U.S. patent application number 10/872460 was filed with the patent office on 2004-12-09 for light pipe and polarized-light source.
This patent application is currently assigned to NITTO DENKO CORPORATION. Invention is credited to Miyatake, Minoru, Sakuramoto, Takafumi.
Application Number | 20040246581 10/872460 |
Document ID | / |
Family ID | 27552774 |
Filed Date | 2004-12-09 |
United States Patent
Application |
20040246581 |
Kind Code |
A1 |
Miyatake, Minoru ; et
al. |
December 9, 2004 |
Light pipe and polarized-light source
Abstract
A light pipe is obtained by laminating on one or both surfaces
of a light-transmitting resin plate a polarized-light scattering
plate having fine birefringent domains dispersed therein and hence
showing anisotropy in scattering. The polarized-light scattering
plate comprises a transparent film having fine domains dispersed
therein comprising a liquid crystal polymer which exhibits nematic
at temperatures lower than the glass transition temperature of the
polymer constituting matrix of the transparent film and has a glass
transition temperature of 50.degree. C. or higher. The light pipe
as a laminate may further comprise a specular reflection layer, a
polarization-retaining lens and a light diffusion layer laminated
thereon. The light pipe may further comprise a light source mounted
at least on one side face thereof to provide a planar
polarized-light source.
Inventors: |
Miyatake, Minoru; (Osaka,
JP) ; Sakuramoto, Takafumi; (Osaka, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
NITTO DENKO CORPORATION
|
Family ID: |
27552774 |
Appl. No.: |
10/872460 |
Filed: |
June 22, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10872460 |
Jun 22, 2004 |
|
|
|
09569024 |
May 11, 2000 |
|
|
|
Current U.S.
Class: |
359/487.02 ;
359/487.06; 359/489.14; 359/493.01 |
Current CPC
Class: |
G02B 5/0257 20130101;
G02B 5/0263 20130101; G02B 5/0278 20130101; G02B 5/0284 20130101;
G02B 6/0056 20130101; G02B 6/0051 20130101; G02B 5/0242 20130101;
G02B 5/3008 20130101; G02B 6/0053 20130101 |
Class at
Publication: |
359/495 ;
359/483 |
International
Class: |
G02F 001/1335; G02B
005/30 |
Foreign Application Data
Date |
Code |
Application Number |
May 12, 1999 |
JP |
P. HEI. 11-131429 |
May 12, 1999 |
JP |
P .HEI. 11-131430 |
May 19, 1999 |
JP |
P. HEI. 11-138102 |
Jun 14, 1999 |
JP |
P. HEI. 11-166727 |
Jun 21, 1999 |
JP |
P. HEI. 11-174368 |
Jul 12, 1999 |
JP |
P. HEI. 11-197083 |
Claims
1. A light pipe comprising: a light-transmitting resin plate; and a
polarized-light scattering plate laminated on at least one surface
of said light-transmitting resin plate, said polarized-light
scattering plate having fine birefringent domains dispersed therein
to exhibit anisotropy in scattering depending on a polarization
direction.
2. A light pipe according to claim 1, wherein said polarized-light
scattering plate comprises a transparent film having fine domains,
difference in refractive index between the fine domains and other
portion of said transparent film is 0.03 or more in an optical
axial direction .DELTA.n1 which exhibits maximum value among the
difference in refractive index in various light axes of fine
domains, the difference in refractive indices of each of two other
axial directions .DELTA.n2 and .DELTA.n3 perpendicular to .DELTA.n1
direction .DELTA.n2 is 50% or less of .DELTA.n1, and .DELTA.n2 and
.DELTA.n3 are equal to each other.
3. A light pipe according to claim 2, wherein .DELTA.n1 direction
in the polarized-light scattering plate is parallel to a surface of
said transparent film.
4. (canceled).
5. A polarized-light source comprising: a light pipe according to
any one of claims 2 to 3; a light source disposed at least on one
side face of said light pipe; and a specular reflection layer
provided on one of both surfaces of said light pipe.
6. A light pipe comprising: a light-transmitting resin plate; and a
polarized-light scattering plate laminated on at least one surface
of said light-transmitting resin plate, said polarized-light
scattering plate having fine birefringent domains dispersed therein
to exhibit anisotropy in scattering depending on a polarization
direction, wherein said polarized-light scattering plate comprises
a transparent film having the fine domains comprising a liquid
crystal polymer which exhibits nematic at temperatures lower than a
glass transition temperature of the polymer constituting other
portion of the transparent film and has a glass transition
temperature of 50.degree. C. or higher.
7. A light pipe according to claim 6, wherein the polymer
constituting the transparent film has a deflection temperature of
80.degree. C. or higher under load and the glass transition
temperature of 110.degree. C. or higher.
8. A light pipe according to claim 1, wherein difference in
refractive index between the fine domains and other portion of said
transparent film is 0.03 or more in an optical axial direction
.DELTA.n1 which exhibits maximum value among the difference in
refractive index in various light axes of fine domains, the
difference in refractive indices of each of two other axial
directions .DELTA.n2 and .DELTA.n3 perpendicular to .DELTA.n1
direction .DELTA.n2 is 50% or less of .DELTA.n1, and .DELTA.n2 and
.DELTA.n3 are equal to each other.
9. A light pipe according to claim 8, wherein .DELTA.n1 direction
in the transparent film is parallel to a surface of said
transparent film.
10. (canceled).
11. A polarized-light source comprising: a light pipe according to
any one of claims 6 to 9 a light source disposed at least on one
side face of said light pipe; and a specular reflection layer
provided on one of both surfaces of said light pipe.
12. A light pipe comprising: a laminate having a birefringent
light-transmitting resin plate, and a polarized-light scattering
plate laminated on at least one surface of said light-transmitting
resin plate, said polarized-light scattering plate having fine
birefringent domains dispersed therein to exhibit anisotropy in
scattering depending on a polarization direction; and a specular
reflection layer provided on one surface of said laminate.
13. A light pipe according to claim 12, wherein a phase difference
due to birefringence of the light-transmitting resin plate is 50 nm
or more based on an average phase difference in a plane of said
light-transmitting resin plate.
14. A light pipe according to claim 13, wherein a retardation axis
of the light-transmitting resin plate and a light axis of the
polarized-light scattering plate in the laminate cross each other
at an angle of 5 degrees or more.
15. A polarized-light source comprising: a light pipe according to
any one of claims 12 to 14; and a light source disposed at least on
one side face of said light pipe.
16. A light pipe comprising: a laminate having a light-transmitting
resin plate, and a polarized-light scattering plate laminated on at
least one surface of said light-transmitting resin plate, said
polarized-light scattering plate having fine birefringent domains
dispersed therein to exhibit anisotropy in scattering depending on
a polarization direction; a specular reflection layer provided on a
first surface of said laminate; and a polarization-retaining light
diffusion layer provided on second surface of said laminate.
17. A light pipe according to claim 16, wherein said light
diffusion layer comprises one of (i) an optically isotropic
light-transmitting resin layer having transparent particles of a
refractive index ratio of from 0.9 to 1.1 dispersed therein and
(ii) an optically isotropic light-transmitting resin layer having a
finely roughened surface structure.
18. A light pipe according to claim 17, wherein said optically
isotropic light-transmitting resin is at least one of cellulose
triacetate-based resin, methyl polymethacrylate, polycarbonate and
norbornene-based resin.
19. A polarized-light source comprising: a light pipe according to
any one of claims 16 to 18; and a light source disposed at least on
one side face of said light pipe.
20. A light pipe comprising: a laminate having a light-transmitting
resin plate, and a polarized-light scattering plate laminated on at
least one surface of said light-transmitting resin plate, said
polarized-light scattering plate having fine birefringent domains
dispersed therein to exhibit anisotropy in scattering depending on
a polarization direction; a specular reflection layer provided on a
first surface of said laminate; and a polarization-retaining lens
sheet provided on a second surface of said laminate.
21. A light pipe according to claim 20, wherein said lens sheet
comprises one or more resins having a low birefringence.
22. A light pipe according to claim 20, wherein said lens sheet
comprises at least one of a cellulose triacetate-based resin,
methyl polymethacrylate, polycarbonate and norbornene-based
resin.
23. A light pipe according to claim 20, wherein said lens sheet has
a linear or dotted roughened structure provided on one surface
thereof.
24. A light pipe according to claim 23, wherein said lens sheet has
a linear roughened structure and a linear direction is parallel to
or perpendicular to a light axis of the polarized-light scattering
plate.
25. A light pipe according to claim 20, further comprising a
polarization-retaining light diffusion layer is provided between
said lens sheet and said laminate or on an emission side of said
lens sheet.
26. A polarized-light source comprising: a light pipe according to
any one of claims 20 to 25; and a light source disposed on one side
face of said light pipe.
27. A light pipe comprising: a light-transmitting resin plate; a
polarized-light scattering plate laminated on at least one surface
of said light-transmitting resin plate, said polarized-light
scattering plate having fine birefringent domains dispersed therein
to exhibit anisotropy in scattering depending on a polarization
direction; and a light path interposed between said
light-transmitting resin plate and said polarized-light scattering
plate to thereby partially bond said said light-transmitting resin
plate and said polarized-light scattering plate in close
contact.
28. A light pipe according to claim 27, wherein said light path
comprises a convex portion in a roughened structure provided on one
of the light-transmitting resin plate and the polarized-light
scattering plate, and said roughened structure has a rectangular
section comprising a flat surface on concave and convex portions
thereof.
29. A light pipe according to claim 27, wherein there is a
variation of distribution density of light path.
30. A light pipe according to claim 27, wherein length of said
light path is from 0.5 to 1,000 .mu.m.
31. A light pipe according to claim 27, wherein the
light-transmitting resin plate side of the light path has a section
having a continuous primary differential curve free of acute
corner.
32. A light pipe according to claim 27, wherein said light path is
made of an adhesive material.
33. A light pipe according to claim 27, further comprising a
polarization-retaining reflection layer on one of both surfaces of
said light pipe.
34. A light pipe according to claim 27, further comprising a
polarization-retaining light diffusion layer on one of both
surfaces of said light pipe.
35. A light pipe according to claim 27, further comprising a
polarization-retaining lens sheet on one of both surfaces of said
light pipe.
36. A polarized-light source comprising: light pipe according to
any one of claims 27 to 35; and a light source provided at least on
one side face of said light pipe.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a light pipe and a planar
polarized-light source which can convert incident light received
from its side face to linearly polarized light having uniform
brightness which is then emitted from both surfaces thereof under
control over oscillating surfaces so that they are suitable for the
formation of back light for liquid crystal display device.
[0003] The present application is based on Japanese Patent
Applications No. Hei. 11-131429, 11-131430, 11-138102, 11-166727,
11-174368 and 11-197083, which are incorporated herein by
reference.
[0004] 2. Description of the Related Art
[0005] As a side light type light-pipe which can be used as back
light for liquid crystal device there has heretofore been known a
device comprising a light-emitting means made of reflecting dots or
the like provided on a light-transmitting resin plate having an
arrangement such that transmitted light produced by total
reflection is emitted from one of two surfaces of the plate by
scattering or the like. However, the foregoing emitted light is
natural light which has little or no polarization and thus needs to
be converted to linearly polarized light through a polarizing plate
before liquid crystal display. Therefore, the foregoing device is
disadvantageous in that the polarizing plate causes absorption loss
that prevents the percent utilization of light from exceeding
50%.
