U.S. patent application number 12/523223 was filed with the patent office on 2010-04-01 for polarizing fiber, polarizer, polarizing plate, laminated optical film, and image display.
This patent application is currently assigned to NITTO DENKO CORPORATION. Invention is credited to Yasuko Iwakawa, Minoru Miyatake, Akinori Nishimura, Masashi Shinagawa.
Application Number | 20100079862 12/523223 |
Document ID | / |
Family ID | 40156147 |
Filed Date | 2010-04-01 |
United States Patent
Application |
20100079862 |
Kind Code |
A1 |
Miyatake; Minoru ; et
al. |
April 1, 2010 |
POLARIZING FIBER, POLARIZER, POLARIZING PLATE, LAMINATED OPTICAL
FILM, AND IMAGE DISPLAY
Abstract
As the polarizing fiber of the present invention, the cross
sectional form perpendicular to the longitudinal direction has a
sea-island structure, and the cross sectional form is continuously
made up in the longitudinal direction. A resin (sea component) that
constitutes the sea region of the sea-island structure comprises a
dichroic dye, and a resin (island component) that constitutes the
island regions of the sea-island structure is a transparent resin.
The polarizing fiber of the present invention may be used as a
forming material of a polarizer, for example. By using the above
polarizing fiber, a polarizer wherein unevenness of the
transmittance is small and cracks are less generated may be
formed.
Inventors: |
Miyatake; Minoru;
(Ibaraki-shi, JP) ; Nishimura; Akinori;
(Ibaraki-shi, JP) ; Shinagawa; Masashi;
(Ibaraki-shi, JP) ; Iwakawa; Yasuko; (Ibaraki-shi,
JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW, SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
NITTO DENKO CORPORATION
Ibaraki-shi, Osaka
JP
|
Family ID: |
40156147 |
Appl. No.: |
12/523223 |
Filed: |
June 4, 2008 |
PCT Filed: |
June 4, 2008 |
PCT NO: |
PCT/JP2008/060262 |
371 Date: |
August 11, 2009 |
Current U.S.
Class: |
359/485.01 |
Current CPC
Class: |
D01F 8/06 20130101; G02B
27/28 20130101; G02B 5/3025 20130101; D01D 5/36 20130101; D01F 8/10
20130101; G02B 5/30 20130101 |
Class at
Publication: |
359/488 |
International
Class: |
G02B 5/30 20060101
G02B005/30 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 19, 2007 |
JP |
2007-161408 |
Claims
1. A polarizing fiber having an absorption axis in the longitudinal
direction thereof, wherein the cross sectional form perpendicular
to the longitudinal direction has a sea-island structure, and the
cross sectional form is continuously made up in the longitudinal
direction, and wherein a resin (sea component) that constitutes the
sea region of the sea-island structure comprises a dichroic dye,
and a resin (island component) that constitutes the island regions
of the sea-island structure is a transparent resin.
2. The polarizing fiber according to claim 1, wherein when the
refractive index of the island component in the direction
perpendicular to the longitudinal direction is represented by
n.sub.i1 and the refractive index of the sea component in the
direction perpendicular to the longitudinal direction is
represented by n.sub.s1, the difference between the refractive
indexes, .DELTA.n.sub.1=|n.sub.s1-n.sub.i1|, is 0.02 or less, and
when the refractive index of the island component in the
longitudinal direction is represented by n.sub.i2 and the
refractive index of the sea component in the longitudinal direction
is represented by n.sub.s2, the difference between the refractive
indexes, .DELTA.n.sub.2=|n.sub.s2-n.sub.i2|, is 0.03 or more and
0.05 or less.
3. The polarizing fiber according to claim 1, wherein the number of
the island regions is 2 or more, and further the long diameter of
each of the island regions is from 0.1 to 8.0 .mu.m.
4. The polarizing fiber according to claim 1, wherein the resin
that constitutes the sea region is polyvinyl alcohol or ethylene
vinyl alcohol copolymer.
5. A polarizer in a sheet form, wherein the polarizing fiber as
recited in claim 1 is arranged or laminated in parallel to the
longitudinal direction thereof, and is further enveloped in a
transparent isotropic material.
6. The polarizer according to claim 5, wherein when the refractive
index of the isotropic material is represented by n.sub.m and the
refractive index of the sea component in the direction
perpendicular to the longitudinal direction is represented by
n.sub.s1, the difference between the refractive indexes,
.DELTA.n.sub.3=|n.sub.s1-n.sub.m|, is 0.02 or less.
7. A polarizing plate, having a transparent protective film on at
least one surface of the polarizer as recited in claim 5.
8. A laminated optical film, having the polarizer as recited in
claim 5.
9. An image display, having the polarizer as recited in claim
5.
10. A laminated optical film, having the polarizing plate as
recited in claim 7.
11. An image display, having the polarizing plate as recited in
claim 7.
12. An image display, having the laminated optical film as recited
in claim 8.
13. An image display, having the polarizer as recited in claim
6.
14. A laminated optical film, having the polarizer as recited in
claim 6.
Description
TECHNICAL FIELD
[0001] The present invention relates to a polarizing fiber, a
polarizer, a polarizing plate, a laminated optical film, and an
image display. More specifically, the present invention relates to
a polarizing fiber preferably used to produce a polarizer wherein
unevenness of the transmittance is small and cracks are less
generated.
BACKGROUND ART
[0002] In general, liquid crystal displays have a liquid crystal
panel wherein a laminated optical film comprising a polarizer is
adhered onto each of two surfaces of a liquid crystal cell, and the
liquid crystal cell is made of a liquid crystal material sandwiched
between two glass plates. As this polarizer, there is generally
used a drawn film obtained by dyeing a polyvinyl alcohol (PVA)
based film with iodine or the like, and then drawing the film
uniaxially. This polarizer is a polarizer exhibiting absorption
dichroism.
[0003] As the display performance of liquid crystal displays has
been improved in recent years, polarizers which have a higher
transmittance and a higher polarization degree have been desired.
In order to obtain a polarizer high in transmittance, a film which
is made of a polyvinyl alcohol based material having a high
polymerization degree is used. Moreover, in order to obtain a
polarizer high in polarization degree, a film which is drawn at a
higher draw ratio is used (see, for example, Patent Document
1).
[0004] However, it is known that a break called crack is easily
generated in any films drawn at a high draw ratio. This crack is
generated in parallel to the direction in which the film is drawn.
It is guessed that this crack is generated since the film-drawn
direction and the direction perpendicular thereto are different
from each other in thermal shrinkage behavior or the linear
expansion coefficient. The crack is more easily generated in a film
drawn at a higher draw ratio. When a polarizer wherein a crack is
generated is used, the display performance of the liquid crystal
display is damaged.
[0005] On the other hand, a large-area polarizer that can be used
in a large-sized liquid crystal televisional image-receiver has
been desired as the size of liquid crystal televisional
image-receivers has been becoming large. This is because it is
preferred that the polarizer used in a liquid crystal display or
the like be seamless. However, about large-area drawn films, the
probability of the generation of a crack therein becomes high when
the films are produced. Furthermore, in order to produce large-area
drawn films, a large-scale drawing facility is required. In order
to arrange this drawing facility, a large facility investment is
required.
[0006] Thus, for example, a technique disclosed in Patent Document
2 is known as a method that neither causes the generation of a
crack nor requires any large drawing facility. Specifically, Patent
Document 2 proposes a technique of using a polarizing fiber to form
a polarizing woven cloth, and coating this polarizing woven cloth
with a transparent resin to form a polarizing filter. According to
this technique, no drawn film is used; thus, the filter is not
cracked in light of the structure thereof, and further no
large-scale drawing facility is required.
[0007] However, the polarizing filter described in Patent Document
2 is not developed for being used in a liquid crystal display. For
this reason, in the polarizing filter, the presence distribution of
its polarizing fibers varies, so that the unevenness of transmitted
light emerges remarkably. Moreover, in the polarizing filter, light
is refracted or reflected on the interfaces between the polarizing
fibers and the transparent resin in accordance with the difference
between the refractive indexes of the polarizing fibers and that of
the coating transparent resin. For this polarizing filter, the
transmittance and the polarization degree thereof are not
sufficient for liquid crystal displays. Accordingly, the polarizing
filter described in Patent Document 2 cannot be used as it is for a
liquid crystal display.
[0008] Further, as the method for dyeing a polarizing fiber, a
method of kneading a resin and a dye, and then spinning the kneaded
product, or a method of forming pellets (chips) dyed with a dye in
advance and then blending the pellets when a fiber spinning is made
is known (see, for example, Patent Documents 3 and 4). However, in
any one of the methods, it is necessary for adjusting the color
tone of a polarizer to incorporate plural dyes to a polarizing
fiber therefor during producing the fiber. Therefore, according to
the methods, after the production of a polarizing fiber, the color
tone thereof cannot be adjusted.
