U.S. patent application number 10/681384 was filed with the patent office on 2007-10-18 for polarizer, optical film, and image display.
Invention is credited to Kazunori Futamura, Takashi Kamijo, Minoru Miyatake.
Application Number | 20070242353 10/681384 |
Document ID | / |
Family ID | 34222094 |
Filed Date | 2007-10-18 |
United States Patent
Application |
20070242353 |
Kind Code |
A1 |
Kamijo; Takashi ; et
al. |
October 18, 2007 |
POLARIZER, OPTICAL FILM, AND IMAGE DISPLAY
Abstract
A polarizer including a film having a structure having a minute
domain dispersed in a matrix formed of a translucent water-soluble
resin including an iodine light absorbing material, provides a high
polarization degree in short wavelength side. The polarizer has a
high transmittance and a high polarization degree, and is able to
control unevenness of the transmittance in the case of black
display.
Inventors: |
Kamijo; Takashi; (Osaka,
JP) ; Miyatake; Minoru; (Osaka, JP) ;
Futamura; Kazunori; (Osaka, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW
SUITE 700
WASHINGTON
DC
20036
US
|
Family ID: |
34222094 |
Appl. No.: |
10/681384 |
Filed: |
October 9, 2003 |
Current U.S.
Class: |
359/487.06 |
Current CPC
Class: |
G02B 5/3033 20130101;
G02F 1/133528 20130101 |
Class at
Publication: |
359/491 |
International
Class: |
G02B 5/30 20060101
G02B005/30 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 8, 2002 |
JP |
2002-294396 |
Jul 1, 2003 |
JP |
2003-189191 |
Sep 22, 2003 |
JP |
2003-329744 |
Claims
1. A polarizer comprising a monolayer film comprising a continuous
phase and a dispersed phase, wherein the continuous phase comprises
a matrix formed of a translucent water-soluble resin including an
iodine light absorbing material, wherein the dispersed phase
comprises a minute domain dispersed in the matrix, and wherein an
absorption axis of the iodine light absorbing material is oriented
in a direction of an axis showing a maximum refractive index
difference between the birefringent material forming the minute
domain and the translucent water-soluble resin.
2. A polarizer comprising a monolayer film comprising a continuous
phase and a dispersed phase, wherein the continuous phase comprises
a matrix formed of a translucent water-soluble resin including an
iodine light absorbing material, wherein the dispersed phase
comprises a minute domain dispersed in the matrix, and wherein the
minute domain is formed of an oriented birefringent material.
3. The polarizer according to claim 2, wherein the birefringent
material shows liquid crystalline properties at least in an
orientation processing step.
4. The polarizer according to claim 2, wherein the minute domain
has 0.02 or more of birefringence.
5. The polarizer according to claim 2, wherein in a refractive
index difference between the birefringent material forming the
minute domain and the translucent water-soluble resin in each
optical axis direction, a refractive index difference
(.DELTA.n.sup.1) in direction of axis showing a maximum is 0.03 or
more, and a refractive index difference (.DELTA.n.sup.2) between
the .DELTA.n.sup.1 direction and a direction of axes of two
directions perpendicular to the .DELTA.n.sup.1 direction is 50% or
less of the .DELTA.n.sup.1.
6. (canceled)
7. The polarizer according to claim 1, wherein the film is
manufactured by stretching.
8. A polarizer comprising a monolayer film comprising a continuous
phase and a dispersed phase, wherein the continuous phase comprises
a matrix formed of a translucent water-soluble resin including an
iodine light absorbing material, wherein the dispersed phase
comprises a minute domain dispersed in the matrix, and wherein the
minute domain has a length of 0.05 through 500 .mu.m in a direction
perpendicular to the direction of an axis showing a maximum
refractive index difference between the birefringent material
forming the minute domain and the translucent water-soluble
resin.
9. The polarizer according to claim 1, wherein the iodine light
absorbing material has an absorbing band at least in a band of 400
nm through 700 nm wavelength range.
10. A polarizer comprising a monolayer film comprising a continuous
phase and a dispersed phase, wherein the continuous phase comprises
a matrix formed of a translucent water-soluble resin including an
iodine light absorbing material, wherein the dispersed phase
comprises a minute domain dispersed in the matrix, and wherein a
transmittance to a linearly polarized light in a transmission
direction is 80% or more, a haze value is 5% or less, and a haze
value to a linearly polarized light in an absorption direction is
30% or more.
11. A polarizing plate having a transparent protective layer formed
at least on one side of the polarizer according to claim 1.
12. An optical film having at least one of the polarizer according
to claim 1 or the polarizing plate according to claim 11.
13. An image display comprising at least one of the polarizer
according to claim 1 or the polarizing plate according to claim
11.
14. An image display comprising the optical film according to claim
12.
15. A polarizer according to claim 1, wherein the minute domains
are dispersed throughout the matrix.
16. A polarizer according to claim 1, wherein the iodine light
absorbing material is dispersed throughout the matrix.
17. A polarizer according to claim 1, wherein the minute domains
and the iodine light absorbing material are dispersed throughout
the matrix.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a polarizer. This invention
also relates to a polarizing plate and an optical film using the
polarizer concerned. Furthermore, this invention relates to an
image display, such as a liquid crystal display, an organic
electroluminescence display, a CRT and a PDP using the polarizing
plate and the optical film concerned.
[0003] 2. Description of the Prior Art
[0004] Liquid crystal display are rapidly developing in market,
such as in clocks and watches, cellular phones, PDAs,
notebook-sized personal computers, and monitor for personal
computers, DVD players, TVs, etc. In the liquid crystal display,
visualization is realized based on a variation of polarization
state by switching of a liquid crystal, where polarizers are used
based on a display principle thereof. Particularly, usage for TV
etc. increasingly requires display with high luminance and high
contrast, polarizers having higher brightness (high transmittance)
and higher contrast (high polarization degree) are being developed
and introduced.
[0005] As polarizers, for example, since it has a high
transmittance and a high polarization degree, polyvinyl alcohols
having a structure in which iodine is absorbed and then stretched,
that is, iodine based polarizers are widely used (for example,
Japanese Patent Laid-Open No. 2001-296427). However, since the
iodine based polarizers have relatively low polarization degrees in
short wavelength side, they have problems in hue, such as blue
omission in black display, and yellowing in white display, in short
wavelength side.
[0006] Iodine based polarizers may easily give unevenness in a
process of iodine absorption. Accordingly, there has been a problem
that the unevenness is detected as unevenness in transmittance
particularly in the case of black display, causing to decrease of
visibility. For example, as methods for solving the problems,
several methods have been proposed that an amount of absorption of
iodine absorbed to the iodine based polarizer is increased and
thereby a transmittance in the case of black display is set not
higher than sensing limitations of human eyes, and that stretching
processes generating little unevenness itself are adopted. However,
the former method has a problem that it decreases a transmittance
in the case of white display, while decreasing a transmittance of
black display, and as a result darkens the display itself. And
also, the latter method has a problem that it requires replacing a
process itself, worsening productivity.
SUMMARY OF THE INVENTION
[0007] This invention aims at providing an iodine based polarizer
having a high polarization degree in short wavelength side.
[0008] Moreover, this invention aims at providing an iodine based
polarizer having a high transmittance and a high polarization
degree, and being able to control unevenness of the transmittance
in the case of black display.
[0009] Besides, this invention aims at providing a polarizing plate
and an optical film using the polarizer concerned. Furthermore,
this invention aims at providing an image display using the
polarizer, the polarizing plate, and the optical film
concerned.
[0010] As a result of examination wholeheartedly performed by the
present inventors that the above-mentioned subject should be
solved, it was found out that the above-mentioned purpose might be
attained using polarizers shown below, leading to completion of
this invention.
[0011] That is, this invention relates to a polarizer comprising a
film having a structure having a minute domain dispersed in a
matrix formed of a translucent water-soluble resin including an
iodine light absorbing material.
[0012] The minute domain of the above-mentioned polarizer is
preferably formed by an oriented birefringent material. The
above-mentioned birefringent material preferably shows liquid
crystallinity at least in orientation processing step.
[0013] The above-mentioned polarizer of this invention has an
iodine based polarizer formed by a translucent water-soluble resin
and an iodine based light absorbing material as a matrix, and has
dispersed minute domains in the above-mentioned matrix. Minute
domains are preferably formed by oriented materials having
birefringence, and particularly minute domains are formed
preferably with materials showing liquid crystallinity. Thus, in
addition to function of absorption dichroism by iodine based light
absorbing materials, characteristics of having function of
scattering anisotropy improve polarization performance according to
synergistic effect of the two functions, and as a result a
polarizer having both of transmittance and polarization degree, and
excellent visibility may be provided.
[0014] Iodine based light absorbing material means chemical species
comprising iodine and absorbs visible light, and it is thought
that, in general, they are formed by interaction between
translucent water-soluble resins (particularly polyvinyl alcohol
based resins) and poly iodine ions (I.sub.3.sub.-, I.sub.5.sub.-,
etc.). An iodine based light absorbing material is also called an
iodine complex. It is thought that poly iodine ions are generated
from iodine and iodide ions.
[0015] Scattering performance of anisotropic scattering originates
in refractive index difference between matrixes and minute domains.
For example, if materials forming minute domains are liquid
crystalline materials, since they have higher wavelength dispersion
of .DELTA.n compared with translucent water-soluble resins as a
matrix, a refractive index difference in scattering axis becomes
larger in shorter wavelength side, and, as a result, it provides
more amounts of scattering in shorter wavelength. Accordingly, an
improving effect of large polarization performance is realized in
shorter wavelengths, compensating a relative low level of
polarization performance of an iodine based polarizer in a side of
shorter wavelength, and thus a polarizer having high polarization
and neutral hue may be realized.
[0016] In the above-mentioned polarizer, It is preferable that the
minute domains have a birefringence of 0.02 or more. In materials
used for minute domains, in the view point of gaining larger
anisotropic scattering function, materials having the
above-mentioned birefringence may be preferably used.
[0017] In the above-mentioned polarizer, in a refractive index
difference between the birefringent material forming the minute
domains and the translucent water-soluble resin in each optical
axis direction, a refractive index difference (.DELTA.n.sup.1) in
direction of axis showing a maximum is 0.03 or more, and a
refractive index difference (.DELTA.n.sup.2) between the
.DELTA.n.sup.1 direction and a direction of axes of two directions
perpendicular to the .DELTA.n.sup.1 direction is 50% or less of the
.DELTA.n.sup.1
[0018] Control of the above-mentioned refractive index difference
(.DELTA.n.sup.1) and (.DELTA.n.sup.2) in each optical axis
direction into the above-mentioned range may provide a scattering
anisotropic film having function being able to selectively scatter
only linearly polarized light in the .DELTA.n.sup.1 direction, as
is submitted in U.S. Pat. No. 2,123,902 specification. That is, on
one hand, having a large refractive index difference in the
.DELTA.n.sup.1 direction, it may scatter linearly polarized light,
and on the other hand, having a small refractive index difference
in the .DELTA.n.sup.2 direction, it may transmit linearly polarized
light. Moreover, refractive index differences (.DELTA.n.sup.2) in
the directions of axes of two directions perpendicular to the
.DELTA.n.sup.1 direction are preferably equal.
