U.S. patent application number 09/072402 was filed with the patent office on 2001-11-29 for liquid crystal device with composite layer of cured resin pillars and liquid crystal phase and method of producing the same.
Invention is credited to HATANO, TAKUJI, OKADA, MASAKAZU.
Application Number | 20010046009 09/072402 |
Document ID | / |
Family ID | 14774966 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010046009 |
Kind Code |
A1 |
HATANO, TAKUJI ; et
al. |
November 29, 2001 |
LIQUID CRYSTAL DEVICE WITH COMPOSITE LAYER OF CURED RESIN PILLARS
AND LIQUID CRYSTAL PHASE AND METHOD OF PRODUCING THE SAME
Abstract
(1) A liquid crystal device comprises a pair of substrates; and
a composite layer disposed between the pair of substrates, the
composite layer including a resin phase and a liquid crystal phase
of a liquid crystal material exhibiting cholesteric characteristic,
the composite layer having an area defining one pixel, and the area
including a plurality of regions being different from each other in
condition of the resin phase. (2) A method of producing a liquid
crystal device comprises the steps of defining an area
corresponding to one pixel; and forming a plurality of regions of
composite layer in the area, the composite layer including a resin
phase and a liquid crystal phase of a liquid crystal material
exhibiting cholesteric characteristic, and each of the regions
being different from the others in condition of the resin phase.
The step of forming the regions may include the steps of supplying
a composition of the liquid crystal material and the resin material
into a space between the paired substrates; and separating the
liquid crystal material in a region corresponding to each of the
regions from the resin under a condition different from the others.
If the resin material is a photo-curing resin material, the
separating step may include the steps of masking the composition
with a mask having a plurality of regions, each of which has a
plurality of openings and is different from the others in condition
of the openings; and exposing the composition to light through the
mask.
Inventors: |
HATANO, TAKUJI; (OSAKA,
JP) ; OKADA, MASAKAZU; (KYOTO-SHI, JP) |
Correspondence
Address: |
SIDLEY AUSTIN BROWN & WOOD
717 NORTH HARWOOD
SUITE 3400
DALLAS
TX
75201
US
|
Family ID: |
14774966 |
Appl. No.: |
09/072402 |
Filed: |
May 4, 1998 |
Current U.S.
Class: |
349/86 |
Current CPC
Class: |
G02F 1/13718 20130101;
G02F 2203/30 20130101; G02F 1/13394 20130101; G02F 1/133377
20130101 |
Class at
Publication: |
349/86 |
International
Class: |
G02F 001/1333 |
Foreign Application Data
Date |
Code |
Application Number |
May 9, 1997 |
JP |
9-119981 |
Claims
What is claimed is:
1. A liquid crystal device comprising: a pair of substrates; and a
composite layer disposed between said pair of substrates, said
composite layer including a resin phase and a liquid crystal phase
of a liquid crystal material exhibiting cholesteric characteristic,
said composite layer having an area defining one pixel, and said
area including a plurality of regions being different from each
other in condition of said resin phase.
2. The liquid crystal device according to claim 1, wherein an
intensity of said resin phase in each of said regions is different
from those in the other regions.
3. The liquid crystal device according to claim 1, wherein a
configuration of said resin phase in each of said regions is
different from those in the other regions.
4. The liquid crystal device according to claim 1, wherein said
composite layer includes a plurality of resin pillars as said resin
phase.
5. The liquid crystal device according to claim 4, wherein an
intensity of said resin pillars in each of said regions is
different from those in the other regions.
6. The liquid crystal device according to claim 4, wherein a pitch
of said resin pillars in each of said regions is different from
those in the other regions.
7. The liquid crystal device according to claim 4, wherein a
density of said resin pillars in each of said regions is different
from those in the other regions.
8. The liquid crystal device according to claim 4, wherein a
configuration of said resin pillar in each of said regions is
different from those in the other regions.
9. The liquid crystal device according to claim 1, wherein said
liquid crystal material includes a nematic liquid crystal material
and a chiral ingredient.
10. The liquid crystal device according to claim 1, wherein said
liquid crystal material exhibiting cholesteric characteristic has a
selective reflection wavelength in a visible range.
11. The liquid crystal device according to claim 1, wherein said
liquid crystal material in all the regions in said area
corresponding to one pixel can be set to a focal conic state.
12. The liquid crystal device according to claim 1, wherein each of
said substrates has an electrode, and said area is sandwiched
between said electrodes.
13. A method of producing a liquid crystal device comprising the
steps of: defining an area corresponding to one pixel; and forming
a plurality of regions of composite layer in said area, said
composite layer including a resin phase and a liquid crystal phase
of a liquid crystal material exhibiting cholesteric characteristic,
and each of said regions being different from the others in
condition of said resin phase.
14. The method of producing the liquid crystal device according to
claim 13, wherein an intensity of said resin phase in each of said
regions is different from those in the other regions.
15. The method of producing the liquid crystal device according to
claim 13, wherein a configuration of said resin phase in each of
said regions is different from those in the other regions.
16. The method of producing the liquid crystal device according to
claim 13, wherein said composite layer includes a plurality of
resin pillars as said resin phase.
17. The method of producing the liquid crystal device according to
claim 16, wherein an intensity of said resin pillars in each of
said regions is different from those in the other regions.
18. The method of producing the liquid crystal device according to
claim 16, wherein a pitch of said resin pillars in each of said
regions is different from those in the other regions.
19. The method of producing the liquid crystal device according to
claim 16, wherein a density of said resin pillars in each of said
regions is different from those in the other regions.
20. The method of producing the liquid crystal device according to
claim 16, wherein a configuration of said resin pillar in each of
said regions is different from those in the other regions.
21. The method of producing the liquid crystal device according to
claim 13, wherein said liquid crystal material exhibiting
cholesteric characteristic includes a nematic liquid crystal
material and a chiral ingredient.
22. The method of producing the liquid crystal device according to
claim 13, wherein said liquid crystal material exhibiting
cholesteric characteristic has a selective reflection wavelength in
a visible range.
23. The method of producing the liquid crystal device according to
claim 13, wherein said area is defined between a pair of
substrates; and said step of forming said regions includes the
steps of: providing a composition of the liquid crystal material
and a resin material between the pair of substrates, and separating
the liquid crystal material in a region corresponding to each of
said regions from the resin under a condition different from those
in the other regions.
24. The method of producing the liquid crystal device according to
claim 23, wherein said resin material is a photo-curing resin
material; and said separating step comprises the steps of: masking
said composition with a mask having a plurality of regions each
having a plurality of openings and being different from the others
in condition of said openings; and exposing said composition to
light through said mask.
25. The method of producing the liquid crystal device according to
claim 24, wherein said openings in said mask can provide said
composite layer including a plurality of resin pillars as the resin
phase.
26. The method of producing the liquid crystal device according to
claim 25, wherein a pitch of said openings in each of said regions
in said mask is different from those in the other regions.
27. The method of producing the liquid crystal device according to
claim 25, wherein a density of said openings in each of said
regions in said mask is different from those in the other
regions.
28. The method of producing the liquid crystal device according to
claim 25, wherein a configuration of said opening in each of said
regions in said mask is different from those in the other
regions.
29. The method of producing the liquid crystal device according to
claim 24, wherein said photo-curing resin material is monomers
and/or oligomers of monofunctional or multifunctional acrylate or
methacrylate.
30. The method of producing the liquid crystal device according to
claim 13, wherein said area is defined between a first substrate
and a provisional substrate; and said step of forming the regions
includes the steps of: (1) supplying the resin material to a space
between said first substrate and said provisional substrate; (2)
curing said resin material in a region corresponding to each of
said regions under a condition different from those in the other
regions; (3) removing said provisional substrate; (4) removing an
uncured resin material; (5) supplying the liquid crystal material
into a space formed by said cured resin; and (6) arranging a second
substrate at a position previously occupied by said provisional
substrate and holding said resin and said liquid crystal material
between said first and second substrates.
31. The method of producing the liquid crystal device according to
claim 30, wherein said resin material is a photo-curing resin
material; and said step (2) comprises the steps of: masking said
resin material with a mask having a plurality of regions each
having a plurality of openings and being different from the others
in condition of said openings, and exposing said resin material to
light through said mask.
32. The method of producing the liquid crystal device according to
claim 31, wherein said openings in said mask can provide said
composite layer including a plurality of resin pillars as the resin
phase.
33. The method of producing the liquid crystal device according to
claim 32, wherein a pitch of said openings in each of said regions
in said mask is different from those in the other regions.
34. The method of producing the liquid crystal device according to
claim 32, wherein a density of said openings in each of said
regions in said mask is different from those in the other
regions.
35. The method of producing the liquid crystal device according to
claim 32, wherein a configuration of said opening in each of said
regions in said mask is different from those in the other
regions.
36. The method of producing the liquid crystal device according to
claim 31, wherein said photo-curing resin material is monomers
and/or oligomers of monofunctional or multifunctional acrylate or
methacrylate.
