U.S. patent application number 11/065452 was filed with the patent office on 2005-10-20 for fixed abrasive grinding/polishing tool.
This patent application is currently assigned to HITACHI MAXELL, LTD.. Invention is credited to Ikeno, Junichi, Kishimoto, Mikio, Oshita, Tadashi.
Application Number | 20050229499 11/065452 |
Document ID | / |
Family ID | 34431663 |
Filed Date | 2005-10-20 |
United States Patent
Application |
20050229499 |
Kind Code |
A1 |
Kishimoto, Mikio ; et
al. |
October 20, 2005 |
Fixed abrasive grinding/polishing tool
Abstract
A fixed abrasive grinding/polishing tool containing cerium oxide
particles each being in the plate shape and having an average
particle size in an in-plane direction of the plate-form particles
of 10 nm to 200 nm, which are bonded together with a water-soluble
polymer.
Inventors: |
Kishimoto, Mikio; (Osaka,
JP) ; Oshita, Tadashi; (Osaka, JP) ; Ikeno,
Junichi; (Saitama-shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
HITACHI MAXELL, LTD.;
Junichi IKENO
|
Family ID: |
34431663 |
Appl. No.: |
11/065452 |
Filed: |
February 25, 2005 |
Current U.S.
Class: |
51/298 |
Current CPC
Class: |
B24B 37/245 20130101;
B24D 11/001 20130101; B24D 3/32 20130101 |
Class at
Publication: |
051/298 |
International
Class: |
B24B 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 1, 2004 |
JP |
P2004-108946 |
Claims
What is claimed is:
1. A fixed abrasive grinding/polishing tool for grinding or
polishing a substrate, wherein said tool comprises cerium oxide
particles having an average particle size of 10 nm to 200 nm and a
binder comprising a water-soluble polymer.
2. The fixed abrasive grinding/polishing tool according to claim 1,
wherein each of the cerium oxide particles in plate form and a
ratio of the maximum length in the in-plane direction of the
plate-form particle to a thickness thereof is from 2 to 20.
3. The fixed abrasive grinding/polishing tool according to claim 1,
comprising said cerium oxide particles as a main component and
further comprising additional oxide particles which are at least
one selected from the group consisting of zirconium oxide
particles, aluminum oxide particles and iron oxide particles.
4. The fixed abrasive grinding/polishing tool according to claim 3,
wherein said additional oxide particles have an average particle
size of 10 nm to 200 nm.
5. The fixed abrasive grinding/polishing tool according to claim 3,
wherein said additional oxide particles are in the plate form and
have a ratio of the maximum length in the in-plane direction of the
plate-form particle thereof to a thickness thereof of from 2 to
20.
6. The fixed abrasive grinding/polishing tool according to claim 3,
wherein a content of the additional oxide particles is from 1 to
50% by weight relative to a weight of the cerium oxide
particles.
7. The fixed abrasive grinding/polishing tool according to claim 1,
wherein a content of the water-soluble polymer is from 0.5 to 30%
by weight and a content of the cerium oxide particles is from 50 to
99% by weight based on the total weight of the particles and
binder.
8. The fixed abrasive grinding/polishing tool according to claim 1,
wherein the binder further comprises an organic solvent soluble
polymer.
9. The fixed abrasive grinding/polishing tool according to claim 1,
wherein the cerium oxide particles have a narrow particle size
distribution.
10. The fixed abrasive grinding/polishing tool according to claim
3, wherein the zirconium oxide particles, aluminum oxide particles
and/or the iron oxide particles have a narrow particle size
distribution.
11. The fixed abrasive grinding/polishing tool according to claim
1, wherein the water-soluble polymer is a metal alginate.
12. The fixed abrasive grinding/polishing tool according to claim
11, wherein the metal is an alkali or alkaline earth metal.
13. A method of producing a fixed abrasive grinding/polishing tool,
comprising a step of combining cerium oxide particles having an
average particle size of 10 nm to 200 nm with a binder comprising a
water-soluble polymer.
14. The method according to claim 13, further comprising:
dissolving the water-soluble polymer with a solvent to form a
solution, dispersing the cerium oxide particles each being in the
shape of a plate into said solution into which the water-soluble
polymer is dissolved to form a dispersion, forming said dispersion
into a specific shape to form an intermediate product so that said
plate-shaped cerium oxide particles are aligned substantially in a
specific direction.
15. The method according to claim 13, further comprising: combining
additional oxide particles which are at least one selected from the
group consisting of zirconium oxide particles, aluminum oxide
particles and iron oxide particle, each being in the shape of a
plate, with the cerium oxide particles.
16. The method according to claim 14, further comprising: removing
solvent in the dispersion to increase the concentration of binder
and particles in the dispersion, aligning the orientation of the
particles using electrophoresis.
17. The method according to claim 15, further comprising:
dissolving the water-soluble polymer with a solvent to form a
solution, dispersing the cerium oxide particles and the additional
oxide particles each being in the shape of a plate into said
solution into which the water-soluble polymer is dissolved to form
a dispersion, forming said dispersion into a specific shape to form
an intermediate product so that said plate-shaped oxide particles
are aligned substantially in a specific direction, removing solvent
in the dispersion to increase the concentration of binder and
particles in the dispersion, aligning the orientation of the
particles using electrophoresis.
18. The method according to claim 13, wherein the water-soluble
binder comprises a metal alginate.
19. The method according to claim 18, wherein the metal is an
alkali or alkaline earth metal.
20. A method of increasing the smoothness of a surface of a
substrate, comprising contacting the fixed abrasive
grinding/polishing tool according to claim 1 with the surface of
the substrate to smoothen said surface.
21. The method according to claim 20, wherein the substrate is
silica.
22. A product made by a process comprising contacting the fixed
abrasive grinding/polishing tool according to claim 1 with a
surface of the product to smoothen said surface.
23. The product according to claim 22, wherein the smoothened
surface of the product is made of silica.
Description
[0001] This application claims priority to Japanese Patent
Application No. 2004-108946, which is herein incorporated by
reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a fixed abrasive
grinding/polishing tool for grinding or polishing a workpiece, and
particularly, to a fixed abrasive grinding/polishing tool using
cerium oxide particles as main abrasive grains.
[0004] 2. Description of the Background Art
[0005] It is increasingly desired to decrease the thickness of a
silicon wafer, and various methods are proposed to this end. A
grinding stone using diamond abrasive grains is commonly used
because of its high grinding efficiency, but grinding marks remain
on a workpiece after grinding and it is necessary to carry out
mirror polishing with a different grinding means using slurry
abrasive grains to remove the grinding marks. That is, totally
different methods should be used to perform grinding, which makes
the grinding process complicated. As a result, the grinding
efficiency is reduced and thus grinding costs increase.
[0006] In the grinding method using slurry abrasive grains, good
surface smoothness is obtained after grinding, but grinding speed
is low and thus grinding efficiency is low.
[0007] In decreasing the thickness of a quartz crystal wafer, a
slurry containing cerium oxide particles having a particle size of
about 1 .mu.m dispersed therein is used. However, further
improvement of the grinding efficiency is required. In this
connection, it may be a great problem from the environmental view
to treat a great amount of the waste slurry discharged in the
polishing process.
