U.S. patent application number 14/722398 was filed with the patent office on 2015-09-10 for liquid crystal display.
The applicant listed for this patent is Japan Display Inc.. Invention is credited to Masaya TAMAKI.
Application Number | 20150253619 14/722398 |
Document ID | / |
Family ID | 49113837 |
Filed Date | 2015-09-10 |
United States Patent
Application |
20150253619 |
Kind Code |
A1 |
TAMAKI; Masaya |
September 10, 2015 |
LIQUID CRYSTAL DISPLAY
Abstract
A liquid crystal display is provided including an anisotropic
scatterer provided on a front substrate side of a front substrate,
wherein the anisotropic scatterer includes low refractive index
regions and high refractive index regions, wherein high-low-index
boundaries are disposed between the low refractive index regions
and high refractive index regions, and wherein the anisotropic
scatterer is disposed such that ambient light is scattered when
light is incident from a direction substantially following the
direction that the high-low-index boundaries extend, and such that
the light is transmitted when light is incident from a direction
substantially perpendicular to the direction that the
high-low-index boundaries extends.
Inventors: |
TAMAKI; Masaya; (Kanagawa,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Japan Display Inc. |
Tokyo |
|
JP |
|
|
Family ID: |
49113837 |
Appl. No.: |
14/722398 |
Filed: |
May 27, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13743013 |
Jan 16, 2013 |
9069209 |
|
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14722398 |
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Current U.S.
Class: |
349/112 |
Current CPC
Class: |
G02F 1/13363 20130101;
G02F 1/133504 20130101; G02F 2203/02 20130101 |
International
Class: |
G02F 1/1335 20060101
G02F001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 12, 2012 |
JP |
2012-054242 |
Claims
1. A liquid crystal display which is a reflective liquid crystal
display, comprising: a front substrate; a rear substrate; and a
liquid crystal material layer disposed between the front substrate
and the rear substrate, wherein an anisotropic scatterer, which is
disposed such that a direction where scattering characteristics are
the maximum is aligned with a normal observing direction, is
provided on a front substrate side of the front substrate, wherein
the anisotropic scatterer includes low refractive index regions and
high refractive index regions, wherein high-low-index boundaries
are disposed between the low refractive index regions and high
refractive index regions, and wherein the anisotropic scatterer is
disposed such that ambient light is scattered when light is
incident from a direction substantially following the direction
that the high-low-index boundaries extend, and such that the light
is transmitted when light is incident from a direction
substantially perpendicular to the direction that the
high-low-index boundaries extends.
2. The liquid crystal display according to claim 1, wherein the
anisotropic scatterer is disposed such that ambient light, which is
reflected on a front surface side of the rear substrate and is
incident on the anisotropic scatterer, is scattered when emitted
toward the front substrate side.
3. The liquid crystal display according to claim 1, wherein the
anisotropic scatterer is formed by laminating a plurality of
scattering members.
4. The liquid crystal display according to claim 1, wherein the
liquid crystal display performs grayscale display using an area
ratio grayscale method.
5. The liquid crystal display according to claim 1, wherein the
anisotropic scatterer is disposed such that ambient light from
outside is incident on the anisotropic scatter and scattered before
being reflected by a front surface side of the rear substrate.
6. The liquid crystal display according to claim 1, wherein the low
refractive index regions and the high refractive index regions are
tilted such that the high-low-index boundaries and thickness
direction of the anisotropic scatter form an angle.
7. The liquid crystal display according to claim 6, wherein the
anisotropic scatterer has a configuration in which the low
refractive index regions and the high refractive index regions are
formed in a louver shape.
8. The liquid crystal display according to claim 6, wherein the
anisotropic scatterer has a configuration in which each of the high
refractive index regions form a columnar region and the low
refractive index regions surround the high refractive index
regions.
9. An anisotropic scatterer provided in a reflective liquid crystal
display, the anisotropic scatterer being disposed in the reflective
liquid crystal display such that a direction where scattering
characteristics are the maximum is aligned with a normal observing
direction, the anisotropic scatterer comprising: low refractive
index regions; and high refractive index regions, wherein
high-low-index boundaries are disposed between the low refractive
index regions and high refractive index regions, and wherein the
anisotropic scatterer is disposed such that ambient light is
scattered when light is incident from a direction substantially
following the direction that the high-low-index boundaries extend,
and such that the light is transmitted when light is incident from
a direction substantially perpendicular to the direction that the
high-low-index boundaries extends.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 13/743,013, filed on Jan. 16, 2013, which
claims priority to Japanese Priority Patent Application JP
2012-054242 filed in the Japan Patent Office on Mar. 12, 2012, the
entire content of which is hereby incorporated by reference.
BACKGROUND
[0002] The present disclosure relates to a liquid crystal display.
More specifically, the present disclosure relates to a reflective
liquid crystal display which displays images by controlling the
reflectance of ambient light.
[0003] A reflective liquid crystal display includes a pixel
electrode or a reflective film which reflects ambient light, and
changes states of a liquid crystal material layer so as to control
the reflectance of ambient light, thereby displaying images. The
reflective liquid crystal display can achieve low power
consumption, a thinner display, and light weight, and is thus used
as, for example, a display device of a portable electronic
apparatus. In addition, for example, as disclosed in
JP-A-2005-148424, there has been proposed a liquid crystal display
of a so-called area ratio grayscale method in which each pixel
(each subpixel in color display) has a set of pixel electrodes, a
voltage applied to the set of pixel electrodes is controlled for
each pixel electrode so as to vary the area of a region provided
for display, thereby performing grayscale display.
[0004] In the reflective liquid crystal display, for example, if a
potential of a common electrode varies due to exposure to ambient
light for a long time or the like, a difference occurs in voltages
applied to the liquid crystal material layer (liquid crystal
applied voltage) in positive polarity side display and negative
polarity side display when polarity inversion driving is performed,
and thereby flickering occurs. Therefore, there is a demand for a
configuration in which flickering is difficult to view with respect
to variations in a potential of the common electrode. In order to
make flickering difficult to view, it is effective to perform a
design such that the vicinity of an extreme value of a liquid
crystal applied voltage-reflectance curve is set as an operation
point, and thus a brightness variation is not viewed even if some
potential variations occur.
