U.S. patent application number 10/566714 was filed with the patent office on 2006-09-21 for polarizing film, laminated film, and liquid crystal display.
This patent application is currently assigned to NITTO DENKO CORPORATION. Invention is credited to Kuniaki Ishibashi, Hiroyuki Yoshimi.
Application Number | 20060210803 10/566714 |
Document ID | / |
Family ID | 34137934 |
Filed Date | 2006-09-21 |
United States Patent
Application |
20060210803 |
Kind Code |
A1 |
Ishibashi; Kuniaki ; et
al. |
September 21, 2006 |
Polarizing film, laminated film, and liquid crystal display
Abstract
The invention provides a polarizing film comprising: a long
polymer film; and a dichroic substance, wherein the polarizing film
has an absorption axis in the TD direction of the polarizing
film.
Inventors: |
Ishibashi; Kuniaki; (Osaka,
JP) ; Yoshimi; Hiroyuki; (Osaka, 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: |
34137934 |
Appl. No.: |
10/566714 |
Filed: |
August 5, 2004 |
PCT Filed: |
August 5, 2004 |
PCT NO: |
PCT/JP04/11579 |
371 Date: |
February 1, 2006 |
Current U.S.
Class: |
428/411.1 |
Current CPC
Class: |
Y10T 428/1041 20150115;
Y10T 428/31504 20150401; B32B 33/00 20130101; G02B 5/3033 20130101;
C09K 2323/031 20200801; B32B 38/0012 20130101 |
Class at
Publication: |
428/411.1 |
International
Class: |
B32B 9/04 20060101
B32B009/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 8, 2003 |
JP |
2003-289612 |
Jul 23, 2004 |
JP |
2004-215159 |
Claims
1. A polarizing film comprising: a long polymer film; and a
dichroic substance, wherein the polarizing film has an absorption
axis in the TD direction of the polarizing film.
2. The polarizing film according to claim 1, wherein the length in
the MD direction of the polarizing film is not smaller than five
times as long as the length in the TD direction of the polarizing
film.
3. The polarizing film according to claim 1, wherein the polarizing
film is produced by stretching the long polymer film in the TD
direction.
4. The polarizing film according to claim 1, wherein the polarizing
film is produced by: stretching the long polymer film in the TD
direction; and shrinking the long polymer film in the MD
direction.
5. The polarizing film according to claim 1, wherein the polarizing
film is produced by dyeing the long polymer, which is stretched in
the TD direction, with a iodine by using an aqueous solution
containing the iodine.
6. The polarizing film according to claim 1, wherein the polarizing
film is produced by dyeing the long polymer, which is stretched in
the TD direction and shrunk in the MD direction, with a iodine by
using an aqueous solution containing the iodine.
7. The polarizing film according to claim 5, wherein the polarizing
film is produced by dyeing the long polymer film with the iodine by
applying the aqueous solution containing the iodine onto the long
polymer film.
8. A laminated film comprising: a polarizing film according to
claim 1; and a retardation film having a slow axis in the MD
direction, which comprises a long polymer film, wherein the MD
direction of the polarizing film corresponds to the MD direction of
the retardation film.
9. The laminated film according to claim 8, wherein the retardation
film comprises a uniaxially stretched film.
10. The laminated film according to claim 8, wherein the
retardation film comprises an optically uniaxial layer comprising a
liquid crystal material.
11. The laminated film according to claim 8, wherein the
retardation film comprises a birefringent layer comprising a
non-liquid crystal material having a birefringence of not lower
than 0.005.
12. The laminated film according to claim 8, wherein the
retardation film is a composite film comprising a birefringent
layer provided on a birefringent polymer film.
13. The laminated film according to claim 11 or 12, wherein the
birefringent layer comprises a solid polymer containing at least
one selected from: polyetherketone; polyamide; polyester;
polyimide; polyamideimide; and polyesterimide.
14. The laminated film according to claim 13, wherein the
birefringent layer is a solid polymer comprising polyimide.
15. The laminated film according to claim 11 or 12, wherein the
birefringent layer has a relationship nx>ny>nz, wherein nx is
the maximum in-plane refractive index, ny is an in-plane refractive
index in a direction perpendicular to the direction of nx, and nz
is a thicknesswise refractive index.
16. A liquid crystal display comprising a polarizing film according
to claim 1 that is disposed outside of a liquid crystal cell.
17. A liquid crystal display comprising a laminated film according
to claim 8 that is disposed outside of a liquid crystal cell.
18. A process for producing a polarizing film comprising: unrolling
a polymer film successively; stretching the polymer film in the TD
direction; and dyeing the stretched film.
19. The process for producing a polarizing film according to claim
18; wherein the stretching in the TD direction is carried out by a
tenter stretching machine.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a polarizing film suitable
for the increase in screen size of a liquid crystal display, a
laminated film suitable for optically compensating a retardation
due to a liquid crystal cell, and a liquid crystal display having
these films arranged.
BACKGROUND ART
[0002] In IPS mode or VA mode liquid crystal display, polarizers
are arranged on front and rear surfaces of a liquid crystal cell so
that absorption axes (vibrating directions of light to cause
absorption) become perpendicular to each other. A long polarizing
film prepared by dyeing a polyvinyl alcohol film or the like with a
dichroic substance has been heretofore formed in such a manner that
the long film is uniaxially stretched in the lengthwise direction
of the long film. In this case, the absorption axis of the
polarizing film appears in the lengthwise direction.
[0003] In use of the conventional long polarizing film, the long
film is cut into film pieces by a predetermined size. The film
pieces are used in combination so that the lengthwise direction
based on the long film, which is the direction of flow of the film
at the time of production of the film (MD direction: Machine
Direction), corresponds to a direction perpendicular to the
lengthwise direction (TD direction: Transverse Direction). Thus,
the orthogonal relation between the absorption axes thereof on the
front and rear surfaces of the liquid crystal cell can be achieved.
Incidentally, hereinafter, the MD direction is referred to as
"lengthwise direction" and the TD direction is referred to as
"widthwise direction", simply.
[0004] Accordingly, in the aforementioned method, the polarizing
film pieces are used to have the relation in which the polarizing
film pieces are rotated by 90 degrees on the basis of the
absorption axes. Therefore, when polarizing film pieces of the same
size are prepared to be applied to the front and rear surfaces of
the liquid crystal cell, the width (widthwise length) of the long
film is a limit size thereof. In this case, a sufficient widthwise
length could not be obtained in the conventional polarizing film
since shrinkage occurred in the widthwise direction in a uniaxial
stretching step or the like. Then, there was a problem that it was
difficult to increase the screen size of liquid crystal display and
particularly to obtain a sufficient transverse length. There is a
limitation in enlarging of the conventional long film in the
widthwise direction because of accuracy in processing into the
polarizing film such as the accuracy of orientation, the degree of
polarization, etc.
[0005] On the other hand, for optical compensation of the
retardation due to the liquid crystal cell, particularly for
compensation of the viewing angle, the polarizing film and the
retardation film are needed so that the slow axis of the
retardation film (the direction of the maximum in-plane refractive
index) becomes perpendicular to the absorption axis of the
polarizing film. In this case, it is advantageous that the
polarizing film and the retardation film each provided in the form
of rolls can be laminated each other as long films from the point
of view of efficiency in production of a laminated film comprising
the laminate thereof.
[0006] The above can be achieved by stretching a long film in the
widthwise direction to form a retardation film having a slow axis
in the widthwise direction. In this case, there was a drawback that
the direction of the slow axis was apt to vary because of a boing
phenomenon that the center portion of the film progressed compared
with the case where the long film is stretched in the lengthwise
direction to provide a retardation film having a slow axis in the
lengthwise direction.
[0007] [Reference 1] JP 3-24502
[0008] [Reference 2] JP 3-33719
DISCLOSURE OF THE INVENTION
[0009] An object of the invention is to provide a polarizing film
in which: the transverse size thereof can be arbitrarily set to
form the orthogonal relation between absorption axes thereof in
front and rear surfaces of a liquid crystal cell; increase in
screen size of liquid crystal display, especially a screen having
an arbitrary transverse size can be achieved; the polarizing film
and a retardation film can be laminated each other as long films,
and a laminated film comprising the laminate can be produced
efficiently, and to develop a laminated film in which the
retardation due to the liquid crystal cell can be highly optically
compensated to attain widening of the viewing angle or the
like.
[0010] That is, the object of the invention can be achieved by the
provision of a polarizing film, a retardation film, a laminated
film as a laminate of the polarizing film and the retardation film,
a liquid crystal display, and a process for producing the
polarizing film as follows.
[0011] 1. A polarizing film comprising: a long polymer film; and a
dichroic substance, wherein the polarizing film has an absorption
axis in the TD direction of the polarizing film.
[0012] 2. The polarizing film according to item 1, wherein the
length in the MD direction of the polarizing film is not smaller
than five times as long as the length in the TD direction of the
polarizing film.
[0013] 3. The polarizing film according to item 1, wherein the
polarizing film is produced by stretching the long polymer film in
the TD direction.
[0014] 4. The polarizing film according to item 1, wherein the
polarizing film is produced by: stretching the long polymer film in
the TD direction; and shrinking the long polymer film in the MD
direction.
[0015] 5. The polarizing film according to item 1, wherein the
polarizing film is produced by dyeing the long polymer, which is
stretched in the TD direction, with a iodine by using an aqueous
solution containing the iodine.
[0016] 6. The polarizing film according to item 1, wherein the
polarizing film is produced by dyeing the long polymer, which is
stretched in the TD direction and shrunk in the MD direction, with
a iodine by using an aqueous solution containing the iodine.
[0017] 7. The polarizing film according to item 5, wherein the
polarizing film is produced by dyeing the long polymer film with
the iodine by applying the aqueous solution containing the iodine
onto the long polymer film.
[0018] 8. A laminated film comprising: a polarizing film according
to item 1; and a retardation film having a slow axis in the MD
direction, which comprises a long polymer film, wherein the MD
direction of the polarizing film corresponds to the MD direction of
the retardation film.
[0019] 9. The laminated film according to item 8, wherein the
retardation film comprises a uniaxially stretched film.
[0020] 10. The laminated film according to item 8, wherein the
retardation film comprises an optically uniaxial layer comprising a
liquid crystal material.