[0008] Despite the demand for the further improvements in grinding
efficiency, currently, any fixed abrasive grinding/polishing tool
meeting the needs in the market has not been developed because of
the problem arising from the fact that the surface smoothness is
decreased after grinding as a grinding efficiency is increased.
[0009] JP-A-2003-73656 discloses active abrasive grains and a
grinding stone or the like comprising the same capable of grinding
a workpiece by a mechanochemical action. The abrasive grains and
the grinding stone have been developed by one of the present
inventors, and the grinding stone is produced by mixing glass beads
and a water-soluble polymer binder such as sodium alginate and
processing the obtained mixture to a desired state using
electrophoresis. JP-A-2003-73656 also describes that the active
abrasive grains constituting the grinding stone exhibit an
excellent grinding ability by the mechanochemical action and, an
excellent mirror surface can be formed although the grinding method
using the grinding stone exerts grinding rather than polishing.
[0010] Furthermore, JP-A-2003-049158 and JP-A-2003-206475 disclose
cerium oxide particles each of which has a plate form and an
average particle size of 10 to 200 nm in the direction of the plate
plane. The description of how to make the cerium oxide particles as
both generically and specifically taught in these references is
herein incorporated by reference.
[0011] The conventional fixed abrasive grinding/polishing tools, as
described above, generally have a problem that the tools easily
cause marks on the surface of a workpiece despite the high grinding
efficiency exhibited by the tools, which leads to poor smoothness
on the ground surface. On the other hand, the slurry abrasive grain
used in a wet method has a defect that the slurry has low and
inferior grinding efficiency although it can easily form the
smoothly ground surface. In the current state of the art, there has
not yet been provided any fixed abrasive grinding/polishing tool
that has an excellent grinding ability and can achieve excellent
surface smoothness on the workpiece after grinding.
SUMMARY OF THE INVENTION
[0012] Accordingly, an object of the present invention is to
provide a fixed abrasive grinding/polishing tool capable of
realizing excellent surface smoothness after grinding, which has
never been obtained with a conventional grinding stone, while
maintaining the excellent grinding ability of grinding stones by
employing cerium oxide particles having specific particle shapes
and specific particle sizes as abrasive grains and binding the
cerium oxide particles with a water-soluble polymer.
[0013] According to the present invention, it has been found that
an excellent grinding performance, which has never been obtained
with the conventional tool of this kind, can be achieved by
employing the cerium oxide particles having a plate-shape and an
average particle size of 10 to 200 nm in the direction of a plate
plane as abrasive grains in a fixed abrasive grinding/polishing
tool. Preferably the average particle size of the cerium oxide
particles is from 20 to 180 nm, more preferably from 40 to 160 nm.
Such cerium particles are described in JP-A-2003-049158 and
JP-A-2003-206475.
[0014] That is, usually, as the particle sizes of abrasive grains
are smaller, the smoothness of a ground surface is usually better,
but the grinding efficiency is lower. On the contrary, the abrasive
grains of the present invention are fine particles and have an
average particle size of 10 to 200 nm, and when the particles are
plate shaped, they exhibit an excellent grinding ability by using
the edges of the plate-form particles, although the particles are
fine particles. In this way, the present inventors, for the first
time, have succeeded in rendering two seemingly contradictory
characteristics of a grinding stone, that is, both a high grinding
efficiency and excellent surface smoothness after grinding can be
obtained together by employing the cerium oxide particles having a
specific shape and specific particle sizes.
[0015] Cerium oxide particles each having a plate shape, which are
employed in the present invention, are characterized in that they
not only exhibit an especially excellent grinding action with using
their edges, but also show a large chemical grinding action. The
present invention, for the first time, achieves simultaneously the
excellent mechanical grinding ability with using their edges and
the excellent chemical grinding ability owned by cerium oxide.
[0016] In the fixed abrasive grinding/polishing tool of the present
invention, the cerium oxide particles further comprise other
particles formed of at least one oxide selected from the group
consisting of aluminum oxide, zirconium oxide and iron oxide,
wherein the cerium oxide particles remain as the main component
according to a kind of a workpiece to be ground or polished,
grinding conditions, etc. The use of the additional oxide in the
particles can improve the grinding ability of the tool in
comparison with the tool using only the cerium oxide particles each
of the present invention, since the mechanical grinding ability of
the additional oxide particles is added.
[0017] For example, the fixed abrasive grinding/polishing tool of
the present invention may be produced as follows:
[0018] The particles of the oxides each having a plate shape as the
abrasive grains are dispersed in the solution of a water-soluble
polymer such as sodium alginate so that the abrasive grains are
bonded together with the water-soluble polymer. Then, water is
removed from the dispersion, and the residual bound abrasive grains
are shaped in the specific form of the tool. When the tool of the
specific shape is shaped using an electrophoresis phenomenon, the
plate-shaped particles are orientated in a specific direction so
that their edges align well, and they are easily closely packed.
Therefore, the fixed abrasive grinding/polishing tool can exert
better performance.
[0019] Accordingly, the fixed abrasive grinding/polishing tool of
the present invention is used as a grinding stone and can realize
the excellent grinding efficiency and surface smoothness
simultaneously. In addition, the fixed abrasive grinding/polishing
tool of the present invention can also be used in the presence of
water like the conventional slurry abrasive grains. In this case,
the chemical polishing action of cerium oxide is enhanced by the
presence of water. When water is used, even a trace of water has a
great effect and an amount of water can be adjusted arbitrarily
depending on an application or a purpose of the use. The fixed
abrasive grinding/polishing tool of the present invention can be
used either as a grinding stone or in the presence of water, which
enables the fixed abrasive grinding/polishing tool to be a tool
used in a wide variety of applications.
[0020] While the advantages of the use of the plate-form cerium
oxide particles have been mainly explained in the above
description, the use of cerium oxide particles each having a plate
shape exerts the mechanical grinding ability induced by the edges
of the particles as described above. Furthermore, with a
construction in which the cerium oxide particles having an average
particle size of 10 nm to 200 nm of the present invention are bound
together with the water-soluble polymer, the inherent chemical
grinding ability induced by the fine particles is emphasized to
exert the excellent grinding and polishing properties, which have
never been achieved with the conventional fixed abrasive
grinding/polishing tools. Therefore, the fixed abrasive
grinding/polishing tool of the present invention is not limited to
the use of the plate-form cerium oxide particles, but the important
characteristics of the present invention resides in that cerium
oxide particles having an average particle size of 10 nm to 200 nm
are bound together with a water-soluble polymer.
[0021] In the case of the fixed abrasive grinding/polishing tool of
the present invention, the cerium oxide particles as constituent
particles not only exert an excellent mechanical grinding ability
when the edges of the particles are effectively used, but also
exert an excellent chemical grinding ability based on the chemical
characteristic thereof. Since the particle size is small and from
10 to 200 nm, excellent surface smoothness is obtained after
grinding of a workpiece. Accordingly, the present invention can
provide a grinding stone which is excellent in grinding efficiency
and also in surface smoothness after grinding simultaneously. Here,
the term "plate-shape" or "plate-form" means that a ratio of the
maximum length in the in-plane direction of the plate-form particle
to the thickness thereof is from 2 to 20. Preferably the ratio is
from 3 to 18, more from 5 to 15. A particle diameter or size herein
used is an average of the diameters of 100 particles the photograph
of which is taken with a high resolution transmission electron
microscope. The thickness thereof is measured by dispersing
particles in a binder, coating the dispersion on a sheet and then
observing the sections thereof with a high resolution transmission
electron microscope.
