TECHNICAL FIELD
[0001 ] The present invention relates to an illumination unit and a display which each
include a light modulation device exhibiting a scattering property or transparency with
respect to light.
BACKGROUND ART
[0002] In recent years, improvements in image quality and energy conservation of
liquid crystal displays have been accelerated , and systems achieving an improvement
in dark-room contrast by modulating light intensity in a partial region of a backlight
have been proposed. As a main technique of achieving an improvement in dark-room
contrast, some of light-emitting diodes (LEDs) used as light sources of a backlight are
driven to modulate backlight light based on a display image. Moreover, in largescreen
liquid crystal displays, as in the case of small-screen liquid crystal displays, a
reduction in profile has been strongly desired ; therefore, attention has been given not to
a system in which cold cathode fluorescent lamps (CCFLs) or LEDs are disposed
directly below a liquid crystal panel, but to an edge light system in which a light source
is disposed on an edge of a light guide plate. However , in the edge light system, it is
difficult to perform a partial drive to modulate light intensity in a partial region of the
light source.
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[Citation list]
[Patent Literature]
[0003 ] [PTL 1] Japanese Unexamined Patent Application Publication No. H6-
347790
SUMMARY OF INVENTION
[0004] As a technique of extracting light propagating through a light guide plate, for
example, PTL 1 proposes a display using a polymer dispersed liquid crystal (PDLC)
allowed to switch between a transmission state and a scattering state. This technique is
proposed to reduce glare or the like, and is a technique of switching between the
transmission state and the scattering state by applying a voltage to a partial region of
the PDLC. However, in a backlight in PTL 1, there is an issue that light absorption by
an electrode is considerably large, and light extraction efficiency is not increased much.
Moreover, in the backlight, there is an issue that as light absorption by the electrode
has wavelength dependence, chromaticity of illumination light varies with increasing
distance from a light source mounted on an edge of a light guide plate.
[0005] The present invention is made to solve the above -described issues, and it is an
object of the invention to provide an illumination unit and a display which are capable
of further uniformizing chromaticity of illumination light in a plane while suppressing
a reduction in light extraction efficiency.
[0006] An illumination unit of the invention includes a first transparent substrate and
a second transparent substrate disposed to be separated from and face each other and a
light source emitting light to an end surface of the first transparent substrate or the
second transparent substrate . The illumination unit further includes an electrode
4
disposed on a surface of the first transparent substrate or the second transparent
substrate and generating an electric field in a direction parallel to the surface of the
first transparent substrate, and a light modulation layer disposed in a gap between the
first transparent substrate and the second transparent substrate and exhibiting a
scattering property or transparency with respect to light from the light source,
depending on magnitude of the electric field.
[0007] A display of the invention includes a display panel including a plurality of
pixels arranged in a matrix and being driven based on an image signal, and an
illumination unit illuminating the display panel. The illumination unit included in the
display includes the same components as those in the above-described illumination
unit.
[0008] In the illumination unit and the display of the invention, the electrode is
disposed on only the surface of one of the first transparent substrate and the second
transparent substrate allowing the light modulation layer to be sandwiched
therebetween. Therefore, a light absorption amount by the electrode when light
emitted from the light source repeatedly passes through the electrode in the light
modulation device while propagating through the light guide plate is smaller,
compared to the case where the electrodes are disposed on the surfaces of both of the
transparent substrates in the light modulation device. Further, as the light absorption
amount by the electrode is small, a change in chromaticity of illumination light in a
plane is also small.
[0009] In the illumination unit and the display of the invention, the electrode may be
configured of a first electrode having comb teeth which extend in a first direction and a
second electrode having comb teeth which are disposed alternately with the comb teeth
5
of the first electrode. The first direction here may be parallel to a side surface facing
the light source of side surfaces of the first transparent substrate or may be parallel to a
normal to a side surface facing the light source of side surfaces of the first transparent
substrate.
[0010] According to the illumination unit and the display of the invention, the
electrode is disposed on only the surface of one of the first transparent substrate and
the second transparent substrate allowing the light modulation layer to be sandwiched
therebetween; therefore, the light absorption amount by the electrode and a change in
chromaticity of illumination light in a plane are allowed to be reduced. As a result,
chromaticity of illumination light in a plane is allowed to be further uniformized while
suppressing a reduction in light extraction efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] [FIG. 1] FIG. 1 is a sectional view illustrating an example of a configuration
of a backlight according to a first embodiment of the invention.
[FIG. 2] FIG. 2 is a perspective view illustrating an example of a configuration of a
light source in FIG. 1.
[FIG. 3] FIG. 3 is a perspective view illustrating an example of a configuration of an
electrode in FIG. 1.
[FIG. 4] FIG. 4 is a perspective view illustrating another example of the configuration
of the electrode in FIG. 3.
[FIG. 5] FIG. 5 is a sectional view illustrating another example of the configuration of
the backlight in FIG. 1.
[FIG. 6] FIG. 6 is a schematic view for describing a configuration when a voltage is
6
not applied to a light modulation device in FIG. 1.
[FIG. 7] FIG. 7 is a schematic view for describing a configuration when a voltage is
applied to the light modulation device in FIG. 1.
[FIG. 8] FIG. 8 is a schematic view for describing a function of the backlight in FIG. 1.
[FIG. 9] FIG. 9 is a sectional view for describing a step of manufacturing the backlight
in FIG. 1.
[FIG. 10] FIG. 10 is a sectional view for describing a manufacturing step following
FIG. 9.
[FIG. 11] FIG. 11 is a sectional view for describing a manufacturing step following
FIG. 10.
[FIG. 12] FIG. 12 is a sectional view illustrating an example of a configuration of a
backlight according to a second embodiment of the invention.
[FIG. 13] FIG. 13 is a schematic view for describing a configuration when a voltage is
not applied to a light modulation device in FIG. 12.
[FIG. 14] FIG. 14 is a schematic view for describing a configuration when a voltage is
applied to the light modulation device in FIG. 12.
[FIG. 15] FIG. 15 is a perspective view illustrating another example of the
configuration of the electrode in FIG. 1.
[FIG. 16] FIG. 16 is a perspective view illustrating another example of the
configuration of the electrode in FIG. 15.
[FIG. 17] FIG. 17 is a schematic view for describing an example of a configuration
when a voltage is not applied to the light modulation device in the case where the
electrode has the configuration illustrated in FIGs. 15 and 16.
[FIG. 18] FIG. 18 is a schematic view for describing an example of a configuration
7
when a voltage is applied to the light modulation device in the case where the electrode
has the configuration illustrated in FIGs. 15 and 16.
[FIG. 19] FIG. 19 is a schematic view for describing another example of the
configuration when a voltage is not applied to the light modulation device in the case
where the electrode has the configuration illustrated in FIGs. 15 and 16.
[FIG. 20] FIG. 20 is a schematic view for describing another example of the
configuration when a voltage is applied to the light modulation device in the case
where the electrode has the configuration illustrated in FIGs. 15 and 16.
[FIG. 21] FIG. 21 is a perspective view illustrating a modification of a configuration
of a light guide plate in FIGs. 1 and 12.
[FIG. 22] FIG. 22 is a perspective view illustrating another modification of the
configuration of the light guide plate in FIGs. 1 and 12.
[FIG. 231 FIG. 23 is a schematic view illustrating a state where light propagates
through the light guide plate in FIGs. 21 and 22.
[FIG. 24] FIG. 24 is a schematic view illustrating a state where light is partially
emitted from the light guide plate in FIGs. 21 and 22.
[FIG. 25] FIG. 25 is a sectional view illustrating a first modification of the
configuration of the backlight in FIGs. 1 and 12.
[FIG. 26] FIG. 26 is a sectional view illustrating a second modification of the
configuration of the backlight in FIGs. 1 and 12.
[FIG. 27] FIG. 27 is a sectional view illustrating a third modification of the
configuration of the backlight in FIGs. 1 and 12.
[FIG. 28] FIG. 28 is a sectional view illustrating an example of a display as an
application example.
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DESCRIPTION OF EMBODIMENTS
[0012] Embodiments of the invention will be described in detail below referring to
the accompanying drawings . It is to be noted that description will be given in the
following order.
1. First Embodiment (FIGs. 1 to 11)
An example in which a light modulation device including a horizontal
alignment film is disposed in a backlight
2. Second Embodiment (FIGs. 12 to 14)
An example in which a light modulation device including a vertical alignment
film is disposed in a backlight.
3. Modifications
An example in which a direction of comb teeth of an electrode is different
(FIGs. 15 and 16)
An example in which an alignment state in a light modulation layer is
different (FIGs. 17 to 20)
An example in which strip-like projections are formed on a top surface of a
light guide plate (FIGs. 21 to 24)
An example in which the position of a light modulation device is different
(FIGs. 25 to 27)
4. Application Example (FIG. 28)
An example in which a backlight of any of the above-described embodiments
and the like is used as a light source of a display
[0013] (1. First Embodiment)
9
FIG. 1(A) is a sectional view illustrating an example of a schematic
configuration of a backlight I (an illumination unit) according to a first embodiment of
the invention. FIG. 1(B) is a sectional view illustrating an example of a specific
configuration of the backlight 1 in FIG. 1(A). It is to be noted that FIGs. 1(A) and (B)
are schematic illustrations, and dimensions and shapes in the illustrations are not
necessarily the same as actual dimensions and shapes. The backlight 1 illuminates, for
example, a liquid crystal display panel or the like from a back side thereof, and
includes a light guide plate 10, a light source 20 disposed on a side surface of the light
guide plate 10, a light modulation device 30 and a reflective plate 40 disposed behind
the light guide plate 10, and a drive circuit 50 driving the light source 20 and the light
modulation device 30.
[0014] The light guide plate 10 guides light from the light source 20 disposed on the
side surface of the light guide plate 10 to a top surface of the light guide plate 10. The
light guide plate 10 has a shape corresponding to a display panel (not illustrated)
disposed on the top surface of the light guide plate 10, for example, a rectangular
parallelepiped shape surrounded by a top surface, a bottom surface, and side surfaces.
It is to be noted that a side surface where light from the light source 20 enters of the
side surfaces of the light guide plate 10 is hereinafter referred to as light incident
surface I OA. In the light guide plate 10, one or both of the top surface and the bottom
surface have a predetermined patterned shape, and the light guide plate 10 has a
function of scattering and uniformizing light incident from the light incident surface
10A. It is to be noted that, in the case where a voltage applied to the backlight 1 is
modulated to uniformize luminance, a flat light guide plate which is not patterned may
be used as the light guide plate 10. The light guide plate 10 also functions as a
10
supporting body supporting an optical sheet (for example, a diffuser plate, a diffuser
sheet, a lens film, or a polarization splitter sheet) disposed between the display panel
and the backlight 1. The light guide plate 10 is formed by mainly including a
transparent thermoplastic resin such as a polycarbonate resin (PC) or an acrylic resin
(polymethylmethacrylate (PMMA)).
[0015] As illustrated in FIG. 2(A), the light source 20 is configured of a linear light
source 21 and a reflective mirror 22. The linear light source 21 is configured of, for
example, a hot cathode fluorescent lamp (HCFL) or a CCFL. The reflective mirror 22
reflects, to the light incident surface 10A, light toward a direction not directly entering
the light incident surface l0A in light emitted from the linear light source 21. For
example, as illustrated in FIG. 2(B) or 2(C), the light source 20 may be configured of a
plurality of point-like light sources 23 arranged in one line. The point-like light
sources 23 each emit light to the light incident surface 10A, and each are configured of,
for example, a light-emitting device having a light emission spot on a surface facing
the light incident surface 10A. Examples of such a light-emitting device include an
LED and a laser diode (LD).
[0016] For example, as illustrated in, FIG. 2(B) or 2(C), every two or more point-like
light sources 23 in the plurality of point-like light sources 23 may be arranged on one
common substrate 24. In this case, a light source block 25 is configured of one
substrate 24 and two or more point-like light sources 23 arranged on the substrate 24.