[0021] 11. The laminated film according to item 8, wherein the
retardation film comprises a birefringent layer comprising a
non-liquid crystal material having a birefringence of not lower
than 0.005.
[0022] 12. The laminated film according to item 8, wherein the
retardation film is a composite film comprising a birefringent
layer provided on a birefringent polymer film.
[0023] 13. The laminated film according to item 11 or 12, wherein
the birefringent layer comprises a solid polymer containing at
least one selected from: polyetherketone; polyamide; polyester;
polyimide; polyamideimide; and polyesterimide.
[0024] 14. The laminated film according to item 13, wherein the
birefringent layer is a solid polymer comprising polyimide.
[0025] 15. The laminated film according to item 11 or 12, wherein
the birefringent layer has a relationship nx>ny>nz, wherein
nx is the maximum in-plane refractive index, ny is an in-plane
refractive index in a direction perpendicular to the direction of
nx, and nz is a thicknesswise refractive index.
[0026] 16. A liquid crystal display comprising a polarizing film
according to item 1 that is disposed outside of a liquid crystal
cell.
[0027] 17. A liquid crystal display comprising a laminated film
according to item 8 that is disposed outside of a liquid crystal
cell.
[0028] 18. A process for producing a polarizing film comprising:
unrolling a polymer film successively; stretching the polymer film
in the TD direction; and dyeing the stretched film.
[0029] 19. The process for producing a polarizing film according to
item 18; wherein the stretching in the TD direction is carried out
by a tenter stretching machine.
BEST MODE FOR CARRYING OUT THE INVENTION
[0030] The invention will be described below specifically.
[0031] The invention provides: a polarizing film comprising a long
polymer film, wherein the film includes a dichroic substance and
the polarizing film has an absorption axis in the widthwise
direction thereof; a laminated film comprising: the polarizing
film; and a retardation film having a slow axis in the lengthwise
direction, which comprises a long polymer film, laminated on the
polarizing film so that the lengthwise directions of these films
correspond each other; a liquid crystal display comprising the
polarizing film or the laminated film disposed outside of a liquid
crystal; and a process for producing the polarizing film.
[0032] The polarizing film according to the invention is a
polarizing film comprising a long polymer film, wherein the film
includes a dichroic substance and the polarizing film has an
absorption axis in the widthwise direction thereof.
[0033] The kind of the polymer for forming the film is not
particularly limited, and a suitable material such as a
homopolymer, a copolymer, or a mixture of two or more kinds of
polymers can be used as the polymer. Generally, one kind or two or
more kinds selected from hydrophilic macromolecules and polyesters
such as polyvinyl alcohol, partially formalized polyvinyl alcohol,
ethylene-vinyl alcohol copolymer, and partially saponified
ethylene-vinyl acetate copolymer may be used.
[0034] The long polymer film preferably has a length not smaller
than five times as long as the width of the long polymer film, more
preferably from 10-to 100,000 times as long as the width of the
long polymer film, still more preferably from 30 to 5000 times as
long as the width of the long polymer film. The long polymer film
may be provided as a roll of film. The width of the film can be
determined suitably in accordance with the purpose of use of the
polarizing film to be formed, or the like. Generally, the width is
preferably from 5 mm to 5 m, more preferably from 30 cm to 3 m,
still more preferably from 50 cm to 2 m.
[0035] The polarizing film can be formed by: dyeing the long
polymer film with a dichroic substance; and stretching the long
polymer film in a widthwise direction. Then an absorption type
polarizing film that exhibits characteristic of transmitting
linearly polarized light when natural light is incident to the
polarizing film can be obtained. The respective steps may be
performed simultaneously on the whole of the long film or may be
performed partially and repetitively so successively as to be
applied on the whole of the long film.
[0036] The step of stretching the long film in the widthwise
direction aims at providing an absorption axis in the widthwise
direction of the long film. In the invention, the polarizing film
can be formed by a process according to the background art except
that the polarizing film is stretched in the widthwise direction so
that an absorption axis is provided in the widthwise direction.
Accordingly, one suitable kind or two or more suitable kinds
selected from iodine, dichroic dyes, etc. can be, for example, used
as the dichroic substance.
[0037] Examples of the method used in the dyeing step with the
dichroic substance include: a method of introducing and immersing
the long polymer film into an aqueous solution containing a
dichroic substance; and a method of applying the aqueous solution
on the long polymer film. The dyeing step may be performed before
or after the step of stretching the polymer film in the widthwise
direction or during the stretching step. It is preferable from the
point of view of improvement in the degree of polarization based on
prevention of dyeing irregularity that the dyeing step is performed
after the stretching step.
[0038] For example, the step of stretching the long polymer film in
the widthwise direction can be performed by a tenter stretching
machine. Examples of the stretching method includes: a dry type
heating method for heating the polymer film in the atmospheric air
to a temperature lower than the melting temperature of the polymer
film, especially to a temperature not lower than the glass
transition temperature of the polymer film; and a wet type
stretching method for stretching the polymer film in an aqueous
solution-containing boric acid or the like.
[0039] It is preferable from the point of view of obtaining a high
polarization degree polarizing film highly uniaxially oriented in
the widthwise direction that the long polymer film is shrunk in the
lengthwise direction (longitudinal shrinking) in addition to
stretching in the widthwise direction (transverse stretching). The
combination step of transverse stretching and longitudinal
shrinking can be performed by a simultaneous or sequential biaxial
process using a biaxial stretching machine such as a pantograph
type machine or a spindle type machine.
[0040] The stretching ratio in the widthwise direction can be
determined suitably. Generally, it is preferable from the point of
view of orientation accuracy, spreading effect, etc. that the
stretching ratio in the widthwise direction is from 1.1 to 20 times
as long as the initial width, more preferably from 1.5 to 10 times,
still more preferably from 2 to 7 times. Incidentally, when
longitudinal shrinking is combined with transverse stretching as
described above, it is preferable from the point of view of
improvement in the degree of orientation, etc. that the
longitudinal shrinking ratio is from 70 to 99% as large as the
initial length (100%), more preferably from 75 to 98%, especially
preferably from 80 to 97%. In general, the thickness of the
polarizing film is preferably from 1 to 200 pm, more preferably
from 3 to 150 .mu.m, more preferably from 5 to 80 .mu.m. The
thickness of the polarizing film is not limited thereto.
Incidentally, as described above, the polarizing film may be
crosslinked by additional use of a crosslinking agent such as boric
acid.
[0041] The polarizing film may have a transparent protective
layer(s) provided on a single surface or on both surfaces of the
polarizing film if necessary. Each transparent protective layer may
be provided for various purposes of reinforcement of the polarizing
film, improvement in heat resistance and humidity resistance,
improvement in handling property and durability, etc. A suitable
transparent substance may be used for forming the transparent
protective layer. Especially, a polymer etc. excellent in
transparency, mechanical strength, heat stability, moisture
sealability, etc. may be used preferably.
[0042] Examples of the polymer include: an acetate resin such as
triacetyl cellulose; a polyester resin; a polyether-sulfone resin;
a polycarbonate resin; a polyamide resin; a polyimide resin; a
polyolefin resin; an acrylic resin; and a heat-curable or
ultraviolet-curable resin such as an acrylic resin, a urethane
resin, an acryl-urethane resin, an epoxy resin, and a silicone
resin.
[0043] The transparent protective layer can be formed by a suitable
method such as a method of applying a polymer or a method of
laminating a polymer as a film through an adhesive layer. The
adhesive layer is not particularly limited. For example, a layer
made of an adhesive agent of an acrylic polymer or a vinyl alcohol
polymer or made of an adhesive agent containing boric acid or
borax, and an aqueous crosslinking agent of a vinyl alcohol polymer
such as glutaraldehyde, melamine or oxalic acid is preferred from
the point of view of the laminating process exhibiting peel
resistance to humidity and heat.
[0044] The thickness of the transparent protective layer can be
arbitrarily determined but is generally set to be preferably not
larger than 300 .mu.m, more preferably from 1 to 200 .mu.m, more
preferably from 5 to 100 .mu.m. Incidentally, when transparent
protective layers are provided on both surfaces of the polarizing
film, the transparent protective layers may made of different
polymers etc. between the front and rear surfaces of the polarizing
film.
[0045] For example, a hard coating treatment, an anti-reflection
treatment, an anti-sticking treatment and other various treatment
for diffusion, anti-glare, etc. may be applied to the polarizing
film. The hard coating treatment is provided for preventing a
surface of a polarizing film from being injured. For example, the
hard coating treatment can be made by a method in which a cured
coat or film made from a suitable ultraviolet-curable resin such as
a silicone resin, a urethane resin, an acrylic resin or an epoxy
resin and excellent in hardness, slip characteristic, etc. is
applied on a surface of a transparent protective film.
[0046] The anti-reflection treatment is provided for preventing
external light from being reflected on a surface of the polarizing
film. For example, the anti-reflection treatment can be achieved in
such a manner that a coherent film such as a coat layer of a
fluorine polymer or a multilayer metal deposition film or an
anti-reflection film according to the background art is formed
suitably.
[0047] The anti-sticking treatment is provided for preventing a
layer from being stuck closely to an adjacent layer. The anti-glare
treatment is provided for preventing visual recognition of light
transmitted through the polarizing film from being disturbed by
external light reflected on a surface of the polarizing film. For
example, the anti-glare treatment can be made in such a suitable
manner that a resin coating layer containing transparent fine
particles or a fine roughness structure is given to a surface by a
suitable method such as embossing, sandblasting or etching to
thereby diffuse light reflected on the surface.
[0048] For example, transparent fine particles having an average
particle size of from 0.5 to 20 .mu.m can be used as the
transparent fine particles. Examples of the transparent fine
particles include: inorganic fine particles which are made of
silica, calcium oxide, alumina, titania, zirconia, tin oxide,
indium oxide, cadmium oxide, antimony oxide, etc. and which may be
electrically conductive; and crosslinked or non-crosslinked organic
fine particles made of a suitable polymer such as polymethyl
methacrylate or polyurethane. One kind or two or more kinds of
suitable fine particles may be used. The amount of use of the
transparent fine particles is generally selected to be preferably
from 2 to 70 parts by weight, more preferably from 5 to 50 parts by
weight with respect to 100 parts by weight of the transparent
resin.