[0019] In order to obtain high scattering anisotropy, a refractive
index difference (.DELTA.n.sup.1) in a .DELTA.n.sup.1 direction is
set 0.03 or more, preferably 0.05 or more, and still preferably
0.10 or more. A refractive index difference (.DELTA.n.sup.2) in two
directions perpendicular to the .DELTA.n.sup.1 direction is 50% or
less of the above-mentioned .DELTA.n.sup.1, and preferably 30% or
less.
[0020] In iodine based light absorbing material in the
above-mentioned polarizer, an absorption axis of the material
concerned preferably is orientated in the .DELTA.n.sup.1
direction.
[0021] The iodine based light absorbing material in a matrix is
orientated so that an absorption axis of the material may become
parallel to the above-mentioned .DELTA.n.sup.1 direction, and
thereby linearly polarized light in the .DELTA.n.sup.1 direction as
a scattering polarizing direction may be selectively absorbed. As a
result, on one hand, a linearly polarized light component of
incident light in a .DELTA.n.sup.2 direction is not scattered or
hardly absorbed by the iodine light absorbing material as in
conventional iodine based polarizers without anisotropic scattering
performance. On the other hand, a linearly polarized light
component in the .DELTA.n.sup.1 direction is scattered, and is
absorbed by the iodine based light absorbing material. Usually,
absorption is determined by an absorption coefficient and a
thickness. In such a case, scattering of light greatly lengthens an
optical path length compared with a case where scattering is not
given. As a result, polarized component in the .DELTA.n.sup.1
direction is more absorbed as compared with a case in conventional
iodine based polarizers. That is, higher polarization degrees may
be attained with same transmittances.
[0022] Descriptions for ideal models will, hereinafter, be given.
Two main transmittances usually used for linear polarizer (a first
main transmittance k.sub.1 (a maximum transmission
direction=linearly polarized light transmittance in a
.DELTA.n.sup.2 direction), a second main transmittance k.sub.2 (a
minimum transmission direction=linearly polarized light
transmittance in a .DELTA.n.sup.1 direction)) are, hereinafter,
used to give discussion.
[0023] In commercially available iodine based polarizers, when
iodine based light absorbing materials are oriented in one
direction, a parallel transmittance and a polarization degree may
be represented as follows, respectively:
parallel transmittance=0.5.times.((k.sub.1).sup.2+(k.sub.2).sup.2)
and
polarization degree=(k.sub.1-k.sub.2)/(k.sub.1+k.sub.2).
[0024] On the other hand, when it is assumed that, in a polarizer
of this invention, a polarized light in a .DELTA.n.sup.1 direction
is scattered backscattering strength to incident light strength is
preferably 30% or less, and more preferably 20% or less.
[0025] As the above-mentioned polarizers, films manufactured by
stretching may suitably be used.
[0026] In the above-mentioned polarizer, minute domains preferably
have a length in a .DELTA.n.sup.2 direction of 0.05 through 500
.mu.m.
[0027] In order to scatter strongly linearly polarized light having
a plane of vibration in a .DELTA.n.sup.1 direction in wavelengths
of visible light band, dispersed minute domains have a length
controlled to 0.05 through 500 .mu.m in a .DELTA.n.sup.2 direction,
and preferably controlled to 0.5 through 100 .mu.m. When the length
in the .DELTA.n.sup.2 direction of the minute domains is too short
a compared with wavelengths, scattering may not fully provided. On
the other hand, when the length in the .DELTA.n.sup.2 direction of
the minute domains is too long, there is a possibility that a
problem of decrease in film strength or of liquid crystalline
material forming minute domains not fully oriented in the minute
domains may arise.
[0028] In the above-mentioned polarizer, iodine light absorbing
materials having an absorption band at least in a wavelength range
of 400 through 700 nm may be used.
[0029] In the above-mentioned polarizers, a transmittance to a
linearly polarized light in a transmission direction is 80% or
more, a haze value is 5% or less, and a haze value to a linearly
polarized light in an absorption direction is 30% or more.
[0030] An iodine polarizer of this invention having the
above-mentioned transmittance and haze value has a high
transmittance and excellent visibility for linearly polarized light
in a transmission direction, and has strong optical diffusibility
for linearly polarized light in an absorption direction. Therefore,
without sacrificing other optical properties and using a simple
method, it may demonstrate a high transmittance and a high
polarization degree, and may control unevenness of the
transmittance in the case of black display.
[0031] As a polarizer of this invention, a polarizer is preferable
that has as high as possible transmittance to linearly polarized
light in a transmission direction, that is, linearly polarized
light in a direction perpendicular to a direction of maximal
absorption of the above-mentioned iodine based light absorbing
material, and that has 80% or more of light transmittance when an
optical intensity of incident linearly polarized light is set to
100. The light transmittance is preferably 85% or more, and still
preferably 88% or more. Here, a light transmittance is equivalent
to a value Y calculated from a spectral transmittance in 380 nm
through 780 nm measured using a spectrophotometer with an
integrating sphere based on CIE 1931 XYZ standard colorimetric
system. In addition, since about 8% through 10% is reflected by an
air interface on a front surface and rear surface of a polarizer,
an ideal limit is a value in which a part for this surface
reflection is deducted from 100%.
[0032] It is desirable that a polarizer does not scatter linearly
polarized light in a transmission direction in the view point of
obtaining clear visibility of a display image. Accordingly, the
polarizer preferably has 5% or less of haze value to the linearly
polarized light in the transmission direction, more preferably 3%
or less, and still more preferably 1% or less. On the other hand,
in the view point of covering unevenness by a local transmittance
variation by scattering, a polarizer desirably scatters strongly
linearly polarized light in a absorption direction, that is,
linearly polarized light in a direction for a maximal absorption of
the above-mentioned iodine based light absorbing material.
Accordingly, a haze value to the linearly polarized light in the
absorption direction is preferably 30% or more, more preferably 40%
or more, and still more preferably 50% or more. In addition, the
haze value here is measured based on JIS K 7136 (how to obtain a
haze of plastics-transparent material).
[0033] The above-mentioned optical properties are obtained by
compounding a function of scattering anisotropy with a function of
an absorption dichroism of the polarizer. As is indicated in U.S.
Pat. No. 2,123,902 specification, Japanese Patent Laid-Open No.
9-274108, and Japanese Patent Laid-Open No. 9-297204, same
characteristics may probably be attained also in a way that a
scattering anisotropic film having a function to selectively
scatter only linearly polarized light, and a dichroism absorption
type polarizer are superimposed in an axial arrangement so that an
axis providing a greatest scattering and an axis providing a
greatest absorption may be parallel to each other. These methods,
however, require necessity for separate formation of a scattering
anisotropic film, have a problem of precision in axial joint in
case of superposition, and furthermore, a simple superposition
method does not provide increase in effect of the above-mentioned
optical path length of the polarized light absorbed as is expected,
and as a result, the method cannot easily attain a high
transmission and a high polarization degree.
[0034] Besides, this invention relates to a polarizing plate which
having a transparent protection layer at least on one side of the
above-mentioned polarizer.
[0035] Moreover, this invention relates to an optical film
characterized by being laminated with at least one of the
above-mentioned polarizer and the above-mentioned polarizing
plate.
[0036] Furthermore, this invention relates to an image display
characterized by using the above-mentioned polarizer, the
above-mentioned polarizing plate, or the above-mentioned optical
film.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 is conceptual top view showing an example of a
polarizer of this invention;
[0038] FIG. 2A and FIG. 2B are graphs showing polarized light
absorption spectra of polarizers in Example 1 and Comparative
example 1; and
[0039] FIG. 3A and FIG. 3B are graphs showing polarized light
absorption spectra of polarizers in Example 3 and Comparative
example 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] A polarizer of this invention will, hereinafter, be
described referring to drawings. FIG. 1 is a conceptual top view of
a polarizer of this invention, and the polarizer has a structure
where a film is formed with a translucent water-soluble resin 1
including an iodine based light absorbing material 2, and minute
domains 3 are dispersed in the film concerned as a matrix.
[0041] FIG. 1 shows an example of a case where the iodine based
light absorbing material 2 is oriented in a direction of axis
(.DELTA.n.sup.1 direction) in which a refractive index difference
between the minute domain 3 and the translucent water-soluble resin
1 shows a maximal value. In minute domain 3, a polarized component
in the .DELTA.n.sup.1 direction are scattered. In FIG. 1, the
.DELTA.n.sup.1 direction in one direction in a film plane is an
absorption axis. In the film plane, a .DELTA.n.sup.2 direction
perpendicular to the .DELTA.n.sup.1 direction serves as a
transmission axis. Another .DELTA.n.sup.2 direction perpendicular
to the .DELTA.n.sup.1 direction is a thickness direction.
[0042] As translucent water-soluble resins 1, resins having
translucency in a visible light band and dispersing and absorbing
the iodine based light absorbing materials may be used without
particular limitation. For example, polyvinyl alcohols or
derivatives thereof conventionally used for polarizers may be
mentioned. As derivatives of polyvinyl alcohol, polyvinyl formals,
polyvinyl acetals, etc. may be mentioned, and in addition
derivatives modified with olefins, such as ethylene and propylene,
and unsaturated carboxylic acids, such as acrylic acid, methacrylic
acid, and crotonic acid, alkyl esters of unsaturated carboxylic
acids, acrylamides etc. may be mentioned. Besides, as translucent
water-soluble resin 1, for example, polyvinyl pyrrolidone based
resins, amylose based resins, etc. may be mentioned. The
above-mentioned translucent water-soluble resin may be of resins
having isotropy not easily generating orientation birefringence
caused by molding deformation etc., and of resins having anisotropy
easily generating orientation birefringence.
[0043] In materials forming minute domains 3, it is not limited
whether the material has birefringence or isotropy, but materials
having birefringence is particularly preferable. Moreover, as
materials having birefringence, materials (henceforth, referred to
as liquid crystalline material) showing liquid crystallinity at
least at the time of orientation treatment may preferably used.
That is, the liquid crystalline material may show or may lose
liquid crystallinity in the formed minute domain 3, as long as it
shows liquid crystallinity at the orientation treatment time.
[0044] As materials forming minute domains 3, materials having
birefringences (liquid crystalline materials) may be any of
materials showing nematic liquid crystallinity, smectic liquid
crystallinity, and cholesteric liquid crystallinity, or of
materials showing lyotropic liquid crystallinity. Moreover,
materials having birefringence may be of liquid crystalline
thermoplastic resins, and may be formed by polymerization of liquid
crystalline monomers. When the liquid crystalline material is of
liquid crystalline thermoplastic resins, in the view point of
heat-resistance of structures finally obtained, resins with high
glass transition temperatures may be preferable. Furthermore, it is
preferable to use materials showing glass state at least at room
temperatures. Usually, a liquid crystalline thermoplastic resin is
oriented by heating, subsequently cooled to be fixed, and forms
minute domains 3 while liquid crystallinity are maintained.