37. The method of producing the liquid crystal device according to
claim 13, wherein said area is defined between a first substrate
and a provisional substrate; said step of forming the regions
includes the steps of: (1) supplying the resin material to a space
between said first substrate and said provisional substrate, (2)
curing the resin material in a region corresponding to each of said
regions under a condition different from those in the other
regions, (3) removing said provisional substrate, (4) removing an
uncured resin material, (5) arranging a second substrate at a
position previously occupied by said provisional substrate and
holding the resin between the first and second substrates, and (6)
supplying said liquid crystal material into a space between said
first and second substrates; and said liquid crystal phase is set
to be continuously present in said composite layer.
38. The method of producing the liquid crystal device according to
claim 37, wherein said resin material is a photo-curing resin
material; and said step (2) comprises the steps of: masking said
resin material with a mask having a plurality of regions each
having a plurality of openings and being different from the others
in condition of said openings, and exposing said resin material to
light through said mask.
39. The method of producing the liquid crystal device according to
claim 38, wherein said openings in said mask can provide said
composite layer including a plurality of resin pillars as the resin
phase.
40. The method of producing the liquid crystal device according to
claim 39, wherein a pitch of said openings in each of said regions
in said mask is different from those in the other regions.
41. The method of producing the liquid crystal device according to
claim 39, wherein a density of said openings in each of said
regions in said mask is different from those in the other
regions.
42. The method of producing the liquid crystal device according to
claim 39, wherein a configuration of said opening in each of said
regions in said mask is different from those in the other
regions.
43. The method of producing the liquid crystal device according to
claim 38, wherein said photo-curing resin material is monomers
and/or oligomers of monofunctional or multifunctional acrylate or
methacrylate.
44. The method of producing the liquid crystal device according to
claim 13, wherein said area is defined between a pair of
substrates; said step of forming the regions includes the steps of;
(1) supplying the resin material into a space between said paired
substrates, (2) curing the resin material in a region corresponding
to each of said regions under a condition different from those in
the other regions, (3) removing an uncured resin material, and (4)
supplying said liquid crystal material into a space between said
paired substrates; and said liquid crystal phase is set to be
continuously present in said composite layer.
45. The method of producing the liquid crystal device according to
claim 44, wherein said resin material is a photo-curing resin
material; and said step (2) comprises the steps of: masking said
resin material with a mask having a plurality of regions each
having a plurality of openings and being different from the others
in condition of said openings, and exposing said resin material to
light through said mask.
46. The method of producing the liquid crystal device according to
claim 45, wherein said openings in said mask can provide said
composite layer including a plurality of resin pillars as the resin
phase.
47. The method of producing the liquid crystal device according to
claim 46, wherein a pitch of said openings in each of said regions
in said mask is different from those in the other regions.
48. The method of producing the liquid crystal device according to
claim 46, wherein a density of said openings in each of said
regions in said mask is different from those in the other
regions.
49. The method of producing the liquid crystal device according to
claim 46, wherein a configuration of said opening in each of said
regions in said mask is different from those in the other
regions.
50. The method of producing the liquid crystal device according to
claim 45, wherein said photo-curing resin material is monomers
and/or oligomers of monofunctional or multifunctional acrylate or
methacrylate.
51. The method of producing the liquid crystal device according to
claim 13, wherein said area is defined on a first substrate; and
said step of forming said regions comprises the steps of: (1)
providing a mask having a plurality of regions each having a
plurality of openings and being different from the others in
condition of said openings, and (2) applying the resin onto the
first substrate in accordance with the openings of said mask.
52. The method of producing the liquid crystal device according to
claim 51, wherein said step of forming said regions further
includes the steps of: (1) supplying the liquid crystal material
into a space formed by said resin; and (2) holding said resin and
said liquid crystal material between said first substrate and a
second substrate.
53. The method of producing the liquid crystal device according to
claim 51, wherein said step of forming said regions further
includes the steps of: (1) holding the resin between said first
substrate and a second substrate, and (2) supplying the liquid
crystal material into a space between said first and second
substrates; and said liquid crystal phase is set to be continuously
present in said composite layer.
54. The method of producing the liquid crystal device according to
claim 51, wherein said resin is thermoplastic resin.
55. The method of producing the liquid crystal device according to
claim 51, wherein said resin is thermosetting resin.
Description
[0001] This application is based on application No. 9-119981
(119981/1997) Pat. filed in Japan, the contents of which is hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a liquid crystal device
having a composite layer, which includes a liquid crystal phase of
a liquid crystal material exhibiting a cholesteric characteristic
and a resin phase, and a method of producing the same.
[0004] 2. Description of the Background Art
[0005] Various kinds of liquid crystal display devices having a
memory effect have already been proposed.
[0006] U.S. Pat. No. 3,578,844 has disclosed a liquid crystal
device, in which cholesteric liquid crystal material capsuled with
a polymer such as gelatin or gum arabi is held between a pair of
substrates. This liquid crystal device has a memory effect, and
performs a predetermined display when supplied with a voltage, as
disclosed therein. The state of the display is stably maintained
even after the cease of application of the voltage. This liquid
crystal device performs the display by utilizing a difference in
quantities of reflected light, which is caused by changing, in
accordance with the voltage application, the orientation state of
cholesteric liquid crystal material having a selective reflection
wavelength in a visible range.
[0007] The liquid crystal device, which has the composite layer
including the polymer material and the cholesteric liquid crystal
material, can perform a high resolution display by simple matrix
driving without requiring a memory element such as TFT, MIM.
However, it has an insufficient self-holding property or
form-keeping property, and therefore is liable to change its
display state when a pressure is externally applied thereto. Also,
it cannot achieve a sufficient contrast.
[0008] A reflective liquid crystal device utilizing selective
reflection of the cholesteric liquid crystal material changes the
display state in accordance with a planar orientation in which
helical axes of liquid crystal molecules are perpendicular to the
substrate and a focal conic orientation in which the helical axes
are irregularly directed or are substantially parallel to the
substrate. If the helical axes of liquid crystal molecules are
oriented excessively uniformly in the planar orientation, the
displayed appearance is significantly affected by a viewing angle.
For example, even if the device is transparent in appearance when
viewed perpendicularly to the substrate, it exhibits an opaque
appearance as the viewing direction shifts from the direction
vertical to the substrate.
[0009] Further, in the cholesteric liquid crystal material which
selectively reflects the light in the visible range, a color tone
can be adjusted by controlling the helical pitch length. However,
control of the brightness is difficult, and display in half
brightness and multi-tone of brightness is difficult.
[0010] Regarding the dependency on the viewing angle, U.S. Pat. No.
5,437,811 has disclosed that the dependency on the viewing angle is
improved in a liquid crystal device in which a chiral nematic
liquid crystal material containing resin added thereto at a rate of
10% by weight or less with respect to the whole weight and
exhibiting a cholesteric characteristic is held between a pair of
substrates. In this liquid crystal device, addition of a small
amount of resin causes a mutual action between the resin and the
liquid crystal material at a region near the resin, and thereby the
liquid crystal near the resin exhibits a less responsibility with
respect to an applied electric field, compared with the liquid
crystal material remote from the resin so that the dependency on
the viewing angle is improved.
[0011] According to the above method in which a small amount of
resin is added to the liquid crystal material, however, a
self-holding property cannot be achieved sufficiently because the
amount of the added resin is small. Therefore, a state of display
is liable to change due to a pressure applied to the substrate
surface. Although this problem can be avoided by increasing an
amount of the added resin, this causes other problems such as
rising of a required drive voltage and lowering of a contrast.
[0012] Meanwhile, U.S. Pat. No. 5,473,450 has disclosed a liquid
crystal device having a composite film or layer which includes
resin partitions formed between pixels or picture elements as well
as liquid crystal regions formed between the partitions. This
partition structure is formed in such a manner that a solution of
liquid crystal material and resin is radiated with ultraviolet rays
through a photomask so that a portion radiated with ultraviolet
rays is cured to form a resin wall which corresponds to the
photomask and forms the above partition structure.
[0013] The liquid crystal device having the above partition
structure of resin can suppress flow of the liquid crystal
material, and therefore has a high self-holding property. Further,
the forms of the liquid crystal regions can be uniform and can be
positioned accurately. Therefore, drive voltages for the respective
liquid crystal regions can be uniform so that it is possible to
reduce the drive voltage required for simultaneously operating all
the liquid crystal regions. Since each liquid crystal region has a
relatively large size defined by the partition, the device can
provide a better contrast than a liquid crystal device in which
fine liquid crystal regions are arranged in resin portions. Such an
advantage can also be achieved that sealing is not required at the
periphery of the substrate.
[0014] However, these do not overcome the problem that the half
tone display and therefore multi-tone display is difficult because
the cholesteric liquid crystal material exhibits a bistability.