SUMMARY
[0005] However, typically, if the vicinity of an extreme value of
the liquid crystal applied voltage-reflectance curve is to be set
as an operation point, a liquid crystal applied voltage has to be
set to be high, and thus power consumption is increased. In order
to prevent this, it is possible to reduce a liquid crystal applied
voltage by changing a design of optical members or the like forming
the liquid crystal display; however, in this case, there is a
problem in that, when the liquid crystal display is observed from a
normal observing direction, flickering is not viewed, but, when the
liquid crystal display is observed from a deviated direction,
flickering is viewed.
[0006] It is therefore desirable to provide a reflective liquid
crystal display, capable of achieving a low voltage of a liquid
crystal applied voltage, in which flickering is not viewed in both
a case where the liquid crystal display is observed from a normal
observing direction and a case where the liquid crystal display is
observed from a deviated direction.
[0007] An embodiment of the present disclosure is directed to a
liquid crystal display which is a reflective liquid crystal
display, including a front substrate; a rear substrate; and a
liquid crystal material layer disposed between the front substrate
and the rear substrate, wherein an optical design is performed such
that an extreme value of a liquid crystal applied
voltage-reflectance curve in a state of being observed from a
normal observing direction is shifted further to a lower voltage
side than an extreme value of a liquid crystal applied
voltage-reflectance curve in a state of being observed from a
direction deviated from the normal observing direction, and wherein
an anisotropic scatterer disposed such that a direction where
scattering characteristics are the maximum is aligned with the
normal observing direction is provided on the front substrate
side.
[0008] In the liquid crystal display according to the embodiment of
the present disclosure, an optical design is performed such that an
extreme value of a liquid crystal applied voltage-reflectance curve
in a state of being observed from a normal observing direction is
shifted further to a lower voltage side than an extreme value of a
liquid crystal applied voltage-reflectance curve in a state of
being observed from a direction deviated from the normal observing
direction, and an anisotropic scatterer disposed such that a
direction where scattering characteristics are the maximum is
aligned with the normal observing direction is provided on the
front substrate side. Thereby, it is possible to achieve a low
voltage for a liquid crystal applied voltage and to thereby reduce
power consumption. In addition, since the strength of light in a
direction deviated from the normal observing direction is
relatively weakened, flickering is not viewed even if the liquid
crystal display is observed from a direction deviated from the
normal observing direction.
[0009] Additional features and advantages are described herein, and
will be apparent from the following Detailed Description and the
figures.
BRIEF DESCRIPTION OF THE FIGURES
[0010] FIG. 1A is a schematic perspective view of a liquid crystal
display according to a reference example.
[0011] FIG. 1B is a schematic cross-sectional view of the liquid
crystal display according to the reference example.
[0012] FIG. 2A is a schematic plan view illustrating a structure of
a pixel.
[0013] FIG. 2B is a schematic diagram illustrating a method of
controlling a voltage applied to a pixel electrode.
[0014] FIG. 3A is a schematic waveform diagram illustrating a
potential difference between a common electrode and a pixel
electrode according to inversion driving.
[0015] FIG. 3B is a schematic graph illustrating a relationship
between a voltage applied to the liquid crystal material layer
(liquid crystal applied voltage) and the reflectance, and a
relationship between a variation in a liquid crystal applied
voltage and a variation in the reflectance.
[0016] FIG. 4 is a schematic graph illustrating how the
relationship between the liquid crystal applied voltage and the
reflectance varies when the liquid crystal display in which a
certain design condition is applied to an optical member or the
like is rotated.
[0017] FIG. 5 is a schematic diagram illustrating an optical design
of the liquid crystal display.
[0018] FIG. 6 is a schematic graph illustrating how the
relationship between the liquid crystal applied voltage and the
reflectance varies when the liquid crystal display in which a
certain design condition different from that of FIG. 4 is applied
to the optical member or the like is rotated.
[0019] FIG. 7 is a schematic diagram illustrating an optical design
of the liquid crystal display.
[0020] FIG. 8 is a schematic exploded perspective view illustrating
a liquid crystal display according to a first embodiment.
[0021] FIG. 9A is a schematic perspective view illustrating a
structure of the liquid crystal display.
[0022] FIG. 9B is a schematic cross-sectional view illustrating a
structure of an anisotropic scatterer according to the first
embodiment.
[0023] FIGS. 9C and 9D are schematic perspective views illustrating
a disposition of a low refractive index region and a high
refractive index region in the anisotropic scatterer.
[0024] FIG. 10 is a schematic diagram illustrating a relationship
between incident light and scattered light in the anisotropic
scatterer.
[0025] FIG. 11 is a schematic cross-sectional view of the liquid
crystal display according to the first embodiment.
[0026] FIGS. 12A to 12C are schematic diagrams and the like
illustrating characteristics of the anisotropic scatterer.
[0027] FIG. 13A is a schematic perspective view illustrating a
positional relationship between cases where a liquid crystal
display from which the anisotropic scatterer is omitted is observed
from a normal observing direction and is observed from another
direction.
[0028] FIG. 13B is a schematic graph of a liquid crystal applied
voltage-reflectance curve in the liquid crystal display from which
the anisotropic scatterer is omitted.
[0029] FIG. 14A is a schematic perspective view illustrating a
positional relationship between cases where the liquid crystal
display according to the first embodiment is observed from a normal
observing direction and is observed from another direction.
[0030] FIG. 14B is a schematic graph of a liquid crystal applied
voltage-reflectance curve in the liquid crystal display according
to the first embodiment.
[0031] FIG. 15A is a schematic cross-sectional view of a liquid
crystal display according to a reference example.
[0032] FIG. 15B is a graph which compares the reflectance
characteristics between the liquid crystal display shown in FIG. 11
and the liquid crystal display shown in FIG. 15A.
