U.S. patent application number 12/634258 was filed with the patent office on 2010-04-08 for polarizer, method of manufacturing the same, polarizing plate, optical film, and image display.
This patent application is currently assigned to NITTO DENKO CORPORATION. Invention is credited to Takahisa Konishi, Yuuji Saiki, Hideyuki Usui, Takemichi Yoshida.
Application Number | 20100085641 12/634258 |
Document ID | / |
Family ID | 33307961 |
Filed Date | 2010-04-08 |
United States Patent
Application |
20100085641 |
Kind Code |
A1 |
Saiki; Yuuji ; et
al. |
April 8, 2010 |
POLARIZER, METHOD OF MANUFACTURING THE SAME, POLARIZING PLATE,
OPTICAL FILM, AND IMAGE DISPLAY
Abstract
A polarizer of the invention comprises a polyvinyl alcohol-based
film which is at least dyed with at least iodine and uniaxially
stretched, having a single transmittance of 43% or more, a
polarizing efficiency of 99.9% or more, and a dichroic ratio of 30
or more, wherein the dichroic ratio is calculated from a parallel
transmittance (Tp) and a crossed transmittance (Tc) at a wavelength
of 440 nm, and have good hue.
Inventors: |
Saiki; Yuuji; (Ibaraki-shi,
JP) ; Usui; Hideyuki; (Ibaraki-shi, JP) ;
Konishi; Takahisa; (Ibaraki-shi, JP) ; Yoshida;
Takemichi; (Ibaraki-shi, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW, SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
NITTO DENKO CORPORATION
Osaka
JP
|
Family ID: |
33307961 |
Appl. No.: |
12/634258 |
Filed: |
December 9, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10553958 |
Oct 19, 2005 |
7651643 |
|
|
PCT/JP2004/005548 |
Apr 19, 2004 |
|
|
|
12634258 |
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Current U.S.
Class: |
359/487.01 |
Current CPC
Class: |
G02B 5/3033
20130101 |
Class at
Publication: |
359/491 |
International
Class: |
G02B 5/30 20060101
G02B005/30; G02B 1/08 20060101 G02B001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 21, 2003 |
JP |
2003-115650 |
Claims
1. A polarizer, comprising a polyvinyl alcohol-based film which is
at least dyed with at least iodine and uniaxially stretched, having
a single transmittance of 43% or more, a polarizing efficiency of
99.9% or more, and a dichroic ratio of 30 or more, wherein the
dichroic ratio is calculated from a parallel transmittance (Tp) and
a crossed transmittance (Tc) at a wavelength of 440 nm according to
the following formula: dichroic
ratio={log.sub.10(1/k.sub.2)}/{log.sub.10(1/k.sub.1)}, where
k.sub.1=1/2 {square root over (
)}2.times.[(Tp+Tc).sup.1/2+(Tp-Tc).sup.1/2] and k.sub.2=1/2 {square
root over ( )}2.times.[(Tp+Tc).sup.1/2-(Tp-Tc).sup.1/2] and a
potassium content is of 0.2 to 0.6% by weight.
2. The polarizer according to claim 1, wherein an iodine content is
of 1.5 to 2.5% by weight.
3. A polarizing plate, comprising the polarizer according to claim
1 and a transparent protective film provided on at least one side
of the polarizer.
4. The polarizing plate according to claim 3, wherein a single
transmittance is of 43% or more, a polarizing efficiency is of
99.9% or more, and a dichroic ratio is of 30 or more, wherein the
dichroic ratio is calculated from a parallel transmittance (Tp) and
a crossed transmittance (Tc) at a wavelength of 440 nm according to
the following formula: dichroic
ratio={log.sub.10(1/k.sub.2)}/{log.sub.10(1/k.sub.1)}, where
k.sub.1=1/2 {square root over (
)}2.times.[(Tp+Tc).sup.1/2+(Tp-Tc).sup.1/2] and k.sub.2=1/2 {square
root over ( )}2.times.[(Tp+Tc).sup.1/2-(Tp-Tc).sup.1/2].
5. An optical film, comprising the polarizer according to claim 1
and at least one other optical layer laminated with the polarizer
or the polarizing plate.
6. An image display, comprising at least one piece of the polarizer
according to claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. Ser.
No. 10/553,958, filed Oct. 19, 2005, which is a National Phase
filing of PCT/JP2004/005548, filed on Apr. 19, 2004, which is based
on and claims the benefit of priority from Japanese Patent
Application No. 2003-115650, filed Apr. 21, 2003, the entire
contents of which being incorporated herein by reference.
TECHNICAL FIELD
[0002] The invention relates to a polarizer and a method of
manufacturing the same. The invention also relates to a polarizing
plate using the polarizer and to an optical film using the
polarizing plate or the like. The invention further relates to an
image display such as a liquid crystal display, an organic
electro-luminescent (EL) display and a Plasma Display Panel (PDP)
using the polarizing plate, the optical film, or the like.
BACKGROUND ART
[0003] Conventionally, image displays such as liquid crystal
displays use polarizing plates comprising a laminate of a polarizer
and a protective film such as a triacetyl cellulose film. The
polarizer is produced by dyeing a polyvinyl alcohol-based film with
a dichroic dye such as iodine and then stretching it in an aqueous
boric acid solution. The hue of the polarizing plate significantly
influences the due of liquid crystal displays.
[0004] Conventional polarizing plates, however, have low
transmittance at wavelengths from 400 nm to 500 nm with respect to
the transmission spectrum in the parallel Nicol configuration and
thus show a yellow hue in the parallel Nicol configuration. On the
other hand, high transmittance is performed at wavelengths from 400
nm to 500 nm with respect to the transmission spectrum in the
crossed Nicol configuration and thus shows a blue hue in the
crossed Nicol configuration. Thus, there has been a problem that
conventional liquid crystal displays using such polarizing plates
can become slightly yellow when white viewing and can become blue
when black viewing.
[0005] As a method of producing neutral gray display when white
viewing or black viewing, a method is disclosed including treating
an iodine-dyed, uniaxially-stretched, polyvinyl alcohol-based film
in an aqueous boric acid solution containing a specific amount of
potassium iodide and controlling the treatment temperature in each
step (for example, Japanese Patent Application Laid-Open (JP-A) No.
2002-169024). According to the method as disclosed in the
publication, however, the resulting hue is not sufficiently good in
each of the parallel and crossed Nicol configurations.
[0006] There has also been a problem that iodine-type polarizers do
not have sufficient durability and two pieces of such polarizers in
the crossed Nicol configuration can cause polarization dropout at
long wavelengths and can be discolored red when placed in a heated
environment. About this problem, a polarizer containing an
appropriate amount of zinc ions is proposed (for example, Japanese
Patent Nos. 1308919 and 1606999 and JP-A No. 2002-35512). These
patent literatures disclose that long wavelength polarization
dropout can be prevented when polarizers are allowed to stand under
high temperature conditions. According to these patent literatures,
however, it is needed to make polarizers contain zinc ions, and
thus there are problems about the zinc precipitate on the surface
of polarizers, the complicated control of concentration, and skin
irritation.
DISCLOSURE OF INVENTION
[0007] It is an object of the invention to provide a polarizer
having good hue. It is another object of the invention to provide a
polarizer having good hue and good durability.
[0008] It is also another object of the invention to provide a
method of manufacturing a polarizer having good hue. It is still
another object of the invention to provide a method of
manufacturing a polarizer having good hue and good durability.
[0009] It is a further object of the invention to provide a
polarizing plate using such a polarizer. It is a further object of
the invention to provide an optical film using such a polarizer or
polarizing plate and to provide an image display using such a
polarizer, polarizing plate or optical film.
[0010] In order to solve the above problems, the inventors have
made active investigations and have finally found that the
polarizer and the method of manufacturing a polarizer as described
below can fulfill the above objects, thereby completing the
invention.
[0011] That is, the invention is directed to a polarizer:
comprising a polyvinyl alcohol-based film which is at least dyed
with at least iodine and uniaxially stretched,
[0012] having a single transmittance of 43% or more, a polarizing
efficiency of 99.9% or more, and
[0013] a dichroic ratio of 30 or more, wherein the dichroic ratio
is calculated from a parallel transmittance (Tp) and a crossed
transmittance (Tc) at a wavelength of 440 nm according to the
following formula:
dichroic ratio={log.sub.10(1/k2)}/{log.sub.10(1/k1)}, where
k1=1/2 {square root over ( )}2.times.[(Tp+Tc)1/2+(Tp-Tc)1/2]
and
k2=1/2 {square root over ( )}2.times.[(Tp+Tc)1/2-(Tp-Tc)1/2].