[0049] The anti-glare layer may serve as a diffusing layer (having
a viewing angle compensating function, etc.) for diffusing light
transmitted through the polarizing film to thereby widen the
viewing angle. Incidentally, the layers such as the hard coating
layer, the anti-reflection layer, the anti-sticking layer, the
diffusing layer and the anti-glare layer may be provided as optical
layers made of sheets etc. having these layers so as that each
optical layer is provided separately from the transparent
protective film. Accordingly, the polarizing film may have an
optical layer for controlling glaring, scattering, etc. concerned
with resolution by using diffusion, scattering, refraction, etc. or
may have an optical layer for controlling the viewing angle.
[0050] A retardation layer(s) can be laminated on a single surface
or both surfaces of the polarizing film to thereby put a laminated
film into practice. In this case, a retardation film made of a long
polymer film and having a slow axis in the lengthwise direction may
be used so that the long polarizing film and the long retardation
film are laminated so that the lengthwise directions of the two
films correspond to each other. Thus, the laminated film in which
the absorption axis of the polarizing film is perpendicular to the
slow axis of the retardation film can be formed at excellent
production efficiency.
[0051] For example, the retardation film having a slow axis in the
lengthwise direction can be formed by a roll type longitudinal
stretching method in which when a long polymer film is conveyed
through a plurality of rolls, circumferential velocities of
conveyance rolls are made different to load tension in the
lengthwise direction of the film to stretch the film longitudinally
uniaxially. In the longitudinal stretching, a retardation film
excellent in uniformity of axes of orientation can be obtained by
the stretching process having necking suppressed, so that a
laminated film useful as a highly accurate viewing angle
compensating film or the like can be obtained.
[0052] A polymer exhibiting positive birefringence to increase the
refractive index in the stretching direction may be preferably used
as the polymer for forming the retardation film. Examples of the
polymer include: norbornene polymer; polycarbonate;
polyether-sulfone; polysulfone; polyolefin; acrylic polymer;
cellulose resin; pollyarylate; polystyrene; polyvinyl alcohol;
polyvinyl chloride; polyvinylidene chloride; and acetate polymer.
The film may be formed by use of one kind or two or more kinds of
these polymers.
[0053] The length and width of the long polymer film for forming
the retardation film can be determined in accordance with those of
the long polymer film for forming the polarizing film.
Incidentally, a suitable film-forming method such as a casting
method or an extrusion method such as a flow-out film-forming
method, a roll coating method or a flow coating method can be used
for forming the long polymer film. A film formed by a solution
film-forming method such as a casting method may be used preferably
from the point of view of mass production of polarizing films or
retardation films uniform in thickness, orientation distortion,
etc. For the formation of the film, various additives such as a
stabilizer, a plasticizer, metals, etc. may be mixed if
necessary.
[0054] In the roll type longitudinal stretching method, the film is
preferably stretched while heated in order to reduce variation in
the stretching process. A suitable method such as a method using a
heat roll, a method of heating the atmosphere or a method using the
two methods in combination can be used for heating the film. In
this case, the temperature for the stretching process can be set in
accordance with the background art. The temperature may be selected
to be preferably lower than the melting temperature of the polymer
for forming the film, more preferably near to the glass transition
temperature, especially preferably not lower than the glass
transition temperature.
[0055] The retardation film having a slow axis in the lengthwise
direction may be a film having an optically uniaxial layer A made
of a liquid crystal material instead of the uniaxially stretched
film or containing the uniaxially stretched film. A suitable
material such as nematic liquid crystal exhibiting liquid crystal
characteristic can be used for forming the uniaxial layer A.
Especially, a layer of a liquid crystal polymer is preferred from
the point of view of durability, etc. For example, the retardation
film can be obtained in a suitable form such as the uniaxial layer
A applied on a support film or the uniaxial layer A molded into a
film.
[0056] A suitable film can be used as the support film without any
particular limitation. The uniaxial layer A may be integrated with
the support film or may be used as a film molding separated from
the support film. In the former case where the uniaxial film A is
integrated with the support film, the retardation generated in the
support film by the stretching process or the like may be used. The
latter case where the uniaxial film A is separated from the support
film is advantageous to the case where the retardation generated in
the support film by the stretching process or the like is
inconvenient.
[0057] Incidentally, in the former case of the integrated type with
the support film, a transparent polymer base material may be
preferably used as the support film. Examples of the polymer for
forming the base material include: materials listed in the
transparent protective layer and the uniaxially stretched
retardation film; and liquid crystal polymers.
[0058] The retardation film having a slow axis in the lengthwise
direction may be a film having a birefringent layer B made of a
non-liquid crystal material having a birefringence (.DELTA.n) not
lower than 0.005. The retardation film can be obtained in a
suitable form such as the birefringent layer B applied on a support
film or the birefringent layer B molded into a film. In the case
where the birefringent layer B is applied on the support film, a
film exhibiting birefringence may be used as the support film so as
to provide a composite film having the birefringent layer B
provided on a birefringent polymer film.
[0059] The support film and the film molding of the birefringent
layer B can comply with the case where the uniaxial layer A is
provided. The birefringent polymer film for forming the composite
film is not particularly limited but may comply with the support
film or the like. In this case, the birefringence may be generated
so that the target retardation characteristic is provided by a
suitable biaxial stretching method such as a simultaneous biaxial
stretching method using a roll type longitudinal stretching method,
a tenter transverse stretching method or a full tenter method or a
sequential biaxial stretching method using a roll tenter
method.
[0060] The non-liquid crystal material for forming the birefringent
layer B is not particularly limited either but a suitable material
may be used as the non-liquid crystal material. Especially, one
kind or two or more kinds selected from polyetherketone,
especially, polyaryl ether ketone, polyamide, polyester, polyimide,
polyamideimide, polyesterimide, etc. may be used preferably from
the point of view of the formability of the birefringent layer
having a birefringence (.DELTA.n) not lower than 0.005.
Incidentally, the birefringence .DELTA.n is defined by
.DELTA.n=(nx+ny)/2-nz in which nx and ny are in-plane refractive
indices of the layer, and ny is a thicknesswise refractive
index.
[0061] A specific example of the polyetherketone, especially,
polyaryl ether ketone includes a material having a constitutional
repeating unit, for example, represented by the following general
formula (1) (JP 2001-49110). ##STR1##
[0062] In the general formula (1), X is halogen, an alkyl group or
an alkoxy group, and the number q of bonds of X to the benzene
ring, that is, the number q of substituents of hydrogen atoms in
the position where a p-tetrafluorobenzoylene group and an
oxyalkylene group do not bond to each other is an integer of from 0
to 4. Moreover, R.sup.1 is a compound (group) represented by the
following general formula (2) in which m is 0 or 1, and n expresses
the degree of polymerization and is preferably from 2 to 5000, more
preferably from 5 to 500. ##STR2##
[0063] Examples of the halogen as X in the general formula (1)
include a fluorine atom, a bromine atom, a chlorine atom, an iodine
atom, etc. Especially, a fluorine atom is preferred. An example of
the alkyl group includes a straight-chain or branch-chain alkyl
group preferably having 1-6 carbon atoms, more preferably having
1-4 carbon atoms, such as a methyl group, an ethyl group, a propyl
group, an isopropyl group, a butyl group, etc. Especially, a
halogenated alkyl group such as a methyl group, an ethyl group or a
trifluoromethyl group is preferred.
[0064] Further, an example of the alkoxy group includes a
straight-chain or branch-chain alkoxy group preferably having 1-6
carbon atoms, more preferably having 1-4 carbon atoms, such as a
methoxy group, an ethoxy group, a propoxy group, an isopropoxy
group, a butoxy group, etc. Especially, a halogenated alkoxy group
such as a methoxy group, an ethoxy group or a trifluoromethoxy
group is preferred. In the above description, the especially
preferred X is a fluorine atom.
[0065] On the other hand, X' in the group represented by the
general formula (2) is halogen, an alkyl group or an alkoxy group,
and the number q' of bonds of X' to the benzene ring is an integer
of from 0 to 4. The halogen, the alkyl group or the alkoxy group as
X' is the same as listed in X.
[0066] Preferably, X' is a fluorine atom, a halogenated alkyl group
such as a methyl group, an ethyl group or a trifluoromethyl group
thereof or a halogenated alkoxy group such as a methoxy group, an
ethoxy group or a trifluoromethoxy group thereof. More preferably,
X' is a fluorine atom.
[0067] Incidentally, in the general formula (1), X and X' may be
equal to each other or may be different from each other. In the
general formulae (1) and (2), X or X' the number of which is two or
more in a molecule on the basis of the fact that q or q' in the
general formulae (1) and (2) is not smaller than 2 may be
independently equal to the other or may be different from the
other.
[0068] Especially preferred R.sup.1 is a group represented by the
following general formula (3). ##STR3##
[0069] In the general formulae (2) and (3), R.sup.2 is a divalent
aromatic group, and P is 0 or 1. Examples of the divalent aromatic
group include an (o, m or p-)phenylene group, a naphthalene group,
a biphenyl group, an anthracene group, an (o, m or p-)terphenyl
group, a phenanthrene group, a dibenzofuran group, a biphenyl ether
group, a biphenyl sulfone group, divalent aromatic groups
represented by the following formulae, and so on. Incidentally, the
divalent aromatic group may be provided in the form in which each
hydrogen directly bonded to the aromatic rings of the divalent
aromatic group may be replaced by the halogen, the alkyl group or
the alkoxy group. ##STR4##
[0070] In the above description, preferred examples of the divalent
aromatic group (R.sup.2) are represented by the following formulae.
##STR5##
[0071] Polyaryl ether ketone represented by the general formula (1)
may be formed from the same constitutional repeating units or may
have two kinds or three or more kinds of different constitutional
repeating units. In the latter case, the respective constitutional
repeating units may be provided in the form of blocks or may be
provided at random.
[0072] Based on the above description the preferred example of
polyaryl ether ketone represented by the general formula (1) is
represented by the following general formula (4). ##STR6##
[0073] Preferred polyaryl ether ketone in the case where the
terminal group in a molecule is included is represented by the
following general formula (5) in accordance with the general
formula (1) or represented by the following formula (6) in
accordance with the general formula (4). Each of these is provided
in the form in which a fluorine atom is bonded to the
p-tetrafluorobenzoylene group side in a molecule while a hydrogen
atom is bonded to the oxyalkylene group side in the molecule.