[0006] Under the foregoing circumstances, a system comprising in
addition to the foregoing arrangement a polarized-light converting
means having a polarized-light separating plate which utilizes
Brewster angle to give linearly polarized light and a retarder
plate in combination has been proposed (JP-A-6-18873 (The term
"JP-A" as used herein means an "unexamined published Japanese
patent application"), JP-A-6-160840, JP-A-6-265892, JP-A-7-72475,
JP-A-7-261122, JP-A-7-270792, JP-A-9-54556, JP-A-9-105933,
JP-A-9-138406, JP-A-9-152604, JP-A-9-293406, JP-A-9-326205,
JP-A-10-78581). However, such a back light cannot provide
sufficient polarization and can hardly give control over the
polarization direction. Thus, such a back light can hardly be put
in practical use.
SUMMARY OF THE INVENTION
[0007] An object of the present invention is to provide a light
pipe comprising a light-transmitting resin plate and a
polarized-light scattering plate laminated on one side or both
sides of the light-transmitting resin plate. The polarized-light
scattering plate has fine birefringent domains dispersed therein to
exhibit a scattering anisotropy attributed to polarization
direction.
[0008] In accordance with the present invention, in the foregoing
arrangement, when natural light is received at a side face,
linearly polarized light can be efficiently emitted from both
surfaces without the necessity of forming a special light-emitting
means such as reflecting dots on a light-transmitting resin plate.
Further, when the linearly polarized light passes through the
optical axis of a polarized-light scattering plate additionally
used, linearly polarized light having the corresponding oscillation
direction can be obtained. Accordingly, the oscillation direction
of linearly polarized light can be arbitrarily changed by
controlling the optical axis of the polarized-light scattering
plate. Moreover, polarized-light can be emitted from one surface of
such a light pipe with a specular reflection layer provided on the
other to enhance the emission efficiency per surface, making it
possible to provide linearly polarized light having excellent
diffusion properties. By disposing a liquid crystal display element
on the light pipe in such an arrangement that the optical axis of
the two elements are parallel to each other, brightness nearly
twice ordinary value can be accomplished.
[0009] In the foregoing description, incident light which has been
received at a side face of the light pipe is transmitted by the
interior of the light pipe while repeating total reflection due to
the difference of refractive index from air, and then enters into
the polarized-light scattering plate. Among the components of
incident light received by the polarized-light scattering plate,
linearly polarized light having an oscillation plane parallel to
the axial direction (.DELTA.n1 direction) showing the maximum
difference of refractive index (.DELTA.n1) from fine domains is
selectively strongly scattered. A part of the linearly polarized
light components which is reflected at an angle smaller than the
total reflection angle is emitted by the light pipe. In this
arrangement, light is screened on the specular reflection layer
side, and then supplied into the opposing side (the other surface
of the light pipe free of specular reflection layer). Thus, light
emission is concentrated at the other side of the light pipe.
Accordingly, linearly polarized light can be diffused from one
surface of the light pipe through a light diffusion layer without
drastically deteriorating polarization degree and then emitted with
a good uniformity.
[0010] On the other hand, the light which has been scattered at a
great angle in .DELTA.n1 direction, the light which has satisfied
the requirements for .DELTA.n1 direction but has not been
scattered, and the light having the oscillation direction other
than .DELTA.n1 direction are confined in the light pipe by which
they are transmitted while repeating total reflection. In this
manner, these components wait for an opportunity of being
depolarized by the difference in birefringence phase due to
polarized-light scattering plate and satisfying the requirements
for .DELTA.n1 direction to emit themselves. By repeating this
process, linearly polarized light having a predetermined
oscillation plane can be efficiently emitted from the light
pipe.
[0011] The foregoing polarized-light scattering plate preferably
comprises a transparent film having fine domains dispersed therein
comprising a liquid crystal polymer which exhibits nematic at
temperatures lower than the glass transition temperature of the
polymer constituting matrix of the transparent film and has a glass
transition temperature of 50.degree. C. or higher.
[0012] In this arrangement, a light pipe having an excellent heat
resistance can be obtained. The light pipe thus obtained is little
liable to deformation and deterioration of function even when
subject to temperature rise after a prolonged operation of light
source. Thus, the light pipe of the invention is excellent in
durability, particularly in thermal stability.
[0013] The present invention further provides a light pipe
comprising as a laminate the foregoing polarized-light scattering
plate having a specular reflection layer provided on one surface
thereof and at least one polarization-retaining lens sheet provided
on the other and a planar polarized-light source comprising a light
source provided at least on one side face of the light pipe. The
path of emitted light can be controlled by the
polarization-retaining lens sheet to obtain linearly polarized
light excellent in directivity to the front. By disposing a liquid
crystal element on the polarization-retaining lens sheet,
brightness 1.5 or more times the ordinary value can be
realized.
[0014] The present invention further provides a light pipe
comprising a laminate having a birefringent light-transmitting
resin plate, and a polarized-light scattering plate having fine
birefringent domains dispersed therein and showing anisotropy in
scattering depending on the polarization direction provided on one
or both surfaces thereof, said laminate comprising a specular
reflection layer provided on one surface thereof, and a planar
polarized-light source comprising a light source provided at least
on one side face of the light pipe. In this arrangement, the
light-transmitting resin plate makes the use of its birefringence
to efficiently eliminate polarization and hence increase the
foregoing opportunity of emission, making it possible to raise
brightness.
[0015] The present invention further provides a light pipe
comprising a light-transmitting resin plate, and a polarized-light
scattering plate having fine birefringent domains dispersed therein
and showing anisotropy in scattering depending on the polarization
direction partially provided in close contact with one or both
surfaces thereof with a light path provided interposed therebetween
and a planar polarized-light source comprising a light source
provided at least on one side face of the light pipe.
[0016] In accordance with the present invention, the light pipe can
receive natural light at its side face and then efficiently emit
linearly polarized light from both surfaces thereof with a good
uniformity in brightness.
[0017] In some detail, incident light which has been received at a
side face of the light-transmitting resin plate is transmitted by
the interior of the resin plate while repeating total reflection
due to the difference of refractive index from air, and then
undergoes scattering through the light path to enter into the
polarized-light scattering plate through which it is then emitted
from the light pipe. Accordingly, the amount of incident light and
hence brightness can be controlled by the area of contact with the
light path.
[0018] Features and advantages of the invention will be evident
from the following detailed description of the preferred
embodiments described in conjunction with the attached
drawings.
BRIEF DESCRIPTION OF THE INVENTION
[0019] In the accompanying drawings:
[0020] FIG. 1 is a sectional view of an embodiment of the light
pipe according to the present invention;
[0021] FIG. 2 is a sectional view of another embodiment of the
light pipe according to the present invention;
[0022] FIG. 3 is a sectional view of an embodiment of the planar
polarized-light source according to the present invention;
[0023] FIG. 4 is a sectional view of another embodiment of the
planar polarized-light source according to the present
invention;
[0024] FIG. 5 is a sectional view of a further embodiment of the
planar polarized-light source according to the present
invention;
[0025] FIG. 6 is a sectional view of a still further embodiment of
the planar polarized-light source according to the present
invention; and
[0026] FIG. 7 is a diagram illustrating the sectional shape of the
light path.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The light pipe according to the present invention comprises
a light-transmitting resin plate and a polarized-light scattering
plate having fine birefringent domains dispersed therein and
showing anisotropy in scattering depending on the polarization
direction and laminated on one or both surfaces of the
light-transmitting resin plate. An embodiment of the light pipe is
shown in FIGS. 1 and 2. The reference numeral 1 indicates a
light-transmitting resin plate, the reference numeral 3 indicates a
polarized-light scattering plate, and the reference numeral 2
indicates an optional adhesive layer.
[0028] The polarized-light scattering plate 3 comprises a
transparent film having fine domains comprising a liquid crystal
polymer dispersed therein which exhibits nematic at temperatures
lower than the glass transition temperature of the polymer
constituting the film (matrix polymer) and has a glass transition
temperature of 50.degree. C. or higher.
[0029] The light pipe as a laminate may further comprise a specular
reflection layer provided on one surface thereof and at least one
polarization-retaining light diffusion layer provided on the other.
An embodiment of this arrangement is shown in FIG. 3. The reference
numeral 4 indicates a laminate (polarized-light scattering plate),
the reference numeral 6 indicates a specular reflection layer, and
the reference numeral 7 indicates a light diffusion layer. FIG. 3
illustrates an embodiment of the planar polarized-light source
comprising the foregoing light pipe. The reference numeral 5
indicates a light source.
[0030] The foregoing laminate may further comprise a
polarization-retaining lens sheet provided on the other surface
thereof. In FIG. 4, the reference numeral 8 indicates a lens
sheet.
[0031] The light pipe according to the present invention may
further comprise the foregoing polarized-light scattering plate
provided partially in close contact with one or both surfaces of
the light-transmitting resin plate with a light path provided
interposed therebetween. An embodiment of this arrangement is shown
in FIG. 6. The reference numeral 1 indicates a light-transmitting
resin plate, the reference numeral 9 indicates a light path, and
the reference numeral 3 indicates a polarized-light scattering
plate. These components form a laminate 4 as light pipe having
least required units. FIG. 6 illustrates an embodiment of the
planar polarized-light source comprising the foregoing light
pipe.
[0032] As the light-transmitting resin plate there may be used any
tabular material formed by a proper material showing transparency
to predetermined wavelength of light from the light source. For
visible light range, for example, a tabular material made of
acrylic resin, polycarbonate resin, styrenic resin,
norbornene-based resin, epoxy resin or the like may be preferably
used. From the standpoint of light transmittance, tabular material
made of a resin having as small refractive index as possible is
preferred. Further, taking into account durability, a tabular
material made of a resin having an excellent heat resistance is
preferred.
[0033] As the light-transmitting resin plate there may be used one
which exhibits in-plane birefringence for the purpose of
eliminating polarization of light transmitted by the interior of
the light pipe to increase the opportunity of emission from the
polarized-light scattering plate and hence enhance brightness. In
order to efficiently eliminate polarization, a material having a
phase difference due to birefringence of 50 nm or more, preferably
60 nm or more, particularly 70 nm or more as calculated in terms of
average phase difference in plane is preferably used. Further, in
order to prevent uneven brightness, a material having as small
uneven phase difference as possible is preferably used.
[0034] The formation of the birefringent light-transmitting resin
plate can be accomplished by any proper method such as method
involving the development of orientation birefringence by strain or
the like during the formation of -plate, method involving
stretching, method involving rolling and method involving
orientation of resin under the action of electric field or magnetic
field. Particularly preferred among these methods is the method
involving the development of orientation birefringence by strain or
the like from the standpoint of mass production of resin plate.
From this standpoint of view, an acrylic resin, polycarbonate resin
or the like is preferably used.
[0035] In order to maintain the desired polarization properties of
the emitted light, a resin plate having as small in-plane phase
difference as possible is preferably used. From this standpoint of
view, a material which is little liable to orientation
birefringence due to strain or the like during the formation of
plate, particularly polymethyl methacrylate or norbornene-based
resin, is preferably used. Such a resin can be fairly formed into
plate.