[0009] Thus, proposed is a technique of using a polarizing fiber
and a birefringent fiber together, thereby overcoming the
unevenness of the transmittance, preventing the refraction or
reflection of light on the interface between the polarizing fiber
and a transparent resin, and making it possible to adjust the color
tone of the polarizing fiber after the fiber is made into a fiber
spinning (see, for example, Patent Document 5).
[0010] Patent Document 1: JP-A-8-190015
[0011] Patent Document 2: JP-A-6-130223
[0012] Patent Document 3: JP-A-10-130946
[0013] Patent Document 4: JP-A-10-170720
[0014] Patent Document 5: JP-A-2006-126313
DISCLOSURE OF THE INVENTION
[0015] However, when the birefringent fiber in the technique of
Patent Document 5 is formed into a thickness (diameter) giving a
good scattering efficiency, the strength of the birefringent fiber
becomes insufficient. It is therefore difficult to produce
practically a birefringent fiber having a thickness giving a good
scattering efficiency. Also, in the technique of Patent Document 5,
it is also difficult to arrange the polarizing fiber and the
birefringent fiber evenly in parallel to the longitudinal
direction.
[0016] A first object of the present invention is to provide a
polarizing fiber that makes it possible to form easily a
birefringent fiber having a thickness (diameter) giving a good
scattering efficiency and further exhibits the same effect as a
case where a polarizing fiber and a birefringent fiber are evenly
arranged in parallel to the longitudinal direction thereof.
[0017] A second object of the present invention is to provide a
polarizer, a polarizing plate, a laminated optical film, and an
image display in each of which the above-mentioned polarizing fiber
is used.
[0018] A polarizing fiber of the present invention has an
absorption axis in the longitudinal direction wherein the cross
sectional form perpendicular to the longitudinal direction thereof
has a sea-island structure, and the cross sectional form is
continuously made up in the longitudinal direction. Also, a resin
(sea component) that constitutes the sea region of the sea-island
structure comprises a dichroic dye, and a resin (island component)
that constitutes the island regions of the sea-island structure is
a transparent resin.
[0019] In the polarizing fiber, the cross section perpendicular to
the longitudinal direction has a sea-island structure, and further
the fiber has an absorption axis in the longitudinal direction
along which the cross sectional form is continuously formed. The
polarizing fiber of this structure can easily be formed by an
extrusion molding by using a nozzle for multiple spinning.
Additionally, the resin (island component) that constitutes the
island regions is a transparent resin. This functions in the same
manner as conventional birefringent fibers. The island regions are
formed in the sea region (polarizing resin). Therefore, the
polarizing fiber can be made finer as compared with a case where a
birefringent fiber is solely formed as in the prior art.
Accordingly, a polarizing fiber having a cross sectional diameter
giving a good scattering efficiency is easily obtained.
[0020] The phrase "the cross section has a sea-island structure"
refers to a structure that a form of a cross section comprises a
sea region made of the same component, the region being compared to
a sea, and island regions made of a component different from the
sea component, the regions being compared to islands, wherein the
island regions are surrounded by the sea region and further the
island regions do not contact each other.
[0021] Furthermore, the polarizing fiber of the present invention
has an absorption axis in the longitudinal direction. When the
polarizing fiber is arranged or laminated in parallel to the
longitudinal direction, a polarizer can easily be formed. Moreover,
the polarizing fiber of the present invention envelops therein a
transparent resin (island component) functioning as a birefringent
fiber. Therefore, the ratio between the region (sea component)
corresponding to a conventional polarizing fiber, and the regions
(island component) corresponding to a conventional birefringent
fiber is constant at all times. Accordingly, in the polarizing
fiber of the present invention, the polarizing-fiber-corresponding
region and the birefringent-fiber-corresponding regions can be
uniformly arranged in parallel to the longitudinal direction.
[0022] In the polarizing fiber of the present invention, the resin
(sea component) that constitutes the sea region of the sea-island
structure comprises a dichroic dye, and the resin (island
component) that constitutes the island regions of the sea-island
structure is a transparent resin. Accordingly, polarized light
parallel to the longitudinal direction is absorbed in the sea
region. On the other hand, polarized light that has reached the
island regions are reflected, diffused, or scattered on/in the
island regions. The optical path of the polarized light which has
been changed by the reflection, diffusion, or scattering is
returned to the sea region again. As a result, the polarized light
parallel to the longitudinal direction remains in the polarizing
fiber for a long period. Thus, the probability that the polarized
light parallel to the longitudinal direction is absorbed in the
polarizing fiber becomes higher as compared with a case where a
polarizing fiber has no island regions. On the other hand, the
polarized light in the direction perpendicular to the longitudinal
direction is neither absorbed in the sea region nor the island
regions, so as to go straight and permeate therethrough.
Accordingly, the polarizing fiber of the present invention has a
greater polarizing performance than conventional polarizing fibers
having no island regions.
[0023] In the polarizing fiber of the present invention, the cross
sectional form is continuously made up in the longitudinal
direction. Therefore, the polarizing fiber has no difference
between optical properties (has uniform optical properties) at all
positions along the longitudinal direction in the same fiber.
Accordingly, a polarizer having uniform optical properties can be
produced by arranging or laminating the polarizing fiber in
parallel to the longitudinal direction.
[0024] The polarizing fiber of the present invention makes it
possible to form a birefringent fiber having a thickness (diameter)
giving a good scattering efficiency, and further exhibits the same
effect as a case where a polarizing fiber and a birefringent fiber
are evenly arranged in parallel to the longitudinal direction
thereof. The use of the polarizing fiber of the present invention
makes it possible to produce a polarizer wherein the polarization
degree is excellent, the unevenness of the transmittance is small,
and cracks are less generated.
[0025] In the preferable polarizing fiber of the present invention,
when the refractive index of the island component in the direction
perpendicular to the longitudinal direction is represented by nil
and the refractive index of the sea component in the direction
perpendicular to the longitudinal direction is represented by
n.sub.s1, the difference between the refractive indexes,
.DELTA.n.sub.1=|n.sub.s1-n.sub.i1|, is 0.02 or less, and when the
refractive index of the island component in the longitudinal
direction is represented by nit and the refractive index of the sea
component in the longitudinal direction is represented by n.sub.s2,
the difference between the refractive indexes,
.DELTA.n.sub.2=|n.sub.s2-n.sub.i2|, is 0.03 or more and 0.05 or
less.
[0026] In the preferable polarizing fiber, the difference
.DELTA.n.sub.1 between the refractive indexes in the direction
perpendicular to the longitudinal direction is 0.02 or less.
Therefore, in the polarizing fiber, polarized light in the
direction perpendicular to the longitudinal direction can be
further restrained from being reflected, diffused, or scattered
on/in the interfaces between the sea component and the island
component of the polarizing fiber. Thus, the polarized light in the
direction perpendicular to the longitudinal direction goes straight
and permeates therethrough without being absorbed in the sea
component.
[0027] On the other hand, in the preferable polarizing fiber, the
difference .DELTA.n.sub.2 between the refractive indexes in the
longitudinal direction is 0.03 or more. Therefore, in the
polarizing fiber, polarized light parallel to the longitudinal
direction is easily reflected, diffused, or scattered on/in the
interfaces between the sea component and the island component of
the polarizing fiber. Thus, the polarizing fiber of the present
invention has still larger polarizing performances than
conventional polarizing fibers having no island regions.
[0028] As another preferable polarizing fiber of the present
invention, the number of the island regions is 2 or more, and
further the long diameter of each of the island regions is from 0.1
to 8.0 .mu.m.
[0029] In another preferable polarizing fiber, the number of the
island regions (hereinafter referred to as the island number) is 2
or more; therefore, polarized light that permeates through the
polarizing fiber and is parallel to the longitudinal direction
easily undergoes multiple reflection, multiple diffusion or
multiple scattering. Thus, the probability that the polarized light
parallel to the longitudinal direction is absorbed in the sea
component becomes still higher.
[0030] When the long diameter of the islands is shorter than about
1/10 of the wavelength of the light, the polarized light is hardly
scattered. In another preferable embodiment, the long diameter of
the island regions is 0.1 .mu.m or more (this is longer than 1/10
of visible ray wavelengths); therefore, the polarizing fiber causes
polarized light to be scattered.
[0031] On the other hand, if the long diameter of the islands is
too large, the island number per filament of the polarizing fiber
becomes relatively small, so that polarized light hardly undergoes
multiple reflection, multiple diffusion or multiple scattering. In
this case, the presence distribution of the islands becomes sparse
so that the uneven of transmittance easily generates. In another
preferred embodiment, the long diameter of each of the islands is
8.0 .mu.m or less; thus, the long diameters of the islands are not
too large. As a result, the above-mentioned bad results can be
restrained.
[0032] In another preferable polarizing fiber of the present
invention, the above resin that constitutes the sea region is
polyvinyl alcohol, or ethylene vinyl alcohol copolymer.
