U.S. patent application number 16/216274 was filed with the patent office on 2019-04-18 for polarizing plate.
This patent application is currently assigned to NITTO DENKO CORPORATION. The applicant listed for this patent is NITTO DENKO CORPORATION. Invention is credited to Naotaka Higuchi, Keisuke Kimura, Yoshitsugu Kitamura, Shinobu Nagano, Kota Nakai, Eiko Suefusa, Katsunori Takada.
Application Number | 20190113659 16/216274 |
Document ID | / |
Family ID | 57153336 |
Filed Date | 2019-04-18 |
United States Patent
Application |
20190113659 |
Kind Code |
A1 |
Takada; Katsunori ; et
al. |
April 18, 2019 |
POLARIZING PLATE
Abstract
A primary object of the present invention is to provide a
polarizing plate excellent in durability. A polarizing plate (100)
according to an embodiment of the present invention includes: a
polarizer (10); and a protective film (21 and 22) arranged on at
least one side of the polarizer (10). The polarizing plate (100)
has a dimensional change ratio of -0.2% or more in a transmission
axis direction thereof when the polarizing plate (100) cut into a
size measuring 100 mm by 100 mm is bonded to a glass plate with a
pressure-sensitive adhesive and the following operation is repeated
100 times: the polarizing plate (100) bonded to the glass plate is
left to stand under an atmosphere at -40.degree. C. for 30 minutes
and then left to stand under an atmosphere at 85.degree. C. for 30
minutes.
Inventors: |
Takada; Katsunori;
(Ibaraki-shi, JP) ; Higuchi; Naotaka;
(Ibaraki-shi, JP) ; Nakai; Kota; (Ibaraki-shi,
JP) ; Nagano; Shinobu; (Ibaraki-shi, JP) ;
Suefusa; Eiko; (Ibaraki-shi, JP) ; Kitamura;
Yoshitsugu; (Ibaraki-shi, JP) ; Kimura; Keisuke;
(Ibaraki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NITTO DENKO CORPORATION |
Osaka |
|
JP |
|
|
Assignee: |
NITTO DENKO CORPORATION
Osaka
JP
|
Family ID: |
57153336 |
Appl. No.: |
16/216274 |
Filed: |
December 11, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15290775 |
Oct 11, 2016 |
|
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16216274 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B32B 2038/047 20130101;
B32B 2551/00 20130101; Y10T 428/24273 20150115; Y10T 428/24777
20150115; B32B 27/306 20130101; B32B 3/266 20130101; Y10S 428/91
20130101; G02B 1/14 20150115; B32B 3/02 20130101; B32B 2307/42
20130101; B32B 7/12 20130101; B32B 2038/0028 20130101; B32B
2038/042 20130101; B32B 2307/518 20130101; B32B 38/0036 20130101;
G02B 5/3033 20130101; B32B 27/16 20130101; B32B 2329/04 20130101;
G02B 5/305 20130101; B32B 2307/734 20130101; B32B 27/08 20130101;
Y10T 428/24322 20150115; B32B 38/0004 20130101 |
International
Class: |
G02B 1/14 20060101
G02B001/14; B32B 3/26 20060101 B32B003/26; G02B 5/30 20060101
G02B005/30; B32B 3/02 20060101 B32B003/02; B32B 38/00 20060101
B32B038/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 4, 2015 |
JP |
2015-216399 |
Claims
1. A polarizing plate, comprising: a polarizer; and a protective
film arranged on at least one side of the polarizer, wherein the
polarizer has a thickness of 20 .mu.m or less, wherein the
polarizing plate has a dimensional change ratio of -0.2% or more in
a transmission axis direction thereof; wherein the dimensional
change ratio is measured by cutting the polarizing plate to 100 mm
by 100 mm while bonded to a glass plate with a pressure-sensitive
adhesive and an operation wherein the polarizing plate bonded to
the glass plate is left to stand under an atmosphere at -40.degree.
C. for 30 minutes and then left to stand under an atmosphere at
85.degree. C. for 30 minutes, is repeated 100 times.
2. The polarizing plate according to claim 1, wherein the
polarizing plate has the dimensional change ratio of 0.1% or
less.
