U.S. patent application number 15/306362 was filed with the patent office on 2017-02-16 for polarizer, polarizing plate, and image display apparatus.
This patent application is currently assigned to NITTO DENKO CORPORATION. The applicant listed for this patent is NITTO DENKO CORPORATION. Invention is credited to Kota Nakai, Yuki Nakano, Daisuke Ogomi, Yuji Saiki, Masahiro Yaegashi.
Application Number | 20170045657 15/306362 |
Document ID | / |
Family ID | 54332564 |
Filed Date | 2017-02-16 |
United States Patent
Application |
20170045657 |
Kind Code |
A1 |
Ogomi; Daisuke ; et
al. |
February 16, 2017 |
POLARIZER, POLARIZING PLATE, AND IMAGE DISPLAY APPARATUS
Abstract
There is provided a polarizer that can realize the
multi-functionalization and high-functionalization of an electronic
device, such as an image display apparatus. A polarizer according
to an embodiment of the present invention includes a resin film
containing a dichromatic substance, wherein the polarizer has a low
dichromatic substance concentration portion whose content of the
dichromatic substance is relatively low in the resin film. In the
polarizer according to an embodiment of the present invention, the
low dichromatic substance concentration portion has a content of an
alkali metal and/or an alkaline earth metal of 3.6 wt % or
less.
Inventors: |
Ogomi; Daisuke;
(Ibaraki-shi, JP) ; Saiki; Yuji; (Ibaraki-shi,
JP) ; Yaegashi; Masahiro; (Ibaraki-shi, JP) ;
Nakai; Kota; (Ibaraki-shi, JP) ; Nakano; Yuki;
(Ibaraki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NITTO DENKO CORPORATION |
Ibaraki-shi, Osaka |
|
JP |
|
|
Assignee: |
NITTO DENKO CORPORATION
Ibaraki-shi, Osaka
JP
|
Family ID: |
54332564 |
Appl. No.: |
15/306362 |
Filed: |
April 23, 2015 |
PCT Filed: |
April 23, 2015 |
PCT NO: |
PCT/JP2015/062358 |
371 Date: |
October 24, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 5/3025 20130101;
H01L 51/5281 20130101; G02F 1/133528 20130101; G02B 5/3033
20130101 |
International
Class: |
G02B 5/30 20060101
G02B005/30 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 25, 2014 |
JP |
2014-091842 |
Apr 22, 2015 |
JP |
2015-087686 |
Claims
1. A polarizer, comprising a resin film containing a dichromatic
substance, the polarizer having, in the resin film, a low
dichromatic substance concentration portion whose content of the
dichromatic substance is relatively low, wherein the low
dichromatic substance concentration portion has a content of an
alkali metal and/or an alkaline earth metal of 3.6 wt % or
less.
2. The polarizer according to claim 1, wherein the low dichromatic
substance concentration portion is formed by bringing a basic
solution into contact with the resin film.
3. The polarizer according to claim 2, wherein the basic solution
comprises an aqueous solution containing a hydroxide of the alkali
metal and/or the alkaline earth metal.
4. The polarizer according to claim 1, wherein the low dichromatic
substance concentration portion has a dichromatic substance content
of 1.0 wt % or less.
5. The polarizer according to claim 1, wherein the low dichromatic
substance concentration portion has a transmittance of 50% or
more.
6. The polarizer according to claim 1, wherein the polarizer has a
thickness of 30 .mu.m or less.
7. The polarizer according to claim 1, wherein the low dichromatic
substance concentration portion corresponds to a camera portion of
an image display apparatus on which the polarizer is mounted.
8. A polarizing plate, comprising the polarizer of claim 1.
9. An image display apparatus, comprising the polarizing plate of
claim 8.
Description
TECHNICAL FIELD
[0001] The present invention relates to a polarizer, a polarizing
plate, and an image display apparatus. More specifically, the
present invention relates to a polarizer having a non-polarizing
portion, and a polarizing plate and an image display apparatus each
using such polarizer.
BACKGROUND ART
[0002] Some of the image display apparatus of a cellular phone, a
notebook personal computer (PC), and the like have mounted thereon
internal electronic parts, such as a camera. Various investigations
have been made for the purpose of improving, for example, the
camera performance of any such image display apparatus (for
example, Patent Literatures 1 to 5). However, an additional
improvement in camera performance or the like has been desired in
association with rapid widespread use of a smart phone and a touch
panel-type information processing apparatus. In addition, a
polarizing plate partially having polarization performance has been
required in order to correspond to the diversification of the
shapes of the image display apparatus and the
high-functionalization thereof.
CITATION LIST
Patent Literature
[0003] [PTL 1] JP 2011-81315 A
[0004] [PTL 2] JP 2007-241314 A
[0005] [PTL 3] US 2004/0212555 A1
[0006] [PTL 4] JP 2012-137738 A
[0007] [PTL 5] KR 10-2012-0118205 A
SUMMARY OF INVENTION
Technical Problem
[0008] The present invention has been made to solve the
above-mentioned problems of the related art, and a primary object
of the present invention is to provide a polarizer that can realize
the multi-functionalization and high-functionalization of an
electronic device, such as an image display apparatus.
Solution to Problem
[0009] A polarizer according to an embodiment of the present
invention includes a resin film containing a dichromatic substance,
the polarizer having, in the resin film, a low dichromatic
substance concentration portion whose content of the dichromatic
substance is relatively low. In the polarizer, the low dichromatic
substance concentration portion has a content of an alkali metal
and/or an alkaline earth metal of 3.6 wt % or less.
[0010] In one embodiment of the present invention, the low
dichromatic substance concentration portion is formed by bringing a
basic solution into contact with the resin film.
[0011] In one embodiment of the present invention, the basic
solution comprises an aqueous solution containing a hydroxide of
the alkali metal and/or the alkaline earth metal.
