U.S. patent application number 16/864192 was filed with the patent office on 2020-08-20 for polarizing plate and circularly polarizing plate.
The applicant listed for this patent is Sumitomo Chemical Company, Limited. Invention is credited to Nobuyuki HATANAKA.
Application Number | 20200264460 16/864192 |
Document ID | 20200264460 / US20200264460 |
Family ID | 1000004810779 |
Filed Date | 2020-08-20 |
Patent Application | download [pdf] |
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United States Patent
Application |
20200264460 |
Kind Code |
A1 |
HATANAKA; Nobuyuki |
August 20, 2020 |
POLARIZING PLATE AND CIRCULARLY POLARIZING PLATE
Abstract
A polarizing plate including a substrate and a polarizer is
provided. The polarizer has a polarizing layer having a thickness
of 5 .mu.m or less in which a dichroic dye is oriented. The
absorbance in the absorption axis direction (A1) of the polarizer
at a wavelength of 380 to 760 nm is 0.3 or more and 1.5 or less,
and the absorbance in the transmission axis direction (A2) is 0.001
or more and 0.15 or less.
Inventors: |
HATANAKA; Nobuyuki; (Osaka,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sumitomo Chemical Company, Limited |
Tokyo |
|
JP |
|
|
Family ID: |
1000004810779 |
Appl. No.: |
16/864192 |
Filed: |
May 1, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15558756 |
Sep 15, 2017 |
10690953 |
|
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PCT/JP2016/057221 |
Mar 8, 2016 |
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16864192 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 51/50 20130101;
H01L 51/5281 20130101; G02B 5/30 20130101; H01L 51/56 20130101;
H01L 51/5293 20130101; G02F 1/133528 20130101; G02F 1/13363
20130101; G02F 1/1335 20130101; G02B 5/305 20130101 |
International
Class: |
G02F 1/1335 20060101
G02F001/1335; H01L 51/50 20060101 H01L051/50; G02B 5/30 20060101
G02B005/30; H01L 51/56 20060101 H01L051/56; H01L 51/52 20060101
H01L051/52; G02F 1/13363 20060101 G02F001/13363 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 16, 2015 |
JP |
2015-051786 |
Claims
1.-8. (canceled)
9. A polarizing plate comprising a substrate and a polarizer,
wherein the polarizer has a polarizing layer having a thickness of
5 .mu.m or less in which a dichroic dye is oriented, an absorbance
in the absorption axis direction (A1) of the polarizer at a
wavelength of 380 to 760 nm is 0.3 or more and 1 or less, and an
absorbance in a transmission axis direction (A2) is 0.001 or more
and 0.10 or less, and wherein the dichroic dye includes: (i) a dye
represented by formula (1): ##STR00023## wherein Y is a group
represented by one of formulas (Y1) and (Y2): ##STR00024## L is an
oxygen atom or --NR--, R is a hydrogen atom or an alkyl group
having 1 to 4 carbon atoms, R.sup.1 is a group represented by one
of formulas (R.sup.1-1), (R.sup.1-2) and (R.sup.1-3): ##STR00025##
wherein each ma represents an integer of 0 to 10, R.sup.2 is a
group represented by one of formulas (R.sup.2-1), (R.sup.2-2),
(R.sup.2-3), (R.sup.2-4), (R.sup.2-5) and (R.sup.2-6): ##STR00026##
and wherein each mb is an integer of 0 to 10; and (ii) a dye
represented by formula (2): ##STR00027## wherein n is 1 or 2,
Ar.sup.1 and Ar.sup.3 each represents a group represented by one of
formulas (AR-1), (AR-2), (AR-3) and (AR-4): ##STR00028## Ar.sup.2
is a group represented by one of formulas (AR2-1), (AR2-2) and
(AR2-3): ##STR00029## A.sub.1 and A.sub.2 each represents a group
represented by one of formulas (A-1) to (A-9): ##STR00030## and
wherein me is an integer of 0 to 10.
10. The polarizing plate according to claim 9, wherein the
azobenzene site of the dye represented by formula (1) has trans
geometric isomerism.
11. The polarizing plate according to claim 9, wherein in the
formula (1), Y is a group represented by the formula (Y1).
12. The polarizing plate according to claim 9, wherein the
polarizing layer comprises a polymer of a polymerizable liquid
crystal compound exhibiting a smectic liquid crystal phase.
13. The polarizing plate according to claim 9, wherein the alkyl
group is selected from the group consisting of a methyl group, an
ethyl group, an n-propyl group, an isopropyl group, an n-butyl
group, an isobutyl group and a t-butyl group.
14. The polarizing plate according to claim 9, wherein R.sup.1 is a
group represented by one of the formulas (R.sup.1-2) and
(R.sup.1-3).
15. The polarizing plate according to claim 9, wherein in formula
(R.sup.1-2), each ma represents an integer of 0 to 5.
16. The polarizing plate according to claim 9, wherein R.sup.2 is a
group represented by one of the formulas (R.sup.2-2), (R.sup.2-5)
and (R.sup.2-6).
17. The polarizing plate according to claim 9, wherein in formulas
(R.sup.2-1), (R.sup.2-2), (R.sup.2-3), (R.sup.2-5) and (R.sup.2-6),
each mb is an integer of 0 to 5.
18. The polarizing plate according to claim 9, wherein the
azobenzene site of the dye represented by formula (2) has trans
geometric isomerism.
19. The polarizing plate according to claim 9, wherein the dichroic
dye is an organic dye.
20. The polarizing plate according to claim 9, wherein the
polymerizable liquid crystal compound is a compound exhibiting a
higher smectic liquid crystal phase.
21. The polarizing plate according to claim 9, wherein L is an
oxygen atom.
22. The polarizing plate according to claim 9, wherein the dye
represented by formula (1) is a compound represented by one of
formulas (1-1) to (1-8): ##STR00031##
23. The polarizing plate according to claim 9, wherein the dye
represented by formula (2) is a compound represented by one of
formulas (2-11) to (2-36): ##STR00032## ##STR00033##
24. The polarizing plate according to claim 9, wherein the
polarizer exhibits a Bragg peak in X-ray diffraction
measurement.
25. A circularly polarizing plate comprising the polarizing plate
according to claim 9 and a 1/4 wavelength plate.
26. The circularly polarizing plate according to claim 25, wherein
a birefringence of the 1/4 wavelength plate to light having a
wavelength of 450 nm, a birefringence to light having a wavelength
of 550 nm, and a birefringence to light having a wavelength of 650
nm have reverse wavelength dispersibility satisfying relationships
represented by the following expressions (II) and (III):
.DELTA.n(450)/.DELTA.n(550).ltoreq.1.00 (II)
1.00.ltoreq..DELTA.n(650)/.DELTA.n(550) (III) wherein
.DELTA.n(.lamda.) represents a birefringence to light having a
wavelength .lamda. nm.
Description
TECHNICAL FIELD
[0001] The present invention relates to polarizing plates and
circularly polarizing plates.
BACKGROUND ART
[0002] Circularly polarizing plates are used in organic
electroluminescent (EL) image displaying devices to prevent
reflection of external light in bright places. As such circularly
polarizing plates, a polarizing plate in which poly(vinyl alcohol)
(PVA) is dyed with iodine (iodine-PVA polarizing plate) is known,
for example (see Patent Literature 1).
[0003] Particularly in the case where a circularly polarizing plate
is used in the organic EL image displaying device, a polarizing
plate having low absorbance is desired so as not to absorb light
emitted from an organic EL element. In the case of the iodine-PVA
polarizing plate, the absorbance can be reduced through a reduction
in dyeing concentration of iodine.
CITATION LIST
Patent Literature
[0004] Patent Literature 1: JP 07-142170 A
SUMMARY OF INVENTION
Technical Problem
[0005] However, such an iodine-PVA polarizing plate having low
iodine concentration has problems such that iodine sublimates and
denatures, causing change of color, in some environments for use,
and warpage generates as a result of relaxing the stretch of PVA.
Moreover, it is difficult to form the iodine-PVA polarizing plate
into a thin film, and the iodine-PVA polarizing plate has a
limitation in applications to display devices required for more
reduced profiles.
[0006] Accordingly, an object of the present invention is to
provide a polarizing plate and a circularly polarizing plate having
high light absorbing selectivity even in the form of a thin film,
and having high heat resistance.
Solution to Problem
[0007] The present invention includes the following aspects.
[1] A polarizing plate comprising a substrate and a polarizer,
wherein the polarizer has a polarizing layer having a thickness of
5 .mu.m or less in which a dichroic dye is oriented, and an
absorbance in the absorption axis direction (A1) of the polarizer
at a wavelength of 380 to 760 nm is 0.3 or more and 1.5 or less,
and an absorbance in a transmission axis direction (A2) is 0.001 or
more and 0.15 or less. [2] The polarizing plate according to [1],
wherein the dichroic dye is an organic dye. [3] The polarizing
plate according to [1] or [2], wherein the polarizing layer
comprises a polymer of a polymerizable liquid crystal compound. [4]
The polarizing plate according to [3], wherein the polymerizable
liquid crystal compound is a compound exhibiting a smectic liquid
crystal phase. [5] The polarizing plate according to [4], wherein
the polymerizable liquid crystal compound is a compound exhibiting
a higher smectic liquid crystal phase. [6] The polarizing plate
according to any one of [1] to [4], wherein the polarizer exhibits
a Bragg peak in X-ray diffraction measurement. [7] A circularly
polarizing plate comprising the polarizing plate according to any
one of [1] to [6], and a 1/4 wavelength plate. [8] The circularly
polarizing plate according to [7], wherein a birefringence of the
1/4 wavelength plate to light having a wavelength of 450 nm, a
birefringence to light having a wavelength of 550 nm, and a
birefringence to light having a wavelength of 650 nm have reverse
wavelength dispersibility satisfying relationships represented by
the following expressions (II) and (III):
.DELTA.n(450)/.DELTA.n(550).ltoreq.1.00 (II)
1.00.ltoreq..DELTA.n(650)/.DELTA.n(550) (III)
wherein .DELTA.n(.lamda.) represents a birefringence to light
having a wavelength .lamda. nm.
Advantageous Effect of Invention
[0008] According to the present invention, a polarizing plate and
circularly polarizing plate can be provided which have high light
absorbing selectivity even in the form of a thin film, and have
high heat resistance.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 is a sectional view schematically illustrating one
embodiment of a polarizing plate.
[0010] FIG. 2 is a sectional view schematically illustrating one
embodiment of a circularly polarizing plate.
[0011] FIG. 3 is a sectional view schematically illustrating one
embodiment of a circularly polarizing plate.
[0012] FIG. 4 is a sectional view schematically illustrating one
embodiment of a circularly polarizing plate.
