U.S. patent application number 11/512166 was filed with the patent office on 2006-12-28 for process of producing optical element and optical element.
This patent application is currently assigned to Dai Nippon Printing Co., Ltd.. Invention is credited to Kouji Ishizaki, Masanori Umeya.
Application Number | 20060292296 11/512166 |
Document ID | / |
Family ID | 19141480 |
Filed Date | 2006-12-28 |
United States Patent
Application |
20060292296 |
Kind Code |
A1 |
Ishizaki; Kouji ; et
al. |
December 28, 2006 |
Process of producing optical element and optical element
Abstract
A liquid crystal layer is formed on an alignment substrate 13 by
the use of a photo-curing chiral nematic liquid crystal having
cholesteric regularity, or the like, and liquid crystalline
molecules in the liquid crystal layer are aligned by the
alignment-regulating action of the alignment substrate 13. A
predetermined amount of radiation 20 is applied to the liquid
crystal layer formed on the alignment substrate 13 to
three-dimensionally cross-link and cure the liquid crystal layer,
thereby forming a cholesteric layer 12 in the semi-cured state.
Thereafter, the semi-cured cholesteric layer 12 formed on the
alignment substrate 13 is brought into contact with an organic
solvent 21 under the specific conditions. There is thus finally
obtained an optical element 10 comprising the cholesteric layer 12
formed on the alignment substrate 13.
Inventors: |
Ishizaki; Kouji; (Tokyo-To,
JP) ; Umeya; Masanori; (Tokyo-To, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
Dai Nippon Printing Co.,
Ltd.
Tokyo-To
JP
|
Family ID: |
19141480 |
Appl. No.: |
11/512166 |
Filed: |
August 30, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10274373 |
Oct 21, 2002 |
7118795 |
|
|
11512166 |
Aug 30, 2006 |
|
|
|
Current U.S.
Class: |
427/162 ;
427/331; 427/487 |
Current CPC
Class: |
Y10T 428/10 20150115;
G02B 5/3016 20130101; C09K 2323/00 20200801; Y10T 428/24479
20150115 |
Class at
Publication: |
427/162 ;
427/487; 427/331 |
International
Class: |
B05D 5/06 20060101
B05D005/06; B05D 1/40 20060101 B05D001/40; C08F 2/46 20060101
C08F002/46; B05D 3/00 20060101 B05D003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 23, 2001 |
JP |
2001-324808 |
Claims
1. A process of producing an optical element, comprising: the first
step of forming a radiation-curing liquid crystal layer having
cholesteric regularity on an alignment substrate having an aligning
function; the second step of applying a predetermined amount of
radiation to the liquid crystal layer formed on the alignment
substrate to cure the liquid crystal layer, thereby forming a
cholesteric layer in the semi-cured state; and the third step of
bringing the semi-cured cholesteric layer formed on the alignment
substrate into contact with an organic solvent; wherein the amount
of radiation to be applied to the liquid crystal layer in the
second step is changed to control a selective reflection wave range
of the cholesteric layer.
2. The process according to claim 1, wherein the radiation is
applied, in the second step, in different amounts to different
regions on the surface of the liquid crystal layer so that these
regions can have different selective reflection wave ranges.
3. The process according to claim 1, wherein the radiation to be
applied to the liquid crystal layer in the second step is light
selected from the group consisting of ultraviolet light, an
electron beam, visible light and infrared light.
4. The process according to claim 1, wherein the liquid crystal
layer formed in the first step comprises a chiral nematic liquid
crystal obtained by adding a chiral agent to a nematic liquid
crystal.
5. A process of producing an optical element, comprising: the first
step of forming a first radiation-curing liquid crystal layer
having cholesteric regularity on an alignment substrate having an
aligning function; the second step of applying a predetermined
amount of radiation to the first liquid crystal layer formed on the
alignment substrate to cure the first liquid crystal layer, thereby
forming a first cholesteric film in the semi-cured state; the third
step of bringing the semi-cured first cholesteric film formed on
the alignment substrate into contact with an organic solvent; the
fourth step of forming a second radiation-curing liquid crystal
layer having cholesteric regularity on the first cholesteric film
that has been brought into contact with the organic solvent; the
fifth step of applying a predetermined amount of radiation to the
second liquid crystal layer formed on the first cholesteric film to
cure the second liquid crystal layer, thereby forming a second
cholesteric film in the semi-cured state; and the sixth step of
bringing the semi-cured second cholesteric film formed on the first
cholesteric film into contact with an organic solvent; wherein the
amount of radiation to be applied to the first or second liquid
crystal layer in the second or fifth step is changed to control a
selective reflection wave range of the first or second cholesteric
film.
6. The process according to claim 5, wherein the radiation to be
applied to the first and second liquid crystal layer in the second
and fifth steps is light selected from the group consisting of
ultraviolet light, an electron beam, visible light and infrared
light.
7. The process according to claim 5, wherein the first and second
liquid crystal layers formed in the first and fourth steps comprise
a chiral nematic liquid crystal obtained by adding a chiral agent
to a nematic liquid crystal.