3. A polarizing plate, comprising: a polarizer; and a protective
film arranged on at least one side of the polarizer, wherein the
polarizer has a thickness of 20 .mu.m or less, wherein the
polarizing plate has a dimensional change ratio of -0.2% or more in
a transmission axis direction thereof; wherein the dimensional
change ratio is measured by cutting the polarizing plate to 100 mm
by 100 mm while bonded to a glass plate with a pressure-sensitive
adhesive and an operation wherein the polarizing plate bonded to
the glass plate is left to stand under an atmosphere at -40.degree.
C. for 30 minutes and then left to stand under an atmosphere at
85.degree. C. for 30 minutes, is repeated 100 times, and the
polarizing plate has one selected from the group consisting of a
through-hole formed therein, a site having an outer edge forming a
substantially V-shape that is convex inward in a surface direction,
and the combination of the through-hole and the site.
4. A polarizing plate, comprising: a polarizer; and a protective
film arranged on at least one side of the polarizer, wherein the
polarizing plate has a dimensional change ratio of -0.2% or more in
a transmission axis direction thereof; wherein the dimensional
change ratio is measured by cutting the polarizing plate to 100 mm
by 100 mm while bonded to a glass plate with a pressure-sensitive
adhesive and an operation wherein the polarizing plate bonded to
the glass plate is left to stand under an atmosphere at -40.degree.
C. for 30 minutes and then left to stand under an atmosphere at
85.degree. C. for 30 minutes, is repeated 100 times, and the
polarizing plate has one selected from the group consisting of a
through-hole formed therein, a site having an outer edge forming a
substantially V-shape that is convex inward in a surface direction,
and the combination of the through-hole and the site.
5. The polarizing plate according to claim 1, further comprising a
second protective film, wherein the second protective film is
arranged on another side of the polarizer that is opposite to the
protective film.
6. The polarizing plate according to claim 1, wherein the
polarizing plate has the dimensional change ratio of -0.1 to
0.1%.
7. The polarizing plate according to claim 1, wherein the
polarizing plate has a dimensional change ratio of -0.6 to 0% in an
absorption axis direction, wherein the dimensional change ratio in
an absorption axis direction is measured by cutting the polarizing
plate to 100 mm by 100 mm while bonded to a glass plate with a
pressure sensitive adhesive and an operation wherein the polarizing
plate bonded to the glass plate is left to stand under an
atmosphere at -40.degree. C. for 30 minutes and then left to stand
under an atmosphere at 85.degree. C. for 30 minutes, is repeated
100 times.
8. The polarizing plate according to claim 3, further comprising a
second protective film, wherein the second protective film is
arranged on another side of the polarizer that is opposite to the
protective film.
9. The polarizing plate according to claim 3, wherein the
polarizing plate has the dimensional change ratio of -0.1 to
0.1%.
10. The polarizing plate according to claim 3, wherein the
polarizing plate has a dimensional change ratio of -0.6 to 0% in an
absorption axis direction, wherein the dimensional change ratio in
an absorption axis direction is measured by cutting the polarizing
plate to 100 mm by 100 mm while bonded to a glass plate with a
pressure sensitive adhesive and an operation wherein the polarizing
plate bonded to the glass plate is left to stand under an
atmosphere at -40.degree. C. for 30 minutes and then left to stand
under an atmosphere at 85.degree. C. for 30 minutes, is repeated
100 times.
11. The polarizing plate according to claim 4, further comprising a
second protective film, wherein the second protective film is
arranged on another side of the polarizer that is opposite to the
protective film.
12. The polarizing plate according to claim 4, wherein the
polarizing plate has the dimensional change ratio of -0.1 to
0.1%.
13. The polarizing plate according to claim 4, wherein the
polarizing plate has a dimensional change ratio of -0.6 to 0% in an
absorption axis direction, wherein the dimensional change ratio in
an absorption axis direction is measured by cutting the polarizing
plate to 100 mm by 100 mm while bonded to a glass plate with a
pressure sensitive adhesive and an operation wherein the polarizing
plate bonded to the glass plate is left to stand under an
atmosphere at -40.degree. C. for 30 minutes and then left to stand
under an atmosphere at 85.degree. C. for 30 minutes, is repeated
100 times.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a Divisional of U.S. application Ser. No. 15/290,775
filed on Oct. 11, 2016, which claims priority over Japanese
application No. 2015-216399 filed on Nov. 4, 2015, the entire
contents of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention relates to a polarizing plate.
