U.S. patent application number 16/767733 was filed with the patent office on 2020-11-12 for circularly polarizing plate.
This patent application is currently assigned to NITTO DENKO CORPORATION. The applicant listed for this patent is NITTO DENKO CORPORATION. Invention is credited to Kozo Nakamura, Peng Wang, Michael Welch, Shijun Zheng.
Application Number | 20200355962 16/767733 |
Document ID | / |
Family ID | 1000005018167 |
Filed Date | 2020-11-12 |
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United States Patent
Application |
20200355962 |
Kind Code |
A1 |
Nakamura; Kozo ; et
al. |
November 12, 2020 |
CIRCULARLY POLARIZING PLATE
Abstract
Provided is a circularly polarizing plate that is excellent in
antireflection characteristic, and that can be produced at low
cost. The circularly polarizing plate of the present invention
includes in the stated order: a polarizer; a retardation layer
(20a) configured to function as a .lamda./4 plate; and a colored
layer, wherein an angle formed by an absorption axis of the
polarizer and a slow axis of the retardation layer (20a) is from
35.degree. to 55.degree., wherein the colored layer has an
absorption peak in a wavelength band in a range of from 580 nm to
610 nm, and wherein the colored layer contains a compound X
represented by the general formula (I) or the general formula
(II).
Inventors: |
Nakamura; Kozo;
(Ibaraki-shi, JP) ; Wang; Peng; (San Diego,
CA) ; Welch; Michael; (San Diego, CA) ; Zheng;
Shijun; (San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NITTO DENKO CORPORATION |
Ibaraki-shi, Osaka |
|
JP |
|
|
Assignee: |
NITTO DENKO CORPORATION
Ibaraki-shi, Osaka
JP
|
Family ID: |
1000005018167 |
Appl. No.: |
16/767733 |
Filed: |
November 29, 2018 |
PCT Filed: |
November 29, 2018 |
PCT NO: |
PCT/JP2018/043980 |
371 Date: |
May 28, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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62592223 |
Nov 29, 2017 |
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62672956 |
May 17, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02F 1/133536 20130101;
G02F 2202/28 20130101; G02F 2001/133638 20130101; G02F 2001/133541
20130101; G02F 1/133634 20130101; G02F 1/133533 20130101 |
International
Class: |
G02F 1/1335 20060101
G02F001/1335; G02F 1/13363 20060101 G02F001/13363 |
Claims
1. A circularly polarizing plate, comprising in the stated order: a
polarizer; a retardation layer "a" configured to function as a
.lamda./4 plate; and a colored layer, wherein an angle formed by an
absorption axis of the polarizer and a slow axis of the retardation
layer "a" is from 35.degree. to 55.degree., wherein the colored
layer has an absorption peak in a wavelength band in a range of
from 580 nm to 610 nm, and wherein the colored layer contains a
compound X represented by the following general formula (I) or
general formula (II): ##STR00032## in the formula (I), R.sub.1,
R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7, and R.sub.8
each independently represent a hydrogen atom, a halogen atom, a
substituted or unsubstituted alkyl group having 1 or more and 20 or
less carbon atoms, a substituent represented by the formula (a), or
a substituent represented by the formula (b), R.sub.1 and R.sub.2
form a saturated cyclic skeleton including 5 or 6 carbon atoms, and
R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7, and R.sub.8 each
independently represent a hydrogen atom, a halogen atom, which is
preferably Cl, a substituted or unsubstituted alkyl group having 1
or more and 20 or less carbon atoms, a substituent represented by
the formula (a), or a substituent represented by the formula (b),
R.sub.2 and R.sub.3 form a saturated cyclic skeleton including 5 to
7 carbon atoms, and R.sub.1, R.sub.4, R.sub.5, R.sub.6, R.sub.7,
and R.sub.8 each independently represent a hydrogen atom, a halogen
atom, which is preferably Cl, a substituted or unsubstituted alkyl
group having 1 or more and 20 or less carbon atoms, a substituent
represented by the formula (a), or a substituent represented by the
formula (b), R.sub.5 and R.sub.6 form a saturated cyclic skeleton
including 5 or 6 carbon atoms, and R.sub.1, R.sub.2, R.sub.3,
R.sub.4, R.sub.7, and R.sub.8 each independently represent a
hydrogen atom, a halogen atom, which is preferably Cl, a
substituted or unsubstituted alkyl group having 1 or more and 20 or
less carbon atoms, a substituent represented by the formula (a), or
a substituent represented by the formula (b), R.sub.6 and R.sub.7
form a saturated cyclic skeleton including 5 to 7 carbon atoms, and
R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.8 each
independently represent a hydrogen atom, a halogen atom, which is
preferably Cl, a substituted or unsubstituted alkyl group having 1
or more and 20 or less carbon atoms, a substituent represented by
the formula (a), or a substituent represented by the formula (b),
R.sub.1 and R.sub.2 form a saturated cyclic skeleton including 5 or
6 carbon atoms, R.sub.5 and R.sub.7 form a saturated cyclic
skeleton including 5 or 6 carbon atoms, and R.sub.3, R.sub.4,
R.sub.7, and R.sub.8 each independently represent a hydrogen atom,
a halogen atom, which is preferably Cl, a substituted or
unsubstituted alkyl group having 1 or more and 20 or less carbon
atoms, a substituent represented by the formula (a), or a
substituent represented by the formula (b), or R.sub.2 and R.sub.3
form a saturated cyclic skeleton including 5 to 7 carbon atoms,
R.sub.5 and R.sub.7 form a saturated cyclic skeleton including 5 to
7 carbon atoms, and R.sub.1, R.sub.4, R.sub.5, and R.sub.8 each
independently represent a hydrogen atom, a halogen atom, which is
preferably Cl, a substituted or unsubstituted alkyl group having 1
or more and 20 or less carbon atoms, a substituent represented by
the formula (a), or a substituent represented by the formula (b);
and in the formula (II), R.sub.4 and R.sub.8 each independently
represent a hydrogen atom, or a substituted or unsubstituted alkyl
group having 1 or more and 20 or less carbon atoms.
2. The circularly polarizing plate according to claim 1, wherein a
laminate including the polarizer and the colored layer has a
polarization degree of 99.9% or more.
3. The circularly polarizing plate according to claim 1, further
comprising a retardation layer "b" configured to function as a
.lamda./2 plate between the polarizer and the retardation layer "a"
configured to function as a .lamda./4 plate, wherein the angle
formed by the absorption axis of the polarizer and the slow axis of
the retardation layer "a" is from 65.degree. to 85.degree., and
wherein an angle formed by the absorption axis of the polarizer and
a slow axis of the retardation layer "b" is from 10.degree. to
20.degree..
4. The circularly polarizing plate according to claim 1, wherein
the colored layer further has an absorption peak in a wavelength
band in a range of from 440 nm to 510 nm.
5. The circularly polarizing plate according to claim 1, wherein
the retardation layer "a" configured to function as a .lamda./4
plate has a ratio Re(450)/Re(550) of 0.5 or more and less than 1.0,
and wherein the retardation layer "a" has an Nz coefficient of from
0.3 to 0.7.
6. An image display apparatus, comprising the circularly polarizing
plate of claim 1.
7. The image display apparatus according to claim 6, further
comprising an image display panel, wherein the image display panel
has a visible light reflectance of 20% or more.
Description
TECHNICAL FIELD
[0001] The present invention related to a circularly polarizing
plate.
BACKGROUND ART
[0002] In recent years, the number of opportunities for a smart
device typified by a smartphone and a display apparatus, such as a
digital signage or a window display, to be used under strong
ambient light has been increasing. Along with the increase, a
problem, such as ambient light reflection or background reflection,
due to the display apparatus itself or a reflector used in the
display apparatus, such as a touch panel portion, a glass
substrate, or metal wiring, has been occurring. In view of the
foregoing, it has been known that such phenomenon is prevented by
arranging a circularly polarizing plate including a .lamda./4 plate
on the viewer side of the apparatus. A circularly polarizing plate
obtained as described below has been known as a general circularly
polarizing plate. A retardation film (typically a .lamda./4 plate)
typified by a cycloolefin (COP)-based resin film is laminated so
that its slow axis may form an angle of about 45.degree. with
respect to the absorption axis of a polarizer. The retardation film
made of a COP-based resin has been known to have such a so-called
flat wavelength dispersion characteristic that its retardation
value does not depend on the wavelength of measurement light and is
substantially constant. When a circularly polarizing plate
including a retardation film having such flat wavelength dispersion
characteristic is used in a display apparatus, a problem in that an
excellent reflection hue is not obtained occurs.
[0003] To solve such problem as described above, there has been
proposed a circularly polarizing plate including a retardation film
having such so-called reverse wavelength dispersion dependency
(reverse wavelength dispersion characteristic) that its retardation
value increases in accordance with an increase in wavelength of
measurement light (e.g., Patent Literature 1). However, the use of
the retardation film having a reverse wavelength dispersion
characteristic is disadvantageous in terms of cost. In addition,
when the film is applied to a reflector having a high reflectance,
a problem in that it is particularly difficult to adjust the hue of
the reflector occurs.
CITATION LIST
Patent Literature
[0004] [PTL 1] JP 2006-171235 A
SUMMARY OF INVENTION
Technical Problem
[0005] The present invention has been made to solve the
conventional problems, and a primary object of the present
invention is to provide a circularly polarizing plate that is
excellent in antireflection characteristic, that has a neutral
reflection hue, and that can be produced at low cost.
