U.S. patent application number 11/946694 was filed with the patent office on 2008-06-19 for non-magnetic plate-form particles, method for producing the same, and abrasive, abrasive member and abrasive liquid comprising the same.
Invention is credited to Kimihiko Kaneno, Nobuko Kasajima, Mikio Kishimoto, Yasumori Maeda, Yuko Sawaki.
Application Number | 20080141594 11/946694 |
Document ID | / |
Family ID | 39525454 |
Filed Date | 2008-06-19 |
United States Patent
Application |
20080141594 |
Kind Code |
A1 |
Kishimoto; Mikio ; et
al. |
June 19, 2008 |
NON-MAGNETIC PLATE-FORM PARTICLES, METHOD FOR PRODUCING THE SAME,
AND ABRASIVE, ABRASIVE MEMBER AND ABRASIVE LIQUID COMPRISING THE
SAME
Abstract
An aqueous solution of a metal salt to an alkaline aqueous
solution to forma hydroxide or a hydrate of a metal, and the
hydroxide or hydrate of the metal is heated at a temperature of 110
to 300.degree. C. in the presence of water. Then, the hydroxide or
hydrate of the metal is filtered and dried and then further heated
at a temperature of 300 to 1200.degree. C. in an air to form oxide
particles such as the particles of cerium oxide, zirconium oxide,
aluminum oxide silicon oxide, iron oxide, etc. Thereby the
particles of cerium oxide, zirconium oxide, aluminum oxide silicon
oxide, iron oxide, etc. having a plate-form shape and a particle
size of from 10 nm to 100 nm in the plate direction of the particle
are obtained. The non-magnetic particles, in particular, plate-form
oxide particles of the present invention have a uniform particle
size distribution, are less sintered or agglomerated, and have good
crystallinity.
Inventors: |
Kishimoto; Mikio;
(Moriya-shi, JP) ; Kasajima; Nobuko;
(Nagaokakyo-shi, JP) ; Sawaki; Yuko; (Otokuni-gun,
JP) ; Kaneno; Kimihiko; (Nagaokakyo-shi, JP) ;
Maeda; Yasumori; (Osaka, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
39525454 |
Appl. No.: |
11/946694 |
Filed: |
November 28, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10490630 |
Mar 25, 2004 |
|
|
|
PCT/JP02/08171 |
Aug 9, 2002 |
|
|
|
11946694 |
|
|
|
|
Current U.S.
Class: |
51/309 |
Current CPC
Class: |
B24D 3/00 20130101; C09K
3/1409 20130101 |
Class at
Publication: |
51/309 |
International
Class: |
B24D 3/02 20060101
B24D003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 28, 2001 |
JP |
P2001-300632 |
Oct 1, 2001 |
JP |
P2001-305138 |
Claims
1. An abrasive member comprising a support and an abrasive layer
which is formed on said support and which comprises a binder and an
abrasive dispersed in the binder, wherein said abrasive comprises
non-magnetic plate-form particles wherein a particle has a
plate-form shape, and a particle size is from 10 nm to 100 nm in
the plate direction of the particle.
2. The abrasive member according to claim 1, wherein the
non-magnetic plate-form particles are oxide particles.
3. The abrasive member according to claim 2, wherein said oxide
particles are at least one kind of oxide particles selected from
the group consisting of cerium oxide particles, zirconium oxide
particles, aluminum oxide particles, silicon oxide particles and
iron oxide particles.
4. The abrasive member according to claim 2, wherein said oxide
particles are at least one kind of oxide particles selected from
the group consisting of cerium oxide particles, zirconium oxide
particles, aluminum oxide particles and silicon oxide
particles.
5. The abrasive member according to claim 2, wherein said oxide
particles are iron oxide particles at least 50% of which have pores
in the thickness direction of the particles.
6. The abrasive member according to claim 1, wherein the plate-form
shape of the particle is a polygon.
7. The abrasive member according to claim 6, wherein the plate-form
shape of the particle is a hexagon.
8. The abrasive member according to claim 6, wherein the plate-form
shape of the particle is a rectangle.
9. The abrasive member according to claim 6, wherein the plate-form
shape of the particle is a disc or an elliptic plate.
Description
[0001] This application is a Divisional of co-pending application
Ser. No. 10/490,630 filed on Mar. 25, 2004 and for which priority
is claimed under 35 U.S.C. .sctn. 120. Application Ser. No.
10/490,630 is the national phase of PCT International Application
No. PCT/JP02/08171 filed on Aug. 9, 2002 under 35 U.S.C. .sctn.
371. The entire contents of each of the above-identified
applications are hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to non-magnetic plate-form
particles having a novel particle shape, which are useful as an
abrasive for an abrasive member or an abrasive liquid, as an
additive to coating type recording media, or as an additive to
functional films such as optical films, and a method for producing
such non-magnetic plate-form particles and the applications
thereof. In particular, the present invention relates to
non-magnetic particles of cerium oxide, zirconium oxide, aluminum
oxide, silicon oxide, iron oxide, etc., which have a novel particle
shape and a specific particle size.
BACKGROUND ART
[0003] Non-magnetic particles such as cerium oxide particles,
zirconium oxide particles, aluminum oxide particles, silicon oxide
particles, iron oxide particles, etc. are used in a wide variety of
applications, for example, as abrasives of abrasive members such as
abrasive sheets, abrasive films, abrasive tapes, abrasive tools,
etc., or abrasive liquids, as additives to various coating type
recording media, and the like.
[0004] Cerium oxide, zirconium oxide, aluminum oxide and silicon
oxide are preferably used in applications which require high
abrading rates, since they have high Mohs' hardness, while iron
oxide is preferably used in applications which require mild
abrasion.
[0005] For producing such non-magnetic oxide particles, various
methods are known.
[0006] (1) Cerium Oxide
[0007] Cerium oxide particles are usually prepared by milling
cerium oxide, which is produced sintering, with a ball mill, etc.
to obtain fine particles. However, the cerium oxide particles
prepared by such a method has abroad particle size distribution. In
addition, since the particles are mechanically ground, the lower
limit of the particle size is in a submicron order and it is
difficult to further decrease the particle size.
[0008] Apart from the above method, it is also known that a cerium
salt such as cerium carbonate is thermally oxidized in an air to
obtain cerium oxide particles. This method has an advantage over
the milling method in that the finer particle scan be easily
obtained. However, the particles tend to be sintered together, and
thus it is difficult to uniformly disperse the particles in a
liquid medium when they are used in an abrasive liquid.
[0009] For example, JP-A-10-106990 and JP-A-11-181405 heat cerium
carbonate in an air to obtain cerium oxide, and then mechanically
mill cerium oxide to obtain fine particles. In the former patent
application, JP-A-10-106990, cerium oxide is milled with a ball
mill, and the resulting particles have a primary particle size of
200 nm. The particle shape of cerium oxide prior to ball milling is
spherical. According to the latter patent application
JP-A-11-181405, after sintering, the cerium oxide particles are jet
milled to decrease the particle size. However, the resulting cerium
oxide particles contain unmilled particles having a large particle
size of 1 to 3 .mu.m and 0.5 to 1 .mu.m besides small particles
having a particle size corresponding to a primary particle
size.
[0010] JP-A-9-27402 discloses a method for preparing cerium oxide
particles comprising ball milling cerium carbonate as a raw
material and thermally treating the milled material in an air. As
described in this patent application, the cerium oxide particles
prepared by this method have a primary particle size of 20 nm but
contain secondary particles having a size of 0.2 to 0.3 .mu.m. The
particle shape is not described in detail. For example,
JP-A-10-102039 describes that an aspect ratio is from 1 to 2. A
particle having such an aspect ratio is close to a granule or a
particle rather than a plate.
[0011] As described above, since the conventional methods
essentially use mechanical grinding to decrease the particle sizes,
particles having a specific particle shape cannot be obtained, and
those having a narrow particle size distribution are hardly
obtained. Furthermore, since mechanical impact is applied to the
particles, the cerium oxide particles tend to be distorted so that
their crystallinity may be deteriorated. The crystallinity of
cerium oxide particles is very important when they are used as an
abrasive. Although the conventional cerium oxide particles may have
a spectrum assigned to cerium oxide in an X-ray diffraction
analysis, they are not satisfactory in their crystallinity as the
abrasive.
[0012] Usually, the cerium oxide particles tend to contain elements
other than cerium, which are contained in a raw material. That is,
it is difficult to obtain high purity cerium oxide. The purity of
cerium oxide is important, particularly when the cerium oxide
particles are used in the form of a chemical polishing liquid.
[0013] (2) Zirconium Oxide
[0014] Zirconium oxide particles are used as an abrasive of an
abrasive sheet, an abrasive liquid, etc., and the zirconium oxide
particles used as the abrasive are often produced by grinding a
zirconium oxide ingot to obtain fine particles. When the fine
particles are produced with mechanical means, the lower limit of
the size of the fine particles is limited. For example,
JP-A-8-113773 abrades the surface of a silicon plate with zirconium
oxide particles, which have a particle size of 7.0 .mu.m.
[0015] JP-A-2000-204353 discloses an aqueous dispersion comprising
a mixture of organic particles of silica, alumina or zirconia, and
polymer particles. The specification of this patent application
describes an average particle size of the inorganic particles in
the range of 0.12 to 0.8 .mu.m.
[0016] Hitherto, the zirconium oxide particles are not used as an
abrasive material by themselves, but rather they are used in
combination with other abrasive particles such as aluminum oxide
particles, silicon oxide particles, etc. This may be because the
conventional zirconium oxide particles do not have satisfactory
properties such as a particle size or a particle shape as an
abrasive.
[0017] (3) Aluminum Oxide
[0018] Aluminum oxide is widely used as an abrasive of an abrasive
sheet, an abrasive liquid, etc., and various methods are known as
the production method of aluminum oxide particles. In general,
aluminum oxide, which is prepared by sintering, is milled with a
ball mill, etc. to obtain fine particles. However, the aluminum
oxide particles produced by such a method have a broad particle
size distribution. In addition, since the particles are
mechanically ground, the lower limit of the particle size is in a
submicron order and it is difficult to further decrease the
particle size.
[0019] Alternatively, aluminum oxide particles can be produced by
precipitating aluminum hydroxide by a neutralization reaction and
thermally treating precipitated aluminum hydroxide. However, this
method can produce aluminum oxide particles having a small particle
size, but the particle shapes are irregular so that the resulting
particles do not have sufficient abrasion ability when used as an
abrasive. Furthermore, secondary particles tend to be formed by
agglomeration of particles. Thus, a large amount of energy and a
long time are required to disperse the particles in a liquid medium
particularly and obtain a homogeneous dispersion, when an abrasive
liquid is prepared. For example, JP-A-7-315833 discloses that
plate-form aluminum oxide, which is prepared by sintering, is
finely milled with a non-metallic medium for a long time to break
agglomeration. However, the fine particles have the lower limit of
a particle size and the obtained aluminum oxide particles have
inherently a broad particle size distribution, since this method
produces fine particles by milling.
[0020] The production of plate-form aluminum oxide using a
hydrothermal method has been known for a long time. For example,
JP-B-37-7750 and JP-B-39-13465 describe the production of
plate-form alumina. However, the particle size of plate-form
alumina obtained is from several microns to several hundred
microns, and such a method is unsatisfactory to obtain fine
particles.
[0021] Additionally, it is known to hydrothermally treating
aluminum hydroxide, the particle size of which has been adjusted in
a submicron order, in water or an alkaline aqueous medium at a high
temperature of 350.degree. C. or higher to obtain plate-form
aluminum oxide in the submicron order (see, for example,
JP-A-5-17132 and JP-A-6-316413). This method uses the hydrothermal
reaction which easily produces plate-form aluminum oxide having
good crystallinity to transform aluminum hydroxide to aluminum
oxide. Therefore, the reaction should be carried out at a high
temperature and a special reactor, which can withstand a high
pressure, should be used. Furthermore, since this method uses the
hydrothermal reaction, it is suitable for the production of
aluminum oxide particles having a large particle size in the
submicron order, but may be less suitable for the production of
aluminum oxide fine particles having a size of 100 nm or less.
[0022] The fine particles of aluminum oxide having a particle size
of 100 nm or less, good crystallinity and a narrow particle size
distribution has been sought for the provision of an abrasive for
an abrasive sheet or liquid for finishing, but aluminum oxide
particles satisfying such a requirement has not bee developed as
explained above.
[0023] (4) Silicon Oxide
[0024] Silicon oxide is also well known as an abrasive for an
abrasive sheet, an abrasive liquid, etc. For example, fumed silica
and colloidal silica are general products which are commercially
available from various producers. A huge number of patent
applications relating to abrasive sheets or abrasive liquids
comprising such silicon oxide particles have been filed.
[0025] For example, JP-A-8-336758 and JP-A-9-248771 relate to an
abrasive sheet comprising colloidal silica particles having a size
of several ten nanometers as an abrasive, and describe that such an
abrasive sheet is particularly useful for polishing the edge face
of an optical connector ferrule. JP-A-8-267356 describes that a
silicon wafer is polished using colloidal silica of 10 to 100 nm as
an abrasive. JP-A-7-221059 describes that a semiconductor wafer is
polished with colloidal silica having a specific shape.
Furthermore, JP-A-6-313164 describes that a colloidal silica slurry
comprising colloidal silica of several ten nanometers as an
abrasive is effective to abrade a metal surface.
[0026] As described above, it is well known that the silicon oxide
particles are useful as an abrasive, and the above patent
publications describe that a spherical particle shape or a particle
shape as close as possible to a spherical shape are effective.
[0027] On the other hand, the kinds of materials to be abraded or
polished has been increased year by year, and abrading
specifications required for such an increased number of materials
have been diversified. To satisfy such requirements for the various
abrading specifications, in the case of silicon oxide, the
composition and surface structure of an abrasive sheet or the
composition of an abrasive slurry has been improved rather than the
improvement of the particles. However, insofar as the silicon oxide
particles having a spherical shape and a particle size of several
ten namometers, the improvements have limits, and it is difficult
to cope with the abrasion in special applications.
[0028] (5) Iron Oxide
[0029] The inventors developed a novel iron oxide having a plate
shape and pores in the thickness direction of the plate-form
particles. Such a novel iron oxide are disclosed in JP-A-61-266311
and JP-A-61-266313, in which plate-form goethite particles are
heated, dehydrated and reduced to form porous plate-form magnetite
particles and then the magnetite particles are modified with
cobalt, and these patent applications propose the use of the
obtained iron oxide particles in magnetic recording.
[0030] JP-B-3-21489 describes annular oxide powder produced from
plate-form goethite particles, and proposes the use of such an
oxide as electric materials (e.g. magnetic powder, etc.), pigments
for reinforcing paints, reinforcing materials for composite
materials, medical materials, and soon. In this JP-B publication,
an aqueous solution of iron chloride is dropwise added to an
aqueous solution containing sodium hydroxide and an alkylamine to
precipitate iron hydroxide, which is aged, washed and subjected to
pH adjustment, followed by the hydrothermal treatment, to obtain
plate form plate-form goethite. When the plate-form goethite is
heated and dehydrated to obtain magnetic powder particles such as
hematite particles, magnetite particles, .gamma.-iron oxide
particles, etc., which have pores at their centers.
DISCLOSURE OF THE INVENTION
[0031] One object of the present invention is to provide
non-magnetic oxides having a specific particle size and a specific
particle shape, such as the particles of cerium oxide, zirconium
oxide, aluminum oxide, silicon oxide and iron oxide, which are
useful as abrasive particles for abrasive sheets, abrasive liquids
(slurry-form abrasives), etc., additives for coating type magnetic
recording media, and also additives for functional optical films,
as well as a method for producing such non-magnetic particles and
the use thereof.
[0032] To achieve the above object, extensive studies have been
made. As a result, a novel production method, which is entirely
different from conventional production methods of non-magnetic
oxide particles have been completed. Consequently, non-magnetic
particles having a plate-form shape and a particle size of 10 to
100 nm, for example, cerium oxide particles, zirconium oxide
particles, aluminum oxide particles, silicon oxide particles and
iron oxide particles have been developed.
[0033] That is, the plate-form on-magnetic particles of the present
invention is characterized in that the particle shape is plate-form
and the particle size is 11 nm to 110 nm. Such non-magnetic
particles include cerium oxide particles, zirconium oxide
particles, aluminum oxide particles, silicon oxide particles and
iron oxide particles having a plate-form shape and a particle size
of 10 to 100 nm.
[0034] According to the present invention, the oxide particles
cerium oxide particles, zirconium oxide particles, aluminum oxide
particles, silicon oxide particles and iron oxide particles having
the specific particle shape and the specific particle size can be
produced by adding an aqueous solution of a metal salt or a
non-metal salt to an alkaline aqueous solution to obtain a
hydroxide or hydrate of the metal or non-metal element, heating the
hydroxide or hydrate at a temperature of 110 to 300.degree. C. in
the presence of water, filtrating and drying the product and then
heating the product at a temperature of 300 to 1200.degree. C. in
an air.
