LIQUID CRYSTAL PHASE

Abstract: A liquid crystal phase consisting of at least three components A, B and C, each of which contains one or more compounds, wherein component A has a viscosity of at most about 25 mPa.s at 20 DEG , a clearing point of at most 130 DEG and a dielectric anisotropy between about -2 and about +2, component B has a dielectric anisotropy above about +8, component C has a clearing point of more than 130 DEG and a dielectric anisotropy between about -2 and about +2, characterized in that component A contains at least one compound of formula (III), in which R<1> is alkyl of 1 to 12 C atoms, in which in addition one or two non-adjacent CH2 groups can be replaced by O atoms, -CO-, -O-CO-, -CO-O- and/or -CH=CH- groups, R<2> has one of the meanings of R<1>, A<3> is ( alpha ) or ( beta ), Z<1> is -CO-O-, -O-CO- or -CH2CH2-, o is 1 or, if A<3> is ( gamma ), also 2, Cy is trans-1,4-cyclohexylene, and Phe is 1,4-phenylene, has suitable material properties for use in supertwisted nematic cells.

Description: Liquid crystal phase The invention relates to liquid crystal phases (LC phases) having elastic and dielectric properties appropriate for use in supertwisted nematic cells. Liquid crystal display cells can be made to support more than 90° of twist in the liquid crystal layer by a com¬ bination of offset alignment directions at the surfaces, and incorporation of chiral additives. If the twist angle is increased in this way, the slope of the thre- shold characteristic increases and eventually becomes vertical. Further increase of the twist angle will result in bistable behaviour, but at the onset of bistability the very steep switching curve allows high level multi¬ plex drive using conventional RMS waveforms. The limit to the increase of twist angle is set by a scattering texture which becomes stabilised as the cholesteric pitch is shortened; the effect can be alleviated but not eli¬ minated by increasing the surface tilt in the cell. The term "supertwisted nematic cell" includes all cells with clearly more than 90° of twist, e.g. the cells using a Guest-Host mode (CM. Waters, V. Brim ell and E.P. Raynes, Proc. 3. Int. Display Research Conference, Kobe (1983) 396; CM. Waters, V. Brimmell and E.P. Raynes, Proc. SID 25/4 (1984) 261), a birefringence mode (T.J. Scheffer and J. Nehring, Appl. Phys. Lett. 45 (1984) 1021; T.J. Scheffer and J. Nehring, J. Appl. Phys. 58 (1985) 3022), Black & White STN-LCD's (optical mode interference) (M. Schadt and F. Leenhouts, Appl. Phys. Lett. 50 (1987) 236; K. Kawasaki, K. Yamada, R. Watanabe and K. Mizunoya, Proc. SID *87 Digest (1987) 391), HBE- LCD's (K. Kinugawa, Y. Kando, M. Kanasaki, H. Kawakami and E. Kaneko), Double Layer Black & White STN LCD's (K. Katoh, Y. Endo, M. Akatsuka, M. Ohgawara and K. Sawada). By comparison with the standard twisted nematic display, the supertwist nematic cell has important differences in behaviour. Because light guiding through the highly twisted structure is imperfect, the cells are commonly operated in a variable birefringence mode and this, together with a strong dependence of threshold voltage on cell thickness, means that a high accuracy of cell spacing is required. In order to minimise the change in materials properties with temperature, a relatively high clearing point is desirable in the mixture. A near optimal optical performance can be obtained, e.g. by setting dΔn = 0.73 for the 270° twist cell and adjusting the polariser orientation if necessary to obtain the best contrast. Because of the large number of interacting cell