U.S. patent application number 12/744551 was filed with the patent office on 2010-11-25 for method of producing polishing sheet.
This patent application is currently assigned to NIHON MICRO COATING CO., LTD.. Invention is credited to Kazunori Tani, Nobuyoshi Watanabe.
Application Number | 20100293865 12/744551 |
Document ID | / |
Family ID | 40678428 |
Filed Date | 2010-11-25 |
United States Patent
Application |
20100293865 |
Kind Code |
A1 |
Watanabe; Nobuyoshi ; et
al. |
November 25, 2010 |
METHOD OF PRODUCING POLISHING SHEET
Abstract
A polishing sheet, having polishing particles fixed to a base
sheet in a single-layer formation by an adhesive agent so as to be
mutually separated in the direction of their plane and having
cutting edges exposed and arranged to be coplanar, is produced by
forming on a provisional base sheet a film of a provisional
adhesive agent of a thickness smaller than the average diameter of
the polishing particles, dispersing the polishing particles onto
the film of the provisional adhesive agent so as to contact the
provisional base sheet, pressing the base sheet covered with the
adhesive agent onto the polishing particles with the adhesive agent
facing towards the polishing particles, hardening the pressed
adhesive agent, and removing the provisional base sheet and the
film of the provisional adhesive agent. The polishing particles are
charged in a same polarity when dispersed.
Inventors: |
Watanabe; Nobuyoshi; (Tokyo,
JP) ; Tani; Kazunori; (Tokyo, JP) |
Correspondence
Address: |
Weaver Austin Villeneuve & Sampson LLP
P.O. BOX 70250
OAKLAND
CA
94612-0250
US
|
Assignee: |
NIHON MICRO COATING CO.,
LTD.
Tokyo
JP
|
Family ID: |
40678428 |
Appl. No.: |
12/744551 |
Filed: |
November 20, 2008 |
PCT Filed: |
November 20, 2008 |
PCT NO: |
PCT/JP2008/071082 |
371 Date: |
July 16, 2010 |
Current U.S.
Class: |
51/297 |
Current CPC
Class: |
B24D 11/001 20130101;
B24D 18/0054 20130101 |
Class at
Publication: |
51/297 |
International
Class: |
B24D 11/00 20060101
B24D011/00; B24D 3/00 20060101 B24D003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2007 |
JP |
2007-307730 |
Claims
1. A polishing sheet comprising a base sheet and polishing
particles fixed to the base sheet in a single-layer formation by an
adhesive agent, edge parts of said polishing particles being
arranged to be coplanar and being distributed separatedly.
2. A method of producing a polishing sheet characterized as having
polishing particles fixed to a base sheet in a single-layer
formation by an adhesive agent, edge parts of said polishing
particles being arranged to be coplanar and being distributed
separatedly, said method comprising: a first step of forming on a
provisional base sheet a film of a provisional adhesive agent with
thickness less than the average particle diameter of the polishing
particles; a second step of distributing the polishing particles on
the film of provisional adhesive agent so as to contact the
provisional base sheet; a third step of pressing a base sheet
covered with an adhesive agent such that said adhesive agent faces
the polishing particles; a fourth step of hardening the adhesive
agent that has been compressed; and a fifth step of peeling off
said provisional base sheet after said adhesive agent has been
hardened and further removing said film of provisional adhesive
agent.
3. The method of producing a polishing sheet described in claim 2
characterized wherein the thickness of said provisional adhesive
agent is 1/10 or more and 2/3 of less of the average diameter of
said polishing particles.
4. The method of producing a polishing sheet described in claim 2
or 3 characterized wherein the polishing particles are charged in a
same polarity.
5. The method of producing a polishing sheet described in claim 4
characterized wherein the polishing particles charged in said same
polarity are dispersed onto aid film of said provisional adhesive
agent on said provisional base sheet while maintaining said
provisional base sheet at a ground potential such that said
polishing particles are mutually separated and come into contact
with said provisional base sheet.
6. The method of producing a polishing sheet described in claim 5
characterized wherein the polishing particles are charged in the
same polarity at a charging potential of 1-50 kV.
7. The method of producing a polishing sheet described in any of
claims 2-6 characterized wherein the film of said provisional
adhesive agent formed on the provisional base sheet comprises a
water-soluble or organic acid water-soluble film.
8. The method of producing a polishing sheet described in any of
claim 7 characterized wherein the water-soluble or organic acid
water-soluble film comprises polysaccharides, pastes, starches,
chitin or chitosan.
9. The method of producing a polishing sheet described in any of
claim 8 characterized wherein the water-soluble film comprises
glycogen, cellulose, dextran, dextrine, polyvinyl alcohol, or
starches generated from plants.
10. The method of producing a polishing sheet described in any of
claims 4-6 further comprising the step of maintaining an inner wall
of a dispersion device for dispersing said polishing particles
charged in said same polarity onto said film of said provisional
adhesive agent on said provisional base sheet in the same polarity
as the polarity of said polishing particles.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] This invention relates to a polishing sheet for smoothly
polishing a magnetic disk substrate, a silicon wafer, a glass
substrate for a display device, the end surface of optical fibers
and the surface of a variety of objects to be polished such as a
lens, and more particularly a polishing sheet for polishing a
target object to be polished extremely precisely, as well as a
method of its production.