[0035] Herein, the "metal salt or non-metal salt" or the "metal or
non-metal element" are used since cerium, zirconium, aluminum and
iron are metal elements while silicon may not be a metal element.
That is, the "non-metal element" primarily means silicon, and the
"non-metal salt" primarily means a salt comprising silicon, or a
silicon salt. Hereinafter, for simplicity, the "metal or non-metal
element" will be referred to as "metal", while the "metal salt or
non-metal salt" will be referred to as "metal salt".
[0036] Since the method of the present invention uses a high purity
metal salt such as a chloride or a nitrate of the metal, the
product contains substantially no element which has adverse effects
on the abrading properties of the product. In addition, chlorine
atoms or nitric acid contained in the raw materials do not
substantially remain in the finally obtained particles of cerium
oxide, zirconium oxide, aluminum oxide, silicon oxide and iron
oxide, since they are removed by dissipation with heating. Thus,
quite high purity non-magnetic oxide particles can be obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 is an X-ray diffraction spectrum of the cerium oxide
particles obtained in Example 1.
[0038] FIG. 2 is a transmission electron microscopic photograph of
the cerium oxide particles obtained in Example 1 (magnification:
200,000 times).
[0039] FIG. 3 is a transmission electron microscopic photograph of
the cerium oxide particles obtained in Example 2 (magnification:
200,000 times).
[0040] FIG. 4 is a transmission electron microscopic photograph of
the cerium oxide particles obtained in Example 3 (magnification:
200,000 times).
[0041] FIG. 5 is an X-ray diffraction spectrum of the zirconium
oxide particles obtained in Example 8.
[0042] FIG. 6 is a transmission electron microscopic photograph of
the zirconium oxide particles obtained in Example 8 (magnification:
200,000 times).
[0043] FIG. 7 is a transmission electron microscopic photograph of
the zirconium oxide particles obtained in Example 9 (magnification:
200,000 times).
[0044] FIG. 8 is an X-ray diffraction spectrum of the aluminum
oxide particles obtained in Example 15.
[0045] FIG. 9 is a transmission electron microscopic photograph of
the aluminum oxide particles obtained in Example 15 (magnification:
200,000 times).
[0046] FIG. 10 is an X-ray diffraction spectrum of the aluminum
oxide particles obtained in Example 16.
[0047] FIG. 11 is a transmission electron microscopic photograph of
the aluminum oxide particles obtained in Example 17 (magnification:
200,000 times).
[0048] FIG. 12 is a transmission electron microscopic photograph of
the aluminum oxide particles obtained in Example 18 (magnification:
200,000 times).
[0049] FIG. 13 is an X-ray diffraction spectrum of the aluminum
oxide particles obtained in Example 20.
[0050] FIG. 14 is a transmission electron microscopic photograph of
the aluminum oxide particles obtained in Example 20 (magnification:
200,000 times).
[0051] FIG. 15 is a transmission electron microscopic photograph of
the silicon oxide particles obtained in Example 22 (magnification:
200,000 times).
[0052] FIG. 16 is a transmission electron microscopic photograph of
the iron oxide particles obtained in Example 28 (magnification:
200,000 times).
[0053] FIG. 17 is a transmission electron microscopic photograph of
the iron oxide particles obtained in Example 29 (magnification:
200,000 times).
BEST EMBODIMENTS FOR CARRYING OUT THE INVENTION
[0054] According to the method of the present invention, in the
first step, an aqueous solution of a salt of cerium, zirconium,
aluminum, silicon or iron is added to an alkaline aqueous solution
to form a hydroxide or hydrate of the metal, and the hydroxide or
hydrate of the metal is heated at a temperature of 110 to
300.degree. C. in the presence of water. Thereby, the metal
hydroxide or metal hydrate particles having the desired particle
shape and the intended particle size are obtained. Then, in the
second step, the hydroxide or hydrate of the metal is heated in the
air to obtain the particles of cerium oxide, zirconium oxide,
aluminum oxide, silicon oxide or iron oxide, which have a uniform
particle size distribution and are rarely sintered or
agglomerated.
[0055] In the above method, when the hydroxide or hydrate of the
metal is optionally aged between the first and second steps, the
particles have the more-uniform particle size and better plate-form
shape.
[0056] The present invention successfully developed the particles
of cerium oxide, zirconium oxide, aluminum oxide, silicon oxide and
iron oxide having a plate-form shape and a particle size of 10 to
100 nm, which cannot be produced by the conventional methods, based
on the innovative idea that the step for adjusting the shape and
size of the particles (the first step) and the step for deriving
the inherent properties of the material to the maximum (the second
step) are separately carried out.
[0057] Herein, the term "plate-form" means that a ratio of the
maximum diameter to the thickness of the particle (plate ratio)
exceeds 1. The plate ratio preferably exceeds 2 and is up to 100,
more preferably from 3 to 50, particularly preferably from 5 to 30.
When the plate ratio is 2 or less, some particles may project above
the surface of the coated layer when the particles are used to
produce the abrasive sheet so that such particles may damage a
material to be abraded. When the plate ratio exceeds 100, the
particles may be broken during abrading so that debris tend to
damage the material to be abraded.
[0058] The particles of cerium oxide, zirconium oxide, aluminum
oxide, silicon oxide or iron oxide, which are produced by the
method described above, are characterized by that they rarely
sintered or agglomerated together, have a narrow particle size
distribution and a plate-form shape. Because of these
characteristics, the non-magnetic oxide particles of the present
invention have excellent properties, which cannot be possessed by
the conventional non-magnetic particles, when they are used as
abrasive particles of the abrasive sheet or abrasive liquid,
additives of various coating type magnetic recording media and also
additives of various optical films.
[0059] When the particles of cerium oxide, zirconium oxide,
aluminum oxide, silicon oxide or iron oxide according to the
present invention are used as an abrasive or an additive, they are
preferably crystalline. Although the conventional non-magnetic
particles may have a spectrum specific to the non-magnetic oxide
particles in an X-ray diffraction analysis or the like, they may
not have a sufficient crystallinity, and thus, they are not always
satisfactory when used as the abrasive or additive.
[0060] The cerium oxide particles can be used as an abrasive for
chemical polishing. In such an application, the purity of cerium
oxide is important, and high purity cerium oxide is required.
However, the cerium oxide particles produced by the conventional
method do not have a satisfactory purity. In contrast therewith,
the cerium oxide particles of the present invention have the
satisfactory purity. In this view point, the cerium oxide particles
of the present invention are suitable as an abrasive for chemical
polishing.
[0061] The present inventors have studied particle shapes which
exhibit good properties as abrasives. As a result, it has been
found that the edges of the plate-form particles effectively
contribute to the function as abrasive particles, when observed
with an electron microscope.
[0062] Accordingly, the present invention firstly succeeded in the
production of particles of cerium oxide, zirconium oxide, aluminum
oxide, silicon oxide or iron oxide, which have the specific
particle shape. The oxide particles produced according to the
present invention are used as abrasive particles highly suitable
for polishing semiconductors, optical fibers, lenses, etc. and also
used in a wide variety of applications, for example, as particulate
additives of coating type magnetic media, and further as
particulate additives of functional optical films by making use of
the specific particle shape.
[0063] The plate-form non-magnetic oxide particles of the present
invention can be roughly classified in to those having
substantially no pores such as the particles of cerium oxide,
zirconium oxide, aluminum oxide and silicon oxide, and those having
pores such as the iron oxide particles. The former particles having
substantially no pores are preferably used as additive particles of
the coating type magnetic recording media or the functional optical
films. In addition, the former particles are preferably used in
fields in which the coloring should be avoided for example, in the
functional films, since they are not colored. The "plate-form oxide
particles having substantially no pores" mean that, when 300
particles are observed, the number of oxide particles having pores
in the thickness direction of the plate is 10% or less.
[0064] In the method of the present invention, a compound
comprising cerium, zirconium, aluminum, silicon or iron as a raw
material is dissolved in water, and then drop wise added to an
alkaline aqueous solution to form the precipitate of the hydroxide
or hydrate of the above metal element. The alkaline aqueous
solution, which is used to form the precipitate, is not limited. A
hydroxyalkylamine is preferably added to the alkaline aqueous
solution, since the plate-form particles having a narrow particle
size distribution are easily obtained, when the hydroxyalkylamine
is added. The suspension containing the hydroxide or hydrate is
hydrothermally treated, for example, in an autoclave. Prior to the
hydrothermal treatment, the suspension may preferably aged, since
the oxide particles having good crystallinity and a narrow particle
size distribution can be easily obtained. After the hydrothermal
treatment, the particles are washed with water, filtrated and then
dried. The dried particles are further heated to obtain the
particles of cerium oxide, zirconium oxide, aluminum oxide, silicon
oxide or iron oxide.
[0065] The method for producing the non-magnetic plate-form
particles (oxide particles) and the use of the non-magnetic
plate-form particles produced by such a method will be explained in
detail.
[0066] Preparation of Precipitate:
[0067] The chloride, nitrate or sulfate of cerium, zirconium,
aluminum or iron, or sodium silicate is dissolved in water to form
an aqueous solution containing metal ions (aqueous solution of
metal salt). Separately, an alkaline aqueous solution is prepared.
As an alkali, sodium hydroxide, potassium hydroxide, lithium
hydroxide, or aqueous ammonia is preferably used. To the alkaline
aqueous solution, an alkylamine, which is a crystal growth
regulator, may be added, since particles having good plate-form
shape can be obtained. Examples of the alkylamine include
monoethanolamine, triethanolamine, isobutanolamine, propanolamine,
etc. Among them, ethanolamine is particularly preferable since the
particles having better plate-form shape can be obtained.
[0068] Next, the aqueous solution of the metal salt is dropwise
added to the alkaline aqueous solution to form the precipitate of
the metal hydroxide or hydrate. Preferably, pH of the suspension
containing the precipitate is adjusted in a range of 8 to 11, and
the suspension is aged at room temperature for about one day. The
adjustment of pH and the aging of the suspension are effective to
obtain the oxide particles having good plate-form shape and a
narrow particle size distribution.
[0069] Hydrothermal Treatment:
[0070] The suspension containing the precipitated hydroxide or
hydrate of the metal is hydrothermally treated in an autoclave,
etc. In this hydrothermal treatment, the suspension is preferably
washed with water to remove by-products or residual materials, and
then the pH of the suspension is readjusted with sodium hydroxide,
etc., although the suspension as such may be hydro thermally
treated. After the readjustment, the pH of the suspension is
preferably from 7 to 11. When the pH value in this step is lower
than 7, the crystal of the material does not grow sufficiently in
the hydrothermal treatment. When the pH value in this step exceeds
11, the particle size distribution may be broadened, or the
particles having the small size as intended may hardly be obtained.
The pH is more preferably from 7 to 10.
[0071] A temperature in the hydrothermal treatment is preferably
from 110 to 300.degree. C. When the temperature is less than
110.degree. C., the hydroxide or hydrate of the metal having the
specific shape may not be obtained. A temperature exceeding
300.degree. C. has no advantage, since a pressure generated
increases so that an expensive apparatus should be used.
[0072] The hydrothermal treatment time is preferably from 1 to 4
hours. When the hydrothermal treatment time is too short, the
particles do not grow sufficiently to the specific shape. When the
hydrothermal treatment time is too long, there is no drawback but
the production costs increase.
[0073] Heating:
[0074] After the hydrothermal treatment, the hydroxide or hydrate
of the metal is filtrated and dried, and then heated. Before
filtration, the pH of the suspension is preferably adjusted in a
neutral range around 6 to 9 by washing with water. When the pH is
hither than this range, sodium, etc. may remain and cause sintering
of the particles in the subsequent heat treatment, or interfere
with the crystal growth of the particles.
[0075] In the case of cerium, zirconium, aluminum and iron, the
hydroxide or hydrate of such a metal may be silicated by adding a
silicon compound such as sodium silicate. The silication is
effective for maintaining the finally obtained particles of cerium
oxide, zirconium oxide, aluminum oxide or iron oxide in the
specific shape.
[0076] After the filtration and drying, the hydroxide or hydrate of
the metal is heated to obtain the oxide particles. The heating
atmosphere is not limited, but the heating in an air is preferable,
since the heating cost is lowest. The temperature in this heating
step is preferably from 300 to 1500.degree. C. When this
temperature is lower than 300.degree. C., oxide particles having a
plate-form shape and also good crystallinity may not be obtained.
When this temperature is higher than 150.degree. C., the particle
size increases due to sintering, or the particle size distribution
is broadened. By such a heating treatment, the particles of cerium
oxide, zirconium oxide, aluminum oxide, iron oxide or silicon oxide
are obtained. When the unreacted compounds are removed by washing
with water and the like, the oxide particles having a higher purity
can be obtained. Thus, the oxide particles are preferably washed
with water in the final step, when they are used as an abrasive for
chemical polishing and so on.
[0077] To obtain the oxide particles having both the plate-form
shape and the good crystallinity, the above heating treatment is an
effective method. However, in the case of cerium oxide and
zirconium oxide, oxide particles having the fluorite structure,
which is the inherent structure of these oxides, can be obtained
without heating treatment. In such a case, the plate-form particles
can be obtained without heating although depending on the
conditions of aging and hydrothermal treatment. In the case of
silicon oxide, the plate-form silicon oxide particles having a
composition of SiO.sub.2 can be produced without heating treatment.
The plate-form particles, which are obtained without heating
treatment, are usually fine particles having a particle size of 10
nm. Therefore, such fine particles are preferably used in the form
of a slurry without drying.
[0078] The oxide particles obtained by the above process have a
particle size of 10 nm to 100 nm, preferably 20 nm to 90 nm, which
is preferable when they are used as an abrasive of a finish
polishing sheet or an abrasive liquid. When the oxide particles are
analyzed with X-ray diffraction, an X-ray diffraction spectrum has
clear peaks corresponding to the crystal structure of CeO.sub.2 or
ZrO.sub.2 having the fluorite structure in the case of cerium oxide
or zirconium oxide. Furthermore, when the oxide particles are
observed with an electron microscope, crystal boundaries are
clearly seen. These data indicate that the oxide particles produced
according to the present invention have the excellent
crystallinity, which cannot be attained by the conventional
methods.
[0079] In the case of aluminum oxide, the heating treatment can
provide the plate-form particles with good crystallinity which have
any crystal structure such as .gamma.-Al.sub.2O.sub.3,
.delta.-Al.sub.2O.sub.3, .theta.-Al.sub.2O.sub.3,
.alpha.-Al.sub.2O.sub.3, etc. For example, alumina having a single
crystal structure of .gamma.-alumina, .delta.-alumina,
.theta.-alumina or .alpha.-alumina, or a mixture of two or more
types of alumina having different crystal structures can be
prepared by adding an aqueous solution of an aluminum salt to an
alkaline aqueous solution to form the hydroxide or hydrate of
aluminum, heating the hydroxide or hydrate of aluminum at a
temperature of 110 to 300.degree. C. in the presence of water,
filtering and drying the particles to obtain boehmite particles,
heating the boehmite particles in an air at a temperature of 300 to
1200.degree. C. or 400 to 1500.degree. C., and optionally washing
the produced particles to remove products other than aluminum
oxides or residual materials.
[0080] In the case of silicon oxide, clear diffraction peaks
showing crystals may not be found in an X-ray diffraction spectrum.
However, it is confirmed that the silicon oxide particles
substantially have the composition of SiO.sub.2 by a fluorescent
X-ray analysis.
[0081] Use of Non-Magnetic Plate-Form Particles:
[0082] The non-magnetic particles, i.e. the oxide particles (e.g.
cerium oxide particles, zirconium oxide particles, aluminum oxide
particles, silicon oxide particles and iron oxide particles), which
are produced by the method described above, have the specific shape
and the specific particle size. Therefore, when they are used as an
abrasive of an abrasive member or an abrasive liquid, they exhibit
excellent abrading or polishing properties without damaging
materials to be abraded, which cannot be achieved by the
conventional particulate abrasive. That is, when the conventional
particulate abrasive is used, it is difficult to form a smoothly
abraded or polished surface of a material without damage while
maintaining the abrading properties. However, when the oxide
particles of the present invention are used, it is possible to
abrade the surface of a material without damaging the surface by
making use of flat surfaces of the plates while abrading the
material surface with the edges of the plate-form particles. The
abrasive member includes a variety of items having various forms
such as a sheet (abrasive sheet), a tape (abrasive tape), a disc
(abrasive disc), a card, a rod, or any other solid forms.
[0083] In addition, according to the present invention, the
non-magnetic plate-form particles include oxide particles in which
pores are easily formed in the thickness direction of a plate such
as iron oxide particles. Such pores are formed since the plate-form
particles of the hydroxide are dehydrated in the heating treatment.
