U.S. patent application number 10/611934 was filed with the patent office on 2004-01-22 for microcapsule composition for electrophoretic displays.
Invention is credited to Kanbe, Sadao, Kawai, Hideyuki, Kushino, Mitsuo, Matsumoto, Makoto.
Application Number | 20040012106 10/611934 |
Document ID | / |
Family ID | 30437487 |
Filed Date | 2004-01-22 |
United States Patent
Application |
20040012106 |
Kind Code |
A1 |
Kanbe, Sadao ; et
al. |
January 22, 2004 |
Microcapsule composition for electrophoretic displays
Abstract
The present invention provides: a microcapsule composition for
electrophoretic displays; a production process for the microcapsule
composition for the electrophoretic displays; a production process
for a sheet for the electrophoretic displays; and a handling method
for microcapsules for the electrophoretic displays; wherein the
microcapsule composition contains microcapsules and, when used for
the electrophoretic displays, can make them as excellent as
conventional in various performances (e.g. longtime stability of
displaying, respondability of displaying, contrast, and number of
times of display rewritability) and, particularly above all, can
make the electrophoretic displays exhibit a very high performance
as to the contrast. The present invention composition is a
composition used for preparation of a coating liquid and comprises
an aqueous medium and microcapsules for the electrophoretic
displays, wherein the microcapsules include a shell and a
dispersion that is capsuled in the shell, wherein the dispersion
includes a solvent and electrophoretic fine particles that are
dispersed in the solvent; with the composition being characterized
by: being a product as obtained without involving the step of
drying the microcapsules; and having a microcapsule content of 30
to 80 weight %.
Inventors: |
Kanbe, Sadao; (Suwa-shi,
JP) ; Kawai, Hideyuki; (Suwa-shi, JP) ;
Kushino, Mitsuo; (Kawabe-gun, JP) ; Matsumoto,
Makoto; (Suita-shi, JP) |
Correspondence
Address: |
ROYLANCE, ABRAMS, BERDO & GOODMAN, L.L.P.
1300 19TH STREET, N.W.
SUITE 600
WASHINGTON,
DC
20036
US
|
Family ID: |
30437487 |
Appl. No.: |
10/611934 |
Filed: |
July 3, 2003 |
Current U.S.
Class: |
264/4 ;
428/402.2 |
Current CPC
Class: |
G02F 1/16757 20190101;
Y10T 428/2984 20150115; G02F 1/167 20130101; Y10T 428/2982
20150115; Y10T 428/2989 20150115; Y10T 428/254 20150115 |
Class at
Publication: |
264/4 ;
428/402.2 |
International
Class: |
B01J 013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 16, 2002 |
JP |
2002-207328 |
Claims
What is claimed is:
1. A microcapsule composition for electrophoretic displays, which
is a composition used for preparation of a coating liquid and
comprises an aqueous medium and microcapsules for the
electrophoretic displays, wherein the microcapsules include a shell
and a dispersion that is capsuled in the shell, wherein the
dispersion includes a solvent and electrophoretic fine particles
that are dispersed in the solvent; with the microcapsule
composition: being a product as obtained without involving the step
of drying the microcapsules; and having a microcapsule content of
30 to 80 weight %.
2. A microcapsule composition according to claim 1, wherein the
microcapsules have a volume-average particle diameter of 30 to 150
.mu.m and a particle diameter distribution by volume such that: not
less than 80 volume % of the microcapsules are present within the
particle diameter range of .+-.40% of the maximum-peak particle
diameter around the maximum-peak particle diameter.
3. A microcapsule composition according to claim 1, wherein the
total content of the microcapsules and the aqueous medium in the
composition is not less than 90 weight %.
4. A production process for a microcapsule composition for
electrophoretic displays, wherein the microcapsule composition
includes an aqueous medium and microcapsules for the
electrophoretic displays, wherein the microcapsules include a shell
and a dispersion that is capsuled in the shell, wherein the
dispersion includes a solvent and electrophoretic fine particles
that are dispersed in the solvent; with the production process
comprising: the dispersing step of dispersing the electrophoretic
fine particles into the solvent; and the microcapsuling step of
capsuling an electrophoretic fine particle dispersion into the
shell in the presence of the aqueous medium, thereby obtaining a
preparation liquid including the microcapsules and the aqueous
medium, wherein the electrophoretic fine particle dispersion is
obtained in the dispersing step; wherein: the composition having a
microcapsule content of 30 to 80 weight % is obtained without
involving the step of drying the microcapsules.
5. A production process according to claim 4, which further
comprises: the wet classification step of treating the preparation
liquid to classify the microcapsules; and the concentration step of
reducing the aqueous medium from a dispersion resultant from the
classification step, thereby concentrating the dispersion.
6. A production process according to claim 5, wherein the
preparation liquid to be used in the wet classification step has a
microcapsule concentration of not more than 15 weight %.
7. A production process for a sheet for electrophoretic displays,
which comprises the steps of: coating a coating liquid containing a
microcapsule composition for the electrophoretic displays; and
drying the resultant coating film; thereby producing the sheet for
the electrophoretic displays; with the production process: using,
as the composition, the microcapsule composition as recited in
claim 1; and further comprising the step of preparing the coating
liquid by mixing the composition in such an amount that the coating
liquid will have a microcapsule content of 25 to 65 weight %.
8. A handling method for microcapsules for electrophoretic
displays, wherein the microcapsules include a shell and a
dispersion that is capsuled in the shell, wherein the dispersion
includes a solvent and electrophoretic fine particles that are
dispersed in the solvent, in which handling method the
microcapsules are handled in the form of a microcapsule composition
such that: the microcapsules are present in an aqueous medium; and
the microcapsule composition has a microcapsule content of 30 to 80
weight %.
Description
BACKGROUND OF THE INVENTION
[0001] A. Technical Field
[0002] The present invention relates to: a microcapsule composition
for electrophoretic displays; a production process for the
microcapsule composition for the electrophoretic displays; a
production process for a sheet for the electrophoretic displays;
and a handling method for microcapsules for the electrophoretic
displays.
[0003] B. Background Art
[0004] Electrophoretic displays are non-light-emitting type display
devices which utilize electrophoretic phenomena of pigment
particles in a dispersion including a colored solvent and
electrophoretic pigment particles that are dispersed in the
solvent. The electrophoretic displays have many excellent
properties, such as wide visual-sight angle, longtime
memorizability without supply of electric power, and low
consumption of electric power. Particularly above all, notice is
drawn to microcapsules having a structure such that the above
dispersion is sealed in a capsule shell to be a partition material
(for example, refer to Japanese Patent No. 2551783), because such
microcapsules are useful for obtaining display devices having
flexibility further in addition to the above properties. There is
expected further technical development into fields of so-called
digital papers (e.g. paper-like displays and rewritable
papers).
[0005] By the way, as to the electrophoretic displays using the
microcapsules which are mentioned above as the display devices to
which notice is drawn in recent years, indeed there might have been
seen great enhancements in various functions such as longtime
stability of displaying, respondability, contrast, and number of
times of display rewritability, when compared with conventional
electrophoretic displays without any microcapsule. However, the
realization of further enhancement of the above various functions
is in demand for making the displays utilizable universally for
various uses as the displaying devices in the future and also for
producing various applied examples. Particularly above all, as to
the contrast that has a great influence upon image vividness, it is
strongly desired to further enhance its performance.
SUMMARY OF THE INVENTION
[0006] A. Object of the Invention
[0007] An object of the present invention is to provide: a
microcapsule composition for electrophoretic displays; a production
process for the microcapsule composition for the electrophoretic
displays; a production process for a sheet for the electrophoretic
displays; and a handling method for microcapsules for the
electrophoretic displays; wherein the microcapsule composition
contains microcapsules and, when used for the electrophoretic
displays, can make them as excellent as conventional in various
performances (e.g. longtime stability of displaying, respondability
of displaying, contrast, and number of times of display
rewritability) and, particularly above all, can make the
electrophoretic displays exhibit a very high performance as to the
contrast.
[0008] B. Disclosure of the Invention
[0009] The present inventors diligently studied to solve the
above-mentioned problems.
[0010] As a result, they have thought what influence will be
exercised on the microcapsules themselves in stages of various
treatments as required for using the microcapsules actually as
constitutional elements of the electrophoretic displays should be
newly studied in consideration also from the viewpoint of such as
performances of the resultant displays. The reasons for this
thought are as follows. Making mention of studies which have
hitherto be made about the microcapsules for the electrophoretic
displays, almost all of them are studies about electrophoretic fine
particles to be sealed into the microcapsules and a dispersion
including the electrophoretic fine particles or about
constitutional elements and physical structures of the
microcapsules, and there has been no especial study about, when the
microcapsules as once prepared by sealing the dispersion in so as
to form the capsules are thereafter actually used as constitutional
elements of the electrophoretic displays, then what influence the
various treatments as meanwhile carried out will exercise on the
microcapsules themselves and further on performances of the
displays using the microcapsules.
[0011] Thus, the present inventors have actually repeated various
experiments and studies. As a result, they have noticed that there
are some problems and points to be improved.
[0012] Specifically, the microcapsules have hitherto been processed
by the following steps. In the case where the microcapsules have
been prepared by microcapsulation in a liquid phase such as an
aqueous medium, the microcapsules are thereafter removed by
separating only the microcapsules from the resultant preparation
liquid after the above preparation, and then subjected to such as
drying to thereby form them into a finely particulate powder, or
the above preparation liquid is subjected to such as centrifugal
separation to thereby remove a major proportion of the liquid to
thus isolate the microcapsules (for example, refer to WO 00/20922).
In addition, in the case where the microcapsules have been prepared
by microcapsulation in a gas phase, usually the microcapsules are
thereafter recovered as they are, and then subjected to such as
drying to thereby form them into a finely particulate powder. Then,
both in the above cases, the microcapsules which are in such a
state as dried are thereafter treated such as by classification
when the occasion demands, and then mixed and dispersed into a
predetermined binder to thereby form them into a paint. Thereafter
this paint is coated onto such as electrode sheets to thus provide
the microcapsules to the displays.
[0013] However, when the isolated microcapsules which are in such a
state as dried are mixed and dispersed into the binder, a dispersed
state which is uniform to a certain extent is desired. However, too
much power is necessary for actually dispersing the microcapsules
in such a way. The cause is such that the microcapsules are once
put in such a state as dried, and that much aggregation (secondary
aggregation) takes place. Then, the present inventors have found
that: too much power as above causes an excessive load onto the
microcapsules; and, after all, in the stage when the microcapsules
have finally been provided to the displays, unimaginably many of
the microcapsules have already been destroyed. As a result, all
such damage to the microcapsules is a cause of hindering the
enhancement of the contrast.