[0022] When the cerium oxide particles are used as main particles
and the additional plate-form particles of a specific oxide such as
aluminum oxide are simultaneously used in an adequate amount, the
grinding properties can enhanced as compared with a case where only
the plate-form cerium oxide particles are used because of the
mechanical grinding ability of the additional oxide particles.
[0023] In addition, in the fabrication of the grinding stone as
described above, there can be obtained a fixed abrasive
grinding/polishing tool exerting the excellent grinding ability by
the use of an electrophoresis phenomenon.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a transmission electron microphotograph of cerium
oxide particles prepared in Example 1 (magnification of
2.times.10.sup.5);
[0025] FIG. 2 is an X-ray diffraction pattern of cerium oxide
prepared in Example 1; and
[0026] FIG. 3 is a transmission electron microphotograph of cerium
oxide particles obtained in Example 2 (magnification of
2.times.10.sup.5).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The fixed abrasive grinding/polishing tool of the present
invention uses cerium oxide particles developed independently as
described above, that is, cerium oxide particles each having a
plate shape and an average particle size of 10 to 200 nm, which are
bonded together with a water-soluble polymer. Thus, the fixed
abrasive grinding/polishing tool of the present invention
simultaneously realizes a high grinding efficiency and an excellent
surface smoothness of a workpiece to be ground or polished.
[0028] The cerium oxide particles each having a peculiar shape and
a specific particle size used in the present invention may be
produced as follows:
[0029] The aqueous solution of a cerium salt is added to an alkali
aqueous solution, the obtained hydroxide or hydrate of cerium is
heated in a first temperature range of 110 to 300.degree. C. in the
presence of water, followed by filtration and drying. The first
temperature range is preferably from 120 to 250.degree. C., more
preferably from 130 to 200.degree. C. This is followed by a heat
treatment in a second temperature range of 200 to 1500.degree. C.
in the air. The second temperature range is preferably from 300 to
1200.degree. C., more preferably from 400 to 1000.degree. C.
[0030] Specifically, in the first step, the desired shapes and
sizes of particles are obtained in a hydrothermal reaction
treatment, in which the hydroxide or the hydrate, which has been
obtained by adding the aqueous solution of the metal salt to the
alkali aqueous solution, is heated in a temperature range of 110 to
300.degree. C.
[0031] In this step, since a pH value at which the hydroxide or the
hydrate are precipitated is different according to a kind of a
metal, pH control is of importance. For example, since aluminum
hydroxide or hydrate is dissolved and not precipitated in either an
acidic or alkaline pH range, a pH value should be controlled in a
neutral range. Since cerium hydroxide or hydrate is dissolved and
not precipitated in a neutral region, a pH value should be
controlled in the alkaline range. In order to obtain a hydroxide or
a hydrate each particle of which is in a desired shape and particle
size by the hydrothermal reaction, a pH control is an important
factor in this reaction.
[0032] Then, in the second step, the hydroxide or the hydrate is
heated in the air to obtain plate-form cerium oxide particles
having an average particle size of 10 nm to 200 nm and a uniform
particle size distribution. The resulting cerium oxide particles
hardly suffer from sintering or agglomeration and have good
crystallinity.
[0033] By employing the production method comprising the above two
steps, the plate-form cerium oxide particles having an average
particle size of 10 nm to 200 nm, which has been unable to obtain
according to the conventional production methods, The fixed
abrasive grinding/polishing tool of the present invention is
fabricated as follows:
[0034] The cerium oxide particles obtained as described above are
dispersed in the solution of a water-soluble polymer, and the
plate-form cerium oxide particles are bonded together with the
water-soluble polymer. Since the fixed abrasive grinding/polishing
tool of the present invention uses a water-soluble polymer as a
binder, it has an advantage that the environmental burden is small
in the manufacturing process. Also, the water soluble binder is
preferred over non-water soluble binders, since the substrate is
preferably washed with water as the substrate is being smoothed. By
using a water soluble binder, the binder slowly dissolves, leaving
more cerium oxide exposed to the substrate. Also, by using a water
soluble binder, the binder that scuffs off the tool during
polishing is dissolved and is therefore easily handled.
[0035] Lastly, the water soluble binder is preferred to comprise a
polymer having ionic character along the length of the polymer
(i.e., ionic groups are part of the backbone and/or pendant
groups). By having this ionic character, cerium oxide particles
bound by the polymer can be physically attracted to an electrode
having an opposite charge to the charge of the polymer using
electrophoresis, which will be described, infra.
[0036] The kind of the water-soluble polymer is not limited.
Preferred examples of the water-soluble polymer include a metal
alginate, wherein the metal can be at least one of Na, K and
NH.sub.3, polyvinyl alcohol, etc. Among them, sodium alginate is a
material contained in seaweeds and thus is particularly preferable
as a harmless polymer binder having ionic character along the
length of the polymer.
[0037] However, a binder may not be specifically limited to a
water-soluble polymer in the fabrication of the grinding stone
according to the present invention. Needless to say, various kinds
of polymer binders to be dissolved in an organic solvent may be
used in combination with the water-soluble polymer. For example,
polymer binders such as vinyl chloride polymers, polyurethanes,
acrylic polymers, urethane polymers, and nitrocellulose may be
used.
[0038] The cerium oxide particles used in the present invention are
characterized in that they have an excellent mechanical grinding
action and also a chemical polishing action. Furthermore, the fixed
abrasive grinding/polishing tool of the present invention can have
further improved mechanical grinding ability, when the additional
plate-form particles of a metal oxide such as at least one of
aluminum oxide, zirconium oxide or iron oxide are used together
with the cerium oxide particles.
[0039] More concretely, the fixed abrasive grinding/polishing tool
of the present invention can be fabricated as described below:
[0040] Firstly, a solution in which the prescribed amount of the
water-soluble polymer is dissolved is prepared, and the prescribed
amount of the plate-form oxide particles are dispersed in the
solution. No specific limitation is imposed on a dispersing method,
and a uniform dispersion is prepared using any of a ball mill, a
paint conditioner, etc.
[0041] The content of the water-soluble polymer in the fixed
abrasive grinding/polishing tool is preferably from 0.5 to 30% by
weight, more preferably from 1 to 25% by weight and particularly
preferably from 2 to 20% by weight, based on the total weight of
oxide particles and binder. When the content of the water-soluble
polymer is low, the plate-form particles are weakly bonded, and the
particles easily drop during grinding. On the other hand, when the
content of the water-soluble polymer is excessively high, the
viscosity of a dispersion is high and it is difficult to uniformly
disperse the particles.
[0042] The content of all of the oxide particles is preferably from
50 to 99% by weight, more preferably from 60 to 97% by weight and
particularly preferably from 75 to 95% by weight based on the total
weight of oxide particles and binder. When the content of the oxide
particles is less than the above range, the grinding efficiency is
unsatisfactory. When this content is excessively high, the bonding
of the particles with the polymer deteriorates, and thus the
particles easily drop off.
[0043] The content of cerium oxide particles is preferably not less
than 50% by weight of all of oxide particles. When the content is
less than 50% by weight, mechanochemical efficiency is
unsatisfactory.