[0015] The resin partitions may be formed by a polymerization phase
separating method. However, this method may suffer from such a
problem that an uncured raw material of resin remains in the liquid
crystal material so that the remaining ingredient lowers the phase
transition temperature (clearing point) of the liquid crystal
material, and/or shifts the selective reflection wavelength of the
liquid crystal material. According to this method, the liquid
crystal material is liable to be taken into the resin wall or
partition, which may lower the strength, the durability and the
adhesivity to the substrate of the resin. Further, the range from
which resin material can be selected is restricted to a certain
extent.
SUMMARY OF THE INVENTION
[0016] An object of the invention is to provide a liquid crystal
device which can easily perform a multi-tone display using a liquid
crystal material which exhibits cholesteric characteristic as well
as a method of producing the same.
[0017] It is also an object of the invention to provide a method of
producing a liquid crystal device having a pair of substrates and a
composite layer, which is held between the substrates and includes
a resin phase and a liquid crystal phase of a liquid crystal
material exhibiting cholesteric characteristic, and particularly a
method capable of producing a liquid crystal device which is not
influenced by an uncured resin material and has a resin phase not
containing liquid crystal material, and capable of selecting a
resin material from a wide range.
[0018] According to an aspect of the invention, there is provided a
liquid crystal device comprising a pair of substrates; and a
composite layer disposed between said pair of substrates, said
composite layer including a resin phase and a liquid crystal phase
of a liquid crystal material exhibiting cholesteric characteristic,
said composite layer having an (at least one) area defining one
pixel, said area including a plurality of regions being different
from each other in condition of said resin phase.
[0019] According to another aspect of the invention, there is
provided a method of producing a liquid crystal device comprising
the steps of defining an (at least one) area corresponding to one
pixel; and forming a plurality of regions of composite layer in
said area, said composite layer including a resin phase and a
liquid crystal phase of a liquid crystal material exhibiting
cholesteric characteristic, and each of said regions being
different from the others in condition of said resin phase.
[0020] The step of forming the regions may include the steps of
supplying a composition of the liquid crystal material and the
resin material to a space between the paired substrates, and
separating the liquid crystal material in a region corresponding to
each of said regions from the resin under a condition different
from those in the other regions. In this case, said area is defined
between the paired substrates.
[0021] The step of forming the regions may include the steps of
supplying the resin material to a space between a first substrate
and a provisional substrate; curing the resin material in a region
corresponding to each of said regions under a condition different
from those in the other regions; removing the provisional
substrate; removing an uncured resin material; supplying the liquid
crystal material into a space formed by the cured resin; and
arranging a second substrate at a position previously occupied by
the provisional substrate and holding the resin and the liquid
crystal material between the first and second substrates. In this
case, said area is defined between the first substrate and the
provisional substrate.
[0022] The step of forming the regions may include the steps of
supplying the resin material to a space between a first substrate
and a provisional substrate; curing the resin material in a region
corresponding to each of said regions under a condition different
from those in the other regions; removing the provisional
substrate; removing an uncured resin material; arranging a second
substrate at a position previously occupied by the provisional
substrate and holding the resin between the first and second
substrates; and supplying the liquid crystal material into a space
between the first and second substrates. In this case, said area is
defined between the first substrate and the provisional substrate.
The liquid crystal phase is set to be continuously present in the
composite layer.
[0023] In the structure wherein the liquid crystal phase is
continuously present in the composite layer, the step of forming
the regions may include the steps of supplying the resin material
into a space between the paired substrates, curing the resin
material in a region corresponding to each of said regions under a
condition different from those in the other regions; removing an
uncured resin material; and supplying the liquid crystal material
into a space between the paired substrates. In this case, said area
is defined between the paired substrates. The liquid crystal phase
is set to be continuously present in the composite layer.
[0024] The step of forming said regions may include the steps of
providing a mask having a plurality of regions each having a
plurality of openings and being different from the others in
condition of said openings; and applying a resin onto a first
substrate in accordance with the openings of said mask. In this
case, said area is defined on the first substrate. The step of
forming said regions may further include the steps of supplying the
liquid crystal material into a space formed by the resin; and
holding the resin and the liquid crystal material between the first
substrate and a second substrate. Alternatively, if the liquid
crystal phase is set to be continuously present in the composite
layer, the step of forming said regions may further include the
steps of sandwiching the resin between the first substrate and a
second substrate; and supplying the liquid crystal material into a
space between the first and second substrates.
[0025] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description when taken in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1(A) is a cross section showing an example of a liquid
crystal device of an embodiment of the invention and more
specifically showing a portion corresponding to one pixel, and FIG.
1(B) is a cross section of the liquid crystal device taken along
line X-X' in FIG. 1(A);
[0027] FIG. 2(A) is a graph schematically showing a relationship
between a magnitude of a pulse voltage applied to a composite layer
of the liquid crystal device shown in FIGS. 1(A) and 1(B) and
reflectances of regions A1-A4, and FIG. 2(B) is a graph
schematically showing a relationship between the magnitude of the
pulse voltage and the reflectance of the whole pixel including the
regions A1-A4;
[0028] FIG. 3 shows a photomask used for producing the liquid
crystal device of a specific embodiment of the invention;
[0029] FIG. 4 shows a relationship between voltages applied on
various regions and the luminous reflectances of the regions in the
liquid crystal device produced with the photomask shown in FIG.
3;
[0030] FIG. 5 shows a relationship between voltages applied on
various regions and the luminous reflectances of the regions in a
liquid crystal device of another specific embodiment of the
invention;
[0031] FIGS. 6(A), 6(B) and 6(C) show manners of producing the
liquid crystal device of the embodiment of the invention including
a step of preparing, in advance, a resin phase;
[0032] FIG. 7 shows a structure of a resin phase of still another
specific embodiment of the invention in which ultraviolet-light
irradiation for curing the resin is performed for an increased
time;
[0033] FIG. 8(A) shows another example of a pattern of openings in
a photomask, and FIG. 8(B) shows a structure of a resin phase
formed with the photomask having the opening pattern shown in FIG.
8(A); and
[0034] FIG. 9 shows a pattern of a mask used in yet another
specific embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] A liquid crystal device of an embodiment of the invention
includes a pair of substrates, and a composite layer disposed
between the paired substrates. The composite layer includes a resin
phase and a liquid crystal phase of a liquid crystal material
exhibiting a cholesteric characteristic or phase. The composite
layer has an (at least one) area defining one pixel and including a
plurality of regions being different from each other in condition
or state of the resin phase.
[0036] The resin phase may be a resin wall. The resin wall may take
the form of, e.g., pillars, a network, a wall providing a
continuous liquid crystal region, a partition dispersing the liquid
crystal material to a plurality of regions in one pixel. The resin
wall usually extends between the paired substrates. The resin wall
in the partition form may be formed in a non-display region between
the pixels, and the resin wall in any one of the foregoing forms
may be formed within one pixel. In any case, the resin wall has
such a form that the composite layer can have a sufficient
self-holding property, and an external pressure can hardly change
the state of display even if the substrate holding the composite
layer is made of a flexible material.
[0037] In particular, the resin wall preferably takes the form of
pillars or columns. This is because the pillar form can increase
the area of contact with the liquid crystal material and therefore
can promote a mutual reaction with the liquid crystal material so
that the memory effect of the liquid crystal material exhibiting
the cholesteric characteristic is stabilized. As will be described
later, the pillar form offers such an advantage that a difference
between drive voltages required for the respective regions, which
are different in form of the resin wall and others from each other,
can be increased, and a dependency on a viewing angle can be
effectively improved. Such an advantage can also be achieved that
production of a gas bubble in the composite layer is suppressed. In
this case, the resin wall can be formed by polymerization phase
separation from a mixture of the liquid crystal material and the
resin material (i.e., a resin raw material), and also can be formed
by forming resin pillars between the paired substrates, and
thereafter supplying the liquid crystal material into a space
between the substrates, as will be described later.
[0038] A spacing by the resin wall is determined such that, in the
process of forming the resin wall by the polymerization phase
separation by exposure through a mask, which will be described
later, the raw material of resin does not flocculate due to a
concentration difference during the phase separation, and that the
raw material of resin does not remain a space formed by the resin
wall, which may occur by polymerization or the like due to an
influence of light diffraction at the mask boundary during exposure
through the mask. The spacing depends on the kind of resin, the
kind of liquid crystal material, the polymerization speed of the
resin material and others.
[0039] Each of the regions may be different in strength and/or form
(configuratin) of the resin phase. If the composite layer has a
plurality of resin pillars as the resin phase, the intensity or
strength of the resin pillar is determined, for example, by the
pitch and density of the resin pillars. Thus, in the structure
employing the composite layer which has a plurality of resin
pillars as the resin phase, each region may be different in pitch,
density and/or form (configuratin) of the resin pillars from the
others.