[0014] Based on such findings, the present inventors further
studied. As a result, they have thought out a microcapsule
composition in which the microcapsules are allowed to coexist with
a considerably large quantity of aqueous medium in order to put the
microcapsules to use for the electrophoretic displays without
carrying out an operation such as of directly mixing the binder
with the isolated microcapsules themselves which are in such a
state as dried. That is to say, the present inventors have thought
that: the microcapsules should be used for preparation of a coating
liquid in the form of a composition such that the surfaces of the
microcapsules are put in a state sufficiently wetted with the
considerably large quantity of aqueous medium; and such a
composition is a novel form that has actually never existed; and
this form would be a clue to direct solution of the problems. Then,
the present inventors have further found out that the content of
the microcapsules in the composition should be limited into a
specific range. That is to say, the present inventors have found
out that: if such a microcapsule composition is used for the
preparation of the coating liquid, the prior art problems can be
solved at a stroke.
[0015] In addition, the present inventors have found that: in the
case where the microcapsulation is carried out in a liquid phase
such as an aqueous medium to prepare the microcapsules, if as
conventional the microcapsules are separated from the prepared
mixture liquid (preparation liquid) and thereafter dried, then not
only does it take labor and costs, but also the microcapsules, as
originally prepared so as to have softness to a certain extent,
easily adhere to each other when once dried, so that much
aggregation (secondary aggregation) inevitably takes place. Then,
the aggregation (secondary aggregation) of the microcapsules more
easily proceeds because of such as generation of static electricity
in the subsequent dry classification apparatus, and the accuracy of
the classification is extremely difficult to enhance. Furthermore,
in the case of the dry classification, the friction or shock is
directly applied to the microcapsule surfaces, and it is therefore
inevitable for the microcapsule to be damaged to a certain extent.
The present inventors have guessed that: considerably much of the
destruction or damage of the microcapsules in the stage when the
microcapsules have been provided to the displays is caused by the
above damage during the dry classification. In addition, if the
classification of the microcapsules is carried out by the dry
classification, the achievement of a high accurate classification
is hindered by the difference in specific gravity between the
microcapsules and a gas or by an influence of the cohesive strength
due to such as electrostatic force and van der Waals force. As a
result, all of such deterioration of the classification accuracy
and the above damage to the microcapsules is a cause of hindering
the enhancement of the contrast.
[0016] As a method for obtaining the aforementioned microcapsule
composition (to which the present inventors have hereupon directed
their attention) in a state more optimum for putting this
composition to use for the electrophoretic displays, the present
inventors have thought out, on the basis of the above findings, a
method in which the microcapsule composition comprising the
microcapsules and the aqueous medium is obtained by subjecting the
microcapsule composition to necessary treatment (e.g.
classification) in a state of the above-mentioned prepared
preparation liquid including the microcapsules and the aqueous
medium. Specifically, the present inventors have guessed that the
classification treatment of the microcapsules should be applied
either to the above-mentioned prepared preparation liquid itself
including the microcapsules and the aqueous medium or to such as a
dilution of this preparation liquid. Because the classification
treatment is applied to the preparation liquid, it inevitably
follows that the classification is carried out in a wet manner.
However, because such as separation and drying of the microcapsules
are not carried out as conventional and because the classification
is not the dry classification, the classification of the
microcapsules can be carried out with good accuracy, and further it
is also possible to greatly reduce the damage to the
microcapsules.
[0017] In addition, the microcapsule content is usually very low in
the above state of the preparation liquid just after the above
preparation. In the case where a coating liquid is prepared from
such a preparation liquid and then used for the electrophoretic
displays, not only is it impossible to provide the microcapsules to
the electrophoretic displays at an appropriate density, but also
the coating liquid has such an excessively low solid content as to
be difficult to utilize. Therefore, conventionally, the
microcapsules are once isolated from the preparation liquid and
then mixed with a binder in a state of dried particles in such an
amount that the concentration will be a desirable value. However,
the present inventors have thought that: if the above preparation
liquid is subjected to treatment of reducing the amount of the
aqueous medium (so-called concentration treatment), then the above
problems can be solved. In addition, the present inventors have
thought that it is favorable to carry out the concentration
treatment to such an extent that the content of the microcapsules
in the composition will be in a specific range. If the microcapsule
composition as obtained in this way is used for the preparation of
the coating liquid, then the microcapsules can be mixed and
dispersed very easily and uniformly, and further the
above-mentioned damage to the microcapsules can effectively be
inhibited (the amount of the damaged microcapsules can greatly be
reduced). In addition, it is also possible to provide the
electrophoretic displays with the microcapsules dispersed at an
appropriate density, and therefore the microcapsule composition is
excellent also in a sense of aptitude for the use for the
electrophoretic displays. As a result, various performances (e.g.
contrast and image quality of the electrophoretic displays) can
greatly be enhanced. That is to say, the present inventors have
thought that, if in the above way the microcapsule composition
having a microcapsule content in a specific range is prepared from
the above preparation liquid (favorably by subjecting this
preparation liquid to the classification in a wet manner and to the
concentration of reducing the aqueous medium) after the preparation
of the microcapsules, then the above effects are all actualized and
the aforementioned problems can be solved at a stroke.
[0018] Furthermore, the present inventors have found out a handling
method for microcapsules, in which the custody, preservation,
transportation, and other various handling of the microcapsules are
carried out in the optimum state so that more excellent
electrophoretic displays can be obtained when the microcapsules as
prepared by the microcapsulation by various production processes in
a liquid phase or gas phase are used for the electrophoretic
displays. Specifically, the present inventors have thought that the
prepared microcapsules should be handled in the form of the
composition in which the microcapsules are allowed to coexist with
the aqueous medium. In addition, the present inventors have further
found out that the microcapsule content in the above composition
should be in a specific range. The same effects as those of the
microcapsule composition as obtained by the above production
process can be obtained by handling the microcapsules in this
way.
[0019] Furthermore, the present inventors have completed a
production process for a sheet for electrophoretic displays as
usage of the present invention microcapsule composition.
[0020] That is to say, a microcapsule composition for
electrophoretic displays, according to the present invention, is a
composition used for preparation of a coating liquid and comprises
an aqueous medium and microcapsules for the electrophoretic
displays, wherein the microcapsules include a shell and a
dispersion that is capsuled in the shell, wherein the dispersion
includes a solvent and electrophoretic fine particles that are
dispersed in the solvent; with the microcapsule composition being
characterized by: being a product as obtained without involving the
step of drying the microcapsules; and having a microcapsule content
of 30 to 80 weight %.
[0021] In the present invention microcapsule composition for the
electrophoretic displays, it is favorable that the microcapsules
have a volume-average particle diameter of 30 to 150 .mu.m and a
particle diameter distribution by volume such that: not less than
80 volume % of the microcapsules are present within the particle
diameter range of .+-.40% of the maximum-peak particle diameter
around the maximum-peak particle diameter.
[0022] In the present invention microcapsule composition for the
electrophoretic displays, it is favorable that the total content of
the microcapsules and the aqueous medium in the composition is not
less than 90 weight %.
[0023] A production process for the microcapsule composition for
the electrophoretic displays, according to the present invention,
is a production process for the microcapsule composition including
an aqueous medium and microcapsules for the electrophoretic
displays, wherein the microcapsules include a shell and a
dispersion that is capsuled in the shell, wherein the dispersion
includes a solvent and electrophoretic fine particles that are
dispersed in the solvent; with the production process being
characterized by comprising: the dispersing step of dispersing the
electrophoretic fine particles into the solvent; and the
microcapsuling step of capsuling an electrophoretic fine particle
dispersion into the shell in the presence of the aqueous medium,
thereby obtaining a preparation liquid including the microcapsules
and the aqueous medium, wherein the electrophoretic fine particle
dispersion is obtained in the dispersing step; with the production
process further being characterized in that: the composition having
a microcapsule content of 30 to 80 weight % is obtained without
involving the step of drying the microcapsules.
[0024] In the present invention production process for the
microcapsule composition for the electrophoretic displays, it is
favorable that this process further comprises: the wet
classification step of treating the preparation liquid to classify
the microcapsules; and the concentration step of reducing the
aqueous medium from a dispersion resultant from the classification
step, thereby concentrating the dispersion.
[0025] In the present invention production process for the
microcapsule composition for the electrophoretic displays, it is
favorable that the preparation liquid to be used in the wet
classification step has a microcapsule concentration of not more
than 15 weight %.
[0026] A production process for a sheet for the electrophoretic
displays, according to the present invention, comprises the steps
of: coating a coating liquid containing a microcapsule composition
for the electrophoretic displays; and drying the resultant coating
film; thereby producing the sheet for the electrophoretic displays;
with the production process being characterized by: using, as the
composition, the above present invention microcapsule composition
for the electrophoretic displays; and further comprising the step
of preparing the coating liquid by mixing the composition in such
an amount that the coating liquid will have a microcapsule content
of 25 to 65 weight %.
[0027] A handling method for microcapsules for the electrophoretic
displays, according to the present invention, is a handling method
for the microcapsules including a shell and a dispersion that is
capsuled in the shell, wherein the dispersion includes a solvent
and electrophoretic fine particles that are dispersed in the
solvent. This handling method is characterized in that the
microcapsules are handled in the form of a microcapsule composition
such that: the microcapsules are present in an aqueous medium; and
the microcapsule composition has a microcapsule content of 30 to 80
weight %.
[0028] These and other objects and the advantages of the present
invention will be more fully apparent from the following detailed
disclosure.
DETAILED DESCRIPTION OF THE INVENTION
[0029] Hereinafter, detailed descriptions are specifically given
about the present invention microcapsule composition for the
electrophoretic displays, the present invention production process
for the microcapsule composition for the electrophoretic displays,
the present invention production process for the sheet for the
electrophoretic displays, and the present invention handling method
for the microcapsules for the electrophoretic displays. However,
the scope of the present invention is not bound to these
descriptions in any way. And other than the following illustrations
can also be carried out appropriately within the scope not
departing from the spirit of the present invention.
[0030] The present invention production process for the
microcapsule composition for the electrophoretic displays (which
may hereinafter be referred to as the present invention production
process for the composition) is a production process for the
microcapsule composition including an aqueous medium and
microcapsules for the electrophoretic displays, wherein the
microcapsules include a shell and a dispersion that is capsuled in
the shell, wherein the dispersion includes a solvent and
electrophoretic fine particles that are dispersed in the solvent.
This production process is characterized by comprising the
below-mentioned dispersing step and microcapsuling step and further
characterized in that: the composition having a microcapsule
content of 30 to 80 weight % is obtained without involving the step
of drying the microcapsules.
[0031] In the present invention, the dispersing step is a step of
dispersing the electrophoretic fine particles into the solvent. The
dispersing liquid resultant from this step is a dispersion to be
finally capsuled in the microcapsules for the electrophoretic
displays.
[0032] The solvent will do if it is a solvent having hitherto been
used conventionally and generally for dispersions for the
electrophoretic displays. Therefore, the solvent is not especially
limited. High-insulating organic solvents are favorable.