[0012] In one embodiment of the present invention, the low
dichromatic substance concentration portion has a dichromatic
substance content of 1.0 wt % or less.
[0013] In one embodiment of the present invention, the low
dichromatic substance concentration portion has a transmittance of
50% or more.
[0014] In one embodiment of the present invention, the polarizer
has a thickness of 30 .mu.m or less.
[0015] In one embodiment of the present invention, the low
dichromatic substance concentration portion corresponds to a camera
portion of an image display apparatus on which the polarizer is
mounted.
[0016] According to another aspect of the present invention, there
is provided a polarizing plate. The polarizing plate includes the
above described polarizer.
[0017] According to still another aspect of the present invention,
there is provided an image display apparatus. The image display
apparatus includes the above described polarizing plate.
Advantageous Effects of Invention
[0018] According to the present invention, there can be provided
the polarizer that can achieve the multi-functionalization and
high-functionalization of an electronic device. The polarizer of
the present invention has a low dichromatic substance concentration
portion having a content of the dichromatic substance relatively
lower than that of another portion of the resin film. When the
content of the dichromatic substance is relatively lower than that
of another portion, the transmittance of the low concentration
portion can increase. Further, the polarizer of the present
invention is excellent in dimensional stability (e.g., dimensional
stability under a humidified environment) of the low concentration
portion. The polarizer of the present invention can be suitably
used in an electronic device. For example, when the low
concentration portion corresponds to the camera portion of an image
display apparatus, the polarizer can secure a transmission
property, and moreover, the polarizer can optimize brightness and a
tint at the time of photographing, and prevent the distortion of an
image to contribute to an improvement in camera performance.
Further, the polarizer of the present invention can be suitably
used not only in a reception-type electronic device, such as video
apparatus or monitor, but also in a transmission-type electronic
device, such as an LED light source or an infrared sensor, and an
image display apparatus that secures a transmission property to a
naked eye and the straightness of light.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 is a plan view of a polarizer according to one
embodiment of the present invention.
[0020] FIG. 2(a) is an observation photograph for illustrating the
transparent portion of the polarizing plate of Example 1 before a
humidity test, and FIG. 2(b) is an observation photograph for
illustrating the transparent portion of the polarizing plate of
Example 1 after the humidity test.
[0021] FIG. 3(a) is an observation photograph for illustrating the
transparent portion of the polarizing plate of Comparative Example
2 before a humidity test, and FIG. 3(b) is an observation
photograph for illustrating the transparent portion of the
polarizing plate of Comparative Example 2 after the humidity
test.
DESCRIPTION OF EMBODIMENTS
[0022] Embodiments of the present invention are described below.
However, the present invention is not limited to these
embodiments.
[0023] A. Polarizer
[0024] FIG. 1 is a plan view of a polarizer according to one
embodiment of the present invention. A polarizer 1 includes a resin
film containing a dichromatic substance. The polarizer (resin film)
1 has formed therein a low concentration portion 2 having a
relatively low content of the dichromatic substance. Specifically,
the polarizer 1 has formed therein the low concentration portion 2
having a content of the dichromatic substance lower than that of
another portion 3. The low concentration portion can function as a
non-polarizing portion. With such construction, a problem in terms
of quality, such as cracking, delamination (interlayer peeling), or
adhesive protrusion, is avoided as compared to the case where a
through-hole is formed mechanically (e.g., by a method involving
mechanically punching out the through-hole in the polarizer through
the use of, for example, chisel punching, a plotter, or a water
jet). In addition, the content of the dichromatic substance itself
of the low concentration portion is low, and hence the transparency
of the non-polarizing portion is satisfactorily maintained as
compared to the case where the non-polarizing portion is formed by
the decomposition of the dichromatic substance with laser light or
the like.
[0025] In the illustrated example, the low concentration portion 2
of a small circular shape is formed at a central portion in the
upper end portion of the resin film, but the number, arrangement,
shape, size, and the like of the low concentration portion can be
appropriately designed. The design is performed in accordance with,
for example, the position, shape, and size of the camera portion of
an image display apparatus on which the polarizer is mounted.
Specifically, the design is performed so that the low concentration
portion may not correspond to the position except the camera (e.g.,
image display portion) of the image display apparatus on which the
polarizer is mounted.
[0026] The transmittance of the low concentration portion (e.g., a
transmittance measured with light having a wavelength of 550 nm at
23.degree. C.) is preferably 50% or more, more preferably 60% or
more, still more preferably 75% or more, particularly preferably
90% or more. With such transmittance, desired transparency can be
secured. For example, when the low concentration portion is caused
to correspond to the camera portion of an image display apparatus,
an adverse effect on the photographing performance of the camera
can be prevented.
[0027] The polarizer (except the low concentration portion)
preferably shows absorption dichroism in the wavelength range of
from 380 nm to 780 nm. The single axis transmittance (Ts) of the
polarizer (except the low concentration portion) is preferably 39%
or more, more preferably 39.5% or more, still more preferably 40%
or more, particularly preferably 40.5% or more. A theoretical upper
limit for the single axis transmittance is 50%, and a practical
upper limit therefor is 46%. In addition, the single axis
transmittance (Ts) is a Y value measured with the two-degree field
of view (C light source) of JIS Z 8701 and subjected to visibility
correction, and can be measured with, for example, a
microspectroscopic system (manufactured by Lambda Vision Inc.,
LVmicro). The polarization degree of the polarizer (except the low
concentration portion) is preferably 99.8% or more, more preferably
99.9% or more, still more preferably 99.95% or more.