[0033] FIG. 16 is a schematic exploded perspective view
illustrating a liquid crystal display according to a modified
example.
DETAILED DESCRIPTION
[0034] Hereinafter, the present disclosure will be described based
on embodiments. The present disclosure is not limited to the
embodiment, and various numerical values or materials in the
embodiment are examples. In the following description, the same
constituent elements or constituent elements having the same
function are given the same reference numerals, and repeated
description will be omitted. In addition, the description will be
made in the following order.
[0035] 1. Description of overall liquid crystal display according
to embodiment of present disclosure
[0036] 2. Description of liquid crystal display according to
reference example
[0037] 3. First embodiment (and others)
[0038] [Description of Overall Liquid Crystal Display According to
Embodiment of Present Disclosure]
[0039] As described above, in the liquid crystal display according
to the embodiment of the present disclosure, an optical design is
performed such that an extreme value of a liquid crystal applied
voltage-reflectance curve in a state of being observed from a
normal observing direction is shifted further to a lower voltage
side than an extreme value of a liquid crystal applied
voltage-reflectance curve in a state of being observed from a
direction deviated from the normal observing direction. This
optical design can be realized by appropriately setting, for
example, the specification of an optical member such as a phase
difference plate used in the liquid crystal display, or the
specification of a surface treatment of an alignment layer which
defines an alignment state of liquid crystal molecules forming the
liquid crystal material layer.
[0040] In the liquid crystal display according to the embodiment of
the present disclosure, an in-plane direction region of the
anisotropic scatterer may be formed as a region in which low
refractive index regions and high refractive index regions are
mixed. The anisotropic scatterer may be configured to be disposed
such that ambient light incident from the outside is scattered when
transmitted through the anisotropic scatterer, but is preferably
configured to be disposed such that ambient light which is
reflected on the rear substrate side is incident on the anisotropic
scatterer and is scattered when emitted to the outside. Since
reflectance of light is higher in the latter configuration, an
image observed from a direction deviated from the normal observing
direction is relatively darkened, and thus flickering when
observation is performed from the deviated direction is not
viewed.
[0041] In the liquid crystal display according to the embodiment of
the present disclosure including the above-described preferable
configurations, the anisotropic scatterer may be formed by
laminating a plurality of scattering members.
[0042] Alternatively, in the liquid crystal display according to
the embodiment of the present disclosure including the
above-described preferable configurations, the liquid crystal
display may perform grayscale display using an area ratio grayscale
method. For example, each pixel (in color display, each subpixel)
may include a set of pixel electrodes of which the area is
increased by about twice, and a voltage applied to the set of the
pixel electrodes may be controlled for each pixel electrode so as
to vary the area of a region provided for display.
[0043] The anisotropic scatterer may be formed using a composition
or the like including a photoreactive compound. For example, a base
material including a composition expressing some extent of
reflectance variations before and after photopolymerization is
irradiated with light such as ultraviolet rays from a predetermined
direction, thereby obtaining an anisotropic scatterer. As a
material forming the composition, a material producing some extent
of reflectance variations in a portion undergoing photoreaction and
a portion not undergoing the photoreaction may be appropriately
selected and used from a well-known material such as a polymer with
functional groups for radical polymerization or cationic
polymerization.
[0044] Alternatively, for example, a base material including a
composition in which a photoreactive compound and non-photoreactive
polymer are mixed is irradiated with light such as ultraviolet rays
from a predetermined direction, thereby obtaining an anisotropic
scatterer. The non-photoreactive polymer may be appropriately
selected and used from well-known materials such as, for example,
an acryl resin or a styrene resin.
[0045] The base material including the composition may be obtained
by coating the composition on a film-shaped base made of, for
example, a polymer material using a well-known coating method.
[0046] An in-plane direction region of the anisotropic scatterer
including the above-described composition may be formed as a region
in which low refractive index regions and high refractive index
regions are mixed. Typically, the anisotropic scatterer is formed
such that the boundary between the low refractive index region and
the high refractive index region forms a predetermined angle with
respect to the thickness direction of the anisotropic scatterer.
Depending on cases, this angle may be continuously varied in the
in-plane direction.
[0047] A refractive index difference between the low refractive
index region and the high refractive index region is typically
preferably 0.01 or more, more preferably 0.05 or more, and most
preferably 0.10 or more.
[0048] Although, depending on a material forming the anisotropic
scatterer or a manufacturing method thereof, the portion undergoing
photoreaction and the portion not undergoing photoreaction may
respectively form louver-shape regions, for example, as shown in
FIG. 9C described later, or may form a columnar region and a
peripheral region surrounding the columnar region as shown in FIG.
9D described later.
[0049] The liquid crystal display according to the embodiment of
the present disclosure may perform monochrome display and color
display. The pixel electrode itself may reflect light as a
reflective electrode, or a reflective film may reflect light
through a combination of a transparent pixel electrode and the
reflective film. An operation mode of the liquid crystal display is
not particularly restricted as long as there is no hindrance in a
display operation as the reflective type. For example, the liquid
crystal display may be driven in a so-called VA mode or ECB
mode.
[0050] For example, a transflective liquid crystal display having
both a reflective display region and a transmissive display region
in a pixel is well known. Depending on cases, the liquid crystal
display may be a transflective liquid crystal display. In other
words, the "reflective type" also includes the "transflective
type".
[0051] A shape of the liquid crystal display is not particularly
restricted, and may be a transversely long rectangular shape or a
longitudinally long rectangular shape. When the number M.times.N of
pixels of the liquid crystal display is indicated by (M,N), for
example, in a case of the transversely long rectangular shape,
several resolutions for image display, such as, (640,480),
(800,600), and (1024,768) are exemplified as a value of (M,N), and,
in a case of the longitudinally long rectangular shape, resolutions
obtained by exchanging the values are exemplified, but the number
thereof is not limited to these values.
[0052] A driving circuit driving the liquid crystal display may
include various circuits. They may be formed using well-known
circuit elements.
