U.S. patent application number 10/939486 was filed with the patent office on 2005-09-15 for liquid crystal display element and manufacturing method thereof.
This patent application is currently assigned to FUJI XEROX CO., LTD.. Invention is credited to Arisawa, Hiroshi, Harada, Haruo.
Application Number | 20050200775 10/939486 |
Document ID | / |
Family ID | 34918638 |
Filed Date | 2005-09-15 |
United States Patent
Application |
20050200775 |
Kind Code |
A1 |
Harada, Haruo ; et
al. |
September 15, 2005 |
Liquid crystal display element and manufacturing method thereof
Abstract
The invention discloses a liquid crystal display element
including: a pair of display substrates each having a support and
an electrode provided on one surface of the support; and a display
layer provided between the electrodes of the pair of display
substrates, wherein the display layer contains gelatin and liquid
crystal drops or microcapsules; and the liquid crystal drops or
microcapsules are densely arrayed in a monolayer, and a method of
manufacturing the liquid crystal display element, including:
applying to a surface of one of the display substrates which
surface has the electrode, a coating solution in which liquid
crystal drops or microcapsules are dispersed in a solution
containing gelatin and a solvent, thereby forming a coating layer;
and evaporating the solvent in the coating layer at a temperature
not less than the freezing point of the gelatin to provide a
display layer between the electrodes of the display substrates.
Inventors: |
Harada, Haruo; (Ebina-shi,
JP) ; Arisawa, Hiroshi; (Ebina-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
FUJI XEROX CO., LTD.
Minato-ku
JP
|
Family ID: |
34918638 |
Appl. No.: |
10/939486 |
Filed: |
September 14, 2004 |
Current U.S.
Class: |
349/86 |
Current CPC
Class: |
G02F 1/1334 20130101;
G02F 1/13718 20130101 |
Class at
Publication: |
349/086 |
International
Class: |
G02F 001/1333 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 15, 2004 |
JP |
2004-72928 |
Claims
What is claimed is:
1. A liquid crystal display element comprising: a pair of display
substrates each having a support and an electrode provided on one
surface of the support; and a display layer provided between the
electrodes of the pair of display substrates, wherein the display
layer contains gelatin and one of liquid crystal drops and liquid
crystal microcapsules; and the one of the liquid crystal drops and
the liquid crystal microcapsules is densely arrayed in a
monolayer.
2. A liquid crystal display element according to claim 1, wherein
the one of the liquid crystal drops and liquid crystal
microcapsules is in a monodispersed state with uniform particle
diameters.
3. A liquid crystal display element according to claim 2, wherein
the one of the liquid crystal drops and the liquid crystal
microcapsules is prepared by a film-emulsifying process.
4. A liquid crystal display element according to claim 1, wherein
the gelatin is prepared by acid-treating cattle bone.
5. A liquid crystal display element according to claim 1, wherein
liquid crystal used for the one of the liquid crystal drops and the
liquid crystal microcapsules is selected from the group consisting
of cholesteric liquid crystal, nematic liquid crystal, guest liquid
crystal and host liquid crystal.
6. A liquid crystal display element according to claim 1, further
comprising a light shielding layer on one electrode of the pair of
display substrates.
7. A liquid crystal display element according to claim 6, further
comprising a bonding layer between the light shielding layer and
the display layer.
8. A liquid crystal display element according to claim 1, further
comprising a bonding layer between the display layer and at least
one of the electrodes.
9. A liquid crystal display element according to claim 6, further
comprising a bonding layer between the light shielding layer and
one of the electrodes.
10. A liquid crystal display element according to claim 6, further
comprising a photoconductive layer between the light shielding
layer and one of the electrodes.
11. A liquid crystal display element according to claim 1, wherein
the one of the liquid crystal drops and the liquid crystal
microcapsules has a uniform size.
12. A liquid crystal display element according to claim 1, wherein
liquid crystal used for the one of the liquid crystal drops and the
liquid crystal microcapsules is cholesteric liquid crystal.
13. A method of manufacturing a liquid crystal display element
according to claim 1, comprising: applying to a surface of one of
display substrates each having a support and an electrode provided
on one surface of the support, which surface has the electrode, a
coating solution for a display layer in which one of liquid crystal
drops and liquid crystal microcapsules is dispersed in a solution
containing gelatin and a solvent, the gelatin, the solvent, and the
one of the liquid crystal drops and the liquid crystal
microcapsules being in an adjusted mix proportion, thereby forming
a coating layer; and evaporating the solvent in the coating layer
at a temperature equal to or higher than the freezing point of the
gelatin to provide a display layer between the electrodes of the
display substrates.
14. A method of manufacturing a liquid crystal display element
according to claim 13, wherein a coating portion is retained in an
atmosphere of which the vapor pressure is the same as or close to
the saturation vapor pressure of the solvent in a part or the total
of time that the solvent is evaporated.
15. A method of manufacturing a liquid crystal display element
according to claim 13, wherein vibration is applied to the coating
layer in a part or the total of time that the solvent is
evaporated.
16. A method of manufacturing a liquid crystal display element
according to claim 13, wherein the one of the liquid crystal drops
and the liquid crystal microcapsules is prepared by a
film-emulsifying process.
17. A method of manufacturing a liquid crystal display element
according to claim 13, wherein a ratio A.sub.L of an area covered
by the one of the liquid crystal drops and the liquid crystal
microcapsules to a coated area, calculated by the following formula
(1), is adjusted to a range of the following formula (2), when a
ratio of volume of nonvolatile components to volume of the coating
solution for the display layer is denoted as Sr, a ratio of volume
of the one of the liquid crystal drops and the liquid crystal
microcapsules to volume of the nonvolatile components is denoted as
Lr, an average particle diameter of the one of the liquid crystal
drops and the liquid crystal microcapsule is denoted as D.sub.L
.mu.m, and a wet coating thickness on the one of the display
substrates is denoted as t.sub.W .mu.m.
A.sub.L=(3/2).multidot.(t.sub.W.m- ultidot.Sr.multidot.Lr/D.sub.L)
Formula (1) 0.8<A.sub.L<1.0 Formula (2)
18. A method of manufacturing a liquid crystal display element
according to claim 17, wherein the ratio Lr of volume of the one of
the liquid crystal drops and the liquid crystal microcapsules to
volume of the nonvolatile components is adjusted to 0.9 or
less.
19. A method of manufacturing a liquid crystal display element
according to claim 13, wherein the temperature of the coating
solution for the display layer is adjusted to a range of 40 to
60.degree. C.
20. A method of manufacturing a liquid crystal display element
according to claim 13, wherein the coating layer is dried at a
temperature in a range of 40 to 60.degree. C.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority under 35 USC 119 from
Japanese Patent Application No. 2004-72928, the disclosure of which
is incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a liquid crystal display
element having a display layer including liquid crystal drops or
liquid crystal microcapsules, and a manufacturing method
thereof.
[0004] 2. Description of the Related Art
[0005] The large quantity of paper consumed mainly in offices has
become problematic, owing to both the destruction of forest
resources to obtain the raw material for paper pulp as well as
environmental pollution arising from the disposal and incineration
of refuse. However, consumption of paper meant to be short-lived
documentation for temporary viewing of electronic information has
tended to increase more and more with the spread of personal
computers and the development of information-based society, as with
the Internet. It is therefore desirable that a rewritable display
medium be developed to replace paper.
[0006] In recent years, cholesteric liquid crystal display elements
have been notable for such merits as a memory property capable of
retaining the display without a power source, a bright display
gained from non-use of a polarizing plate, and color display being
possible even without use of a color filter.
[0007] Cholesteric liquid crystal, in which liquid crystal
molecules have a helical structure, causes a selective reflection
phenomenon where incident light is divided into right-hand
circularly polarized light and left-hand circularly polarized
light, and a circularly polarized light component corresponding to
the torsional direction of the helix undergoes Bragg reflection,
and the rest of the light is transmitted. The central wavelength
.lambda. and the reflected wavelength width .DELTA..lambda. of
reflected light are denoted as .lambda.=n.multidot.p and
.DELTA..lambda.=.DELTA.n.multidot.p respectively where helical
pitch is p, average refractive index is n and double refractive
index is .DELTA.n, and reflected light from a cholesteric liquid
crystal layer exhibits vibrant color depending on the helical
pitch.
