Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
2001-04-18
2003-06-10
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
C349S062000, C349S065000, C349S071000, C362S035000
Reexamination Certificate
active
06577359
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflective liquid crystal display apparatus of a front-lighting type.
2. Description of the Related Art
Conventional liquid crystal display apparatuses include a semitransparent type liquid crystal display apparatus having a back lighter. In such a liquid crystal display apparatus, light from the back lighter arranged behind the liquid crystal panel travels through a semitransparent reflector to the back side of the liquid crystal panel.
Recently, a semitransparent type liquid crystal display apparatus having a front lighter has been proposed.
FIG. 11
illustrates an example of such a liquid crystal display apparatus. The liquid crystal display apparatus D includes a liquid crystal panel
41
which comprises a pair of transparent plates
40
a
,
40
b
, and liquid crystal C filled therebetween. The liquid crystal panel
41
has a front surface (upper surface in this figure) on which a first polarizer
43
a
and a light guide panel
42
are disposed, and a rear surface on which a second polarizer
43
b
and a reflector
44
are disposed.
The light guide panel
42
may be a transparent, generally planar plate, but has one surface which is formed with a plurality of projections
45
. Each of the projections
45
is triangular, in cross section, including a first inclined surface
45
a
and a second inclined surface
45
b
which are different in the direction and angle of inclination. The projections
45
, each of which extends in the widthwise direction of the light guide plate
42
, are constantly spaced in a predetermined direction. Point light sources
46
are provided beside the light guide plate
42
.
With the liquid crystal display apparatus D, when the light sources
46
are turned on to perform image display, light from the light sources
46
travels within the light guide panel
42
while being totally reflected by the inner surfaces of the projections
45
of the light guide panel
42
. The light reflected by the projections
45
exits the light guide panel downwardly to enter the first polarizer
43
a
, the liquid crystal panel
41
, and the second polarizer
43
b
, and is then reflected upwardly by the reflector
44
. The light reflected by the reflector
44
travels again through the second polarizer
43
b
, the liquid crystal panel
41
and the first polarizer
43
a
to be emitted to the front side of the liquid crystal display apparatus D.
On the other hand, when image display is performed utilizing external light (e.g. sunlight or light from interior lighting) only, the external light travels downwardly to penetrate the light guide panel
42
, the first polarizer
43
a
, the liquid crystal panel
41
and the second polarizer
43
b
. The light is then reflected by the reflector
44
upwardly to travel again through the second polarizer
43
b
, the liquid crystal panel
41
, the first polarizer
43
a
and the light guide panel
42
to be emitted to the front side of the liquid crystal display apparatus D.
With the above-described liquid crystal display apparatus D in which the light guide panel
42
is formed with projections on its front surface, visibility of the display may often be deteriorated depending on the direction in which the user views the display. For example, in the case where the user views the liquid crystal panel
41
obliquely from the upper right in
FIG. 11
(See an arrow E), external light impinging on the light guide panel
42
is partially reflected by the second inclined surfaces
45
b
of the projections
45
and then by the first inclined surfaces
45
a
to travel toward the user's eyes.
Further, when the light sources
46
are turned on, light from the light sources
46
enters the light guide panel
42
to be totally reflected within the light guide panel
42
. At that time, however, the light vertically impinging on the second inclined surfaces
45
b
is not totally reflected by the second inclined surfaces
45
but exits the light guide panel
42
to travel toward the user's eyes. As a result, the contrast at the liquid crystal panel
41
is deteriorated, which leads to deteriorated visibility. Such a problem is peculiar to the liquid crystal display apparatus D which includes the light guide panel
42
formed with projections
45
.
In the above-described liquid crystal display apparatus D, external light or light from the light sources
46
is utilized to view the liquid crystal panel
41
, as described above. However, in the case where a mobile phone, for example, incorporating the liquid crystal display apparatus D is used utilizing sunlight and the user moves from a light place with sunlight to a dark place such as shade, it may be impossible to obtain sufficient light for visibility at the liquid crystal panel
41
. Therefore, it is difficult for the user to view the letters or images displayed at the liquid crystal panel
41
, so that the light sources
46
need to be turned on. In this way, the mobile phone incorporating the above-described liquid crystal display apparatus D is not conveniently usable.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a liquid crystal display apparatus which is capable of eliminating or reducing the problems described above.
In accordance with a first aspect of the present invention, there is provided a liquid crystal display apparatus comprising: a liquid crystal panel; a transparent light guide panel disposed in front of the liquid crystal panel and having at least one irregular surface for emitting light entering from a light source toward the liquid crystal panel; and a reflector disposed behind the liquid crystal panel for reflecting light passing through the light guide panel and the liquid crystal panel toward the liquid crystal panel and the light guide panel; wherein the irregular surface of the light guide panel is partially formed with an absorbing layer for absorbing external light.
In the prior art structure which is not provided with an absorbing layer, external light may be reflected on the light guide panel to deteriorate the visibility depending on the direction in which the user views the liquid crystal panel. However, in accordance with the present invention, the light guide panel has a surface which is partially formed with an absorbing layer for absorbing external light. Therefore, the external light impinging on the absorbing layer of the light guide panel is absorbed by the layer without being reflected. Thus, the absorbing layer prevents the contrast deterioration to enhance the display quality of the liquid crystal panel.
Preferably, the irregular surface of the light guide panel may include a plurality of projections each of which is triangular in cross section with two inclined surfaces differing from each other in direction and angle of inclination, and the absorbing layer may be provided on a steeper inclined surface of each projection.
Preferably, the absorbing layer may be formed by applying a black coating onto the steeper inclined surface.
The steeper inclined surface of each said projection may be located farther away from the light source than the other inclined surface.
Alternatively, the steeper inclined surface of each said projection may be located closer to the light source than the other inclined surface.
Preferably, the irregular surface of the light guide panel may include a plurality of cylindrical projections each having a circumferential side surface on which the absorbing layer is formed.
The irregular surface of the light guide panel may be oriented away from the liquid crystal panel.
The irregular surface of the light guide panel may face toward the liquid crystal panel.
In accordance with a second aspect of the present invention, there is provided a liquid crystal display apparatus comprising a liquid crystal panel; a transparent light guide panel disposed in front of the liquid crystal panel and having at least one irregular surface for emitting light entering from a light source toward the liquid crystal panel
Bednarek Michael D.
Dudek James
Rohm & Co., Ltd.
Schechter Andrew
Shaw Pittman LLP
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