[0053] A variety of conditions shown in the present specification
are satisfied in a case of being substantially established as well
as in a case of being strictly established. Presence of a variety
of variations occurring in design or manufacturing is allowed.
[0054] [Description of Liquid Crystal Display According to
Reference Example]
[0055] First, for better understanding of the present disclosure, a
liquid crystal display according to a reference example will be
described.
[0056] FIG. 1A is a schematic perspective view of a liquid crystal
display according to the reference example. FIG. 1B is a schematic
cross-sectional view of the liquid crystal display according to the
reference example.
[0057] The liquid crystal display 901 according to the reference
example is a reflective liquid crystal display having a display
region 11 in which pixels 12 are arranged. The liquid crystal
display 901 is driven by driving circuits and the like (not shown).
Ambient light such as, for example, sunlight or illumination light
is incident on the display region 11. For convenience of the
description, the display region 11 is set to be parallel to the X-Y
plane, and a direction where an image is observed is set to +Z
direction. The description will be made assuming that the ambient
light is incident with a predetermined polar angle (for example, 30
degrees) from a direction of the azimuth 90 degrees, but this is
only an example.
[0058] The liquid crystal display 901 has a rectangular shape, and
sides thereof are indicated by the reference numerals 13A, 13B, 13C
and 13D. The side 13C is a front side, and the side 13A is a side
opposite to the side 13C. For example, the sides 13A and 13C are
about 12[cm], and the sides 13B and 13D are about 16[cm], but the
lengths thereof are not limited to these values.
[0059] As shown in FIG. 1B, the liquid crystal display 901 includes
a front substrate 18, a rear substrate 14, and a liquid crystal
material layer 17 disposed between the front substrate 18 and the
rear substrate 14. The reference numeral 17A schematically
indicates liquid crystal molecules forming the liquid crystal
material layer 17. The liquid crystal material layer 17 is provided
at a predetermined thickness using spacers and the like (not
shown). The reference numeral 10 shown in FIG. 1B indicates a
portion including the front substrate 18, the rear substrate 14,
and the liquid crystal material layer 17 disposed between the front
substrate 18 and the rear substrate 14 in the liquid crystal
display 901. Similarly, the reference numeral 20 indicates a
portion including a 1/4 waveform plate 21, a 1/2 waveform plate 22,
and a polarization plate 23 in the liquid crystal display 901. The
liquid crystal display 901 is driven, for example, in an ECB
mode.
[0060] For example, a planarization film 15 made of a polymer
material such as an acryl resin is formed on the rear substrate 14
made of a glass material, and pixel electrodes (reflective
electrodes) 16 made of a metal material such as aluminum is formed
thereon.
[0061] A surface of the pixel electrode 16 is formed in a specular
form. For example, an element such as a TFT is connected to the
pixel electrode 16 in order to control electrical connection
between signal lines for supplying an image signal and the pixel
electrode 16. In addition, in FIG. 1B, TFTs, various wires such as
signal lines or scanning lines for controlling conduction states of
the TFTs, a common electrode or color filters provided on the front
substrate 18, an alignment layer for defining an initial alignment
state of the liquid crystal material layer 17, and the like are not
shown.
[0062] The ambient light incident from the outside is linearly
polarized in a predetermined direction by the polarization plate
23, rotates its polarization plane by 90 degrees in the 1/2
waveform plate 22, and is then circularly polarized by the 1/4
waveform plate 21. The ambient light which has been circularly
polarized is transmitted through the liquid crystal material layer
17 and is reflected by the pixel electrode 16. The reflected
ambient light is transmitted through the liquid crystal material
layer 17, further transmitted through the 1/4 waveform plate 21 and
the 1/2 waveform plate 22, arrives at the polarization plate 23,
and is emitted toward the outside. It is possible to control an
amount where ambient light reflected by the pixel electrode 16 is
transmitted through the polarization plate 23 by controlling a
voltage applied to the pixel electrode 16 or the like so as to
control an alignment state of the liquid crystal molecules 17A in
the liquid crystal material layer 17.
[0063] FIG. 2A is a schematic plan view illustrating a structure of
the pixel. FIG. 2B is a schematic diagram illustrating a method of
controlling a voltage applied to the pixel electrode.
[0064] As shown in FIG. 2A, the pixel 12 includes a set of a red
display subpixel 12R, a green display subpixel 12G, and a blue
display subpixel 12B. The liquid crystal display 901 performs
grayscale display using an area ratio grayscale method. For this
reason, the pixel electrodes 16 of each subpixel include a set of
electrodes of which the area is increased by about twice. FIG. 2A
shows an example of the case of including a set of five electrodes
16A, 16B, 16C, 16D and 16E. Voltages applied to the electrodes 16A,
16B, 16C, 16D and 16E are controlled, for example, depending on
values of corresponding bits of a digitalized image signal.
[0065] With reference to FIG. 2B, a description will be made of a
configuration of a case where control is performed based on, for
example, an image signal of 5 bits. The electrode 16E of which the
area is the largest is controlled based on MSB of the image signal,
and, as the area is decreased, the electrodes are controlled based
on lower bits. The electrode 16A of which the area is the smallest
is controlled based on LSB of the image signal. Specifically, one
of, for example, a voltage V.sub.com with the same value as a
voltage applied to the common electrode, a voltage
V.sub.com+V.sub.d with a positive polarity, and a voltage
V.sub.com-V.sub.d with a negative polarity is applied to each
electrode according to a value of a corresponding bit of the image
signal from a driving circuit 100. Thereby, polarity inversion
driving is performed, for example, for each frame.
[0066] A voltage applied to each of the electrodes 16A, 16B, 16C,
16D and 16E is controlled, and thereby it is possible to control
the area of a region provided for display. In addition, in the
following description, in a case where it is not necessary to
differentiate the electrodes 16A, 16B, 16C, 16D and 16E from each
other, they are simply referred to as a pixel electrode 16. In
addition, description will be made assuming that the liquid crystal
display 901 is driven in a normally white mode, but this is only an
example.