The substrate 24 is, for example, a circuit board on which wiring electrically
connecting the point-like light sources 23 and the drive circuit 50 to each other is
installed, and the respective point-like light sources 23 are mounted on the circuit
board. The respective point-like light sources 23 arranged on the common substrate 24
11
(the respective point-like light sources 23 in one light source block 25) are collectively
(not independently) driven by the drive circuit 50, and are connected to one another in
parallel or in series (not illustrated). Moreover, the point-like light sources 23 arranged
on different substrates 24 (the point-like light sources 23 in respective light source
blocks 25) may be collectively (not independently) driven by the drive circuit 50, and
are connected to one another, for example, in parallel as illustrated in FIG. 2(B), or in
series (not illustrated). For example, the point-like light sources 23 arranged on
different substrates 24 (the point-like light sources 23 in respective light source blocks
25) may be driven by the drive circuit 50 independently of one light source block 25 to
another. At this time, for example, as illustrated in FIG. 2(C), the point-like light
sources 23 arranged on different substrates 24 (the point-like light sources 23 in
respective light source blocks 25) are connected to different current paths.
[0017] As illustrated in FIGs. 2(A) to 2(C), the light source 20 may be disposed on
only one side surface of the light guide plate 10, or although not illustrated, the light
sources 20 may be disposed on two side surfaces, three side surfaces, or all side
surfaces of the light guide plate 10.
[0018] The reflective plate 40 returns light leaked from behind the light guide plate
10 through the light modulation device 30 to the light guide plate 10, and has, for
example, functions such as reflection, diffusion, and scattering. The reflective plate 40
allows light emitted from the light source 20 to be efficiently used, and is also useful to
improve front luminance. The reflective plate 40 is made of, for example, foamed PET
(polyethylene terephthalate), a silver-evaporated film, a multilayer reflective film, or
white PET.
[0019] In the embodiment, the light modulation device 30 is in close contact with a
12
back side (the bottom surface) of the light guide plate 10 without an air layer in
between, and is bonded to the back side of the light guide plate 10 with, for example,
an adhesive (not illustrated) in between. For example, as illustrated in FIG. 1(B), the
light modulation device 30 is configured by arranging a transparent substrate 31, an
electrode 32, an alignment film 33, a light modulation layer 34, an alignment film 35,
and a transparent substrate 36 in order from a side closer to the reflective plate 40.
[0020] The transparent substrates 31 and 36 support the light modulation layer 34,
and are typically configured of substrates transparent to visible light, for example,
glass plates or plastic films. The electrode 32 is disposed on a surface located closer to
the light modulation layer 34 of the transparent substrate 31, and has a configuration
allowing an electric field to be generated in the light modulation layer 34 in a direction
parallel to a surface of the transparent substrate 31. More specifically, for example, as
illustrated in a part of the light modulation device 30 in FIG. 3(A), the electrode 32
includes a first electrode 32A having comb teeth which extend in one direction (a first
direction) in a plane and a second electrode 32B having comb teeth which are arranged
alternately with the comb teeth of the first electrode 32A. For example, as illustrated
in FIGs. 3(B) and (C), the comb teeth of the first electrode 32A and the second
electrode 32B extend in a direction parallel to an extending direction of the light source
20 when the light source 20 is disposed close to only one side surface of the light
modulation device 30 or when the light sources 20 are arranged close to two side
surfaces facing each other of the side surfaces of the light modulation device 30.
[0021] For example, as illustrated in FIGs. 3(A) to (C), the first electrode 32A and
the second electrode 32B each may be configured of a single structure formed on an
entire surface of the transparent substrate 31. Moreover, for example, as illustrated in
13
FIGS. 4(A) to (C), the first electrode 32A and the second electrode 32B each may be
configured of a plurality of structures (sub-electrodes 32A' and 3213'). Each of the subelectrodes
32A' has comb teeth extending in one direction (the first direction) in a
plane, and each of the sub-electrodes 32B' has comb teeth arranged alternately with the
comb teeth of the sub-electrode 32A'. It is to be noted that a pair of the sub-electrodes
32A' and 3213' engaged in each other is referred to as sub-electrode pair 32C.
[0022] A plurality of sub-electrode pairs 32C may be arranged in one direction in a
plane, for example, as illustrated in FIGs. 4(A) and (B), or in a matrix, for example, as
illustrated in FIG. 4(C). It is to be noted that an arrangement direction in FIG. 4(A)
corresponds to a direction parallel to an extending direction of the light source 20 when
the light source 20 is disposed on only one side surface of the light guide plate 10, or
when the light sources 20 are arranged on two side surfaces facing each other of the
side surfaces of the light guide plate 10. Moreover, an arrangement direction in FIG.
4(B) corresponds to a direction orthogonal to the extending direction of the light
source 20 when the light source 20 is disposed on only one side surface of the light
guide plate 10, or when the light sources 20 are arranged on two side surfaces facing
each other of the side surfaces of the light guide plate 10. Further, an arrangement
direction in FIG. 4(C) corresponds to two directions including a direction parallel to
the extending direction of the light source 20 and the direction orthogonal to the
extending direction of the light source 20 when the light source 20 is disposed on only
one side surface of the light guide plate 10, or when the light sources 20 are arranged
on two side surfaces facing each other of the side surfaces of the light guide plate 10.
[0023] The electrode 32 is made of a transparent conductive material, for example,
indium tin oxide (ITO). However, the electrode 32 may not be made of a transparent
14
material, and may be made of, for example, metal. It is to be noted that when the
electrode 32 is made of metal, the electrode 32 also has a function of reflecting light
entering the light modulation device 30 from behind the light guide plate 10 as in the
case of the reflective plate 40. Therefore, in this case, for example, as illustrated in
FIG. 5, the reflective plate 40 may not be included.
[0024] In the case where the first electrode 32A and the second electrode 32B are
configured of a plurality of sub-electrodes 32A' and 32B', respectively, portions facing
the sub-electrode pairs 32C of the light modulation device 30 when the sub-electrode
pairs 32C are viewed from a direction of a normal to the light modulation device 30
configure light modulation cells 30S. For example, a portion indicated by a broken
line in FIG. 1(B) configures the light modulation cell 305. The light modulation cells
30S are allowed to be separately and independently driven by applying a
predetermined voltage to the sub-electrodes 32A' and 32B', and exhibit transparency or
a scattering property with respect to light from the light source 20, depending on a
voltage value applied to the sub-electrodes 32A' and 32B'. It is to be noted that
transparency and the scattering property will be described in more detail when the light
modulation layer 34 is described.
[0025] The alignment films 33 and 35 align, for example, a liquid crystal or a
monomer used in the light modulation layer 34. Kinds of alignment films include a
vertical alignment film and a horizontal alignment film, and in the embodiment,
horizontal alignment films are used as the alignment films 33 and 35. Examples of the
horizontal alignment films include an alignment film formed by performing a rubbing
process on polyimide, polyamide imide, polyvinyl alcohol, or the like, and an
alignment film provided with a groove by transfer or etching. Other examples of the
15
horizontal alignment films include an alignment film formed by obliquely evaporating
an inorganic material such as silicon oxide, a diamond-like carbon alignment film
formed by ion beam irradiation, and an alignment film provided with an electrode
pattern slit. In the case where plastic films are used as the transparent substrates 31
and 36, in a manufacturing process, polyamide imide capable of forming a film at a
temperature of 100°C or less is preferably used for the alignment films 33 and 35,
because a firing temperature after coating surfaces of the transparent substrates 31 and
36 with the alignment films 33 and 35 is preferably as low as possible.
[0026] Moreover, it is only necessary for both of vertical and horizontal alignment
films to have a function of aligning a liquid crystal and a monomer, and reliability,
which is necessary for a typical liquid crystal display, with respect to repeated voltage
application is not necessary. It is because reliability with respect to voltage application
after forming a device is determined by an interface between a resultant formed by
polymerizing a monomer, and a liquid crystal. Moreover, even if the alignment films
33 and 35 are not used, for example, when an electric field or a magnetic field is
applied between the first electrode 32A and the second electrode 32B (or the subelectrodes
32A' and 3213'), a liquid crystal or a monomer used in the light modulation
layer 34 is allowed to be aligned. In other words, while an electric field or a magnetic
field is applied between the first electrode 32A and the second electrode 32B (or the
sub-electrodes 32A' and 3213), the alignment state of the liquid crystal or the monomer
under voltage application is allowed to be fixed by ultraviolet irradiation. In the case
where a voltage is used to form the alignment films 33 and 35, an electrode for
alignment and an electrode for drive may be separately formed, or as a liquid crystal
material, a dual-frequency liquid crystal allowing the sign of dielectric constant
16
anisotropy to be inverted by a frequency may be used. Moreover, in the case where a
magnetic field is used to form the alignment films 33 and 35, for the alignment films
33 and 35, a material with large magnetic susceptibility anisotropy is preferably used,
and, for example, a material with a large number of benzene rings is preferably used.
[0027] The light modulation layer 34 exhibits a scattering property or transparency
with respect to light from the light source 20 depending on magnitude of an electric
field. More specifically, the light modulation layer 34 exhibits transparency with
respect to light from the light source 20 when a voltage is not applied to the electrode
32 and exhibits the scattering property when a voltage is applied to the electrode 32.
For example, as illustrated in FIG. 1(B), the light modulation layer 34 is a composite
layer including a bulk 34A and a plurality of microparticles 34B dispersed in the bulk
34A. The bulk 34A and the microparticles 34B have optical anisotropy.
[0028] FIG. 6 schematically illustrates an example of an alignment state in the bulk
34A and the microparticles 34B when a voltage is not applied between the first
electrode 32A and the second electrode 32B (or the sub-electrodes 32A' and 3213'). An
ellipsoid 134A in FIG. 6 is an example of a refractive index ellipsoid exhibiting
refractive index anisotropy of the bulk 34A when a voltage is not applied between the
first electrode 32A and the second electrode 32B (or the sub-electrodes 32A' and 3213').
An ellipsoid 134B in FIG. 6 is an example of a refractive index ellipsoid exhibiting
refractive index anisotropy of the microparticle 34B when a voltage is not applied
between the first electrode 32A and the second electrode 32B (or the sub-electrodes
32A' and 3213'). The refractive index ellipsoid is a tensor ellipsoid representing a
refractive index of linearly polarized light incident from various directions, and when a
section of an ellipsoid from a light incident direction is observed, the refractive index
17
is allowed to be geometrically learned.
[0029] FIG. 7 schematically illustrates an example of an alignment state in the bulk
34A and the microparticles 34B when a voltage is applied between the first electrode
32A and the second electrode 32B (or the sub-electrodes 32A' and 3213'). An ellipsoid
134A in FIG. 7 is an example of a refractive index ellipsoid exhibiting refractive index
anisotropy of the bulk 34A when a voltage is applied between the first electrode 32A
and the second electrode 32B (or the sub-electrodes 32A' and 32B'). An ellipsoid
134B in FIG. 7 is an example of a refractive index ellipsoid exhibiting refractive index
anisotropy of the microparticle 34B when a voltage is applied between the first
electrode 32A and the second electrode 32B (or the sub-electrodes 32A' and 3213').
[0030] For example, as illustrated in FIG. 6, the bulk 34A and the microparticle 34B
are structured to allow the direction of an optical axis AXI of the bulk 34A (a long
axis of the ellipsoid 134A) and the direction of an optical axis AX2 of the
microparticle 34B (a long axis of the ellipsoid 134B) to coincide with (be parallel to)
each other when a voltage is not applied between the first electrode 32A and the
second electrode 32B (or the sub-electrodes 32A' and 3213'). It is to be noted that the
optical axes AX1 and AX2 each indicate a line parallel to a travel direction of a light
beam allowing a refractive index to have one value irrespective of polarization
direction. Moreover, it is not necessary for the directions of the optical axis AX1 and
the optical axis AX2 to consistently coincide with each other when a voltage is not
applied between the first electrode 32A and the second electrode 32B (or the subelectrodes
32A' and 3213'), and the directions of the optical axis AX1 and the optical
axis AX2 may be slightly deviated from each other due to, for example, a
manufacturing error.
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[0031] Moreover, the optical axis AX2 is parallel to the light incident surface IOA of
the light guide plate 10 as well as parallel to a surface of the transparent substrate 31
when a voltage is not applied between the first electrode 32A and the second electrode
32B (or the sub-electrodes 32A' and 3213'). In other words, when a voltage is not
applied between the first electrode 32A and the second electrode 32B (or the subelectrodes
32A' and 3213), the optical axis AX2 is parallel to a plane including the first
electrode 32A and the second electrode 32B (or the sub-electrodes 32A' and 32B') as
well as parallel to an extending direction of comb teeth of the first electrode 32A and
the second electrode 32B (or the sub-electrodes 32A' and 32B').