[0014] In iodine-dyed and uniaxially-stretched polyvinyl
alcohol-based films (polarizers), the adsorbed iodine forms
polyiodine complexes of I3- and I5-. I3- has a broad absorption
peak at about 470 nm, and I5- has a broad absorption peak in the
wavelength range from 600 to 700 nm. In conventional polarizers,
however, the alignment of I3- is poor at short wavelengths from 400
nm to 500 nm, and thus conventional polarizers have low dichroic
ratios in the wavelength range from 400 nm to 500 nm. Therefore,
conventional polarizers have low transmittance and show a yellow
color at wavelengths from 400 nm to 500 nm with respect to the
transmission spectrum in the parallel Nicol configuration and have
high transmittance and show a blue color at wavelengths from 400 nm
to 500 nm with respect to the transmission spectrum in the crossed
Nicol configuration.
[0015] The low dichroic ratio of the polarizer is attributable to
the poor alignment of I3-. Thus, if the alignment of I3- is
improved and the dichroic ratio is increased, the polarizer can
have improved its hue. Since cold-cathode fluorescent tubes
especially for use in liquid crystal displays have bright lines at
wavelengths of 440 nm, 550 nm and 610 nm, the short wavelength
properties of iodine-type polarizers, generally, are particularly
important at 440 nm.
[0016] It is conceived that if the dichroic ratio is 30 or more at
a wavelength of 440 nm, the above problem with hue can be solved.
Conventionally, however, polarizers are required to lower single
transmittance in order to have a dichroic ratio of 30 or more at a
wavelength of 440 nm. Such a lowered single transmittance is not
preferred in terms of optical properties. The single transmittance
is preferable 43% or more in terms of optical properties.
Conventionally, it has been impossible to coexistence the dichroic
ratio at a wavelength of 440 nm to 30 or more and the simple
transmittance of 43% or more.
[0017] The polarizer of the invention has good alignment of I3-, a
single transmittance of 43% or more, a polarizing efficiency of
99.9% or more, and a dichroic ratio of 30 or more at a wavelength
of 440 nm. The polarizer of the invention has good optical
properties and improved hue neutral in both parallel and crossed
Nicol configurations. The single transmittance is 43% or more,
preferably 43.5% or more. The polarizing efficiency is 99.9% or
more, preferably 99.92% or more. The dichroic ratio at a wavelength
of 440 nm is 30 or more, preferably 34 or more. Conventionally, it
has been difficult to obtain a dichroic ratio of 30 or more at a
wavelength of 440 nm, because it has been difficult to improve the
alignment of I3-.
[0018] The polarizer preferably has an iodine content of 1.5 to
2.5% by weight and a potassium content of 0.2 to 0.6% by
weight.
[0019] Polarizers are discolored red when kept at high
temperatures. It is conceived that I5- having absorption at long
wavelengths is decomposed or lowered in alignment.
[0020] Polarizers are produced by stretching iodine-dyed polyvinyl
alcohol-based films in an aqueous solution containing, for example,
boric acid and potassium iodide. In this process, the transmittance
is determined by the stretch ratio, the iodine concentration or the
like, while the polarizing efficiency varies with the concentration
of potassium iodide. That is, it is conceived that the polarizing
efficiency increase with the amount of potassium iodide in a
polarizer, but if the amount of potassium iodide is increased too
much, the polarizer is discolored red when kept at high
temperatures.
[0021] In this point of view, the content of iodine in the
polarizer is preferably from 1.5 to 2.5% by weight, more preferably
from 1.7 to 2.4% by weight, still more preferably from 2 to 2.3% by
weight. If the iodine content is too high, the polarizing plate has
insufficient durability and is easily discolored red at high
temperatures. If the iodine content is too low, the polarizing
efficiency is easily lowered. The content of potassium in the
polarizer is preferably from 0.2 to 0.6% by weight, more preferably
from 0.3 to 0.58% by weight, still more preferably from 0.4 to
0.57% by weight. If the potassium content is too high, the
polarizing plate has insufficient durability and is easily
discolored red at high temperatures. If the potassium content is
too low, the polarizing efficiency is easily lowered.
[0022] The invention is also directed to a method of manufacturing
a polarizer, comprising the steps of:
[0023] dyeing a polyvinyl alcohol-based film with iodine;
[0024] uniaxially stretching the iodine-dyed polyvinyl
alcohol-based film in an aqueous boric acid solution containing
potassium iodide at a concentration of 4% by weight or more;
and
[0025] subsequently washing the film with an aqueous solution
containing an iodide at a concentration of 0.8% by weight or
more.
[0026] In the method of manufacturing the polarizer, the aqueous
boric acid solution (a stretching bath) used in the uniaxially
stretching step preferably contains the iodide at a concentration
of 4 to 12% by weight.
[0027] In the method of manufacturing the polarizer, the aqueous
iodide solution (a washing bath) used in the washing step
preferably contains the iodide at a concentration of 0.8 to 2.5% by
weight.
[0028] Typically, polarizers are produced by dyeing a polyvinyl
alcohol-based film with iodine and uniaxially stretching. After the
polyvinyl alcohol-based film is dyed with iodine, I5-, which gives
a blue color, is generated with stretching the film or immersing
the film in an aqueous boric acid solution. On the other hand, when
the polarizer is immersed in an aqueous solution of an iodide such
as potassium iodide to be impregnated with iodine ions, I3- is
generated to give neutral hue. Since I3- is relatively poor in
alignment, in comparison with I5-, the dichroic ratios of
polarizers prepared by conventional manufacturing methods are
relatively low at short wavelengths and relatively high at long
wavelengths.
[0029] The method of manufacturing polarizer according to the
invention is based on the finding that the alignment of the
polyiodine complex is better in the case that the polyvinyl
alcohol-based film is aligned by stretching or the like after the
polyiodine complex is generated than in the case that the
polyiodine complex is generated after the polyvinyl alcohol-based
film is aligned by stretching or the like in the conventional
manner. Specifically, the polyvinyl alcohol-based film is stretched
after a large amount of I3- is generated in the aqueous boric acid
solution (the stretching bath) containing an iodide at a
concentration of 4% by weight or more, I3- having good alignments
is performed and high dichroic ratios is obtained at short
wavelengths from 400 nm to 500 nm. In addition, the film is washed
in the aqueous solution (the washing bath) of an iodide at a
concentration of 0.8% by weight or more so that excess I3- is
washed off and the film retain I3- in good alignments, and thus the
amounts of I3- and I5- is controlled. If the concentration of the
iodide in the stretching bath or the washing bath is too low, the
amount of I3- is too small, and thus the polarizing plate has a
blue hue. The concentration of the iodide in the stretching bath is
4% by weight or more, preferably 4.5% by weight or more, more
preferably 5% by weight or more. The concentration of the iodide in
the washing bath is 0.8% by weight or more, preferably 1.0% by
weight or more, more preferably 1.2% by weight or more.
[0030] On the other hand, if the concentration of the iodide in the
stretching bath or the washing bath is higher than a certain level,
it is difficult to obtain a further effect, and the polarizer has a
yellow hue and the hue in the crossed Nicol configuration tends to
be discolored red when kept in a high temperature atmosphere for a
long time. The concentration of the iodide in the stretching bath
is generally 15% by weight or less and preferably 12% by weight or
less, preferably 11% by weight or less, more preferably 10% by
weight or less, from the above point of view. The concentration of
the iodide in the washing bath is generally 6% by weight or less
and preferably 2.5% by weight or less, preferably 2.3% by weight or
less, more preferably 2% by weight or less.
[0031] The method of manufacturing polarizer comprises the step of
drying after the step of washing with the aqueous iodide solution.
The drying step is preferably performed at 70.degree. C. or less in
order to produce a highly durable polarizer.
[0032] In the method of manufacturing the polarizer, the iodide is
preferably potassium iodide. Examples of the iodide for use in the
stretching or washing bath include a variety of iodides such as
potassium iodide, sodium iodide, lithium iodide, zinc iodide,
calcium iodide, and cobalt iodide. In particular, potassium iodide
is preferred because it hardly precipitates on the surface of
films. When an iodide other than potassium iodide is used, the
amount of the iodide is preferably adjusted such that the
concentration of the iodine ions in the polyvinyl alcohol-based
film is equal to the corresponding concentration in the case of
potassium iodide, depending on the molecular weight and
dissociation constant of the iodide, and the degree of swelling of
the polyvinyl alcohol-based film or the like.