The oxide particles having pores do not lose the characteristics of
the oxide particles of the present invention such as abrading
properties. When a part of the iron elements are substituted with
other metal element such as aluminum, zirconium, etc., the hardness
of the iron oxide particles can be controlled so that the abrading
properties are adjusted according to the application of the
abrasive.
[0084] An abrasive liquid, that is, a slurry-form abrasive, can be
prepared by dispersing the non-magnetic plate-form particles of the
present invention in a liquid medium preferably in the presence of
a dispersant. The abrasive particles, that is, the cerium oxide
particles, zirconium oxide particles, aluminum oxide particles,
silicon oxide particles and iron oxide particles have different
hardness. Thus, when two or more kinds of the oxide particles are
used in combination, the hardness of the abrasive can be precisely
adjusted, so that the abrasive liquids suitable for a wide variety
of applications can be prepared. In particular, when the general
purpose colloidal silica and the abrasive particles according to
the present invention are used together, the additional abrading
properties can be imparted to the abrasive liquid in addition to
the less satisfactory abrading properties of the colloidal silica.
Therefore, the abrasive liquid can be used in a wider variety of
applications. When such a mixture is used, the abrasive liquid has
very good stability since the abrasive particles are no sintered or
agglomerated together and have a uniform particle size distribution
so that the different particles are not separated in the
liquid.
[0085] The non-magnetic plate-form particles of the present
invention are very useful as additive particles of coating type
magnetic recording media. In this case, the plate-form particles
having no pore are preferable, since the acicular particles of a
magnetic powder are trapped in the pores of the non-magnetic
particles so that the orientation of the magnetic powder may be
disturbed, and furthermore, the thickness of a magnetic layer may
fluctuate.
[0086] The magnetic layer of coating type magnetic recording media
is made thinner and thinner because of the requirement for high
density recording. Hitherto, particulate aluminum oxide, silicon
oxide and iron oxide have been used as additives of the coating
type magnetic recording media. When the thickness of the magnetic
layer is decreased, such particulate additives protrude from the
surface of the magnetic layer so that the surface smoothness of the
magnetic layer is deteriorated and the noise is increased. When the
plate-form particles of the present invention are used, the planes
of the plate-form particles can be aligned in parallel with the
plane of the magnetic layer. Therefore, the magnetic recording
media comprising a magnetic layer with a smooth surface can be
produced while maintaining the cleaning function of the additive
particles.
[0087] Furthermore, the oxide particles of the present invention
have good light transmission based on the optical properties
inherent to the oxide materials and also the plate-form shape, when
they are used as additives of various functional films such as
optical films. That is, when the planes of the plate-form particles
are aligned in parallel with the plane of the functional film, the
transparent functional film having good light transmittance while
exhibiting the interaction with light, which is inherent to the
materials, can be obtained. Accordingly, a large variety of films,
for example, an anti-reflection film having a plurality of coatings
comprising oxide particles of the present invention which have
different refractive indices, and a film having a high refractive
index and good light transmittance can be provided.
[0088] Thus, the oxide particles of the present invention can find
a large number of applications.
[0089] It is possible to form a coating film having a very small
mechanical or thermal deformation rate in a specific direction
using the isotropy in the plate of the particle due to the
plate-form.
[0090] In this case, the color less plate-form particles such as
the particles of aluminum oxide, zirconium oxide, cerium oxide and
silicon oxide are preferably used, since the coating film is not
colored. When the particles have pores, they may cause the
fluctuation of a refractive index or the decrease of the
transparency. Thus, the particles having no pore are
preferable.
[0091] As explained above, the oxide particles of the present
invention have the plate-form shape and an average particle size of
10 nm to 100 nm, and also they have a very good particle size
distribution. When such particles are used, the properties of
products comprising the oxide particles are significantly improved
in comparison with those comprising the conventional oxide
particles, and the oxide particles can exploit novel applications
which cannot be exploited by the conventional oxide particles.
EXAMPLES
[0092] Hereinafter, the Examples of the present invention will be
illustrated together with the Comparative Examples.
(1) Examples of Cerium Oxide Particles
Example 1
[0093] An alkaline aqueous solution was prepared by dissolving
sodium hydroxide (0.75 mol) and 2-aminoethanol (100 ml) in water
(800 ml). Separately, an aqueous cerium chloride solution was
prepared by dissolving cerium chloride (III) heptahydrate (0.074
mol) in water (400 ml). To the alkaline aqueous solution was added
dropwise the aqueous cerium chloride solution to form a precipitate
containing cerium hydroxide at about 25.degree. C. The pH of the
suspension was 10.8. The precipitate in the form of a suspension
was aged for 20 hours and washed with water until the pH of the
suspension reached 7.9.
[0094] Next, the supernatant was removed, and the suspension of the
precipitate was charged in an autoclave and subjected to
hydrothermal reaction at 200.degree. C. for 2 hours.
[0095] The resultant product was filtered and dried at 90.degree.
C. in an air. The resultant solid was lightly crushed in a mortar
and heated in an air at 600.degree. C. for one hour to obtain
cerium oxide particles. After the heating treatment, the cerium
oxide particles were washed with water using an ultrasonic
disperser, and filtered and dried so as to remove the unreacted
substances and the residue.
[0096] The resultant cerium oxide particles were subjected to X-ray
diffractometry, and a spectrum corresponding to cerium oxide with a
fluorite structure was clearly observed (see FIG. 1). The
crystallite size was calculated from the width of a peak
corresponding to the plane (111) of cerium oxide according to the
Scherre method. As a result, the crystallite size was 12.7 nm.
Further, the shapes of the cerium oxide particles were observed
with a transmission electron microscope, and were found to be
hexagonal plate-form particles with a particle size of 10 to 20
nm.
[0097] FIG. 1 shows the X-ray diffraction spectrum of the cerium
oxide particles, and FIG. 2 shows the transmission electron
microphotograph (magnification: 200,000 times). The synthesis
conditions for the cerium oxide particles, the crystal structure
found by the X-ray diffraction, the average particle sizes and the
shapes of the particles found based on the transmission electron
microphotograph, and the crystallite size calculated from the X-ray
diffraction peak width are summarized in Table 1.
Example 2
[0098] Cerium oxide particles were prepared by forming a
precipitate containing cerium hydroxide, washing it with water,
filtering, drying and subjecting it to heating treatment in the
same manner as in the synthesis of the cerium oxide particles of
Example 1, except that the heating temperature of the product of
hydrothermal treatment was changed from 600.degree. C. to
800.degree. C.
[0099] The X-ray diffraction spectrum of the resultant cerium oxide
particles were measured, and a spectrum corresponding to cerium
oxide with a fluorite structure was observed as in Example 1. The
crystallite size calculated from the width of a peak corresponding
to the plane (111) according to the Scherre method was 17.2 nm.
Further, the shapes of the cerium oxide particles were observed
with a transmission electron microscope and found to be hexagonal
particles with a particle size of 10 to 25 nm.
[0100] FIG. 3 shows the transmission electron microphotograph of
the cerium oxide particles (magnification: 200,000 times). The
synthesis conditions, the crystal structure observed by X-ray
diffraction, the average particle sizes and the shapes of the
particles found based on the transmission electron microphotograph,
and the crystallite size calculated from the X-ray diffraction peak
width are summarized in Table 1.
Example 3
[0101] Cerium oxide particles were prepared by forming a
precipitate containing cerium hydroxide, washing it with water,
filtering, drying and subjecting it to heating treatment in the
same manner as in the synthesis of the cerium oxide particles of
Example 1, except that the heating temperature of the product of
hydrothermal treatment was changed from 600.degree. C. to
1,000.degree. C.
[0102] The X-ray diffraction spectrum of the resultant cerium oxide
particles was measured, and a spectrum corresponding to cerium
oxide with a fluorite structure were observed as in Example 1. The
crystallite size calculated from the width of a peak corresponding
to the plane (111) according to the Scherre method was 32.4 nm.
Further, the shapes of the cerium oxide particles were observed
with a transmission electron microscope and found to be hexagonal
or rectangle plate-form particles with a particle size of 50 to 100
nm.
[0103] FIG. 4 shows the transmission electron microphotograph of
the cerium oxide particles (magnification: 200,000 times). The
synthesis conditions, the crystal structure observed by X-ray
diffraction, the average particle sizes and the shapes of the
particles found based on the transmission electron microphotograph,
and the crystallite size calculated from the X-ray diffraction peak
width are summarized in Table 1.
Example 4
[0104] In the synthesis of the cerium oxide particles of Example 1,
the precipitate was subjected to hydrothermal treatment and then,
washed with water in an amount 500 times larger than the volume of
the suspension, filtered and dried. The pH of the washed
precipitate was 7.5. The steps following the heating treatment were
carried out in the same manner as in Example 1 to obtain cerium
oxide particles.
[0105] The X-ray diffraction spectrum of the resultant cerium oxide
particles was measured, and a spectrum corresponding to cerium
oxide with a fluorite structure was observed. The crystallite size
calculated from the width of a peak corresponding to the plane
(111) according to the Scherre method was 11.5 nm. Further, the
shapes of the cerium oxide particles were observed with a
transmission electron microscope and found to be hexagonal
plate-form particles with a particle size of 10 to 15 nm.
[0106] The synthesis conditions, the crystal structure observed by
X-ray diffraction, the average particle sizes and the shapes of the
particles found based on the transmission electron microphotograph,
and the crystallite size calculated from the X-ray diffraction peak
width are summarized in Table 1.
Example 5
[0107] Cerium oxide particles were prepared by forming a
precipitate containing cerium hydroxide, washing with water,
filtering, drying and subjecting the same to heating treatment in
the same manner as in the synthesis of the cerium oxide particles
of Example 1, except that an aqueous 4N sodium silicate solution
(0.04 g) and then an aqueous 0.8N hydrochloric acid solution were
further added to the product of the hydrothermal treatment, so as
to adjust the pH to 7.4.
[0108] The X-ray diffraction spectrum of the resultant cerium oxide
particles was measured, and a spectrum corresponding to cerium
oxide with a fluorite structure was observed. The crystallite size
calculated from the width of a peak corresponding to the plane
(111) according to the Scherre method was 10.6 nm. Further, the
shapes of the cerium oxide particles were observed with a
transmission electron microscope and found to be hexagonal
plate-form particles with a particle size of 10 to 15 nm.
[0109] The synthesis conditions, the crystal structure observed by
X-ray diffraction, the average particle sizes and the shapes of the
particles found based on the transmission electron microphotograph,
and the crystallite size calculated from the X-ray diffraction peak
width are summarized in Table 1.
Example 6
[0110] Cerium oxide particles were prepared in the same manner as
in the synthesis of the cerium oxide particles of Example 1, except
that after the product was subjected to heating treatment at
600.degree. C. in an air, it was washed with water by using an
ultrasonic disperser.
[0111] The X-ray diffraction spectrum of the resultant cerium oxide
particles was measured, and a spectrum corresponding to cerium
oxide with a fluorite structure was observed. The crystallite size
calculated from the width of a peak corresponding to the plane
(111) according to the Scherre method was 12.3 nm. Further, the
shapes of the cerium oxide particles were observed with a
transmission electron microscope and found to be hexagonal
plate-form particles with a particle size of 10 to 20 nm.
[0112] The synthesis conditions, the crystal structure observed by
X-ray diffraction, the average particle sizes and the shapes of the
particles found based on the transmission electron microphotograph,
and the crystallite size calculated from the X-ray diffraction peak
width are summarized in Table 1.
Example 7
[0113] Cerium oxide particles were prepared in the same manner as
in the synthesis of the cerium oxide particles of Example 1, except
that the amount of sodium hydroxide added was changed to 0.90 mol
from 0.75 mol, and that no 2-aminoethanol was added. The pH of the
precipitate was 10.5. Then, the suspension of the precipitate was
aged, subjected to hydrothermal treatment, washed with water,
filtered, dried and further subjected to a heating treatment to
obtain the cerium oxide particles.
[0114] The X-ray diffraction spectrum of the resultant cerium oxide
particles was measured, and a spectrum corresponding to cerium
oxide with a fluorite structure was observed. The crystallite size
calculated from the width of a peak corresponding to the plane
(111) according to the Scherre method was 20.1 nm. Further, the
shapes of the cerium oxide particles were observed with a
transmission electron microscope and found to be hexagonal
plate-form particles with a particle size of 20 to 30 nm, although
the particle size distribution was slightly wider.
[0115] The synthesis conditions, the crystal structure observed by
X-ray diffraction, the average particle sizes and the shapes of the
particles found based on the transmission electron microphotograph,
and the crystallite size calculated from the X-ray diffraction peak
width are summarized in Table 1.
Comparative Example 1
[0116] Cerium oxide particles were prepared in the same manner as
in the synthesis of the cerium oxide particles of Example 1, except
that the hydrothermal treatment of the precipitate containing
cerium hydroxide was not done. The precipitate containing cerium
hydroxide was directly washed with water, filtered, dried and
subjected to a heating treatment to obtain the cerium oxide
particles.
[0117] The X-ray diffraction spectrum of the resultant cerium oxide
particles was measured. While a spectrum corresponding to cerium
oxide with a fluorite structure was observed, the crystallite size
was too large to be calculated from the width of a peak
corresponding to the plane (111). Further, the shapes of the cerium
oxide particles were observed with a transmission electron
microscope and found to be sintered or be coarse and large
particles with a particle size of 1 to 10 .mu.m in a very wide
particle size distribution.
[0118] The synthesis conditions, the crystal structure observed by
X-ray diffraction, the average particle sizes and the shapes of the
particles found based on the transmission electron microphotograph,
and the crystallite size calculated from the X-ray diffraction peak
width are summarized in Table 1.
(X-ray Diffraction Spectrum of Cerium Oxide Particles)
[0119] FIG. 1 is a graph of the X-ray diffraction spectrum of the
cerium oxide particles prepared in Example 1, showing peaks
corresponding to the crystal structure of the cerium oxide with the
fluorite structure. Since similar results were obtained from all
the particles of Examples and Comparative Examples, it can be
confirmed that all the particles prepared in Examples and
Comparative Examples were cerium oxide particles.
(Results of Observation of Cerium Oxide Particles with a
Transmission Electron Microscope)
[0120] FIGS. 2 to 4 are the transmission electron microphotographs
of the cerium oxide particles prepared in Examples 1 to 3,
respectively. In Examples 1 to 3, the temperatures for the heating
treatments after the hydrothermal treatments are 600.degree. C.,
800.degree. C. and 10,000.degree. C., respectively. It is seen
that, with an increase in the temperature for the heating
treatment, the average particle size tends to increase from about
10 nm to about 100 nm. This fact proves that the crystals of the
cerium oxide particles are growing in the course of the heating
treatment.
[0121] The synthesis conditions for the cerium oxide particles of
Examples and Comparative Examples, the crystal structures thereof
examined based on the X-ray diffraction, and the average particle
sizes and shapes thereof evaluated from the transmission electron
microphotographs are summarized in Table 1. Each of the particle
sizes evaluated from the above photographs was determined from the
average particle size of 300 particles.
TABLE-US-00001 TABLE 1 Temp. (.degree. C.)/ Temp. time (hr.)
(.degree. C.)/ Crystal PH in of hydro- time (hr.)
growth-controlling precipitating thermal of heating agent step
treatment treatment Ex. 1 2-amino-ethanol 10.8 200/2 600/1 Ex. 2
2-amino-ethanol 10.8 200/2 800/1 Ex. 3 2-amino-ethanol 10.8 200/2
1,000/1 Ex. 4 2-amino-ethanol 10.8 200/2 600/1 Ex. 5
2-amino-ethanol & 10.8 200/2 600/1 sodium silicate Ex. 6
2-amino-ethanol 10.8 200/2 600/1 Ex. 7 None 10.5 200/2 600/1 Com.
Ex. 1 2-amino-ethanol 10.8 no 600/1 treatment Average Crystal
particle Shape of Crystallite structure size (nm) particle size
(nm) Ex. 1 fluorite 14 hexagonal 13 structure plate Ex. 2 fluorite
18 hexagonal 17 structure plate Ex. 3 fluorite 55
hexagonal-rectangle 32 structure plate Ex. 4 fluorite 13 hexagonal
12 structure plate Ex. 5 fluorite 12 hexagonal 11 structure plate
Ex. 6 fluorite 14 hexagonal 12 structure plate Ex. 7 fluorite 24
hexagonal 20 structure plate Com. Ex. 1 fluorite 3 .mu.m
agglomerated >1,000 structure
[0122] As is apparent from Table 1, all the cerium oxide particles
obtained in the above Examples are plate-form shaped, having a
fluorite structure inherent to cerium oxide, and the particle sizes
thereof are within the range optimal for use not only in abrasive
members such as abrasive sheets and abrasive liquids but also in
magnetic tapes and a variety of optical films which are formed by
making good use of the plate-form shapes of the particles. On the
other hand, the cerium oxide particles obtained in Comparative
Example 1 have very large particle sizes, although having the
fluorite structure, and also have a very wide particle size
distribution and thus are not suitable for use in abrasive members
and the like.