[0044] The dispersion obtained as described above can also be used
as slurry abrasive grains. Preferably the dispersion is shaped in a
specific form using the electrophoresis phenomenon. No specific
limitation is placed on the electrophoresis method. For example, an
apparatus can be used, in which a cylindrical positive electrode
rod is placed at the center of an electrophoresis bath and a
negative electrode is installed so as to surround the positive
electrode. That is, the dispersion is charged in the
electrophoresis bath and a voltage is applied between the positive
electrode and the negative electrode while rotating the positive
electrode rod. Thereby, the plate-form cerium oxide particles which
are covered with the water-soluble polymer are adsorbed and
deposited on the peripheral surface of the positive electrode
rod.
[0045] The orientation of the particles will now be discussed. The
plate-form oxide particles of the present invention have a
characteristic such that when the particles are adsorbed and
deposited using the electrophoresis, the plate-form particles align
on the positive electrode rod with the planes of the particles
being substantially aligned in a specific direction, i.e.,
substantially in parallel with each other. In other words, it is
preferred that the particles are not randomly oriented.
[0046] With such an alignment, since the edge faces of the
plate-form particles align in a specific direction, the fixed
abrasive grinding/polishing tool thus prepared exhibits improved
grinding efficiency in practical use by edge-on grinding. However,
it should be noted that the inventive fixed abrasive
grinding/polishing tool can also be used to smooth the surface of
the substrate when the particles are randomly oriented.
[0047] In another embodiment of the invention, the fixed abrasive
grinding/polishing tool includes at least one other particle in
addition to cerium oxide particles wherein said at least one other
particle is selected from the group consisting of aluminum oxide,
zirconium oxide and iron oxide. The additional aluminum oxide
particles and/or zirconium oxide particles can be in the same
plate-shape and having the same average particle size range and
thickness range as that described herein for cerium oxide, and
wherein these particles are preferably oriented in a similar
fashion to the cerium oxide particles for edge-on grinding.
[0048] Once the plate-form cerium oxide particles which are covered
with the water-soluble polymer are adsorbed and deposited on the
peripheral surface of the positive electrode rod, the positive
electrode rod is pulled out from the dispersion and then removed
from the intermediate product consisting of the plate-form oxide
particles bound with the water-soluble polymer to obtain the
intermediate product in the prescribed shape. In this example, the
intermediate product is deposited on the outer surface of the
positive electrode rod. Therefore, the substantially cylindrical
form intermediate product corresponding to the shape of the
positive electrode rod is produced. The intermediate product is cut
to pieces with an arbitrary size and dried in the air to obtain the
fixed abrasive grinding/polishing tool of the present
invention.
[0049] In the above example, a cylindrical intermediate product is
fabricated using the electrophoresis phenomenon. Needless to say,
by changing the shape of the positive electrode or the intermediate
product, a grinding stone having an adequate shape such as a disk,
prism or others and an adequate size may be fabricated.
Furthermore, in order to obtain a closely packed grinding stone
from the plate-form oxide particles, the electrophoresis phenomenon
is one of useful methods, while for example, simple press molding
can also fabricate a grinding stone without using the
electrophoresis phenomenon. A fabricating method using the press
molding only has an advantage in simplicity and ease of the
fabrication process.
[0050] The fixed abrasive grinding/polishing tool of the present
invention can achieve the excellent grinding efficiency and the
surface smoothness at the same time when it is used as a grinding
stone. Furthermore, the tool of the present invention can also be
used in the presence of water. In this case, the amount of water is
adjusted so that the chemical polishing action of cerium oxide is
realized in the presence of water. Accordingly, the fixed abrasive
polishing tool of the present invention can be used as a grinding
stone or in the presence of water depending on an application and a
purpose thereof. That is, the fixed abrasive grinding/polishing
tool is a fixed abrasive grinding/polishing tool which can be used
in a wide variety of applications.
[0051] When the cerium oxide particles according to the present
invention are used, the mechanical grinding ability are exerted
using the edges of the particles having the plate shape. However,
only with a construction in which the cerium oxide particles having
an average particle size of 10 nm to 200 nm of the present
invention are bound together with the water-soluble polymer, the
chemical grinding ability is enhanced because of the small particle
size, so that the excellent grinding/polishing ability, which has
never been achieved by the conventional fixed abrasive
grinding/polishing tool, is exerted.
[0052] The important steps of the production method of the present
invention will be explained further in detail.
[0053] Preparation of Plate-Form Cerium Oxide Particles, etc.
[0054] (Preparation of Precipitates)
[0055] A cerium salt such as cerium chloride, cerium nitrate,
cerium sulfate or the like is dissolved in water to obtain an
aqueous solution containing cerium ions (an aqueous cerium salt
solution). Among the cerium salts, cerium chloride is most
preferable, since cerium oxide particles with a narrow particle
size distribution can be obtained. As an alkali, an aqueous
solution of sodium hydroxide, potassium hydroxide, lithium
hydroxide, ammonia or the like is preferably used.
[0056] The aqueous cerium salt solution is drop wise added to the
alkali aqueous solution to precipitate the hydroxide or hydrate of
cerium. The pH value of the suspension containing the precipitate
is adjusted in a range of from 8 to 11, and the suspension is
preferably aged at room temperature for about one day. The pH value
adjustment and aging are effective for obtaining cerium oxide
particles with a higher crystallinity in the subsequent heat
treatment at a relatively low temperature.
[0057] (Hydrothermal Treatment)
[0058] The suspension containing the precipitate of the hydroxide
or hydrate of cerium is subjected to a hydrothermal treatment using
an autoclave, etc., In the hydrothermal treatment, while the
suspension containing the precipitate as such may be directly
subjected to the hydrothermal treatment, preferably by-products
and/or residues other than the precipitate are removed by washing
with water and then the pH value is adjusted again with sodium
hydroxide, etc. The pH value at this time is preferably from 7 to
11. When pH is lower than 7, crystals may insufficiently grow in
the hydrothermal treatment. When it exceeds 11, the particle size
distribution is broadened and it is difficult to obtain the
designed particles with a small particle size.
[0059] A temperature in the hydrothermal treatment is preferably
from 110.degree. C. to 300.degree. C. When the temperature is lower
than 110.degree. C., a hydroxide or a hydrate of cerium having a
plate shape is hardly obtained. When it exceeds 300.degree. C., an
apparatus used for the hydrothermal treatment is expensive since it
should withstand a high pressure generated at such a high
temperature.
[0060] A time for the hydrothermal treatment is preferably from 1
hour to 4 hours. If the hydrothermal treatment time is very short,
growth of particles with a specific shape is insufficient. When it
is very long, a production cost increases without any merit.
[0061] (Heat Treatment)
[0062] After the hydrothermal treatment, the particles of cerium
hydroxide or hydrate are filtered and dried and then subjected to a
heat treatment. Prior to filtration, the pH value is preferably
adjusted in a neutral range of from 6 to 9 by washing with water.
When the particles are washed with water, impurities which have an
adverse influence such as sintering in the heat treatment, for
example, sodium, chlorine and the like are removed.
[0063] The particles are preferably treated with silica by further
adding a silicon compound such as sodium silicate to the particles
of cerium hydroxide or hydrate. The silica treatment is effective
for maintaining the specific shape of the cerium oxide particles
which are the final desired products.