Although liquid crystalline monomers after orienting can form
minute domains 3 in the state of fixed by polymerization,
cross-linking, etc., some of the formed minute domains 3 may lose
liquid crystallinity.
[0045] As the above-mentioned liquid crystalline thermoplastic
resins, polymers having various skeletons of principal chain types,
side chain types, or compounded types thereof may be used without
particular limitation. As principal chain type liquid crystal
polymers, polymers, such as condensed polymers having structures
where mesogen groups including aromatic units etc. are combined,
for example, polyester based, polyamide based, polycarbonate based,
and polyester imide based polymers, may be mentioned. As the
above-mentioned aromatic units used as mesogen groups, phenyl
based, biphenyl based, and naphthalene based units may be
mentioned, and the aromatic units may have substituents, such as
cyano groups, alkyl groups, alkoxy groups, and halogen groups.
[0046] As side chain type liquid crystal polymers, polymers having
principal chain of, such as polyacrylate based, polymethacrylate
based, poly-alpha-halo acrylate based, poly-alpha-halo cyano
acrylate based, polyacrylamide based, polysiloxane based, and poly
malonate based principal chain as a skeleton, and having mesogen
groups including cyclic units etc. in side chains may be mentioned.
As the above-mentioned cyclic units used as mesogen groups,
biphenyl based, phenyl benzoate based, phenylcyclohexane based,
azoxybenzene based, azomethine based, azobenzene based, phenyl
pyrimidine based, diphenyl acetylene based, diphenyl benzoate
based, bicyclo hexane based, cyclohexylbenzene based, terphenyl
based units, etc. may be mentioned. Terminal groups of these cyclic
units may have substituents, such as cyano group, alkyl group,
alkenyl group, alkoxy group, halogen group, haloalkyl group,
haloalkoxy group, and haloalkenyl group. Groups having halogen
groups may be used for phenyl groups of mesogen groups.
[0047] Besides, any mesogen groups of the liquid crystal polymer
may be bonded via a spacer part giving flexibility. As spacer
parts, polymethylene chain, polyoxymethylene chain, etc. may be
mentioned. A number of repetitions of structural units forming the
spacer parts is suitably determined by chemical structure of
mesogen parts, and the number of repeating units of polymethylene
chain is 0 through 20, preferably 2 through 12, and the number of
repeating units of polyoxymethylene chain is 0 through 10, and
preferably 1 through 3.
[0048] The above-mentioned liquid crystalline thermoplastic resins
preferably have glass transition temperatures of 50.degree. C. or
more, and more preferably 80.degree. C. or more. Furthermore they
have approximately 2,000 through 100,000 of weight average
molecular weight.
[0049] As liquid crystalline monomers, monomers having
polymerizable functional groups, such as acryloyl groups and
methacryloyl groups, at terminal groups, and further having mesogen
groups and spacer parts including the above-mentioned cyclic units
etc. may be mentioned. Crossed-linked structures may be introduced
using polymerizable functional groups having two or more acryloyl
groups, methacryloyl groups, etc., and durability may also be
improved.
[0050] Materials forming minute domains 3 are not entirely limited
to the above-mentioned liquid crystalline materials, and non-liquid
crystalline resins may be used if they are different materials from
the matrix materials. As the above-mentioned resins, polyvinyl
alcohols and derivatives thereof, polyolefins, polyallylates,
polymethacrylates, polyacrylamides, polyethylene terephthalates,
acrylic styrene copolymes, etc. may be mentioned. Moreover,
particles without birefringence may be used as materials for
forming the minute domains 3. As fine-particles concerned, resins,
such as polyacrylates and acrylic styrene copolymers, may be
mentioned. A size of the fine-particles is not especially limited,
and particle diameters of 0.05 through 500 .mu.m may be used, and
preferably 0.5 through 100 .mu.m. Although it is preferable that
materials for forming minute domains 3 is of the above-mentioned
liquid crystalline materials, non-liquid crystalline materials may
be mixed and used to the above-mentioned liquid crystalline
materials. Furthermore, as materials for forming minute domains 3,
non-liquid crystalline materials may also be independently
used.
[0051] In a polarizer of this invention, while producing a film in
which a matrix is formed with a translucent water-soluble resin 1
including an iodine based light absorbing material 2, minute
domains 3 (for example, an oriented birefringent material formed
with liquid crystalline materials) are dispersed in the matrix
concerned. Moreover, the above-mentioned refractive index
difference (.DELTA.n.sup.1) in a .DELTA.n.sup.1 direction and a
refractive index difference (.DELTA.n.sup.2) in a .DELTA.n.sup.2
direction are controlled to be in the above-mentioned range in the
film.
[0052] Manufacturing process of a polarizer of this invention is
not especially limited, and for example, the polarizer of this
invention may be obtained using following production processes:
[0053] (1) a process for manufacturing a mixed solution in which a
material for forming minute domains is dispersed in a translucent
water-soluble resin forming a matrix (description is, hereinafter,
to be provided, with reference to an example of representation, for
a case where a liquid crystalline material is used as a material
forming the minute domains. A case by a liquid crystalline material
will apply to a case by other materials.);
(2) a process in which a film is formed with the mixed solution of
the above-mentioned (1);
(3) a process in which the film obtained in the above-mentioned
(2) is oriented (stretched); and
(4) a process in which an iodine based light absorbing material is
dispersed (dyed) in the translucent water-soluble resin forming the
above-mentioned matrix.
In addition, an order of the processes (1) to (4) may suitably be
determined.
[0054] In the above-mentioned process (1), a mixed solution is
firstly prepared in which a liquid crystalline material forming
minute domains is dispersed in a translucent water-soluble resin
forming a matrix. A method for preparing the mixed solution
concerned is not especially limited, and a method may be mentioned
of utilizing a phase separation phenomenon between the
above-mentioned matrix component (a translucent water-soluble
resin) and a liquid crystalline material. For example, a method may
be mentioned in which a material having poor compatibility between
the matrix component as a liquid crystalline material is selected,
a solution of the material forming the liquid crystalline material
is dispersed using dispersing agents, such as a surface active
agent, in a water solution of the matrix component. In preparation
of the above-mentioned mixed solution, some of combinations of the
translucent material forming the matrix, and the liquid crystal
material forming minute domains do not require a dispersing agent.
An amount used of the liquid crystalline material dispersed in the
matrix is not especially limited, and a liquid crystalline material
is 0.01 through 100 part(s) by weight to a translucent
water-soluble resin 100 parts by weight, and preferably it is 0.1
through 10 part(s) by weight. The liquid crystalline material is
used in a state dissolved or not dissolved in a solvent. Examples
of solvents, for example, include: water, toluene, xylene, hexane
cyclohexane, dichloromethane, trichloromethane, dichloroethane,
trichloroethane, tetrachloroethane, trichloroethylene, methyl ethyl
ketone, methylisobutylketone, cyclohexanone, cyclopentanone,
tetrahydrofuran, ethyl acetate, etc. Solvents for the matrix
components and solvents for the liquid crystalline materials may be
of same, or may be of different solvents.
[0055] In the above-mentioned process (2), in order to reduce
foaming in a drying process after a film formation, it is desirable
that solvents for dissolving the liquid crystalline material
forming a minute domains is not used in preparation of the mixed
solution in the process (1). When solvents are not used, for
example, a method may be mentioned in which a liquid crystalline
material is directly added to an aqueous solution of a translucency
material forming a matrix, and then is heated above a liquid
crystal temperature range in order to disperse the liquid
crystalline material uniformly in a smaller state.
[0056] In addition, a solution of a matrix component, a solution of
a liquid crystalline material, or a mixed solution may include
various kinds of additives, such as dispersing agents, surface
active agents, ultraviolet absorption agents, flame retardants,
antioxidants, plasticizers, mold lubricants, other lubricants, and
colorants in a range not disturbing an object of this
invention.
[0057] In the process (2) for obtaining a film of the
above-mentioned mixed solution, the above-mentioned mixed solution
is heated and dried to remove solvents, and thus a film with minute
domains dispersed in the matrix is produced. As methods for
formation of the film, various kinds of methods, such as casting
methods, extrusion methods, injection molding methods, roll molding
methods, and flow casting molding methods, may be adopted. In film
molding, a size of minute domains in the film is controlled to be
in a range of 0.05 through 500 .mu.m in a .DELTA.n.sup.2 direction.
Sizes and dispersibility of the minute domains may be controlled,
by adjusting a viscosity of the mixed solution, selection and
combination of the solvent of the mixed solution, dispersant, and
thermal processes (cooling rate) of the mixed solvent and a rate of
drying. For example, a mixed solution of a translucent
water-soluble resin that has a high viscosity and generates high
shearing force and that forms a matrix, and a liquid crystalline
material forming minute domains is dispersed by agitators, such as
a homogeneous mixer, being heated at a temperature in no less than
a range of a liquid crystal temperature, and thereby minute domains
may be dispersed in a smaller state.
[0058] The process (3) giving orientation to the above-mentioned
film may be performed by stretching the film. In stretching,
uniaxial stretching, biaxial stretching, diagonal stretching are
exemplified, but uniaxial stretching is usually performed. Any of
dries type stretching in air and wet type stretching in an aqueous
system bath may be adopted as the stretching method. When adopting
a wet type stretching, an aqueous system bath may include suitable
additives (boron compounds, such as boric acid; iodide of alkali
metal, etc.) A stretching ratio is not especially limited, and in
usual a ratio of approximately 2 through 10 times is preferably
adopted.
[0059] This stretching may orient the iodine based light absorbing
material in a direction of stretching axis. Moreover, the liquid
crystalline material forming a birefringent material is oriented in
the stretching direction in minute domains by the above-mentioned
stretching, and as a result birefringence is demonstrated.
[0060] It is desirable the minute domains may be deformed according
to stretching. When minute domains are of non-liquid crystalline
materials, approximate temperatures of glass transition
temperatures of the resins are desirably selected as stretching
temperatures, and when the minute domains are of liquid crystalline
materials, temperatures making the liquid crystalline materials
exist in a liquid crystal state such as nematic phase or smectic
phase or an isotropic phase state, are desirably selected as
stretching temperatures. When inadequate orientation is given by
stretching process, processes, such as heating orientation
treatment, may separately be added.