[0008] Cholesteric liquid crystal having positive dielectric
anisotropy can exist in the following three states: a planar state
where the helical axis is perpendicular to a cell surface as shown
in FIG. 10A and the above-mentioned selective reflection phenomenon
is caused with respect to incident light, a focal conic state where
the helical axis is substantially parallel to the cell surface as
shown in FIG. 10B and incident light is transmitted while being
somewhat subjected to forward scattering, and a homeotropic state
where a liquid crystal director turns in the direction of an
electric field with a deformed helical structure as shown in FIG.
10C and where incident light is transmitted substantially
completely.
[0009] Of the three states, the planar state and the focal conic
state can bistably exist without voltage. The state of orientation
of cholesteric liquid crystal, therefore, is not univocally
determined for voltage applied to a liquid crystal layer, the state
of orientation of which changes from a planar state to a focal
conic state and then to a homeotropic state, in that order, as an
applied voltage is increased in a case where the planar state is
the initial state, and changes from a focal conic state to a
homeotropic state, in that order, as an applied voltage is
increased in a case where the focal conic state is the initial
state. On the other hand, in a case where voltage applied to a
liquid crystal layer is abruptly brought to 0, the planar state and
the focal conic state are maintained in these respective states,
while the homeotropic state changes into the planar state. The
three states can be made to undergo mutual transition by the
magnitude of applied pulse voltage.
[0010] FIG. 11 shows this electrooptical response. In FIG. 11, the
curve A denotes the case where the initial state is the planar
state and the curve B denotes the case where the initial state is
the focal conic state.
[0011] A range denoted as (a) in FIG. 11 shows the planar state or
the focal conic state (selective reflection state or transmission
state), a range denoted as (b) shows a transition region, a range
denoted as (c) shows the focal conic state (transmission state), a
range denoted as (d) shows a transition region and a range denoted
as (e) shows the homeotropic state, which changes into the planar
state (selective reflection state) at a voltage of 0. Vpf,90,
Vpf,10, Vfh,10 and Vh,90 signify voltage at which normalized
reflectance is 90 or 10 (normalized reflectance of 90 or more is
regarded as the selective reflection state and that of 10 or less
is regarded as the transmission state) before and after the two
transition regions.
[0012] A layer for absorbing light of the same wavelength as at
least the selective reflection color is disposed on the back of a
cholesteric liquid crystal layer, so that a reflection type memory
display utilizing the planar state and the focal conic state can be
achieved.
[0013] A cholesteric liquid crystal display element can have a
structure in which liquid crystal is contained in space formed
between a pair of display substrates to form a continuous phase, or
have a structure such as a PDLC (Polymer Dispersed Liquid Crystal)
structure in which drop-like cholesteric liquid crystal is
dispersed in a polymeric binder or a PDMLC (Polymer Dispersed
Microencapsulated Liquid Crystal) structure in which
microencapsulated cholesteric liquid crystal is dispersed in a
polymeric binder (for example, refer to Japanese Patent Application
Publication (JP-B) No. 7-009512, Japanese Patent Application
Laid-Open (JP-A) No. 09-236791 and Japanese Patent No. 3178530
(paragraphs 0159 to 0161)).
[0014] The use of the PDLC or PDMLC structure restrains the
flowability of liquid crystal, and thus disorder of an image due to
bending and pressure decreases, achieving a flexible medium. The
direct laminating of multiple cholesteric liquid crystal layers
allows realization of color display, and also laminating with a
photoconductive layer allows realization of a display element for
addressing an image with light signals. In addition, a display
layer can be formed with a thick-film printing technique so as to
offer the advantage of the manufacturing method thereof being
simplified to achieve low cost.
[0015] However, a cholesteric liquid crystal display element having
a PDLC or PDMLC structure has problems in that selective reflection
color in the planar state is low in brightness and color purity so
as not to allow a clear color display, and that light transmittance
in the focal conic state is poor such that contrast decreases due
to a turbid black display in a display element provided with a
black light-absorbing layer on the back thereof.
[0016] The reason why selective reflection color in the planar
state is low in brightness as described above is that, as shown in
FIG. 12, an area 32y of disordered orientation occurs in the
vicinity of an interface of each liquid crystal drop or liquid
crystal microcapsule 32 which has a curved surface such as being in
a spherical shape, and an effective selective reflection area 32x
reduces in the planar state. This also results in unnecessary
scattered light in the focal conic state. An effective means for
reducing this defect is to render the diameters of the liquid
crystal drops larger and uniform and to decrease the total area of
interfaces as much as possible. However, the problem arises of
surface irregularities of a display layer becoming large due to the
enlarged liquid crystal drops as described below.
[0017] As shown in FIGS. 13 and 14, conventional structures
including PDLC and PDMLC are manufactured by applying a coating
solution for a display layer to a display substrate 10 with a
coating device 60 (FIGS. 13A and 14A), evaporating a solvent 35 by
heating and decompressing (FIGS. 13B and 14B). Within the coating
solution, the liquid crystal drops or the liquid crystal
microcapsules 32 are dispersed in an aqueous solution of a polymer
serving as a binder. Refer to JP-B No. 7-009512, JP-A No. 09-236791
and Japanese Patent No. 3178530 (paragraphs 0159 to 0161)). FIG. 13
shows an example of polydispersion where the liquid crystal drops
or the liquid crystal microcapsules are not uniform in particle
diameter, while FIG. 14 shows an example of monodispersion where
the particle diameters are uniform.
[0018] In the case of FIG. 13, when the concentration of
nonvolatile components (non-evaporable components) in a coating
film is increased by evaporating the solvent, the flowability of a
coating layer decreases, causing a phenomenon called flocculation
where multiple liquid crystal drops or liquid crystal microcapsules
flow integrally, as shown by 33 in FIG. 13B. Drying progresses in a
state where individual dispersed liquid crystal drops cannot freely
move, and thus the obtained display layer has a structure in which
multiple liquid crystal drops or liquid crystal microcapsules are
in an accumulated state, and additionally, a leveling effect on the
liquid surface does not sufficiently come to bear, whereby a film
is produced which easily obtains large surface irregularities in
the liquid crystal drop layer, causing a particular disadvantage
which will be mentioned later.
[0019] The flocculation also occurs in a case where the liquid
crystal drops 32 dispersed as shown in FIG. 14 have uniform and
large particle diameters. The larger and more uniform the particle
diameters are of the dispersed liquid crystal drops, the greater
the tendency is for surface irregularities to become large in a
liquid crystal drop layer.
[0020] When surface irregularities in the liquid crystal drop layer
are large, as shown in FIG. 15, a bonding layer 16 cannot
completely cover all of the irregularities and an undesirable air
layer 38 occurs between the bonding layer 16 and a display layer 30
at the time that opposite display substrates 10 and 20 are
laminated. A desirable voltage cannot be applied to areas including
air. The areas thus remain in the planar state which is obtained
after coating, do not act and cause unnecessary selective
reflection light. Light reflected at the interface between the
bonding layer 16 and the air layer 38, or between the air layer 38
and the display layer 30, becomes unnecessary backward scattered
light, which particularly causes decrease in light transmittance in
the focal conic state and a turbid black display as described
above.
[0021] In addition, the reason why color purity is low in
conventional PDLC and PDMLC structures is as follow. As shown in
FIGS. 13 to 15, light which has passed through cholesteric liquid
crystal is slightly forward scattered when liquid crystal drops are
not orderly arrayed in a monolayer. The forward scattered light
enters a second liquid crystal drop layer at a smaller incident
angle. A phenomenon where the liquid crystal drops in second or
more layers reflect light of a shorter wavelength than the original
helical pitch according to Bragg's condition
(.lambda.=n.multidot.P.multidot.cos .theta.) in addition to the
original selective reflection light undesirably occurs in a state
of liquid crystal drops being accumulated in the direction of
thickness, decreasing the color purity of reflection color observed
as a result.
[0022] Problems have been described so far with regard to a
cholesteric liquid crystal display element. Also with regard to the
display element of a PDLC or PDMLC structure using nematic liquid
crystal or guest-host liquid crystal, when the liquid crystal drops
are not orderly arrayed in a monolayer, there is occasionally a
problem of large surface irregularities in a liquid crystal drop
layer causing incorporation of air at the time that opposite
substrates are laminated, and of a varying abundance ratio of
liquid crystal to a polymeric binder in the direction of thickness
deteriorating threshold steepness.