TECHNICAL BACKGROUND
[0002] While polishing particles as small as possible are used for
polishing the surface of a target object smoothly and flatly,
methods of polishing may be roughly classified into the free
particle method which is carried out by supplying polishing
particles to the target object from outside and the fixed particle
method carried out by using a polishing sheet having polishing
particles fixed to a substrate. The fixed particle method is widely
used because it does not require a large amount of polishing
material, unlike the free particle method, and also because
polishing sheets of various shapes for having polishing materials
affixed to can be realized.
[0003] The substrate for a polishing sheet for use in the fixed
particle method is made of a material such as organic resins such
as polyethylene terephthalate, woven and unwoven cloths, and fine
particles of an inorganic polishing material such as alumina,
silica and diamond are fixed on this substrate by means of a binder
such as a resin.
[0004] The polishing performance of a polishing sheet varies
significantly, depending on the polishing particles themselves,
their mixing ratio with the resin, the thickness of fixing, etc.
and particularly on the characteristics of the polishing particles.
Important factors of the characteristics of polishing particles
include their material, size and shape but the manner in which the
individual particles are arranged in the layer where the polishing
particles are affixed becomes another important factor for having
their characteristics fully utilized even after the particles
themselves are optimally selected.
[0005] Especially for the purpose of polishing a target object at
an extremely high level of precision, arrangements of particles
wherein the individual particles are fixed to the substrate in an
aggregated form are not desirable. There are many situations in
which the particles are not uniformly arranged if they are viewed
microscopically. It is likely that aggregations of particles are
formed, and the arrangement includes clumps that are scattered
around.
[0006] When the polishing particles are thus arranged, the surface
roughness of the polishing sheet becomes uneven, and only polishing
operations of the kind resulting in scratches on the surface of the
target object are possible.
[0007] In view of the above, polishing sheets having the particle
diameters of the polishing particles made as uniform as possible
for eliminating the generation of such flaws and also having
polishing particles fixed in a single layer have been proposed
(Patent References 1 and 2). There have been known, for example,
polishing sheets with a single-particle layer such as shown in FIG.
2 of Patent Reference 1 and polishing sheets with a single diamond
layer such as shown in FIG. 1 of Patent Reference 2.
[0008] It is disclosed in Patent Reference 1 that a single-particle
layer can be obtained easily merely by mixing a binder with
polishing particles and applying the mixture to a substrate,
without explaining any application method requiring any particular
inventive details. Patent Reference 2, on the other hand, describes
a special method for obtaining a single-particle layer, disclosing
a method of fixing polishing particles by electrodeposition inside
an electrolyte solution having the polishing particles dispersed
therein or by roll-coating a mixture of an organic binder and
polishing particles.
[0009] Although polishing tapes having polishing particles in a
single-particle layer formation have been disclosed, as explained
above, the individual polishing particles in these prior art
examples are found to be covered with the binder on the side of the
surface contacting the object to be polished, if seen
microscopically. By the method disclosed in Patent Reference 1, for
example, it can be seen from its FIG. 2 that the surfaces of the
polishing particles on the side contacting the object to be
polished are covered with the binder indicated by dotted lines
since a mixture of the binder and the polishing particles is simply
applied. If polishing particles are thus covered with a binder that
does not contribute to the polishing, their polishing performance
is significantly affected negatively.
[0010] As for Patent Reference 2, although polishing particles are
described as if not covered by the binder, the inventors herein
discovered by an investigation that the binders remain on the
surfaces of the polishing particles if the mixture of the binder
and the polishing particles is simply applied.
[0011] Even if a classification process is carried out for making
the sizes of the polishing particles uniform, there is a limit to
the degree of classification and the polishing particles have a
specified size distribution. If polishing particles having a finite
size distribution are simply applied, the protruding edge parts of
the polishing particles on the side contacting the object to be
polished (or the contacting parts with the object to be polished)
have different heights and not on a perfectly straight line, if
observed microscopically. It is not desirable at the time of
polishing to have coexisting together both polishing particles that
contact the target object and contribute to the polishing and
polishing particles that do not make any contact with the object
and do not contribute to the polishing. The edge parts of polishing
particles that will contact the object to be polished will be
hereinafter referred to as the cutting edges, and if cutting edges
are on a straight line, it will be said that the cutting edges are
uniform, or even.
[0012] In view of the above, a method of removing the binder
attached to the surfaces of the polishing particles after a
single-particle layer has been formed has been devised in order to
realize a condition of polishing particles fixed in a
single-particle layer with the cutting edges of the individual
polishing particles not covered with any binder or electrodeposited
material that would adversely affect the polishing performance
(Patent Reference 3). According to this method, after a mixture of
the binder and the polishing particles is applied, this mixture is
exposed to ultraviolet light for removing the binder on the
particle surfaces such that the surfaces of the single-layer
polishing particles become exposed and the adverse effect on the
polishing performance will be prevented.