##STR7##
[0074] On the other hand, a specific example of the polyamide or
polyester includes a material having a constitutional repeating
unit represented by the following general formula (7). ##STR8##
[0075] In the general formula (7), B is halogen, an alkyl group or
halogenated alkyl group having 1-3 carbon atoms, a phenyl group
replaced by one kind or two or more kinds of these, or a phenyl
group not replaced, and z is an integer of from 0 to 3.
[0076] E is a covalent bond, an alkenyl group or halogenated
alkenyl group having 2 carbon atoms, a CH.sub.2 group, a
C(CX.sub.3) .sub.2 group, a CO group, an O atom, an S atom, an
SO.sub.2 group, an Si(R).sub.2 group, or an NR group. In the
C(CX.sub.3).sub.2 group, X is a hydrogen atom or halogen. In the
Si(R).sub.2 group and the NR group, R is an alkyl group or
halogenated alkyl group having 1-3 carbon atoms. Incidentally, E is
located in a meta or para position with respect to the carbonyl or
Y group. The halogen is a fluorine atom, a chlorine atom, an iodine
atom or a bromine atom (hereinafter this rule applies to the
general formula (7)).
[0077] Moreover, Y is an O atom or an NH group. A is a hydrogen
atom, halogen, an alkyl group or halogenated alkyl group having 1-3
carbon atoms, a nitro group, a cyano group, a thioalkyl group
having 1-3 carbon atoms, an alkoxy group or halogenated alkoxy
group having 1-3 carbon atoms, an aryl group or halogenated aryl
group, an alkyl ester group having 1-9 carbon atoms, an aryl ester
group or substitutional derivative having 1-12 carbon atoms, or an
aryl amide group or substitutional derivative having 1-12 carbon
atoms.
[0078] Moreover, n is an integer of from 0 to 4, p is an integer of
from 0 to 3, q is an integer of from 1 to 3, and r is an integer of
from 0 to 3. Preferred polyamide or polyester is a material having
a constitutional repeating unit represented by the general formula
(8) in which both r and q are equal to 1 and in which at least one
of the biphenyl rings is replaced in the 2 and 2' positions.
##STR9##
[0079] In the general formula (8), m is an integer of from o to 3,
preferably 1 or 2, and each of x and y is 0 or 1 but both x and y
are not equal to 0 simultaneously. Incidentally, other symbols are
synonymous with those in the general formula (7) but E has a
para-oriented covalent bond with the carbonyl or Y group.
[0080] In the general formulae (7) and (8), when the number of B,
E, Y or A is two or more in a molecule, B, E, Y or A may be the
same or may be different. Similarly, z, n, m, x or y may be the
same or may be different. Incidentally, in this case, B, E, Y, A,
z, n, m, x and y can be judged independently.
[0081] The polyamide or polyester represented by the general
formula (7) may be formed from the same constitutional repeating
units or may have two kinds or three or more kinds of different
constitutional repeating units. In the latter case, the respective
constitutional repeating units may be provided in the form of
blocks or may be provided at random.
[0082] On the other hand, the specific example of polyimide is a
material having one or more constitutional repeating units each
containing a condensation polymerization product of
9,9-bis(aminoaryl)fluorine and aromatic tetracarboxylic dianhydride
and represented by the following general formula (9). ##STR10##
[0083] In the general formula (9), R is a hydrogen atom, halogen, a
phenyl group, a phenyl group replaced by an alkyl group having 1-4
halogens or 1-10 carbon atoms, or an alkyl group having 1-10 carbon
atoms. The four R can be determined independent of one another, so
that replacement can be made in a range of from 0 to 4. The
substituents may be preferably the same as described above but may
partially contain different materials. Incidentally, the halogen is
a fluorine atom, a chlorine atom, an iodine atom or a bromine atom
(hereinafter the same rule applies to the general formula (9)).
[0084] Z is a three-substitution aromatic group having 6-20 carbon
atoms. Preferred Z include a pyromellitic group, a polycyclic
aromatic group or substitutional derivative such as a naphthylene
group, a fluorenylene group, a benzofluorenylene group or an
antrathenylene group, and a group represented by the following
general formula (10). Incidentally, examples of the substituents in
the substitutional derivative of the polycyclic aromatic group
include halogen, and an alkyl group or fluorinated alkyl group
having 1-10 carbon atoms. ##STR11##
[0085] In the general formula (10), D is a covalent bond, a
C(R.sup.2).sub.2 group, a CO group, an O atom, an S atom, an
SO.sub.2 group, an Si(C.sub.2H.sub.5).sub.2 group, an
N(R.sup.3).sub.2 group, or a combination thereof, and m is an
integer of from 1 to 10. Incidentally, each of the R.sup.2 is
independently selected from a hydrogen atom and a C(R.sup.4).sub.3
group. Each of the R.sup.3 is independently selected from a
hydrogen atom, an alkyl group having about 1-20 carbon atoms and an
aryl group having about 6-20 carbon atoms. Each of the R.sup.4 is
independently selected from a hydrogen atom, a fluorine atom and a
chlorine atom.
[0086] Examples of polyimide other than the above description
include materials having units represented by the following general
formulae (11) and (12). Especially, polyimide having the unit
represented by the general formula (13) is preferred. ##STR12##
[0087] In the general formulae (11), (12) and (13), each of T and L
is halogen, an alkyl group or halogenated alkyl group having 1-3
carbon atoms, a phenyl group replaced by one kind or two or more
kinds of these, or a phenyl group not replaced. The halogen is a
fluorine atom, a chlorine atom, an iodine atom or a bromine atom
(hereinafter this rule applies to the general formulae (11), (12)
and (13)), and z is an integer of from 0 to 3.
[0088] Moreover, each of G and J is a covalent bond or junctional
bond, a CH.sub.2 group, a C(CX.sub.3).sub.2 group, a CO group, an O
atom, an S atom, an SO.sub.2 group, an Si(C.sub.2H.sub.5).sub.2
group, or an N(CH.sub.3) group. In the C(CX.sub.3).sub.2 group, X
is a hydrogen atom or halogen (hereinafter this rule applies to the
general formulae (11), (12) and (13)).
[0089] A is a hydrogen atom, halogen, an alkyl group or halogenated
alkyl group, a nitro group, a cyano group, a thioalkyl group, an
alkoxy group or halogenated alkyl group, an aryl group or
halogenated aryl group, or an alkyl ester group or substitutional
derivative.
[0090] R is a hydrogen atom, halogen, a phenyl group or
substitutional phenyl group such as phenyl halide, or an alkyl
group or substitutional alkyl group such as alkyl halide, n is an
integer of from 0 to 4, p is an integer of from 0 to 3, and q is an
integer of from 1 to 3.
[0091] Incidentally, in the case where a plurality of T, A, R or L
are provided independently in a molecule in the general formulae
(11), (12) and (13), the plurality of T, A, R or L may be the same
or may be different. Similarly, a plurality of z, n or m may be the
same or may be different. Incidentally, in this case, T, A, R, L,
z, n and m are judged independent of one another.
[0092] The polyimide represented by the general formula (9), (11),
(12) or (13) may be formed from the same constitutional repeating
units or may have two kinds or three or more kinds of different
constitutional repeating units. The different constitutional
repeating units may be formed by copolymerization of one kind or
two or more kinds selected from acid dianhydride or/and diamine
other than the above description. Aromatic diamine is especially
preferred as the diamine. In the latter case where different
constitutional repeating units are provided, the respective
constitutional repeating units may be provided in the form of
blocks or may be provided at random.
[0093] Examples of the acid dianhydride for forming the different
constitutional repeating units include pyromellitic dianhydride,
3,6-diphenylpyromellitic dianhydride,
3,6-bis(trifluoromethyl)pyromellitic dianhydride,
3,6-dibromopyromellitic dianhydride, 3,6-dichloropyromellitic
dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride,
2,3,3',4'-benzophenonetetracarboxylic dianhydride,
2,2',3,3'-benzophenonetetracarboxylic dianhydride,
3,3',4,4'-biphenylcarboxylic dianhydride, and
bis(2,3-dicarbophenyl)methane dianhydride.
[0094] Examples of the acid dianhydride further include
bis(2,5,6-trifluoro-3,4-dicarboxyphenyl)methane dianhydride,
2,2-bis(3,4-dicarboxyphenyl)-1,1,3,3-hexafluoropropane dianhydride,
bis(3,4-dicarboxyphenyl)ether dianhydride (4,4'-oxydipththalic
anhydride), bis(3,4-dicarboxyphenyl)sulfone diamhydride
(3,3',4,4'-diphenylsulfonetetracarboxylic anhydride), and
4,4'-[4,4'-isopropylidene-di(p-phenyleneoxy)]bis(phthalic
anhydride).
[0095] Examples of the acid dianhydride further include
N,N-(3,4-dicarboxyphenyl)-N-methylamine dianhydride,
bis(3,4-dicarboxyphenyl)diethylsilane dianhydride, naphthalene
tetracarboxylic dianhydride such as
2,3,6,7-naphthalene-tetracarboxylic dianhydride and
1,2,5,6-naphthalene-tetracarboxilic dianhydride,
2,6-dicholo-naphthalene-1,4,5,8-tetracarboxylic dianhydride, and
heterocyclic aromatic tetracarboxylic dianhydride such as
thiophene-2,3,4,5-tetracarboxylic dianhydride,
pyrazine-2,3,5,6-tetracarboxylic dianhydride and
pyridine-2,3,5,6-tetracarboxylic dianhydride.
[0096] The acid dianhydride to be preferably used is
2,2'-substitutional dianhyride such as
2,2'-dibromo-4,4',5,5'-biphenyltetracarboxylic dianhydride,
2,2'-dichloro-4,4',5,5'-biphenyltetracarboxylic dianhydride, and
2,2'-trihalo-substitutional dianhydride. Especially,
2,2-bis(trifluoromethyl)-4,4',5,5'-biphenyltetracarboxylic
dianhydride is preferred.
[0097] On the other hand, examples of the diamine for forming the
different constitutional repeating units include: benzene diamine
such as (o, m or p-)phenylene diamine, 2,4-diaminotoluene,
1,4-diamino-2-methoxybenzene, 1,4-diamino-2-phenylbenzene, and
1,3-diamino-4-chlorobenzebe; 4,4'-diaminobiphenyl;
4,4'-diaminophenylmethane; 2,2-bis(4-aminophenyl)propane;
2,2-bis(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane;
4,4-diaminodiphenyl ether; 3,4'-diaminodiphenyl ether;
1,3-bis(3-aminophenoxy)benzene; 1,3-bis(4-aminophenoxy)benzene; and
1,4-bis(4-aminophenoxy)benzene.