[0033] Favorable examples of the high-insulating organic solvents
include one member alone or mixtures selected from the group
consisting of: aromatic hydrocarbons, such as o-, m-, or p-xylene,
toluene, benzene, dodecylbenzene, hexylbenzene, phenylxylylethane,
and naphthenic hydrocarbons; aliphatic hydrocarbons, such as
cyclohexane, n-hexane, kerosine, and paraffinic hydrocarbons;
various esters, such as ethyl acetate and butyl acetate; ketones,
such as acetone, methyl ethyl ketone, and methyl isobutyl ketone;
alcoholic solvents, such as methanol, ethanol, isopropanol,
octanol, and methyl cellosolve; halogenated hydrocarbons, such as
chlorobutane, chloroform, trichloroethylene,
trichlorofluoroethylene, trichloroethane, carbon tetrachloride,
cyclohexyl chloride, chlorobenzene, 1,1,2,2-tetrachloroethylene,
trichlorofluoroethane, tetrafluorodibromoethane, bromoethane,
tetrafluorodifluoroethane, methylene iodide, triiodosilane, and
methyl iodide; and carbon disulfide. Of the above, such as
long-chain-alkylbenzenes (e.g. dodecylbenzene and hexylbenzene) and
phenylxylylethane are more favorable because they have a high
boiling point and also a high flash point, and further have almost
no toxicity. These solvents may be used either alone respectively
or in combinations with each other.
[0034] The amount of the solvent as used is favorably adjusted so
as to be in the range of 40 to 95 weight %, more favorably 50 to 92
weight %, still more favorably 60 to 90 weight %, relative to the
entire dispersion as obtained. In the case where the above amount
is smaller than 40 weight %, the viscosity of the dispersion rises
so much as to lower the electrophoretic ability of the
electrophoretic fine particles. In the case where the above amount
is larger than 95 weight %, the concentration of the
electrophoretic fine particles is so low that the contrast cannot
be obtained sufficiently.
[0035] The solvent is favorably a colorless and transparent
solvent, and may, for example, get colored when the occasion
demands.
[0036] In the case where the solvent is a colored one, there is no
especial limitation on the dye used for the coloring. However,
oil-soluble dyes are favorable, and such as azo dyes and
anthraquinone dyes are more favorable particularly in respect of
being easy to use. Specific favorable examples thereof include: as
yellow dyes, azo compounds (e.g. Oil Yellow 3G (produced by Orient
Chemical Co., Ltd.)); as yellowish brown dyes, azo compounds (e.g.
Fast Orange G (produced by BASF)); as blue dyes, anthraquinones
(e.g. Macrorex Blue RR (produced by Bayer)); as green dyes,
anthraquinones (e.g. Sumiplast Green G (produced by Sumitomo
Chemical Co., Ltd.)); as brown dyes, azo compounds (e.g. Oil Brown
GR (produced by Orient Chemical Co., Ltd.)); as red dyes, azo
compounds (e.g. Oil Red 5303 (produced by Arimoto Chemical Co.,
Ltd.) and Oil Red 5B (produced by Orient Chemical Co., Ltd.)); as
purple dyes, anthraquinones (e.g. Oil Violet #730 (produced by
Orient Chemical Co., Ltd.)); as black dyes, azo compounds (e.g.
Sudan Black X60 (produced by BASF); and mixtures of Macrorex Blue
FR as an anthraquinone (produced by Bayer) and Oil Red XO as an azo
compound (produced by Kanto Chemical Co., Ltd.). These dyes may be
used either alone respectively or in combinations with each
other.
[0037] The above dye is usually used in an amount of favorably 0.1
to 10 parts by weight, more favorably 0.5 to 10 parts by weight,
still more favorably 1 to 10 parts by weight, per 100 parts by
weight of the solvent. In the case where the amount of the above
dye as used is smaller than 0.1 part by weight, the coloring
ability is so insufficient that the contrast to the electrophoretic
fine particles cannot sufficiently be obtained. In the case where
the above amount is larger than 10 parts by weight, the costs
increase more than is necessary.
[0038] The electrophoretic fine particles will do if they are
electrophoretic pigment particles, namely, colored particles that
display plus or minus polarity in the dispersion. Although there is
no especial limitation on their kinds, specifically there are
favorably used such as white particles (e.g. Titanium Oxide) and
black particles (e.g. Carbon Black and Titanium Black), and there
may also be used other particles as mentioned below. These may be
used either alone respectively or in combinations with each
other.
[0039] In the case of using the fine particles of the titanium
oxide, there is no especial limitation on the kind of the titanium
oxide. That will do if it is titanium oxide as generally used as a
white pigment, and the titanium oxide may be either a rutile type
or anatase type. However, in the case of considering such as
discoloration of colorants due to photoactive performance of the
titanium oxide, the rutile type titanium oxide displaying low
photoactive performance is favorable, and there is more favorable
titanium oxide as processed by such as Si treatment, Al treatment,
Si--Al treatment, or Zn--Al treatment for further lowering the
photoactive performance.
[0040] As the electrophoretic fine particles, other particles
besides the above fine titanium oxide particles, Carbon Black, and
Titanium Black may be used together, and the above other particles
may be used instead of such as the titanium oxide. The above other
particles are, favorably, pigment particles similarly to such as
the fine titanium oxide particles. In addition, there is not always
necessity for the above other particles to have the electrophoretic
ability similarly to such as the fine titanium oxide particles. If
necessary, the electrophoretic ability may be given by some
hitherto publicly known method.
[0041] Although there is no especial limitation on the above other
particles, specific favorable examples thereof include: as white
particles other than the above titanium oxide, inorganic pigments
(e.g. Barium Sulfate, Zinc Oxide, and Zinc White); as yellow
particles, inorganic pigments (e.g. Yellow Iron Oxide, Cadmium
Yellow, Titanium Yellow, and Chrome Yellow) and organic pigments,
such as insoluble azo compounds (e.g. Fast Yellow), condensed azo
compounds (e.g. Chromophthal Yellow), azo complex salts (e.g.
Benzimidazolone Azo Yellow), condensed polycyclics (e.g. Flavans
Yellow), Hansa Yellow, naphthol yellow, nitro compounds, and
pigment yellow; as yellowish brown particles, inorganic pigments
(e.g. Molybdate Orange) and organic pigments, such as azo complex
salts (e.g. Benzimidazolone Azo Orange) and condensed polycyclics
(e.g. Pelinon Orange); as red particles, inorganic pigments (e.g.
Ferric Oxide Red and Cadmium Red) and organic pigments, such as
dyeing lakes (e.g. Madder Lake), soluble azo compounds (e.g. Lake
Red), insoluble azo compounds (e.g. naphthol red), condensed azo
compounds, (e.g. Chromophthalo Scarlet Red), condensed polycyclics
(e.g. Tioindigo Voldor), quinacridone pigments (e.g. Cinquasia Red
Y and Fastpermanent Red), and azo pigments (e.g. Permanent Red and
Fast Slow Red); as purple particles, inorganic pigments (e.g.
Manganese Violet) and organic pigments, such as dyeing lakes (e.g.
Rhodamine Lake) and condensed polycyclics (e.g. Dioxadine Violet);
as blue particles, inorganic pigments (e.g. Iron Blue, Ultramarine,
Cobalt Blue, and Cerlian Blue) and organic pigments, such as
phthalocyanines (e.g. Phthalocyanine Blue), indanthrenes (e.g.
Indanthrene Blue), and alkali blue; as green particles, inorganic
pigments (e.g. Emerald Green, Chrome Green, Chromium Oxide, and
Viridian) and organic pigments, such as azo complex salts (e.g.
Nickel Azo Yellow), nitroso compounds (e.g. Pigment Green and
Naphthol Green), and phthalocyanines (e.g. Phthalocyanine Green);
and as black particles other than the above Carbon Black and
Titanium Black, inorganic pigments (e.g. Iron Black) and organic
pigments (e.g. Aniline Black). These may be used either alone
respectively or in combinations with each other.
[0042] Although there is no especial limitation on the particle
diameters of the electrophoretic fine particles, their
volume-average particle diameter is favorably in the range of 0.1
to 5 .mu.m, more favorably 0.2 to 3 .mu.m. In the case where the
above particle diameter (volume-average particle diameter) is
smaller than 0.1 .mu.m, there is a possibility that: the hiding
performance is not sufficiently obtained in a displaying portion of
the electrophoretic displays, so that the coloring degree is
lowered, and there cannot be obtained electrophoretic displays
having high contrast. In the case where the above particle diameter
is larger than 5 .mu.m, there is a possibility that there may occur
necessity to raise the coloring degree of the particles themselves
(the pigment concentration) more than is necessary, and besides,
there is also a possibility that the smooth electrophoretic
property of the fine particles may be lowered.
[0043] The concentration of the electrophoretic fine particles in
the dispersion is favorably in the range of 5 to 60 weight %, more
favorably 5 to 50 weight %, still more favorably 5 to 40 weight %.
In the case where the above concentration of the electrophoretic
fine particles is less than 5 weight %, there is a possibility
that: neither the coloring nor the hiding performance is
sufficiently exhibited by the electrophoretic fine particles in a
displaying portion of the electrophoretic displays, so that a
sufficient contrast cannot be obtained, and therefore a vivid
displaying cannot be obtained. In the case where the above
concentration is more than 60 weight %, there is a possibility that
the viscosity during the dispersing treatment may be so high as to
overload the dispersing apparatus, and besides, there is a
possibility of aggregating the electrophoretic fine particles when
high energy is applied to the displaying portion of the
electrophoretic displays, or there is a possibility that the
response rate (respondability of displaying) of the electrophoretic
fine particles may be lowered in a portion to which a voltage is
applied.
[0044] In the dispersing step, the dispersion as obtained can
include some other component besides the above solvent and
electrophoretic fine particles when the occasion demands. However,
there is no especial limitation on such as its kind. Examples of
the above other component include dispersants. The dispersants may
be included either before or after the electrophoretic fine
particles are dispersed into the solvent, and there is no especial
limitation.
[0045] There is no especial limitation on the above dispersants.
The dispersants will do if they are dispersants usable
conventionally and generally for assisting the particles in being
dispersed in the solvent. Specific favorable examples thereof
include: anionic surfactants soluble in the dispersion, cationic
surfactants, amphoteric surfactants, nonionic surfactants,
fluorosurfactants, sorbitan fatty acid ester surfactants (e.g.
sorbitan sesquioleate), dispersants (e.g. block polymers and graft
polymers), and various coupling agents. These may be used either
alone respectively or in combinations with each other. Of the above
dispersants, the coupling agents are more favorable because they
also enhance the dispersing stability when the charges are applied.
If the fine particles are treated with the coupling agents, a
coating layer of the coupling agent is formed on surfaces of the
fine particles.
[0046] There is no especial limitation on the kinds of the above
coupling agents. However, favorable examples thereof include: (1)
silane coupling agents; (2) titanate coupling agents; (3) aluminum
coupling agents; (4) vinyl-group-containing coupling agents; (5)
coupling agents containing at least one group selected from among
an amino group, a quaternary ammonium salt, a carboxyl group, and a
phosphoric acid group; (6) coupling agents containing an amino
group or a glycidyl group at their end; and (7) organosilazanes.
The titanate coupling agents and the aluminum coupling agents are
more favorable. Coupling agents belonging to the above various
coupling agents and also containing a long-chain alkyl group are
still more favorable. Titanate coupling agents and aluminum
coupling agents also containing a long-chain alkyl group are
particularly favorable. The above coupling agents may be used
either alone respectively or in combinations with each other.