[0033] The polyvinyl alcohol or the ethylene vinyl alcohol
copolymer is actually used as the raw material of a polarizer, and
is versatile and inexpensive.
[0034] In another aspect of the present invention, a polarizer is
provided.
[0035] As the polarizer of the present invention, the above
polarizing fiber is arranged or laminated in parallel to the
longitudinal direction, and the polarizing fiber is further
enveloped in a transparent isotropic material to be sheet form.
[0036] In the preferable polarizer of the present invention, when
the refractive index of the isotropic material is represented by
n.sub.m and the refractive index of the sea component in the
direction perpendicular to the longitudinal direction is
represented by n.sub.s1, the difference between the refractive
indexes, .DELTA.n.sub.3=|n.sub.s1-n.sub.m |, is 0.02 or less.
[0037] In the preferable polarizer, the difference .DELTA.n.sub.3
between the refractive index of the sea component in the direction
perpendicular to the longitudinal direction and that of the
isotropic material is 0.02 or less; therefore, polarized light in
the direction perpendicular to the longitudinal direction can be
restrained from being reflected, diffused, or scattered on the
interface between the sea component and the isotropic material.
Thus, the polarizer becomes high in transmittance, and easily
transmits polarized light in the direction perpendicular to the
longitudinal direction.
[0038] In another aspect of the present invention, a polarizing
plate is provided.
[0039] The polarizing plate of the present invention has a
transparent protective film on at least one surface of the
polarizer.
[0040] In another aspect of the present invention, a laminated
optical film is provided.
[0041] The laminated optical film of the present invention has the
above polarizer or the above polarizing plate.
[0042] In another aspect of the present invention, an image display
is provided.
[0043] The image display of the present invention has at least one
selected from the group consisting of the above polarizer, the
above polarizing plate, and the above laminated optical film.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] FIG. 1 is a perspective view illustrating a polarizing fiber
according to an embodiment.
[0045] FIG. 2A is a view of a partial cross section of the
polarizing fiber, which is a plane perpendicular to the
longitudinal direction of the fiber, and FIG. 2B is a partial side
view of the polarizing fiber.
[0046] FIG. 3 is a perspective view illustrating a polarizer
according to an embodiment.
[0047] FIG. 4 is a view of a partial cross section illustrating a
polarizing plate according to an embodiment.
[0048] FIG. 5 is a view of a partial cross section illustrating a
laminated optical film according to an embodiment.
[0049] FIG. 6 is a view of a partial cross section illustrating an
image display according to an embodiment.
BEST MODE FOR CARRYING OUT THE INVENTION
[0050] With reference to FIGS. 1 to 6, the following will describe
embodiments of a polarizing fiber, a polarizer, a polarizing plate,
a laminated optical film, and an image display wherein the present
invention is embodied.
[Polarizing Fiber]
[0051] As illustrated in FIG. 1, in a polarizing fiber 1 according
to the present embodiment, its cross section perpendicular to the
longitudinal direction thereof has a sea-island structure, and
further the cross sectional form is continuously made up in the
longitudinal direction. A resin (sea component) that constitutes
the sea region of the sea-island structure comprises a dichroic
dye. The sea region 11 comprising the dichroic dye has an
absorption axis in the longitudinal direction.
[0052] A resin (island component) that constitutes the island
regions 12 of the sea-island structure is a transparent resin. The
refractive index of the sea component in the longitudinal direction
is largely different from that of the island component in the
longitudinal direction. On the other hand, the refractive index of
the sea component in the direction perpendicular to the
longitudinal direction is equal to or approximate to that of the
island component in the direction perpendicular to the longitudinal
direction (the refractive index of the polarizing fiber 1 in the
cross sectional direction).
[0053] The difference .DELTA.n.sub.2 between the refractive index
of the sea component in the longitudinal direction and the
refractive index of the island component in the longitudinal
direction (.DELTA.n.sub.2=|n.sub.s2-n.sub.i2|) is preferably 0.03
or more and 0.05 or less and more preferably 0.035 or more and
0.045 or less.
[0054] The symbol "n.sub.s2" represents the refractive index of the
sea component in the longitudinal direction and the symbol
"n.sub.i2" represents the refractive index of the island component
in the longitudinal direction.
[0055] The difference .DELTA.n.sub.1 between the refractive index
of the sea component in the direction perpendicular to the
longitudinal direction and the refractive index of the island
component in the direction perpendicular to the longitudinal
direction (.DELTA.n.sub.1=|n.sub.s1-n.sub.i1|) is preferably 0.02
or less and more preferably 0.01 or less.
[0056] The symbol "n.sub.s1" represents the refractive index of the
sea component in the direction perpendicular to the longitudinal
direction and the symbol "n.sub.i1" represents the refractive index
of the island component in the direction perpendicular to the
longitudinal direction.
[0057] The resin that constitutes the sea component is not limited
in the kind thereof as far as the resin has light transmissivity in
the visible light range, can be made into a fibrous form, and has
the property that a dichroic dye can be dispersed. As these resins,
for example, a polyvinyl alcohol and a derivative thereof used as a
polarizer conventionally may be cited. As the derivative of the
polyvinyl alcohol, polyvinyl formal, polyvinyl acetal, and the like
may be cited. As the derivative of the polyvinyl alcohol, olefin
such as ethylene, propylene; unsaturated carboxylic acid such as
acrylic acid, methacrylic acid, crotonic acid; alkyl ester of the
unsaturated carboxylic acid; polyvinyl alcohol modified by
acrylamide may be cited. As the derivative of the polyvinyl
alcohol, polyvinyl pyrolidone based resin, amylose based resin, and
the like may be cited. Among them, the resin that constitutes the
sea component is preferably the polyvinyl alcohol. The resin is
preferably a copolymer made from ethylene and vinyl alcohol from
the viewpoint of melt spinning.
[0058] When the sea-island structure is formed by extrusion
molding, it is preferable that the resin that constitutes the sea
component is close to the resin that constitutes the island
component in melt viscosity and melt flow index.
[0059] As the above dichroic dye, it is not particularly limited,
but the compound which can absorb a certain wavelength in the
visible light region is preferable.
[0060] In accordance with classification according to chemical
structure, as the dichroic dye, an azo based pigment, an
anthraquinone based pigment, a perylene based pigment, an
indanthrone based pigment, an imidazole based pigment, an indigoid
based pigment, an oxazine based pigment, a phthalocyanine based
pigment, a triphenylmethane based pigment, a pyrazolone based
pigment, a stilbene based pigment, a diphenylmethane based pigment,
a naphthoquinone based pigment, a methocyanine based pigment, a
quinophthalone based pigment, a xanthene based pigment, an alizarin
based pigment, an acridine based pigment, a quinonimine based
pigment, a thiazole based pigment, a methine based pigment, a nitro
based pigment, a nitroso based pigment, and the like may be
cited.
[0061] These dichroic dyes may be used singly or in combination of
two or more kinds.
[0062] Next, with reference to FIG. 2, the following will describe
the behavior of light entered to the polarizing fiber.
[0063] The light entered into the polarizing fiber 1 can be
considered to be light separated vectorially into a linearly
polarized light 21 parallel to the cross sectional direction of the
polarizing fiber 1 and a linearly polarized light 22 parallel to
the longitudinal direction of the polarizing fiber 1.
[0064] In FIGS. 2A and 2B, the incident light is illustrated such
that the advancing direction of the incident light is defined as Z
direction, the direction parallel to the cross sectional direction
of the polarizing fiber 1 is defined as X direction, and the
direction parallel to the longitudinal direction of the polarizing
fiber 1 is defined as Y direction. Near the root of an arrow
representing each of the linearly polarized light 21 and 22, small
arrows representing the direction of the polarized light are
drawn.
[0065] The linearly polarized light 21 (referred to as the X
polarized light) parallel to the cross sectional direction of the
polarizing fiber 1 is a polarized light in the direction
perpendicular to the absorption axis direction of the sea region
11. Accordingly, the X polarized light permeates through the
polarizing fiber 1 without being absorbed in the sea region 11. As
described above, the refractive index of the resin that constitutes
the sea component in the cross sectional direction (the X
direction) is substantially equal to that of the resin that
constitutes the island component in the cross sectional direction
(the X direction). Therefore, in the interfaces between the sea
region 11 and the island regions 12 also, the X polarized light
permeates through the polarizing fiber 1 without being reflected,
diffused, or scattered. Furthermore, the island regions 12 are made
of the transparent resin; therefore, the X polarized light
permeates through the polarizing fiber 1 without causing any
especial problem. Thus, the X polarized light permeates into the
polarizing fiber 1 without receiving any effect substantially.
[0066] On the other hand, the linearly polarized light 22 (referred
to as the Y polarized light) parallel to the longitudinal direction
of the polarizing fiber 1 is a polarized light in the direction
parallel to the absorption axis direction of the sea region 11.