[0040] Further, the composite layer may contain a large number of
liquid crystal droplets or a large number of liquid crystal
microcapsules dispersed in the resin phase. In this case, a
plurality of regions, which are different in diameter or the like
of the liquid crystal droplet or liquid crystal capsule from each
other, are present in the area corresponding to one pixel,
similarly to the foregoing cases.
[0041] The paired substrates may have electrodes, respectively,
between which the foregoing area is defined. The area in the
composite layer corresponds to one pixel formed by these
electrodes. If the substrate is transparent, the transparent
electrode is employed. The transparent electrode may be made of ITO
(Indium Tin Oxide), SnO.sub.2, InO.sub.3 or the like, or may be
made of a thin metal film.
[0042] The electrodes can form the pixel by employing such a
structure that at least one of the electrodes takes the form of a
matrix, or that one of the electrodes is formed of a large number
of parallel line-like members, and the other is formed of a large
number of parallel line-like members perpendicular to them.
[0043] The liquid crystal device of the embodiment of the invention
can be manufactured by the steps of defining the area corresponding
to one pixel, and forming the plurality of regions of the composite
layer in the defined area.
[0044] The step of forming the regions may include the steps of
supplying a composition of the liquid crystal material and the
resin material (i.e., the raw material of the resin) into a space
between paired substrates; and separating the liquid crystal
material in a region corresponding to each of the regions from the
resin under a condition different from those in the other regions.
In this case, the foregoing area is defined between the paired
substrates.
[0045] If the resin material is a photo-curing resin material, the
separating step may include the steps of masking the composition
with a mask having a plurality of regions, each of which has a
plurality of openings and is different from the others in condition
of the openings; and exposing the composition to light through the
mask.
[0046] More specifically, the liquid crystal device of the
embodiment of the invention can be manufactured, for example, by
the following method. A pair of plates provided with electrodes are
prepared. At least one of the plates provided with electrodes is
transparent. These plates and a spacer disposed therebetween are
attached together with inner sides of the electrodes directed
inward. A space between the plates is filled with a mixture liquid.
The mixture liquid is made of a liquid crystal material exhibiting
cholesteric characteristic at a room temperature, monomers and/or
oligomers of a raw material of photo-curing resin (e.g., raw
material of ultraviolet-curing resin) and a polymerization
initiator mixed at a predetermined ratio. Then, a photomask having
a predetermined pattern is disposed outside the transparent plate,
and radiation is performed with rays (e.g., ultraviolet rays)
having a predetermined intensity of illumination through the
photomask at a temperature equal to or higher than the clearing
point of the liquid crystal material exhibiting cholesteric
characteristic. Thereby, the resin monomers or the like are cured
at a portion radiated with the rays so that phase separation occurs
between the liquid crystal material and the resin, and the resin
phase corresponding to the mask form is formed.
[0047] If the resin phase is made of a plurality of resin pillars,
each region in the foregoing mask may be different in pitch,
density and/or form of the openings from the others, whereby the
pitch, density and/or forms (configurations) of the resin pillars
formed at each region in the composite layer may be different from
that (or those) of the others.
[0048] If the resin phase is in the network form, the resin phase
is formed such that a plurality of regions, which are different in
density of mesh openings or the like from each other, are present
in the area corresponding to one pixel. More specifically, in the
process of the polymerization phase separation which is performed
by radiating the composition of the liquid crystal material and the
resin material of the photo-curing resin with light, an ND filter
having portions providing different light transmittances from each
other in one pixel is laid on the plate. Thereby, growth of the
resin can be controlled in several different manners in the area
corresponding to one pixel so that the network resin phase made of
several portions having different densities or the like of mesh
openings from each other can be formed in the area corresponding to
one pixel. In the structure where the composite layer includes the
liquid crystal droplets dispersed in the resin phase, this
composite layer can be formed by the phase separation method. In
this case, the intended structure can be formed by performing the
phase separation that a plurality of regions, which are different
in diameter or the like are present in the area corresponding to
one pixel.
[0049] Furthermore, in the structure where the composite layer
includes the liquid crystal microcapsules dispersed in the resin
phase, the composite layer can be formed by spreading a resin
material, dispersing a plurality of microcapsules on the spread
resin material so that microcapsules different in diameter are
respectively located in regions of the area corresponding to one
pixel, and then curing the resin material.
[0050] The "plates" holding the composite layer may conceptually
include flexible or less flexible plate-like members, flexible
films or the like. For example, one of the paired plates may be a
plate having a hardness which allows holding of the composite
layer, and the other may be a member such as a film for protecting
the composite layer.
[0051] If the plate nearer to the exposure light source were thick,
it would be impossible to form the resin phase having an intended
form due to an influence of spreading and diffraction of exposure
rays. Therefore, the thickness of the plate nearer to the exposure
light source is preferably about 0.5 mm or less, although it
depends on an optical system for the exposure. More preferably, it
is about 0.2 mm or less. The exposure is preferably performed by
projection exposure because it is less affected by stray light.
However, contact exposure may be employed, in which case the plate
near the light source preferably has a thickness equal to or
smaller than a thickness which is about ten times larger than the
minimum form of the mask pattern (minimum size of the exposure
opening pitch).
[0052] For curing the raw material of resin by radiation of light
(e.g., ultraviolet rays), the plate near the light source is
preferably made of a material which neither scatters nor absorbs
the light (e.g., ultraviolet rays). For example, it may be glass,
polyethylene terephthalate, polycarbonate, polyether sulfone or the
like.
[0053] The foregoing liquid crystal material exhibiting cholesteric
characteristic may be, for example, a cholesteric liquid crystal
material or a chiral nematic liquid crystal material made of a
nematic liquid crystal material and a chiral ingredient added
thereto for providing a predetermined helical pitch length.
[0054] The nematic liquid crystal material may be a material
containing, e.g., cyanobiphenyl, tolane or pyrimidine, and having a
positive dielectric anisotropy. More specifically, MN1000XX
(manufactured by Chisso Co., Ltd.) as well as ZLI-1565 and BL-009
(both manufactured by Merck Co., Ltd.) may be available. The chiral
ingredient may be a compound having asymmetric carbon and inducing
an optical rotation. More specifically, S-811, S-1011, CB15, CE2
(all manufactured by Merck Co., Ltd.) and others may be available.
Cholesteric nonanoate (manufactured by Merck Co., Ltd.) of
cholesteric liquid crystal material may be used as a chiral
ingredient. The property of MN1000XX is disclosed in U.S. Pat. No.
5,731,861.
[0055] The raw resin material may preferably be ultraviolet-curing
monomers and/or oligomers, and more specifically may preferably be
monomers and/or oligomers of monofunctional or multifunctional
acrylate or methacrylate in view of a mutual action with the liquid
crystal material, reliability, adhesivity to the plate and
others.
[0056] The polymerization initiator may be a material which induces
radical polymerization of resin when radiated with light (e.g.,
ultraviolet light). More specifically, the polymerization initiator
may be, for example, DAROCUR 1173 or IRGACUR 184 (both manufactured
by Chiba Gaigy Co., Ltd) which induces radical polymerization of
resin when radiated with ultraviolet light.
[0057] The polymerization phase separation is performed at a
temperature that the liquid crystal material attains an isotropic
phase, i.e., a temperature equal to or higher than the clearing
point of the liquid crystal material. If performed at a temperature
lower than the above, partial separation of the liquid crystal
material occurs during the polymerization phase separation so that
ultraviolet rays are scattered, resulting in lowering of the
contrast. Also, the separated liquid crystal material may adhere
onto the plate, and thereby may reduce the adhesivity between the
plate and the composite layer.
[0058] For cutting the component of light scattered due to a
disclination between liquid crystal domains in the liquid crystal
phase, a minute amount of dye may be added into the liquid crystal
material, or a color filter may be arranged outside the plate on
the light reflecting side. The dye may have such characteristics
that can absorb spectral rays of the wavelengths other than
spectral rays to be selectively reflected by the liquid crystal
material. This can improve the contrast. In this case, the dye may
be taken into either the liquid crystal phase or the resin phase.
The dye to be added to the liquid crystal phase or the resin phase
may be dichroic pigment for a liquid crystal display such as SI-426
or M-483 (both manufactured by Mitsui Toatsu Senryo Co., Ltd.).
[0059] The spacer may be made of plastics, glass or the like, and
for example, may be sprayed on the plate in advance, or may be
mixed to the raw material of resin in advance. The spacer has a
diameter substantially equal to or slight smaller than an intended
thickness of the composite layer. This is because that the
thickness of the composite layer is substantially determined by the
height of the resin phase, but slightly exceeds the height of the
resin phase.
[0060] In the structure where the liquid crystal device using the
liquid crystal material exhibiting cholesteric characteristic is to
be driven by application of the voltage, two kinds of, i.e., high
and low pulse voltages are applied to switch the orientation state
of the liquid crystal molecules between the planar orientation
state and the focal conic orientation state. The switched state is
stably held even after stop of voltage application.
