
Besides, Inventors discovered that the speed of the substitution
can be dropped by adding to the polyurethane resin solution the
control organic solvent, (a) which can be uniformly dispersed to
the DMF without re-solidifying the polyurethane resin dissolved in
the DMF, and (b) of which solubility to water is smaller than that
of the DMF.
[0047] In the present embodiment, the resin emulsion 45 is obtained
by adding the control organic solvent to the polyurethane resin
solution. Since the solubility to water of the control organic
solvent is smaller than that of the DMF, the elution of the control
organic solvent into water (the coagulation liquid 25) delays
comparing with that of the DMF. Since the control organic solvent
is blended with the resin emulsion 45, an amount of the DMF in the
resin emulsion 45 becomes small. Accordingly, the speed of the
substitution between the DMF plus the control organic solvent and
the coagulation liquid 25 is delayed, so that the formation of the
large cells is eliminated. Thus, the polishing layer that a
thickness thereof is larger than that of the skin layer and that
the foams 3 are dispersed approximately uniformly is formed inside
the skin layer in the polyurethane resin. Because the speed of the
substitution between the DMF plus the control organic solvent and
the coagulation liquid 25 is low, a space volume of the foams 3
becomes larger than that of the foams formed at the skin layer
which is formed soon after soaking into the coagulation liquid 25.
Further, since the foams 3 are formed according to the deliquoring
of the DMF and the control organic solvent, the foams 3 are
communicated so as to form the network by the continuous holes of
which diameter is smaller than that of the space volume of the
foams 3. Therefore, the obtained polyurethane resin has the
approximately uniform foam structure in the direction of a
thickness thereof and has the approximately uniform foam structure
without the large cells within a range of not less than 50 .mu.m
from a surface thereof for polishing the material to be
polished.
[0048] In the polishing pad 1 having the obtained polyurethane
resin, the polishing liquid which is supplied at the time of
polishing is reserved by the foams 3 formed at the polishing layer.
The polishing liquid is allowed to move via the continuous holes
communicated between the foams 3 and it is supplied to a face of
the material to be polished via the open portions 4. Accordingly,
since the polishing liquid is supplied between the face of the
material to be polished and the surface of the polishing pad 1, the
face of the material to be polished is polished approximately
evenly so that waviness of the face of the material to be polished
is improved. Further, since the polishing pad 1 has the
approximately uniformly formed polishing layer with the thickness
of not less than 50 .mu.m, even if the polishing layer is worn away
at the time of polishing, the structure of the surface does not
change within a range of the thickness of the polishing layer.
Therefore, the polishing pad 1 can polish the material to be
polished stably according to the thickness of the polishing layer,
so that a life of the polishing pad 1 is enhanced.
(Second Embodiment)
[0049] Next, a second 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.
In a manufacturing method of the polishing pad according to this
embodiment, re-solidification of the polyurethane resin is delayed
by a high density DMF in a coagulation liquid, in stead of adding
the control organic solvent to the polyurethane resin solution
explained in the first embodiment. Incidentally, in this
embodiment, the same apparatus and members as those in the first
embodiment are denoted by the same reference numerals and an
explanation thereof is omitted, and only different portions will be
explained. Further, in this embodiment, examples where the DMF
densities in the coagulation liquid are 20 weight % and 40 weigh %
are shown just for simplification in explanation, however, the DMF
density is allowed to take in a range of from 20 weight % to 50
weight % as will be explained later.
[0050] The resin emulsion 45 is prepared by adding additives after
dissolving the polyurethane resin into the DMF. The resin emulsion
45 is diluted by the DMF in order to control viscosity thereof in
the film forming process. In order to delay the re-solidification
of the polyurethane resin, the coagulation liquid 25 is prepared by
blending water and the DMF such that the density of the DMF becomes
20 weight % or 40 weight %.
[0051] In the second embodiment, since elution of the DMF to the
resin emulsion 45 is restrained by setting the density of the DMF
in the coagulation liquid high, the speed of the substitution
between the DMF in the resin emulsion 45 and the coagulation liquid
25 is delayed. Accordingly, since the re-solidification of the
polyurethane resin becomes slow, the obtained polyurethane resin
has the polishing layer which is disposed inside the skin layer and
which is not formed the large cells, and the polishing layer has
the approximately uniform foam structure in which the foams 3 are
dispersed approximately uniformly in the direction of its
thickness.