DESCRIPTION OF EMBODIMENTS
[0013] The polarizing plate according to the present embodiment
comprises a substrate and a polarizer, wherein the polarizer has a
polarizing layer having a thickness of 5 .mu.m or less in which a
dichroic dye is oriented, and the polarizer has an absorbance (A1)
at a wavelength of 380 to 760 nm of 0.3 or more and 1.5 or less in
the absorption axis direction and an absorbance (A2) of 0.001 or
more and 0.15 or less in the transmission axis direction.
[0014] 1. Polarizer
[0015] The polarizer according to the present embodiment has a
polarizing layer having a thickness of 5 .mu.m or less in which a
dichroic dye is oriented. This polarizing layer can be formed using
a composition comprising a dichroic dye (hereinafter, referred to
as "composition for forming a polarizer" in some cases).
[0016] 1-1. Dichroic Dye
[0017] It is preferred that a dichroic dye having absorption at a
wavelength in the range of 380 to 800 nm can be used, and it is
preferred that an organic dye be used. Examples of the dichroic dye
include azo compounds.
[0018] As the azo compounds, a dichroic dye (1) having an
absorption maximum at a wavelength in the range of 380 to 550 nm
can be used. Examples of the dichroic dye (1) include a compound
represented by the following formula (1) (hereinafter, referred to
as "compound (1)" in some cases). It is preferred that the
azobenzene site of the compound (1) have trans geometric
isomerism.
##STR00001##
[0019] In the formula (1), Y is a group represented by the
following formula (Y1) or (Y2), preferably a group represented by
the formula (Y1):
##STR00002##
[0020] In the formula (Y1) and the formula (Y2), the straight lines
at both ends represent direct links, the direct link on the left
bonds to a phenylene group having an azo group, and the direct link
on the right bonds to a phenylene group having R.sup.2. L is an
oxygen atom or --NR--, and R is a hydrogen atom or an alkyl group
having 1 to 4 carbon atoms. Examples of the alkyl group include a
methyl group, an ethyl group, an n-propyl group, an isopropyl
group, an n-butyl group, an isobutyl group, and a t-butyl group.
Among these, it is preferred that L be an oxygen atom or --NH--,
and it is more preferred that L be an oxygen atom.
[0021] R.sup.1 is a group represented by the following formula
(R.sup.1-1), (R.sup.1-2), or (R.sup.1-3), and is preferably a group
represented by the formula (R.sup.1-2) or (R.sup.1-3). In the
formulas, * represents a direct link.
##STR00003##
[0022] In the group represented by the formula (R.sup.1-2), it is
preferred that ma's each represent an integer of 0 to 10, and it is
more preferred that ma's each represent an integer of 0 to 5. The
two ma's may be the same or different, but it is preferred that
these be the same.
[0023] R.sup.2 is a group represented by the formula (R.sup.2-1),
(R.sup.2-2), (R.sup.2-3), (R.sup.2-4), (R.sup.2-5), or (R.sup.2-6),
it is preferred that R.sup.2 be a group represented by the formula
(R.sup.2-2), (R.sup.2-5), or (R.sup.2-6), and it is more preferred
that R.sup.2 be a group represented by the formula (R.sup.2-6).
##STR00004##
[0024] In the case where R.sup.2 is a group represented by the
formula (R.sup.2-1), (R.sup.2-2), (R.sup.2-3), (R.sup.2-5), or
(R.sup.2-6), it is preferred that mb comprised in the group be an
integer of 0 to 10, and it is more preferred that mb comprised in
the group be an integer of 0 to 5.
[0025] Examples of the compound (1) include the compounds
represented by the following formulas (1-1) to (1-8):
##STR00005##
[0026] Among these, as the compound (1), the compounds represented
by the formulas (1-1), (1-2), (1-3), (1-5), (1-7), and (1-8) are
preferred, and the compounds represented by the formulas (1-1),
(1-2), (1-3), and (1-7) are more preferred.
[0027] Here, a method of producing the compound (1) will be
described. The compound (1) can be produced, for example, from a
compound [compound (1X)] represented by the formula (1X) and a
compound [compound (1Y)] represented by the formula (1Y) by the
reaction shown in the following schema:
##STR00006##
[0028] In the above schema, R.sup.1, R.sup.2 and Y have the same
meanings as defined above, and Re.sup.1 and Re.sup.2 are groups
which will react with each other to form a group represented by Y.
Examples of the combination of Re.sup.1 and Re.sup.2 include a
combination of a carboxy group and a hydroxyl group, a combination
of a carboxy group and an amino group (where the amino group may be
replaced by R), a combination of a carbonyl halide group and a
hydroxyl group, a combination of a carbonyl halide group and an
amino group (where the amino group may be replaced by R), a
combination of a carbonyloxyalkyl group and a hydroxyl group, and a
combination of a carbonyloxyalkyl group and an amino group (where
the amino group may be replaced by R). Examples of R include alkyl
groups having 1 to 4 carbon atoms. Moreover, although the compound
(1X) having R.sup.1 and the compound (1Y) having R.sup.2 have been
described here, a compound having R.sup.1 protected with an
appropriate protecting group and a compound having R.sup.2
protected with an appropriate protecting group can be reacted with
each other, and then an appropriate deprotection reaction can be
performed to produce the compound (1).
[0029] For the reaction condition when the compound (1X) and the
compound (1Y) are reacted, an optimal known condition can be
appropriately selected according to the types of the compound (1X)
and the compound (1Y).
[0030] Examples of the reaction condition when Re.sup.1 is a
carboxy group, Re.sup.2 is a hydroxyl group, and Y is
--C(.dbd.O)--O-- include a condition for condensation in a solvent
in the presence of an esterification condensing agent. Examples of
the solvent include solvents which can dissolve both of the
compound (1X) and the compound (1Y), such as chloroform. Examples
of the esterification condensing agent include
diisopropylcarbodiimide (IPC). Herein, it is preferred that a base
such as dimethylaminopyridine (DMAP) be further used in
combination. Although the reaction temperature is selected
according to the types of the compound (1X) and the compound (1Y),
the reaction temperature is a temperature, for example, in the
range of -15 to 70.degree. C., preferably 0 to 40.degree. C. The
reaction time is in the range of 15 minutes to 48 hours, for
example.
[0031] The reaction time can be determined by appropriately
sampling the reaction mixture which is being reacted, and checking
the degree of loss of the compound (1X) and the compound (1Y) and
the degree of generation of the compound (1) by a known analysis
unit such as liquid chromatography and gas chromatography.
[0032] The compound (1) can be extracted from the reaction mixture
after the reaction by a known method such as recrystallization,
reprecipitation, extraction, and a variety of chromatographic
methods, or a combination of these operations.
[0033] As the azo compound, a dichroic dye (2) having an absorption
maximum at a wavelength in the range of 550 to 700 nm can be
used.
[0034] The dichroic dye (2) may comprise a dichroic dye (2-1)
having an absorption maximum at a wavelength in the range of 550 to
600 nm and/or a dichroic dye (2-2) having an absorption maximum at
a wavelength in the range of 600 to 700 nm. It is more preferred
that the dichroic dye (2-1) have an absorption maximum at a
wavelength in the range of 570 to 600 nm, and it is more preferred
that the dichroic dye (2-2) have an absorption maximum having a
wavelength in the range of 600 to 680 nm.
[0035] Examples of the dichroic dye (2) include a compound
represented by the following formula (2)(hereinafter, referred to
as "compound (2)" in some cases). It is preferred that the
azobenzene site of the compound (2) have trans geometric isomerism.
In the formula (2), n is 1 or 2.
##STR00007##
[0036] Ar.sup.1 and Ar.sup.3 each represent a group represented by
the formula (AR-1), (AR-2), (AR-3), or (AR-4). * represents a
direct link.
##STR00008##
[0037] Ar.sup.2 is a group represented by the formula (AR2-1),
(AR2-2), or (AR2-3).
##STR00009##
[0038] A.sub.1 and A.sub.2 each represent a group represented by
each of the formulas (A-1) to (A-9). In the formulas (A-2), (A-3),
(A-5), and (A-6), me is an integer of 0 to 10; if two mc's are in
the same group, these two mc's are the same or different.
##STR00010##
[0039] The compound (2) which can be used as the dichroic dye (2-1)
is determined by combining Ar.sup.1, Ar.sup.2, and Ar.sup.3 such
that the compound (2) has an absorption maximum at a wavelength in
the range of 550 to 600 nm. Similarly, the compound (2) which can
be used as the dichroic dye (2-2) is determined by combining
Ar.sup.1, Ar.sup.2, and Ar.sup.3 such that the compound (2) has an
absorption at a wavelength in the range of 600 to 700 nm.
[0040] Specifically showing the compound (2), examples thereof
include compounds represented by the formulas (2-11) to (2-39).
##STR00011## ##STR00012##
[0041] Among the specific examples of the compound (2), the
compound represented by the formulas (2-12), (2-13), (2-18),
(2-20), (2-21), (2-22), (2-23), (2-24), (2-26), (2-27), (2-28),
(2-29), and (2-30) each correspond to the dichroic dye (2-1), and
compounds represented by the formulas (2-31), (2-32), (2-33),
(2-34), (2-35), and (2-36) each correspond to the dichroic dye
(2-2). Although the compounds represented by the formulas (2-11).
(2-15), and (2-16) are not a dye having an absorption at a
wavelength of 550 to 700 nm, these can be used in combination with
another dichroic dye.
[0042] Among these specific examples of the compound (2), the
compounds represented by the formulas (2-15), (2-16), (2-18),
(2-20), (2-21), (2-22), (2-23), (2-27), (2-29), (2-31), (2-32),
(2-33), (2-34), and (2-35) are preferred as the dichroic dye
(2).
[0043] The dichroic dye (2) can be produced, for example, by a
known method described in JP 58-38756 A or JP 63-301850 A.
[0044] The dichroic dyes described above may be used alone or in
combination. In the case where the composition for forming a
polarizer contains two or more dichroic dyes, the content of each
dichroic dye is preferably 3 parts by mass or less, more preferably
0.1 parts by mass or more and 2.5 parts by mass or less, further
more preferably 1 part by mass or more and 1.5 parts by mass or
less relative to 100 parts by mass of a polymerizable liquid
crystal compound described later. If the content of each dichroic
dye is within this range, the dichroic dye(s) in the composition
for forming a polarizer has (have) sufficient solubility to the
solvent; for this reason, a polarizer having no defect generated is
readily obtained when the polarizer is produced using the
composition for forming a polarizer. Thereby, a polarizing plate
having high light absorbing selectivity and high heat resistance in
the form of a thin film is readily produced. The total amount of
the dichroic dyes in the composition for forming a polarizer is
preferably 9 parts by mass or less, more preferably 0.1 parts by
mass or more and 7.5 parts by mass or less, still more preferably 1
part by mass or more and 4.5 parts by mass or less relative to 100
parts by mass of a polymerizable liquid crystal compound described
later.