[0032] On the other hand, the bulk 34A is structured to have a fixed optical axis AXI
irrespective of whether or not a voltage is applied between the first electrode 32A and
the second electrode 32B (or the sub-electrodes 32A' and 3213'). More specifically, the
optical axis AXl is parallel to the light incident surface 10A of the light guide plate 10
as well as parallel to the surface of the transparent substrate 31. In other words, when
a voltage is not applied between the first electrode 32A and the second electrode 32B
(or the sub-electrodes 32A' and 32B'), the optical axis AX1 is parallel to the optical
axis AX2.
[0033] It is to be noted that it is not necessary for the optical axis AX2 to be
consistently parallel to the light incident surface 10A of the light guide plate 10 as well
as the surface of the transparent substrate 31, and the optical axis AX2 may be aligned
in a direction intersecting with one or both of the light incident surface 10A and the
surface of the transparent substrate 31 at a small angle due to, for example, a
manufacturing error.
[0034] In this case, ordinary refractive indices of the bulk 34A and the microparticle
19
34B are preferably equal to each other, and extraordinary refractive indices of the bulk
34A and the microparticle 34B are preferably equal to each other. In this case, for
example, when a voltage is not applied between the first electrode 32A and the second
electrode 32B (or the sub-electrodes 32A' and 32B'), there is little difference in
refractive index in all directions including a front direction and an oblique direction,
and high transparency is obtained. Therefore, light toward the front direction and light
toward the oblique direction pass through the light modulation layer 34 without being
scattered in the light modulation layer 34. As a result, for example, as illustrated in
FIGs. 8(A) and (B), light L from the light source 20 (light from the oblique direction)
is totally reflected by an interface (an interface between the transparent substrate 31 or
the light guide plate 10 and air) of a transparent region (a transmission region 30A) of
the light modulation device 30, and luminance (luminance in black display) in the
transmission region 30A is decreased, compared to the case where the light modulation
device 30 is not included (indicated by an alternate long and short dash line in FIG.
8(B)). It is to be noted that a graph in FIG. 8(B) is obtained by measuring front
luminance in a state where a diffuser sheet 41 is disposed on the light guide plate 10 as
illustrated in FIG. 8(A).
[0035] Moreover, for example, as illustrated in FIG. 7, the bulk 34A and the
microparticles 34B are structured to allow directions of the optical axes AX1 and AX2
to be different from (intersect with or be orthogonal to) each other when a voltage is
applied between the first electrode 32A and the second electrode 32B (or the subelectrodes
32A' and 32B'). Further, for example, the microparticles 34B are structured
to allow the optical axis AX2 to be parallel to the normal to the light incident surface
l0A of the light guide plate 10 as well as parallel to the surface of the transparent
20
substrate 31 when a voltage is applied between the first electrode 32A and the second
electrode 32B (or the sub-electrodes 32A' and 3213'). In other words, when a voltage is
applied between the first electrode 32A and the second electrode 32B (or the subelectrodes
32A' and 3213'), the optical axis AX2 is parallel to a plane including the first
electrode 32A and the second electrode 32B (or the sub-electrodes 32A' and 32B') and
intersects with (or is orthogonal to) an extending direction of comb teeth of the subelectrodes
32A' and 3213'.
[0036] Therefore, when a voltage is applied between the first electrode 32A and the
second electrode 32B (or the sub-electrodes 32A' and 32B'), in the light modulation
layer 34, a difference in refractive index in all directions in a plane parallel to the
surface of the transparent substrate 31 is increased to obtain a high scattering property.
Accordingly, for example, light toward the front direction and light toward the oblique
direction are scattered in the light modulation layer 34. As a result, for example, as
illustrated in FIGS. 8(A) and (B), the light L from the light source 20 (light from the
oblique direction) passes through an interface (an interface between the transparent
substrate 31 or the light guide plate 10 and the air) of a region in a scattering state (a
scattering region 30B) in the light modulation device 30, and light having passed
toward the reflective plate 40 is reflected by the reflective plate 40 to pass through the
light modulation device 30. Therefore, the luminance of the scattering region 30B is
extremely higher than that in the case where the light modulation device 30 is not
included (indicated by an alternate long and short dash line in FIG. 8(B)), and
luminance in white display is partially increased (partial luminance enhancement) by a
reduced amount of the luminance of the transmission region 30A.
[0037] It is to be noted that the ordinary refractive indices of the bulk 34A and the
21
microparticle 34B may be slightly different from each other due to, for example, a
manufacturing error, and are preferably, for example, 0.1 or less, and more preferably
0.05 or less. Moreover, the extraordinary refractive indices of the bulk 34A and the
microparticle 34B may be slightly different from each other due to, for example, a
manufacturing error, and are preferably, for example, 0.1 or less, and more preferably
0.05 or less.
[0038] Moreover, a refractive index difference (=extraordinary refractive
index-ordinary refractive index) in the bulk 34A and a refractive index difference
(=extraordinary refractive index-ordinary refractive index) in the microparticle 34B
are preferably as large as possible, and are preferably 0.05 or over, more preferably 0.1
or over, and still more preferably 0.15 or over. In the case where the refractive index
differences in the bulk 34A and the microparticle 34B are large, the scattering power
of the light modulation layer 34 is enhanced to allow light guide conditions to be easily
disrupted, thereby allowing light from the light guide plate 10 to be easily extracted.
[0039] Further, the bulk 34A and the microparticle 34B have different response
speeds with respect to an electric field. The bulk 34A has, for example, a streaky
structure or a porous structure which does not respond to an electric field, or a rod-like
structure having a response speed slower than that of the microparticle 34B. The bulk
34A is formed of, for example, a polymer material obtained by polymerizing a lowmolecular
monomer. The bulk 34A is formed, for example, by polymerizing, by one
or both of heat and light, a material (for example, a monomer) with orientation and
polymerization which is aligned along the alignment direction of the microparticles
34B or the alignment directions of the alignment films 33 and 35.
[0040] On the other hand, the microparticles 34B mainly include, for example, a
22
liquid crystal material, and have a response speed sufficiently higher than that of the
bulk 34A. Examples of the liquid crystal material (liquid crystal molecules) included
in the microparticles 34B include rod-like molecules. As liquid crystal molecules
included in the microparticles 34B, liquid crystal molecules having positive dielectric
constant anisotropy (a so-called positive type liquid crystal) are preferably used.
[0041] In this case, when a voltage is not applied between the first electrode 32A and
the second electrode 32B (or the sub-electrodes 32A' and 3213'), the long-axis
directions of the liquid crystal molecules in the microparticles 34B are parallel to the
optical axis AX1. At this time, the long axes of the liquid crystal molecules in the
microparticles 34B are parallel to the light incident surface I OA of the light guide plate
10 as well as parallel to the surface of the transparent substrate 31. Moreover, when a
voltage is applied between the first electrode 32A and the second electrode 32B (or the
sub-electrodes 32A' and 3213'), the long-axis directions of the liquid crystal molecules
in the microparticles 34B intersect with (or is orthogonal to) the optical axis AX1. At
this time, the long axes of the liquid crystal molecules in the microparticles 34B are
parallel to the normal to the light incident surface 1OA of the light guide plate 10 as
well as parallel to the surface of the transparent substrate 31.
[0042] The above-described monomer having orientation and polymerization may be
a material having optical anisotropy and forming a composite material with a liquid
crystal; however, a low-molecular monomer which is cured with ultraviolet light is
preferable in this embodiment. It is preferable that, in a state where no voltage is
applied, directions of optical anisotropy of the liquid crystal and a resultant (a polymer
material) formed by polymerizing a low-molecular monomer coincide with each other;
therefore, before curing the low-molecular monomer with ultraviolet light, the liquid
23
crystal and the low-molecular monomer are preferably aligned in the same direction.
In the case where a liquid crystal is used as the microparticles 34B, when the liquid
crystal includes rod-like molecules, the used monomer material preferably has a rodlike
shape. As described above, a material having both of polymerization and liquid
crystal properties is preferably used as the monomer material, and, for example, the
monomer material preferably includes one or more functional groups selected from the
group consisting of an acrylate group, a methacrylate group, an acryloyloxy group, a
methacryloyloxy group, a vinyl ether group, and an epoxy group as polymerizable
functional groups. These functional groups are allowed to be polymerized by
ultraviolet, infrared, or electron irradiation, or by heating. To suppress a reduction in
the degree of alignment under ultraviolet irradiation, a liquid crystal material having a
polyfuncitonal group may be added. In the case where the bulk 34A has the abovedescribed
streaky structure, as the material of the bulk 34A, a bifunctional liquid
crystal monomer is preferably used. Moreover, a monofunctional monomer may be
added to the material of the bulk 34A to adjust a temperature at which liquid crystal
properties are exhibited, or a tri- or more-functional monomer may be added to the
material of the bulk 34A to improve crosslink density.
[00431 For example, the drive circuit 50 controls the magnitude of a voltage applied
to the first electrode 32A and the second electrode 32B (or the sub-electrodes 32A' and
32B') to allow the optical axes AX2 of the microparticles 34B in one light modulation
cell 30S to be parallel or substantially parallel to the optical axis AX1 of the bulk 34A,
as well as to allow the optical axes AX2 of the microparticles 34B in another light
modulation cell 30S to intersect with or be orthogonal to the optical axis AX1 of the
bulk 34A. In other words, the drive circuit 50 allows, by electric field control, the
24
direction of the optical axis AXl of the bulk 34A and the directions of the optical axes
AX2 of the microparticles 34B to coincide with (or substantially coincide with) each
other or to be different from (or orthogonal to) each other.
[0044] Moreover, for example, when the electrode 32 is configured of a plurality of
sub-electrode pairs 32C and the sub-electrode pairs 32C are arranged in a direction
parallel to the normal to the light incident surface 10A, the drive circuit 50 applies, to
the sub-electrode pairs 32C, a voltage with a peal, value, a duty ratio, and a frequency
one or more of which are modulated according to a distance from the light source 20 to
the sub-electrode pairs 32C. For example, the voltage is modulated to enhance the
scattering property of the light modulation cell 30S with increasing distance from the
light source 20. Further, the drive circuit 50 may apply, to the sub-electrode pairs 32C,
a voltage with the peak value, the duty ratio, and the frequency one or more of which
are modulated with consideration given to not only the distance from the light source
20 but also an externally supplied image signal.
[0045] Moreover, for example, when the light source 20 is configured of a plurality
of light source blocks 25 capable of being driven independently of each other, the drive
circuit 50 may apply, to respective light source blocks 25, a voltage or a current with a
peak value, a duty ratio, and a frequency one of which is modulated according to a
distance from the light source 20 to a sub-electrode pair 32C to which a voltage is to be
applied and an externally supplied image signal.
[0046] Next, a method of manufacturing the backlight 1 according to the
embodiment will be described below referring to FIGs. 9(A) to (C) to FIGs. 11(A) to
(C).
[0047] First, a transparent conductive film 32D made of ITO or the like is formed on
25
the transparent substrate 31 configured of a glass substrate or a plastic film substrate
(refer to FIG. 9(A)). Next, a patterned resist layer (not illustrated) is formed on the
transparent conductive film 32D, and then the transparent conductive film 32D is
selectively etched with use of the resist layer as a mask. As a result, the electrode 32 is
formed (refer to FIG. 9(B)).
[0048] Next, after an entire surface of the transparent substrate 31 is coated with the
alignment film 33, the alignment film 33 is dried and fired (refer to FIG. 9(C)). In the
case where a polyimide-based material is used as the alignment film 33, NMP (Nmethyl-
2-pyrrolidone) is often used as a solvent; however, at this time, a temperature
of approximately 200°C is necessary under an atmosphere. It is to be noted that, in this
case, when a plastic substrate is used as the transparent substrate 31, the alignment film
33 may be vacuum-dried and fired at 100°C. After that, a rubbing process is
performed on the alignment film 33. Therefore, the alignment film 33 functions as an
alignment film for horizontal alignment.