2. Description of the Related Art
[0003] A polarizing plate has been used in an image display
apparatus (e.g., a liquid crystal display apparatus) of a cellular
phone, a notebook personal computer, or the like. In recent years,
the use of the polarizing plate in, for example, a meter display
portion of an automobile or a smart watch has been desired, and
hence the formation of the polarizing plate into a shape except a
rectangular shape and the formation of a through-hole in the
polarizing plate have been desired. However, when any such form is
adopted, a problem in terms of durability is liable to occur. With
a view to improving the durability, for example, there has been
proposed a method involving thermally treating a polarizer at a
temperature of 95.degree. C. or more, and laminating a protective
film on the thermally treated polarizer to provide a polarizing
plate (see Japanese Patent Application Laid-open No. Hei 7-333425).
However, a further improvement in durability has been required.
SUMMARY OF THE INVENTION
[0004] The present invention has been made to solve the problem,
and a primary object of the present invention is to provide a
polarizing plate excellent in durability.
[0005] As a result of their extensive investigations, the inventors
have paid attention to the fact that when a polarizing plate is
bonded to any other member (e.g., a glass plate) through
intermediation of a pressure-sensitive adhesive layer, the
polarizing plate side of the pressure-sensitive adhesive layer is
deformed (shrunk) by a change in external environment, and a stress
produced by the deformation is related to the durability of the
polarizing plate (the occurrence of a crack), and have found that
when the dimensional change ratio of the polarizing plate is
controlled, the occurrence of a stress between the respective
members is suppressed and hence the object can be achieved. Thus,
the inventors have completed the present invention.
[0006] A polarizing plate according to an embodiment of the present
invention includes: a polarizer; and a protective film arranged on
at least one side of the polarizer. The polarizing plate has a
dimensional change ratio of -0.2% or more in a transmission axis
direction thereof when the polarizing plate cut into a size
measuring 100 mm by 100 mm is bonded to a glass plate with a
pressure-sensitive adhesive and the following operation is repeated
100 times: the polarizing plate bonded to the glass plate is left
to stand under an atmosphere at -40.degree. C. for 30 minutes and
then left to stand under an atmosphere at 85.degree. C. for 30
minutes. In one embodiment of the present invention, the polarizer
has a thickness of 20 .mu.m or less. In one embodiment of the
present invention, the polarizing plate is subjected to a heat
treatment under conditions of a temperature in a range of from
50.degree. C. to 120.degree. C. and a time period of 1 hour or more
and 100 hours or less. In one embodiment of the present invention,
the polarizing plate has formed therein a through-hole. In one
embodiment of the present invention, the polarizing plate includes
a site having an outer edge forming a substantially V-shape that is
convex inward in a surface direction. In one embodiment of the
present invention, the polarizing plate has the dimensional change
ratio of 0.1% or less.
[0007] According to the present invention, the polarizing plate
excellent in durability can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a plan view of a polarizing plate according to one
embodiment of the present invention.
[0009] FIG. 2 is a partially enlarged sectional view of the
polarizing plate illustrated in FIG. 1.
[0010] FIG. 3 is a plan view of a polarizing plate according to
another embodiment of the present invention.
[0011] FIG. 4A is a photograph for showing the periphery of a
through-hole of the polarizing plate of Example 1 after a heat
cycle test, FIG. 4B is a photograph for showing the periphery of a
through-hole of the polarizing plate of Example 2 after a heat
cycle test, FIG. 4C is a photograph for showing the periphery of a
through-hole of the polarizing plate of Example 3 after a heat
cycle test, and FIG. 4D is a photograph for showing the periphery
of a through-hole of the polarizing plate of Comparative Example 1
after a heat cycle test.
[0012] FIG. 5A is a photograph for showing the state of the
periphery of an end side of the polarizing plate along the
transmission axis direction of the test sample of Example 1 after
the heat cycle test, and FIG. 5B is a photograph for showing the
state of the periphery of an end side of the polarizing plate along
the absorption axis direction thereof.
[0013] FIG. 6A is a photograph for showing the state of the
periphery of an end side of the polarizing plate along the
transmission axis direction of the test sample of Comparative
Example 1 after the heat cycle test, and FIG. 6B is a photograph
for showing the state of the periphery of an end side of the
polarizing plate along the absorption axis direction thereof.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] Embodiments of the present invention are described below.
However, the present invention is not limited to these
embodiments.
A. Polarizing Plate
[0015] FIG. 1 is a plan view of a polarizing plate according to one
embodiment of the present invention, and FIG. 2 is a partially
enlarged sectional view of the polarizing plate illustrated in FIG.