[0013] This method, however, takes a long time for removing the
binder from the particle surfaces and hence is not suitable for
mass production. Since the ultraviolet light will affect not only
the particle surfaces but also the side surfaces of the polishing
particles, furthermore, the portions of the binder serving to
firmly hold the polishing particles are also lost, making it easier
for the polishing particles to drop off.
[0014] There are other methods of forming a single layer with the
surfaces of polishing particles exposed, besides those described
above (Patent Reference 4). According to a method disclosed in
Patent Reference 4, polishing particles are firstly mixed with a
first binder with low viscosity into the form of slurry and this
slurry is applied to a substrate such that the polishing particles
will form a single layer. This is then dried such that the binder
will shrink and the surface of each polishing particle will project
out from the binder part. Next, these projecting parts are pushed
into a second binder with high viscosity such that these projecting
parts become covered. As the second binder is dried, each of the
polishing particles comes to be held more strongly by the second
binder with stronger viscosity than by the first binder with weaker
viscosity. As the first binder is peeled off, the polishing
particles are still held by the second binder, forming a single
layer with their surfaces exposed.
[0015] By this method, however, the first binder is not necessarily
peeled off easily from the polishing particles. It is likely that
there results a polishing sheet with the first binder still
remaining thereon to cover the particle surfaces.
[0016] The polishing means according to Patent Reference 5, on the
other hand, has a plurality of polishing composites exposed on the
surface of a polishing sheet, distributed at uniform intervals but
is less than acceptable because the device itself becomes
complicated and there is no guarantee that the front edges of the
polishing composites would become arranged evenly.
[0017] Patent Reference 1: Japanese Patent Publication Tokkai
1-234169
[0018] Patent Reference 2: Japanese Patent Publication Tokkai
4-129660
[0019] Patent Reference 3: Japanese Patent Publication Tokkai
2-243271
[0020] Patent Reference 4: Japanese Patent Koho 3314154
[0021] Patent Reference 5: Japanese Patent Publication
Tokkai5-253852
DETAILED DESCRIPTION OF THE INVENTION
Problem to be Solved by the Invention
[0022] For forming polishing particles in a single layer and to
further obtain a polishing sheet with the surfaces of cutting edges
not covered with the binder and completely exposed, as explained
above, conventional methods can provide a single-particle layer but
allow polishing debris to remain on the surfaces of the cutting
edges. Conventional methods for removing remaining polishing debris
are less than perfect in the debris-removing performance and are
not suited for mass production.
[0023] If the cutting edges are not evenly arranged, the natural
polishing capability of polishing particles cannot be fully
realized. On polishing sheets produced by a conventional method,
furthermore, neighboring polishing particles are frequently in
mutual contact as seen in the direction of their plane. As a
mechanism for generating polishing flaws which are problematical in
a polishing operation, it is known that remaining polishing debris
can be one of the causes. In order to eliminate polishing flaws due
to such a mechanism, it is necessary to efficiently discharge such
polishing debris. Since a polishing operation is usually carried
out by applying a load on the target object to be polished or on
the polishing sheet, the target object and the polishing sheet are
in a tight contact with each other, making it difficult for the
polishing debris to be discharged. In the case of conventional
examples with neighboring polishing particles mutually contacting
as seen in the direction of their plane, the discharge of polishing
debris becomes even more difficult.
[0024] It is therefore an object of this invention to provide a
polishing sheet (1) having exposed cutting edges of polishing
particles, (2) having even cutting edges and (3) capable of
efficiently discharging debris of polishing.
Means for Solving the Problem
[0025] In view of the object described above, the present invention
provides a polishing sheet comprising polishing particles fixed to
a base sheet in a single-layer formation by an adhesive agent,
parts of the polishing particles contacting a target object to be
polished and being exposed from the adhesive material and edge
parts of the polishing particles being mutually separated and
arranged to be coplanar.
[0026] The invention further provides a method of producing a
polishing sheet comprising polishing particles fixed to a base
sheet in a single-layer formation by an adhesive agent, parts of
the polishing particles contacting an object to be polished and
being exposed from the adhesive material and edge parts of the
polishing particles being arranged to be coplanar, the method
comprising a first step of forming on a provisional base sheet a
film of a provisional adhesive agent of a thickness smaller than
the average diameter of the polishing particles, a second step of
dispersing the polishing particles onto the film of the provisional
adhesive agent so as to contact the provisional base sheet, a third
step of pressing the base sheet covered with the adhesive agent
onto the polishing particles with the adhesive agent facing towards
the polishing particles, a fourth step of hardening the pressed
adhesive agent, and a fifth step of peeling off the provisional
base sheet and further removing the film of the provisional
adhesive agent after the adhesive agent hardens.
