Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-10-04
2004-03-16
Ngo, Julie (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S062000, C349S098000, C349S112000, C349S115000, C349S119000
Reexamination Certificate
active
06707519
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a liquid crystal device, and particularly to a transflective liquid crystal device having both the reflective display function of performing display by reflecting light, which is incident on a liquid crystal layer from a front side of liquid crystal cell, by a transflective layer, and the transmissive display function of performing display by transmitting light, which is incident on the liquid crystal layer from a back side, through the transflective layer. The present invention also relates to an electronic apparatus using the liquid crystal device.
2. Background Art
Although a reflective liquid crystal device is generally used for the display unit of a portable electronic apparatus, it has a problem in that a display cannot be recognized in the dark because of the use of external light incident on a liquid crystal layer from the front side of a liquid crystal cell. Therefore, a transflective liquid crystal device has been proposed in which a display can be recognized by using external light, like a reflective liquid crystal device, in the light, and using light emitted from an illumination device arranged on the back side of a liquid crystal cell in the dark.
The transflective liquid crystal device comprises a polarizer, a transflector, and the illumination device, which are arranged in this order on the back side of the liquid crystal cell, as disclosed in Japanese Unexamined Utility Model Publication No. 57-49271. In this liquid crystal device, in bright reflective display is performed by reflecting the external light incident on the liquid crystal layer from the front side of the liquid crystal cell by a transflector, and in dark surroundings, transmissive display is performed by transmitting the light emitted from the illumination device through the transflector.
An example of other transflective liquid crystal devices is the transflective liquid crystal device disclosed in Japanese Unexamined Patent Publication No. 8-292413, which is aimed at improving the brightness of reflective display. This transflective liquid crystal device comprises a transflector, a retardation plate, a polarizer, and a back light, which are arranged on the back side of the liquid crystal cell in this order, wherein in light surroundings, external light incident on the liquid crystal layer from the front side of the liquid crystal cell is reflected by the transflector to perform reflective display, and in dark surroundings, the light emitted from the back light is transmitted through the transflector to perform transmissive display. Such a structure produces brighter reflective display than the aforementioned liquid crystal device because no polarizer is present between the liquid crystal cell and the transflector.
However, the transflective liquid crystal device disclosed in the above publication comprises a transparent substrate interposed between the liquid crystal layer and the transflector, and thus causes a double image due to parallax when reflective display is performed. Particularly, a color liquid crystal device comprising a combination of the transflective liquid crystal device disclosed in the above publication and color filters has the high possibility that the color filter through which light incident on the liquid crystal layer from the front side of the liquid crystal cell passes, and the color filter through which the incident light passes after being reflected by the transflector are different, thereby causing the problem of paling a display color.
In order to solve this problem, Japanese Unexamined Patent Publication Nos. 7-318929 and 7-333598 disclose the invention of a transflective liquid crystal device including a transflector arranged in a liquid crystal cell in order to remove parallax.
In the transflective liquid crystal devices disclosed in Japanese Unexamined Patent Publication Nos. 7-318929 and 7-333598, i.e., transflective liquid crystal devices performing reflective display without using the polarizer provided on the back side of the liquid crystal cell, when the light, which is incident from the front side of the liquid crystal cell and passes through the liquid crystal layer is reflected by the transflector, the light is preferably changed to circularly polarized light or elliptically polarized light with high ellipticity in a dark display state, and changed to linearly polarized light or elliptically polarized light with low ellipticity in a bright display state. This is because when circularly polarized light or elliptically polarized light with high ellipticity, which is reflected by the transflector, again passes through the liquid crystal layer, the light is changed to linearly polarized light perpendicular to the transmission axis of the polarizer provided on the front side of the liquid crystal cell or elliptically polarized light with low ellipticity, and absorbed by the polarizer, thereby realizing good contrast properties.
On the other hand, the light transmitted through the transflector from the back side of the liquid crystal cell is constantly in the same polarization state without dependency of the display states.
In the transflective liquid crystal devices disclosed in Japanese Unexamined Patent Publication Nos. 7-318929 and 7-333598, no optical element for changing polarization of the light incident on the liquid crystal layer is provided between the polarizer provided on the back side of the liquid crystal cell and the transflector, and thus linearly polarized light transmitted through the polarizer provided on the back side of the liquid crystal cell is constantly incident on the liquid crystal layer. Therefore, by preferable setting for reflective display in which the light reflected by the transflector is changed to circularly polarized light or elliptically polarized light with high ellipticity in the dark display state, the contrast properties of transmissive display deteriorate.
This is because linearly polarized light incident on the liquid crystal layer from the back side of the liquid crystal cell, in the dark display state, is changed to circularly polarized light or elliptically polarized light with high ellipticity when passing through the liquid crystal layer, and thus part of the light is transmitted through the polarizer provided on the front side of the liquid crystal cell.
SUMMARY OF THE INVENTION
The present invention has been achieved for solving the above problems, and a first object of the invention is to obtain a transflective liquid crystal device exhibiting good contrast properties in transmissive display, and a second object of the invention is to obtain a transflective liquid crystal device causing no double image due to parallax.
In order to achieve the objects, the liquid crystal device according to the present invention has a reflective display function of performing display by reflecting light, which is incident on a liquid crystal layer from one side of liquid crystal cell, by a transflective layer, and the transmissive display function of performing display by transmitting light, which is incident on the liquid crystal layer from the other side opposite to the one side, through the transflective layer. According to the liquid crystal device, a first display state as a bright display state and a second display state as a dark display state can be selected by changing the voltage applied to the liquid crystal layer; and in the second display state, the light incident on the liquid crystal layer from the one side of the liquid crystal cell passes through the liquid crystal layer and is reflected by the transflective layer to be changed to circularly polarized light or elliptically polarized light with the predetermined rotational direction. The liquid crystal device has a first polarizer provided on the one side, and an optical element provided on the other side, for polarizing the light incident on the transflective layer from the other side into a light with a predetermined rotational direction.
In the first liquid crystal device, the t
Maeda Tsuyoshi
Okamoto Eiji
Okumura Osamu
Seki Takumi
Harness & Dickey & Pierce P.L.C.
Ngo Julie
Seiko Epson Corporation
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