U.S. patent application number 09/370427 was filed with the patent office on 2002-01-10 for liquid crystal composition and liquid crystal light modulating device.
Invention is credited to IWAMATSU, MASAKO, KOBAYASHI, NOBUYUKI, UEDA, HIDEAKI.
Application Number | 20020003600 09/370427 |
Document ID | / |
Family ID | 26459422 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020003600 |
Kind Code |
A1 |
IWAMATSU, MASAKO ; et
al. |
January 10, 2002 |
LIQUID CRYSTAL COMPOSITION AND LIQUID CRYSTAL LIGHT MODULATING
DEVICE
Abstract
A reflective type liquid crystal display which has a liquid
crystal composition exhibiting a cholesteric phase in a room
temperature and a columnar structure between substrates with ITO
electrodes thereon. The liquid crystal composition is a chiral
nematic liquid crystal composition which is produced by adding a
chiral agent at a ratio within a range from 10 wt % to 45 wt % to
nematic liquid crystal which contains a nematic liquid crystal
component with a polar group at not less than 25 wt % and of which
transition temperature to isotropic phase is within a range from
70.degree. C. to 150.degree. C. The anisotropy of refractive index
of the liquid crystal composition is 0.10 to 0.22, and the
anisotropy of dielectric constant is 5 to 30.
Inventors: |
IWAMATSU, MASAKO;
(TOYONAKA-SHI, JP) ; KOBAYASHI, NOBUYUKI;
(KOBE-SHI, JP) ; UEDA, HIDEAKI; (KISHIWADA-SHI,
JP) |
Correspondence
Address: |
SIDLEY AUSTIN BROWN & WOOD
717 NORTH HARWOOD
SUITE 3400
DALLAS
TX
75201
US
|
Family ID: |
26459422 |
Appl. No.: |
09/370427 |
Filed: |
August 9, 1999 |
Current U.S.
Class: |
349/175 |
Current CPC
Class: |
C09K 19/42 20130101;
C09K 19/586 20130101; G02F 1/13718 20130101; C09K 19/46
20130101 |
Class at
Publication: |
349/175 |
International
Class: |
G02F 001/13 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 18, 1998 |
JP |
10-231921 |
Apr 28, 1999 |
JP |
11-122268 |
Claims
What is claimed is:
1. A liquid crystal composition which exhibits a cholesteric phase
in a room temperature, comprising: nematic liquid crystal which
contains a nematic liquid crystal component with a polar group at
not less than 25 wt % and of which transition temperature to
isotropic phase is within a range from 70.degree. C. to 150.degree.
C.; and a chiral agent which is added to the nematic liquid crystal
at a ratio within a range from 10 wt % to 45 wt %; wherein said
liquid crystal composition has an anisotropy of refractive index of
0.10 to 0.22 and an anisotropy of dielectric constant of 5 to
30.
2. A liquid crystal composition as claimed in claim 1, wherein the
liquid crystal component with a polar group in the nematic liquid
crystal contains a liquid crystal ester compound or a liquid
crystal pyrimidine compound.
3. A liquid crystal composition as claimed in claim 1, wherein the
liquid crystal component with a polar group in the nematic liquid
crystal contains a liquid crystal compound with at least one polar
group selecting from the group consisting of fluorine, fluoroalkyl
and cyano.
4. A liquid crystal composition as claimed in claim 3, wherein the
liquid crystal component with a polar group in the nematic liquid
crystal is a compound selecting from the group consisting of liquid
crystal tolan compounds, liquid crystal ester compounds and liquid
crystal pyrimidine compounds.
5. A liquid crystal composition as claimed in claim 1, wherein the
anisotropy of refractive index is within a range from 0.12 to
0.20.
6. A liquid crystal composition as claimed in claim 1, wherein the
chiral agent is contained in the liquid crystal composition at a
ratio within a range from 12 wt % to 35 wt %.
7. A liquid crystal composition as claimed in claim 1, which
contains a plurality of chiral agents.
8. A liquid crystal light modulating device comprising: a pair of
substrates, at least one of which is light transmitting; the liquid
crystal composition as claimed in claim 1 provided between the
substrates; and a space maintaining member provided between the
substrates.
Description
[0001] This application is based on applications No. 10-231921 and
No. 11-122268 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
composition which exhibits a cholesteric phase in a room
temperature and a reflective type liquid crystal light modulating
device provided with the liquid crystal composition.
[0004] 2. Description of Related Art
[0005] Recently, studies have been made to develop reflective
liquid crystal displays by using chiral nematic liquid crystal
which is produced by adding a chiral agent to nematic liquid
crystal to cause the liquid crystal to exhibit a cholesteric phase
in a room temperature. Such a liquid crystal display makes a
display by switching between a planar state (color) and a
focal-conic state (transparent) in accordance with the level of the
pulse voltage applied thereto. The planar state and the focal-conic
state can be maintained after the application of the pulse voltage
(which is referred to as bistability or non-volatility), whereby
the display can be maintained even after stoppage of the
application of the voltage.
[0006] At present, however, in such a reflective liquid crystal
display, the reflectance is low, and the contrast between the
planar state and the focal-conic state is not sufficiently high,
and liquid crystal displays of this type which are satisfactory in
performance such as color purity (excitation purity), etc. are yet
to be developed. To this type of liquid crystal displays, it is
also important to have a wide temperature range in which practical
display performance is possible.
SUMMARY OF THE INVENTION
[0007] It is an object of the present invention to provide a liquid
crystal composition which, when it is used for a liquid crystal
light modulating device such as a liquid crystal display, is good
in color purity, reflectance, etc., has a wide temperature range
which permits practical display performance and is driven by a low
voltage.
[0008] Another object of the present invention is to provide a
liquid crystal light modulating device which is good in color
purity, reflectance, etc., has a wide temperature range which
permits practical display performance and is driven by a low
voltage.