Solution to Problem
[0006] According to one embodiment of the present invention, there
is provided a circularly polarizing plate, including in the stated
order: a polarizer; a retardation layer "a" configured to function
as a .lamda./4 plate; and a colored layer, wherein an angle formed
by an absorption axis of the polarizer and a slow axis of the
retardation layer "a" is from 35.degree. to 55.degree., wherein the
colored layer has an absorption peak in a wavelength band in a
range of from 580 nm to 610 nm, and wherein the colored layer
contains a compound X represented by the following general formula
(I) or general formula (II):
##STR00001##
in the formula (I),
[0007] R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6,
R.sub.7, and R.sub.8 each independently represent a hydrogen atom,
a halogen atom, a substituted or unsubstituted alkyl group having 1
or more and 20 or less carbon atoms, a substituent represented by
the formula (a), or a substituent represented by the formula
(b),
[0008] R.sub.1 and R.sub.2 form a saturated cyclic skeleton
including 5 or 6 carbon atoms, and R.sub.3, R.sub.4, R.sub.5,
R.sub.6, R.sub.7, and R.sub.8 each independently represent a
hydrogen atom, a halogen atom, which is preferably Cl, a
substituted or unsubstituted alkyl group having 1 or more and 20 or
less carbon atoms, a substituent represented by the formula (a), or
a substituent represented by the formula (b),
[0009] R.sub.2 and R.sub.3 form a saturated cyclic skeleton
including 5 to 7 carbon atoms, and R.sub.1, R.sub.4, R.sub.5,
R.sub.6, R.sub.7, and R.sub.8 each independently represent a
hydrogen atom, a halogen atom, which is preferably Cl, a
substituted or unsubstituted alkyl group having 1 or more and 20 or
less carbon atoms, a substituent represented by the formula (a), or
a substituent represented by the formula (b),
[0010] R.sub.5 and R.sub.6 form a saturated cyclic skeleton
including 5 or 6 carbon atoms, and R.sub.1, R.sub.2, R.sub.3,
R.sub.4, R.sub.7, and R.sub.8 each independently represent a
hydrogen atom, a halogen atom, which is preferably Cl, a
substituted or unsubstituted alkyl group having 1 or more and 20 or
less carbon atoms, a substituent represented by the formula (a), or
a substituent represented by the formula (b),
[0011] R.sub.6 and R.sub.7 form a saturated cyclic skeleton
including 5 to 7 carbon atoms, and R.sub.1, R.sub.2, R.sub.3,
R.sub.4, R.sub.5, and R.sub.8 each independently represent a
hydrogen atom, a halogen atom, which is preferably Cl, a
substituted or unsubstituted alkyl group having 1 or more and 20 or
less carbon atoms, a substituent represented by the formula (a), or
a substituent represented by the formula (b),
[0012] R.sub.1 and R.sub.2 form a saturated cyclic skeleton
including 5 or 6 carbon atoms, R.sub.5 and R.sub.6 form a saturated
cyclic skeleton including 5 or 6 carbon atoms, and R.sub.3,
R.sub.4, R.sub.7, and R.sub.8 each independently represent a
hydrogen atom, a halogen atom, which is preferably Cl, a
substituted or unsubstituted alkyl group having 1 or more and 20 or
less carbon atoms, a substituent represented by the formula (a), or
a substituent represented by the formula (b), or
[0013] R.sub.2 and R.sub.3 form a saturated cyclic skeleton
including 5 to 7 carbon atoms, R.sub.6 and R.sub.7 form a saturated
cyclic skeleton including 5 to 7 carbon atoms, and R.sub.1,
R.sub.4, R.sub.5, and R.sub.8 each independently represent a
hydrogen atom, a halogen atom, which is preferably Cl, a
substituted or unsubstituted alkyl group having 1 or more and 20 or
less carbon atoms, a substituent represented by the formula (a), or
a substituent represented by the formula (b); and
[0014] in the formula (II), R.sub.4 and R.sub.8 each independently
represent a hydrogen atom, or a substituted or unsubstituted alkyl
group having 1 or more and 20 or less carbon atoms.
[0015] In one embodiment, a laminate including the polarizer and
the colored layer has a polarization degree of 99.9% or more.
[0016] In one embodiment, the circularly polarizing plate further
includes a retardation layer "b" configured to function as a
.lamda./2 plate between the polarizer and the retardation layer "a"
configured to function as a .lamda./4 plate, wherein the angle
formed by the absorption axis of the polarizer and the slow axis of
the retardation layer "a" is from 65.degree. to 85.degree., and
wherein an angle formed by the absorption axis of the polarizer and
a slow axis of the retardation layer "b" is from 10.degree. to
20.degree..
[0017] In one embodiment, the colored layer further has an
absorption peak in a wavelength band in a range of from 440 nm to
510 nm.
[0018] In one embodiment, the retardation layer "a" configured to
function as a .lamda./4 plate has a ratio Re(450)/Re(550) of 0.5 or
more and less than 1.0, and the retardation layer "a" has an Nz
coefficient of from 0.3 to 0.7.
[0019] According to another embodiment of the present invention,
there is provided an image display apparatus. The image display
apparatus includes the circularly polarizing plate.
[0020] In one embodiment, the image display apparatus further
includes an image display panel, wherein the image display panel
has a visible light reflectance of 20% or more.
Advantageous Effects of Invention
[0021] According to the present invention, the circularly
polarizing plate excellent in antireflection characteristic can be
obtained by forming the colored layer. In addition, the circularly
polarizing plate of the present invention can output light having a
neutral hue through the adjustment of its reflection hue by
appropriate setting of the absorption wavelength of the colored
layer. Further, the use of the circularly polarizing plate of the
present invention can widen the color gamut of the image display
apparatus while preventing a reduction in brightness thereof.
BRIEF DESCRIPTION OF DRAWINGS
[0022] FIG. 1 is a schematic sectional view of a circularly
polarizing plate according to one embodiment of the present
invention.
[0023] FIG. 2 is a schematic sectional view of a circularly
polarizing plate according to another embodiment of the present
invention.
DESCRIPTION OF EMBODIMENTS
[0024] Now, preferred embodiments of the present invention are
described. However, the present invention is not limited to these
embodiments.
DEFINITIONS OF TERMS AND SYMBOLS
[0025] The definitions of terms and symbols in this description are
as described below.
(1) Refractive Index (Nx, Ny, or Nz)
[0026] The symbol "nx" represents a refractive index in the
direction in which a refractive index in a plane becomes maximum
(i.e., a slow axis direction), the symbol "ny" represents a
refractive index in the direction perpendicular to the slow axis in
the plane (i.e., a fast axis direction), and the symbol "nz"
represents a thickness direction refractive index.
(2) In-plane Retardation (Re)
[0027] The symbol "Re(.lamda.)" represents an in-plane retardation
measured with light having a wavelength of .lamda. nm at 23.degree.
C. For example, the symbol "Re(550)" represents an in-plane
retardation measured with light having a wavelength of 550 nm at
23.degree. C. When the thickness of a layer (film) is represented
by d (nm), the Re(.lamda.) is determined from the equation
"Re=(nx-ny).times.d".
(3) Thickness Direction Retardation (Rth)
[0028] The symbol "Rth(.lamda.)" represents a thickness direction
retardation measured with light having a wavelength of .lamda. nm
at 23.degree. C. For example, the symbol "Rth(550)" represents a
thickness direction retardation measured with light having a
wavelength of 550 nm at 23.degree. C. When the thickness of a layer
(film) is represented by d (nm), the Rth(.lamda.) is determined
from the equation "Rth=(nx-nz).times.d".
(4) Nz Coefficient
[0029] An Nz coefficient is determined from the equation
"Nz=Rth/Re".
[0030] A. Circularly Polarizing Plate
A-1. Overall Configuration of Circularly Polarizing Plate
[0031] FIG. 1 is a schematic sectional view of a circularly
polarizing plate according to one embodiment of the present
invention. A circularly polarizing plate 100 of this embodiment
includes a polarizer 10, a retardation layer 20a, and a colored
layer 30 in the stated order. The retardation layer 20a may
function as a .lamda./4 plate. The circularly polarizing plate 100
may be used so that the colored layer 30 may be on a reflector
(e.g., an image display panel, such as a liquid crystal display
panel or an organic EL panel) side, and the polarizer 10 may be on
a viewer side. In one embodiment, the circularly polarizing plate
100 includes a protective film 40 on the surface of the polarizer
10 opposite to the retardation layer 20a. The protective film 40
may be omitted in accordance with, for example, an application or
the configuration of an image display apparatus including the
circularly polarizing plate. In addition, the circularly polarizing
plate may include another protective film (also referred to as
"inner protective film": not shown) between the polarizer and the
retardation layer. In the illustrated example, the inner protective
film is omitted. In this case, the retardation layer 20a may also
function as an inner protective film. With such configuration,
further thinning of the circularly polarizing plate can be
achieved.
[0032] In this embodiment, an angle formed by the absorption axis
of the polarizer 10 and the slow axis of the retardation layer 20a
is from 35.degree. to 55.degree., preferably from 38.degree. to
52.degree., more preferably from 40.degree. to 50.degree., still
more preferably from 42.degree. to 48.degree., particularly
preferably from 44.degree. to 46.degree.. When the angle falls
within such range, a desired circular polarization function can be
achieved. When reference is made to an angle in this description,
the angle comprehends angles in both of clockwise and
counterclockwise directions unless otherwise stated.