[0028] The thickness of the polarizer (resin film) may be set to
any appropriate value. The thickness is typically 0.5 .mu.m or more
and 80 .mu.m or less, preferably 30 .mu.m or less, more preferably
25 .mu.m or less, still more preferably 18 .mu.m or less,
particularly preferably 12 .mu.m or less, more particularly
preferably less than 8 .mu.m. The lower limit value of the
thickness is preferably 1 .mu.m or more. As the thickness becomes
smaller, the low concentration portion can be more satisfactorily
formed. For example, when a basic solution to be described later is
brought into contact with the resin film, the low concentration
portion can be formed in a shorter time period. In addition, the
thickness of the portion with which the basic solution is brought
into contact may be smaller than that of another portion. When the
thickness of the resin film is small, a difference in thickness
between the portion brought into contact with the basic solution
and another portion can be reduced, and hence the bonding of the
polarizer to any other constituent member, such as a protective
film, can be satisfactorily performed.
[0029] Examples of the dichromatic substance include iodine and an
organic dye. The substances may be used alone or in combination. Of
those, iodine is preferably used. This is because the low
concentration portion can be satisfactorily formed by contact with
a basic solution to be described later.
[0030] The low concentration portion is a portion whose content of
the dichromatic substance is lower than that of another portion.
The content of the dichromatic substance of the low concentration
portion is preferably 1.0 wt % or less, more preferably 0.5 wt % or
less, still more preferably 0.2 wt % or less. When the content of
the dichromatic substance of the low concentration portion falls
within such range, desired transparency can be sufficiently
imparted to the low concentration portion. For example, when the
low concentration portion is caused to correspond to the camera
portion of an image display apparatus, photographing performance
extremely excellent from both the viewpoints of brightness and a
tint can be achieved. Meanwhile, a lower limit value for the
content of the dichromatic substance of the low concentration
portion is typically equal to or less than a detection limit. When
iodine is used as the dichromatic substance, an iodine content is
determined from, for example, a calibration curve produced in
advance from an X-ray intensity measured by fluorescent X-ray
analysis through the use of a standard sample.
[0031] A difference between the content of the dichromatic
substance in another portion and the content of the dichromatic
substance in the low concentration portion is preferably 0.5 wt %
or more, more preferably 1 wt % or more. When the difference
between the contents falls within such range, a low concentration
portion having desired transparency can be formed.
[0032] The content of an alkali metal and/or an alkaline earth
metal in the low concentration portion is 3.6 wt % or less,
preferably 2.5 wt % or less, more preferably 1.0 wt % or less,
still more preferably 0.5 wt % or less. When the content of the
alkali metal and/or the alkaline earth metal in the low
concentration portion falls within such range, the shape of the low
concentration portion formed by contact with a basic solution to be
described later can be satisfactorily maintained (i.e., a low
concentration portion having excellent dimensional stability can be
achieved). The content can be determined from, for example, a
calibration curve produced in advance from an X-ray intensity
measured by fluorescent X-ray analysis through the use of a
standard sample. Such content can be achieved by reducing the
content of the alkali metal and/or the alkaline earth metal in a
contact portion in the contact with the basic solution to be
described later.
[0033] Any appropriate resin may be used as a resin for forming the
resin film. A polyvinyl alcohol-based resin (hereinafter referred
to as "PVA-based resin") is preferably used as the resin. Examples
of the PVA-based resin include polyvinyl alcohol and an
ethylene-vinyl alcohol copolymer. The polyvinyl alcohol is obtained
by saponifying polyvinyl acetate. The ethylene-vinyl alcohol
copolymer is obtained by saponifying an ethylene-vinyl acetate
copolymer. The saponification degree of the PVA-based resin is
typically 85 mol % or more and less than 100 mol %, preferably from
95.0 mol % to 99.95 mol %, more preferably from 99.0 mol % to 99.93
mol %. The saponification degree may be determined in conformity
with JIS K 6726-1994. The use of the PVA-based resin having such
saponification degree can provide a polarizer excellent in
durability. When the saponification degree is too high, there is a
risk of gelation.
[0034] The average polymerization degree of the PVA-based resin may
be appropriately selected depending on purposes. The average
polymerization degree is typically from 1,000 to 10,000, preferably
from 1,200 to 4,500, more preferably from 1,500 to 4,300. The
average polymerization degree may be determined in conformity with
JIS K 6726-1994.
[0035] B. Method of Producing Polarizer
[0036] The low concentration portion can be formed by bringing a
basic solution into contact with the resin film containing the
dichromatic substance. Further, such content of the alkali metal
and/or the alkaline earth metal as described above in the low
concentration portion can be achieved by reducing the content of
the alkali metal and/or the alkaline earth metal in a contact
portion with the basic solution. Therefore, a method of producing
the polarizer of the present invention includes: bringing the basic
solution into contact with the resin film containing the
dichromatic substance; and reducing the content of the alkali metal
and/or the alkaline earth metal in the contact portion.
[0037] B-1. Contact of Basic Solution
[0038] As described above, the low concentration portion is formed
by bringing the basic solution into contact with the resin film
containing the dichromatic substance. When iodine is used as the
dichromatic substance, the contact of the basic solution with a
desired portion of the resin film can easily reduce the iodine
content of the contact portion. Specifically, the contact can cause
the basic solution to permeate into the resin film. An iodine
complex in the resin film is reduced by a base in the basic
solution to become an iodine ion. The reduction of the iodine
complex to the iodine ion can increase the transmittance of the
contact portion. Then, iodine that has become the iodine ion moves
from the resin film into the solvent of the basic solution. The
transparency of the low concentration portion thus obtained can be
satisfactorily maintained. Specifically, when the transmittance is
increased by breaking the iodine complex, iodine remaining in the
resin film may form the iodine complex again in association with
the use of the polarizer to reduce the transmittance, but when the
iodine content is reduced, such problem is prevented.
[0039] Any appropriate method may be adopted as a method of
bringing the basic solution into contact with the resin film.
Examples thereof include: a method involving dropping, applying, or
spraying the basic solution onto the resin film; and a method
involving immersing the resin film in the basic solution.
