Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1997-08-19
2001-05-15
Malinowski, Walter (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S098000
Reexamination Certificate
active
06233029
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a display device and, more preferably, to a reflection-type liquid-crystal display device.
DESCRIPTION OF RELATED ART
A conventional liquid-crystal display device using a transmission polarized light axis changing means having a polarized light axis of a TN (Twisted Nematic) liquid crystal, STN (Super-Twisted Nematic) liquid crystal, or the like employs a structure in which the transmission polarized light axis changing means is sandwiched by two polarizers. For this reason, good efficiency of light cannot be obtained, and, especially in the reflection type, a dark display is posed as a problem.
Therefore, it is an object of the present invention to provide a display device, using a transmission polarized light axis changing element, which provides a bright display.
SUMMARY OF THE INVENTION
The principle of the present invention will be described below with reference to
FIGS. 1 and 2
.
FIGS. 1 and 2
are views for explaining the principle of a display device according to the present invention. Liquid-crystal display devices shown in
FIGS. 1 and 2
illustrate the principle of the present invention. The present invention is not limited to the liquid-crystal display devices shown in
FIGS. 1 and 2
as a matter of course.
Referring to
FIG. 1
, in this liquid-crystal display device, a TN liquid crystal
140
is used as a transmission polarized light axis changing element. A polarizer
130
is arranged above the TN liquid crystal
140
. The polarizer
130
transmits linearly polarized light of a predetermined first direction of incident light, and absorbs linearly polarized light of a direction perpendicular to the linearly polarized light of the first direction. A light-scattering layer
150
, a polarized light separator
160
, a colored layer
170
, and a reflecting plate
180
are arranged in this order under the TN liquid crystal
140
. The following description is performed on the assumption that the left side of the liquid-crystal display device serves as a voltage applied portion
110
and the right side serves as a voltage non-applied portion
120
.
The polarized light separator
160
comprises a (¼) &lgr; plate
162
and a cholesteric liquid-crystal layer
164
. The cholesteric liquid crystal reflects a circularly polarized light which has a wavelength equal to the pitch of the liquid crystal and has the same rotational direction as that of the liquid crystal, and transmits other light. Therefore, for example, when a left-rotational cholesteric liquid crystal having a pitch of 5000 Å is used as the cholesteric liquid-crystal layer
164
, an element which reflects left-circularly polarized light having a wavelength of 5,000 Å and transmits right-circularly polarized light and left-circularly polarized light having other wavelengths is obtained. In addition, when left-rotational cholesteric liquid crystal is used, and its pitch is changed within the cholesteric liquid crystal over the whole wavelength range of visible light, an element which reflects left-circularly polarized light over not only a single color but also white light and transmits right-circularly polarized light is obtained.
In the polarized light separator
160
obtained by combining the cholesteric liquid-crystal layer
164
and the (¼) &lgr; plate
162
described above, when linearly polarized light of a predetermined third direction is incident from the (¼) &lgr; plate
162
, the linearly polarized light is changed by the (¼) &lgr; plate
162
into left-circularly polarized light, reflected by the cholesteric liquidcrystal layer
164
, and emitted again as linearly polarized light of the predetermined third direction by the (¼) &lgr; plate
162
. When linearly polarized light of a second direction perpendicular to the third direction is incident, the linearly polarized light is changed by the (¼) &lgr; plate
162
into right-circularly polarized light and transmitted through the cholesteric liquid-crystal layer
164
. In response to light being incident from the lower side of the cholesteric liquid-crystal layer
164
, linearly polarized light of the second direction is emitted upward from the (¼) &lgr; plate
162
.
In this manner, the polarized light separator
160
obtained by combining the cholesteric liquid-crystal layer
164
and the (¼) &lgr; plate
162
is a polarized light separation means which transmits a linearly polarized light component of the predetermined second direction of light being incident from the (¼) &lgr; plate
162
, reflects a linearly polarized light component of the third direction perpendicular to the predetermined second direction, emits linearly polarized light of the second direction to the (¼) &lgr; plate
162
in response to light being incident from the cholesteric liquid-crystal layer
164
. As a polarized light separation means having this function, in addition to the polarized light separator
160
obtained by combining the cholesteric liquid-crystal layer
164
and the (¼) &lgr; plate
162
described above, a means using a film obtained by stacking a large number of films (U.S. Pat. No. 4,974,219), a means for separating reflection polarized light from transmission polarized light by using an angle of polarization (SID 92 DIGEST pp. 427 to 429) and a means using a hologram are known.
Referring to
FIG. 1
again, in the voltage nonapplied portion
120
on the right, natural light
121
is changed by the polarizer
130
into linearly polarized light of a direction parallel to the drawing surface. Thereafter, the light is twisted at 90° in polarization direction by the TN liquid crystal
140
to be linearly polarized light of a direction perpendicular to the drawing surface, the linearly polarized light is changed by the (¼) &lgr; plate
162
into left-circularly polarized light, and the left-circularly polarized light is reflected by the cholesteric liquid-crystal layer
164
to be incident on the (¼) &lgr; plate
162
again. The left-circularly polarized light is changed by the (¼) &lgr; plate
162
into linearly polarized light of a direction perpendicular to the drawing surface, and the linearly polarized light is twisted in polarization direction by the TN liquid crystal
140
to be linearly polarized light of a direction parallel to the drawing surface. The linearly polarized light is emitted from the polarizer
130
as linearly polarized light of a direction parallel to the drawing surface. In this manner, in a voltage non-applied state, since incident light is reflected by the polarized light separator
160
, a bright display is obtained. Since the light-scattering layer
150
is formed between the (¼) &lgr; plate
162
and the TN liquid crystal
140
, the state of the reflected light from the polarized light separator
160
is changed from a specular state to a white state.
In the voltage applied portion
110
on the left, natural light
111
is changed by the polarizer
130
into linearly polarized light of a direction parallel to the drawing surface. Thereafter, the linearly polarized light is transmitted through the TN liquid crystal
140
without changing the polarization direction and changed by the (¼) &lgr; plate
162
into right-circularly polarized light, and the right-circularly polarized light is transmitted through the cholesteric liquid-crystal layer
164
. The right-circularly polarized light transmitted through the cholesteric liquid-crystal layer
164
is partially reflected by the coloring layer
170
, incident on the (¼) &lgr; plate
162
again, and changed by the (¼) &lgr; plate
162
into linearly polarized light of a direction parallel to the drawing surface. The linearly polarized light is transmitted through the TN liquid crystal
140
without changing the polarization direction and emitted from the polarizer
130
as linearly polarized light of the direction parallel to the drawing surface. The right-circularly polarized light transmitted throug
Iijima Chiyoaki
Tsuchihashi Toshihiko
Malinowski Walter
Oliff & Berridg,e PLC
Seiko Epson Corporation
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