[0064] After filtration and drying, the particles of cerium
hydroxide or hydrate can be heat treated to form cerium oxide
particles. No specific limitation is placed on an atmosphere in the
heat treatment. Preferably, the heat treatment is carried out in
the air since the production cost can be made lowest. The heat
treatment temperature is preferably from 300.degree. C. to
1200.degree. C. When the temperature is lower than 300.degree. C.,
crystalline cerium oxide particles are hardly obtained. When it
exceeds 1200.degree. C., particle sizes grow larger by sintering or
a particle size distribution is broadened. While the cerium oxide
particles are obtained by the heat treatment, the cerium oxide
particles with higher purity are obtained if unreacted materials
are removed by washing with water. Therefore, the cerium oxide
particles are preferably washed with water in the final step for
use as an abrasive.
[0065] The cerium oxide particles obtained are particles having an
average particle size of 10 nm to 200 nm and each having a plate
shape and thus the optimal particles for use in the fixed abrasive
grinding/polishing tool.
[0066] In an embodiment of the invention, the cerium oxide
particles have a narrow particle size distribution. Preferably, 50%
of the particles have an average particle size which is within
.+-.50% of the mean average particle size. More preferably, 60% of
the particles have an average particle size which is within .+-.50%
of the mean average particle size. Most preferably, 70% of the
particles have an average particle size which is within .+-.50% of
the mean average particle size.
[0067] In the X-ray diffraction of the cerium oxide particles
according to the present invention, peaks corresponding to the
crystalline structure of CeO.sub.2 having the CaF.sub.2 (fluorite)
structure are clearly observed. Furthermore, crystal boundaries are
clearly observed with an electron microscope, which means that the
particles are plate-form particles having an extremely good
crystallinity, which has never been obtained according to the
conventional method.
[0068] The above description relates to the preparation of the
plate-form cerium oxide particles. However, plate-form particles of
aluminum oxide, zirconium oxide and iron oxide can also be prepared
by a method analogous to the above-described method (see
JP-A-2003-049158 and JP-A-2003-206475).
[0069] Preparation of Dispersion for Fixed Abrasive
Grinding/Polishing Tool:
[0070] Hereinafter, one example of the preparing method of a
dispersion for fabricating a fixed abrasive grinding/polishing tool
will be explained using the cerium oxide particles prepared by the
above method according to the present invention.
[0071] Sodium alginate is dissolved in a prescribed amount of
water. The amount of sodium alginate is preferably from 0.1 to 2%
by weight based on the amount of water. When the amount of sodium
alginate is less than 0.1% by weight, it is difficult to disperse
cerium oxide particles uniformly in water and the cerium oxide
particles easily settle. When the amount of sodium alginate exceeds
2% by weight, the viscosity increases, and the dispersibility of
the cerium oxide particle worsens.
[0072] Then, the cerium oxide particles are added to and dispersed
in the aqueous solution of sodium alginate. The amount of cerium
oxide particles to be added is preferably from 1 to 20% by weight
based on the prescribed amount of water. When the amount of the
cerium oxide particles is less than 1% by weight, a high grinding
efficiency as the fixed abrasive grinding/polishing tool may hardly
be obtained. When the amount of the cerium oxide particles exceeds
20% by weight, the cerium oxide particles are hardly be dispersed
uniformly and thus a uniform dispersion may not be obtained.
[0073] No specific limitation is placed on a dispersing method, and
various dispersing apparatuses such as a ball mill, a paint
conditioner, a disper and the like can be used. Among them, a paint
conditioner is preferable. A dispersing time may depend on a
dispersing machine. For example, when a paint conditioner is used,
a dispersion time is preferably from 1 to 10 hours.
[0074] Then, the dispersion in a container is placed on a hot plate
and heated while stirring to evaporate water and to concentrate the
dispersion. A weight after the evaporation and concentration is
preferably from a half to one tenth of the weight of the dispersion
prior to the evaporation of water. When the concentration is less
than the range, the filling property of the cerium oxide particles
may be low in the fabrication of an intermediate product using an
electrophoresis phenomenon described later or the cerium oxide
particles in the dispersion tend to settle. When the concentration
exceeds the range, the transfer of the cerium oxide particles by
the electrophoresis phenomenon is difficult, and thus the
productivity of the intermediate product decreases.
[0075] When the contents of sodium alginate and cerium oxide
particles in the dispersion after evaporation and concentration are
adjusted in a range of from 0.2 to 5% by weight and of 2 to 60% by
weight, respectively, based on the total weight of the dispersion,
the efficiency in the production of the intermediate product using
the electrophoresis phenomenon is greatly increased, and the fixed
abrasive grinding/polishing tool fabricated using the intermediate
product has the excellent balance between the grinding ability and
the retention of the cerium oxide particles in the tools.
[0076] Fabrication of Intermediate Product from Cerium Oxide and
Water-Soluble Polymer Mixture Using Electrophoresis:
[0077] The dispersion obtained by evaporation and concentration as
described above is charged in a glass beaker. A metal positive
electrode rod is inserted in the dispersion, and a metal negative
electrode is positioned so that it spirally surrounds the positive
electrode. A direct-current voltage is applied between the
electrodes while rotating the positive electrode rod. The applied
voltage differs according to the sizes and shapes of the electrodes
and a distance between the electrodes. Preferably, the voltage is
from 1 to 20 V. An electric current is usually from about 0.1 to 3
A. In this step, the cerium oxide particles covered with the
water-soluble polymer are electrically attracted to the positive
electrode rod and deposited thereon, and the thickness of the layer
of deposited particles increases as time passes.
[0078] Fabrication of Fixed Abrasive Grinding/Polishing Tool:
[0079] The cerium oxide particles covered with the water-soluble
polymer are deposited to a proper thickness according to the
above-described method. Thereafter, the positive electrode rod is
pulled out from the dispersion, the positive electrode rod is then
removed from the cylindrical deposit of the cerium oxide particles,
and the deposit is cut at a proper length. The cut piece is dried
at room temperature in the air. Then, the dried piece is polished
to smoothen its outer surface to finally finish the dried piece
into a desired tool.
EXAMPLES
[0080] Hereinafter, the present invention will be illustrated by
the following examples, which do not limit the scope of the
invention in any way.
Example 1
[0081] Preparation of Plate-Form Cerium Oxide Particles:
[0082] In 800 ml of water, 0.90 mole of sodium hydroxide was
dissolved to prepare an alkali aqueous solution. Separately, 0.074
mole of cerium chloride (III) heptahydrate was dissolved in 400 ml
of water to prepare the aqueous solution of cerium chloride. The
latter solution of cerium chloride was drop wise added to the
former alkali aqueous solution at about 25.degree. C. to prepare
precipitates containing cerium hydroxide. The pH value of the
mixture at this time was 10.5. The precipitate was aged for 20
hours in the state of a suspension.
[0083] Then, the supernatant liquid was removed and thereafter, the
suspension of the precipitate was placed in an autoclave and
subjected to a hydrothermal treatment at 180.degree. C. for 2
hours.
[0084] The product from the hydrothermal treatment was washed with
water, filtered and dried at 90.degree. C. in the air. The dried
product was slightly crushed with a mortar and then heat treated at
600.degree. C. for 1 hour in the air to obtain cerium oxide
particles. After the heat treatment, the particles were washed with
water using a supersonic wave dispersing apparatus to remove the
unreacted products and residues, followed by filtration and
drying.
