Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2003-01-07
2004-05-11
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S063000, C349S064000, C349S160000
Reexamination Certificate
active
06734934
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an external type liquid crystal display including a liquid crystal cell having a pair of opposing transparent substrates with a liquid crystal layer held therebetween, and a reflector provided on an outer surface of the liquid crystal cell. The invention more particularly relates to a liquid crystal display having improved visibility by providing the liquid crystal cell with a light scattering characteristic.
2. Description of the Related Art
Liquid crystal displays are generally divided into semi-transmissive or transmissive type displays having a backlight and reflective type displays. The reflective type liquid crystal display utilizes only external light such as sunlight and illumination for display and does not use a backlight. This type of display is widely used for mobile information terminals that should be thin and lightweight, and operate with low power consumption. The reflective type liquid crystal display includes a reflector that reflects incoming light from the display surface side for display. Some reflectors have a mirror surface and others have an irregular surface. The reflector having, an irregular surface is more suitable for obtaining a wider viewing angle than the reflector with a mirror surface.
FIG. 4
is a schematic sectional view of a conventional reflective type liquid crystal display including a reflector with an irregular surface. The conventional liquid crystal display
200
includes a liquid crystal cell
220
, and a front light
210
provided in front of the liquid crystal cell
220
(in the upper part of FIG.
4
).
The conventional front light
210
includes a light guide plate
212
, and a light source
213
of a cold cathode tube provided at the side end face
212
a
of the light guide plate
212
. The light guide plate
212
has an emission surface
212
b
as a lower surface (the surface on the side of the liquid crystal cell
220
), from which light is emitted. The surface on the opposite, side to the emission surface
212
b
(the upper surface of the light guide plate
212
) is a prism surface
212
c
that can change the optical path of light propagating through the light guide plate
212
toward the emission surface
212
b.
The liquid crystal cell
220
has first and second opposing substrates
221
and
222
joined to each other by a seal member
224
and having a liquid crystal layer
223
therebetween. There are display circuits
226
and
227
on the first and second substrates
221
and
222
on the side of the liquid crystal layer
223
(at the inner side). A reflector
230
is provided on the side of the first substrate
221
opposite to the liquid crystal layer
223
(at the outer side) through an adhesive layer
231
. The reflector
230
includes a reflector substrate
228
having one irregular surface, and a reflection layer
229
formed on the irregular surface of the reflector substrate
228
. The reflection layer
229
is located on the side of the first substrate
221
.
In the liquid crystal display
200
having the above structure, when the front light
210
is turned on, light emitted from the light source
213
is propagated in the light guide plate
212
and emitted from the emission surface
212
b
. The light emitted from the emission surface
212
b
is let into the liquid crystal cell
220
as the illumination light, sequentially passed through the second substrate
222
, the display circuit
226
, the liquid crystal layer
223
, the display circuit
227
, the first substrate
221
, and the adhesive layer
231
and reflected by the reflection layer
229
. The reflected light is returned to the outer side of the liquid crystal cell
220
(the side of the front light
210
), and reaches the viewer through the emission surface
212
b
and the prism surface
212
c
of the front light
210
. In this way, the displayed content at the liquid crystal cell
220
is viewed by the viewer.
When sunlight is used for display rather than turning on the front light
210
, sunlight comes into the liquid crystal cell
220
through the prism surface
212
c
and the emission surface
212
b
of the front light
210
, and light reflected by the reflection layer
229
is viewed by the viewer similarly to the above described case.
However, the on going development and designing of the reflective type liquid crystal displays including the reflector with the irregular reflection surface aims at forming fine irregularities (raise and recessed portions) on the reflection surface to adjust the angle of the reflected light and controlling the irregular geometry to control even the directivity of the reflected light. The fine irregularities on the reflection surface surely improve the controllability of the reflected light, but there is a problem that a spectrum is more likely to occur under intense sunlight, which could cause a rainbow-like pattern (hereinafter simply as “rainbow”) to be observed on the display screen, in other words, the visibility is lowered.
SUMMARY OF THE INVENTION
The present invention is directed to a solution to the above problem, and a liquid crystal display including a reflector having an irregular surface that can prevent a rainbow from appearing on the screen is provided.
In order to solve the above problem, the liquid crystal display according to the invention includes a pair of opposing transparent substrates having a liquid crystal layer held therebetween. An outer surface of one of the transparent substrates serves as a light scattering surface having a light scattering characteristic. A reflector having an irregular reflection surface is provided on the light scattering surface so that the reflection surface is on the side of the light scattering surface.
The liquid crystal display according to the invention includes the light scattering surface between the reflection surface and the liquid crystal layer, and therefore light reflected by the reflection surface of the reflector is scattered as it passes through the light scattering surface, despite a spectrum caused at the irregularities at the reflection surface. Therefore, the rainbow is prevented from being generated at the display screen.
According to the invention, the light scattering surface preferably has irregularities.
In this manner, the outer surface of one of the transparent substrates on the side (light scattering surface) having the reflector is provided with irregularities, so that the surface may have a preferable light scattering characteristic.
According to the invention, the haze of the light, scattering surface is preferably in the range from 15% to 30%.
As will be described, the haze is an index of the degree of light scattering. When the outer surface (light scattering surface) of the above-mentioned one transparent substrate has too small a light scattering characteristic, there is not a sufficient rainbow elimination effect at the display screen. Meanwhile, when the light scattering characteristic is too large, the display characteristic at the screen is significantly lowered. When the haze at the outer surface (light scattering surface) of the above mentioned one transparent substrate is in the range from 15% to 30%, the display characteristic of the liquid crystal display can be restrained from being lowered, while the rainbow at the display screen can be prevented.
According to the invention, the reflector is provided on the light scattering surface through the adhesive layer and the difference between the refractive index of one transparent substrate having the light scattering surface and the refractive index of the adhesive layer is preferably at least 0.01.
In this way, the refractive indexes of the light scattering surface and the adhesive layer can be different, so that light reflected by the reflection surface of the reflector can effectively be scattered at the light scattering surface, and the rainbow can be prevented from being generated.
The thickness of one transparent substrate having the light scattering surface is preferably smaller tha
Tanada Tetsushi
Yoshii Katsumasa
Alps Electric Co. ,Ltd.
Chowdhury Tarifur R.
Schechter Andrew
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