[0027] According to this invention, a water-soluble or organic acid
water-soluble film is formed on the surface of the provisional base
sheet to a thickness of 1/10 or more and 2/3 of less of the average
diameter of the polishing particles, these polishing particles are
charged negatively or positively in a same polarity, the container
of the dispersion device for dispersing the polishing particles is
also charged in the same polarity, the base sheet is maintained at
the ground potential as the polishing particles are dispersed onto
this water-soluble or organic acid water-soluble film such that the
edges of these polishing particles will contact the provisional
base sheet, a resin for fixing the polishing particles is pressed
against the polishing particles from the side opposite from the
provisional base sheet, and the provisional base sheet is peeled
off and this film is removed after this resin is hardened. By this
novel method, it is possible to obtain a polishing tape with a
superior polishing performance.
[0028] According to the method of this invention, a provisional
base sheet for fixing the polishing particles is firstly prepared
and this is coated with a water-soluble or organic acid
water-soluble thin film. Next, the polishing particles are
dispersed onto this water-soluble or organic acid water-soluble
film. The polishing particles are electrostatically charged
negatively or positively in the same polarity, and the provisional
base plate is electrically maintained at the ground potential as
the polishing particles are dispersed.
[0029] Since the inner wall of the device for carrying out the
electrostatic dispersion is also charged in the same polarity as
the polishing particles at this time, the polishing particles can
be dispersed efficiently over the base sheet without becoming
adhered to the inner walls of the container. The polishing
particles are buried into the water-soluble or organic acid
water-soluble film so as to contact the provisional base plate as
the thickness of the water-soluble or organic acid water-soluble
film and the potential difference between the potential for the
electrostatic charging and the ground potential are properly
selected, portions of the polishing particles on the opposite side
from the provisional base sheet projecting from the water-soluble
or organic acid water-soluble film.
[0030] Next, an adhesive agent such as a resin is applied so as to
cover the projected portions of the polishing particles. This
adhesive agent is hardened so as to strongly secure the polishing
particles. Next, the provisional base sheet is peeled off and the
water-soluble or organic acid water-soluble film is finally
dissolved in water or an acid such that an ideal sheet is obtained
with the polishing particles mutually separated in the direction of
their plane and the cutting edges arranged uniformly. In what
follows, this novel technology and the product that can be produced
thereby will be described in detail.
EFFECTS OF THE INVENTION
[0031] The present invention provides a polishing sheet capable of
efficiently polishing a target object with a good surface roughness
without generating polishing flaws.
[0032] The present invention makes it possible in particular to
obtain polishing sheet having polishing particles mutually
separated as seen in the direction of their plane by using a
water-soluble or organic acid water-soluble material as the
provisional adhesive agent, charging the polishing particles at the
same time in a same polarity and maintaining the base sheet at the
ground potential. Moreover, the cutting edges are completely
exposed and arranged uniformly such that a superior polishing
capability is exhibited as a polishing sheet.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a partially sectional view of a polishing sheet
embodying this invention.
[0034] FIGS. 2A, 2B, 2C, 2D, 2E, 2F, 2G and 2H are schematic
drawings for explaining the production process of a polishing sheet
according to this invention.
[0035] FIG. 3 is a schematic drawing for showing the structure of a
dispersing device for dispersing polishing particles
electrostatically according to this invention.
[0036] FIG. 4 is a photographic image showing the distribution of
polishing particles after they are dispersed according to this
invention.
[0037] FIG. 5 is a schematic diagonal view of a test piece
fabrication device using a polishing sheet of this invention.
BEST EMBODIMENT OF THE INVENTION
[0038] A preferred embodiment of this invention is described next
with reference to the drawings.
[0039] FIG. 1 is a partially sectional view of a polishing sheet
embodying this invention, FIGS. 2A through 2H are schematic
drawings for explaining the production process of a polishing sheet
according to this invention, FIG. 3 is a schematic drawing for
showing the structure of a dispersing device for dispersing
polishing particles electrostatically according to this invention,
FIG. 4 is a photographic image showing the distribution of
polishing particles after they are dispersed according to this
invention, and FIG. 5 is a schematic diagonal view of a test piece
fabrication device using a polishing sheet of this invention.
[0040] As shown in FIG. 1, a polishing sheet of this invention has
a layer of adhesive resin 5 tightly adhering to one of the surfaces
of a base sheet 4, which is a base material in the form of a film,
and firmly fixing polishing particles 31-33.
[0041] Examples of the material for the base sheet 4 include
polyester resins such as polyethylene terephthalate and
polyethylene naphthalate, polyolefin resins such as polyethylene
and polypropylene, polystyrene, vinyl chloride, polyvinyl alcohol,
acryl resins having methacryl alcohol as principal component, and
polycarbonates.
[0042] The polishing particles 31-33 are formed in a
single-particle layer without forming aggregations, each having on
the opposite side from the base sheet 4 a cutting edge which
contacts an imaginary line 35. In other words, the cutting edges
are in a completely uniform condition and not covered by anything
that may adversely affect the polishing performance. Moreover,
these polishing particles 31-33 are fixed such that mutually
adjacent ones of them are not tightly in contact with each other
but are separated from each other. Thus, the cutting edges of all
polishing particles for contacting a target object to be polished
are not only arranged to be coplanar but are separated one from
another.