[0067] Next, with reference to FIGS. 3A and 3B, a relationship
between a liquid crystal applied voltage-reflectance curve and
flickering will be described.
[0068] FIG. 3A is a schematic waveform diagram illustrating a
potential difference between the common electrode and the pixel
electrode according to the inversion driving. FIG. 3B is schematic
graphs illustrating a relationship between a voltage applied to the
liquid crystal material layer (liquid crystal applied voltage) and
the reflectance, and a relationship between a variation in a liquid
crystal applied voltage and a variation in the reflectance.
[0069] For example, if a potential of the common electrode varies
from V.sub.com to V.sub.com' due to the liquid crystal display 901
being exposed to ambient light for a long time or the like,
flickering occurs when black display is performed. In other words,
as shown in FIG. 3A, a liquid crystal applied voltage V.sub.1 in
positive polarity driving and a liquid crystal applied voltage
V.sub.2 in negative polarity driving have different values, and
thus a difference .DELTA.V between the liquid crystal applied
voltages occurs.
[0070] The graph on the upper part of FIG. 3B is a schematic graph
of a liquid crystal applied voltage-reflectance curve. A variation
in the reflectance due to the difference .DELTA.V between the
liquid crystal applied voltages can be reduced by setting a voltage
V.sub.d to a value close to an extreme value of the liquid crystal
applied voltage-reflectance curve.
[0071] The graph on the lower part of FIG. 3B shows reflectance
variations caused by the difference .DELTA.V in cases where the
voltage V.sub.d is set to a voltage V.sub.d.sub.--.sub.1 around an
extreme value of the liquid crystal applied voltage-reflectance
curve and is set to a value V.sub.d.sub.--.sub.2 distant from the
extreme value. As is clear from the graphs, a reflectance variation
.DELTA.RE.sub.1 in a case where the voltage V.sub.d is set to a
value V.sub.d.sub.--.sub.1 is smaller than a reflectance variation
.DELTA.RE.sub.2 in a case where the voltage V.sub.d is set to a
value V.sub.d.sub.--.sub.2. As such, even if the same difference
.DELTA.V occurs, it is possible to reduce occurrence of flickering
due to the inversion driving by setting the voltage V.sub.d to a
value around the extreme value of the liquid crystal applied
voltage-reflectance curve. Particularly, it is not necessary to
apply a voltage for intermediate grayscale display to the liquid
crystal material layer 17 in a general area ratio grayscale method
with MIP (Memory In Pixel), and thus flickering is further
difficult to view. In addition, the liquid crystal display
according to the embodiment of the present disclosure is not
limited to a liquid crystal display of the area ratio grayscale
method.
[0072] Next, an optical design of the liquid crystal display
according to the reference example will be described. First, an
example of the general optical design will be described with
reference to FIGS. 4 and 5, and, then an example of the optical
design for shifting an extreme value of the liquid crystal applied
voltage-reflectance curve to a low voltage side will be described
with reference to FIGS. 6 and 7.
[0073] FIG. 4 is a schematic graph illustrating how the
relationship between the liquid crystal applied voltage and the
reflectance varies when the liquid crystal display in which a
certain design condition is applied to an optical member or the
like is rotated. FIG. 5 is a schematic diagram illustrating an
optical design of the liquid crystal display.
[0074] Details of the optical design will be described. As shown in
FIG. 5, a polarization axis of the polarization plate 23 is set to
form an angle of 35 degrees, a polarization axis of the 1/2
waveform plate 22 is set to form an angle of 50 degrees, and a
polarization axis of the 1/4 waveform plate 21 is set to form an
angle of -70 degrees, with respect to the X axis. A rubbing
direction in the alignment layer (not shown) on the rear substrate
14 side forms an angle of -128.5 degrees with respect to the X
axis. In addition, a rubbing direction in the alignment layer (not
shown) on the front substrate 18 side is set such that the liquid
crystal molecules 17A are twisted by 63 degrees in the clockwise
direction when viewed by an observer. FIG. 4 is a graph regarding
the liquid crystal display 901 for which the above-described
optical design is performed.
[0075] FIG. 4 shows a liquid crystal applied voltage-reflectance
curve when the liquid crystal display 901 is rotated with respect
to the Z axis as shown in FIGS. 1A and 1B. Specifically, FIG. 4
shows a liquid crystal applied voltage-reflectance curve when the
liquid crystal display 901 is rotated by 0 degrees, a liquid
crystal applied voltage-reflectance curve when the liquid crystal
display 901 is rotated by 15 degrees, a liquid crystal applied
voltage-reflectance curve when the liquid crystal display 901 is
rotated by 30 degrees, and a liquid crystal applied
voltage-reflectance curve when the liquid crystal display 901 is
rotated by 50 degrees.
[0076] As is clear from the graph, in the optical design, a value
where the liquid crystal applied voltage-reflectance curve becomes
an extreme value does not vary much even if the liquid crystal
display 901 is rotated. In addition, unless the liquid crystal
applied voltage is set to a relatively high value (in the example
shown in the figure, about 4.3 V), the liquid crystal applied
voltage does not becomes a value around the extreme value of the
liquid crystal applied voltage-reflectance curve. Therefore, in the
design condition shown in FIG. 4, if the voltage V.sub.d is
intended to be set to a value around the extreme value of the
liquid crystal applied voltage-reflectance curve, the power
consumption is increased. In addition, for example, if the liquid
crystal applied voltage is set to a relatively low value (in the
example shown in the figure, about 3.3 V), a reflectance variation
caused by the difference .DELTA.V between liquid crystal applied
voltages due to the polarity inversion driving is increased.
Further, the difference .DELTA.V shown in FIG. 4 is schematically
shown and is only an example. This is also the same for FIG. 6
described later.
[0077] FIG. 6 is a schematic graph illustrating how the
relationship between the liquid crystal applied voltage and the
reflectance varies when the liquid crystal display in which a
certain design condition different from that of FIG. 4 is applied
to the optical member or the like is rotated. FIG. 7 is a schematic
diagram illustrating an optical design of the liquid crystal
display.