[0061] The liquid crystal material exhibiting cholesteric
characteristic selectively reflects the rays of a wavelength
corresponding to a product of the helical pitch length and the
average refractive index of the liquid crystal material when it is
in the planar orientation wherein the helical axes are oriented
perpendicularly to the substrate. Therefore, by employing the
liquid crystal materials of which selective reflection wavelengths
are in a red range, a blue range and a green range, respectively,
the liquid crystal materials in the planar orientation selectively
reflect the rays of the respective wavelengths to perform display
in red, blue and green. By layering the liquid crystal layers of
the respective colors, display in multiple colors can be performed.
By setting the selective reflection wavelength in a range such as
an infrared range, a transparent appearance is exhibited. In the
structure employing a chiral nematic liquid crystal material, the
helical pitch length can be controlled by controlling an amount of
added chiral ingredient, whereby the selective reflection
wavelength can be controlled.
[0062] The liquid crystal material exhibiting cholesteric
characteristic exhibits an opaque appearance by scattering the
incident rays when it is in the focal conic state and thus its
helical axes are oriented irregularly. If the liquid crystal
material exhibiting cholesteric characteristic has the selective
reflection wavelength, for example, in a visible range, it has a
short helical pitch length so that the scattering is reduced.
Therefore, the helical axes are oriented substantially parallel to
the plate. In this case, a nearly transparent appearance can be
exhibited.
[0063] Accordingly, by switching the state between the planar state
and the focal conic state, it is possible to perform the display
between the selective reflection state (planar state) and the
transparent state (focal conic state), display between the
transparent state (planar state) and the opaque state (focal conic
state) and others. The selective reflection wavelength may be set
in a visible range, and a background layer of an appropriate color
may be arranged outside the plate remote from the viewing side.
Thereby, the display can be performed between the selective
reflection state (planar state) and the background color state
(focal conic state) and others.
[0064] In the liquid crystal device of the embodiment of the
invention, the liquid crystal material exhibiting cholesteric
characteristic may have, typically, the selective reflection
wavelength in the visible range.
[0065] FIG. 1(A) shows a cross section of a liquid crystal device
of an embodiment of the invention thus formed, and particularly
shows a portion corresponding to one pixel. In the liquid crystal
device, a pair of transparent substrates or plates 1a and 1b, which
are provided with transparent electrodes 2a and 2b in matrix forms,
respectively, are attached together with the transparent electrodes
2a and 2b directed inward, and a composite layer 3 is held between
the plates 1a and 1b. A black light absorber layer 4 is disposed
outside the plate 1b. The composite layer 3 in this embodiment is
formed of a liquid crystal phase 3a and a resin phase 3b is formed
of resin pillars. Four regions A1, A2, A3 and A4 which are
different in diameter and form of the resin pillar 3b from each
other are present in one pixel. FIG. 1B shows, on a reduced scale,
a cross section of the composite layer 3 taken along line X-X' in
FIG. 1(A).
[0066] As shown in FIG. 1(A), each resin pillar has a slightly
sloped end. Therefore, when a voltage is applied across the
transparent electrodes 2a and 2b, an electric field produced
thereby crosses the resin pillar 3b and the voltage applied is
divided between the liquid crystal phase 3a and the resin pillar
3b. The sloped structure of the end is formed by the following
reason. Since the rays (e.g., ultraviolet rays) are radiated from
outside one of the plates, the space in which polymerization of
resin monomers or the like is achieved expands during the
polymerization. Thus, the resin wall has an expanded structure at
the ray radiation side where the polymerization started first. For
achieving uniform polymerization, it is preferable that the rays
for radiation are parallel rays. However, the form of the resin
pillar can be controlled by controlling the diverging angle and
incident angle of the rays.
[0067] According to the liquid crystal device of the embodiment of
the invention, each pixel in the composite layer includes the
plurality of regions different in state or condition of the resin
phase from each other. Therefore, the applied voltage is divided by
the resin phase to various extents depending on the regions, and
the voltage actually applied to the liquid crystal material in each
region differs from the voltages applied to the liquid crystal
material in the other regions. In the structure wherein the resin
phase is formed of the resin pillar, the composite layer includes
the plurality of regions which are different, e.g., in density,
arrangement pitch and/or form of the resin pillars so that the
degree or extent of division of the applied voltage, which is
caused in each region by the inclination of the end of the resin
pillar, differs from those in the other regions, and therefore the
magnitude of the voltage which is actually applied to the liquid
crystal material in each region differs from those in the other
regions. Movement of the liquid crystal molecules is restricted by
a mutual action (anchoring) with the resin phase to an extent,
which depends on the form and others of the resin phase. As a
result, the drive voltage required for setting each region to an
intended state differs from that for the other regions, and the
regions exhibit different reflectances, respectively, when the
predetermined voltage is applied thereto.
[0068] FIG. 2(A) schematically shows a relationship between the
magnitude of the pulse voltage applied between the transparent
electrodes 2a and 2b in the liquid crystal device in FIG. 1(A) and
the reflectances of the regions A1-A4. In this liquid crystal
device, the selective reflection wavelength of the liquid crystal
material is outside the infrared range so that the liquid crystal
material exhibits a transparent appearance when it is in the planar
state, and exhibits an opaque appearance when it is in the focal
conic state. The liquid crystal material is in the planar state
when it is in the initial state. As shown in FIG. 2(A), the voltage
attaining the focal conic state (low-reflectance state) and the
voltage attaining the planar state (high-reflectance state) again
in each region differ from those in the other regions.
[0069] FIG. 2(B) schematically shows a relationship between the
magnitude of the pulse voltage and the reflectance in the whole
pixel including regions A1-A4. The reflectance in the whole pixel
is an average value of the reflectances of the respective regions.
Therefore, many reflectance states are present between the state
that all the regions A1-A4 are in the planar state and the state
that all the regions A1-A4 are in the focal conic state.
Accordingly, a multi-tone display can be performed by controlling
the magnitude of the voltage applied to the composite layer. For
example, a cholesteric liquid crystal material which is controlled
to have the selective reflection wavelength in a green range may be
used, whereby a multi-tone display can be performed between the
green and the black.
[0070] It is assumed that, in the composite layer (pixel) of the
liquid crystal device shown in FIGS. 1(A) and 1(B), the regions A4
requires a voltage V1 for changing from the planar state to the
focal conic state, and this voltage V1 is higher than the voltages
required by the other regions for changing their states in the same
manner. Also, it is assumed that the region A1 in the pixel
requires a voltage V2 for returning from the focal conic state to
the planar state, and this voltage V2 is lower than the voltages
required by the other regions for returning in the same manner. In
this case, it is preferable that the voltage V1 is lower than the
voltage V2 because this relationship can set all the regions to the
focal conic state and can attain the state of the lowest
reflectance.
[0071] The liquid crystal device of the embodiment of the invention
has the resin phase and therefore a high self-holding property, and
can suppress change in display state which may be caused by an
externally applied pressure even if the plate is soft. In an
extreme case, the composite layer may be held between the paired
film-like plates to provide the liquid crystal device having a
sheet-like form.
[0072] Owing to presence of the resin phase, the orientation of the
liquid crystal molecules in the planar state is disarranged so that
the dependency on the viewing angle is improved.
[0073] In the method of producing the liquid crystal device of the
embodiment of the invention, the foregoing step of forming the
regions may include the steps of (1) supplying the resin material
into a space between a first substrate and a provisional substrate,
(2) curing the resin material in a region corresponding to each of
said regions under a condition different from those in the other
regions; (3) removing the provisional substrate; (4) removing an
uncured resin material; (5) supplying the liquid crystal material
into a space formed by the cured resin; and (6) arranging a second
substrate at a position previously occupied by the provisional
substrate, and holding the resin and the liquid crystal material
between the first and second plates. In this case, said area is
defined between the first substrate and the provisional
substrate.
[0074] In particular, if the resin material is a photo-curing resin
material, the above step (2) may include the steps of masking the
resin material with a mask having a plurality of regions, each of
which has a plurality of openings and is different from the others
in condition of the openings; and exposing said resin material to
light through said mask.
[0075] More specifically, a transparent plate (first plate), which
is provided with a transparent electrode, a provisional plate and
spacers disposed therebetween are attached together with the
electrode directed inward. A space between the plates is filled
with a mixture liquid. The mixture liquid is made of monomers
and/or oligomers of a raw material, e.g., of ultraviolet-curing
resin and a polymerization initiator mixed at a ratio from 1% to 3%
by weight with respect to the whole weight. Then, a photomask
having a predetermined pattern is located outside the first plate,
and radiation is performed with ultraviolet rays having a
predetermined intensity of illumination through the photomask.
Thereby, the resin monomers and/or oligomers are cured at a portion
radiated with the rays so that the resin phase is formed.
[0076] The conditions similar to those for forming of the resin
phase by the polymerization phase separating method already
described may be employed with respect to available liquid crystal
material exhibiting cholesteric characteristic, raw resin material,
form of the resin phase, polymerization initiator, plates,
electrodes, spacer and photomask as well as dye, color filter or
the like for cutting scattered components of the light.