Description
[0001] This is a Divisional of application Ser. No. 10/274,373
filed Oct. 21, 2002. The entire disclosure of the prior application
is hereby incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a process of producing an
optical element such as a circular-polarization-controlling
element, and particularly relates to a process of producing an
optical element by the use of a radiation-curing liquid crystalline
material having cholesteric regularity, and to an optical
element.
[0004] 2. Description of Related Art
[0005] Optical elements comprising liquid crystal layers having
cholesteric regularity (cholesteric layers) are widely used as
circular-polarization-controlling elements (circularly polarizing
plates, color filters, etc.) for use in liquid crystal
displays.
[0006] To produce an optical element, such as a circularly
polarizing plate that reflects all visible light, a reflection-type
color filter on which each pixel is composed of regions having
selective reflection wave ranges equal to the wave ranges of red
(R), green (G) and blue (B) colors, or an optical element that is
used in a transmission or semi-transmission liquid crystal display
in order to improve light utilization efficiency, it is necessary
to form a cholesteric layer having a broadened selective reflection
wave range or a cholesteric layer having selective reflection wave
ranges controlled to be equal to the wave ranges of red, green and
blue colors. For this reason, there has been demanded a method of
controlling the selective reflection wave range of a cholesteric
layer with ease and high precision.
[0007] To fulfil this demand, the following methods have been
proposed so far: (1) a method in which optically active groups
composing the cholesteric structure of a cholesteric layer are
modified or deactivated to change the selective reflection wave
range of the cholesteric layer (Japanese Laid-Open Patent
Publication No. 54905/1998), and (2) a method in which a liquid
crystal layer having cholesteric regularity is brought into contact
with a solvent or solvent mixture to broaden its selective
reflection wave range (Japanese Laid-Open Patent Publication No.
316755/1998).
[0008] However, the above two methods are disadvantageous as
described below. In the method (1), in which optically active
groups in a cholesteric layer are modified or deactivated, the
modified or deactivated molecules become impurities to lower the
stability of the cholesteric layer itself. If such a cholesteric
layer is incorporated into a liquid crystal display, the display
cannot clearly display an image. With the method (2), on the other
hand, only a cholesteric layer having lowered intensity of color is
obtained. If such a cholesteric layer is incorporated into a liquid
crystal display, the display cannot clearly display an image.
SUMMARY OF THE INVENTION
[0009] The present invention was accomplished in the light of the
aforementioned drawbacks in the related art. An object of the
present invention is therefore to provide a process of producing an
optical element, which makes it possible to control the selective
reflection wave range of a cholesteric layer with ease and high
precision and to easily produce an optical element excellent in
both optical stability and intensity of color, suitable for a
liquid crystal display or the like; and an optical element.
[0010] A first aspect of the present invention is a process of
producing an optical element, comprising the steps of: forming a
radiation-curing liquid crystal layer having cholesteric regularity
on an alignment substrate having an aligning function; applying a
predetermined amount of radiation to the liquid crystal layer
formed on the alignment substrate to cure the liquid crystal layer,
thereby forming a cholesteric layer in the semi-cured state; and
bringing the semi-cured cholesteric layer formed on the alignment
substrate into contact with an organic solvent; wherein the amount
of radiation to be applied to the liquid crystal layer is changed
to control the selective reflection wave range of the cholesteric
layer.
[0011] A second aspect of the present invention is a process of
producing an optical element, comprising the steps of: forming a
first radiation-curing liquid crystal layer having cholesteric
regularity on an alignment substrate having an aligning function;
applying a predetermined amount of radiation to the first liquid
crystal layer formed on the alignment substrate to cure the first
liquid crystal layer, thereby forming a first cholesteric film in
the semi-cured state; bringing the semi-cured first cholesteric
film formed on the alignment substrate into contact with an organic
solvent; forming a second radiation-curing liquid crystal layer
having cholesteric regularity on the first cholesteric film that
has been brought into contact with the organic solvent; applying a
predetermined amount of radiation to the second liquid crystal
layer formed on the first cholesteric film to cure the second
liquid crystal layer, thereby forming a second cholesteric film in
the semi-cured state; and bringing the semi-cured second
cholesteric film formed on the first cholesteric film into contact
with an organic solvent; wherein the amount of radiation to be
applied to the first and/or second liquid crystal layer is changed
to control the selective reflection wave range of the first and/or
second cholesteric film.
[0012] According to the first aspect of the present invention, the
selective reflection wave range of the cholesteric layer can be
controlled by varying the amount of radiation to be applied to the
liquid crystal layer formed on the alignment substrate, so that it
is possible to control the selective reflection wave range of the
cholesteric layer with ease and high precision. It is therefore
possible to easily produce an optical element that comprises a
cholesteric layer having the desired selective reflection wave
range and that is excellent in both optical stability and intensity
of color.