[0098] Examples of the diamine further include:
4,4'-bis(4-aminophenoxy)biphenyl; 4,4'-bis(3-aminophenoxy)biphenyl;
2,2-bis(4-[4-aminophenoxy)phenyl]propane;
2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane;
4,4'-diaminodiphenylthio ether; 4,4'-diaminodiphenyl sulfone;
2,2'-diaminobenzophenone; 3,3'-diaminobenzophenone; naphthalene
diamine such as 1,8-diaminonaphthalene, and 1,5-diaminonaphthalene;
and heterocyclic aromatic diamine such as 2,6-diaminopyridine,
2,4-diaminopyridine, and 2,4-diamino-S-triazine.
[0099] An example of the polyimide to be preferably used is
heat-resistant solvent-soluble polyimide prepared by use of
aromatic acid dianhydride such as
2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride,
4,4'-bis(3,4-dicarboxyphenyl)-2,2-diphenylpropane dianhydride,
naphthalenetetracarboxylic anhydride, and
bis(3,4-dicarboxyphenyl)sulfone dianhydride.
[0100] Another example of the polyimide to be preferably used is
heat-resistant solvent-soluble polyimide prepared by use of
aromatic diamine such as 4,4'-(9-fluorenylidene)-dianiline,
2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl,
3,3'-dichloro-4,4'-diaminodiphenylmethane,
2,2'-dichloro-4,4'-diaminobiphenyl,
2,2',5',5'-tetrachlorobenzidine,
2,2-bis(4-aminophenoxyphenyl)propane,
2,2-bis(4-aminophenoxyphenyl)hexafluoropropane,
1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, and
1,3-bis(3-aminophenoxy)benzene, as the diamine.
[0101] On the other hand, the polyamideimide or polyesterimide is
not particularly limited but one kind or two or more kinds of
suitable polyamideimide or polyesterimide may be used. Especially,
polyamideimide described in JP 61-162512, polyesterimide described
in JP 64-38472 etc. may be used preferably.
[0102] The molecular weight of the polymer for forming the
birefringent layer B is not particularly limited but it is
preferable that the polymer exhibits a solid state at room
temperature and is soluble in a solvent. Especially, the
weight-average molecular weight is preferably from 10,000 to
1,600,000, more preferably from 20,000 to 500,000, especially
preferably from 50,000 to 200,obo from the point of view of film
strength, prevention of cracking caused by stretching and
shrinking, distortion, etc. in the form of a film, solubility
(anti-gelation) to the solvent, and so on. Incidentally, the
weight-average molecular weight is a value measured by a gel
permeation chromatography (GPC) in the condition that
dimethylformamide is used as a solvent is used while polyethylene
oxide is used as a standard sample.
[0103] A solid polymer of polyaryl ether ketone, polyamide,
polyester, polyimide, polyamideimide or polyesterimide as described
above may be used singly or two or more kinds of these materials
may be used in combination for forming the retardation film. For
example, a mixture of two or more kinds of solid polymers having
different functional groups, such as a mixture of polyaryl ether
ketone and polyamide may be used. Particularly, a solid polymer of
polyimide is more excellent than the conventional solid polymer of
polycarbonate because the thickness of the retardation film can be
reduced while the same effect can be kept.
[0104] Moreover, one kind or two or more kinds of suitable polymers
other than the aforementioned polymers may be used additionally as
long as the orientation of the solid polymer is not reduced
remarkably. Incidentally, examples of the additional polymer
include thermoplastic resins such as polyethylene, polypropylene,
polystyrene, polymethyl methacrylate, ABS resin, AS resin,
polyacetate, polycarbonate, polyamide, polyethylene terephthalate,
polybutylene terephthalate, polyphenylene sulfide,
polyether-sulfone, polyketone, polyimide, polycyclohexanedimethanol
terephthalate, polyarylate, and liquid crystal polymer (inclusive
of photopolymerizable liquid crystal monomer).
[0105] Examples of the additional polymer further include
heat-curable resins such as an epoxy resin, a phenol resin, and a
novolac resin. The amount of use of the additional polymer is not
particularly limited if the orientation is not reduced remarkably.
Generally, the amount of use of the additional polymer is not
larger than 50% by weight, preferably not larger than 40% by
weight, especially preferably not larger than 30% by weight.
[0106] The formation of a transparent film as a base of the
retardation film can be performed in such a manner that a solid
polymer is liquefied and spread and then the spread layer is
solidified. For the formation of the transparent film, various
additives such as a stabilizer, a plasticizer, metals, etc. may be
mixed if necessary. A suitable method such as a method of heating
the thermoplastic solid polymer to melt it, or a method of
dissolving the solid polymer in a solvent to prepare a solution can
be used for liquefying the solid polymer.
[0107] Accordingly, in the former melt solution, the solidification
of the spread layer can be performed in such a manner that the
spread layer is cooled. In the latter solution, the solidification
of the spread layer can be performed in such a manner that the
solvent is removed from the spread layer to dry the spread layer.
One kind or two or more kinds of suitable methods such as a natural
drying (air drying) method, a heat drying method, especially a heat
drying method at 40 to 200.degree. C., a suction drying method,
etc. can be used for the drying. The method of applying a polymer
solution is preferred from the point of view of production
efficiency and suppression of optical anisotropy.
[0108] Examples of the solvent include: halogenated hydrocarbons
such as chloroform, dichloromethane, carbon tetrachloride,
dichloroethane, tetrachloroethane, trichloroethylene,
tetrachloroethylene, chlorobenzene, and ortho-dichlorobenzene;
phenols such as phenol, and para-chlorophenol; aromatic
hydrocarbons such as benzene, toluene, xylene, methoxybenzene, and
1,2-dimethoxybenzene; ketones such as acetone, methylethyl ketone,
methylisobutyl ketone, cyclohexanone, cyclopentanone, 2-pyrolidone,
and N-methyl-2-pyrolidone; and esters such as ethyl acetate, and
butyl acetate.
[0109] Examples of the solvent further include: alcohols such as
t-butyl alcohol, glycerin, ethylene glycol, triethylene glycol,
ethylene glycol monoethyl ether, diethylene glycol dimethyl ether,
propylene glycol, dipropylene glycol, and 2-methyl-2,4-pentandiol;
amides such as dimethylformamide, and dimethylacetoamide; nitrites
such as acetonitrile, and butyronitrile; ethers such as diethyl
ether, dibutyl ether, and tetrahydrofuran; and others such as
methylene chloride, carbon disulfide, ethylcellosolve, and
butylcellosolve.
[0110] The solvent may be used singly or a suitable combination of
two or more kinds of solvents may be used. The solution is prepared
in such a manner that preferably 2 to 100 parts by weight of a
solid polymer, more preferably 5 to 50 parts by weight of a solid
polymer, especially preferably 10 to 40 parts by weight of a solid
polymer are dissolved in 100 parts by weight of a solvent from the
point of view of viscosity suitable for the formation of a
film.
[0111] A suitable film-forming method such as a casting method or
an extrusion method such as a spin coating method, a roll coating
method, a flow coating method, a printing method, a dip coating
method, a flow-out film-forming method, a bar coating method, a
gravure printing method, etc. can be used for spreading the
liquefied solid polymer. Especially, a solution film-forming method
such as a casting method can be used preferably from the point of
view of mass production of films little in thickness variation,
orientation distortion variation, etc.
[0112] It is preferable from the point of view of achieving good
contrast liquid crystal display in a wide viewing angle that the
birefringent layer B has the relation nx>ny>nz in which nx is
the maximum in-plane refractive index, ny is an in-plane refractive
index in a direction perpendicular to the direction of nx, and nz
is a thicknesswise refractive index. A retardation film having the
birefringent layer B having the relation nx>ny>nz or a
laminated film using the retardation film can be used particularly
preferably in a VA mode or OCB mode liquid crystal display.
[0113] For example, the relation nx>ny>nz can be achieved by
applying an extending process or/and a contracting process to a
film. For example, the extending process can be performed as a
stretching process etc. One kind or two or more kinds of suitable
methods such as sequential type or simultaneous type biaxial
stretching methods and free end type or fixed end type uniaxial
stretching methods can be used for the stretching process. The
temperature for the stretching process can be determined in
conformity to the background art. Generally, the temperature is
preferably near to the glass transition temperature of the solid
polymer for forming the transparent film and more preferably not
lower than the glass transition temperature and lower than the
melting temperature.
[0114] On the other hand, for example, the contracting process can
be performed by a method in which a transparent film is applied and
formed on a base material so that size change caused by the
temperature change of the base material etc. is used for making
shrinking force act. In this case, a base material to which
shrinkability of a heat-shrinkable film etc. is given can be used.
In this case, it is preferable that a stretching machine or the
like is used for controlling the rate of shrinkage.
[0115] The preferred method for producing the retardation film
having the birefringent layer B is a method comprising the steps
of: dissolving a solid polymer in a solvent to liquefy the solid
polymer; spreading the liquefied polymer on a support film; drying
the liquefied polymer to solidify the liquefied polymer; and
orienting molecules in a plane by applying either or both of an
extending process and a shrinking process to a transparent film or
coating film made of the solidified polymer so that the
characteristic nx>ny>nz is provided. According to this
method, the transparent film can be processed in a state in which
the transparent film is supported by the support film. This method
is excellent in production efficiency, processing accuracy etc., so
that continuous production can be achieved.
[0116] The retardation film may be formed from the transparent film
integrated with the support film or may be formed from the
transparent film separated from the support film. In the former
case where the transparent film is integrated with the support
film, a retardation generated in the support film by the stretching
process or the like can be used as a retardation in the retardation
film. This retardation film is a composite film. The latter case
where the transparent film is separated from the support film is
advantageous to the case where the retardation generated in the
support film by the stretching process or the like is inconvenient.
Incidentally, a film made of the aforementioned solid polymer may
be also used as the support film in the composite film.
[0117] The polymer described in Japanese Patent Laid-Open No.