[0061] In addition to the above-mentioned stretching, function of
external fields, such as electric field and magnetic field, may be
used for orientation of the liquid crystalline material. Moreover,
liquid crystalline materials mixed with light reactive substances,
such as azobenzene, and liquid crystalline materials having light
reactive groups, such as a cinnamoyl group, introduced thereto are
used, and thereby these materials may be oriented by orientation
processing with light irradiation etc. Furthermore, a stretching
processing and the above-mentioned orientation processing may also
be used in combination. When the liquid crystalline material is of
liquid crystalline thermoplastic resins, it is oriented at the time
of stretching, cooled at room temperatures, and thereby orientation
is fixed and stabilized. Since target optical property will be
demonstrated if orientation is carried out, the liquid crystalline
monomer may not necessarily be in a cured state. However, in liquid
crystalline monomers having low isotropic transition temperatures,
a few temperature rise provides an isotropic state. In such a case,
since anisotropic scattering may not be demonstrated but conversely
polarized light performance deteriorates, the liquid crystalline
monomers are preferably cured. Besides, many of liquid crystalline
monomers will be crystallized when left at room temperatures, and
then they will demonstrate anisotropic scattering and polarized
light performance conversely deteriorate, the liquid crystalline
monomers are preferably cured. In the view point of these
phenomena, in order to make orientation state stably exist under
any kind of conditions, liquid crystalline monomers are preferably
cured. In curing of a liquid crystalline monomer, for example,
after the liquid crystalline monomer is mixed with
photopolymerization initiators, dispersed in a solution of a matrix
component and oriented, in either of timing (before dyed or after
dyed by iodine based light absorbing materials), the liquid
crystalline monomer is cured by exposure with ultraviolet radiation
etc. to stabilize orientation. Desirably, the liquid crystalline
monomer is cured before dyed with iodine based light absorbing
materials.
[0062] As a process (4) in which the iodine based light absorbing
material is dispersed in the translucent water-soluble resin used
for forming the above-mentioned matrix, in general, a method in
which the above-mentioned film is immersed into a bath of aqueous
system including iodine dissolved with auxiliary agents of iodide
of alkali metals, such as potassium iodide may be mentioned. As
mentioned above, an iodine based light absorbing material is formed
by interaction between iodine dispersed in the matrix and the
matrix resin. Timing of immersing may be before or after the
above-mentioned stretching process (3). The iodine based light
absorbing material is, in general, remarkably formed by being
passed through a stretching process. A concentration of the aqueous
system bath including iodine, and a percentage of the auxiliary
agents, such as iodide of alkali metals may not especially be
limited, but general iodine dyeing techniques may be adopted, and
the above-mentioned concentration etc. may arbitrarily be
changed.
[0063] Moreover, a percentage of the iodine in the polarizer
obtained is not especially limited, but a percentage of the
translucent water-soluble resin and the iodine is preferably
controlled to be 0.05 through 50 part(s) by weight grade to the
translucent water-soluble resin 100 parts by weight, and more
preferably 0.1 through 10 parts(s) by weight.
[0064] In production of the polarizer, processes for various
purposes (5) may be given other than the above-mentioned processes
(1) through (4). As a process (5), for example, a process in which
a film is immersed in water bath and swollen may be mentioned for
the purpose of mainly improving iodine dyeing efficiency of the
film. Besides, a process in which a film is immersed in a water
bath including arbitrary additives dissolved therein may be
mentioned. A process in which a film is immersed in an aqueous
solution including additives, such as boric acid and borax, for the
purpose of cross-linking a water-soluble resin (matrix) may be
mentioned. Moreover, for the purpose of mainly adjusting an amount
balance of the dispersed iodine based light absorbing materials,
and adjusting a hue, a process in which a film is immersed to an
aqueous solution including additives, such as an iodide of an
alkaline metals may be mentioned.
[0065] As for the process (3) of orienting (stretching) of the
above-mentioned film, the process (4) of dispersing and dyeing the
iodine based light absorbing material to a matrix resin and the
above-mentioned process (5), so long as each of the processes (3)
and (4) is provided at least 1 time, respectively, a number, order
and conditions (a bath temperature, immersion period of time, etc.)
of the processes, may arbitrarily be selected, each process may
separately be performed and furthermore a plurality of processes
may simultaneously be performed. For example, a cross-linking
process of the process (5) and the stretching process (3) may be
carried out simultaneously.
[0066] In addition, although the iodine based light absorbing
material used for dyeing, boric acid used for cross-linking are
permeated into a film by immersing the film in an aqueous solution
as mentioned above, instead of this method, a method may be adopted
that arbitrary types and amounts may be added before film formation
of the process (2) and before or after preparation of a mixed
solution in the process (1). And both methods may be used in
combination. However, when high temperatures (for example, no less
than 80.degree. C.) is required in the process (3) at the time of
stretching etc., in the view point of heat resistance of the iodine
based light absorbing material, the process (4) for dispersing and
dyeing the iodine based light absorbing material may be desirably
performed after the process (3).
[0067] A film given the above treatments is desirably dried using
suitable conditions. Drying is performed according to conventional
methods.
[0068] A thickness of the obtained polarizer (film) is not
especially limited, in general, but it is 1 .mu.m through 3 mm,
preferably 5 .mu.m through 1 mm, and more preferably 10 through 500
.mu.m.
[0069] A polarizer obtained in this way does not especially have a
relationship in size between a refractive index of the birefringent
material forming minute domains and a refractive index of the
matrix resin in a stretching direction, whose stretching direction
is in a .DELTA.n.sup.1 direction and two directions perpendicular
to a stretching axis are .DELTA.n.sup.2 directions. Moreover, the
stretching direction of an iodine based light absorbing material is
in a direction demonstrating maximal absorption, and thus a
polarizer having a maximally demonstrated effect of absorption and
scattering may be realized.
[0070] Since a polarizer obtained by this invention has equivalent
functions as in existing absorbed type polarizing plates, it may be
used in various applicable fields where absorbed type polarizing
plates are used without any change.
[0071] The above-described polarizer may be used as a polarizing
plate with a transparent protective layer prepared at least on one
side thereof using a usual method. The transparent protective layer
may be prepared as an application layer by polymers, or a laminated
layer of films. Proper transparent materials may be used as a
transparent polymer or a film material that forms the transparent
protective layer, and the material having outstanding transparency,
mechanical strength, heat stability and outstanding moisture
interception property, etc. may be preferably used. As materials of
the above-mentioned protective layer, for example, polyester type
polymers, such as polyethylene terephthalate and
polyethylenenaphthalate; cellulose type polymers, such as diacetyl
cellulose and triacetyl cellulose; acrylics type polymer, such as
poly methylmethacrylate; styrene type polymers, such as polystyrene
and acrylonitrile-styrene copolymer (AS resin); polycarbonate type
polymer may be mentioned. Besides, as examples of the polymer
forming a protective film, polyolefin type polymers, such as
polyethylene, polypropylene, polyolefin that has cyclo-type or
norbornene structure, ethylene-propylene copolymer; vinyl chloride
type polymer; amide type polymers, such as nylon and aromatic
polyamide; imide type polymers; sulfone type polymers; polyether
sulfone type polymers; polyether-ether ketone type polymers; poly
phenylene sulfide type polymers; vinyl alcohol type polymer;
vinylidene chloride type polymers; vinyl butyral type polymers;
allylate type polymers; polyoxymethylene type polymers; epoxy type
polymers; or blend polymers of the above-mentioned polymers may be
mentioned. Films made of heat curing type or ultraviolet ray curing
type resins, such as acryl based, urethane based, acryl urethane
based, epoxy based, and silicone based, etc. may be mentioned.
[0072] Moreover, as is described in Japanese Patent Laid-Open
Publication No. 2001-343529 (WO 01/37007), polymer films, for
example, resin compositions including (A) thermoplastic resins
having substituted and/or non-substituted imido group is in side
chain, and (B) thermoplastic resins having substituted and/or
non-substituted phenyl and nitrile group in sidechain may be
mentioned. As an illustrative example, a film may be mentioned that
is made of a resin composition including alternating copolymer
comprising iso-butylene and N-methyl maleimide, and
acrylonitrile-styrene copolymer. A film comprising mixture extruded
article of resin compositions etc. may be used.
[0073] As a transparent protection film, if polarization property
and durability are taken into consideration, cellulose based
polymer, such as triacetyl cellulose, is preferable, and especially
triacetyl cellulose film is suitable. In general, a thickness of a
transparent protection film is 500 .mu.m or less, preferably 1
through 300 .mu.m, and especially preferably 5 through 300 .mu.m.
In addition, when transparent protection films are provided on both
sides of the polarizer, transparent protection films comprising
same polymer material may be used on both of a front side and a
back side, and transparent protection films comprising different
polymer materials etc. may be used.
[0074] Moreover, it is preferable that the transparent protection
film may have as little coloring as possible. Accordingly, a
protection film having a phase difference value in a film thickness
direction represented by Rth=[(nx+ny)/2-nz].times.d of -90 nm
through +75 nm (where, nx and ny represent principal indices of
refraction in a film plane, nz represents refractive index in a
film thickness direction, and d represents a film thickness) may be
preferably used. Thus, coloring (optical coloring) of polarizing
plate resulting from a protection film may mostly be cancelled
using a protection film having a phase difference value (Rth) of
-90 nm through +75 nm in a thickness direction. The phase
difference value (Rth) in a thickness direction is preferably -80
nm through +60 nm, and especially preferably -70 nm through +45
nm.
[0075] A hard coat layer may be prepared, or antireflection
processing, processing aiming at sticking prevention, diffusion or
anti glare may be performed onto the face on which the polarizing
film of the above described transparent protective film has not
been adhered.
[0076] A hard coat processing is applied for the purpose of
protecting the surface of the polarizing plate from damage, and
this hard coat film may be formed by a method in which, for
example, a curable coated film with excellent hardness, slide
property etc. is added on the surface of the protective film using
suitable ultraviolet curable type resins, such as acrylic type and
silicone type resins. Antireflection processing is applied for the
purpose of antireflection of outdoor daylight on the surface of a
polarizing plate and it may be prepared by forming an
antireflection film according to the conventional method etc.
Besides, a sticking prevention processing is applied for the
purpose of adherence prevention with adjoining layer.
[0077] In addition, an anti glare processing is applied in order to
prevent a disadvantage that outdoor daylight reflects on the
surface of a polarizing plate to disturb visual recognition of
transmitting light through the polarizing plate, and the processing
may be applied, for example, by giving a fine concavo-convex
structure to a surface of the protective film using, for example, a
suitable method, such as rough surfacing treatment method by
sandblasting or embossing and a method of combining transparent
fine particle. As a fine particle combined in order to form a fine
concavo-convex structure on the above-mentioned surface,
transparent fine particles whose average particle size is 0.5 to 50
.mu.m, for example, such as inorganic type fine particles that may
have conductivity comprising silica, alumina, titania, zirconia,
tin oxides, indium oxides, cadmium oxides, antimony oxides, etc.,
and organic type fine particles comprising cross-linked of
non-cross-linked polymers may be used. When forming fine
concavo-convex structure on the surface, the amount of fine
particle used is usually about 2 to 50 weight part to the
transparent resin 100 weight part that forms the fine
concavo-convex structure on the surface, and preferably 5 to 25
weight part. An anti glare layer may serve as a diffusion layer
(viewing angle expanding function etc.) for diffusing transmitting
light through the polarizing plate and expanding a viewing angle
etc.
[0078] In addition, the above-mentioned antireflection layer,
sticking prevention layer, diffusion layer, anti glare layer, etc.
may be built in the protective film itself, and also they may be
prepared as an optical layer different from the protective
layer.
[0079] Adhesives are used for adhesion processing of the above
described polarizing film and the transparent protective film. As
adhesives, isocyanate derived adhesives, polyvinyl alcohol derived
adhesives, gelatin derived adhesives, vinyl polymers derived latex
type, aqueous polyesters derived adhesives, etc. may be mentioned.