[0052] Incidentally, in the above embodiments, the polyurethane
resin sheet was exemplified as the elastic plastic foam sheet,
however, this invention is not limited to this exemplification. For
example, a resin, which forms a continuous foam body, such as a
polyester resin and the like may be used. In a case that the
polyester resin is used, continuous foams may be easily formed
according to the wet film forming process. Further, in the above
embodiments, the wet film forming process was exemplified in the
process for manufacturing the polyurethane sheet, however, the dry
film forming process may be used. At this time, for example,
hydrophilic activator or the like for promoting foaming may be
added to form the continuous foam body.
[0053] Further, in the above embodiments, the polishing pad 1 that
the polyurethane resin is re-solidified onto the base material 43
which is the supporting member 7 was shown, however, this invention
is not confined to the same. For example, as shown in FIG. 4A, the
sheet shaped polyurethane resin may have large cells 5 which are
approximately as long as a half of the thickness of the
polyurethane resin and which are positioned below the foams 3. At
this time, a polishing pad may be obtained by pasting the
supporting member 7 and the double adhesive tape 8 to a side of the
large cells 5 in the sheet shaped polyurethane resin. In such a
polishing pad, since a layer that the large cells 5 are formed in
the polyurethane resin functions as an elastic layer which gives
elasticity to the polishing pad, the polishing sheet can contact
the material to be polished approximately equally at the time of
polishing. Accordingly, this polyurethane sheet is integrally form
by the polishing layer and the elastic layer. Furthermore, as shown
in FIG. 4B, the polishing pad may have a multi-layer (three-layer)
structure where a conventional sheet shaped polyurethane resin 6
that the large cells 5 are formed is pasted to the polyurethane
sheet 2 that the foams 3 are formed, and the supporting member 7
and the double adhesive tape 8 are pasted to an opposite side of
the polyurethane sheet 2 of the polyurethane resin 6. Since the
polyurethane sheet 2 functions like the skin layer, a polishing pad
equivalent to the conventional polishing pad of which the skin
layer is made thicker may be obtained. In that case, the polishing
pad may further have a flexible film 14 made of polyolefin, etc.
between the polyurethane sheet 2 and the polyurethane resin 6. A
face of the polishing sheet is hardly influenced by a shape of the
material to be polished at a time of contacting the polishing sheet
with the material to be polished.
[0054] Furthermore, in the above embodiments, the sheet shaped
polyurethane resin where the buffing treatment was conducted to the
surface at the side of polishing face P was shown, however, this
invention is not limited to the same. For example, the skin layer
may be removed by a cutter or by means of laser beams. It is
without saying that the polishing pad can be used without
conducting the buffing treatment. In such a polishing pad, since
the surface of the skin layer is flat, if only the surface of the
skin layer is removed by dressing (slight surface sanding), the
skin layer can reserve the polishing liquid. Such a polishing pad
can polish the material to be polished with the skin layer whose
surface is flat, and even if the skin layer is worn away, the
polishing pad can continue to polish the material to be polished
with the polishing layer.
[0055] Further, as shown in FIG. 4A, the polishing pad may have a
groove 16 for accommodating and discharging shavings occurred from
the material to be polished formed at the polishing layer (and the
skin layer) of the polyurethane sheet 2. In such a polishing pad,
since the shavings are removed from the polishing face P via the
groove 16, occurrence of defects at the face of the material to be
polished can be prevented. The groove 16 also contributes to a
supply of the polishing liquid. Such a groove may be formed by a
mechanical or chemical method such as machine work, laser beam
work, or etching work. The width, the depth, or the number of the
grooves is not limited, but it is preferable that the groove(s) can
remove the shavings without obstructing polishing characteristics
such as flatness, a polishing rate, and the like. The grooves may
be formed like a lattice, concentric circulars, radial straight
lines, or a combination of these. It is desirable that the
groove(s) is/are continuous from an inner side to an outer side of
the polishing pad.
[0056] Further, in the above embodiments, the film made of the PET
for the base material 43 was shown, however, this invention is not
limited to the same. For example, a flexible film made of
polyolefin and the like, a nonwoven fabric or a woven fabric made
of synthetic fiber and the like, may be used. In a case that such a
film is used for the base material 43, after coating the resin
emulsion 45 and re-solidifying the polyurethane resin, a film of
the polyurethane sheet 2 may only be obtained by peeling off from
the base material 43. The obtained film of the polyurethane sheet 2
may be used for the polishing pad as a single substance. In such a
case, the supporting member 7 such as, for example, a high hardness
resin film made of the PET and the like, a nonwoven or woven fabric
made of synthetic fiber, or the conventional polyurethane foam
sheet may be pasted to the film of the polyurethane sheet 2.