[0049] Next, spacers 38 allowing a cell gap to be formed are sprayed on the
alignment film 33 by a dry method or a wet method (refer to FIG. 10(A)). It is to be
noted that, in the case where the light modulation cells 30S are formed by a vacuum
bonding method, the spacers 38 may be mixed in a mixture which is to be dropped.
Alternatively, columnar spacers may be formed by a photolithography method, instead
of the spacers 38.
[0050] Then, the alignment film 35 formed by a method similar to the abovedescribed
method is coated with a sealant pattern 39 for bonding and preventing
leakage of the liquid crystal in, for example, a frame shape (refer to FIG. 10(B)). The
sealant pattern 39 is allowed to be formed by a dispenser method or a screen printing
26
method.
[0051] The vacuum bonding method (a one-drop-fill (ODF) method) will be
described below; however, the light modulation cells 30S may also be formed by a
vacuum injection method, a roll bonding method, or the like.
[0052] First, a mixture 42 of a liquid crystal and a monomer, corresponding to a
volume determined by a cell gap, a cell area, or the like, is dropped uniformly on a
plane (refer to FIG. 10(C)). The mixture 42 is preferably dropped with use of a linear
guide precise dispenser; however, a die coater or the like may be used with use of the
sealant pattern 39 as a bank.
[0053] The above-described materials may be used as the liquid crystal and the
monomer, and a weight ratio of the liquid crystal to the monomer is within a range of
98:2 to 50:50, preferably within a range of 95:5 to 75:25, and more preferably within a
range of 92:8 to 85:15. A drive voltage is allowed to be decreased by increasing the
ratio of the liquid crystal; however, when the liquid crystal is increased too much, the
liquid crystal tends to have difficulty in returning to a transparent state, such as a
reduction in whiteness under voltage application or a decrease in the response speed
after turning the voltage off.
[0054] In addition to the liquid crystal and the monomer, a polymerization initiator is
added to the mixture 42. A monomer ratio of the added polymerization initiator is
adjusted within a range of 0.1 to 10 wt%, depending on a used ultraviolet wavelength.
A polymerization inhibitor, a plasticizer, a viscosity modifier, or the like may be
further added to the mixture 42, as necessary. When the monomer is a solid or gel at
room temperature, a cap, a syringe, and a substrate are preferably warmed.
[0055] After the transparent substrates 31 and 36 are put in a vacuum bonding
27
system (not illustrated), evacuation is performed to bond the transparent substrates 31
and 36 (refer to FIG. 11(A)). After that, a resultant is released to the atmosphere to
uniformize the cell gap by uniform pressurization under atmospheric pressure. The
cell gap may be appropriately selected based on a relationship between white
luminance (whiteness) and the drive voltage; however, the cell gap is within a range of
5 to 40 μm, preferably within a range of 6 to 20 μm, and more preferably within a
range of 7 to 10 pin.
[0056] After bonding, an alignment process is preferably performed as necessary
(not illustrated). In the case where light leakage occurs by an insertion of a bonded
cell between crossed-Nicols polarizers, the cell may be heated for a predetermined
time or be left at room temperature to be aligned. After that, the monomer is irradiated
with ultraviolet light L3 to be polymerized (refer to FIG. 11(B)). Thus, the light
modulation device 30 is manufactured.
[0057] It is preferable to prevent the temperature of the cell from being changed
under ultraviolet irradiation. An infrared out filter is preferably used, or an UV-LED
or the like is preferably used as a light source. Ultraviolet irradiance exerts an
influence on an organization structure of a composite material; therefore, the
ultraviolet irradiance is preferably adjusted appropriately based on a used liquid crystal
material or a used monomer material, and a composition thereof, and the ultraviolet
irradiance is preferably within a range of 0.1 to 500 mW/cm2, and more preferably
within a range of 0.5 to 30 mW/cm2. There is a tendency that the lower the ultraviolet
irradiance is, the lower the drive voltage becomes, and preferable ultraviolet irradiance
is allowed to be selected in terms of both of productivity and properties.
[0058] Then, the light modulation device 30 is bonded to the light guide plate 10
28
(refer to FIG. 11(C)). Bonding may be carried out by sticking or adhesion; however, it
is preferable that the light modulation device 30 be adhered or stuck with a material
having a refractive index which is as close to a refractive index of the light guide plate
10 and a refractive index of a substrate material of the light modulation device 30 as
possible. Finally, leading lines (not illustrated) are attached to a lower electrode 32.
Thus, the backlight 1 according to the embodiment is manufactured.
[0059] Although the process of forming the light modulation device 30, and finally
bonding the light modulation device 30 to the light guide plate 10 is described, the
transparent substrate 36 on which the alignment film 35 is formed may be bonded in
advance to the surface of the light guide plate 10 to form the backlight 1. Moreover,
the backlight 1 may be formed by one of a sheet-feeding method and a roll-to-roll
method.
[0060] Next, functions and effects of the backlight 1 according to the embodiment
will be described below.
[0061] In the backlight 1 according to the embodiment, a voltage is applied between
the sub-electrodes 32A' and 313' of respective light modulation cells 30S to allow the
optical axes AX2 of the microparticles 34B in one light modulation cell 30S to be
parallel or substantially parallel to the optical axis AXI of the bulk 34A, and to allow
the optical axes AX2 of the microparticles 34B in another light modulation cell 30S to
intersect with or be orthogonal to the optical axis AX1 of the bulk 34A. As a result,
light emitted from the light source 20 and entering into the light guide plate 10 passes
through the transmission region 30A where the optical axes AXl and AX2 are parallel
or substantially parallel to each other of the light modulation device 30. On the other
hand, light emitted from the light source 20 and entering into the light guide plate 10 is
29
scattered in the scattering region 30B where the optical axes AXI and AX2 intersect
with or are orthogonal to each other of the light modulation device 30. Light having
passed through a bottom surface of the scattering region 30B in the scattered light is
reflected by the reflective plate 40 to be returned to the light guide plate 10 again, and
then the light is emitted from a top surface of the backlight 1. Moreover, light toward
a top surface of the scattering region 30B in the scattered light passes through the light
guide plate 10, and then is emitted from the top surface of the backlight 1. Thus, in the
embodiment, light is hardly emitted from the top surface of the transmission region
30A, and light is emitted from the top surface of the scattering region 30B.
Accordingly, a modulation ratio in a front direction is increased.
[0062] Typically, PDLC is a composite layer which is formed by mixing the liquid
crystal material and an isotropic low-molecular material, and causing phase separation
by ultraviolet irradiation, drying of a solvent, or the like, and has microparticles of the
liquid crystal material dispersed in a polymer material. The liquid crystal material in
the composite layer is aligned in random directions under no voltage application, and
thus exhibits the scattering property, but on the other hand, under voltage application,
the liquid crystal material is aligned in an electric field direction; therefore, in the case
where the ordinary refractive index of the liquid crystal material and the refractive
index of the polymer material are equal to each other, the liquid crystal material
exhibits high transparency in the front direction (in a direction of a normal to the
PDLC). However, in this liquid crystal material , a difference between the
extraordinary refractive index of the liquid crystal material and the refractive index of
the polymer material becomes pronounced in an oblique direction ; therefore, even if
the liquid crystal material has transparency in the front direction , the liquid crystal
30
material exhibits the scattering property in the oblique direction.
[0063] A typical light modulation device using the PDLC often has a configuration
in which the PDLC is sandwiched between two glass plates on which transparent
conductive films are formed. When light obliquely enters from air into the light
modulation device with the above-described configuration, the light incident from the
oblique direction is refracted by a refractive index difference between the air and the
glass plate to enter into the PDLC at a smaller angle. Therefore, large scattering does
not occur in such a light modulation device. For example, when light enters from air at
an angle of 80°, the incident angle of the light to the PDLC is reduced to
approximately 40° by refraction at a glass interface.
[0064] However, in an edge-light system with use of a light guide plate, as light
enters through the light guide plate, the light crosses the PDLC at a large angle of
approximately 80°. Accordingly, a difference between the extraordinary refractive
index of the liquid crystal material and the refractive index of the polymer material is
large, and light crosses the PDCL at a larger angle, thereby causing a longer optical
path subjected to scattering. For example, in the case where microparticles of a liquid
crystal material having an ordinary refractiveindex of 1.5 and an extraordinary
refractive index of 1.65 are dispersed in a polymer material having a refractive index
of 1.5, there is no refractive index difference in the front direction (the direction of the
normal to the PDLC), but the refractive index difference is large in the oblique
direction. Therefore, the scattering property in the oblique direction is not allowed to
be reduced, thereby causing low view angle characteristics. Further, in the case where
an optical film such as a diffuser film is disposed on the light guide plate, oblique leak
light is diffused also in the front direction by the diffuser film or the like, thereby
31
causing an increase in light leakage in the front direction and a decrease in a
modulation ratio in the front direction.
[0065] On the other hand, in the embodiment, as the bulk 34A and the microparticles
34B each include mainly an optical anisotropic material, the scattering property in an
oblique direction is reduced, thereby enabling to improve transparency. For example,
when the bulk 34A and the microparticles 34B include mainly the optical anisotropic
materials with ordinary refractive indices which are equal to each other and
extraordinary refractive indices which are also equal to each other, the directions of the
optical axes of the bulk 34A and the microparticles 34B coincide with or substantially
coincide with each other in a region where a voltage is not applied between the subelectrodes
32A' and 32B'. Therefore, the refractive index difference is reduced or
eliminated in all directions including the front direction (a direction of the normal to
the light modulation device 30) and the oblique direction, thereby obtaining high
transparency. As a result, the leakage of light in a range having a large view angle is
allowed to be reduced or substantially eliminated, and view angle characteristics are
allowed to be improved.
[0066] For example, when a liquid crystal having an ordinary refractive index of 1.5
and an extraordinary refractive index of 1.65, and a liquid crystal monomer having an
ordinary refractive index of 1.5 and an extraordinary refractive index of 1.65 are mixed,
and the liquid crystal monomer is polymerized in a state where the liquid crystal and
the liquid crystal monomer are aligned by an alignment film or an electric field, the
optical axis of the liquid crystal and the optical axis of a polymer formed by
polymerizing the liquid crystal monomer coincide with each other. Therefore, the
refractive indices are allowed to coincide with each other in all directions, thereby
32
enabling to achieve a state where transparency is high, and to further improve the view
angle characteristics.
[0067] Moreover, in the embodiment, for example, as illustrated in FIGs. 8(A) and
(B), luminance in the transmission region 30A (luminance in black display) is lower,
compared to the case where the light modulation device 30 is not included (indicated
by the alternate long and short dash line in FIG. 8(B)). On the other hand, luminance
in the scattering region 30B is significantly increased, compared to the case where the
light modulation device 30 is not included (indicated by the alternate long and short
dash line in FIG. 8(B)), and luminance in white display is partially increased (partial
luminance enhancement) by a reduced amount of the luminance of the transmission
region 30A.
[0068] The partial luminance enhancement is a technique of enhancing luminance
when white display is partially performed, compared to the case where white display is
performed on an entire screen. The partial luminance enhancement is generally used in
a CRT, a PDP, or the like. However, in a liquid crystal display, as a backlight
uniformly emits light in an entire surface thereof irrespective of an image, the
luminance is not allowed to be partially enhanced. When an LED backlight in which a
plurality of LEDs are two-dimensionally arranged is used as the backlight, some of the
LEDs are allowed to be turned off. However, in such a case, diffusion light from dark
regions in which the LEDs are turned off disappears; therefore, the luminance becomes
lower, compared to the case where all of the LEDs are turned on. Also, the luminance
may be increased by increasing a current applied to some LEDs which are turned on;
however, in such a case, a large current flows for an extremely short time, thereby
causing an issue in terms of load and reliability of a circuit.
33
[0069] On the other hand, in the embodiment, as the bulk 34A and the microparticles
34B each include mainly the optical anisotropic material, the scattering property in the
oblique direction is suppressed to reduce leak light from the light guide plate in a dark
state. Therefore, as light is guided from a part in a partially-dark state to a part in a
partially-bright state, partial luminance enhancement is achievable without increasing
electric power supplied to the backlight 1.