[0023] JP-A No. 09-90321 describes a method in which liquid crystal
microcapsules of a uniform size formed from liquid crystal drops
coated with a medium having a constant thickness are formed into a
monolayer. This method involves immersing a substrate in an
emulsion in which liquid crystal microcapsules are dispersed, and
pulling the substrate up from the emulsion at a constant velocity
to form the monolayer on the substrate.
[0024] This method, however, employs the flow accumulation
principle where a substrate is pulled out of an emulsion, and
according to the wettability of the substrate surface, particles
accumulate where the substrate, solution, and air are in contact
due to tension acting between the particles partially immersed in
the solution. Therefore, the film-forming rate is low, and the
method requires much time. Consequently this method is not suitable
for manufacturing a large surface-area device. In addition, a
complicated mechanism is required, such as a feedback device for
controlling the pull-up rate while observing the state of the
coating film. Moreover, a process of applying a polymer solution
after forming the monolayer is additionally required to flatten the
surface of the coating film.
[0025] JP-A No. 2002-270495 describes a leveling method at the time
that a coating solution is applied to a semiconductor wafer. With
this leveling method, a coating solution applied to a semiconductor
wafer is spread by a traveling wave that is generated by a
traveling-wave generator (a piezoelectric element). The coating
solution is spread within an environment where the atmosphere is
pressurized to be equal to or more than the saturation vapor
pressure of the coating solution so that no solvent vaporizes and
thereby leveling is effectively performed. JP-A No. 2002-270495,
however, gives no disclosure that liquid crystal drops or liquid
crystal microcapsules, obtained from a coating solution containing
particulates such as liquid crystal drops or liquid crystal
microcapsules, are arrayed in a monolayer.
[0026] Accordingly, the invention has been made in view of the
above-mentioned problems and there are needs for a liquid crystal
display element that is superior in contrast, by forming a flat
film in which liquid crystal drops or liquid crystal microcapsules
are densely arrayed in a monolayer, and for a method of simply
manufacturing such a liquid crystal display element with a large
surface area.
SUMMARY OF THE INVENTION
[0027] The above-mentioned needs are met by providing the following
liquid crystal display element and manufacturing method
thereof.
[0028] A first aspect of the present invention provides a liquid
crystal display element including: a pair of display substrates
each having a support and an electrode provided on one surface of
the support; and a display layer provided between the electrodes of
the pair of display substrates, wherein the display layer contains
gelatin and liquid crystal drops or liquid crystal microcapsules;
and the liquid crystal drops or the liquid crystal microcapsules
are densely arrayed in a monolayer.
[0029] A second aspect of the invention provides a method of
manufacturing the liquid crystal display element, including:
applying to a surface of one of display substrates each having a
support and an electrode provided on one surface of the support,
which surface has the electrode, a coating solution for a display
layer in which liquid crystal drops or liquid crystal microcapsules
are dispersed in a solution containing gelatin and a solvent, the
gelatin, the solvent, and the liquid crystal drops or the liquid
crystal microcapsules being in an adjusted mix proportion, thereby
forming a coating layer; and evaporating the solvent in the coating
layer at a temperature equal to or higher than the freezing point
of the gelatin to provide a display layer between the electrodes of
the display substrates.
[0030] With regard to the liquid crystal display element of the
invention, monodispersed liquid crystal drops or liquid crystal
microcapsules are densely arrayed in a monolayer and the surface of
the display layer is flat, whereby the problem can be avoided which
arises in a case where polydispersed liquid crystal drops or liquid
crystal microcapsules conventionally having a curved interface such
as a spherical or elliptical shape are arrayed in multilayers and
surface irregularities of a display layer are large. That is, the
use of cholesteric liquid crystal as the liquid crystal allows a
liquid crystal display element where the effective selective
reflection area within liquid crystal drops or liquid crystal
microcapsules is large (selective reflection color is bright), the
color purity of reflection color does not decrease, unnecessary
selective reflection does not occur, and a superior display is
enabled that does not suffer from a turbid black display. The use
of nematic liquid crystal and guest-host liquid crystal as the
liquid crystal allows a liquid crystal display element having a
superior threshold steepness.
[0031] The method of manufacturing the liquid crystal display
element of the invention allows a superior liquid crystal display
element with a large surface area as described above to be simply
manufactured.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] Preferred embodiments of the invention will be described in
detail based on the following figures, wherein:
[0033] FIG. 1 is a conceptual view showing an example of the
display element of the invention, which display element has a
display layer containing liquid crystal drops;
[0034] FIG. 2 is a conceptual view showing an example of the
display element of the invention, which display element has a
display layer containing liquid crystal microcapsules;
[0035] FIG. 3 is a conceptual view showing an example of the
display element of the invention, in which optical writing is
performed;
[0036] FIG. 4A is a conceptual view showing the application step of
the method for manufacturing the liquid crystal display element of
the invention, and FIG. 4B is a conceptual view showing the drying
step of the method of the invention;
[0037] FIGS. 5A to 5C are graphs showing change of arithmetic mean
roughness Ra on a display layer surface with respect to drying
temperature;
[0038] FIG. 6A shows the micrograph of a coating layer after an
application step has been completed in Example 1, FIG. 6B shows the
micrograph of the coating layer after a retaining step has been
completed in Example 1, and FIG. 6C shows the micrograph of the
coating layer after a drying step has been completed in Example
1;
[0039] FIG. 7A shows the image of a display layer obtained in
Example 1 which image is observed by a three-dimensional laser
microscope, FIG. 7B shows the image of a display layer obtained in
Comparative Example 1 which image is observed by the
three-dimensional laser microscope, and FIG. 7C shows the image of
a display layer obtained in Comparative Example 2 which image is
observed by the three-dimensional laser microscope;
[0040] FIG. 8A shows a graph in which the image of FIG. 7A is shown
by surface profile, FIG. 8B shows a graph in which the image of
FIG. 7B is shown by surface profile, and FIG. 8C shows a graph in
which the image of FIG. 7C is shown by surface profile;
[0041] FIG. 9 is a graph showing reflection spectra of display
elements of Example 1 and Comparative Examples 1 and 2 in a planar
state and a focal conic state;
[0042] FIGS. 10A to 10C are views showing array states of
cholesteric liquid crystal;
[0043] FIG. 11 is a graph showing an electrooptical response of
cholesteric liquid crystal having positive dielectric
anisotropy;
[0044] FIG. 12 is a conceptual view showing liquid crystal drops in
the display layer of a conventional display element.
[0045] FIG. 13A shows the application step of a conventional method
of manufacturing a display layer in which liquid crystal is
polydispersed, and FIG. 13B shows the drying step of the
method;
[0046] FIG. 14A shows the application step of another conventional
method of manufacturing a display layer in which liquid crystal is
monodispersed, and FIG. 14B shows the drying step of the
method;
[0047] FIG. 15 is a conceptual view showing that black reflectance
deteriorates when surface irregularities in a liquid crystal drop
layer are large in a conventional display device; and
[0048] FIG. 16 is a conceptual view showing a process in which a
coating layer containing a dispersing element is dried.
DETAILED DESCRIPTION OF THE INVENTION
[0049] The liquid crystal display element (occasionally,
hereinafter referred to as the "display element") of the invention
includes a pair of display substrates each having a support and at
least one electrode provided on one surface of the support; and a
display layer provided between the electrodes of the pair of
display substrates, and the display layer contains gelatin and
liquid crystal drops or liquid crystal microcapsules; and the
liquid crystal drops or the liquid crystal microcapsules are
densely arrayed in a monolayer.
[0050] The display element of the invention may have a light
shielding layer on the electrode(s) of a display substrate on a
non-display surface side, and a bonding layer between the light
shielding layer and the display layer, or between the electrode(s)
and the display layer, if necessary.
[0051] The type of liquid crystal used in the display element of
the invention is not particularly limited, and cholesteric liquid
crystal, nematic liquid crystal and guest-host liquid crystal can
be used. Embodiments of the display element of the invention which
embodiments include cholesteric liquid crystal will be described
below.
[0052] The embodiments of the display element of the invention are
described in figures. FIG. 1 shows a first embodiment of the
display element of the invention.