[0043] The adhesive resin 5 is selected for its adhesive
characteristic to the base sheet 4 from a wide range of materials
such that any commonly used kind may be used. Moreover, it is
preferable to use a UV resin for the purpose of its hardening.
[0044] FIGS. 2A-2H show schematically the production process of a
polishing sheet according to this invention.
[0045] FIG. 2H is a schematic view of a polishing sheet as finally
produced as a product, comprising a base sheet 4, polishing
particles 31-33 and an adhesive resin 5 for securely fixing the
polishing particles 31-33. The cutting edges of the polishing
particles 31-33 contact a target object 8 to be polished.
[0046] Such a polishing sheet is produced by going through steps
shown in FIGS. 2A through 2G. Firstly, a provisional base sheet 1
is prepared. Materials of various kinds such as polymer, Si wafer
and metals may be used for the provisional base sheet 1. Although
there is no strict limit on the material itself to be used, it is
necessary to make its surface smooth. The degree of smoothness
depends on the size of the polishing particles to be used but if
the average diameter of the polishing particles is 20 microns, the
average surface roughness may be about 1 micron or less and if the
average diameter of the polishing particles is 5 microns, the
smoothness may be 0.5 micron or less.
[0047] Next, a thin film 2 of a provisional adhesive agent (also
hereinafter referred to simply as "the film") which is
water-soluble or soluble in an organic acid, having the function of
provisionally adhering onto the provisional base sheet 1, is
applied to the provisional base sheet 1. Polysaccharides, pastes,
starches, gelatins, etc. may be used as the water-soluble film
material. More specifically, polysaccharides such as glycogen,
cellulose, dextran and dextrine, water-soluble polymers (pastes)
such as polyvinyl alcohol, acryl polymers and polyethylene oxides,
starches generated from plants such as corns and potatoes, and
gelatins comprising animal protein may be mentioned.
[0048] Those materials not easily soluble in water but soluble in
solutions having an organic acid added to them are also useful. Use
may be made, for example, of chitin and
poly-.beta.1,4-glucosamine(chitosan) obtained by removing acetyl
group from chitin. Chitosan, in particular, is soluble in vinegar
and it is suitable for the purpose of the present invention since
it has no problem also from the point of view of safety.
[0049] Any known method may be used for applying such film 2 of a
provisional adhesive agent soluble in water or organic acid water,
but the spray coating and roll coating methods are generally known
methods. The thickness of this film 2 is controlled by the
concentration of the liquid, the application temperature and the
application speed. It is preferable to adjust the thickness to
1/10-2/3 of the average diameter of the polishing particles.
[0050] Next, polishing particles 31-33 are buried into the
water-soluble or organic acid water-soluble film 2, as shown in
FIG. 2B. The material for the polishing particles may be selected
according to the relationship between the target object to be
polished and the polishing performance of the polishing particles.
Inorganic particles of alumina, silica, diamond, boron nitride and
silicon carbide and organic particles of cross-linked acryl resins,
cross-linked polystyrene resins and melamine resins may be
used.
[0051] For burying the polishing particles into the water-soluble
or organic acid water-soluble film 2 as a single-particle layer,
the electrostatic dispersion method of electrostatically charging
the polishing particles and holding the base sheet 1 at the ground
potential may be used. The electrostatic dispersion method is
carried out by using a device shown in FIG. 3.
[0052] FIG. 3 is a plan view of the dispersion device for the
electrostatic dispersion of the polishing particles, comprising a
supply unit 10 and a dispersing unit 20. Polishing particles are
supplied into an adjustment chamber 11 from a supply hopper 12 and
then charged positively or negatively in a single polarity inside a
pressure-transporting pipe 16. The polarity into which the
polishing particles are to be charged depends on the material of
the polishing particles. If the polishing particles are diamond,
for example, they are charged negatively. If they are alumina, a
positive potential is selected.
[0053] The level of charging of the polishing particles is detected
by a charge sensor 15 and the quantity of particle supply is
controlled by the supply control box 13 such that the level of
charging will take upon a suitable value. The polishing particles
with the supply quantity thus controlled are dispersed towards a
substrate stage 22 from the dispersion nozzle 21 through the
pressure-transporting pipe 16. Since the inner walls of the
container of the dispersion device are charged in the same polarity
as the polishing particles, the polishing particles are subjected
to a repulsive force from the inner walls and hence efficiently
reach the provisional base sheet 1 without becoming attached to the
inner walls of the container.
[0054] Methods of preventing pressure loss inside the
pressure-transporting pipe for accelerating friction with the inner
walls of the pressure-transporting pipe include (a) providing the
interior of the pressure-transporting pipe with the function of
supplying a supplementary gas (dry air, nitrogen gas, etc.), (b)
providing a negative pressure inside the pressure-transporting
pipe, and (c) adding a plurality of branches to the
pressure-transporting pipe for increasing the friction
efficiency.