[0085] The X-ray diffraction of the obtained cerium oxide particles
was measured and the obtained spectrum corresponded to that of
cerium oxide having the fluorite structure.
[0086] The shapes of the particles were observed with a
transmission electron microscope (a field emission electron
microscope HF-200 of Hitachi Ltd.) at a magnification of
2.times.10.sup.5, and it was found that each particle had a plate
shape and the particles had an average particle size of 21 nm.
Here, an average particle size was obtained by taking a
transmission electron microphotograph of 100 particles, measuring
the maximum particle size of each particle and then averaging the
measured particle sizes of 100 particles.
[0087] The ratio of the maximum length in the in-plane direction of
the plate-form particles to the thickness thereof was about 5. This
ratio was obtained by observing the section with the same electron
microscope as used above at a magnification of
5.times.10.sup.6.
[0088] FIG. 1 shows the photograph of the cerium oxide particles of
this Example taken with a transmission electron microscope at a
magnification of 2.times.10.sup.5 and FIG. 2 shows the X-ray
diffraction pattern of the cerium oxide particles of this
Example.
[0089] (Preparation of Dispersion Using Plate-Form Cerium Oxide
Particles and Water-Soluble Polymer)
[0090] In 560 g of water, 3 g of sodium alginate as a water-soluble
polymer was dissolved. To the solution, 37 g of the plate-form
cerium particles (abrasive grains) prepared in the previous step
were added, and the mixture was dispersed for 2 hours using a paint
conditioner. Further, 200 g of zirconia beads each having a
diameter of 1 mm as a dispersion medium was added to the pot for
the paint conditioner. With the dispersing treatment applied, the
individual cerium oxide particles were dispersed in the aqueous
solution of sodium alginate to obtain a uniform dispersion.
[0091] Then, the dispersion was taken out from the pot, 300 g of
the dispersion was charged in a 500 cm.sup.3 glass beaker, and
water was evaporated from the dispersion while stirring on a hot
plate until the total weight of the content in the pot decreased to
75 g.
[0092] Fabrication of Intermediate Product From Plate-Form Cerium
Oxide Particles and Water-Soluble Polymer Using
Electrophoresis:
[0093] The concentrated dispersion from the previous step was
transferred into a 100 cm.sup.3 glass beaker and a positive
electrode rode and a negative electrode were set therein. The
positive electrode rod was a brass rod having a diameter of 4 mm
and a length of 10 cm. The negative electrode was a spirally shaped
brass rod and disposed along the inner wall of the beaker.
[0094] A voltage of 10 V was applied between the positive electrode
and the negative electrode using a direct current power supply with
a low voltage. A current flowing between the electrodes was from
about 0.7 to 0.1 A. In this state, the positive electrode rod was
rotated and the direct-current voltage was applied for 30 minutes
to deposit the cerium oxide particles each having a plate shape
covered by sodium alginate on the outer surface of the positive
electrode rod. The thickness of the layer of deposit particles was
about 4 mm and the diameter thereof was about 12 mm.
[0095] Fabrication of Fixed Abrasive Grinding/Polishing Tool:
[0096] The positive electrode rod was pulled out from the deposit
prepared in the previous step, and the hollow cylindrical deposit
was cut with a disposable blade so that a height of the cut piece
was about 1 cm. The cylindrical intermediate product was dried at
room temperature in the air for about one day. The intermediate
product shrank due to drying to obtain a cylindrical product having
a diameter of about 8 mm and a height of about 7 mm, which
consisted of the plate-form cerium particles bound with sodium
alginate. The circumferential surface and end surfaces were
smoothed using a polishing tape to complete a fixed abrasive
grinding/polishing tool.
Example 2
[0097] A precipitate containing cerium hydroxide was produced in
the same way as that in Example 1 except that, in preparation of
plate-form cerium particles in Example 1, conditions for a
hydrothermal treatment of the suspension of the precipitate were
changed to 200.degree. C. and 2 hours from 180.degree. C. and 2
hours and conditions for heat treatment in the air were changed to
800.degree. C. and 1 hour from 600.degree. C. and 1 hour, and then
washing with water, filtration and drying followed and further, a
heat treatment followed to prepare cerium oxide particles.
[0098] The obtained cerium oxide particles were measured on X-ray
diffraction pattern to observe a spectrum corresponding to cerium
oxide having the fluorite structure, similar to that in Example 1.
Observation on shapes with a transmission electron microscope was
conducted with findings that the particles were of an average
particle size of 58 nm each having a plate shape. FIG. 3 shows a
transmission electron microphotograph of cerium oxide particles at
a magnification of 2.times.10.sup.5. A ratio of the maximum length
the in-plane direction of a plate-form particle to a thickness
thereof was about 8.
[0099] A dispersion was prepared using the cerium oxide particles
and a water-soluble polymer in the same method as that adopted in
Example 1 and an intermediate product was produced from the
plate-form cerium oxide particles and the water-soluble polymer
using electrophoresis, from which a fixed abrasive
grinding/polishing tool was fabricated.
Example 3
[0100] A dispersion was prepared and concentrated in the same way
as that adopted in Example 1 except that in preparation of the
dispersion using the plate-form cerium oxide particles having an
average particle size of 21 nm and the water-soluble polymer in
Example 1, the amount of sodium alginate added as a water-soluble
polymer into 560 g of water was changed to 1.5 g from 3 g. An
intermediate product was prepared from the mixture of plate-form
cerium oxide particles and the water-soluble polymer under the same
conditions as in Example 1 to complete a fixed abrasive
grinding/polishing tool.
Example 4
[0101] A dispersion was prepared and concentrated in the same way
as that adopted in Example 1 except that in preparation of the
dispersion using the plate-form cerium oxide particles having an
average particle size of 21 nm and the water-soluble polymer in
Example 1, the amount of sodium alginate added as a water-soluble
polymer into 560 g of water was changed to 4.5 g from 3 g. An
intermediate product was prepared from the mixture of plate-form
cerium oxide particles and the water-soluble polymer under the same
conditions as in Example 1 to complete a fixed abrasive
grinding/polishing tool.
Example 5
[0102] A dispersion was prepared and concentrated in the same way
as that adopted in Example 1 except that in preparation of the
dispersion using the plate-form cerium oxide particles having an
average particle size of 21 nm and the water-soluble polymer in
Example 1, the amount of cerium oxide particles added into 560 g of
water was changed to 18.5 g from 3.7 g. An intermediate product was
prepared from the mixture of plate-form cerium oxide particles and
the water-soluble polymer under the same conditions as in Example 1
to complete a fixed abrasive grinding/polishing tool.
Example 6
[0103] A dispersion was prepared and concentrated in the same way
as that adopted in Example 2 except that in preparation of the
dispersion using the plate-form cerium oxide particles having an
average particle size of 58 nm and the water-soluble polymer in
Example 2, an amount of sodium alginate added as a water-soluble
polymer into 560 g of water was changed to 4.5 g from 3 g. An
intermediate product was prepared from a mixture of plate-form
cerium oxide particles and a water-soluble polymer under the same
conditions as in Example 2 to complete a fixed abrasive
grinding/polishing tool.