[0036] The shape of the light-transmitting resin plate can be
properly determined depending on the size of liquid crystal cell,
the characteristics of light source, the degree of uniformity in
brightness of emitted light, etc. and thus is not specifically
limited. From the standpoint of formability or the like, tabular or
wedge-shaped plate is preferably used. The thickness of the
light-transmitting resin plate can be properly determined depending
on the size of light source and liquid crystal cell and thus is not
specifically limited. However, the light-transmitting resin plate
is preferably as thin as possible for the purpose of reducing the
thickness and weight of the light pipe and is specifically 10 mm or
less, particularly from 0.5 to 5 mm.
[0037] The formation of the light-transmitting resin plate can be
accomplished by any proper method such as injection molding method,
casting method, extrusion method, flow casting method, roll coating
method, transfer molding method and reaction injection molding
method (RIM). For the formation of the light-transmitting resin
plate, a proper additive such as discoloration inhibitor, oxidation
inhibitor, ultraviolet absorber and release agent may be added to
the material.
[0038] On the other hand, as the polarized-light scattering plate
there may be used any proper material which comprises fine
birefringent domains dispersed therein to exhibit anisotropy in
scattering depending on the polarization direction. An examples of
the polarized-light scattering plate is a transparent film having
fine birefringent domains dispersed therein.
[0039] For example, there may be used one comprising a transparent
film having fine domains comprising a liquid crystal polymer
dispersed therein which exhibits nematic at temperatures lower than
the glass transition temperature of the polymer constituting the
film and has a glass transition temperature of 50.degree. C. or
higher and showing anisotropy in scattering depending on the
polarization direction. In this arrangement, a polarized-light
scattering plate excellent in heat resistance can be obtained,
making it possible to form a light pipe excellent in thermal
stability.
[0040] The formation of the foregoing polarized-light scattering
plate showing anisotropy in scattering can be accomplished by any
proper method such as method which comprises subjecting one or more
proper materials having excellent transparency such as polymer and
liquid crystal to proper orientation by stretching or the like in
such a combination that regions having different birefringences are
formed to obtain an oriented film.
[0041] Examples of the foregoing combination include combination of
polymer and liquid crystal, combination of isotropic polymer and
anisotropic polymer, and combination of anisotropic polymers. From
the standpoint of dispersion distribution of fine domains, a
combination causing phase separation is preferably used. The
dispersion distribution of fine domains can be controlled by the
compatibility of the materials to be combined. Phase separation can
be accomplished by any proper method such as method which comprises
solubilizing noncompatible materials with a solvent and method
which comprises heating and melting noncompatible materials in
admixture.
[0042] In the case where orientation is carried out by stretching
in the foregoing combination, the desired polarized-light
scattering plate can be formed by stretching at arbitrary
temperature and stretching ratio if the combination of polymer and
liquid crystal and the combination of isotropic polymer and
anisotropic polymer are used or by properly controlling the
stretching conditions if the combination of anisotropic polymers is
used. Anisotropic polymers can be classified as positive or
negative according to the change of refractive index in the
stretching direction. In the present invention, both positive and
negative anisotropic polymers can be used. Any of combination of
positive anisotropic polymers, combination of negative anisotropic
polymer and combination of positive anisotropic polymer and
negative anisotropic polymer can be used.
[0043] Examples of the foregoing polymers include ester-based
polymer such as polyethylene terephthalate and polyethylene
naphthalate, styrene-based polymer such as polystyrene and
acrylonitrile-styrene copolymer (AS polymer), olefinic polymer such
as polyethylene, polypropylene, polyolefin having cyclo or
norbornene structure and ethylene-propylene copolymer, acrylic
polymer such as polymethyl methacrylate, cellulose-based polymer
such as cellulose biacetate and cellulose triacetate, and
amide-based polymer such as nylon and aromatic polyamide.
[0044] Further examples of the foregoing transparent polymer
include thermosetting or ultraviolet-curing polymers such as
carbonate-based polymer, vinyl chloride-based polymer, imide-based
polymer, sulfon-based polymer, polyether sulfone, polyether ether
ketone, polyphenylene sulfide, vinyl alcohol-based polymer,
vinylidene chloride-based polymer, vinyl butyral-based polymer,
arylate-based polymer, polyoxymethylene, silicone-based polymer,
urethane-based polymer, ether-based polymer, vinyl acetate-based
polymer, blend of the foregoing polymers, phenolic polymer,
melamine-based polymer, acrylic polymer, urethane-based polymer,
urethane acryl-based polymer, epoxy-based polymer, and
silicone-based polymer.
[0045] In particular, a polymer excellent in transparency in a
desired wavelength range such as visible light range is preferred.
In order to obtain a polarized-light scattering plate excellent in
thermal stability, there is preferably used a polymer having a
deflection temperature of 80.degree. C. or higher under load and a
glass transition temperature of 110.degree. C. or higher, more
preferably 115.degree. C. or higher, particularly 120.degree. C. or
higher. The measurement of deflection temperature under load is
conducted according to JIS K 7207. In some detail, a-heat transfer
medium in a heating bath is heated at a rate of 2.degree. C./min
while a specimen having a height of 10 mm in the heating bath is
under the application of a bending stress of 18.5 kgf/cm.sup.2. The
temperature of the heat transfer medium at which the deflection of
the specimen reached 0.32 mm is defined as deflection temperature
under load.
[0046] Examples of the liquid crystal include low molecular liquid
crystal or crosslinkable liquid crystal monomer which exhibits
nematic or smectic at room temperature or high temperatures such as
cyanobiphenyl-based compound, cyanophenylcyclohexane-based
compound, cyanophenylester-based compound, benzoic acid
phenylester-based compound, phenylpyrimidine-based compound and
mixture thereof, and liquid crystal polymer which exhibits nematic
or smectic at room temperature or high temperatures. The foregoing
crosslinkable liquid crystal monomer is normally subjected to
orientation followed by crosslinking by a proper means such as heat
and light to become a polymer.
[0047] In order to obtain a polarized-light scattering plate
excellent in heat resistance, durability, etc., it is preferred
that a polymer having a glass transition temperature of 50.degree.
C. or higher, more preferably 80.degree. C. or higher, particularly
120.degree. C. or higher, and a crosslinkable liquid crystal
monomer or liquid crystal polymer be used in combination. As the
liquid crystal polymer there may be any proper material such as
main-chain type compound and side-chain type compound. The kind of
the liquid crystal polymer is not specifically limited.
[0048] The formation of the polarized-light scattering plate by a
liquid crystal polymer can be accomplished by a process which
comprises mixing one or more polymers and one or more liquid
crystal polymers for forming fine domains, forming a polymer film
having the liquid crystal polymer dispersed therein in the form of
minute region, and then subjecting the polymer film to proper
orientation to form regions having different birefringences.
[0049] From the standpoint of ease of control over the foregoing
refractive index differences .DELTA.n1 and .DELTA.n2 by
orientation, as the liquid crystal polymer for forming fine domains
there may be used one which has a glass transition temperature of
50.degree. C. and exhibits nematic at temperatures lower than the
glass transition temperature of the polymer constituting the film.
The kind of the liquid crystal polymer to be used herein is not
specifically limited. A proper liquid crystal polymer of main-chain
type or side-chain type which exhibits such properties can be
used.
[0050] Specific examples of the foregoing liquid crystal polymer
include a side-chain liquid crystal polymer having a monomer unit
represented by the following general formula. The side-chain type
liquid crystal polymer may be a proper thermoplastic polymer such
as homopolymer and copolymer having such a monomer unit. In
particular, such a thermoplastic polymer excellent in monodomain
orientability is preferred. 1
[0051] In the foregoing general formula, X represents a skeleton
group forming the main chain of the liquid crystal polymer which
may be formed by a proper connecting chain such as linear, branched
and cyclic chain. Examples of the skeleton group include
polyacrylate, polymethacrylate, poly-.alpha.-haloacrylate,
poly-.alpha.-cyanoacrylate, polyacrylamide, polyacryloylnitrile,
polymethacrylonitrile, polyamide, polyester, polyurethane,
polyether, polyimide, and polycyloxane.
[0052] Y represents a spacer group branched from the main chain.
From the standpoint of formability of polarized-light scattering
plate such as ease of control over refractive index. Examples of
the spacer group include ethylene, propylene, butylene, pentylene,
hexylene, octylene, decylene, undecylene, dodecylene, octadecylene,
ethoxyethylene, and methoxybutylene.
[0053] On the other hand, Z represents a mesogen group for
imparting liquid crystal orientability (nematic orientability).
Examples of the mesogen group will be given below. 2
[0054] In the foregoing compounds, the terminal substituent A may
be a proper group such as cyano group, alkyl group, alkenyl group,
alkoxy group, oxalkyl group and haloalkyl group, haloalkoxy group
and haloalkenyl group having one or more hydrogen atoms substituted
by fluorine or chlorine.
[0055] The spacer group Y and the mesogen group Z may be connected
to each other via an ether bond, i.e., --O--. The phenyl group in
the mesogen group Z may have one or more hydrogen atoms substituted
by halogen. The halogen to be used is preferably. chlorine or
fluorine.
[0056] The formation of the polarized-light scattering plate by the
foregoing nematically orientable liquid crystal polymer can be
accomplished, e.g., by a process which comprises mixing a polymer
for forming a polymer film and a liquid crystal polymer, forming a
polymer film having the liquid crystal polymer dispersed therein in
the form of minute region, subjecting the polymer film to heat
treatment so that the liquid crystal polymer for forming fine
domains is oriented in liquid-crystalline arrangement, and then
cooling the polymer film so that orientation is fixed.
[0057] In particular, the formation of the polarized-light
scattering plate can be accomplished, e.g., by a process which
comprises mixing one or more polymers for forming a film and one or
more liquid crystal polymers for forming fine domains which
exhibits nematic at temperatures lower than the glass transition
temperature of the foregoing polymer and has a glass transition
temperature of 50.degree. C. or higher, forming a polymer film
having the liquid crystal polymer dispersed therein in the form of
minute region, subjecting the polymer film to heat treatment so
that the liquid crystal polymer for forming fine domains is
oriented in nematic liquid crystal phase, and then cooling the
polymer film so that the orientation is fixed.
[0058] In order to obtain a polarized-light scattering plate
excellent in heat resistance and durability, there is preferably
used a liquid crystal polymer having a glass transition temperature
of 60.degree. C. or higher, more preferably 70.degree. C. or
higher, particularly 80.degree. C. or higher. From the standpoint
of ease of formation of fine domains having an excellent uniformity
in particle diameter distribution, thermal stability, formability
into film and ease of orientation, a liquid crystal polymer having
a polymerization degree of 8 or more, preferably 10 or more,
particularly from 15 to 5,000 is desirable.
[0059] From the standpoint of dispersion distribution of fine
domains in the light pipe thus obtained, the polymer for forming a
film and the liquid crystal polymer for forming fine domains are
preferably used in such a combination that phase separation takes
place. The dispersion distribution of fine domains can be
controlled by compatibility attained by such a combination. Phase
separation can be accomplished, e.g., by any proper method such as
method which comprises solubilizing noncompatible materials with a
solvent and method which comprises heating and melting
noncompatible materials in admixture.