[0033] The circularly polarizing plate of the present invention may
typically function as an antireflection film by being arranged on
the viewer side of an image display apparatus. The circularly
polarizing plate of the present invention exhibits an excellent
antireflection function while being suppressed in visible light
transmittance reduction (i.e., a brightness reduction) because the
circularly polarizing plate includes the colored layer, and the
colored layer contains a specific coloring matter to be described
later (coloring matter represented by the general formula (I) or
(II)) to absorb light having a specific wavelength. Even when the
circularly polarizing plate of the present invention is applied to
an image display apparatus including a reflector having a high
reflectance (e.g., a reflectance of 20% or more), reflected light
from the reflector can be sufficiently shielded. In addition, when
the colored layer selectively absorbs light in a specific
wavelength range (from 580 nm to 610 nm) and is suppressed in
unneeded absorption in a wavelength range except the specific
wavelength range, a circularly polarizing plate having the
following features can be obtained: its reflection hue can be
appropriately adjusted; and the circularly polarizing plate can
contribute to the widening of the color gamut of an image display
apparatus, and to an improvement in brightness thereof. According
to the present invention, the color gamut of the image display
apparatus can be significantly widened without the use of a
high-cost technology (an organic EL technology or a quantum dot
technology). In other words, when a liquid crystal display panel is
combined with the circularly polarizing plate of the present
invention, color gamut widening comparable to (or comparable to or
more than) that of an image display apparatus formed by the organic
EL technology or the quantum dot technology can be achieved at low
cost. Needless to say, further color gamut widening can be achieved
by combining the circularly polarizing plate of the present
invention with the organic EL technology, the quantum dot
technology, or the like.
[0034] FIG. 2 is a schematic sectional view of a circularly
polarizing plate according to another embodiment of the present
invention. A circularly polarizing plate 100' of this embodiment
further includes another retardation layer 20b between the
polarizer 10 and the retardation layer 20a (.lamda./4 plate). The
other retardation layer 20b functions as a .lamda./2 plate. In this
description, for convenience, the retardation layer 20a (.lamda./4
plate) is sometimes referred to as "first retardation layer", and
the other retardation layer 20b (.lamda./2 plate) is sometimes
referred to as "second retardation layer". The circularly
polarizing plate 100' of the illustrated example includes the
protective film 40 on the side of the polarizer 10 opposite to the
other retardation layer 20b. In addition, the circularly polarizing
plate may include another protective film (also referred to as
"inner protective film": not shown) between the polarizer and the
retardation layer 20a. In the illustrated example, the inner
protective film is omitted. In this case, the other retardation
layer (second retardation layer) 20b may also function as an inner
protective film.
[0035] In this embodiment, the angle formed by the absorption axis
of the polarizer 10 and the slow axis of the first retardation
layer 20a is preferably from 65.degree. to 85.degree., more
preferably from 72.degree. to 78.degree., still more preferably
about 75.degree.. Further, an angle formed by the absorption axis
of the polarizer 10 and the slow axis of the second retardation
layer 20b is preferably from 10.degree. to 20.degree., more
preferably from 13.degree. to 17.degree., still more preferably
about 15.degree.. When the two retardation layers are arranged at
such axial angles as described above, a circularly polarizing plate
having an extremely excellent circular polarization characteristic
(consequently, an extremely excellent antireflection
characteristic) in a wide band can be obtained.
[0036] In one embodiment, the circularly polarizing plate of the
present invention is free of any other retardation layer except the
retardation layer that may function as a .lamda./4 plate and the
retardation layer that may function as a .lamda./2 plate. The
circularly polarizing plate of the present invention can be
produced at low cost because the circularly polarizing plate may
have an excellent antireflection function, an excellent
hue-adjusting function, and an excellent color gamut-widening
function without including any other retardation layer.
[0037] The polarization degree of a laminate "x" including the
polarizer and the colored layer is preferably 99.9% or more, more
preferably 99.95% or more, still more preferably 99.99% or more.
The laminate "x" is obtained by: producing the same polarizer and
colored layer as the polarizer and the colored layer forming the
circularly polarizing plate; and laminating the polarizer and the
colored layer. The laminate "x" may include any other layer (e.g.,
a protective film) that does not affect the polarization degree. In
one embodiment, when a colored layer having a low haze value is
formed, the depolarization of light passing the colored layer is
suppressed, and hence the polarization degree of the laminate "x"
can be increased. The use of the polarizer and the colored layer
forming the laminate "x" having a high polarization degree can
provide a circularly polarizing plate that exhibits an excellent
antireflection function. The upper limit value of the polarization
degree of the laminate "x" is, for example, 99.9990. The
polarization degree of the laminate "x" may be determined from the
following equation by measuring the single layer transmittance
(Ts), parallel transmittance (Tp), and cross transmittance (Tc) of
the laminate "x" with an ultraviolet-visible spectrophotometer
(manufactured by JASCO Corporation, product name: "V-7000
SERIES").
Polarization degree(P) (%)={(Tp-Tc)/(Tp+Tc)}.sup.1/2.times.100
[0038] The parallel transmittance (Tp) and the cross transmittance
(Tc) are measured by causing polarized light to enter from the
colored layer side of the laminate "x". In addition, the Ts, the
Tp, and the Tc are Y values measured with the two-degree field of
view (C light source) of JIS Z 8701 and subjected to visibility
correction.
[0039] In one embodiment, the outermost surface (e.g., a surface
serving as a viewer side) of the circularly polarizing plate is
subjected to a low-reflection treatment, and hence the circularly
polarizing plate includes a low-reflection-treated layer on the
outermost surface. Examples of the low-reflection treatment
include: a method including bonding an antireflection film to the
outermost surface; a method including forming a thin film from, for
example, a low-refractive index resin provided with voids, such as
a fluorine resin or hollow silica, through a wet process, such as
coating or application (e.g., Patent Literature: JP 2013-64934 A);
and a method including providing a multilayer antireflection film
through the combination of a dry process and the wet process, such
as coating or application (e.g., Patent Literature: JP 2002-243906
A).
A-2. Polarizer and Protective Film
[0040] Any appropriate polarizer is used as the polarizer. Examples
thereof include polyene-based alignment films, such as: a product
obtained by causing a hydrophilic polymer film, such as a polyvinyl
alcohol-based film, a partially formalized polyvinyl alcohol-based
film, or an ethylene-vinyl acetate copolymer-based partially
saponified film, to adsorb a dichroic substance, such as iodine or
a dichroic dye, and uniaxially stretching the resultant; a
dehydration-treated product of polyvinyl alcohol; and a
dehydrochlorination-treated product of polyvinyl chloride. Of
those, a polarizer obtained by causing the polyvinyl alcohol-based
film to adsorb the dichroic substance, such as iodine, and
uniaxially stretching the resultant is particularly preferred
because of its high polarization dichroic ratio. The thickness of
the polarizer is preferably from 0.5 .mu.m to 80 .mu.m.
[0041] The polarizer obtained by causing the polyvinyl
alcohol-based film to adsorb iodine and uniaxially stretching the
resultant is typically produced by: immersing polyvinyl alcohol in
an aqueous solution of iodine to dye the polyvinyl alcohol; and
stretching the dyed polyvinyl alcohol so that the polyvinyl alcohol
may have a length 3 to 7 times as long as its original length. The
stretching may be performed after the dyeing, the stretching may be
performed while the dyeing is performed, or the dyeing may be
performed after the stretching. The polarizer is produced through a
treatment, such as swelling, cross-linking, adjustment, water
washing, or drying, in addition to the stretching and the dyeing.
For example, when the polyvinyl alcohol-based film is washed with
water by being immersed in the water before the dyeing,
contamination and an antiblocking agent on the surface of the
polyvinyl alcohol-based film can be washed off. Moreover, the
polyvinyl alcohol-based film can be swollen to prevent its dyeing
unevenness or the like. The polyvinyl alcohol-based film may be a
single-layer film (typical film obtained by film forming), or may
be a polyvinyl alcohol-based resin layer applied and formed onto a
resin substrate. A technology involving producing a polarizer from
the single-layer polyvinyl alcohol-based film is well known in the
art. A technology involving producing a polarizer from the
polyvinyl alcohol-based resin layer applied and formed onto the
resin substrate is described in, for example, JP 2009-098653 A.
[0042] The polarizer preferably shows absorption dichroism at any
wavelength in the wavelength range of from 380 nm to 780 nm. The
single layer transmittance of the polarizer is preferably from 38%
to 45.5%, more preferably from 40% to 45%.
[0043] The polarization degree of the polarizer is preferably 99.9%
or more, more preferably 99.95% or more. When the polarization
degree falls within such ranges, a circularly polarizing plate that
exhibits a desired circular polarization function and that is
excellent in antireflection characteristic can be obtained.
[0044] Any appropriate film is used as the protective film.