[0047] As is mentioned above, the reason that the coupling agents
containing a long-chain alkyl group are favorable can be
exemplified by such that: the affinity is raised by such as
long-chain-alkylbenzenes which are high safe solvents, and
therefore such coupling agents have high effects of raising the
dispersing stability of the electrophoretic fine particles.
[0048] Although there is no especial limitation on the silane
coupling agents, favorable examples thereof include: silane
coupling agents containing such as a vinyl group, an amino group, a
glycidyl group, and a thiol group; and silane coupling agents
containing a long-chain alkyl group. These may be used either alone
respectively or in combinations with each other.
[0049] Although there is no especial limitation on the titanate
coupling agents, favorable examples thereof include compounds as
represented by the following general formula (1):
(RO).sub.m--Ti--X.sub.a (1)
[0050] (where: R denotes an alkyl group having 1 to 4 carbon atoms;
X denotes an alkyl group having 8 to 18 carbon atoms, a fatty acid
residue, a hydroxyphenyl group, or a hydrocarbon residue; m denotes
an integer of 1 to 4; and a denotes an integer of 1 to 3). Specific
favorable examples of the titanate coupling agents as represented
by the above general formula (1) include isopropyl.triisostearoyl
titanate, isopropyl tridecylbenzenesulfonyl titanate,
isopropyl.tris(dioctylpyrophosphate) titanate,
isopropyl.trioctanoyl titanate, isopropyl.dimethacryl.isostearo- yl
titanate, isopropyl.diacryl.isostearoyl titanate,
isopropyl.tris(dioctylphosphate) titanate, isopropyl.tricumylphenyl
titanate, isopropyl.tris(N-aminoethyl) titanate,
tetraisopropyl.bis(dioct- ylphosphite) titanate,
tetraoctyl.bis(ditridecylphosphite) titanate,
tetra(2,2-diallyloxymethyl-1-butyl).bis(di-tridecyl)phosphite
titanate, bis(dioctylpyrophosphate) oxyacetate titanate,
dicumylphenyl.oxyacetate titanate, diisostearoylethylene titanate,
and bis(dioctylpyrophosphate) ethylene titanate. Incidentally,
these are, for example, commercially available in the trade name of
Plemact from Ajinomoto Co., Inc. These may be used either alone
respectively or in combinations with each other.
[0051] Although there is no especial limitation on the aluminum
coupling agents, favorable examples thereof include hitherto
publicly known various aluminum chelates, alkyl acetoacetate
aluminum diisopropylate, and aluminum.bis(ethyl
acetate).diisopropylate. These may be used either alone
respectively or in combinations with each other.
[0052] Although there is no especial limitation on the
vinyl-group-containing coupling agents, favorable examples thereof
include: alkoxysilanes, such as vinyltrimethoxysilane and
dimethylvinylmethoxysilane; chlorosilanes, such as
vinyltrichlorosilane and dimethylchlorosilane; methacryloxysilanes,
such as .gamma.-methacryloxypropyltrimethoxysilane and
.gamma.-methacryloxypropyl- methyldimethoxysilane; quaternary
ammonium salts, such as
N-.beta.-(N-vinylbenzylaminoethyl)-.gamma.-aminopropyltrimethoxysilane;
and titanates, such as isopropyl dimethacryl isostearoyl titanate
and isopropyl diacryl isostearoyl titanate. These may be used
either alone respectively or in combinations with each other.
[0053] The coupling agents containing at least one group selected
from among an amino group, a quaternary ammonium salt, a carboxyl
group, and a phosphoric acid group are charge-donating agents.
Although not especially limited, specific favorable examples
thereof include: silanes, such as
.gamma.-aminopropyltriethoxysilane and
octadecyldimethyl[3-(trimethoxysil- yl)propyl]ammonium chloride;
titanates, such as isopropyl triisostearoyl titanate and
isopropyl.tris(dioctylpyrophosphate) titanate. These may be used
either alone respectively or in combinations with each other.
[0054] Although there is no especial limitation on the coupling
agents containing an amino group or a glycidyl group at their end,
favorable examples thereof include: silane coupling agents, such as
.gamma.-aminopropyltriethoxysilane and
.gamma.-glycidoxypropyltrimethoxys- ilane; and titanate coupling
agents such as isopropyl.tris(N-aminoethyl) titanate. These may be
used either alone respectively or in combinations with each
other.
[0055] Although there is no especial limitation on the
organosilazanes, it is enough that they are hitherto publicly known
organosilazane compounds. Favorable examples thereof include
compounds represented by the following formulas (a), (b), and (c)
as described in JP-A-008637/1988.
[(CH.sub.3).sub.3Si].sub.2NH (a)
[(C.sub.2H.sub.5).sub.3Si].sub.2NH (b)
[(C.sub.3H.sub.7).sub.3Si].sub.2NH (c)
[0056] These may be used either alone respectively or in
combinations with each other.
[0057] Although there is no especial limitation on the coupling
agents containing a long-chain alkyl group, favorable examples
thereof include: alkoxysilanes, such as propyltrimethoxysilane,
butyltrimethoxysilane, hexyltrimethoxysilane,
decyltrimethoxysilane, dodecyltrimethoxysilane,
hexadecyltrimethoxysilane, and octadecyltrimethoxysilane;
chlorosilanes, such as propyldodecyltrichlorosilane,
butyltrichlorosilane, hexyltrichlorosilane, decyltrichlorosilane,
dodecyltrichlorosilane, hexadecyltrichlorosilane, and
octadecyltrichlorosilane; fluorosilanes, such as
trifluoropropyltrimethoxysilane, trifluoropropyltrichlorosilane,
tridecafluorooctyltrimethoxysilane,
tridecafluorooctyltrichlorosilane,
heptadecafluorodecyltrimethoxysilane, and
heptadecafluorodecyltrichlorosi- lane; and titanates, such as
isopropyl triisostearoyl titanate and isopropyl trioctanoyl
titanate. Of these coupling agents containing a long-chain alkyl
group, such as the alkoxysilanes, the chlorosilanes, and the
fluorosilanes are more favorable. These may be used either alone
respectively or in combinations with each other.
[0058] Although there is no especial limitation on the method for
dispersing the electrophoretic fine particles into the solvent in
the dispersing step, it is enough that this method is a method as
conventionally used when desirable particles are dispersed into
some solvent. Specific examples thereof include: a method that
involves the steps of charging an ultrasonic bath with such as the
fine titanium oxide particles, the solvent, and the coupling agent
as raw components, and then ultrasonically dispersing the resultant
mixture under stirred conditions; a method that involves the step
of making a dispersion with a dispersing machine such as a paint
shaker, a ball mill, and a sand grind mill; a dry method that
involves the step of, while forcibly stirring the solvent and the
fine particles with such as a V-blender, spraying the coupling
agent thereonto by dry air or nitrogen gas; a wet method that
involves the steps of properly dispersing the fine particles into
the solvent to thereby form a slurry, and then adding thereto the
coupling agent; and a spraying method that involves the step of,
while vigorously stirring the preheated solvent and fine particles,
spraying the coupling agent thereonto.
[0059] The microcapsuling step in the present invention is a step
of capsuling an electrophoretic fine particle dispersion into the
shell (capsule shell) in the presence of the aqueous medium,
wherein the electrophoretic fine particle dispersion is obtained in
the aforementioned dispersing step. The preparation liquid
including the aqueous medium and the microcapsules as prepared by
the microcapsulation is obtained by this step.
[0060] There is no especial limitation on the method for carrying
out the above capsulation. It is enough that the method for
carrying out the microcapsulation is adopted by appropriately
selecting it from among conventional and publicly known methods.
Specific examples thereof include so-called interfacial
precipitation methods (e.g. a coacervation method (phase separation
method), a melting-decomposition-cooling method, powdery bed
method) and so-called interfacial reaction methods (e.g. a
interfacial polymerization method, an in-situ method, a
coating-film (covering) method by curing in liquids (orifice
method), and an interfacial reaction method (inorganochemical
reaction method)). Of the above, the coacervation method (phase
separation method), the in-situ method, the interfacial
polymerization method, and the melting-decomposition-cooling method
are more favorable. In these various production processes, the
microcapsulation is carried out in the presence of the aqueous
medium, thereby obtaining the preparation liquid including the
microcapsules and the aqueous medium.
[0061] Although there is no especial limitation on the aqueous
medium usable in the above various production processes, specific
usable examples thereof include: water; mixed liquids of water and
hydrophilic solvents (e.g. alcohols, ketones, esters, and glycols);
solutions as obtained by dissolving water-soluble polymers (e.g.
PVA (polyvinyl alcohol), CMC (carboxymethyl cellulose), gelatins,
and gum arabic) into water; solutions as obtained by adding
surfactants (e.g. anionic surfactants, cationic surfactants, and
nonionic surfactants) to water; or liquids as obtained by combining
these aqueous mediums.
[0062] Although there is no especial limitation on the amount of
the dispersion (obtained in the above dispersing step) to be
dispersed into the aqueous medium, specifically this dispersion is
favorably used in an amount of 20 to 200 parts by weight, more
favorably 30 to 150 parts by weight, per 100 parts by weight of the
aqueous medium. In the case where the above amount is smaller than
20 parts by weight, there is a possibility that the resultant
microcapsules may have such a broad particle diameter distribution
as to cause the lowering of the production efficiency. In the case
where the above amount is larger than 200 parts by weight, there is
a possibility that: a reversed suspension may be formed, and
therefore the microcapsules cannot be produced.
[0063] The raw material of the capsule shell will do if it is the
same as used for hitherto publicly known microcapsules. Thus, there
is no especial limitation. In the case of using the coacervation
method, examples of raw materials that are favorably used include
anionic substances (e.g. gum arabic, sodium alginate, copolymers of
styrene-maleic anhydride, copolymers of vinyl methyl ether-maleic
anhydride, phthalate esters of starch, and polyacrylic acid). In
the case of using the in-situ method, examples of raw materials
that are favorably used include melamine-formalin resins
(melamine-formalin prepolymers). In the case of using the
interfacial polymerization method, hydrophilic polymers (e.g.
polyamines, glycols, and polyphenols) and hydrophobic polymers
(e.g. polybasic acid halides, bisharofolmerl, and polyisocyanates)
are favorably used as the raw materials to form a capsule shell
made of such as polyamides, epoxy resins, polyurethanes, and
polyureas.
[0064] Such as polyamines may further be added to these raw
materials of the capsule shell, whereby there can be obtained
microcapsules having a capsule shell which is excellent in such as
heat-resistant preservability. The amount of such as polyamines to
be used will do if it is to such an extent as not to extremely
damage desirable shell properties derived from the above raw
material of the capsule shell.