[0123] As is understood from the foregoing description, the cerium
oxide particles of the present invention satisfy the conditions of
plate-form shaped particles and a very small particle size of 100
nm or less. Therefore, it becomes possible to use the cerium oxide
particles of the present invention for quite new applications which
have been believed to be impossible to realize.
(2) Examples of Zirconium Oxide Particles
Example 8
[0124] An alkaline aqueous solution was prepared by dissolving
sodium hydroxide (0.75 mol) and 2-aminoethanol (100 ml) in water
(800 ml). Separately, an aqueous zirconium chloride solution was
prepared by dissolving zirconium chloride (IV) (0.074 mol) in water
(400 ml). To the alkaline aqueous solution was added dropwise the
aqueous zirconium chloride solution to form a precipitate
containing zirconium hydroxide at about 25.degree. C. The pH of the
suspension was 10.8. The precipitate in the state of a suspension
was aged for 20 hours and then washed with water until the pH
reached 7.8.
[0125] Next, the supernatant was removed, and the suspension of the
precipitate was charged in an autoclave and subjected to a
hydrothermal treatment at 20.degree. C. for 2 hours.
[0126] The resultant product was filtered, dried, lightly crushed
in a mortar, and subjected to a heating treatment at 600.degree. C.
in an air for one hour to obtain zirconium oxide particles. After
the heating treatment, the zirconium oxide particles were further
washed with water using an ultrasonic disperser, filtered and dried
so as to remove the unreacted substances and the residue.
[0127] As a result of the measurement of the X-ray diffraction
spectrum of the resultant zirconium oxide particles, a spectrum
corresponding to zirconium oxide with a fluorite structure was
clearly observed. The shapes of the zirconium oxide particles were
observed with a transmission electron microscope. As a result, they
are hexagonal plate-form particles with a particle size of 10 to 20
nm. FIG. 5 shows the X-ray diffraction spectrum of the zirconium
oxide particles, and FIG. 6 shows the transmission electron
microphotograph of the particles (magnification: 200,000 times).
The synthesis conditions for preparing the zirconium oxide
particles, the crystal structure of the particles examined by X-ray
diffraction, and the average particle size and the shape of the
particles found from the transmission electron microphotograph of
the particles are summarized in Table 2.
Example 9
[0128] Zirconium oxide particles were obtained by forming a
precipitate containing zirconium hydroxide, washing the precipitate
with water, filtering and drying the product and subjecting the
product to a heating treatment in the same manner as in the
synthesis of the zirconium oxide particles of Example 8, except
that the temperature for the heating treatment of the product of
the hydrothermal treatment was changed from 600.degree. C. to
800.degree. C.
[0129] As a result of the measurement of the X-ray diffraction
spectrum of the resultant zirconium oxide particles, a spectrum
corresponding to zirconium oxide with a fluorite structure was
clearly observed, as well as Example 8. The shapes of the zirconium
oxide particles were further observed with a transmission electron
microscope. As a result, they are hexagonal plate-form particles
with a particle size of 20 to 30 nm. FIG. 7 shows the transmission
electron microphotograph of the particles (magnification: 200,000
times). The synthesis conditions, the crystal structure of the
particles examined by X-ray diffraction, and the average particle
size and the shape of the particles found from the transmission
electron microphotograph of the particles are summarized in Table
2.
Example 10
[0130] Zirconium oxide particles were obtained by forming a
precipitate containing zirconium hydroxide, washing the precipitate
with water, filtering and drying the product and subjecting the
product to a heating treatment in the same manner as in the
synthesis of the zirconium oxide particles of Example 8, except
that the temperature for the heating treatment of the product of
the hydrothermal treatment was changed from 600.degree. C. to
1,000.degree. C.
[0131] As a result of the measurement of the X-ray diffraction
spectrum of the resultant zirconium oxide particles, a spectrum
corresponding to zirconium oxide with a fluorite structure was
clearly observed, as well as Example 8. The shapes of the zirconium
oxide particles were further observed with a transmission electron
microscope. As a result, they are hexagonal plate-form particles
with a particle size of 50 to 100 nm. The synthesis conditions, the
crystal structure of the particles examined by X-ray diffraction,
and the average particle size and the shape of the particles found
from the transmission electron microphotograph of the particles are
summarized in Table 2.
Example 11
[0132] Zirconium oxide particles were obtained in the same manner
as in Example 8, except that the product of the hydrothermal
treatment was washed with water in an amount 500 times larger than
the volume of the suspension of the precipitate, filtered and
dried, and that the pH after the washing was 7.5, provided that the
following steps after the heating treatment were carried out in the
same manner as in Example 8.
[0133] As a result of the measurement of the X-ray diffraction
spectrum of the resultant zirconium oxide particles, a spectrum
corresponding to zirconium oxide with a fluorite structure was
observed. The shapes of the zirconium oxide particles were further
observed with a transmission electron microscope. As a result, they
are hexagonal plate-form particles with a particle size of 10 to 15
nm. The synthesis conditions, the crystal structure of the
particles examined by X-ray diffraction, and the average particle
size and the shape of the particles found from the transmission
electron microphotograph of the particles are summarized in Table
2.
Example 12
[0134] Zirconium oxide particles were obtained by forming a
precipitate containing zirconium hydroxide, washing the precipitate
with water, filtering and drying the product and subjecting the
product to a heating treatment in the same manner as in the
synthesis of the zirconium oxide particles of Example 8, except
that an aqueous 4N sodium silicate solution (0.04 g) and an aqueous
0.8N hydrochloric acid solution were further added to the product
of the hydrothermal treatment so as to adjust the pH to 7.4.
[0135] As a result of the measurement of the X-ray diffraction
spectrum of the resultant zirconium oxide particles, a spectrum
corresponding to zirconium oxide with a fluorite structure was
observed. The shapes of the zirconium oxide particles were further
observed with a transmission electron microscope. As a result, they
are hexagonal plate-form particles with a particle size of 10 to 15
nm. The synthesis conditions, the crystal structure of the
particles examined by X-ray diffraction, and the average particle
size and the shape of the particles found from the transmission
electron microphotograph of the particles are summarized in Table
2.
Example 13
[0136] Zirconium oxide particles were obtained in the same manner
as in the synthesis of the zirconium oxide particles of Example 8,
except that after the product was subjected to a heating treatment
at 600.degree. C. in an air, it was further washed with water using
an ultrasonic disperser.
[0137] As a result of the measurement of the X-ray diffraction
spectrum of the resultant zirconium oxide particles, a spectrum
corresponding to zirconium oxide with a fluorite structure was
observed. The shapes of the zirconium oxide particles were further
observed with a transmission electron microscope. As a result, they
are hexagonal plate-form particles with a particle size of 10 to 20
nm. The synthesis conditions, the crystal structure of the
particles examined by X-ray diffraction, and the average particle
size and the shape of the particles found from the transmission
electron microphotograph of the particles are summarized in Table
2.
Example 14
[0138] Zirconium oxide particles were obtained as follows:
[0139] A precipitate was formed in the same manner as in the
synthesis of the zirconium oxide particles of Example 8, except
that the amount of sodium hydroxide added was changed from 0.75 mol
to 0.90 mol, and that no 2-aminoethanol was added. The suspension
of the precipitate was aged, and then subjected to a hydrothermal
treatment, washed with water, filtered and dried. The resulting
product was further subjected to a heating treatment to obtain the
zirconium oxide particles.
[0140] As a result of the measurement of the X-ray diffraction
spectrum of the resultant zirconium oxide particles, a spectrum
corresponding to zirconium oxide with a fluorite structure was
clearly observed. The shapes of the zirconium oxide particles were
further observed with a transmission electron microscope. As a
result, they were found to be hexagonal plate-form particles with a
particle size of 15 to 25 nm, although having a slightly wide
particle size distribution. The synthesis conditions, the crystal
structure of the particles examined by X-ray diffraction, and the
average particle size and the shape of the particles found from the
transmission electron microphotograph of the particles are
summarized in Table 2.
Comparative Example 2
[0141] Zirconium oxide particles were obtained as follows:
[0142] A precipitate containing zirconium hydroxide was formed and
was directly washed with water, filtered and dried without
undergoing a hydrothermal treatment, and then was subjected to a
heating treatment in the same manner as in Example 8, to obtain the
zirconium oxide particles.
[0143] As a result of the measurement of the X-ray diffraction
spectrum of the resultant zirconium oxide particles, a spectrum
corresponding to zirconium oxide with a fluorite structure was
observed. The shapes of the zirconium oxide particles were observed
with a transmission electron microscope. As a result, they were
found to be sintered or be coarse particles which had a very wide
particle size distribution of 1 to 10 .mu.m, including very fine
particles and coarse particles formed due to sintering or
agglomeration. The synthesis conditions for preparing the zirconium
oxide particles, the crystal structure of the particles examined by
X-ray diffraction, and the average particle size and the shape of
the particles found from the transmission electron microphotograph
of the particles are summarized in Table 2.
(X-Ray Diffraction Spectrum of Zirconium Oxide Particles)
[0144] FIG. 5 shows the X-ray diffraction spectrum of the zirconium
oxide particles obtained in Example 8, indicating peaks which
correspond to the crystal structure of zirconium oxide. Since
similar effects could be obtained from all the particles of
Examples, it is seen that all the particles of Examples were
zirconium oxide particles.
(Results of Observation of Zirconium Oxide Particles with a
Transmission Electron Microscope)
[0145] FIGS. 6 and 7 are the transmission electron micro
photographs of the zirconium oxide particles obtained in Examples 8
and 9, respectively. The plate-form zirconium oxide particles were
clearly observed from the photographs. In this regard, the average
particle size evaluated from the photograph was determined from the
average particle size of 300 particles in the photograph.
TABLE-US-00002 TABLE 2 Temp. (.degree. C.)/ Temp. time (hr.)
(.degree. C.)/ Crystal PH in of hydro- time (hr.)
growth-controlling precipitating thermal of heating agent step
treatment treatment Ex. 8 2-amino-ethanol 10.8 200/2 600/1 Ex. 9
2-amino-ethanol 10.8 200/2 800/1 Ex. 10 2-amino-ethanol 10.8 200/2
1,000/1 Ex. 11 2-amino-ethanol 10.8 200/2 600/1 Ex. 12
2-amino-ethanol & 10.8 200/2 600/1 sodium silicate Ex. 13
2-amino-ethanol 10.8 200/2 600/1 Ex. 14 None 10.9 200/2 600/1 Com.
Ex. 2 2-amino-ethanol 10.8 no 600/1 treatment Av. Crystal particle
structure Shape of particle size (nm) Ex. 8 fluorite hexagonal
plate 19 structure Ex. 9 fluorite hexagonal plate 25 structure Ex.
10 fluorite hexagonal plate 70 structure Ex. 11 fluorite hexagonal
plate 13 structure Ex. 12 fluorite hexagonal plate 12 structure Ex.
13 fluorite hexagonal plate 15 structure Ex. 14 fluorite hexagonal
plate 20 structure Com. Ex. 2 fluorite agglomerated >1,000
structure
[0146] As is apparent from Table 2, all the zirconium oxide
particles obtained in the above Examples are plate-form shaped,
having high crystallinity, and the particle sizes thereof were
within the ranges optimal for use not only in abrasive members such
as abrasive sheets and abrasive liquids but also in magnetic tapes
and a variety of optical films which are formed by making good use
of the shapes of the plate particles. On the other hand, the
zirconium oxide particles obtained in Comparative Example 2 have
very large particle sizes and have a very wide particle size
distribution and thus are not suitable for use in abrasive members
and the like.
[0147] As is understood from the foregoing description, the
zirconium oxide particles of the present invention satisfy the
conditions of plate-form shaped particles and a very small particle
size of 100 nm or less. Therefore, it becomes possible to use the
zirconium oxide particles of the present invention for quite new
applications which have been believed to be impossible to
realize.
(3) Examples of Aluminum Oxide Particles
Example 15
[0148] An alkaline aqueous solution was prepared by dissolving
sodium hydroxide (0.75 mol) and 2-aminoethanol (100 ml) in water
(800 ml). Separately, an aqueous aluminum chloride solution was
prepared by dissolving aluminum chloride (III) heptahydrate (0.074
mol) in water (400 ml). To the alkaline aqueous solution was added
dropwise the aqueous aluminum chloride solution to form a
precipitate containing aluminum hydroxide at about 25.degree. C.
Then, hydrochloric acid was added dropwise to the precipitate to
adjust the pH of the suspension to 10.2. The precipitate in the
state of a suspension was aged for 20 hours and then washed with
water in an amount about 1,000 times larger than the volume of the
suspension.
[0149] Next, the supernatant was removed, and the pH of the
suspension of the precipitate was adjusted to 10.0 by using an
aqueous sodium hydroxide solution. The precipitate was charged in
an autoclave and subjected to a hydrothermal treatment at
200.degree. C. for 2 hours.
[0150] The resultant product was filtered, dried at 90.degree. C.
in an air, lightly crushed in a mortar, and subjected to a heating
treatment at 600.degree. C. in an air for one hour to obtain
aluminum oxide particles. After the heating treatment, the aluminum
oxide particles were washed with water using an ultrasonic
disperser, filtered and dried so as to remove the unreacted
substances and the residue.
[0151] As a result of the measurement of the X-ray diffraction
spectrum of the resultant aluminum oxide particles, a spectrum
corresponding to .gamma.-alumina was observed. The shapes of the
aluminum oxide particles were observed with a transmission electron
microscope. As a result, they were found to be rectangle plate-form
particles with a particle size of 30 to 50 nm.
[0152] FIG. 8 shows the X-ray diffraction spectrum of the aluminum
oxide particles, and FIG. 9 shows the transmission electron
microphotograph of the particles (magnification: 200,000 times).
The synthesis conditions for preparing the aluminum oxide
particles, the crystal structure of the particles examined by X-ray
diffraction, and the average particle size and the shape of the
particles found from the transmission electron microphotograph of
the particles are summarized in Table 3.
Example 16
[0153] Aluminum oxide particles were obtained by forming a
precipitate containing aluminum hydroxide, washing the precipitate
with water, filtering and drying the product and subjecting the
product to a heating treatment in the same manner as in the
synthesis of the aluminum oxide particles of Example 15, except
that the temperature for the heating treatment of the product of
the hydrothermal treatment was changed from 600.degree. C. to
1,000.degree. C.
[0154] As a result of the measurement of the X-ray diffraction
spectrum of the resultant aluminum oxide particles, a spectrum
corresponding to 6-alumina which had a peak intensity higher than
that of the spectrum observed in Example 15. The shapes of the
aluminum oxide particles were observed with a transmission electron
microscope. As a result, they are rectangle plate-form particles
with a particle size of 30 to 50 nm, as well as Example 15.
[0155] FIG. 10 shows the X-ray diffration spectrum of the aluminum
oxide particles. The synthesis conditions for preparing the
aluminum oxide particles, the crystal structure of the particles
examined by X-ray diffraction, and the average particle size and
the shape of the particles found from the transmission electron
microphotograph of the particles are summarized in Table 3.
Example 17
[0156] Aluminum oxide particles were obtained by forming a
precipitate containing aluminum hydroxide, washing the precipitate
with water, filtering and drying the product and subjecting the
product to a heating treatment in the same manner as in the
synthesis of the aluminum oxide particles of Example 15, except
that the time for the hydrothermal treatment was changed from 2
hours to 4 hours.
[0157] As a result of the measurement of the X-ray diffraction
spectrum of the resultant aluminum oxide particles, a spectrum
corresponding to .gamma.-alumina was observed, as well as Example
15. The shapes of the aluminum oxide particles were further
observed with a transmission electron microscope. As a result, they
were rectangle plate-form particles with a particle size of 10 to
20 nm.
[0158] FIG. 11 is the transmission electron microphotograph of the
aluminum oxide particles (magnification: 200,000 times). The
synthesis conditions, the crystal structure of the particles
examined by X-ray diffraction, and the average particle size and
the shape of the particles found from the transmission electron
microphotograph of the particles are summarized in Table 3.
Example 18
[0159] Aluminum oxide particles were obtained in the same manner as
in Example 15 except for the following. That is, a precipitate
containing aluminum hydroxide was formed by adding dropwise the
aqueous aluminum chloride solution to the alkaline solution, and
was adjusted in pH to 8.3 by adding dropwise hydrochloric acid. The
precipitate was aged, washed with water in an amount about 1,000
times larger than the volume of the suspension of the precipitate,
and again adjusted in pH to 8.1 by adding an aqueous sodium
hydroxide solution. The steps following the hydrothermal treatment
were carried out in the same manner as in Example 15 to obtain the
aluminum oxide particles.
[0160] As a result of the measurement of the X-ray diffraction
spectrum of the resultant aluminum oxide particles, a spectrum
corresponding to .gamma.-alumina was observed, as well as Example
15. The shapes of the aluminum oxide particles were observed with a
transmission electron microscope. As a result, they are hexagonal
plate-form particles with a particle size of 65 to 85 nm.