[0013] According to the second aspect of the present invention, the
selective reflection wave ranges of the plurality of cholesteric
films that constitute the cholesteric layer can be controlled by
varying the amount of radiation to be applied to the liquid crystal
layer formed on the alignment substrate or on the first cholesteric
film, so that it is possible to control the selective reflection
wave ranges of the plurality of cholesteric films with ease and
high precision. It is therefore possible to easily produce an
optical element that comprises a cholesteric layer composed of a
laminate of a plurality of cholesteric films having different
selective reflection wave ranges and that is excellent in both
optical stability and intensity of color.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] In the drawings,
[0015] FIG. 1 is a cross-sectional view illustrating an optical
element according to a first embodiment of the present
invention;
[0016] FIG. 2 is a view illustrating an example of a process of
producing the optical element shown in FIG. 1;
[0017] FIG. 3 is a diagram showing the selective reflection wave
ranges of cholesteric layers before and after bringing them into
contact with an organic solvent;
[0018] FIG. 4 is a view illustrating another example of a process
of producing the optical element shown in FIG. 1;
[0019] FIG. 5 is a cross-sectional view illustrating an optical
element according to a second embodiment of the present
invention;
[0020] FIG. 6 is a diagram showing the selective reflection wave
range of a cholesteric layer composed of a laminate of a plurality
of cholesteric films;
[0021] FIG. 7 is a view illustrating an example of a process of
producing the optical element shown in FIG. 5;
[0022] FIG. 8 is a diagram showing the selective reflection wave
ranges of the cholesteric layers in Example 1 before and after
bringing them into contact with an organic solvent;
[0023] FIG. 9 is a diagram showing the selective reflection wave
ranges of the cholesteric layers in Example 2 before and after
bringing them into contact with an organic solvent; and
[0024] FIG. 10 is a diagram showing the selective reflection wave
range of the cholesteric layer in Example 3, composed of a laminate
of two cholesteric films.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0025] By referring to the accompanying drawings, embodiments of
the present invention will be described hereinafter.
First Embodiment
[0026] First of all, an optical element according to a first
embodiment of the present invention will be described.
[0027] As shown in FIG. 1, an optical element 10 according to the
first embodiment of the present invention is composed of: an
alignment substrate 13 prepared by conducting alignment treatment;
and a cholesteric layer 12 laminated to the alignment substrate
13.
[0028] The cholesteric layer 12 is made from a radiation-curing
liquid crystalline material having cholesteric regularity, and has
the polarized-light-separating property, that is, the property of
separating a component circularly polarized in one direction from a
component circularly polarized in the opposite direction according
to the physical orientation (planar orientation) of liquid
crystalline molecules in the liquid crystalline material. Namely,
light entering into the cholesteric layer 12 along the helical axis
of the planar orientation is split into right-handed circularly
polarized component and left-handed circularly polarized component;
one of these circularly polarized components is transmitted and the
other one is reflected. This phenomenon is widely known as circular
dichroism. If the direction of rotation of the circularly
polarizing component is selected properly in terms of the direction
of incident light, only a circularly polarized component rotated in
the same direction as that of the helical axis of the cholesteric
layer 12 is selectively reflected. Notes that the chiral pitch of
liquid crystalline molecules in the cholesteric layer 12 determines
the center wavelength of the selective reflection wave range of the
cholesteric layer 12.
[0029] It is preferable to use, as the liquid crystalline material
for forming the cholesteric layer 12, a cholesteric liquid crystal
(chiral nematic liquid crystal) obtained by adding a chiral agent
to a nematic liquid crystal (see Japanese Laid-Open Patent
Publication No. 345160/2000). It is preferable that both the
nematic liquid crystal and chiral agent in the liquid crystalline
material have polymerizable groups or groups containing
polymerizable groups. It is also preferable that a
photopolymerization initiator be added to the liquid crystalline
material.
[0030] Specifically, a liquid crystal containing a compound
represented by the following chemical formula (1): ##STR1## and a
compound represented by the following chemical formula (2):
##STR2## in a weight ratio between 99:1 and 50:50 can be used as
the nematic liquid crystal. In the above chemical formulas (1) and
(2), R.sup.1, R.sup.2 and R.sup.3 independently represent hydrogen
or methyl group; X represents hydrogen, chlorine, bromine, iodine,
an alkyl group having 1 to 4 carbon atoms, methoxy group, cyano
group or nitro group; and a, b and c are an integer of 2 to 12.
[0031] Further, it is preferable to use, as the chiral agent, a
compound represented by the following chemical formula (3) or (4):
##STR3## or achiral dopant-added liquid crystal "S-811"
(manufactured by Merck KGaA, Germany). In the above chemical
formulas (3) and (4), R.sup.4 represents hydrogen or methyl group;
d and e are an integer of 2 to 12; and Y represents a divalent
group selected from the following groups (i) to (xxiv): ##STR4##
##STR5##
[0032] Next, by referring to FIGS. 2(a), 2(b) and 2(c), a process
of producing the optical element 10 according to the first
embodiment of the present invention, having the above-described
constitution, will be described.