[0033] In the method of manufacturing the polarizer, the iodine
dyeing step may be performed together with the stretching step.
While the stretching may be performed in a pre-step before the step
in the aqueous boric acid solution (the stretching bath), the
stretching in the pre-step is preferably performed together with
the iodine dyeing step in terms of preventing wrinkling of the film
swelling in water.
[0034] The polarizer obtained by the above manufacturing method
preferably has a single transmittance of 43% or more, a polarizing
efficiency of 99.9% or more, and a dichroic ratio of 30 or more in
terms of good hue, wherein the dichroic ratio is calculated from a
parallel transmittance (Tp) and a crossed transmittance (Tc) at a
wavelength of 440 nm according to the following formula:
dichroic ratio={log.sub.10(1/k2)}/{log.sub.10(1/k1)}, where k1=1/2
{square root over ( )}2.times.[(Tp+Tc)1/2+(Tp-Tc)1/2] and
k2=1/2 {square root over ( )}2.times.[(Tp+Tc)1/2-(Tp-Tc) 1/2].
[0035] In terms of durability, the polarizer obtained by the above
manufacturing method preferably has an iodine content of 1.5 to
2.5% by weight and a potassium content of 0.2 to 0.6% by
weight.
[0036] The invention is also directed to a polarizer obtained by
the above manufacturing method.
[0037] The invention is also directed to a polarizing plate
comprising the above polarizer and a transparent protective film
provided on at least one side of the polarizer. The polarizing
plate preferably has the above characteristics (a single
transmittance of 43% or more, a polarizing efficiency of 99.9% or
more and a dichroic ratio of 30 or more at a wavelength of 440
nm).
[0038] The invention is also directed to an optical film comprising
the above polarizer or the above polarizing plate and at least one
other optical layer laminated with the polarizer or the polarizing
plate.
[0039] The invention is also directed to an image display
comprising at least one piece of the above polarizer, the above
polarizing plate or the above optical film.
BEST MODE FOR CARRYING OUT THE INVENTION
[0040] Polyvinyl alcohol or any derivative thereof may be used as a
material for the polyvinyl alcohol-based film suited for the
polarizer of the invention. Examples of the polyvinyl alcohol
derivative include polyvinyl formal, polyvinyl acetal, and those
modified with an olefin such as ethylene and propylene, an
unsaturated carboxylic acid such as acrylic acid, methacrylic acid
and crotonic acid, an alkyl ester thereof, acrylamide, or the like.
The polyvinyl alcohol having a degree of polymerization of from
about 1,000 to about 10,000 and a saponification degree of from
about 80 to about 100% by mole, is generally used.
[0041] The polyvinyl alcohol-based film may contain any additive
such as a plasticizer. Examples of the plasticizer include polyols
such as glycerol, diglycerol, triglycerol, ethylene glycol,
propylene glycol, and polyethylene glycol and condensation products
thereof. While the amount of the plasticizer is not to be limited,
the content of the plasticizer in the polyvinyl alcohol-based film
is preferably 20% by weight or less.
[0042] In general, an about 30 to 150 unstretched polyvinyl
alcohol-based film is used.
[0043] The polyvinyl alcohol-based film (unstretched film) is
subjected to a process including the steps of: dyeing the polyvinyl
alcohol-based film with iodine; uniaxially stretching the
iodine-dyed polyvinyl alcohol-based film in an aqueous boric acid
solution (a stretching bath) containing an iodide at a
concentration of 4% by weight or more; and then washing the film
with an aqueous solution (a washing bath) of an iodide at a
concentration of 0.8% by weight or more.
[0044] The iodine dyeing process is generally performed by
immersing the polyvinyl alcohol-based film in an iodine solution.
If an aqueous iodine solution is used as the iodine solution, the
aqueous iodine solution contains iodine and iodine ions derived
from an iodide such as potassium iodide serving as a dissolution
aid. The iodine concentration is preferably from about 0.01 to
about 0.5% by weight, more preferably from 0.02 to 0.4% by weight,
still more preferably from 0.2 to 0.38% by weight, further more
preferably from 0.2 to 0.35% by weight. The iodide (such as
potassium iodide) concentration is preferably from about 0.01 to
about 10% by weight, more preferably from 0.02 to 8% by weight.
[0045] In the iodine dyeing process, a temperature of the iodine
solution is generally of about 20 to 50.degree. C., preferably of
25 to 40.degree. C. The immersion time period is generally from
about 10 to about 300 seconds, preferably from 20 to 240
seconds.
[0046] Before the iodine dyeing process, the polyvinyl
alcohol-based film may be immersed in water for water-washing. If
the polyvinyl alcohol-based film is washed with water, surface
stain or antiblocking agents can be washed off from the polyvinyl
alcohol-based film. In addition, the polyvinyl alcohol-based film
may be allowed to swell so that unevenness such as uneven dyeing
can be effectively prevented.
[0047] The iodine-dyed polyvinyl alcohol-based film is then
uniaxially stretched of an aqueous boric acid solution (a
stretching bath) containing an iodide. As described above, an
iodide concentration of the stretching bath is of 4% by weight or
more, preferably of 4 to 12% by weight, more preferably of 4.5 to
11% by weight, still more preferably of 5 to 10% by weight.
[0048] A boric acid concentration of the stretching bath is
generally of 2 to 8% by weight, preferably of 2.5 to 7% by weight,
more preferably of 3 to 6% by weight. If the boric acid
concentration is too low, the polarizing efficiency tends to be
degraded. If the boric acid concentration is too high, stretching
hardly to perform.
[0049] In the uniaxial stretching process, the iodine-dyed
polyvinyl alcohol-based film is immersed in the stretching bath.
The stretch ratio is generally from about 4 to about 7, preferably
from 5 to 6.8, more preferably from 5.5 to 6.5. The stretched film
preferably has a thickness of about 5 to about 80 .mu.m.
[0050] The stretching in the stretching bath may be performed in a
multistage manner. Stretching may also be performed before the
stretching in the stretching bath. If stretching is performed
before the stretching in the stretching bath, the stretching in the
stretching bath should be controlled such that the total stretch
ratio with respect to the unstretched film is 4 to 7 after the
stretching in the stretching bath. A stretch ratio in the
pre-stretching before the stretching in the stretching bath is of 4
or less, specifically of 2.8 to 3.8. The pre-stretching before the
stretching in the stretching bath is preferably performed together
with the iodine dyeing step.
[0051] A temperature of the aqueous boric acid solution (the
stretching bath) is not to be limited, for example, of 30.degree.
C. or higher, preferably of 40 to 85.degree. C. The immersion time
period is generally from 10 to 1,200 seconds, preferably from 30 to
600 seconds.
[0052] The film is then subjected to the step of washing with the
aqueous iodide solution. The aqueous iodide solution (the washing
bath) has an iodide concentration of 0.8% by weight or more, as
described above, preferably of 0.8 to 2.5% by weight, more
preferably of 0.8 to 2.3% by weight, still more preferably of 0.8
to 2.1% by weight. The temperature of the aqueous iodide solution
(the washing bath) is generally from about 15 to about 60.degree.
C., preferably from 25 to 40.degree. C. The immersion time period
is generally from about 1 to about 120 seconds, preferably from 3
to 90 seconds.
[0053] The film may be then subjected to the drying step. The
drying step is preferably performed at 70.degree. C. or lower, more
preferably at 60.degree. C. or lower, more preferably at 45.degree.
C. or lower. The drying time period is preferably 10 minutes or
less, more preferably 5 minutes or less.