[0077] Then, the provisional plate is peeled off with the resin
phase remained on the first plate. This processing of peeling off
the provisional plate can be performed easily by employing, for
example, such a simple manner that a thin layer of peeling agent
(e.g., Ceparack RA450 manufactured by Yamaichi Kagaku Kogyo Co.,
Ltd.) is applied to the provisional plate in advance for reducing
the adhesivity between the provisional plate and the composite
layer, or that a polyethylene terephthalate (PET) film having a
good releasing property is used as the provisional plate, although
not restricted to these manners. Further, a coupling agent (e.g.,
Sila-Ace S710 manufactured by Chisso Co., Ltd.) may be spread on
the first plate in advance for improving the adhesivity between the
resin phase and the first plate.
[0078] Then, an uncured raw resin material is removed by washing
with organic solvent. The organic solvent is required not to affect
the formed resin phase, and may be ethanol, methanol, isopropyl
alcohol (IPA), hexane or the like.
[0079] Then, a space in the resin phase is filled with the liquid
crystal material after removing the uncured resin material by
washing, and the resin and liquid crystal material are sandwiched
between the first plate and a new plate (second plate) provided
with an electrode. The peripheries of the plates are sealed with an
adhesive or the like. If the resin phase has a wall form sealing
the peripheries of the plates, the foregoing sealing with the
adhesive is not necessary.
[0080] In the manner described above, the liquid crystal device is
produced. In this liquid crystal device, the composite layer
including the liquid crystal phase of the liquid crystal material
exhibiting cholesteric phase and the resin phase is held between
the plates, and the composite layer has an (at least one) area
defining one pixel and including a plurality of regions being
different from each other in condition of the resin phase.
[0081] In the above method, the liquid crystal material may be
supplied into the space between the first and second plates after
removing the uncured resin material, arranging the second plate and
holding the resin phase between the first and second plates. In
this case, the resin phase may take the form of pillars or a
network, and the liquid crystal phase may be continuously present
without being divided by the resin phase.
[0082] According to the method described above, there is no
possibility that an uncured raw resin material remains in the
liquid crystal phase, and it is possible to avoid lowering of the
phase transition temperature of the liquid crystal material,
shifting of the selective reflection wavelength and others, which
may be caused by the residue. There is no possibility that the
liquid crystal material is taken into the resin phase so that it is
possible to avoid disadvantages such as lowering of the intensity
of the resin phase, lowering of the durability of the resin phase
and lowering of the adhesivity of the resin phase to the plates,
which may be caused by mixing of the liquid crystal material into
the resin phase. If the polymerization phase separation method is
employed for forming the resin phase, the resin material can be
selected only from a restricted range, for example, due to such
reasons that a compatibility between the liquid crystal material
and the raw resin material is required, and that some kinds of
materials of the liquid crystal and resin do not allow the phase
separation. However, the above method allows selection of the resin
material from a wide range for producing the liquid crystal
device.
[0083] In the method of manufacturing the liquid crystal device of
the embodiment of the invention, the foregoing step of forming the
regions may include the steps of (1) supplying the resin material
into a space between paired plates, (2) curing the resin material
in a region corresponding to each of said regions under a condition
different from those in the other regions; (3) removing an uncured
resin material; and (4) supplying the liquid crystal material into
the space between the paired plates. In this case, the area is
defined between the paired plates. The resin phase may be set to
take the form of, e.g., pillars or a network, and the liquid
crystal phase may be set to be continuously present without being
divided by the resin phase.
[0084] Particularly, if the resin material is a photo-curing resin
material, the foregoing step (2) may include the steps of masking
the resin material with a mask having a plurality of regions, each
of which has a plurality of openings and is different from the
others in condition of the openings; and exposing the resin
material to light through the mask.
[0085] More specifically, a pair of transparent plates, which are
provided with transparent electrodes, and a spacer disposed
therebetween are attached together with the electrodes directed
inward. A space between the plates is filled with a mixture liquid.
The mixture liquid is made of monomers and/or oligomers of a raw
material, e.g., of ultraviolet-curing resin and a polymerization
initiator mixed at a ratio from 1% to 3% by weight with respect to
the whole weight. Then, a photomask having a predetermined pattern
is located outside the first plate, and radiation is performed with
ultraviolet rays having a predetermined intensity of illumination
through the photomask. Thereby, the resin monomers and/or oligomers
are cured at a portion radiated with the rays so that the resin
phase is formed.
[0086] Then, similarly to the above method employing the
provisional plate, an uncured raw resin material is removed by
washing. Then, a space in the resin phase is filled with the liquid
crystal material after removing the uncured resin material by
washing, and the peripheries of the plates are sealed with an
adhesive or the like. If the resin phase has a wall form sealing
the peripheries of the plates, the foregoing sealing with the
adhesive is not necessary.
[0087] The conditions similar to those for forming the resin phase
by foregoing method using the provisional plate may be employed
with respect to available liquid crystal material exhibiting
cholesteric characteristic, raw resin material, form of the resin
phase, polymerization initiator, plates, electrodes, spacer and
photomask as well as dye, color filter or the like for cutting
scattered components of the light.
[0088] Similar to the foregoing method, this method can achieve the
following advantages. There is no possibility that an uncured raw
resin material remains in the liquid crystal phase, and it is
possible to avoid lowering of the phase transition temperature of
the liquid crystal material, shifting of the selective reflection
wavelength and others, which may be caused by the residue. There is
no possibility that the liquid crystal material is taken into the
resin phase so that it is possible to avoid disadvantages such as
lowering of the intensity of the resin phase, lowering of the
durability of the resin phase and lowering of the adhesivity of the
resin phase to the plates, which may be caused by mixing of the
liquid crystal material into the resin phase. Compared with the
polymerization phase separation method, the above method allows
selection of the resin material from a wide range for producing the
liquid crystal device.
[0089] In the method of producing the liquid crystal device of the
embodiment of the invention, the step of forming the regions may
include the steps of: providing a mask having a plurality of
regions, each of which has a plurality of openings and is different
from the others in condition of the openings; and applying the
resin onto a first plate in accordance with the openings of the
mask. In this case, the foregoing area is defined on the first
plate.
[0090] The step of forming the regions may further include the
steps of supplying the liquid crystal material into the space
formed by the resin, and holding the resin and the liquid crystal
material between the first plate and a second plate.
[0091] Alternatively, if the composite layer is set to include the
liquid crystal phase which is continuously present without being
divided by the resin phase takes the form of, e.g., pillars or a
network, the step of forming the regions may further include the
steps of holding the resin between the first plate and a second
plate, and supplying the liquid crystal material into the space
between the first and second plates.
[0092] More specifically, the resin is applied onto the first plate
by a printing method, in which printing on the plate is performed
by squeezing the resin with a squeezee through a screen plate or a
metal mask. When squeezing the resin with the squeezee, the plate
may be supported by a plate-like support member, if necessary.
[0093] The resin used in this method is not restricted to the
photo-curing resin. With respect to the thermal characteristics,
the resin may be either a thermosetting resin or a thermoplastic
resin. The thermosetting resin may be epoxy resin or acrylic resin.
The thermoplastic resin may be polyvinyl chloride resin,
polyvinylidene chloride resin, polyvinyl acetate resin,
polymethacrylic acid ester resin, polyacrylic acid ester resin,
polystyrene resin, polyamide resin, polyethylene resin,
polypropylene resin, fluorocarbon resin, polyurethane,
polyacrylonitrile resin, polyvinyl ether resin, polyvinyl ketone
resin, polyether resin, polyvinyl pyrrolidone resin, saturated
polyester resin, polycarbonate resin, chlorinated polyether resin
or the like. Only one kind of resin may be selected from the above,
or two or more kinds of resin may be selected from the above for
use in combination. It is desired to use the thermosetting resin
which has a softening point higher than the transition temperature
of the liquid crystal material to the isotropic phase.
[0094] When actually used, it is desired to prepare a paste of the
resin, for example, by solving the resin with appropriate solvent.
It is preferable that the resin applied onto the plate has a height
which is larger than the intended thickness of the composite layer
but does not exceed a value five times larger than the same. More
preferably, the resin applied onto the plate has a height which is
larger than the intended thickness of the composite layer but does
not exceed a value three times larger than the same.
[0095] By a known spraying method such as a wet method or a dry
method, the spacers are sprayed onto at least one of the plates,
and the pair of plates are overlaid on each other to form an empty
cell. The plates are arranged such that the surfaces provided with
the electrodes are opposed to each other. Overlaying of the plates
may be performed in a reduced pressure. This can suppress mixing of
an air into the resin phase. The spacers may be mixed, in advance,
into the resin. The spacers may be contained in both the resin
phase and the liquid crystal phase.