[0161] FIG. 12 shows the transmission electron microphotograph of
the particles (magnification: 200,000 times). The synthesis
conditions, the crystal structure of the particles examined by
X-ray diffraction, and the average particle size and the shape of
the particles found from the transmission electron microphotograph
of the particles are summarized in Table 3.
Example 19
[0162] Aluminum oxide particles were obtained in the same manner as
in Example 15, except the following. A precipitate was subjected to
a hydrothermal treatment, and thereto was added an aqueous 4N
sodium silicate solution (0.04 g). The mixture was sufficiently
stirred, and to the reaction solution was added gradually an
aqueous 0.8N hydrochloric acid solution while stirring the
solution, so as to adjust the pH of the solution to 7.5. Other than
those, the formation of the precipitate containing aluminum
hydroxide, the washing of the precipitate with water, and the
filtering, drying and heating treatment of the product were carried
out in the same manner as in the synthesis of the aluminum oxide
particles of Example 15 to obtain the aluminum oxide particles.
[0163] As a result of the measurement of the X-ray diffraction
spectrum of the resultant aluminum oxide particles, a spectrum
corresponding to .gamma.-alumina was observed. The shapes of the
aluminum oxide particles were observed with a transmission electron
microscope. As a result, they are rectangle plate-form particles
with a particle size of 30 to 50 nm.
[0164] The synthesis conditions, the crystal structure of the
particles examined by X-ray diffraction, and the average particle
size and the shape of the particles found from the transmission
electron microphotograph of the particles are summarized in Table
3.
Example 20
[0165] The aluminum oxide particles obtained in Example 15 were
further subjected to a heating treatment at 1,250.degree. C. in an
air for one hour. As a result of the measurement of the X-ray
diffraction spectrum of the resultant aluminum oxide particles, a
spectrum corresponding to .alpha.-alumina was observed. The shapes
of the aluminum oxide particles were observed with a transmission
electron microscope. As a result, they are rectangle plate-form
particles with a particle size of 40 to 60 nm.
[0166] FIG. 13 shows the X-ray diffraction spectrum of the aluminum
oxide particles, and FIG. 14 shows the transmission electron
microphotograph of the particles (magnification: 200,000 times).
The synthesis conditions, the crystal structure of the particles
examined by X-ray diffraction, and the average particle size and
the shape of the particles found from the transmission electron
microphotograph of the particles are summarized in Table 3.
Example 21
[0167] Aluminum oxide particles were obtained as follows:
[0168] A precipitate was formed in the same manner as in the
synthesis of the aluminum oxide particles of Example 15, except
that the amount of sodium hydroxide added was changed from 0.75 mol
to 0.90 mol, and that no 2-aminoethanol was added. The suspension
of the precipitate was aged, and then subjected to a hydrothermal
treatment, washed with water, filtered and dried. The resulting
product was further subjected to a heating treatment to obtain the
aluminum oxide particles.
[0169] As a result of the measurement of the X-ray diffraction
spectrum of the resultant aluminum oxide particles, a spectrum
corresponding to .gamma.-alumina was observed. The shapes of the
aluminum oxide particles were observed with a transmission electron
microscope. As a result, they were found to be rectangle plate-form
particles with a particle size of 40 to 60 nm, which was a slightly
wide particle size distribution.
[0170] The synthesis conditions, the crystal structure of the
particles examined by X-ray diffraction, and the average particle
size and the shape of the particles found from the transmission
electron microphotograph of the particles are summarized in Table
3.
Comparative Example 3
[0171] Aluminum oxide particles were obtained in the same manner as
in the synthesis of the aluminum oxide particles of Example 15,
except that the temperature for the heating treatment was changed
from 600.degree. C. to 300.degree. C.
[0172] As a result of the measurement of the X-ray diffraction
spectrum of the resultant aluminum oxide particles, it was found
that the transformation of the crystal structure to aluminum oxide
was insufficient, and a spectrum corresponding to aluminum
hydroxyoxide (boehmite: AlO(OH)) was observed.
[0173] The synthesis conditions, the crystal structure of the
particles examined by X-ray diffraction, and the average particle
size and the shape of the particles found from the transmission
electron microphotograph of the particles are summarized in Table
3.
Comparative Example 4
[0174] A precipitate containing aluminum hydroxide was formed under
the same conditions as in Example 15, and was washed with water in
an amount about 1,000 times larger than the volume of the
suspension of the precipitate. Then, the pH of the suspension was
again adjusted to 10.0 by adding an aqueous sodium hydroxide
solution as in Example 15. Next, the suspension of the precipitate
was subjected to a heating treatment at 90.degree. C. for 2 hours,
instead of a hydrothermal treatment in an autoclave. The resultant
product was filtered, dried at 90.degree. C. in an air, lightly
crushed in a mortar, and subjected to a heating treatment at
60.degree. C. in an air for one hour as in Example 1 to obtain
aluminum oxide particles. After the heating treatment, the aluminum
oxide particles were further washed with water, using an ultrasonic
disperser, filtered and dried so as to remove the unreacted
substance and the residue.
[0175] As a result of the measurement of the X-ray diffraction
spectrum of the resultant aluminum oxide particles, a spectrum
corresponding to .gamma.-alumina was observed. The shapes of the
aluminum oxide particles were observed with a transmission electron
microscope. As a result, the shapes of the particles were granular
or mass-like irregular and had a wide particle size distribution
including fine particles with a particle size of about 20 nm, and
sintered or agglomerated particles with a particle size of several
micrometers.
[0176] The synthesis conditions for preparing the aluminum oxide
particles, the crystal structure of the particles examined by X-ray
diffraction, and the average particle size and the shape of the
particles found from the transmission electron microphotograph of
the particles are summarized in Table 3.
(Results of Observation of Aluminum Oxide Particles with a
Transmission Electron Microscope)
[0177] FIGS. 9, 11, 12 and 14 are the transmission electron
microphotographs of the aluminum oxide particles obtained in
Examples 15, 17, 18 and 20, respectively.
[0178] The hydrothermal treatments of Examples 15 and 17 were
carried out for 2 hours and 4 hours, respectively. In this regard,
it is seen that, as the time of the hydrothermal treatment
increases, the average particles size of the aluminum oxide
particles formed after the heating treatment tends to decrease from
about 45 nm to about 16 nm. This tendency indicates that, when the
crystal growth of aluminum oxide during the hydrothermal treatment
is sufficient, the crystal growth thereof tends to be suppressed
during the following heating treatment, and that, when the crystal
growth of aluminum oxide during the hydrothermal treatment, on the
contrary, is suppressed, the crystal growth thereof tends to be
facilitated during the following heating treatment.
[0179] As described above, one of the features of the process of
the present invention is that the step for regulating the shapes
and a particle size of the particles is done separately from the
step for extracting the properties inherent to the material to the
maximum. The initial step of the hydrothermal treatment has a close
relationship with the post-step of the heating treatment in an air,
and this relationship was, for the first time, discovered in the
present invention.
[0180] Further, in Examples 15 and 18, the pH values of the
precipitates found in the aging and the hydrothermal treatment are
10.2 and 8.3, respectively. The shapes of the aluminum particles
are rectangle plate-form at pH 10.2, and are hexagonal plate-form
at pH 8.3. The particle size tends to diminish and the particle
shape tends to transform from hexagonal plates to rectangle plates,
as the pH increases. In the state of the present art, the causes of
the change in particle size and the transformation of the particle
shape depending on the pH of the precipitate in the aging and the
hydrothermal treatment are not elucidated. However, it is one of
the distinguishing features of the process of the present
invention, which is not found in other conventional processes, that
the particle shape and the average particle size can be changed
while the plate-form shapes of the particles being maintained, by
controlling the values of pH in the aging or the hydrothermal
treatment.
[0181] The synthesis conditions for preparing the aluminum oxide
particles, the crystal structure of the particles examined by X-ray
diffraction, and the average particle size and the shape of the
particles found from the transmission electron microphotograph of
the particles are summarized in Table 3. In this regard, the
average particle size evaluated from the photograph was determined
from the average particle size of 300 particles in the
photograph.
(X-Ray Diffraction Spectrum of Aluminum Oxide Particles)
[0182] FIGS. 8, 10 and 13 show the X-ray diffraction spectra of the
aluminum oxide particles obtained in Examples 15, 16 and 20, which
correspond to the X-ray diffraction spectra of .gamma.-alumina,
.delta.-alumina and .alpha.-alumina, respectively. These results
suggest that when the conditions of the heating treatment are
controlled, it is possible to obtain aluminum oxide particles with
desired crystal structures without changing the particle size and
particle shape of the aluminum oxide particles. This point is also
one of the distinguishing features of the present invention.
TABLE-US-00003 TABLE 3 Temp. (.degree. C.)/ Temp. time (hr.)
(.degree. C.)/ Crystal PH in of hydro- time (hr.)
growth-controlling precipitating thermal of heating agent step
treatment treatment Ex. 15 2-amino-ethanol 10.2 200/2 600/1 Ex. 16
2-amino-ethanol 10.2 200/2 1,000/1 Ex. 17 2-amino-ethanol 10.2
200/4 600/1 Ex. 18 2-amino-ethanol 8.3 200/2 600/1 Ex. 19
2-amino-ethanol & 10.2 200/2 600/1 sodium silicate Ex. 20
2-amino-ethanol 10.2 200/2 1,250/1 Ex. 21 None 10.6 200/2 600/1
Com. Ex. 3 2-amino-ethanol 10.2 200/2 300/1 Com. Ex. 4
2-amino-ethanol 10.2 no 600/1 treatment Av. Crystal particle
structure Shape of particle size (nm) Ex. 15 .gamma.-alumina
rectangle plate 45 Ex. 16 .delta.-alumina rectangle plate 40 Ex. 17
.gamma.-alumina rectangle plate 16 Ex. 18 .gamma.-alumina hexagonal
plate 70 Ex. 19 .gamma.-alumina rectangle plate 35 Ex. 20
.alpha.-alumina rectangle plate 48 Ex. 21 .gamma.-alumina rectangle
plate 52 Com. Ex. 3 boehmite rectangle plate 42 Com. Ex. 4
.gamma.-alumina agglomerated 500
[0183] As is apparent from Table 3, all the aluminum oxide
particles obtained in the above Examples were plate-form shaped,
and it is known from the X-ray diffraction analyses that it is
possible to control the crystal structure of aluminum oxide
particles to .gamma., .delta., .alpha. or the like by controlling
the conditions for the heating treatment.
[0184] On the other hand, aluminum oxide particles could not be
obtained in Comparative Example 3, and the resultant particles were
left to be the aluminum hydroxyoxide particles (boehemite
particles). Further, the aluminum oxide particles of Comparative
Example 4 had a very wide particle size distribution: the sintered
or agglomerated particles with very large particle sizes were
included. Thus, it is seen that the aluminum oxide particles of
Comparative Example 4 are not suitable for use as additives such as
abrasive members and the like.
[0185] The particle sizes of the aluminum oxide particles of the
present invention are within the ranges optimal for not only
abrasive members such as abrasive sheets and abrasive liquids but
also additive particles for magnetic tapes and a variety of
functional sheets. Hitherto, aluminum oxide particles which
concurrently have plate-form shapes and particle sizes of so fine
as 100 nm or less have not been realized, and will be used for
quite new applications which are believed to be impossible so
far.
(4) Examples of Silicon Oxide Particles
Example 22
[0186] An alkaline aqueous solution was prepared by dissolving
sodium metasilicate (0.074 mol) and 2-aminoethanol (100 ml) in
water (800 ml). Separately, an aqueous 1N hydrochloric acid
solution (400 ml) was prepared. To the alkaline aqueous solution
was added dropwise the aqueous hydrochloric acid solution until the
pH of the resulting suspension was adjusted to 8.3, to form a
precipitate containing silicon hydroxide at about 25.degree. C.
Then, the precipitate in the state of the suspension was aged for
20 hours and then washed with water until the pH reached 7.6.
[0187] Next, the supernatant was removed, and the suspension of the
precipitate was charged in an autoclave and subjected to a
hydrothermal treatment at 200.degree. C. for 2 hours.
[0188] The resultant product was filtered, dried at 90.degree. C.
in an air, lightly crushed in a mortar, and subjected to a heating
treatment at 800.degree. C. in an air for one hour to obtain
silicon oxide particles.
[0189] The shapes of the silicon oxide particles were observed with
a transmission electron microscope. As a result, they were almost
disk-like particles with a particle size of 30 to 40 nm.
[0190] FIG. 15 shows the transmission electron microphotograph of
the particles (magnification: 200,000 times). The synthesis
conditions for preparing the silicon oxide particles, the crystal
structure of the particles examined by X-ray diffraction, and the
average particle size and the shape of the particles found from the
transmission electron microphotograph of the particles are
summarized in Table 4.
Example 23
[0191] Silicon oxide particles were obtained by forming a
precipitate containing silicon hydroxide, washing the precipitate
with water, filtering, drying and subjecting the product to a
heating treatment in the same manner as in the synthesis of the
silicon oxide particles of Example 22, except that the temperature
for the heating treatment of the product of the hydrothermal
treatment was changed from 800.degree. C. to 600.degree. C.
[0192] The shapes of the silicon oxide particles were observed with
a transmission electron microscope. As a result, they were almost
disc-like particles with a particle size of 15 to 25 nm. The
synthesis conditions for preparing the silicon oxide particles, the
crystal structure of the particles examined by X-ray diffraction,
and the average particle size and the shape of the particles found
from the transmission electron microphotograph of the particles are
summarized in Table 4.
Example 24
[0193] Silicon oxide particles were obtained by forming a
precipitate containing silicon hydroxide, washing the precipitate
with water, filtering, drying and subjecting the product to a
heating treatment in the same manner as in the synthesis of the
silicon oxide particles of Example 22, except that the temperature
for the heating treatment of the product of the hydrothermal
treatment was changed from 800.degree. C. to 1,000.degree. C.
[0194] The shapes of the silicon oxide particles were observed with
a transmission electron microscope. As a result, they were almost
disc-like particles with a particle size of 70 to 100 nm. The
synthesis conditions for preparing the silicon oxide particles, the
crystal structure of the particles examined by X-ray diffraction,
and the average particle size and the shape of the particles found
from the transmission electron microphotograph of the particles are
summarized in Table 4.
Example 25
[0195] Silicon oxide particles were obtained as follows:
[0196] In the synthesis of the silicon oxide particles of Example
22, the product of the hydrothermal treatment was washed with water
in an amount 500 times larger than the volume of the suspension of
the precipitate, and filtered and dried. The pH of the product
found after the washing was 7.5. The steps following the heating
treatment were carried out in the same manner as in Example 22.
[0197] The shapes of the silicon oxide particles were observed with
a transmission electron microscope. As a result, they were almost
disc-like particles with a particle size of 30 to 40 nm. The
synthesis conditions for preparing the silicon oxide particles, the
crystal structure of the particles examined by X-ray diffraction,
and the average particle size and the shape of the particles found
from the transmission electron microphotograph of the particles are
summarized in Table 4.
Example 26
[0198] Silicon oxide particles were obtained in the same manner as
in Example 22, except that the particles obtained by the heating
treatment at 80.degree. C. in an air for one hour were further
washed water, using an ultrasonic disperser.
[0199] The shapes of the silicon oxide particles were observed with
a transmission electron microscope. As a result, they were almost
disc-like particles with a particle size of 30 to 40 nm. The
synthesis conditions for preparing the silicon oxide particles, the
crystal structure of the particles examined by X-ray diffraction,
and the average particle size and the shape of the particles found
from the transmission electron microphotograph of the particles are
summarized in Table 4.
Example 27
[0200] A precipitate containing silicon hydroxide was formed by
adding dropwise an aqueous 1N hydrochloric acid solution to an
aqueous sodium metasilicate solution until the pH reached 7.5, in
the same manner as in the synthesis of the silicon oxide particles
of Example 22, except that the alkaline aqueous solution prepared
by dissolving only sodium metasilicate (0.074 mol) in water (800
ml) without 2-aminoethanol was used instead of the alkaline aqueous
solution of sodium metasilicate (0.074 mol) and 2-aminoethanol (100
ml) in water (800 ml). Then, the resulting precipitate in the state
of the suspension was aged for 20 hours and then washed with water
until the pH reached 7.6.
[0201] Next, the supernatant was removed, and the suspension of the
precipitate was charged in an autoclave and subjected to a
hydrothermal treatment at 200.degree. C. for 2 hours.
[0202] The shapes of the resultant silicon oxide particles were
observed with a transmission electron microscope. As a result, they
were almost disk-like particles with a particle size of 20 to 30
nm, although having a slightly wide particle size distribution. The
synthesis conditions for preparing the silicon oxide particles, the
crystal structure of the particles examined by X-ray diffraction,
and the average particle size and the shape of the particles found
from the transmission electron microphotograph of the particles are
summarized in Table 4.