[0053] The display element of the first embodiment has a display
layer containing liquid crystal drops. In FIG. 1, the numeral 100
denotes a display element, the numerals 10 and 20 denote a pair of
display substrates, and each of the numerals 11 and 21 denotes a
support and the numerals 12 and 22 denote electrodes provided on
the supports 11 and 21. The display substrates 10 and 20 are
disposed so that the respective electrodes face each other. The
numeral 14 denotes a light shielding layer provided on the
electrode on a non-display surface side. The numeral 30 denotes a
display layer, which contains cholesteric liquid crystal drops 32
and a polymeric binder 34, and cholesteric liquid crystal is
denoted by 32a. The numeral 16 denotes a bonding layer formed
between the light shielding layer 14 and the display layer 30. In
this embodiment, the state of orientation of the cholesteric liquid
crystal is controlled by applying voltage between the electrodes,
and thereby incident light is selectively reflected by the
cholesteric liquid crystal as shown in FIG. 1.
[0054] Since liquid crystal drops or liquid crystal microcapsules
in the display layer of the display element of the invention are
arrayed in a monolayer as described above, an area of disordered
orientation is decreased in the vicinity of an interface of each
liquid crystal drop or microcapsule, and thereby an effective
reflection area is increased, which achieves bright display and
restrains decrease in color purity caused by multiple reflection.
In addition, surface irregularities becomes smaller, whereby
adhesion between the bonding layer and the display layer can be
improved at the time of lamination, and turbidity of black display
caused by unnecessary selectively reflected light and interfacial
reflected light can be reduced.
[0055] FIG. 2 shows a second embodiment of the display element of
the invention.
[0056] This embodiment is different from the first embodiment only
in that a display layer in which liquid crystal microcapsules are
retained and dispersed in a polymeric binder. In each of the liquid
crystal microcapsules, a polymeric shell encapsulates cholesteric
liquid crystal. In FIGS. 1 and 2, members having the same reference
numeral are the same. In FIG. 2, the numerals 36, 36a and 36b
denote liquid crystal microcapsules, cholesteric liquid crystal and
the polymeric shell of each liquid crystal microcapsule,
respectively.
[0057] FIG. 3 shows a third embodiment of the display element of
the invention.
[0058] A display element shown in FIG. 3 is different from the
display element of FIG. 2 only in that a photoconductive layer 40
is provided between the electrode 12 and the light shielding layer
14. The state of orientation of the cholesteric liquid crystal is
controlled by applying bias voltage between the electrodes 12 and
22 and irradiating the photoconductive layer 40 with writing
light.
[0059] Next, each of the members employed in the display element
described above is described.
[0060] The support is made of an insulating material, for example,
glass, silicon or a polymer such as polyethylene terephthalate,
polysulfone, polyether sulfone and polycarbonate. The polymer can
be in the form of a film. At least a support on a display surface
side is made of a material which transmits incident light and
reflected light. A known functional film such as a stain preventing
film, an abrasion-resistant film, a reflection preventing film
and/or a gas barrier film may be formed on the surface of the
support, if necessary.
[0061] The electrode is made of an electrically conductive
material, for example, a metal such as gold or aluminum, a metal
oxide such as indium oxide or tin oxide, or a conductive organic
polymer such as polypyrrole, polyacethylene or polyaniline. At
least an electrode on the display surface side is made of a
material which transmits incident light and reflected light. A
known functional film such as an adhesion improving film, the
reflection preventing film and/or the gas barrier film may be
formed on the surface of the electrode, if necessary.
[0062] The display layer has a structure in which drops or
microcapsules of liquid crystal such as cholesteric (including
chiral nematic) liquid crystal are retained and dispersed in a
polymeric binder. The liquid crystal drops or the liquid crystal
microcapsules in the display layer preferably have a uniform
size.
[0063] The cholesteric liquid crystal can be a material in which a
chiral component such as a steroid cholesterol derivative or an
optically active material including Schiff base, an azo compound,
an ester compound, or a biphenyl compound is added to nematic
liquid crystal, smectic liquid crystal or mixed liquid crystal
thereof, such as Schiff base, an azo compound, an azoxy compound, a
benzoate compound, a biphenyl compound, a terphenyl compound, a
cyclohexyl carboxylate compound, a phenylcyclohexane compound, a
biphenylcyclohexane compound, a pyrimidine compound, a dioxane
compound, a cyclohexyl cyclohexane ester compound, a
cyclohexylethane compound, a cyclohexane compound, a tolane
compound, an alkenyl compound, a stilbene compound, or a condensed
polycyclic compound.
[0064] The polymeric binder is gelatin. The gelatin preferably has
a high gel strength and a low sol viscosity as described later.
Gelatin having high-molecular-weight .beta. chain or .gamma. chain
which is a multimer of .alpha. chain, and gelatin having a large
residue of .alpha. chain and including small amount of
low-molecular-weight components which are obtained by cleavage of
the main chain of .alpha. chain .alpha. are suitable for such
gelatin. Specifically, a gelatin material manufactured by
acid-treating cattle bone is suitable for the above gelatin and is
particularly preferable because of its high gel strength and its
low sol viscosity. A first extract is preferable, which is
initially extracted at the time that collagen serving as a raw
material is hydrolyzed. In order to prevent ion contamination of
liquid crystal materials, ion components remaining in gelatin may
be removed by using a known technique such as ion exchange
resin.
[0065] The bonding layer is made of the material to bring the
display layer into close contact with the light shielding layer due
to heat or pressure, such as a urethane resin, an epoxy resin, an
acrylic resin or a silicone resin. A position at which the bonding
layer is interposed is not limited to those in the above-described
embodiments. The bonding layer may be interposed between the
electrode and the display layer, or between the electrode and the
light shielding layer. The bonding layer disposed between the
electrode and the display layer is made of a material which
transmits at least incident light and reflected light.
[0066] The light shielding layer is made of an insulating material,
for example, an inorganic pigment such as a cadmium pigment, a
chromium pigment, a cobalt pigment, a manganese pigment, or a
carbon pigment, an organic dye or pigment such as an azo compound,
an anthraquinone compound, an indigo compound, a triphenylmethane
compound, a nitro compound, a phthalocyanine compound, a perylene
compound, a pyrrolopyrrole compound, a quinacridone compound, a
polycyclic quinone compound, a squarylium compound, an azulenium
compound, a cyanine compound, a pyrylium compound, or an anthrone
compound, or a material in which any of these is dispersed in a
polymeric binder. The light shielding layer absorbs at least
reflected light.
[0067] The photoconductive layer is made of an inorganic
photoconductor such as a-Si:H, a-Se, Te--Se, As.sub.2Se.sub.3, CdSe
or CdS, or an organic photoconductor in which a charge generating
material such as an azo pigment, a phthalocyanine pigment, a
perylene pigment, a quinacridone pigment, a pyrrolopyrrole pigment,
an indigo pigment, or an anthrone pigment is combined with a charge
transport material such as arylamine, hydrazone, triphenylmethane,
or PVK.
[0068] Next, a method of manufacturing the display layer of the
display element will be described. First, preparation of a coating
solution for the display layer will be described.
[0069] [Preparation of Coating Solution for Display Layer]
[0070] First, a method of preparing liquid crystal drops and liquid
crystal microcapsules will be described.
[0071] <Preparation of Liquid Crystal Drop Emulsion>
[0072] A liquid crystal drop emulsion is prepared by emulsifying
and dispersing a disperse phase including at least cholesteric
liquid crystal in a continuous phase that is incompatible with the
disperse phase, such as an aqueous phase, in a drop-like state. In
emulsification, a process in which the disperse phase is mixed with
the continuous phase and then is dispersed therein as minute
droplets by a mechanical shearing force of for example, a
homogenizer, or a film-emulsifying process in which the disperse
phase is allowed to pass through a porous film, extruded into the
continuous phase and dispersed as minute droplets can be conducted.
In particular, the film-emulsifying process is preferable since
particle size variation of emulsified droplets are smaller to form
liquid crystal drops having a uniform particle size. Trace of a
surfactant and/or a protective colloid for stabilizing
emulsification may be mixed with the continuous phase at the time
of emulsification.
[0073] <Preparation of Liquid Crystal Microcapsule
Slurry>
[0074] For preparation of liquid crystal microcapsules each having
a polymeric shell that encaupsulates cholesteric liquid crystal, a
known microencapsulating process such as a phase separation
process, an interfacial polymerization process, or an in-situ
polymerization process can be employed. Specifically, liquid
crystal drops manufactured above are dispersed in a solution
containing a polymeric shell material or thermoseting the polymeric
shell material to form a polymeric shell on the periphery of each
liquid crystal drop. When urethane/urea polymeric shells are
manufactured, it is preferable that liquid crystal drops including
a polyisocyanate compound are prepared and added to a solution
containing polyhydric alcohol and that urethane/urea forming
reaction is caused.