Specific examples of a material serving as a main component of such
film include: cellulose-based resins, such as triacetyl cellulose
(TAC); and transparent resins, such as (meth)acrylic,
polyester-based, polyvinyl alcohol-based, polycarbonate-based,
polyamide-based, polyimide-based, polyether sulfone-based,
polysulfone-based, polystyrene-based, polynorbornene-based,
polyolefin-based, and acetate-based resins. Examples thereof also
include thermosetting resins or UV-curable resins, such as acrylic,
urethane-based, acrylic urethane-based, epoxy-based, and
silicone-based resins. Examples thereof also include glassy
polymers, such as a siloxane-based polymer. In addition, a polymer
film described in JP 2001-343529 A (WO 01/37007 A1) may also be
used. For example, a resin composition containing a thermoplastic
resin having a substituted or unsubstituted imide group in a side
chain thereof, and a thermoplastic resin having a substituted or
unsubstituted phenyl group and a nitrile group in side chains
thereof may be used as a material for the film, and the resin
composition is, for example, a resin composition including: an
alternating copolymer formed of isobutene and N-methylmaleimide;
and an acrylonitrile-styrene copolymer. The polymer film may be,
for example, an extrusion molded product of the resin composition.
Any appropriate pressure-sensitive adhesive layer or adhesive layer
is used in the lamination of the polarizer and the protective film.
The pressure-sensitive adhesive layer is typically formed of an
acrylic pressure-sensitive adhesive. The adhesive layer is
typically formed of a polyvinyl alcohol-based adhesive.
[0045] A-3. First Retardation Layer (Retardation Layer configured
to function as .lamda./4 Plate)
[0046] As described above, the first retardation layer may function
as a .lamda./4 plate. The in-plane retardation Re(550) of such
first retardation layer is from 100 nm to 180 nm, preferably from
110 nm to 170 nm, more preferably from 120 nm to 160 nm,
particularly preferably from 135 nm to 155 nm. The first
retardation layer typically has a refractive index ellipsoid of
nx>ny=nz or nx>ny>nz. For example, the equation "ny=nz" as
used herein comprehends not only a case in which the ny and the nz
are strictly equal to each other but also a case in which the ny
and the nz are substantially equal to each other. The Nz
coefficient of the first retardation layer is, for example, from
0.9 to 2, preferably from 1 to 1.5, more preferably from 1 to
1.3.
[0047] The thickness of the first retardation layer may be set so
that the layer may most appropriately function as a .lamda./4
plate. In other words, the thickness may be set so that a desired
in-plane retardation may be obtained. Specifically, the thickness
is preferably from 10 .mu.m to 80 .mu.m, more preferably from 10
.mu.m to 60 .mu.m, most preferably from 30 .mu.m to 50 .mu.m.
[0048] The first retardation layer may show such a reverse
wavelength dispersion characteristic that its retardation value
increases in accordance with an increase in wavelength of
measurement light, may show such a positive wavelength dispersion
characteristic that the retardation value reduces in accordance
with an increase in wavelength of the measurement light, or may
show such a flat wavelength dispersion characteristic that the
retardation value remains substantially unchanged irrespective of
the wavelength of the measurement light.
[0049] In one embodiment, the first retardation layer shows a flat
wavelength dispersion characteristic. The adoption of the first
retardation layer showing a flat wavelength dispersion
characteristic can achieve an excellent antireflection
characteristic and an excellent reflection hue in an oblique
direction. In addition, the circularly polarizing plate of the
present invention can achieve an excellent reflection hue even
through the use of the first retardation layer showing a flat
wavelength dispersion characteristic. The circularly polarizing
plate using the first retardation layer showing a flat wavelength
dispersion characteristic is advantageous in terms of cost. In this
embodiment, the ratio Re(450)/Re(550) of the first retardation
layer is preferably from 0.99 to 1.03, and the ratio
Re(650)/Re(550) thereof is preferably from 0.98 to 1.02.
[0050] In another embodiment, the first retardation layer shows a
reverse wavelength dispersion characteristic. The adoption of the
first retardation layer showing a reverse wavelength dispersion
characteristic can improve a reflection hue in a front direction.
In addition, the adoption of the first retardation layer showing a
reverse wavelength dispersion characteristic can improve any other
characteristic (e.g., a brightness) while maintaining a practical
reflection hue. In this embodiment, the ratio Re(450)/Re(550) of
the first retardation layer is preferably 0.5 or more and less than
1.0, more preferably from 0.7 to 0.95. In addition, the ratio
Re(650)/Re(550) of the first retardation layer is preferably more
than 1 and 1.2 or less, more preferably from 1.01 to 1.15. In this
embodiment, the Nz coefficient of the first retardation layer is
preferably from 0.3 to 0.7, more preferably from 0.4 to 0.6, still
more preferably from 0.45 to 0.55, particularly preferably about
0.5. When the Nz coefficient falls within such ranges, a more
excellent reflection hue can be achieved.
[0051] The .lamda./4 plate is preferably a stretched film of a
polymer film. Specifically, the .lamda./4 plate is obtained by
appropriately selecting the kind of the polymer and a stretching
treatment (e.g., a stretching method, a stretching temperature, a
stretching ratio, or a stretching direction).
[0052] Any appropriate resin is used as a resin forming the polymer
film. Specific examples thereof include resins each forming a
positive birefringent film, such as a cycloolefin-based resin, such
as polynorbornene, a polycarbonate-based resin, a cellulose-based
resin, a polyvinyl alcohol-based resin, and a polysulfone-based
resin. Of those, a norbornene-based resin and a polycarbonate-based
resin are preferred. Details about the resin forming the polymer
film are described in, for example, JP 2014-010291 A, the
description of which is incorporated herein by reference.
[0053] The polynorbornene refers to a (co)polymer obtained by using
a norbornene-based monomer having a norbornene ring as part or the
entirety of starting materials (monomers). Examples of the
norbornene-based monomer include: norbornene, alkyl and/or
alkylidene substituted products thereof, such as
5-methyl-2-norbornene, 5-dimethyl-2-norbornene,
5-ethyl-2-norbornene, 5-butyl-2-norbornene, and
5-ethylidene-2-norbornene, and polar group (e.g., halogen)
substituted products thereof; dicyclopentadiene and
2,3-dihydrodicyclopentadiene; dimethanooctahydronaphthalene, alkyl
and/or alkylidene substituted products thereof, and polar group
(e.g., halogen) substituted products thereof, such as
6-methyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene,
6-ethyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene,
6-ethylidene-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene,
6-chloro-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene,
6-cyano-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene,
6-pyridyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene,
and
6-methoxycarbonyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalen-
e; and trimers or tetramers of cyclopentadiene, such as
4,9:5,8-dimethano-3a,4,4a,5,8,8a,9,9a-octahydro-1H-benzoindene and
4,11:5,10:6,9-trimethano-3a,4,4a,5,5a,6,9,9a,10,10a,11,11a-dodecahydro-1H-
-cyclopentaanthracene.
[0054] Various products are commercially available as the
polynorbornene. Specific examples thereof include: products
available under the product names "ZEONEX" and "ZEONOR" from Zeon
Corporation; a product available under the product name "Arton"
from JSR Corporation; a product available under the product name
"TOPAS" from TICONA; and a product available under the product name
"APEL" from Mitsui Chemicals, Inc.
[0055] An aromatic polycarbonate is preferably used as the
polycarbonate-based resin. The aromatic polycarbonate may be
typically obtained by a reaction between a carbonate precursor and
an aromatic dihydric phenol compound. Specific examples of the
carbonate precursor include phosgene, a bischloroformate of a
dihydric phenol, diphenyl carbonate, di-p-tolyl carbonate,
phenyl-p-tolyl carbonate, di-p-chlorophenyl carbonate, and
dinaphthyl carbonate. Of those, phosgene and diphenyl carbonate are
preferred. Specific examples of the aromatic dihydric phenol
compound include 2,2-bis(4-hydroxyphenyl)propane,
2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane,
bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane,
2,2-bis(4-hydroxyphenyl)butane,
2,2-bis(4-hydroxy-3,5-dimethylphenyl)butane,
2,2-bis(4-hydroxy-3,5-dipropylphenyl)propane,
1,1-bis(4-hydroxyphenyl)cyclohexane, and
1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane. Those
compounds may be used alone or in combination thereof. Of those,
2,2-bis(4-hydroxyphenyl)propane,
1,1-bis(4-hydroxyphenyl)cyclohexane, and
1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane are preferably
used. Of those, 2,2-bis(4-hydroxyphenyl)propane and
1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane are
particularly preferably used in combination thereof.
[0056] Examples of the stretching method include lateral uniaxial
stretching, fixed-end biaxial stretching, and sequential biaxial
stretching. The fixed-end biaxial stretching is specifically, for
example, a method including stretching the polymer film in its
short direction (lateral direction) while causing the film to
travel in its lengthwise direction. The method may be apparently
lateral uniaxial stretching. Oblique stretching may also be
adopted. The adoption of the oblique stretching can provide an
elongate stretched film having an alignment axis (slow axis) at a
predetermined angle with respect to its widthwise direction.
[0057] The thickness of the stretched film is typically from 5
.mu.m to 80 .mu.m, preferably from 15 .mu.m to 60 .mu.m, more
preferably from 25 .mu.m to 45 .mu.m.
[0058] A-4. Second Retardation Layer (Retardation Layer Configured
to Function as .lamda./2 Plate)
[0059] As described above, the second retardation layer may
function as a .lamda./2 plate. The in-plane retardation Re(550) of
such second retardation layer is preferably from 180 nm to 300 nm,
more preferably from 210 nm to 280 nm, most preferably from 230 nm
to 240 nm. It is preferred that the second retardation layer
typically have a refractive index ellipsoid of nx>ny=nz. The Nz
coefficient of the second retardation layer is, for example, from
0.9 to 2, preferably from 1 to 1.5, more preferably from 1 to
1.3.