[0065] Favorable examples of the above polyamines include:
aliphatic amines, such as ethylenediamine, diethylenetriamine,
triethylenetetramine, tetraethylenepentamine, 1,3-propylenediamine,
and hexamethylenediamine; epoxy compound addition products from
aliphatic polyamines, such as poly(1 to 5)alkylene(C.sub.2 to
C.sub.6)polyamine-alkylene(C.sub.2 to C.sub.18) oxide addition
products; aromatic polyamines, such as phenylenediamine,
diaminonaphthalene, and xylylenediamine; alicyclic polyamines such
as piperazine; and heterocyclic diamines such as
3,9-bis-aminopropyl-2,4,8,10-tetraoxaspiro-- [5.5]undecane. These
may be used either alone respectively or in combinations with each
other.
[0066] Although there is no especial limitation on the amount of
the raw material of the capsule shell to be used, this amount is
specifically in the range of favorably 1 to 50 parts by weight,
more favorably 5 to 30 parts by weight, per 1 part by weight of the
electrophoretic fine particle dispersion. In the case where the
above amount to be used is outside the above range, there is a
possibility that the below-mentioned desirable thickness of the
capsule shell cannot be obtained.
[0067] In the microcapsuling step, when the occasion demands, there
can be appropriately used other components besides the above
aqueous medium, the above raw material of the capsule shell, and
the above dispersion as obtained in the dispersing step.
[0068] Although there is no especial limitation on the shape of the
microcapsules as obtained in the microcapsuling step, it is
favorable to appropriately set conditions in such a manner that the
microcapsules will be the shape of particles such as true
spheres.
[0069] Although there is no especial limitation on the
volume-average particle diameter of the microcapsules as obtained
in the microcapsuling step, specifically it is favorable to
appropriately set conditions (e.g. diameters of particles dispersed
in the dispersion) in such a manner that the above volume-average
particle diameter will be in the range of 5 to 300 .mu.m, more
favorably 10 to 200 .mu.m, still more favorably 15 to 150 .mu.m. In
the case where the volume-average particle diameter of the
microcapsules is smaller than 5 .mu.m, there is a possibility that:
when the microcapsules are put to use for the electrophoretic
displays, the displaying concentration cannot sufficiently be
obtained in the displaying portion of the electrophoretic displays.
In the case where the volume-average particle diameter of the
microcapsules is larger than 300 .mu.m, there is a possibility that
there may occur problems in the mechanical strength of the
microcapsules themselves, and besides, there is a possibility that:
when the microcapsules are put to use for the electrophoretic
displays, the electrophoretic properties of such as the fine
titanium oxide particles in the dispersion as sealed in the
microcapsules may not sufficiently be displayed, and the starting
voltage for displaying may also increase.
[0070] Although there is no especial limitation on the thickness of
the capsule shell of the microcapsules as obtained in the
microcapsuling step, specifically it is favorable to appropriately
set conditions (e.g. the amount of the raw material of the capsule
shell to be used) in such a manner that the above thickness will be
in the range of 0.1 to 5 .mu.m, more favorably 0.1 to 4 .mu.m,
still more favorably 0.1 to 3 .mu.m. In the case where the
thickness of the capsule shell is less than 0.1 .mu.m, there is a
possibility that the strength as the capsule shell may not
sufficiently be obtained. In the case where the thickness of the
capsule shell is more than 5 .mu.m, there is a possibility that:
the transparency may be lowered so much as to cause the lowering of
the contrast, and beside, the softness of the microcapsules
themselves may be lowered so much as to result in insufficient
adhesion to such as electrode films.
[0071] In the present invention production process for the
composition, it is important that the microcapsule content in the
composition as obtained is adjusted in the range of 30 to 80 weight
%, favorably 35 to 80 weight %, more favorably 40 to 70 weight %.
In the case where the above content is less than 30 weight %, there
is a possibility that: when the composition is formed into a paint,
the microcapsule concentration may become so low that the
microcapsules are difficult to arrange in a layer densely by the
side of each other on a surface to be coated, thus resulting in
occurrence of spaces to cause a lack of displaying and therefore to
cause the lowering of the contrast and the image defect (displaying
defect). In addition, in the case where the above content is more
than 80 weight %, there is a possibility such that: the
microcapsules may mutually aggregate to cause problems in the
dispersibility when the composition is formed into a paint; or the
image defect (displaying defect) may be caused in the case where
the microcapsules cannot sufficiently be dispersed; or, if the
microcapsules are strongly dispersed, they may be damaged so much
that the electrophoretic fine particle dispersion leaks from inside
the microcapsules due to the pressure as applied by laminating an
electrode film to be a counter electrode. Because of these
problems, the resultant electrophoretic displays cannot
sufficiently obtain the contrast, and have a lot of image defects
(displaying defects).
[0072] In the present invention, it is important that: as mentioned
above, the microcapsules to be used for the preparation of the
coating liquid are produced not in the form of the isolated
microcapsules which are in such a state as dried, but in the form
of a composition such that the surfaces of the microcapsules are
put in a state sufficiently wetted with a considerably large
quantity of aqueous medium. Such a production process can reduce
the labor and costs as needed for separating and then drying the
microcapsules as conventional, and besides, can further reduce
damage as done to the microcapsules by such as friction or shock
accompanying the drying. Then, for example, as mentioned below, the
resultant composition can display excellent effects when used for
the preparation of the coating liquid as it is. Incidentally, in
the present invention, it is necessary that the microcapsules to be
used for the preparation of the coating liquid are produced in the
form of a composition such that the surfaces of the microcapsules
are put in a state sufficiently wetted with a considerably large
quantity of aqueous medium. In addition, from the view point of the
labor and costs as needed for separating and then drying the
microcapsules and from the view point of the damage as done to the
microcapsules by such as friction or shock accompanying the drying,
it is necessary that the above composition is produced without
involving the step of drying the microcapsules.
[0073] Although there is no especial limitation on the method for
adjusting the microcapsule content in the range of 30 to 80 weight
% in the composition as obtained, the microcapsule content in the
composition is favorably adjusted in the range of 30 to 80 weight %
by carrying out the concentration step of reducing the aqueous
medium. However, in the case where the preparation liquid as
obtained in the microcapsuling step has already been a composition
having a microcapsule content of 30 to 80 weight %, such as the
above concentration step is not necessary to carry out.
[0074] The above concentration step may be applied either to the
preparation liquid as obtained in the microcapsuling step or to a
dispersion as obtained by classification in the below-mentioned wet
classification step.
[0075] The above concentration step is a step in which a treatment
of reducing the amount of the aqueous medium is applied either to
the preparation liquid resultant from the microcapsuling step
(preparation liquid including the prepared microcapsules and the
aqueous medium) or to the dispersion as obtained by classification
in the below-mentioned wet classification step. That is to say, the
above concentration step is a step of reducing the aqueous medium
from the above preparation liquid or dispersion, thereby raising
the microcapsule content. Usually in the case of considering that
the composition including the microcapsules and the aqueous medium
is put to use for the electrophoretic displays, then the
microcapsule concentration is often too low in the preparation
liquid as it is after having been obtained by the microcapsuling
step. If such a preparation liquid is used as it is, for example,
there are problems in that: when this preparation liquid is put to
use in the form mixed into the binder, even if this mixing and the
dispersing itself of the microcapsules are easy, it is after all
impossible to provide the microcapsules to the electrophoretic
displays at a sufficient density, and therefore the product quality
is deteriorated. If the aqueous medium is reduced in the above
concentration step in such a manner that the microcapsule
concentration will be in a specific range, then the above problems
can easily be solved. In addition, for example, when compared with
such as a method in which microcapsules as once powdered by drying
are dispersed into the binder, a method in which microcapsules are
dispersed by mixing the binder with a concentrate of the above
preparation liquid can greatly lessen the damage to the
microcapsules and also can easily uniformly disperse the
microcapsules.
[0076] Favorably, if the concentration step is carried out, then
the composition including the microcapsules and the aqueous medium
is obtained in a state where the microcapsule content is raised to
a desirable range. Therefore, the labor, time, and costs for the
transportation, storage, and other handling of the above
composition per unit quantity of the microcapsules can be reduced,
and besides, it is possible to achieve the productivity enhancement
and the cost reduction as to final products such as the
electrophoretic displays.
[0077] Although there is no especial limitation on the
concentration method, specific examples thereof include a suction
filtration method, a pressurizing filtration method, a centrifugal
sedimentation method, a centrifugal filtration method, and a filter
press method.
[0078] In the present invention production process for the
composition, the wet classification step is favorably carried out
before the above concentration step. In this case, it follows that
the above concentration step is applied to a dispersion resultant
from the classification in the wet classification step.
[0079] The above wet classification step is a step of carrying out
a treatment of applying the classification of the microcapsules to
the preparation liquid resultant from the microcapsuling step,
namely, the preparation liquid including the prepared microcapsules
and the aqueous medium. The classification is wet classification
because the above preparation liquid is classified. Specifically,
the wet classification step is, for example, a classification step
of carrying out the classification treatment of the above
preparation liquid either as it is or after having diluted it with
such as any aqueous medium, whereby the microcapsules in the
preparation liquid are classified so as to have desirable particle
diameters or a desirable particle diameter distribution.
[0080] The wet classification can be carried out by methods or with
apparatuses, which methods and apparatuses involve manners such as
a sieving manner (filtration manner), a centrifugal sedimentation
manner, and a natural sedimentation manner. The sieving manner can
effectively be used for microcapsules having relatively large
particle diameters.
[0081] As to the classification in the sieving manner, it is
efficient and favorable to carry out this classification under
application of vibration.
[0082] Examples of the classification in the centrifugal
sedimentation manner include a batch manner (e.g. bucket type) and
a continuous manner (e.g. cyclone type). The classification in the
continuous manner is a manner in which the classification is
carried out by utilizing the difference in specific gravity between
the microcapsules with a high-speed rotating stream. This manner
can continuously carry out the classification and therefore enables
industrial mass production.
[0083] As to such a wet classification, it is favorable, for
solving problems such as of mutual aggregation of particles and
clogging, that the classification operation is carried in a state
where the microcapsule particle concentration is low in the
preparation liquid. This particle concentration is favorably not
more than 15 weight %, more favorably not more than 10 weight %,
still more favorably not more than 5 weight %.
[0084] In order that the microcapsule particle concentration in the
preparation liquid during the wet classification step can be in the
above-mentioned low range, when the occasion demands, the
preparation liquid may be diluted by adding thereto the aqueous
medium before the wet classification step.
[0085] The present invention production process for the composition
may further comprise other steps besides the above various steps
when the occasion demands. Examples thereof include a step of
washing the microcapsules.
[0086] The present invention microcapsule composition for the
electrophoretic displays (which may hereinafter be referred to as
the present invention microcapsule composition or as the present
invention composition) is a composition used for the preparation of
the coating liquid and comprises the aqueous medium and the
microcapsules for the electrophoretic displays, wherein the
microcapsules include the shell and the dispersion that is capsuled
in the shell, wherein the dispersion includes the solvent and the
electrophoretic fine particles that are dispersed in the solvent;
with the microcapsule composition being characterized by: being a
product as obtained without involving the step of drying the
microcapsules; and having a microcapsule content of 30 to 80 weight
%.
[0087] The microcapsules for the electrophoretic displays, as
referred to in the present invention microcapsule composition, may
be conventional and publicly known microcapsules for the
electrophoretic displays if the microcapsules are products as
obtained without involving the step of drying the microcapsules.