1. A polarizing plate 100 is suitably used in the meter panel of an
automobile. The polarizing plate 100 includes a first display
portion 50 and a second display portion 60 that are continuously
arranged, and through-holes 51 and 61 for fixing various meter
needles are formed around the centers of the respective display
portions.
[0016] The diameter of each of the through-holes is, for example,
from 0.5 mm to 100 mm. The outer edge of each of the display
portions 50 and 60 is formed into an arc shape along the rotational
direction of a meter needle.
[0017] The polarizing plate 100 includes a polarizer 10, a first
protective film 21 arranged on one side of the polarizer 10, and a
second protective film 22 arranged on the other side of the
polarizer 10. The protective films 21 and 22 are each typically
bonded to the surface of the polarizer 10 through intermediation of
an adhesive layer, though the layer is not shown. Although the
protective films are arranged on both sides of the polarizer in
this illustrated example, a protective film may be arranged only on
one side thereof.
[0018] The polarizing plate of the present invention has a
dimensional change ratio in its transmission axis direction of
-0.2% or more, preferably -0.1% or more, more preferably -0.05% or
more when the polarizing plate is cut into a size measuring 100 mm
by 100 mm and the cut polarizing plate is bonded to a glass plate
with a pressure-sensitive adhesive, and in the state, the following
operation is repeated 100 times (change ratio of a dimension after
a heat cycle test to that before the test): the polarizing plate is
left to stand under an atmosphere at -40.degree. C. for 30 minutes
and then left to stand under an atmosphere at 8.5.degree. C. for 30
minutes. Meanwhile, the dimensional change ratio in the
transmission axis direction is, for example, 0.1% or less. A
polarizing plate satisfying such dimensional change ratio can have
excellent durability. Specifically, the polarizing plate satisfying
such dimensional change ratio shows an extremely small change in
shape due to a change in external environment, and hence when the
polarizing plate is bonded to any other member (e.g., the glass
substrate of a liquid crystal cell or the like) through
intermediation of a pressure-sensitive adhesive layer, an influence
on the adjacent pressure-sensitive adhesive layer is extremely
small. Accordingly, a change in shape of the pressure-sensitive
adhesive layer due to the change in external environment is
suppressed, and hence the occurrence of a stress between the
respective members (e.g., a stress produced when the modulus of
elasticity of the pressure-sensitive adhesive layer increases at
low temperature) can be prevented. As a result, a crack does not
occur in the polarizing plate and hence the polarizing plate can
have extremely excellent durability.
[0019] The dimensional change ratio in the absorption axis
direction of the polarizing plate after the heat cycle test to that
before the test is, for example, from -0.6% to 0%. The dimensional
change ratio may be determined from the following equation.
Dimensional change ratio (%)={(dimension after heat cycle
test/dimension before heat cycle test)-1}.times.100
[0020] When a through-hole is formed like the illustrated example,
the position of the through-hole may be appropriately set in
accordance with, for example, the applications of the polarizing
plate. The crack is liable to occur by using the peripheral edge of
the through-hole as a starting point, and the tendency may be more
remarkable as the position of the through-hole becomes more distant
from the outer edge of the polarizing plate. As a result, as the
position of the through-hole becomes more distant from the outer
edge of the polarizing plate (e.g., its distance from the outer
edge of the polarizing plate is 15 mm or more), a
durability-improving effect exhibited by the fact that the
dimensional change ratio is controlled can be more significantly
obtained. As in the peripheral edge of the through-hole, a site
whose outer edge forms a V-shape (including an R-shape) that is
convex inward in a surface direction, such as a boundary portion 41
or 42 between the respective display portions, is also liable to be
the starting point of the crack.
[0021] The polarizing plate of the present invention is not limited
to the construction of the illustrated example and may be
appropriately changed. For example, the shape of the polarizing
plate, the presence or absence of the through-holes, the shapes and
sizes of the through-holes, and the number and formation positions
of the through-holes may be appropriately changed. Specifically,
there is given a mode in which V-shaped portions 43 and 44 that are
convex inward in the surface direction are formed so as to be
adjacent to each other, and a notch 45 is formed as illustrated in
FIG. 3.
A-1. Polarizer
[0022] The polarizer typically includes a resin film containing a
dichromatic substance. 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.
