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EP0098070A2 Expired / Lapsed EP ⏱️ 0.0 years remaining

Liquid crystal devices

Assignee: Qinetiq Ltd
•
Filing: 1983-06-10
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Granted: —
•
Expires: 2003-06-10
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Abstract

Abstract A liquid crystal device comprises a layer of long pitch cholesteric liquid crystal material incorporating a pleochroic dye. The layer is contained between two cell walls surface treated to align liquid crystal molecules in a tilted homogeneous structure. The surface alignment and natural pitch of the cholesteric material are matched to provide a progressive molecular twist of between pi and 2 pi , preferably about 3 pi /2, with a uniform tilt direction. The ratio of natural pitch P divided by thickness d of the liquid crystal layer is arranged to lie between 0.5 and 1.0, with a value of d less than 20 mu m. Both low tilt and high tilt surface alignment may be used separately or in combination. Polarisers may be used to enhance contrast between ON and OFF states. The device has a sharp transmission/voltage characteristic which enables it to be used in large multiplex addressed matrix displays.

Inventors

  • 👤 Colin Martin Waters
  • 👤 Edward Peter Raynes

Bibliographic Details

Application Number —
Jurisdiction EP
Data Source google_patents
Last Synchronized 2026-10-27 15:02
CPC Classifications
G; G02; G02F; G02F1/00; G02F1/01; G02F1/13; G02F1/133; G02F1/137; G02F1/13725; C; C09; C09K; C09K19/00; C09K19/02; C09K19/0208; C09K19/52; C09K19/60; G02F1/1333; G02F1/1347; G02F1/13475

Claims Analysis

Total Claims: 10
Claim 1
Independent Claim 139 words
A liquid crystal device comprising a layer of long pitch cholesteric liquid crystal material of positive dielectric anisotropy and incorporating an amount of a pleochroic dye contained between two cell walls bearing electrode structures and being surface treated to align liquid crystal molecules in a tilted homogeneous structure characterised in that the surface alignment and natural pitch p of the cholesteric material are matched to provide a progressive molecular twist of greater than π and less than 2 π radians across the layer with a uniform tilt direction, the ratio of layer thickness d divided by pitch p lying between C.5 and 1.0 with a value of d less than 20 um whereby the device may be switched directly between a light transmissive ON state and a non transmissive OFF state with a sharp transmission/voltage characteristics without substantial hysteresis.
Claim 2
Dependent Claim 139 words
A liquid crystal device comprising a layer of long pitch cholesteric liquid crystal material of positive dielectric anisotropy and incorporating an amount of a pleochroic dye contained between two cell walls bearing electrode structures and being surface treated to align liquid crystal molecules in a tilted homogeneous structure characterised in that the surface alignment and natural pitch p of the cholesteric material are matched to provide a progressive molecular twist of greater than π and less than 2 π radians across the layer with a uniform tilt direction, the ratio of layer thickness d divided by pitch p lying between C.5 and 1.0 with a value of d less than 20 um whereby the device may be switched directly between a light transmissive ON state and a non transmissive OFF state with a sharp transmission/voltage characteristics without substantial hysteresis.
Claim 3
Dependent Claim 13 words
The device of claim 1 wherein the molecular twist is about 3 π/2.
Claim 4
Dependent Claim 28 words
The device of claim 1 wherein the surface treatment provides a liquid crystal molecular tilt up to 5 0 and the ratio d/p lies between 0.5 and 0.75.
Claim 5
Dependent Claim 29 words
4 . The device of claim 1 wherein the surface treatment provides a liquid crystal molecular tilt of between 5 0 and 70 on at least one cell wall.
Claim 6
Dependent Claim 12 words
The device of claim 1 and further comprising at least one polariser.
Claim 7
Dependent Claim 14 words
The device of claim 1 and further comprising a reflector optically behind the cell.
Claim 8
Dependent Claim 26 words
The device of claim 1 arranged optically in series with at least one other device of claim 1 with different colour dyes in the different cells.
Claim 9
Dependent Claim 53 words
The device of claim 1 wherein the electrode structure on one cell wall is arranged in a first series of m separate electrodes and the electrode structure on the other cell wall is arranged in a second series of n separate electrodes to form an m x n matrix of separate addressable elements.
Claim 10
Dependent Claim 41 words
The device of claim 8 wherein the first and second series of electrodes are connected to two sets of driver circuits controlled by a logic circuit for repetitively applying voltages from a voltage source to the electrodes in a multiplexed sequence.

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