[0033] A glass substrate provided with a polyimide (PI) film that
has been subjected to rubbing treatment, a supporting film having
the function of aligning liquid crystalline molecules, or the like
is prepared as the alignment substrate 13 prepared by conducting
alignment treatment. On top of this alignment substrate 13, a
liquid crystal layer is formed by the use of a radiation-curing
liquid crystal having cholesteric regularity (a photo-curing chiral
nematic liquid crystal, or the like). Liquid crystalline molecules
in the liquid crystal layer are aligned by the alignment-regulating
action of the alignment substrate 13, where the liquid crystal
layer is subjected to heat treatment, if necessary. A predetermined
amount of radiation 20 is applied to the liquid crystal layer
formed on the alignment substrate 13 to three-dimensionally
cross-link and cure the liquid crystal layer. A cholesteric layer
12 in the semi-cured state is thus formed (FIG. 2(a)). The
radiation 20 herein used is to induce photopolymerization reaction
or the like in the radiation-curing liquid crystal, and ultraviolet
light, an electron beam, visible light, infrared light (heat rays),
or the like can be used as the radiation. In the case where
ultraviolet light is used to cure the liquid crystal, it is
preferable to add a photopolymerization initiator in the liquid
crystalline material beforehand. The amount of the radiation 20 to
be applied varies depending on whether the photopolymerization
initiator has been added or not, or on the amount of the
photopolymerization initiator added or the type of the radiation to
be applied. It is, however, preferable to apply the radiation 20 in
an amount of approximately 0.01 to 10000 mJ/cm.sup.2, for example.
By "three-dimensional crosslinking" is herein meant that a
photo-curing monomer, oligomer or polymer is three-dimensionally
polymerized to give a network structure. If such a network
structure is formed, the state of the liquid crystalline material
from which the cholesteric layer 12 has been formed is optically
fixed; and a film that is easy to handle as an optical film and
that is stable at normal temperatures can be obtained.
[0034] Examples of supporting films that can be used for the
alignment substrate 13 include films of plastics such as polyimide,
polyamideimide, polyamide, polyether imide, polyether ether ketone,
polyether ketone, polyketone sulfide, polyether sulfone,
polysulfone, polyphenylene sulfide, polyphenylene oxide,
polyethylene terephthalate, polybutylene terephthalate,
polyethylene naphthalate, polyacetal, polycarbonate, polyacrylate,
acrylic resins, polyvinyl alcohol, polypropylene, cellulose,
triacetyl cellulose, partially saponified triacetyl cellulose,
epoxy resins, and phenol resins. These plastic films may be used as
a laminate of two or more films and also as uniaxially or biaxially
oriented ones. The supporting film may be treated in advance to
make its surface hydrophilic or hydrophobic. Although it may not be
necessary to separately impart the function of aligning liquid
crystalline molecules to the supporting film depending on the
composition of the liquid crystal contained in the liquid
crystalline material, it is preferable to impart this function to
the supporting film before applying the liquid crystalline material
to the supporting film. To impart the function of aligning liquid
crystalline molecules, an alignment layer is laminated to the
supporting film, or the supporting film or the alignment layer
laminated to the supporting film is rubbed. It is also possible to
impart this function to the supporting film by obliquely depositing
silicon oxide on the supporting film. Polyimide, polyamide,
polyvinyl alcohol or the like is usually used for forming the
alignment layer. Rubbing treatment is usually carried out in the
following manner: a rubbing cloth made from rayon, cotton,
polyamide, or the like is wrapped around a metallic roll, and this
roll is rotated with its surface in contact with a film of
polyimide or the like, or a film of polyimide or the like is
conveyed with the roll fixed, thereby rubbing the film surface with
the rubbing cloth.
[0035] Thereafter, the cholesteric layer 12 in the semi-cured
state, formed on the alignment substrate 13, is brought into
contact with an organic solvent 21 (FIG. 2 (b)). To bring the
cholesteric layer 12 into contact with the organic solvent 21, a
variety of development methods such as immersion and spin shower,
as well as various of coating methods such as spin coating, die
coating and cast coating may be adopted. In this process, uncured
portions of the semi-cured cholesteric layer 12 are extracted;
extracted herein are uncured portions of both the nematic liquid
crystal and chiral agent, which are the chief components of the
cholesteric layer 12. When a smaller amount of ultraviolet light is
applied to the cholesteric layer 12, a larger part of the
cholesteric layer 12 remains uncured, and vice versa. [Therefore,
in the case where the semi-cured cholesteric layer 12 formed by the
application of a small amount of radiation 20 is brought into
contact with an organic solvent, uncured portions of the
cholesteric layer 12 are extracted in a large amount, and the
cholesteric layer 12 is entirely thinned. As a result, the chiral
pitch becomes short, and the selective reflection wave range is
shifted to the shorter wavelength side. The degree of shift in
wavelength thus varies depending upon the state of curing
(proportion of uncured portions) of the cholesteric layer 12,
regardless of the conditions under which the cholesteric layer 12
is brought into contact with an organic solvent, and the selective
reflection wave range of the cholesteric layer 12 is controlled by
the degree of this shift (see FIG. 3).]