The above-described adhesives are usually used as adhesives
comprising aqueous solution, and usually contain solid of 0.5 to
60% by weight.
[0080] A polarizing plate of the present invention is manufactured
by adhering the above described transparent protective film and the
polarizing film using the above described adhesives. The
application of adhesives may be performed to any of the transparent
protective film or the polarizing film, and may be performed to
both of them. After adhered, drying process is given and the
adhesion layer comprising applied dry layer is formed. Adhering
process of the polarizing film and the transparent protective film
may be performed using a roll laminator etc. Although a thickness
of the adhesion layer is not especially limited, it is usually
approximately 0.1 to 5 .mu.m.
[0081] A polarizing plate of the present invention may be used in
practical use as an optical film laminated with other optical
layers. Although there is especially no limitation about the
optical layers, one layer or two layers or more of optical layers,
which may be used for formation of a liquid crystal display etc.,
such as a reflector, a transflective plate, a retardation plate (a
half wavelength plate and a quarter wavelength plate included), and
a viewing angle compensation film, may be used. Especially
preferable polarizing plates are; a reflection type polarizing
plate or a transflective type polarizing plate in which a reflector
or a transflective reflector is further laminated onto a polarizing
plate of the present invention; an elliptically polarizing plate or
a circular polarizing plate in which a retardation plate is further
laminated onto the polarizing plate; a wide viewing angle
polarizing plate in which a viewing angle compensation film is
further laminated onto the polarizing plate; or a polarizing plate
in which a brightness enhancement film is further laminated onto
the polarizing plate.
[0082] A reflective layer is prepared on a polarizing plate to give
a reflection type polarizing plate, and this type of plate is used
for a liquid crystal display in which an incident light from a view
side (display side) is reflected to give a display. This type of
plate does not require built-in light sources, such as a backlight,
but has an advantage that a liquid crystal display may easily be
made thinner. A reflection type polarizing plate may be formed
using suitable methods, such as a method in which a reflective
layer of metal etc. is, if required, attached to one side of a
polarizing plate through a transparent protective layer etc.
[0083] As an example of a reflection type polarizing plate, a plate
may be mentioned on which, if required, a reflective layer is
formed using a method of attaching a foil and vapor deposition film
of reflective metals, such as aluminum, to one side of a matte
treated protective film. Moreover, a different type of plate with a
fine concavo-convex structure on the surface obtained by mixing
fine particle into the above-mentioned protective film, on which a
reflective layer of concavo-convex structure is prepared, may be
mentioned. The reflective layer that has the above-mentioned fine
concavo-convex structure diffuses incident light by random
reflection to prevent directivity and glaring appearance, and has
an advantage of controlling unevenness of light and darkness etc.
Moreover, the protective film containing the fine particle has an
advantage that unevenness of light and darkness may be controlled
more effectively, as a result that an incident light and its
reflected light that is transmitted through the film are diffused.
A reflective layer with fine concavo-convex structure on the
surface effected by a surface fine concavo-convex structure of a
protective film may be formed by a method of attaching a metal to
the surface of a transparent protective layer directly using, for
example, suitable methods of a vacuum evaporation method, such as a
vacuum deposition method, an ion plating method, and a sputtering
method, and a plating method etc.
[0084] Instead of a method in which a reflection plate is directly
given to the protective film of the above-mentioned polarizing
plate, a reflection plate may also be used as a reflective sheet
constituted by preparing a reflective layer on the suitable film
for the transparent film. In addition, since a reflective layer is
usually made of metal, it is desirable that the reflective side is
covered with a protective film or a polarizing plate etc. when
used, from a viewpoint of preventing deterioration in reflectance
by oxidation, of maintaining an initial reflectance for a long
period of time and of avoiding preparation of a protective layer
separately etc.
[0085] In addition, a transflective type polarizing plate may be
obtained by preparing the above-mentioned reflective layer as a
transflective type reflective layer, such as a half-mirror etc.
that reflects and transmits light. A transflective type polarizing
plate is usually prepared in the backside of a liquid crystal cell
and it may form a liquid crystal display unit of a type in which a
picture is displayed by an incident light reflected from a view
side (display side) when used in a comparatively well-lighted
atmosphere. And this unit displays a picture, in a comparatively
dark atmosphere, using embedded type light sources, such as a back
light built in backside of a transflective type polarizing plate.
That is, the transflective type polarizing plate is useful to
obtain of a liquid crystal display of the type that saves energy of
light sources, such as a back light, in a well-lighted atmosphere,
and can be used with a built-in light source if needed in a
comparatively dark atmosphere etc.
[0086] The above-mentioned polarizing plate may be used as
elliptically polarizing plate or circularly polarizing plate on
which the retardation plate is laminated. A description of the
above-mentioned elliptically polarizing plate or circularly
polarizing plate will be made in the following paragraph. These
polarizing plates change linearly polarized light into elliptically
polarized light or circularly polarized light, elliptically
polarized light or circularly polarized light into linearly
polarized light or change the polarization direction of linearly
polarization by a function of the retardation plate. As a
retardation plate that changes circularly polarized light into
linearly polarized light or linearly polarized light into
circularly polarized light, what is called a quarter wavelength
plate (also called .lamda./4 plate) is used. Usually,
half-wavelength plate (also called .lamda./2 plate) is used, when
changing the polarization direction of linearly polarized
light.
[0087] Elliptically polarizing plate is effectively used to give a
monochrome display without above-mentioned coloring by compensating
(preventing) coloring (blue or yellow color) produced by
birefringence of a liquid crystal layer of a super twisted nematic
(STN) type liquid crystal display. Furthermore, a polarizing plate
in which three-dimensional refractive index is controlled may also
preferably compensate (prevent) coloring produced when a screen of
a liquid crystal display is viewed from an oblique direction.
Circularly polarizing plate is effectively used, for example, when
adjusting a color tone of a picture of a reflection type liquid
crystal display that provides a colored picture, and it also has
function of antireflection. For example, a retardation plate may be
used that compensates coloring and viewing angle, etc. caused by
birefringence of various wavelength plates or liquid crystal layers
etc. Besides, optical characteristics, such as retardation, may be
controlled using laminated layer with two or more sorts of
retardation plates having suitable retardation value according to
each purpose. As retardation plates, birefringence films formed by
stretching films comprising suitable polymers, such as
polycarbonates, norbornene type resins, polyvinyl alcohols,
polystyrenes, poly methyl methacrylates, polypropylene;
polyallylates and polyamides; oriented films comprising liquid
crystal materials, such as liquid crystal polymer; and films on
which an alignment layer of a liquid crystal material is supported
may be mentioned. A retardation plate may be a retardation plate
that has a proper phase difference according to the purposes of
use, such as various kinds of wavelength plates and plates aiming
at compensation of coloring by birefringence of a liquid crystal
layer and of visual angle, etc., and may be a retardation plate in
which two or more sorts of retardation plates is laminated so that
optical properties, such as retardation, may be controlled.
[0088] The above-mentioned elliptically polarizing plate and an
above-mentioned reflected type elliptically polarizing plate are
laminated plate combining suitably a polarizing plate or a
reflection type polarizing plate with a retardation plate. This
type of elliptically polarizing plate etc. may be manufactured by
combining a polarizing plate (reflected type) and a retardation
plate, and by laminating them one by one separately in the
manufacture process of a liquid crystal display. On the other hand,
the polarizing plate in which lamination was beforehand carried out
and was obtained as an optical film, such as an elliptically
polarizing plate, is excellent in a stable quality, a workability
in lamination etc., and has an advantage in improved manufacturing
efficiency of a liquid crystal display.
[0089] A viewing angle compensation film is a film for extending
viewing angle so that a picture may look comparatively clearly,
even when it is viewed from an oblique direction not from vertical
direction to a screen. As such a viewing angle compensation
retardation plate, in addition, a film having birefringence
property that is processed by uniaxial stretching or orthogonal
bidirectional stretching and a bidirectionally stretched film as
inclined orientation film etc. may be used. As inclined orientation
film, for example, a film obtained using a method in which a heat
shrinking film is adhered to a polymer film, and then the combined
film is heated and stretched or shrinked under a condition of being
influenced by a shrinking force, or a film that is oriented in
oblique direction may be mentioned. The viewing angle compensation
film is suitably combined for the purpose of prevention of coloring
caused by change of visible angle based on retardation by liquid
crystal cell etc. and of expansion of viewing angle with good
visibility.
[0090] Besides, a compensation plate in which an optical anisotropy
layer consisting of an alignment layer of liquid crystal polymer,
especially consisting of an inclined alignment layer of discotic
liquid crystal polymer is supported with triacetyl cellulose film
may preferably be used from a viewpoint of attaining a wide viewing
angle with good visibility.
[0091] The polarizing plate with which a polarizing plate and a
brightness enhancement film are adhered together is usually used
being prepared in a backside of a liquid crystal cell. A brightness
enhancement film shows a characteristic that reflects linearly
polarized light with a predetermined polarization axis, or
circularly polarized light with a predetermined direction, and that
transmits other light, when natural light by back lights of a
liquid crystal display or by reflection from a back-side etc.,
comes in. The polarizing plate, which is obtained by laminating a
brightness enhancement film to a polarizing plate, thus does not
transmit light without the predetermined polarization state and
reflects it, while obtaining transmitted light with the
predetermined polarization state by accepting a light from light
sources, such as a backlight. This polarizing plate makes the light
reflected by the brightness enhancement film further reversed
through the reflective layer prepared in the backside and forces
the light re-enter into the brightness enhancement film, and
increases the quantity of the transmitted light through the
brightness enhancement film by transmitting a part or all of the
light as light with the predetermined polarization state. The
polarizing plate simultaneously supplies polarized light that is
difficult to be absorbed in a polarizer, and increases the quantity
of the light usable for a liquid crystal picture display etc., and
as a result luminosity may be improved. That is, in the case where
the light enters through a polarizer from backside of a liquid
crystal cell by the back light etc. without using a brightness
enhancement film, most of the light, with a polarization direction
different from the polarization axis of a polarizer, is absorbed by
the polarizer, and does not transmit through the polarizer. This
means that although influenced with the characteristics of the
polarizer used, about 50 percent of light is absorbed by the
polarizer, the quantity of the light usable for a liquid crystal
picture display etc. decreases so much, and a resulting picture
displayed becomes dark. A brightness enhancement film does not
enter the light with the polarizing direction absorbed by the
polarizer into the polarizer but reflects the light once by the
brightness enhancement film, and further makes the light reversed
through the reflective layer etc. prepared in the backside to
re-enter the light into the brightness enhancement film. By this
above-mentioned repeated operation, only when the polarization
direction of the light reflected and reversed between the both
becomes to have the polarization direction which may pass a
polarizer, the brightness enhancement film transmits the light to
supply it to the polarizer. As a result, the light from a backlight
may be efficiently used for the display of the picture of a liquid
crystal display to obtain a bright screen.