[0070] Moreover, in the embodiment, the electrode 32 is disposed on only the
surface of the transparent substrate 31 in the pair of transparent substrates 31 and 36
which allow the light modulation layer 34 to be sandwiched therebetween. Therefore,
for example, in the case where the electrode 32 is configured of an ITO film, a light
absorption amount by the electrode 32 when light emitted from the light source 20
repeatedly passes through the electrode 32 in the light modulation device 30 while
propagating through the light guide plate 10 is smaller, compared to the case where the
electrodes are disposed on the surfaces of both of the transparent substrates 31 and 36
in the light modulation device 30. Further, as the light absorption amount by the
electrode 32 is small, a change in chromaticity of illumination light in a plane is also
small. As a result, chromaticity of illumination light is allowed to be further
uniformized in a plane while suppressing a reduction in light extraction efficiency.
[00711 (2. Second Embodiment)
FIG. 12(A) is a sectional view illustrating an example of a schematic
configuration of a backlight 2 (an illumination unit) according to a second embodiment
of the invention. FIG. 12(B) is a sectional view illustrating an example of a specific
configuration of the backlight 2 in FIG. 12(A). It is to be noted that FIGs. 12(A) and
(B) are schematic illustrations, and dimensions and shapes in the illustrations are not
34
necessarily the same as actual dimensions and shapes.
[0072] The backlight 2 according to the embodiment is distinguished from the
backlight 1 according to the above-described first embodiment and modifications
thereof by the fact that a light modulation device 60 is included instead of the light
modulation device 30. Description will be given of, mainly, points different from the
above-described embodiment, and points common to the above-described embodiment
will not be further described.
[0073] In the embodiment, the light modulation device 60 is in close contact with a
back side (the bottom surface) of the light guide plate 10 without an air layer in
between, and is bonded to the back side of the light guide plate 10 with, for example,
an adhesive (not illustrated) in between. For example, as illustrated in FIG. 12(B), the
light modulation device 60 is configured by arranging the transparent substrate 31, the
electrode 32, an alignment film 63, a light modulation layer 64, an alignment film 65,
and the transparent substrate 36 in order from a side closer to the reflective plate 40.
[0074] The alignment films 63 and 65 align, for example, a liquid crystal or a
monomer used in the light modulation layer 64. Kinds of alignment films include a
vertical alignment film and a horizontal alignment film, and in the embodiment,
vertical alignment films are used as the alignment films 63 and 65. The vertical
alignment films may be made of a silane coupling material, polyvinyl alcohol (PVA), a
polyimide-based material, a surfactant, or the like. Moreover, when plastic films are
used as the transparent substrates 31 and 36, it is preferable that in a manufacturing
process, a firing temperature after coating the surfaces of the transparent substrates 31
and 36 with the alignment films 63 and 65 be as low as possible; therefore, a silane
coupling material capable of using an alcohol-based solvent is preferably used as the
35
alignment films 63 and 65.
[0075] It is to be noted that as the vertical alignment films, vertical alignment films
having a function of providing a pretilt to liquid crystal molecules in contact therewith
may be used. Examples of a method of developing a pretilt function in the vertical
alignment film include rubbing. The above-described vertical alignment films may
have, for example, a function of allowing long axes of liquid crystal molecules in
proximity to the vertical alignment film to intersect with a normal to the vertical
alignment film at a slight angle.
[0076] However, when the vertical alignment films are used as the alignment films
63 and 65, as liquid crystal molecules included in microparticles 64B which will be
described later, liquid crystal molecules having negative dielectric constant anisotropy
(a so-called negative type liquid crystal) are used in some cases, but in the embodiment,
liquid crystal molecules having positive dielectric constant anisotropy (a so-called
positive type liquid crystal) are used.
[0077] Next, the light modulation layer 64 in the embodiment will be described
below. For example, as illustrated in FIG. 12(B), the light modulation layer 64 is a
composite layer including a bulk 64A and a plurality of microparticles 64B dispersed
in the bulk 64A. The bulk 64A and the microparticles 64B have optical anisotropy.
[0078] FIG. 13 schematically illustrates an example of an alignment state in the bulk
64A and the microparticles 64B when a voltage is not applied between the first
electrode 32A and the second electrode 32B (or the sub-electrodes 32A' and 3213'). An
ellipsoid 164A in FIG. 13 represents an example of a refractive index ellipsoid
exhibiting refractive index anisotropy of the bulk 64A when a voltage is not applied
between the first electrode 32A and the second electrode 32B (or the sub-electrodes
36
32A' and 3213'). An ellipsoid 164B in FIG. 13 represents an example of a refractive
index ellipsoid exhibiting refractive index anisotropy of the microparticle 64B when a
voltage is not applied between the first electrode 32A and the second electrode 32B (or
the sub-electrodes 32A' and 32B').
[0079] FIG. 14 schematically illustrates an example of an alignment state in the bulk
64A and the microparticles 64B when a voltage is applied between the first electrode
32A and the second electrode 32B (or the sub-electrodes 32A' and 32B'). An ellipsoid
164A in FIG. 14 represents an example of a refractive index ellipsoid exhibiting
refractive index anisotropy of the bulk 64A when a voltage is applied between the first
electrode 32A and the second electrode 32B (or the sub-electrodes 32A' and 32B'). An
ellipsoid 164B in FIG. 14 represents an example of a refractive index ellipsoid
exhibiting refractive index anisotropy of the microparticle 64B when a voltage is
applied between the first electrode 32A and the second electrode 32B (or the subelectrodes
32A' and 32B').
[0080] For example, as illustrated in FIG. 13, the bulk 64A and the microparticle
64B are structured to allow the direction of an optical axis AX3 of the bulk 64A (a
long axis of the ellipsoid 164A) and the direction of an optical axis AX4 of the
microparticle 64B (a long axis of the ellipsoid 164B) to coincide with (be parallel to)
each other when a voltage is not applied between the first electrode 32A and the
second electrode 32B (or the sub-electrodes 32A' and 32B'). It is to be noted that the
optical axes AX3 and AX4 each indicate a line parallel to a travel direction of a light
beam allowing a refractive index to have one value irrespective of polarization
direction. Moreover, it is not necessary for the directions of the optical axis AX3 and
the optical axis AX4 to consistently coincide with each other when a voltage is not
37
applied between the first electrode 32A and the second electrode 32B (or the subelectrodes
32A' and 32B'), and the direction of the optical axis AX3 and the direction
of the optical axis AX4 may be slightly deviated from each other due to, for example, a
manufacturing error.
[0081] Moreover, the optical axis AX4 is parallel to the light incident surface l0A of
the light guide plate 10 as well as parallel to a normal to the surface of the transparent
substrate 31 when a voltage is not applied between the first electrode 32A and the
second electrode 32B (or the sub-electrodes 32A' and 32B'). In other words, when a
voltage is not applied between the first electrode 32A and the second electrode 32B (or
the sub-electrodes 32A' and 3213'), the optical axis AX4 is orthogonal to a plane
including the first electrode 32A and the second electrode 32B (or the sub-electrodes
32A' and 32B`).
[0082] On the other hand, the bulk 64A is structured to have a fixed optical axis AX3
irrespective of whether or not a voltage is applied between the first electrode 32A and
the second electrode 32B (or the sub-electrodes 32A' and 32B'). More specifically,
the optical axis AX3 is parallel to the light incident surface 10A of the light guide plate
10 as well as parallel to the normal to the surface of the transparent substrate: 31. In
other words, when a voltage is not applied between the first electrode 32A and the
second electrode 32B (or the sub-electrodes 32A' and 32B'), the optical axis AX3 is
parallel to the optical axis AX4.
[0083] It is to be noted that it is not necessary for the optical axis AX4 to be
consistently parallel to the light incident surface 10A of the light guide plate 10 as well
as the normal to the surface of the transparent substrate 31, and the optical axis AX4
may be aligned in a direction intersecting with one or both of the light incident surface
38
l0A and the normal to the surface of the transparent substrate 31 at a small angle due
to, for example, a manufacturing error.
[0084] In this case, ordinary refractive indices of the bulk 64A and the microparticle
64B are preferably equal to each other, and extraordinary refractive indices of the bulk
64A and the microparticle 64B are preferably equal to each other. In this case, for
example, when a voltage is not applied between the first electrode 32A and the second
electrode 32B (or the sub-electrodes 32A' and 32B'), there is little difference in
refractive index in all directions including the front direction and the oblique direction,
and high transparency is obtained. Therefore, for example, light toward the front
direction and light toward the oblique direction pass through the light modulation layer
64 without being scattered in the light modulation layer 64. As a result, as illustrated
in FIGs. 8(A) and (B), the light L from the light source 20 (light from the oblique
direction) is totally reflected by an interface (an interface between the transparent
substrate 31 or the light guide plate 10 and the air) of a transparent region (the
transmission region 30A) in the light modulation device 60, and luminance (luminance
in black display) of the transmission region 30A is decreased, compared to the case
where the light modulation device 60 is not included (indicated by the alternate long
and short dash line in FIG. 8(B)).
[0085]- Moreover, for example, as illustrated in FIG. 14, the bulk 64A and the
microparticle 64B are structured to allow the directions of the optical axis AX3 and the
optical axis AX4 to be different from (intersect with or be orthogonal to) each other
when a voltage is applied between the first electrode 32A and the second electrode 32B
(or the sub-electrodes 32A' and 32B'). Further, for example, the microparticles 64B
are structured to allow the optical axis AX4 to be parallel to the normal to the light
39
incident surface I OA of the light guide plate 10 as well as parallel to the surface of the
transparent substrate 31 when a voltage is applied between the first electrode 32A and
the second electrode 32B (or the sub-electrodes 32A' and 321'). In other words, when
a voltage is applied between the first electrode 32A and the second electrode 32B (or
the sub-electrodes 32A' and 32B'), the optical axis AX4 is parallel to a plane including
the first electrode 32A and the second electrode 32B (or the sub-electrodes 32A' and
3213') as well as intersects with (or is orthogonal to) the extending direction of comb
teeth of the sub-electrodes 32A' and 3213'.
[0086] Therefore, when a voltage is applied between the first electrode 32A and the
second electrode 32B (or the sub-electrodes 32A' and 3213'), in the light modulation
layer 64, a difference in refractive index in all directions in a plane which is parallel to
the normal to the light incident surface IOA as well as is orthogonal to the surface of
the transparent substrate 31 is increased to obtain a high scattering property.
Accordingly, for example, light toward the front direction and light toward the oblique
direction are scattered in the light modulation layer 64. As a result, for example, as
illustrated in FIGs. 8(A) and (B), the light L from the light source 20 (light from the
oblique direction) passes through an interface (an interface between the transparent
substrate 31 or the light guide plate 10 and the air) of the scattering region 30B, and
light having passed toward the reflective plate 40 is reflected by the reflective plate 40
to pass through the light modulation device 60. Therefore, the luminance of the
scattering region 30B is extremely higher than that in the case where the light
modulation device 60 is not included (indicated by the alternate long and short dash
line in FIG. 8(B)), and luminance in white display is partially increased (partial
luminance enhancement) by a reduced amount of the luminance of the transmission
40
region 30A.
[0087] It is to be noted that the ordinary refractive indices of the bulk 64A and the
microparticle 64B may be slightly different from each other due to, for example, a
manufacturing error, and are preferably, for example, 0.1 or less, and more preferably
0.05 or less. Moreover, the extraordinary refractive indices of the bulk 64A and the
microparticle 64B may be slightly different from each other due to, for example, a
manufacturing error, and are preferably, for example, 0.1 or less, and more preferably
0.05 or less.
[0088] Moreover, a refractive index difference (=extraordinary refractive
index-ordinary refractive index) in the bulk 64A and a refractive index difference
(=extraordinary refractive index-ordinary refractive index) in the microparticle 64B
are preferably as large as possible, and are preferably 0.05 or over, more preferably 0.1
or over, and still more preferably 0.15 or over. In the case where the refractive index
differences in the bulk 64A and the microparticle 64B are large, the scattering power
of the light modulation layer 34 is enhanced to allow light guide conditions to be easily
disrupted, thereby allowing light from the light guide plate 10 to be easily extracted.