2001-343529 (WO 01/37007), for example, a resin composition
containing (1) a thermoplastic resin having substitution or/and
non-substitution imide groups in a side chain, and (2) a
thermoplastic resin having substitution or/and non-substitution
phenyl and nitrile groups in the chain side and including the
aforementioned 1 and 2 can be used for forming the support film.
Such a film can be used for supporting the optically uniaxial layer
A made of the liquid crystal layer.
[0118] Incidentally, a specific example of the resin composition is
a resin composition containing an isobutene-N-methyl maleimide
crosslinked polymer and an acrylonitrile-styrene copolymer. The
support film can be prepared as a film etc. made of a mixture
extrudate of the resin composition etc. Incidentally, the polymer
can be used for forming the transparent film.
[0119] The preferred retardation characteristic of the retardation
film having a slow axis in the lengthwise direction from the point
of view of the optically compensating effect or the like exhibits
preferably Re of from 5 to 1,000 nm, more preferably Re of from 10
to 800 nm, especially preferably Re of 20 to 500 nm in
(nx-ny)d=.DELTA.nd=Re and (nx-nz)d=Rz in which nx and ny are
in-plane refractive indices, nz is a thicknesswise refractive
index, and d is the thickness of the retardation film. Rz is
preferably from 5 to 5,000 nm, more preferably from 10 to 3,000 nm,
especially preferably from 30 to 1,000 nm.
[0120] The magnitudes of Re and Rz can be controlled in accordance
with the kind of the polymer, the method of forming the spread
layer such as the method of applying the liquefied polymer, the
method of solidifying the spread layer such as the drying
condition, the thickness of the film to be formed, the stretching
condition, and so on.
[0121] In general, the thickness of the retardation film is
preferably from 5 to 300 .mu.m, more preferably from 10 to 200
.mu.m, especially preferably from 20 to 150 .mu.m. The thickness of
the birefringent layer B provided as a coating film on the support
film is preferably from 0.5 to 30 .mu.m, more preferably from 1 to
25 .mu.m, especially preferably from 2 to 20 .mu.m in general.
[0122] For lamination of the polarizing film and the retardation
film, the retardation film can be made to serve as a transparent
protective layer in the polarizing film. In this case, the
thickness of the laminated film and, accordingly, the thickness of
the liquid crystal display or the like can be reduced.
[0123] For the formation of a laminated film, that is, for
lamination of a polarizing film and one or two or more retardation
films, an adhesive layer or a pressure-sensitive adhesive layer can
be used if necessary. Such a laminated film can be preferably used
for compensating the retardation caused by the birefringence of the
cell for the purpose of widening the viewing angle of the liquid
crystal cell, improving contrast, etc.
[0124] For practical use of the polarizing film or the laminated
film, an adhesive layer or pressure-sensitive adhesive layer or
adhesive layers or pressure-sensitive adhesive layers can be
provided on a single surface or on both surfaces of another member
such as a liquid crystal cell for the purpose of bonding the film
to the other member such as the liquid crystal cell. For the
formation of the pressure-sensitive adhesive layer, it is possible
to use a transparent pressure-sensitive adhesive made of a suitable
polymer such as an acrylic polymer, a silicone polymer, polyester,
polyurethane, polyether, synthetic rubber, etc. Especially, an
acrylic pressure-sensitive adhesive is preferred from the point of
view of optical transparency, tackiness, weather resistance,
etc.
[0125] Suitable additives such as natural and synthetic resins,
fillers and pigments of glass fiber, glass beads, metal powder and
another inorganic powder, colorants and antioxidants, etc. can be
mixed with the pressure-sensitive adhesive layer if necessary.
Transparent fine particles may be contained in the
pressure-sensitive adhesive layer to provide the pressure-sensitive
adhesive layer as a layer exhibiting light-diffusing
characteristic. In the case where the pressure-sensitive adhesive
later is exposed out of surface, it is preferable that a separator
or the like is temporarily fixed to prevent the surface of the
pressure-sensitive adhesive layer from contamination or the like
until the tack adhesive layer is put into practical use.
[0126] Although the formation of the laminated film can be
performed by a successively individual laminating method in a
process of production of a liquid crystal display or the like,
previous lamination has an advantage that efficiency in production
of the liquid crystal display or the like can be improved by
excellence in quality stability, laminating workability, etc.
[0127] The polarizing film or the laminated film according to the
invention can be preferably used for forming various display
devices such as a liquid crystal display. For application to such
various display devices, one layer or two or more layers selected
from other optical layers such as a reflection plate, a
semi-transmissive reflection plate, a brightness enhancement film,
another retardation plate, a diffusion control film, a polarizing
and scattering film, etc. may be laminated through an adhesive
layer or a pressure-sensitive adhesive layer to provide an optical
member if necessary. Suitable bonding means such as the
aforementioned pressure-sensitive adhesive layer can be used for
the lamination.
[0128] The reflection plate is provided on the polarizing film for
forming a reflective polarizing film. The reflective polarizing
film is generally used for forming a liquid crystal display
(reflective liquid crystal display) of the type in which' the
reflective polarizing film is disposed on the back side of a liquid
crystal cell and reflects incident light from the viewing side
(display side). The reflective polarizing film has an advantage
that internal provision of a light source such as a backlight unit
can be dispensed with to attain reduction in thickness of the
Iiquid-crystal display.
[0129] The formation of the reflective polarizing film can be
performed by a suitable method such as a method of providing a
reflection layer made of metal or the like on a single surface of
the polarizing film through a transparent protective layer or the
like if necessary. A specific example of the method is a method in
which a sheet of foil or a vapor-deposition film made of a
reflective metal such as aluminum is provided on a single surface
of a transparent protective layer matted if necessary.
[0130] The reflection layer may be of a light-diffusing type. For
example, the light-diffusing type reflection layer can be obtained
by a method in which transparent fine particles are contained in a
transparent protective layer to form a surface of the transparent
protective layer as a fine roughness structure and in which a
reflection layer is formed on the transparent protective layer so
that the fine roughness structure is reflected on the transparent
protective layer. The reflection layer having the surface of the
fine roughness structure has an advantage that the reflection layer
diffuses incident light by irregular reflection to prevent
directivity and glaring appearance and suppress variation in
brightness and darkness. The reflection layer on which the fine
roughness structure is reflected can be formed in such a manner
that a metal reflection layer is provided on the fine roughness
structure by a suitable method such as a vapor deposition method or
a plating method such as a vacuum vapor deposition method, an
ion-plating method, a sputtering method, etc.
[0131] Incidentally, the reflection layer can be provided in the
form of a reflection sheet or the like by a method of providing the
reflection layer on a suitable film instead of the method of
directly providing the reflection layer on the transparent
protective layer of the polarizing film. The form of use of the
reflection layer of metal having a reflection surface coated with a
film, a polarizing film, etc. is preferred from the point of view
of prevention of reduction in reflectance due to oxidation,
long-term persistence of initial reflectance, avoidance of separate
provision of a protective layer, and so on.
[0132] The reflection layer may be of a semi-transmissive type made
of a half-mirror or the like and capable of reflecting light and
transmitting light. The semi-transmissive polarizing film is also
generally used for forming a display device of the type in which
the semi-transmissive polarizing film is disposed on the back side
of a liquid crystal cell so that incident light from the viewing
side (display side) is reflected to achieve display when the liquid
crystal display is used in a relatively bright atmosphere whereas a
built-in light source such as a backlight unit disposed on the back
side of the semi-transmissive polarizing film is used to achieve
display when the liquid crystal display is used in a relatively
dark atmosphere. Accordingly, the semi-transmissive polarizing film
is useful for forming a display device of the type in which energy
caused by use of the light source such as a backlight unit can be
saved in the bright atmosphere whereas the built-in light source
can be used in the relatively dark atmosphere.
[0133] On the other hand, the brightness enhancement film is used
for suppressing absorption loss etc. due to the polarizing film to
attain enhancement in luminance. A suitable film can be used as the
brightness enhancement film. Incidentally, an example of the
brightness enhancement film is a film (e.g. "D-BEF" manufactured by
3M) exhibiting characteristic of transmitting linearly polarized
light with a predetermined axis of polarization but reflecting
other light components, such as a multilayer thin film of
dielectrics or a multilayer laminate of thin films different in
refractive index anisotropy.
[0134] Another example of the brightness enhancement film is a film
exhibiting characteristic of reflecting either of left-handed and
right-handed circularly polarized light components but transmitting
the other light components, such as a cholesteric liquid crystal
layer, especially a cholesteric liquid crystal polymer-oriented
film or the oriented liquid crystal layer supported on a film base
(e.g. "PCF350" manufactured by NITTO DENKO CORP. or "Transmax"
manufactured by MERCK & CO., INC.). The chlesteric liquid
crystal type film may be used in combination with a quarter-wave
plate in accordance with necessity for the purpose of converting
circularly polarized light into linearly polarized light.
[0135] As the retardation plate, there may be used a plate
exhibiting a suitable retardation, such as a stretched film of any
kind of polymer by a suitable uniaxial or biaxial method, a polymer
film oriented in the Z axis, a liquid crystal macromolecular layer,
etc. besides the quarter-wave plate. The diffusion control film is
used for controlling glaring, scattering light etc. concerned with
the viewing angle and resolution. An optically functional film
using diffusion, scattering or/and refraction is used as the
diffusion control film. The polarizing and scattering film is
provided as a film containing a scattering substance so that
scattering anisotropy occurs in polarized light in accordance with
the direction of vibration. The polarizing and scattering film is
used for controlling polarized light.
[0136] Although the optical member provided as a laminate of two
optical layers or three or more optical layers can be formed by a
successively individually laminating method in a process of
production of a liquid crystal display or the like, a previously
laminated optical member has an advantage that efficiency in
production of the liquid crystal display or the like can be
improved because of excellence in quality stability, assembling
workability, etc.
[0137] A pressure-sensitive adhesive layer or an adhesive layer for
bonding the optical member to another member such as another
optical layer or a liquid crystal cell can be provided on a
necessary surface of the optical member. The adhesive layer can be
formed in accordance with the above description. Especially, a
pressure-sensitive adhesive layer low in hygroscopicity and
excellent in heat resistance may be used preferably from the point
of view of prevention of a foaming phenomenon and a peeling
phenomenon due to hygroscopicity, reduction in optical
characteristic and prevention of a warp of the liquid crystal cell
due to the thermal expansion difference or the like, the
formability of a display device excellent in quality and
durability, and so on. Transparent fine particles may be mixed with
the pressure-sensitive adhesive layer or the adhesive layer so that
the pressure-sensitive adhesive layer or the adhesive layer can
exhibit light-diffusing characteristic.