[0009] In order to attain the objects, a liquid crystal composition
according to the present invention is a chiral nematic liquid
crystal composition which exhibits a cholesteric phase in a room
temperature and is produced by adding a chiral agent at a ratio
within a range from 10 wt % to 45 wt % to nematic liquid crystal
which contains a nematic liquid crystal component with a polar
group at not less than 25 wt % and of which transition temperature
to isotropic phase is within a range from 70.degree. C. to
150.degree. C. The anisotropy of refractive index of the liquid
crystal composition is 0.10 to 0.22, and the anisotropy of
dielectric constant is 5 to 30.
[0010] A liquid crystal light modulating device according to the
present invention comprises the above-described liquid crystal
composition and a space maintaining member between a pair of
substrates at least one of which is light transmitting.
[0011] As the nematic liquid crystal component with a polar group,
nematic liquid crystal with a polar bonding group in the molecular
structure and nematic liquid crystal with a polar group as a
substituent can be used. For example, a liquid crystal ester
compound with an ester bonding group, a compound with a polar group
in the molecule such as a liquid crystal pyrimidine compound of a
pyrimidine structure, a liquid crystal tolan compound, a liquid
crystal ester compound, a liquid crystal pyrimidine compound or the
like which has a polar group such as a fluorine atom, a fluoroalkyl
group, a cyano group as a substituent can be named.
[0012] As the other component of the nematic liquid crystal, it is
preferred to use nematic liquid crystal with a low viscosity. For
example, a liquid crystal tolan compound with alkyl groups at both
ends, a liquid crystal phenylcyclohexane (PCH) compound with alkyl
groups at both ends, etc. can be named as the nematic liquid
crystal with a low viscosity. Further, a liquid crystal polycyclic
(tricyclic or more) compound with no polar groups may be added so
as to control the transition temperature to isotropic phase, or a
liquid crystal tolan compound with no polar groups or a liquid
crystal polycyclic compound may be added so as to control the
anisotropy of refractive index.
[0013] If the anisotropy of refractive index is too low, the
quantity of scattered light will be small. Consequently, coloring
in the planar state will be weak, and the reflectance will not be
sufficient. On the other hand, if the anisotropy of refractive
index is too high, the quantity of scattered light will be too
large, and the transparency or the black display in the focal-conic
state will be bad. Consequently, the display performance will be
poor. According to the present invention, the anisotropy of
refractive index is regulated to a value within a range from 0.1 to
0.22. Thereby, both the color portions and the transparent portions
are good in reflectance, and satisfactory contrast can be
obtained.
[0014] Also, the anisotropy of dielectric constant is regulated to
be not more than 30. Thereby, when a liquid crystal light
modulating device is fabricated by use of the liquid crystal
composition, the peripheral materials such as a sealing material
are prevented from diffusing into the liquid crystal, and the
reliability of the device can be improved. If the anisotropy of
dielectric constant is less than 5, a high driving voltage will be
necessary. If the transition temperature to isotropic phase of the
nematic liquid crystal is lower than 70.degree. C., the temperature
range which permits practical display performance will be narrow.
If the transition temperature to isotropic phase is higher than
150.degree. C., the liquid crystal will be crystallized easily by
addition of a chiral agent.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] These and other objects and features of the present
invention will be apparent from the following description with
reference to the accompanying drawings, in which:
[0016] FIG. 1 is composed of 1a and 1b which are sectional views of
a liquid crystal display as the first embodiment, FIG. 1a showing
the liquid crystal display in a planar state and FIG. 1b showing
the liquid crystal display in a focal-conic state;
[0017] FIG. 2 is a sectional view of a liquid crystal display as
the second embodiment; and
[0018] FIG. 3 is a sectional view of a liquid crystal display as
the third embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] Preferred embodiments of a liquid crystal composition and a
liquid crystal light modulating device according to the present
invention are described with reference to the accompanying
drawings.
Structure and Display Operation of the First Embodiment
[0020] FIG. 1 is a sectional view of a liquid crystal display
according to the first embodiment of the present invention. FIG. 1a
shows a planar state (RGB coloring state) in which a high pulse
voltage is applied to the liquid crystal display, and FIG. 1b shows
a focal-conic state (transparent/black display state) in which a
low pulse voltage is applied to the liquid crystal display. The
liquid crystal display has non-volatility, and the planar state and
the focal-conic state are maintained even after stoppage of the
application of the pulse voltage.
[0021] In FIG. 1, the numbers 11 and 12 are transparent substrates,
on which transparent electrodes 13 and 14 are formed, respectively.
The electrodes 13 and 14 are in the form of strips, and the
respective electrode strips 13 and 14 are arranged in parallel. The
extending direction of the electrode strips 13 and the extending
direction of the electrode strips 14 cross each other, and the
electrodes 13 and 14 face each other. It is preferred that an
insulating layer 15 is provided on the electrode strips 13. In
addition, on the reverse side of the substrate 12, a visible light
absorbing layer 16 is provided if necessary.
[0022] The number 20 is a columnar structure serving as a space
maintaining member, and the number 21 is a liquid crystal
composition which exhibits a cholesteric phase in a room
temperature. The materials of these members and combinations
thereof will be described later and further specific descriptions
will be made referring to examples. The number 24 denotes a seal
which is to seal the liquid crystal composition 21 between the
substrates 11 and 12. The number 25 denotes a pulse electric source
and applies a pulse voltage to the electrodes 13 and 14.
[0023] In the liquid crystal display of the above structure, a
display is made by application of a pulse voltage from the electric
source 25 to the electrodes 13 and 14. Specifically, if the liquid
crystal composition 21 is one which exhibits a cholesteric phase,
when a pulse voltage with comparatively high energy is applied
thereto, the liquid crystal comes to a planar state and selectively
reflects light of a wavelength determined by the cholesteric pitch
and the refractive index. When a pulse voltage with comparatively
low energy is applied, the liquid crystal comes to a focal-conic
state and becomes transparent. Each of the states is maintained
even after stoppage of the application of the voltage.