There is no especial limitation on such as: from what material, by
what production process, and via what production steps the
microcapsules are products as obtained. In addition, the
microcapsules may appropriately be processed by such as the
classification treatment when the occasion demands in consideration
of purposes of their use. The microcapsules are favorably the
microcapsules for the electrophoretic displays in the microcapsule
composition as obtained by the present invention production
process. That is to say, the present invention microcapsule
composition is favorably the microcapsule composition as obtained
by the present invention production process.
[0088] Although there is no especial limitation on the aqueous
medium as referred to in the present invention composition,
specifically the same as the aqueous mediums used in the present
invention production process are favorable.
[0089] The present invention composition can appropriately further
comprise other components besides the aqueous medium and the
microcapsules for the electrophoretic displays when the occasion
demands.
[0090] The present invention microcapsule composition is
characterized by having a microcapsule content of 30 to 80 weight
%, more favorably 35 to 80 weight %, still more favorably 40 to 80
weight %, of the entire composition. In the case where the above
content is less than 30 weight %, there is a possibility that: when
the composition is formed into a paint, the microcapsule
concentration may become so low that the microcapsules are
difficult to arrange in a layer densely by the side of each other
on a surface to be coated, thus resulting in occurrence of spaces
to cause a lack of displaying and therefore to cause the lowering
of the contrast and the image defect (displaying defect). In
addition, in the case where the above content is more than 80
weight %, there is a possibility such that: the microcapsules may
mutually aggregate to cause problems in the dispersibility when the
composition is formed into a paint; or the image defect (displaying
defect) may be caused in the case where the microcapsules cannot
sufficiently be dispersed; or, if the microcapsules are strongly
dispersed, they may be damaged so much that the electrophoretic
fine particle dispersion leaks from inside the microcapsules due to
the pressure as applied by laminating an electrode film to be a
counter electrode. Because of these problems, the resultant
electrophoretic displays cannot sufficiently obtain the contrast,
and have a lot of image defects (displaying defects).
[0091] In the present invention microcapsule composition, it is
favorable that the microcapsules in the composition have a
volume-average particle diameter of 30 to 150 .mu.m and a particle
diameter distribution by volume such that: not less than 80 volume
% of the microcapsules are present, within the particle diameter
range of .+-.40% of the maximum-peak particle diameter (particle
diameter corresponding to the maximum peak in the particle diameter
frequency distribution by particle volume) around the maximum-peak
particle diameter.
[0092] The above volume-average particle diameter is more favorably
in the range of 50 to 150 .mu.m. In the case where this
volume-average particle diameter is smaller than 30 .mu.m, there is
a possibility that there cannot be obtained electrophoretic
displays having a sufficient contrast. In the case where the
volume-average particle diameter is larger than 150 .mu.m, there is
a possibility that there may occur problems in the strength of the
microcapsules.
[0093] The above particle diameter distribution by volume is
favorably a particle diameter distribution such that: not less than
80 volume % (more favorably not less than 85 volume %) of the
microcapsules are present within the particle diameter range of "a
particle diameter length corresponding to .+-.40% of the
maximum-peak particle diameter" around the maximum-peak particle
diameter in the particle diameter frequency distribution by
particle volume. In the case where the above ratio is less than 80
volume %, there is a possibility that: when the composition is
formed into a paint and then coated, the microcapsules may be
coated not in a layer but partially in a multilayer including at
least two layers.
[0094] In the present invention microcapsule composition, the total
content of the microcapsules and the aqueous medium in the
composition is favorably not less than 90 weight %, more favorably
not less than 93 weight %, still more favorably not less than 95
weight %, particularly favorably not less than 98 weight %. In the
case where the above content is less than 90 weight %, there is a
possibility that the effects of the present invention cannot be
displayed sufficiently when the composition is provided to the
electrophoretic displays.
[0095] In the case where the present invention microcapsule
composition is (either as it is or after having been mixed with
such as the binder) put to use for the electrophoretic displays,
there can be produced the electrophoretic displays that are
excellent in various performances (e.g. longtime stability of
displaying, respondability, and number of times of display
rewritability) and exhibit excellent performances particularly in
such as contrast and image vividness. In the case where the
electrophoretic displays are produced from the present invention
microcapsule composition, for example, there can favorably be cited
a method that involves the steps of: coating the above composition
(either as it is or after having mixed it with such as the binder)
onto such as a film having a transparent electrode; and thereafter
laminating another film onto the resultant coated surface as
provided with the microcapsules. In the case where the
above-mentioned microcapsule composition is used in this method,
the above coating liquid can be made to have moderate thixotropy in
viscosity, and the above coated surface can be made to be a coated
surface which has little unevenness and is so homogeneous as to be
decreased also in localization and aggregation of the microcapsule
particles.
[0096] As an example of favorable usage of the present invention
microcapsule composition, there can be cited the production process
for a sheet for the electrophoretic displays. Specifically, this
process comprises the steps of: preparing a coating liquid
containing the present invention microcapsule composition in a
specific ratio; and then coating the prepared coating liquid onto a
substrate; and then drying the resultant coating film, thereby
producing the sheet for the electrophoretic displays.
[0097] That is to say, the present invention production process for
the sheet for the electrophoretic displays (which may hereinafter
be referred to as the present invention production process for the
sheet) comprises the steps of: coating a coating liquid containing
a microcapsule composition for the electrophoretic displays; and
drying the resultant coating film; thereby producing the sheet for
the electrophoretic displays; with the production process being
characterized by: using, as the composition, the present invention
microcapsule composition for the electrophoretic displays; and
further comprising the step of preparing the coating liquid by
mixing the composition in such an amount that the coating liquid
will have a microcapsule content of 25 to 65 weight %.
[0098] In the present invention production process for the sheet,
there is first prepared the coating liquid containing the present
invention microcapsule composition for the electrophoretic
displays. Specifically, the coating liquid is prepared, if
necessary, by adding such as a binder, an additive, and an aqueous
medium (e.g. aqueous medium for dilution) to the present invention
microcapsule composition for the electrophoretic displays.
[0099] Examples of the aforementioned binder include water-soluble
type binders and emulsion type binders.
[0100] Examples of the water-soluble type binders include
water-soluble alkyd resins, water-soluble acrylic-modified alkyd
resins, water-soluble oil-free alkyd resins (water-soluble
polyester resins), water-soluble acrylic resins, water-soluble
epoxy ester resins, and water-soluble melamine resins.
[0101] Examples of the emulsion type binders include alkyl
(meth)acrylate copolymer dispersions, vinyl acetate resin
emulsions, vinyl acetate copolymer resin emulsions, ethylene-vinyl
acetate copolymer resin emulsions, acrylate ester (co)polymer resin
emulsions, styrene-acrylate ester copolymer resin emulsions, epoxy
resin emulsions, urethane resin emulsions, acrylic-silicone
emulsions, and fluororesin emulsions.
[0102] Examples of the aforementioned additive include
viscosity-adjusting agents (thickeners), dispersants/wetting
agents, defoamers, and mildew-proofing agents/antiseptics. In the
case where the coating liquid contains these additives, there is no
especial limitation on their contents if they are in such a range
that there can be obtained a coating liquid having desirable
performances.
[0103] Examples of the viscosity-adjusting agents (thickeners)
include: cellulosic viscosity-adjusting agents (thickeners), such
as carboxymethyl cellulose, methyl cellulose, and hydroxyethyl
cellulose; polycarboxylic viscosity-adjusting agents (thickeners),
such as poly(sodium acrylate), alkaline-soluble emulsions, and
associated type alkaline-soluble emulsions; polyethylene-glycolic
viscosity-adjusting agents (thickeners), such as polyethylene
glycol, polyethylene glycol alkyl ethers, polyethylene glycol alkyl
esters, and associated type polyethylene glycol derivatives; other
water-soluble polymers such as polyvinyl alcohol; and smectite type
viscosity-adjusting agents (thickeners), such as montmorillonite,
hectorite, and saponite. These can be used either alone
respectively or in combinations with each other.
[0104] Examples of the dispersants/wetting agents include:
poly(acrylate salts) and styrene-maleic acid copolymer salts;
formalin condensation products from naphthalenesulfonate salts;
long-chain-alkyl organic sulfonate salts; polyphosphate salts;
long-chain-alkylamine salts; poly(alkylene oxides); polyoxyalkylene
alkyl ethers; sorbitan fatty acid esters; fluorosurfactants, such
as perfluoroalkyl-group-containing salts,
perfluoroalkyl-group-containing esters, and
perfluoroalkyl-group-containi- ng oligomers; acetylenediol; and
acetylene glycol. These can be used either alone respectively or in
combinations with each other.
[0105] Examples of the defoamers include siliconic defoamers,
pluronic type defoamers, mineral oil type defoamers, polyesteric
defoamers and polyetheric defoamers. These can be used either alone
respectively or in combinations with each other.
[0106] Examples of the mildew-proofing agents/antiseptics include
organic nitrogen-sulfur compounds, organic nitrogen-halogen
compounds, hexadienoic acid chloride salts, cresolic compounds,
brominated compounds, aldehydic compounds, benzimidazolic
compounds, halogenated cyclic sulfur compounds, organic arsenic
compounds, organic copper compounds, chloroisothiazolone, and
isothiazolone. These can be used either alone respectively or in
combinations with each other.
[0107] As to the coating liquid as referred to in the present
invention, it is favorable to uniformly disperse the microcapsules
into the coating liquid in order to obtain a coating film in which
the microcapsules are uniformly present. Examples of its means
include addition of such as the dispersants/wetting agents and the
viscosity-adjusting agents (thickeners), which are cited above as
examples of the aforementioned additives.
[0108] Examples of the aforementioned aqueous medium include the
same aqueous mediums as mentioned above.
[0109] When the aforementioned coating liquid is prepared, the
aforementioned composition is mixed in such an amount that the
coating liquid will have a microcapsule content of 25 to 65 weight
%, favorably 30 to 60 weight %, more favorably 30 to 55 weight %,
still more favorably 35 to 50 weight %. In the case where the
coating liquid has a microcapsule content of less than 25 weight %,
there is a possibility that: the microcapsule concentration may
become so low that the microcapsules are difficult to arrange in a
layer densely by the side of each other on a surface to be coated,
thus resulting in occurrence of spaces to cause a lack of
displaying and therefore to cause the lowering of the contrast and
the image defect (displaying defect). In addition, in the case
where the coating liquid has a microcapsule content of more than 65
weight %, there is a possibility such that: the microcapsules may
mutually aggregate to cause problems in the dispersibility in the
coating liquid; or the image defect (displaying defect) may be
caused in the case where the microcapsules cannot sufficiently be
dispersed; or, if the microcapsules are strongly dispersed, they
may be damaged so much that the electrophoretic fine particle
dispersion leaks from inside the microcapsules due to the pressure
as applied by laminating an electrode film to be a counter
electrode. Because of these problems, the resultant electrophoretic
displays cannot sufficiently obtain the contrast, and have a lot of
image defects (displaying defects).