Example 7
[0104] In preparation of the dispersion using the plate-form cerium
oxide particles and the water-soluble polymer in Example 1, 3 g of
sodium alginate as a water-soluble polymer was dissolved into 560 g
of water. Then, to the solution, were added 29.6 g of the cerium
oxide particle prepared in Example 2 having an average particle
size of 58 nm and 7.4 g of plate-form aluminum oxide
(.gamma.-alumina) having an average particle size of 80 nm and a
ratio of the maximum length in the in-plane direction of a
plate-form particle was about 10.
[0105] The plate-form aluminum oxide particles were produced as
follows:
[0106] In 800 ml of water, 0.75 mole of sodium hydroxide was
dissolved to prepare an aqueous alkaline solution. Separately,
0.074 mole of aluminum (III) chloride heptahydrate was dissolved in
400 ml of water.
[0107] To the aqueous alkaline solution, the aqueous solution of
aluminum chloride was drop wise added to form a precipitate
containing aluminum hydroxide, and the pH of the suspension
containing the precipitate was adjusted to 10.2 by the drop wise
addition of hydrochloric acid. The suspension containing the
precipitate was aged for 20 hours, and then washed with water in an
amount of about 1,000 times volume of the suspension.
[0108] Thereafter, the supernatant was discarded and the pH of the
suspension containing the precipitate was adjusted to 10.0 with an
aqueous solution of sodium hydroxide. Then, the suspension was
placed in an autoclave and subjected to the hydrothermal treatment
at 200.degree. C. for 2 hours. After that, the hydrothermal product
was recovered by filtration and dried in an air at 90.degree. C.,
slightly comminuted with a mortar and heated in the air at
600.degree. C. for 1 hour to obtain plate-form aluminum oxide
particles.
[0109] A dispersion and a fixed abrasive grinding/polishing tool
were fabricated in the same methods as those adopted in Example
1.
Example 8
[0110] A dispersion and a fixed abrasive grinding/polishing tool
were fabricated in same ways as those adopted in Example 7 except
that 7.4 g of plate-form zirconium oxide particles having an
average diameter of 20 nm and a ratio of the maximum length in the
in-plane direction of a plate-form particle to a thickness thereof
of about 3 was added in place of the addition of 7.4 g of
plate-form aluminum oxide particles having an average particle size
of 80 nm.
[0111] The plate-form zirconium oxide particles were produced as
follows:
[0112] In 800 ml of water, 0.75 mole of sodium hydroxide was
dissolved to prepare an aqueous alkaline solution. Separately,
0.074 mole of zirconium (IV) chloride was dissolved in 400 ml of
water.
[0113] To the aqueous alkaline solution, the aqueous solution of
zirconium chloride was drop wise added to form a precipitate
containing aluminum hydroxide. The pH of the suspension containing
the precipitate was 10.8. The suspension containing the precipitate
was aged for 20 hours, and then washed with water until the pH
reduced to 7.8.
[0114] Thereafter, the supernatant was discarded and the suspension
was placed in an autoclave and subjected to the hydrothermal
treatment at 200.degree. C. for 2 hours. After that, the
hydrothermal product was recovered by filtration and dried in an
air at 90.degree. C., slightly comminuted with a mortar and heated
in the air at 600.degree. C. for 1 hour to obtain plate-form
zirconium oxide particles.
Example 9
[0115] A dispersion and a fixed abrasive grinding/polishing tool
were fabricated in same ways as those adopted in Example 7 except
that 7.4 g of plate-form iron oxide particles having an average
diameter of 50 nm and a ratio of the maximum length in the in-plane
direction of a plate-form particle to a thickness thereof of about
5 was added in place of the addition of 7.4 g of plate-form
aluminum oxide particles having an average particle size of 80
nm.
[0116] The plate-form iron oxide particles were produced as
follows:
[0117] In 800 ml of water, 0.75 mole of sodium hydroxide and 100 ml
of 2-aminoethanol were dissolved to prepare an aqueous alkaline
solution. Separately, 0.074 mole of ferric chloride hexahydrate was
dissolved in 400 ml of water.
[0118] The aqueous alkaline solution and the aqueous solution of
the ferric chloride were maintained at 15.degree. C., and the
aqueous solution of ferric chloride was drop wise added to the
aqueous alkaline solution to form a precipitate containing ferric
hydroxide. The suspension containing the precipitate was aged for
20 hours, and then washed with water in an amount of about 1,000
times volume of the suspension.
[0119] Thereafter, the supernatant was discarded and the pH of the
suspension was adjusted to 11.3 with an aqueous solution of sodium
hydroxide. The suspension was then placed in an autoclave and
subjected to the hydrothermal treatment at 200.degree. C. for 2
hours to obtain plate-form goethite (.alpha.-FeOOH). The goethite
was recovered by filtration and dried in an air at 90.degree. C.,
slightly comminuted with a mortar and heated in the air at
600.degree. C. for 1 hour to obtain plate-form .alpha.-iron oxide
particles.
Example 10
[0120] A precipitate containing cerium hydroxide was produced in
the same way as that adopted in Example 1, washing with water,
filtration and drying were applied, thereafter a heat treatment
followed to prepare cerium oxide particles, except that conditions
for the heat treatment in the air were changed to 300.degree. C.
and 1 hour from 600.degree. C. and 1 hour without conducting the
hydrothermal treatment on the suspension of precipitate. The
obtained cerium oxide particles were measured on an X-ray
diffraction pattern to observe a spectrum corresponding to cerium
oxide particles having the fluorite structure, similar to that in
Example 1. The shapes of the particles were observed with a
transmission electron microscope with the result that the shapes
are spherical or of other particulate shapes and an average
particle size was 30 nm.
[0121] A dispersion using the cerium oxide particles and a
water-soluble polymer was prepared in the same method as that
adopted in Example 1 and an intermediate product was obtained from
the mixture of spherical or other particulate shaped cerium oxide
particles and a water-soluble polymer with electrophoresis to
produce a fixed abrasive grinding/polishing tool.
Comparative Example 1
[0122] Three grams of sodium alginate as a water-soluble polymer
was dissolved in 260 g of water. To the solution, was added 37 g of
commercially available diamond abrasive particles (an average
particle size of 0.1 .mu.m shown in a catalogue) and the particles
were dispersed while stirring for 1 hour. The dispersion was placed
on a hot plate to evaporate off water till stirring is
impossible.
[0123] The concentrated mixture was shaped into a cylinder and the
cylinder was dried at room temperature in the same way as that
adopted in Example 1 and the intermediate product was smoothed on
the cylindrical surface and both end surfaces with a polishing tape
or the like to complete a fixed abrasive grinding/polishing tool.
That is, in Comparative Example 1, the diamond particles were used
as abrasive particles and fixed with a water-soluble polymer to
fabricate the tool.
Comparative Example 2
[0124] Three grams of sodium alginate as a water-soluble polymer
was dissolved into 260 g of water. To the solution, was added 37 g
of commercially available .alpha.-alumina abrasive grains (an
average particle size of 0.2 .mu.m shown in a catalogue) and the
particles were dispersed while stirring for 1 hour. The dispersion
was placed on a hot plate to evaporate off water till stirring is
impossible.