[0040] At the time of the contact of the basic solution, the resin
film may be protected with any appropriate protective material so
that the basic solution may not be brought into contact with a
portion except a desired portion (the concentration of the
dichromatic substance may not reduce). Specific examples of the
protective material for the resin film include a protective film
and a surface protective film. Some of the protective films may
each be utilized as it is as a protective film for the polarizer.
The surface protective film is temporarily used at the time of the
production of the polarizer. The surface protective film is
typically bonded to the resin film through intermediation of a
pressure-sensitive adhesive layer because the film is removed from
the resin film at any appropriate timing. Another specific example
of the protective material is a photoresist.
[0041] Any appropriate basic compound may be used as the basic
compound. Examples of the basic compound include: hydroxides of
alkali metals, such as sodium hydroxide, potassium hydroxide, and
lithium hydroxide; hydroxides of alkaline earth metals, such as
calcium hydroxide; inorganic alkali metal salts, such as sodium
carbonate; organic alkali metal salts, such as sodium acetate; and
ammonia water. Of those, hydroxides of alkali metals and/or
alkaline earth metals are preferably used, and sodium hydroxide,
potassium hydroxide, and lithium hydroxide are more preferably
used. The dichromatic substance can be efficiently ionized, and
hence the low concentration portion can be formed more easily.
Those basic compounds may be used alone or in combination.
[0042] Any appropriate solvent may be used as the solvent of the
basic solution. Specific examples thereof include water, alcohols,
such as ethanol and methanol, ethers, benzene, chloroform, and
mixed solvents thereof. Of those, water or an alcohol is preferably
used because the ionized dichromatic substance can satisfactorily
migrate to the solvent.
[0043] The concentration of the basic solution is, for example,
from 0.01 N to 5 N, preferably from 0.05 N to 3 N, more preferably
from 0.1 N to 2.5 N. When the concentration falls within such
range, a desired low concentration portion can be satisfactorily
formed.
[0044] The liquid temperature of the basic solution is, for
example, from 20.degree. C. to 50.degree. C. The time period for
which the resin film and the basic solution are brought into
contact with each other can be set in accordance with the thickness
of the resin film, the kind of the basic compound, and the
concentration of the basic solution, and is, for example, from 5
seconds to 30 minutes.
[0045] In one embodiment, at the time of the contact of the basic
solution, the surface of the resin film is covered with a surface
protective film so that at least part thereof may be exposed. The
polarizer of the illustrated example is produced by, for example,
bonding a surface protective film having formed therein a
through-hole having a small circular shape to the resin film, and
bringing the basic solution into contact with the resultant. At
that time, the other side of the resin film (the side on which the
surface protective film is not arranged) is also preferably
protected. When the resin film has an elongated shape, the
lamination of the resin film and the protective material is
preferably performed by a roll-to-roll process. The term
"roll-to-roll" as used herein means that roll-shaped films are
laminated with their longitudinal directions aligned with each
other while being conveyed. Through-holes are formed in the
elongated surface protective film in, for example, the lengthwise
direction and/or widthwise direction thereof at a predetermined
interval.
[0046] The thickness of the surface protective film is typically
from 20 .mu.m to 250 .mu.m, preferably from 30 .mu.m to 150 .mu.m.
The surface protective film is preferably a film having a high
hardness (e.g., modulus of elasticity). This is because the
deformation of the through-holes can be prevented. As materials for
forming the surface protective film, there are given, for example:
an ester-based resin, such as a polyethylene terephthalate-based
resin; a cycloolefin-based resin, such as a norbornene-based resin;
an olefin-based resin, such as polypropylene; a polyamide-based
resin; a polycarbonate-based resin; and a copolymer resin thereof.
Of those, an ester-based resin (in particular, a polyethylene
terephthalate-based resin) is preferred.
[0047] When the basic solution is brought into contact with the
resin film, the resin film is preferably brought into a state in
which the film can be used as a polarizer. Specifically, the film
is preferably subjected to various treatments, such as a swelling
treatment, a stretching treatment, a dyeing treatment with the
dichromatic substance, a cross-linking treatment, a washing
treatment, and a drying treatment. When the resin film is subjected
to the various treatments, the resin film may be a resin layer
formed on a substrate. A laminate of the substrate and the resin
layer can be obtained by, for example, a method involving applying
an application liquid containing a material for forming the resin
film to the substrate, or a method involving laminating the resin
film on the substrate.
[0048] The dyeing treatment is typically performed by causing the
dichromatic substance to adsorb to the resin film. A method for the
adsorption is, for example, a method involving immersing the resin
film in a dyeing liquid containing the dichromatic substance, a
method involving applying the dyeing liquid to the resin film, or a
method involving spraying the dyeing liquid on the resin film. Of
those, the method involving immersing the resin film in the dyeing
liquid is preferred. This is because the dichromatic substance can
satisfactorily adsorb thereto.
[0049] When iodine is used as the dichromatic substance, an aqueous
solution of iodine is preferably used as the dyeing liquid. The
compounding amount of iodine is preferably from 0.04 part by weight
to 5.0 parts by weight with respect to 100 parts by weight of
water. The aqueous solution of iodine is preferably compounded with
an iodide in order that the solubility of iodine in water may be
increased. Potassium iodide is preferably used as the iodide. The
compounding amount of the iodide is preferably from 0.3 part by
weight to 15 parts by weight with respect to 100 parts by weight of
water.
[0050] In the stretching treatment, typically, the resin film is
uniaxially stretched at from 3 times to 7 times. A stretching
direction can correspond to the absorption axis direction of the
polarizer to be obtained.
[0051] Boric acid may be incorporated into the resin film by the
various treatments. For example, when a boric acid solution (e.g.,
an aqueous solution of boric acid) is brought into contact with the
resin film at the time of the stretching treatment or the
cross-linking treatment, boric acid may be incorporated into the
resin film. The boric acid content of the resin film is, for
example, from 10 wt % to 30 wt %. In addition, a boric acid content
in the contact portion with the basic solution is, for example,
from 5 wt % to 12 wt %.