[0096] Then, the paired plates which are overlaid on each other are
heated while applying a pressure from the opposite sides so that
the resin is softened. This application of the pressure is
performed, for example, by applying the pressure to the paired
plates by a pneumatic cylinder, moving the paired plates between
paired rollers which are opposed together with a predetermined
space therebetween, or by putting a plate member on the paired
plates and moving a roller bearing a predetermined load over the
plate member. When using the pneumatic cylinder, the paired plates
may be held between paired plate members to which the pressure is
applied from the pneumatic cylinder, if necessary. The heating may
be performed, for example, by performing the above application of
the pressure within a constant temperature chamber kept at a
predetermined temperature, or by heating the plate members or
rollers used for pressure application to a predetermined
temperature. Thereafter, the plate pair is cooled so that the resin
can be solidified.
[0097] The liquid crystal material is supplied into the empty cell
thus formed in a known vacuum injection method. When supplying the
liquid crystal material, the plates may be heated to a temperature
lower than the softening point of the resin.
[0098] Instead of injection of the liquid crystal material,
droplets of the liquid crystal material may be supplied onto one of
the plates before overlaying the plates on each other, in which
case the plates may likewise be heated to a temperature higher than
the transition temperature of the liquid crystal material to the
isotropic phase.
[0099] Instead of the printing method in which the resin is applied
in accordance with the openings of the mask, the resin may be
applied onto the first plate, e.g., by a dispensing method, an ink
jet method or a transfer method. These methods are likewise
performed to form finally the plurality of regions different from
the others in condition of the resin phase in the area
corresponding to one pixel. The dispensing method and the ink jet
method are performed in such a manner that resin paste or the like
is injected onto the plate from a nozzle. The transfer method is
performed in such a manner that the resin is applied onto a plate
member or a roller, and then is transferred onto the plate.
[0100] The kinds of available resin, spacer, methods of heating and
pressuring the plates, method of supplying the liquid crystal
material and others are similar to those in the printing
method.
[0101] Similarly to the foregoing method, this method can achieve
the following advantages. There is no possibility that an uncured
raw resin material remains in the liquid crystal phase, and it is
possible to avoid lowering of the phase transition temperature of
the liquid crystal, shifting of the selective reflection wavelength
and others, which may be caused by the residue. There is no
possibility that the liquid crystal material is taken into the
resin phase so that it is possible to avoid disadvantages such as
lowering of the intensity of the resin phase, lowering of the
durability of the resin phase and lowering of the adhesivity of the
resin phase to the plates, which may be caused by mixing of the
liquid crystal material into the resin phase. Compared with the
polymerization phase separating method, the resin material can be
selected from a wide range for producing the liquid crystal
device.
[0102] Specific embodiments of the invention will now be described
below. The invention is, however, not restricted to them.
Embodiment 1
[0103] A mixture, which included the nematic liquid crystal
material MN1000XX and ZLI-1565 mixed at a weight ratio of 1:1, was
mixed with the chiral material, which was a mixture of CN and S811
mixed at a weight ratio of 2:1, to produce a chiral nematic liquid
crystal material A. This liquid crystal material A contained the
chiral material at 35.4% by weight with respect to the whole
mixture, and had the selective wavelength of 560 nm. The clearing
point of the liquid crystal material A was 61.3.degree. C. This
liquid crystal material A and photo-curing resin, i.e., monomers of
2, 4-dibromophenol epoxy acrylate were mixed at a weight ratio of
8:2 to prepare a mixture. This mixture was supplied into a space
between the plates of 0.2 mm in thickness, which carried spacers of
10 .mu.m and were provided with a pair of transparent electrodes.
Then, a photomask shown in FIG. 3 was arranged on the outside of
one of the plates, and the plate was radiated with ultraviolet rays
(15 mW/cm.sup.2) through the photomask to cause polymerization of
the resin monomers at a temperature of 65.degree. C. To prevent
reflection of the ultraviolet rays, a black absorbing layer was
disposed on the background in this processing of radiating the
ultraviolet rays. For simplicity reason, FIG. 3 shows a portion of
the photomask corresponding to one pixel, but the actual photomask
had a large number of portions corresponding to that shown in FIG.
3.
[0104] The photomask shown in FIG. 3 has four regions B1, B2, B3
and B4 corresponding to one pixel. These regions B1, B2, B3 and B4
are different from each other in an arrangement pitch P of the
openings, which correspond to resin pillars having a square cross
section, respectively, and are also different from each other in a
size d of one side of the opening. The region B1 has the pitch P of
30 .mu.m and the size d of 10 .mu.m (opening rate of 89%). The
region B2 has the pitch P of 40 .mu.m and the size d of 15 .mu.m
(opening rate of 86%). The region B3 has the pitch P of 60 .mu.m
and the size d of 25 .mu.m (opening rate of 82%). The region B4 has
the pitch P of 100 .mu.m and the size d of 50 .mu.m (opening rate
of 75%).
[0105] After cooling the composite layer, the structure of the
resin phase was observed with a polarization microscope. As a
result, an isotropic resin region and a fan shape of the liquid
crystal material in the focal conic orientation were found from
either side of the plates, and it was found that the resin phase in
the pillar form was formed.
[0106] A high voltage pulse of .+-.200 V and 5 msec was applied
across the electrodes of this liquid crystal device to form the
planar orientation in the entire region, and then the peak value of
the pulse voltage was changed to change the state of the liquid
crystal material. Thereby, a multi-tone display could be performed.
The luminous reflectances of the portions corresponding to the
regions B1-B4 were measured with a spectrocolorimeter CM-1000
(manufactured by Minolta Co., Ltd., reflection type). However, it
was difficult to measure the reflectance of the portions
corresponding to the regions B1-B4 because an area of each portion
was excessively small. Therefore, four kinds of photomasks, which
had the same opening pitches P and the side length d of the opening
as the regions B1-B4, respectively, were prepared, and four kinds
of liquid crystal devices having the composite layers, each of
which was formed of a single region, were prepared with these
photomasks, respectively. The measurement of the reflectances were
performed with these composite layers, respectively. The
relationship between the magnitude of the voltage and the luminous
reflectances of the respective regions are shown in FIG. 4. Since
the respective regions exhibited different reflectance curves,
respectively, it can be understood that the multi-tone display can
be performed by providing a plurality of regions corresponding to
the regions B1-B4 in one pixel.
[0107] Similarly to the foregoing, another liquid crystal device
having the composite layer was prepared with a photomask, which had
four regions C1, C2, C3 and C4 (corresponding to the regions B1,
B2, B3 and B4, respectively) for one pixel. These regions C1, C2,
C3 and C4 were different from each other in pitch P of the openings
for exposure and length d of one side of the opening, which
corresponded to the resin pillars each having a square cross
section, respectively. The region C1 had the pitch P of 20 .mu.m
and the length d of 10 .mu.m, the region C2 had the pitch P of 40
.mu.m and the length d of 20 .mu.m, the region C3 had the pitch P
of 60 .mu.m and the length d of 30 .mu.m, and the region C4 had the
pitch P of 100 .mu.m and the length d of 50 .mu.m. The regions C1,
C2, C3 and C4 had the same opening rate of 75%.
[0108] Measurement was carried out on this liquid crystal device in
the same manner as the foregoing. The relationship between the
magnitude of the pulse voltage and the luminous reflectances of the
respective regions are shown in FIG. 5. Similarly to the foregoing
case, the respective regions exhibit different reflectance curves,
and therefore it can be understood that a multi-tone display can be
performed by providing the regions corresponding to the regions
C1-C4 in one pixel. This liquid crystal device was different from
the liquid crystal device produced with the photomask shown in FIG.
3 in pitch, form and others of the resin pillars in each region,
and therefore was different in required drive voltage. The luminous
reflectances of the respective portions corresponding to the
regions C1-C4 were measured in the same manner as the measurement
of the luminous reflectances of the portions corresponding to the
respective regions B1-B4.
[0109] From FIGS. 4 and 5, it can be seen that the region having
resin pillars, which have a smaller thickness (length d of one side
of the resin pillar) and are arranged at a smaller pitch P and
therefore at a higher density, requires a higher drive voltage.
[0110] Referring to FIG. 6, another specific embodiment will be
described below.
Embodiment 2
[0111] A glass plate provided with a transparent electrode having a
sheet resistance of 100 .OMEGA. and a thickness of 120 .mu.m was
prepared as a first plate 5a. A mixture of monofunctional acrylate
monomers R128H (manufactured by Nippon Kayaku Co., Ltd.) and
polymerization initiator IRGACURE 184 (manufactured by Chiba Gaigy
Co., Ltd.) added at a ratio of 5% by weight with respect to the
whole weight was spread on the side of the first plate carrying the
transparent electrode, and was held between the first plate and the
provision plate formed of a PET film 5b with spacers of 10 .mu.m
therebetween.