[0060] The formation of the foregoing polymer film having fine
domains dispersed therein, i.e., film to be oriented, can be
accomplished, e.g., by any proper method such as casting method,
extrusion method, injection molding method, rolling method and flow
casting method. Alternatively, the formation of the foregoing
polymer film can be accomplished by a method which comprises
spreading the polymer in the form of monomer, and then subjecting
the material to heat treatment or irradiation with ultraviolet rays
or the like to form a film.
[0061] In order to obtain a polarized-light scattering plate
excellent in uniformity in distribution of fine domains, there is
preferably used a method which comprises subjecting a mixture of
film-forming materials with a solvent to casting or flow casting to
form a film. In this case, the size and distribution of fine
domains can be controlled by the kind of the solvent, the viscosity
of the mixture, the drying rate of the mixture-spread layer, etc.
For example, the reduction of the area of fine domains can be
advantageously accomplished by lowering the viscosity of the
mixture or raising the drying rate of the mixture-spread layer.
[0062] The thickness of the film to be oriented can be properly
determined. In practice, however, it is preferably from 1 .mu.m to
3 mm, more preferably from 5 .mu.m to 1 mm, particularly from 10
.mu.m to 500 .mu.m from the standpoint of orientability. During the
formation of film, the material may comprise a proper additive such
as dispersant, surface active agent, ultraviolet absorber, color
toner, fire retardant, release agent and oxidation inhibitor
incorporated therein.
[0063] Orientation can be accomplished by one or more proper
methods which allow control over refractive index by orientation
such as stretching method or rolling method such as uniaxial,
biaxial, successive biaxial or Z-axis method, method which
comprises applying an electric field or magnetic field to the
material at a temperature of not lower than glass transition
temperature or liquid crystal transition temperature, and then
rapidly cooling the material to fix orientation, method involving
flow orientation during film forming and method involving
self-orientation of liquid crystal according to slight orientation
of isotropic polymer. Accordingly, the polarized-light scattering
plate thus obtained may be a stretched film or unstretched film. In
the case where a stretched film is produced, a brittle polymer,
too, may be used. However, a polymer excellent in extensibility is
particularly desirable.
[0064] In the case where the fine domains are made of the foregoing
liquid crystal polymer, there may be used-a method which comprises
heating the material to a temperature at which the liquid crystal
polymer to be dispersed and distributed in the polymer film in the
form of fine domains shows a desired liquid crystal phase such as
nematic phase so that it is melted, subjecting the material to
orientation under the action of an orientation regulating force,
and then rapidly cooling the material so that orientation is fixed.
The orientation of fine domains is preferably in the state of as
monodomain as possible to inhibit scatter of optical
properties.
[0065] As the orientation regulating force there may be used a
proper regulating force capable of orienting liquid crystal polymer
such as stretching force to be used in a method involving
stretching a polymer film at a proper draw ratio, shearing force to
be used during the film formation and electric or magnetic field.
One or more of these regulating forces can be acted upon the
polymer film to orient the liquid crystal polymer.
[0066] Accordingly, the portion other than the fine domains in the
polarized-light scattering plate, i.e., matrix of the transparent
film (polymer film portion) may exhibit birefringence or may be
isotropic. The polarized-light scattering plate which entirely
exhibits birefringence can be obtained by subjecting an
orientation-birefringent film-forming polymer to molecular
orientation during the foregoing film-forming process. If
necessary, the polymer may be subjected to a known orientation such
as stretching so that it is rendered birefringent or controlled in
birefringence.
[0067] The polarized-light scattering plate which is isotropic in
regions other than the fine domains can be obtained by subjecting
an isotropic film-forming polymer to stretching at temperatures of
not higher than the glass transition temperature of the
polymer.
[0068] A preferred embodiment of the polarized-light scattering
plate is controlled such that in the axial direction (.DELTA.n1
direction) which is maximum among the difference in refractive
index in the various light axes of fine domains between the fine
domains and other portions as the polymer film portion, i.e.,
.DELTA.n1, .DELTA.n2 and .DELTA.n3, .DELTA.n1 is 0.03 or more, and
in the two other axial directions perpendicular to .DELTA.n1
direction (.DELTA.n2 and .DELTA.n3 directions) .DELTA.n2 and
.DELTA.n3 each are 50% or less of .DELTA.n1. .DELTA.n2 and
.DELTA.n3 are preferably equal to each other.
[0069] By using the foregoing refractive index, linearly polarized
light in .DELTA.n1 direction is strongly scattered at an angle
smaller than the total reflection angle, making it possible to
increase the amount of light emitted from the light pipe. Linearly
polarized light in other directions can hardly be scattered and
thus is repeatedly totally reflected, making it possible to confine
itself in the light pipe.
[0070] In the foregoing description, the difference between the
refractive index of the fine domains in the various axial
directions and that of portions other than the-fine domains means
the difference between the refractive index of the fine domains in
the various directions and the average refractive index of the
polymer film if the film-forming polymer is optically isotropic. If
the film-forming polymer is optically anisotropic, it means the
difference between the refractive index of the polymer film in the
main optical axial direction and that of the fine domains in the
main optical axial direction because the two main optical
directions are usually the same.
[0071] From the standpoint of the foregoing total reflection, the
refractive index difference .DELTA.n1 in .DELTA.n1 direction is
preferably properly great, more preferably from 0.035 to 1,
particularly from 0.045 to 0.5. The refractive index differences
.DELTA.n2 and .DELTA.n3 in .DELTA.n2 and .DELTA.n3 directions,
respectively, are each preferably properly small. These refractive
index differences can be controlled by adjusting the refractive
index of the material used or conducting the foregoing
orientation.
[0072] Since the foregoing .DELTA.n1 direction corresponds to the
oscillation plane of linearly polarized light emitted by the light
pipe, it is preferably parallel to the surface of the
polarized-light scattering plate. .DELTA.n1 direction in plane may
be proper depending on the desired liquid crystal cell or the
like.
[0073] From the standpoint of homogeneity in scattering effect, the
fine domains are preferably dispersed and distributed in the
polarized-light scattering plate as homogeneously as possible. The
size of the fine domains, particularly .DELTA.n1 direction, which
is the scattering direction, is related to back scattering
(reflection) or dependence on wavelength.
[0074] From the standpoint of enhancement of percent utilization of
light, prevention of coloring due to dependence on wavelength,
prevention of obstruction of vision of fine domains by sight,
prevention of obstruction of clear display, film-forming properties
and film strength, the preferred size of the fine domains,
particularly the preferred length of .DELTA.n1 direction, is from
0.05 to 500 .mu.m, more preferably from 0.1 to 250 .mu.m,
particularly from 1 to 100 .mu.m. Although the fine domains are
usually present in the polarized-light scattering plate in the form
of domain, its length .DELTA.n2 direction is not specifically
limited.
[0075] The proportion of the fine domains in the polarized-light
scattering plate can be properly determined by the scattering
properties in .DELTA.n1 direction. In practice, however, it is
preferably from 0.1 to 70% by weight, more preferably from 0.5 to
50% by weight, particularly from 1 to 30% by weight, taking into
account the film strength as well.
[0076] The polarized-light scattering plate can be formed in the
form of single layer made of the foregoing film showing
birefringence. Two or more of such a film can be laminated to form
the polarized-light scattering plate. The lamination of these films
makes it possible to exert a synergistic scattering effect greater
than developed by the increase of the thickness. The lamination may
be conducted such that the films are arranged at arbitrary angle
such as .DELTA.n1 or .DELTA.n2 direction. From the standpoint of
enhancement of scattering effect, the lamination is preferably
conducted such that .DELTA.n1 direction of two vertically adjacent
layers are parallel to each other. The laminated number of films is
an arbitrary number of 2 or more.
[0077] The films to be laminated may have the same or different
.DELTA.n1 or .DELTA.n2 directions. The .DELTA.n1 direction or the
like of the vertically adjacent layers are as parallel to each
other as possible. However, deviation due to error in working is
tolerated. When .DELTA.n1 direction or the like scatters, the
values of .DELTA.n1 direction may be averaged.
[0078] The films to be laminated are bonded to each other with an
adhesive layer in such an arrangement that the total reflection
surface is the outermost surface. As the adhesive there may be used
any proper adhesive such as hot-melt adhesive and tacky adhesive.
In order to inhibit reflection loss, an adhesive layer having as
small refractive index difference from the foregoing films as
possible is preferably used. These films may be bonded to
themselves or using the polymer for forming fine domains.
[0079] The light pipe preferably has a phase difference as a whole
or in part because polarization can be properly eliminated while
light is being transmitted by the interior of the light pipe to
advantage from the standpoint of percent utilization of light.
Since the retardation axis of the scattering light pipe and the
polarization axis (oscillation plane) of the linearly polarized
light are essentially perpendicular to each other, it is thought
that polarization conversion due to phase difference can hardly
take place but a slight scattering causes the change of apparent
angle that results in polarization conversion.
[0080] From the standpoint of the foregoing polarization
conversion, it is usually preferred that there occur an in-plane
phase difference of 5 nm or more, though depending on the thickness
of the scattering light pipe. The phase difference can be imparted
by a proper method such as method which comprises allowing
birefringent particles to be incorporated in the scattering light
pipe, method which comprises attaching birefringent particles to
the surface of the scattering light pipe, method which comprises
rendering the polymer film birefringent and combination
thereof.
[0081] The light pipe according to the present invention comprises
a laminate of a light-transmitting resin plate and a
polarized-light scattering plate. For the formation of the light
pipe of the invention, it is preferred that the light-transmitting
resin plate 1 and the polarized-light scattering plate 3 be bonded
to each other with an adhesive or the like having a refractive
index as close to that of the two layers as possible to inhibit
reflection by the interface of the light-transmitting resin plate 1
with the polarized-light scattering plate 3 as much as possible,
i.e., to facilitate the transmission of light between the
light-transmitting resin plate and the polarized-light scattering
plate and hence realize the total reflection by both surfaces of
the light pipe made of a close laminate of the two layers, as shown
in FIG. 1. Bonding is effective from the standpoint of prevention
of deviation of axis. For the formation of the light pipe, a
polarized-light scattering plate 3 may be provided on both surfaces
of the light-transmitting resin plate 1 as shown in FIG. 2.
[0082] For the formation of the laminate of light-transmitting
resin plate and polarized-light scattering plate, it is preferred
that the light-transmitting resin plate and the polarized-light
scattering plate be arranged such that the average retardation axis
of the light-transmitting resin plate and the optical axis
(oscillation plane of emitted polarized-light) cross at an angle of
5 degrees or more, more preferably from 10 to 80 degrees,
particularly from 15 to 75 degrees, in order to efficiently
eliminate the polarization of transmitted light.
[0083] For the foregoing bonding, a proper adhesive such as
transparent adhesive (e.g., acrylic adhesive, silicone adhesive,
polyester-based adhesive, polyurethane-based adhesive,
polyether-based adhesive, rubber adhesive) may be used as in the
case of the foregoing laminate type polarized-light scattering
plate. Thus, there is no special restriction on bonding. From the
standpoint of prevention of change of optical characteristics, an
adhesive requiring no high temperature prolonged curing and drying
process is preferred. Further, an adhesive which is not liable to
floating or peeling under heating or moistening conditions is
preferred.
