Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified...
Reexamination Certificate
1999-11-30
2001-09-11
Wu, Shean C. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
C252S299010, C252S299630
Reexamination Certificate
active
06287647
ABSTRACT:
This application is based on application No. 10-344392 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal composition, and more particularly to a liquid crystal composition exhibiting a cholesteric phase in a room temperature. Further to this, the present invention also relates to a liquid crystal display using the above liquid crystal, and more particularly to a bistable/reflective type liquid crystal display.
2. Description of Related Art
Recently, studies have been made to develop reflective liquid crystal displays by using chiral nematic liquid crystal which is produced by adding a chiral agent to nematic liquid crystal to cause the liquid crystal to exhibit a cholesteric phase in a room temperature. Such a liquid crystal display makes a display by switching between a planar state and a focal-conic state in accordance with the level of the pulse voltage applied thereto.
At the present, however, in such a reflective liquid crystal display, the response speed to application of a voltage is low, and the contrast between the planar state and the focal-conic state is not sufficiently high. Liquid crystal displays of this type which satisfactorily complies with these demands and can be driven by a low voltage are yet to be developed.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide an improved liquid crystal composition, and liquid crystal display using the same.
Other object of the present invention is to provide a liquid crystal display which can be driven by a low voltage, responds to application of the voltage at a high speed and has high contrast between the planar state and the focal-conic state.
In order to attain at least one of the above mentioned objects, a liquid crystal display according to the present invention comprises: a pair of substrates, at least one of which is transparent; and between the substrates, a liquid crystal composition which exhibits a cholesteric phase and contains a liquid crystal mixture containing a liquid crystal phenylcyclohexane compound at approximately 45 to 60 wt % and a liquid crystal tolan compound at approximately 5 to 15 wt %.
Liquid crystal phenylcyclohexane compounds and liquid crystal tolan compounds have relatively large anisotropy of refractive index and have low viscosity. Liquid crystal containing these compounds, therefore, can be driven by a low voltage, and the response to application of the voltage is speedy. Also, because the reflectance in the coloring state is large, the contrast is high. Including a large volume of liquid crystal phenylcyclohexane compound, of which anisotropy of dielectric constant is large, in the liquid crystal is especially advantageous to lower the driving voltage.
If a liquid crystal phenylcyclohexane compound is contained too much (approximately 60 wt % or more), however, the compatibility of the liquid crystal with the peripheral material such as a sealant will be high, and the peripheral material may fuse into the liquid crystal composition, which will cause deterioration of display performance. If a liquid crystal tolan compound is contained too much (approximately 15 wt % or more), the anisotropy of dielectric constant of the liquid crystal will be small, and a higher voltage will be necessary to drive the liquid crystal. It is preferred that the total content of the liquid crystal phenylcyclohexane compound and the liquid crystal tolan compound is not more than approximately 70 wt % of the liquid crystal mixture.
The chiral agent is added to nematic liquid crystal so that the liquid crystal can exhibit a cholesteric phase in a room temperature. The wavelength of light selectively reflected by the liquid crystal can be adjusted by altering the content of the chiral agent. According to the present invention, preferably, at least two kinds of chiral agents are used in combination. The use of at least two chiral agents is advantageous in the following points: the necessary volume of chiral agents is smaller; the driving voltage is low; and the reflectance, the color purity and the contrast are improved.
The liquid crystal composition may contain a coloring agent, and in this case, the color purity in the coloring state is improved. Further, it is preferred that an insulating layer is formed on at least one of the substrates on the electrodes. This insulating layer improves the insulation performance and the gas barrier performance. An alignment controlling layer or a color filter may be formed on the inner surface of at least one of the substrates.
Also, a polymeric structure may be provided between the substrates. The polymeric structure is composed of a plurality of columns, such as cylinders, square poles, elliptic cylinders, which may be arranged either at random or in a specified pattern. With the polymeric structure, the gap between the substrates can be maintained stably, the arrangement of the liquid crystal composition becomes stable, and variations in reflectance, etc. can be minimized.
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Iwamatsu Masako
Kobayashi Nobuyuki
Ueda Hideaki
Burns Doane , Swecker, Mathis LLP
Minolta Co. , Ltd.
Wu Shean C.
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