[0045] 1-2. Polymerizable Liquid Crystal Compound
[0046] It is preferred that the polarizer according to the present
embodiment have a polarizing layer comprising a polymer of a
polymerizable liquid crystal compound. Namely, the composition for
forming a polarizer can contain the dichroic dye with the
polymerizable liquid crystal compound.
[0047] The polymerizable liquid crystal compound is a liquid
crystal compound which can be polymerized in the state where it is
oriented, and has a polymerizable group in the molecule. The
composition for forming a polarizer containing the polymerizable
liquid crystal compound forms a cured film by polymerizing the
polymerizable liquid crystal compound in the state where the
polymerizable liquid crystal compound is oriented. It is
particularly preferred that the polymerizable group be a radical
polymerizable group. The radical polymerizable group refers to a
group related with a radical polymerization reaction.
[0048] The polymerizable liquid crystal compound may be a compound
having a liquid crystal phase of nematic phase (hereinafter,
referred to as "nematic liquid crystal phase" in some cases), a
compound having a liquid crystal phase of smectic phase
(hereinafter, referred to as "smectic liquid crystal phase" in some
cases), or a compound having both of the nematic liquid crystal
phase and the smectic liquid crystal phase; a polymerizable smectic
liquid crystal compound having at least the smectic liquid crystal
phase is preferred. The composition for forming a polarizer
comprising the polymerizable smectic liquid crystal compound, with
an interaction with the dichroic dye, produces a polarizer having
favorable neutral color phase properties and higher polarizing
performance.
[0049] As the smectic liquid crystal phase of the polymerizable
smectic liquid crystal compound, a higher smectic liquid crystal
phase is more preferred. The higher smectic liquid crystal phase
herein refers to the smectic B phase, the smectic D phase, the
smectic E phase, the smectic F phase, the smectic G phase, the
smectic H phase, the smectic I phase, the smectic J phase, the
smectic K phase, and the smectic L phase; among these, the smectic
B phase, the smectic F phase, and the smectic I phase are more
preferred.
[0050] If the smectic liquid crystal phase of the polymerizable
liquid crystal compound is one of these higher smectic liquid
crystal phases, a polarizer having a higher orientation order can
be produced. Moreover, a polarizer produced from such a higher
smectic liquid crystal phase having a higher orientation order
exhibits a Bragg peak derived from a higher structure such as a
hexatic phase or a crystal phase in the X-ray diffraction
measurement. The Bragg peak is a peak derived from a surface
periodic structure of a molecular orientation, and according to the
composition for forming a polarizer according to the present
embodiment, a polarizer having a periodic interval of 3.0 to 5.0
angstroms can be obtained.
[0051] Whether the polymerizable liquid crystal compound has a
nematic liquid crystal phase or a smectic liquid crystal phase can
be verified as follows, for example. An appropriate substrate is
prepared, and the composition for forming a polarizer is applied to
the substrate to form a coating; then, the workpiece is heat
treated or treated under reduced pressure on the condition
inhibiting the polymerization of the polymerizable liquid crystal
compound to remove the solvent contained in the coating.
Subsequently, the liquid crystal phase expressed by heating the
coating formed on the substrate to an isotropic temperature, and
gradually cooling the coating is examined through observation of
the texture with a polarizing microscope, X-ray diffraction
measurement, or differential scanning calorimetry. In this
examination, for example, a polymerizable liquid crystal compound
exhibiting the nematic liquid crystal phase through cooling of the
compound and exhibiting the smectic liquid crystal phase through
further cooling thereof is particularly preferred. In the nematic
liquid crystal phase and the smectic liquid crystal phase, that the
polymerizable liquid crystal compound and the dichroic dye are not
phase separated can be verified through surface observation with a
variety of microscopes or measurement of the degree of scattering
with a haze meter, for example.
[0052] Examples of the polymerizable liquid crystal compound
include a compound represented by the formula (4) (hereinafter,
referred to as "compound (4)" in some cases):
U.sup.1--V.sup.1--W.sup.1--X.sup.1--Y.sup.1--X.sup.2--Y.sup.2--X.sup.3---
W.sup.2--V.sup.2--U.sup.2 (4).
[0053] In the formula (4), X.sup.1, X.sup.2, and X.sup.3 each
independently represent an optionally substituted 1,4-phenylene
group or an optionally substituted cyclohexane-1,4-diyl group. At
least one of X.sup.1, X.sup.2, and X.sup.3 is preferably an
optionally substituted cyclohexane-1,4-diyl group, and X.sup.1 or
X.sup.3 is particularly preferably an optionally substituted
cyclohexane-1,4-diyl group. --CH.sub.2-- forming the optionally
substituted cyclohexane-1,4-diyl group may be replaced by --O--,
--S--, or --NR--. R is an alkyl group having 1 to 6 carbon atoms or
a phenyl group.
[0054] The optionally substituted cyclohexane-1,4-diyl group is
preferably an optionally substituted trans-cyclohexane-1,4-diyl
group, and more preferably a trans-cyclohexane-1,4-diyl group
having no substituent. In the formula (4), at least two of X.sup.1,
X.sup.2, and X.sup.3 may be an optionally substituted 1,4-phenylene
group, and is preferably a 1,4-phenylene group having no
substituent.
[0055] Examples of the substituent which the optionally substituted
1,4-phenylene group or the optionally substituted
cyclohexane-1,4-diyl group optionally has include alkyl groups
having 1 to 4 carbon atoms such as a methyl group, an ethyl group,
and a butyl group; a cyano group, and halogen atoms.
[0056] In the formula (4), Y.sup.1 and Y.sup.2 each independently
represent --CH.sub.2CH.sub.2--, --CH.sub.2O--, --COO--, --OCOO--,
single bond, --N.dbd.N--, --CR.sup.a.dbd.CR.sup.b--, --C.ident.C--,
or --CR.sup.a.dbd.N--. R.sup.a and R.sup.b each independently
represent a hydrogen atom or an alkyl group having 1 to 4 carbon
atoms. Y.sup.1 is preferably --CH.sub.2CH.sub.2--, --COO--, or a
single bond; Y.sup.2 is preferably --CH.sub.2CH.sub.2--, --COO--,
or --CH.sub.2O--.
[0057] In the formula (4), U.sup.1 is a hydrogen atom or a
polymerizable group, preferably a polymerizable group. U.sup.2 is a
polymerizable group. U.sup.1 and U.sup.2 are both preferably a
polymerizable group, more preferably a photopolymerizable group.
The photopolymerizable group refers to a group which can be
involved in a polymerization reaction by an active radical or an
acid generated from a photopolymerization initiator described
later. It is advantageous that the polymerizable liquid crystal
compound having a photopolymerizable group can be polymerized under
a condition at lower temperature.
[0058] The polymerizable groups of U.sup.1 and U.sup.2 may be
different, but it is preferred that polymerizable groups of U.sup.1
and U.sup.2 be groups of the same type. Examples of the
polymerizable group include a vinyl group, a vinyloxy group, a
1-chlorovinyl group, an isopropenyl group, a 4-vinylphenyl group,
an acryloyloxy group, a methacryloyloxy group, an oxiranyl group,
and an oxetanyl group. Among these, an acryloyloxy group, a
methacryloyloxy group, a vinyloxy group, an oxiranyl group, and an
oxetanyl group are preferred, and an acryloyloxy group is more
preferred as the polymerizable group.
[0059] In the formula (4), V.sup.1 and V.sup.2 each independently
represent an optionally substituted alkanediyl group having 1 to 20
carbon atoms, where --CH.sub.2-- forming the alkanediyl group may
be replaced by --O--, --S--, or --NH--. Examples of the alkanediyl
group having 1 to 20 carbon atoms include a methylene group, an
ethylene group, a propane-1,3-diyl group, a butane-1,3-diyl group,
a butane-1,4-diyl group, a pentane-1,5-diyl group, a
hexane-1,6-diyl group, a heptane-1,7-diyl group, an octane-1,8-diyl
group, a decane-1,10-diyl group, a tetradecane-1,14-diyl group, and
an icosane-1,20-diyl group. V.sup.1 and V.sup.2 are an alkanediyl
group having preferably 2 to 12 carbon atoms, more preferably 6 to
12 carbon atoms. Examples of the substituent that the alkanediyl
group having 1 to 20 carbon atoms optionally has can include a
cyano group and halogen atoms. It is preferred that the alkanediyl
group be not replaced, and it is more preferred that the alkanediyl
group be not replaced and be linear.
[0060] In the formula (4), W.sup.1 and W.sup.2 each independently
represent a single bond, --O--, --S--, --COO--, or --OCOO--, and
W.sup.1 and W.sup.2 are preferably a single bond or --O--.
[0061] Examples of the compound (4) include compounds represented
by the formulas (4-1) to (4-43). If a specific example of the
compound (4) has a cyclohexane-1,4-diyl group, it is preferred that
the cyclohexane-1,4-diyl group be a trans body.
##STR00013## ##STR00014## ##STR00015## ##STR00016##
[0062] These polymerizable liquid crystal compounds can be used
alone or in the form of a mixture thereof in the composition for
forming a polarizer. In the case where two or more of the
polymerizable liquid crystal compounds are mixed, it is preferred
that at least one of them be the compound (4). As the mixing ratio
(mass ratio) when two of the polymerizable liquid crystal compounds
are mixed, the ratio of polymerizable liquid crystal compound other
than the compound (4): compound (4) is usually 1:99 to 50:50,
preferably 5:95 to 50:50, more preferably 10:90 to 50:50.
[0063] Among these compounds (4), the compounds represented by the
formulas (4-5), (4-6), (4-7), (4-8), (4-9), (4-10), (4-11), (4-12),
(4-13), (4-14), (4-15), (4-22), (4-24), (4-25), (4-26), (4-27),
(4-28), and (4-29) are preferred. By the interaction with another
polymerizable liquid crystal compound, these compounds can be
readily polymerized under a temperature condition lower than the
crystal phase transition temperature thereof, namely, in the state
where the liquid crystal state of a higher smectic phase is
sufficiently kept. Specifically, these compounds can be polymerized
under a temperature condition of 70.degree. C. or less, preferably
60.degree. C. or less in the state where the liquid crystal state
of a higher smectic phase is sufficiently kept.
[0064] The proportion of the polymerizable liquid crystal compound
contained in the composition for forming a polarizer is preferably
50 to 99.9% by mass, more preferably, 80 to 99.9% by mass relative
to the solid content of the composition for forming a polarizer. If
the proportion of the polymerizable liquid crystal compound
contained is within this range, the orientation properties of the
polymerizable liquid crystal compound tend to be enhanced. The
solid content refers to the total amount of the component excluding
volatility components such as a solvent from the composition for
forming a polarizer.