[0057] Furthermore, in the above embodiments, the coating of the
resin emulsion 45 by the knife coater 46 was exemplified, however,
for example, a reverse coater or a roll coater may be used. Any
coater may be used as long as it can allow uniform coating to the
base material. Besides, in the above embodiments, the cylinder type
drying machine 50 for drying the polyurethane resin was shown,
however, this invention is not limited to this. For example, a hot
air drying machine may be used instead.
[0058] Further, in the first embodiment, the example where, after
the polyurethane resin is dissolved into the DMF, the control
organic solvent is added thereto, was explained, however, this
invention is not limited to this. For example, the polyurethane
resin may be dissolved to a mixed solvent which is mixed by the DMF
and the control organic solvent.
[0059] Furthermore, in the second embodiment, the example where the
DMF density of the coagulation liquid 25 was set to 20 weight % or
40 weight % was explained, however, this invention is not limited
to the same. Inventors have confirmed that the formation of the
large cells is eliminated as long as the DMF density of the
coagulation liquid 25 ranges from 20 to 50 weight %.
[0060] Next, examples of the polishing pad 1 manufactured according
to the above embodiments will be explained. Incidentally, a
comparative example of the polishing pad manufactured for
comparison will also be described.
(EXAMPLE 1)
[0061] As shown in the following Table 1, in Example 1, polyester
MDI (diphenylmethane diisocyanate) polyurethane resin was uses as
the polyurethane resin according to the first embodiment. The resin
emulsion 45 was prepared by adding and blending ethyl acetate of 45
parts as the control organic solvent, a DMF dispersing liquid of 40
weight parts including carbon black of 30% as the pigment, and a
hydrophobic activator of 2 weight parts as the film-forming
stabilizer, to 30% polyurethane resin solution of 100 weight parts.
The coagulation liquid 25 was heated to 40 degrees Celsius. The
polishing pad 1 was manufactured by, after coating the resin
emulsion 45 onto the flexible film to form the film the
polyurethane sheet 2, pasting the film made of the PET as the
supporting member 7 to the polyurethane sheet 2 which was peeled
off from the flexible film. Incidentally, in Table 1, X expresses
the number of adding parts of the ethyl acetate to the polyurethane
resin solution of 100 parts. When X is short of 45, the DMF of
(45-X) parts was added.
1 TABLE 1 NUMBER OF ADDING PARTS OF ETHYL ACETATE (X) COMPARATIVE 0
EXAMPLE 1 EXAMPLE 2 10 EXAMPLE 3 20 EXAMPLE 4 30 EXAMPLE 5 40
EXAMPLE 1 45
(EXAMPLES 2 TO 5)
[0062] As shown in Table 1, in Examples 2 to 5, the same conditions
as those in Example 1 were employed except for a difference in the
number of adding parts of the ethyl acetate. The number of adding
parts of the ethyl acetate was respectively set to 10 (parts) in
Example 2; 20 (parts) in Example 3; 30 (parts) in Example 4; and 40
(parts) in Example 5.
(COMPARATIVE EXAMPLE 1)
[0063] As shown in Table 1, in Comparative Example 1, the same
conditions as those in Example 1 were employed other than adding
the DMF of 45 parts, instead of adding the ethyl acetate.
Therefore, the polyurethane sheet according to Comparative Example
1 was manufactured by the conventional manufacturing method which
does not add the control organic solvent.
(EXAMPLE 6)
[0064] As shown in the following Table 2, in Example 6, water and
the DMF were blended for the coagulation liquid 25 such that the
DMF density is set to 40 weight % according to the second
embodiment, and a temperature of the coagulation liquid 25 was set
to 20 degrees Celsius.
2 TABLE 2 DMF DENSITY OF TEMPERATURE OF COAGULATION COAGULATION
LIQUID (%) LIQUID (.degree. C.) EXAMPLE 6 40 20 EXAMPLE 7 20 50
EXAMPLE 8 1 70
(EXAMPLES 7 and 8)
[0065] As shown in Table 2, in Examples 7 and 8, the same
conditions as those in Example 6 were employed except for the DMF
density and the temperature of the coagulation liquid 25. In
Example 7, the DMF density was set to 20 weight % and the
temperature was set to 50 degrees Celsius; and in Example 8, the
DMF density was set to 1 weight % and the temperature was set to 70
degrees Celsius.
[0066] (Evaluation of Foam Structure)
[0067] Each foaming structure in the manufactured polishing pads
according to Examples and Comparative Example was evaluated by
observing the sections of the polyurethane sheets 2 with an
electron microscope. Regarding Example 1 to Examples 5 and
Comparative Example 1, evaluation results about
existence/nonexistence of the large cells and film forming
characteristic are shown in the following Table 3, and regarding
Example 6 to Example 8, evaluation results about
existence/nonexistence of the large cells are shown in the
following Table 4.
