Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-12-28
2001-07-10
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S086000, C349S033000, C349S166000, C345S211000
Reexamination Certificate
active
06259498
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a display device using a mixture of a liquid crystal and minute solid particles.
Accompanying the progress of data processing apparatus, there has been an increasing demand for display devices requiring only a small power consumption and having a small thickness. Among such display devices, extensive study and development have been made on liquid crystal display devices as a type of display device satisfying such a demand. Particularly, display devices using a low-molecular weight liquid crystal have been commercialized and come into wide use in the society. A low-molecular weight liquid crystal allows an easy control of molecular orientation electrically but generally lacks a memory characteristic, i.e., a property of retaining its molecular orientation even after removal of a voltage applied thereto. Accordingly, for a continuous picture display, power supply to the liquid crystal cannot be interrupted, so that it is difficult to substantially suppress the power consumption.
For solving the above-mentioned problem, a number of new type liquid crystal display devices using a low-molecular weight liquid crystal and yet capable of exhibiting a memory characteristic have been proposed.
For example, Japanese Laid-Open Patent Application (JP-A) 5-61021 has proposed an electric field control of orientation state of nematic liquid crystal molecules around minute particles to realize a transparent state and a light scattering state. In this system, no alignment film or rubbing thereof is used for facilitating the control of alignment or orientation of nematic liquid crystal molecules. In this system, no change in distribution of minute particles in a direction of extension of electrodes is utilized. The system uses a nematic liquid crystal so that a substantial memory characteristic is not imparted and a continual voltage supply is required for maintaining a display state, thus requiring a substantial power consumption.
JP-A 8-269453 has proposed an electric field control according to a double frequency drive mode of a mixture of a liquid crystal exhibiting a positive or a negative dielectric anisotropy depending on a drive frequency region and flat-shaped minute particles showing affinity to the liquid crystal, to realize a transparent state and a light-scattering state. Also in this system, no alignment film or rubbing thereof is used for facilitating the control of alignment or orientation of nematic liquid crystal molecules. In this system, no change in distribution of minute particles in a direction of extension of electrodes is utilized. The system is restricted to the use of a specific liquid crystal composition, and therefor the latitude of material selection is narrow. As special minute particles requiring chemical treatments for providing the affinity and conversion into a flat shape in order to impart a memory characteristic are used, the production cost is increased.
JP-A 7-318982 also discloses a display device using a liquid crystal composition comprising a low-molecular weight liquid crystal and flat-shaped particles exhibiting affinity to the liquid crystal. When supplied with a voltage of several tens volt, the liquid crystal composition assumes a state of transmittance different from that before the voltage supply. The resultant state is retained even after removal of the voltage, so that the liquid crystal composition using a low-molecular weight liquid crystal is allowed to exhibit a memory characteristic. However, this system does not utilize a change in distribution of minute particles in a direction of electrodes. No alignment film or rubbing thereof is used for facilitating control of alignment or orientation of liquid crystal molecules.
Moreover, the above-proposed system involves a problem that a reversible change in transmittance cannot be realized only by electrical stimulation. More specifically, in order to remove a memory state formed by voltage application, it is necessary to impart a stimulation or external force other than an electric field to the liquid crystal composition. Two types of stimulation other than electric field are disclosed. One is heating of the liquid crystal composition for converting the liquid crystal composition into isotopic liquid, thereby destroying the liquid crystal texture formed by voltage application. The other is application of a mechanical stimulation, such as shearing, vibration or impact, for destroying the liquid crystal texture formed by voltage application.
SUMMARY OF THE INVENTION
In view of the above-mentioned problems of the prior art, an object of the present invention is to provide a display device using a low-molecular weight liquid crystal capable of causing a transition between two states having a memory characteristic only by application of electrical stimulation.
According to the present invention, there is provided a display device, comprising: a pair of oppositely disposed substrates each having an opposing electrode thereon so as to form a hollow cell including a gap between the electrodes, a mixture disposed to fill the hollow cell and comprising a low-molecular weight liquid crystal and minute solid particles having sizes smaller than the gap, and voltage application means for applying voltages between the opposing electrodes so as to selectively provide a state of localization and a state of dispersion of the minute solid particles between the oppositely disposed substrates thereby developing a transparent state and an opaque state, respectively, of the mixture.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
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patent: 40 41 682 (1992-06-01), None
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patent: 0 782 123 (1997-07-01), None
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patent: 7-318982 (1995-12-01), None
patent: 8-269453 (1996-10-01), None
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Parker Kenneth
Qi Mike
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