[0055] The charged particles led to the dispersion nozzle 21 of the
dispersion chamber 20 are blown onto the substrate 23 together with
a compressed gas discharged through gas nozzles provided around the
dispersion nozzle 21. Dry air and nitrogen gas from an ordinary
high-pressure container may be used as the compressed gas.
[0056] The provisional base sheet 1 with the water-soluble or
organic acid water-soluble film 2 applied thereto is set on the
substrate stage 22 and is maintained at a ground potential. The
polishing particles dispersed from the dispersion nozzle 21 are
charged by a potential of the same polarity at 1-50 kV. For this
reason, the individual polishing particles remain as individual
particles as they fly onto the water-soluble or organic acid
water-soluble film 2 on the provisional base sheet 1 under the
influence of the repulsive electrostatic force so as to be released
from their aggregated condition. Since the inner walls of the
electrostatic dispersion chamber 20 are also maintained at a
potential of the same polarity as the polishing particles, the
polishing particles dispersed from the dispersion nozzle 21 fly
onto the water-soluble or organic acid water-soluble film 2 without
becoming attached to the inner walls of the dispersion chamber 20,
resulting in a high yield.
[0057] What is important here is that the provisional base sheet 1
and the water-soluble or organic acid water-soluble film 2 are
maintained at the ground potential. The polishing particles,
maintained at a same priority, are strongly attracted
electrostatically by and fly towards the water-soluble or organic
acid water-soluble film 2 maintained at the ground potential and
collide with it with large kinetic energy.
[0058] Since the water-soluble or organic acid water-soluble film 2
is soft, the polishing particles having large kinetic energy become
easily buried inside the water-soluble or organic acid
water-soluble film 2, their front edges contacting the provisional
base sheet 1 and coming to be uniformly arranged, as shown in FIG.
2B.
[0059] Potential of 1 kV or more will be sufficient for achieving
this effect. The same effect may be had with a potential in excess
of 50 kV but since it becomes difficult to design a device as a
practical matter, the present invention limits this potential to be
within the range of 1-50 kV.
[0060] As compared to this method of this invention for dispersing
polishing particles, conventional methods cannot provide a strong
attractive force on polishing particles towards the provisional
base sheet onto which the polishing particles are to become
provisionally attached. If the polishing particles are merely
dropped by the gravitational force, they merely become attached to
the provisional adhesive agent without passing through this
provisional adhesive agent to reach the provisional base sheet.
[0061] Since the polishing particles are charged in the same
polarity, furthermore, they repel one another when they reach the
water-soluble or organic acid water-soluble film 2 and do not newly
form aggregations. Thus, they become temporarily fixed as a
single-particle layer inside the film 2 of the provisional adhesive
agent.
[0062] Moreover, since the polishing particles which have reached
the water-soluble or organic acid water-soluble film 2 become
temporarily fixed while remaining charged in the same polarity,
they become fixed while remaining separated as seen in the
direction of their plane. Thus, a polishing sheet with the
polishing particles separated at effective distances among
themselves for efficient discharge can be obtained.
[0063] In summary, a polishing sheet as shown in FIG. 2H can
finally be obtained with cutting edges arranged uniformly and the
polishing particles separated in the direction of their plane in a
single-particle layer formation because the electrostatic
dispersion is carried out onto the water-soluble or organic acid
water-soluble film 2.
[0064] The thickness of the water-soluble or organic acid
water-soluble film 2 is determined according to the size of the
polishing particles, preferably being 1/10-2/3 of the average
diameter of the polishing particles. The reason for this preference
is, as shown in FIG. 2D, such that 9/10-1/3 of the polishing
parties would be covered by the adhesive resin 5 in the following
step.
[0065] In order to make the size distribution of polishing
particles small for the convenience of producing a single-particle
layer, polishing particles conventionally used to be classified by
having both very large and very small particles eliminated. Thus,
polishing particles of the selected class were relatively
expensive. According to the present invention, large particles
merely stick out more from the water-soluble or organic acid
water-soluble film and the portions that stick out are eventually
covered by the adhesive resin 5 and hence present no problem. Very
small particles will become buried inside the water-soluble or
organic acid water-soluble film 2 and will have no cutting edges
appearing and hence may be eliminated but if it is only small
particles that are to be eliminated in a classification process, it
is cost-wise still advantageous compared to the conventional method
of eliminating both large and small particles.
[0066] Aside from the electrostatic dispersion process for the
polishing particles, a base sheet 4 coated with an adhesive resin 5
as shown in FIG. 2C is prepared. This is the base sheet 4 that will
remain in the final product and may comprise polyester resins such
as polyethylene terephthalate and polyethylene naphthalate,
polyolefin resins such as polyethylene and polypropylene,
polystyrene, vinyl chloride, polyvinyl alcohol, acryl resins having
methacryl alcohol as principal component, and polycarbonates.