[0036] Any organic solvent can be used as the organic solvent 21 in
the above process as long as it can dissolve the cholesteric layer
12. Specific examples of such organic solvents include:
hydrocarbons such as benzene, toluene, xylene, n-butyl benzene,
diethyl benzene and tetralin; ethers such as methoxybenzene,
1,2-dimethoxybenzene and diethylene glycol dimethyl ether; ketones
such as acetone, methyl ethyl ketone, methyl isobutyl ketone,
cydlohexanone and 2,4-pentanedione; esters such as ethyl acetate,
ethylene glycol monomethyl ether acetate, propylene glycol
monomethyl ether acetate, propylene glycol monoethyl ether acetate
and .gamma.-butyrolactone; amide-type solvents such as
2-pyrrolidone, N-methyl-2-pyrrolidone, dimethylformamide and
dimethylacetamide; halogen-containing solvents such as chloroform,
dichloromethane, carbon tetrachloride, dichloroethane,
tetrachloroethane, trichloroethylene, tetrachloroethylene,
chlorobenzene and orthodichloro-benzene; alcohols such as t-butyl
alcohol, diacetone alcohol, glycerin, monoacetin, ethylene glycol,
triethylene glycol, hexylene glycol, ethylene glycol monomethyl
ether, ethyl Cellosolve and butyl Cellosolve; and phenols such as
phenol and para-chlorophenol. These solvents can be used either
singly or in combination. Such inconveniences that the liquid
crystal cannot fully be dissolved in one solvent and that one
solvent is likely to dissolve the supporting film, which will be
described later, can be avoided by the use of a mixture of two or
more solvents. of the above-enumerated solvents, hydrocarbons and
glycol monoether acetates are preferred as solvents to be used
singly; and mixtures of ethers or ketones and glycols are preferred
as solvent mixtures.
[0037] An optical element 10 containing the cholesteric layer 12
formed on the alignment substrate 13 is thus finally obtained (FIG.
2(c)). It is preferable to subject the cholesteric layer 12 to
drying and re-alignment treatment at a predetermined temperature,
thereby stabilizing the optical properties of the cholesteric layer
12. It is also preferable that, after the drying and re-alignment
treatment is completed, a predetermined amount of radiation
(ultraviolet light or the like) be applied to the cholesteric layer
12 in the air, more preferably in an inert atmosphere, to re-cure
the cholesteric layer 12.
[0038] In the above production process, the crystalline material
for forming the cholesteric layer 12 may be made into a coating
liquid by dissolving it in a solvent. In this case, it is necessary
to add the drying step of evaporating the solvent before
three-dimensionally crosslinking the liquid crystal layer by the
application of radiation 20. As such a solvent, the above-mentioned
material for the organic solvent 21 can be used. In this case, the
concentration of the solution cannot be specified sweepingly
because it depends on the solubility of the liquid crystal in the
solvent and the desired thickness of the liquid crystal layer to be
formed. In general, however, the concentration is adjusted so that
it will fall in the range of 1 to 60% by weight, preferably in the
range of 3 to 40% by weight. Surface active agents, etc. may be
added to the liquid crystal solution in order to make it easy to
apply the solution. Examples of surface active agents that can be
added to the liquid crystal solution include: cationic surface
active agents such as imidazoline, quaternary ammonium salts,
alkylamine oxides and polyamine derivatives; anionic surface active
agents such as polyoxyethylene-polyoxypropylene condensation
products, primary or secondary alcohol ethoxylates, alkylphenol
ethoxylates, polyethylene glycol and its esters, sodiumlauryl
sulfate, ammonium lauryl sulfate, amine lauryl sulfate,
alkyl-substituted aromatic sulfonates, alkyl phosphates, and
aliphatic or aromatic sulfonic acid-formalin condensation products;
amphoteric surface active agents such as laurylamidopropylbetaine
and laurylaminoacetic acid betaine; nonionic surface active agents
such as polyethylene glycol fatty esters and polyoxyethylene
alkylamines; and fluorine-containing surface active agents such as
perfluoroalkyl sulfonates, perfluoroalkyl carboxylates,
perfluoroalkyl ethyleneoxide adducts, perfluoroalkyl
trimethylammonium salts, oligomers containing perfluoroalkyl groups
and hydrophilic groups, oligomers containing perfluoroalkyl groups
and lipophilic groups, and urethanes containing perfluoroalkyl
groups. The amount of a surface active agent to be added varies
depending upon the type of the surface active agent, the type of
the curing liquid crystal, the type of the solvent, and the type of
the glass substrate or supporting film to which the liquid crystal
solution is applied; and, in general, it is from 10 wt. ppm to 10%
by weight, preferably from 100 wt. ppm to 5% by weight, more
preferably from 0.1 to 1% by weight of the liquid crystal contained
in the solution.
