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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resin substrate capable of transmitting
an incident light from the lateral face backwards efficiently, and a
liquid crystal display device of transmission type or
transmission/reflection type that is superior in the display quality,
employing the resin substrate as a cell substrate.
The present application is based on Japanese Patent Application No.
2000-185977, which is incorporated herein by reference.
2. Description of the Related Art
Nowadays, a liquid crystal display device is made smaller in thickness and
weight for the purposes of suppressing the increased weight along with the
larger size of a TV or personal computer screen, or reducing the size or
weight of a portable personal computer or portable telephone. As
illustrated in FIGS. 5 to 7, a conventional sidelight type light
conducting plate 83 with a front light 8 or a back light 8 is difficult to
reduce in thickness and weight. By the way, the side-light type light
conducting plate may have a thickness of 1 mm or more due to the necessity
of light transmission, and usually have a thickness of 3 mm or more when a
light diffusion plate, a reflector or a prism sheet is disposed thereon.
Reference numeral 81 denotes a light source and reference numeral 82
denotes a light source holder.
In view of the above, a liquid crystal display device of reflection type
has been proposed (Unexamined Japanese Patent Publication No. Hei.
5-158033) in which a lighting device is disposed on the lateral face of a
liquid crystal display panel, an illuminating light from its lateral face
is transmitted all over the panel, while being totally reflected at a cell
substrate on the visible side, its reflected light being scattered with a
reflector of rough face type and used for the display. This is aimed at
employing the liquid crystal panel also as a light conducting plate of the
side-light type, and omitting the conducting plate for accomplishment of
the liquid crystal display device of thin and light weight structure. Note
that the transmission of light is carried by the entire liquid crystal
display panel, principally the cell substrate of the liquid crystal cell.
In the previously noted patent publication, a glass plate is proposed as
the cell substrate, but the present inventors attempted to use a resin
substrate to further reduce the weight. However, it was found that there
was the problem with the conventional resin substrate, satisfying the
required characteristics such as transparency, thermal resistance,
chemical resistance, surface smoothness, and gas barrier property, that
the light transmission efficiency was lower, and the display was darker as
being farther away from the lighting device, with great differences in
brightness on the panel face.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a liquid crystal
display device of the transmission type or transmission/reflection type
that is superior in the luminance and uniformity and has an excellent
display quality by producing a resin substrate that is superior in the
backward transmission efficiency of a light that is incident upon the
lateral face, while utilizing the advantages of thin type and light weight
structure.
This invention provides a liquid crystal display device having a resin
substrate wherein a transparent resin plate has at least a conductive
layer via a transparent layer with a lower refractive index than the resin
plate, and a liquid crystal display panel comprising at least a liquid
crystal cell with a liquid crystal carried between a visible side
substrate and a back side substrate that are disposed with electrodes on
their substrates opposed to one another, wherein one or both of the
visible side substrate and the back side substrate is or are the resin
substrate.
With the resin substrate of the invention, the transparent layer of low
refractive index totally reflects an incident light upon the lateral face
to be confined within the substrate and transmitted in a side direction
(backwards) efficiently. Since the increased amount of weight is roughly
equal to the weight of the transparent layer of low refractive index, the
liquid crystal display device is superior in the thin and lightweight
structure. As a result, the liquid crystal cell is formed using the resin
substrate as the cell substrate, whereby an incident light from the
lighting device placed on the lateral face of the liquid crystal display
panel can be efficiently transmitted via the substrate backwards. The
optical path of the transmitted light is converted via the appropriate
optical path converting means in the visible direction, whereby the screen
is wholly bright and the good display quality with excellent uniformity of
brightness can be accomplished. Also, the liquid crystal display device of
the thin type with the lateral face arrangement of the lighting device can
be formed.
As previously described, if the transparent layer of low refractive index
does not exist, the transmitted light within the panel is incident upon
the liquid crystal layer and the color filter layer usually adjacently
disposed, the absorption component of light incident upon the polarizer is
increased due to birefringence of the liquid crystal layer, or the
backward transmission efficiency is remarkably decreased due to the light
absorption with the color filter layer, whereby the screen is darker as
being farther away from the lighting device, and the uniformity of
luminance is significantly lost, resulting in unfavorable display.