[0092] A diffusion plate may also be prepared between brightness
enhancement film and the above described reflective layer, etc. A
polarized light reflected by the brightness enhancement film goes
to the above described reflective layer etc., and the diffusion
plate installed diffuses passing light uniformly and changes the
light state into depolarization at the same time. That is, the
diffusion plate returns polarized light to natural light state.
Steps are repeated where light, in the unpolarized state, i.e.,
natural light state, reflects through reflective layer and the
like, and again goes into brightness enhancement film through
diffusion plate toward reflective layer and the like. Diffusion
plate that returns polarized light to the natural light state is
installed between brightness enhancement film and the above
described reflective layer, and the like, in this way, and thus a
uniform and bright screen may be provided while maintaining
brightness of display screen, and simultaneously controlling
non-uniformity of brightness of the display screen. By preparing
such diffusion plate, it is considered that number of repetition
times of reflection of a first incident light increases with
sufficient degree to provide uniform and bright display screen
conjointly with diffusion function of the diffusion plate.
[0093] The suitable films are used as the above-mentioned
brightness enhancement film. Namely, multilayer thin film of a
dielectric substance; a laminated film that has the characteristics
of transmitting a linearly polarized light with a predetermined
polarizing axis, and of reflecting other light, such as the
multilayer laminated film of the thin film having a different
refractive-index anisotropy (D-BEF and others manufactured by 3M
Co., Ltd.); an aligned film of cholesteric liquid-crystal polymer;
a film that has the characteristics of reflecting a circularly
polarized light with either left-handed or right-handed rotation
and transmitting other light, such as a film on which the aligned
cholesteric liquid crystal layer is supported (PCF350 manufactured
by NITTO DENKO CORPORATION, Transmax manufactured by Merck Co.,
Ltd., and others); etc. may be mentioned.
[0094] Therefore, in the brightness enhancement film of a type that
transmits a linearly polarized light having the above-mentioned
predetermined polarization axis, by arranging the polarization axis
of the transmitted light and entering the light into a polarizing
plate as it is, the absorption loss by the polarizing plate is
controlled and the polarized light can be transmitted efficiently.
On the other hand, in the brightness enhancement film of a type
that transmits a circularly polarized light as a cholesteric
liquid-crystal layer, the light may be entered into a polarizer as
it is, but it is desirable to enter the light into a polarizer
after changing the circularly polarized light to a linearly
polarized light through a retardation plate, taking control an
absorption loss into consideration. In addition, a circularly
polarized light is convertible into a linearly polarized light
using a quarter wavelength plate as the retardation plate.
[0095] A retardation plate that works as a quarter wavelength plate
in a wide wavelength ranges, such as a visible-light band, is
obtained by a method in which a retardation layer working as a
quarter wavelength plate to a pale color light with a wavelength of
550 nm is laminated with a retardation layer having other
retardation characteristics, such as a retardation layer working as
a half-wavelength plate. Therefore, the retardation plate located
between a polarizing plate and a brightness enhancement film may
consist of one or more retardation layers.
[0096] In addition, also in a cholesteric liquid-crystal layer, a
layer reflecting a circularly polarized light in a wide wavelength
ranges, such as a visible-light band, may be obtained by adopting a
configuration structure in which two or more layers with different
reflective wavelength are laminated together. Thus a transmitted
circularly polarized light in a wide wavelength range may be
obtained using this type of cholesteric liquid-crystal layer.
[0097] Moreover, the polarizing plate may consist of multi-layered
film of laminated layers of a polarizing plate and two of more of
optical layers as the above-mentioned separated type polarizing
plate. Therefore, a polarizing plate may be a reflection type
elliptically polarizing plate or a semi-transmission type
elliptically polarizing plate, etc. in which the above-mentioned
reflection type polarizing plate or a transflective type polarizing
plate is combined with above described retardation plate
respectively.
[0098] Although an optical film with the above described optical
layer laminated to the polarizing plate may be formed by a method
in which laminating is separately carried out sequentially in
manufacturing process of a liquid crystal display etc., an optical
film in a form of being laminated beforehand has an outstanding
advantage that it has excellent stability in quality and assembly
workability, etc., and thus manufacturing processes ability of a
liquid crystal display etc. may be raised. Proper adhesion means,
such as an adhesive layer, may be used for laminating. On the
occasion of adhesion of the above described polarizing plate and
other optical films, the optical axis may be set as a suitable
configuration angle according to the target retardation
characteristics etc.
[0099] In the polarizing plate mentioned above and the optical film
in which at least one layer of the polarizing plate is laminated,
an adhesive layer may also be prepared for adhesion with other
members, such as a liquid crystal cell etc. As pressure sensitive
adhesive that forms adhesive layer is not especially limited, and,
for example, acrylic type polymers; silicone type polymers;
polyesters, polyurethanes, polyamides, polyethers; fluorine type
and rubber type polymers may be suitably selected as a base
polymer. Especially, a pressure sensitive adhesive such as acrylics
type pressure sensitive adhesives may be preferably used, which is
excellent in optical transparency, showing adhesion characteristics
with moderate wettability, cohesiveness and adhesive property and
has outstanding weather resistance, heat resistance, etc.
[0100] Moreover, an adhesive layer with low moisture absorption and
excellent heat resistance is desirable. This is because those
characteristics are required in order to prevent foaming and
peeling-off phenomena by moisture absorption, in order to prevent
decrease in optical characteristics and curvature of a liquid
crystal cell caused by thermal expansion difference etc. and in
order to manufacture a liquid crystal display excellent in
durability with high quality.
[0101] The adhesive layer may contain additives, for example, such
as natural or synthetic resins, adhesive resins, glass fibers,
glass beads, metal powder, fillers comprising other inorganic
powder etc., pigments, colorants and antioxidants. Moreover, it may
be an adhesive layer that contains fine particle and shows optical
diffusion nature.
[0102] Proper method may be carried out to attach an adhesive layer
to one side or both sides of the optical film. As an example, about
10 to 40 weight % of the pressure sensitive adhesive solution in
which a base polymer or its composition is dissolved or dispersed,
for example, toluene or ethyl acetate or a mixed solvent of these
two solvents is prepared. A method in which this solution is
directly applied on a polarizing plate top or an optical film top
using suitable developing methods, such as flow method and coating
method, or a method in which an adhesive layer is once formed on a
separator, as mentioned above, and is then transferred on a
polarizing plate or an optical film may be mentioned.
[0103] An adhesive layer may also be prepared on one side or both
sides of a polarizing plate or an optical film as a layer in which
pressure sensitive adhesives with different composition or
different kind etc. are laminated together. Moreover, when adhesive
layers are prepared on both sides, adhesive layers that have
different compositions, different kinds or thickness, etc. may also
be used on front side and backside of a polarizing plate or an
optical film. Thickness of an adhesive layer may be suitably
determined depending on a purpose of usage or adhesive strength,
etc., and generally is 1 to 500 .mu.m, preferably 5 to 200 .mu.m,
and more preferably 10 to 100 .mu.m.
[0104] A temporary separator is attached to an exposed side of an
adhesive layer to prevent contamination etc., until it is
practically used. Thereby, it can be prevented that foreign matter
contacts adhesive layer in usual handling. As a separator, without
taking the above-mentioned thickness conditions into consideration,
for example, suitable conventional sheet materials that is coated,
if necessary, with release agents, such as silicone type, long
chain alkyl type, fluorine type release agents, and molybdenum
sulfide may be used. As a suitable sheet material, plastics films,
rubber sheets, papers, cloths, no woven fabrics, nets, foamed
sheets and metallic foils or laminated sheets thereof may be
used.
[0105] In addition, in the present invention, ultraviolet absorbing
property may be given to the above-mentioned each layer, such as a
polarizer for a polarizing plate, a transparent protective film and
an optical film etc. and an adhesive layer, using a method of
adding UV absorbents, such as salicylic acid ester type compounds,
benzophenol type compounds, benzotriazol type compounds, cyano
acrylate type compounds, and nickel complex salt type
compounds.
[0106] An optical film of the present invention may be preferably
used for manufacturing various equipment, such as liquid crystal
display, etc. Assembling of a liquid crystal display may be carried
out according to conventional methods. That is, a liquid crystal
display is generally manufactured by suitably assembling several
parts such as a liquid crystal cell, optical films and, if
necessity, lighting system, and by incorporating driving circuit.
In the present invention, except that an optical film by the
present invention is used, there is especially no limitation to use
any conventional methods. Also any liquid crystal cell of arbitrary
type, such as TN type, and STN type, .pi. type may be used.
[0107] Suitable liquid crystal displays, such as liquid crystal
display with which the above-mentioned optical film has been
located at one side or both sides of the liquid crystal cell, and
with which a backlight or a reflector is used for a lighting system
may be manufactured. In this case, the optical film by the present
invention may be installed in one side or both sides of the liquid
crystal cell. When installing the optical films in both sides, they
may be of the same type or of different type. Furthermore, in
assembling a liquid crystal display, suitable parts, such as
diffusion plate, anti-glare layer, antireflection film, protective
plate, prism array, lens array sheet, optical diffusion plate, and
backlight, may be installed in suitable position in one layer or
two or more layers.
[0108] Subsequently, organic electro luminescence equipment
(organic EL display) will be explained. Generally, in organic EL
display, a transparent electrode, an organic luminescence layer and
a metal electrode are laminated on a transparent substrate in an
order configuring an illuminant (organic electro luminescence
illuminant). Here, an organic luminescence layer is a laminated
material of various organic thin films, and much compositions with
various combination are known, for example, a laminated material of
hole injection layer comprising triphenylamine derivatives etc., a
luminescence layer comprising fluorescent organic solids, such as
anthracene; a laminated material of electronic injection layer
comprising such a luminescence layer and perylene derivatives;
etc.; laminated material of these hole injection layers,
luminescence layer, and electronic injection layer etc.
[0109] An organic EL display emits light based on a principle that
positive hole and electron are injected into an organic
luminescence layer by impressing voltage between a transparent
electrode and a metal electrode, the energy produced by
recombination of these positive holes and electrons excites
fluorescent substance, and subsequently light is emitted when
excited fluorescent substance returns to ground state. A mechanism
called recombination which takes place in a intermediate process is
the same as a mechanism in common diodes, and, as is expected,
there is a strong non-linear relationship between electric current
and luminescence strength accompanied by rectification nature to
applied voltage.
[0110] In an organic EL display, in order to take out luminescence
in an organic luminescence layer, at least one electrode must be
transparent. The transparent electrode usually formed with
transparent electric conductor, such as indium tin oxide (ITO), is
used as an anode. On the other hand, in order to make electronic
injection easier and to increase luminescence efficiency, it is
important that a substance with small work function is used for
cathode, and metal electrodes, such as Mg--Ag and Al--Li, are
usually used.
[0111] In organic EL display of such a configuration, an organic
luminescence layer is formed by a very thin film about 10 nm in
thickness. For this reason, light is transmitted nearly completely
through organic luminescence layer as through transparent
electrode. Consequently, since the light that enters, when light is
not emitted, as incident light from a surface of a transparent
substrate and is transmitted through a transparent electrode and an
organic luminescence layer and then is reflected by a metal
electrode, appears in front surface side of the transparent
substrate again, a display side of the organic EL display looks
like mirror if viewed from outside.