[0065] The polymerizable liquid crystal compound can be produced by
a known method described in Lub et al. Recl. Trav. Chim. Pays-Bas,
115, 321-328 (1996), or JP 4719156 B, for example.
[0066] 1-3. Solvent
[0067] It is preferred that the composition for forming a polarizer
comprises a solvent. As the solvent, a solvent that can completely
dissolve the dichroic dye and the polymerizable liquid crystal
compound is preferred. Moreover, it is preferred that the solvent
be inactive to the polymerization reaction of the polymerizable
liquid crystal compound comprised in the composition for forming a
polarizer.
[0068] Examples of the solvent include alcohol solvents such as
methanol, ethanol, ethylene glycol, isopropyl alcohol, propylene
glycol, ethylene glycol methyl ether, ethylene glycol butyl ether,
and propylene glycol monomethyl ether; ester solvents such as ethyl
acetate, butyl acetate, ethylene glycol methyl ether acetate,
.gamma.-butyrolactone, propylene glycol methyl ether acetate, and
ethyl lactate; ketone solvents such as acetone, methyl ethyl
ketone, cyclopentanone, cyclohexanone, 2-heptanone, and methyl
isobutyl ketone; aliphatic hydrocarbon solvents such as pentane,
hexane, and heptane; aromatic hydrocarbon solvents such as toluene
and xylene; nitrile solvents such as acetonitrile; ether solvents
such as tetrahydrofuran and dimethoxyethane; and chlorine
containing solvents such as chloroform and chlorobenzene. These
solvents may be used alone or in combination.
[0069] The content of the solvent is preferably 50 to 98% by mass
relative to the total amount of the composition for forming a
polarizer. In other words, the solid content of the composition for
forming a polarizer is preferably 2 to 50% by mass. If the solid
content is 2% by mass or more, a polarizing plate having a thin
profile, which is one of the objects of the present invention, is
readily obtained. Moreover, if the solid content is 50% by mass or
less, the viscosity of the composition for forming a polarizer
reduces; therefore, the thickness of the polarizer becomes
approximately uniform, and unevenness barely occurs in the
polarizer. The solid content can be determined in consideration of
the thickness of the polarizer.
[0070] 1-4. Additives
[0071] The composition for forming a polarizer according to the
present embodiment can optionally comprise additives. Examples of
the additives include polymerization initiators, light sensitizers,
polymerization inhibitors, and leveling agents.
[0072] 1-4-1. Polymerization Initiator
[0073] It is preferred that the composition for forming a polarizer
contain a polymerization initiator. The polymerization initiator is
a compound which can initiate the polymerization reaction of the
polymerizable liquid crystal compound. As the polymerization
initiator, photopolymerization initiators are preferred because
these can initiate the polymerization reaction under low
temperature conditions. Specifically, compounds which generate an
active radical or an acid by the action of light are used as the
photopolymerization initiator. Among these photopolymerization
initiators, polymerization initiators which generate active
radicals by the action of light are more preferred.
[0074] Examples of the polymerization initiator include benzoin
compounds, benzophenone compounds, alkylphenone compounds,
acylphosphine oxide compounds, triazine compounds, iodonium salts,
and sulfonium salts.
[0075] Examples of the benzoin compounds include benzoin, benzoin
methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and
benzoin isobutyl ether.
[0076] Examples of the benzophenone compounds include benzophenone,
methyl o-benzoylbenzoate, 4-phenylbenzophenone,
4-benzoyl-4'-methyldiphenyl sulfide,
3,3',4,4'-tetra(tert-butylperoxycarbonyl)benzophenone, and
2,4,6-trimethylbenzophenone.
[0077] Examples of the alkylphenone compounds include oligomers of
diethoxyacetophenone,
2-methyl-2-morpholino-1-(4-methylthiophenyl)propane-1-one,
2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butane-1-one,
2-hydroxy-2-methyl-1-phenylpropane-1-one,
1,2-diphenyl-2,2-dimethoxyethane-1-one,
2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]propane-1-one,
1-hydroxycyclohexylphenyl ketone, and
2-hydroxy-2-methyl-I-[4-(1-methyl vinyl)phenyl]propane-1-one.
[0078] Examples of the acylphosphine oxide compounds include
2,4,6-trimethylbenzoyldiphenylphosphine oxide, and
bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.
[0079] Examples of the triazine compounds include
2,4-bis(trichloromethyl)-6-(4-methoxyphenyl)-1,3,5-triazine,
2,4-bis(trichloromethyl)-6-(4-methoxynaphthyl)-1,3,5-triazine,
2,4-bis(trichloromethyl)-6-(4-methoxystyryl)-1,3,5-triazine,
2,4-bis(trichloromethyl)-6-[2-(5-methylfuran-2-yl)ethenyl]-1,3,5-triazine-
,
2,4-bis(trichloromethyl)-6-[2-(furan-2-yl)ethenyl]-1,3,5-triazine,
2,4-bis(trichloromethyl)-6-[2-(4-diethylamino-2-methylphenyl)ethenyl]-1,3-
,5-triazine, and
2,4-bis(trichloromethyl)-6-[2-(3,4-dimethoxyphenyl)ethenyl]-1,3,5-triazin-
e.
[0080] Commercially available polymerization initiators can also be
used as the polymerization initiator. Examples of the commercially
available polymerization initiators include "IRGACURE 907",
"IRGACURE 184", "IRGACURE 651", "IRGACURE 819", "IRGACURE 250", and
"IRGACURE 369" (BASF Japan Ltd.); "SEIKUOL BZ", "SEIKUOL Z",
"SEIKUOL BEE" (Seiko Chemical Co., Ltd.); "Kayacure BP100" (NIPPON
KAYAKU Co., Ltd.); "UVI-6992" (made by Dow Chemical Company);
"Adeka OPTOMER SP-152", "Adeka OPTOMER SP-170" (ADEKA Corporation);
"TAZ-A" and "TAZ-PP" (DKSH Japan); and "TAZ-104" (SANWA Chemical
Co., Ltd.).
[0081] In the case where the composition for forming a polarizer
contains the polymerization initiator, the content can be
appropriately adjusted according to the type and the amount of the
polymerizable liquid crystal compound contained in the composition
for forming a polarizer; the content of the polymerization
initiator relative to the total of 100 parts by mass of the
polymerizable liquid crystal compound is usually 0.1 to 30 parts by
mass, preferably 0.5 to 10 parts by mass, more preferably 0.5 to 8
parts by mass. If the content of the polymerizable initiator is
within this range, the polymerizable liquid crystal compound can be
polymerized without disturbing the orientation thereof; for this
reason, the content of the polymerizable initiator within this
range is preferred.
[0082] 1-4-2. Light Sensitizer
[0083] The composition for forming a polarizer, if containing the
photopolymerization initiator, may further contain a light
sensitizer. Examples of the light sensitizer include xanthone and
xanthone compounds such as thioxanthone (such as
2,4-diethylthioxanthone and 2-isopropylthioxanthone); anthracene
and anthracene compounds such as alkoxy group-containing
anthracenes (such as dibutoxyanthracene); and phenothiazine and
rubrene.
[0084] In the case where the composition for forming a polarizer
contains the photopolymerization initiator and the light
sensitizer, the polymerization reaction of the polymerizable liquid
crystal compound contained in the composition for forming a
polarizer is more accelerated. The content of the light sensitizer
can be appropriately adjusted according to the type and the amount
of the photopolymerization initiator and the polymerizable liquid
crystal compound used in combination; the content is usually 0.1 to
30 parts by mass, preferably 0.5 to 10 parts by mass, more
preferably 0.5 to 8 parts by mass relative to 100 parts by mass of
the polymerizable liquid crystal compound.
[0085] 1-4-3. Polymerization Inhibitor
[0086] The composition for forming a polarizer may contain a
polymerization inhibitor to stably progress the polymerization
reaction of the polymerizable liquid crystal compound. The degree
of polymerization reaction of the polymerizable liquid crystal
compound can be controlled by the polymerization inhibitor.
[0087] Examples of the polymerization inhibitor include radical
scavengers such as hydroquinone, alkoxy group-containing
hydroquinones, alkoxy group-containing catechols (such as
butylcatechol), pyrogallol, and
2,2,6,6-tetramethyl-1-piperidinyloxy radicals; thiophenols;
.beta.-naphthylamines, and .beta.-naphthols.
[0088] In the case where the composition for forming a polarizer
comprises the polymerization inhibitor, the content can be
appropriately adjusted according to the type and the amount of the
polymerizable liquid crystal compound to be used and the content of
the light sensitizer; the content is usually 0.1 to 30 parts by
mass, preferably 0.5 to 10 parts by mass, more preferably 0.5 to 8
parts by mass relative to 100 parts by mass of the polymerizable
liquid crystal compound. If the content of the polymerization
inhibitor is within this range, the polymerizable liquid crystal
compound can be polymerized without disturbing the orientation
thereof; for this reason, the content of the polymerizable
inhibitor within this range is preferred.
[0089] 1-4-4. Leveling Agent
[0090] It is preferred that the composition for forming a polarizer
contain a leveling agent. The leveling agent has a function to
adjust the fluidity of the composition for forming a polarizer to
provide a smoother coating obtained by applying the composition for
forming a polarizer; examples thereof can include surfactants.
Examples of the leveling agent include leveling agents containing
polyacrylate compounds as a main component, and leveling agents
containing fluorine atom-containing compounds as a main
component.
[0091] Examples of the leveling agents containing polyacrylate
compounds as a main component include "BYK-350", "BYK-352",
"BYK-353", "BYK-354", "BYK-355", "BYK-358N", "BYK-361N", "BYK-380",
"BYK-381", and "BYK-392" [BYK Chemie GmbH].
[0092] Examples of the leveling agents containing fluorine
atom-containing compounds as a main component include Megafac
"R-08", "R-30", "R-90", "F-410", "F-411", "F-443", "F-445",
"F-470", "F-471", "F-477", "F-479", "F-482", and "F-483" [made by
DIC Corporation]; Surflon "S-381", "S-382", "S-383", "S-393",
"SC-101", "SC-105", "KH-40", and "SA-100" [AGC SEIMI CHEMICAL CO.,
LTD.]; "E1830", "E5844" [DAIKIN INDUSTRIES, LTD.]; EFTOP "EF301",
"EF303", "EF351", and "EF352" [Mitsubishi Materials Electronic
Chemicals Co., Ltd.].