[0052] B-2. Reduction of Content of Alkali Metal and/or Alkaline
Earth Metal
[0053] After the contact with the basic solution, the content of an
alkali metal and/or an alkaline earth metal in the resin film is
reduced in a contact portion with which the basic solution has been
brought into contact. The reduction in content of the alkali metal
and/or the alkaline earth metal can provide a low concentration
portion excellent in dimensional stability. Specifically, the shape
of the low concentration portion formed by the contact with the
basic solution can be maintained as it is even under a humidified
environment.
[0054] When the basic solution is brought into contact with the
resin film, a hydroxide of the alkali metal and/or the alkaline
earth metal may remain in the contact portion. In addition, when
the basic solution is brought into contact with the resin film, a
metal salt of the alkali metal and/or the alkaline earth metal may
be produced in the contact portion. Any such metal salt may produce
a hydroxide ion, and the produced hydroxide ion may act on
(decompose or reduce) the dichromatic substance (e.g., an iodine
complex) present around the contact portion to expand a
non-polarizing region (low concentration region). Therefore, it is
assumed that the reduction in content of the alkali metal salt
and/or the alkaline earth metal salt suppresses temporal expansion
of the non-polarizing region and hence enables the maintenance of a
desired shape of the non-polarizing portion.
[0055] The metal salt that may produce a hydroxide ion is, for
example, a borate. The borate may be produced by the neutralization
of boric acid in the resin film with the basic solution (a solution
of a hydroxide of an alkali metal and/or a hydroxide of an alkaline
earth metal). For example, when the polarizer is placed under a
humidified environment, the borate (metaborate) may be hydrolyzed
to produce a hydroxide ion as represented by the following
formulae.
##STR00001##
(In the formulae, X represents an alkali metal or an alkaline earth
metal).
[0056] In the method of producing the polarizer of the present
invention, the content of the alkali metal and/or the alkaline
earth metal in the contact portion is reduced so that the content
may be 3.6 wt % or less, preferably 2.5 wt % or less, more
preferably 1.0 wt % or less, still more preferably 0.5 wt % or
less.
[0057] The alkali metal and/or the alkaline earth metal may be
incorporated into the resin film in advance by subjecting the film
to the various treatments for turning the film into a polarizer.
For example, potassium may be incorporated into the resin film by
bringing a solution of an iodide, such as potassium iodide, into
contact with the film. The alkali metal and/or the alkaline earth
metal to be typically incorporated into the polarizer as described
above may not adversely affect the dimensional stability of the low
concentration portion.
[0058] A method involving bringing a treatment liquid into contact
with the contact portion with the basic solution is preferably used
as the method for the reduction. According to such method, the
alkali metal and/or the alkaline earth metal is caused to migrate
from the resin film toward the treatment liquid, and hence the
content thereof can be reduced.
[0059] Any appropriate method may be adopted as a method for the
contact of the treatment liquid. Examples thereof include: a method
involving dropping, applying, or spraying the treatment liquid onto
the contact portion with the basic solution; and a method involving
immersing the contact portion with the basic solution in the
treatment liquid.
[0060] In the case where the resin film is protected with any
appropriate protective material at the time of the contact of the
basic solution, the treatment liquid is preferably brought into
contact as it is with the contact portion (particularly when the
temperature of the treatment liquid is 50.degree. C. or more).
According to such mode, reductions in polarization characteristics
by the treatment liquid can be prevented in a portion except the
contact portion with the basic solution.
[0061] The treatment liquid may contain any appropriate solvent.
Examples of the solvent include water, alcohols, such as ethanol
and methanol, ethers, benzene, chloroform, and mixed solvents
thereof. Of those, water or an alcohol is preferably used from the
viewpoint of efficiently causing the alkali metal and/or the
alkaline earth metal to migrate. Any appropriate water may be used
as the water. Examples thereof include tapwater, pure water, and
deionized water.
[0062] The temperature of the treatment liquid at the time of its
contact is, for example, 20.degree. C. or more, preferably
50.degree. C. or more, more preferably 60.degree. C. or more, still
more preferably 70.degree. C. or more. With such temperature, the
alkali metal and/or the alkaline earth metal can be efficiently
caused to migrate toward the treatment liquid. Specifically, the
swelling ratio of the resin film is significantly increased, and
hence the alkali metal and/or the alkaline earth metal in the resin
film can be physically removed. Meanwhile, the temperature of the
water is substantially 95.degree. C. or less.
[0063] A contact time may be appropriately adjusted in accordance
with, for example, the contact method, the temperature of the
treatment liquid (water), and the thickness of the resin film. For
example, when the resin film is immersed in warm water, the contact
time is preferably from 10 seconds to 30 minutes, more preferably
from 30 seconds to 15 minutes, still more preferably from 60
seconds to 10 minutes.
[0064] In one embodiment, an acidic solution is used as the
treatment liquid. The use of the acidic solution can neutralize the
hydroxide of the alkali metal and/or the alkaline earth metal
remaining in the resin film to chemically remove the alkali metal
and/or the alkaline earth metal in the resin film.
[0065] Any appropriate acidic compound may be used as an acidic
compound in the acidic solution. Examples of the acidic compound
include: inorganic acids, such as hydrochloric acid, sulfuric acid,
nitric acid, hydrogen fluoride, and boric acid; and organic acids,
such as formic acid, oxalic acid, citric acid, acetic acid, and
benzoic acid. The acidic compound in the acidic solution is
preferably an inorganic acid, more preferably hydrochloric acid,
sulfuric acid, or nitric acid. One kind of those acidic compounds
may be used alone, or two or more kinds thereof may be used in
combination.
[0066] An acidic compound having an acidity stronger than that of
boric acid is preferably used as the acidic compound. This is
because the compound can also act on the metal salt (borate) of the
alkali metal and/or the alkaline earth metal. Specifically, the
compound can liberate boric acid from any such borate to chemically
remove the alkali metal and/or the alkaline earth metal in the
resin film.