[0023] Any appropriate resin may be used as a resin for forming the
resin film. A hydrophilic resin (e.g., a polyvinyl alcohol
(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 from 85
mol % to 100 mol %, preferably 95.0 mol % or more, more preferably
99.0 mol % or more, particularly preferably 99.93 mol % or more.
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.
[0024] 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 6,000, more preferably from 2,000 to 5,000. The
average polymerization degree may be determined in conformity with
JIS K 6726-1994.
[0025] The polarizer preferably shows absorption dichroism in the
wavelength range of from 380 nm to 780 nm. The single axis
transmittance (Ts) of the polarizer is preferably 40% or more, more
preferably 41% or more, still more preferably 42% or more,
particularly preferably 43% 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
may be measured with, for example, a spectrophotometer
(manufactured by JASCO Corporation, V7100). The polarization degree
of the polarizer is preferably 99.8% or more, more preferably 99.9%
or more, still more preferably 99.95% or more.
[0026] The thickness of the polarizer may be set to any appropriate
value. The thickness is typically from 1 .mu.m to 80 .mu.m,
preferably from 3 .mu.m to 40 .mu.m. In one embodiment, the
thickness of the polarizer is 20 .mu.m or less, preferably 18 .mu.m
or less, more preferably 15 .mu.m or less. The use of the polarizer
having such thickness can satisfactorily achieve the dimensional
change ratio without performing a heat treatment to be described
later.
[0027] The polarizer may be typically obtained by subjecting the
resin film to 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. The number of times of each of the treatments,
the order in which the treatments are performed, the timings of the
treatments, and the like may be appropriately set. When the resin
film is subjected to each of the treatments, the film may be a
resin layer formed on a substrate.
[0028] The cross-linking treatment is performed by, for example,
bringing a boric acid solution (e.g., an aqueous solution of boric
acid) into contact with the resin film. In addition, when a wet
stretching system is adopted in the stretching treatment, the
stretching is preferably performed while a boric acid solution is
brought into contact with the resin film. In ordinary cases, the
resin film is uniaxially stretched at from 3 times to 7 times from
the viewpoint that excellent polarization characteristics are
obtained. A stretching direction in the stretching treatment may
correspond to the absorption axis direction of the polarizer to be
obtained. The transmission axis direction thereof may be
perpendicular to the absorption axis direction. In one embodiment,
while an elongated resin film is conveyed in its lengthwise
direction, the film is stretched in the conveying direction (MD).
In this case, the absorption axis direction of the polarizer to be
obtained may be the lengthwise direction (MD), and the transmission
axis direction thereof may be a widthwise direction (TD).
[0029] A-2. Protective Film
[0030] As the formation materials of the protective film, there are
given, for example, a cellulose-based resin, such as diacetyl
cellulose or triacetyl cellulose (TAC), 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. The term
"(meth)acrylic resin" refers to an acrylic resin and/or a
methacrylic resin.
[0031] The thickness of the protective film is preferably from 10
.mu.m to 200 .mu.m. A surface-treated layer may be formed on one
side of the protective film (side on which the polarizer is not
arranged). Specifically, the side may be subjected to a hard coat
treatment, an antireflection treatment, or a treatment intended for
diffusion or anti-glaring. In addition, the protective film may
function as a retardation film. When the protective films are
arranged on both sides of the polarizer like the illustrated
example, the constructions (including a formation material and a
thickness) of both the films may be identical to each other, or may
be different from each other.
[0032] As described above, the protective film is typically bonded
to the surface of the polarizer through intermediation of the
adhesive layer. Any appropriate adhesive may be adopted as an
adhesive to be used in the bonding of the protective film. For
example, an aqueous adhesive, a solvent-based adhesive, or an
active energy ray-curable adhesive is used. An adhesive containing
a PVA-based resin is preferably used as the aqueous adhesive.
[0033] B. Method of Producing Polarizing Plate
[0034] The polarizing plate of the present invention is produced by
any appropriate method as long as the dimensional change ratio can
be achieved. In one embodiment, the polarizing plate of the present
invention is produced by a method involving: preparing a polarizing
film laminate including a polarizer and a protective film arranged
on at least one side of the polarizer; and shrinking the polarizing
film laminate as required.
[0035] The polarizing film laminate is typically produced by
bonding the protective film to one side, or each of both sides, of
the polarizer.