[0093] In the case where the composition for forming a polarizer
contains the leveling agent, the content is usually 0.3 parts by
mass or more and 5 parts by mass or less, preferably 0.5 parts by
mass or more and 3 parts by mass or less relative to 100 parts by
mass of the polymerizable liquid crystal compound. If the content
of the leveling agent is within this range, the horizontal
alignment of the polymerizable liquid crystal compound tends to be
easy, and the resulting polarizer tends to be smoother. If the
content of the leveling agent to the polymerizable liquid crystal
compound exceeds the range, unevenness tends to be generated in the
resulting polarizer. The composition for forming a polarizer may
contain two or more leveling agents.
[0094] In the polarizer according to the present embodiment, the
absorbance (A1) at a wavelength of 380 to 760 nm in the absorption
axis direction is 0.3 or more and 1.5 or less, preferably 0.3 or
more and 1.0 or less, more preferably 0.33 or more and 0.9 or less,
still more preferably 0.36 or more and 0.85 or less. The absorbance
(A2) in the transmission axis direction is 0.001 or more and 0.15
or less, preferably 0.001 or more and 0.10 or less, more preferably
0.002 or more and 0.05 or less, still more preferably 0.005 or more
and 0.040 or less.
[0095] The absorbances can be appropriately adjusted by adjusting
the type of the dichroic dye comprised in the polarizer, the amount
of the dichroic dye, or the solid content or the amount applied of
the composition for forming a polarizer to control the thickness of
the polarizer.
[0096] 2. Method of Forming Polarizer
[0097] A method of forming a polarizer using the composition for
forming a polarizer will be described. In such a method, a
polarizer is formed by applying the composition for forming a
polarizer to a substrate, preferably a transparent substrate.
[0098] 2-1. Substrate
[0099] A transparent substrate refers to a substrate having a
transparency which enables transmission of light, particularly
visible light. The transparency refers to properties that the
transmittance to light beams at a wavelength ranging from 380 to
780 nm is 80% or more. Specifically, examples of the transparent
substrate can include glass substrates and plastic substrates; the
transparent substrate is preferably a plastic substrate. Examples
of the plastics forming the plastic substrates include polyolefins
such as polyethylene, polypropylene, and norbornene-based polymers;
cyclic olefin resins; poly(vinyl alcohol); poly(ethylene
terephthalate); polymethacrylic acid esters; polyacrylic acid
esters; cellulose esters such as triacetyl cellulose, diacetyl
cellulose, and cellulose acetate propionate; poly(ethylene
naphthalate); polycarbonate; polysulfone; polyethersulfone;
poly(ether ketone); poly(phenylene sulfide), and poly(phenylene
oxide). Among these, especially preferred is cellulose ester,
cyclic olefin resins, poly(ethylene terephthalate), or
polymethacrylic acid ester because these are easily available from
the market or has high transparency. A support substrate may be
bonded to the transparent substrate because the transparent
substrate is easily handled during manufacturing of the polarizer
without generating breakage of the transparent substrate during
transportation or storage of the transparent substrate. Moreover,
as described later, retardation properties may be given to the
plastic substrate during manufacturing of a circularly polarizing
plate from a polarizer. In this case, the retardation properties
may be given by stretching the plastic substrate.
[0100] In the case where the retardation properties are given to
the plastic substrate, a plastic substrate composed of cellulose
ester or a cyclic olefin resin is preferred because the retardation
value is readily controlled.
[0101] The cellulose ester is a compound having at least part of
hydroxyl groups comprised in cellulose subjected to acetic acid
esterification. Cellulose ester films composed of such cellulose
esters are easily available from the market. Examples of
commercially available triacetyl cellulose films include "Fujitac
film" (FUJIFILM Corporation; and "KC8UX2M", "KC8UY", and "KC4UY"
(Konica Minolta Opto Products Co., Ltd.). Such commercial triacetyl
cellulose films can be used as the transparent substrate as they
are, or when necessary, after the retardation properties are given.
Moreover, after the surface of the transparent substrate prepared
may be subjected to a surface treatment such as an anti-glare
treatment, a hardcoat treatment, a charge prevention treatment, or
a reflection prevention treatment, the transparent substrate
prepared can be used as a transparent substrate.
[0102] As described above, a method of stretching a plastic
substrate can be used to give the retardation properties to the
plastic substrate. All of the plastic substrates composed of
thermoplastic resins can be subjected to the stretch treatment;
plastic substrates composed of cyclic olefin resins are more
preferred because the retardation properties are readily
controlled. The cyclic olefin resins refer to resins composed of
polymers or copolymers of cyclic olefins such as norbornene and
polycyclic norbornene-based monomers. The cyclic olefin resin may
partially comprise a ring opened portion, or a cyclic olefin resin
comprising a ring opened portion may be hydrogenated. The cyclic
olefin resin may be a copolymer of a cyclic olefin and a linear
olefin or a vinylated aromatic compound (such as styrene), for
example, because the transparency is not remarkably impaired and
the moisture absorbing properties are not remarkably increased.
Moreover, the cyclic olefin resin may have a polar group introduced
into the molecule.
[0103] In the case where the cyclic olefin resin is a copolymer of
a cyclic olefin and a linear olefin or an aromatic compound having
a vinyl group, examples of the linear olefin include ethylene and
propylene, and examples of the vinylated aromatic compound include
styrene, .alpha.-methylstyrene, and alkyl-substituted styrene. In
such a copolymer, the proportion of the content of the structural
unit derived from the cyclic olefin is in the range of 50 mol % or
less, for example, about 15 to 50 mol % relative to all of the
structural units of the cyclic olefin resin. In the case where the
cyclic olefin resin is a ternary copolymer obtained from a cyclic
olefin, a linear olefin, and a vinylated aromatic compound, for
example, the proportion of the content of the structural unit
derived from the linear olefin is about 5 to 80 mol % relative to
all of the structural units of the cyclic olefin resin, and the
proportion of the content of the structural unit derived from the
vinylated aromatic compound is about 5 to 80 mol %. Such a ternary
copolymer cyclic olefin resin has an advantage that the amount of
expensive cyclic olefin to be used can be relatively reduced during
manufacturing of the cyclic olefin resin.
[0104] The cyclic olefin resins are easily available from the
market. Examples of the commercially available cyclic olefin resins
include "Topas" [Ticona GmbH (Germany)]; "ARTON" [JSR Corporation];
"ZEONOR" and "ZEONEX" [ZEON Corporation]; and "APEL" [made by
Mitsui Chemicals, Inc.]. Such a cyclic olefin resin can be formed
into a film (cyclic olefin resin film) by a known film forming unit
such as solvent casting or melt extrusion. Moreover, cyclic olefin
resin films already commercially available in the form of a film
can also be used. Examples of the commercially available cyclic
olefin resin films include "Esushina" and "SCA40" [SEKISUI CHEMICAL
CO., LTD.]; "ZEONOR films" [Optes K.K.]; and "ARTON films" [JSR
Corporation].
[0105] Subsequently, a method of giving the retardation properties
to the plastic substrate will be described. The retardation
properties can be given to the plastic substrate by a known
stretching method. For example, a roll (winding body) around which
the plastic substrate is wound in the form of a roll is prepared;
the plastic substrate is continuously fed from the winding body,
and the fed plastic substrate is conveyed to a heating furnace. The
setting temperature of the heating furnace is in the range of a
temperature near the glass transition temperature of the plastic
substrate (.degree. C.) to [glass transition temperature+100]
(.degree. C.), preferably a temperature near the glass transition
temperature (.degree. C.) to [glass transition temperature+50]
(.degree. C.). In the heating furnace, a monoaxial or biaxial heat
stretching treatment is performed through adjustment of the
conveying direction or tension with an inclination at any angle
during stretching in the traveling direction of the plastic
substrate or a direction orthogonal to the traveling direction. The
stretch ratio is usually in the range of about 1.1 to 6, preferably
about 1.1 to 3.5. Moreover, a method of stretching the plastic
substrate in an oblique direction is not particularly limited as
long as the method can continuously incline the orientation axis at
a desired angle; a known stretching method can be used. Examples of
such a stretching method can include methods described in JP
50-83482 A and JP 02-113920 A.
[0106] It is preferred that the thickness of the transparent
substrate be thinner because of a weight enabling practical
handling and ensuring sufficient transparency; however, if the
transparent substrate is excessively thin, the strength tends to be
reduced, resulting in inferior processability. The appropriate
thickness of the glass substrate is, for example, about 100 to 3000
.mu.m, preferably about 100 to 1000 .mu.m. The appropriate
thickness of the plastic substrate is, for example, about 5 to 300
.mu.m, preferably about 20 to 200 .mu.m. It is preferred that the
thickness of the transparent substrate in the case where the
polarizing plate according to the present embodiment is used as a
circularly polarizing plate described later, particularly as a
circularly polarizing plate in applications to mobiles be about 20
to 100 pun. In the case where the retardation properties are given
to the film by stretching, the thickness after stretching is
determined according to the thickness before stretching or the
stretch ratio.
[0107] FIG. 1 is a sectional view schematically illustrating one
embodiment of a polarizing plate 10 according to the present
invention. The polarizing plate 10 includes a substrate 1, and a
polarizer (polarizing layer) 3 disposed on the substrate 1. In the
polarizer 3, a dichroic dye 3a is oriented. An oriented layer 2
described later may be formed on the substrate 1.
[0108] 2-2. Orientation Layer
[0109] It is preferred that an oriented layer be formed on the
substrate used in manufacturing of the polarizer. In this case, the
composition for forming a polarizer is applied onto the oriented
layer. For this reason, it is preferred that the oriented layer
have solvent resistance so as not to dissolve by application of the
composition for forming a polarizer. Moreover, it is preferred that
the oriented layer have heat resistance in a heat treatment for
removal of the solvent and orientation of liquid crystals. The
oriented layer can be formed of an orienting polymer.
[0110] Examples of the orienting polymer include polyamide,
gelatins, polyimide, polyamic acid, poly(vinyl alcohol),
alkyl-modified poly(vinyl alcohol), polyacrylamide, polyoxazole,
polyethyleneimine, polystyrene, polyvinylpyrrolidone, polyacrylic
acid, and polyacrylic acid esters. Among these, poly(vinyl alcohol)
is preferred. These orienting polymers may be used alone or in the
form of a mixture thereof.
[0111] The orienting polymer can be applied onto the substrate as
an orienting polymer composition which the orienting polymer is
dissolved in a solvent (solution comprising the orienting polymer)
to form an oriented layer on the substrate. Examples of the solvent
include water; alcohol solvents such as methanol, ethanol, ethylene
glycol, isopropyl alcohol, propylene glycol, methyl cellosolve,
butyl cellosolve, and propylene glycol monomethyl ether; ester
solvents such as ethyl acetate, butyl acetate, ethylene glycol
methyl ether acetate, .gamma.-butyrolactone, propylene glycol
methyl ether acetate and ethyl lactate; ketone solvents such as
acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, methyl
amyl ketone, and methyl isobutyl ketone; aliphatic hydrocarbon
solvents such as pentane, hexane and heptane; aromatic hydrocarbon
solvents such as toluene and xylene, nitrile solvents such as
acetonitrile; ether solvents such as tetrahydrofuran and
dimethoxyethane; and chlorine-substituted hydrocarbon solvents such
as chloroform and chlorobenzene. These solvents can be used alone
or in combination.