and ma¬ terial properties which contribute to the performance of the supertwisted nematic display, it is highly difficult to select combinations of materials to suit the para¬ meters of the cell for best performance. There is thus still a great need for liquid crystal phases having suitable material properties for use in supertwisted nematic display cells. The invention has for its object to prepare liquid crystal phases which have a nematic phase including room temperature and exhibit elastic and dielectric properties appropriate for use in supertwist cells. It has now been found that the liquid crystal phases having particularly favorable combinations of material properties are obtained when they consist of at least three components A, B, and C, each of which contains one or more compounds, wherein component A has a visco¬ sity of at most about 25 mPa.s at 20°, a clearing point of at most 130° and a dielectric anisotropy between about -2 and about +2, component B has a dielectric anisotropy above about +8, component C has a clearing point of more than 130° and a dielectric anisotropy between about -2 and about +2, characterized in that component A contains at least one compound of the formula III in which R is alkyl of 1 to 12 C atoms, in which in addition one or two nonadjacent CE groups can be replaced by 0 atoms, -CO-, -0-CO-, -CO-O- and/or -CH=CH- groups, R 2 has one of the meanings of R1, F A ,3- is -< >- or -(o) I-(θ)-, Z 1 is -CO-O-, -O-CO- or -CH 2 CH 2 -, is 1 or, if A J is --<<t0>>--,, also 2, Cy is trans-l,4-cyclohexylene, and Phe is 1,4-phenylene. The liquid crystal phases according to the invention exhibit favorable elastic constants, i.e. relatively low K-. , and K 7 ? values, relatively high K-,., values and very favorable K 33 /K- 1 and K 33 /K„ 2 relationship for use in supertwisted nematic cells. The invention thus provides the above-described liquid crystal phases for use in supertwisted nematic cells which may also contain one or more suitable chiral additives to obtain the desired d/p relationship. The invention further provides supertwisted nematic liquid crystal display elements, in particular super¬ twisted nematic display elements which contain such phases. Such phases preferably consist of at least about 10 wt.% of component A, at least about 15 wt.% of component B and at least about 5 wt.% of component C and particularly of about 40 to 70 % wt.% (favorably about 50 wt.%) of component A, about 30 to 50 wt.% (favorably about 40 wt.%; of component B and about 5 to 30 wt.% (favorably about 10 wt.%) of component C The amount of compounds of formula III in the total mixture conveniently amounts to at least about 10 wt.% and preferably about 20 to 60 wt.% (favorably about 50 wt. %: Compounds having the above properties required for the components A, B and C are basically known to the person skilled in the art. The total mixture must have nematic or cholesteric properties. Component A can be nematic or of monotropic liquid crystalline behaviour or, as long as the total mixture is nematic, also smectic. How- ever, there are preferred those mixtures in which at least one compound of component A is enantiotropic liquid crystalline and there are especially preferred those mix¬ tures in which components A, B and C are enantiotropic liquid crystalline. Compounds and mixtures which are suitable as component A, B and C are to a large extent known and many of them are also commercially available. The following compounds or their mixtures are especially suitable for or as components A: R 1 -Cy-Phe-R 