[0036] The polarizing film laminate is shrunk as required. The
shrinkage of the polarizing film laminate can provide a polarizing
plate that can satisfactorily achieve the dimensional change ratio
irrespective of, for example, the thickness of the polarizer. A
method for the shrinkage is typically, for example, a method
involving heating the polarizing film laminate. A heating
temperature is, for example, from 50.degree. C. to 120.degree. C.,
preferably from 70.degree. C. to 90.degree. C. When the temperature
falls within such range, the polarizing film laminate can be
efficiently shrunk while its optical characteristics (e.g., a hue,
a transmittance, and a polarization degree) are secured. A heating
time is, for example, from 1 hour to 100 hours, preferably 2 hours
or more, more preferably 10 hours or more. The heating may be
performed in one stage, or may be performed in a plurality of
stages. In addition, the heating temperature may be kept
substantially constant, or may be changed continuously or in a
stepwise manner.
[0037] A shrinkage ratio is preferably 0.2% or more, more
preferably 0.3% or more in, for example, the transmission axis
direction of the polarizer in the polarizing film laminate.
Meanwhile, the shrinkage ratio in the transmission axis direction
is, for example, 0.6% or less. With such shrinkage ratio, it can be
judged that the polarizing film laminate is shrunk to a sufficient
level. The polarizing film laminate may shrink in its absorption
axis direction to a larger extent than in the transmission axis
direction, and hence at the initial stage of the shrinkage, a
dimension in the transmission axis direction of the polarizing film
laminate apparently increases for the time being in some cases. In
any such case, as the shrinkage progresses, the dimension in the
transmission axis direction may reduce from a dimension at the time
of the initiation of the shrinkage (at the time of the initiation
of the heating).
[0038] A shrinkage ratio in the absorption axis direction of the
polarizing film laminate is preferably 0.3% or more, more
preferably 0.4% or more. Meanwhile, the shrinkage ratio in the
absorption axis direction is, for example, 1.0% or less. The
shrinkage ratio may be determined from the following equation.
Shrinkage ratio (%)={1-(dimension after heating/dimension before
heating)}.times.100
[0039] The polarizing plate of the present invention can be formed
into a desired shape because the polarizing plate has excellent
durability. A method of forming the polarizing plate into the
desired shape is typically, for example, a method involving cutting
(punching) the polarizing film laminate. When the polarizing film
laminate is shrunk, the cutting may be performed before the
shrinkage, or may be performed after the shrinkage. The cutting is
preferably performed after the shrinkage from the viewpoint that
the forming into the desired shape is performed more
accurately.
[0040] Any appropriate method may be adopted as a cutting
(punching) method. For example, a method involving irradiating the
laminate with laser light or a method involving using a cutting
blade (punching die), such as a Thomson blade or a pinnacle blade,
is given. The laser light irradiation provides a smooth cut surface
and can suppress the occurrence of the starting point of a crack
(initial crack), and hence can contribute to a further improvement
in durability. Even when the cutting blade is used (even when the
initial crack occurs), the dimensional change ratio is controlled
and hence excellent durability can be obtained.
[0041] Any appropriate laser may be adopted as the laser as long as
the polarizing film laminate (polarizing plate) can be cut. A laser
that can emit light having a wavelength in the range of from 150 nm
to 11 .mu.m is preferably used. Specific examples thereof include a
gas laser, such as a CO.sub.2 laser, a solid laser, such as an YAG
laser, and a semiconductor laser. Of those, a CO.sub.2 laser is
preferably used.
[0042] A condition for the laser light irradiation may be set to
any appropriate condition depending on, for example, the laser to
be used. When the CO.sub.2 laser is used, an output condition is
preferably from 10 W to 1,000 W, more preferably from 100 W to 400
W.
[0043] C. Usage
[0044] The polarizing plate of the present invention is bonded to
any other member (e.g., the glass substrate of a liquid crystal
cell or the like) through intermediation of, for example, a
pressure-sensitive adhesive layer. The thickness of the
pressure-sensitive adhesive layer is preferably from 4 .mu.m to 50
.mu.m. An acrylic pressure-sensitive adhesive is preferably used as
a pressure-sensitive adhesive forming the pressure-sensitive
adhesive layer. The polarizing plate of the present invention may
adopt the form of a polarizing plate with a pressure-sensitive
adhesive layer having the pressure-sensitive adhesive layer
arranged on at least one side thereof in advance.