[0075] A material that is not dissolved in a liquid crystal
material to be encapsulated is employed for the polymeric shell.
Examples thereof include gelatin, a cellulose derivative,
gelatin-gum arabic, gelatin-Guerin's gum, gelatin-peptone,
gelatin-carboxymethyl cellulose, polystyrene, polyamide, nylon,
polyester, polyphenyl ester, polyurethane, polyurea,
melamine-formalin resin, phenol-formalin resin, urea-formalin
resin, acrylic resin, and methacrylic resin.
[0076] <Concentration>
[0077] Next, when the concentration of nonvolatile components
(non-evaporable components) in the cholesteric liquid crystal drop
emulsion or the cholesteric liquid crystal microcapsule slurry
manufactured above is lower than the necessary, the cholesteric
liquid crystal drop emulsion or cholesteeric liquid crystal
microcapsule slurry is concentrated to obtain a coating solution
for a display layer having a desired concentration of the
nonvolatile components. For concentration, a process in which the
emulsion or slurry is allowed to stand or centrifuged to cause
precipitation or sedimentation due to the difference between
specific gravity of the continuous phase and that of the
cholesteric liquid crystal drops or the cholesteric liquid crystal
microcapsules and to separate and remove the continuous phase, or a
process of filtering the emulsion or slurry with a membrane filter
can be conducted.
[0078] <Preparation of Coating Solution for Display
Layer>
[0079] A gelatin binder is added to the liquid crystal drop
emulsion or the liquid crystal microcapsule slurry thus obtained to
prepare a coating solution for a display layer.
[0080] In the invention, the liquid crystal drops or the liquid
crystal microcapsules are applied to a substrate to form a
monolayer in which they are dense. The content of each component in
the crystal drop emulsion or the liquid crystal microcapsule slurry
is measured with a densitometer or a gravimeter, and the mix ratio
of the gelatin binder, a solvent, and the liquid crystal drops or
the liquid crystal microcapsules in the coating solution for the
display layer is adjusted on the basis of the measured
contents.
[0081] Given that the ratio of volume of nonvolatile components to
volume of a coating solution for a display layer is denoted as Sr,
that the ratio of volume of liquid crystal drops or liquid crystal
microcapsules to volume of the nonvolatile components is denoted as
Lr, that the average particle diameter (.mu.m) of the liquid
crystal drops or the liquid crystal microcapsules is denoted as
D.sub.L and that a wet coating thickness (.mu.m) on the substrate
is denoted as t.sub.W, the ratio A.sub.L of an area covered by the
liquid crystal drops or the liquid crystal microcapsules to a
coated area is denoted as follows:
A.sub.L=(3/2)-(t.sub.W.multidot.Sr.multidot.Lr/D.sub.L) Formula
(1)
[0082] The coating solution for the display layer is preferably
adjusted so that A.sub.L satisfies the following range:
0.8<A.sub.L<1.0 Formula (2)
[0083] Sr means Y/X when the amount of nonvolatile components
remaining after the solvent has been vaporized from X cc of the
coating solution for the display layer is Y cc, while Lr means Z/Y
when Z cc of the liquid crystal drops or the liquid crystal
microcapsules are contained in Y cc of the nonvolatile
components.
[0084] The ratio Lr of volume of the liquid crystal drops or the
liquid crystal microcapsules to volume of the nonvolatile
components is preferably adjusted at 0.9 or less in order to
prevent the drops or microcapsules from being broken by
pressure.
[0085] The coating solution for the display layer is prepared by
adjusting the mix quantities of the gelatin binder and the solvent
with respect to the liquid crystal drop emulsion or the liquid
crystal microcapsule slurry on the basis of the calculated mix
ratio. The coating solution may contain trace of a known property
modifier, such as a thickening agent, a wettability improving agent
and/or a drying rate regulating agent.
[0086] The solvent to be employed in the invention dissolves
gelatin, but, in the case of liquid crystal drops, does not
dissolve liquid crystal, or, in the case of liquid crystal
microcapsules, does not dissolve at least the polymeric shells of
the microcapsules. Water or a mixture of water and alcohol such as
methanol, ethanol or glycol is properly used as the solvent to be
employed in the invention.
[0087] Next, a step of applying the coating solution for the
display layer and a step of drying the resultant coating will be
described.
[0088] <Application Step>
[0089] The coating solution for the display layer having an
adjusted concentration as described above is applied to a display
substrate with a known device which can form a layer made of the
coating solution and having a desired wet thickness, such as an
applicator, an edge coater, a screen coater, a roll coater, a
curtain coater, or a die coater. It is necessary to heat gelatin to
a temperature equal to or higher than the freezing point thereof so
as to make the gelatin sol, which is flowable. Therefore, the
temperature of the coating solution for the display layer is
preferably set at a value within the range of 40 to 60.degree.
C.
[0090] <Drying Step>
[0091] Next, a drying step is conducted in which the solvent is
evaporated from the coating layer formed on the display substrate
by the application step. In this step, the display layer needs to
be heated to a temperature equal to or higher than the freezing
point of gelatin, and the temperature of the coating layer is
preferably set at a temperature within the range of 40 to
60.degree. C. Examples of a heating apparatus include an oven, a
hot air blowing apparatus, and a hot plate.
[0092] When drying is conducted under this condition, the solvent
evaporates and relative positions of uniformly dispersed liquid
crystal drops or microcapsules gradually change to naturally form a
monolayer. If this change is insufficient and multilayers may be
formed, vibration such as mechanical vibration is effectively
applied to the coating layer by a supersonic wave vibrator in a
part or the total of the drying step. When the solvent has
completely evaporated, a polymer-dispersed display layer can be
obtained which has a flat surface with small surface
irregularities, and which is a monolayer in which the liquid
crystal drops or microcapsules are dense.
[0093] When the drying rate is too high, the liquid crystal drops
or microcapsules tend to have distorted shapes due to intense
liquid flow at dried end portions, and thus the direction of
orientation of liquid crystal tends to incline with respect to a
substrate surface. Here, for example, when cholesteric liquid
crystal is used, selectively reflected light has large dependence
on angle of visibility. Accordingly, rapid evaporation of the
solvent is preferably restrained by mildly drying the coating
layer. In order to restrain the rapid evaporation of the solvent,
it is preferable that a coating portion is retained in an
atmosphere in which vapor pressure thereof is the same as or close
to the saturation vapor pressure of the solvent. This is achieved
by using a process of retaining the coating portion in a vessel
having as small capacity as possible, a process of retaining the
coating portion in a chamber having a portion for generating steam
of the solvent, or a process of setting the saturation vapor
pressure of the solvent at a value equal to or lower than
atmospheric pressure.
[0094] A case in which a coating portion made of a coating solution
for a display layer including liquid crystal drops dispersed in a
solution including a gelatin binder and a solvent is retained in a
vessel with as small capacity as possible will be described while
referring to FIG. 4. FIG. 4A is a conceptual view showing an
application step. In FIG. 4A, the numerals 10, 39, 37, 32 and 60
represent a display substrate, a coating layer, a continuous phase,
liquid crystal drops and a coating device, respectively. The
gelatin binder and the solvent are included in the continuous phase
37. The liquid crystal drops 32 are dispersed in the coating layer.
FIG. 4B shows a drying step. As shown in FIG. 4B, the coating layer
is retained in a closed vessel 70. The atmosphere therein is such
that the vapor pressure of the solvent is close to the saturation
vapor pressure thereof due to initial evaporation of the solvent.
In this state, the solvent does not rapidly evaporate from the
coating layer, and thereby each of the liquid crystal drops does
not distort due to absence of intense liquid flow. As the solvent
evaporates, the thickness of the coating film decreases, which
causes the liquid crystal drops to gradually shift and form into a
monolayer. When the solvent has completely evaporated, a display
layer can be obtained which has a flat surface with small
irregularities, and in which the liquid crystal drops are arrayed
in the polymeric binder in a monolayer.
[0095] FIGS. 5A to 5C show change of arithmetic mean roughness Ra
on the display layer surface with respect to drying temperature.