[0039] According to the first embodiment of the present invention,
the selective reflection wave range of the cholesteric layer 12 can
be controlled by changing the amount of the radiation 20 to be
applied to the liquid crystal layer formed on the alignment
substrate 13, so that it is possible to control the selective
reflection wave range of the cholesteric layer 12 with ease and
high precision. It is therefore possible to easily produce an
optical element 10 that comprises a cholesteric layer 12 having the
desired selective reflection wave range and that is excellent in
both optical stability and intensity of color.
[0040] In the aforementioned first embodiment, the radiation 20 is
evenly applied to the entire surface of the liquid crystal layer
formed on the alignment substrate 13. The present invention is not
limited to this; and the radiation 20 may be applied in different
amounts to different regions on the surface of the liquid crystal
layer as shown in FIGS. 4(a), 4(b) and 4(c) so that these regions
can have different selective reflection wave ranges. By doing so,
it becomes possible to produce a color filter or the like having a
cholesteric layer 12 on which each pixel has selective reflection
wave ranges equal to the wave ranges of red (R), green (G) and blue
(B) colors. [In this case, the cholesteric layer 12 is formed by
bringing, under the specific conditions, the uniformly deposited
liquid crystal layer into contact with an organic solvent, and the
final thickness of the cholesteric layer 12 differs as shown in
FIG. 4(c) according to the regions to which the radiation has been
applied in different amounts.]
Second Embodiment
[0041] Next, the second embodiment of the present invention will be
described by referring to FIGS. 5 to 7. The second embodiment of
the invention is basically the same as the first embodiment shown
in FIGS. 1 to 4, except that the cholesteric layer 12 is composed
of a laminate of a plurality of cholesteric films 12' and 12''. It
is noted that like reference characters designate like or
corresponding parts throughout several views and that those parts
that have been explained in connection with the first embodiment
will not be explained any more in detail in the description of the
second embodiment.
[0042] As shown in FIG. 5, an optical element 10 according to the
second embodiment of the present invention is composed of: an
alignment substrate 13 prepared by conducting alignment treatment;
and a cholesteric layer 12 laminated to the alignment substrate 13.
The cholesteric layer 12 is composed of a laminate of a plurality
of cholesteric films 12' and 12'' having different chiral pitches,
and has a broad selective reflection wave range covering the
selective reflection wave range of the cholesteric film 12' and
that of the cholesteric film 12'' (see FIG. 6).
[0043] Next, a process of producing the optical element 10
according to the second embodiment of the present invention, having
the above-described constitution, will be described by referring to
FIGS. 7(a)-7(f).
[0044] A glass substrate provided with a polyimide (PI) film that
has been subjected to rubbing treatment, a supporting film having
the function of aligning liquid crystalline molecules, or the like
is prepared as the alignment substrate 13 prepared by conducting
alignment treatment. On top of this alignment substrate 13, a first
liquid crystal layer is formed by the use of a photo-curing chiral
nematic liquid crystal having cholesteric regularity. Liquid
crystalline molecules in the first liquid crystal layer are aligned
by the alignment-regulating action of the alignment substrate 13,
where the first liquid crystal layer is subjected to heat
treatment, if necessary. A predetermined amount (e.g., from 0.01 to
10000 mJ/cm.sup.2) of radiation 20 is applied to the first liquid
crystal layer formed on the alignment substrate 13 to
three-dimensionally cross-link and cure the first liquid crystal
layer. A first cholesteric film 12' is thus formed in the
semi-cured state (FIG. 7(a)).
[0045] It is possible to use, as the supporting film for use as the
alignment substrate 13, any of those materials that are mentioned
in the above description of the first embodiment.
[0046] Thereafter, the semi-cured first cholesteric film 12' formed
on the alignment substrate 13 is brought into contact with an
organic solvent 21 (FIG. 7(b)).
[0047] There is thus obtained an optical element containing the
first cholesteric film 12' formed on the alignment substrate 13
(FIG. 7(c)). It is preferable to subject the first cholesteric film
12' to drying and re-alignment treatment at a predetermined
temperature, thereby stabilizing the optical properties of the
first cholesteric film 12'. It is also preferable that, after the
drying and re-alignment treatment is completed, a predetermined
amount of radiation (ultraviolet light or the like) be applied to
the first cholesteric film 12' in the air, more preferably in an
inert atmosphere, to re-cure the first cholesteric film 12'. Any
organic solvent can be used as the organic solvent in the above
process as long as it can dissolve the first cholesteric film 12';
and one of the organic solvents enumerated in the above description
of the first embodiment, for example, can be used.
[0048] Next, by the use of a photo-curing chiral nematic liquid
crystal or the like having cholesteric regularity, a second liquid
crystal layer is formed on the first cholesteric film 12' provided
on the alignment substrate 13. Liquid crystalline molecules in the
second crystal layer are aligned by the alignment-regulating action
of the first cholesteric film 12', where the second crystal layer
is subjected to heat treatment, if necessary. Prior to the
formation of the second liquid crystal layer, a polyimide (PI) film
may be formed on the first cholesteric film 12' and rubbed. A
predetermined amount of radiation 20 is applied to the second
liquid crystal layer formed on the first cholesteric film 12' to
three-dimensionally cross-link and cure the second liquid crystal
layer. A second cholesteric film 12'' is thus formed in the
semi-cured state (FIG. 7 (d)).
