Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-09-22
2001-04-17
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S099000, C349S113000, C349S118000, C349S121000, C252S299100
Reexamination Certificate
active
06219122
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflective liquid crystal display device having a bright light display and high contrast among the characteristics of the bright light display, and, a wide angle of view on the display plane in vertical and horizontal directions, and superior visual characteristics.
2. Description of the Related Art
In general, liquid crystal display devices are either a semi-transmissive or transmissive type having a backlight, or a reflective type. Reflective liquid crystal display devices produce a display without a backlight by using only ambient light, such as sunlight or artificial light, and are widely used in, for example, portable information terminals or the like that need a low profile, light weight, and low power consumption.
FIG. 10
is a schematic cross-sectional view showing the configuration of a well-known type of reflective liquid crystal display device. In particular, the device in this example is a passive-matrix STN (Super-Twisted Nematic) type.
In this reflective liquid crystal display device, a liquid crystal cell
72
for a reflective STN mode and a retardation film
73
are placed in that order on the surface of a lower polarizing plate
70
of a reflection plate
71
, and an upper polarizing plate
74
is further placed on the retardation film
73
.
In the liquid crystal cell
72
, a lower glass substrate
75
, a color filter
76
, a lower transparent electrode layer
78
, a lower alignment layer
79
, an upper alignment layer
80
placed opposing the lower alignment layer
79
with a space therebetween, an upper transparent electrode layer
81
, and an upper glass substrate
82
are laid in that order on the surface of the lower polarizing plate
70
. An STN liquid crystal layer
83
is interposed between the lower and upper alignment layers
79
and
80
. An overcoat layer (not shown) made of silica or acrylic resin is provided between the color filter
76
and the lower transparent electrode layer
78
.
The retardation film
73
compensates for the phase difference of light passing through the STN liquid crystal, thereby preventing the display from taking on a blue or yellow tint.
The liquid crystal display device is generally required to have high display performance, such as having high resolution, high contrast, a bright screen, vivid colors, high visibility, and a wide angle of view.
When the conventional reflective liquid crystal display device is applied to a display section of a portable information terminal or the like, however, a high-contrast region of the display screen in the horizontal direction is large, whereas a high-contrast region in the vertical direction is small. Therefore, the angle of view on the display screen in the vertical direction is narrow, the dependence on the angle of view is great, and visual characteristics are unsatisfactory. Moreover, light display (white display) is darker than that of a transmissive liquid crystal display device equipped with a high-intensity backlight.
Accordingly, it has been suggested that the white display during the application of a selection voltage be brightened by removing the lower polarizing plate
70
placed between the liquid crystal cell
72
and the reflection plate
71
, and by using only the upper polarizing plate
74
on the retardation film
73
. In such a reflective liquid crystal display device, however, removing one of the polarizing plates not only brightens the light display, but also brightens the dark display (black display), which results in a loss of contrast.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a reflective liquid crystal display device that having a bright white display and high contrast among the characteristics the of bright white display, a wide angle of view on the display plane in vertical and horizontal directions, and excellent visual characteristics.
In order to achieve the above object, according to an aspect of the present invention, there is provided a reflective liquid crystal display device, wherein a transparent electrode and an alignment layer are placed in that order from the inner side the of transparent substrates on opposite sides of a liquid crystal layer in a liquid crystal cell of a normally black display type, a transparent electrode and an alignment layer are placed in that order from the inner side of the other transparent substrate, and two retardation films and a polarizing plate are placed in that order from the outer side of the other transparent substrate in the liquid crystal cell, wherein a retardation &Dgr;nd
LC
of the liquid crystal cell ranges from 705 nm to 890 nm, and wherein, when an alignment direction a of the alignment layer on the side of the other transparent substrate and an alignment direction b of the alignment layer on the side of one of the transparent substrates are viewed from the light incident side, and the direction between the alignment directions a and b that bisects the interior angle, which is formed by an intersection O of the alignment directions a and b, and the alignment directions a and b, is designated a normal direction X, a retardation &Dgr;nd
RF1
of the retardation film adjacent to the other transparent substrate ranges from 195 nm to 280 nm, an angle &phgr;
RF1
formed by a delayed phase axis of the retardation film with respect to the normal direction X ranges from 75° to 115°, counterclockwise, as viewed from the light incident side, a retardation &Dgr;nd
RF2
of the retardation film adjacent to the polarizing plate ranges from 310 nm to 415 nm, an angle &phgr;
RF2
formed by a delayed phase axis of the retardation film with respect to the normal direction X ranges from 130° to 180°, counterclockwise, as viewed from the light incident side, and an angle formed by an absorption axis of the polarizing plate with respect to the normal direction X ranges from 80° to 130° or 170° to 220°, counterclockwise, as viewed from the light incident side.
According to the reflective liquid crystal display device of the present invention, in the liquid crystal cell of the normally black display type, the transparent electrode and the alignment layer are placed in that order from the inner side of one of the transparent substrates on opposite sides of the liquid crystal layer, the transparent electrode and the alignment layer are placed in that order from the inner side of the other transparent substrate, and two retardation films and the polarizing plate are placed in that order from the outer side of the other transparent substrate of the liquid crystal cell. Therefore, only a single polarizing plate is used, which makes it possible to improve transmittance in a voltage applied state (when a selection voltage is applied), and to brighten the white display. As a result, the contrast is improved, and excellent display characteristics are obtained.
In particular, &Dgr;nd
LC
of the liquid crystal cell ranges from 705 nm to 890 nm, &Dgr;nd
RF1
of the retardation film adjacent to the other transparent substrate ranges from 195 nm to 280 nm, and the angle &phgr;
RF1
formed by the delayed phase axis of the retardation film with respect to the normal direction X ranges from 75° to 115°, counterclockwise, as viewed from the light incident side. &Dgr;nd
RF2
of the retardation film adjacent to the polarizing plate ranges from 310 nm to 415 nm, and the angle &phgr;
RF2
formed by the delayed phase axis of the retardation film with respect to the normal direction X ranges from 130° to 180° counterclockwise, as viewed from the light incident side. The angle &phgr;
Pol
formed by the absorption axis of the polarizing plate with respect to the normal direction X ranges from 80° to 130° or 170° to 220°, counterclockwise, as viewed from the light incident side. The above settings make the white display brighter, and improves contrast.
In the reflective liquid crystal display device having the above-described configuration, it is preferable t
Hoshino Toshiaki
Kano Mitsuru
Ohizumi Mitsuo
Uchida Tatsuo
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Ngo Julie-Huyen L.
Sikes William L.
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