[0084] From the foregoing standpoint of view, there is preferably
used an acrylic adhesive comprising as a base polymer an acrylic
polymer having a weight-average molecular weight of 100,000 or more
obtained by the copolymerization of a (meth)acrylic acid alkylester
having an alkyl group having 20 or less carbon atoms such as
methyl, ethyl and butyl and an acrylic monomer comprising a
modified component such as (meth)acrylic acid and (meth)acrylic
acid hydroxyethyl in such a combination that the resulting glass
transition temperature is 0.degree. C. or lower. Such an acrylic
adhesive is also advantageous in that it is excellent in
transparency, weathering resistance and heat resistance.
[0085] The provision of the adhesive layer on the
light-transmitting resin plate and/or the polarized-light
scattering plate can be accomplished by any proper method. Examples
of such a method include a method which comprises dissolving or
dispersing an adhesive component in proper solvents such as toluene
and ethyl acetate, singly or in admixture, to prepare an adhesive
solution having a concentration of from about 10 to 40% by weight,
and then providing the adhesive solution directly on a
light-transmitting resin plate or polarized-light scattering plate
by any proper spreading method such as casting method and coating
method, and a method which comprises forming an adhesive layer on a
separator in the same manner as mentioned above, and then
transferring the adhesive layer onto a light-transmitting resin
plate or polarized-light scattering plate. The adhesive layers to
be provided may be laminating layers having different compositions
or kinds.
[0086] The thickness of the adhesive layer can be properly
determined by adhesivity or the like. It is normally from 1 to 500
.mu.m. The adhesive layer may comprise a filler such as natural or
synthetic resin, glass fiber, glass beads, metal powder and other
inorganic powder or a proper additive such as pigment, colorant and
oxidation inhibitor incorporated therein as necessary. Further, the
adhesive layer may comprise finely divided particles incorporated
therein to exhibit light diffusion properties.
[0087] The light pipe according to the present invention acts to
convert incident light received at its side face to linearly
polarized light which is then emitted from both surfaces thereof as
mentioned above and thus can be preferably used to form a planar
polarized-light source. The planar polarized-light source can be
formed by disposing a light source 5 at least on one side face of
the light pipe 4 as shown in FIG. 3.
[0088] In order to obtain a planar polarized-light source having
excellent brightness, it is preferred that a specular reflection
layer 6 be provided on one surface of the light pipe 4 as shown in
FIG. 3. In this arrangement, the light emitted from the reflection
layer side can be inverted by the specular reflection layer and
concentrated onto one surface of the light pipe without changing
its polarization state, making it possible to enhance
brightness.
[0089] As the foregoing light source there may be used any proper
light source which can be disposed on the side face of the light
pipe, such as (cold, hot) cathode ray tube, linear or planar array
of light-emitting diodes and incandescent lamp. In particular, cold
cathode ray tube is preferred from the standpoint of light emission
efficiency, reduction of consumption of electric power and
reduction of diameter. The light source may be disposed on plural
side faces such as two opposing side faces or three side faces to
enhance brightness or uniformity. In the case where three sides
faces are used, a U-shaped tube may be used.
[0090] For the formation of the planar polarized-light source, if
necessary, a proper auxiliary means such as reflector 51
surrounding the light source 5 may be disposed to introduce
scattered light from the light source into the side face of the
light pipe as shown in FIG. 3. As such a reflector there may be
normally used a resin sheet provided with a thin metal layer having
a high reflectance or a metal foil. The reflector may extend to the
lower surface of the light pipe to act as a reflection layer as
well. The reflector is useful also as a light source fixing
means.
[0091] On the other hand, the foregoing specular reflection layer 6
is preferably as specular as possible from the standpoint of
retention of polarization. From this standpoint of view, a
reflecting surface made of metal is particularly preferred. As such
a metal there may be used any proper metal such as aluminum,
silver, chromium, gold, copper, tin, zinc, indium, palladium,
platinum and alloy thereof.
[0092] The reflection layer 6 may be formed by vacuum-evaporating
such a metal on the light pipe to a small thickness so that it is
kept in direct contact with the light pipe. However, the
vacuum-deposited metal can hardly make total reflection. The
reflection layer makes some absorption of light. Therefore,
absorption loss can be apprehended taking into account the
repetition by total reflection. In order to inhibit absorption
loss, the arrangement is preferably such that the reflector is
merely superposed on the light pipe so that an air layer is
provided interposed therebetween. Accordingly, from this standpoint
of view, the reflector is preferably formed by sputtering or
vacuum-evaporating a metal onto the supporting substrate to a small
thickness. Alternatively, a tabular metal material such as metal
foil and rolled sheet of metal is preferably used. As the
supporting substrate for reflector there may be used a proper
material such as glass plate and resin sheet. In particular, a
resin sheet having silver or aluminum vacuum-deposited thereon is
preferably used from the standpoint of reflectance, tint and
handleability. The reflection layer may be disposed either surface
of the light pipe.
[0093] For the formation of the planar polarized-light source, one
or more proper optical layers such as diffusion layer 7 as shown in
FIG. 3 may be disposed at a proper position. The optical layer to
be used herein is not specifically limited. For example, a proper
material such as optical layer used to form a liquid crystal
display device may be used. FIG. 5 is an embodiment of the planar
polarized-light source free of light diffusion layer 7.
[0094] The polarization-retaining light diffusion layer 7 to be
provided on the other surface of the light pipe 4 as laminate,
i.e., the surface of the light pipe on which the foregoing specular
reflection layer is not provided, is intended to diffuse light
(linearly polarized light) emitted by the laminate while
maintaining its polarization as much as possible and hence
uniformalize emission, making it possible to enhance its
visibility.
[0095] Further, the light diffusion layer may be also disposed as
necessary for the purpose of enhancing visibility by relaxation of
sight through concave-convex pattern on lens sheet described
later.
[0096] In the present invention, in order to efficiently utilize
linearly polarized light emitted by the light pipe, if an optical
layer, particularly polarizing plate is provided on the emission
side of the light pipe, the optical layer to be disposed between
the polarizing plate and the light pipe is preferably one which
exhibits an excellent light transmittance and maintains the linear
polarization (polarization degree) of emitted light as much as
possible without eliminating it. In particular, the optical layer
preferably exhibits a total light transmittance of 80% or more,
more preferably 85% or more, particularly 90% or more and a percent
leakage (transmittance) of 5% or less, more preferably 2% or less,
particularly 1% or less, as developed by the elimination of
polarization through the arrangement disposed of cross-Nicol.
[0097] In the light of the fact that the elimination of
polarization is usually made by birefringence or multiple
scattering, the optical layer showing polarization-retaining
properties can be realized by lowering birefringence as much as
possible or reducing the number of average reflections (scattering)
in the orbit of rays. From this standpoint of view, the optical
layer is preferably formed by a resin having a low birefringence
(resin having a good optical isotropy) such as cellulose
triacetate-based resin, methyl polymethacrylate, polycarbonate and
norbornene-based resin. One or more of these resins may be
used.
[0098] The light diffusion layer excellent in
polarization-retaining properties can be provided with a finely
roughened structure on the surface thereof by a proper method such
as method which comprises allowing transparent particles to be
dispersed in a layer made of a resin having a small birefringence
and method which comprises roughening the surface of a resin layer.
Examples of the transparent particles employable herein include
finely divided particles of material which may be electrically
conductive, such as silica, glass, titania, zirconia, tin oxide,
indium oxide, cadmium oxide and antimony oxide, and finely divided
particles made of crosslinked or uncrosslinked polymer such as
acrylic polymer, polyacrylonitrile, polyester, epoxy resin,
melamine-based resin, urethane based resin, polycarbonate,
polystyrene, silicone-based resin, benzoguanamine,
melamine-benzoguanamine condensate and benzoguanamine-formaldehyde
condensate. One or more of these compounds may be used.
[0099] The diameter of the transparent particles is preferably from
1 to 20 .mu.m from the standpoint of diffusibility of light and
uniformity in diffusion. The shape of the particles is arbitrary.
In practice, however, spherical particles or secondary aggregates
thereof may be used. In particular, from the standpoint of
polarization-retaining properties, transparent particles having a
refractive index ratio of from 0.9 to 1.1 to resin is preferably
used.
[0100] The formation of the light diffusion layer having
transparent particles incorporated therein can be accomplished by
any proper conventional method such as method which comprises
mixing a molten resin solution with transparent particles, and then
extruding the mixture to form a sheet or the like, method which
comprises incorporating transparent particles in a resin solution
or monomer, casting the mixture into a sheet, and then optionally
subjecting the sheet to polymerization and method which comprises
applying a resin solution having transparent particles incorporated
therein to a predetermined surface or polarization-retaining
supporting film.
[0101] On the other hand, the formation of the light diffusion
layer having a finely roughened structure on the surface thereof
can be accomplished by any proper method such as method which
comprises roughening the surface of a sheet made of an optically
isotropic light-transmitting resin by buffing using sandblast or
the like or embossing and method which comprises forming a
light-transmitting material layer having protrusions on the surface
of the foregoing sheet. However, a method which comprises forming a
roughness (protrusion) having a great difference in refractive
index between bubble such as air or titanium oxide particles and
light-transmitting resin is not desirable because it can easily
eliminate polarization.
[0102] Referring to the finely roughened structure on the surface
of the light diffusion layer, the surface roughness of the light
diffusion layer is preferably from not less than the wavelength of
incident light to not more than 100 .mu.m and nonperiodic from the
standpoint of diffusibility of light or uniformity in diffusion.
For the formation of the foregoing transparent
particle-incorporated type or roughened surface type light
diffusion layer, it is preferred that the base layer made of
light-transmitting resin be prevented from suffering from the rise
in phase difference due to optical elasticity or orientation as
much as possible from the standpoint of polarization-retaining
properties or the like.
[0103] One or more such light diffusion layers may be provided on
the emission side of the laminate. Two or more light diffusion
layers,if any,may be the same or different. However, these light
diffusion layers preferably have the foregoing
polarization-retaining properties as a whole. It is preferred that
the light diffusion layer be arranged with a gap formed with
respect to the laminate as in the case of the foregoing specular
reflection layer. The gap is preferably sufficiently greater than
the wavelength of incident light from the standpoint of total
reflection.
[0104] The polarization-retaining lens sheet 8 to be provided on
the other surface of the laminate 4 in the embodiment of FIG. 4,
i.e., on the surface of the laminate free of specular reflection
layer, is intended to control the light path of scattered emitted
light (linearly polarized light) from the laminate while
maintaining the polarization degree thereof as much as possible,
thereby improving the directivity to the front to advantage in
vision and hence allowing the intensity peak of scattered emitted
light to appear in the front direction.
[0105] As the lens sheet there may be used any proper material
capable of controlling the light path of incident light received at
one surface thereof and efficiently emitting it from the other in
the direction as perpendicular to the surface of the sheet as
possible (forward direction). Thus, the lens sheet is not
specifically limited. Accordingly, any material having various lens
forms used in the conventional side light type light pipe may be
used except for polarization-retaining properties
(JP-A-5-169015).
[0106] As the lens sheet to be used herein there may be used one
having an -excellent light transmittance which prevents the
elimination of polarization properties of emitted light, e.g.,
having a total light transmittance of 80% or more, preferably 85%
or more, particularly 90% or more and a percent leakage
(transmittance) of 5% or less, more preferably 2% or less,
particularly 1% or less, as developed by the elimination of
polarization through the arrangement of cross-Nicol.