FIG. 5A shows a graph of gelatin having a gel strength of 160 g and
a sol viscosity of 30 mp, and obtain by acid-treating pig skin, and
FIG. 5B shows a graph of gelatin having a gel strength of 285 g and
a sol viscosity of 46 mp, and obtained by alkali-treating cattle
bone and skin, and FIG. 5C shows a graph of gelatin having a gel
strength of 314 g and a sol viscosity of 32 mp, and obtained by
acid-treating cattle bone. In all of FIGS. 5A and 5C, the
arithmetic mean roughness decreases at drying temperatures equal to
or higher than the freezing point of the gelatin, at which sol-gel
change occurs, with a range (20 to 30.degree. C.) close to the
freezing point being a transition region. In addition, gelatin
having the relationship of FIG. 5A or FIG. 5C and a low sol
viscosity forms a more flat surface with smaller surface
irregularities than gelatin having the relationship of FIG. 5B and
a high sol viscosity. On the other hand, the mark "x" in FIG. 5
shows that liquid crystal droplets escape from the dried display
layer and appear on the surface of the dried display layer at
temperatures represented by the mark. This phenomenon easily occurs
when gelatin having the relationship of FIG. 5A and a low gel
strength is used.
[0096] It is found from above that a gelatin material to be
employed in the invention preferably has a high gel strength and a
low sol viscosity such as gelatin used in FIG. 5C.
[0097] The reason why the above-mentioned drying behavior, which is
a characteristic of the invention, occurs cannot strictly be
clarified. However, when the mix proportion of the coating solution
for the display layer is adjusted at a value out of the
predetermined range, that is, when the ratio A.sub.L of the area
covered by the liquid crystal drops to the coated area is made to
be not more than 0.8 or not less than 1.0, void portions including
no liquid crystal drop or multilayered portions in which liquid
crystal drops accumulate in the direction of thickness uniformly
occur in the overall display layer. From this fact, it is found
that the same flow accumulation principle as in JP-A No. 09-90321
does not work. The reason for this is as follows. In the flow
accumulation process, liquid crystal drops gather at dry end
portions to form a monolayer film. Accordingly, when the area
covered by the liquid crystal drops is not equal to the coated area
as described above, monolayer portions occur at the end portions of
a coated surface and void portions or multilayered portions occur
at the central portion of the coated surface.
[0098] Meanwhile, even when the specific gravity of a liquid
crystal material is substantially the same as that of a gelatin
aqueous solution in the invention, a flat display layer can be
obtained in which the liquid crystal drops or microcapsules are
densely arrayed in a monolayer. From this fact, it is found that
the reason why the liquid crystal drops are densely arrayed in a
monolayer in the drying step is not that the liquid crystal drops
naturally settle on a substrate surface or naturally precipitate on
a liquid surface due to the difference between the specific gravity
of the liquid crystal drops and that of a binder solution.
[0099] The reason why this phenomenon occurs in the invention is
thought as shown in FIG. 16. Given that the difference between the
specific gravity of a continuous phase and that of a dispersing
element is disregarded, flow behavior of the dispersing element in
a process where a coating solution containing the dispersing
element is dried depends on balance between flow resistance
resulting from the viscosity of the continuous phase and pushing
force toward the inside of the coating layer which force results
from surface tension of the coating solution.
[0100] Even when the concentration of gelatin which is in a sol
state is increased, the viscosity thereof less changes than a
general water-soluble polymer such as PVA. Therefore, the gelatin
keeps a low viscosity even at a high concentration. Accordingly,
even when the solvent in the coating layer is evaporated and the
concentration of gelatin in the coating layer rises, the flow
resistance of the coating layer does not easily increase and then
liquid crystal drops easily flow until the drying process is almost
finished.
[0101] When drying progresses and begins to shift from a stage in
which moisture movement in the surface or the portion of a coating
which portion is near the surface determines a drying rate to a
stage in which moisture movement in the portion disposed inside of
the coating determines a drying rate, the moisture content of the
coating layer surface has decreased and the concentration of
gelatin in the surface or the portion near the surface of the
coating has become higher than that of the inside. A
three-dimensional structure of the gelatin is gradually formed on
the surface with the increase of the gelatin concentration, so that
surface tension sharply increases.
[0102] That is, the process of drying gelatin used as a binder at a
temperature equal to or higher than the freezing point thereof
according to the invention can more rise the ratio of surface
tension to viscosity in the drying process than a process of drying
gelatin at a temperature equal to or lower than the freezing point
thereof, or a process in which other water-soluble polymer is used
as a binder. Consequently, the following is thought. The ratio of
pushing force to flow resistance is so large that the liquid
crystal drops are pressed toward the inside of the coating layer
while rearrayed. Therefore, a leveling effect of flattening the
coating surface acts greatly.
[0103] According to the above consideration, it is preferable to
employ gelatin having a gel strength, which affects surface
tension, as high as possible and a sol viscosity, which affects
flow resistance, as low as possible in order to obtain a greater
leveling effect.
EXAMPLES
[0104] The invention will be more specifically described
hereinafter by referring to examples but is not limited
thereto.
Example 1
[0105] Preparation of Coating Solution for Display Layer
[0106] 77.5 mass % of nematic liquid crystal (E7 (trade name)
manufactured by Merck & Co., Inc.), 18.8 mass % of a chiral
agent 1 (CB15 (trade name) manufactured by Merck & Co., Inc.)
and 3.7 mass % of a chiral agent 2 (R1011 (trade name) manufactured
by Merck & Co., Inc.) are mixed to prepare cholesteric liquid
crystal that selectively reflects light of green color.
[0107] The cholesteric liquid crystal is emulsified in a 0.25 mass
% aqueous solution of sodium dodecylbenzenesulfonate at a nitrogen
pressure of 0.12 kgf/cm.sup.2 with a membrane emulsification device
(MICRO KIT (trade name) manufactured by SPG TECHNOLOGY Co., Ltd.)
which includes a ceramic porous film having a pore side of 4.2
.mu.m. The state of dispersion of the resultant emulsion, which
includes cholesteric liquid crystal drops haing an average size of
14.9 .mu.m and a size standard deviation of 1.32 .mu.m, is close to
monodisperse.
[0108] Next, the emulsion is allowed to stand so as to cause the
cholesteric liquid crystal drops to settle. The resultant
supernatant is removed to obtain a condensed emulsion. The ratio of
volume of the cholesteric liquid crystal drops to that of the
condensed emulsion is measured with a densitometer (DMA35n (trade
name) manufactured by Nihon SiberHegner K.K.) and found to be
0.535.
[0109] The ratio A.sub.L of an area covered by the liquid crystal
drops to a coated area and a wet coating thickness are set at 0.95
and 90 .mu.m, respectively. The ratio (Sr.times.Lr) of volume of
the cholesteric liquid crystal drops to that of a coating solution
for a display layer is calculated from the above-mentioned formula
(1), the average size (14.9 .mu.m) of the cholesteric liquid
crystal drops and the wet coating thickness (90 .mu.m) on a display
substrate, and found to be 0.10 (10 vol %). On the basis of this
value, 4 parts by mass of a 7.7 mass % aqueous solution of
acid-treated bone gelatin having a gel strength of 314 g and a sol
viscosity of 32 mp and manufactured by Nippi, Incorporated is added
to one part by mass of the condensed emulsion so as to obtain a
coating solution for a display layer in which the ratio of volume
of nonvolatile components (non-evaporable components) to that of
the coating solution for the display layer is approximately 0.15
and in which the ratio of volume of the cholesteric liquid crystal
to that of the nonvolatile components is approximately 0.70.
[0110] Manufacture of Display Layer
[0111] <Application Step>
[0112] The coating solution for the display layer is heated to
50.degree. C. to make gelatin contained therein sol and the heated
coating solution is applied to a PET display substrate (Highbeam
(trade name) manufactured by Toray Industries, Inc.) having ITO
transparent electrodes sputtered and a thickness of 125 .mu.m with
an applicator which has a micrometer and in which the gap between
the applicator and the substrate surface is adjusted so that a wet
coating thickness of 90 .mu.m can be obtained. FIG. 6A shows the
transmission micrograph of the resultant coating. The cholesteric
liquid crystal drops are uniformly dispersed in the coating.
[0113] <Drying Step>
[0114] Subsequently, the display substrate to which the coating
solution for the display layer has been applied is put on a hot
plate kept at 50.degree. C. and the hot plate is covered with a
polyethylene case. In this state, the display substrate is retained
for 15 minutes. FIG. 6B shows the transmission micrograph of the
coating, which is being dried. The cholesteric liquid crystal drops
are gradually changed into a monolayer while the relative positions
thereof change little by little. When the coating film has been
completely dried by further evaporating the solvent contained in
the coating, the film has shrunk and the thickness thereof has
decreased and the cholesteric liquid crystal takes planar
orientation and provides selectively reflected light of green
color. As shown in the reflective micrograph of FIG. 6C, the dried
coating film has become a display layer in which the cholesteric
liquid crystal drops are densely arrayed in a monolayer.