[0054] The above-described polarizer may be used as a polarizing
plate with a transparent protective film prepared at least on one
side thereof using a usual method. The transparent protective film
may be prepared as an application layer by polymers, or a laminated
layer of films. Proper transparent materials may be used as a
transparent polymer or a film material that forms the transparent
protective film, and the material having outstanding transparency,
mechanical strength, heat stability and outstanding moisture
interception property, etc. may be preferably used. As materials of
the above-mentioned protective film, for example, polyester type
polymers, such as polyethylene terephthalate and
polyethylenenaphthalate; cellulose type polymers, such as diacetyl
cellulose and triacetyl cellulose; acrylics type polymer, such as
poly methylmethacrylate; styrene type polymers, such as polystyrene
and acrylonitrile-styrene copolymer (AS resin); polycarbonate type
polymer may be mentioned. Besides, as examples of the polymer
forming a protective film, polyolefin type polymers, such as
polyethylene, polypropylene, polyolefin that has cyclo- type or
norbornene structure, ethylene-propylene copolymer; vinyl chloride
type polymer; amide type polymers, such as nylon and aromatic
polyamide; imide type polymers; sulfone type polymers; polyether
sulfone type polymers; polyether-ether ketone type polymers; poly
phenylene sulfide type polymers; vinyl alcohol type polymer;
vinylidene chloride type polymers; vinyl butyral type polymers;
arylate type polymers; polyoxymethylene type polymers; epoxy type
polymers; or blend polymers of the above-mentioned polymers may be
mentioned. Films made of heat curing type or ultraviolet ray curing
type resins, such as acryl based, urethane based, acryl urethane
based, epoxy based, and silicone based, etc. may be mentioned. The
transparent protective film may also be in the form of a cured
layer of thermosetting resins or ultraviolet curing resins, such as
acrylic resins, urethane resins, acrylic urethane resins, epoxy
resins, and silicone resins.
[0055] Moreover, as is described in Japanese Patent Laid-Open
Publication No. 2001-343529 (WO 01/37007), polymer films, for
example, resin compositions including (A) thermoplastic resins
having substituted and/or non-substituted imido group is in side
chain, and (B) thermoplastic resins having substituted and/or
non-substituted phenyl and nitrile group in sidechain may be
mentioned. As an illustrative example, a film may be mentioned that
is made of a resin composition including alternating copolymer
comprising iso-butylene and N-methyl maleimide, and
acrylonitrile-styrene copolymer. A film comprising mixture extruded
article of resin compositions etc. may be used. These films have
small retardation and small photoelastic coefficient, and thus
prevent defects such as unevenness which would otherwise be caused
by distortion of the polarizing plate, and also have small water
vapor permeability, and thus have good durability under moistening
conditions.
[0056] While the thickness of the protective film may be specified
as needed, generally, is from about 1 to about 500 .mu.m in terms
of strength, processability such as handleability, and thin layer
formability, preferably from 1 to 300 .mu.m, more preferably from 5
to 200 .mu.m.
[0057] Moreover, it is preferable that the protective film may have
as little coloring as possible. Accordingly, a protective film
having a retardation value in a film thickness direction
represented by Rth=[(nx+ny)/2-nz].times.d of -90 nm through +75 nm
(where, nx and ny represent principal indices of refraction in a
film plane, nz represents refractive index in a film thickness
direction, and d represents a film thickness) may be preferably
used. Thus, coloring (optical coloring) of polarizing plate
resulting from a protective film may mostly be cancelled using a
protective film having a retardation value (Rth) of -90 nm through
+75 nm in a thickness direction. The retardation value (Rth) in a
thickness direction is preferably -80 nm through +60 nm, and
especially preferably -70 nm through +45 nm.
[0058] As a transparent protective film, if polarization property
and durability are taken into consideration, cellulose based
polymer, such as triacetyl cellulose, is preferable, and especially
triacetyl cellulose film is suitable. In addition, when transparent
protective films are provided on both sides of the polarizer,
transparent protective films comprising same polymer material may
be used on both of a front side and a back side, and transparent
protective films comprising different polymer materials etc. may be
used.
[0059] A hard coat layer may be prepared, or antireflection
processing, processing aiming at sticking prevention, diffusion or
anti glare may be performed onto the face on which the polarizing
film of the above described transparent protective film has not
been adhered.
[0060] A hard coat processing is applied for the purpose of
protecting the surface of the polarizing plate from damage, and
this hard coat film may be formed by a method in which, for
example, a curable coated film with excellent hardness, slide
property etc. is added on the surface of the protective film using
suitable ultraviolet curable type resins, such as acrylic type and
silicone type resins. Antireflection processing is applied for the
purpose of antireflection of outdoor daylight on the surface of a
polarizing plate and it may be prepared by forming an
antireflection film according to the conventional method etc.
Besides, a sticking prevention processing is applied for the
purpose of adherence prevention with adjoining layer.
[0061] In addition, an anti glare processing is applied in order to
prevent a disadvantage that outdoor daylight reflects on the
surface of a polarizing plate to disturb visual recognition of
transmitting light through the polarizing plate, and the processing
may be applied, for example, by giving a fine concavo-convex
structure to a surface of the protective film using, for example, a
suitable method, such as rough surfacing treatment method by
sandblasting or embossing and a method of combining transparent
fine particle. As a fine particle combined in order to form a fine
concavo-convex structure on the above-mentioned surface,
transparent fine particles whose average particle size is 0.5 to 50
.mu.m, for example, such as inorganic type fine particles that may
have conductivity comprising silica, alumina, titania, zirconia,
tin oxides, indium oxides, cadmium oxides, antimony oxides, etc.,
and organic type fine particles comprising cross-linked of
non-cross-linked polymers may be used. When forming fine
concavo-convex structure on the surface, the amount of fine
particle used is usually about 2 to 50 weight parts to the
transparent resin 100 weight part that forms the fine
concavo-convex structure on the surface, and preferably 5 to 25
weight parts. An anti glare layer may serve as a diffusion layer
(viewing angle expanding function etc.) for diffusing transmitting
light through the polarizing plate and expanding a viewing angle
etc.
[0062] In addition, the above-mentioned antireflection layer,
sticking prevention layer, diffusion layer, anti glare layer, etc.
may be built in the protective film itself, and also they may be
prepared as an optical layer different from the protective
film.
[0063] Adhesives are used for adhesion processing of the above
described polarizing film and the transparent protective film. As
adhesives, isocyanate derived adhesives, polyvinyl alcohol derived
adhesives, gelatin derived adhesives, vinyl polymers derived latex
type, aqueous polyesters derived adhesives, etc. may be mentioned.
The above-described adhesives are usually used as adhesives
comprising aqueous solution.
[0064] A polarizing plate of the present invention is manufactured
by adhering the above described transparent protective film and the
polarizing film using the above described adhesives. The
application of adhesives may be performed to any of the transparent
protective film or the polarizing film, and may be performed to
both of them. After adhered, drying process is given and the
adhesion layer comprising applied dry layer is formed. Adhering
process of the polarizing film and the transparent protective film
may be performed using a roll laminator etc. Although a thickness
of the adhesion layer is not especially limited, it is usually
approximately 0.1 to 5 p.m.
[0065] A polarizing plate of the present invention may be used in
practical use as an optical film laminated with other optical
layers. Although there is especially no limitation about the
optical layers, one layer or two layers or more of optical layers,
which may be used for formation of a liquid crystal display etc.,
such as a reflector, a transflective plate, a retardation plate (a
half wavelength plate and a quarter wavelength plate included), and
a viewing angle compensation film, may be used. Especially
preferable polarizing plates are; a reflection type polarizing
plate or a transflective type polarizing plate in which a reflector
or a transflective reflector is further laminated onto a polarizing
plate of the present invention; an elliptically polarizing plate or
a circular polarizing plate in which a retardation plate is further
laminated onto the polarizing plate; a wide viewing angle
polarizing plate in which a viewing angle compensation film is
further laminated onto the polarizing plate; or a polarizing plate
in which a brightness enhancement film is further laminated onto
the polarizing plate.
[0066] A reflective layer is prepared on a polarizing plate to give
a reflection type polarizing plate, and this type of plate is used
for a liquid crystal display in which an incident light from a view
side (display side) is reflected to give a display. This type of
plate does not require built-in light sources, such as a backlight,
but has an advantage that a liquid crystal display may easily be
made thinner. A reflection type polarizing plate may be formed
using suitable methods, such as a method in which a reflective
layer of metal etc. is, if required, attached to one side of a
polarizing plate through a transparent protective film etc.
[0067] As an example of a reflection type polarizing plate, a plate
may be mentioned on which, if required, a reflective layer is
formed using a method of attaching a foil and vapor deposition film
of reflective metals, such as aluminum, to one side of a matte
treated protective film. Moreover, a different type of plate with a
fine concavo-convex structure on the surface obtained by mixing
fine particle into the above-mentioned protective film, on which a
reflective layer of concavo-convex structure is prepared, may be
mentioned. The reflective layer that has the above-mentioned fine
concavo-convex structure diffuses incident light by random
reflection to prevent directivity and glaring appearance, and has
an advantage of controlling unevenness of light and darkness etc.
