Patent ID: 7115307

Claim:
A nematic liquid crystal medium with weak zenithal anchoring energy for bistable display devices, comprising: a) at least 40% by weight of compounds with strong molecular polarisability (Δε>10) and strong dipole moment (μ>1D), however with weak zenithal anchoring, the compounds including: AI compounds selected from the group consisting of 4-pentyl-4′-cyanobiphenyl, 4-heptyl-4′-cyanobiphenyl, 3-fluoro-4-cyanophenyl-4′-ethylbenzoate, 3-fluoro-4-cyanophenyl-4′-propylbenzoate, 3-fluoro-4′-cyanophenyl-4′-butylbenzoate and 3-fluoro-4-cyanophenyl-4′-pentylbenzoate; and AII or AIV compounds selected from the group consisting of 4-cyanophenyl-4′-trans-butyl-cyclohexylbenzoate, 3-fluoro-4-cyanophenyl-4′-trans-pentyl-cyclohexylbenzoate and 4-pentyl-trans-cyclohexyl-benzoate-4′-phenyl-carboxylate of 4-cyano-3-fluorobenzene b) 0 to 50% by weight of compounds with weak anchoring selected from the group consisting of 4-pentylphenyl-4′-pentylcyclohexyl-carboxylate, 4-pentylphenyl-4′-propylcyclohexylcarboxylate, 4,4′-bis(4-propyl-cyclohexyl)-3-fluorobiphenyl, 4,4′-bis(4-propyl-cyclohexyl)-biphenyl, 4-pentylphenyl-4′-propylcyclohexylcarboxylate, 4-pentylphenyl-4′-propylphenylcarboxylate, 4-pentylphenyl-4′-pentylphenylcarboxylate, 4-propylphenylethynyl-4′-butylphenyl and 4-hexylcarboxyphenylethynyl-4′-hexylcarboxylphenyl; wherein the relative proportions of the above-mentioned compounds used in the composition of the nematic liquid crystal mixture are determined to simultaneously obtain the following physical characteristics for the said mixture: a nematic-isotropic liquid transition temperature (T N-I ) of the liquid crystal mixture greater than or equal to +50° C., a nematic range ΔT TN of the liquid crystal mixture 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.). a weak zenithal anchoring on at least one of the plates of the bistable display, characterised by a breaking voltage U λ/2 >25 volts for a cell with thickness d such that Δn d =295 nm (value measured at a temperature of +20° C.).