[0107] Since the elimination of polarization takes place by
birefringence or multiple scattering, the foregoing lens sheet
showing polarization-retaining properties can be realized by
lowering the birefringence as much as possible or reducing the
number of average reflections (scattering) in the orbit of light
ray. In some detail, the lens sheet can be formed by one or more of
the polymers exemplified with reference to the light-transmitting
resin plate or scattering polarization plate, particularly resins
having a low birefringence (resins having a good optical isotropy)
such as celluose triacetate-based resin, methyl polymethacrylate,
polycarbonate and norbornene-based resin.
[0108] As the lens sheet there may be used one having a proper lens
form such as one having many convex type or refractive index
distribution type (GI type) regions the refractive index of which
is controlled by a photopolymer or the like, particularly minute
lens regions formed on the surface or inside a transparent resin
substrate optionally comprising resins having different refractive
indexes, one having lens regions formed by filling many
through-holes provided in a transparent resin substrate with a
polymer having a different refractive index from that of the resin
and one having a single layer of many spherical lens fixed with a
thin layer. From the standpoint of control over the light path
utilizing the difference in refractive index, the lens sheet is
preferably in a form having a particular lens structure 81 of a
roughened structure on either or both surfaces, particularly either
surface of the sheet 8 as shown in FIG. 4.
[0109] The roughened structure forming the foregoing lens form may
be arbitrary so far as it acts to control the light path of light
transmitted by the sheet and converge the transmitted light toward
the front. Examples of the roughened structure include a striped or
lattice-shaped alignment of linear grooves or protrusions having a
triangular section, and a dotted alignment of many conical minute
protrusions having a bottom such as triangular pyramid,
quadrangular pyramid and polyangular pyramid. The linear or dotted
roughened structure may be a spherical lens, nonspherical lens or
semi-cylindrical lens. Thus, a proper lens form may be used.
[0110] The formation of the foregoing lens sheet having a linear or
dotted roughened structure can be accomplished by a proper method
such as method which comprises packing a resin solution or a
resin-forming monomer into a mold for forming a predetermined
roughened structure, and then optionally subjecting the material to
polymerization to transfer the roughened pattern to the material
and method which comprises hot-pressing a resin sheet against the
mold to transfer the roughened pattern to the resin sheet. The lens
sheet-may be formed by the same kind of material as the supporting
sheet, e.g., one obtained by providing the supporting sheet with a
lens form. Alternatively, two or more different resin layers may be
laminated to form a lens sheet.
[0111] One or more lens sheets may be disposed on the emission side
of the laminate. Two or more lens sheets, if any, may be the same
or different. However, these layers preferably maintain
polarization-retaining properties as a whole. When the lens sheet
is disposed adjacent to the laminate (light pipe), the arrangement
is preferably such that a gap is formed therebetween. The gap is
preferably sufficiently greater than the wavelength of incident
light from the standpoint of total reflection.
[0112] In the case where the lens form in the lens sheet is made of
a linear roughened structure, the linear direction of the lens form
is preferably arranged parallel to or perpendicular to the optical
axis of the polarized-light scattering plate (oscillation plane of
emitted polarized-light) from the standpoint of control over the
light path toward the front. In the case where two or more such
lens sheets are arranged, the arrangement is preferably such that
the linear direction of two vertically adjacent layers cross each
other from the standpoint of control over the light path.
[0113] As shown in FIG. 4, one or more polarization-retaining light
diffusion layers 7 mentioned above may be disposed between the lens
sheet and the laminate or on the emission side of the lens sheet,
on the emission side of the laminate 4 as light pipe, together with
the lens sheet 8 for the purpose of diffusing emitted light
(linearly polarized light) while maintaining its polarization as
much as possible to uniformalize emission or relax vision of
pattern of lens sheet, thereby enhancing visibility.
[0114] The light diffusion layer may be disposed as an independent
layer made of tabular material or may be disposed as a dependent
layer integrated with the lens sheet. In the case where the light
diffusion layer is disposed adjacent to the laminate, the
arrangement is preferably such that a gap is formed therebetween as
in the case of lens sheet. Two or more light diffusion layers, if
any, may be the same or different. However, these layers preferably
maintain polarization-retaining properties as a whole.
[0115] The optical layer to be arranged far from the light pipe may
be bonded to the laminate with an adhesive layer or the like as
necessary. However, the optical layer having a roughened surface
structure such as the foregoing roughened surface type light
diffusion layer and lens sheet having a roughened structure is
preferably arranged so as to have a gap. Accordingly, the optical
layer such as light diffusion layer may be arranged as an
independent layer made of tabular material or may be arranged as a
dependent layer integrated closely with other optical layers.
[0116] In the case where the light diffusion layer 7 and the lens
sheet 8 are used in combination as shown in FIG. 4, one or more
light diffusion layers may be disposed between the lens sheet and
the light pipe and/or on the emission side of the lens sheet.
Referring to the lens sheet having a lens form comprising a linear
roughened structure, the arrangement is preferably such that the
linear direction of the lens form is parallel to or perpendicular
to the optical axis of the polarized-light scattering plate from
the standpoint of control over the light path toward the front.
When two or more such lens sheets are arranged, the arrangement is
preferably such that the linear direction of two vertically
adjacent layers cross each other from the standpoint of efficiency
in control over the light path.
[0117] The light pipe shown in FIG. 6 comprises a laminate 4 having
a polarized-light scattering plate 3 partially kept in close
contact with one or both surfaces of the light-transmitting resin
plate 1 with a light path 9 which also acts as an adhesive layer
provided therebetween as shown in FIG. 6 for the purpose of
controlling the amount of transmitted light received at the
polarized-light scattering plate from the light-transmitting resin
plate.
[0118] In accordance with the foregoing description, the use of an
isolation arrangement such that the light-transmitting resin plate
and the polarized-light scattering plate are disposed with a gap
interposed therebetween makes it possible to satisfy requirements
for total reflection and hence keep the transmitted light in the
light-transmitting resin plate. Further, the transmitted light can
be scattered through the light path so that it is introduced from
the light-transmitting resin plate to the polarized-light
scattering plate through the light path. During this process, by
adjusting the disposition of the light path, the amount of light
received at the polarized-light scattering plate from the
light-transmitting resin plate can be controlled, hence making it
possible to uniformalize brightness on the light pipe.
[0119] The light path may be eventually interposed between the
light-transmitting resin plate and the polarized-light scattering
plate. Accordingly, the light path can be formed by any proper
method. For example, the formation of the light-transmitting resin
plate or polarized-light scattering plate may be accompanied by the
formation of a roughened structure on one or both surfaces thereof
to form a roughened structure integrally with the
light-transmitting resin plate or polarized-light scattering plate,
thereby laminating the light-transmitting resin plate and the
polarized-light scattering plate with the roughened structure
interposed therebetween.
[0120] Alternatively, the light-transmitting resin plate and the
polarized-light scattering plate may be laminated with the
interposition of a sheet having a roughened structure formed as a
light path. Further, the light-transmitting resin plate and the
polarized-light scattering plate may be laminated with the
interposition of a roughened structure which has been patternwise
coated through a mask onto one or both surfaces of the
light-transmitting resin plate or polarized-light scattering plate.
Accordingly, the light path may be formed integrally with the
light-transmitting resin plate or polarized-light scattering plate
or separately of the light-transmitting resin plate or
polarized-light scattering plate.
[0121] The light path may be in a proper form such that the
light-transmitting resin plate and the polarized-light scattering
plate can be partially connected to each other, e.g., dotted form
or striped form. From the standpoint of controllability over the
amount of incident light by contact with the light-transmitting
resin plate or polarized-light scattering plate, the light path is
preferably formed flat on the contact surface thereof.
[0122] In the case where the light path is provided as convex
portion constituting the roughened structure on the surface of the
light-transmitting resin plate or polarized-light scattering plate,
it preferably has a roughened structure having a rectangular
section as shown in FIG. 7 from the standpoint of adhesion of the
convex portion and total reflection by the concave portion between
the convex portions. In some detail, the concave portion 91 and the
convex portion 92 (light path 9) have flat surfaces 93 and 95.
Accordingly, the area at which the light-transmitting resin plate
and the polarized-light scattering plate are not in close contact
with the light path preferably has a flat surface from the
standpoint of total reflection.
[0123] The foregoing flat surface may have a finely roughened
structure developed by roughening. However, the flat surface is
preferably as smooth as possible from the standpoint of total
reflection or close contact. In particular, the flat surface as
contact surface in the light path is preferably arranged flat so as
to be kept in close contact with the light-transmitting resin plate
or polarized-light scattering plate.
[0124] Further, the light-transmitting resin plate side of the
light path made of the concave portion 91 as shown in FIG. 7
preferably has a section having a continuous primary differential
curve and a corner portion 94 having an easy curve. If the corner
portion on the light-transmitting resin plate side of the light
path has a sharp angle, it can cause the generation of bright point
and bright line.
[0125] The disposition of the light path can be properly determined
by the desired amount of incident light to be received by the
polarized-light scattering plate. In the present invention, when a
light source is disposed at the side face of the light pipe to form
a planar polarized-light source, there normally shows a tendency
that the brightness increases toward the light source. In order to
uniformalize the brightness of the entire emission surface of the
light pipe, the arrangement is preferably such that there is a
variation of distribution density of light path, particularly such
that the distribution density of light path per area of plane
increases with distance from the light source. The distribution
density of light path may vary stepwise or continuously.
[0126] The length of the light path as the difference in height
between the concave portion and the convex portion in the roughened
structure, i.e., the thickness of the gap between the
light-transmitting resin plate and the polarized-light scattering
plate at the position where there is no light path is preferably
small from the standpoint of reduction of the thickness of the
light pipe. When the thickness of the gap is great, light leaks
more through this portion to make a pool of light, lowering the
percent utilization of light. In order to prevent the reduction of
percent utilization of light and secure a gap greater than the
wavelength of the transmitted light, thereby obtaining the
foregoing total reflection efficiency, the length of the light path
is preferably from 0.5 to 1,000 .mu.m, more preferably 500 .mu.m or
less, particularly from 1 to 100 .mu.m.
[0127] The partial contact of the light-transmitting resin plate
with the polarized-light scattering plate through the light path is
preferably accomplished by bonding the two components at their
interface to inhibit reflection by the interface as much as
possible and hence facilitate the transmission of light by the
light path from the light-transmitting resin plate to the
polarized-light scattering plate. The bonding is advantageous from
the standpoint of prevention of deviation of axis.
[0128] For the bonding, any proper adhesive such as tacky adhesive,
hot-melt adhesive, ultraviolet-curing adhesive and thermosetting
adhesive may be used as in the case of the foregoing lamination
type polarized-light scattering plate. An adhesive material having
an excellent transparency and a refractive index as close to that
of these components as possible is preferably used. In this case,
as shown in FIG. 6, such an adhesive may be used to form the light
path 9 with which the light-transmitting resin plate 1 and the
polarized-light scattering plate 3 are bonded to each other.
[0129] For the formation of the planar polarized-light source, one
or more proper optical layers may be disposed at any proper
position. The optical layer is not specifically limited. For
example, any proper optical layer such as polarizing plate,
retarder plate and liquid crystal cell used in the formation of
liquid crystal display device may be used. In this case, the
foregoing lens sheet and light diffusion layer may be kept in close
contact with the upper optical layer with an adhesive layer or the
like interposed therebetween. In the case of lens sheet having a
roughened structure or roughened surface type light diffusion
layer, however, the arrangement is preferably such that the
foregoing gap is provided.