Features and advantages of the invention will be evident from the following
detailed description of the preferred embodiments described in conjunction
with the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a cross-sectional view illustrating a resin substrate;
FIG. 2 is a cross-sectional view illustrating a liquid crystal display
device;
FIG. 3 is a cross-sectional view illustrating another liquid crystal
display device;
FIG. 4 is a cross-sectional view illustrating a further liquid crystal
display device;
FIG. 5 is a cross-sectional view of the conventional Example;
FIG. 6 is a cross-sectional view of another conventional example;
FIG. 7 is a cross-sectional view of a further conventional example;
FIG. 8 is an explanatory view of an optical path in an example; and
FIG. 9 is an explanatory view of an optical path in the conventional
example.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A resin substrate of the invention is a transparent resin plate having at
least a conductive layer via a transparent layer with a lower refractive
index than the resin plate. FIG. 1 illustrates an example of the resin
substrate 1. Reference numeral 11 denotes the transparent resin plate; 12
denotes the transparent layer of low refractive index; 13 denotes the
conductive layer; 14 denotes an oriented film; 15 denotes a color filter
layer; 16 denotes a gas barrier layer; and 17 denotes a hard coat layer.
The transparent resin plate may be composed of one or more appropriate
resins, but not limited specifically. In this connection, examples of
resin may include acetate resin, polyester resin, polyether sulfone resin,
polycarbonate resin, polyamide resin, polyimide resin, polyolefine resin,
acrylic resin, polyether resin, polyvinyl chloride, styrene resin,
norbornene resin, and other thermosetting or ultraviolet ray setting
resins such as acrylic, urethane, acrylic urethane, epoxy, and silicone.
Particularly, the transparent resin plate used for a cell substrate is
preferably excellent in the respects of the transparency and the
mechanical strength rather than the transmittance of the illuminating
light or display light, and the cell strength. Further, it is preferably
superior in the optical isotropy in order to reduce the optical loss by
suppressing the birefringence in the light transmission direction or the
thickness direction as much as possible. Further, the transparent resin
plate is preferably excellent in the thermal resistance such as heat
stability, the chemical resistance, the gas barrier ability against oxygen
or water content, and the surface smoothness. In the respect of the
thermal resistance, the transparent resin plate is desirably made of resin
having a glass transition temperature of 90.degree. C. or higher, more
preferably 100.degree. C. or higher, or most preferably 120.degree. C. or
higher, such as epoxy resin, from the viewpoint of the heating temperature
when forming the transparent layer of low refractive index, the conductive
layer or the color filter layer.
The thickness of the transparent resin plate is not specifically limited,
and may be appropriately selected depending on the strength for the
purposes of use. For the cell substrate, the thickness may be typically 10
.mu.m to 5 mm, preferably 50 .mu.m to 2 mm, and more preferably 100 .mu.m
to 1 mm, from the respect of balancing the sealing strength of liquid
crystal, the light transmission efficiency, and the thin type and light
weight structure. Particularly when employed as the transmission substrate
of an incident light from the lighting device, a greater cross section is
more beneficial from the respects of the light incidence efficiency and
transmission efficiency, and accordingly a greater thickness is more
preferable.
On the other hand, a smaller thickness is more beneficial from the respect
of the thin type and lightweight structure, as described before. Note that
the transparent resin plate may be even in thickness, or may partially
vary in thickness. When used as the transmission substrate, the
transparent resin substrates having partially different thickness, for
example, a wedge shape in cross section, may be favorable in the respect
of increasing the incidence efficiency of transmitted light with an
inclined arrangement of optical path converting means.
The transparent layer of low refractive index on one side or both sides of
the transparent resin plate is provided as the layer having a lower
refractive index than the transparent resin plate. Thereby, when an
incident light from the lateral face via the lighting device 7 is
transmitted into the transparent resin plate (or cell substrate) 11, its
transmitted light is totally reflected due to a difference in refractive
index between the resin plate 11 and the transparent layer 12, and
confined within the transparent resin plate, so that the transmitted light
is passed to the opposite lateral face (backward) efficiently, as shown as
the polygonal line arrow .alpha.0' in FIG. 8.