[0024] It has been found that an intermediate state between the
focal-conic state and the planar state exists, and by applying a
pulse voltage with medium energy to the liquid crystal, a display
with a medium tone is possible. In the intermediate state, the
focal-conic state and the planar state mix together, and this
intermediate state is maintained even after stoppage of the
application of the voltage. Further, as FIG. 1 shows, when the
visible light absorbing layer 16 is provided, a black display is
made in the focal-conic state.
[0025] In the liquid crystal display, the intersections of the
electrode strips 13 and 14 are display pixels. In the following
paragraphs, the area where light modulation is carried out by the
liquid crystal is referred to as display area, and the periphery of
the display area is a non-display area in which light modulation is
not carried out.
Substrate
[0026] At least one of the substrates 11 and 12 must be light
transmitting. For a transparent substrate, not only glass but also
flexible material such as polycarbonate, polyether sulfone,
polyethylene terephthalate, etc. can be used.
Electrode
[0027] For the electrodes 13 and 14, transparent conductive films
typically of ITO (indium tin oxide), metal such as aluminum,
silicone, etc., photoconductive films of amolphous silicone, BSO
(bismuth silicone oxide) etc. can be used. In order to form the
electrodes 13 and 14 in a matrix, for example, an ITO film is
formed on each of the substrates 11 and 12 by sputtering, and the
ITO film is patterned by photolithography.
Insulating Layer, Alignment Controlling Layer
[0028] The insulating layer 15 is an inorganic film of e.g.
silicone oxide or an organic film of e.g. polyimide resin, epoxy
resin, acrylic resin or urethane resin. The insulating layer 15
functions as a preventive of short-circuit between the electrodes
13 and 14 and as a gas barrier layer to improve the reliability of
the liquid crystal. Also, if polyimide resin or silicone resin is
used, the layer 15 also functions as an alignment controlling
layer. In addition, if a coloring agent is added, it will also
functions as a color filter. Further, the polymeric material which
is used for the columnar structure 20 can be used for the
insulating layer 15.
Spacers
[0029] Although they are not shown in the drawings, spacers may be
provided between the substrates 11 and 12. The spacers are
spherical and made of resin or inorganic oxide. The spacers are to
maintain the gap between the substrates 11 and 12 even. It is
possible to use the spherical spacers as a space maintaining member
instead of the columnar structure 20.
Liquid Crystal Composition
[0030] The liquid crystal composition is a chiral nematic liquid
crystal composition which is produced by adding a chiral agent at a
ratio within a range from 10 wt % to 45 wt % to nematic liquid
crystal which contains a nematic liquid crystal component with
large polarization at not less than 25 wt %, desirably 30 to 90 wt
%, and more desirably 45 to 80 wt % and of which transition
temperature to isotropic phase is within a range from 70.degree. C.
to 150.degree. C. The anisotropy of refractive index of the chiral
nematic liquid crystal composition is 0.10 to 0.22, and the
anisotropy of dielectric constant is 5 to 30. Further, a dye may be
added.
[0031] The wavelength to be selectively reflected by the liquid
crystal composition can be controlled by changing the content of
the chiral agent in the liquid crystal composition. In general, by
increasing the content of the chiral agent, the wavelength to be
reflected by the liquid crystal composition becomes shorter. The
wavelength to be selectively reflected by the liquid crystal
composition means the peak wavelength in the visible light
wavelength range of the reflectance spectrum in the planar state of
the liquid crystal realized by application of a high pulse voltage
to the electrodes 13 and 14.
[0032] The following general chemical formula (A) and specific
chemical formulas (A.sub.1) through (A.sub.2) show liquid crystal
tolan compounds which are usable as nematic liquid crystal. The
compounds shown by the chemical formulas (A.sub.21), (A.sub.31)
through (A.sub.33), (A.sub.39) through (A.sub.47), (A.sub.61)
through (A.sub.76), (A.sub.78), (A.sub.79), (A.sub.83) through
(A.sub.89), (A.sub.100) through (A.sub.106) correspond to nematic
liquid crystal with a polar group. 1
[0033] R: alkyl, alkenyl or a alkoxyl with one to ten crbons
[0034] X: fluorine or hydrogen
[0035] Y: cyclohexyl, bicyclohexyl or single bond
[0036] Z: fluorine, fluoroalkyl, cyano, or alkyl, alkenyl or
alkoxyl with one to ten carbons, or the group shown by the
following chemical formula 2
[0037] R.sub.1, R.sub.2: hydrogen, halogen or alkyl with one to ten
carbons
[0038] n: 1 or 2 3
[0039] The following general chemical formula (B) and specific
chemical formulas (B.sub.1) through (B.sub.84) show liquid crystal
ester compounds which are usable as nematic liquid crystal with a
polar group.
R.sub.3--A--Ar.sub.1--COO--Ar.sub.2--(R.sub.4).sub.n (B)
[0040] R.sub.3, R.sub.4: fluorne, fluoroalkyl, cyano, or alkyl,
alkenyl or alkoxyl with one to ten carbons
[0041] n: 1 or 2
[0042] A, Ar.sub.2: phenylene or cyrclohexyl
[0043] Ar.sub.1: cyclohexyl, phenylene or single bond 4
[0044] The following general chemical formula (C) and specific
chemical formulas (C.sub.1) through (C.sub.86) show liquid crystal
pyrimidine compounds which are usable as nematic liquid crystal
with a polar group. 5
[0045] A, A': single bond or phenylene except that both are
phenylene
[0046] R.sub.1, R.sub.2: hydrogen, fluorine, cyano or alkyl with
one to ten carbons except that both are hydrogen
[0047] n: integer from 2 to 10 6
[0048] Chiral nematic liquid crystal has an advantage of changing
the pitch of its helical structure by changing the content of the
chiral agent, whereby the wavelength to be reflected by the liquid
crystal can be controlled. In general, the pitch of the helical
structure of liquid crystal molecules is expressed by the term
"helical pitch" which is defined by the distance between molecules
which are at an angle of 360.degree. to each other along the
helical structure.