2 R 1 -Cy-Cy-R 2 R 1 -Cy-Phe-Phe-R 2 R 1 -Cy-Cy-Phe-R 2 Preferred compounds of the formula III are those of the formulae IIla to Illg: R 1 -Cy-Cy-OOC-PheF-R 2 Ilia R 1 -Cy-Cy-CH 2 CH 2 -Phe-F-R 2 IIlb R 1 -Cy-Cy-COO-PheF-R 2 IHe R 1 -Cy-COO-PheF-R 2 IIId R 1 -Cy-CH 2 CH 2 -PheF-R 2 IHe F R 1 -Cy-COO-Phe—(—Phe-R 2 11If R 1 -Cy-CH 2 CH 2 -Phe-|—Phe-R 2 Illg wherein PheF iiss -- -<θ0V>- oorr --(ζθ)V-,, pprreeffeerraabbllyy --<o0}>--, and F F -Phe—I—Phe is Compounds of the formulae HIc, Hid and Illg are particularly preferred. Component A has favorably a viscosity of at most about 20, in particular at most 18 mPa.s at 20° and a clear¬ ing point of at most 120°. For or as component B there are suitable, for example, known compounds containing 2 or 3 p-phenylene or trans-l,4-cyclohexylene groups, a polar end group and optionally a lateral halogen substituent. Compounds which are suitable for or as components B are, for example, the known compounds of formula I and/or in which R is alkyl of 1 to 12 C atoms, in which in addition one or two non- adjacent CH_ groups can be re¬ placed by 0 atoms, -CO-, -O-CO-, -CO-O- and/or -CH=CH- groups, A and A are each, independently of each other, Cy, Dio, Pyr or Phe, Z is -CO-O-, -O-CO-, CH -0-, -0-CH 2 - or a single bond, X 1 is F, Cl or -CN, X 2 is F or Cl, m is 0 or 1, Cy is trans-l,4-cyclohexylene, Pyr is pyrimidine-2,5-diyl or pyridine- 2,5-diyl, Dio is trans-l,3-dioxane-2,5-diyl and he is 1,4-phenylene. R 1 -A 4 -Phe-CN II in which A 4 is Cy, Cy-CH 2 CH 2 , Phe, Dio, Phe-COO, Cy-COO, Phe-Phe, Phe-COO-Phe, Cy-Phe-COO-Phe, Phe-Phe-COO-Phe, Cy-Cy, Cy-Cy-CH 2 CH 2 , Cy-CH 2 CH 2 -Cy, Cy-Phe or Cy-COO-Phe and R , Cy and Phe have the meanings indicated above. Further compounds which are suitable for or as com¬ ponents are R 1 - H >-^ )»-CN and/or in which R has the meaning indicated above. Compounds which are suitable for or as components C are, for example, the known compounds of the following formulae: R -Cy-Phe- ■Phe-Cy-R ^ R 1 -Phe-Phe-Z 1 -< £ -R 2 R 1 -Cy-Z 1 -Phe-Phe-Cy-R 2 Component C has favorably a clearing point of at least about 140°. Preferably component C contains at least one compound with a clearing point of at least 180°, preferably of at least 200°. Further compounds which are suitable for or as compo¬ nents C are those of the formula IV R 1 -A 2 -(Z 2 -A 2 ) 2 -R 2 IV m which Z 2 independently is -CO-O- or -0-CO-, 2 is Cy or Phe and R 1 and R2 independently have the mean¬ ings indicated above. The individual compounds of the formula I to IV of the liquid crystal phases according to the invention are either known or preparable by methods which are easily derivable by those skilled in the art from the prior art, since they are based on standard methods described in the literature. Corresponding compounds of the formula I are described for example in German Patent Applications P 34 05 914 and P 35 15 633; in European Patent Specification 0,019,665; in S.M. Kelly and Hp. Schad, Helvetica Chimica Acta, 6 , 1580-1587 (1984); in S.M. Kelly, ibid, 61_, 1572-1579 (1984); in Japanese Offenlegungsschrift 59-191,789 and European Offenlegungsschriften 0,099,099 and 0,119,756. Compounds of the formula II are described for example in German Offenlegungsschriften 29 44 905, 31 12 185, 31 46 249, 31 50 761, 31 50 763, 32 07 114, 32 27 916, 33 02 218, 33 34 054, in European Offenlegungs- schrift 0,122,389, in U.S. Patent 4,322,354 and in Japanese Offenlegungsschrift 56-164,179. It was found, surprisingly, that the combination accord¬ ing to the invention of components A, B and C gives