[0089] Further, the bulk 64A and the microparticle 64B have different response
speeds with respect to an electric field. The bulk 64A has, for example, a streaky
structure or a porous structure which does not respond to an electric field, or a rod-like
structure having a response speed slower than that of the microparticle 64B. The bulk
64A is formed of, for example, a polymer material obtained by polymerizing a lowmolecular
monomer. The bulk 64A is formed, for example, by polymerizing, by one
or both of heat and light, a material (for example, a monomer) with orientation and
polymerization which is aligned along the alignment direction of the microparticles
41
64B or the alignment directions of the alignment films 63 and 65. On the other hand,
the microparticles 64B mainly include, for example, a liquid crystal material, and have
a response speed sufficiently higher than that of the bulk 64A. Examples of the liquid
crystal material (liquid crystal molecules) included in the microparticles 64B include
rod-like molecules.
[0090] In this case, when a voltage is not applied between the first electrode 32A and
the second electrode 32B (the sub-electrodes 32A' and 3213'), the long-axis directions
of the liquid crystal molecules in the microparticles 64B are parallel to the optical axis
AX3. At this time, the long axes of the liquid crystal molecules in the microparticles
64B are parallel to the light incident surface 10A of the light guide plate 10 as well as
parallel to the direction of the normal to the surface of the transparent substrate 31.
Moreover, when a voltage is applied between the first electrode 32A and the second
electrode 32B (or the sub-electrodes 32A' and 3213'), the long-axis directions of the
liquid crystal molecules in the microparticles 64B intersect with (or are orthogonal to)
the optical axis AX3. At this time, the long axes of the liquid crystal molecules in the
microparticles 64B are parallel to the normal to the light incident surface 10A of the
light guide plate 10 as well as parallel to the surface of the transparent substrate 31.
[0091] The above-described monomer having orientation and polymerization may be
a material having optical anisotropy and forming a composite material with a liquid
crystal; however, a low-molecular monomer which is cured with ultraviolet light is
preferable in this embodiment. It is preferable that, in a state where no voltage is
applied, directions of optical anisotropy of the liquid crystal and a resultant (a polymer
material) formed by polymerizing a low-molecular monomer coincide with each other;
therefore, before curing the low-molecular monomer with ultraviolet light, the liquid
42
crystal and the low-molecular monomer are preferably aligned in the same direction.
In the case where a liquid crystal is used as the microparticles 64B, when the liquid
crystal includes rod-like molecules, the used monomer material preferably has a rodlike
shape. As described above, a material having both of polymerization and liquid
crystal properties is preferably used as the monomer material, and, for example, the
monomer material preferably includes one or more functional groups selected from the
group consisting of an acrylate group, a methacrylate group, an acryloyloxy group, a
methacryloyloxy group, a vinyl ether group, and an epoxy group as polyincrizable
functional groups. These functional groups are allowed to be polymerized by
ultraviolet, infrared, or electron irradiation, or by heating. To suppress a reduction in
the degree of alignment under ultraviolet irradiation, a liquid crystal material having a
polyfuncitonal group may be added. In the case where the bulk 64A has the abovedescribed
streaky structure, as the material of the bulk 64A, a bifunctional liquid
crystal monomer is preferably used. Moreover, a monofunctional monomer may be
added to the material of the bulk 64A to adjust a temperature at which liquid crystal
properties are exhibited, or a tri- or more-functional monomer may be added to the
material of the bulk 64A to improve crosslink density.
[0092] Next, functions and effects of the backlight 2 according to the embodiment
will be described below.
[0093] In the backlight 2 according to the embodiment, a voltage is applied between
the sub-electrodes 32A' and 3213' of respective light modulation cells 30S to allow the
optical axes AX4 of the microparticles 64B in one light modulation cell 30S to be
parallel or substantially parallel to the optical axis AX3 of the bulk 64A, and to allow
the optical axes AX4 of the microparticles 64B in another light modulation cell 30S to
43
intersect with or be orthogonal to the optical axis AX3 of the bulk 64A. As a result,
light emitted from the light source 20 and entering into the light guide plate 10 passes
through the transmission region 30A where the optical axes AX3 and AX4 are parallel
or substantially parallel to each other of the light modulation device 60. On the other
hand, light emitted from the light source 20 and entering into the light guide plate 10 is
scattered in the scattering region 30B where the optical axes AX3 and AX4 intersect
with or are orthogonal to each other of the light modulation device 30. Light having
passed through a bottom surface of the scattering region 30B in the scattered light is
reflected by the reflective plate 40 to be returned to the light guide plate 10 again, and
then the light is emitted from a top surface of the backlight 2. Moreover, light toward
a top surface of the scattering region 30B in the scattered light passes through the light
guide plate 10, and then is emitted from the top surface of the backlight 2. Thus, in the
embodiment, light is hardly emitted from the top surface of the transmission region
30A, and light is emitted from the top surface of the scattering region 30B.
Accordingly, a modulation ratio in a front direction is increased.
[0094] On the other hand, in the embodiment, as the bulk 64A and the microparticles
64B each include mainly an optical anisotropic material, the scattering property in an
oblique direction is reduced, thereby enabling to improve transparency. For example,
the bulk 64A and the microparticles 64B include mainly the optical anisotropic
materials with ordinary refractive indices which are equal to each other and
extraordinary refractive indices which are also equal to each other, and in addition
thereto, the directions of the optical axes of the bulk 64A and the microparticles 64B
coincide with or substantially coincide with each other in a region where a voltage is
not applied between the sub-electrodes 32A' and 3213'. Therefore, the refractive index
44
difference is reduced or eliminated in all directions including the front direction (a
direction of the normal to the light modulation device 60) and the oblique direction,
thereby obtaining high transparency. As a result, the leakage of light in a range having
a large view angle is allowed to be reduced or substantially eliminated, and view angle
characteristics are allowed to be improved.
[0095] For example, when a liquid crystal having an ordinary refractive index of 1.5
and an extraordinary refractive index of 1.65, and a liquid crystal monomer having an
ordinary refractive index of 1.5 and an extraordinary refractive index of 1.65 are mixed,
and the liquid crystal monomer is polymerized in a state where the liquid crystal and
the liquid crystal monomer are aligned by an alignment film or an electric field, the
optical axis of the liquid crystal and the optical axis of a polymer formed by
polymerizing the liquid crystal monomer coincide with each other. Therefore, the
refractive indices coincide with each other in all directions, thereby enabling to achieve
a state where transparency is high, and to further improve the view angle
characteristics.
[0096] Moreover, in the embodiment, for example, as illustrated in FIGs. 8(A) and
(B), luminance in the transmission region 30A (luminance in black display) is lower,
compared to the case where the light modulation device 60 is not included (indicated
by the alternate long and short dash line in FIG. 8(B)). On the other hand, luminance
in the scattering region 30B is significantly increased, compared to the case where the
light modulation device 60 is not included (indicated by the alternate long and short
dash line in FIG. 8(B)), and luminance in white display is partially increased (partial
luminance enhancement) by a reduced amount of the luminance of the transmission
region 30A. It is because as the bulk 64A and the microparticles 64B each include
45
mainly the optical anisotropic material, the scattering property in the oblique direction
is suppressed to reduce leak light from the light guide plate in a dark state. Therefore,
as light is guided from a part in a partially-dark state to a part in a partially-bright state,
partial luminance enhancement is achievable without increasing electric power
supplied to the backlight 2.
[0097] Moreover, in the embodiment, the electrode 32 is disposed on only the
surface of the transparent substrate 31 in the pair of transparent substrates 31 and 36
which allow the light modulation layer 64 to be sandwiched therebetween. Therefore,
for example, in the case where the electrode 32 is configured of an ITO film, a light
absorption amount by the electrode 32 when light emitted from the light source 20
repeatedly passes through the electrode 32 in the light modulation device 60 while
propagating through the light guide plate 10 is smaller, compared to the case where the
electrodes are disposed on the surfaces of both of the transparent substrates 31 and 36
in the light modulation device 60. Further, as the light absorption amount by the
electrode 32 is small, a change in chromaticity of illumination light in a plane is also
small. As a result, chromaticity of illumination light is allowed to be further
uniformized while suppressing a reduction in light extraction efficiency.
[0098] (3. Modifications)
[First Modification]
In the above-described embodiments, the comb teeth of the first electrode 32A
and the second electrode 32B extend in a direction parallel to the extending direction
of the light source 20; however, for example, as illustrated in FIGs. 15(A) and (B),
they may extend in a direction intersecting with the extending direction of the light
source 20. At this time, the first electrode 32A and the second electrode 32B each may
46
be configured of, for example, a single structure formed on an entire surface of the
transparent substrate 31 as illustrated in FIGs. 15(A) to (C), or may be configured of,
for example, a plurality of structures (sub-electrodes 32A' and 3213') as illustrated in
FIGs. 16(A) to (C).
[0099] FIG. 17 schematically illustrates an example of an alignment state in the bulk
34A and the microparticles 34B when a voltage is not applied to the first electrode 32A
and the second electrode 32B (or the sub-electrodes 32A' and 3213'). FIG. 18
schematically illustrates an example of an alignment state in the bulk 34A and the
microparticles 34B when a voltage is applied to the first electrode 32A and the second
electrode 32B (or the sub-electrodes 32A' and 32B').
[0100] For example, as illustrated in FIG. 17, the bulk 34A and the microparticle
34B are structured to allow the direction of the optical axis AX1 of the bulk 34A (the
long axis of the ellipsoid 134A) and the direction of the optical axis AX2 of the
microparticle 34B (the long axis of the ellipsoid 134B) to coincide with (be parallel to)
each other when a voltage is not applied between the first electrode 32A and the
second electrode 32B (or the sub-electrodes 32A' and 3213').
[0101] Moreover, the optical axis AX2 is parallel to the normal to the light incident
surface 1OA of the light guide plate 10 as well as parallel to the surface of the
transparent substrate 31 when a voltage is not applied between the first electrode 32A
and the second electrode 32B (or the sub-electrodes 32A' and 3213'). In other words,
when a voltage is not applied between the first electrode 32A and the second electrode
32B (or the sub-electrodes 32A' and 3213'), the optical axis AX2 is parallel to a plane
including the first electrode 32A and the second electrode 32B (or the sub-electrodes
32A' and 3213') as well as parallel to the extending direction of the comb teeth of the
47
first electrode 32A and the second electrode 32B (or the sub-electrodes 32A' and 3213').
It is to be noted that it is not necessary for the directions of the optical axis AXl and
the optical axis AX2 to consistently coincide with each other when a voltage is not
applied between the first electrode 32A and the second electrode 32B (or the subelectrodes
32A' and 3213'), and the direction of the optical axis AX1 and the direction
of the optical axis AX2 may be slightly deviated from each other due to, for example, a
manufacturing error.
[0102] On the other hand, for example, the bulk 34A is structured to have a fixed
optical axis AX1 irrespective of whether or not a voltage is applied between the first
electrode 32A and the second electrode 32B (or the sub-electrodes 32A' and 3213').
More specifically, the optical axis AXl is parallel to the normal to the light incident
surface 10A of the light guide plate 10 as well as parallel to the surface of the
transparent substrate 31. In other words, when a voltage is not applied between the
first electrode 32A and the second electrode 32B (or the sub-electrodes 32A' and 32B'),
the optical axis AX1 is parallel to the optical axis AX2. It is to be noted that it is not
necessary for the optical axis AX2 to be consistently parallel to the normal to the light
incident surface 10A of the light guide plate 10 as well as the surface of the transparent
substrate 31, and the optical axis AX2 may be aligned in a direction intersecting with
one or both of the normal to the light incident surface 10A and the surface of the
transparent substrate 31 at a small angle due to, for example, a manufacturing error.
[0103] Moreover, for example, as illustrated in FIG. 18, the bulk 34A and the
microparticles 34B are structured to allow directions of the optical axes AX1 and AX2
to be different from (intersect with or be orthogonal to) each other when a voltage is
applied between the first electrode 32A and the second electrode 32B (or the sub48
electrodes 32A' and 32B'). Further, for example, the microparticles 34B are structured
to allow the optical axis AX2 to be parallel to the light incident surface 1OA of the
light guide plate 10 as well as parallel to the surface of the transparent substrate 31
when a voltage is applied between the first electrode 32A and the second electrode 32B
(or the sub-electrodes 32A' and 32B'). In other words, when a voltage is applied
between the first electrode 32A and the second electrode 32B (or the sub-electrodes
32A' and 32B'), the optical axis AX2 is parallel to a plane including the first electrode
32A and the second electrode 32B (or the sub-electrodes 32A' and 3213') and intersects
with (or is orthogonal to) the extending direction of comb teeth of the sub-electrodes
32A' and 3213'.
