Patent ID: 7335405

Claim:
In a bistable liquid crystal device comprising a liquid crystal composition being situated between two substrates, forming a cell, electrode structures with alignment layers on the inner side of said substrates, whereby at least one alignment layer comprises a weak zenithal anchoring characterised by a breaking voltage U λ/2 <25 Volts for a cell with thickness d such that Δnd=275 nm (value measured at T=20° C.), that permits the compounds of said liquid crystal composition to adopt at least two different stable states and to switch between the two stable states when suitable electric signal is applied to said electrodes, the improvement wherein said liquid crystal composition has: a nematic—isotropic liquid transition temperature (T N-1 ) greater than or equal to +50° C., a positive dielectric anisotropy larger than or equal to 8×10 −11 F/m (value measured at a temperature of +20° C.) and said liquid crystal composition includes: a) at least 40% by weight of compounds with strong molecular polarisability (Δ∈>10) and strong dipole moment (μ>1D), however with weak zenithal anchoring, chosen from among compounds with the following formulas (AI, AII, AIII and AIV): in which:R 1 is a —CN or a —NCS polar group or a fluorine atom, R 2 represents an alkyl chain containing 1 to 12 carbon atoms, R 3 is an alkyl chain containing 1 to 12 carbon atoms or a cycloaliphatic radical, Z 1 is a —C≡C—group or a single bond, Z 2 and Z 3 are identical or different, and are —COO—groups or single bonds, and X 1 is a fluorine or hydrogen atom; b) 0 to 50% by weight of compounds with weak anchoring chosen from among compounds with the following formulas (BI, El and FI): in which: R 4 and R 5 are identical or different and are selected from the group constituted by cycloaliphatic radicals, and R—, or RO—, or R—COO—radicals, where R represents an alkyl chain with 1 to 12 carbon atoms, R 6 represents an alkyl chain with 1 to 12 carbon atoms or an alkoxy group with 1 to 12 carbon atoms, Z 4 is a —C∈C—group, a —CH 2 -CH 2 —group, a —COO—group or a single bond and X 1 is a fluorine or an hydrogen atom; c) 0 to about 20% by weight of compounds comprising dipoles chosen from among compounds with the following formulas (CI and CII): in which: R 1 is a —CN group, a —NCS group or a fluorine atom, R′ 1 is a —CN group, a —NCS group or a fluorine atom or a radical —OR, wherein R is an alkyl chain containing 1 to 12 carbon atoms possibly substituted by fluorine atom(s), R 5 is an alkyl chain containing 1 to 12 carbon atoms, R 6 is an alkyl chain or an alkoxy chain containing 1 to 12 carbon atoms, Z 5 is a —CH 2 -CH 2 —group, a —COO—group or a single bond, X 1 and X 2 are identical or different, and are a fluorine or an hydrogen atom; d) 0 to 5% by weight of compounds with the following formulas (DI and DII): where: R 1 is a —CN or a —NCS polar group or a fluorine atom, R 2 is an alkyl chain containing 1 to 12 carbon atoms, Z 2 is a —COO—group or a single bond, X 1 and X 2 are identical or different, and are a fluorine or hydrogen atoms.