[0125] The concentrated mixture was worked into a cylinder and the
cylinder was dried at room temperature in the same way as that
adopted in Example 1 and the intermediate product was smoothed on
the cylindrical surface and both end surfaces with a polishing tape
or the like to complete a fixed abrasive grinding/polishing tool.
That is, in Comparative Example 2, the .alpha.-alumina abrasive
grains were used as abrasive particles and fixed with a
water-soluble polymer to fabricate the tool.
[0126] Evaluation of Grinding Ability
[0127] To evaluate the grinding performances of the fixed abrasive
grinding/polishing tools produced in the Examples and Comparative
Examples described above, a workpiece was actually ground using
each fabricated tool to evaluate the grinding ability thereof The
evaluation of the grinding ability was conducted on a silicon wafer
of 4 inch (about 10.16 mm) in diameter as a workpiece. An apparatus
examining the grinding ability was a fiber polisher (SFP-120A
manufactured by Seiko Giken Co., Ltd.). In grinding, four tools
fabricated according to the above described method were fixed along
the inner peripheral wall with a diameter of about 5 cm of a
circular metal surface plate (the upper surface plate) of about 18
cm in diameter in the fiber polisher at equal intervals between
adjacent tools using an adhesive. On the other hand, a silicon
wafer was fixed on the lower surface plate of about 12 cm in
diameter and the upper surface plate on which the tools were fixed
were placed on the silicon wafer to thereby press the tools, that
is, grinding stones, to the surface of the silicon wafer by the
weight of the upper surface plate itself. Then, the upper surface
plate was fixed and the lower surface plate was rotated at 75 rpm
to grind the surface of the silicon wafer fixed on the lower
surface plate.
[0128] A grinding efficiency was evaluated in a way such that a
rhombic indent was formed on the surface of the silicon wafer with
a Knoop hardness meter (with a model number of HM-122) manufactured
by Akashi K.K. and a reduction in depth of the indent, that is a
grinding depth, was measured as grinding progresses for
evaluation.
[0129] A surface smoothness after grinding was measured on a
surface roughness Ra (center line average height) of the silicon
wafer using a non-contact surface roughness meter (New View 5000
manufactured by Zygo Corp.) and the surface smoothness was
evaluated with the measured Ra.
[0130] Table 1 shows the kinds, average particle sizes and amounts
of abrasive grains, and the contents of abrasive grains and of the
water-soluble polymer in the grinding stones and in Table 2, there
is shown evaluation the results of grinding conducted using the
fixed abrasive grinding/polishing tools obtained in the Examples
and Comparative Examples. Grinding depths and Ra values on the
ground surfaces shown in Table 2 were measured when grinding was
conducted for 30 minutes. The larger the grinding depth, the higher
the grinding efficiency, while the smaller the Ra value, the better
surface smoothness.
1TABLE 1 Content of Amount abrasive of grains in Contents of
abrasive grinding water-soluble Kind of abrasive grains grains
stones polymer Ex. No. (av. particle sizes) (wt. %) (wt. %) (wt. %)
Ex. 1 Plate-form cerium oxide 100 92.5 7.5 (21 nm) Ex. 2 Plate-form
cerium oxide 100 92.5 7.5 (58 nm) Ex. 3 Plate-form cerium oxide 100
96.1 3.9 (21 nm) Ex. 4 Plate-form cerium oxide 100 89.2 10.8 (21
nm) Ex. 5 Plate-form cerium oxide 100 86.0 14.0 (21 nm) Ex. 6
Plate-form cerium oxide 100 89.2 10.8 (58 nm) Ex. 7 Plate-form
cerium oxide 80/20 92.5 7.5 (58 nm)/plate-form aluminum oxide (80
nm) Ex. 8 Plate-form cerium oxide 80/20 92.5 7.5 (58 nm)/plate-form
zirconium oxide (20 nm) Ex. 9 Plate-form cerium oxide 80/20 92.5
7.5 (58 nm)/plate-form iron oxide (50 nm) Ex. 10
Spherical-particulate 100 92.5 7.5 shaped cerium oxide (30 nm)
Comp. Diamond particles 100 92.5 7.5 Ex. 1 (0.1 .mu.m) Comp.
Particulate shaped 100 92.5 7.5 Ex. 2 .alpha.-alumina (0.2
.mu.m)
[0131]
2TABLE 2 Grinding efficiency Surface smoothness Ra (grinding depth,
.mu.m) (nm) Example 1 0.14 0.8 Example 2 0.22 2.1 Example 3 0.18
1.5 Example 4 0.14 0.9 Example 5 0.12 0.8 Example 6 0.20 1.8
Example 7 0.18 2.8 Example 8 0.21 3.1 Example 9 0.16 2.0 Example 10
0.10 1.8 Comparative Example 1 0.35 >100 Comparative Example 2
0.02 3.6
[0132] As is clear from Table 2, it is seen that the fixed abrasive
grinding/polishing tools comprising the plate-form cerium oxide
particles obtained in Examples 1 to 5 are grinding stones having
good balance between the grinding efficiency and the surface
smoothness after grinding. The abrasive grains exhibit an excellent
grinding efficiency despite the fact that the abrasive grains are
fine in size based on the synergistic effect of the excellent
mechanical grinding ability using the particle edges due to the
plate-form shape of each of cerium oxide particles as abrasive
grains and the inherent chemical grinding ability owned by cerium
oxide particles. The excellent surface smoothness is achieved by
the action of cerium oxide particles that are extremely fine
particles having an average particle size of 20 nm to 60 nm.
[0133] The fixed abrasive grinding/polishing tools of Examples 7 to
9 used as the stones contained the plate-form cerium oxide
particles as the main constituent particles, and in addition
thereto, the plate-form aluminum oxide particles, plate-form
zirconium oxide particles and plate-form iron oxide particles. The
tools are inferior to a grinding stone using only plate-form cerium
oxide particles in surface smoothness, which is because silicon
wafers were used as workpieces. It was confirmed that the tools of
the Examples exhibit an excellent grinding performance according to
the kind of a workpiece to be ground or polished, or conditions for
grinding. Therefore, the construction of a grinding stone according
to the present invention can be preferably selected according to
purposes or applications. While the evaluation results in the
Examples were investigated about the grinding ability as the
grinding stone, it is also possible to grind in the presence of
water added. The conditions for grinding can be arbitrarily set:
such as those for dry grinding, grinding in the presence of water
or a grinding at high temperature and humidity.
[0134] Although the fixed abrasive grinding/polishing tool of
Example 10 using the cerium oxide particles having other
particulate shapes is slightly inferior to the tool using the
plate-form cerium oxide particles in the grinding ability, the tool
exhibits an excellent grinding ability in comparison with the tools
using the conventional kinds of abrasive grains shown in
Comparative Examples 1 and 2.
[0135] On the other hand, although the fixed abrasive
grinding/polishing tool of Comparative Example 1 using the diamond
abrasive grains is high in the grinding ability reflecting the high
hardness of the diamond particles, grinding marks are clearly left
after grinding, rendering the surface smoothness extremely
poor.
[0136] Although the fixed abrasive grinding/polishing tool of
Comparative Example 2 using the .alpha.-alumina particles is
relatively good in surface smoothness, the grinding efficiency is
very low. This is because the .alpha.-alumina particles lack an
inherent chemical grinding ability while they have a comparatively
high hardness.
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