[0115] FIGS. 7A and 8A show the image of the obtained display layer
which image is observed by a three-dimensional laser microscope
(VK8500 (trade name) manufactured by KEYENCE Corporation) and
measured values of surface profile thereof, respectively. It is
found that a flat surface having small irregularities can be
achieved.
[0116] Another PET substrate (Highbeam (trade name) manufactured by
Toray Industries, Inc.) having ITO transparent electrodes sputtered
and a thickness of 125 .mu.m is used as another display substrate.
A polyvinyl alcohol aqueous solution with dispersed carbon black
pigment particles is applied to the substrate by a spin coating
method to form a light shielding layer having a thickness of 2.0
.mu.m.
[0117] An urethane laminating agent (LX719/KY-90 (trade name)
manufactured by Dainippon Ink and Chemicals, Incorporated) is
applied to the light shielding layer by a spin coating method to
form a bonding layer having a thickness of 1 .mu.m.
[0118] The two display substrates thus manufactured are superposed
so that the display layer and the bonding layer face each other.
The resultant is made to pass through a laminator kept at
100.degree. C. to bond these display substrates. A display element
is thus obtained.
Comparative Example 1
[0119] A display substrate with a display layer is prepared in the
same manner as in Example 1, except that drying temperature is set
at 18.degree. C. which is not more than the freezing point of
gelatin.
[0120] FIGS. 7B and 8B show the image of the obtained display layer
which image is observed by a three-dimensional laser microscope
(VK8500 (trade name) manufactured by KEYENCE Corporation) and
measured values of surface profile thereof, respectively. It is
found that the resultant surface has larger irregularities and is
less smooth than in Example 1.
[0121] Another PET substrate (Highbeam (trade name) manufactured by
Toray Industries, Inc.) having ITO transparent electrodes sputtered
and a thickness of 125 .mu.m is used as another display substrate.
A polyvinyl alcohol aqueous solution with dispersed carbon black
pigment particles is applied to the substrate by a spin coating
method to form a light shielding layer having a thickness of 2.0
.mu.m.
[0122] An urethane laminating agent (LX719/KY-90 (trade name)
manufactured by Dainippon Ink and Chemicals, Incorporated) is
applied to the light shielding layer by a spin coating method to
form a bonding layer having a thickness of 1 .mu.m.
[0123] The two display substrates thus manufactured are superposed
so that the display layer and the bonding layer face each other.
The resultant is made to pass through a laminator kept at
100.degree. C. to bond these display substrates. A display element
is thus obtained.
Comparative Example 2
[0124] A mixed solution of one part by mass of the same cholesteric
liquid crystal as in Example 1, and 8 parts by mass of a 5.0 mass %
aqueous solution of partially saponified PVA having a
polymerization degree of 500 and manufactured by Wako Pure Chemical
Industries, Ltd. is emulsified at 10000 rpm with a homogenizer (GLH
type manufactured by Omni Co.) to obtain a coating solution for a
display layer in which the ratio of volume of nonvolatile
components to that of the coating solution for the display layer is
approximately 0.15 and in which the ratio of volume of the
cholesteric liquid crystal to that of the nonvolatile components is
approximately 0.70.
[0125] The obtained coating solution emulsion for the display
layer, which includes cholesteric liquid crystal drops having an
average size of 12.3 .mu.m and a size standard deviation of 5.6
.mu.m, is in a polydispersed state.
[0126] The coating solution for the display layer kept at room
temperature is applied to a PET substrate (trade name: Highbeam,
manufactured by Toray Industries, Inc.) having ITO transparent
electrodes sputtered and a thickness of 125 .mu.m with an
applicator which has a micrometer and in which the gap between the
applicator and the substrate surface is adjusted so that a wet
coating thickness of 100 .mu.m can be obtained.
[0127] Subsequently, this substrate is put on a hot plate kept at
60.degree. C. to evaporate moisture in the resultant coating film.
A display layer is thus obtained.
[0128] FIGS. 7C and 8C show the image of the obtained display layer
which image is observed by a three-dimensional laser microscope
(VK8500 (trade name) manufactured by KEYENCE Corporation) and
measured values of surface profile thereof, respectively. It is
found that the surface has larger irregularities and is less smooth
than in Example 1, though the irregularities are smaller than in
Comparative Example 1.
[0129] Another PET substrate (Highbeam (trade name) manufactured by
Toray Industries, Inc.) having ITO transparent electrodes sputtered
and a thickness of 125 .mu.m is used as another display substrate.
A polyvinyl alcohol aqueous solution with dispersed carbon black
pigment particles is applied to the substrate by a spin coating
method to form a light shielding layer having a thickness of 2.0
.mu.m.
[0130] An urethane laminating agent (LX719/KY-90 (trade name)
manufactured by Dainippon Ink and Chemicals, Incorporated) is
applied to the light shielding layer by a spin coating method to
form a bonding layer having a thickness of 1 .mu.m.
[0131] The two display substrates thus manufactured are superposed
so that the display layer and the bonding layer face each other.
The resultant is made to pass through a laminator kept at
100.degree. C. to bond these display substrates. A display element
is thus obtained.
Example 2
[0132] A cholesteric liquid crystal emulsion is prepared in the
same manner as in Example 1. A water-soluble melamine-formalin
resin (MX-035 (trade name) manufactured by Sanwa Chemical
Industries, Ltd.) is added thereto such that the amount of the
resin is one fifth of that of the cholesteric liquid crystal in
terms of part by mass. They are reacted at 65.degree. C. for 3
hours to obtain a slurry including microcapsules each of which has
a shell made of the melamine-formalin resin and encapsulating the
cholesteric liquid crystal. The average size of the microcapsules
is 15.2 .mu.m.
[0133] Next, the slurry is allowed to stand so as to the
microcapsules to settle. The resultant supernatant is removed to
obtain a condensed slurry. The ratio of volume of the microcapsules
to that of the condensed slurry is measured with a densitometer
(DMA35n (trade name) manufactured by Nihon SiberHegner K.K.) and
found to be 0.482.
[0134] The ratio A.sub.L of an area covered by the liquid crystal
micrcapsules to a coated area and a wet coating thickness are set
at 0.95 and 90 .mu.m, respectively. The ratio (Sr.times.Lr) of
volume of the cholesteric liquid crystal microcapsules to that of a
coating solution for a display layer is calculated from the
above-mentioned formula (1), the average size (15.2 .mu.m) of the
cholesteric liquid crystal microcapsules and the wet coating
thickness (90 .mu.m) on a display substrate, and found to be 0.10
(10 vol %). On the basis of this value, 3.5 parts by mass of a 7.9
mass % aqueous solution of acid-treated bone gelatin having a gel
strength of 314 g and a sol viscosity of 32 mp and manufactured by
Nippi, Incorporated is added to one part by mass of the condensed
slurry so as to obtain a coating solution for a display layer in
which the ratio of volume of nonvolatile components to that of the
coating solution for the display layer is approximately 0.15 and in
which the ratio of volume of the cholesteric liquid crystal
microcapsules to that of the nonvolatile components is
approximately 0.70.
[0135] The coating solution for the display layer is heated to
50.degree. C. to make gelatin contained therein sol and the heated
coating solution is applied to a PET display substrate (Highbeam
(trade name) manufactured by Toray Industries, Inc.) having ITO
transparent electrodes sputtered and a thickness of 125 .mu.m with
an applicator which has a micrometer and in which the gap between
the applicator and the substrate surface is adjusted so that a wet
coating thickness of 90 .mu.m can be obtained.
[0136] Subsequently, the display substrate to which the coating
solution for the display layer has been applied is retained in a
chamber kept at a high temperature of 50.degree. C. and a high
humidity of 85% RH for 20 minutes. As the coating film is dried,
the film shrinks and the thickness thereof decreases. When the
coating film has been completely dried, the cholesteric liquid
crystal takes planar orientation and the film provides selectively
reflected light of green color. A display layer in which the
cholesteric liquid crystal microcapsules are densely arrayed in a
monolayer is thus obtained.
[0137] Another PET substrate (Highbeam (trade name) manufactured by
Toray Industries, Inc.) having ITO transparent electrodes sputtered
and a thickness of 125 .mu.m is used as another display substrate.