[0130] The various layers constituting the light pipe or planar
polarized-light source each may comprise an ultraviolet absorber
such as salicylic acid ester-based compound, benzophenol-based
compound, benzotriazole-based compound, cyano acrylate-based
compound and nickel complex-based compound incorporated therein to
have an ultraviolet-absorbing capability as necessary.
[0131] As mentioned above, the light pipe and planar
polarized-light source according to the present invention can
provide linearly polarized light with its oscillation plane
(polarization axis) being properly controlled and thus can be used
for proper devices and purposes utilizing linearly polarized light
as in the formation of liquid crystal display device by making the
use of its advantages.
EXAMPLE 1
[0132] A 20 wt-% dichloromethane solution of 200 parts (hereinafter
by weight) of an AS resin (Stylak AS, produced by ASAHI CHEMICAL
INDUSTRY CO., LTD.) and 800 parts of a polycarbonate (Panlite,
produced by TEIJIN LTD.) was subjected to casting to form a polymer
film having a thickness of 80 .mu.m which was then stretched at a
temperature of 80.degree. C. and a draw ratio of 2.5 and rapidly
cooled to obtain a polarized-light scattering plate.
[0133] The foregoing polarized-light scattering plate comprised
fine domains made of AS resin dispersed in a film made of
polycarbonate in domain pattern and exhibited refractive index
differences .DELTA.n1 of 0.05, .DELTA.n2 of 0.001 and .DELTA.n3 of
0.001. The average diameter of the foregoing fine domains was
measured by coloring based on phase difference under polarization
microscope. As a result, the length in .DELTA.n1 direction was
about 8 .mu.m.
[0134] Subsequently, the foregoing polarized-light scattering plate
was bonded to one surface of an acrylic resin plate (produced by
Mitsubishi Rayon Co., Ltd.) in such an arrangement that its
.DELTA.n1 direction crossed the side face at an angle of 45 degrees
to obtain a light pipe. A cold cathode ray tube was then fixed to
one side face of the light pipe with a lamp reflector made of a
matted PET-based reflection sheet. A specular reflection sheet
comprising a PET sheet having silver vacuum-evaporated thereon was
disposed on the lower surface of the polarized-light scattering
plate to obtain a planar polarized-light source.
COMPARATIVE EXAMPLE 1
[0135] A planar light source was obtained in the same manner as in
Example 1 except that there was used a light pipe obtained by
printing a reflective ink comprising titanium white incorporated
therein on one surface of an acrylic resin plate having a thickness
of 2 mm in a dotted pattern and then disposing a white reflecting
plate made of a foamed PET on the same surface of the acrylic resin
plate.
Evaluation Test 1
[0136] The planar (polarized-) light sources obtained in Example 1
and Comparative Example 1 were each visually observed for
brightness in the forward direction and in oblique directions. As a
result, the two light sources exhibited almost the same brightness
in the forward direction. However, the planar polarized-light
source of Example 1 exhibited an excellent brightness over a wider
angle range than Comparative Example 1 when observed obliquely.
[0137] On the other hand, a polarizing plate having a transmission
axis in the direction of 45 degrees was disposed on the planar
(polarized-)light source. The planar (polarized-)light source was
then measured for brightness in the same manner as mentioned above.
As a result, the light source of Comparative Example 1 showed an
approximately halved brightness due to the disposition of the
polarizing plate while the planar polarized-light source of Example
1 showed little brightness drop and thus exhibited a brightness
approximately double that of Comparative Example 1.
EXAMPLE 2
[0138] A 20 wt-% dichloromethane solution of 950 parts of a
norbornene-based resin having a deflection temperature of
165.degree. C. and a glass transition temperature of 182.degree. C.
(Arton, produced by JSR Inc.) and 50 parts of a liquid crystal
polymer represented by the following general formula having a glass
transition temperature of 80.degree. C. and a nematic
liquid-crystallization temperature of from 100.degree. C. to
290.degree. C. was subjected to casting to form a polymer film
having a thickness of 100 .mu.m which was then stretched at a
temperature of 180.degree. C. and a draw ratio of 3 and rapidly
cooled to obtain a polarized-light scattering plate. 3
[0139] The foregoing polarized-light scattering plate comprised a
liquid crystal polymer dispersed in a transparent film made of
norbornene-based resin in a pattern of domains having almost the
same shape which are longitudinal in the stretching direction and
exhibited refractive index differences .DELTA.n1 of 0.23, .DELTA.n2
of 0.029 and .DELTA.n3 of 0.029. The average diameter of the
foregoing fine domains was measured by coloring based on phase
difference under polarization microscope. As a result, the length
in .DELTA.n1 direction was about 5 .mu.m.
[0140] Subsequently, the foregoing polarized-light scattering plate
was bonded to one surface of an acrylic resin plate (produced by
Mitsubishi Rayon Co., Ltd.) in such an arrangement that its
.DELTA.n1 direction crossed the side face at an angle of 45 degrees
to obtain a light pipe. A cold cathode ray tube was then fixed to
one side face of the light pipe with a lamp reflector made of a
matted PET-based reflection sheet. A specular reflection sheet
comprising a PET sheet having silver vacuum-evaporated thereon was
disposed on the lower surface of the polarized-light scattering
plate to obtain a planar polarized-light source.
COMPARATIVE EXAMPLE 2
[0141] A planar light source was obtained in the same manner as in
Example 2 except that there was used a light pipe obtained by
printing a reflective ink comprising titanium white incorporated
therein on one surface of an acrylic resin plate having a thickness
of 2 mm in a dotted pattern and then disposing a white reflecting
plate made of a foamed PET on the same surface of the acrylic resin
plate.
Evaluation Test 2
[0142] The planar (polarized-)light sources obtained in Example 2
and Comparative Example 2 were each visually observed for
brightness in the forward direction and in oblique directions. As a
result, the two light sources exhibited almost the same brightness
in the forward direction. However, the planar polarized-light
source of Example 2 exhibited an excellent brightness over a wider
angle range than Comparative Example 2 when observed obliquely.
[0143] On the other hand, a polarizing plate having a transmission
axis in the direction of 45 degrees was disposed on the planar
(polarized-)light source. The planar (polarized-)light source was
then measured for brightness in the same manner as mentioned above.
As a result, the light source of Comparative Example 2 showed an
approximately halved brightness due to the disposition of the
polarizing plate while the planar polarized-light source of Example
2 showed little brightness drop and thus exhibited a brightness
approximately double that of Comparative Example 2. The planar
polarized-light source of Example 2 was allowed to stand in a
80.degree. C. atmosphere for 100 hours, and then operated again. As
a result, the planar polarized-light source of Example 2 showed no
brightness drop.
[0144] As obvious from the foregoing description, when the planar
polarized-light source according to the present invention is used
as a backlight for liquid crystal display device, a very bright
display can be realized. Further, the planar polarized-light source
according to the present invention exhibits an excellent thermal
stability and thus can retain its function over an extended period
of time.
EXAMPLE 3
[0145] A 20 wt-% dichloromethane solution of 950 parts of a
norbornene-based resin having a glass transition temperature of
182.degree. C. (Arton, produced by JSR Inc.) and 50 parts of a
liquid crystal polymer represented by the same general formula as
in Example 2 was subjected to casting to form a polymer film having
a thickness of 100 .mu.m which was then stretched at a temperature
of 180.degree. C. and a draw ratio of 3 and rapidly cooled to
obtain a polarized-light scattering plate. The polarized-light
scattering plate thus obtained exhibited the same refractive index
differences .DELTA.n1, .DELTA.n2 and .DELTA.n3 and average minute
region diameter as in Example 2.
[0146] Subsequently, the foregoing polarized-light scattering plate
was bonded to one surface of an acrylic resin plate (produced by
Mitsubishi Rayon Co., Ltd.) in such an arrangement that its
.DELTA.n1 direction crossed the side face at an angle of 45 degrees
to obtain a laminate. A specular reflection sheet comprising a PET
sheet having silver vacuum-evaporated thereon was then disposed on
the lower surface of the laminate. At the same time, a light
diffusion plate was disposed on the upper surface of the laminate
to obtain a light pipe. A cold cathode ray tube was then fixed to
one side face of the light pipe with a lamp reflector made of a
matted PET-based reflection sheet.
[0147] The foregoing light diffusion plate had been obtained by a
process which comprises adding 30 parts of silicone particles
having an average diameter of 4 .mu.m to 70 parts of an
ultraviolet-curing epoxy resin, stirring the mixture to cause
defoaming, applying the material to one surface of a 80 .mu.m thick
cellulose triacetate film to a thickness of 30 .mu.m, and then
irradiating the coated material with light from a high voltage
mercury vapor lamp at an accumulated dose of 1,000 mJ/cm.sup.2 so
that it was cured. In the light diffusion plate, the ratio of
refractive index of silicone particles to cured epoxy resin was
0.95. The amount of light leaked due to elimination of polarization
in an arrangement comprising the light diffusion plate interposed
between polarizers of cross nicol was 0.7% of the total amount of
incident light.
EXAMPLE 4
[0148] A light pipe and a planar polarized-light source were
obtained in the same manner as in Example 3 except that as the
light diffusion plate there was used one having a finely roughened
surface structure obtained by a process which comprises stirring 10
parts of silica particles having an average diameter of 1.8 .mu.m,
100 parts of an ultraviolet-curing acrylurethane-based oligomer and
3 parts of benzophenone with ethylene acetate at a high speed to
obtain a dispersion having a solid content of 50% by weight,
applying the dispersion to one surface of a cellulose triacetate
film having a thickness of 80 .mu.m, drying the coated material so
that the thickness of the coating film reached 4 .mu.m, and then
irradiating the coated material with light from a high voltage
mercury vapor lamp at an accumulated dose of 150 mJ/cm.sup.2 so
that it was cured.
[0149] The light diffusion plate showed a silica particle to cured
resin refractive index ratio of 0.93. The amount of light leaked
due to elimination of polarization was 1.0% of the total amount of
incident light. The light diffusion plate exhibited a surface
roughness Ra (value averaged over 10 points according to JIS B
0601) of 1.5 .mu.m as determined by a surface roughness meter.
COMPARATIVE EXAMPLE 3
[0150] A planar light source was obtained in the same manner as in
Example 3 except that there was used a light pipe obtained by
printing a reflective ink comprising titanium white incorporated
therein on one surface of an acrylic resin plate having a thickness
of 2 mm in a dotted pattern and then disposing a white reflecting
plate made of a foamed PET on the same surface of the acrylic resin
plate.
COMPARATIVE EXAMPLE 4
[0151] A light pipe and a planar polarized-light source were
obtained in the same manner as in Example 4 except that there was
used a light diffusion plate comprising a polyester film instead of
cellulose triacetate film and hence allowing leakage of light due
to elimination of polarization in an amount of 5.2% of the total
amount of incident light.
COMPARATIVE EXAMPLE 5
[0152] A light pipe and a planar polarized-light source were
obtained in the same manner as in Example 3 except that there was
disposed no light diffusion plate.