[0060] The thickness of the second retardation layer may be set so
that the layer may most appropriately function as a .lamda./2
plate. In other words, the thickness may be set so that a desired
in-plane retardation may be obtained. Specifically, the thickness
is preferably from 0.5 .mu.m to 5 .mu.m, more preferably from 1
.mu.m to 4 .mu.m, most preferably from 1.5 .mu.m to 3 .mu.m.
[0061] Any appropriate material may be adopted as a material for
the second retardation layer as long as such characteristics as
described above are obtained. A liquid crystal material is
preferred, and a liquid crystal material whose liquid crystal phase
is a nematic phase (nematic liquid crystal) is more preferred. The
use of the liquid crystal material can make a difference between
the nx and ny of the second retardation layer to be obtained much
larger than that of a non-liquid crystal material. As a result, the
thickness of the second retardation layer for obtaining a desired
in-plane retardation can be markedly reduced. For example, a liquid
crystal polymer or a liquid crystal monomer may be used as such
liquid crystal material. The mechanism via which the liquid
crystallinity of the liquid crystal material is expressed may be
any one of a lyotropic mechanism and a thermotropic mechanism. In
addition, the alignment state of the liquid crystal material is
preferably homogeneous alignment. In addition, the resin forming
the polymer film may be used as the material for the second
retardation layer.
[0062] The second retardation layer may show such a reverse
wavelength dispersion characteristic that its retardation value
increases in accordance with an increase in wavelength of
measurement light, may show such a positive wavelength dispersion
characteristic that the retardation value reduces in accordance
with an increase in wavelength of the measurement light, or may
show such a flat wavelength dispersion characteristic that the
retardation value remains substantially unchanged irrespective of
the wavelength of the measurement light. The layer preferably shows
a flat wavelength dispersion characteristic. The adoption of a
.lamda./2 plate having a flat wavelength dispersion characteristic
can achieve an excellent antireflection characteristic and an
excellent reflection hue in an oblique direction. The ratio
Re(450)/Re(550) of the retardation layer is preferably from 0.99 to
1.03, and the ratio Re(650)/Re(550) thereof is preferably from 0.98
to 1.02.
[0063] A-5. Colored Layer
[0064] The colored layer contains one or more kinds of coloring
materials. In the coloring material, the coloring material is
typically present in a matrix.
[0065] As described above, the colored layer has an absorption peak
in the wavelength band in the range of from 580 nm to 610 nm. The
formation of such colored layer can improve the antireflection
function of the circularly polarizing plate while suppressing a
reduction in visible light transmittance (i.e., a reduction in
brightness) thereof. In addition, when the wavelength of light to
be absorbed by the layer is adjusted, a reflection hue can be made
neutral, and hence a circularly polarizing plate reduced in
coloring can be obtained. The absorption spectrum of the layer may
be measured with a spectrophotometer (manufactured by Hitachi
High-Technologies Corporation, product name: "U-4100").
[0066] The ratio (A.sub.545/A.sub.max) of the absorbance A.sub.545
of the peak of the colored layer at a wavelength of 545 nm to the
absorbance A.sub.max of the highest absorption peak of the colored
layer at a wavelength of from 580 nm to 610 nm is preferably 0.13
or less, more preferably 0.1 or less, still more preferably 0.08 or
less, particularly preferably 0.05 or less. When a colored layer
having a small absorbance at a wavelength of 545 nm as described
above is formed, a circularly polarizing plate that can contribute
to the widening of the color gamut of an image display apparatus by
absorbing light that is not needed for color representation can be
obtained. In addition, the layer hardly absorbs light emitted from
a light source whose wavelength is around 545 nm at which a
visibility is high, and hence can be suppressed in brightness
reduction.
[0067] In the colored layer, the half width of the absorption peak
in the wavelength range of from 580 nm to 610 nm is preferably 35
nm or less, more preferably 30 nm or less, still more preferably 25
nm or less, particularly preferably 20 nm or less. When the half
width falls within such ranges, a circularly polarizing plate that
can contribute to the widening of the color gamut of an image
display apparatus can be obtained.
[0068] In one embodiment, the colored layer is free of an
absorption peak in the range of from 530 nm to 570 nm. More
specifically, the colored layer is free of an absorption peak
having an absorbance of 0.1 or more in the range of from 530 nm to
570 nm. The formation of such colored layer can provide a
circularly polarizing plate that can contribute to the widening of
the color gamut of an image display apparatus.
[0069] In one embodiment, the colored layer further has an
absorption peak in a wavelength band in the range of from 440 nm to
510 nm. That is, in this embodiment, the colored layer has
absorption peaks in the wavelength bands in the ranges of from 440
nm to 510 nm and from 580 nm to 610 nm. With such configuration,
the color mixing of red light and green light, and that of green
light and blue light can be satisfactorily prevented. When the
circularly polarizing plate configured as described above is used
as an antireflection film for an image display apparatus, the color
gamut of the image display apparatus can be widened, and hence
bright and vivid image quality can be obtained. A colored layer
having two or more absorption peaks as described above may be
obtained by using a plurality of kinds of coloring materials.
[0070] The transmittance of the colored layer at an absorption peak
is preferably from 0% to 80%, more preferably from 0% to 70%. When
the transmittance falls within such ranges, the above-mentioned
effect of the present invention becomes more significant.
[0071] The visible light transmittance of the colored layer is
preferably from 30% to 90%, more preferably from 30% to 80%. When
the visible light transmittance falls within such ranges, a
circularly polarizing plate that can exhibit an antireflection
function while being suppressed in brightness reduction can be
obtained.
[0072] The haze value of the colored layer is preferably 15% or
less, more preferably 10% or less, still more preferably 5% or
less. When the haze value of the colored layer is set within such
ranges, the depolarization of circularly polarized light that has
passed the first retardation layer (and the second retardation
layer) is prevented, and as a result, a circularly polarizing plate
having an excellent antireflection characteristic can be obtained.
Although the haze value of the colored layer is preferably as small
as possible, its lower limit is, for example, 0.1%.
[0073] The thickness of the colored layer is preferably from 1
.mu.m to 100 .mu.m, more preferably from 2 .mu.m to 30 .mu.m.
[0074] A-5-1. Coloring Material
[0075] The colored layer contains, as a coloring material, a
compound X represented by the following general formula (I) or
general formula (II). The compound X is a compound having an
absorption peak in the wavelength band in the range of from 580 nm
to 610 nm.
##STR00002##
in the formula (I),
[0076] R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6,
R.sub.7, and R.sub.8 each independently represent a hydrogen atom,
a halogen atom, a substituted or unsubstituted alkyl group having 1
or more and 20 or less carbon atoms, a substituent represented by
the formula (a), or a substituent represented by the formula
(b),
[0077] R.sub.1 and R.sub.2 form a saturated cyclic skeleton
including 5 or 6 carbon atoms, and R.sub.3, R.sub.4, R.sub.5,
R.sub.6, R.sub.7, and R.sub.8 each independently represent a
hydrogen atom, a halogen atom, which is preferably Cl, a
substituted or unsubstituted alkyl group having 1 or more and 20 or
less carbon atoms, a substituent represented by the formula (a), or
a substituent represented by the formula (b),
[0078] R.sub.2 and R.sub.3 form a saturated cyclic skeleton
including 5 to 7 carbon atoms, and R.sub.1, R.sub.4, R.sub.5,
R.sub.6, R.sub.7, and R.sub.8 each independently represent a
hydrogen atom, a halogen atom, which is preferably Cl, a
substituted or unsubstituted alkyl group having 1 or more and 20 or
less carbon atoms, a substituent represented by the formula (a), or
a substituent represented by the formula (b),
[0079] R.sub.5 and R.sub.6 form a saturated cyclic skeleton
including 5 or 6 carbon atoms, and R.sub.1, R.sub.2, R.sub.3,
R.sub.4, R.sub.7, and R.sub.8 each independently represent a
hydrogen atom, a halogen atom, which is preferably Cl, a
substituted or unsubstituted alkyl group having 1 or more and 20 or
less carbon atoms, a substituent represented by the formula (a), or
a substituent represented by the formula (b),
[0080] R.sub.6 and R.sub.7 form a saturated cyclic skeleton
including 5 to 7 carbon atoms, and R.sub.1, R.sub.2, R.sub.3,
R.sub.4, R.sub.5, and R.sub.8 each independently represent a
hydrogen atom, a halogen atom, which is preferably Cl, a
substituted or unsubstituted alkyl group having 1 or more and 20 or
less carbon atoms, a substituent represented by the formula (a), or
a substituent represented by the formula (b),
[0081] R.sub.1 and R.sub.2 form a saturated cyclic skeleton
including 5 or 6 carbon atoms, R.sub.5 and R.sub.6 form a saturated
cyclic skeleton including 5 or 6 carbon atoms, and R.sub.3,
R.sub.4, R.sub.7, and R.sub.8 each independently represent a
hydrogen atom, a halogen atom, which is preferably Cl, a
substituted or unsubstituted alkyl group having 1 or more and 20 or
less carbon atoms, a substituent represented by the formula (a), or
a substituent represented by the formula (b), or
[0082] R.sub.2 and R.sub.3 form a saturated cyclic skeleton
including 5 to 7 carbon atoms, R.sub.6 and R.sub.7 form a saturated
cyclic skeleton including 5 to 7 carbon atoms, and R.sub.1,
R.sub.4, R.sub.5, and R.sub.8 each independently represent a
hydrogen atom, a halogen atom, which is preferably Cl, a
substituted or unsubstituted alkyl group having 1 or more and 20 or
less carbon atoms, a substituent represented by the formula (a), or
a substituent represented by the formula (b); and
[0083] in the formula (II), R.sub.4 and R.sub.8 each independently
represent a hydrogen atom, or a substituted or unsubstituted alkyl
group having 1 or more and 20 or less carbon atoms.