[0110] In the present invention production process for the sheet,
subsequently, the prepared coating liquid is coated onto the
substrate and then dried, thereby producing the sheet for the
electrophoretic displays.
[0111] Examples of the aforementioned substrate include transparent
conductive films (e.g. PET films with ITO), films having a
conductive layer (e.g. copper-laminated polyimide films), and films
as coated with metal foils (e.g. aluminum foil) or conductive
polymers (e.g. polyacetylene, polyaniline, and polypyrrole). There
is no especial limitation on the method for coating the coating
liquid onto the substrate, and the coating liquid may be coated by
hitherto publicly known methods.
[0112] There is no especial limitation on the conditions of the
aforementioned drying step. However, the drying step may be carried
out in the temperature range of favorably 15 to 150.degree. C.
(more favorably 20 to 120.degree. C.) for favorably 1 to 60 minutes
(more favorably 5 to 45 minutes).
[0113] The present invention handling method for the microcapsules
for the electrophoretic displays (which may hereinafter be referred
to as the present invention handling method) is a handling method
for the microcapsules including the shell and the dispersion that
is capsuled in the shell, wherein the dispersion includes the
solvent and the electrophoretic fine particles that are dispersed
in the solvent, in which handling method the microcapsules are
handled by custody, preservation, transportation, and other various
handling in the form of the microcapsule composition such that: the
microcapsules are present in the aqueous medium; and the
microcapsule composition has a microcapsule content of 30 to 80
weight %.
[0114] The microcapsules for the electrophoretic displays, as
handled by the present invention handling method, will do if the
microcapsules are conventional and publicly known microcapsules for
the electrophoretic displays. There is no especial limitation on
such as: from what material, by what production process, and via
what production steps the microcapsules are products as obtained.
In addition, the microcapsules may appropriately be processed by
such as the classification treatment when the occasion demands in
consideration of purposes of their use. Specifically, for example,
microcapsules for the electrophoretic displays, which are obtained
by once being prepared by microcapsulation and thereafter being
isolated and then being dried and then being classified in a dry
manner, can also be used as the microcapsules (as referred to in
the present invention handling method) for the electrophoretic
displays. However, the microcapsules are favorably the
microcapsules for the electrophoretic displays in the microcapsule
composition as obtained by the above present invention production
process.
[0115] Examples of the handling, as referred to in the present
invention, include packing into containers, repacking between
containers, and measuring besides the above-mentioned custody,
preservation, and transportation.
[0116] Although there is no especial limitation on the aqueous
medium as referred to in the present invention handling method,
specifically the same as the aqueous mediums used in the above
present invention production process are favorable.
[0117] In the present invention handling method, the microcapsules
for the electrophoretic displays are handled in the presence of the
aqueous medium. However, other components can appropriately be used
besides the aqueous medium when the occasion demands.
[0118] In addition, in the present invention handling method, the
microcapsules are handled in the form of the microcapsule
composition having a microcapsule content of 30 to 80 weight % of
the entire composition including such as the aqueous medium as
well. However, the above content is more favorably in the range of
35 to 80 weight %, still more favorably 40 to 80 weight %. In the
case where the above content is less than 30 weight %, there is a
possibility that: when the composition is formed into a paint, the
microcapsule concentration may become so low that the microcapsules
are difficult to arrange in a layer densely by the side of each
other on a surface to be coated, thus resulting in occurrence of
spaces to cause a lack of displaying and therefore to cause the
lowering of the contrast and the image defect (displaying defect).
In addition, in the case where the above content is more than 80
weight %, there is a possibility such that: the microcapsules may
mutually aggregate to cause problems in the dispersibility when the
composition is formed into a paint; or the image defect (displaying
defect) may be caused in the case where the microcapsules cannot
sufficiently be dispersed; or, if the microcapsules are strongly
dispersed, they may be damaged so much that the electrophoretic
fine particle dispersion leaks from inside the microcapsules due to
the pressure as applied by laminating an electrode film to be a
counter electrode. Because of these problems, the resultant
electrophoretic displays cannot sufficiently obtain the contrast,
and have a lot of image defects (displaying defects).
[0119] (Effects and Advantages of the Invention):
[0120] The present invention can provide: a microcapsule
composition for electrophoretic displays; a production process for
the microcapsule composition for the electrophoretic displays; a
production process for a sheet for the electrophoretic displays;
and a handling method for microcapsules for the electrophoretic
displays; wherein the microcapsule composition contains
microcapsules and, when used for the electrophoretic displays, can
make them as excellent as conventional in various performances
(e.g. longtime stability of displaying, respondability of
displaying, contrast, and number of times of display rewritability)
and, particularly above all, can make the electrophoretic displays
exhibit a very high performance as to the contrast.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0121] Hereinafter, the present invention is more specifically
illustrated by the following examples of some preferred embodiments
in comparison with comparative examples not according to the
present invention. However, the present invention is not limited to
these examples in any way. Incidentally, for the sake of
convenience, the units "part(s) by weight" and "liter(s)" may
hereinafter be abbreviated simply to "part(s)" and "L"
respectively.
EXAMPLE 1
[0122] A four-necked flask of 500 mL was charged with 30 g of
titanium oxide (produced by Ishihara Sangyo Kaisha, Ltd., trade
name: Tipaque CR-97), 261 g of dodecylbenzene, and 2 g of titanate
coupling agent (produced by Ajinomoto Co., Inc., trade name:
Plemact TTS), and then these materials were mixed by stirring.
Thereafter, the flask was put into an ultrasonic bath (produced by
Yamato Co., Ltd., product name: BRANSON 5210) of 55.degree. C., and
then the contents of the flask were subjected to a ultrasonically
dispersing treatment under stirred conditions for 2 hours, thus
obtaining a titanium oxide dispersion (1).
[0123] The particle diameters of the titanium oxide in the above
dispersion (1) were measured. As a result, the volume-average
particle diameter was 0.34 .mu.m. The particle diameter
distribution was measured with a Shimadzu
centrifugal-sedimentation-type particle diameter distribution
measurement apparatus SA-CP3 (produced by Shimadzu
Corporation).
[0124] Into this dispersion (1), 6 g of anthraquinone blue oil dye
was dissolved, thus obtaining a blue-colored dispersion (1) for
electrophoretic displays.
[0125] Under stirring with a disper (produced by Tokushu Kika Kogyo
Co., Ltd., product name: ROBOMICS), 105 g of the dispersion (1) for
electrophoretic displays as heated to 55.degree. C. was added to an
aqueous solution which had beforehand been prepared by dissolving
5.5 g of gum arabic and 5.5 g of gelatin into 60 g of water and
then maintained at 43.degree. C. The stirring speed was gradually
raised to stir the resultant mixture at 1,050 r.p.m. for 60
minutes, thus obtaining a suspension.
[0126] While 300 mL of warm water of 43.degree. C. was added to
this suspension, the stirring speed was gradually lowered to 500
r.p.m. Furthermore, 0.75 ML of 10% aqueous NaCO.sub.3 solution was
added thereto, and thereafter the resultant mixture was maintained
for 30 minutes. Then, 11 mL of 10% acetic acid solution was added
thereto at a constant rate over a period of 25 minutes, and then
the resultant mixture was cooled to not higher than 10.degree.
C.
[0127] The mixture was maintained in the cooled state for 2 hours,
and then 3 mL of 37% formalin solution was added thereto at a
constant rate in 30 seconds, and then 22 mL of 10% aqueous
NaCO.sub.3 solution was further added thereto at a constant rate
over a period of 25 minutes.
[0128] The resultant mixture was cooled to ordinary temperature
under stirred conditions and then aged for 20 hours, thus preparing
microcapsules (1) and further obtaining a microcapsule dispersion
(1). The microcapsules (1) included a shell and the aforementioned
dispersion (1) for electrophoretic displays that was capsuled in
the shell. In the microcapsule dispersion (1), the above
microcapsules (1) were dispersed.
[0129] At that point of time, the particle diameters of the
microcapsules (1) were measured with a laser-diffraction/scattering
type particle-diameter-distribution measurement apparatus, HORIBA
LA-910 (produced by Horiba Seisakusho Co., Ltd.),. As a result, the
volume-average particle diameter was 67 .mu.m.
[0130] The microcapsule dispersion (1) as obtained was diluted with
1,500 g of water to which 1.25 mL of 10% aqueous NaCO.sub.3
solution had been added. The resultant dilution was passed through
a mesh sieve having a mesh opening size of 85 .mu.m, and then
placed into a separatory funnel, and then left stationary. Then, 7
hours later, the lower liquid of the separated upper and lower
liquids was extracted. To the residual upper liquid, there was
added 1,500 g of water to which 1.25 mL of 10% aqueous NaCO.sub.3
solution had been added. These materials were uniformly mixed by
hand shaking to thereby carry out re-dispersion, and thereafter
left stationary. A sequence of the above operations of the
stationary leaving, the extraction of the lower liquid, and the
re-dispersion of the upper liquid were repeated three times, thus
completing the wet classification.
[0131] The microcapsule dispersion (1) which had been subjected to
the above wet classification was concentrated by suction
filtration, thus obtaining a microcapsule composition (1) as a
filtrated cake including the classified microcapsules (1). The
classified microcapsules (1) had a volume-average particle diameter
of 74.6 .mu.m and the maximum-peak particle diameter of 77.2 .mu.m
(incidentally, the above maximum-peak particle diameter is a
particle diameter corresponding to the maximum peak in the particle
diameter distribution by volume; the same definition is hereinafter
applied). In addition, the particle diameter distribution by volume
was such that: 85 volume % of the microcapsules were present within
the particle diameter range of .+-.40% of the maximum-peak particle
diameter around the maximum-peak particle diameter. Furthermore,
the microcapsules (1) were present at a content of 45 weight % in
the above microcapsule composition (1). These results are listed in
Table 1.
EXAMPLE 2
[0132] A titanium oxide dispersion (2) was obtained by the same
procedure as of Example 1 except to replace the dodecylbenzene with
Highsol SA296 (produced by Nisseki Kagaku Co., Ltd.).
[0133] The particle diameters of the titanium oxide in the above
dispersion (2) were measured in the same way as of Example 1. As a
result, the volume-average particle diameter was 0.27 .mu.m.
[0134] Into this dispersion (2), 6 g of anthraquinone blue oil dye
was dissolved, thus obtaining a blue-colored dispersion (2) for
electrophoretic displays.
[0135] Thereafter, the same procedure as of Example 1 was carried
out except that: the dispersion (2) for electrophoretic displays
was used instead of the dispersion (1) for electrophoretic
displays, and the stirring with the diaper at 1,050 r.p.m. for 60
minutes was changed to the stirring at 800 r.p.m. for 60 minutes.
Thereby, microcapsules (2) were prepared, and further a
microcapsule dispersion (2) was obtained. The microcapsules (2)
included a shell and the aforementioned dispersion (2) for
electrophoretic displays that was capsuled in the shell. In the
microcapsule dispersion (2), the above microcapsules (2) were
dispersed.