LC phases for use in supertwisted nematic cells which on the one hand have favorable elastic properties, wide mesophase ranges with low melting points and low smectic-nematic transition temperatures and on the other hand are capable of multiplexed drive by virtue of their good electro-optic steepness and viewing angle characteristic. The LC phases according to the invention preferably con¬ tain at least two compounds, in particular at least three compounds, of the formula III and preferably at least two compounds, in particular at least three com- pounds, selected from the formulae I and II. Preferably at least one compound of formula I is present. X 1 i.s preferably CN. X2 i.s preferably fluori■ne. Z is pre¬ ferably -CO-O-. R is preferably alkyl, alkenyl, alkoxy or alkoxymethyl in each case with 1 to 7 C atoms, in particular alkyl or alkoxymethyl. (A°) -A is preferably Phe, CyPhe, PhePhe or PyrPhe, in particular Phe or CyPhe. Preferred compounds of the formula I are those of the partial formulae la to Is: x 2 x 2 R -O >-<≤>- χl !• x 2 R 00-0-<£$- χl x 2 R -{ ^ "{2^" co °-(£)- χl xi x 2 R -{^— { ~ COO-^-X 1 Ij x 2 - ii - X 2 R-{o - o)-coo-^o^-χ i Io 2 X^ The group is preferably F Cl F / -(θ -CN, -(θJ- CN or -< 0 >-F. R is preferably straight-chain alkyl of 2 to 7 C atoms. Z is in the case of compounds of the formula I preferab¬ 2 llyy --CCOO--OO--, -CH 2 -0- or a single bond. X is preferably fluorine. Of the foregoing partial formulae, those of the formu¬ lae la, lb, Ic, Id, Ie, Ig, Ih, Ii, Ij , Ik, II, I , Io, Ip, Ir and Is are preferred. Particular preference is given to those of the partial formulae Ia-Ic, Ig, Ih, Im and Ip. In the case of the compounds of the foregoing partial formulae, R is a straight-chain alkyl group, prefer¬ ably of 1 to 7 C atoms, in which in addition a CH» group can also be replaced by -O- or -CH=CH-. Parti¬ cularly preferred groups R are methyl, ethyl, n-propyl, n-butyl, n-pentyl and n-heptyl. In the case of compounds of the foregoing partial formulae with two groups R, both groups R each have independently of each other one of the abovementioned meanings. In the compounds of the formula III R 1 and R2 are each independently preferably alkyl, alkoxy or alkoxymethyl with each up to 7 C atoms. In the compounds of the formula IV R 1 and R2 have the preferred meanings indicated above. Preferred compounds of the formula IV are those of the partial formulae IVa to IVf: R -Phe-COO-Phe-COO-Phe-R 2 IVa R 1 -Cy-COO-Phe-COO-Phe-R 2 IVb 1 ? R -Phe-COO-Cy-COO-Phe-R IVc R 1 -Phe-OOC-Cy-COO-Phe-R 2 IVd R 1 -Cy-COO-Cy-COO-Phe-R 2 IVe R 1 -Cy-COO-Phe-COO-Cy-R 2 IVf Of the foregoing partial formulae, those of the formu¬ lae IVa, IVb and IVd are preferred. When the alkyl groups in the compounds of formulae I to IV contain 3 or more carbon atoms, these can be arranged in a straight or branched chain. However, the phases according to the invention did not use any components which contain more than one branched alkyl group. Such branched alkyl groups for the purposes of the present invention contain not more than one chain branching; preferably this is a methyl or ethyl group in the 1- or 2-position of carbon skeleton, so that suitable branched alkyl groups are in particular: 2- methylpropyl, 2-methylbutyl, 1-methylpentyl, 2-methyl- pentyl, 1-methylhexyl. Generally the liquid crystal dielectrics according to the invention contain only one component having a branched-chain alkyl radical in order to induce, if desired, optical activity. For this pur¬ pose, normally not more than 10 percent by weight, preferably 