[0112] In an organic EL display containing an organic electro
luminescence illuminant equipped with a transparent electrode on a
surface side of an organic luminescence layer that emits light by
impression of voltage, and at the same time equipped with a metal
electrode on a back side of organic luminescence layer, a
retardation plate may be installed between these transparent
electrodes and a polarizing plate, while preparing the polarizing
plate on the surface side of the transparent electrode.
[0113] Since the retardation plate and the polarizing plate have
function polarizing the light that has entered as incident light
from outside and has been reflected by the metal electrode, they
have an effect of making the mirror surface of metal electrode not
visible from outside by the polarization action. If a retardation
plate is configured with a quarter wavelength plate and the angle
between the two polarization directions of the polarizing plate and
the retardation plate is adjusted to .pi./4, the mirror surface of
the metal electrode may be completely covered.
[0114] This means that only linearly polarized light component of
the external light that enters as incident light into this organic
EL display is transmitted with the work of polarizing plate. This
linearly polarized light generally gives an elliptically polarized
light by the retardation plate, and especially the retardation
plate is a quarter wavelength plate, and moreover when the angle
between the two polarization directions of the polarizing plate and
the retardation plate is adjusted to .pi./4, it gives a circularly
polarized light.
[0115] This circularly polarized light is transmitted through the
transparent substrate, the transparent electrode and the organic
thin film, and is reflected by the metal electrode, and then is
transmitted through the organic thin film, the transparent
electrode and the transparent substrate again, and is turned into a
linearly polarized light again with the retardation plate. And
since this linearly polarized light lies at right angles to the
polarization direction of the polarizing plate, it cannot be
transmitted through the polarizing plate. As the result, mirror
surface of the metal electrode may be completely covered.
EXAMPLES
[0116] Examples of this invention will, hereinafter, be shown, and
specific descriptions will be provided. In addition, "part(s)" in
following sections represents part(s) by weight.
Example 1
[0117] A liquid crystalline monomer having acryloyl groups at both
of terminal groups of a mesogen group (nematic liquid crystal
temperature range: 60 through 125.degree. C.) and a surface active
agent (manufactured by Kao Corporation, EMASOL L10) were blended by
a weight ratio of 30:1 to prepare a tetrahydrofuran solution having
30% by weight of solid content. A polyvinyl alcohol aqueous
solution having a polyvinyl alcohol resin with a 2400 of degree of
polymerization and a 98.5% of degrees of saponification dissolved
therein and having 13% by weight of solid content, and the
above-mentioned tetrahydrofuran solution were mixed so as to give
(polyvinyl alcohol):(liquid crystalline monomer)=100:3 (weight
ratio), and they were agitated with a homogeneous mixer to obtain a
mixed solution. Then, after the mixed solution concerned was held
for 30 minutes at 90.degree. C. to vaporize tetrahydrofuran off and
cooled at room temperature (23.degree. C.), the mixed solution was
coated using a casting method, subsequently dried to obtain a
cloudy film with a thickness of 70 .mu.m. This film was uniaxially
stretched by 3 times at 110.degree. C. to obtain a stretched film
(the stretched film produced at this time is referred to as Film
A).
[0118] Film A has scattering anisotropy, and when a polarized light
with a plane of vibration parallel to a stretching direction
enters, the light was scattered, and on the other side, when a
polarized light with a plane of vibration perpendicular to the
direction entered, the light was not scattered. When the film A was
observed with a polarization microscope, it was identified that
countless minute domains of a liquid crystalline monomer dispersed
in a polyvinyl alcohol matrix were formed. This liquid crystalline
monomer was oriented in a stretching direction, and it had an
average size of the minute domains of 5 through 10 .mu.m in the
stretching direction (.DELTA.n.sup.2 direction).
[0119] Refractive indexes of the matrix and of the minute domains
were separately measured respectively. Measurement was performed at
20.degree. C. First, an independent refractive index of the
polyvinyl alcohol film stretched by a same stretching condition
(stretched 3 times at 110.degree. C.) was measured using an Abbe
refractometer (measurement light: 589 nm) to obtain a refractive
index=1.54 in the stretching direction (.DELTA.n.sup.1 direction),
and a refractive index of .DELTA.n.sup.2 direction=1.52. Moreover,
the liquid crystalline monomer was measured for refractive indexes
(n.sub.e: extraordinary refractive index, and n.sub.o: ordinary
refractive index). The liquid crystalline monomer oriented and
coated on a high refractive index glass to which perpendicular
orientation processing was given was measured for n.sub.o using an
Abbe refractometer (measurement light: 589 nm). On the other hand,
the liquid crystalline monomer was introduced into a liquid crystal
cell to which horizontal orientation processing was given, a
retardation (.DELTA.n.times.d) was measured using an automatic
birefringence measuring apparatus (manufactured by Oji Scientific
Instruments, automatic birefringence meter KOBRA 21 ADH), a cell
gap (d) was separately measured using an optical interference
method, and then .DELTA.n was calculated from the phase
difference/cell gap. This sum of .DELTA.n and n.sub.o was defined
as n.sub.e. A value n.sub.e (equivalent to a refractive index in a
.DELTA.n.sup.1 direction)=1.654 and n.sub.o (equivalent to a
refractive index in a .DELTA.n.sup.2 direction)=1.523 were
obtained. Therefore, calculated results of
.DELTA.n.sup.1=1.654-1.54=0.114, .DELTA.n.sup.2=1.523-1.52=0.003
were obtained.
[0120] Then, Film A was sequentially immersed in each of following
baths. That is, (a) swelling was performed in a water bath at
30.degree. C.;
[0121] (b) dyeing was performed at 30.degree. C. in an aqueous
solution (0.32% by weight of concentration) in which
iodine:potassium iodide=1:7 (weight ratio) were dissolved; (c)
cross-linking was performed in an aqueous solution bath of 3% by
weight boric acid; and (d) hue adjustment was performed at
30.degree. C. in an aqueous solution bath of potassium iodide of 3%
by weight, and thereby a polarizer of this invention was
obtained.
Comparative Example 1
[0122] Except that the tetrahydrofuran solution including the
liquid crystalline monomer was not mixed with the polyvinyl alcohol
aqueous solution in Example 1, and the polyvinyl alcohol aqueous
solution was independently used, a same method as in Example 1 was
repeated to produce a film. A same stretching as in Example 1 was
provided to the film to produce a stretched film. In addition, the
obtained stretched film was dyed as in Example 1 using completely
same processes as (a) through (d), and polarizer was obtained.
Example 2
[0123] Except that the polyvinyl alcohol aqueous solution and the
tetrahydrofuran solution were mixed so as to be polyvinyl
alcohol:liquid crystalline monomer=100:10 (weight ratio), a same
method as in Example 1 was repeated to obtain a mixed solution. And
except for having used the mixed solution concerned, a same method
as in Example 1 was repeated to obtain a stretched film.
[0124] The stretched film had scattering anisotropy as in Example
1, when a polarized light with a plane of vibration parallel to a
stretching direction enters, the light was scattered, and on the
other side, when a polarized light with a plane of vibration
perpendicular to the direction entered, the light was not
scattered. When the stretched film was observed with a polarization
microscope, it was identified that countless minute domains of a
liquid crystalline monomer dispersed in a polyvinyl alcohol matrix
were formed. This liquid crystalline monomer was oriented in a
stretching direction, and it had an average size of the minute
domains of 3 through 5 .mu.m in the stretching direction
(.DELTA.n.sup.2 direction). Subsequently, the stretched film was
sequentially immersed in each of baths of (a) through (d) as in
Example 1, iodine dyeing was performed to obtain a polarizer of
this invention.
Example 3
[0125] A polyvinyl alcohol aqueous solution of 13% by weight of
solid content in which a polyvinyl alcohol resin having a degree of
polymerization of 2400 and a 98.5% of a degrees of saponification
were dissolved; a liquid crystalline monomer (nematic liquid
crystal temperature range is 40 through 70.degree. C.) having
acryloyl groups at each terminal of both of a mesogen group; and
glycerin were mixed so as to be polyvinyl alcohol:liquid
crystalline monomer:glycerin=100:3:15 (weight ratio), and the
mixture was heated more than a liquid crystal temperature range,
and was agitated with a homogeneous mixer to obtain a mixed
solution. After degassing of bubbles existing in the mixed solution
concerned by left to stand at room temperature (23.degree. C.), the
mixed solution was coated by a casting method, and a cloudy mixed
film having a thickness of 70 .mu.m was obtained after drying. The
mixed film was heat-treated for 10 minutes at 130.degree. C.
[0126] Each of following processes was given to the above-mentioned
mixed film, and stretched in a wet state: (a) the film was immersed
in 30.degree. C. water bath, swelled and stretched to 3 times; (b)
it was immersed and dyed in an aqueous solution (0.32% by weight of
concentration) of iodine:potassium iodide=1:7 (weight ratio) at
30.degree. C.; (c) the film was immersed in an aqueous solution of
boric acid of 3% by weight at 30.degree. C., and cross-linked; (d)
furthermore, the film was immersed in an aqueous solution of boric
acid of 4% by weight at 60.degree. C., and stretched twice (total
stretching to 6 times); and (e) the obtained film was immersed in
an aqueous solution bath of potassium iodide of 5% by weight at
30.degree. C., and hue adjustment was given. Then, it was dried for
4 minutes at 50.degree. C., and a polarizer of this invention was
obtained.
(Identification of Anisotropic Scattering Expression, and
Measurement of Refractive Index)
[0127] The above-mentioned mixed film was stretched on same
conditions as in the above-mentioned wet type stretching except for
using only water as an aqueous solution in the process (b) (with no
dyeing). It was confirmed that desired scattering anisotropy was
demonstrated by the stretched film obtained as in Example 1.
Therefore, it was identified that the above-mentioned polarizer
served as a desired polarizer in which both of absorption
anisotropy and scattering anisotropy were demonstrated.
[0128] When the polarizer obtained was observed with a polarization
microscope, it was identified that countless minute domains of a
liquid crystalline monomer dispersed in a polyvinyl alcohol matrix
were formed. This liquid crystalline monomer was oriented in a
stretching direction, and it had an average size of the minute
domains of 1 through 3 .mu.m in the stretching direction
(.DELTA.n.sup.2 direction).
[0129] Refractive indexes of the matrix and the minute domains were
separately measured respectively. Measurement of refractive index
was performed by a same method as in Example 1. Firstly, except for
using only water as an aqueous solution in the process (b) (with no
dyeing), stretching was performed on same conditions as in the
above-mentioned wet type stretching to obtain an independently
stretched film of polyvinyl alcohol film. The film was measured for
refractive indexes with Abbe refractometer (measurement light: 589
nm) to obtain a refractive index in the stretching direction
(.DELTA.n.sup.1 direction)=1.54 and a refractive index in the
.DELTA.n.sup.2 direction=1.52. Moreover, the liquid crystalline
monomer was measured for refractive indexes (n.sub.e: extraordinary
index, and n.sub.o: ordinary index) to obtain n.sub.e (equivalent
to a refractive index in the .DELTA.n.sup.1 direction)=1.66 and
n.sub.o (equivalent to a refractive index in the .DELTA.n.sup.2
direction)=1.53. Therefore, calculated results of
.DELTA.n.sup.1=1.66-1.54=0.12 and .DELTA.n.sup.2=1.53-1.52=0.01
were obtained. It was identified that desired anisotropic
scattering was demonstrated from the above results.