A polyvinyl alcohol aqueous solution with dispersed carbon black
pigment particles is applied to the substrate by a spin coating
method to form a light shielding layer having a thickness of 2.0
.mu.m.
[0138] An urethane laminating agent (LX719/KY-90 (trade name)
manufactured by Dainippon Ink and Chemicals, Incorporated) is
applied to the light shielding layer by a spin coating method to
form a bonding layer having a thickness of 1 .mu.m.
[0139] The two display substrates thus manufactured are superposed
so that the display layer and the bonding layer face each other.
The resultant is made to pass through a laminator kept at
100.degree. C. to bond these display substrates. A display element
is thus obtained.
Example 3
[0140] An adduct (Takenate D110N (trade name) manufactured by
Takeda Chemical Industries, Ltd.) of xylene diisocyanate to
trimethylolpropane at a ratio of 3:1 and ethyl acetate are added to
the same cholesteric liquid crystal as in Example 1 so that the
amount of each of these components is one fifth of that of the
cholesteric liquid crystal in terms of part by mass. The resultant
is stirred to obtain a uniform solution serving as an oil
phase.
[0141] One part by mass of ethyl acetate is added to 10 parts by
mass of a 1.0 mass % aqueous solution of partially saponified PVA
having a polymerization degree of 500 and manufactured by Wako Pure
Chemical Industries, Ltd., and the resultant is stirred at
70.degree. C. and then cooled down to room temperature. Another
uniform solution serving as an aqueous phase is obtained by
removing a part of ethyl acetate which part has not been
dissolved.
[0142] The oil phase is emulsified in the aqueous phase at a
nitrogen pressure of 0.10 kgf/cm.sup.2 with a membrane
emulsification device (MICRO KIT (trade name) manufactured by SPG
TECHNOLOGY Co., Ltd.) which includes a ceramic porous film having a
pore diameter of 4.2 .mu.m.
[0143] The state of dispersion of the resultant emulsion, which
includes oil phase droplets having an average size of 15.7 .mu.m
and a size standard deviation of 1.81 .mu.m, is close to
monodisperse.
[0144] Next, one gram of a 10 mass % aqueous solution of
1,4-butanediol is dripped into the emulsion and the resultant is
stirred at 70.degree. C. for 90 minutes to cause polymerization
reaction. A slurry including liquid crystal microcapsules each of
which has a shell made of the resultant urethane urea resin and
encapsulating the cholesteric liquid crystal. The average size of
the liquid crystal microcapsules is 14.3 .mu.m.
[0145] The liquid crystal microcapsule slurry is diluted with a
large quantity of water. The resultant is stirred and then
centrifuged with a centrifugal separator so as to settle the liquid
crystal microcapsules. The resultant supernatant is removed to
obtain a condensed slurry including the liquid crystal
microcapsules. This process is repeated twice to remove a part of
polyvinyl alcohol and ethyl acetate. A liquid crystal microcapsule
slurry is thus obtained. The ratio of volume of the liquid crystal
microcapsules to that of the slurry is measured with a densitometer
(DMA35n (trade name) manufactured by Nihon SiberHegner K.K.) and
found to be 0.505.
[0146] The ratio A.sub.L of an area covered by the liquid crystal
micrcapsules to a coated area and a wet coating thickness are set
at 0.95 and 90 .mu.m, respectively. The ratio (Sr.times.Lr) of
volume of the cholesteric liquid crystal microcapsules to that of a
coating solution for a display layer is calculated from the
above-mentioned formula (1), the average size (14.3 .mu.m) of the
cholesteric liquid crystal microcapsules and the wet coating
thickness (90 .mu.m) on a display substrate, and found to be 0.10
(10 vol %). On the basis of this value, 3.7 parts by mass of a 7.8
mass % aqueous solution of acid-treated bone gelatin having a gel
strength of 314 g and a sol viscosity of 32 mp and manufactured by
Nippi, Incorporated is added to one part by mass of the slurry so
as to obtain a coating solution for a display layer in which the
ratio of volume of nonvolatile components to that of the coating
solution for the display layer is approximately 0.15 and in which
the ratio of volume of the cholesteric liquid crystal microcapsules
to that of the nonvolatile components is approximately 0.70.
[0147] The coating solution for the display layer is heated to
50.degree. C. to make gelatin contained therein sol and the heated
coating solution is applied to a PET display substrate (Highbeam
(trade name) manufactured by Toray Industries, Inc.) having ITO
transparent electrodes sputtered and a thickness of 125 .mu.m with
an applicator which has a micrometer and in which the gap between
the applicator and the substrate surface is adjusted so that a wet
coating thickness of 90 .mu.m can be obtained.
[0148] Subsequently, dimethyl silicone oil (KF96 (trade name)
manufactured by Shin-Etsu Chemical Co., Ltd.) is applied to a
supersonic wave vibrating plate (UI304 (trade name) manufactured by
Sharp Corporation) and the substrate to which the coating solution
for the display layer has been applied is put on the supersonic
wave vibrating plate. The supersonic wave vibrating plate is
covered with a polyethylene case. The supersonic wave vibrating
plate is retained in an oven kept at 50.degree. C. for 15 minutes
while supersonic wave is being applied to the substrate. As the
coating film is dried, the film shrinks and the thickness thereof
decreases. When the coating film has been completely dried, the
cholesteric liquid crystal takes planar orientation and the film
provides selectively reflected light of green color. A display
layer in which the cholesteric liquid crystal microcapsules are
densely arrayed in a monolayer is thus obtained.
[0149] A glass substrate manufactured by EHC Corporation and having
ITO transparent electrodes sputtered and a thickness of 1.1 .mu.m
is used as another display substrate. A solution including as a
solvent butanol and also including polyvinyl butyral in which a
titanyl phthalocyanine pigment having a high sensitivity with
respect to visible light having wavelengths of 600 nm or more is
dispersed is applied to the substrate by a spin coating method to
form a layer having a thickness of 200 nm. Thereafter, a solution
including as a solvent monochlorobenzene and also includeing
bisphenol Z polycarbonate in which N,N'-bis(3-methylphenyl)-1,-
1'-biphenyl-4,4'-diamine is dispersed is applied to the layer by a
spin coating method to form another layer having a thickness of 3
.mu.m. Furthermore, a solution including as a solvent butanol and
also including polyvinyl butyral in which a titanyl phthalocyanine
pigment having a high sensitivity with respect to visible light
having wavelengths of 600 nm or more is dispersed is applied to the
resultant layer by a spin coating method to form still another
layer having a thickness of 200 nm. A photoconductive layer is thus
formed.
[0150] A polyvinyl alcohol aqueous solution with dispersed carbon
black pigment particles is applied to the photoconductive layer by
a spin coating method to form a light shielding layer having a
thickness of 2.0 .mu.m. Moreover, an urethane laminating agent
(LX719/KY-90 (trade name) manufactured by Dainippon Ink and
Chemicals, Incorporated) is applied to the light shielding layer by
a spin coating method to form a bonding layer having a thickness of
1 .mu.m.
[0151] The two display substrates thus manufactured are superposed
so that the display layer and the bonding layer face each other.
The resultant is made to pass through a laminator kept at
100.degree. C. to bond these display substrates. A display element
is thus obtained.
[0152] Measurement of Display Properties
[0153] The display properties of the display elements of Example 1,
and Comparative Examples 1 and 2 which are in a planar state or a
focal conic state are measured with an integrating sphere type
spectrocolorimeter (CM2022 (trade name) manufactured by KONICA
MINOLTA HOLDINGS, INC.). FIG. 9 shows the measured results of
reflection spectra, and Table 1 shows reflectance (Rpeak) and color
purity (C*) at a peak wavelength in a planar state, and luminous
reflectance Y value (Ymin) in a focal conic state, which are
obtained from the reflection spectra.
[0154] As is clear from Table 1, the display element of the
invention has high reflectance and high chroma in a bright state
due to planar, and low reflectance in a dark state due to focal
conic. On the contrary, the display elements of Comparative
Examples 1 and 2 have low reflectance in a planar state, and high
reflectance in a focal conic state.
1 TABLE 1 Bright Reflectance Color Purity Black Reflectance Rpeak
C* Ymin Example 1 26.3% 39.1 1.81 Comparative 22.9% 29.9 4.42
Example 1 Comparative 25.3% 19.8 2.83 Example 2
* * * * *