Moreover, the protective film containing the fine particle has an
advantage that unevenness of light and darkness may be controlled
more effectively, as a result that an incident light and its
reflected light that is transmitted through the film are diffused.
A reflective layer with fine concavo-convex structure on the
surface effected by a surface fine concavo-convex structure of a
protective film may be formed by a method of attaching a metal to
the surface of a transparent protective film directly using, for
example, suitable methods of a vacuum evaporation method, such as a
vacuum deposition method, an ion plating method, and a sputtering
method, and a plating method etc.
[0068] Instead of a method in which a reflection plate is directly
given to the protective film of the above-mentioned polarizing
plate, a reflection plate may also be used as a reflective sheet
constituted by preparing a reflective layer on the suitable film
for the transparent film. In addition, since a reflective layer is
usually made of metal, it is desirable that the reflective side is
covered with a protective film or a polarizing plate etc. when
used, from a viewpoint of preventing deterioration in reflectance
by oxidation, of maintaining an initial reflectance for a long
period of time and of avoiding preparation of a protective film
separately etc.
[0069] In addition, a transflective type polarizing plate may be
obtained by preparing the above-mentioned reflective layer as a
transflective type reflective layer, such as a half-mirror etc.
that reflects and transmits light. A transflective type polarizing
plate is usually prepared in the backside of a liquid crystal cell
and it may form a liquid crystal display unit of a type in which a
picture is displayed by an incident light reflected from a view
side (display side) when used in a comparatively well-lighted
atmosphere. And this unit displays a picture, in a comparatively
dark atmosphere, using embedded type light sources, such as a back
light built in backside of a transflective type polarizing plate.
That is, the transflective type polarizing plate is useful to
obtain of a liquid crystal display of the type that saves energy of
light sources, such as a back light, in a well-lighted atmosphere,
and can be used with a built-in light source if needed in a
comparatively dark atmosphere etc.
[0070] The above-mentioned polarizing plate may be used as
elliptically polarizing plate or circularly polarizing plate on
which the retardation plate is laminated. A description of the
above-mentioned elliptically polarizing plate or circularly
polarizing plate will be made in the following paragraph. These
polarizing plates change linearly polarized light into elliptically
polarized light or circularly polarized light, elliptically
polarized light or circularly polarized light into linearly
polarized light or change the polarization direction of linearly
polarization by a function of the retardation plate. As a
retardation plate that changes circularly polarized light into
linearly polarized light or linearly polarized light into
circularly polarized light, what is called a quarter wavelength
plate (also called 214 plate) is used. Usually, half-wavelength
plate (also called .lamda./2 plate) is used, when changing the
polarization direction of linearly polarized light.
[0071] Elliptically polarizing plate is effectively used to give a
monochrome display without above-mentioned coloring by compensating
(preventing) coloring (blue or yellow color) produced by
birefringence of a liquid crystal layer of a super twisted nematic
(STN) type liquid crystal display. Furthermore, a polarizing plate
in which three-dimensional refractive index is controlled may also
preferably compensate (prevent) coloring produced when a screen of
a liquid crystal display is viewed from an oblique direction.
Circularly polarizing plate is effectively used, for example, when
adjusting a color tone of a picture of a reflection type liquid
crystal display that provides a colored picture, and it also has
function of antireflection. For example, a retardation plate may be
used that compensates coloring and viewing angle, etc. caused by
birefringence of various wavelength plates or liquid crystal layers
etc. Besides, optical characteristics, such as retardation, may be
controlled using laminated layer with two or more sorts of
retardation plates having suitable retardation value according to
each purpose. As retardation plates, birefringence films formed by
stretching films comprising suitable polymers, such as
polycarbonates, norbornene type resins, polyvinyl alcohols,
polystyrenes, poly methyl methacrylates, polypropylene;
polyallylates and polyamides; oriented films comprising liquid
crystalline materials, such as liquid crystal polymer; and films on
which an alignment layer of a liquid crystalline material is
supported may be mentioned. A retardation plate may be a
retardation plate that has a proper retardation according to the
purposes of use, such as various kinds of wavelength plates and
plates aiming at compensation of coloring by birefringence of a
liquid crystal layer and of visual angle, etc., and may be a
retardation plate in which two or more sorts of retardation plates
is laminated so that optical properties, such as retardation, may
be controlled.
[0072] The above-mentioned elliptically polarizing plate and an
above-mentioned reflected type elliptically polarizing plate are
laminated plate combining suitably a polarizing plate or a
reflection type polarizing plate with a retardation plate. This
type of elliptically polarizing plate etc. may be manufactured by
combining a polarizing plate (reflected type) and a retardation
plate, and by laminating them one by one separately in the
manufacture process of a liquid crystal display. On the other hand,
the polarizing plate in which lamination was beforehand carried out
and was obtained as an optical film, such as an elliptically
polarizing plate, is excellent in a stable quality, a workability
in lamination etc., and has an advantage in improved manufacturing
efficiency of a liquid crystal display.
[0073] A viewing angle compensation film is a film for extending
viewing angle so that a picture may look comparatively clearly,
even when it is viewed from an oblique direction not from vertical
direction to a screen. As such a viewing angle compensation
retardation plate, in addition, a film having birefringence
property that is processed by uniaxial stretching or orthogonal
biaxial stretching and a biaxially stretched film as inclined
orientation film etc. may be used. As inclined orientation film,
for example, a film obtained using a method in which a heat
shrinking film is adhered to a polymer film, and then the combined
film is heated and stretched or shrunk under a condition of being
influenced by a shrinking force, or a film that is oriented in
oblique direction may be mentioned. The viewing angle compensation
film is suitably combined for the purpose of prevention of coloring
caused by change of visible angle based on retardation by liquid
crystal cell etc. and of expansion of viewing angle with good
visibility.
[0074] Besides, a compensation plate in which an optical anisotropy
layer consisting of an alignment layer of liquid crystal polymer,
especially consisting of an inclined alignment layer of discotic
liquid crystal polymer is supported with triacetyl cellulose film
may preferably be used from a viewpoint of attaining a wide viewing
angle with good visibility.
[0075] The polarizing plate with which a polarizing plate and a
brightness enhancement film are adhered together is usually used
being prepared in a backside of a liquid crystal cell. A brightness
enhancement film shows a characteristic that reflects linearly
polarized light with a predetermined polarization axis, or
circularly polarized light with a predetermined direction, and that
transmits other light, when natural light by back lights of a
liquid crystal display or by reflection from a back-side etc.,
comes in. The polarizing plate, which is obtained by laminating a
brightness enhancement film to a polarizing plate, thus does not
transmit light without the predetermined polarization state and
reflects it, while obtaining transmitted light with the
predetermined polarization state by accepting a light from light
sources, such as a backlight. This polarizing plate makes the light
reflected by the brightness enhancement film further reversed
through the reflective layer prepared in the backside and forces
the light re-enter into the brightness enhancement film, and
increases the quantity of the transmitted light through the
brightness enhancement film by transmitting a part or all of the
light as light with the predetermined polarization state. The
polarizing plate simultaneously supplies polarized light that is
difficult to be absorbed in a polarizer, and increases the quantity
of the light usable for a liquid crystal picture display etc., and
as a result luminosity may be improved. That is, in the case where
the light enters through a polarizer from backside of a liquid
crystal cell by the back light etc. without using a brightness
enhancement film, most of the light, with a polarization direction
different from the polarization axis of a polarizer, is absorbed by
the polarizer, and does not transmit through the polarizer. This
means that although influenced with the characteristics of the
polarizer used, about 50 percent of light is absorbed by the
polarizer, the quantity of the light usable for a liquid crystal
picture display etc. decreases so much, and a resulting picture
displayed becomes dark. A brightness enhancement film does not
enter the light with the polarizing direction absorbed by the
polarizer into the polarizer but reflects the light once by the
brightness enhancement film, and further makes the light reversed
through the reflective layer etc. prepared in the backside to
re-enter the light into the brightness enhancement film. By this
above-mentioned repeated operation, only when the polarization
direction of the light reflected and reversed between the both
becomes to have the polarization direction which may pass a
polarizer, the brightness enhancement film transmits the light to
supply it to the polarizer. As a result, the light from a backlight
may be efficiently used for the display of the picture of a liquid
crystal display to obtain a bright screen.