Example 4
[0130] Except that fine-particles with globular form (mean diameter
of 2 .mu.m) of acrylic styrene with refractive index 1.51 were used
instead of the liquid crystalline monomer in Example 3 and mixed so
that polyvinyl alcohol:fine-particles with globular form=100:2
(weight ratio), same method as in Example 3 was repeated to obtain
a mixed solution. Moreover, a same method as in Example 3 was
repeated using the mixed solution concerned to produce a mixed
film. In addition, same method as in Example 3 was repeated on the
mixed film obtained, and completely same wet type stretching as by
(a) through (e) was given to obtain a polarizer.
.DELTA.n.sup.1=0.03 (=1.54-1.51), and .DELTA.n.sup.2=0.01
(=1.52-1.51). As a result, it has confirmed that desired
anisotropic scattering was demonstrated.
Comparative Example 2
[0131] Same operations as in Example 3 were repeated except for a
film being produced in Example 3 using the polyvinyl alcohol
aqueous solution itself. In addition, same method as in Example 3
was repeated on the mixed film obtained, and completely same wet
type stretching as by (a) through (e) was given to obtain a
polarizer.
(Evaluation)
[0132] Polarizers (sample) obtained in Examples and Comparative
examples were measured for optical properties using a
spectrophotometer with integrating sphere (manufactured by Hitachi
Ltd. U-4100). Transmittance to each linearly polarized light was
measured under conditions in which a completely polarized light
obtained through Glan Thompson prism polarizer was set as 100%.
Transmittance was calculated based on CIE 1931 standard
colorimetric system, and is shown with Y value, for which relative
spectral responsivity correction was carried out. Notation k.sub.1
represents a transmittance of a linearly polarized light in a
maximum transmittance direction, and k.sub.2 represents a
transmittance of a linearly polarized light perpendicular to the
direction.
[0133] A polarization degree P was calculated with an equation
P={(k.sub.1-k.sub.2)/(k.sub.1+k.sub.2)}.times.100. A transmittance
T of a simple substance was calculated with an equation
T=(k.sub.1+k.sub.2)/2.
[0134] Furthermore, polarizers obtained in Example 1, Comparative
example 1, Example 3, and Comparative example 2 were measured for a
polarized light absorption spectrum using a spectrophotometer
(manufactured by Hitachi Ltd. U-4100) with Glan Thompson prism.
FIG. 2 shows polarized light absorption spectra of polarizers
obtained in Example 1 and Comparative example 1. And FIG. 3 shows
polarized light absorption spectra of polarizers obtained in
Example 3 and Comparative example 2. "MD polarized lights" in FIG.
2 (a) and FIG. 3 (a) represent polarized light absorption spectra
when a polarized light with a plane of vibration parallel to a
stretching axis enters, and "TD polarized lights" in FIG. 2 (b) and
FIG. 3 (b) represent polarized light absorption spectra when a
polarized light with a plane of vibration perpendicular to a
stretching axis enters.
[0135] In TD polarized lights (=transmission axis of polarizer), in
visible range whole band, while absorbance of the polarizers in
Example 1 and Comparative example 1 showed almost equal value, in
MD polarized lights (=absorption of polarizer+scattering axis),
absorbance in the polarizer of Example 1 exceeded absorbance of the
polarizer in Comparative example 1 in shorter wavelength side. That
is, the above-mentioned result shows that light polarizing
performance of the polarizer in Example 1 exceeded performance of
the polarizer in Comparative example 1 in a short wavelength side.
Since all conditions, such as stretching and dyeing, are equivalent
in Example 1 and Comparative example 1, it is thought that
orientation of iodine based light absorbing materials is also
equivalent. Therefore, as mentioned above, a rise of absorbance in
MD polarized light of the polarizer of Example 1 shows that light
polarizing performance improved by an effect caused by an effect of
anisotropic scattering having been added to absorption by iodine.
Also in polarizer obtained in Example 3, and polarizer obtained in
Comparative example 2, it is shown, as in the above-mentioned
results, that light polarizing performance of Example 3 improved as
compared with Comparative example 2.
[0136] In haze values, a haze value to a linearly polarized light
in a maximum transmittance direction, and a haze value to a
linearly polarized light in an absorption direction (a
perpendicular direction). Measurement of a haze value was performed
according to JIS K7136 (how to obtain a haze of
plastics-transparent material), using a haze meter (manufactured by
Murakami Color Research Institute HM-150). A commercially available
polarizing plate (NPF-SEG1224DU manufactured by NITTO DENKO CORP.:
43% of simple substance transmittances, 99.96% of polarization
degree) was arranged on a plane of incident side of a measurement
light of a sample, and stretching directions of the commercially
available polarizing plate and the sample (polarizer) were made to
perpendicularly intersect, and a haze value was measured. However,
since quantity of light at the time of rectangular crossing is less
than limitations of sensitivity of a detecting element when a light
source of the commercially available haze meter is used, light by a
halogen lamp which has high optical intensity provided separately
was made to enter with a help of an optical fiber device, thereby
quantity of light was set as inside of sensitivity of detection,
and subsequently a shutter closing and opening motion was manually
performed to obtain a haze value to be calculated.
[0137] In evaluation of unevenness, in a dark room, a sample
(polarizer) was arranged on an upper surface of a backlight used
for a liquid crystal display, furthermore, a commercially available
polarizing plate (NPF-SEG1224DU by NITTO DENKO CORP.) was laminated
as an analyzer so that a polarized light axis may intersect
perpendicularly. And a level of the unevenness was visually
observed on following criterion using the arrangement.
X: a level in which unevenness may visually be recognized
[0138] O: a level in which unevenness may not visually be
recognized TABLE-US-00001 TABLE 1 Transmittance of linearly
polarized light (%) Single haze value (%) Maximum Perpendicular
substance Maximum transmission direction transmittance Polarization
transmission Perpendicular direction (k.sub.1) (k.sub.2) (%) degree
(%) direction direction Unevenness Example 1 82.80 1.40 42.10 96.70
2.7 47.0 .largecircle. Comparative 83.00 1.65 42.30 96.10 0.4 0.3 X
Example 1 Example 2 84.20 1.20 42.70 97.20 1.9 54.1 .largecircle.
Example 3 87.00 0.035 43.52 99.92 1.8 61.0 .largecircle. Example 4
86.50 0.087 43.29 99.80 4.2 70.5 .largecircle. Comparative 87.00
0.043 43.52 99.90 0.3 0.2 X Example 2
[0139] In Examples 1 and 2 and Comparative example 1, although
single substance transmittances are almost equal to each other,
Examples 1 and 2 have higher polarization degrees, and demonstrate
excellent polarized light characteristics, as shown in
above-mentioned Table 1. Also in Examples 3 and 4 and Comparative
example 2, although single substance transmittances are almost
equal to each other, Examples 3 and 4 have higher polarization
degrees, and demonstrate excellent polarized light
characteristics.
[0140] Moreover, polarizers in Examples have a higher haze value of
transmittance at the time of a rectangular crossing, and unevenness
by variation is covered by scattering and cannot be recognized
clearly as compared with the polarizer in Comparative examples.
[0141] Next, a triacetyl cellulose film (80 .mu.m thickness) was
adhered to both sides of polarizers in Examples and Comparative
examples using a water-soluble adhesive, dried, and the adhered
films were used as a polarizing plate. The obtained polarizing
plate was exchanged for a polarizing plate on a backlight side of a
commercially available twist nematic liquid crystal panel, and was
mounted side by side. This was set in a state of black display in a
dark room and level of unevenness was observed, and unevenness was
not observed at all but very excellent visibility was confirmed as
compared with polarizing plates prepared with polarizers in
Comparative examples, when polarizing plates prepared with
polarizers in Examples were mounted.
[0142] As a polarizer having a similar structure as a structure of
a polarizer of this invention, a polarizer in which a mixed phase
of a liquid crystalline birefringent material and an absorption
dichroism material is dispersed in a resin matrix is disclosed in
Japanese Patent Laid-Open No. 2002-207118, whose effect is similar
as that of this invention. However, as compared with a case where
an absorption dichroism material exists in dispersed phase as in
Japanese Patent Laid-Open No. 2002-207118, since in a case where an
absorption dichroism material exists in a matrix layer as in this
invention a longer optical path length may be realized by which a
scattered polarized light passes absorption layer, more scattered
light may be absorbed. Therefore, this invention may demonstrate
much higher effect of improvement in light polarizing performance.
This invention may be realized with simple manufacturing
process.
[0143] Although an optical system to which a dichroic dye is added
to either of continuous phase or dispersed phase is disclosed in
Japanese Patent Laid-Open No. 2000-506990, this invention has large
special feature in a point of using not dichroic dye but iodine.
The following advantages are realized when using not dichroic dye
but iodine. (1) Absorption dichroism demonstrated with iodine is
higher than by dichroic dye. Therefore, polarized light
characteristics will also become higher if iodine is used for a
polarizer obtained. (2) Iodine does not show absorption dichroism,
before being added in a continuous phase (matrix phase), and after
being dispersed in a matrix, an iodine based light absorbing
material showing dichroism is formed by stretching. This point is
different from a dichroic dye having dichroism before being added
in a continuous phase. That is, iodine exists as iodine itself,
when dispersed in a matrix. In this case, in general, iodine has a
far effective diffusibility in a matrix compared with a dichroic
dye. As a result, iodine based light absorbing material is
dispersed to all corners of a film more excellently than dichroic
dye. Therefore, an effect of increasing optical path length by
scattering anisotropy can be utilized for maximum, which increases
polarized light function.
[0144] A background of invention given in Japanese Patent Laid-Open
No. 2000-506990 describes that optical property of a stretched film
in which liquid droplets of a liquid crystal are arranged in a
polymer matrix is indicated by Aphonin et al. However, Aphonin et
al. has mentioned an optical film comprising a matrix phase and a
dispersed phase (liquid crystal component), without using a
dichroic dye, and since a liquid crystal component is not a liquid
crystal polymer or a polymerized liquid crystal monomer, a liquid
crystal component in the film concerned has a sensitive
birefringence typically depending on temperatures. On the other
hand, this invention provides a polarizer comprising a film having
a structure where minute domains are dispersed in a matrix formed
of a translucent water-soluble resin including an iodine based
light absorbing material, furthermore, in a liquid crystalline
material of this invention, in the case of a liquid crystal
polymer, after it is orientated in a liquid crystal temperature
range, cooled to room temperatures and thus orientation is fixed,
in the case of a liquid crystal monomer, similarly, after
orientation, the orientation is fixed by ultraviolet curing etc.,
birefringence of minute domains formed by a liquid crystalline
material does not change by the change of temperatures.
* * * * *