Evaluation Test 3
[0153] The planar (polarized-)light sources obtained in Examples 3
and 4 and Comparative Examples 3 to 5 were each measured for
brightness on the central portion thereof in the forward direction
and uniformity in brightness on the plane by means of a brightness
meter (BM-7, produced by TOPCON CORP.). The proportion of these
measurements based on Comparative Example 1 was determined. The
results are set forth in the table below. The figure in parentheses
each indicate the proportion of brightness determined when the
polarizing plate is disposed on the planar light source in such an
arrangement that the transmission axis lies at an angle of 45
degrees based on Comparative Example 1.
1 Front brightness (polarizing plate disposed) Uniformity Example 3
110 (100) Good Example 4 90 (80) Good Comparative 100 (40) Good
Example 3 Comparative 90 (50) Good Example 4 Comparative 60 (50)
Poor Example 5
[0154] The comparison with Comparative Example 5 in the table below
shows that the disposition of the light diffusion plate makes it
possible to drastically enhance the front brightness as well as the
uniformity in brightness on the plane. The comparison of the
examples with Comparative Example 3 shows that the examples emit
linearly polarized light and exhibit a drastically enhanced
brightness through the polarizing plate. The comparison of the
examples with Comparative Example 4 shows that if the light
diffusion plate eliminates polarization, the advantage of emitting
linearly polarized light cannot be made the use of. It is thus made
obvious that when the planar polarized-light source according to
the present invention is used as a backlight for liquid crystal
display device, a brightness twice or more times ordinary value
(Comparative Example 3) can be realized, making it possible to
accomplish a very bright display excellent in uniformity.
EXAMPLE 5
[0155] A laminate (light pipe) was obtained by laminating a
polarized-light scattering plate obtained in the same manner as in
Example 3 with the same acrylic resin plate as used in Examples 1
and 3 in the same manner as in Examples 1 and 3. A specular
reflection sheet comprising a PET sheet having silver
vacuum-evaporated thereon was then disposed on the lower surface of
the laminate. At the same time, a light diffusion plate was
disposed on the upper surface of the laminate to obtain a light
pipe. A cold cathode ray tube was then fixed to one side face of
the light pipe with a lamp reflector made of a matted PET-based
reflection sheet.
[0156] The foregoing lens sheet had been obtained by providing on
one surface of a cellulose triacetate resin film having a thickness
of 80 .mu.m a lens form having a striped alignment of linear
protrusions made of a photosetting epoxy resin having a triangular
section with a vertical angle of 90 degrees and a height of 80
.mu.m arranged at an interval of 350 .mu.m. The arrangement was
such that the lens form lies at the upper side and the direction of
stripes is parallel to the foregoing .DELTA.n2 direction. The lens
sheet thus obtained exhibits a transmittance (hereinafter the
amount of light leaked due to elimination of polarization) of 1.0%
of the total amount of incident light as determined by an
integrating sphere when disposed between cross nicols and thus is
excellent in polarization-retaining properties.
EXAMPLE 6
[0157] A light pipe and a planar polarized-light source were
obtained in the same manner as in Example 1 except that a light
diffusion plate obtained by a process which comprises adding 30
parts of silicone particles having an average diameter of 4 .mu.m
to 70 parts of an ultraviolet-curing epoxy resin, stirring the
mixture to cause defoaming, applying the material to one surface of
a 80 .mu.m thick cellulose triacetate film to a thickness of 30
.mu.m, and then irradiating the coated material with light from a
high voltage mercury vapor lamp at an accumulated dose of 1,000
mJ/cm.sup.2 so that it was cured was disposed between the laminate
and the lens sheet. The foregoing light diffusion plate allowed
leakage of light due to elimination of polarization in an amount of
0.7% of the total amount of incident light.
COMPARATIVE EXAMPLE 6
[0158] A planar light source was obtained in the same manner as in
Example 5 except that there was used a light pipe obtained by
printing a reflective ink comprising titanium white incorporated
therein on one surface of an acrylic resin plate having a thickness
of 2 mm in a dotted pattern and then disposing a white reflecting
plate made of a foamed PET on the same surface of the acrylic resin
plate.
COMPARATIVE EXAMPLE 7
[0159] A light pipe and a planar polarized-light source were
obtained in the same manner as in Example 5 except that there was
used a lens sheet comprising a polyester film instead of cellulose
triacetate film and hence allowing leakage of light due to
elimination of polarization in an amount of 6.2% of the total
amount of incident light.
Evaluation Test 4
[0160] The planar (polarized-)light sources obtained in Examples 5
and 6 and Comparative Examples 6 and 7 were each measured for
brightness on the central portion thereof in the forward direction
and brightness in the forward direction with a commercially
available absorption type polarizing plate having a transmittance
of 44% and a polarization degree of 99% being disposed on the
planar light source in such an arrangement that the transmission
axis lies at an angle of 45 degrees by means of a brightness meter
(BM-7, produced by TOPCON CORP.). The proportion of these
measurements based on Comparative Example 6, which was free of
polarizing plate, was determined. The results are set forth in the
table below.
2 Front brightness With no polarizing With polarizing plate
disposed plate disposed Example 5 95 76 Example 6 98 77 Comparative
100 44 Example 6 Comparative 95 48 Example 7
[0161] The results in the table above shows that the examples can
emit linearly polarized light and exhibits a drastically enhanced
brightness through the polarizing plate. Further, the comparison of
the examples with Comparative Example 7 shows that if the light
diffusion plate eliminates polarization, the advantage of emitting
linearly polarized light cannot be made the use of. It is thus made
obvious that when the planar polarized-light source according to
the present invention is used as a backlight for liquid crystal
display device, a brightness 1.5 or more times ordinary value
(Comparative Example 1) can be realized, making it possible to
accomplish a very bright display. In Example 6, which comprised a
light diffusion plate incorporated therein, the vision of linear
pattern on the lens sheet was relaxed, enhancing visibility.
EXAMPLE 7
[0162] The same polarized-light scattering plate as obtained in
Example 3 was bonded to one surface of a commercially available
polycarbonate plate having a thickness of 2 mm with an acrylic
adhesive layer in such an arrangement that its .DELTA.n1 direction
crossed the side face at an angle of 45 degrees to obtain a
laminate. A specular reflection sheet comprising a PET sheet having
silver vacuum-evaporated thereon was disposed on the lower surface
of the laminate to obtain a light pipe. A cold cathode ray tube was
then fixed to one side face of the laminate with a lamp reflector
made of a matted PET-based reflection sheet. The average phase
difference in the plane of the foregoing polycarbonate plate was 80
nm, and the average retardation axis was parallel to its side face
(0 degree direction).
COMPARATIVE EXAMPLE 8
[0163] A planar light source was obtained in the same manner as in
Example 7 except that there was used a light pipe obtained by
printing a reflective ink comprising titanium white incorporated
therein on one surface of an acrylic resin plate having a thickness
of 2 mm in a dotted pattern and then disposing a white reflecting
plate made of a foamed PET on the same surface of the acrylic resin
plate.
COMPARATIVE EXAMPLE 9
[0164] A light pipe and a planar polarized-light source were
obtained in the same manner as in Example 7 except that an acrylic
resin plate (in-plane average phase difference: 5 nm or less) was
used instead of the polycarbonate plate.
Evaluation Test 5
[0165] A commercially available absorption type polarizing plate
was disposed on the planar (polarized-)light sources obtained in
Example 7 and Comparative Examples 8 and 9 in such an arrangement
that the transmission axis lies at an angle of 45 degrees. These
arrangements were each visually measured for brightness in the
forward direction. As a result, brightness decreased in the order
of Example 1, Comparative Example 9 and Comparative Example 8. The
difference in brightness was definitely viewed also visually. The
difference in brightness between Comparative Example 9 and
Comparative Example 8 was obviously greater than that between
Example 7 and Comparative Example 9.
[0166] As can be seen in the foregoing description, when there is
disposed no polarizing plate, the brightness of Example 7 and
Comparative Examples 8 and 9 in the forward direction as viewed
visually are almost the same and thus can be hardly distinguished.
It can be seen that the difference in brightness between Example 7
and Comparative Example 8 in the arrangement having a polarizing
plate makes it possible to drastically enhance brightness of
linearly polarized light through the polarizing plate in Example 7.
As mentioned above, when the planar polarized-light source
according to the present invention is used as a backlight for
liquid crystal display device, the brightness can be drastically
enhanced, making it possible to accomplish a very bright
display.
EXAMPLE 8
[0167] A toluene solution of a hot-melt resin (Evaflex, produced by
Du Pont) was applied to one surface of the same polarized-light
scattering plate as obtained in Example 3 through a mask pattern
having many through-holes having a diameter of 1 mm formed therein,
and then dried to form a light path having a height of 10 .mu.m
which is sparse on the light source side thereof and dense on the
opposing side thereof.
[0168] The foregoing polarized-light scattering plate was then
hot-pressed onto one surface of an acrylic resin plate having a
thickness of 2 mm (produced by Mitsubishi Rayon Co., Ltd.) with the
light path interposed therebetween in such an arrangement that its
.DELTA.n1 direction crossed the side face thereof where the light
source is disposed at an angle of 45 degrees to obtain a light
pipe. A specular reflection sheet comprising a PET sheet having
silver vacuum-evaporated thereon was disposed on the lower surface
of the light pipe. At the same time, a cold cathode ray tube was
then fixed to one side face of the light pipe with a lamp reflector
made of a matted PET-based reflection sheet to obtain a planar
polarized-light source.
COMPARATIVE EXAMPLE 10
[0169] A planar light source was obtained in the same manner as in
Example 8 except that there was used a light pipe obtained by
printing a reflective ink comprising titanium white incorporated
therein on one surface of an acrylic resin plate having a thickness
of 2 mm in a dotted pattern and then disposing a white reflecting
plate made of a foamed PET on the same surface of the acrylic resin
plate.
COMPARATIVE EXAMPLE 11
[0170] A light pipe and a planar polarized-light source were
obtained in the same manner as in Example 8 except that a hot-melt
adhesive was applied to the entire one surface of the
polarized-light scattering plate and the polarized-light scattering
plate was then entirely bonded to the acrylic resin plate with the
hot-melt adhesive layer interposed therebetween.
Evaluation Test 6
[0171] A commercially available absorption type polarizing plate
having a transmittance of 44% and a polarization degree of 99% was
disposed on the planar (polarized-)light sources obtained in
Example 8 and Comparative Examples 10 and 11 in such an arrangement
that the transmission axis lies at an angle of 45degrees. These
arrangements were each visually measured for brightness. As a
result, the comparison with Comparative Example 10 shows that
Example 8 and Comparative Example 11 show a drastically brightness
through the polarizing plate and thus can emit linearly polarized
light from the planar source.
[0172] On the other hand, Comparative Example 11 is brighter toward
the light source and less bright with distance from the light
source, showing a great variation of brightness. However, Example 8
shows no visual difference in brightness on the entire surface
thereof and thus is excellent in uniformity in brightness. As
mentioned above, when the planar polarized-light source according
to the present invention is used as a backlight for liquid crystal
display device, the percent utilization of light can be drastically
enhanced, making it possible to accomplish a bright display having
an excellent uniformity in brightness and a good visibility.
[0173] Although the invention has been described in its preferred
form with a certain degree of particularity, it is understood that
the present disclosure of the preferred form can be changed in the
details of construction and in the combination and arrangement of
parts without departing from the spirit and the scope of the
invention as hereinafter claimed.
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