[0049] A chiral agent, when it is added to nematic liquid crystal,
twists molecules of the nematic liquid crystal. In other words, by
adding a chiral agent to nematic liquid crystal, the liquid crystal
molecules are arranged in a helical structure with a specified
twisting pitch, whereby the liquid crystal exhibits a cholesteric
phase.
[0050] Various well-known chiral agents, for example, biphenyl
compounds with an optically active group at an end, tarphenyl
compounds, ester compounds, pyrimidine compounds, azoxy compounds,
tolan compounds, etc. are usable as the chiral agent in this
embodiment. Also, cholesteric liquid crystal with a cholesteric
ring, of which typical example is cholesteric nonanolate, can be
used.
[0051] It is possible to add a plurality of chiral agents to
nematic liquid crystal. In such a case, the combination may be of
chiral agents of the same kind in optical rotatory power or may be
of chiral agents of different kinds in optical rotatory power. The
use of a combination of a plurality of chiral agents has advantages
of changing the transition temperature to isotropic phase of the
cholesteric liquid crystal, of reducing the variation of the
wavelength to be reflected in accordance with the temperature
change and of changing the properties, such as the anisotropy of
dielectric constant, the anisotropy of refractive index, the
viscosity, etc., of the cholesteric liquid crystal, i.e., of
improving the performance as a display. The content of the chiral
agent(s) is within a range from 10 wt % to 45 wt %, desirably 12 to
45 wt %, more desirably 15 to 45 wt % and further more desirably 20
to 40 wt %. If the content of the chiral agent(s) is 10 wt % or
less, the liquid crystal may not reflect light of the desirable
wavelength, and if the content of the chiral agent(s) is 45 wt % or
more, the liquid crystal may not exhibit a cholesteric phase and
may be solidified.
[0052] The following chemical formulas (D.sub.1) through (D.sub.6)
show exemplary chiral agents. 7
[0053] As the dye to be added, various well-known dyes can be used,
and ones which are compatible with liquid crystal are preferable.
For example, azo compounds, quinon compounds, anthraquinon
compounds, dichroic dyes, etc. are usable, and two or more of these
dyes can be used. The content of the dye(s) is preferably not more
than 3 wt %.
[0054] If a color filter is provided instead of adding one or more
dyes, the filter layer may be formed by adding a dye to a
transparent substance. The filter layer also may be a thin film of
a substance which is essentially colored or functions as a dye. It
is obvious that the same effect can be obtained merely by using
such a filter layer as one of the substrates.
Columnar Structure
[0055] First, the configuration of the columnar structure 20 is
described. The columnar structure 20 is composed of columns, for
example, cylinders, square poles or elliptic cylinders which are
arranged in a specified pattern such as a grating or stripes.
Preferably, the arrangement of the columns is not random. For
example, the columns may be arranged at uniform intervals, at
gradually changing intervals, in periodically repeating specified
patterns or the like. The arrangement is preferably such a type
which enables the substrates 11 and 12 to keep a suitable gap
between each other and will never be obstructive to image display.
If the columnar structure 20 occupies 1% to 40% of the display
area, the device can maintain sufficient strength and make
satisfactory performance as a display device.
[0056] Next, the material is described. The columnar structure 20
is made of a polymeric composition which is produced by adding a
polymerization initiator to polymeric monomer. The polymeric
composition is, for example, photosetting resin in the market which
is produced by mixing photosetting monomer or oligomer with a
photopolymerization initiator. A photopolymerization method in
which light is radiated to photosetting resin facilitates the
columnar structure 20 to be formed in a desired pattern. Materials
of which main components are acrylic ester compounds are especially
suited for the columnar structure 20. An acrylic ester compound is
an acrylate compound or a methacrylate compound which has two or
more allyl groups. It may contain an aromatic ring or the like in
the main chain between the allyl groups. Also, it may contain a
divalent group such as CO, CO.sub.2, CH.sub.2, O or the like in the
main chain. Further, epoxy acrylate compounds, urethane acrylate
compounds, etc. are included in acrylate compounds.
[0057] Next, the method of forming the columnar structure 20 is
described.
[0058] First, an ultraviolet-ray setting compound (columnar
structure composition) is filled between one of the substrates with
ITO electrodes thereon and a mask with a specified pattern.
Alternatively, an ultraviolet-ray setting compound is coated on the
ITO electrodes on one of the substrates, and a mask is covered
thereon. Then, ultraviolet rays are radiated. Next, the mask is
removed, and the compound is removed from the non-radiated portions
by a specified solvent. Then, the substrate is dried, so that the
compound is hardened to be made into a columnar structure.
[0059] Thereafter, the liquid crystal composition is filled between
the substrates which sandwich the columnar structure by a vacuum
injection method. Alternatively, the liquid crystal composition is
dropped on one of the substrates, and while the other substrate is
laid over and joined to the substrate, the liquid crystal
composition is spread between the substrates.
[0060] The following method is also possible: a mixture of a liquid
crystal material and a photosetting resin material is filled
between glass substrates; while a photomask is covered on one of
the substrates, light is radiated, so that the resin is polymerized
and separated from the liquid crystal. Thus, the resin part is
formed as the columnar structure 20.
[0061] Further, in order to regulate the gap between the substrates
more accurately, spacers with a smaller size than the thickness of
the resin, for example, glass fiber, ball glass, ceramic powder or
spherical particles of an organic material is/are arranged between
the substrates in forming the columnar structure. Thereby, the gap
between the substrates is hardly changed by heat and/or pressure,
and voltage unevenness, chromatic unevenness, etc. can be
prevented.