Comparative Example 5
[0203] A precipitate containing silicon hydroxide was formed and
directly washed with water, filtered, dried and subjected to a
heating treatment in the same manner as in the synthesis of the
silicon oxide particles of Example 22, except that the hydrothermal
treatment of the precipitate was not carried out. Thus, silicon
oxide particles were obtained.
[0204] The shapes of the resultant silicon oxide particles were
observed with a transmission electron microscope. As a result, it
was found that the particles were sintered or agglomerated
particles, and thus, that such particles had a very wide particle
size distribution of 1 to 10 .mu.m. The synthesis conditions for
preparing the silicon oxide particles, the crystal structure of the
particles examined by X-ray diffraction, and the average particle
size and the shape of the particles found from the transmission
electron microphotograph of the particles are summarized in Table
4. The average particle size evaluated from the transmission
electron microphotograph was calculated from 300 particles in the
photograph.
(Results of Observation of Silicon Oxide Particles with a
Transmission Electron Microscope)
[0205] FIG. 15 is the transmission electron microphotograph of the
silicon oxide particles obtained in Example 22. It is seen from the
photograph that the silicon oxide particles were almost disc-like
shaped particles with a particle size of 30 to 40 nm. Hitherto, it
has been very difficult to form such plate-form silicon oxide
particles with very small particle sizes by any of conventional
processes, and the process of the present invention has, for the
first time, succeeded in forming such particles.
TABLE-US-00004 TABLE 4 Temp. (.degree. C.)/ Temp. time (hr.)
(.degree. C.)/ Crystal PH in of hydro- time (hr.)
growth-controlling precipitating thermal of heating agent step
treatment treatment Ex. 22 2-amino-ethanol 8.3 200/2 800/1 Ex. 23
2-amino-ethanol 8.3 200/2 600/1 Ex. 24 2-amino-ethanol 8.3 200/2
1,000/1 Ex. 25 2-amino-ethanol 8.3 200/2 800/1 Ex. 26
2-amino-ethanol 8.3 200/2 80/1 Ex. 27 No addition 7.5 200/2 80/1
Com. Ex. 5 2-amino-ethanol 8.3 No 800/1 treatment Crystal Shape of
Av. particle structure particle size (nm) Ex. 22 amorphous
disc-like 34 Ex. 23 amorphous disc-like 21 Ex. 24 amorphous
disc-like 85 Ex. 25 amorphous disc-like 34 Ex. 26 amorphous
disc-like 31 Ex. 27 amorphous disc-like 22 Com. Ex. 5 amorphous
agglomerated >1,000
[0206] As is apparent from Table 4, the silicon oxide particles
obtained in the above Examples were found to be amorphous in
crystal structure from the X-ray diffraction spectra, however, had
plate-form shapes. Such plate-form shaped silicon oxide particles
have been realized by the present invention for the first time.
[0207] On the other hand, the silicon oxide particles of
Comparative Example 5 had large particle sizes due to the sintering
or agglomeration, and also had a very wide particle size
distribution. Therefore, the silicon oxide particles of Comparative
Example are not suitable for the use as abrasive members and the
like.
[0208] The particle sizes of the silicon oxide particles of the
present invention are within the ranges optimal for not only
abrasive members for abrasive sheets and abrasive liquids but also
additive particles for magnetic tapes and a variety of functional
sheets. Hitherto, silicon oxide particles which concurrently have
unique plate-form shapes and particle sizes of so fine as 100 nm or
less have not been realized, and will find quite new applications
which are believed to be impossible so far.
(5) Examples of Iron Oxide Particles
Example 2
[0209] The following two different aqueous solutions were
prepared.
TABLE-US-00005 Solution A: Ferric chloride
(FeCl.sub.3.cndot.6H.sub.2O) 20 g Water 500 cc Solution B: Sodium
hydroxide 30 g Monoethanolamine 50 cc Water 1,000 cc
[0210] The solution A was added dropwise into the solution B in
about one hour while stirring and maintaining the solutions A and B
at 12.degree. C. After completion of the dropwise addition, the
mixture was further stirred for one hour. The resultant precipitate
was left to stand at room temperature for about 20 hours, washed
with pure water, adjusted in pH to 11.3 by the addition of an
aqueous sodium hydroxide solution, and subjected to a hydrothermal
treatment at 150.degree. C. for one hour in an autoclave.
Plate-form goethite (.alpha.-FeOOH) was obtained by this treatment.
To the goethite was added a sodium silicate solution in an amount
of 1 wt. % in terms of SiO.sub.2 based on the weight of the
goethite, while being stirred. Hydrochloric acid was added to the
solution to adjust the pH to 7.3. Thus, the resultant particles
were coated with SiO.sub.2, and filtered, dried and dehydrated by
heating at 600.degree. C. in an air for one hour. Plate-form
.alpha.-iron oxide particles (.alpha.-Fe.sub.2O.sub.3) were
obtained by this heating treatment.
[0211] The resultant plate-form .alpha.-iron oxide particles were
disc-like or hexagonal plate-form particles with an average
particle size of 65 nm which had pores with diameters of about 30
nm at and around their center portions. It is seen from the X-ray
diffraction spectrum that they were alpha hematite having corundum
structures.
[0212] FIG. 16 is the electron microphotograph of the iron oxide
particles. The synthesis conditions for their on oxide particles,
the crystal structure thereof, and the average particle size and
shape thereof found from the transmission electron microphotograph
are summarized in Table 5.
Example 29
[0213] A precipitate was formed in the same manner as in Example
28, except that the temperature for maintaining both solutions A
and B during the dropwise addition of the solution A into the
solution B was changed from 12.degree. C. to 18.degree. C. The
resultant precipitate was then subjected to a hydrothermal
treatment, and dehydrated by heating in the same manner as in
Example 28 to obtain disc-like or hexagonal plate-form iron oxide
particles with an average particle size of 90 nm, having pores
therein. The iron oxide particles were found to be alpha hematite
with a corundum structure, from the X-ray diffraction spectrum.
[0214] FIG. 17 is the electron microphotograph of the iron oxide
particles. The synthesis conditions for the iron oxide particles,
the crystal structure thereof, and the average particle size and
shape thereof found from the transmission electron microphotograph
are summarized in Table 5.
Comparative Example 6
[0215] A precipitate was formed by adding dropwise the solution A
into the solution B as in the synthesis of the iron oxide particles
of Example 28, and the precipitate was coated with SiO.sub.2
without undergoing the hydrothermal treatment, filtered, dried and
dehydrated by heating at 600.degree. C. in an air for one hour.
[0216] Iron oxide particles obtained by this heating treatment had
granular shapes and an average particle size of 60 nm, and were not
plate-form shaped unlike the particles of Examples 28 and 29. The
synthesis conditions for the iron oxide particles, the crystal
structure thereof, and the average particle size and shape thereof
found from the transmission electron microphotograph are summarized
in Table 5.
(Results of Observation of Iron Oxide Particles with a Transmission
Electron Microscope)
[0217] FIGS. 16 and 17 are the transmission electron
microphotographs of the iron oxide particles obtained in Examples
28 and 29, respectively. The iron oxide particles of Example 28
shown in FIG. 16 were found to be plate-form particles with an
average particle size of 65 nm, and the iron oxide particles of
Example 29 shown in FIG. 17 were found to be plate-form particles
with an average particle size of 90 nm. Either of the iron oxide
particles have pores therein. The pores were formed because of the
dehydration while the plate-form goethite particles obtained by the
hydrothermal treatment were being subjected to the heating
treatment. The shapes and sizes of the pores formed by heating and
dehydrating the plate-form hydroxide particles vary depending on
the types of materials used: i.e., such pores include from very
fine micro pores to relatively large pores as found in the
plate-form iron oxide particles of the present invention. However,
the formation of such pores does not impair the features of the
plate-form particles, such as abrading properties, etc., of the
present invention, in any way.
TABLE-US-00006 TABLE 5 Temp. (.degree. C.)/ Temp. PH/temp. time
(hr.) (.degree. C.)/ Crystal (.degree. C.) in of hydro- time (hr.)
growth-controlling precipitating thermal of heating agent step
treatment treatment Ex. 28 2-amino-ethanol & 11.3/12 150/2
600/1 sodium silicate Ex. 29 2-amino-ethanol & 11.3/18 150/2
600/1 sodium silicate Com. Ex. 6 2-amino-ethanol & 11.3/12 No
600/1 sodium treatment silicate Crystal Shape of Av. particle
structure particle size (nm) Ex. 28 .alpha.-Fe.sub.2O.sub.3
disc-like to 65 hexagonal plate Ex. 29 .alpha.-Fe.sub.2O.sub.3
disc-like to 90 hexagonal plate Com. Ex. 6 .alpha.-Fe.sub.2O.sub.3
granular 60
[0218] As is apparent from Table 5, the iron oxide particles
obtained in the above Examples were found to have a corundum
structure and to be plate-form particles. Iron oxide particles with
such shapes have been realized for the first time by the present
invention.
[0219] On the other hand, the iron oxide particles of Comparative
Example 6 were granular and were not formed with such plate-form
shapes as seen in the present invention.
[0220] The particle sizes of the iron oxide particles of the
present invention are within the ranges optimal for not only
abrasive members for abrasive sheets and abrasive liquids but also
additive particles for magnetic tapes and a variety of functional
sheets. Hitherto, silicon oxide particles which concurrently have
unique plate-form shapes and particle sizes of so fine as 100 nm or
less have not been realized, and will find quite new applications
which are believed to be impossible so far.
(6) Examples of Application to Abrasive Tape
[0221] Next, examples of application of the plate-form oxide
particles of the present invention to an abrasive tape as one of
abrasive members will be described. The abrasive tape is provided
by forming an abrasive layer containing an abrasive material on the
surface of a film-like or sheet-like support, and cutting the
resulting lamination sheet into tapes with predetermined widths.
The only different point of the abrasive tape from an abrasive
sheet and an abrasive film is in the form thereof. Accordingly, the
application of the plate-form oxide particles of the present
invention to abrasive sheets and abrasive films also provides
similar effects as described in the following examples.
Examples 30 to 44, and Comparative Examples 7 to 16
[0222] Abrasive coating liquids for abrasive layers, having the
following compositions, were prepared by using the plate-form oxide
particles of the present invention and the oxide particles of
Comparative Examples, respectively.
[0223] The oxide particles used in the experiments were prepared by
carrying out the experiments of Example 1 and the like on larger
scales. (The rest were done in the same manner.)
Components of a Coating Liquid for Forming an Abrasive Layer
TABLE-US-00007 [0224] Non-magnetic oxide particles 200 parts Vinyl
chloride-vinyl acetate copolymer 30 parts ("VAGH" manufactured by
UCC) Polyurethane resin 25 parts ("Viron UR8300" manufactured by
TOYOBO CO., LTD.) Methyl ethyl ketone 150 parts Toluene 150 parts
Cyclohexanone 130 parts ("Parts" are "wt. parts", unless otherwise
specified.)
[0225] The above components of the coating liquid were mixed and
stirred, and the resulting mixture was dispersed in a sand mill to
prepare a coating liquid for use in forming an abrasive layer. The
coating liquid was applied on one side of a support of a
polyethylene terephthalate film with a thickness of 75 .mu.m so
that the thickness of the resultant layer of the coating liquid
could be 10 .mu.m after calendered. The layer was dried and
planished by calendering. The resultant lamination sheet was cut
into tapes with predetermined widths to provide abrasive tapes.
[0226] Table 6 shows the kinds of the abrasive tapes and the main
properties of the oxide particles used in these abrasive tapes.
TABLE-US-00008 TABLE 6 Properties of Oxide Particles Used Average
Ex. No./Com. Ex. Shape of particle No. Kind Particles size (nm) Ex.
30 Ex. 1 cerium oxide hexagonal plate 13 Ex. 31 Ex. 3 cerium oxide
hexagonal-rectangle 32 plate Ex. 32 Ex. 7 cerium oxide hexagonal
plate 20 C. Ex. 7 C. Ex. 1 cerium oxide agglomerated >1,000 C.
Ex. 8 -- cerium oxide granular ca. 100 Ex. 33 Ex. 8 zirconium oxide
hexagonal 19 plate-form Ex. 34 Ex. 9 zirconium oxide hexagonal 25
plate-form Ex. 35 Ex. 14 zirconium oxide hexagonal 20 plate-form C.
Ex. 9 C. Ex. 2 zirconium oxide agglomerated >1,000 C. Ex. 10 --
zirconium oxide granular ca. 40 Ex. 36 Ex. 15 aluminum oxide
rectangle 38 (.gamma.-alumina) plate-form Ex. 37 Ex. 17 aluminum
oxide rectangle 17 (.gamma.-alumina) plate-form Ex. 38 Ex. 18
aluminum oxide hexagonal 70 (.gamma.-alumina) plate-form Ex. 39 Ex.
20 aluminum oxide rectangle 48 (.alpha.-alumina) plate-form Ex. 40
Ex. 21 aluminum oxide rectangle 52 (.gamma.-alumina) plate-form C.
Ex. 11 C. Ex. 4 aluminum oxide agglomerated 500 (.gamma.-alumina)
C. Ex. 12 -- aluminum oxide granular ca. 80 (.alpha.-alumina) Ex.
41 Ex. 22 silicon oxide disc-like 34 (amorphous) Ex. 42 Ex. 27
silicon oxide disc-like 22 (amorphous) C. Ex. 13 C. Ex. 5 silicon
oxide agglomerated >1,000 (amorphous) C. Ex. 14 -- silicon oxide
spherical ca. 10 (colloidal silica) Ex. 43 Ex. 28 iron oxide
rectangle-hexagonal 65 (.alpha.-hematite) plate-form Ex. 44 Ex. 29
iron oxide rectangle-hexagonal 90 (.alpha.-hematite) plate-form C.
Ex. 15 C. Ex. 6 iron oxide granular 60 (.alpha.-hematite) C. Ex. 16
-- iron oxide cubic 150 (.alpha.-hematite)
[0227] Examples and Comparative Examples in the right side of the
column "Example/Comparative Example" in Table 6 mean that the oxide
particles obtained in these Examples and Comparative Examples were
used. Also, in Table 6, the abrasive tapes of Comparative Examples
8, 10, 12, 14 and 16 were made, using cerium oxide particles,
zirconium oxide particles, aluminum oxide particles, silicon oxide
particles and iron oxide particles, respectively, which were all
commercially available and were compounded in the same components
by the same method as used in the foregoing coating liquid for
forming the abrasive layer. These oxide particles are all
commercially available and sold as so-called fine particles with
spherical, granular or cubic shapes. The abrasive tapes using these
commercially available oxide particles were made for comparing the
abrading properties of the abrasive tapes using the plate-form
oxide particles featured by the present invention.
[0228] The abrasive tapes using the oxide particles of Examples and
Comparative Examples were subjected to glass-flawing tests
according to the following method, and the performance thereof were
evaluated. The results are shown in Table 7.
(Flawing Test)
[0229] Both ends of an abrasive tape were fixed on a glass plate,
and a glass ball with a diameter of 5 mm (NIKKATO CORPORATION) was
reciprocally slid 100 times at a sliding speed of 3,000 mm/min.
with a sliding scale of 20 mm under a load of 20 g, on the abrasive
tape impregnated with water, using a surface tester ("HEIDON-14DR"
manufactured by Shintokagaku). Then, the abrasion degree of the
glass ball was observed with a microscope and evaluated based on
five criteria. In this regard, the abrasion degree is larger as the
criterion value increases. The abrasion flaws were evaluated based
on four criteria by observing the surface of the glass ball with a
microscope. The criteria of the abrasion flaws were determined as
follows. [0230] A: No flaw found on the surface of the glass ball.
[0231] B: Two or less flaws found on the surface of the glass ball.
[0232] C: Three or four flaws found on the surface of the glass
ball. [0233] D: Five or more flaws found on the surface of the
glass ball.
TABLE-US-00009 [0233] TABLE 7 Abrasion degree Evaluation of flaws
Ex. 30 ca. 3 A Ex. 31 3 or 4 B or A Ex. 32 ca. 3 B or A Com. Ex. 7
ca. 4 D Com. Ex. 8 3 or 4 C Ex. 33 ca. 3 A Ex. 34 3 or 4 B or A Ex.
35 ca. 3 B or A Com. Ex. 9 4 or 5 D Com. Ex. 10 ca. 4 C Ex. 36 3 or
4 B or A Ex. 37 ca. 3 B or A Ex. 38 4 or 5 B Ex. 39 3 or 4 B or A
Ex. 40 ca. 4 B Com. Ex. 11 ca. 5 D Com. Ex. 12 ca. 5 D Ex. 41 ca. 3
A Ex. 42 2 or 3 A Com. Ex. 13 ca. 3 C Com. Ex. 14 ca. 2 A Ex. 43
ca. 3 A Ex. 44 3 or 4 B or A Com. Ex. 15 ca. 3 B Com. Ex. 16 3 or 4
C
[0234] The results of Tables 6 and 7 clearly show the difference
between the abrasive tapes using the plate-form oxide particles of
the present invention and the abrasive tapes using the oxide
particles of Comparative Examples which were subjected to the
heating treatments alone without the hydrothermal treatments in
case where the oxide particles of the same oxide were used in both
cases. In other words, the abrasive tapes using the plate-form
oxide particles of the present invention show less flaws while
maintaining appropriate abrading properties, and thus were well
balanced. On the other hand, the abrasive tapes using the oxide
particles of Comparative Examples were found to be unsuitable for
use in the abrasive tapes, since they were very susceptible to
flawing in spite of their higher abrading properties because of
their larger particle sizes.