When used as the cell substrate, the transparent layer of low refractive
index prevents the transmission state from partially changing and prevents
the transmitted light from decreasing or being less uniform because the
transmitted light being incident on the liquid crystal layer is
birefringent or scattered. Thereby, the transparent layer of low
refractive index prevents the display from being darker or the display
quality from degrading because the display near the lighting device is
ghosting in the rear. Further, when the color filter is disposed, it is
aimed at avoiding the reduction of the transmitted light by preventing the
transmitted light from being abruptly absorbed. In the liquid crystal
display device as taught in JP 5-158033, in which an incident light from
the lighting device is transmitted through the liquid crystal layer, the
transmitted light is scattered by the liquid crystal layer, resulting in
the non-uniform transmission state, causing the non-uniform emergent light
or ghost, the displayed image being difficult to see.
The transparent layer of low refractive index can be formed by suitable
methods, including vacuum deposition or spin coating, employing an
appropriate material with a lower refractive index than the transparent
resin plate, such as an inorganic or organic dielectric with low
refractive index. The materials or the forming methods are not
specifically limited. When employed as the cell substrate, the transparent
layer of low refractive index made of inorganic dielectric is preferable
from the respect of stability in forming the electrodes.
A greater difference in refractive index between the transparent layer and
the transparent resin plate is more beneficial from the respect of the
backward transmission efficiency with an extended range of angles capable
of total reflection. The difference in refractive index is 0.05 or more,
preferably 0.1 or greater, and more preferably from 0.12 to 0.5. The
difference in refractive index of the above value has less effect on the
display quality in the reflection mode due to an external light, when the
transparent resin plate is employed for the cell substrate. In this
connection, when the difference in refractive index is equal to 0.1, the
reflection factor of external light on its interface is 0.1% or less,
resulting in extremely small decrease in brightness or contrast due to its
reflection loss.
As illustrated in FIG. 1, the transparent layer 12 of low refractive index
is arranged between the transparent resin plate 11 and the conductive
layer 13, due to the confinement effect of the transmitted light and to
prevent the intrusion into the liquid crystal layer, when employed as the
cell substrate. Also, when the color filter layer 15 is disposed between
the transparent resin plate 11 and the conductive layer 13, as illustrated
in FIG. 1, it is preferably positioned closer to the resin plate 11 to
prevent the absorption loss of the transmitted light with the color filter
layer. Accordingly, usually, the transparent layer 12 of low refractive
index is directly provided on the transparent resin plate 11. In this
case, it is more beneficial to prevent scattering of the transmitted light
as an affixed plane of the transparent layer on the transparent resin
plate is smoother, and hence the transparent layer is smoother, and from
the viewpoint of preventing influence on the display light when employed
as the cell substrate.
The thickness of the transparent layer of low refractive index is favorably
greater from the respect of maintaining the total reflection effect,
because too thin layer may reduce the confinement effect due to the
exudation phenomenon of wave motion. Its thickness may be appropriately
determined in view of the total reflection effect, but typically may be
quarter wavelength (about 100 nm) or greater, preferably half wavelength
(190 nm) or greater, and more preferably one wavelength (380 nm) or
greater on the basis of the optical path length calculated by refractive
index .times.layer thickness from the respect of the total reflection
effect for a visible light having a wavelength from 380 nm to 780 nm,
particularly a light having a wavelength of 380 nm on the shorter
wavelength side. Further, it is preferably 600 nm or greater.
The conductive layer provided via the transparent layer of low refractive
index on the transparent resin plate may be appropriately prepared
according to the purposes of using the resin substrate, including the
electrode for use in the cell substrate, the light reflection layer or
electrode therefor, prevention of electrification, and shielding the
electromagnetic wave. Accordingly, the conductive layer may be formed of a
suitable material as conventionally employed for the transparent layer
made of, for example, ITO (indium tin oxide), or an opaque layer of the
light reflection type with the metallic thin film.
The resin substrate of the invention can be employed for a variety of
purposes as conventionally pursued, and particularly can be utilized for
the uses of entering the light from the lateral face and transmitting it
backward, such as the cell substrate in the liquid crystal cell, because
the backward transmission efficiency of the incident light on the lateral
face as above described is excellent. For the actual utilization, one or
more appropriate functional layers, including the color filter layer 15,
the gas barrier layer 16 and the hard coat layer 17, can be provided at
suitable locations as needed, as illustrated in FIG. 1.
The color filter layer 15 is provided for coloring the liquid crystal
display, and usually interposed between the transparent layer of low
refractive index 12 and the conductive film 13, as above described. Also,
when employed as the liquid crystal cell substrate, an oriented film 14
composed of a rubbing film to orient the liquid crystal may be provided.