[0136] At that point of time, the particle diameters of the
microcapsules (2) were measured in the same way as of Example 1. As
a result, the volume-average particle diameter was 105 .mu.m.
[0137] The microcapsule dispersion (2) as obtained was diluted with
1,500 g of water to which 1.25 mL of 10% aqueous NaCO.sub.3
solution had been added. The resultant dilution was passed through
a mesh sieve having a mesh opening size of 130 .mu.m. Thereafter,
microcapsules having particle diameters of not larger than 70 .mu.m
were removed with a continuous wet classification apparatus,
Sanitary Cyclone (produced by Nippo Co., Ltd.).
[0138] The microcapsule dispersion (2) which had been subjected to
the above wet classification was concentrated by suction
filtration, thus obtaining a microcapsule composition (2) as a
filtrated cake including the classified microcapsules (2). The
classified microcapsules (2) had a volume-average particle diameter
of 113.2 .mu.m and the maximum-peak particle diameter of 118.7
.mu.m. In addition, the particle diameter distribution by volume
was such that: 81 volume % of the microcapsules were present within
the particle diameter range of .+-.40% of the maximum-peak particle
diameter around the maximum-peak particle diameter. Furthermore,
the microcapsules (2) were present at a content of 58 weight % in
the above microcapsule composition (2). These results are listed in
Table 1.
EXAMPLE 3
[0139] In the same way as of Example 1, microcapsules (3) were
prepared, and further a microcapsule dispersion (3) was obtained.
In the microcapsule dispersion (3), the above microcapsules (3)
were dispersed.
[0140] At that point of time, the particle diameters of the
microcapsules (3) were measured in the same way as of Example 1. As
a result, the volume-average particle diameter was 65 .mu.m.
[0141] The microcapsule dispersion (3) as obtained was subjected to
wet classification in the same way as of Example 1.
[0142] The microcapsule dispersion (3) which had been subjected to
the above wet classification was concentrated by suction filtration
in the same way as of Example 1 except that the suction amount was
reduced. Thus, there was obtained a microcapsule composition (3) as
a filtrated cake including the classified microcapsules (3). The
classified microcapsules (3) had a volume-average particle diameter
of 70.7 .mu.m and the maximum-peak particle diameter of 75.5 .mu.m.
In addition, the particle diameter distribution by volume was such
that: 88 volume % of the microcapsules were present within the
particle diameter range of .+-.40% of the maximum-peak particle
diameter around the maximum-peak particle diameter. Furthermore,
the microcapsules (3) were present at a content of 33 weight % in
the above microcapsule composition (3). These results are listed in
Table 1.
EXAMPLE 4
[0143] In the same way as of Example 2, microcapsules (4) were
prepared, and further a microcapsule dispersion (4) was obtained.
In the microcapsule dispersion (4), the above microcapsules (4)
were dispersed.
[0144] At that point of time, the particle diameters of the
microcapsules (4) were measured in the same way as of Example 2. As
a result, the volume-average particle diameter was 112 .mu.m.
[0145] The microcapsule dispersion (4) as obtained was subjected to
wet classification in the same way as of Example 2 except that:
there was used a mesh having a mesh opening size of 140 .mu.m, and
microcapsules having particle diameters of not larger than 80 .mu.m
were removed.
[0146] The microcapsule dispersion (4) which had been subjected to
the above wet classification was concentrated by suction filtration
in the same way as of Example 2 except that the suction amount was
increased. Thus, there was obtained a microcapsule composition (4)
as a filtrated cake including the classified microcapsules (4). The
classified microcapsules (4) had a volume-average particle diameter
of 121.8 .mu.m and the maximum-peak particle diameter of 128.1
.mu.m. In addition, the particle diameter distribution by volume
was such that: 80 volume % of the microcapsules were present within
the particle diameter range of .+-.40% of the maximum-peak particle
diameter around the maximum-peak particle diameter. Furthermore,
the microcapsules (4) were present at a content of 75 weight % in
the above microcapsule composition (4). These results are listed in
Table 1.
Comparative Example 1
[0147] In the same way as of Example 1, microcapsules (c1) were
prepared, and further a microcapsule dispersion (c1) was obtained.
In the microcapsule dispersion (c1), the above microcapsules (c1)
were dispersed.
[0148] At that point of time, the particle diameters of the
microcapsules (c1) were measured in the same way as of Example 1.
As a result, the volume-average particle diameter was 67 .mu.m, and
the maximum-peak particle diameter was 65.1 .mu.m. In addition, the
particle diameter distribution by volume was such that: 51 volume %
of the microcapsules were present within the particle diameter
range of .+-.40% of the maximum-peak particle diameter around the
maximum-peak particle diameter.
[0149] The microcapsule dispersion (c1) as obtained was filtrated
and then dried, thus obtaining a powder of the microcapsules (c1).
These results are listed in Table 1.
Comparative Example 2
[0150] The powder of the microcapsules (c1) as obtained in
Comparative Example 1 was passed through a mesh having a mesh
opening size of 85 .mu.m, thus obtaining microcapsules (c2) of
Comparative Example 2. In the above operation of passing the powder
through the mesh having a mesh opening size of 85 .mu.m, aggregates
remaining on the mesh were seen in a large amount.
[0151] The amount of the powder of the microcapsules (c2) as
obtained through the mesh was 31 weight % of the entire powder of
the microcapsules (c1).
[0152] The particle diameters of the microcapsules (c2) were
measured in the same way as of Example 1. As a result, the
volume-average particle diameter was 67 .mu.m, and the maximum-peak
particle diameter was 61.9 .mu.m. In addition, the particle
diameter distribution by volume was such that: 53 volume % of the
microcapsules were present within the particle diameter range of
.+-.40% of the maximum-peak particle diameter around the
maximum-peak particle diameter. These results are listed in Table
1.
[0153] Electrophoretic displays (1) to (4), (c1), and (c2) were
produced in the following procedure from the microcapsule
compositions (1) to (4) and powdery microcapsules (c1) and (c2),
respectively, as obtained in the above ways.
[0154] First of all, a coating liquid was prepared as follows. Any
one of the microcapsule compositions (1) to (4) or the powdery
microcapsules (c1) or (c2) were mixed with an acrylic emulsion for
binders (solid component concentration: 45 weight %) in such an
amount that the weight ratio of microcapsules/acrylic emulsion for
binders would be as listed in Table 2. Water was further added to
the resultant mixture in such an amount that the microcapsule
content in the coating liquid would be as listed in Table 2. Thus,
coating liquids (1) to (4), (c1), and (c2) were prepared.
[0155] Next, the prepared coating liquid was coated onto an
ITO-having PET film with an applicator and thereafter dried at
90.degree. C. for 10 minutes, thus preparing a coated sheet (sheet
for electrophoretic displays). Subsequently, another ITO-having
film was piled and thereby laminated onto the coated side of this
coated sheet, thus obtaining an electrophoretic display as equipped
with counter electrodes.
[0156] The case where the microcapsule content is too low in the
microcapsule composition results inevitably in a low solid
component concentration of the coating liquid, also. Accompanying
it, the viscosity of the coating liquid also decreases so much that
the leveling ability is deteriorated when the coating liquid is
coated. In addition, the resultant coating film is also so thin
that spaces between the microcapsules are opened so wide that the
microcapsules fall into a "sparse" state. Dense existence of the
microcapsules on the coated surface enhances the displaying
properties and remarkably acts upon the contrast above all.
[0157] As to each of the electrophoretic displays (1) to (4), (c1),
and (c2) as obtained, a direct current voltage of 30 V was applied
between both electrodes for 1 second, and thereafter the contrast
was measured. As to the contrast, the reflectances of blue and
white displays were measured with a Macbeth spectrophotometric
densitometer, SpectroEye (produced by Gretag Macbeth), and the
contrast was represented by the ratio (contrast) between these
reflectances (ratio (contrast) between reflectances=white
reflectance/blue reflectance). Incidentally, the ratio between
reflectances is a value as obtained by: measuring a reflectance of
a display (e.g. blue) when the direct current voltage is applied
between the counter electrodes of the electrophoretic display; and
subsequently measuring a reflectance of a display (e.g. white) when
the polarity is reversed to apply the direct current voltage; and
then calculating the ratio between both reflectances. It is
hereupon prescribed that the reflectance should be measured as to
one entire face of the electrophoretic display.
[0158] In addition, the coated surface was optically magnified with
a microscope (produced by Highlocks Co., Ltd., product name: Power
High Scope KH-2700) to observe and evaluate a state of rows of the
microcapsules and a damaged or defective (non-electrophoretic)
state of the microcapsules on the following standards.
[0159] Their results are listed in Table 1.
[0160] (State of Rows of Microcapsules):
[0161] .circleincircle.: The microcapsules are densely packed
without spaces, and there is also little overlap between the
microcapsules, and there are no aggregates.
[0162] .largecircle.: The microcapsules are in a dense state as a
whole, but there are some "sparse" portions. There are also some
overlap portions between the microcapsules, but there are no
aggregates.
[0163] .DELTA.: There are also dense portions, but there are also
considerably many "sparse" portions. There is little overlap
between the microcapsules, but aggregates are seen.
[0164] X: The microcapsules are sparse, and there are few dense
portions. There are also considerably many aggregates.
[0165] (Damage or Defect (Non-electrophoresis) of
Microcapsules):
[0166] There was counted the number of damaged or defective
(non-electrophoretic) microcapsules existing in any five visual
fields (200 to 400 microcapsules existed per one visual field)
under 200 magnifications.
1 TABLE 1 Ratio of microcapsules present within particle diameter
range of .+-.40% of Volume- Maximum- maximum-peak average peak
particle Ratio Number of Microcapsule particle particle diameter
(contrast) State of rows damaged or content diameter diameter
around it between of defective (wt %) (.mu.m) (.mu.m) (vol. %)
reflectances microcapsules microcapsules Example 1 45 74.6 77.2 85
5.6 .circleincircle. 6 Example 2 68 113.2 118.7 81 7.2
.circleincircle. 8 Example 3 33 70.7 75.5 88 4.7 .largecircle. 13
Example 4 75 121.8 128.1 80 6.9 .largecircle. 11 Comparative 100
62.1 65.1 51 2.1 X 36 Example 1 Comparative 100 60.3 61.9 53 2.8
.DELTA. 28 Example 2
[0167]
2 TABLE 2 Microcapsules/ Microcapsule acrylic content emulsion in
coating Microcapsules for binders liquid used (weight ratio)
(weight %) Coating liquid (1) Microcapsule 10/2 40 composition (1)
Coating liquid (2) Microcapsule 10/4 45 composition (2) Coating
liquid (3) Microcapsule 10/0.5 30 composition (3) Coating liquid
(4) Microcapsule 10/1 60 composition (4) Coating liquid (c1)
Microcapsules 10/4 50 (c1) Coating liquid (c2) Microcapsules 10/4
40 (c2)
[0168] Various details of the invention may be changed without
departing from its spirit not its scope. Furthermore, the foregoing
description of the preferred embodiments according to the present
invention is provided for the purpose of illustration only, and not
for the purpose of limiting the invention as defined by the
appended claims and their equivalents.
* * * * *