[0235] In case where the abrasive tapes were made using the
commercially available oxide particles of the same oxide and sold
as very fine particles, such abrasive tapes were satisfactory in
balance between the abrading properties and the degree of abrasion.
However, the abrasive sheets made using the commercially available
oxide particles were inferior in total evaluation of the
properties, to the abrasive tapes made using the plate-form oxide
particles with a particle size of 10 to 100 nm of the present
invention.
[0236] This may be because the commercially available oxide
particles were granular, spherical or cubic, while the oxide
particles of the present invention were plate-form shaped. In
particular, when the plate-form oxide particles of the present
invention are used, the abrading properties are imparted to the
tape, since the edges of the plate-form particles are effectively
utilized, and the plate-form faces of the plate-form particles
improve the conditions for contact with a surface to be polished.
As a result, the excellent abrasive performance as mentioned above
can be imparted.
[0237] Although it seems to be meaningless to make comparison
between each of the oxide particles of the present invention, the
aluminum oxide particles and the zirconium oxide particles have
relatively higher abrading properties, and the cerium oxide
particles, the iron oxide particles and the silicon oxide particles
have relatively lower abrading properties. On the other hand, the
evaluation of the flaw degrees of the above oxide particles is
reversed to the evaluation of the abrading properties thereof.
Therefore, the appropriate selection of the oxide particles in
accordance with the end use is important. However, the abrasive
tapes made using any of the plate-form oxide particles of the
present invention with a particle size of 10 to 100 nm are superior
in total evaluation of the properties, to the abrasive tapes made
using the conventional granular, spherical or cubic oxide particles
as mentioned above.
[0238] The foregoing Examples are described as being applied to the
abrasive sheets by making good use of the excellent abrading
properties of the oxide particles of the present invention. The
oxide particles of the present invention, however, are not
necessarily applied to the sheets, and are, of course, applied to
abrasive liquids and abrasive slurry. That is, by making good use
of the unique shapes of the non-magnetic oxide particles of the
present invention, the oxide particles of the present invention can
exhibit excellent properties as particles for abrasive members,
independently of the final form thereof.
[0239] As mentioned above, it can be understood that the use of the
plate-form cerium oxide, zirconium oxide, aluminum oxide, silicon
oxide and iron oxide particles of the present invention with a
particle size of 10 to 100 nm can provide good-balanced abrasive
sheets which show less flaws due to abrasion while maintaining high
abrading properties.
(7) Examples of Application to a Coating Type Magnetic Recording
Medium (Magnetic Tape)
[0240] Next, description is made on an example of applying the
plate-form oxide particles of the present invention to an additive
for a coating type magnetic tape as one of coating type magnetic
recording media.
Examples 45 to 49 and Reference Example 1
Components of Coating Composition for Primer Layer
TABLE-US-00010 [0241] (1) Oxide particles (see Table 8 below) 76
parts Carbon black 24 parts (average particle size: 25 nm, and: oil
absorption 55 g/cc) Stearic acid (lubricant) 2.0 parts Vinyl
chloride-hydroxypropyl acrylate copolymer 8.8 parts (content of
--SO.sub.3Na groups: 0.7 .times. 10.sup.-4 eq./g)
Polyester-polyurethane resin 4.4 parts (content of --SO.sub.3Na
groups: 1.0 .times. 10.sup.-4 eq./g) Cyclohexanone 25 parts Methyl
ethyl ketone 40 parts Toluene 10 parts (2) Butyl stearate
(lubricant) 1 part Cyclohexanone 70 parts Methyl ethyl ketone 50
parts Toluene 20 parts (3) Polyisocyanate (crosslinking agent) 2.0
parts Cyclohexanone 10 parts Methyl ethyl ketone 15 parts
Toluene
[0242] Toluene
Components of Coating Composition for Magnetic Layer
TABLE-US-00011 [0243] (1) Ferromagnetic iron metal powder 100 parts
[Co/Fe: 25 wt. %, Y/Fe: 9.3 wt. %, Al/Fe: 3.5 wt. %, Ca/Fe: 0 wt.
%, .sigma.s: 155 A m.sup.2/kg, Hc: 188.2 kA/m, pH: 9.4, average
major axis length: 0.10 .mu.m] Vinyl chloride-hydroxypropyl
acrylate copolymer 12.3 parts (content of --SO.sub.3Na groups: 0.7
.times. 10.sup.-4 eq./g) Polyester-polyurethane resin 5.5 parts
(content of --SO.sub.3Na groups: 1.0 .times. 10.sup.-4 eq./g)
.alpha.-alumina (average particle size: 0.12 m) 10.0 parts Carbon
black 1.0 part (average particle size: 75 nm, and DBP oil
absorption: 72 cc/100 g) Metal acid phosphate 2 parts Amide
palmitate 1.5 parts n-Butyl stearate 1.0 part Tetrahydrofuran 65
parts Methyl ethyl ketone 245 parts Toluene 85 parts (2)
Polyisocyanate (crosslinking agent) 2.0 parts Cyclohexanone 167
parts
[0244] A coating composition for a primer layer was prepared from
the above components of the coating composition for the primer
layer, as follows: Firstly, the components (1) were kneaded with a
kneader, and thereto were added the components (2). The mixture was
stirred and dispersed for a residence time of 60 minutes in a sand
mill. To the mixture were added the components (3), and they were
stirred and filtered to give the coating composition for the primer
layer. Separately, a coating composition for a magnetic layer was
prepared from the above components of the coating composition for
the magnetic layer, as follows: Firstly, the components (1) were
kneaded with a kneader and dispersed for a residence time of 45
minutes in a sand mill. To the dispersion were added the components
(2), and the mixture was stirred and filtered to give the magnetic
coating composition.
[0245] Next, the above coating composition for the primer layer was
applied on a non-magnetic substrate composed of a polyethylene
naphthalate film (PEN having a thickness of 6.2 .mu.m, a humidity
expansion coefficient of 5.6.times.10.sup.-6% RH, a thermal
expansion coefficient of -7.4.times.10.sup.-6/.degree. C., MD of
6.50 GPa, and MD/TD of 0.54, manufactured by Teijin Limited,
provided that MD means the Young's modulus of the film in the
film-drawing direction (the lengthwise direction), and that TD
means the Young's modulus in a direction orthogonal to the
film-drawing direction (the widthwise direction)), so that the
resultant primer layer of the coating composition could be 1.8 m
after dried and calendered. The above magnetic coating composition
was applied on the primer layer by the wet-on-wet method, so that
the resultant magnetic layer could have a thickness of 0.15 .mu.m
after subjected to an orientation treatment in a magnetic field,
dried and calendered. The magnetic layer was orientated in a
magnetic field and dried with a drier to give a magnetic sheet. The
orientation treatment in the magnetic field was carried out by
disposing N--N opposed magnets (5 kG) in front of the drier, and
disposing two pairs of N--N opposed magnets (5 kG) at an interval
of 50 cm and at positions 75 cm before a position where the dryness
of the coating layer was felt with one's finger within the drier.
The coating rate was 100 m/min.
Components of Coating Composition for Backcoat Layer
TABLE-US-00012 [0246] Carbon black (average particle size: 25 nm)
80 parts Carbon black (average particle size: 370 nm) 20 parts
Nitrocellulose 44 parts Polyurethane resin (containing SO.sub.3Na
groups) 30 parts Cyclohexanone 260 parts Toluene 260 parts Methyl
ethyl ketone 525 parts
[0247] The above components of the coating composition for the
backcoat layer were dispersed in a sand mill for a residence time
of 45 minutes, and thereto was added polyisocyanate (13 parts) as a
crosslinking agent, and the mixture was filtered to obtain the
coating composition for the backcoat layer. This coating
composition was applied to the other surface of the magnetic sheet
reverse to the magnetic layer formed thereon so that the resultant
backcoat layer could have a thickness of 0.5 .mu.m after dried and
calendered. The resultant magnetic sheet was planished with a
seven-staged calender comprising metallic rolls, at 100.degree. C.
under a linear pressure of 150.times.9.8 N/cm (150 kg/cm). The
resultant magnetic sheet (for magnetic tapes) was wound onto a core
and aged at 70.degree. C. for 72 hours.
[0248] Next, the magnetic sheet was cut into a plurality of
magnetic tapes each having a width of 1/2 inch using a slitting
system. The resultant magnetic tape was wound onto a reel and
assembled in a casing body to finish a magnetic tape cartridge for
use in a computer (or a computer tape).
[0249] The computer tape thus obtained was evaluated with respect
to the basic properties such as reproducing output properties,
error rate, servo properties, etc. Above all, off-track amount
which would give serious influence on the servo properties is
particularly described. The off-track amount is greatly influenced
by the properties of the non-magnetic particles used in the primer
layer. In this context, several comparisons for evaluating
off-track amounts were made between the use of each of the
plate-form oxide particles of the present invention as non-magnetic
particles for the primer layer and the use of conventional
needle-like .alpha.-iron oxide particles therefor. The off-track
amounts of these cases were measured by the following method.
(Measurement of Off-Track Amount)
[0250] Recording (at a recording wavelength of 0.55 .mu.m) was made
on a computer tape at a temperature of 10.degree. C. and a humidity
of 10% RH by using an adapted LTO drive (in which the recording
track width was 20.6 .mu.m, and the reproducing track width, 12
.mu.m), and then, reproducing was made from the same computer tape
at a temperature of 10.degree. C. and a humidity of 10% RH, and at
a temperature of 29.degree. C. and a humidity of 80% RH,
respectively, so as to calculate a reproduction ratio. The
off-track amount was determined from such a reproduction ratio. In
this connection, when a LTO drive having recording tracks with a
width of 80 .mu.m and reproducing tracks with a width of 50 .mu.m
was used, almost no decrease in output due to off-track (1% or
less) occurred.
[0251] Table 8 shows the results of the comparisons for evaluating
off-track amounts which were made between the use of each of the
plate-form oxide particles of the present invention as the oxide
particles for the primer layer and the use of the conventional
acicular .alpha.-iron oxide particles for the primer layer.
TABLE-US-00013 TABLE 8 Oxide particles used in a primer layer
Off-track Particle amount Kind Shape size (nm) Ex. No. (%) Ex. 45
cerium hexagonal 32 Ex. 3 2.7 oxide to rectangle Ex. 46 zirconium
hexagonal 23 Ex. 9 2.8 oxide Ex. 47 aluminum rectangle 38 Ex. 15
1.9 oxide Ex. 48 silicon disc-like 22 Ex. 22 2.2 oxide Ex. 49 iron
rectangle 65 Ex. 28 3.6 oxide to hexagonal Ref. iron acicular 120
-- 6.7 Ex. 1 oxide (.alpha.-Fe.sub.2O.sub.3)
[0252] As is apparent from Table 8, the off-track amount was
smaller when the plate-form particles with a particle size of 10 to
100 nm according to the present invention were used as then
on-magnetic oxide particles of the primer layer, as compared with
the use of the conventional needle-like oxide particles.
[0253] In general, off-track does not cause so serious problems in
case where the width of the recording tracks is sufficiently wide.
However, problems caused by off-track becomes serious as the width
of the recording tracks becomes narrower. When the off-track amount
is larger, an off-track error arises, and thus, it becomes
impossible to carry out normal servo control. This problem occurs
in common in both of the magnetic servo system and the optical
servo system, of which the optical servo system is far more
markedly influenced by the off-track amount, because the mass of a
whole of the magnetic head array used in the optical servo system
is larger than that of the magnetic head array used in the magnetic
serve system.
[0254] The use of the plate-form oxide particles of the present
invention makes it possible to decrease PES (a standard deviation
of positional shift), and makes it hard to cause off-track even if
the recording track width is as narrow as 21 .mu.m or less and also
even if a change in temperature occurs. Thus, it becomes possible
to provide a magnetic tape and a magnetic tape cartridge with
excellent servo properties and a lower error rate.
[0255] This may be assumed that the plate-form shapes of the
particles facilitate the array of the plate-form faces of the
particles in parallel to the coating surface in the coating layer,
and consequently that the anisotropy of elastic modulus is small in
the interior of the tape. In addition, the particles of the present
invention have a small particle size of 10 to 100 nm and also have
plate-form shapes, and therefore have larger surface are as. As a
result, such particles can more firmly be bound with a binder, and
thus can provide an excellent magnetic tape with less thermal and
mechanical deformation.
[0256] In the above Examples, the use of the plate-form particles
of the present invention in the primer layers are described.
However, other than the primer layers, the addition of the
plate-form particles of the present invention in the magnetic
layers and the backcoat layers is, of course, effective. That is,
when the non-magnetic oxide particles of the present invention are
used in magnetic tapes by making good use of their plate-form
shapes, the most distinguished feature of the present invention in
contrast to the granular shapes, plate-form needle shapes or cubic
shapes of the conventional non-magnetic oxide particles, the
resultant magnetic tapes show far less deformation due to a change
in temperature or humidity or far less mechanical deformation, and
thus are optimal for high density recording.
[0257] Further, the use of the non-magnetic oxide particles of the
present invention in the magnetic layer provides a magnetic tape
with less thermal and mechanical deformation as mentioned above,
and the magnetic layer containing such oxide particles can also act
as an abrasive material as described in Examples of the abrasive
tape. The action as the abrasive is more effectively exhibited as
the thickness of the magnetic layer reduces. In particular, when
the thickness of the magnetic layer is so thin as 0.1 .mu.m or
less, the granular or spherical particles used so far as the
additive in such a magnetic layer protrude from the surface of the
magnetic layer, and thus, the surface smoothness of the magnetic
layer degrades. By contrast, the non-magnetic oxide particles of
the present invention are plate-form shaped, having a particle size
of 10 to 100 nm, and therefore, such particles do not protrude from
the surface of the magnetic layer, or, even if protrude, the degree
of the protrusion is far smaller in comparison with the
conventional oxide particles. Therefore, the magnetic layer
according to the present invention can have excellent surface
smoothness while maintaining the abrading property.
(8) Application of the Non-Magnetic Plate-Form Oxide Particles to
an Abrasive Liquid
[0258] Next, the application of the plate-form oxide particles of
the present invention to an abrasive liquid is described.
Example 50
[0259] A slurry-like abrasive liquid was prepared as follows by
using the cerium oxide particles obtained in Example 1 as abrasive
particles.
[0260] To a solution of polyammonium acrylate (3 g) in pure water
(300 cc) were added the plate-form cerium oxide particles (24 g)
obtained by the foregoing method, and the mixture was dispersed at
3,000 rpm for one hour with a homomixer. The resultant slurry-like
abrasive liquid was very stable and showed almost no precipitate
therein even after left to stand for one day.
Example 51
[0261] A slurry-like abrasive liquid was prepared as follows by
using the silicon oxide particles obtained in Example 22 as
abrasive particles.
[0262] To a solution of polyammonium acrylate (3 g) in pure water
(300 cc) were added the above silicon oxide particles (24 g) in the
same manner as in Example 50, and a slurry-like abrasive liquid was
prepared in the same manner as in Example 50. The resultant
slurry-like abrasive liquid was very stable and showed almost no
precipitate therein even after left to stand for one day.
Example 52
[0263] A slurry-like abrasive liquid was prepared as follows by
using the zirconium oxide particles obtained in Example 8 as
abrasive particles.
[0264] To a solution of polyammonium acrylate (3 g) in pure water
(300 cc) were added the above zirconium oxide particles (24 g) in
the same manner as in Example 50, and a slurry-like abrasive liquid
was prepared in the same manner as in Example 50. The resultant
slurry-like abrasive liquid was very stable and showed almost no
precipitate therein even after left to stand for one day.
Example 53
[0265] A slurry-like abrasive liquid was prepared as follows by
using the aluminum oxide particles obtained in Example 15 as
abrasive particles.
[0266] To a solution of polyammonium acrylate (3 g) in pure water
(300 cc) were added the above aluminum oxide particles (24 g) in
the same manner as in Example 50, and a slurry-like abrasive liquid
was prepared in the same manner as in Example 50. The resultant
slurry-like abrasive liquid was very stable and showed almost no
precipitate therein even after left to stand for one day.
Example 54
[0267] Plate-form .alpha.-iron oxide particles obtained by the
following method were used instead of the cerium oxide particles
used in Example 50.