[0067] An indicator of the acidity is, for example, an acid
dissociation constant (pKa), and an acidic compound having a pKa
smaller than the pKa of boric acid (9.2) is preferably used.
Specifically, the pKa is preferably less than 9.2, more preferably
5 or less. The pKa may be measured with any appropriate measuring
apparatus, and reference may be made to a value disclosed in a
literature, such as "Handbook of Chemistry: Pure Chemistry, 5th
ed." (edited by The Chemical Society of Japan, Maruzen Publishing
Co., Ltd.). In addition, in the case of an acidic compound that
dissociates in a multi-stages, its pKa value may change in each
stage. When such acidic compound is used, such a compound that any
one of the pKa values in the respective stages falls within the
range is used. The pKa as used herein refers to a value in an
aqueous solution at 25.degree. C.
[0068] A difference between the pKa of the acidic compound and the
pKa of boric acid is, for example, 2.0 or more, preferably from 2.5
to 15, more preferably from 2.5 to 13. When the difference falls
within such range, the alkali metal and/or the alkaline earth metal
can be efficiently caused to migrate toward the treatment liquid,
and as a result, a desired content of the alkali metal and/or the
alkaline earth metal in the low concentration portion can be
achieved.
[0069] Examples of the acidic compound that may satisfy the pKa
include inorganic acids, such as hydrochloric acid (pKa: -3.7),
sulfuric acid (pK.sub.2: 1.96), nitric acid (pKa: -1.8), hydrogen
fluoride (pKa: 3.17), and boric acid (pKa: 9.2), and organic acids,
such as formic acid (pKa: 3.54), oxalic acid (pK.sub.1: 1.04,
pK.sub.2: 3.82), citric acid (pK.sub.1: 3.09, pK.sub.2: 4.75,
pK.sub.3: 6.41), acetic acid (pKa: 4.8), and benzoic acid (pKa:
4.0).
[0070] The solvent of the acidic solution (treatment liquid) is as
described above, and also in this mode in which the acidic solution
is used as the treatment liquid, the physical removal of the alkali
metal and/or the alkaline earth metal in the resin film may
occur.
[0071] The concentration of the acidic solution is, for example,
from 0.01 N to 5 N, preferably from 0.05 N to 3 N, more preferably
from 0.1 N to 2.5 N.
[0072] The liquid temperature of the acidic solution is, for
example, from 20.degree. C. to 50.degree. C. The time period for
which the resin film and the acidic solution are brought into
contact with each other can be set in accordance with the thickness
of the resin film, the kind of the acidic compound, and the
concentration of the acidic solution, and is, for example, from 5
seconds to 30 minutes.
[0073] The polarizer of the present invention can be obtained by
subjecting the resin film containing the dichromatic substance to
those treatments. The resin film may be further subjected to any
appropriate other treatment in addition to the treatments. Examples
of the other treatment include the removal of the basic solution
and/or the acidic solution, and washing.
[0074] A method for the removal of the basic solution and/or the
acidic solution is specifically, for example, removal by wiping
with a waste cloth or the like, removal by suction, natural drying,
heat drying, blow drying, or vacuum drying. The drying temperature
is, for example, from 20.degree. C. to 100.degree. C.
[0075] The washing treatment is performed by any appropriate
method. Examples of a solution to be used in the washing treatment
include pure water, alcohols, such as methanol and ethanol, an
acidic aqueous solution, and mixed solvents thereof. The washing
treatment may be performed in any appropriate stage. The washing
treatment may be performed a plurality of times.
[0076] B. Polarizing Plate
[0077] A polarizing plate of the present invention includes the
polarizer. The polarizing plate of the present invention is
typically used under a state in which a protective film is
laminated on at least one side thereof. As materials for forming
the protective film, there are given, for example, a
cellulose-based resin, such as diacetyl cellulose or triacetyl
cellulose, a (meth)acrylic resin, a cycloolefin-based resin, an
olefin-based resin, such as polypropylene, an ester-based resin,
such as a polyethylene terephthalate-based resin, a polyamide-based
resin, a polycarbonate-based resin, and copolymer resins
thereof.
[0078] The surface of the protective film on which the polarizer is
not laminated may have formed thereon a hard coat layer as a
surface-treated layer, or may be subjected surface treatment such
as an antireflection treatment or a treatment intended for
diffusion or for antiglare.
[0079] The thickness of the protective film is preferably from 10
.mu.m to 100 .mu.m. The protective film is typically laminated on
the polarizer through intermediation of an adhesion layer
(specifically an adhesive layer or a pressure-sensitive adhesive
layer). The adhesive layer is typically formed of a PVA-based
adhesive or an active energy ray-curable adhesive. The
pressure-sensitive adhesive layer is typically formed of an acrylic
pressure-sensitive adhesive.
[0080] C. Image Display Apparatus
[0081] An image display apparatus of the present invention includes
the polarizing plate. Examples of the image display apparatus
include a liquid crystal display apparatus and an organic EL
device. Specifically, the liquid crystal display apparatus includes
a liquid crystal panel including: a liquid crystal cell; and the
polarizer arranged on one side, or each of both sides, of the
liquid crystal cell. The organic EL device includes an organic EL
panel including the polarizer arranged on a viewer side. The
polarizer is arranged so that its low concentration portion may
correspond to the camera portion of an image display apparatus on
which the polarizer is mounted.