0.5 to 3 percent by weight, of a component having a branched alkyl radical are added. In the compounds of the foregoing partial formulae, F -<° °>- or -<£>^° Preferred phases according to the invention contain compounds of the formula III in wich R is n-alkyl and R 2 i.s n-alkyl, n-alkoxy or n-alkanoyloxy. R 1 and R2 are preferably n-alkyl or n-alkoxy of m each case 2 to 7 C atoms. The preparation of the phases according to the in¬ vention is effected in the conventional manner. In general, the desired amount of the components which is used in the smaller amount is dissolved in the compo¬ nents which constitutes the main constituent, preferably at elevated temperature. If this temperature is chosen to be above the clear point of the main constituent, the completeness of the process of dissolving can be observed particularly easily. However, it is also possible to mix solutions of the components in a suitable organic solvent, for example acetone, chloroform or methanol, and to remove the sol¬ vent after thorough mixing, for example by distillation under reduced pressure. It is self-evident that with this method it must be ensured that the solvent does not introduce any contaminants or undesirable dopants. By means of suitable additives the liquid crystal phases according to the invention can be modified in such a way that they can be used in any hitherto disclosed kind of supertwisted nematic liquid crystal display element. The production of a supertwisted nematic electro-optical cell containing a phase in accordance with the inven¬ tion can also be carried out in a manner known per se; for example, by evacuating a suitable cell and intro¬ ducing the mixture into the evacuated cell. The examples below serve to illustrate the invention without limiting it. In the examples, the melting point and clear point of a liquid crystal substance are given in degrees Celsius. The percentages are by weight. The values of the threshold voltages relate to an angle of observation of 0°, 10 % contrast and 20 °C and are voltages in a 90° twist cell. Example 1 A liquid crystal phase consisting of 3 % of 4-cyanobiphenyl-4'-yl p-(n-heptylphenyl)-benzoate 10 % of 2-fluoro-4-pentylphenyl p-(heptylphenyl)-benzoate 14 % of 4-cyano-4'-(trans-4-pentylcyclohexyl)-biphenyl 7 % of 4-cyano-3-fluorophenyl p-propylbenzoate 2 % of 4-cyano-3-fluorophenyl p-ethylbenzoate 10 % of 2-fluoro-4-pentylphenyl trans-4-(trans-4-pentyl- cyclohexyl)-cyclohexane carboxylate 14 % of 2-p-cyanophenyl-5-propyl-l,3-dioxane 8 % of 2-fluoro-4-pentylphenyl trans-4-propylcyclohexane carboxylate 16 % of 2-fluoro-4-pentylphenyl trans-4-pentylcyclohexane carboxylate and 16 % of 2-fluoro-4-pentylphenyl trans-4-heptylcyclohexane carboxylate has a clearing point of 85.4°, an optical anisotropy of 0.131, a viscosity of 54.3 mPa.s at 20°, a threshold voltage of 2.22 volt, a dielectric anisotropy of +11.1, and 33 /K 1:L of 1.18. Example 2 A liquid crystal phase consisting of 8.6 % of l-(trans-4-propylcyclohexyl)-2-(4'-pentyl-2'- fluorobiphenyl-4-yl)-ethane 8.7 % of l-(trans-4-propylcyclohexyl)-2-(4'-ethyl-2'- fluorobiphenyl-4-yl)-ethane 8.7 % of l-(trans-4-pentylcyclohexyl)-2-(4'-ethyl-2'- fluorobiphenyl-4-yl)-ethane 6 % of 4-ethyl-4'-cyanobiphenyl 20 % of 2-p-cyanophenyl-5-propyl-l,3-dioxane 20 % of 2-p-cyanophenyl-5-pentyl-l,3-dioxane 9 9 % % of trans-4-(trans-4-propylcyclohexane)-propoxy- cyclohexane 2 % of 4-cyanobiphenyl-4'-yl p-(heptylphenyl)-benzoate 4 % of 4,4'-Bis-(trans-4-propylcyclohexyl)-biphenyl 4 % of 4-(trans-4-pentylcyclohexyl)-4'-(trans-4-propyl- cyclohexyl)-biphenyl