[0112] As the orienting polymer composition, a commercially
available oriented film material may be used as it is. Examples of
the commercially available oriented film material include SUNEVER
(registered trademark, made by Nissan Chemical Industries, Ltd.)
and OPTOMER (registered trademark, made by JSR Corporation).
[0113] Examples of the method of forming an oriented layer on a
substrate include a method of applying an orienting polymer
composition or a commercially available oriented film material onto
a substrate, and annealing the coating. The thickness of the
thus-obtained oriented layer is usually in the range of 10 nm to
10000 nm, preferably 10 nm to 1000 nm.
[0114] To give an orientation restraining force to the oriented
layer, when necessary, performing rubbing (rubbing method) is
preferred. By giving the orientation restraining force, the
polymerizable liquid crystal compound can be oriented in a desired
direction.
[0115] Examples of the method of giving an orientation restraining
force by the rubbing method include a method of preparing a
rotating rubbing roll wrapped with a rubbing cloth, placing a
laminate composed of a substrate and a coating for forming an
oriented layer formed on the substrate on a stage, and conveying
the laminate to the rotating rubbing roll to contact the coating
for forming an oriented layer with the rotating rubbing roll.
[0116] The oriented layer may be a photo-oriented layer. The
photo-oriented layer refers to an oriented layer having an
orientation restraining force given by applying a composition
comprising a polymer or monomer having a photoreactive group and a
solvent (hereinafter, referred to as "composition for forming a
photo-oriented layer" in some cases) to a substrate, and
irradiating the coating with polarized light (preferably, polarized
UV). The photoreactive group refers to a group in which a liquid
crystal orientation ability is generated through irradiation of
light. Specifically, the photoreactive group refers to a group
which triggers orientation induction of molecules generated through
irradiation of light or a photoreaction causing the liquid crystal
orientation ability such as an isomerization reaction, a
dimerization reaction, a photocrosslinking reaction, or a
photodecomposition reaction. A photoreactive group triggering a
dimerization reaction or a photocrosslinking reaction is preferred
because its orientation is high, and the smectic liquid crystal
state in the formation of the polarizer is kept. As the
photoreactive group, groups having unsaturated bond, particularly
double bond are preferred, and groups having at least one selected
from the group consisting of groups having carbon-carbon double
bond (C.dbd.C bond), carbon-nitrogen double bond (C.dbd.N bond),
nitrogen-nitrogen double bond (N.dbd.N bond), and carbon-oxygen
double bond (C.dbd.O bond) are more preferred.
[0117] Examples of the photoreactive groups having C.dbd.C bond
include a vinyl group, a polyene group, a stilbene group, a
stilbazole group, a stilbazolium group, a chalcone group, and a
cinnamoyl group. Examples of the photoreactive groups having
C.dbd.N bond include groups having a structure such as an aromatic
Schiff base and an aromatic hydrazone. Examples of the
photoreactive groups having N.dbd.N bond include an azobenzene
group, an azonaphthalene group, an aromatic heterocyclic azo group,
a bisazo group, a formazan group and groups having azoxybenzene as
a basic structure. Examples of the photoreactive groups having
C.dbd.O bond include a benzophenone group, a coumarin group, an
anthraquinone group, and a maleimide group. These groups may have a
substituent such as an, alkyl group, an alkoxy group, an aryl
group, an allyloxy group, a cyano group, an alkoxycarbonyl group, a
hydroxyl group, a sulfonate group, or an alkyl halide group. Among
these, photoreactive groups which can cause the photodimerization
reaction are preferred, and a cinnamoyl group and a chalcone group
are preferred because the irradiation intensity of polarized light
needed for photo-orientation is relatively low and a photo-oriented
layer having high thermal stability and stability over time is
obtained. Furthermore, as a polymer having a photoreactive group, a
polymer having a cinnamoyl group in which the terminal site of the
polymer side chain has a cinnamic acid structure is more
preferred.
[0118] As the solvent for the composition for forming a
photo-oriented layer, solvents which dissolve polymers and monomers
having a photoreactive group are preferred; examples of the solvent
for the composition for forming a photo-oriented layer include the
solvents used in the orienting polymer composition described
above.
[0119] The content of the polymer or monomer having a photoreactive
group in the composition for forming a photo-oriented layer can be
appropriately adjusted according to the type of the polymer or
monomer having a photoreactive group or the thickness of the
photo-oriented layer to be manufactured; in terms of the solid
content, at least 0.2% by mass is preferred, and the range of 0.3
to 10% by mass is more preferred. A polymer material, such as
poly(vinyl alcohol) or polyimide, or a light sensitizer may be
comprised in the composition for forming a photo-oriented layer in
the range not remarkably impairing the properties of the
photo-oriented layer.
[0120] As a method of applying the orienting polymer composition or
the composition for forming a photo-oriented layer onto a
substrate, a known method is used, for example, a coating method
such as spin coating, extrusion, gravure coating, die coating, bar
coating, and an applicator method, or a printing method such as
flexography. In the case where the manufacturing of the polarizer
is performed by a roll-to-roll continuous manufacturing method, as
an application method, usually, gravure coating, die coating, or a
printing method such as flexography is used.
[0121] If masking is performed when rubbing or irradiation with
polarized light is performed, a plurality of regions (patterns)
having different orientation directions can also be formed.
[0122] 2-3. Method of Manufacturing Polarizing Plate
[0123] The composition for forming a polarizer is applied onto the
substrate or the oriented layer formed on the substrate to obtain
the coating. Examples of the method of applying the composition for
forming a polarizer include the same methods as those exemplified
as the method of applying the orienting polymer composition or
composition for forming a photo-oriented layer onto the
substrate.
[0124] Next, a dry coating film is formed by drying and removing
the solvent on the condition in which the polymerizable liquid
crystal compound comprised in the coating is not polymerized.
Examples of the drying method include spontaneous drying, air blow
drying, drying by heating, and drying under reduced pressure.
[0125] As a preferred form, the liquid crystal state of the
polymerizable liquid crystal compound comprised in the dry coating
film is once converted into nematic liquid crystals, and then the
nematic liquid crystal phase is transited to the smectic liquid
crystal phase. To form the smectic liquid crystal phase through the
nematic liquid crystal phase, a method of heating the polymerizable
liquid crystal compound comprised in the dry coating film to a
temperature showing the nematic liquid crystal phase or higher, and
then cooling the polymerizable liquid crystal compound to a
temperature showing the smectic liquid crystal phase is used, for
example.
[0126] In the case where the polymerizable liquid crystal compound
in the dry coating film is converted into the smectic liquid
crystal phase or the polymerizable liquid crystal compound is
converted into the smectic liquid crystal phase through the nematic
liquid crystal phase, the condition to control the liquid crystal
state (heating condition) can be determined by measuring the phase
transition temperature of the polymerizable liquid crystal
compound. The measurement condition of the phase transition
temperature will be described in Examples of this
specification.
[0127] Next, a polymerization step of the polymerizable liquid
crystal compound will be described. Here, a method of containing a
photopolymerization initiator in the composition for forming a
polarizer, converting the liquid crystal state of the polymerizable
liquid crystal compound in the dry coating film into the smectic
liquid crystal phase, and then photopolymerizing the polymerizable
liquid crystal compound while keeping the liquid crystal state of
the smectic liquid crystal phase will be described in detail.
[0128] The light with which the dry coating film is irradiated in
the photopolymerization is appropriately selected from the group
consisting of visible light, ultraviolet light, laser light, and
active electron beams according to the type of photopolymerization
initiator comprised in the dry coating film, the type of the
polymerizable liquid crystal compound (particularly, the type of
polymerizable group which the polymerizable liquid crystal compound
has), and the amount thereof. Among these, ultraviolet light is
preferred because the progress of the polymerization reaction is
easy to control and apparatuses widely used in the field as an
apparatus according to photopolymerization can be used.
Accordingly, it is preferred that the types of the polymerizable
liquid crystal compound and the photopolymerization initiator
contained in the composition for forming a polarizer be selected so
as to enable photopolymerization using ultraviolet light. Moreover,
when the polymerizable liquid crystal compound is polymerized, the
polymerization temperature can be also controlled by cooling the
dry coating film by the irradiation with ultraviolet light and a
cooling unit. Even if a substrate having relatively low heat
resistance is used, an advantage is provided by use of such a
cooling unit as long as the polymerization of the polymerizable
liquid crystal compound can be performed at lower temperature, in
that a polarizer can be appropriately formed. A patterned polarizer
can be also obtained by performing masking or developing during the
photopolymerization.
[0129] By performing the photopolymerization described above, the
polymerizable liquid crystal compound is polymerized while keeping
the nematic liquid crystal phase or the smectic liquid crystal
phase, preferably, the higher smectic liquid crystal phase already
exemplified, forming a polarizer. The polarizer obtained by
polymerizing the polymerizable liquid crystal compound while the
smectic liquid crystal phase is kept has an advantage in that this
polarizer has higher polarization performance than that of a
conventional host-guest polarizer, namely, a polarizer obtained by
polymerizing the polymerizable liquid crystal compound while the
liquid crystal state of the nematic liquid crystal phase is kept.
Furthermore, the polarizer has an advantage in that the strength is
higher than that of a polarizer in which only a lyotropic dichroic
dye is applied.
[0130] The thickness of the polarizer is in the range of preferably
0.5 .mu.m or more and 5 .mu.m or less, more preferably 1 .mu.m or
more and 5 .mu.m or less. Accordingly, the thickness of the coating
for forming a polarizer is determined in consideration of the
thickness of the polarizer obtained. The thickness of the polarizer
can be determined by measurement with an interference film
thickness meter, a laser microscope, or a stylus type film
thickness meter.
[0131] It is particularly preferred that the formed polarizer be a
polarizer which obtains the Bragg peak in the X-ray diffraction
measurement as described above. Examples of the polarizer which
obtains the Bragg peak include polarizers showing a diffraction
peak derived from a hexatic phase or a crystal phase.
[0132] The polarizer according to the present embodiment has
favorable neutral color phase properties. The polarizer having
favorable neutral color phase properties is a polarizer in which
the color coordinates a* value and b* value in the L*a*b*(Lab)
color system satisfy the relationships represented by the following
formulas (1F) and (2 F).