[0084] The saturated cyclic skeleton (number of carbon atoms: 5 or
6) formed so as to include R.sub.1 and R.sub.2, and the saturated
cyclic skeleton (number of carbon atoms: 5 or 6) formed so as to
include R.sub.5 and R.sub.6 may each have a substituent. The
substituent is, for example, an alkyl group having 1 to 4 carbon
atoms. In addition, the saturated cyclic skeleton (number of carbon
atoms: 5 to 7) formed so as to include R.sub.2 and R.sub.3, and the
saturated cyclic skeleton (number of carbon atoms: 5 to 7) formed
so as to include R.sub.6 and R.sub.7 may each have a substituent.
The substituent is, for example, an alkyl group having 1 to 4
carbon atoms.
[0085] In one embodiment, R.sub.4 and/or R.sub.8 has a benzene ring
or a naphthalene ring as a substituent.
[0086] Specific examples of the compound X represented by the
formula (I) or (II) include compounds represented by the following
general formulae (I-1) to (I-27) and (II-1). The absorption peak of
the compound X is shown in each of the following tables. With
regard to each of the formulae (I-1) to (I-23), an absorption peak
obtained by measuring the absorbance of a film formed of a resin
composition prepared by mixing aliphatic polycarbonate with the
compound X is shown, and with regard to each of the formulae (I-24)
to (I-27) and (II-1), an absorption peak obtained by measuring the
absorbance of a film formed of a resin composition prepared by
mixing a polymethyl methacrylate resin with the compound X is
shown.
TABLE-US-00001 Absorption peak NO. Compound X (nm) I-1 ##STR00003##
596 nm (APC) I-2 ##STR00004## 595 nm (APC) I-3 ##STR00005## 582 nm
(APC) I-4 ##STR00006## 585 nm (APC) I-5 ##STR00007## 585 nm (APC)
I-6 ##STR00008## 575 nm (APC) I-7 ##STR00009## 585 nm (APC) I-8
##STR00010## 587 nm (APC) I-9 ##STR00011## 587 nm (APC) I-10
##STR00012## 588 nm (APC) I-11 ##STR00013## 588 nm (APC) I-12
##STR00014## 589 nm (APC) I-13 ##STR00015## 592 nm (APC) I-14
##STR00016## 591 nm (APC) I-15 ##STR00017## 595 nm (APC) I-16
##STR00018## 595 nm (APC) I-17 ##STR00019## 596 nm (APC) I-18
##STR00020## 614 nm (APC) I-19 ##STR00021## 581 nm (APC) I-20
##STR00022## 591 nm (APC) I-21 ##STR00023## 593 nm (APC) I-22
##STR00024## 594 nm (APC) I-23 ##STR00025## 594 nm (APC) I-24
##STR00026## 592 nm I-25 ##STR00027## 593 nm I-26 ##STR00028## 594
nm I-27 ##STR00029## 594 nm II-1 ##STR00030## 597 nm
[0087] The content of the compound X is preferably from 0.01 part
by weight to 50 parts by weight, more preferably from 0.05 part by
weight to 10 parts by weight, still more preferably from 0.1 part
by weight to 5 parts by weight, particularly preferably from 0.1
part by weight to 1 part by weight with respect to 100 parts by
weight of a matrix material.
[0088] The colored layer may further contain a compound having an
absorption peak in the wavelength band in the range of from 440 nm
to 510 nm. For example, an anthraquinone-based, oxime-based,
naphthoquinone-based, quinizarin-based, oxonol-based, azo-based,
xanthene-based, or phthalocyanine-based compound (dye) is used as
such compound.
[0089] The content of the compound having an absorption peak in the
wavelength band in the range of from 440 nm to 510 nm is preferably
from 0.01 part by weight to 50 parts by weight, more preferably
from 0.01 part by weight to 25 parts by weight with respect to 100
parts by weight of the matrix material.
[0090] A-5-2. Matrix
[0091] The matrix may be a pressure-sensitive adhesive, or may be a
resin film. The matrix is preferably a pressure-sensitive
adhesive.
[0092] When the matrix is a pressure-sensitive adhesive, any
appropriate pressure-sensitive adhesive may be used as the
pressure-sensitive adhesive. The pressure-sensitive adhesive
preferably has transparency and optical isotropy. Specific examples
of the pressure-sensitive adhesive include a rubber-based
pressure-sensitive adhesive, an acrylic pressure-sensitive
adhesive, a silicone-based pressure-sensitive adhesive, an
epoxy-based pressure-sensitive adhesive, and a cellulose-based
pressure-sensitive adhesive. Of those, a rubber-based
pressure-sensitive adhesive or an acrylic pressure-sensitive
adhesive is preferred.
[0093] A rubber-based polymer serving as the rubber-based
pressure-sensitive adhesive is a polymer showing rubber elasticity
in a temperature region around room temperature. Preferred examples
of the rubber-based polymer (A) include a styrene-based
thermoplastic elastomer (A1), an isobutylene-based polymer (A2),
and a combination thereof.
[0094] Examples of the styrene-based thermoplastic elastomer (A1)
may include styrene-based block copolymers, such as a
styrene-ethylene-butylene-styrene block copolymer (SEBS), a
styrene-isoprene-styrene block copolymer (SIS), a
styrene-butadiene-styrene block copolymer (SBS), a
styrene-ethylene-propylene-styrene block copolymer (SEPS, a
hydrogenated product of SIS), a styrene-ethylene-propylene block
copolymer (SEP, a hydrogenated product of a styrene-isoprene block
copolymer), a styrene-isobutylene-styrene block copolymer (SIBS),
and a styrene-butadiene rubber (SBR). Of those, a
styrene-ethylene-propylene-styrene block copolymer (SEPS, a
hydrogenated product of SIS), a styrene-ethylene-butylene-styrene
block copolymer (SEBS), and a styrene-isobutylene-styrene block
copolymer (SIBS) are preferred because the copolymers each have
polystyrene blocks at both ends of a molecule thereof and have a
high cohesive force as a polymer. A commercial product may be used
as the styrene-based thermoplastic elastomer (A1). Specific
examples of the commercial product include SEPTON and HYBRAR
manufactured by Kuraray Co., Ltd., Tuftec manufactured by Asahi
Kasei Chemicals Corporation, and SIBSTAR manufactured by Kaneka
Corporation.
[0095] The weight-average molecular weight of the styrene-based
thermoplastic elastomer (A1) is preferably from about 50,000 to
about 500,000, more preferably from about 50,000 to about 300,000,
still more preferably from about 50,000 to about 250,000. The
weight-average molecular weight of the styrene-based thermoplastic
elastomer (A1) preferably falls within such ranges because both of
the cohesive force and viscoelasticity of the polymer can be
achieved.
[0096] A styrene content in the styrene-based thermoplastic
elastomer (A1) is preferably from about 5 wt % to about 70 wt %,
more preferably from about 5 wt % to about 40 wt %, still more
preferably from about 10 wt % to about 20 wt %. The styrene content
in the styrene-based thermoplastic elastomer (A1) preferably falls
within such ranges because viscoelasticity based on a soft segment
can be secured while a cohesive force based on a styrene moiety is
maintained.
[0097] Examples of the isobutylene-based polymer (A2) may include
polymers each including isobutylene as a constituent monomer and
having a weight-average molecular weight (Mw) of preferably 500,000
or more. The isobutylene-based polymer (A2) may be a homopolymer of
isobutylene (polyisobutylene, PIB) or may be a copolymer including
isobutylene as amain monomer (i.e., a copolymer obtained by
copolymerizing isobutylene at a ratio of more than 50 mol %).
Examples of such copolymer may include a copolymer of isobutylene
and normal butylene, a copolymer of isobutylene and isoprene (e.g.,
a butyl rubber, such as a regular butyl rubber, a chlorinated butyl
rubber, a brominated butyl rubber, or a partially cross-linked
butyl rubber), and vulcanized products and modified products
thereof (e.g., a product modified with a functional group, such as
a hydroxyl group, a carboxyl group, an amino group, or an epoxy
group). Of those, polyisobutylene (PIB) is preferred because the
polyisobutylene is free of a double bond in its main chain, and is
excellent in weatherability. A commercial product may be used as
the isobutylene-based polymer (A2). The commercial product is
specifically, for example, OPPANOL manufactured by BASF.
[0098] The weight-average molecular weight (Mw) of the
isobutylene-based polymer (A2) is preferably 500,000 or more, more
preferably 600,000 or more, still more preferably 700,000 or more.
In addition, the upper limit of the weight-average molecular weight
(Mw) is preferably 5,000,000 or less, more preferably 3,000,000 or
less, still more preferably 2,000,000 or less. When the
weight-average molecular weight of the isobutylene-based polymer
(A2) is set to 500,000 or more, a pressure-sensitive adhesive that
is more excellent in durability at the time of its high-temperature
storage can be obtained.