Preparation of Plate-Form .alpha.-Iron Oxide Particles
[0268] An alkaline aqueous solution was prepared by dissolving
sodium hydroxide (0.75 mol) and 2-aminoethanol (100 ml) in water
(800 ml). Separately, an aqueous ferric chloride solution was
prepared by dissolving ferric chloride (III) hexahydrate (0.074
mol) in water (400 ml). The alkaline aqueous solution and the
aqueous ferric chloride solution were cooled to 5.degree. C., and
to the alkaline aqueous solution was added dropwise the aqueous
ferric chloride solution under cooling so that the resultant
solution was not warmed to 8.degree. C. or higher, since this
dropwise addition increased the temperature of the solution due to
the heat of reaction. Thus, precipitate containing ferric hydroxide
was prepared. The pH of the precipitate was 11.3. The precipitate
in the state of a suspension was aged for 20 hours and then washed
with water until the pH was adjusted to 7.5.
[0269] Next, the supernatant was removed, and the suspension of the
precipitate was charged in an autoclave and subjected to a
hydrothermal treatment at 150.degree. C. for 2 hours.
[0270] The resultant product was filtered, dried at 90.degree. C.
in an air, lightly crushed in a mortar, and subjected to a heating
treatment at 600.degree. C. in an air for one hour to obtain
.alpha.-iron oxide particles. After the heating treatment, the
.alpha.-iron oxide particles were further washed with water using
an ultrasonic disperser, filtered and dried so as to remove the
unreacted substances and the residue.
[0271] As a result of the measurement of the X-ray diffraction
spectrum of the resultant .alpha.-iron oxide particles, a spectrum
corresponding to an .alpha.-hematite structure was clearly
observed. The shapes of the .alpha.-iron oxide particles were
further observed with a transmission electron microscope. As a
result, they were hexagonal plate-form particles with a particle
size of 30 to 40 nm.
Preparation of Slurry-Like Abrasive Liquid
[0272] To a solution of polyammonium acrylate (3 g) in pure water
(300 cc) were added the plate-form .alpha.-iron oxide particles (24
g) obtained by the above method, in the same manner as in Example
50, and a slurry-like abrasive liquid was prepared in the same
manner as in Example 50. The resultant slurry-like abrasive liquid
was very stable and showed almost no precipitate therein even after
left to stand for one day.
Comparative Example 17
Use of Cerium Oxide Particles as Abrasive Particles
[0273] Cerium carbonate was used as a salt of cerium instead of the
cerium oxide particles (prepared in Example 1) used in Example 50,
and this salt of cerium was oxidized by heating at 600.degree. C.
in an air, to obtain cerium oxide particles. The resultant cerium
oxide particles were coarse particles with particle sizes of
submicron, and thus were further milled in an aqueous medium with a
ball mill to obtain fine particles. The resultant cerium oxide
particles obtained by the milling contained from very fine
particles with a particle size of 0.1 m to particles with a
particle size of 1 .mu.m which might be the agglomerates of the
primary particles.
[0274] The shapes of the cerium oxide particles were mass-like and
irregular.
Preparation of Slurry-Like Abrasive Liquid
[0275] To a solution of polyammonium acrylate (3 g) in pure water
(300 cc) were added the above cerium oxide particles (24 g) in the
same manner as in Example 50, and a slurry-like abrasive liquid was
prepared in the same manner as in Example 50. The resultant
slurry-like abrasive liquid had unstable properties and formed
precipitate in short time when dispersed and then left to stand,
and the cerium oxide particles accumulated on the bottom of the
container.
Comparative Example 18
Use of Silicon Oxide Particles as Abrasive Particles
[0276] Commercially available colloidal silica was used. As a
result of the observation of the colloidal silica with a
transmission electron microscope, the colloidal silica particles
were substantially spherical, having the particle size distribution
from 10 to 100 nm.
Preparation of Slurry-Like Abrasive Liquid
[0277] To a solution of polyammonium acrylate (3 g) in pure water
(300 cc) were added the above colloidal silica particles (24 g) in
the same manner as in Example 50, and a slurry-like abrasive liquid
was prepared in the same manner as in Example 50. The resultant
slurry-like abrasive liquid had considerably stable properties and
formed a little precipitate after left to stand for one day.
Comparative Example 19
Use of Zirconium Oxide Particles as Abrasive Particles
[0278] The zirconium oxide particles prepared in Comparative
Example 2 were used.
[0279] A precipitate containing zirconium hydroxide was formed, and
was directly washed with water without undergoing a hydrothermal
treatment, filtered and dried in the same manner as in the
synthesis of the zirconium oxide particles of Example 8, and the
resultant particles were subjected to a heating treatment in the
same manner as in Example 8 to obtain zirconium oxide
particles.
[0280] As a result of the measurement of the X-ray diffraction
spectrum of the resultant zirconium oxide particles, peaks
corresponding to zirconium oxide were observed. The shapes of the
zirconium oxide particles were observed with a transmission
electron microscope. As a result, they were found to have a very
wide particle size distribution which included very fine particles
and coarse particles formed due to sintering or agglomeration.
[0281] The zirconium oxide particles were further milled in an
aqueous medium with a ball mill to obtain fine particles. The
resultant zirconium oxide particles obtained by milling had a wide
particle size distribution of from 0.1 .mu.m to 1 .mu.m. The shapes
of the zirconium oxide particles were mass-like and irregular.
Preparation of Slurry-Like Abrasive Liquid
[0282] To a solution of polyammonium acrylate (3 g) in pure water
(300 cc) were added the above zirconium oxide particles (24 g) in
the same manner as in Example 50, and a slurry-like abrasive liquid
was prepared in the same manner as in Example 50. The resultant
slurry-like abrasive liquid had unstable properties and formed
precipitate in short time when dispersed and then left to stand,
and the zirconium oxide particles accumulated on the bottom of the
container.
Comparative Example 20
Use of Aluminum Oxide Particles as Abrasive Particles
[0283] The aluminum oxide particles prepared in Comparative Example
4 were used. A precipitate containing aluminum hydroxide was formed
under the same conditions as those in Example 15, and washed with
water in an amount about 1,000 times larger than the volume of the
suspension of the precipitate, and then filtered without undergoing
a hydrothermal treatment, and dried at 90.degree. C. in an air. The
solid precipitate was lightly crushed in a mortar and was subjected
to a heating treatment at 600.degree. C. in an air for one hour in
the same manner as in Example 15 to obtain aluminum oxide
particles. To remove the unreacted substance and the residue, the
aluminum oxide particles were further washed with water using an
ultrasonic disperser, and filtered and dried.
[0284] The aluminum oxide particles were milled in an aqueous
medium with a ball mill to obtain fine particles. As a result of
the measurement of the X-ray diffraction spectrum of the resultant
aluminum oxide particles obtained by the pulverization, a spectrum
corresponding to .gamma.-alumina was observed. As a result of the
observation thereof with a transmission electron microscope, they
had a wide particle size distribution including very fine particles
with particles sizes of about 20 nm and particles with a particle
size of 1 .mu.m which might be sintered body or agglomeration of
the primary particles. The shapes of the aluminum oxide particles
were mass-like and irregular.
Preparation of Slurry-Like Abrasive Liquid
[0285] To a solution of polyammonium acrylate (3 g) in pure water
(300 cc) were added the above aluminum oxide particles (24 g) in
the same manner as in Example 53, and a slurry-like abrasive liquid
was prepared in the same manner as in Example 53. The resultant
slurry-like abrasive liquid had unstable properties and formed
precipitate in short time when dispersed and then left to stand,
and the aluminum oxide particles accumulated on the bottom of the
container.
Comparative Example 21
Use of .alpha.-Iron Oxide Particles as Abrasive Particles
[0286] Commercially available .alpha.-iron oxide particles were
used. The .alpha.-iron oxide particles of this type were sold on
the market for use as abrasive particles to be added to magnetic
tapes or the like. When the shapes of the particles were observed
with a transmission electron microscope, they were spherical or
granular, and had a narrow particle size distribution of from 0.2
to 0.3 .mu.m.
Preparation of Slurry-Like Abrasive Liquid
[0287] To a solution of polyammonium acrylate (3 g) in pure water
(300 cc) were added the above .alpha.-iron oxide particles (24 g)
in the same manner as in Example 50, and a slurry-like abrasive
liquid was prepared in the same manner as in Example 50. The
resultant slurry-like abrasive liquid had relatively stable
properties and formed a little precipitate after left to stand for
several hours.
Example 55
Abrasive Particles Used
[0288] The cerium oxide particles used in Example 50 and the
colloidal silica used in Comparative Example 18 were mixed for use.
The mixing proportions of the cerium oxide particles and the
colloidal silica particles were 70% by weight and 30% by weight,
respectively.
Preparation of Slurry-Like Abrasive Liquid
[0289] To a solution of polyammonium acrylate (3 g) in pure water
(300 cc) were added the above cerium oxide particles (16.8 g) and
the above colloidal silica (7.2 g) in the same manner as in Example
50, and a slurry-like abrasive liquid was prepared in the same
manner as in Example 50. The resultant slurry-like abrasive liquid
was very stable and formed almost no precipitate after left to
stand for one day.
(Evaluation)
[0290] A porous abrasive pad made of a urethane resin was applied
to a glass plate with a thickness of 10 mm. The slurry-like
abrasive liquid prepared in each of the above Examples and
Comparative Examples was added dropwise onto this pad at a rate of
10 cc/min., while a glass ball with a diameter of 6.25 mm was
rotated thereon at 30 rpm under a load of 20 g for 2 minutes with a
surface meter ("HEIDON-14DR" manufactured by Shintokagaku). Then,
the degree of the abrasion of the glass ball, and the abrasion
flaws on the surface of the glass ball were observed with a
microscope, and then evaluated based on four criteria of A, B C and
D as described below.
A: markedly abraded D: hardly abraded B and D: medium states
between A and D, provided that B indicates that the abrasion degree
was higher than C.
[0291] Five or more abrasion flaws on the surface of the glass ball
was evaluated as D; 3 to 4 abrasion flaws thereon, as C; 2 or less
abrasion flaws thereon, as B; and no abrasion flaw thereon, as A.
The results of the evaluation of the abrading properties are shown
in Table 9.
TABLE-US-00014 TABLE 9 Abrasive particles Abrading property
Particle Stability Degree of Flaws due to Kind Shape size of slurry
abrasion abrasion Ex. 50 Cerium Hexagonal 10 to 20 nm Very B A
oxide plate stable Ex. 51 Silicon Disc-like 30 to 40 nm Very B A
oxide plate stable Ex. 52 Zirconium Hexagonal 10 to 20 nm Very B A
oxide plate stable Ex. 53 Aluminum Rectangle 30 to 50 nm Very A B
oxide plate stable Ex. 54 .alpha.-iron Hexagonal 30 to 40 nm Very B
A oxide plate stable Ex. 55 Cerium Hexagonal 0 to 20 nm Very B A
oxide & plate & & 10 stable Silicon spherical to 100 nm
oxide Com. Ex. Cerium Irregular 0.1 to 1 .mu.m Unstable C C 17
oxide Com. Ex. Silicon Spherical 10 to Stable B B 18 oxide 100 nm
Com. Ex. Zirconium Irregular 0.1 to 1 .mu.m Unstable B D 19 oxide
Com. Ex. Aluminum Irregular 20 nm to Unstable A D 20 oxide 1 .mu.m
Com. Ex. .alpha.-iron Spherical 0.2 to Relatively C C 21 oxide 0.3
.mu.m stable
[0292] It is seen from the results of Table 9 that the slurry-like
abrasive liquids of the above Examples are very stable. This is
because the particle sizes thereof are as small as several tens
nanometers, and also because they are abrasive particles which show
almost no sintering or agglomeration and thus have very excellent
dispersibility. In addition, their abrading properties are good
despite of their small particle sizes. This is because the edge
portions of the particles are increased because of their plate-form
shapes, resulting in improved abrading power. Although some of the
particles of Examples are slightly lower in abrading power, their
abrading power is considered to be further improved, if the
conditions such as the number of rotations, loads to be applied,
etc. are optimized for the abrasive liquids.
[0293] Further, no flaw due to the abrasion is caused by any of the
abrasive liquids of Examples, since their particle sizes are so
small as several tens nanometers and also have narrow particle size
distributions. Therefore, no abrasion flaw is caused by such coarse
particles that would be often mixed in the very fine particles of
the conventional abrasive members.
[0294] On the other hand, the abrasive liquid of Comparative
Example 18 using the colloidal silica are relatively good in
abrading power and in the number of abrasion flaws, and thus is
well balanced. However, as compared with the abrasive liquid of
Example 51 using the silicon oxide particles of the same kind, the
abrasive liquid of Comparative Example 18 is inferior as a
whole.
[0295] The abrasive liquid of Comparative Example 21 using the
.alpha.-iron oxide particles is considered to be relatively well
balanced. However, higher abrading power can not be expected from
this abrasive liquid, because the hardness of iron oxides
themselves is intrinsically low. By contrast, the abrasive liquid
of Example 54 using the 1-iron oxide particles are greatly improved
in abrading power and in the number of abrasion flaws, as compared
with the abrasive liquid of Comparative Example 21, since the edge
portions of the abrasive particles of this Example are increased
because of their plate-form particle shapes.
[0296] The abrasive liquid of Comparative Example 17 using the
cerium oxide particles is relatively well balanced in abrading
properties, but is unsatisfactory as a whole. By contrast, the
abrasive liquid of Example 50 using the cerium oxide particles of
the same kind is greatly improved in abrading power and in the
number of the abrasion flaws, and thus, it is seen that the
plate-form cerium oxide particles of this Example are especially
suitable for the slurry-like abrasive liquid.
[0297] The abrasive liquid of Comparative Example 19 using the
zirconium oxide particles and the abrasive liquid of Comparative
Example 20 using the aluminum oxide particles are relatively high
in abrading power, but cause lots of abrasion flaws. This is
because the hardness of zirconium oxide and aluminum oxide are
intrinsically high, and also because it is considered that the
coarse particles mixed in the zirconium oxide particles and the
aluminum oxide particles of Comparative Examples caused the lots of
abrasion flaws. By contrast, the abrasive liquid of Example 52
using the plate-form zirconium oxide particles and the abrasive
liquid of Example 53 using the plate-form aluminum oxide particles
exhibited excellent abrading power without causing abrasion flaws,
because of their plate-form shapes with very small particle sizes
and their very narrow particle size distributions.
[0298] Furthermore, as shown in Example 55, the use of the mixture
of the plate-form particles of the present invention and the
general-purpose abrasive particles makes it possible to provide
abrasive members capable of flexibly corresponding to a variety of
articles to be polished.
(9) Other Applications
[0299] The non-magnetic plate-form particles of the present
invention can be applied to not only abrasive tapes, magnetic tapes
and abrasive liquids, but also various types of functional optical
films such as antireflection films, UV- or infrared-shielding
films, etc. Specifically, the non-magnetic plate-form particles
(particularly oxide particles) are easy to array with their
plate-form faces in parallel to the surface of a film because of
their plate-form shapes. As a result, the light transmission
through the film is improved. That is, when light transmits the
non-magnetic plate-form particles in the film, the inherent
properties of the non-magnetic plate-form particles are fully
exhibited due to the interaction between light and the non-magnetic
plate-form particles.
[0300] For example, the lamination of a layer of the plate-form
silicon oxide particles having a low refractive index and a layer
of the plate-form zirconium oxide particles having a high
refractive index provides a high performance antireflection film
having a very high transparency which has not been obtained from
the conventional granular or spherical oxide particles. Further,
the use of the plate-form iron oxide particles makes it possible to
provide an UV-screening film having a high transmittance.
Furthermore, when a high density coating film is formed from a
mixture of the plate-form zirconium oxide particles and the
plate-form cerium oxide particles both of which have high
refractive indexes, by making good use of their plate-form shapes,
the resultant coating film is transparent and has a very high
refractive index, comparable to a film formed by sputtering,
although it is formed by coating.
EFFECT OF THE INVENTION
[0301] As has been fully described above, according to the
processes of the present invention, there can be provided
plate-form shaped non-magnetic particles with a particle size of 10
to 100 nm in the plate-form face directions, specifically the
plate-form particles of oxides such as cerium oxide, zirconium
oxide, aluminum oxide, silicon oxide, iron oxide, etc., which
hitherto have not been obtained by any of the conventional
processes. The non-magnetic plate-form particles, particularly the
plate-form oxide particles, of the present invention have a uniform
particle size distribution and rarely suffer from sintering or
agglomeration thereof, thus having a good crystallinity. The
application of such non-magnetic plate-form particles of the
present invention to, for example, abrasive tapes, abrasive sheets,
abrasive films and abrasive members of abrasive tools, functional
optical films such as magnetic tapes, etc. greatly improves the
properties thereof, as compared with the application of the
conventional oxide particles thereto. As is understood from the
above, it is expected that the non-magnetic plate-form particles of
the present invention will find quite novel uses or applications
which are believed to be impossible so far.
* * * * *