The oriented film is usually formed on the conductive film 13 used as the
electrode as illustrated. Note that when employed as the cell substrate,
the gas barrier layer is usually provided outside the cell, and the hard
coat layer is provided on the surface outside the cell, as illustrated.
The liquid crystal display device of the invention has a liquid crystal
display panel comprising at least a liquid crystal cell with a liquid
crystal carried between a visible side substrate and a back side substrate
that are disposed with electrodes on their substrates opposed to one
another, wherein one or both of the visible side substrate and the back
side substrate is or are the resin substrate with the transparent layer of
low refractive index. Its example is shown in FIGS. 2, 3 and 4. Reference
numeral 10 denotes the liquid crystal display panel; 1 denotes the visible
side substrate composed of the resin substrate with the transparent layer
of low refractive index; 2 denotes the cell substrate on the back side
that is the opposite side; and 3 denotes the liquid crystal layer.
Reference numeral 21 denotes the substrate; 23 denotes the electrode; 24
denotes the oriented film; 26 denotes the gas barrier layer; and 27
denotes the hard coat layer.
The liquid crystal display panel 10 is not specifically limited in its
kind, except for the liquid crystal cell in which the resin substrate with
the transparent layer of low refractive index is employed for at least one
of the cell substrate, and can be appropriately used. In this connection,
the specific examples of the liquid crystal display panel may include a
twist type or a non-twist type, a guest host type, or a ferroelectric
liquid crystal, and the types using the light diffusion, such as a TN type
liquid crystal display panel, an STN type liquid crystal display panel, a
vertical orientation type display panel, a HAN type display panel, and an
OCB type display panel, on the basis of the orientation of the liquid
crystal. The driving methods for the liquid crystal may be appropriately
employed, such as an active matrix method or a passive matrix method, for
example. Driving the liquid crystal can be usually made via the electrodes
13, 23 provided inside a pair of cell substrates 1, 2 as illustrated in
FIG. 2.
In the case where the resin substrate of the invention is not employed on
the visible side or back side substrate, the other substrate may be made
of a suitable material such as glass or resin. From the viewpoint of light
weight, both substrates on the visible side and the back side maybe
preferably made of resin. Also, the other substrate is necessary to be
transparent when the illuminating light or display light needs to be
transmitted, whereas it may be opaque, if there is no need of transmitting
the light such as the reflection type liquid crystal cell in which the
electrode serving as the reflection layer is provided within the cell.
In this connection, the liquid crystal display panel as illustrated in FIG.
2 has both substrates 11, 21 on the visible side and the back side, and
both electrodes 13, 23 provided inside them, consisting of the
transmission type liquid crystal cell composed of the transparent layer,
and is a front light transmission/reflection type with the reflection
layer 6 disposed on the back side of the liquid crystal cell employing the
resin substrate 1 of the invention on the visible side substrate. Also,
the liquid crystal display panel as illustrated in FIG. 3 has the
electrode 23' provided inside the back side substrate consisting of the
reflection type liquid crystal cell made of a metal thin film serving as
the light reflection layer, and is the front light transmission/reflection
type.
Accordingly, in the case of the liquid crystal display panel of
transmission/reflection type as illustrated in FIG. 3, the transparent
substrate 21 is employed for the back side substrate as illustrated, but
because of no need of transmitting the light, the substrate maybe opaque
as previously described. Also, when the substrate with the gas shield and
abrasion resistance properties is employed, the gas barrier layer 26 or
the hard coat layer 27 as illustrated may be omitted to make the display
panel thinner.
On the other hand, in a liquid crystal display panel as illustrated in FIG.
4, both substrates 21, 11 on the visible side and the back side, and both
electrodes 23, 13 provided inside them are composed of a liquid crystal
cell of transmission type made up of a transparent layer, and the resin
substrate 1 according to the invention is employed for the substrate on
the back side. In this illustrated example, the reflection layer 6 is
disposed on the back side of the liquid crystal cell, whereby the liquid
crystal display panel of the transmission/reflection type with the
back-light is provided, but the liquid crystal display panel of the
transmission type may be provided without the reflection layer.
In forming the liquid crystal display device, one or more appropriate
optical layers such as the polarizer, phase retarder, light diffusion
layer or optical path converting means may be provided on one side or both
sides of the liquid crystal cell, as needed, and a lighting device may be
provided on one or more lateral faces of the liquid crystal display panel.