[0078] Details of the optical design will be described. As shown in
FIG. 7, a polarization axis of the polarization plate 23 is set to
form an angle of 26 degrees, a polarization axis of the 1/2
waveform plate 22 is set to form an angle of 40 degrees, and a
polarization axis of the 1/4 waveform plate 21 is set to form an
angle of -84 degrees, with respect to the X axis. A rubbing
direction in the alignment layer (not shown) on the rear substrate
14 side forms an angle of -158.5 degrees with respect to the X
axis. In addition, a rubbing direction in the alignment layer (not
shown) on the front substrate 18 side is set such that the liquid
crystal molecules 17A are twisted by 70 degrees in the clockwise
direction when viewed by an observer. FIG. 6 is a graph regarding
the liquid crystal display 901 for which the above-described
optical design is performed.
[0079] FIG. 6 also additionally shows a liquid crystal applied
voltage-reflectance curve when the liquid crystal display 901 is
rotated by 70 degrees and by 90 degrees with respect to the Z
axis.
[0080] As is clear by comparing the characteristics shown in FIG.
4, in the characteristics shown in FIG. 6, a value of the liquid
crystal applied voltage where the liquid crystal applied
voltage-reflectance curve becomes an extreme value is varied by
changing a rotation angle of the liquid crystal display 901. In
addition, it can be seen that the extreme value of the liquid
crystal applied voltage-reflectance curve when a rotation angle is
small is shifted to a low voltage side. For example, when attention
is paid to the liquid crystal applied voltage-reflectance curve
with the rotation angle 15 degrees, a reflectance variation caused
by the difference .DELTA.V between liquid crystal applied voltages
due to the polarity inversion driving is small even if a liquid
crystal applied voltage is set to a relatively low value (in the
example shown in the figure, 3.3 V).
[0081] For example, if an optical design is configured to be
entirely shifted by 15 degrees such that the characteristics
indicated by the liquid crystal applied voltage-reflectance curve
with the rotation angle 15 degrees shown in FIG. 6 are expressed
without rotating the liquid crystal display, it is possible to
shift an extreme value of the liquid crystal applied
voltage-reflectance curve in a state of being observed from a
normal observing direction (for example, a direction of the polar
angle 0 degrees) to a low voltage. In the liquid crystal display
configured in this way, it is possible to reduce power consumption
while setting the voltage V.sub.d to a value around an extreme
value of the liquid crystal applied voltage-reflectance curve.
However, for example, the characteristics at the rotation angle 70
degrees shown in FIG. 6 are expressed at the rotation angle 55
degrees. Therefore, there is a problem in that flickering is viewed
in a case where the liquid crystal display is observed from a
direction different from the normal observing direction, for
example, from an obliquely transverse direction. Next, a liquid
crystal display according to a first embodiment for solving the
above-described problem will be described.
First Embodiment
[0082] The first embodiment of the present disclosure relates to a
display device.
[0083] FIG. 8 is a schematic exploded perspective view illustrating
a liquid crystal display according to the first embodiment.
[0084] A liquid crystal display 1 according to the first embodiment
basically has a configuration in which an anisotropic scatterer is
added to the liquid crystal display 901 described in the reference
example. Specifically, the anisotropic scatterer is further
provided on the front substrate side of the liquid crystal display
which has a configuration in which an optical design is shifted
such that the characteristics indicated by the liquid crystal
applied voltage-reflectance curve with the rotation angle 15
degrees shown in FIG. 6 are shown without rotating the liquid
crystal display.
[0085] The reference numeral 10A shown in FIG. 8 indicates a
portion including the front substrate 18, the rear substrate 14,
and the liquid crystal material layer 17 disposed between the front
substrate 18 and the rear substrate 14 which form the liquid
crystal display for which the above-described optical design has
been performed. Similarly, the reference numeral 20A shown in FIG.
8 indicates a portion including a 1/4 waveform plate 21, a 1/2
waveform plate 22, and a polarization plate 23 which form the
liquid crystal display for which the above-described optical design
has been performed. An anisotropic scatterer 30 is disposed on the
front substrate 18 side, more specifically, between the front
substrate 18 and the 1/4 waveform plate 21 as shown in FIG. 11
described later.
[0086] As such, the liquid crystal display 1 is a reflective liquid
crystal display including the front substrate 18, the rear
substrate 14, and the liquid crystal material layer 17 disposed
between the front substrate 18 and the rear substrate 14. In
addition, an optical design is performed such that an extreme value
of a liquid crystal applied voltage-reflectance curve in a state of
being observed from a normal observing direction (for example, a
direction of the polar angle 0 degrees) is shifted further to a low
voltage side than an extreme value of a liquid crystal applied
voltage-reflectance curve in a state of being observed from a
direction deviated from the normal observing direction.
[0087] FIG. 9A is a schematic perspective view illustrating a
structure of the liquid crystal display. FIG. 9B is a schematic
cross-sectional view illustrating a structure of the anisotropic
scatterer according to the first embodiment. FIGS. 9C and 9D are
schematic perspective views illustrating a disposition of a low
refractive index region and a high refractive index region in the
anisotropic scatterer.
[0088] The anisotropic scatterer 30 shown in FIG. 8 or 9A has a
sheet shape (film shape) with the thickness of, for example, 0.02
to 0.5 [mm] Although a detailed description is made referring to
FIGS. 12A to 12C described later, the anisotropic scatterer 30 is
disposed such that a direction where scattering characteristics are
the maximum is aligned with the normal observing direction.
[0089] As shown in FIG. 9B, an in-plane direction region of the
anisotropic scatterer 30 is formed as a region in which low
refractive index regions 31 and high refractive index regions 32
are mixed, for example, at the order of microns. In addition, there
may be a configuration of being mixed at the order of microns or
less. Further, for simplicity of illustration, in FIGS. 9A to 9D, a
transparent film and the like which form a base of the anisotropic
scatterer 30 are not shown.