Structure of the Second Embodiment
[0062] FIG. 2 is a sectional view of a liquid crystal display as
the second embodiment of the present invention. FIG. 2 shows the
planar state (when a high pulse voltage is applied) of the liquid
crystal display. This liquid crystal display is basically the same
as the first embodiment shown by FIG. 1. In the second embodiment,
the columnar structure is not provided in the display area. In FIG.
2, the same members are provided with the same reference symbols as
in FIG. 1.
Structure of the Third Embodiment
[0063] FIG. 3 is a sectional view of a liquid crystal display as
the third embodiment of the present invention. FIG. 3 shows the
planar state (when a high pulse voltage is applied) of the liquid
crystal display. In this liquid crystal display, between the
substrates 11 and 12, a small columnar structure 20', of which
columns extend to the middle of the gap between the substrates 11
and 12, is formed. In FIG. 3, the same members are provided with
the same reference symbols as in FIG. 2.
Structure of the Fourth Embodiment
[0064] The fourth embodiment is a liquid crystal display which is
of the same structure as the first embodiment. In the fourth
embodiment, the columnar structure is formed by a screen printing
method.
[0065] In the screen printing method, a screen with a specified
pattern is covered on the electrodes on one of the substrates, and
a printing material (columnar structure composition) is laid on the
screen. Then, a squeegee is moved under a specified pressure, at a
specified angle and at a specified speed. Thereby, the material is
transferred onto the substrate through the pattern of the screen.
Next, the transferred material is heated to be hardened and is
dried.
[0066] In a case of forming a columnar structure in a screen
printing method, the resin material is not necessarily photosetting
resin, and thermosetting resin such as epoxy resin, acrylic resin,
etc. and thermoplastic resin can be used. As thermoplastic resin,
polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl
acetate resin, polyester methacrylate resin, polyester acrylate
resin, polystyrene resin, polyamide resin, polyethylene resin,
polypropyrene resin, fluororesin, polyurethane resin,
polyacrylonitrile resin, polyvinyl ether resin, polyvinyl keton
eresin, polyether resin, polyvinyl pyloridone resin, saturated
polyester resin, polycarbonate resin, polyether cholorine resin,
etc. can be named. It is preferred that such resin is used in a
state of paste, and the paste of resin can be obtained, for
example, by dissolving resin in a suitable solvent.
[0067] After the formation of the columnar structure on one of the
substrates by the above-described method, spacers are dispersed on
at least one of the substrates. Then, the two substrates are laid
on each other with the respective sides with electrodes thereon
facing each other, whereby a hollow cell is fabricated. The
laminated substrates are pressed from both sides and heated,
whereby the resin material of the columnar structure is softened,
and thereafter, the substrates are cooled, whereby the resin
material is hardened again.
Experimental Example 1
[0068] To a nematic liquid crystal mixture (which contains a
component with a polar group at 58 wt %) which contains the liquid
crystal ester compounds of the chemical formulas (B.sub.9),
(B.sub.10), (B.sub.11), (B.sub.12), (B.sub.13), (B.sub.65) and
(B.sub.66) at 58 wt % and of which transition temperature to
isotropic phase is 102.degree. C., the chiral agent of the chemical
formula (D.sub.6) and the chiral agent of the chemical formula
(D.sub.1) were added at 29.3 wt % and 3.3 wt %, respectively. Thus,
a liquid crystal composition which selectively reflects light of
550 nm was prepared. With respect to this chiral nematic liquid
crystal composition, the anisotropy of refractive index was 0.120;
the anisotropy of dielectric constant was 20; and the transition
temperature to isotropic phase was 90.degree. C. Spacers were
provided between glass substrates with electrodes thereon so that
the gap could be regulated to 7 .mu.m, and the liquid crystal
composition was filled between the substrates. Further, on the side
opposite the light incidence side, a light absorbing layer of black
was provided. In this way, a liquid crystal display of the
structure shown by FIG. 2 was produced.
[0069] In the liquid crystal display, when a pulse voltage of 60V
was applied between the electrodes for five milliseconds, the
liquid crystal came to a planar state (showed green). At that time,
the Y value was 17.8; the reflectance was 30%; and the color purity
was 78.9%. When a pulse voltage of 30V was applied for five
milliseconds, the liquid crystal came to a focal-conic state
(transparent), and the Y value was 2.38. Accordingly, the contrast
was 7.48.
[0070] The Y value (luminous reflectance) and the color purity
(excitation purity) were measured by use of a spectrocolorimeter
CM-3700d (made by Minolta Co., Ltd.) which has a white light
source. In the experimental examples and comparative examples
below, the same spectrocolorimeter was used.
Experimental Example 2
[0071] To a nematic liquid crystal mixture (which contains a
component with a polar group at 49 wt %) which contains the liquid
crystal pyrimidine compounds of the chemical formulas (C.sub.14),
(C.sub.22), (C.sub.23) and (C.sub.24) at 29 wt % and the liquid
crystal tolan compounds with a polar group of the chemical formulas
(A.sub.43), (A.sub.44) and (A.sub.45) at 20 wt % and of which
transition temperature to isotropic phase is 130.degree. C., the
chiral agent of the chemical formula (D.sub.3) and the chiral agent
of the chemical formula (D.sub.1) were added at 15.8 wt % and 17.5
wt %, respectively. Thus, a liquid crystal composition which
selectively reflects light of 550 nm was prepared. With respect to
this chiral nematic liquid crystal composition, the anisotropy of
refractive index was 0.215; the anisotropy of dielectric constant
was 8; and the transition temperature to isotropic phase was
75.degree. C. Spacers were provided between glass substrates with
electrodes thereon so that the gap could be regulated to 7 .mu.m,
and the liquid crystal composition was filled between the
substrates. Further, on the side opposite the light incidence side,
a light absorbing layer of black was provided. In this way, a
liquid crystal display of the structure shown by FIG. 2 was
produced.