[0104] FIG. 19 schematically illustrates an example of an alignment state in the bulk
64A and the microparticles 64B in the above-described modification when a voltage is
not applied to the first electrode 32A and the second electrode 32B (or the subelectrodes
32A' and 3213'). FIG. 20 schematically illustrates an example of an
alignment state in the bulk 64A and the microparticles 64B in the above-described
modification when a voltage is applied between the first electrode 32A and the second
electrode 32B (or the sub-electrodes 32A' and 32B').
[0105] For example, as illustrated in FIG. 19, the bulk 64A and the microparticle
64B are structured to allow the direction of the optical axis AX3 of the bulk 64A (the
long axis of the ellipsoid 164A) and the direction of the optical axis AX4 of the
microparticle 64B (the long axis of the ellipsoid 164B) to coincide with (be parallel to)
each other when a voltage is not applied between the first electrode 32A and the
second electrode 32B (or the sub-electrodes 32A' and 32B'). Moreover, it is not
necessary for the directions of the optical axis AX3 and the optical axis AX4 to
49
consistently coincide with each other when a voltage is not applied between the first
electrode 32A and the second electrode 32B (or the sub-electrodes 32A' and 3213'), and
the direction of the optical axis AX3 and the direction of the optical axis AX4 may be
slightly deviated from each other due to, for example, a manufacturing error.
[0106] Moreover, the optical axis AX4 is parallel to the light incident surface 10A of
the light guide plate 10 as well as parallel to the normal to the surface of the
transparent substrate 31 when a voltage is not applied between the first electrode 32A
and the second electrode 32B (or the sub-electrodes 32A' and 3213'). In other words,
when a voltage is not applied between the first electrode 32A and the second electrode
32B (or the sub-electrodes 32A' and 3213'), the optical axis AX4 is orthogonal to a
plane including the first electrode 32A and the second electrode 32B (or the subelectrodes
32A' and 32B').
[0107] On the other hand, the bulk 64A is structured to have a fixed optical axis AX3
irrespective of whether or not a voltage is applied between the first electrode 32A and
the second electrode 32B (or the sub-electrodes 32A' and 32B'). More specifically, the
optical axis AX3 is parallel to the light incident surface 10A of the light guide plate 10
as well as parallel to the normal to the surface- of the transparent substrate 31. In other
words, when a voltage is not applied between the first electrode 32A and the second
electrode 32B (or the sub-electrodes 32A' and 3213'), the optical axis AX3 is parallel to
the optical axis AX4.
[0108] It is to be noted that it is not necessary for the optical axis AX4 to be
consistently parallel to the light incident surface 10A of the light guide plate 10 as well
as the normal to the surface of the transparent substrate 31, and the optical axis AX4
may be aligned in a direction intersecting with one or both of the light incident surface
50
1OA and the normal to the surface of the transparent substrate 31 at a small angle due
to, for example, a manufacturing error.
[0109] Moreover, for example, as illustrated in FIG. 20, the bulk 64A and the
microparticles 64B are structured to allow directions of the optical axis AX3 and the
optical axis AX4 to be different from (intersect with or be orthogonal to) each other
when a voltage is applied between the first electrode 32A and the second electrode 32B
(or the sub-electrodes 32A' and 32B'). Further, for example, the microparticles 64B
are structured to allow the optical axis AX4 to be parallel to the light incident surface
IOA of the light guide plate 10 as well as parallel to the surface of the transparent
substrate 31 when a voltage is applied between the first electrode 32A and the second
electrode 32B (or the sub-electrodes 32A' and 3213'). In other words, when a voltage is
applied between the first electrode 32A and the second electrode 32B (or the subelectrodes
32A' and 3213'), the optical axis AX4 is parallel to a plane including the first
electrode 32A and the second electrode 32B (or the sub-electrodes 32A' and 3213') as
well as intersects with (or is orthogonal to) the extending direction of comb teeth of the
sub-electrodes 32A' and 32B'.
[0110] In the above-described modification, when the alignment states in the bulk
34A and the microparticles 34B or the alignment states in the bulk 64A and the
microparticles 64B are as illustrated in the above FIGS. 17 to 19, the luminance in the
scattering region 30B is significantly increased, compared to the case where the light
modulation devices 30 and 60 are not included (indicated by the alternate long and
short dash line in FIG. 8(B)), and luminance in white display is partially increased
(partial luminance enhancement) by a reduced amount of the luminance of the
transmission region 30A.
51
[0111] Moreover, in the above-described modification, as in the case of the abovedescribed
embodiments and the like, the electrode 32 is disposed on only the surface of
the transparent substrate 31 in the pair of transparent substrates 31 and 36. Therefore,
for example, in the case where the electrode 32 is configured of an ITO film, a light
absorption amount by the electrode 32 when light emitted from the light source 20
repeatedly passes through the electrode 32 in the light modulation device 30 or 60
while propagating through the light guide plate 10 is smaller, compared to the case
where the electrodes are disposed on the surfaces of both of the transparent substrates
31 and 36 in the light modulation device 30 or 60. Further, as the light absorption
amount by the electrode 32 is small, a change in chromaticity of illumination light in a
plane is also small. As a result, chromaticity of illumination light is allowed to be
further uniformized while suppressing a reduction in light extraction efficiency.
[0112] [Second Modification]
In the above-described embodiments and modifications thereof, as the light
guide plate 10, a light guide plate with a pattern shape allowing light incident from the
light incident surface 10A to be scattered to be uniformized, or a flat light guide plate
without such a pattern shape is used; however, for example, as illustrated in FIG.
21(A), a light guide plate having a plurality of strip-like projections 11 on a top surface
thereof may be used. It is to be noted that, for example, as illustrated in FIG. 21(B),
the light guide plate 10 may have a plurality of strip-like projections 11 on a bottom
surface thereof. Moreover, for example, the light guide plate 10 may have a plurality
of strip-like projections 11 in the light guide plate 10 (not illustrated). Further, the
light guide plate 10 may be hollow, or may be densely packed.
[0113] The respective projections 11 extend in a direction parallel to the normal to
52
the light incident surface 10A, and, for example, as illustrated in FIGs. 21(A) and (B),
the projections 11 are successively formed from one side surface of the light guide
plate 10 to another side surface facing the side surface. A section in an arrangement
direction of each of the projections 11 has, for example, a rectangular shape, a
trapezoidal shape, or a triangular shape. In the case where the section in the
arrangement direction of each projection 11 has a rectangular shape, a rectilinear
propagation property of light is extremely high, and the projections 11 are suitable for
a large-scale backlight. In the case where the section in the arrangement direction of
each projection 11 has a trapezoidal shape, processing of a die used to form each
projection 11 by injection molding, extrusion molding, heat-press molding, or the like
is easy, and mold releasability in molding is high, and yields and molding speed are
allowed to be improved because of a reduction in defects.
[0114] A flat surface may or may not be disposed between adjacent projections 11.
The height of each of the projections 11 maybe uniform or nonuniform in a plane. For
example, as illustrated in FIGs. 22(A), when one side surface of the light guide plate
10 is the light incident surface 10A, the height of each of the projections 11 may be
smaller on a side closer to the light incident surface 10A, and be higher on a side closer
to a side surface facing the light incident surface 1OA. Moreover, for example,
although not illustrated, when a pair of facing side surfaces of the side surfaces of the
light guide plate 10 are light incident surfaces 10A, the height of each of the
projections I1 may be lower at and in proximity to both of the light incident surfaces
10A, and be higher in other regions. The height at and in proximity to the light
incident surface 10A of each of the projections 11 may be zero or substantially zero.
For example, as illustrated in FIG. 22(B), the height of each of the projections 11 may
53
be increased from a side closer to the light incident surface 1OA to a side surface facing
the light incident surface IOA. At this time, the height of each of the projections 11
may be uniform in a midway from the light incident surface l0A to the side surface
facing the light incident surface 10A. It is to be noted that a plurality of projections 11
with a nonuniform height as illustrated in FIGs. 22(A) and (B) may be disposed in a
region other than the top surface of the light guide plate 10, and, for example, the
plurality of projections 11 with a nonuniform height may be disposed on the bottom
surface of the light guide plate 10 or in the light guide plate 10.
[0115] As described above, when the height of each of the projections 11 (in other
words, the depth of a groove formed between the projections 11) varies, the rectilinear
propagation property of light is allowed to vary. For example, as illustrated in FIGS.
21(A) and (B), in the case where the projections I 1 are disposed on and in proximity to
the light incident surface 10A, and the light source 20 is configured of a plurality of
light source blocks 25 capable of being driven independently of one another, for
example, as illustrated in FIG. 23(A), when one light source block 25 illuminates, light
Ll emitted from the light source block 25 propagates through the light guide plate 10
while not spreading too much in a horizontal direction (a width direction). In this case,
a dark region may be generated between the point-like light sources 21 in proximity to
the light incident surface 10A, and in this case, image quality may be degraded.
Therefore, in such a case, for example, as illustrated in FIGs. 22(A) and (B), the height
of each of the projections I1 is preferably lower or zero at and in proximity to the light
incident surface 10A. In doing so, for example, as illustrated in FIG. 23(B), the light
L1 emitted from the light source block 25 is allowed to be spread in the horizontal
direction (the width direction) at a divergent angle of the point-like light source 23 at
54
and in proximity to the light incident surface 10A, thereby enabling to propagate with a
substantially uniform width in a region farther from the light incident surface 10A.
[0116] In this case, in the case were the electrode 32 is configured of a plurality of
sub-electrode pairs 32C, when light emitted from the light source block 25 propagates
through the light guide plate 10 as described above, partial lighting is allowed to be
performed by applying a voltage to one sub-electrode pair 32C.
[0117] For example, in the case where the plurality of sub-electrode pairs 32C (light
modulation cells 30S) extend in a direction parallel to the light incident surface 1OA
and are arranged in a direction parallel to the normal to the light incident surface 1 OA,
and a voltage is applied to only one light modulation cell 30S, as illustrated in FIG.
24(A), the light L1 emitted from one light source block 25 is mostly emitted from a
section where light emitted from one light source block 25 passes of the light
modulation cell 30S to which the voltage is applied. In this case, in a section profile of
luminance in a direction parallel to the light incident surface I OA in FIG. 24(A), a
boundary between a lighting section and a non-lighting section is moderately blurred;
therefore, it is difficult to visually identify the boundary. As a result, contrast is
allowed to be improved without reducing image quality.
[0118] Moreover, for example, in the case were the plurality of sub-electrode pairs
32C (the light modulation cells 30S) extend in a direction parallel to the normal to the
light incident surface IOA and are arranged in a direction parallel to the light incident
surface 10A, and a voltage is applied to only one light modulation cell 30S, as
illustrated in FIG. 24(B), the light Ll emitted from one light source block 25 is mostly
emitted from a section where light emitted from one light source block 25 passes (for
example, the entire light modulation cell 30S to which the voltage is applied) of the
55
light modulation cell 30S to which the voltage is applied.
[0119] Further, for example, in the case where the plurality of sub-electrode pairs
32C (the light modulation cells 30S) are two-dimensionally arranged and a voltage is
applied to only one light modulation cell 30S, as illustrated in FIG. 24(C), the light Ll
emitted from one light source block 25 is mostly emitted from a section where light
emitted from one light source block 25 passes (for example, the entire light modulation
cell 30S to which the voltage is applied) of the light modulation cell 30S to which the
voltage is applied.
[0120] In the above-described respective examples, in the case where the height of
each of the projections 11 of the light guide plate 10 is smaller at and in proximity to
the light incident surface 10A, even if a voltage is applied to the light modulation cells
30S in proximity to the light incident surface 10A to allow the light Ll to be emitted
from a section in proximity to the light incident surface 1OA, in-plane luminance of the
light Ll (illumination light) emitted from the light modulation cells 30A is allowed to
be further uniformized.
[0121] [Third Modification]
In the above-described embodiments and modifications thereof, the light
modulation devices 30 and 60 each are in close contact with and are bonded to the
back side (the bottom surface) of the light guide plate 10 without an air layer in
between; however, for example, as illustrated in FIG. 25, the light modulation devices
30 and 60 each may be in close contact with and bonded to the top surface of the light
guide plate 10 without an air layer in between. Moreover, for example, as illustrated in
FIG. 26, the light modulation devices 30 and 60 each may be disposed in the light
guide plate 10. However, also in this case, it is necessary for the light modulation
56
devices 30 and 60 to be in close contact with and bonded to the light guide plate 10
without an air layer in between.