[0067] There is no particular limitation on the thickness of the
base sheet 4 but it is preferably within the range of 5 microns or
more and 100 microns less, and more preferably within the range of
10 microns or more and 75 microns or less. The base sheet 4 is
coated with an adhesive resin 5, which serves to fix the polishing
particles in the final product.
[0068] A resin of the common UV-setting type of the thermosetting
type may be used as the adhesive resin 5. UV-setting resins are
particularly preferable because they are easy to process, as will
be described below.
[0069] The base sheet 4 prepared as shown in FIG. 2C is pressed by
a process such as the calendar roll such that its adhesive resin 5
will contact the polishing particles 31-33. By this operation, the
projecting parts of the polishing particles 31-33 not contacting
the water-soluble or organic acid water-soluble film 2 become
buried inside the adhesive resin 5 and will become firmly fixed
after a hardening operation.
[0070] Next, the hardening of the adhesive resin 5 will be
explained. FIG. 2E shows an example wherein the base sheet 4
comprises polyethylene terephthalate which is transmissive to UV
light 6 being irradiated from the back surface to complete the
hardening of the adhesive UV-setting resin 5. In the case of an
adhesive resin not transmissive to UV light, a specified process of
heating and drying may be carried out to obtain the same
result.
[0071] Since the water-soluble or organic acid water-soluble film 2
does not become hardened in this process for hardening the adhesive
resin 5, the peeling of the provisional base sheet 1 and the
removal of the water-soluble or organic acid water-soluble film 2
in the next step can be carried out easily. If an epoxy-type
thermosetting resin with a strong adhesive characteristic is used
instead of the water-soluble or organic acid water-soluble film 2,
such thermosetting resin will also become hardened when the
adhesive resin 5 is hardened such that the peeling of the adhesive
resin 5 and the provisional base sheet 1 becomes difficult, the
cutting edges of the polishing particles remaining covered by this
thermosetting resin and failing to become exposed. It should now be
understood that it is an important novel point of this invention to
use water-soluble or organic acid water-soluble material for the
film 2 of the provisional adhesive agent.
[0072] After the process of hardening the adhesive resin 5 is
completed, the provisional base sheet 1 is peeled off and water or
a liquid organic acid is sprayed on the water-soluble or organic
acid water-soluble film 2. In the case of a film 2 comprising
chitin or chitosan, the film 2 can be easily removed by spraying
vinegar. In the case of a film 2 comprising polysaccharide, paste
or starch, the film 2 can be removed by a spray of water to expose
the cutting edges. The polishing sheet thus obtained comprises a
single-particle layer with cutting edges arranged uniformly, having
no aggregates as shown in FIG. 2H. Since the uniformly arranged
cutting edges contact the target object 8 to be polished, the
target object 8 can be polished efficiently without leaving flaws.
The invention is explained next by way of test examples.
Test Examples
(1) Preparation of Polishing Particles
[0073] Diamond particles of average diameter 10 microns were used
and small particles of less than about 2 microns were removed by a
classifying device of the cyclone type. Many aggregations were
observed after the classification by a microscopic inspection but
they were directly used as polishing particles.
(2) Preparation of Provisional Base Sheet
[0074] A polyethylene terephthalate film with thickness of 50
microns and having good smoothness was used as the provisional base
sheet. As measured preliminarily by a surface roughness meter with
a probe, its average surface roughness Ra was 0.4 microns. In order
to form films of provisional adhesive agents on this film, a
chitosan solution, a 10% aqueous solution of polyvinyl alcohol with
degree of polymerization about 200 and a solution obtained by
dissolving in water corn starch which is a kind of starch were
individually applied to obtain three kinds. Applications were
effected by the spray method and their thickness was adjusted
within the range of 3-5 micros by compiling the conditions of
application and the thickness data measured by a load meter of the
push-in type.
(3) Dispersion of Polishing Particles
[0075] The diamond polishing particles classified as described
above were electrostatically dispersed. The diameter of the
dispersion nozzle was adjusted to 5 mm and each emission was for 5
seconds with a carrier gas at 3 kg/cm.sup.2, and such emission was
repeated 10 times. The charging potential was 5 kV.
(4) Preparation and Compression of Base Sheet and Hardening
[0076] Epoxy-type UV resin was applied as adhesive resin to the
polyethylene terephthalate base sheet with thickness of 75 microns.
Although there was no strict limitation on the thickness of
application, a range of about 10-15 microns was selected. This base
sheet was positioned such that the UV adhesive resin would contact
the polishing particles which had been electrostatically dispersed
to the film of the provisional adhesive agent and pressed. UV light
beams at intervals of 100 mm between them were thereafter projected
from the side of the polyethylene terephthalate base sheet to
completely harden the UV resin serving as the adhesive resin.
(5) Removal of Provisional Base Sheet and Provisional Adhesive
Agent
[0077] The provisional base sheet was peeled off after the
irradiation of the UV light. The peeling was possible by using a
pair of pincers. Since remainders of the provisional adhesive agent
were visible on its surface after the peeling, they were dissolved
in water or an acid. When the provisional adhesive agent was
chitosan, commercially available vinegar was sprayed for 20
minutes. In the case of a 10% aqueous solution of polyvinyl alcohol
with degree of polarization 200, water heated to about 60.degree.
