Nematic liquid crystal composition and bistable nematic liquid crystal display

A nematic liquid crystal composition comprising:

• a) at least 20% by weight of one or more compounds selected from the compound group A:
• wherein:
• R1 is an alkyl group or alkenyl group having 2 to 7 carbon atoms, in which, in addition, one or more methylene groups existing in the alkyl group or alkenyl group may be substituted each independently with an —O—, —COO— or —OCO— where O atoms are not directly linked to each other,
• Z1 represents —CH2CH2—, —COO—, —OCO—, —CH2O—, —OCH2—, —CF2O—, —OCF2—, or a single bond,
• Z2 represents —CH2CH2—, —CH═CH—, —COO—, —OCO—, —CH2O—, —OCH2—, —CF2O—, —OCF2—, or a single bond,
• Z3 represents —COO—, —OCO—, —CH2O—, —OCH2—, —CF2O—, —OCF2—, —C≡C—, or a single bond,
• Z4 and Z5 are each, independently of one another, —CH2CH2—, —COO—, —OCO—, —CH2O—, —OCH2—, —CF2O—, —OCF2—, or a single bond,
• X1 is a cyano group, a fluorine atom, a chlorine atom, a trifluoro methyl group, a trifluoro methoxy group, or a difluoromethoxy group (—OCHF2),
• Y1, Y2, Y3, and Y4 are each, independently of one another, a hydrogen atom, a fluorine atom, a chlorine atom, a trifluoro methyl group, or a trifluoro methoxy group,
• ring T1 is a 1,4-phenylene group or a 1,4-cyclohexylene group, in which among these groups the 1,4-phenylene group may be unsubstituted or may have one or more of a fluorine atom, a chlorine atom, a methyl group, a trifluoro methyl group, or a trifluoro methoxy group as a substituent group,
• m is 0 or 1, and
• p and q are 0 or 1, provided that p+q is 0 or 1;
• b) 5 to 50% by weight of one or more compounds selected from the compound group B:
• wherein:
• R2 and R3 are each, independently of one another, an alkyl group having 1 to 7 carbon atoms or an alkenyl group having 2 to 7 carbon atoms, in which, in addition, one or more methylene groups existing in the alkyl group or alkenyl group may be substituted each independently with an —O—, —COO— or —OCO— where O atoms are not directly linked to each other,
• Z6 is —CH2CH2—, —COO—, —OCO—, —CH2O—, —OCH2—, —CF2O—, —OCF2—, or a single bond,
• Z7 is —CH2CH2—, —CH═CH—, —COO—, —OCO—, —CH2O—, —OCH2—, —CF2O—, —OCF2—, or a single bond,
• Z8 is —COO—, —OCO—, —CH2O—, —OCH2—, —CF2O—, —OCF2—, —C≡C—, or a single bond,
• Z9 and Z19 are each, independently of one another, —CH2CH2—, —COO—, —OCO—, or a single bond
• Y7 to Y14 are each, independently of one another, a hydrogen atom, a methyl group, a fluorine atom, or a chlorine atom, and
• rings T2 and T3 are each, independently of one another, a 1,4-phenylene group or a 1,4-cyclohexylene group, in which among these groups the 1,4-phenylene group may be unsubstituted or may have one or more of a fluorine atom, a chlorine atom, a methyl group, a trifluoro methyl group, or a trifluoro methoxy group as a substituent group, wherein
• the relative proportions of the above-mentioned compounds used in the nematic liquid crystal composition is determined to simultaneously obtain the following physical characteristics for the composition:
• a nematic-isotropic liquid transition temperature (TN-I) of the liquid crystal composition of greater than or equal to 50° C.,
• a nematic temperature range (ΔTN) of the liquid crystal composition of greater than or equal to 50° C.,
• a dielectric anisotropy of larger than or equal to 8×10−11 F/m at 20° C., and
• a weak zenithal anchoring force on at least one of two substrates for a bistable nematic liquid crystal display that confine the composition, being defined by an anchoring breaking voltage Uλ/4 of less than or equal to 25 volts for a cell with a thickness (d) such that the product (Δn·d) of the refractive index anisotropy (Δn) and the thickness (d) is 140 nm at 20° C.