[0099] The content of the rubber-based polymer (A) in the
pressure-sensitive adhesive is preferably 30 wt % or more, more
preferably 40 wt % or more, still more preferably 50 wt % or more,
particularly preferably 60 wt % or more in the total solid content
of the pressure-sensitive adhesive. The upper limit of the content
of the rubber-based polymer is preferably 95 wt % or less, more
preferably 90 wt % or less.
[0100] In the rubber-based pressure-sensitive adhesive, the
rubber-based polymer (A) and any other rubber-based polymer may be
used in combination. Specific examples of the other rubber-based
polymer include: a butyl rubber (IIR), a butadiene rubber (BR), an
acrylonitrile-butadiene rubber (NBR), EPR (binary
ethylene-propylene rubber), EPT (ternary ethylene-propylene
rubber), an acrylic rubber, a urethane rubber, and a
polyurethane-based thermoplastic elastomer; a polyester-based
thermoplastic elastomer; and a blend-based thermoplastic elastomer,
such as a polymer blend of polypropylene and EPT (ternary
ethylene-propylene rubber). The compounding amount of the other
rubber-based polymer is preferably about 10 parts by weight or less
with respect to 100 parts by weight of the rubber-based polymer
(A).
[0101] The acrylic polymer of the acrylic pressure-sensitive
adhesive typically contains an alkyl (meth)acrylate as a main
component, and may contain an aromatic ring-containing
(meth)acrylate, an amide group-containing monomer, a carboxyl
group-containing monomer, and/or a hydroxyl group-containing
monomer as a copolymerization component in accordance with a
purpose. The term "(meth)acrylate" as used herein means an acrylate
and/or a methacrylate. The alkyl (meth)acrylate may be, for
example, an alkyl (meth)acrylate having a linear or branched alkyl
group having 1 to 18 carbon atoms. The aromatic ring-containing
(meth)acrylate is a compound containing an aromatic ring structure
in its structure and containing a (meth)acryloyl group. The
aromatic ring is, for example, a benzene ring, a naphthalene ring,
or a biphenyl ring. The aromatic ring-containing (meth)acrylate
satisfies durability and can alleviate display unevenness due to a
white void of the peripheral portion of an image display apparatus.
The amide group-containing monomer is a compound containing an
amide group in its structure and containing a polymerizable
unsaturated double bond, such as a (meth)acryloyl group or a vinyl
group. The carboxyl group-containing monomer is a compound
containing a carboxyl group in its structure and containing a
polymerizable unsaturated double bond, such as a (meth)acryloyl
group or a vinyl group. The hydroxyl group-containing monomer is a
compound containing a hydroxyl group in its structure and
containing a polymerizable unsaturated double bond, such as a
(meth)acryloyl group or a vinyl group. Details about the acrylic
pressure-sensitive adhesive are described in, for example, JP
2015-199942 A, the description of which is incorporated herein by
reference.
[0102] When the matrix is a resin film, any appropriate resin may
be used as a resin forming the resin film. Specifically, the resin
may be a thermoplastic resin, may be a thermosetting resin, or may
be an active energy ray-curable resin. Examples of the active
energy ray-curable resin include an electron beam-curable resin, a
UV-curable resin, and a visible light-curable resin. Specific
examples of the resin include an epoxy, a (meth)acrylate (e.g.,
methyl methacrylate or butyl acrylate), norbornene, polyethylene,
poly(vinyl butyral), poly(vinyl acetate), polyurea, polyurethane,
aminosilicone (AMS), polyphenylmethylsiloxane, a
polyphenylalkylsiloxane, polydiphenylsiloxane, a
polydialkylsiloxane, silsesquioxane, silicone fluoride, vinyl- and
hydride-substituted silicones, a styrene-based polymer (e.g.,
polystyrene, aminopolystyrene (APS), poly(acrylonitrile ethylene
styrene) (AES)), a polymer having cross-linked with a di functional
monomer (e.g., divinylbenzene), a polyester-based polymer (e.g.,
polyethylene terephthalate), a cellulose-based polymer (e.g.,
triacetyl cellulose), a vinyl chloride-based polymer, an
amide-based polymer, an imide-based polymer, a vinyl alcohol-based
polymer, an epoxy-based polymer, a silicone-based polymer, and an
acrylic urethane-based polymer. Those resins may be used alone or
in combination thereof (e.g., a blend or a copolymer). Those resins
may each be subjected to a treatment, such as stretching, heating,
or pressurization, after forming a film. Of those, a thermosetting
resin or a UV-curable resin is preferred, and a thermosetting resin
is more preferred.
[0103] B. Image Display Apparatus
[0104] An image display apparatus of the present invention includes
an image display panel and the circularly polarizing plate.
Examples of the image display panel include a liquid crystal
display panel and an organic EL panel. The circularly polarizing
plate is arranged on the viewer side of the image display panel,
and is arranged so that the colored layer may be on an image
display panel side, and the polarizer may be on the viewer
side.
[0105] An image display panel having a high reflectance (e.g., an
image display panel that includes, for example, a member formed of
a metal or a member containing a metal, and that has a high
reflectance) is suitably used as the image display panel. The
circularlypolarizingplate of the present invention has an excellent
antireflection characteristic and an excellent hue-adjusting
function. Accordingly, even in an image display apparatus including
the image display panel having a high reflectance, the influence of
ambient light reflection can be effectively reduced. The visible
light reflectance of the image display panel is, for example, 20%
or more, preferably from 40% to 99%.
EXAMPLES
[0106] Now, the present invention is specifically described byway
of Examples. However, the present invention is by no means limited
by these Examples. Methods of measuring the respective
characteristics are as described below.
[0107] [Evaluation]
(1) Measurement of Absorption Spectrum
[0108] A colored layer was dissolved in ethyl acetate to prepare an
evaluation sample.
[0109] The absorption spectrum of the evaluation sample was
measured with a spectrophotometer (manufacturedby Hitachi
High-Technologies Corporation, product name: "U-4100").
(2) Measurement of Color Gamut
[0110] A circularly polarizing plate was arranged on the viewer
side of iPad manufactured by Apple Inc. so that its colored layer
was on an iPad side. Thus, an evaluation sample was obtained.
[0111] In a dark room, chromaticities at the time of the red
display of the evaluation sample, at the time of the blue display
thereof, and at the time of the green display thereof were measured
with a luminance colorimeter (manufactured by Topcon Technohouse
Corporation, product name: "SR-UL1"). A DCI ratio (area B/area A)
was calculated from the area A of a triangle formed by connecting
the chromaticity coordinates of the respective colors, and the area
B of a region where the triangle formed by connecting the
chromaticity coordinates of the respective colors and the color
gamut standard of DCI overlapped each other.
(3) Measurement of Reflectance of Circularly Polarizing Plate
[0112] A circularly polarizing plate was bonded to a reflective
plate (manufactured by Toray Advanced Film Co., Ltd., product name:
"CERAPEEL DMS-X42", total light reflectance: 86%) so that its
colored layer was on a reflective plate side. Thus, an evaluation
sample was produced. The total light reflectance of the evaluation
sample was measured with CM2600-d (manufactured by Konica Minolta,
Inc.).
(4) .DELTA.ab
[0113] The reflection hue (L*a*b* colorimetric system) of the
evaluation sample produced in the (3) was measured with CM2600-d
(manufactured by Konica Minolta, Inc.), and the Lab thereof was
determined from the equation
".DELTA.ab=(a.sup.2+b.sup.2).sup.1/2".
Example 1
(i) Production of Retardation Layer (.lamda./4 Plate)
[0114] Polymerization was performed by using a batch polymerization
apparatus formed of two vertical reactors each including a stirring
blade and a reflux condenser controlled to 100.degree. C.
9,9-[4-(2-Hydroxyethoxy)phenyl]fluorene (BHEPF), isosorbide (ISB),
diethylene glycol (DEG), diphenyl carbonate (DPC), and magnesium
acetate tetrahydrate were loaded into a first reactor so that a
molar ratio "BHEPF/ISB/DEG/DPC/magnesium acetate" became
0.348/0.490/0.162/1.005/1.00.times.10.sup.-5. After air in the
reactor had been sufficiently purged with nitrogen (oxygen
concentration: from 0.0005 vol % to 0.001 vol %), a temperature in
the reactor was warmed with a heating medium, and stirring was
started at the time point when the internal temperature became
100.degree. C. 40 Minutes after the start of the temperature
increase, the internal temperature was caused to reach 220.degree.
C., and such control that the temperature was held was performed.
Simultaneously with the control, the reduction of a pressure in the
reactor was started, and the pressure was set to 13.3 kPa in 90
minutes after the temperature had reached 220.degree. C. Phenol
vapor produced as a by-product of the polymerization reaction was
introduced into the reflux condenser at 100.degree. C. A monomer
component present in a trace amount in the phenol vapor was
returned to the reactor, and the phenol vapor that did not condense
was introduced into a condenser at 45.degree. C. and collected.
[0115] Nitrogen was introduced into the first reactor to return the
pressure to atmospheric pressure once. After that, the oligomerized
reaction liquid in the first reactor was transferred to a second
reactor. Next, the increase of a temperature in the second reactor
and the reduction of a pressure therein were started, and the
internal temperature and the pressure were set to 240.degree. C.
and 0.2 kPa, respectively in 50 minutes. After that, polymerization
was advanced until predetermined stirring power was obtained. At
the time point when the predetermined power was achieved, nitrogen
was introduced into the reactor to return the pressure to
atmospheric pressure. The reaction liquid was extracted in the form
of a strand, and was pelletized with a rotary cutter to provide a
polycarbonate resin having a copolymerization composition
"BHEPF/ISB/DEG" of 34.8/49.0/16.2 [mol %]. The polycarbonate resin
had a reduced viscosity of 0.430 dL/g and a glass transition
temperature of 128.degree. C.