EXAMPLES
Example 1
[0082] An amorphous isophthalic acid-copolymerized polyethylene
terephthalate (IPA-copolymerized PET) film of an elongated shape
(thickness: 100 .mu.m) having a coefficient of water absorption of
0.75% and a Tg of 75.degree. C. was used as a substrate. One
surface of the substrate was subjected to a corona treatment, and
an aqueous solution containing polyvinyl alcohol (polymerization
degree: 4,200, saponification degree: 99.2 mol %) and
acetoacetyl-modified PVA (polymerization degree: 1,200, acetoacetyl
modification degree: 4.6%, saponification degree: 99.0 mol % or
more, manufactured by The Nippon Synthetic Chemical Industry Co.,
Ltd., trade name: "GOHSEFIMER Z-200") at a ratio of 9:1 was applied
to the corona-treated surface and dried at 25.degree. C. to form a
PVA-based resin layer having a thickness of 11 .mu.m. Thus, a
laminate was produced.
[0083] The resultant laminate was subjected to free-end uniaxial
stretching in an oven at 120.degree. C. between rolls having
different peripheral speeds in a longitudinal direction (lengthwise
direction) at 2.0 times (in-air auxiliary stretching).
[0084] Next, the laminate was immersed in an insolubilizing bath
having a liquid temperature of 30.degree. C. (an aqueous solution
of boric acid obtained by compounding 100 parts by weight of water
with 4 parts by weight of boric acid) for 30 seconds
(insolubilizing treatment).
[0085] Next, the laminate was immersed in a dyeing bath having a
liquid temperature of 30.degree. C. while an iodine concentration
and an immersion time were adjusted so that a polarizing plate to
be obtained had a predetermined transmittance. In this example, the
laminate was immersed in an aqueous solution of iodine, which was
obtained by compounding 100 parts by weight of water with 0.2 part
by weight of iodine and 1.5 parts by weight of potassium iodide,
for 60 seconds (dyeing treatment).
[0086] Next, the laminate was immersed in a cross-linking bath
having a liquid temperature of 30.degree. C. (an aqueous solution
of boric acid obtained by compounding 100 parts by weight of water
with 3 parts by weight of potassium iodide and 3 parts by weight of
boric acid) for 30 seconds (cross-linking treatment).
[0087] After that, the laminate was subjected to uniaxial
stretching between rolls having different peripheral speeds in a
longitudinal direction (lengthwise direction) so that a total
stretching ratio became 5.5 times while being immersed in an
aqueous solution of boric acid having a liquid temperature of
70.degree. C. (an aqueous solution obtained by compounding 100
parts by weight of water with 4 parts by weight of boric acid and 5
parts by weight of potassium iodide) (underwater stretching).
[0088] After that, the laminate was immersed in a washing bath
having a liquid temperature of 30.degree. C. (an aqueous solution
obtained by compounding 100 parts by weight of water with 4 parts
by weight of potassium iodide) (washing treatment).
[0089] Subsequently, a PVA-based resin aqueous solution
(manufactured by The Nippon Synthetic Chemical Industry Co., Ltd.,
trade name: "GOHSEFIMER (trademark) Z-200", resin concentration: 3
wt %) was applied to the PVA-based resin layer surface of the
laminate, and a protective film (thickness: 25 .mu.m) was bonded
thereto, followed by the heating of the resultant in an oven
maintained at 60.degree. C. for 5 minutes. After that, the
substrate was peeled from the PVA-based resin layer. Thus, a
polarizing plate (polarizer (transmittance: 42.3%, thickness: 5
.mu.m)/protective film) was obtained.
[0090] An aqueous solution of sodium hydroxide at normal
temperature (1.0 mol/L (1.0 N)) was dropped to the surface of the
polarizing plate having a total thickness of 30 .mu.m obtained in
the foregoing on a polarizer side so as to have a diameter of 4 mm,
and the resultant was left to stand for 60 seconds. After that, the
dropped aqueous solution of sodium hydroxide was removed with a
waste cloth.
[0091] Next, hydrochloric acid at normal temperature (1.0 mol/L
(1.0 N)) was dropped to the contact portion with the aqueous
solution of sodium hydroxide, and the resultant was left to stand
for 30 seconds. After that, the dropped hydrochloric acid was
removed with a waste cloth. Thus, a transparent portion was formed
in the polarizer.
Example 2
[0092] A transparent portion was formed in the polarizer in the
same manner as in Example 1 except that the concentration of the
hydrochloric acid was changed to 0.1 mol/L (0.1 N).
Example 3
[0093] A pressure-sensitive adhesive (acrylic pressure-sensitive
adhesive) was applied to one surface of an ester-based film
(thickness: 38 .mu.m) so as to have a thickness of 10 .mu.m. A
through-hole having a diameter of 4 mm was formed in the
ester-based film with the pressure-sensitive adhesive with a
pinnacle blade.
[0094] The ester-based film was bonded to the polarizer side of the
polarizing plate having a total thickness of 30 .mu.m used in
Example 1 through intermediation of the pressure-sensitive adhesive
layer. Thus, a polarizing film laminate was obtained.
[0095] An aqueous solution of sodium hydroxide at normal
temperature (1.0 mol/L (1.0 N)) was dropped to a portion where the
polarizer was exposed from the ester-based film of the resultant
polarizing film laminate, and the resultant was left to stand for
60 seconds. After that, the dropped aqueous solution of sodium
hydroxide was removed with a waste cloth.
[0096] Next, the polarizing film laminate was immersed in a water
bath set to 55.degree. C. for 60 seconds. After the immersion,
water adhering to its surface was removed with a waste cloth, and
then the ester-based film was peeled. Thus, a transparent portion
was formed in the polarizer.
Example 4
[0097] A transparent portion was formed in the polarizer in the
same manner as in Example 3 except that the temperature of the
water bath was changed to 70.degree. C.
Example 5
[0098] A transparent portion was formed in the polarizer in the
same manner as in Example 3 except that: the temperature of the
water bath was changed to 40.degree. C.; and after the removal of
the water with the waste cloth, hydrochloric acid (1.0 mol/L (1.0
N)) was dropped to the portion where the polarizer was exposed, and
the resultant was left to stand for 30 seconds, followed by the
removal of the hydrochloric acid with a waste cloth.