[0045] Now, the present invention is specifically described by way
of Examples. However, the present invention not limited to these
Examples.
EXAMPLE 1
(Production of Polarizing Film Laminate Sheet)
[0046] A film (thickness: 28 .mu.m) obtained by incorporating
iodine into an elongated PVA-based resin film and uniaxially
stretching the film in its lengthwise direction (MD) was used as a
polarizer.
[0047] A PVA-based adhesive was applied to one side of the
polarizer so that its thickness after drying became 100 nm, and an
elongated TAC film having a thickness of 40 .mu.m was bonded to the
polarizer so that their lengthwise directions were aligned with
each other.
[0048] Subsequently, a PVA-based adhesive was applied to the other
side of the polarizer so that its thickness after drying became 100
nm, and an elongated acrylic film having a thickness of 30 .mu.m
was bonded to the polarizer so that their lengthwise directions
were aligned with each other.
[0049] Thus, a polarizing film laminate sheet having a construction
"TAC film/polarizer/acrylic film" was obtained.
[0050] The resultant polarizing film laminate sheet was cut with a
CO.sub.2 laser (wavelength: 9.35 .mu.m, output: 150 W) to provide a
cut piece of a size measuring 112 mm by 112 mm, the cut piece
having a through-hole having a diameter of 2 mm formed in a site
distant from its outer edge by 55 mm.
[0051] The resultant cut piece was placed under an atmosphere at
85.degree. C. for 50 hours to provide a polarizing plate. The
polarizing plate had a shrinkage ratio in its absorption axis
direction of 0.74% and a shrinkage ratio in its transmission axis
direction of 0.44%, the shrinkage ratios each serving as a ratio of
a dimension after the heating to that before the heating. The
shrinkage ratios each serving as a ratio of a dimension after the
heating to that before the heating were each determined by:
separately preparing a cut piece cut out of the polarizing film
laminate sheet into a size measuring 100 mm by 100 mm (no
through-hole was formed in the cut piece); and measuring the
position of a corner of the cut piece. In this case, the cut piece
was cut out of the sheet so that a pair of sides opposite to each
other corresponded to the transmission axis direction of the
polarizer and another pair of sides opposite to each other
corresponded to the absorption axis direction of the polarizer.
EXAMPLE 2
[0052] A polarizing plate was obtained in the same manner as in
Example 1 except that the resultant cut piece was placed under an
atmosphere at 85.degree. C. for 5 hours. The polarizing plate had a
shrinkage ratio in its absorption axis direction of 0.45% and a
shrinkage ratio in its transmission axis direction of 0.37%, the
shrinkage ratios each serving as a ratio of a dimension after the
heating to that before the heating, and each being measured by the
same method as that of Example 1.
EXAMPLE 3
[0053] A polarizing plate was obtained in the same manner as in
Example 1 except that the resultant cut piece was placed under an
atmosphere at 85.degree. C. for 2.5 hours. The polarizing plate had
a shrinkage ratio in its absorption axis direction of 0.34% and a
shrinkage ratio in its transmission axis direction of 0.25%, the
shrinkage ratios each serving as a ratio of a dimension after the
heating to that before the heating, and each being measured by the
same method as that of Example 1.
EXAMPLE 4
[0054] A polarizing plate was obtained in the same manner as in
Example 1 except that: the size of the cut piece was set to 52 mm
by 52 mm; and the through-hole was formed in a site distant from
the outer edge of the cut piece by 25 mm.
EXAMPLE 5
[0055] A polarizing plate was obtained in the same manner as in
Example 1 except that at the time of the production of the
polarizing film laminate sheet, a polarizer having a thickness of
12 .mu.m was used and the cut piece was not heated.
EXAMPLE 6
[0056] A polarizing plate was obtained in the same manner as in
Example 1 except that at the time of the production of the
polarizing film laminate sheet, a polarizer having a thickness of
18 .mu.m was used, a TAC film having a thickness of 60 .mu.m was
used instead of the acrylic film having a thickness of 30 .mu.m,
and the cut piece was not heated.
COMPARATIVE EXAMPLE 1
[0057] A polarizing plate was obtained in the same manner as in
[0058] Example 1 except that the cut piece was not heated.
COMPARATIVE EXAMPLE 2
[0059] A polarizing plate was obtained in the same manner as in
Example 4 except that the cut piece was not heated.
[0060] The durability of each of the resultant polarizing plates
was evaluated by a heat cycle (HC, heat shock (HS)) test.