[0049] The semi-cured second cholesteric film 12'' formed on the
first cholesteric film 12' is then brought into contact with an
organic solvent 21 (FIG. 7(e)).
[0050] Thus, there is finally obtained an optical element 10
containing the cholesteric films 12' and 12'' on the alignment
substrate 13 (FIG. 7 (f)). It is preferable to subject the second
cholesteric film 12'' to drying and re-alignment treatment at a
predetermined temperature, thereby stabilizing the optical
properties of the second cholesteric film 12''. It is also
preferable that, after the drying and re-alignment treatment is
completed, a predetermined amount of radiation (ultraviolet light
or the like) be applied to the second cholesteric film 12'' in the
air, more preferably in an inert atmosphere, to re-cure the second
cholesteric film 12''. Any organic solvent can be used as the
organic solvent in the above process as long as it can dissolve the
second cholesteric film 12''; and one of the organic solvents
enumerated in the description of the first embodiment, for example,
can be used.
[0051] In the above production process, the liquid crystalline
materials for forming the cholesteric films 12' and 12'' may be
made into coating liquids by dissolving them in solvents, as
mentioned in the above description of the first embodiment. In this
case, it is necessary to add the drying step of evaporating the
solvent before three-dimensionally crosslinking each liquid crystal
layer by the application of radiation 20.
[0052] According to the second embodiment of the present invention,
the selective reflection wave ranges of the plurality of
cholesteric films 12' and 12'' can be controlled by changing the
amount of the radiation 20 to be applied to the liquid crystal
layer formed on the alignment substrate 13 or on the first
cholesteric film 12', so that it is possible to control the
selective reflection wave ranges of the plurality of cholesteric
films 12' and 12'' with ease and high precision. It is therefore
possible to easily produce an optical element 10 that comprises a
cholesteric layer 12 composed of a laminate of a plurality of
cholesteric films 12' and 12'' having different selective
reflection wave ranges and that is excellent in both optical
stability and intensity of color.
EXAMPLES
Example 1
[0053] The aforementioned first embodiment of the invention will
now be explained more specifically by referring to Example 1.
[0054] A photo-curing chiral nematic liquid crystal consisting of
80 parts by weight of a polymerizable nematic liquid crystal, 20
parts by weight of a chiral agent and 1 part by weight of a
photopolymerization initiator was dissolved in toluene to obtain a
25 wt. % toluene solution of the chiral nematic liquid crystal.
[0055] The nematic liquid crystal used was a liquid crystal
containing a compound represented by the following chemical formula
(5): ##STR6## and a compound represented by the following chemical
formula (6): ##STR7## in the weight ratio of 90:10. Further, a
chiral dopant-added liquid crystal "S-811" (manufactured by Merck
KGaA, Germany) was used as the chiral agent; and "Irg 631"
(available from Ciba Specialty Chemicals K.K., Japan) was used as
the photopolymerization initiator.
[0056] On the other hand, a glass substrate was coated with
polyimide (PI); and the polyimide film formed was rubbed in the
definite direction (alignment treatment) to obtain an alignment
substrate.
[0057] The glass substrate having thereon the polyimide (PI) film
that had been subjected to the rubbing treatment was set in a spin
coater; and the polyimide film was spin-coated with the
above-prepared toluene solution so that the thickness of the
solution layer would be from about 3.0 to 5.0 .mu.m.
[0058] The alignment substrate coated with the toluene solution was
then subjected to drying and alignment treatment with heating at
80.degree. C. for 5 minutes. It was visually confirmed that the
liquid crystal layer formed on the alignment substrate was
cholesteric.
[0059] By the use of an ultraviolet light irradiator having an
extra-high pressure mercury vapor lamp, a predetermined amount of
ultraviolet light was applied to the liquid crystal layer to
three-dimensionally cross-link and polymerize the liquid crystal
layer. A cholesteric layer in the semi-cured state was thus formed
on the alignment substrate.
[0060] The semi-cured cholesteric layer formed on the alignment
substrate was immersed in acetone for 5 minutes.
[0061] Thereafter, this cholesteric layer was dried with heating at
60.degree. C. for 15 minutes; and 10000 mJ/cm.sup.2 of ultraviolet
light was applied to the cholesteric layer by an ultraviolet light
irradiator having an extra-high pressure mercury vapor lamp to
re-cure the cholesteric layer, thereby stabilizing the optical
properties of the cholesteric layer.
[0062] Thus, there is finally obtained an optical element having
the cholesteric layer formed on the alignment substrate.
[0063] In the above-described production process, ultraviolet light
was applied in three different amounts, 1 mJ/cm.sup.2, 100
mJ/cm.sup.2 and 10000 mJ/cm.sup.2, to form three cholesteric layers
in the semi-cured state, and the selective reflection wavelengths
(reflection spectra) of the finally-obtained three optical elements
were measured by a spectrophotometer. The results are shown in FIG.