-3.ltoreq.chromaticity a*.ltoreq.3 (1F)
-3.ltoreq.chromaticity b*.ltoreq.3 (2F)
[0133] The color coordinates a* value and b* value are also
referred to as "chromaticity a*" and "chromaticity b*",
respectively. As both of the values a* and b* is closer to 0
(zero), it is determined that the polarizer is a polarizer showing
a neutral color phase. A colorless, favorable, white display is
obtained in display devices including such a polarizer.
[0134] It is more preferred in the color phase of the polarizer if
two polarizers are overlaid such that their absorption axes are
orthogonal to each other, the color phase at this time is
determined in the same manner as above, the "orthogonal a*" and
"orthogonal b*" are calculated, and the orthogonal a* and the
orthogonal b* satisfy the relationships represented by the
following formulas (1F') and the formula (2F'). The orthogonal a*
and the orthogonal b* are indices indicating whether the color
phase of a black display is neutral or not in a display device
including the polarizer. As the orthogonal a* and the orthogonal b*
are both closer to 0 (zero), a colorless, favorable black display
is obtained.
-3.ltoreq.orthogonal a*.ltoreq.3 (1F')
-3.ltoreq.orthogonal b*.ltoreq.3 (2F')
[0135] When polarizers are commercially manufactured, a method
which can continuously form polarizers is required. Such a
continuous manufacturing method is of a roll-to-roll system, and is
referred to as "the present manufacturing method" in some cases. In
the present manufacturing method, a case where the substrate is a
transparent substrate will be mainly described. In the case where
the substrate is a transparent substrate, the final product is a
polarizing plate including a transparent substrate and a
polarizer.
[0136] The present manufacturing method comprises, for example, a
step of preparing a first roll in which a transparent substrate is
wound around a first roll core, a step of continuously feeding the
transparent substrate from the first roll, a step of continuously
forming an oriented layer on the transparent substrate, a step of
continuously applying a composition for forming a polarizer onto
the oriented layer, a step of continuously forming a dry coating
film on the oriented layer by drying the applied composition for
forming a polarizer on a condition in which the polymerizable
liquid crystal compound is not polymerized, a step of converting
the polymerizable liquid crystal compound comprised in the dry
coating film into a nematic liquid crystal phase, preferably a
smectic liquid crystal phase, and polymerizing the polymerizable
liquid crystal compound while keeping the smectic liquid crystal
phase to continuously obtain a film to form a polarizer, and a step
of winding the continuously obtained polarizer around a second roll
core to obtain a second roll.
[0137] The polarizing plate obtained by the present manufacturing
method is a film shape and elongate polarizing film. The polarizing
plate, if used in liquid crystal display devices described later,
are cut into a desired size according to the scale of the liquid
crystal display device used.
[0138] While the polarizing plate can be in the form of a laminate
of transparent substrate/photo-oriented layer/polarizer, the
polarizer can be also obtained as a single layer by releasing the
photo-oriented layer and the transparent substrate. Moreover, the
polarizing plate may have a form composed of a laminate of layers
or films other than transparent substrate/photo-oriented
layer/polarizer. As these layers or films, the polarizing plate may
further include a retardation film, or may further include an
anti-reflective layer or a luminance enhanced film.
[0139] For example, the polarizing plate according to the present
embodiment is a circularly polarizing plate if a 1/4 wavelength
plate is comprised. FIG. 2 is a sectional view schematically
illustrating one embodiment of a circularly polarizing plate 100
according to the present invention. The circularly polarizing plate
100 can comprise a substrate 1 having an oriented layer 2 formed
thereof, a polarizer 3 disposed on the oriented layer 2, and a
retardation film 4 disposed on the surface of the substrate 1
opposite to the surface of the substrate 1 having the oriented
layer 2 formed thereon, the retardation film 4 being a 1/4
wavelength plate. Moreover, the retardation film 4 may be formed on
the side of the polarizer 3. In this case, as illustrated in FIG.
3, a circularly polarizing plate 110 can have a form in which the
substrate 1, the oriented layer 2, the polarizer 3, and the
retardation film 4 are disposed in sequence.
[0140] When the circularly polarizing plate is manufactured, the
substrate 1 or the polarizer 3 and the retardation film 4 may be
bonded using an appropriate pressure-sensitive adhesive through a
pressure-sensitive adhesive layer formed of a pressure-sensitive
adhesive.
[0141] By using a substrate 1 (retardation film 4) having
retardation properties preliminarily given as a transparent
substrate, the transparent substrate itself may comprise a function
as the retardation layer. If the transparent substrate itself is a
retardation film, a circularly polarizing plate or an elliptically
polarizing plate in the form of retardation film/photo-oriented
layer/polarizer can be obtained. For example, in the case where a
monoaxially stretched 1/4 wavelength plate is used as a retardation
film, the circularly polarizing plate can be manufactured by the
roll-to-roll method by setting the irradiation direction of
polarized UV so as to be about 45.degree. to the traveling
direction of the transparent substrate. Thus, as a 1/4 wavelength
plate used in manufacturing of the circularly polarizing plate,
those having properties such that the in-plane retardation value to
visible light is smaller as the wavelength is shorter are
preferred. FIG. 4 is a sectional view schematically illustrating
one embodiment of a circularly polarizing plate 120 in the case
where the substrate itself functions as a retardation film. The
circularly polarizing plate 120 can have a form comprising a
retardation film 4 having an oriented layer 2 formed thereon, and a
polarizer 3 disposed on the oriented layer 2.
[0142] Using 1/2 wavelength plate as a retardation film, a linearly
polarizing plate roll set such that the angle formed by the slow
axis of the 1/2 wavelength plate and the absorption axis of a
polarizer is shifted is produced, and a 1/4 wavelength plate is
further formed on the surface opposite to the surface having the
polarizer thereon; thereby, a broad-band circularly polarizing
plate can be formed.
[0143] It is preferred that the birefringence to light having a
wavelength of 450 nm, the birefringence to light having a
wavelength of 550 nm, and the birefringence to light having a
wavelength of 650 nm of the 1/4 wavelength plate used as the
retardation film have reverse wavelength dispersibility satisfying
the relationships represented by the following expressions (II) and
(III). In the expressions, .DELTA.n(.lamda.) represents the
birefringence to light having a wavelength .lamda. nm.
.DELTA.n(450)/.DELTA.n(550).ltoreq.1.00 (II)
1.00.ltoreq..DELTA.n(650)/.DELTA.n(550) (III)
[0144] Such retardation films having reverse wavelength dispersing
properties can be manufactured by the method described in JP
5463666 B.
[0145] 4. Applications of Polarizing Plate
[0146] The polarizing plate can be used in a variety of display
devices. The display device is a device having a display element,
and comprises a light-emitting element or a light-emitting device
as a light emitting source. Examples of the display device include
liquid crystal display devices, organic electroluminescent (EL)
display devices, inorganic electroluminescent (EL) display devices,
electron emission display devices (such as field emission display
devices (FEDs) and surface field emission display devices (SEDs)),
electronic paper (display devices using electronic ink or
electrophoretic elements), plasma display devices, projection
display devices (such as grating light valve (GLV) display devices,
display devices including digital micromirror devices (DMD)), and
piezoelectric ceramic displays. Examples of the liquid crystal
display devices include transmissive liquid crystal display
devices, semi-transmissive liquid crystal display devices,
reflective liquid crystal display devices, direct-view liquid
crystal display devices, and projection liquid crystal display
devices. These display devices may be display devices which display
two-dimensional images, or may be stereoscopic display devices
which display three-dimensional images. The polarizing plate
according to the present embodiment can be effectively used in
particularly display devices of organic EL display devices or
inorganic EL display devices.
[0147] Examples of the electronic paper include those which display
by optical anisotropy and molecules using orientation of dye
molecules, those which display by particles such as
electrophoresis, movement of particles, rotation of particles, and
phase change, those which display by moving one end of a film,
those which display by coloring of molecules/phase change, those
which display by absorption of light by molecules, and those which
display by binding of electrons and holes to perform self-emission
of light. More specifically, examples thereof include those of
microencapsulated electrophoresis types, horizontal electrophoresis
types, vertical electrophoresis types, spherical twisted ball
types, magnetic twisted ball types, cylindrical twisted ball types,
charged toner types, electronic power fluid types, magnetic
electrophoresis types, magnetic thermosensitive types,
electrowetting types, light scattering types (change in
transparency/cloudiness), cholesteric liquid
crystal/photo-conductive layer types, cholesteric liquid crystal
types, bistable nematic liquid crystal types, high dielectric
liquid crystal types, dichromatic dye and liquid crystal dispersion
types, movable films, color developing and quenching of leuco dyes,
photochromic types, electrochromic types, electrodeposition types,
and flexible organic ELs. The electronic paper may be not only
personally used for texts and images but also used in advertising
displays (signage). According to the polarizing plate according to
the present embodiment, the thickness of the electronic paper can
be reduced.
[0148] As a stereoscopic display device, for example, a method of
alternately disposing different retardation films, such as a
micropole method, is proposed (JP 2002-185983 A); however, by use
of the polarizing plate according to the present embodiment,
patterning is easier by printing, ink-jetting, or photolithography,
and therefore the process of manufacturing a display device can be
shortened, and the retardation film is unnecessary.
EXAMPLES
[0149] Hereinafter, the present invention will be described in more
detail by way of Examples. "%" and "parts" in Examples are % by
mass and parts by mass unless otherwise specified.
[0150] [Measurement of Absorbance]
[0151] The absorbance of the polarizer was measured as follows.
Using an apparatus in which a holder with a polarizer was set in a
spectrophotometer (made by SHIMADZU Corporation, UV-3150), the
absorbance (A1) in the orientation direction of the dichroic dye
(absorption axis direction) and the absorbance (A2) in a plane of
the polarizer and in the direction vertical to the orientation
(transmission axis direction) were measured by a double beam method
in the wavelength range of 380 to 680 nm with a step of 2 nm. To
remove the contribution of the light loss caused by surface
reflection of the polarizing plate, a sample for measurement was
set, zero point correction was performed at 800 nm having no light
absorption, and the measurement was performed.
[0152] [Evaluation of Heat Resistance]
[0153] The surface of a triacetyl cellulose film of a polarizing
plate was bonded to a glass substrate with a pressure-sensitive
adhesive. The absorbance A1 in the absorption axis direction was
then measured at 23.degree. C. by the method (A1 (23.degree. C.)).
Subsequently, the sample was placed in an oven at 85.degree. C. for
100 hours, was extracted, and again the measurement of the
absorbance was performed by the method. The absorbance retention
rate (%) was calculated by the following expression (I):
absorbance retention rate (%) A1(85.degree. C.)/A1(23.degree.
C.).times.100 (I)
where A1 (85.degree. C.) represents the absorbance in the
absorption axis direction after the polarizing plate is kept in the
heat-resistant oven at 85.degree. C. for 100 hours, and A1
(23.degree. C.) represents the absorbance in the absorption axis
direction measured at 23.degree. C. before the heat resistance
test.