C. was sprayed. In the case of a corn starch liquid, the removal of
the provisional adhesive agent was completed to the extent that the
remainder of the provisional adhesive agent was no longer visible
after tap water at room temperature was sprayed for 5 minutes.
(6) Method of Evaluation
[0078] The condition of attachment of the polishing particles after
the series of processes described above was observed
microscopically. FIG. 4 is a microscopic photograph of the
condition of the aforementioned diamond polishing particles having
been dispersed by the electrostatic dispersion method described
above into a film of 10% aqueous solution of polyvinyl alcohol. The
portions appearing white in the photograph are the polishing
particles. As can be seen, no aggregations of the individual
polishing particles are visible and it can be understood that the
polishing particles are formed in a single-particle layer
formation. Moreover, these diamond polishing are separated as seen
in the direction of their plane so as to be in a condition useful
for the discharge of polishing debris.
[0079] A test for polishing performance was carried out as a
bearing ball fabrication test by comparing the stock removal over a
specified length of time, the central line surface roughness (Ra)
and the maximum surface roughness (Rmax).
[0080] A performance test for the polishing tape was carried out by
using steel balls serving as ball bearing (SUJ-2) with diameter 4
mm as test pieces and by polishing them with a ball bearing
fabrication tester 40, as shown in FIG. 5.
[0081] This fabrication tester 40 is adapted to have a polishing
sheet 43 of this invention attached to a rotatable lapping plate
42, to fix a steel ball 44 as described above as a test piece to a
jig 45 and to have a specified load 47 from above onto a polishing
head 42 provided to a principal shaft 46.
[0082] The fabrication test was carried out by rotating the lapping
plate 42, causing the polishing head 41 with the steel ball 44
fixed thereto to contact the surface of the polishing sheet 43
pasted onto the lapping plate 42 at a specified load and to move a
specified distance from a central position to an outer peripheral
position on the lapping plate 42 at a specified speed. The
fabrication process is started and ended automatically by moving up
and down an arm 48 supported around a supporting point 49. After
the fabrication process is completed, the steel ball 44 is removed
from the jig 45, the steel ball 44 is weighed and the change (or
the reduction) in its weight serves as the polished quantity. Five
different steel balls were used for the test and the average value
from them was used for the evaluation.
[0083] The conditions of the test were as follows.
[0084] (6-1) Load: 500 g
[0085] (6-2) Diameter of the lapping plate: 8 inches
[0086] (6-3) Rotary speed of the lapping plate: 300 rpm
[0087] (6-4) Distance of motion from the central position to the
peripheral position: 100 mm
[0088] (6-5) Polishing time: 12 seconds
[0089] The average surface roughness Ra and the maximum surface
roughness Rmax of the polished steel balls were measured by a
surface roughness meter (SURFCON 480A produced by Tokyo Seimitsu
Kabushiki Kaisha).
Comparison Example
[0090] The same UV resin as used in Test Examples was applied as
Comparison Example onto a polyethylene terephthalate film with
thickness 50 microns and diamond polishing particles with average
diameter of 10 microns were further dispersed onto it directly. The
dispersion was carried out by causing these polishing particles to
be emitted from a small opening at an air pressure of 1 kg/mm.sup.2
to cause them to fall freely. The UV resin was thereafter hardened
under the same conditions as used for Test Examples to obtain a
polishing sheet.
(7) Results of Evaluation
[0091] Table 1 shows the results of evaluation of Test and
Comparison Examples.
TABLE-US-00001 TABLE 1 Average surface Maximum surface roughness
(Ra) roughness (Rmax) Stock removal (.mu.m) (.mu.m) (mg/min) Test
Example 0.019 0.119 9.84 Chitosan Test Example 0.021 0.135 9.60
Polyvinyl alcohol Test Example 0.023 0.128 9.32 Corn starch
Comparison 0.296 0.210 8.64 Example
[0092] Although many generated defects were observed in the case of
Comparison Example, only one or two shallow flaws were observable
on Test Examples. It may therefore be concluded that the polishing
sheets according to Test Examples do not generate polishing flaws
and are useful, capable of efficiently carrying out polishing for
obtaining good surface roughness. Especially if a water-soluble or
organic acid water-soluble material is used as the provisional
adhesive agent to charge polishing particles at the same time in a
same polarity and the base sheet is maintained at the ground
potential, a polishing sheet can be obtained with the polishing
particles separated mutually as seen in the direction of their
plane. Moreover, their cutting edges are completely exposed and
arranged uniformly such that the polishing sheet can exhibit
extremely superior performance characteristics.
EXPLANATION OF SYMBOLS
[0093] 1: Provisional base sheet [0094] 2: Film of a provisional
adhesive agent (Film) [0095] 4: Base sheet [0096] 5: Adhesive resin
[0097] 6: UV light [0098] 8: Target object to be polished
* * * * *