Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-09-08
2002-02-26
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S086000, C349S088000, C349S112000, C349S117000
Reexamination Certificate
active
06351298
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to reflective type liquid crystal display devices, and more particularly to reflective type liquid crystal display devices suitable adopted for various kinds of audio-visual appliances, information display devices, and game machines, such as word processors, notebook type personal computers, electronic still cameras, portable video cameras, portable information terminus, vehicle information display devices.
BACKGROUND OF THE INVENTION
FIG. 25
is a cross-sectional view showing an arrangement of a reflective type liquid crystal display device
101
of a Guest Host (GH) mode using a conventional quarter-wavelength plate. The reflective type liquid crystal display device
101
is composed of light-passing substrates
102
and
103
, a liquid crystal layer
104
, transparent electrodes
107
and
109
, orientation films
108
and
110
, a quarter-wavelength plate
111
, and a reflector plate
112
. It is assumed here that the liquid crystal layer
104
flanked by the light-passing substrates
102
and
103
made of glass includes dichroic dye
106
, and the liquid crystal has a positive dielectric constant anisotropy.
The belt-like transparent electrodes
107
and
109
are provided on the respective surfaces
102
a
and
103
a,
of the light-passing substrates
102
and
103
, facing the liquid crystal layer
104
. The light-passing substrates
102
and
103
are disposed so that the transparent electrodes
107
and
109
cross at right angles. The orientation films
108
and
110
are provided on the transparent electrodes
107
and
109
provided on the light-passing substrates
102
and
103
. The surfaces of the orientation films
108
and
110
receive rubbing or other treatment to orientate liquid crystal molecules
105
of the liquid crystal layer
104
parallel to the substrates. The light-passing substrates
102
and
103
are disposed so that the directions in orientation treatment of the orientation films
108
and
110
are parallel to each other. Besides, the quarter-wavelength plate
111
and the reflector plate
112
are disposed in this order on the surface
103
b,
of the light-passing substrate
103
, facing the liquid crystal layer
104
. The quarter-wavelength plate
111
is disposed so that the optic axis thereof forms an angle of 45° to the direction in rubbing orientation treatment of the liquid crystal molecules
105
.
Display in a GH mode exploits the absorption coefficient anisotropy of the dichroic dye added to the liquid crystal layer. For example, if dichroic dye having a bar structure is used, since the dye molecules have properties to become orientated parallel to the liquid crystal molecules, it becomes possible to change the orientation state of the dye molecules by changing the orientation state of the liquid crystal molecules with the application
on-application of an electric field.
For example, since the p type dye has an absorption axis, i.e. a transitional dipole moment, practically parallel to the longer axes of the molecules, the p type dye absorbs the polarization component parallel to the longer axes substantially, but absorbs little of the polarization component perpendicular thereto. The absorption coefficient for light of the dichroic dye varies, in this manner, depending upon the directions of the molecular axes, thereby effecting bright and dark display.
Here, referring to the FIGS.
26
(
a
) and
26
(
b
), the following description will explain the principles of the operation of the reflective type liquid crystal display device
101
. The explanation will deal with the case where the p type dye is used as the dichroic dye
106
and black & white display is carried out.
FIG.
26
(
a
) shows a state where no voltage is applied, while FIG.
26
(
b
) shows a state where voltage is applied. In the state where no voltage is applied, the liquid crystal molecules
105
are orientated along the direction in the orientation treatment of the orientation films
108
and
110
. Therefore, the dichroic dye
106
is also orientated along the direction in the orientation treatment of the orientation films
108
and
110
. Part of incident light
113
on the side of the light-passing substrate
102
, i.e., light
113
a
having the vibration plane parallel to the longer axes of the molecules of the dichroic dye
106
, is absorbed by the dichroic dye
106
. Other part to the light
113
, i.e., light
113
b
having the vibration plane perpendicular to the longer axes of the molecules of the dichroic dye
106
, passes through the liquid crystal layer
104
. The light
113
b
is circularly polarized as it passes the quarter-wavelength plate
111
, and is circularly polarized in the opposite direction as it is reflected by the reflector plate
112
. Subsequently, the light
113
b
becomes light
113
a
having the vibration plane parallel to the longer axes of the molecules of the dichroic dye
106
as it passes the quarter-wavelength plate
111
again, and is absorbed by the dichroic dye
106
. Therefore, the reflective type liquid crystal display device
101
can carry out dark display.
Meanwhile, in the state where voltage is applied, the liquid crystal molecules
105
are orientated along the direction of the electric field. Therefore, the dichroic dye
106
is also orientated along the direction of the electric field. The incident light
113
, is not absorbed by the dichroic dye
106
, passes through the liquid crystal layer
104
, does not change the polarization state thereof as it passes through the quarter-wavelength plate
111
, is reflected by the reflector plate
112
, passes through the quarter-wavelength plate
111
again, and enters the liquid crystal layer
104
. Since the light
113
is not absorbed by the dichroic dye
106
, the light
113
exits the liquid crystal layer
104
without changing at all. Therefore, the reflective type liquid crystal display device
101
can carry out bright display.
The reflective type liquid crystal display device
101
is disclosed, for instance, by Japanese Laid-Open Patent Application No. 52-129450/1977 (Tokukaisho 52-129450). Besides, Japanese Laid-Open Patent Application No. 54-26756/1979 (Tokukaisho 54-26756) discloses technology to carry out dark display with voltage applied and bright display with no voltage applied in the arrangement of the above reflective type liquid crystal display device
101
, by adding dye to Host crystal having an orientation film of slanting perpendicular orientation and having Guest Host liquid crystal of a negative dielectric constant anisotropy.
In the reflective type liquid crystal display device
101
, the performance of the reflector plate
112
dictates display quality. That is, if the reflector plate used for such display principle does not preserve the polarization of incident light, the clockwise polarized light is not effectively transformed to the anti-clockwise polarized light, or vice versa, as mentioned above. As a result, light leaks during dark display, contributing to a reduction of contrast.
An example of reflector members capable of preserving polarization is a flat mirror-surface reflector member. However, the mirror-surface reflector member reflects the images of external objects at the surface thereof, and causes new problems: namely, reflections of nearby objects appear on the surface, overlapping the displayed image in the bright state, and visibility is seriously degraded. The reflector plate therefore has light diffusion characteristics as well.
A reflector plate is essential which can both preserve the light diffusion characteristics and control the polarization. Japanese Laid-Open Patent Application No. 7-218906/1995 (Tokukaihei 7-218906), as an example, discloses a reflector plate composed of a concave-convex portion made of smooth photosensitive resin and a aluminum film provided thereon. The application reports that 50% or more of the polarization should be preserved to achieve the contrast of 4 or more and that 70% or more of the polarization should be preserved to achieve the contrast o
Mitsui Seiichi
Okamoto Masayuki
Ueki Shun
Chowdhury Tarifur R.
Dike Bronstein, Roberts & Cushman IP Group of Edwards & Angell,
Neuner, Esq. George W.
Sikes William L.
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