Accordingly, almost all of the Y polarized light is absorbed in the
sea region 11. As described above, the refractive index of the
resin that constitutes the sea component in the longitudinal
direction (the Y direction) is largely different from the
refractive index of the resin that constitutes the island component
in the longitudinal direction (the Y direction). In the interfaces
between the sea region 11 and the island regions 12, the Y
polarized light is reflected, diffused, or scattered. Accordingly,
the optical path of the Y polarized light is changed every time
when the Y polarized light passes each interface of the sea region
11 and the island regions 12. Thus, the Y polarized light passes
through the long optical path in the polarizing fiber 1, and almost
all of the Y polarized light is absorbed in the sea region 11.
[0067] As the fiber corresponding to the island component in the
present invention, a birefringent fiber is conventionally used.
However, in the present invention, birefringence is not necessarily
essential. As described above, in the polarizing fiber of the
present invention, the refractive index of the sea component in the
longitudinal direction is largely different from that of the island
component in the same direction, and further the refractive index
of the sea component in the direction perpendicular to the
longitudinal direction is equal to or approximate to that of the
island component in the same direction. Thus, the polarizing fiber
can selectively transmit a specific linearly polarized light.
[0068] Accordingly, in the present specification, the transparent
resin that constitutes the island component is referred to as the
"refractive index differed component". When the refractive index
differed component is made into a fibrous form, the fiber is
referred to as the "refractive index differed fiber". However, when
it is formed as a different fiber in the same manner as in the
prior art, the fiber is referred to as a birefringent fiber as ever
in order to avoid confusion.
[0069] The island number (the number of the island regions) per
single polarizing fiber is preferably 2 or more, more preferably 4
or more, and particularly preferably 6 or more. The upper limit of
the island number is not particularly limited, so that the number
may be set in accordance with the thickness of the polarizing fiber
or the island regions. The island number is, for example, 100 or
less.
[0070] The long diameter of the island regions is preferably from
0.1 to 8.0 .mu.m and more preferably from 0.5 to 7.5 .mu.m.
[0071] The long diameter of the island regions means the following:
when the cross sectional form of the island regions is circular,
the diameter thereof; and when the cross sectional form of the
island regions is noncircular (for example, elliptic), the longest
diameter thereof.
[0072] In the present specification, the description of "A to B"
means "A or more and B or less".
[0073] The polarizing fiber 1 according to the above embodiment may
be changed as follows.
[0074] In FIG. 1, the cross sectional form of the polarizing fiber
1, which is a plane perpendicular to the longitudinal direction of
the fiber, is circular. However, the form is not limited thereto,
and may be, for example, elliptic.
[0075] Also, in FIG. 1, the cross sectional form of the island
regions 12, which is a plane perpendicular to the longitudinal
direction, is circular. However, the form is not limited thereto,
and may be, for example, elliptic.
[0076] In FIG. 1, the island regions 12 in the cross section of the
polarizing fiber 1 are arranged approximately concentric from.
However, the island regions 12 may be arranged in a different form.
For example, the island regions 12 may be arranged to be
approximately evenly dispersed, or may be arranged to be dispersed
at random. However, in order to cause multiple reflection, multiple
diffusion, or multiple scattering easily, it is preferred that the
island regions 12 are arranged to be dispersed in an approximately
even form, such as an approximately concentric form.
[Polarizer]
[0077] As illustrated in FIG. 3, a polarizer 3 of the present
invention is a sheet having polarizing fibers 1. The polarizer 3 is
produced by using the polarizing fiber 1 illustrated FIG. 1. In the
polarizer 3 of the present embodiment, the polarizing fibers 1 are
arranged or laminated in parallel to the longitudinal direction of
the polarizer 3, and the polarizing fibers 1 are enveloped in a
transparent isotropic material 2. The polarizer is a sheet having
the optical property of transmitting a certain linearly polarized
light from a natural light or a polarized light.
[0078] In the polarizer 3 of the present embodiment, it is
preferable that the plural polarizing fibers 1 are arranged or
laminated in parallel to the longitudinal direction without
generating any gap. For example, when the two or more polarizing
fibers 1 are laminated in the thickness direction of the polarizer
3, it is preferable that adjacent ones out of the polarizing fibers
1 contact each other. By arranging the polarizing fibers 1 without
generating any gap in this way, a polarizer 3 excellent in
polarization property can be obtained.
[0079] In the present embodiment, the isotropic material 2 and the
raw material of the sea region 11 are selected to set the
difference between the refractive indexes,
.DELTA.n.sub.3=|n.sub.s1-n.sub.m|, to 0.02 or less. Here, the
symbol "n.sub.m" represents the refractive index of the above
isotropic material 2, and the symbol "n.sub.s1" represents the
refractive index of the sea component in the polarizing fibers 1 in
the direction perpendicular to the longitudinal direction.
[0080] By selecting the raw material to set the .DELTA.n.sub.3 to
0.02 or less, the polarized light in the direction perpendicular to
the longitudinal direction can be restrained from being reflected,
diffused, or scattered on the interface between the sea region 11
and the isotropic material 2. As a result, the polarizer 3, which
has a high transmittance and easily transmit the polarized light in
the direction perpendicular to the longitudinal direction can be
provided. In principle, the .DELTA.n.sub.3 is preferably zero.
However, a case where the .DELTA.n.sub.3 does not easily become
zero in fact may be caused; thus, a combination where the
.DELTA.n.sub.3 is as close to zero as possible is investigated
while other requirements are considered.
[0081] When the number of the polarizing fibers 1 is increased in
the polarizer 3, the transmittance of the polarizer 3 is declined.
On the other hand, when the number of the polarizing fibers 1 is
decreased in the polarizer 3, the absorptance of the polarized
light parallel to the longitudinal direction is declined so that
the polarization performance of the polarizer 3 deteriorates.
Accordingly, the number of the polarizing fibers 1 in the polarizer
3 is determined in accordance with the balance between required
transmittance and polarization performance. The balance is varied
also in accordance with the concentration of the dichroic dye in
the sea region, the number of the islands per single polarizing
fiber, the long diameter of the islands, the form of the islands,
and others.
[0082] The polarizer 3 is produced by enveloping the polarizing
fibers 1 in the isotropic material 2 without generating any gap.
When the polarizer 3 is produced, it is not preferable that air
bubbles are put into between the polarizing fibers 1 and the
isotropic material 2, since the gap is generated. When the air
bubbles are put thereinto, the bubbles become isotropic
scattering-points independent of polarized light. Thus, the
polarization performance of the polarizer 3 deteriorates. In order
to prevent the air bubbles from being put thereinto, the used
isotropic material 2 is preferably a material in low viscosity.
[0083] The total thickness of the polarizer 3 of the present
invention is not particularly limited, and is preferably from about
20 to 500 .mu.m. If the thickness of the polarizer 3 is too thin,
the number of the polarizing fibers 1 that can be enveloped becomes
relatively small so that the polarization performance of the
polarizer 3 becomes insufficient. If the thickness of the polarizer
3 is too thick, the handleability is poor and further there are
caused such as a problem that at the time of the production, air
bubbles are easily put thereinto.
[0084] The polarizer 3 according to the embodiment may be changed
as follows.
[0085] The polarizer 3 may be produced by using the polarizing
fibers 1 and wefts to form a woven cloth, and enveloping this woven
cloth in the isotropic material 2. In this case also, it is
preferred that the woven cloth is enveloped in the isotropic
material 2 without generating any gap in the same manner as
described above. Usually, the polarizer 3 is produced in the
following order: the step of forming the woven cloth on ahead, and
the step of enveloping this woven cloth in the isotropic material
2. According to this step-order, the polarizer 3 can be efficiently
produced. However, the parallel property of the polarizing fibers 1
may be somewhat deteriorated since the woven cloth is formed by
weaving.
[0086] The material of the wefts may be an arbitrary transparent
resin. The wefts are preferably threads made of a transparent resin
having a refractive index approximately equal to that of the
isotropic material 2. In this case, the difference between the
refractive index of the wefts and that of the isotropic material 2
is preferably 0.02 or less, more preferably 0.01 or less, and
particular preferably zero. To restrain deterioration in the
polarization property, it is preferable that the wefts be as thin
as possible. However, if the strength of the polarizing fibers 1 is
largely different from that of the wefts, the woven cloth is not
easily formed. Therefore, it is preferable that the long diameter
of the wefts is from about 1 to 30 .mu.m. The cross sectional form
of the wefts is not particularly limited, and is preferably
elliptic from the viewpoint of easiness of the formation thereof.
The weaving manner for the woven cloth may be plain weave, satin
weave, or a manner in which the polarizing fibers 1 are bunched and
then the bunch is woven. When the woven cloth formed in such a
manner is used, deterioration in the polarization property of the
polarizer 3 can be prevented.