3 TABLE 3 FILM FORMING LARGE CHARACTERISTIC CELLS COMPARATIVE GOOD
EXISTED EXAMPLE 1 EXAMPLE 2 GOOD EXISTED EXAMPLE 3 GOOD EXISTED (A
FEW) EXAMPLE 4 GOOD NON EXAMPLE 5 GOOD NON EXAMPLE 1 GOOD NON
[0068] As shown in Table 3, in each Example and Comparative Example
1, the film forming characteristic of each polyurethane sheet 2 was
good, i.e., there was no trouble in forming the film of the
polyurethane sheet 2. Large cells were observed from the
polyurethane sheet 2 of Comparative Example 1 which was
manufactured by the conventional manufacturing method. In contrast,
no large cells were observed from each polyurethane sheet 2 of
Examples 1, 4 and 5 that the ethyl acetate as the control organic
solvent was added to the resin emulsion 45. In the polyurethane
sheet 2 of Example 3, a few of large cells were formed. In the
polyurethane sheet 2 of Example 2, large cells were observed at a
side of the coagulation liquid 25 of the coagulation time (an
opposite side of the base material). FIG. 5 is illustrative
comparison of the observed results. As shown in FIG. 5E, in
Comparative Example 1, large cells shaped like a trigonal pyramid
having a largely rounded configuration at a side of the base
material (a lower side) were formed. In contrast, in Examples 1, 4
and 5, no large cells were formed, but the foams 3 were formed
approximately uniformly in a direction of the thickness of the
polyurethane sheet 2 as shown in FIG. 5A. In Example 3, a few of
large cells 5 were observed at an opposite side of the base
material (an upper side) as shown in FIG. 5B. In Example 2, large
cells 5 of which size (length) is as large as a half of the
thickness of the polyurethane sheet were formed at an opposite side
of the supporting member, and the foams 3 were formed approximately
uniformly at a side of the supporting member as shown in FIG. 5C.
Accordingly, it was confirmed that the large cells are restrained
by setting the adding amount of the ethyl acetate to the
polyurethane resin solution of 100 parts, to a range of from 20
parts to 45 parts.
4 TABLE 4 LARGE CELLS EXAMPLE 6 NON EXAMPLE 7 LARGE CELLS EXISTED
AT UPPER HALF AND CONTINUOUSLY FOAMED BODY EXISTED AT LOWER HALF.
EXAMPLE 8 EXISTED
[0069] As shown in Table 4, in Example 6, no large cells 5 were
observed. (See FIG. 5A.) In Example 7, large cells 5 of which size
is as large as a half of the thickness of the polyurethane sheet
were formed at an opposite side of the supporting member, and the
foams 3 were formed approximately uniformly at a side of the
supporting member. (See FIG. 5C.) In Example 8, as shown in FIG.
5D, large cells 5 of which size is as large as two thirds of the
thickness of the polyurethane sheet were formed at an opposite side
of the supporting member. Accordingly, in a case that the DMF
density of the coagulation liquid 25 is 40 weight %, no large cells
5 are formed even under a normal temperature (20 degrees Celsius),
and a continuously foamed structure that the foams 3 are formed
approximately uniformly is formed. In a case that the DMF density
of the coagulation liquid 25 is set to 20 weight % and the
temperature of the coagulation liquid 25 is set to 50 degrees
Celsius, the large cells 5 of which size (length) is as large as
the thickness are formed (See FIG. 5C.). However, the polishing pad
1 where the polyurethane resin having the large cells 5 is served
as the elastic layer can be obtained by conducting the buffing
treatment to cut off the upper half portion in order to use the
lower half portion as the polishing layer (See FIG. 4B.), or by
utilizing the polyurethane sheet 2 per se such that the lower half
portion functions as the polishing layer (See FIG. 4A.).
[0070] FIGS. 6, 7, and 8 are electron microscopic photographs at a
time of observing each sectional view of the polyurethane sheets 2
used for Example 6 to Example 8. As obvious from FIG. 6, since the
polyurethane sheet 2 of Example 6 has the polishing layer at which
the foam structure is formed approximately uniformly in a direction
of the thickness (a longitudinal direction of FIG. 6), the
polyurethane sheet 2 can be used for polishing until the whole
portion of the polishing layer is worn away. As shown in FIG. 7, in
the polyurethane sheet 2 of Example 7, the large cells 5 of which
size (length) is as large as a half of the thickness of the
polyurethane sheet 2 are formed. As shown in FIG. 8, in the
polyurethane sheet 2 of Example 8, the large cells 5 of which size
(length) is as large as two thirds of the thickness of the
polyurethane sheet 2 are formed. Incidentally, in FIG. 6 to FIG. 8,
the polyurethane sheets 2 before conducting the buffing treatment
are used as samples for observation, so that skin layers 9 are
observed.