Further, a color filter layer may be provided on the cell substrate other
than the resin substrate according to the invention. In this case, the
color filter layer is usually provided between the substrate and the
electrode on the cell substrate. Also, the color filter layer is typically
provided on the visible side substrate, but not limited thereto. In the
illustrated example, reference numeral 4 denotes the polarizer, reference
numeral 5 denotes the optical path converting means, and reference numeral
7 denotes the lighting device.
The polarizer is aimed at producing the display employing the linear
polarization, and the phase retarder is aimed at improving the quality of
display by compensating for a retardation owing to birefringence of the
liquid crystal. Also, the light diffusion layer is aimed at effecting
homogeneous luminance owing to the enlargement of display area with the
diffusion of display light or leveling the bright streak emission via the
optical path converting means, and increasing the quantity of incident
light onto the optical path converting means owing to diffusion of the
transmitted light within the liquid crystal display panel. On the other
hand, the optical path converting means is aimed at regulating the optical
path of an incident light from the lighting device placed on the lateral
face of the liquid crystal display panel, or a transmitted light within
the panel to convert the optical path in a thickness direction of the
liquid crystal display panel to be useful as the display light.
The polarizer may be suitably employed, but particularly is not limited.
From the viewpoint of obtaining the display with excellent contrast ratio
by making a highly linear polarization incident, the polarizer preferably
uses highly polarized films such as absorption type polarized films or
films with a transparent protective layer on one side or either side,
composed of a dichroic material such as iodine or dichroic dye adsorbed to
a hydrophilic polymeric material such as polyvinyl alcohol based film, or
partial formal polyvinyl alcohol based film, or ethylene/vinyl acetate
copolymer based, partially saponified film.
The transparent protective layer is preferably made of a material that is
excellent in the respects of transparency, mechanical strength, thermal
stability, and moisture shield properties. In this connection, examples of
the material may include resins illustrated with the transparent resin
plate. The transparent protective layer may be attached by bonding the
film, or applying the resin liquid.
The polarizer for use, particularly the polarizer on the visible side, may
be subjected to the non-glare treatment or anti-reflection treatment in
order to prevent lower visibility due to surface reflection of the
external light. The non-glare treatment can be applied by making the
surface a refined prismatic structure by various methods including a
surface roughing method such as the sandblasting or embossing finish, and
a blending method of the transparent grains of silica. The anti-reflection
process can be made by forming a deposited film with coherency. Also, the
non-glare treatment or anti-reflection treatment may be effected by
bonding a film with the refined prismatic surface structure or with
coherency. The polarizer may be provided on either side of the liquid
crystal cell, as illustrated in FIGS. 2 and 4, or only on one side of the
liquid crystal cell, as illustrated in FIG. 3.
On the otherhand, the phase retarder may be a birefringent film that is
obtained by uniaxially or biaxially drawing a film made of appropriate
resin as illustrated with the transparent resin plate, an oriented film of
appropriate liquid crystal polymer, nematic or discotic, or its oriented
layer which is supported by the transparent substrate. It may be a film
having the refractive index regulated in a thickness direction under the
action of heat shrinkage force of a thermally shrinkable film. The phase
retarder for compensation is usually disposed between the polarizer on the
visible side or/and on the back side and the liquid crystal cell, as
needed, and maybe suitably used depending on the region of wavelength.
Also, the phase retarder may be composed of two or more layers in
superposition in order to control the optical characteristics such as the
retardation.
Also, the light diffusion layer can be provided by suitable methods with a
coated layer or a diffusion sheet having the refined prismatic surface
structure that is consistent with the non-glare layer. The light diffusion
layer can be formed as the layer also serving as bonding the optical layer
such as the polarizer or the phase retarder as the adhesive layer with
transparent grains, achieving the thin structure. The adhesive layer is
formed using adhesives having suitably a base polymer such as rubber,
acrylic, vinyl alkyl ether, silicone, polyester, polyurethane, polyether,
polyamide, or styrene.
By the way, the adhesives superior in the respects of transparency, weather
proofing, and thermal resistance, are preferably employed, such as acrylic
adhesives with the base polymer having alkyl ester of acrylic acid or
methacrylic acid as a main component. The transparent grains to be blended
into the adhesive layer may be one or more sorts of inorganic grains that
may be conductive, and made of, for example, silica, alumina, titania,
zirconia, tin oxide, indium oxide, cadmium oxide, or antimony oxide, with
an average diameter of 0.5 to 20 .mu.m, or organic grains made of bridged
or unbridged polymer.