[0112] Then, radiation of ultraviolet rays (6 mW/cm.sup.2) was
performed for 4 seconds with a photomask 7 in intimate contact with
the first plate 5a so that the resin was polymerized. The radiation
of ultraviolet rays was performed with a black absorbing layer
disposed on the background so as to prevent reflection of the
ultraviolet rays. A light source was spaced from the plate by 30
cm. The radiation rays were not parallel rays but were diverging
rays.
[0113] The photomask 7 had three regions D1, D2 and D3 for one
pixel. The regions D1, D2 and D3 were different from each other in
pitch P of openings 7a and length d of one side of opening 7a. The
region D1 had the pitch P of 40 .mu.m and the length d of 20 .mu.m,
the region D2 had the pitch P of 60 .mu.m and the length d of 30
.mu.m, and the region D3 had the pitch P of 100 .mu.m and the
length d of 50 .mu.m. These regions had the same opening rate.
[0114] Thereby, a group of the resin pillars of 10 .mu.m in height
was formed correspondingly to the mask pattern. A cross section of
the structure including the resin pillars is fragmentarily shown in
FIG. 6(A). The resin was held between the first plate 5a provided
with an electrode layer 5a' and the PET film 5b, and the resin
pillars 6b were formed at the positions corresponding to the
openings 7a in the photomask 7 which was disposed outside the glass
plate 5a. Each resin pillar 6b had a sloped form diverging toward
the ultraviolet ray source. Uncured resin monomers 6b, were present
between the resin pillars 6b.
[0115] Then, the PET film was peeled off, and the uncured resin
monomers were removed by washing with ethanol. In this state, the
cross section of the structure including the resin pillars are
shown in FIG. 6(B). This structure was observed from the side of
the resin pillars 6b with a scanning electron microscope (SEM). It
was confirmed that the resin remained only in the exposed
portions.
[0116] A mixture, which included the nematic liquid crystal
material MN1000XX and ZLI-1565 mixed at a weight ratio of 1:1, was
mixed with the chiral material, which was a mixture of CN and S811
mixed at a weight ratio of 2:1, to produce a chiral nematic liquid
crystal material A. This liquid crystal material A contained the
chiral material at 35.4% by weight with respect to the whole
mixture, and thereby had the selective reflection wavelength of 560
nm. This liquid crystal material A was applied to spaces between
the resin pillars. A new plate 5c having a new transparent
electrode (second electrode) 5c' was attached to hold the liquid
crystal material A and the resin pillars under pressure between the
first and second plates, and the peripheries of the plates were
sealed with ultraviolet-curing resin. The transparent electrode
layer 5c' was directed inward when holding the resin pillars 6b and
liquid crystal material 6a between the first plate 5a and the
second plate 5c. In this manner, the liquid crystal device having
the composite layer 6, of which cross section is shown in FIG.
6(C), was completed.
[0117] An AC pulse voltage of 5 msec was applied across the
electrodes 5a' and 5c' while changing the magnitude of the voltage
in various manner. When a high voltage pulse of, e.g., 200 V was
applied, the liquid crystal device attained the planar orientation
state, and the composite layer 6 exhibited a green appearance owing
to the selective reflection. When a low voltage pulse of, e.g., 100
V was applied, the composite layer 6 attained a weakly scattering
state and no longer exhibited the colored state. The respective
states were maintained even after 24 hours from stop of the pulse
voltage application. Thereby, it could be found that the display
could be changed between the green and transparent appearances.
[0118] This liquid crystal device could perform a multi-tone
display by applying the pulse voltage of various magnitudes to the
composite layer which was initially in the planar orientation
state. In the same manner as the specific embodiment 1 already
described, the luminous reflectances of the regions D1, D2 and D3
were measured. As a result, the respective regions exhibited
different reflectance curves. From this, it can likewise be
understood that the multi-tone display can be performed by
providing the plurality of regions corresponding to the regions
D1-D3 in one pixel, respectively.
[0119] In the specific embodiment 2, the time for radiation of the
ultraviolet rays was changed from 4 seconds to 7 seconds. In this
case, the resin pillars exhibited the state shown in FIG. 7 after
removing uncured resin monomers by washing the same with ethanol.
In this state, the resin layers were formed even on unexposed
portions of the first plate. As a result, the voltage for selecting
the planar orientation increased.
[0120] In the specific embodiment 2, if the resin wall was formed
with the photomask having a pattern shown in FIG. 8(A), a resin
wall having a partition form shown in FIG. 8(B) was formed, in
which case gas bubbles were liable to be mixed during the step of
supplying the liquid crystal material.
[0121] Still another specific embodiment of the invention will be
described below with reference to FIG. 9. In this embodiment, resin
pillars made of thermoplastic resin were produced by the screen
printing method.
[0122] First, a glass plate (100.times.100), which was provided at
its one surface with an ITO film forming the transparent electrode
film, was processed by the photolithography to pattern the ITO film
into stripes each having a line width of 600 .mu.m and arranged at
a pitch of 640 .mu.m. Then, a spin coat method is executed to form
a silicon oxide insulating film. A pattern of thermoplastic resin,
i.e., polyester resin PES-360S30 (manufactured by Three Bond Co.,
Ltd.) was formed on the silicon oxide insulating film by the screen
printing method as shown in FIG. 9. FIG. 9 shows a portion
corresponding to one pixel defined by the matrix electrodes which
were formed when the other plate provided with a similarly
patterned ITO film and an insulating film thereon was overlaid on
the foregoing glass plate. The region corresponding to one pixel
included four regions E1, E2, E3 and E4 which were different from
each other in arrangement pitch P of the resin pillars and length d
of one side thereof. The region E1 had the pitch P of 30 .mu.m,
length d of 10 .mu.m and opening rate of 89%. The region E2 had the
pitch P of 40 .mu.m, length d of 15 .mu.m and opening rate of 86%.
The region E3 had the pitch P of 60 .mu.m, length d of 25 .mu.m and
opening rate of 82%. The region E4 had the pitch P of 100 .mu.m,
length d of 50 .mu.m and opening rate of 75%. A continuous dam was
simultaneously formed at the outer periphery of the plate except
for a portion providing an inlet of the liquid crystal material.
This dam was likewise made of polyester resin PES-360-30.
[0123] Thereafter, spacers (Micro Pearl SP-2075 manufactured by
Sekisui Fine Chemical Co. Ltd.) having a particle diameter of about
7.5 .mu.m were uniformly sprayed onto the whole surface of the
plate by the dry spraying method at a density of 100
particles/mm.sup.2.
[0124] A glass plate having a similarly patterned ITO film and a
similar insulating film was prepared as the other plate, and was
overlapped with the foregoing plate provided with the
screen-printed resin. These plates were overlapped with each other
such that the ITO patterns thereof were perpendicular to each
other. This assembly was heated to 150.degree. C., i.e., the
softening point of the polyester resin while being pressured for
five minutes with the pressure of 0.2 kg/cm.sup.2. The assembly was
then cooled to a room temperature while maintaining the pressurized
state.
[0125] The liquid crystal material was supplied into empty cells
thus formed by a vacuum injection at a temperature of 60.degree. C.
to form the liquid crystal device. This liquid crystal material was
made of a nematic liquid crystal material E-31LV (manufactured by
Merck Co., Ltd., T.sub.N-I=61.5.degree. C.) and a chiral ingredient
S-811 added thereto at a ratio of 24.5% by weight with respect to
the whole weight. Then, the supply inlet was closed by
ultraviolet-curing resin Photoreck A-704-60 (manufactured by
Sekisui Fine Chemical CO., LTD.).
[0126] Through the foregoing steps, a light modulation device of a
cholesteric liquid crystal material having the selective reflection
wavelength of 550 nm and exhibiting the green reflection color was
produced. A high voltage pulse of .+-.150 V and 5 msec (150 V at a
row side and 0 V at a column side) was applied across the
electrodes of the liquid crystal light modulation device to set the
planar state in all the regions. Then, change in state of the
liquid crystal material was observed while changing the peak value
of the pulse voltage. As a result, it was found that the peak
reflectance changed in accordance with the value of the applied
voltage, and the multi-tone display could be performed. The peak
value of the pulse voltage was changed by changing the voltage
value on the column side.
[0127] An external pressure of 10 kg/cm.sup.2 was applied to the
foregoing liquid crystal light modulation device. After elimination
of the external pressure, it was observed that the distance between
the plates neither increased nor decreased, and no irregularity was
present. Also, no change in drive voltage was caused by the voltage
application. After this liquid crystal light modulation device was
left at -25.degree. C. for 24 hours, occurrence of gas bubbles was
not found.
[0128] The embodiments 1 to 3 have been described in connection
with the examples of liquid crystal devices including the resin
pillars as the resin phase of the composite layer. However, the
invention is not restricted to this. For example, the resin phase
may take another form such as a network form. In this case, the
resin phase has such a structure that a plurality of regions having
different densities of mesh openings are present in one pixel,
whereby a multi-tone display can be performed by controlling the
applied voltage, as can be done also in the foregoing
embodiments.
[0129] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *