Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-09-26
2004-11-23
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S112000, C349S095000, C349S102000
Reexamination Certificate
active
06822711
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-279209, filed Sep. 30, 1999; No. 11-309062, filed Oct. 29, 1999; No. 2000-214589, filed Jul. 14, 2000; No. 2000-214590, filed Jul. 14, 2000; No. 2000-224316, filed Jul. 25, 2000; and No. 2000-234378, filed Aug. 2, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display apparatus performing a reflection display by utilizing an external light.
A liquid crystal display apparatus comprises a liquid crystal element and a pair of polarizing plates arranged to have the liquid crystal element sandwiched therebetween. The liquid crystal element comprises a front transparent substrate on the side of the observation of the display, a rear transparent substrate positioned to face the front transparent substrate, two electrodes mounted to the inner surfaces of the front and rear transparent substrates, respectively, and a liquid crystal layer interposed between these two electrodes. The polarizing state of the transmitting light is controlled by the liquid crystal layer in accordance with the electric field applied between the two electrodes.
A TN (twisted nematic) type is widely used as such a liquid crystal display apparatus. The TN type liquid crystal display apparatus is constructed such that the liquid crystal molecules of the liquid crystal layer included in the liquid crystal element are aligned under the state free from an electric field in a twisted manner with a twisting angle of about 90°. Also, the paired polarizing plates are arranged such that the transmitting axes thereof are substantially parallel to each other or substantially perpendicular to each other.
The liquid crystal display apparatus includes a transmission type in which a transmission display is performed by utilizing an illuminating light emitted from a back light and a reflection type in which a reflection display is performed by utilizing the external light in the environment of use of the liquid crystal display apparatus. The transmission type liquid crystal display apparatus consumes a large amount of an electric power for lighting the back light and, thus, the reflection type liquid crystal display apparatus performing the reflection display by utilizing an external light is advantageous in terms of the power saving.
The conventional reflection type liquid crystal display apparatus is constructed such that a reflecting plate is arranged behind the rear polarizing plate that is arranged behind the liquid crystal element.
In the conventional reflection type liquid crystal display apparatus, the external light incident on the front transparent substrate on the side of observation of the display is allowed to be incident as a linear polarized light on the liquid crystal element by the polarizing function of the front polarizing plate arranged in front of the liquid crystal element. The polarized state of the light incident on the liquid crystal element is controlled by the liquid crystal layer and, then, emitted to the rear side of the liquid crystal element. Among the light emitted to the rear side of the liquid crystal element, the light component transmitted through the rear polarizing plate is reflected by the reflecting plate, and the reflected light is allowed to be transmitted through the rear polarizing plate, the liquid crystal element and the front polarizing plate so as to be emitted to the front side of the display apparatus.
In the conventional reflection type liquid crystal display apparatus, the light of the polarized component along the transmission axis of the front polarizing plate, which is contained in the light incident from the front side, is transmitted through the front polarizing plate so as to be incident on the liquid crystal element, and the light of the polarized component along the absorption axis of the front polarizing plate is absorbed by the front polarizing plate. It follows that about half the light incident from the front side is absorbed by the front polarizing plate and, thus, is made useless. As a result, the conventional reflection type liquid crystal display apparatus is poor in its utilization rate of the incident light, and the light reflected by the reflecting plate so as to be emitted to the front side has a high intensity, resulting in failure to obtain a bright screen.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a liquid crystal display apparatus that permits increasing the brightness of the screen by effectively utilizing the external light incident from the front side and also permits obtaining a good contrast.
According to an aspect of the present invention, which has been accomplished in an attempt to achieve the above-noted object, there is provided a liquid crystal display apparatus, comprising:
a liquid crystal element including a front substrate positioned on the side of an observer and having a first electrode mounted to one surface, a rear substrate having a second electrode arranged to face the first electrode, and a liquid crystal layer interposed between these substrates, the liquid crystal layer controlling the polarized state of the transmitted light in accordance with the electric field applied between the first and the second electrodes;
a first reflection polarizing plate arranged on the front side of the liquid crystal element and reflecting the light of one of the two polarized components of the incident light, the two polarized components being perpendicular to each other, and transmitting the light of the other polarized component; and
a rear member arranged behind the liquid crystal element and reflecting at least a part of the light transmitted through the liquid crystal element so as to be emitted to the rear side.
The liquid crystal display apparatus further comprises a diffusion means arranged on the front side of the reflection polarizing plate and a diffusion layer arranged between the reflection polarizing plate and the liquid crystal element and/or between the liquid crystal element and the rear member. It is desirable for the diffusion layer to be formed of a lens film having micro lenses arranged on one surface.
In the liquid crystal display apparatus of the present invention, another reflection polarizing plate, which transmits the light of one of the two polarized components, which are perpendicular to each other, of the incident light and reflects the light of the other polarized component, is used as the rear member. When the liquid crystal element is of a TN type in which the liquid crystal molecules are twist-aligned with a twisting angle of 90°, the first reflection polarizing plate arranged on the front side of the liquid crystal element is arranged such that the transmission axis of the first reflection polarizing plate is substantially parallel to perpendicular to the aligning direction of the liquid crystal molecules in the vicinity of the front substrate of the liquid crystal element. On the other hand, the second reflection polarizing plate constituting the rear member is arranged such that the transmission axis of the second reflection polarizing plate is substantially parallel or perpendicular to the transmission axis of the first reflection polarizing plate. Further, it is possible to arrange a back light on the front side of the rear member.
The rear member is constructed by a reflection polarizing plate and a light absorbing means. The light absorbing means is formed of a light absorbing film or an absorption polarizing plate that absorbs the light of one the two polarized components, which are perpendicular to each other, of the incident light and transmits the light of the other polarized component. Also, the rear member is constructed by the absorption polarizing plate and a reflection plate arranged on the rear side of the absorption polarizing plate.
According to the liquid crystal display apparatus of present inventio
Ishida Keiichi
Nishino Toshiharu
Sato Kazuhito
Sawano Yoshiaki
Tano Tomoko
Casio Computer Co. Ltd.
Frishauf Holtz Goodman & Chick P.C.
Ton Toan
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