The optical path converting means is aimed at reflecting an incident light
or its transmitted light from the lighting device 7 disposed on the
lateral face of the liquid crystal display panel 10, as indicated by the
polygonal line arrows .alpha.0, .alpha.1 in FIG. 8, and converting the
optical path in a thickness direction of the panel to be useful as the
illuminating light (display light) Hence, it is disposed outside one of
the visible side substrate or back side substrate in the liquid crystal
display panel 10 as illustrated in FIGS. 2 to 4, thereby forming a front
light or a back light.
The optical path converting means 5 may be in a suitable form of reflecting
an incident light from the lighting device 7, and converting the optical
path in a predetermined direction as illustrated in the figure. From the
standpoint of obtaining a display light excellent in the directivity to
the front direction via the optical path conversion, optical path
converting means preferably comprises an optical path converting bevel
opposed to the lateral face with the lighting device, that is, the
incidence lateral face, particularly an optical path converting bevel with
prismatic structures of substantial triangle or pentagon in cross section.
The optical path converting bevel that is preferable from the viewpoint of
directivity to the front direction has an inclination to the plane of
liquid crystal display panel being 35 to 48 degrees, preferably 38 to 45
degrees, and more preferably 40 to 44 degrees. Also, the optical path
converting means has preferably a repetition structure of the optical path
converting bevel from the respect of thin form. Further, the optical path
converting bevel may be formed in a projection (convex) form, but is
favorably formed in a groove (convex) form in order to maintain the
function of bevel to improve the abrasion resistance, because the bevel is
less prone to hurt. In the case where two or more incidence lateral faces
are provided by disposing the lighting devices on two or more lateral
faces of the liquid crystal display panel, the optical path converting
means preferably comprises the optical path converting bevels
corresponding to the number and position of incidence lateral faces, such
as a two-face optical path converting bevel with an equilateral triangle
in cross section.
In the liquid crystal display device of transmission/reflection type as
illustrated in FIGS. 2 to 4, it may be necessary in some cases to see a
display light .alpha.3 via the optical path converting means layer 5 as
indicated by the polygonal line arrow .alpha.2 in FIG. 8, in which case
from the viewpoint of good visibility of the display light, it is
preferable to have optical path converting means of a structure having a
gentle bevel or a flat face between the optical path converting bevels as
illustrated in the figure. Accordingly, when the optical path converting
means has a structure of prismatic structures triangular in cross section
disposed repeatedly and adjacently comprising the optical path converting
bevels and the gentle bevel, the inclination to the panel plane of the
gentle bevel is preferably 10 degrees or less, more preferably 5 degrees
or less, and most preferably 3 degrees or less. A difference in
inclination between gentle bevels adjacently placed is preferably within
one degree, and more preferably as small as 0.3 degree or less.
The optical path converting means of a structure having the optical path
converting bevel can reflect an incident light or its transmitted light
from the lateral face via the optical path converting bevel, convert the
optical path with excellent directivity in the front direction and easily
balance the brightness in a state favorable for both transmission and
reflection modes. However, in the case of a scattering reflection method
via the rough surface, as disclosed in JP 5-158033, the light usable for
the display is the light significantly slanted from the front direction
getting out of the total reflection condition due to scattering and
emerging from the panel, being less favorable to utilize it for the
display, in which the display in the front direction is darker. If the
scattering with the rough surface reflector is stronger, the quantity of
light in the front direction in the reflection mode is reduced, and
unfavorable for the display. Accordingly, in this rough surface scattering
reflection method, the brightness in both transmission and reflection
modes is difficult to balance.
The optical path converting means maybe made of a suitable material
indicating the transparency in accordance with the wavelength region of
the lighting device. In this connection, in a visible light region, the
resins or glasses listed in the transparent resin plate can be employed.
The optical path converting means is preferably made of a material
indicating no or less birefringence. From the viewpoint of suppressing the
quantity of light loss that is confined within the panel due to reflection
at the interface and can not emerge and supplying efficiently an incident
light on the lateral face or its transmitted light to the optical path
converting bevel of the optical path converting means, the optical path
converting means desirably has a refractive index higher than the
transparent layer of low refractive index in the resin substrate, which is
preferably 0.05 or more, and more preferably 0.1 or more.