[0087] The polarizer 3 may be produced by producing several species
of polarizing fibers 1 wherein dichroic dyes comprised in their sea
regions 11 are different from each other, and then combining these
polarizing fibers 1 with each other. By the production in this way,
the absorption wavelength of polarized light can easily be adjusted
and the color tone of polarized light transmitted through the
polarizer 3 can easily be adjusted. By the use of the polarizing
fibers 1 comprising, for example, dichroic dyes described below in
their sea regions 11, a polarizer 3 can be produced wherein the
absorptance of polarized light is approximately constant in the
whole of the visible light range. Firstly, the polarizing fibers 1
comprising a red (R) based dye, a green (G) based dye, and a blue
(B) based dye respectively as the dichroic dye in their sea
components are produced. Next, the individual polarizing fibers 1
are combined with each other to make the absorptance of polarized
light constant in the whole of the visible light range, thereby
producing the polarizer 3. In the case of using, as the red (R)
based, green (G) based and blue (B) based dyes, for example, Congo
Red (manufactured by Kishida Chemical Co., Ltd.), Direct Green 85
(manufactured by Mitsubishi Chemical Corp.), and GREY-B
(manufactured by Clariant (Japan) K.K.), respectively, it is
preferable to combine the individual polarizing fibers 1 with each
other to set the ratio by weight between the individual dyes
R:G:B=30 to 50:40 to 60:10 to 30.
[Polarizing Plate]
[0088] As illustrated in FIG. 4, the polarizing plate 5 according
to the present embodiment has a structure such that the protective
films 4 are laminated on both surfaces of the polarizer 3.
As to the polarizer 3, the polarizing fibers 1 are enveloped in a
transparent isotropic material 2.
[0089] The protective film 4 used in the above polarizing plate 5
is preferably a transparent film. Furthermore, the protective film
4 is preferably a film excellent in mechanical strength, thermal
stability, water blocking property, isotropy, and others. As the
protective film 4, for example, a film made of polyethylene based
polymer such as polyethylene terephthalate, polyethylene
naphthalate; cellulose based polymer such as diacetylcellulose,
triacetylcellulose; acrylic based polymer such as polymethyl
methacrylate; styrene based polymer such as polystyrene,
acrylonitrile-styrene copolymer (AS); polycarbonate based polymer
may be cited. Also, as the above protective layer 4, a film made of
a polyolefin based polymer such as polyethylene, polypropylene,
ethylene-propylene copolymer having a cyclo based or norbornene
structure; vinyl chloride based polymer; amide based polymer such
as nylon, aromatic polyamide; imide based polymer; sulfone based
polymer; polyethersulfone based polymer; polyetheretherketone based
polymer; polyphenylene sulfide based polymer; vinyl alcohol based
polymer; vinylidene chloride based polymer; vinyl butyral based
polymer; acrylate based polymer; polyoxymethylene based polymer;
epoxy based polymer; silicon based polymer may be cited.
[0090] The protective film 4 is preferably a film made of a
cellulose based polymer, such as triacetylcellulose, from the
viewpoint of polarization property, endurance, and others. The
protective film 4 is in particular preferably a triacetylcellulose
film.
[0091] The thickness of the protective film 4 may be set in
arbitrarily. The thickness of the protective film is typically from
about 1 to 500 .mu.m and preferably from 5 to 200 .mu.m from the
viewpoint of strength, handleability, and workability for producing
a thin film.
[0092] The protective film 4 is preferably a colorless film as far
as possible. As the protective film 4, for example, a film having a
retardation value in the thickness direction of from -90 nm to +75
nm may be cited. Here, the retardation value "Rth(590)" in the
thickness direction may be calculated from the expression of
Rth(590)=(nx-nz).times.d. Here, "590" represents a measurement
wavelength, "nx" represents a refractive index of a slow axis
direction of the film in the plane, "nz" represents a refractive
index of the film in the thickness direction, and "d" represents a
thickness of the film.
[0093] The retardation value in the thickness direction of the
protective film 4 is more preferably from -80 nm to +60 nm and
particularly preferably from -70 nm to +45 nm.
[0094] The polarizing plate 5 according to the above embodiment may
be changed as follows.
[0095] In FIG. 4, the polarizing plate 5 is formed in such a manner
that the protective films 4 are laminated on both surfaces of the
polarizer 3. However, the polarizing plate 5 is not limited to this
structure. For example, a protective film 4 may be laminated on
only one of the surfaces of the polarizer 3. In particular, in the
case where a polarizing plate 5 is produced by laminating another
film having some other optical property, no protective film may be
laminated on the other surface of the polarizer 3. When the
protective film 4 is disposed on only one of the surfaces of the
polarizer 3 (in other words, another protective film 4 is not
disposed on the other surface of the polarizer 3) in this way, a
relatively thin polarizing plate 5 can be provided.
[Laminated Optical Film]
[0096] As illustrated in FIG. 5, a laminated optical film 7 of a
present embodiment has a structure such that the protective layer 4
is laminated on only one surface of the polarizer 3 and the optical
film 6 is laminated on the other surface of the polarizer 3.
[0097] As to the polarizer 3, the polarizing fibers 1 are enveloped
in the isotropic material 2.
[0098] The protective film 6 is not particularly limited and
arbitrary one may be used according to necessity. As the optical
film 6, for example, a retardation film, an optical diffusing
layer, and the like may be cited. The optical film 6 may be a
laminate in which plural of same or different films/layers are
combined.
[Image Display]
[0099] The image display of the present invention has at least one
selected from the group consisting of the polarizer, the polarizing
plate, and the laminated optical film. Examples of the image
display include representatively a liquid crystal display, an
organic EL display, and a plasma display.
[0100] As illustrated in FIG. 6, an image display 30 of the present
embodiment is a liquid crystal display. The liquid crystal display
is equipped with: a liquid crystal panel wherein a liquid crystal
cell 9 is sandwiched between two polarizing plates 7; and a
backlight unit 80 disposed on a single side of the liquid crystal
panel. The liquid crystal cell 9 has a structure wherein a liquid
crystal material is confined into between two glass plates. In the
liquid crystal cell 9, the alignment of the liquid crystal material
is changed by applying voltage to the glass plates. As a result,
the cell selectively transmits light.
[0101] The backlight unit 80 is equipped with at least a light
source 81, a reflective film 82, a diffuser 83, a prism sheet 84,
and a brightness enhancement film 85. The optical members
illustrated in FIG. 6, such as the reflective film 82, may be
partially omitted or alternated to some other optical member(s) in
accordance with the illuminating manner of the liquid crystal
display, the driving mode of the liquid crystal cell, or
others.
[0102] The liquid crystal display (image display) according to the
embodiment may be changed as follows.
[0103] The liquid crystal display of the above embodiment is a
transmission type, wherein light is radiated thereto from the
backside of its liquid crystal panel and its display is watched;
however, the liquid crystal display may be a reflection type,
wherein light is radiated thereto from the viewing side of its
liquid crystal panel and its display is watched. Alternatively, the
liquid crystal display may be a semi-transmission type, which has
both natures of the transmission type and the reflection type.
[0104] The backlight unit may be a sidelight type. When the
sidelight type is adopted, the backlight unit has at least a light
conducting plate and a light reflector besides the above-mentioned
structure.
EXAMPLES
[0105] Next, the following will describe the present invention more
specifically by way of Examples and Comparative Examples. The
invention is not limited to these Examples. In the following
description, any "%" described as a unit represents percent by
weight.
Example 1
Polarizing Fiber A
[0106] A nozzle for sea-island composite fiber spinning was used to
extrusion-mold an island component material and a sea component
material described below, thereby producing a polarizing fiber
A.
[0107] The used island component material was a propylene-excessive
ethylene-propylene copolymer having a melting point of 138.degree.
C. and a melt flow index of 25 g/10 min (trade name: "OX1066A",
manufactured by Japan Polypropylene Corp.).
[0108] The used sea component material was a material obtained by
immersing resin pellets of an ethylene-vinyl alcohol copolymer
having a melting point of 181.degree. C. and a melt flow index of
12 g/10 min (trade name: "SOANOL (transliterated) DC3212B",
manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) in a
2% water solution of a dichroic dye (trade name: "Congo Red",
manufactured by Kishida Chemical Co., Ltd.) at 90.degree. C. for 4
hours, washing the pellets with water, and then drying the pellets
sufficiently in a vacuum drier.
[0109] The used nozzle for sea-island composite fiber spinning was
a nozzle for sea-island composite fiber spinning wherein the number
of islands was 12 per fiber cross section.
[0110] A polarizing fiber was obtained by use of the nozzle for
sea-island composite fiber spinning for subjecting the island
component material and the sea component material to melt extrusion
molding with ratio by weight therebetween being 5:5, and pulling
out the resultant at a pulling-out speed of 600 m/min. At this
time, the spinning temperature of the island component was set to
270.degree. C., and the spinning temperature of the sea component
was set to 230.degree. C. Also, the resultant polarizing fiber had
a diameter of 25 .mu.m. This polarizing fiber was drawn 2.5 times
in hot water of 70.degree. C. temperature to obtain a polarizing
fiber A having a diameter of 15 .mu.m.