[0076] A diffusion plate may also be prepared between brightness
enhancement film and the above described reflective layer, etc. A
polarized light reflected by the brightness enhancement film goes
to the above described reflective layer etc., and the diffusion
plate installed diffuses passing light uniformly and changes the
light state into depolarization at the same time. That is, the
diffusion plate returns polarized light to natural light state.
Steps are repeated where light, in the unpolarized state, i.e.,
natural light state, reflects through reflective layer and the
like, and again goes into brightness enhancement film through
diffusion plate toward reflective layer and the like. Diffusion
plate that returns polarized light to the natural light state is
installed between brightness enhancement film and the above
described reflective layer, and the like, in this way, and thus a
uniform and bright screen may be provided while maintaining
brightness of display screen, and simultaneously controlling
non-uniformity of brightness of the display screen. By preparing
such diffusion plate, it is considered that number of repetition
times of reflection of a first incident light increases with
sufficient degree to provide uniform and bright display screen
conjointly with diffusion function of the diffusion plate.
[0077] The suitable films are used as the above-mentioned
brightness enhancement film. Namely, multilayer thin film of a
dielectric substance; a laminated film that has the characteristics
of transmitting a linearly polarized light with a predetermined
polarizing axis, and of reflecting other light, such as the
multilayer laminated film of the thin film having a different
refractive-index anisotropy (D-BEF and others manufactured by 3M
Co., Ltd.); an oriented film of cholesteric liquid-crystal polymer;
a film that has the characteristics of reflecting a circularly
polarized light with either left-handed or right-handed rotation
and transmitting other light, such as a film on which the oriented
cholesteric liquid crystal layer is supported (PCF350 manufactured
by Nitto Denko Corporation, TRANSMAX manufactured by Merck Co.,
Ltd., and others); etc. may be mentioned.
[0078] Therefore, in the brightness enhancement film of a type that
transmits a linearly polarized light having the above-mentioned
predetermined polarization axis, by arranging the polarization axis
of the transmitted light and entering the light into a polarizing
plate as it is, the absorption loss by the polarizing plate is
controlled and the polarized light can be transmitted efficiently.
On the other hand, in the brightness enhancement film of a type
that transmits a circularly polarized light as a cholesteric
liquid-crystal layer, the light may be entered into a polarizer as
it is, but it is desirable to enter the light into a polarizer
after changing the circularly polarized light to a linearly
polarized light through a retardation plate, taking control an
absorption loss into consideration. In addition, a circularly
polarized light is convertible into a linearly polarized light
using a quarter wavelength plate as the retardation plate.
[0079] A retardation plate that works as a quarter wavelength plate
in a wide wavelength ranges, such as a visible-light band, is
obtained by a method in which a retardation layer working as a
quarter wavelength plate to a pale color light with a wavelength of
550 nm is laminated with a retardation layer having other
retardation characteristics, such as a retardation layer working as
a half-wavelength plate. Therefore, the retardation plate located
between a polarizing plate and a brightness enhancement film may
consist of one or more retardation layers.
[0080] In addition, also in a cholesteric liquid-crystal layer, a
layer reflecting a circularly polarized light in a wide wavelength
ranges, such as a visible-light band, may be obtained by adopting a
configuration structure in which two or more layers with different
reflective wavelength are laminated together. Thus a transmitted
circularly polarized light in a wide wavelength range may be
obtained using this type of cholesteric liquid-crystal layer.
[0081] Moreover, the polarizing plate may consist of multi-layered
film of laminated layers of a polarizing plate and two of more of
optical layers as the above-mentioned separated type polarizing
plate. Therefore, a polarizing plate may be a reflection type
elliptically polarizing plate or a semi-transmission type
elliptically polarizing plate, etc. in which the above-mentioned
reflection type polarizing plate or a transflective type polarizing
plate is combined with above described retardation plate
respectively.
[0082] Although an optical film with the above described optical
layer laminated to the polarizing plate may be formed by a method
in which laminating is separately carried out sequentially in
manufacturing process of a liquid crystal display etc., an optical
film in a form of being laminated beforehand has an outstanding
advantage that it has excellent stability in quality and assembly
workability, etc., and thus manufacturing processes ability of a
liquid crystal display etc. may be raised. Proper adhesion means,
such as a pressure sensitive adhesive layer, may be used for
laminating. On the occasion of adhesion of the above described
polarizing plate and other optical films, the optical axis may be
set as a suitable configuration angle according to the target
retardation characteristics etc.
[0083] In the polarizing plate mentioned above and the optical film
in which at least one layer of the polarizing plate is laminated, a
pressure sensitive adhesive layer may also be prepared for adhesion
with other members, such as a liquid crystal cell etc. As pressure
sensitive adhesive that forms pressure sensitive adhesive layer is
not especially limited, and, for example, acrylic type polymers;
silicone type polymers; polyesters, polyurethanes, polyamides,
polyethers; fluorine type and rubber type polymers may be suitably
selected as a base polymer. Especially, a pressure sensitive
adhesive such as acrylics type pressure sensitive adhesives may be
preferably used, which is excellent in optical transparency,
showing adhesion characteristics with moderate wettability,
cohesiveness and adhesive property and has outstanding weather
resistance, heat resistance, etc.
[0084] Moreover, a pressure sensitive adhesive layer with low
moisture absorption and excellent heat resistance is desirable.
This is because those characteristics are required in order to
prevent foaming and peeling-off phenomena by moisture absorption,
in order to prevent decrease in optical characteristics and
curvature of a liquid crystal cell caused by thermal expansion
difference etc. and in order to manufacture a liquid crystal
display excellent in durability with high quality.
[0085] The pressure sensitive adhesive layer may contain additives,
for example, such as natural or synthetic resins, adhesive resins,
glass fibers, glass beads, metal powder, fillers comprising other
inorganic powder etc., pigments, colorants and antioxidants.
Moreover, it may be a pressure sensitive adhesive layer that
contains fine particle and shows optical diffusion nature.
[0086] Proper method may be carried out to attach a pressure
sensitive adhesive layer to one side or both sides of the optical
film. As an example, about 10 to 40 weight % of the pressure
sensitive adhesive solution in which a base polymer or its
composition is dissolved or dispersed, for example, toluene or
ethyl acetate or a mixed solvent of these two solvents is prepared.
A method in which this solution is directly applied on a polarizing
plate top or an optical film top using suitable developing methods,
such as flow method and coating method, or a method in which a
pressure sensitive adhesive layer is once formed on a separator, as
mentioned above, and is then transferred on a polarizing plate or
an optical film may be mentioned.
[0087] A pressure sensitive adhesive layer may also be prepared on
one side or both sides of a polarizing plate or an optical film as
a layer in which pressure sensitive adhesives with different
composition or different kind etc. are laminated together.
Moreover, when pressure sensitive adhesive layers are prepared on
both sides, pressure sensitive adhesive layers that have different
compositions, different kinds or thickness, etc. may also be used
on front side and backside of a polarizing plate or an optical
film. Thickness of a pressure sensitive adhesive layer may be
suitably determined depending on a purpose of usage or adhesive
strength, etc., and generally is 1 to 500 .mu.m, preferably 5 to
200 .mu.m, and more preferably 10 to 100 .mu.m.
[0088] A temporary separator is attached to an exposed side of a
pressure sensitive adhesive layer to prevent contamination etc.,
until it is practically used. Thereby, it can be prevented that
foreign matter contacts pressure sensitive adhesive layer in usual
handling. As a separator, without taking the above-mentioned
thickness conditions into consideration, for example, suitable
conventional sheet materials that is coated, if necessary, with
release agents, such as silicone type, long chain alkyl type,
fluorine type release agents, and molybdenum sulfide may be used.
As a suitable sheet material, plastics films, rubber sheets,
papers, cloths, no woven fabrics, nets, foamed sheets and metallic
foils or laminated sheets thereof may be used.
[0089] In addition, in the present invention, ultraviolet absorbing
property may be given to the above-mentioned each layer, such as a
polarizer for a polarizing plate, a transparent protective film and
an optical film etc. and a pressure sensitive adhesive layer, using
a method of adding UV absorbents, such as salicylic acid ester type
compounds, benzophenol type compounds, benzotriazol type compounds,
cyano acrylate type compounds, and nickel complex salt type
compounds.
[0090] An optical film of the present invention may be preferably
used for manufacturing various equipment, such as liquid crystal
display, etc. Assembling of a liquid crystal display may be carried
out according to conventional methods. That is, a liquid crystal
display is generally manufactured by suitably assembling several
parts such as a liquid crystal cell, optical films and, if
necessity, lighting system, and by incorporating driving circuit.