The optical path converting means can be formed by a cutting method or
other suitable methods. The preferable manufacturing methods from the
standpoint of mass productivity include a transfer method of transferring
a shape by pressing the thermoplastic resin onto a mould capable of
forming a predetermined shape under heating, a filling method of filling a
thermoplastic resin molten by heating or a resin fluidized by heating or
solvent into a mould capable of forming a predetermined shape, and a
polymerization method of polymerizing a liquid resin polymerizable with
the heat, ultraviolet rays or radiant rays by filling or flowing it into a
mould capable of forming a predetermined shape. Accordingly, the optical
path converting means may be formed by attaching its predetermined
conformation directly on the cell substrate, or formed as a transparent
sheet with the predetermined conformation. The thickness of the optical
path converting means may be determined suitably, but typically 30 .mu.m
or less from the respect of thin structure, preferably 5 to 20 .mu.m, and
more preferably 10 to 100 .mu.m.
The optical path converting means is preferably disposed with the face
having the optical path converting means formed outward, as illustrated in
FIGS. 2 to 4, from the standpoints of the higher reflection efficiency via
the optical path converting bevel, or the increased luminance by making
effective use of the incident light on the lateral face. In the case where
the optical path converting means is formed independently as the
transparent sheet as above described, the transparent sheet is preferably
bonded to the liquid crystal display panel via an adhesive layer having a
higher refractive index than the transparent layer of low refractive index
in the resin substrate, particularly an adhesive layer of refractive index
as equivalent as possible to that of the transparent sheet, from the
above-mentioned respects.
Accordingly, the refractive index of the adhesive layer maybe consistent
with that of the optical path converting means. The adhesive layer can be
formed by suitable transparent adhesives, the sort of adhesives being
specifically not limited. From the respect of simplifying the bonding
operation, the bonding method with the adhesive layer is preferred. The
adhesive layer may be consistent as above described, and may be of the
light diffusion type.
The lighting device placed on the lateral face of the liquid crystal
display panel is aimed at making a light for use as the illuminating light
of the liquid crystal display device incident upon the lateral face of the
liquid crystal display panel. Thereby, the liquid crystal display device
can be made a thin and lightweight structure by a combination with the
optical path converting means placed on the panel. In this connection, in
the liquid crystal display panel, as illustrated in FIGS. 2 to 4, there is
a difference in the thickness between the optical path converting means 5
and a side-light light conducting plate 83 which directly leads to a
difference in the thickness of the liquid crystal display device, as will
be clear from the contract with the liquid crystal display panel of
transmission/reflection type using the side-light type conducting plate 83
as illustrated in FIGS. 5 to 7. In FIGS. 5 to 7, reference numeral 25
denotes a color filter layer, reference numeral 8 denotes a lighting
device, reference numeral 81 denotes a light source, reference numeral 82
denotes a holder, and other reference numerals denote the same parts as in
FIGS. 2 to 4.
From the viewpoint of the backward transmission efficiency of an incident
light from the lighting device, the preferred position of the lighting
device is on a lateral face of the cell substrate on the side where the
optical path converting means is provided, in the resin substrate 1
according to the invention as illustrated in FIGS. 2 to 4. In this case,
in order to prevent an incident light from the lighting device entering
the liquid crystal layer, a preferred method of disposing the lighting
device involves extending the lateral face of the cell substrate 1 where
the lighting device is disposed from the lateral face formed by another
cell substrate 2. Accordingly, the substrates on the visible side and the
back side may be different in the size of plane, and are not required to
be equal. As above described, the thickness of the substrates on the
visible side and the back side may be different, and are not required to
be equal.
As previously described, when an incident light .alpha.0 on the lateral
face from the lighting device 7 is transmitted inside the transparent
resin plate 11 via the transparent layer 12 of low refractive index
provided on the resin substrate 1 as indicated by the polygonal line
arrows .beta.0, .alpha.0' in FIG. 8, the transmitted light is totally
reflected owing to a difference in refractive index between the resin
plate 11 and the transparent layer 12, and efficiently confined within the
transparent resin plate to thereby transmit efficiently the transmitted
light .alpha.0' to the opposite lateral face (backward | | |