[0090] The anisotropic scatterer 30 is formed using a composition
or the like including a photoreactive compound. For example, as
shown in FIG. 9C, the anisotropic scatterer 30 may have a
configuration in which the low refractive index regions 31 and the
high refractive index regions 32 are formed in a louver shape, and,
as shown in FIG. 9D, the anisotropic scatterer 30 may have a
configuration in which the low refractive index regions 31 and the
high refractive index regions 32 form columnar regions and
peripheral regions surrounding them. FIG. 9D shows an example of
the case where, for example, a composition portion having undergone
photoreaction has a high refractive index in a columnar region
form.
[0091] FIG. 9C shows that the width of each of the low refractive
index regions 31 in the thickness direction or the width of each of
the high refractive index regions 32 in the thickness direction is
constant, but this is only an example. Similarly, FIG. 9D shows
that the shapes of the column regions are the same, but this is
also only an example.
[0092] As shown in FIGS. 9B to 9D, inside the anisotropic scatterer
30, the low refractive index regions 31 and the high refractive
index regions 32 are formed in a tilt direction such that a
boundary between the low refractive index region 31 and the high
refractive index region 32 forms an angle 8 with respect to the
thickness direction (Z direction) of the anisotropic scatterer 30.
The angle 8 is set to an appropriately preferable value depending
on the specification of the anisotropic scatterer 30.
[0093] For convenience of description, here, the low refractive
index regions 31 and the high refractive index regions 32 are
formed in a louver shape as shown in FIG. 9C, and a direction where
the louver-shape regions extend is set to be parallel to the X
direction. In addition, a description will be made assuming that
the high refractive index region 32 is a region where a base
material produces photoreaction, but this is only an example. A
region where a base material produces photoreaction may be the low
refractive index region 31.
[0094] Here, a relationship between incident light and scattered
light in the anisotropic scatterer will be described with reference
to FIG. 10.
[0095] As shown in FIG. 10, in a case where, in the anisotropic
scatterer 30, light is incident from a direction substantially
following the direction where the boundary between the low
refractive index region 31 and the high refractive index region 32
extends, the light is scattered and is emitted. On the other hand,
light is incident from a direction substantially perpendicular to
the direction where the boundary between the low refractive index
region 31 and the high refractive index region 32 extends, the
light is transmitted as it is.
[0096] In addition, a scattering center axis S (an axis where an
anisotropic scattering characteristic of light which is incident
centering thereon is substantially symmetrical; in other words, an
axis which extends in an incidence direction of most scattered
light) of the anisotropic scatterer 30 is obliquely tilted with
respect to the Z axis direction, but, qualitatively, it is
considered that an axial direction thereof is a direction
substantially following the extending direction of the low
refractive index regions 31 and the high refractive index regions
32. Further, in this case, it is considered that the azimuth where
the scattering center axis S is projected onto the X-Y plane is in
a direction perpendicular to the direction where the louver-shape
regions extend in the case shown in FIG. 9C, and is in a direction
where, when the columnar region is projected onto the X-Y plane, a
shadow thereof extends in the case shown in FIG. 9D. A plane
including the scattering center axis S is parallel to the Y-Z
plane.
[0097] The anisotropic scatterer 30 is disposed such that ambient
light which is reflected on the rear substrate 14 side is incident
on the anisotropic scatterer 30 and is scattered when emitted to
the outside (hereinafter, referred to as "an emission scattering
configuration" in some cases).
[0098] Behaviors of light in the liquid crystal display 1 will be
described with reference to FIGS. 11 to 12C.
[0099] FIG. 11 is a schematic cross-sectional view of the liquid
crystal display according to the first embodiment. FIGS. 12A to 12C
are schematic diagrams illustrating characteristics of the
anisotropic scatterer.
[0100] The anisotropic scatterer 30 shows anisotropy in light
scattering. Therefore, the liquid crystal display 1 including the
anisotropic scatterer 30 is considerably different in light
reflection characteristics in a case where light is incident on the
plane including the scattering center axis S of the anisotropic
scatterer and in a case where light is not incident thereon.
[0101] For example, in a state where the liquid crystal display 1
performs white display, as shown in FIG. 12A, light 1 is incident
at the azimuth 90 degrees and the polar angle 30 degrees, and, in a
case where the intensity of emitted light is observed at an
observing position of the polar angle 0 degrees, a characteristic
as in FIG. 12B is shown. In addition, FIG. 12B shows a normalized
value. In contrast, in a case where the azimuth is changed (for
example, 0 degrees) and light 2 is incident, a characteristic as in
FIG. 12C is shown.
[0102] As such, the liquid crystal display 1 using the anisotropic
scatterer 30 has angle dependency in the light scattering
characteristic, and thus shows a characteristic of strengthening
light in a predetermined direction (the in-plane direction
perpendicular to the plane of the paper in the example shown in
FIGS. 12A to 12C) and of weakening light in a direction deviated
from the predetermined direction. Thereby, flickering when the
liquid crystal display 1 is observed from another direction
different from the normal observing direction is reduced.
Hereinafter, a description thereof will be made with reference to
FIGS. 13A to 14B.
[0103] FIG. 13A is a schematic perspective view illustrating a
positional relationship between cases where a liquid crystal
display from which the anisotropic scatterer is omitted is observed
from a normal observing direction and is observed from another
direction. FIG. 13B is a schematic graph of a liquid crystal
applied voltage-reflectance curve in the liquid crystal display
from which the anisotropic scatterer is omitted.
[0104] In a liquid crystal display 1' which has a configuration
where the anisotropic scatterer 30 is omitted from the liquid
crystal display 1, flickering is viewed in a case of being observed
from another direction (for example, a direction of the polar angle
30 degrees and the azimuth 0 degrees) different from a normal
observing direction (for example, the polar angle 30 degrees and
the azimuth 270 degrees). That is to say, as shown in FIG. 13B, a
reflectance variation .DELTA.RE.sub.2' due to the difference
.DELTA.V between liquid crystal applied voltages when observation
is performed from another direction is much larger than a variation
.DELTA.RE.sub.1' when observation is performed from the normal
observing direction.