[0111] As to the polarizing fiber A, the island number is 12 (the
island number is 2 or more); thus, polarized light that permeates
through the polarizing fiber and is parallel to the longitudinal
direction easily undergoes multiple reflection, multiple diffusion,
or multiple scattering. Thus, the probability that polarized light
is absorbed in the sea component of the polarizing fiber A is still
higher.
[0112] The diameter of the island regions of this polarizing fiber
A was about 1.5 .mu.m. About this polarizing fiber A, the long
diameter of the islands is 0.1 .mu.m or more; thus, it is longer
than the wavelengths of visible light. Therefore, polarized light
may be scattered. Also, about this polarizing fiber A, the long
diameter of the islands is 8.0 .mu.m or less; thus, bad results
based on the matter that the long diameter is too large are
restrained. In other words, in this polarizing fiber A, the island
number per single filament of the polarizing fiber becomes
relatively small, thereby a bad results such that polarized light
does not easily undergo multiple reflection, multiple diffusion, or
multiple scattering, or the transmittance easily becomes uneven on
the basis of a matter that the presence distribution of the islands
becomes thin can be restrained.
[0113] The refractive index n.sub.s1 of the sea component in the
direction perpendicular to the longitudinal direction of the above
polarizing fiber A was 1.51. The refractive index n.sub.s2 of the
sea component in the longitudinal direction was 1.54.
[0114] Further, a fiber comprising only the above island component
material was produced for calculating the .DELTA.n.sub.1 and
.DELTA.n.sub.2.
[0115] Namely, a fiber having a diameter of 100 .mu.m was produced
by the above described same method except that only the island
component material was spun by using the nozzle for monofilament.
The refractive index of the fiber was measured. The refractive
index n.sub.i1 of the island component (fiber) in the direction
perpendicular to the longitudinal direction thereof was 1.50. The
refractive index nit of the island component (fiber) in the
longitudinal direction was 1.51.
[0116] Accordingly,
.DELTA.n.sub.1=|n.sub.s1-n.sub.i1|=|1.51-1.50|=0.01. The difference
.DELTA.n.sub.1 between the refractive indexes in the direction
perpendicular to the longitudinal direction is 0.02 or less, so
that the polarized light in the direction perpendicular to the
longitudinal direction can be restrained from being reflected,
diffused, or scattered on/in the interfaces between the sea
component and the island component in the polarizing fiber A. As a
result, the polarized light in the direction perpendicular to the
longitudinal direction goes straight and permeates therethrough
without being absorbed in the sea component.
[0117] Also, .DELTA.n.sub.2=|n.sub.s2-n.sub.i2|=|1.54-1.51|=0.03.
The difference .DELTA.n.sub.2 between the refractive indexes in the
longitudinal direction is 0.03 or more, so that the polarized light
in longitudinal direction is easily reflected, diffused, or
scattered on/in the interfaces between the sea component and the
island component in the polarizing fiber A. As a result, the
polarizing performance of the polarizing fiber A further becomes
larger than the polarizing performance of a conventional polarizing
fiber, which has no island regions.
[0118] Hereinafter, the measurement method of the above diameter
and the refractive index is described. In the Examples other than
Example 1 and Comparative Examples, the same measurement method was
used.
[0119] The diameter of the polarizing fiber and the diameter of the
island component were measured with a scanning electron microscope
(product name: "S-3000N") manufactured by Hitachi Ltd.
[0120] Each of the refractive indexes was measured by the Becke
line method by using a refractive-index-adjusting solution at
normal temperature (25.degree. C.) with wavelength of 545 nm.
Example 2
Polarizing Fiber B
[0121] A polarizing fiber B was produced by using the same
materials and producing method as in Example 1 except that a dye
(trade name: "DIRECT GREEN 85") manufactured by Mitsubishi Chemical
Corp. was used as a dichroic dye. The producing method and so on in
Example 2 were the same as in Example 1; thus, description thereof
is omitted. Moreover, measured results of the diameters, the island
number and the refractive indexes were also the same; thus,
description thereof is also omitted.
Example 3
Polarizing Fiber C
[0122] A nozzle for core-sheath structure fiber spinning was used
to extrusion-mold an island component material and a sea component
material described below, thereby producing a polarizing fiber C.
The nozzle for core-sheath structure fiber spinning is a nozzle for
sea-island composite fiber spinning wherein the island number is 1.
In the following description, the term "island component" will be
used instead of the term "core component", and the term "sea
component" will be used instead of the term "sheath component"
unless especially necessitated.
[0123] The used island component material was a crystalline
polypropylene having a melting point of 161.degree. C. and a melt
flow index of 26 g/10 min (trade name: "SA03A", manufactured by
Japan Polypropylene Corp.).
[0124] The used sea component material was the same material as the
sea component material described in the Example 1.
[0125] A polarizing fiber was obtained by use of the nozzle for
core-sheath structure fiber spinning for subjecting the island
component material and the sea component material to melt extrusion
molding with ratio by weight therebetween being 3:7, and pulling
out the resultant at a pulling-out speed of 600 m/min. At this
time, the spinning temperature of the island component was set to
230.degree. C., and the spinning temperature of the sea component
was set to 230.degree. C. The resultant polarizing fiber had a
diameter of 25 .mu.m. This polarizing fiber was drawn 2.5 times in
hot water of 70.degree. C. temperature to obtain a polarizing fiber
C having a diameter of 15 .mu.m.
[0126] The diameter of the island regions of this polarizing fiber
C was about 7.0 .mu.m. About this polarizing fiber C, the long
diameter of the islands is 0.1 .mu.m or more; thus, it is longer
than the wavelengths of visible light. Therefore, polarized light
may be scattered. Also, about this polarizing fiber C, the long
diameter of the islands is 8.0 .mu.m or less; thus, the above bad
results based on the matter that the long diameter is too large are
restrained.
[0127] As to the polarizing fiber C, the refractive index n.sub.s1
of the sea component in the direction perpendicular to the
longitudinal direction was 1.51 and the refractive index n.sub.s2
of the sea component in the longitudinal direction was 1.54.
[0128] Further, a fiber comprising only the above island component
material was produced for calculating the .DELTA.n.sub.1 and
.DELTA.n.sub.2.
[0129] Namely, a fiber having a diameter of 100 .mu.m was produced
by the above described same method except that only the island
component material was spun by using the nozzle for monofilament.
The refractive index of the fiber was measured. The refractive
index n.sub.i1 of the island component (fiber) in the direction
perpendicular to the longitudinal direction was 1.49. The
refractive index n.sub.i2 of the island component (fiber) in the
longitudinal direction was 1.50.
[0130] Accordingly, .DELTA.n.sub.1=|n.sub.s1-n.sub.i1|=|1.50-1.49
|=0.02. The difference .DELTA.n.sub.1 between the refractive
indexes in the direction perpendicular to the longitudinal
direction is 0.02 or less, so that the polarized light in the
direction perpendicular to the longitudinal direction can be
restrained from being reflected, diffused, or scattered on/in the
interfaces between the sea component and island component in the
polarizing fiber C. As a result, the polarized light in the
direction perpendicular to the longitudinal direction goes straight
and permeates therethrough without being absorbed in the sea
component.
[0131] Also, .DELTA.n.sub.2=|n.sub.s2-n.sub.i2|=|1.54-1.50|=0.04.
The difference .DELTA.n.sub.2 between the refractive indexes in the
longitudinal direction is 0.03 or more, so that the polarized light
in longitudinal direction is easily reflected, diffused, or
scattered on/in the interfaces between the sea component and the
island component in the polarizing fiber C. As a result, the
polarizing performance of the polarizing fiber C further becomes
larger than the polarizing performance of a conventional polarizing
fiber, which has no island regions.
Example 4
Polarizing Plate D
[0132] A polarizing plate D was produced wherein a
triacetylcellulose film of 40 .mu.m in thickness was laminated as a
protective film on each of both surfaces of a polarizer having the
polarizing fiber A and an isotropic material described below.
[0133] The used isotropic material was a transparent liquid epoxy
resin having the refractive index n.sub.m of 1.51 after the resin
was cured. Specifically, the transparent liquid epoxy resin
comprises 100 parts by weight of an alicyclic epoxy resin, 124
parts by weight of methylhexahydrophthalic anhydride, and 1 part by
weight of tri-n-butylphosphonium bromide.
[0134] Filaments of the polarizing fiber (polarizing fiber A)
produced in Example 1 were arranged in parallel to each other on a
triacetylcellulose film of 40 .mu.m in thickness. Next, the
polarizing fiber was coated with the isotropic material to envelop
the polarizing fiber in the material. Furthermore, a
triacetylcellulose film of 40 .mu.m in thickness was put thereon in
such a manner that air bubbles would not enter the workpiece. In
this way, the polarizing fiber was sandwiched between the two TAC
films. Thereafter, the resultant was subjected to curing treatment
at 100.degree. C. for 5 hours to obtain a polarizing plate D. The
moiety sandwiched between the triacetylcellulose films (that is,
the polarizer) had a thickness of 70 .mu.m. The amount of the
isotropic material used for 100 parts by weight of the polarizing
fiber was 100 parts by weight.