[0154] [Measurement of Film Thickness]
[0155] After the polarizing plate was cut with a microtome, its
carbon deposited cross-section was observed with a scanning
transmission electron microscope (STEM, field emission scanning
electron microscope (FE-STEM), type: "S-5500", made by Hitachi,
Ltd.) to measure the thickness of the polarizer (polarizing
layer).
Example 1
[Preparation of Composition for Forming Photo-Oriented Layer]
[0156] A photo-orienting material (2 parts) represented by the
following formula (3) and o-xylene (98 parts) as a solvent were
mixed, and the resulting mixture was stirred at 80.degree. C. for 1
hour to prepare a composition for forming a photo-oriented layer.
The photo-orienting material represented by the following formula
(3) was synthesized by the method described in JP 2013-33248 A.
##STR00017##
[0157] [Preparation of Composition for Forming Polarizer]
[0158] The following components were mixed, and were stirred at
80.degree. C. for 1 hour to prepare a composition for forming a
polarizer.
TABLE-US-00001 polymerizable liquid crystal compound; compound
represented by the following formula (4-6) 75 parts compound
represented by the following formula (4-7) 25 parts [Chemical
Formula 21] ##STR00018## ##STR00019## dichroic dye; Magenta dye
represented by the following formula (2-18) 1.3 parts Yellow dye
represented by the following formula (2-15) 1.3 parts Cyan dye
represented by the following formula (2-27) 1.3 parts [Chemical
Formula 22] ##STR00020## ##STR00021## ##STR00022## polymerization
initiator;
2-dimethylamino-2-benzyl-1-(4-morpholinophenyl)butane-1-one
(IRGACURE 369; made by BASF Japan Ltd.) 6 parts leveling agent;
polyacrylate compound (BYK-361N; made by BYK-Chemie GmbH) 1.2 parts
solvent; xylene 250 parts
[0159] [Manufacturing of Polarizing Film (Polarizing Plate)]
[0160] A roll of a triacetyl cellulose film (made by KONICA
MINOLTA, INC., KC4 UY-TAC 40 .mu.m) having a width of 600 mm was
continuously fed at a rate of 8 m/min, and the film surface was
subjected to a plasma treatment; then, the composition for forming
a photo-oriented layer was ejected from a slot die coater at a flow
rate of 16 mL/min, and was applied to a region of the film central
portion having a width of 400 mm to form a first coating.
Furthermore, the film was fed into an air-blow drying furnace set
at 100.degree. C. for 2 minutes to remove the solvent; thereby, a
first dry film was formed. Subsequently, the first dry film was
irradiated with UV light polarized in a 45.degree. direction to the
film traveling direction such that the intensity was 20 mJ/cm.sup.2
(in terms of 313 nm); thereby, the orientation restraining force
was given to manufacture a substrate film with a photo-oriented
layer. The composition for forming a polarizer was ejected from the
slot die coater onto the surface of the photo-oriented layer at a
flow rate of 30 mL/min, and was applied to a region of the film
central portion having a width of 400 mm to form a second coating.
Furthermore, the film was fed into an air-blow drying furnace set
at 110.degree. C. for 2 minutes to remove the solvent; thereby, a
second dry film was formed. Subsequently, the film was irradiated
with UV light at 500 mJ/cm.sup.2 (in terms of 365 nm) to polymerize
and cure the polymerizable liquid crystal compound; thereby, a
polarizer was formed. Subsequently, the polarizer was continuously
wound into a roll to manufacture a polarizing film roll having an
absorption axis in a 45.degree. direction. A piece from this long
polarizing film roll thus manufactured into a 3 cm square was used
as a polarizing plate, and a variety of evaluations was performed.
The film thickness of the polarizer, the absorbances of the
dichroic dyes at their maximum absorption wavelengths, and their
absorbance retention rates are shown in Table 1.
Example 2
[0161] A polarizing film roll was manufactured in the same manner
as in Example 1 except that the coating flow rate of the
composition for forming a polarizer was 15 mL/min, and the same
measurement as in Example 1 was performed.
Example 3
[0162] A polarizing film roll was manufactured in the same manner
as in Example 1 except that the amounts of the dichroic dyes to be
mixed were varied as follows, and the same measurement as in
Example 1 was performed.
TABLE-US-00002 Magenta dye represented by the formula (2-18) 2.3
parts Yellow dye represented by the formula (2-15) 2.3 parts Cyan
dye represented by the formula (2-27) 2.3 parts
Example 4
[0163] A polarizing film roll was manufactured in the same manner
as in Example 2 except that the amounts of the dichroic dyes to be
mixed were varied as follows, and the same measurement as in
Example 2 was performed.
TABLE-US-00003 Magenta dye represented by the formula (2-18) 2.3
parts Yellow dye represented by the formula (2-15) 2.3 parts Cyan
dye represented by the formula (2-27) 2.3 parts
Comparative Example 1
[Manufacturing of Iodine PVA Polarizing Plate]
[0164] A poly(vinyl alcohol) film having a thickness of 75 .mu.m at
an average degree of polymerization of about 2400 and a degree of
saponification of 99.9 mol % or more was monoaxially stretched
about 5.5 times by a dry method; furthermore, while the tensed
state was kept, the film was immersed in pure water at 60.degree.
C. for 60 seconds, and then was immersed in an aqueous solution of
iodine/potassium iodide/water having a weight ratio of 0.05/5/100
at 23.degree. C. for 30 seconds. Subsequently, the film was
immersed in an aqueous solution of potassium iodide/boric
acid/water having a weight ratio of 8.5/8.5/100 at 72.degree. C.
for 300 seconds. Subsequently, the film was washed with pure water
at 23.degree. C. for 15 seconds, and was dried at 70.degree. C. for
2 minutes to obtain a polarizer in which iodine was adsorbed on and
oriented in the poly(vinyl alcohol) resin. The polarizer was
measured with a contact film thickness meter; the thickness was 25
.mu.m. Both surfaces of the thus-obtained polarizer were protected
with a saponified triacetyl cellulose film (made by KONICA MINOLTA,
INC., KC4UY-TAC 40 .mu.m) through a poly(vinyl alcohol) adhesive
prepared from 3 parts of carboxyl group-modified poly(vinyl
alcohol) [made by Kuraray Co., Ltd., Kuraray POVAL KL318] and 1.5
parts of a water-soluble polyamide epoxy resin [made by Sumika
Chemtex Company, Limited, Sumirez resin (registered trademark) 650
(aqueous solution having a solid content of 30%)] to manufacture a
polarizing plate. This polarizing plate was sampled, and the same
measurement as in Example 1 was performed; light absorption
attributed to an 13-PVA complex at a maximum absorption wavelength
of 474 nm and light absorption attributed to an I5-PVA complex at a
maximum absorption wavelength of 594 nm were measured.
Comparative Example 2
[0165] A polarizing film was manufactured in the same manner as in
Comparative Example 1 except that the film was immersed in an
aqueous solution of iodine/potassium iodide/water having a weight
ratio of 0.06/6/100 at 23.degree. C. for 30 seconds. This
polarizing film was sampled, and the same measurement as in Example
1 was performed; light absorption attributed to an 13-PVA complex
at a maximum absorption wavelength of 474 nm and light absorption
attributed to an I5-PVA complex at a maximum absorption wavelength
of 594 nm were measured.
Comparative Example 3
[0166] A polarizing film was manufactured in the same manner as in
Comparative Example 1 except that the film was immersed in an
aqueous solution of iodine/potassium iodide/water having a weight
ratio of 0.06/6/100 at 23.degree. C. for 40 seconds. This
polarizing film was sampled, and the same measurement as in Example
1 was performed; light absorption attributed to an 13-PVA complex
at a maximum absorption wavelength of 474 nm and light absorption
attributed to an I5-PVA complex at a maximum absorption wavelength
of 594 nm were measured.
TABLE-US-00004 TABLE 1 After 100 hours Thickness Initial Absorbance
of Dichroic .lamda. retention polarizer dye MAX A1 A2 A1 A2 rate
Example 1 2.0 .mu.m Yellow 410 0.83 0.03 0.81 0.04 97% Magenta 520
0.77 0.02 0.75 0.02 98% Cyan 620 0.81 0.02 0.78 0.02 96% Example 2
1.0 .mu.m Yellow 410 0.42 0.03 0.40 0.03 97% Magenta 520 0.38 0.01
0.38 0.01 98% Cyan 620 0.41 0.01 0.39 0.01 96% Example 3 2.0 .mu.m
Yellow 410 1.47 0.04 1.44 0.03 98% Magenta 520 1.36 0.03 1.32 0.01
97% Cyan 620 1.43 0.03 1.39 0.01 97% Example 4 1.0 .mu.m Yellow 410
0.74 0.03 0.72 0.03 97% Magenta 520 0.69 0.02 0.66 0.01 96% Cyan
620 0.73 0.02 0.71 0.01 97% Comparative 25 .mu.m I3-PVA 474 1.41
0.02 1.24 0.02 88% Example 1 I5-PVA 594 1.53 0.01 1.08 0.01 70%
Comparative 25 .mu.m I3-PVA 474 1.58 0.02 1.51 0.01 95% Example 2
I5-PVA 594 1.73 0.01 1.25 0.02 73% Comparative 25 .mu.m I3-PVA 474
1.75 0.02 1.70 0.02 97% Example 3 I5-PVA 594 1.81 0.01 1.40 0.01
77%
[0167] The polarizing plates in Examples 1 to 4 were thin films,
but had high light absorbing selectivity, and had very high heat
resistance in regions having very low absorbance. Moreover, in the
polarizing plates in Examples 1 to 4, no warpage occurred after the
heat-resistant test, and favorable film shapes were kept.
[0168] In the polarizing plates in Comparative Examples 1 to 3, the
absorbance attributed to the light absorption by the I5-PVA complex
reduced to about 70 to 77% after the heat-resistant test, and the
light absorption at a long wavelength was weaker than that at a
short wavelength; for this reason, the whole polarizing plates had
reddish color phases. Moreover, the polarizing plates in
Comparative Examples 1 to 3 had significant deformation due to heat
of PVA, and significant warpage occurred.
INDUSTRIAL APPLICABILITY
[0169] Since the polarizing plate according to the present
invention has high light absorbing selectivity in the form of a
thin film and has high heat resistance, the polarizing plate
according to the present invention is extremely useful in
manufacturing of liquid crystal display devices, (organic) EL
display devices, and projection liquid crystal display devices.
REFERENCE SIGNS LIST
[0170] 1 . . . substrate, 2 . . . oriented layer, 3 . . .
polarizer, 3a . . . dichroic dye, 4 . . . retardation film, 10 . .
. polarizing plate, 100, 110, 120 . . . circularly polarizing
plate.
* * * * *