[0072] In the liquid crystal display, when a pulse voltage of 80V
was applied between the electrodes for five milliseconds, the
liquid crystal came to a planar state (showed green). At that time,
the Y value was 25.11; the reflectance was 39%; and the color
purity was 72%. When a pulse voltage of 50V was applied for five
milliseconds, the liquid crystal came to a focal-conic state
(transparent), and the Y value was 2.5. Accordingly, the contrast
was 10.04.
Comparative Example 1
[0073] To a nematic liquid crystal mixture (which contains a
component with a polar group at 18 wt %) which contains the liquid
crystal ester compounds of the chemical formulas (B.sub.9),
(B.sub.10), (B.sub.11), (B.sub.12), (B.sub.13), (B.sub.65) and
(B.sub.66) at 18 wt % and of which transition temperature to
isotropic phase is 90.degree. C., the chiral agent of the chemical
formula (D.sub.5) and the chiral agent of the chemical formula
(D.sub.1) were added at 26 wt % and 3.6 wt %, respectively. Thus, a
liquid crystal composition which selectively reflects light of 550
nm was prepared. With this chiral nematic liquid crystal
composition, the anisotropy of referactive index was 0.154; the
anisotropy of dielectric constant was 7; and the transition
temperature to isotropic phase was 70.degree. C. Spacers were
provided between glass substrates with electrodes thereon so that
the gap could be regulated to 7 .mu.m, and the liquid crystal
composition was filled between the substrates. Further, on the side
opposite the light incidence side, a light absorbing layer of black
was provided. In this way, a liquid crystal display of the
structure shown by FIG. 2 was produced.
[0074] In the liquid crystal display, when a pulse voltage of 140V
was applied between the electrodes for five milliseconds, the
liquid crystal came to a planar state (showed green). At that time,
the Y value was 18.5; the reflectance was 24%; and the color purity
was 65%. When a pulse voltage of 90V was applied for five
milliseconds, the liquid crystal came to a focal-conic state
(transparent), and the Y value was 4.5. Accordingly, the contrast
was 4.11.
Experimental Example 3
[0075] To a nematic liquid crystal mixture (which contains a
component with a polar group at 49 wt %) which contains the liquid
crystal pyrimidine compounds of the chemical formulas (C.sub.14),
(C.sub.22), (C.sub.23) and (C.sub.24) at 29 wt % and the liquid
crystal tolan compounds with a polar group of the chemical formulas
(A.sub.43), (A.sub.44) and (A.sub.45) at 20 wt % and of which
transition temperature to isotropic phase is 130.degree. C., the
chiral agent of the chemical formula (D.sub.3) and the chiral agent
of the chemical formula (D.sub.2) were added at 17.8 wt % and 7.6
wt %, respectively. Thus, a liquid crystal composition which
selectively reflects light of 490 nm was prepared. With respect to
this chiral nematic liquid crystal composition, the anisotropy of
refractive index was 0.20; the anisotropy of dielectric constant
was 13.3; and the transition temperature to isotropic phase was
70.degree. C. Spacers were provided between glass substrates with
electrodes thereon so that the gap could be regulated to 5 .mu.m,
and the liquid crystal composition was filled between the
substrates. Further, on the side opposite the light incidence side,
a light absorbing layer of black was provided. In this way, a
liquid crystal display of the structure shown by FIG. 2 was
produced.
[0076] In the liquid crystal display, when a pulse voltage of 60V
was applied between the electrodes for five milliseconds, the
liquid crystal came to a planar state (showed blue). At that time,
the Y value was 9.56; the reflectance was 30%; and the color purity
was 59.6%. When a pulse voltage of 35V was applied for five
milliseconds, the liquid crystal came to a focal-conic state
(transparent), and the Y value was 2.35. Accordingly, the contrast
was 4.07.
Comparative Example 2
[0077] To a nematic liquid crystal mixture (which contains a
component with a polar group at 58 wt %) which contains the liquid
crystal ester compounds of the chemical formulas (B.sub.9),
(B.sub.10), (B.sub.11), (B.sub.12), (B.sub.13), (B.sub.65) and
(B.sub.66) at 58 wt % and of which transition temperature to
isotropic phase is 102.degree. C., the chiral agent of the chemical
formula (D.sub.6) and the chiral agent of the chemical formula
(D.sub.1) were added at 32.5 wt % and 2.9 wt %, respectively. Thus,
a liquid crystal composition which selectively reflects light of
480 nm was prepared. With this chiral nematic liquid crystal
composition, the anisotropy of referactive index was 0.090; the
anisotropy of dielectric constant was 15; and the transition
temperature to isotropic phase was 80.degree. C. Spacers were
provided between glass substrates with electrodes thereon so that
the gap could be regulated to 5 .mu.m, and the liquid crystal
composition was filled between the substrates. Further, on the side
opposite the light incidence side, a light absorbing layer of black
was provided. In this way, a liquid crystal display of the
structure shown by FIG. 2 was produced.
[0078] In the liquid crystal display, when a pulse voltage of 50V
was applied between the electrodes for five milliseconds, the
liquid crystal came to a planar state (showed blue). At that time,
the Y value was 5.54; the reflectance was 22%; and the color purity
was 63.2%. When a pulse voltage of 30V was applied for five
milliseconds, the liquid crystal came to a focal-conic state
(transparent), and the Y value was 2.0. Accordingly, the contrast
was 2.77.