[0116] The resultant polycarbonate resin (10 kg) was dissolved in
methylene chloride (73 kg) to prepare an application liquid. Next,
the application liquid was directly applied onto a shrinkable film
(longitudinally uniaxially stretched polypropylene film,
manufactured by Tokyo Printing Ink Mfg Co., Ltd., product name:
"NOBLEN"). The applied film was dried at a drying temperature of
30.degree. C. for 5 minutes and at a drying temperature of
80.degree. C. for 5 minutes to form a laminate having the
configuration "shrinkable film/birefringent layer". The resultant
laminate was stretched with a simultaneous biaxial stretching
machine at a stretching temperature of 155.degree. C. in its MD
direction at a shrinkage ratio of 0.80 times and in its TD
direction at a stretching ratio of 1.3 times to form a retardation
film A on the shrinkable film. Next, the retardation film was
peeled from the shrinkable film. The retardation film A had a
thickness of 60.0 .mu.m, an Re(550) of 140 nm, an Nz coefficient of
0.5, and a ratio Re(450)/Re(550) of 0.89. The retardation film A
was adopted as a retardation layer (.lamda./4 plate).
[0117] (ii) Production of Polarizer
[0118] An elongate roll of a polyvinyl alcohol (PVA)-based resin
film having a thickness of 30 .mu.m (manufactured by Kuraray Co.,
Ltd., product name: "PE3000") was uniaxially stretched with a roll
stretching machine in its lengthwise direction at a stretching
ratio of 5.9 times in the lengthwise direction. Simultaneously with
the stretching, the film was subjected to swelling, dyeing,
cross-linking, and washing treatments, and was finally subjected to
a drying treatment to produce a polarizer having a thickness of 12
.mu.m.
[0119] Specifically, in the swelling treatment, the film was
stretched at a stretching ratio of 2.2 times while being treated
with pure water at 20.degree. C. Next, in the dyeing treatment, the
film was stretched at a stretching ratio of 1.4 times while being
treated in an aqueous solution at 30.degree. C. containing iodine
and potassium iodide at a weight ratio of 1:7 in which an iodine
concentration was adjusted so that the single layer transmittance
of the polarizer to be obtained became 45.0%. Further, in the
cross-linking treatment, a two-stage cross-linking treatment was
adopted, and in a first-stage cross-linking treatment, the film was
stretched at a stretching ratio of 1.2 times while being treated in
an aqueous solution at 40.degree. C. having dissolved therein boric
acid and potassium iodide. The boric acid content of the aqueous
solution in the first-stage cross-linking treatment was set to 5.0
wt %, and the potassium iodide content thereof was set to 3.0 wt %.
In a second-stage cross-linking treatment, the film was stretched
at a stretching ratio of 1.6 times while being treated in an
aqueous solution at 65.degree. C. having dissolved therein boric
acid and potassium iodide. The boric acid content of the aqueous
solution in the second-stage cross-linking treatment was set to 4.3
wt %, and the potassium iodide content thereof was set to 5.0 wt %.
In addition, in the washing treatment, the film was treated with a
potassium iodide aqueous solution at 20.degree. C. The potassium
iodide content of the aqueous solution in the washing treatment was
set to 2.6 wt %. Finally, in the drying treatment, the film was
dried at 70.degree. C. for 5 minutes to provide the polarizer.
[0120] (iii) Production of Polarizing Plate A
[0121] AHC-TAC film (thickness: 32 .mu.m, corresponding to a
protective film) including a hard coat (HC) layer formed on one
surface of a TAC film by a hard coat treatment was bonded to one
side of the polarizer via a polyvinyl alcohol-based adhesive
through a roll-to-roll process. Thus, an elongate polarizing plate
A having the configuration "protective film/polarizer" was
obtained.
[0122] (iv) Production of Polarizing Plate A with Retardation
Layer
[0123] The polarizing plate and the retardation layer obtained in
the foregoing were each cut into a predetermined size, and the
polarizer surface of the polarizing plate and the retardation layer
were bonded to each other via an acrylic pressure-sensitive
adhesive. Thus, a polarizing plate A with a retardation layer
having the configuration "protective film/polarizer/retardation
layer (.lamda./4 plate)" was obtained. The retardation layer was
cut so that an angle formed by the absorption axis of the polarizer
and the slow axis of the retardation layer became 45.degree. at the
time of the bonding of the polarizing plate and the retardation
layer.
[0124] (v) Formation of Colored Layer
[0125] A coloring matter-containing pressure-sensitive adhesive
containing 0.3 part by weight of a radical generator (benzoyl
peroxide, manufactured by Nippon Oil & Fats Co., Ltd., product
name: "NYPER BMT"), 1 part by weight of an isocyanate-based
cross-linking agent (manufactured by Tosoh Corporation, product
name: "CORONATE L"), 0.25 part by weight of a squaraine compound
represented by the following general formula (I-20), and 0.2 part
by weight of a phenol-based antioxidant (manufactured by BASF Japan
Ltd., product name: "IRGANOX 1010") with respect to 100 parts by
weight of an acrylic polymer obtained by copolymerizing n-butyl
acrylate and a hydroxy group-containing monomer was produced. The
pressure-sensitive adhesive was applied onto a PET substrate
(manufacturedbyMitsubishi Plastics, Inc., product name: "MRF38CK"),
which had been subjected to a treatment for facilitating the
peeling of the pressure-sensitive adhesive, with an applicator so
as to have a thickness of 20 .mu.m, and the adhesive was dried at
155.degree. C. for 2 minutes. After that, the pressure-sensitive
adhesive sample was removed, and the pressure-sensitive adhesive
surface was bonded to the retardation layer side of the polarizing
plate with a retardation layer. Thus, a colored layer (absorption
maximum wavelength: 594 nm) was formed.
[0126] The squaraine compound represented by the general formula
(I-20) was synthesized by the following method.
<Synthesis of Squaraine Compound>
[0127] 1-Phenyl-1,4,5,6-tetrahydrocyclopenta[b]pyrrole was
synthesized by a method described in "M. Beller et. al., J. Am.
Chem. Soc., 2013, 135(30), 11384-11388".
[0128] 300 Milligrams of
1-phenyl-1,4,5,6-tetrahydrocyclopenta[b]pyrrole and 80 mg of
squaric acid were mixed in 5 mL of ethanol, and the mixture was
stirred at 80.degree. C. for 2 hours. After that, the mixture was
cooled to room temperature, and the product was filtered out. The
product that had been filtered out was washed with ethanol, and was
dried under reduced pressure at 70.degree. C. to provide 197 mg of
a squaraine compound. Further, the compound was purified by silica
gel chromatography to provide 120 mg of a squaraine compound.
##STR00031##
[0129] A circularly polarizing plate including the protective film,
the polarizer, the retardation layer (.lamda./4 plate), and the
colored layer was obtained as described above. The resultant
circularly polarizing plate was subjected to the evaluations (2) to
(4). The results are shown in Table 1.
Comparative Example 1
[0130] (i) Production of Polarizing Plate A with Retardation
Layer
[0131] The polarizing plate A with a retardation layer was obtained
in the same manner as in Example 1.
[0132] (ii) Formation of Colored Layer
[0133] A circularly polarizing plate including the protective film,
the polarizer, the retardation layer (.lamda./4 plate), and a
colored layer (absorption maximum wavelength: 595 nm) was obtained
in the same manner as in Example 1 except that 0.25 part by weight
of a porphyrin-based coloring matter (manufactured by Yamamoto
Chemicals, Inc., product name: "PD-320") was used instead of 0.25
part by weight of the squaraine compound represented by the general
formula (I-20). The resultant circularly polarizing plate was
subjected to the evaluations (2) to (4). The results are shown in
Table 1.
Comparative Example 2
[0134] A circularly polarizing plate was obtained in the same
manner as in Example 1 except that the coloring matter (squaraine
compound) was not incorporated into the pressure-sensitive adhesive
forming the colored layer (i.e., a pressure-sensitive adhesive
layer was formed instead of the colored layer). The resultant
circularly polarizing plate was subjected to the evaluations (2) to
(4). The results are shown in Table 1.
TABLE-US-00002 TABLE 1 Color gamut Reflectance (DCI ratio) Coloring
matter (%) .DELTA.ab (%) Example 1 Squaraine compound 2.39 22.3 57
(formula (II)) Comparative Porphyrin-based 2.49 26.7 55 Example 1
coloring matter Comparative -- 2.66 25.1 51 Example 2
[0135] As is apparent from Table 1, according to the present
invention, a circularly polarizing plate that is excellent in
antireflection characteristic, that can output light having a small
Lab and a neutral hue, and that can widen the color gamut of an
image display apparatus can be obtained.
INDUSTRIAL APPLICABILITY
[0136] The circularly polarizing plate of the present invention is
suitably used in an image display apparatus, such as a liquid
crystal display apparatus.
REFERENCE SIGNS LIST
[0137] 10 polarizer [0138] 20a retardation layer [0139] 30 colored
layer [0140] 100 circularly polarizing plate
* * * * *