Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
2000-09-25
2003-10-07
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
C549S090000, C549S315000
Reexamination Certificate
active
06630968
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a technical field of a display device such as a liquid crystal device, and more particularly to a technical field of a transflective monochrome or color display device capable of displaying while switching between a reflective display and a transmissive display, an electronic apparatus using such a display device, and a light guide plate suitable for use in such a display device.
BACKGROUND ART
So far, reflective liquid crystal devices, because of its small power consumption, have come into widespread use as additional sections of portable units, apparatus and others, while there is a problem which arises with the reflective liquid crystal devices, however, in that, because a display is made visible through the use of the external light, the display is unreadable in the dark. For this reason, a transflective liquid crystal device, in which a display is made visible through the use of the external light in the light as in common reflective liquid crystal devices but through the use of an internal light source in the dark, has been proposed as exemplified by Japanese Unexamined Utility Model Publication No. 57-049271. Particularly, in connection with a transflective liquid crystal device utilizing a polarization axis variable means for rotating a polarization axis of a TN (Twisted Nematic) liquid crystal, a STN (Super-Twisted Nematic) liquid crystal or the like, this applicant has proposed a transflective display device using, as a means to better the brightness in the reflective display, a polarized light splitter which causes the reflection of a linearly polarized light component running in a predetermined direction while allowing the transmission of a linearly polarized light component advancing in a direction perpendicular thereto (Japanese Patent Application No. 8-245346). Referring to
FIG. 22
, a description will be made hereinbelow of a transflective display device using this polarized light splitter.
In
FIG. 22
, a TN liquid crystal panel is composed of an upper polarizer
5130
, an upper glass substrate
5302
, a lower glass substrate
5304
, a polarized light splitter
5160
, a semipermeable light absorbing layer
5307
and a light source
5210
. In the illustration, a TN liquid crystal, placed between the upper glass substrate
5302
and the lower glass substrate
5304
, is divided into a voltage non-applied area
5120
and a voltage applied area
5110
.
First, a description will be given hereinbelow of achromatic display of a reflective display. Incident light from the exterior of the display device, indicated as an optical path
5601
, turns through the upper polarizer
5130
to linearly polarized light in a direction parallel with the paper surface, and then form a linearly polarized light component in a direction perpendicular to the paper surface with its polarizing direction being twisted by 90° in the voltage non-applied section
5120
of the TN liquid crystal panel, and further is reflected on the polarized light splitter
5160
in a state of the same linearly polarized light in the direction perpendicular to the paper surface, and again undergoes a twist of 90° in its polarizing direction in the voltage non-applied section
5120
of the TN liquid crystal panel to develop into a linearly polarized light component in a direction parallel with the paper surface, finally going out of the upper polarizer
5130
. Accordingly, no application of a voltage to the TN liquid crystal panel makes a white display. Thus, the white display light is light reflected on the polarized light splitter
5160
, which produces a brighter display than a conventional transflective display device. The light indicated by an optical path
5603
forms linearly polarized light in a direction parallel with the paper surface due to the upper polarizer
5130
, and advances with its polarizing direction remaining intact even in the voltage applied section
5110
of the TN liquid crystal panel and with it remaining the same linearly polarized light in the direction parallel with the paper surface, and further transmits with its polarizing direction being also kept intact even in the polarized light splitter
5160
, thereafter being absorbed by the semipermeable light absorbing layer
5307
to produce a black display.
Secondly, a description will be given hereinbelow of achromatic display of a transmissive display. Light indicated by an optical path
5602
passes through an opening section made in the semipermeable light absorbing layer
5307
and turns to linearly polarized light in a direction parallel with the paper surface in the polarized light splitter
5160
, and then undergoes a twist of 90° in its polarizing direction in the voltage non-applied section
5120
of the TN liquid crystal panel to form linearly polarized light perpendicular to the paper surface, thereafter absorbed in the upper polarizer
5130
to produce a black display. Light indicated by an optical path
5604
comes in through an opening section made in the semipermeable light absorbing layer
5307
turns through the polarized light splitter
5160
to form a linearly polarized light in a direction parallel with the paper surface and passes through the upper polarizer
5130
with its polarizing direction being kept intact even in the voltage applied section
5110
of the TN liquid crystal panel and with it remaining the same linearly polarized light parallel with the paper surface, thus providing a white display.
As described above, the transflective display device (Japanese Patent Application No. 8-245346) this applicant has proposed can accomplish more proper switching between a reflective display and a transmissive display in accordance with ON/OFF of a light source, which provides a relatively bright reflective display.
On the other hand, with the recent progress of portable equipment (portable telephones, PDAS, watches) or OA equipment, a request has existed for coloring in liquid crystal display, and even a requirement for coloring has occurred to equipment using such a transflective liquid crystal device. In general, a color filter is put to use for coloring of display on a liquid crystal device. However, the color filter absorbs light so that the display tends to be dark. Therefore, in order to enhance the utilization efficiency of light, there has sometimes been employed a mode (which will be referred to hereinafter as an “SPD”) in which a polarizer is provided only on the visible side of the liquid crystal device and a reflecting layer is provided on an inner surface of a liquid crystal substrate. In the case of this SPD mode, only one polarizer can improve the utilization efficiency of light. Additionally, for realizing a transflective liquid crystal device with the SPD mode, a hole(s) is made in a portion of the reflecting layer or the reflecting layer is made relatively thin; whereupon, the reflecting layer has a permeable function to enable a transmissive display.
SUMMARY OF THE INVENTION
However, the use of the polarized light splitter shown in
FIG. 22
causes a positive-negative reversal phenomenon due to a difference between incidence on the polarized light splitter from the upper side and incidence from the lower side. Thus, the mode of the positive-negative reversal between a transmissive display and a reflective display creates a problem in that it is unsuitable for the display device depending on the applications of the display device, or is impracticable. Additionally, because of the use of the semipermeable light absorbing layer, the utilization efficiency of light drops, particularly at the transmissive display, it becomes dark.
On the other hand, with the transflective liquid crystal disclosed in Japanese Unexamined Utility Model Publication No. 57-049271, since a thick transparent substrate of a liquid crystal panel is interposed between a liquid crystal layer and a transflective layer, double image or display bleeding occurs due to parallax, particularly for coloring, the color filter cannot exhibit sufficient color development.
Furthermore, the
Iljima Chiyoaki
Tsuchihashi Toshihiko
Harness & Dickey & Pierce P.L.C.
Nguyen Hoan
Seiko Epson Corporation
Ton Toan
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