[0135] As described above, the refractive index n.sub.m of the used
isotropic material is 1.51. As described in the Example 1, the
refractive index n.sub.s1 of the sea component in the direction
perpendicular to the longitudinal direction of the polarizing fiber
A is 1.51. Accordingly, the difference between the refractive
indexes, .DELTA.n.sub.3=|n.sub.s1-n.sub.m|=|1.51-1.51|=0.00. The
.DELTA.n.sub.3 of this polarizing plate D is 0.02 or less, so that
the polarized light in the direction perpendicular to the
longitudinal direction can be restrained from being reflected,
diffused, or scattered on/in the interfaces between the sea
component and the island component in the polarizing plate D. As a
result, the polarizer of the polarizing plate D easily permeates
the polarized light perpendicular to the longitudinal direction and
has a high transmittance.
Example 5
Polarizing Plate E
[0136] A polarizing plate E was produced wherein a
triacetylcellulose film of 40 .mu.m in thickness was laminated as a
protective film on each of both surfaces of a polarizer having the
polarizing fiber C and an isotropic material.
[0137] The producing method of the polarizing plate E and so on
were the same as in Example 4 except that the polarizing fiber C
produced in the Example 3 was used as a polarizing fiber. Thus,
description thereof is omitted. Also, the sea components of the
polarizing fiber A used in the polarizing plate D and the
polarizing fiber C used in the polarizing plate E are the same. The
isotropic material used in the polarizing plate D and the isotropic
material used in the polarizing plate E are the same. Accordingly,
the differences .DELTA.n.sub.3 between the refractive indexes of
the polarizer of the polarizing plate D and the polarizer of the
polarizing plate E are the same and each of the polarizers has a
high transmittance.
Example 6
Polarizing Plate F
[0138] A polarizing plate F was produced wherein a
triacetylcellulose film of 40 .mu.m in thickness was laminated as a
protective layer on each of both surfaces of a polarizer having the
isotropic material, the polarizing fiber A, and the polarizing
fiber B.
[0139] The producing method of the polarizing plate F and so on
were the same as in Example 4 except that the polarizing fiber A
and the polarizing fiber B were used as polarizing fibers so as to
set the ratio by volume of the former to the latter to 48:52. Thus,
description thereof is omitted. The polarizing fiber A and the
polarizing fiber B were evenly dispersed not to cause any
deflection.
[0140] Also, the sea components of the polarizing fiber A and the
polarizing fiber B are the same except that the used dichroic dyes
are different. The isotropic material used in the polarizing plate
D and the isotropic material used in the polarizing plate F are the
same. Accordingly, the differences .DELTA.n.sub.3 between the
refractive indexes of the polarizer of the polarizing plate D and
the polarizer of the polarizing plate E are the same, and each of
the polarizers has a high transmittance.
Example 7
Polarizing Plate G
[0141] A polarizing plate G was produced wherein a
triacetylcellulose film of 40 .mu.m in thickness was laminated as a
protective film on each of both surfaces of a polarizer having an
isotropic material and a woven cloth.
[0142] The polarizer of the polarizing plate G is produced by using
the polarizing fibers A and wefts to form the woven cloth, and
enveloping this woven cloth in the same isotropic material as in
the Example 4.
[0143] The woven cloth used in the polarizing plate G is a woven
cloth formed by weaving warps and wefts as follows in plain weave
construction.
[0144] The warps, they were formed by bunching fifty strands of
polarizing fibers A produced in the Example 1.
[0145] The wefts were produced by melting and spinning resin
pellets of ethylene vinyl alcohol copolymer used as a sea component
of the polarizing fiber A. Here, the resin pellets used in the
wefts did not comprise a dichroic dye. The diameter of each of the
wefts was 50 .mu.m.
[0146] The polarizing plate G was obtained by the same method as in
the above Example 4 except that these warps and wefts were
used.
[0147] The wefts and the sea component of the polarizing fiber A
are the same component except that the wefts do not comprise a
dichoic dye. The isotropic material used in the polarizing plate D
and the isotropic material used in the polarizing plate G are the
same. Accordingly, the differences .DELTA.n.sub.3 between the
refractive indexes of the polarizer of the polarizing plate D and
the polarizer of the polarizing plate G are the same and each of
the polarizers has a high transmittance.
Comparative Example 1
Polarizing Plate H
[0148] An iodine-dyed PVA-based polarizing plate high in
transmittance and polarization degree (trade name: "NPF-SEG1425DU",
manufactured by Nitto Denko Corp.) was used.
Comparative Example 2
Polarizing Fiber I
[0149] Firstly, a polarizing fiber having no sea-island structure
was produced.
[0150] As to producing of the polarizing fiber I of Comparative
Example 2, the material same as the sea component material of the
polarizing fiber A in the Example 1 was used. Namely, the material
of the polarizing fiber I was a material obtained by immersing
resin pellets of an ethylene-vinyl alcohol copolymer having a
melting point of 181.degree. C. and a melt flow index of 12 g/10
min (trade name: "SOANOL (transliterated) DC3212B", manufactured by
Nippon Synthetic Chemical Industry Co., Ltd.) in a 2% water
solution of a dichroic dye (trade name: "Congo Red", manufactured
by Kishida Chemical Co., Ltd.) at 90.degree. C. for 4 hours,
washing the pellets with water, and then drying the pellets
sufficiently in a vacuum drier.
[0151] A polarizing fiber was obtained by use of the nozzle for
monofilament spinning and the same material to melt extrusion
molding, and pulling out the resultant at a pulling-out speed of
600 m/min. At this time, the spinning temperature was set to
230.degree. C. Also, the obtained polarizing fiber had a diameter
of 40 .mu.m. Further, this polarizing fiber was drawn 2.5 times in
hot water of 70.degree. C. temperature to obtain a polarizing fiber
I having a diameter of 25 .mu.m. The refractive index n.sub.p1 of
the polarizing fiber I in the direction perpendicular to the
longitudinal direction was 1.50. The refractive index n.sub.p2 of
the polarizing fiber I in the longitudinal direction was 1.54.
(Birefringent Fiber)
[0152] The same EVA resin pellets used in the above polarizing
fiber I were used except that the resin pellets were not dyed with
a dichroic dye. A birefringent fiber was obtained by use of the
nozzle for monofilament spinning for subjecting undyed resin
pellets to melt extrusion molding, and pulling out the resultant at
a pulling-out speed of 600 m/min. At this time, the spinning
temperature was set to 230.degree. C. This birefringent fiber was
drawn in hot water of 90.degree. C. temperature to obtain a
birefringent fiber having a diameter of 10 .mu.m. The refractive
index n.sub.o1 of the birefringent fiber in the direction
perpendicular to the longitudinal direction was 1.50. The
refractive index n.sub.o2 of the birefringent fiber in the
longitudinal direction was 1.54.
Polarizing Plate J
[0153] A polarizing plate J was produced wherein a
triacetylcellulose film of 40 .mu.m in thickness was laminated as a
protective film on each of both surfaces of the polarizer having
the above polarizing fiber I and the above birefringent fiber.
[0154] The producing method of the polarizing plate J and so on
were the same as in Example 4 except that the polarizing fiber I
and the birefringent fiber were used so as to set the ratio by
volume of the former to the latter to 4:5. Thus, description
thereof is omitted. The polarizing fiber I and the birefringent
fiber were evenly dispersed not to cause any deflection.
[0155] As described above, the refractive index n.sub.m of the used
isotropic material is 1.51. The refractive index n.sub.p1 of the
polarizing fiber I in the direction perpendicular to the
longitudinal direction is 1.50. The difference between the
refractive indexes,
.DELTA.n.sub.3=|n.sub.p1-n.sub.m|=|1.50-1.51|=0.01. Namely, the
.DELTA.n.sub.3 of the polarizing plate J is 0.02 or less, so that
the polarized light in the direction perpendicular to the
longitudinal direction can be restrained from being reflected,
diffused, or scattered on/in the interfaces between the polarizing
fiber I and the isotropic material.
[0156] The refractive index n.sub.o1 of the birefringent fiber in
the direction perpendicular to the longitudinal direction is also
1.50, so that the difference between the refractive indexes,
.DELTA.n.sub.3'=|n.sub.o1-n.sub.m|=|1.50-1.51|=0.01. Namely, the
.DELTA.n.sub.3' of the polarizing plate J is 0.02 or less, so that
the polarized light in the direction perpendicular to the
longitudinal direction can be restrained from being reflected,
diffused, or scattered on/in the interfaces between the
birefringent fiber and the isotropic material.