Comparative Example 3
[0079] To a nematic liquid crystal mixture (which contains a
component with a polar group at 54 wt %) which contains the liquid
crystal pyrimidine compounds of the chemical formulas (C.sub.8),
(C.sub.16), (C.sub.22), (C.sub.23) and (C.sub.24) at 27 wt % and of
which transition temperature to isotropic phase is 68.degree. C.,
the chiral agent of the chemical formula (D.sub.4) and the chiral
agent of the chemical formula (D.sub.1) were added 18.2 wt % and 17
wt %, respectively. Thus, a liquid crystal composition which
selectively reflects light of 490 nm was prepared. With respect to
this chiral nematic liquid crystal composition, the anisotropy of
refractive index was 0.168; the anisotropy of dielectric constant
was 3.8; and the transition temperature to isotropic phase was
50.degree. C. Spacers were provided between glass substrates with
electrodes thereon so that the gap could be regulated to 5 .mu.m,
and the liquid crystal composition was filled between the
substrates. Further, on the side opposite the light incidence side,
a light absorbing layer of black was provided. In this way, a
liquid crystal display of the structure shown by FIG. 2 was
produced.
[0080] In the liquid crystal display, when a pulse voltage of 120V
was applied between the electrodes for five milliseconds, the
liquid crystal came to a planar state (showed blue). At that time,
the Y value was 8.2; the reflectance was 29.7%; and the color
purity was 59%. When a pulse voltage of 60V was applied for five
milliseconds, the liquid crystal came to a focal-conic state
(transparent), and the Y value was 2.34 Accordingly, the contrast
was 3.5.
Experimental Example 4
[0081] To a nematic liquid crystal mixture (which contains a
component with a polar group at 45 wt %) which contains the liquid
crystal pyrimidine compounds of the chemical formulas (C.sub.14),
(C.sub.22) and (C.sub.23) at 21 wt % and the liquid crystal tolan
compounds with a polar group of the chemical formulas (A.sub.43)
and (A.sub.44) at 24 wt % and of which transition temperature to
isotropic phase is 94.degree. C., the chiral agent of the chemical
formula (D.sub.3) and the chiral agent of the chemical formula
(D.sub.2) were added at 17 wt % and 5 wt %, respectively. Thus, a
liquid crystal composition which selectively reflects light of 680
nm was prepared. With respect to this chiral nematic liquid crystal
composition, the anisotropy of refractive index was 0.2; the
anisotropy of dielectric constant was 8; and the transition
temperature to isotropic phase was 70.degree. C. Spacers were
provided between glass substrates with electrodes thereon so that
the gap could be regulated to 7 .mu.m, and the liquid crystal
composition was filled between the substrates. Further, on the side
opposite the light incidence side, a light absorbing layer of black
was provided. In this way, a liquid crystal display of the
structure shown by FIG. 2 was produced.
[0082] In the liquid crystal display, when a pulse voltage of 80V
was applied between the electrodes for five milliseconds, the
liquid crystal came to a planar state (showed red). At that time,
the Y value was 6.04; the reflectance was 31.5%; and the color
purity was 79%. When a pulse voltage of 50V was applied for five
milliseconds, the liquid crystal came to a focal-conic state
(transparent), and the Y value was 1.22. Accordingly, the contrast
was 4.95.
Experimental Example 5
[0083] To a nematic liquid crystal mixture (which contains a
component with a polar group at 66 wt %) which contains the liquid
crystal pyrimidine compounds of the chemical formulas (C.sub.14),
(C.sub.22), (C.sub.23) and (C.sub.24) at 27 wt % and the liquid
crystal tolan compounds with a polar group of the chemical formulas
(A.sub.43), (A.sub.44) and (A.sub.46), (A.sub.85), (A.sub.86) and
(A.sub.87) at 39 wt % and of which transition temperature to
isotropic phase is 122.degree. C., the chiral agent of the chemical
formula (D.sub.3) and the chiral agent of the chemical formula
(D.sub.1) were added at 12.3 wt % and 14.4 wt %, respectively..
Thus, a liquid crystal composition which selectively reflects light
of 680 nm was prepared. With respect to this chiral nematic liquid
crystal composition, the anisotropy of refractive index was 0.18;
the anisotropy of dielectric constant was 8; and the transition
temperature to isotropic phase was 75.degree. C. Spacers were
provided between glass substrates with electrodes thereon so that
the gap could be regulated to 7 .mu.m, and the liquid crystal
composition was filled between the substrates. Further, a color
filter was provided on the light incidence side, and a light
absorbing layer of black was provided on the opposite side. In this
way, a liquid crystal display of the structure shown by FIG. 2 was
produced.
[0084] In the liquid crystal display, when a pulse voltage of 80V
was applied between the electrodes for five milliseconds, the
liquid crystal came to a planar state (showed red). At that time,
the Y value was 6; the reflectance was 32.5%; and the color purity
was 80.5%. When a pulse voltage of 50V was applied for five
milliseconds, the liquid crystal came to a focal-conic state
(transparent), and the Y value was 1.22. Accordingly, the contrast
was 4.91.
Experimental Example 6
[0085] To a nematic liquid crystal mixture (which contains a
component with a polar group at 80 wt %) which contains the liquid
crystal ester compounds of the chemical formulas (B.sub.21),
(B.sub.22), (B.sub.23), (B.sub.24), (B.sub.27) and (B.sub.28) at 52
wt % and the liquid crystal tolan compounds with a polar group of
the chemical formulas (A.sub.43), (A.sub.44) and (A.sub.46) at 28
wt % and of which transition temperature to isotropic phase is
104.degree. C., the chiral agent of the chemical formula (D.sub.3)
and the chiral agent of the chemical formula (D.sub.2) were added
at 8.8 wt % and 3.2 wt %, respectively. Thus, a liquid crystal
composition which selectively reflects light of 680 nm was
prepared. With respect to this chiral nematic liquid crystal
composition, the anisotropy of refractive index was 0.190; the
anisotropy of dielectric constant was 28; and the transition
temperature to isotropic phase was 80.degree. C. Spacers were
provided between glass substrates with electrodes thereon so that
the gap could be regulated to 7 .mu.m, and the liquid crystal
composition was filled between the substrates. Further, a color
filter was provided on the light incidence side, and a light
absorbing layer of black was provided on the opposite side. In this
way, a liquid crystal display of the structure shown by FIG. 2 was
produced.
