Erasable bistable display

Details Erasable bistable display Erasable bistable display

2002-08-26

2004-06-22

Frech, Karl D. (Department: 2876)

Liquid crystal cells, elements and systems

Particular excitation of liquid crystal

Magnetic or pressure excitation

C349S086000, C349S160000

Reexamination Certificate

active

06753933

ABSTRACT:

The invention comprises a liquid crystal display device, which is switchable between a first optical modus and a second optical modus, the display device having a first section and at least part of a display screen being erasable by applying a pressure to the first section.
A bistable liquid crystal display device is disclosed in JP-2000127683. The display is applied in an electronic whiteboard. Whiteboards are used during meetings to write information on. Later the information is scanned and can be printed. A Liquid Crystal Display (LCD) of the polymer stabilized cholesteric texture type (PSCT) is applied for the section of the board which is used to write on. PSCT displays are switchable between a reflective and a transmissive mode. JP-2000127683 discloses that information displayed on such a display can be erased by exerting an external mechanical pressure by means of e.g. a pen. Due to the mechanical pressure, a transition is induced in the liquid crystal fluid as a consequence of which the transmissive state (modus) is changed locally into the reflective state (modus). This phenomenon is used to erase information displayed on the device. Since the pressure is locally exerted the erasing effect also takes place locally and consequently only a small part of the display is erased.
It is an object of the invention to provide a display device in which it is possible to erase information displayed on the device over larger areas or even the whole display area by means of a mechanical pressure. The display device according to the invention is characterized in that the device is provided with an expansion chamber for storing an excess of fluid caused to flow into the expansion chamber by the applied pressure, the fluid flow thus erasing information displayed on the display in a second section of the display device, which is located between the first section and the expansion chamber. The inventors have realized that if the display device is adapted such that a flow of liquid crystal material is caused to occur, this flow may advantageously be used for erasing the whole display area. In view of the presence of the expansion chamber a flow of liquid crystal material from the point of pressure to the expansion chamber will occur and a shear force will act on the liquid crystal. The liquid crystal material becomes ordered in the planar (reflecting) state over the whole area of the display where fluid flow occurs, i.e. the phase transition from the transmissive to the reflective mode occurs and hence the displayed information is erased. Consequently no high electrical erasing voltage is required anymore.
This aspect as well as other aspects of the invention are defined by the independent claims.
Advantageous embodiments of the invention are defined in the dependent claims.
These and other aspects of the invention will be elucidated with reference to the embodiments described hereinafter.


REFERENCES:
patent: 6104448 (2000-08-01), Doane et al.
patent: 6559918 (2003-05-01), Lueder
patent: 2003/0071958 (2003-04-01), Wu et al.
patent: 127683 (2000-05-01), None

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