[0122] Moreover, in the above-described embodiments, no component is specifically
disposed on the light guide plate 10; however, for example, as illustrated in FIG. 27, an
optical sheet 70 (for example, a diffuser plate, a diffuser sheet, a lens film, a
polarization splitter sheet, or the like) may be disposed. In such a case, a part of light
emitted from the light guide plate 10 in an oblique direction rises in the front direction;
therefore, a modulation ratio is allowed to be effectively improved.
[0123] [Fourth Modification]
Moreover, in the above-described respective embodiments and modifications
thereof, one or both of the transparent substrate 31 and the transparent substrate 37
may be integrally formed with the light guide plate 10. For example, in the abovedescribed
embodiments and modifications thereof, in the case where the transparent
substrate 37 is in contact with the light guide plate 10, the transparent substrate 37 may
be integrally formed with the light guide plate 10. At this time, the transparent
substrate 37 corresponds to a specific example of "first transparent substrate" or
"second transparent substrate". Moreover, for example, in the above-described
respective embodiments and modifications thereof, in the case where the transparent
substrate 31 is in contact with the light guide plate 10, the transparent substrate 31 may
be integrally formed with the light guide plate 10. At this time, the transparent
substrate 31 corresponds to a specific example of "first transparent substrate" or
"second transparent substrate". Further, for example, in the above-described respective
embodiments and modifications thereof, in the case where the transparent substrates 31
and 37 are in contact with the light guide plate 10, the transparent substrates 31 and 37
57
may be integrally formed with the light guide plate 10. At this time, the transparent
substrate 31 or the transparent substrate 37 corresponds to a specific example of "first
transparent substrate" or "second transparent substrate".
[0124] (Application Example)
Next, an application example of the backlights 1 and 2 according to the abovedescribed
embodiments will be described below.
[0125] FIG. 28 illustrates an example of a schematic configuration of a display 3
according to the application example. The display 3 includes a display panel 80, and
the backlight 1 or 2 disposed behind the display panel 80.
[0126] The display panel 80 displays an image. The display panel 80 includes a
plurality of pixels which are arranged in a matrix, and is allowed to display an image
by driving the plurality of pixels based on an image signal. The display panel 80 is, for
example, a transmissive liquid crystal display panel, and has a configuration in which a
liquid crystal layer is sandwiched between a pair of transparent substrates. Although
not illustrated, the display panel 80 includes, for example, a polarizer, a transparent
substrate, pixel electrodes, an alignment film, a liquid crystal layer, an alignment film,
a common electrode, a color. filter, a transparent substrate, and a polarizer in order
from a side closer to the backlight 1 or 2.
[0127] The transparent substrates are configured of substrates transparent to visible
light, for example, plate glass . It is to be noted that an active drive circuit (not
illustrated) including TFTs (thin film transistors), wiring, and the like electrically
connected to the pixel electrodes is formed on the transparent substrate located closer
to the backlight 1. The pixel electrodes and the common electrode are made of, for
example, indium tin oxide (ITO). The pixel electrodes are arranged in a lattice
58
arrangement or a delta arrangement on the transparent substrate, and function as
electrodes for respective pixels. On the other hand, the common electrode is formed
on an entire surface of the color filter, and functions as a common electrode facing the
respective pixel electrodes. The alignment films are made of a polymer material such
as polyimide, and perform an alignment process on a liquid crystal. The liquid crystal
layer is made of, for example, a VA (Vertical Alignment) mode, TN (Twisted
Nematic) mode or STN (Super Twisted Nematic) mode liquid crystal, and has a
function of changing the direction of a polarizing axis of emitted light from the
backlight 1 or 2 in each pixel by a voltage applied from the drive circuit (not
illustrated). It is to be noted that liquid crystal alignment is changed in a stepwise
manner to adjust the direction of a transmission axis of each pixel in a stepwise manner.
In the color filter, color filters separating light having passed through the liquid crystal
layer into, for example, three primary colors of red (R), green (G), and blue (B), or
four colors such as R, G, B, and white (W), respectively, are arranged corresponding to
the arrangement of the pixel electrodes. Typical filter arrangements (pixel
arrangements) include a stripe arrangement, a diagonal arrangement, a delta
arrangement, and a rectangular arrangement.
[0128] The polarizers are optical shutters of one kind, and allow only light (polarized
light) in a certain vibration direction to pass therethrough. It is to be noted that the
polarizers may be absorption polarizers absorbing light (polarized light) in a vibration
direction other than a transmission axis, but the polarizers are preferably reflective
polarizers reflecting light toward the backlight 1 or 2 in terms of an improvement in
luminance. The polarizers are disposed to allow their polarizing axes to be different by
90° from each other, thereby allowing emitted light from the backlight 1 to pass
59
therethrough via the liquid crystal layer, or to be shielded.
[0129] For example, the drive circuit 50 controls the magnitude of a voltage applied
to the sub-electrodes 32A' and 3213' of each of the light modulation cells 30S to allow
the optical axes AX2 or AX4 of the microparticles 34B or 64B in a cell corresponding
to a black-display pixel position of the plurality of light modulation cells 30S to be
parallel to the optical axis AXl or AX3 of the bulk 34A or 64A, as well as to allow the
optical axes AX2 or AX4 of the microparticles 34B or 64B in a cell corresponding to a
white-display pixel position of the plurality of light modulation cells 30S to intersect
with the optical axis AXl or AX3 of the bulk 34A or 64A.
[0130] In the application example, as a light source applying light to the display
panel 80, the backlight 1 or 2 according to the above-described embodiments is used.
Therefore, while the leakage of light in a range having a large view angle is allowed to
be reduced or substantially eliminated, display luminance is allowed to be improved.
As a result, a modulation ratio in a front direction is allowed to be increased.
Moreover, partial luminance enhancement is achievable without increasing electric
power supplied to the backlight 1 or 2.
[0131] Moreover, in the application example, the backlight 1 or 2 partially modulates
intensity of light entering into the display panel 80 based on a display image. However,
when an abrupt change in brightness occurs in pattern edge sections of the subelectrodes
32A' and 3213' included in the light modulation device 30 or 60, a boundary
section thereof is observed even in a display image. Therefore, a characteristic, called
blur characteristic, is demanded to change brightness at an electrode boundary section
as monotonously as possible. A diffuser plate with high diffusibility is effectively used
to enhance the blur characteristic; however, when diffusibility is high, total light beam
60
transmittance is reduced, thereby causing a tendency to reduce brightness. Therefore,
in the application example, when a diffuser plate is used as the optical sheet 70, the
total light beam transmittance of the diffuser plate is preferably 50% to 85%, and more
preferably 60% to 80%. Moreover, the blur characteristic is improved with an increase
in spatial distance between the light guide plate 10 and the diffuser plate in the
backlight 1 or 2.
[0132] Further, in the case where a light guide plate including a plurality of
projections 11 on a top surface thereof is used as the light guide plate 10, and an
electrode configured of a plurality of sub-electrode pairs 32C is used as the electrode
32, and a plurality of light source blocks 25 capable of being driven independently of
one another are used as the light source 20, when only some of the light source blocks
25 illuminate and a voltage is applied to some of the sub-electrode pairs 32C, the blur
characteristic is improved. Moreover, when the number of sub-electrode pairs 32C
included in the light modulation device 30 is increased and a voltage applied to
respective sub-electrode pairs 32C is adjusted to change lightness or darkness as
monotonously as possible, the blur characteristic is improved.
61

CLAIMS
1. An illumination unit comprising:
a first transparent substrate and a second transparent substrate disposed to be
separated from and face each other;
a light source emitting light to an end surface of the first transparent substrate
or the second transparent substrate;
an electrode disposed on a surface of the first transparent substrate or the
second transparent substrate and generating an electric field in a direction parallel to
the surface of the first transparent substrate; and
a light modulation layer disposed in a gap between the first transparent
substrate and the second transparent substrate and exhibiting a scattering property or
transparency with respect to light from the light source, depending on magnitude of the
electric field.
2. The illumination unit according to claim 1, wherein
the electrode includes a first electrode having comb teeth which extend in a
first direction and a second electrode having comb teeth which are disposed alternately
with the comb teeth of the first electrode.
3. The illumination unit according to claim 2, wherein
the first direction is parallel to a side surface facing the light source of side
surfaces of the first transparent substrate.
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4. The illumination unit according to claim 2, wherein
the first direction is parallel to a normal to a side surface facing the light
source of side surfaces of the first transparent substrate.
5. The illumination unit according to claim 2, wherein
the first electrode and the second electrode each are configured of a plurality
of sub-electrodes.
6. The illumination unit according to claim 5, wherein
the plurality of sub-electrodes are arranged in a direction parallel to a side
surface facing the light source of side surfaces of the first transparent substrate.
7. The illumination unit according to claim 5, wherein
the plurality of sub-electrodes are arranged in a direction parallel to a normal
to a side surface facing the light source of side surfaces of the first transparent
substrate.
8. The illumination unit according to claim 5, wherein
the plurality of sub-electrodes are two-dimensionally arranged.
9. The illumination unit according to claim 5, comprising a drive circuit
applying a voltage to respective sub-electrodes, the voltage being modulated according
to a distance from the light source.
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10. The illumination unit according to claim 9, wherein
the drive circuit applies a voltage to respective sub-electrodes, the voltage
being modulated according to the distance from the light source and an image signal.
11. The illumination unit according to claim 1, wherein
the light source is configured of a plurality of light source blocks capable of
being driven independently of one another.
12. The illumination unit according to claim 11, wherein
the drive circuit applies, to respective light source blocks, a voltage or a
current being modulated according to a distance from the light source to a subelectrode
to which a voltage is to be applied and an image signal.
13. The illumination unit according to claim 11, wherein
the first transparent substrate or the second transparent substrate has a
plurality of projections extending in a direction parallel to a normal to a side surface
facing the light source of side surfaces of the first transparent substrate or the second
transparent substrate.
14. The illumination unit according to claim 13, wherein
a section in a direction orthogonal to a projection extending direction of each
of the projections has a rectangular shape, a trapezoidal shape, or a triangular shape.
15. The illumination unit according to claim 13, wherein
64
a height of each of the projections is smaller at a shorter distance from the
light source and larger at a longer distance from the light source.
16. The illumination unit according to claim 15 , wherein
the height of each of the projections is zero closest to the light source.
17. The illumination unit according to claim 1, wherein
the light modulation layer exhibits transparency when a voltage is not applied
to the electrode and exhibits a scattering property when a voltage is applied to the
electrode.
18. The illumination unit according to claim 1, wherein
the light modulation layer is configured by including liquid crystal molecules
and a polymer, the liquid crystal molecules having faster response speed with respect
to an electric field generated by the electrode, the polymer having slower response
speed with respect to the electric field generated by the electrode.
19. The illumination unit according to claim 18, wherein
the electrode includes a first electrode having comb teeth extending in a first
direction and a second electrode having comb teeth arranged alternately with the comb
teeth of the first electrode, and
the liquid crystal molecules and the polymer are aligned in an extending
direction of the comb teeth of the first electrode when a voltage is not applied to the
65
electrode.
20. The illumination unit according to claim 18, wherein
the liquid crystal molecules and the polymer are aligned in a direction of a
normal to the first transparent substrate when a voltage is not applied to the electrode.
21. A display comprising:
a display panel including a plurality of pixels arranged in a matrix and being
driven based on an image signal; and
an illumination unit illuminating the display panel,
the illumination unit including
a first transparent substrate and a second transparent substrate disposed to be
separated from and face each other,
a light source emitting light to an end surface of the first transparent substrate
or the second transparent substrate,
an electrode disposed on a surface of the first transparent substrate or the
second transparent substrate and generating an electric field in a direction parallel to
the surface of the first transparent substrate, and
a light modulation layer disposed in a gap between the first transparent
substrate and the second transparent substrate and exhibiting a scattering property or
transparency with respect to light from the light source, depending on magnitude of the
electric field.
Dated this 13/6/2012