[0138] When the pressure-sensitive adhesive layer or the adhesive
layer provided on the polarizing film, the laminated film or the
optical member is exposed out of surface, it is preferable that the
layer is temporarily covered with a separator for the purpose of
anti-contamination or the like until the pressure-sensitive
adhesive layer or the like is put into practical use. The separator
can be obtained by a method in which a coating layer of a suitable
releasant such as a silicone type releasant, a long-chain alkyl
type releasant, a fluorine type releasant, molybdenum sulfide, etc.
is provided on the support film or a suitable sheet of paper or the
like if necessary.
[0139] The polarizing film, the retardation film or each of the
layers such as the transparent protective layer, the
pressure-sensitive adhesive layer, etc. for forming the laminated
film, the optical member, etc. may be provided so that
ultraviolet-absorbing power is given to the film or layer by a
suitable method such as a method in which the film or layer is
treated with an ultraviolet-absorbing agent such as a salicylic
ester compound, a benzophenone compound, a benzotriazole compound,
a cyanoacrylate compound, a nickel complex salt compound, etc.
EXAMPLES
[0140] The present invention is now illustrated in greater detail
with reference to Examples and Comparative Examples, but it should
be understood that the present invention is not to be construed as
being limited thereto.
[0141] Incidentally, in the following description, a polarizer of a
polarizing film stretched in an MD direction in a stretching step
is referred to as "MD polarizer", and a polarizer of a polarizing
film stretched in a TD direction is referred to as "TD polarizer".
A retardation film stretched in the MD direction is referred to as
"MD retardation film", and a retardation film stretched in the TD
direction is referred to as "TD retardation film".
Example 1
[0142] A film was unrolled out successively from a roll of film
made of polyvinyl alcohol (PVA) having the degree of polymerization
of 2400 and having a thickness of 75 .mu.m, a width of 0.3 m and a
length of 500 m. The film was stretched by five times in the
widthwise direction by a tenter stretching machine at 120.degree.
C. Then, the stretched film was immersed in a dye bath of a mixture
of iodine and potassium iodine at 30.degree. C. for 1 minute while
shrinking in the lengthwise direction was suppressed. Then, the
stretched film was immersed in an aqueous solution of 5% potassium
iodide at 30.degree. C. for 5 seconds. Then, the stretched film was
dried at 45.degree. C. for 7 minutes while fixed so that shrinking
of the film was suppressed. The film obtained thus was cut by a
width of 1 m. Triacetyl cellulose (TAC) films were laminated on
both surfaces of the film through PVA water-soluble adhesive
agents. Thus, a TD polarizing film having a three-layer structure
of TAC film/TD polarizer/TAC film was obtained and rolled up.
Comparative Example 1
[0143] A film was unrolled out successively from a roll of film
made of PVA having the degree of polymerization of 2400 and having
a thickness of 75 .mu.m, a width of 1.2 m and a length of 500 m.
The film was stretched by 2.5 times in the lengthwise direction by
a roll type longitudinal stretching method while the film was
immersed in pure water at 30.degree. C. for 1 minute. Then, the
stretched film was stretched by 1.2 times in the lengthwise
direction while immersed in a dye bath of a mixture of iodine and
potassium iodine at 30.degree. C. for 1 minute. Then, the stretched
film was stretched by twice in the lengthwise direction while
immersed in a bath of an aqueous solution of 4% boric acid at
60.degree. C. for 2 minutes. Then, the stretched film was immersed
in an aqueous solution of 5% potassium iodide at 30.degree. C. for
5 seconds. Then, the stretched film was dried at 45.degree. C. for
7 minutes. The film obtained thus was cut by a width of 1 m. TAC
films were stuck onto both surfaces of the film in the same manner
as in Example 1. Thus, an MD polarizing film having a three-layer
structure of TAC film/MD polarizer/TAC film was obtained and rolled
up.
Referential Example 1
[0144] A film was unrolled out successively from a roll of film
made of a norbornene resin film (ARTON manufactured by JSR CORP.)
and having a thickness of 100 pm, a width of 1.2 m and a length of
500 m. The film was stretched by 1.3 times in the lengthwise
direction by a roll type longitudinal stretching method at
170.degree. C. Then, the stretched film was cut by a width of 1 m.
Thus, an (MD) retardation film was obtained and rolled up. The film
had Re of 100 nm. The Re distribution (variation: difference
between a maximum value and a minimum value, this rule applies
hereunder) in the widthwise direction was 5 nm. The slow axis
distribution (in the lengthwise direction) was 1 degree.
[0145] Incidentally, Re (and Rz which will be described later) was
calculated on the basis of refractive indices measured by
KOBRA-21ADH manufactured by OJI SCIENTIFIC INSTRUMENTS. In the
following description, refractive indices were measured in the same
manner.
Referential Example 2
[0146] A (TD) retardation film was obtained in the same manner as
in Referential example 1 except that an ARTON film was stretched by
1.5 times in the width direction by a tenter stretching machine at
175.degree. C. The retardation film was rolled up. The film had Re
of 100 nm. The Re distribution in the widthwise direction was 8 m.
The slow axis distribution (in the widthwise direction) was 2.5
degrees.
Referential Example 3
[0147] A film was unrolled out successively from a roll of TAC film
having a thickness of 50 .mu.m, a width of 1.2 m and a length of
500 m. A cyclohexanone solution of 15% by weight if polyimide
synthesized from 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane and
2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl was successively
applied on the film and was dried at 120.degree. C. for 10 minutes.
Thus, a 6 .mu.m-thick polyimide layer was formed on the film. The
film was stretched by 1.05 times in the lengthwise direction by a
roll type longitudinal stretching method at 150.degree. C. Then,
the stretched film was cut by a width of 1 m. Thus, an (MD)
retardation film was obtained and rolled up. The film had Re of 50
nm and Rz of 280 nm. The Re distribution in the widthwise direction
was 2 nm. The slow axis distribution (in the lengthwise direction)
was 0.5 degrees.
Referential Example 4
[0148] A (TD) retardation film was obtained in the same manner as
in Referential example 3 except that a film was stretched by 1.1
times in the widthwise direction by a tenter stretching machine at
150.degree. C. The retardation film was rolled up. The film had Re
of 50 nm and Rz of 290 nm. The Re distribution in the widthwise
direction was 7 nm. The slow axis distribution (in the lengthwise
direction) was 1.5 degrees.
Referential Example 5
[0149] A film was unrolled out successively from a roll of film
made of a norbornene resin film (ZEONOA manufactured by ZEON CORP.)
and having a thickness of 100 .mu.m, a width of 1.3 m and a length
of 1000 m. The film was stretched by 1.1 times in the lengthwise
direction by a roll type longitudinal stretching method at
140.degree. C. Then, the stretched film was cut by a width of 1 m.
Thus, an (MD) retardation film was obtained and rolled up. The film
had Re of 100 nm. The Re distribution in the widthwise direction
was 4 nm. The slow axis distribution (in the lengthwise direction
was 1.6 degrees.
Referential Example 6
[0150] A film was unrolled out successively from a roll of film
made of a polycarbonate resin film (PF film manufactured by KANEKA
CORP.) and having a thickness of 100 .mu.m, a width of 1.2 m and a
length of 500 m. The film was stretched by 1.15 times in the
lengthwise direction by a roll type longitudinal stretching method
at 150.degree. C. Then, the stretched film was cut by a width of 1
m. Thus, an (MD) retardation film was obtained and rolled up. The
film had Re of 100 nm. The Re distribution in the widthwise
direction was 5 nm. The slow axis distribution (in the lengthwise
direction) was 1.8 degrees.
Referential Example 7
[0151] A film was unrolled out successively from a roll of film
made of a cellulose acetate propionate resin film (KA film
manufactured by KANEKA CORP.) and having a thickness of 100 .mu.m,
a width of 1.2 m and a length of 500 m. The film was stretched by
1.5 times in the lengthwise direction by a roll type longitudinal
stretching method at 150.degree. C. Then, the stretched film was
cut by a width of 1 m. Thus, an (MD) retardation film was obtained
and rolled up. The film had Re of 100 nm. The Re distribution in
the widthwise direction was 5 nm. The slow axis distribution (in
the lengthwise direction) was 1.2 degrees.
Example 2
[0152] While a (TD) polarizing film obtained in Example 1 and an
(MD) retardation film obtained in Referential example 1 were
unrolled out successively from rolls of film respectively, the
films were laminated through an acrylic pressure-sensitive adhesive
layer so that the lengthwise directions of the films were made to
correspond to each other. Thus, a laminated film in which the
absorption axis of the polarizing film was perpendicular to the
slow axis of the retardation film was obtained continuously.
Example 3
[0153] While a (TD) polarizing film obtained in Example 1 and an
(MD) retardation film obtained in Referential example 3 were
unrolled out successively from rolls of film respectively, the
films were laminated through an acrylic pressure-sensitive adhesive
layer so that the lengthwise directions of the films were made to
correspond to each other. Thus, a laminated film in which the
absorption axis of the polarizing film was perpendicular to the
slow axis of the retardation film was obtained continuously.
Example 4
[0154] While a (TD) polarizing film obtained in Example 1 and an
(MD) retardation film obtained in Referential example 5 were
unrolled out successively from rolls of film respectively, the
films were laminated through an acrylic pressure-sensitive adhesive
layer so that the lengthwise directions of the films were made to
correspond to each other. Thus, a laminated film in which the
absorption axis of the polarizing film was perpendicular to the
slow axis of the retardation film was obtained continuously.
Example 5
[0155] While a (TD) polarizing film obtained in Example 1 and an
(MD) retardation film obtained in Referential example 6 were
unrolled out successively from rolls of film respectively, the
films were laminated through an acrylic pressure-sensitive adhesive
layer so that the lengthwise directions of the films were made to
correspond to each other. Thus, a laminated film in which the
absorption axis of the polarizing film was perpendicular to the
slow axis of the retardation film was obtained continuously.