In the present invention, except that an optical film by the
present invention is used, there is especially no limitation to use
any conventional methods. Also any liquid crystal cell of arbitrary
type, such as TN type, and STN type, .pi. type may be used.
[0091] Suitable liquid crystal displays, such as liquid crystal
display with which the above-mentioned optical film has been
located at one side or both sides of the liquid crystal cell, and
with which a backlight or a reflector is used for a lighting system
may be manufactured. In this case, the optical film by the present
invention may be installed in one side or both sides of the liquid
crystal cell. When installing the optical films in both sides, they
may be of the same type or of different type. Furthermore, in
assembling a liquid crystal display, suitable parts, such as
diffusion plate, anti-glare layer, antireflection film, protective
plate, prism array, lens array sheet, optical diffusion plate, and
backlight, may be installed in suitable position in one layer or
two or more layers.
[0092] Subsequently, organic electro luminescence equipment
(organic EL display) will be explained. Generally, in organic EL
display, a transparent electrode, an organic luminescence layer and
a metal electrode are laminated on a transparent substrate in an
order configuring an illuminant (organic electro luminescence
illuminant). Here, an organic luminescence layer is a laminated
material of various organic thin films, and much compositions with
various combination are known, for example, a laminated material of
hole injection layer comprising triphenylamine derivatives etc., a
luminescence layer comprising fluorescent organic solids, such as
anthracene; a laminated material of electronic injection layer
comprising such a luminescence layer and perylene derivatives,
etc.; laminated material of these hole injection layers,
luminescence layer, and electronic injection layer etc.
[0093] An organic EL display emits light based on a principle that
positive hole and electron are injected into an organic
luminescence layer by impressing voltage between a transparent
electrode and a metal electrode, the energy produced by
recombination of these positive holes and electrons excites
fluorescent substance, and subsequently light is emitted when
excited fluorescent substance returns to ground state. A mechanism
called recombination which takes place in a intermediate process is
the same as a mechanism in common diodes, and, as is expected,
there is a strong non-linear relationship between electric current
and luminescence strength accompanied by rectification nature to
applied voltage.
[0094] In an organic EL display, in order to take out luminescence
in an organic luminescence layer, at least one electrode must be
transparent. The transparent electrode usually formed with
transparent electric conductor, such as indium tin oxide (ITO), is
used as an anode. On the other hand, in order to make electronic
injection easier and to increase luminescence efficiency, it is
important that a substance with small work function is used for
cathode, and metal electrodes, such as Mg--Ag and Al--Li, are
usually used.
[0095] In organic EL display of such a configuration, an organic
luminescence layer is formed by a very thin film about 10 nm in
thickness. For this reason, light is transmitted nearly completely
through organic luminescence layer as through transparent
electrode. Consequently, since the light that enters, when light is
not emitted, as incident light from a surface of a transparent
substrate and is transmitted through a transparent electrode and an
organic luminescence layer and then is reflected by a metal
electrode, appears in front surface side of the transparent
substrate again, a display side of the organic EL display looks
like mirror if viewed from outside.
[0096] In an organic EL display containing an organic electro
luminescence illuminant equipped with a transparent electrode on a
surface side of an organic luminescence layer that emits light by
impression of voltage, and at the same time equipped with a metal
electrode on a back side of organic luminescence layer, a
retardation plate may be installed between these transparent
electrodes and a polarizing plate, while preparing the polarizing
plate on the surface side of the transparent electrode.
[0097] Since the retardation plate and the polarizing plate have
function polarizing the light that has entered as incident light
from outside and has been reflected by the metal electrode, they
have an effect of making the mirror surface of metal electrode not
visible from outside by the polarization action. If a retardation
plate is configured with a quarter wavelength plate and the angle
between the two polarization directions of the polarizing plate and
the retardation plate is adjusted to .pi./4, the mirror surface of
the metal electrode may be completely covered.
[0098] This means that only linearly polarized light component of
the external light that enters as incident light into this organic
EL display is transmitted with the work of polarizing plate. This
linearly polarized light generally gives an elliptically polarized
light by the retardation plate, and especially the retardation
plate is a quarter wavelength plate, and moreover when the angle
between the two polarization directions of the polarizing plate and
the retardation plate is adjusted to .pi./4, it gives a circularly
polarized light.
[0099] This circularly polarized light is transmitted through the
transparent substrate, the transparent electrode and the organic
thin film, and is reflected by the metal electrode, and then is
transmitted through the organic thin film, the transparent
electrode and the transparent substrate again, and is turned into a
linearly polarized light again with the retardation plate. And
since this linearly polarized light lies at right angles to the
polarization direction of the polarizing plate, it cannot be
transmitted through the polarizing plate. As the result, mirror
surface of the metal electrode may be completely covered.
EXAMPLES
[0100] The invention is more specifically described by means of
Examples and Comparative Examples below. In each example, "%" means
% by weight. Concerning the stretching bath and the washing bath,
each concentration refers to the concentration of each solute in
the whole of the corresponding solution.
Example 1
[0101] An 80 .mu.m-thick polyvinyl alcohol film (with an average
degree of polymerization of 2400 and a degree of saponification of
99.9%) was uniaxially stretched to 3 times between rolls at
different velocity ratios, while it was immersed at 30.degree. C.
for 60 seconds in an aqueous iodine solution with an iodine
concentration of 0.3% and a potassium iodide concentration of 2% to
be dyed. The film was then stretched such that the total stretch
ratio reached 6, while immersed at 60.degree. C. for 40 seconds in
an aqueous solution (a stretching bath) with a boric acid
concentration of 4% and a potassium iodide concentration of 5%. The
film was then immersed to be washed at 30.degree. C. for 10 seconds
in an aqueous solution of 1.5% potassium iodide (a washing bath).
The film was then dried at 50.degree. C. for 4 minutes to give a
polarizer. Surface-saponified 80 .mu.m-thick triacetyl cellulose
films were adhered to both sides of the resulting polarizer with a
polyvinyl alcohol-based adhesive and then dried at 60.degree. C.
for 4 minutes to form a polarizing plate.
Example 2
[0102] A polarizer was prepared using the process of Example 1
except that an aqueous solution with a boric acid concentration of
4% and a potassium iodide concentration of 10% was alternatively
used as the stretching bath. And a polarizing plate was prepared in
the same manner of Example 1.
Example 3
[0103] A polarizer was prepared using the process of Example 1
except that an aqueous solution with a boric acid concentration of
4% and a potassium iodide concentration of 10% was alternatively
used as the stretching bath and an aqueous solution with a
potassium iodide concentration of 2% was alternatively used as the
washing bath. And a polarizing plate was prepared in the same
manner of Example 1.
Example 4
[0104] A polarizer was prepared using the process of Example 1
except that an aqueous solution with a boric acid concentration of
4% and a potassium iodide concentration of 7% was alternatively
used as the stretching bath and an aqueous solution with a
potassium iodide concentration of 1% was alternatively used as the
washing bath. And a polarizing plate was prepared in the same
manner of Example 1.
Example 5
[0105] A polarizer was prepared using the process of Example 1
except that an aqueous solution with a boric acid concentration of
4% and a potassium iodide concentration of 5% was alternatively
used as the stretching bath and an aqueous solution with a
potassium iodide concentration of 1% was alternatively used as the
washing bath. And a polarizing plate was prepared in the same
manner of Example 1.
Example 6
[0106] A polarizer was prepared using the process of Example 1
except that an aqueous solution with a boric acid concentration of
4% and a potassium iodide concentration of 15% was alternatively
used as the stretching bath. And a polarizing plate was prepared in
the same manner of Example 1.
Example 7
[0107] A polarizer was prepared using the process of Example 1
except that an aqueous solution with a potassium iodide
concentration of 3% was alternatively used as the washing bath. And
a polarizing plate was prepared in the same manner of Example
1.
Example 8
[0108] A polarizer was prepared using the process of Example 1
except that an aqueous iodine solution (controlled to be single
transmittance of 42.5%) with an iodine concentration of 0.4% and a
potassium iodide concentration of 3% was alternatively used as the
aqueous iodine solution. And a polarizing plate was prepared in the
same manner of Example 1.