[0105] FIG. 14A is a schematic perspective view illustrating a
positional relationship between cases where the liquid crystal
display according to the first embodiment is observed from a normal
observing direction and is observed from another direction. FIG.
14B is a schematic graph of a liquid crystal applied
voltage-reflectance curve in the liquid crystal display according
to the first embodiment.
[0106] The anisotropic scatterer 30 shows a characteristic of
strengthening light in a direction toward a predetermined observing
position and weakening light in a direction deviated from the
predetermined observing position. Fundamentally, the closer to the
scattering center axis S and the closer to the plane including the
scattering center axis S (in the example shown in FIGS. 12A to 12C,
the plane parallel to the Y-Z plane), the stronger the light
intensity. Therefore, a reflectance variation .DELTA.RE.sub.2 due
to the difference .DELTA.V between liquid crystal applied voltages
when observation is performed from another direction (for example,
a transverse direction) is smaller than the .DELTA.RE.sub.2' shown
in FIGS. 14A and 14B. Thereby, flickering when observation is
performed from another direction is reduced. A liquid crystal
applied voltage-reflectance curve when observation is performed
from the normal observing direction is shifted further upward than
the liquid crystal applied voltage-reflectance curve shown in FIGS.
14A and 14B. Therefore, it is possible to increase the luminance of
an image observed from a predetermined observing position.
[0107] As described above, the anisotropic scatterer 30 is disposed
such that ambient light which is reflected on the rear substrate 14
side is incident on the anisotropic scatterer 30 and is scattered
when emitted to the outside. In contrast, there may be a
configuration in which ambient light incident from the outside is
incident on the anisotropic scatterer 30 and is scattered when
directing toward the rear substrate 14 side (hereinafter, referred
to as an "incidence scattering configuration" in some cases), but
an image is slightly darkened. In the following, a description
thereof will be made with reference to FIGS. 15A and 15B.
[0108] FIG. 15A is a cross-sectional view of a liquid crystal
display 1'' with a configuration in which a disposition of the
anisotropic scatterer 30 is changed, and ambient light from the
outside is scattered when the ambient light is incident on the
anisotropic scatterer 30.
[0109] In the liquid crystal display 1'', the scattered light is
incident on the pixel electrode 16 and is reflected toward the
front substrate side. Therefore, the light is more widely scattered
than in the liquid crystal display 1 shown in FIG. 11.
[0110] FIG. 15B is a graph which compares the reflectance
characteristics between the liquid crystal display shown in FIG. 11
and the liquid crystal display shown in FIG. 15A.
[0111] As is clear from the graph, the liquid crystal display 1
with the emission scattering configuration shown in FIG. 11 has the
higher reflectance than the liquid crystal display 1'' with the
incidence scattering configuration. Therefore, the liquid crystal
display 1 with the emission scattering configuration has an
advantage in that the luminance of a displayed image can be further
increased.
[0112] In addition, in order to enlarge a scattering range or
reduce an iridescent color, the anisotropic scatterer may have a
structure formed by laminating a plurality of scattering members.
FIG. 16 shows a schematic exploded perspective view of a liquid
crystal display having an anisotropic scatterer with the
above-described configuration.
[0113] In FIG. 16, an anisotropic scatterer 130 is formed by
laminating scattering members 30A and 30B. The scattering members
30A and 30B basically have the same configuration as the
anisotropic scatterer 30. For example, by giving some differences
in directions of scattering center axes of the scattering members
30A and 30B, it is possible to adjust a diffusion range of
light.
[0114] As above, although the embodiment of the present disclosure
has been described in detail, the present disclosure is not limited
to the above-described embodiment and may be variously modified
based on the technical scope of the present disclosure.
[0115] For example, although, in the above-described embodiment,
the anisotropic scatterer is disposed between the front substrate
18 and the 1/4 waveform plate 21, this is only an example. A
location at which the anisotropic scatterer is disposed may be
appropriately determined depending on a design or a specification
of the liquid crystal display.
[0116] In addition, the present disclosure may be implemented as
the following configurations.
[0117] (1) A liquid crystal display which is a reflective liquid
crystal display, including a front substrate; a rear substrate; and
a liquid crystal material layer disposed between the front
substrate and the rear substrate, wherein an optical design is
performed such that an extreme value of a liquid crystal applied
voltage-reflectance curve in a state of being observed from a
normal observing direction is shifted further to a lower voltage
side than an extreme value of a liquid crystal applied
voltage-reflectance curve in a state of being observed from a
direction deviated from the normal observing direction, and wherein
an anisotropic scatterer disposed such that a direction where
scattering characteristics are the maximum is aligned with the
normal observing direction is provided on the front substrate
side.
[0118] (2) The liquid crystal display set forth in (1), wherein an
in-plane direction region of the anisotropic scatterer is formed as
a region in which low refractive index regions and high refractive
index regions are mixed.
[0119] (3) The liquid crystal display set forth in (2), wherein the
anisotropic scatterer is disposed such that ambient light which is
reflected on the rear substrate side is incident on the anisotropic
scatterer and is scattered when emitted to outside.
[0120] (4) The liquid crystal display set forth in (3), wherein the
ambient light reflected on the rear substrate side is incident from
a surface side of which an extent of a reflectance variation around
a boundary between the low refractive index region and the high
refractive index region is relatively large on the anisotropic
scatterer, and is emitted from a surface side of which an extent of
a reflectance variation around the boundary between the low
refractive index region and the high refractive index region is
relatively small.
[0121] (5) The liquid crystal display set forth in (1), wherein the
anisotropic scatterer is formed by laminating a plurality of
scattering members.
[0122] (6) The liquid crystal display set forth in (1), wherein the
liquid crystal display performs grayscale display using an area
ratio grayscale method.
[0123] It should be understood that various changes and
modifications to the presently preferred embodiments described
herein will be apparent to those skilled in the art. Such changes
and modifications can be made without departing from the spirit and
scope of the present subject matter and without diminishing its
intended advantages. It is therefore intended that such changes and
modifications be covered by the appended claims.
* * * * *