[0157] On the other hand, as described above, the refractive index
n.sub.o2 of the birefringent fiber in the longitudinal direction is
1.54, so that the difference between the refractive indexes,
.DELTA.n.sub.4=|n.sub.o2-n.sub.m|=|1.54-1.51|=0.03. The difference
.DELTA.n.sub.4 between the refractive indexes of the polarizing
plate J in the longitudinal direction is 0.03 or more, so that the
polarized light parallel to the longitudinal direction is easily
reflected, diffused, or scattered on/in the interfaces between the
birefringent fiber and the isotropic material.
[0158] The polarizing plate J is produced by coating the polarizing
fiber I and the birefringent fiber with the isotropic material to
envelop the fibers in the material. In the polarizing plate J, the
interfaces of the polarizing fiber I do not directly contact the
interfaces of the birefringent fiber. It is therefore hardly
significant to calculate out .DELTA.n.sub.1=|n.sub.p1-n.sub.o1|,
.DELTA.n.sub.2=|n.sub.p2-n.sub.o2|, and
.DELTA.n.sub.3=|n.sub.p1-n.sub.m|. Thus, the interfaces between the
polarizing fiber I and the birefringent fiber, and the isotropic
material were examined as described above.
[Evaluating Methods]
(Polarization Function of Polarizing Fibers)
[0159] The polarization function of the polarizing fibers of
Examples 1 to 3 and Comparative Example 2 (that is, the polarizing
fibers A, B, C and I) was examined. Specifically, a commercially
available polarizing plate was used to take out a linearly
polarized light in the direction perpendicular to the longitudinal
direction of each of the polarizing fibers. The linearly polarized
light was radiated to the polarizing fiber, and the light
transmitted through the polarizing fiber was observed with the
naked eye. Next, a linearly polarized light parallel to the
longitudinal direction of the polarizing fiber was radiated thereto
in the same way, and the light transmitted through the polarizing
fiber was observed with the naked eye.
(Transmittance and Polarization Degree of Polarizing Plates)
[0160] About the polarizing plates of Examples 4 to 7 and
Comparative Examples 1 to 2 (that is, the polarizing plates D, E,
F, G, H and J), an integrating-sphere-attached spectrophotometer
(product name: "U-4100", manufactured by Hitachi Ltd.) was used to
calculate out the transmittance and the polarization degree at a
wavelength of 550 nm.
(Color Tone of Polarizing Plates)
[0161] About each of the polarizing plates of Examples 4 to 7 and
Comparative Examples 1 to 2, the degree of the color of the plate
was observed with the naked eye.
(Unevenness in Polarizing Plates)
[0162] Each of the polarizing plates of Examples 4 to 7 and
Comparative Examples 1 to 2 was cut into pieces, 5 cm (in the cross
sectional direction).times.20 cm (in the longitudinal or drawn
direction), with pinking shears for handcrafts. Each of the pieces
was attached to a glass plate 0.7 mm in thickness. The resultants
were used as samples. In generally, when such a product is cut with
pinking shears, a crack described below is more easily generated.
Two out of the same samples were made into a cross nicol state, and
then observed on a high-brightness backlight with the naked eye. It
was then checked whether each of the samples (polarizing plates)
turned uneven or not.
(Crack in Polarizing Plates)
[0163] The individual samples were cooled at -30.degree. C. for 60
minutes, and then heated at 80.degree. C. for 60 minutes. This cold
and heat cycle test was conducted 100 times. Thereafter, two of the
same samples were made into a cross nicol state, and then it was
observed whether each of the samples (polarizing plates) was
cracked or not with the naked eye.
[Evaluation Results and Study]
(Polarization Function of Polarizing Fibers)
[0164] When the linearly polarized light in the direction
perpendicular to the longitudinal direction was radiated to each of
the polarizing fibers, the light transmitted through the polarizing
fibers was approximately transparent and colorless about each one
of the polarizing fibers. When the linearly polarized light
parallel to the longitudinal direction was radiated to each of the
polarizing fibers, the light transmitted through each one of the
polarizing fibers was colored in accordance with the absorption
wavelength of the dichroic dye. Accordingly, it is understood that
any one of the polarizing fibers A, B, C and I expressed a
polarization function.
(Transmittance, Polarization Degree of Polarizing Plates, and
Unevenness And Crack Therein)
[0165] The measurement results of the transmittance and
polarization degree of each of the polarizing fibers, and
unevenness and a crack therein are shown in Table 1. About each of
the unevenness and the crack, a case where it was generated is
represented by "x", and a case where it was not generated is
represented by "o".
TABLE-US-00001 Polarizing Structure or the Polarization Samples
fiber like Transmittance degree Unevenness Crack Example 4: A
Sea-island 44.7 99.50 .largecircle. .largecircle. polarizing plate
D Example 5: C Core-sheath 44.1 99.20 .largecircle. .largecircle.
polarizing plate E Example 6: A + B Sea-island 43.0 99.91
.largecircle. .largecircle. polarizing plate F Example 7: A Plain
weave 39.1 99.00 .largecircle. .largecircle. polarizing plate G
Comparative -- Blank 43.5 99.95 .largecircle. X Example 1:
polarizing plate H Comparative I Monofilament 44.5 98.00
.largecircle. .largecircle. Example 2: polarizing plate J
[0166] When Examples 4 to 7 are compared with Comparative Example
1, a crack was generated in Comparative Example 1. Accordingly, it
is understood that the polarizing plate H of Comparative Example 1
may be cracked under the severe conditions (100 cycles of the
cold-heat cycle test). The polarizing-fiber-used polarizing plates,
including Comparative Example 2, were not cracked.
[0167] When Examples 4 to 7 are compared with Comparative Example
2, as to Comparative Example 2, the same dichroic dye as in Example
1 was used and further the transmittance thereof was also
approximately equal to that of Example 1, but a polarization degree
was lower than Examples 4 to 7. The causes therefor are assumed as
follows. Firstly, in Comparative Example 2, it was difficult to
arrange the polarizing fiber and the birefringent fiber evenly and
in parallel to each other when the polarizing plate was produced.
If these cannot be arranged evenly and in parallel to each other,
the difference between the transmittances to the polarized light
parallel to the longitudinal direction of the fiber and that to the
polarized light in the direction perpendicular thereto does not
become large, so that the polarization degree is declined.
Secondly, a problem about the workabilities of the polarizing fiber
and the birefringent fiber is cited. In Comparative Example 2, the
polarizing fiber and the birefringent fiber were separately
produced; thus, it is assumed that a sufficiently fine fiber failed
in being obtained so that scattering in the interface between the
two fibers was not effectively used.
[0168] When Example 4 is compared with Example 5, the polarizing
plate D was slightly better than the polarizing plate E in each of
transmittance and polarization degree although the dichroic dyes
comprised in the polarizing fibers were the same. This would be
because the island number per filament of the polarizing fiber was
one in the polarizing plate E while the island number per filament
of the polarizing fiber was 12 in the polarizing plate D. In other
words, in the polarizing plate D, the island number was 2 or more,
and thus the polarized light that was transmitted through the
polarizing fiber and was parallel to the longitudinal direction
easily underwent multiple reflection, multiple diffusion or
multiple scattering. It is considered that this matter made high
the probability that the polarized light was absorbed in the sea
component of the polarizing plate D.
[0169] When Example 4 is compared with Example 7, the polarizing
plate D was slightly better than the polarizing plate G in each of
transmittance and polarization degree although the same polarizing
fiber A was used. In the polarizer that the polarizing plate D had,
the filaments of the polarizing fiber A were lined with each other
so that the filaments of the fiber A were arranged in parallel to
each other. On the other hand, in the polarizer that the polarizing
plate G had, the polarizing fiber A was made into the woven cloth,
thus, the polarizing fiber A were not arranged in sufficiently
parallel to each other. This matter would be a cause for the above.
However, the polarization degree of the polarizing plate G was
better than that of Comparative Example 2. When the polarizing
fiber A is formed into a woven cloth of plain weave, the
workability thereof is good when a polarizer is made therefrom;
therefore, the polarizing plate G can be more easily produced.
(Color Tone of Polarizing Plates)
[0170] It has been understood from the observation with the naked
eye that the polarizing plate F according to Example 6 was further
restrained from being colored than the polarizing plates D, E, F,
which were corresponding to Examples 4, 5 and 7, respectively. In
the polarizing plate F, the two polarizing fibers A and B were
used. It is therefore suggested that the use of two polarizing
fibers comprising dichroic dyes different from each other makes it
possible to uniform light-absorption-unevenness depending on
wavelengths.
INDUSTRIAL APPLICABILITY
[0171] The polarizing fiber of the present invention may be used as
a forming material of a polarizer, for example.
[0172] By laminating a proper optical member on the polarizer, a
polarizing plate or a laminated optical film may be provided.
[0173] The polarizer, the polarizing plate, and the laminated
optical film may be used for an image display.
* * * * *