[0086] In the liquid crystal display, when a pulse voltage of 60V
was applied between the electrodes for five milliseconds, the
liquid crystal came to a planar state (showed red). At that time,
the Y value was 6.28; the reflectance was 33%; and the color purity
was 83%. When a pulse voltage of 35V was applied for five
milliseconds, the liquid crystal came to a focal-conic state
(transparent), and the Y value was 1.19. Accordingly, the contrast
was 5.28.
Comparative Example 4
[0087] To a nematic liquid crystal mixture (which contains a
component with a polar group at 18 wt %) which contains the liquid
crystal tolan compounds with a polar group of the chemical formulas
(A.sub.21), (A.sub.61) and (A.sub.63) at 18 wt % and of which
transition temperature to isotropic phase is 95.degree. C., the
chiral agent of the chemical formula (D.sub.3) and the chiral agent
of the chemical formula (D.sub.2) were added at 10.9 wt % and 4.6
wt %, respectively. Thus, a liquid crystal composition which
selectively reflects light of 680 nm was prepared. With respect to
this chiral nematic liquid crystal composition, the anisotropy of
refractive index was 0.25; the anisotropy of dielectric constant
was 6.3; and the transition temperature to isotropic phase was
70.degree. C. Spacers were provided between glass substrates with
electrodes thereon so that the gap could be regulated to 7 .mu.m,
and the liquid crystal composition was filled between the
substrates. Further, a color filter was provided on the light
incidence side, and a light absorbing layer of black was provided
on the opposite side. In this way, a liquid crystal display of the
structure shown by FIG. 2 was produced.
[0088] In the liquid crystal display, when a pulse voltage of 120V
was applied between the electrodes for five milliseconds, the
liquid crystal came to a planar state (showed red). At that time,
the Y value was 5.95; the reflectance was 25%; and the color purity
was 81.9%. When a pulse voltage of 80V was applied for five
milliseconds, the liquid crystal came to a focal-conic state
(transparent), and the Y value was 1.75. Accordingly, the contrast
was 3.4.
Comparative Example 5
[0089] To a nematic liquid crystal mixture which contains the
liquid crystal tolan compounds with no polar groups of the chemical
formulas (A.sub.12), (A.sub.24) and (A.sub.38) at 100 wt % and of
which transition temperature to isotropic phase is 65.degree. C.,
the chiral agent of the chemical formula (D.sub.3) and the chiral
agent of the chemical formula (D.sub.6) were added at 12.5 wt % and
5 wt %, respectively. Thus, a liquid crystal composition which
selectively reflects light of 680 nm was prepared. With respect to
this chiral nematic liquid crystal composition, the anisotropy of
refractive index was 0.235; the anisotropy of dielectric constant
was 0 (could not measured); and the transition temperature to
isotropic phase was 50.degree. C. Spacers were provided between
glass substrates with electrodes thereon so that the gap could be
regulated to 7 .mu.m, and the liquid crystal composition was filled
between the substrates. Further, a color filter was provided on the
light incidence side, and a light absorbing layer of black was
provided on the opposite side. In this way, a liquid crystal
display of the structure shown by FIG. 2 was produced.
[0090] In the liquid crystal display, even when a pulse voltage was
applied between the electrodes, any change did not occur to the
liquid crystal.
Experimental Example 7
[0091] To a nematic liquid crystal mixture (which contains a
component with a polar group at 32 wt %) which contains the liquid
crystal tolan compounds with no polar groups of the chemical
formulas (A.sub.1), (A.sub.2), (A.sub.4), (A.sub.7), (A.sub.8),
(A.sub.48), (A.sub.49) and (A.sub.5) at 35 wt %, the liquid crystal
tolan compounds with a polar group of the chemical formulas
(A.sub.43), (A.sub.44) and (A.sub.45) at 15 wt % and the liquid
crystal pyrimidine compounds of the chemical formulas (C.sub.14),
(C.sub.22) and (C.sub.23) at 17 wt % and of which transition
temperature to isotropic phase is 97.degree. C., the chiral agent
of the chemical formula (D.sub.3) and the chiral agent of the
chemical formula (D.sub.1) were added at 12.8 wt % and 14.3 wt %,
respectively. Thus, a liquid crystal composition which selectively
reflects light of 680 nm was prepared. With respect to this chiral
nematic liquid crystal composition, the anisotropy of refractive
index was 0.198; the anisotropy of dielectric constant was 6.8; and
the transition temperature to isotropic phase was 70.degree. C.
Further, a dichroic dye SI426 (made by Mitsui Toatsu Co., Ltd.) was
mixed in the liquid crystal composition at 0.5 wt %. Spacers were
provided between glass substrates with electrodes thereon so that
the gap could be regulated to 7 .mu.m, and the liquid crystal
composition was filled between the substrates. Further, a light
absorbing layer of black was provided on the side opposite the
light incidence side. In this way, a liquid crystal display of the
structure shown by FIG. 2 was produced.
[0092] In the liquid crystal display, when a pulse voltage of 95V
was applied between the electrodes for five milliseconds, the
liquid crystal came to a planar state (showed red). At that time,
the Y value was 6.22; the reflectance was 32.5%; and the color
purity was 79%. When a pulse voltage of 60V was applied for five
milliseconds, the liquid crystal came to a focal-conic state
(transparent), and the Y value was 1.36. Accordingly, the contrast
was 4.57.
[0093] Although the present invention has been described in
connection with the preferred embodiments above, it is to be noted
that various changes and modifications are possible to those who
are skilled in the art. Such changes and modifications are to be
understood as being within the present invention.
* * * * *