8. Shift to the shorter wavelength side was confirmed in the
selective reflection wave range of each cholesteric layer after the
cholesteric layer was brought into contact with the organic
solvent; and the degree of this shift was found to be greater when
the amount of ultraviolet light applied was smaller. In addition,
the bandwidth of the selective reflection wave range was
approximately 80 nm in all cases.
Example 2
[0064] In Example 2, an optical element was produced in the same
manner as that of Example 1 except that 3 parts by weight of "Irg
369" (available from Ciba Specialty chemicals K.K., Japan) was used
as the photopolymerization initiator, instead of 1 part by weight
of "Irg 631."
[0065] In Example 2, ultraviolet light was applied in four
different amounts, 4 mJ/cm.sup.2, 8 mJ/cm.sup.2, 20 mJ/cm.sup.2 and
400 mJ/cm.sup.2, to form four cholesteric layers in the semi-cured
state, and the selective reflection wavelengths (reflection
spectra) of the finally-obtained four optical elements were
measured by a spectrophotometer. The results are shown in FIG. 9.
Similar to Example 1, shift to the shorter wavelength side was
confirmed in the selective reflection wave range of each
cholesteric layer after the cholesteric layer was brought into
contact with the organic solvent. This shift was accomplished with
a smaller amount of ultraviolet light as compared with Example
1.
Example 3
[0066] The aforementioned second embodiment of the present
invention will be explained more specifically by referring to
Example 3.
[0067] A photo-curing chiral nematic liquid crystal consisting of
80 parts by weight of a polymerizable nematic liquid crystal, 20
parts by weight of a chiral agent and 1 part by weight of a
photopolymerization initiator was dissolved in toluene to obtain a
25 wt. % toluene solution of the chiral nematic liquid crystal. The
nematic liquid crystal, the chiral agent and the
photopolymerization initiator used in this example were the same as
those used in Example 1.
[0068] On the other hand, a glass substrate was coated with
polyimide (PI); and the polyimide film formed was rubbed in the
definite direction (alignment treatment) to obtain an alignment
substrate.
[0069] The glass substrate having thereon the polyimide (PI) film
that had been subjected to the rubbing treatment was set in a spin
coater, and the polyimide film was spin-coated with the
above-prepared toluene solution so that the thickness of the
solution layer would be from about 3.0 to 5.0 .mu.m.
[0070] The alignment substrate coated with the toluene solution was
then subjected to drying and alignment treatment with heating at
80.degree. C. for 5 minutes. It was visually confirmed that the
layer formed on the alignment substrate was cholesteric.
[0071] By the use of an ultraviolet light irradiator having an
extra-high pressure mercury vapor lamp, a predetermined amount of
ultraviolet light was applied to the liquid crystal layer to
three-dimensionally cross-link and polymerize the liquid crystal
layer. A first cholesteric film in the semi-cured state was thus
formed on the alignment substrate.
[0072] The semi-cured first cholesteric film formed on the
alignment substrate was immersed in acetone for 5 minutes.
[0073] Thereafter, the first cholesteric film that had been
immersed in acetone was spin-coated with the above-prepared toluene
solution so that the thickness of the solution layer would be from
about 3.0 to 5.0 .mu.m.
[0074] This layer was then subjected to drying and alignment
treatment with heating at 80.degree. C. for 5 minutes. It was
visually observed that the layer formed on the first cholesteric
film was cholesteric.
[0075] By the use of an ultraviolet light irradiator having an
extra-high pressure mercury vapor lamp, a predetermined amount of
ultraviolet light was applied to the liquid crystal layer to
three-dimensionally cross-link and polymerize the liquid crystal
layer. A second cholesteric film in the semi-cured state was thus
formed on the first cholesteric film.
[0076] The semi-cured second cholesteric film formed on the first
cholesteric film was then immersed in acetone for 5 minutes.
[0077] This cholesteric film was dried with heating at 60.degree.
C. for 15 minutes. 10000 mJ/cm.sup.2 of ultraviolet light was then
applied to the cholesteric layer by an ultraviolet light irradiator
having an extra-high pressure mercury vapor lamp to re-cure the
cholesteric layer, thereby stabilizing the optical properties of
the cholesteric layer.
[0078] Thus, there was finally obtained an optical element
containing the cholesteric layer composed of two cholesteric films,
formed on the alignment substrate.
[0079] To form the cholesteric layer in the semi-cured state in the
above process, 100 mJ/cm.sup.2 of ultraviolet light was applied to
the first cholesteric film, while 10000 mJ/cm.sup.2 of ultraviolet
light was applied to the second cholesteric film. The selective
reflection wavelength (reflection spectrum) of the optical element
finally obtained was measured by a spectrophotometer. As a result,
the optical element containing the cholesteric layer composed of
the laminate of the two cholesteric films, formed by applying
ultraviolet light in different amounts, was found to have the
optical properties (broad selective reflection wave range) covering
the optical properties (selective reflection wave range) of the
first cholesteric film and those of the second cholesteric film, as
shown in FIG. 10.
* * * * *