Example 9
[0109] A polarizer was prepared using the process of Example 1
except that an aqueous solution with a boric acid concentration of
4% and a potassium iodide concentration of 2% was alternatively
used as the stretching bath and an aqueous solution with a
potassium iodide concentration of 5% was alternatively used as the
washing bath. And a polarizing plate was prepared in the same
manner of Example 1.
Example 10
[0110] A polarizer was prepared using the process of Example 1
except that an aqueous solution with a potassium iodide
concentration of 2% was alternatively used as the washing bath and
then the drying was performed at 30.degree. C. for 5 minutes. And a
polarizing plate was prepared in the same manner of Example 1.
Comparative Example 1
[0111] A polarizer was prepared using the process of Example 1
except that an aqueous solution with a boric acid concentration of
4% and a potassium iodide concentration of 3% was alternatively
used as the stretching bath. And a polarizing plate was prepared in
the same manner of Example 1.
Comparative Example 2
[0112] A polarizer was prepared using the process of Example 1
except that an aqueous solution with a potassium iodide
concentration of 0.5% was alternatively used as the washing bath.
And a polarizing plate was prepared in the same manner of Example
1.
Comparative Example 3
[0113] A polarizer was prepared using the process of Example 1
except that a pure water was alternatively used as the washing
bath. And a polarizing plate was prepared in the same manner of
Example 1.
Comparative Example 4
[0114] A polarizer was prepared using the process of Example 1
except that an aqueous solution with a boric acid concentration of
4% and a potassium iodide concentration of 3% was alternatively
used as the stretching bath and an aqueous solution with a
potassium iodide concentration of 3% was alternatively used as the
washing bath. And a polarizing plate was prepared in the same
manner of Example 1.
[0115] The polarizing plates prepared in Examples and Comparative
Examples were each evaluated as follows. The results are shown in
Table 1.
(Single Transmittance)
[0116] The transmittance of a single piece of the polarizing plate
was measured using a spectrophotometer (Dot-3C manufactured by
Murakami Color Research Laboratory). The single transmittance of
the polarizing plate is a Y value determined through relative
spectral responsivity correction with 2 degree (C. light source)
according to JIS Z 8701.
(Polarizing Efficiency)
[0117] The parallel transmittance (Tp) of the same two polarizing
plates superimposed with their polarization axes arranged parallel
and the crossed transmittance (Tc) of those superimposed with their
polarization axes arranged perpendicular were measured,
respectively, using the spectrophotometer, and the polarizing
efficiency was calculated using the formula below.
Polarizing efficiency (%)= {square root over (
)}{(To-Do)/(Patch)}.times.100
[0118] The parallel transmittance (Tp) and the crossed
transmittance (Tc) are each a Y value determined through relative
spectral responsivity correction with 2 degree (C. light source)
according to JIS Z 8701.
(Dichroic Ratio at Wavelength of 440 Nm)
[0119] The dichroic ratio was calculated from the parallel
transmittance (Tp) and crossed transmittance (Tc) of the polarizing
plate at a wavelength of 440 nm according to the following
formula:
dichroic ratio={log.sub.10(1/k2)}/{log.sub.10(1l/k1)}, wherein
k1=1/2 {square root over ( )}2.times.[(Tp+Tc)1/2+(Tp-Tc)1/2]
and
k2=1/2 {square root over ( )}2.times.[(Tp+Tc)1/2-(Tp-Tc)1/2]
(Contents of Iodine and Potassium in Polarizer)
[0120] Using the fundamental parameter method (FP method), the
contents (%) of iodine and potassium in the polarizer were
calculated from X-ray fluorescence intensities which were measured
with a X-ray fluorescence spectrometer (ZSX 100e manufacture by
Rigaku Corporation).
(Hue (.DELTA.ab))
[0121] Using a spectrophotometer (Dot-3C manufactured by Murakami
Color Research Laboratory), a value and b value in Hunter color
system were determined (C light source). .DELTA.ab was calculated
from the values according to the following formula:
.DELTA.ab= {square root over ( )}{(parallel a value-crossed a
value)2+(parallel b value-crossed b value)2}
.DELTA.ab indicates a change in chromaticity depending on a change
in brightness of color. The smaller the value is, the better color
reproducibility. In a preferred mode of the invention, .DELTA.ab is
5 or less.
(Durability: Evaluation of Red Discoloration by Heating)
[0122] After the polarizing plate was kept at 85.degree. C. for 24
hours, the hue in the crossed Nicol configuration was visually
evaluated using the following criteria:
.smallcircle..smallcircle.: no red discoloration .smallcircle.: a
little red discoloration .tangle-solidup.: some red discoloration
x: significant red discoloration
TABLE-US-00001 TABLE 1 Potassium Iodide Polariz- Dichroic Iodine
Potassium Concentration (%) Single ing Ratio at Content Content Hue
(NBS) Red Stretch- Wash- Transmit- effi- Wave- of of Parallel
Parallel Crossed Crossed Discolor- ing ing tance ciency length of
Polarizer Polarizer a b a b ation by Bath Bath (%) (%) 440 nm (%)
(%) Value Value Value Value .DELTA.ab Heating Example 1 5 1.5 44.0
99.97 36.5 1.91 0.38 -1.26 2.67 0.57 -1.83 4.86
.smallcircle..smallcircle. Example 2 10 1.5 44.3 99.97 38.6 2.01
0.42 -1.15 2.89 0.63 -1.56 4.79 .smallcircle..smallcircle. Example
3 10 2 44.1 99.98 44.4 2.42 0.56 -1.08 3.24 0.45 -1.05 4.55
.smallcircle. Example 4 7 1 44.0 99.94 34.5 1.52 0.25 -1.31 2.46
0.56 -1.86 4.71 .smallcircle..smallcircle. Example 5 5 1 44.0 99.95
34.8 1.46 0.24 -1.33 2.32 0.57 -2.20 4.90
.smallcircle..smallcircle. Example 6 15 1.5 44.3 99.97 40.3 2.64
0.61 -1.00 3.28 0.79 -1.29 4.91 .tangle-solidup. Example 7 5 3 44.0
99.96 36.5 2.99 0.74 -1.08 3.49 0.56 -1.04 4.82 x Example 8 5 1.5
42.5 99.97 32.6 1.80 0.36 -0.84 3.94 0.46 -0.59 4.71
.smallcircle..smallcircle. Example 9 2 5 44.0 99.95 31.4 2.78 0.66
-1.10 3.88 0.45 -0.83 4.96 x Example 10 5 2 43.9 99.95 40.6 2.21
0.48 -1.24 2.96 0.54 -1.60 4.90 .smallcircle..smallcircle.
Comparative 3 1.5 44.2 99.80 29.4 1.81 0.34 -1.30 2.60 0.75 -2.51
5.51 .smallcircle..smallcircle. Example 1 Comparative 5 0.5 44.4
99.86 27.6 1.11 0.12 -1.47 2.63 1.47 -4.64 7.84
.smallcircle..smallcircle. Example 2 Comparative 5 0 43.9 99.55
21.5 0.91 0.06 -0.70 0.84 6.18 -37.65 39.10
.smallcircle..smallcircle. Example 3 Comparative 3 3 44.1 99.92
28.5 2.70 0.63 -1.19 3.62 0.37 -2.28 6.10 .tangle-solidup. Example
4
[0123] Table 1 indicates that the polarizer or polarizing plate
having a single transmittance of 43% or more, a polarizing
efficiency of 99.9% or more and a 440 nm dichroic ratio of 30 or
more show good hue. As a result of comparing Examples 1 to 5 and 8
with Examples 6, 7 and 9, it is apparent that red discoloration by
heating is inhibited and good durability is obtained to control the
contents of iodine to 1.5 to 2.5% by weight and potassium to 0.2 to
0.6% by weight, respectively.
[0124] Such a polarizer can be obtained by the process including
the steps of uniaxially stretching the film in an aqueous boric
acid solution containing potassium iodide at a concentration of 4%
by weight or more and then washing it with an aqueous solution of
potassium iodide at a concentration of 0.8% by weight or more. If
the potassium iodide concentration of the aqueous boric acid
solution is from 4 to 12% by weight and the concentration of the
aqueous potassium iodide solution is from 0.8 to 2.5% by weight,
the resulting polarizer or polarizing plate has good
durability.
INDUSTRIAL APPLICABILITY
[0125] The polarizer of the invention and the polarizer produced by
the manufacturing method of the invention are suitable and useful
for polarizing plates and optical films using a polarizing plate or
the like and can be applied to image displays such as liquid
crystal displays, organic EL displays and PDPs.
* * * * *