[0071] (Polishing Performance)
[0072] Next, by using the polishing pads of Example 1 and
Comparative Example. 1, polishing work for polishing the aluminum
base plate was conducted under the following polishing conditions,
and polishing performance according to a polishing rate and
waviness was evaluated. Further, regarding polished aluminum base
plates, appearance evaluation about presence/absence of defect
occurrence to surfaces of the aluminum base plates was made.
[0073] <Polishing Conditions>
[0074] Used Polishing Machine: 9B-5P POLISHING MACHINE manufactured
by SPEEDFAM CO., LTD.
[0075] Polishing Speed (Rotating Speed): 30 rpm
[0076] Working Pressure: 90 g/cm.sup.2
[0077] Slurry: alumina slurry (average particle diameter: 0.8
.mu.m)
[0078] Slurry Supplying Amount: 100 cc/min
[0079] Material to be Polished: aluminum base plate for 95 mm.phi.
hard disc (NiP plated magnetic disc substrate)
[0080] Polishing Time: 200 sec.; 240 sec.; 300 sec.
[0081] <Polishing Rate>
[0082] 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.
[0083] <Waviness>
[0084] 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.
[0085] Regarding the polishing performance about the polishing pads
of Example 1 and Comparative Example 1, evaluation results of the
polishing rate is shown in the following Table 5, and evaluation
results of the waviness is shown in the following Table 6,
respectively. In the polishing work according to the polishing pads
of Example 1 and Comparative Example 1, no defects at each of
surfaces of the aluminum base plates were observed.
5 TABLE 5 POLISHING RATE (.mu.m/min.) POLISHING TIME (SEC.) 200 240
300 AVERAGE COMPARATIVE 0.30 0.32 0.32 0.32 EXAMPLE 1 EXAMPLE 1
0.22 0.23 0.19 0.21
[0086] As shown in Table 5, in the polishing pad of Comparative
Example 1 which was manufactured by the conventional manufacturing
method, an average of the polishing rate was 0.32 .mu.m/min. In
contrast, in the polishing pad of Example 1 which was manufactured
by adding the ethyl acetate to the polyurethane resin solution, an
average of the polishing rate became 0.21 .mu.m/min, which went
down to about two thirds of Comparative Example 1. Comparing with
the polishing pad of Comparative Example 1 at which the large cells
5 that reserve the slurry (polishing liquid) are formed, the
polishing pad 1 of Example 1 at which the foams 3 whose size (space
volume) is smaller than that of the large cells 5 are approximately
uniformly formed without such large cells. Accordingly, it is
considered that the polishing rate of Example 1 was lowered since
the foams 3 which reserve the polishing liquid are small and an
actual amount of the polishing liquid which is supplied to the
polishing face becomes small.
6 TABLE 6 COMPARATIVE EXAM- EXAMPLE 1 PLE 1 WAVINESS POLISHING
BEFORE 15.2 16.1 (.ANG.) TIME POLISHING 200 SEC. AFTER 13.8 7.0
POLISHING DIFFERENCE 1.4 9.1 POLISHING BEFORE 14.5 16.5 TIME
POLISHING 240 SEC. AFTER 12.6 6.3 POLISHING DIFFERENCE 1.9 10.2
POLISHING BEFORE 15.7 17.6 TIME POLISHING 300 SEC. AFTER 10.6 5.6
POLISHING DIFFERENCE 5.1 12.0
[0087] As shown in Table 6, in the polishing pad of Comparative
Example 1, improvement in waviness at the polished surface of the
aluminum base plate was small. Even in the polishing time of 300
seconds, the difference of the waviness between before and after
polishing was 5.1 Angstrom and it was small. In contrast, in the
polishing pad 1 of Example 1, waviness at the polished surface of
the aluminum base plate was improved largely and the aluminum base
plate having excellent flatness on its surface could be obtained.
Even in the short polishing time of 200 seconds, the difference of
the waviness was 9.1 Angstrom and it was largely improved. It is
considered that the waviness of the polishing pad 1 of Example 1 is
improved since uniformity of the surface of the polishing pad 1 is
excellent in that only the open portions 4 according to the foams 3
are formed on the surface comparing with the surface of the
polishing pad of Example 1 at which a honeycomb shaped cell
structure according to openings of the large cells 5 is formed.
* * * * *