Example 6
[0099] A transparent portion was formed in the polarizer in the
same manner as in Example 5 except that the temperature of the
water bath was changed to 70.degree. C.
Example 7
[0100] A transparent portion was formed in the polarizer in the
same manner as in Example 3 except that the temperature of the
water bath was changed to 30.degree. C.
Example 8
[0101] A transparent portion was formed in the polarizer in the
same manner as in Example 3 except that the temperature of the
water bath was changed to 40.degree. C.
Comparative Example 1
[0102] An attempt was made to form a transparent portion in the
same manner as in Example 1 except that: pure water was used
instead of the aqueous solution of sodium hydroxide; and the
hydrochloric acid was not brought into contact with the contact
portion.
Comparative Example 2
[0103] A transparent portion was formed in the polarizer in the
same manner as in Example 1 except that the hydrochloric acid was
not brought into contact with the contact portion.
[0104] Each of the polarizing plates of Examples and Comparative
Examples was evaluated for the following items. The results of the
evaluations are summarized in Table 1.
1. Transmittance (Ts)
[0105] Measurement was performed with a spectrophotometer
(manufactured by Murakami Color Research Laboratory, product name:
"DOT-3"). A transmittance (T) is a Y value subjected to visibility
correction with the two-degree field of view (C light source) of
JIS Z 8701-1982.
2. Iodine Content
[0106] An iodine content in the contact portion of a polarizer was
determined by fluorescent X-ray analysis. Specifically, the iodine
content of the polarizer was determined from a calibration curve
produced in advance from the X-ray intensity measured under the
following conditions through the use of a standard sample.
[0107] Analysis apparatus: manufactured by Rigaku Corporation,
X-ray fluorescence (XRF) analysis apparatus, product name
"ZSX100e"
[0108] Anticathode: rhodium
[0109] Dispersive crystal: lithium fluoride
[0110] Excitation light energy: 40 kV-90 mA
[0111] Iodine measured line: I-LA
[0112] Quantification method: FP method
[0113] 2.theta. angle peak: 103.078 deg (iodine)
[0114] Measurement time: 40 seconds
3. Sodium Content
[0115] A sodium content in the contact portion of a polarizer was
determined by fluorescent X-ray analysis. Specifically, the sodium
content of the polarizer was determined from a calibration curve
produced in advance from an X-ray intensity measured under the
following conditions through the use of a standard sample.
[0116] Analysis apparatus: manufactured by Rigaku Corporation,
X-ray fluorescence (XRF) analysis apparatus, product name
"ZSX100e"
[0117] Anticathode: rhodium
[0118] Dispersive crystal: lithium fluoride
[0119] Excitation light energy: 40 kV-90 mA
[0120] Sodium measured line: Na-KA
[0121] Quantification method: FP method
[0122] Measurement time: 40 seconds
4. Sodium Reduction Ratio
[0123] The aqueous solution of sodium hydroxide that had been
brought into contact with a polarizer was removed with a waste
cloth, and the sodium content of the contact portion immediately
after the contact was measured. After that, the sodium content of
the contact portion (transparent portion) of the finally obtained
polarizer was measured. A reduction ratio was calculated from the
following equation by using those measured values.
Reduction ratio=((sodium content of contact portion immediately
after contact)-(sodium content of contact portion(transparent
portion) of resultant polarizer))/(sodium content of contact
portion immediately after contact).times.100
5. Size Change Ratio
[0124] Each of the resultant polarizing plates was placed under a
65.degree. C./90% RH environment for 500 hours. The sizes of its
transparent portion before and after a humidity test were measured,
and a size change ratio was calculated by using the following
equation.
[0125] After the humidity test, edge detection was performed with a
super-high-speed flexible image processing system (manufactured by
Keyence Corporation, trade name: "XG-7500") to draw a boundary line
between the transparent portion and another portion, and the size
of a portion having the maximum size was measured.
Size change ratio (%)=100.times.(size of transparent portion after
humidity test)/(size of transparent portion before humidity
test)
TABLE-US-00001 TABLE 1 Sodium Size Iodine Sodium reduction change
Treatment liquid Transmittance content content ratio ratio Kind
Temperature (%) (wt %) (wt %) (%) (%) Example 1 Hydrochloric Normal
93.5 0.12 0.04 99 100.5 acid temperature Example 2 Hydrochloric
Normal 93.4 0.1 0.04 99 100.6 acid temperature Example 3 Water
55.degree. C. 93.7 0.14 0.61 85 104.8 Example 4 Water 70.degree. C.
93.4 0.1 0.13 97 101.2 Example 5 Water 40.degree. C. 93.1 0.1 0.04
99 100.2 Hydrochloric Normal acid temperature Example 6 Water
70.degree. C. 93.2 0.1 0.04 99 100.4 Hydrochloric Normal acid
temperature Example 7 Water 30.degree. C. 93.1 0.13 3.53 12 125.5
Example 8 Water 40.degree. C. 93.3 0.11 2.29 43 122.3 Comparative
-- -- 42.3 5.1 0.03 -- -- Example 1 Comparative -- -- 93.3 0.11 4.0
-- 130.3 Example 2
[0126] In each of Examples and Comparative Example 2, the iodine
content in the transparent portion was low and hence the portion
was regarded as a low iodine concentration portion. In each of
Examples, the size of the transparent portion was maintained as
compared to Comparative Example 2. As illustrated in FIGS. 2 and 3,
high dimensional stability was observed in each of Examples 1 to
6.
INDUSTRIAL APPLICABILITY
[0127] The polarizer of the present invention is suitably used in
an image display apparatus (a liquid crystal display apparatus or
an organic EL device) with a camera of, for example, a cellular
phone, such as a smart phone, a notebook PC, or a tablet PC.
CITATION LIST
[0128] 1 polarizer (resin film) [0129] 2 low concentration
portion
* * * * *