Example 6
[0156] While a (TD) polarizing film obtained in Example 1 and an
(MD) retardation film obtained in Referential example 7 were
unrolled out successively from rolls of film respectively, the
films were laminated through an acrylic pressure-sensitive adhesive
layer so that the lengthwise directions of the films were made to
correspond to each other. Thus, a laminated film in which the
absorption axis of the polarizing film was perpendicular to the
slow axis of the retardation film was obtained continuously.
Comparative Example 2
[0157] While an (MD) polarizing film obtained in Comparative
Example 1 and a (TD) retardation film obtained in Referential
example 2 were unrolled out successively from rolls of film
respectively, the films were laminated through an acrylic
pressure-sensitive adhesive layer so that the lengthwise directions
of the films were made to correspond to each other. Thus, a
laminated film in which the absorption axis of the polarizing film
was perpendicular to the slow axis of the retardation film was
obtained continuously.
Comparative Example 3
[0158] While an (MD) polarizing film obtained in Comparative
Example 1 and a (TD) retardation film obtained in Referential
example 4 were unrolled out successively from rolls of film
respectively, the films were laminated through an acrylic
pressure-sensitive adhesive layer so that the lengthwise directions
of the films were made to correspond to each other. Thus, a
laminated film in which the absorption axis of the polarizing film
was perpendicular to the slow axis of the retardation film was
obtained continuously.
Comparative Example 4
[0159] An (MD) polarizing film obtained in Comparative Example 1
and an (MD) retardation film obtained in Referential example 1 were
cut into films with a predetermined size. The films were laminated
through an acrylic pressure-sensitive adhesive layer while the
absorption axis of the polarizing film was perpendicular to the
slow axis of the retardation film. Thus, a laminated film was
obtained.
Comparative Example 5
[0160] While an (MD) polarizing film obtained in Comparative
Example 1 and an (MD) retardation film obtained in Referential
example 5 were unrolled out successively from rolls of film
respectively, the films were laminated through an acrylic
pressure-sensitive adhesive layer so that the lengthwise directions
of the films were made to correspond to each other. Thus, a
laminated film in which the absorption axis of the polarizing film
was parallel to the slow axis of the retardation film was obtained
continuously.
Comparative Example 6
[0161] While an (MD) polarizing film obtained in Comparative
Example 1 and an (MD) retardation film obtained in Referential
example 6 were unrolled out successively from rolls of film
respectively, the films were laminated through an acrylic
pressure-sensitive adhesive layer so that the lengthwise directions
of the films were made to correspond to each other. Thus, a
laminated film in which the absorption axis of the polarizing film
was parallel to the slow axis of the retardation film was obtained
continuously.
Comparative Example 7
[0162] While an (MD) polarizing film obtained in Comparative
Example 1 and an (MD) retardation film obtained in Referential
example 7 were unrolled out successively from rolls of film
respectively, the films were laminated through an acrylic
pressure-sensitive adhesive layer so that the lengthwise directions
of the films were made to correspond to each other. Thus,-a
laminated film in which the absorption axis of the polarizing film
was parallel to the slow axis of the retardation film was obtained
continuously.
Evaluation Test 1
[0163] Laminated films obtained in Examples and Comparative
Examples and each having an effective width of 1 m were used in the
following combinations to obtain Samples 1 to 5. The maximum size
of a screen allowed to be formed in the case where the laminated
films were disposed on the viewing side and back side of a VA type
liquid crystal cell having a 16:9 aspect ratio so that the
absorption axes of polarizing films were perpendicular to each
other was examined while these samples were used. Results of the
examination were shown in Table 1. TABLE-US-00001 TABLE 1 Laminated
film Maximum Screen Viewing Side Back Side Size Sample 1
Comparative Example 2 80 inches Example 2 Sample 2 Comparative
Example 3 80 inches Example 3 Sample 3 Comparative Comparative 45
inches Example 2 Example 2 Sample 4 Comparative Comparative 45
inches Example 3 Example 3 Sample 5 Comparative Comparative 45
inches Example 2 Example 4
Evaluation Test 2
[0164] A laminated film obtained in each of Examples and
Comparative Examples and having a predetermined size was disposed
on the back side of a VA type liquid crystal cell available on the
market while a polarizing film obtained in Example 1 was disposed
on the viewing side so that the absorption axis of the polarizing
film was perpendicular to that on the back side. Thus, a liquid
crystal display was formed. In this manner, the following liquid
crystal display Samples 6 to 15 were obtained. The visibility of
display of each of the liquid crystal displays was examined.
Results of the examination were shown in Table 2. TABLE-US-00002
TABLE 2 Laminated film Visibility Sample 6 Example 2 Good Sample 7
Example 3 Good Sample 8 Comparative Example 2 Ununiform Sample 9
Comparative Example 3 Ununiform Sample 10 Example 4 Good Sample 11
Example 5 Good Sample 12 Example 6 Good Sample 13 Comparative
Example 5 Ununiform Sample 14 Comparative Example 6 Ununiform
Sample 15 Comparative Example 7 Ununiform
[0165] It is apparent from the Samples 1 to 5 that the screen size
can be increased when the laminated film (Samples 1 and 2) using
the polarizing film according to the invention is used. It is
apparent from the Samples 6 to 12 that the laminated film (Samples
6, 7 and 10 to 12) according to the invention can achieve good
display because variation in the slow axis of the retardation film
is few. It is apparent from the Samples 10 to 15 that good display
can be achieved when the absorption axis of the polarizing film and
the slow axis of the retardation film are made to be perpendicular
to each other as in the laminated film (Samples 10 to 12) according
to the invention.
[0166] According to the invention, a long polarizing film having an
absorption axis in the widthwise direction can be obtained. The
length in the lengthwise direction, that is, the transverse size
can be set at option. When the polarizing film is combined with a
long polarizing film having-an absorption-axis in the-l-engthwise
direction, the orthogonal relation between the absorption axes in
the front and rear surfaces of a liquid crystal cell can be formed
in accordance with the screen of an arbitrary transverse size. A
large-size screen of liquid crystal display can be achieved.
Widening of the width can be also achieved by stretching in the
widthwise direction. Incidentally, when long polarizing films each
having a width of 1200 mm are used in the aforementioned
combination, a liquid crystal screen of maximum 95 inches in 16:9
aspect ratio can be formed.
[0167] Furthermore, when the long polarizing film is combined with
a long retardation film having a slow axis in the lengthwise
direction, the orthogonal relation between the absorption axis of
the polarizing film and the slow axis of the retardation film can
be formed by such lamination that the lengthwise directions of the
long films are made to correspond to each other, since being a long
polarizing film having an absorption axis in the widthwise
direction. A laminated film made of the laminate can be produced
efficiently in a laminating process in which the long films rolled
up are unrolled out successively.
[0168] Because a film stretched in the lengthwise direction can be
used as a retardation film, variation in the direction of the slow
axis due to the-boing phenomenon hardly occurs so that excellent
axial accuracy can be obtained. There can be obtained a laminated
film in which the retardation in a liquid crystal cell can be
optically compensated with high accuracy to achieve uniform liquid
crystal display and attain widening of the viewing angle.
[0169] While the present invention has been described in detail and
with reference to specific embodiments thereof, it will be apparent
to one skilled in the art that various changes and modifications
can be made therein without departing from the spirit and scope
thereof.
[0170] The present application is based on Japanese Patent
Application Nos. 2003-289612 filed on Aug. 8, 2003 and 2004-215159
filed on Jul. 23, 2004, and the contents thereof are incorporated
herein by reference.
INDUSTRIAL APPLICABILITY
[0171] The polarizing film, the laminated film and the optical
member according to the invention can be preferably used for
forming various devices such as liquid crystal displays. For
example, the polarizing film, the laminated film and the optical
member according to the invention can be used for forming liquid
crystal displays such as a reflective liquid crystal display, a
semi-transmissive liquid crystal display or a
transmissive-reflective double type liquid crystal display in which
a polarizing film is disposed on a single surface of a liquid
crystal cell or polarizing films are disposed on both surfaces of a
liquid crystal cell.
[0172] That is, though a liquid crystal display is generally formed
by suitably assembling constituent parts such as a liquid crystal
cell, a polarizing film or laminated film and an illumination
system in accordance with necessity and incorporating a driving
circuit therein, there is no particular limitation in the invention
except that the polarizing film, laminated film or optical member
according to the invention is provided on at least one outer
surface of a liquid crystal cell. The invention can comply with the
background art. When films are disposed on both surfaces of a
liquid crystal cell, use of a combination of a polarizing film
having an absorption axis in the widthwise direction and a
polarizing film having an absorption axis in the lengthwise
direction is advantageous from the point of view of the formability
of a large-size screen.
[0173] Accordingly, it is possible to form a suitable liquid
crystal display such as a liquid crystal display having one
laminated film or two laminated films disposed on a single surface
or both surfaces of a liquid crystal cell, a liquid crystal display
using a backlight unit or a front light unit as an illumination
system or a transmissive, reflective or transmissive-reflective
double type liquid crystal display using a reflection plate or a
semi-transmissive reflection plate. It is more preferable from the
point of view of the compensating effect or the like that the
laminated film is disposed so that the retardation film of the
laminated film is located between the. liquid crystal cell on the
viewing side or/and back side and the polarizing film, especially
between the liquid crystal cell and the viewing side polarizing
film. For the arrangement of the laminated film, the film provided
in the form of the optical member may be used.
[0174] The liquid crystal cell for forming the liquid crystal
display in the above description can be selected at option. For
example, a suitable type liquid crystal cell such as an active
matrix driving type liquid crystal cell represented by a thin-film
transistor liquid crystal cell, a passive matrix driving type
liquid crystal cell represented by a TN or STN liquid crystal cell,
a VA liquid crystal cell, an OCB liquid crystal cell, an IPS liquid
crystal cell, etc. may be used. Especially, a liquid crystal cell
of the type in which the polarizing film is disposed so that the
absorption axis of the polarizing film becomes parallel to a side
of the liquid crystal cell, such as a VA liquid crystal cell or an
IPS liquid crystal cell may be used preferably.
[0175] In the above description, parts for forming the liquid
crystal display may be laminated integrally or may be separated.
For the formation of the liquid crystal display, suitable optical
elements such as a prism array sheet, a lens array sheet, a
light-diffusing plate, a protective plate, etc. can be disposed
suitably. Such elements may be laminated on the laminated film so
as to be provided in the form of the optical member for forming the
liquid crystal display.
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