[0061] Specifically, each of the resultant polarizing plates was
bonded to a glass plate with an acrylic pressure-sensitive adhesive
(thickness: 20 .mu.m) having a difference between a storage modulus
of elasticity in a high-temperature region (85.degree. C.) and a
storage modulus of elasticity in a low-temperature region
(-40.degree. C.) of less than 1.times.10.sup.9 Pa, having a storage
modulus of elasticity at 25.degree. C. of 1.times.10.sup.5 Pa or
more, and having a storage modulus of elasticity at 85.degree. C.
of less than 1.times.10.sup.6 Pa. Thus, a test sample was obtained.
The storage moduli of elasticity are each determined by performing
measurement with a dynamic viscoelasticity-measuring apparatus
(manufactured by Rheometric Scientific, "Advanced Rheometric
Expansion System (ARES)") under the condition of a frequency of 1
Hz in the range of from -70.degree. C. to 200.degree. C. at a rate
of temperature increase of 5.degree. C./min to calculate a shear
storage modulus.
[0062] The resultant test sample was left to stand under an
atmosphere at -40.degree. C. for 30 minutes and then left to stand
under an atmosphere at 85.degree. C. for 30 minutes. The foregoing
operation was defined as one cycle and the cycle was repeated 100
times. After the heat cycle test, whether or not a crack occurred
in the polarizing plate was observed.
[0063] In addition, the change ratio of a dimension in the
transmission axis direction of the polarizing plate after the heat
cycle test to that before the test was measured. The dimensional
change ratio was determined by: separately preparing a cut piece
cut out of the polarizing film laminate sheet (in each of Examples
1 to 4, out of the polarizing film laminate sheet heated in
advance) into a size measuring 100 mm by 100 mm (no through-hole
was formed in the cut piece); subjecting the cut piece to the heat
cycle test; and measuring the position of a corner of the cut
piece. In this case, the cut piece was cut out of the sheet so that
a pair of sides opposite to each other corresponded to the
transmission axis direction of the polarizer and another pair of
sides opposite to each other corresponded to the absorption axis
direction of the polarizer.
[0064] The dimensional change ratios of Examples and Comparative
Examples are summarized in Table 1.
TABLE-US-00001 TABLE 1 Dimensional change ratio (%) Example 1 0.007
Example 2 -0.08 Example 3 -0.14 Example 4 0.007 Example 5 -0.15
Example 6 -0.15 Comparative Example 1 -0.37 Comparative Example 2
-0.37
[0065] FIG. 4A to FIG. 4D are photographs obtained by observing the
peripheries of the through-holes of the polarizing plates of
Examples 1 to 3 and Comparative Example 1 after the HS tests with
an optical microscope (manufactured by Olympus Corporation, MX61,
magnification: 5). In Comparative Example 1, a crack that can be
visually recognized with the eyes in a clear manner is observed. In
contrast, in Example 1, the occurrence of a crack (including a
microcrack) is not observed. In each of Examples 2 and 3, a
microcrack that cannot be visually recognized with the eyes in a
clear manner is observed, but the occurrence of a crack is
suppressed as compared to Comparative Example 1. The cracks each
occur along a stretching direction.
[0066] In Example 4, as in Example 1, the occurrence of a crack
(including a microcrack) is not observed. In Comparative Example 1,
the crack extends from the through-hole serving as a starting point
to an end side of the polarizing plate. In contrast, in Comparative
Example 2, a crack length is 12 mm.
[0067] In each of Examples 5 and 6, as in Example 1, the occurrence
of a crack (including a microcrack) is not observed.
[0068] FIG. 5A and FIG. 5B are each a photograph for showing the
state of an end portion of the polarizing plate of the test sample
of Example 1 after the HS test, and FIG. 6A and FIG. 6B are each a
photograph for showing the state of an end portion of the
polarizing plate of the test sample of Comparative Example 1 after
the HS test. In Comparative Example 1, a region in which the
pressure-sensitive adhesive layer used at the time of the bonding
of the polarizing plate to the glass plate is exposed is
formed.
[0069] The polarizing plate of the present invention can be
suitably used not only in an image display apparatus (a liquid
crystal display apparatus or an organic EL device) of a rectangular
shape but also in, for example, an image display portion of a
particular shape typified by the meter display portion of an
automobile or a smart watch.
* * * * *