and 9 % of trans-4-pentylcyclohexyl trans-4-(trans-4- butylcyclohexyl)-cyclohexane carboxylate has a clearing point of 86.9°, an optical anisotropy of 0.130, a viscosity of 32.3 mPa.s at 20°, and thre¬ shold voltage of 2.28 volt, a dielectric anisotropy of +11.2 and 33 K 1L of 1.27. Example 3 A liquid crystal phase consisting of 3.0 % of 4-cyanobiphenyl-4'-yl p-(hep ylphenyl)-benzoate 10.0 % of 2-fluoro-4-pentylphenyl p-(heptylphenyl)-benzoate 14.0 % of 4-cyano-4'-(trans-4-pentylcyclohexyl)-biphenyl 7.0 % of 4-cyano-3-fluorophenyl p-propylbenzoate 2.0 % of 4-cyano-3-fluorophenyl p-ethylbenzoate 10.0 % of 2-fluoro-4-pentylphenyl trans-4-(trans-4-pentyl- cyclohexyl)-cyclohexane carboxylate 14.0 % of 2-p-cyanophenyl-5-propyl-l,3-dioxane 12.6 % of p-propylphenyl trans-4-propylcyclohexane carboxylate 15.4 % of p-pentylphenyl trans-4-propylcyclohexane carboxylate and 12.0 % of p-heptylphenyl trans-4-propylcyclohexane carboxylate has a clearing point of 85.2°, an optial anisotropy of 0.131, a viscosity of 45.3 mPa.s at 20°, a threshold voltage of 2.21 volt, a dielectric anisotropy of +11.2, and ^ 33 / ' ^ 11 of 1.16. The mixture of Example 1 is a good starting point when designing supertwisted displays. If the initial test cells containing this phase show insufficient threshold sharpness, the mixture of Example 2 may be added in order to introduce hysteresis and obtain an optimised trans¬ mission vs voltage curve in the test cell. Similarly, the mixture of Example 3 may be added if necessary in order to reduce excess hysteresis. The driving voltage should then be adjusted to provide the correct switch- ing voltages for the tuned cell. The mixtures of Examples 1 to 3 are undoped and suitable chiral additives and have to be used to obtain the de¬ sired d/p relationship. These additives are readily available and known to the skilled worker. The three mixtures may also be mixed together in any pro¬ portion to obtain intermediate properties. Example 4 A liquid crystal phase is prepared consisting of 3 % of 4-cyanobiphenyl-4'-yl p-(n-heptylphenyl)-benzoate 8 % of 2-fluoro-4-pentylphenyl p-(heptylphenyl)-benzoate 14 % of 4-cyano-4'-(trans-4-pentylcyclohexyl)-biphenyl - 7 % of 4-cyano-3-fluorophenyl p-propylbenzoate 2 % of 4-cyano-3-fluorophenyl p-ethylbenzoate 10 % of 2-fluoro-4-pentylphenyl trans-4-(trans-4-pentyl- cyclohexyl)-cyclohexane carboxylate 14 % of 2-p-cyanophenyl-5-propyl-l,3-dioxane 2 % of p-(p-propylphenoxycarbonyl)-phenyl trans-4- cyclohexane carboxylate 8 % of 2-fluoro-4-pentylphenyl trans-4-propylcyclohexane carboxylate 16 % of 2-fluoro-4-pentylphenyl trans-4-pentylcyclohexane carboxylate and 16 % of 2-fluoro-4-pentylphenyl trans-4-heptylcyclohexane carboxylate. Example 5 A liquid crystal phase consisting of 16.6 % of l-(trans-4-propylcyclohexyl)-2-(4'-ethyl-2'- fluorobiphenyl-4-yl)-ethane 16.7 % of l-(trans-4-propylcyclohexyl)-2-(4'-pentyl-2'- fluorobiphenyl-4-yl)-ethane 16.7 % of l-(trans-4-pentylcyclohexyl)-2-(4'-ethyl-2'- fluorobiphenyl-4-yl)-ethane 10 % of 4-ethyl-4'-cyanobiphenyl 10 % of 4-propyl-4'-cyanobiphenyl 15 % of 4-pentyl-4'-cyanobiphenyl 5 % of 4,4'-bis-(trans-4-propylcyclohexyl)-2-fluoro- biphenyl, 5 % of 4,4'-bis-(trans-4-pentylcyclohexyl)-2-fluoro- biphenyl and 5 % of 4-(trans-4-pentylcyclohexyl)-4'-(trans-4-propyl- cyclohexyl)-2-fluorobiphenyl has a clearing point of 97.5°, a transition point smec- tic-nematic of < -20°, a viscosity of 33.1 mPa.s at 20°, an optical anisotropy of 0.179 and shows good properties in SBE devices. Example 6 A liquid crystal phase consisting of 6.6 % of l-(trans-4-propylcyclohexyl)-2-(4'-ethyl-2'- fluorobiphenyl-4-yl)-ethane 6,7 % of l-(trans-4-propylcyclohexyl)-2-(4'-pentyl-2'- fluorobiphenyl-4-yl)-ethane 6.7 % of l-(trans-4-pentylcyclohexyl)-2-(4'-ethyl-2'- fluorobiphenyl-4-yl)-ethane 25 % of l-(trans-4-propylcyclohexyl)-2-(p-cyanophenyl)- ethane 20 % of trans,trans-4-propyl-4'-cyanocyclohexylcyclo- hexane 10 % of 2-p-cyanophenyl-5-propyl-l,3-dioxane 5 % of 4,4'-bis-(trans-4-propylcyclohexyl)-2-fluoro- biphenyl 5 % of 4,4'-bis-(trans-4-pentylcyclohexyl)-2-fluoro- biphenyl 5 % of 4-(trans-4-pentylcyclohexyl)-4*-(trans-4- propylcyclohexyl)-2-fluorobiphenyl 5 % of trans-4-pentylcyclohexyl 4-(trans-4-propylcyclo- hexyl)-cyclohexane carboxylate and 5 % of trans-4-pentylcyclohexyl 4-(trans-4-butylcyclo- hexyl)-eye1ohe ane carboxy1ate shows good properties in SBE devices. Example 7 A liquid crystal phase consisting of 9,2 % of l-(trans-4-propylcyclohexyl)-2-(4'-ethyl-2'- fluorobiphenyl-4-yl)-ethane, 9,1 % of l-(trans-4-propylcyclohexyl)-2-(4'-pentyl-2 '- fluorobiphenyl-4-yl)-ethane, 9,2 % of l-(trans-4-pentylcyclohexyl)-2-(4'-ethyl-2'- fluorobiphenyl-4-yl)-ethane, 22,5 % of l-(trans-4-propylcyclohexyl)-2-(p-cyanophenyl)- ethane, 15 % of trans,trans-4-propyl-4'-cyanocyclohexylcyclo- hexane, 5 % of 2-p-cyanophenyl-5-propyl-l,3-dioxane, 5 % of 4-cyano-3-fluorophenyl p-propylbenzoate, 5 % of 4,4'-Bis-(trans-4-propylcyclohexyl)-2-fluoro- biphenyl, 5 % of 4,4'-Bis-(trans-4-pentylcyclohexyl)-2-fluoro- biphenyl, 5 % of 4-(trans-4-pentylcyclohexyl)-4'-(trans-4-propyl- cyclohexyl)-2-fluorobiphenyl, 5 % of trans-4-pentylcyclohexyl trans-4-(trans-4- propylcyclohexyl)-cyclohexane carboxylate and 5 % of trans-4-pentylcyclohexyl trans-4-(trans-4- butylcyclohexyl)-cyclohexane carboxylate has a clearing point of 96.8°, a transition point smectic- nematic of < -20°, a viscosity of 33.5 mPa.s at 20°, an optical anisotropy of 0.122 and shows good properties in SBE devices. The mixtures of example 7 and example 5 are suitable as a two-bottle system with variable birefringence for STN devices. This system is especially useful for STN dis¬ plays with twist angles of 180 degrees-220 degrees, in- corporating a variable birefringence to allow matching to precise cell twist angle and thickness. Both mix¬ tures are miscible in all proportions, providing a range of Δn from C179 to 0.122, and a near constant threshold voltage of 2.03 V-2.04 V in 180 degrees twist cells (7 μm, 180 °C twist, low surface tilt cell, d/p = 0.375, d.Δn = 0.95). The high clearing points minimise un¬ desirable variation in colour at elevated operating tem¬ peratures. A suitable birefringence for a 7 μm STN cell is obtained by mixing 21.8 parts of the mixture of example 5 with 78.2 parts of the mixture of example 7. The resulting liquid crystal phase shows an optical anisotropy of 0.1357 which gives the optimal optical path difference for a 180° twist STN cell with 7 μm thickness (d.Δn = 0.95). Electro-optical measurements were taken using a white light source in positive contrast mode with both polari- sers parallel and the input polariser was at an angle of 45° to the input director: V 90 , 0 , 20 1. 92 V 10 , 0 , 20 2 . 05 V 90 , 45 , 20 1.86 V 50 , 10 , 20 1. 96 M 1.10 20 M' 1.05 U 20 Example 8 A liquid crystal phase consisting of 25 % of l-(trans-4-ethylcyclohexyl)-2-(4'-ethyl-2'- fluorobiphenyl-4-yl)-ethane, 25 % of l-(trans-4-propylcyclohexyl)-2-(4'-ethyl-2 '- fluorobiphenyl-4-yl)-ethane, 10 % of 4-ethyl-4'-cyanobiphenyl, 15 % of 4-pentyl-4' -cyanobiphenyl, 10 % of l-(trans-4-propylcyclohexyl)-2-(p-cyanophenyl)- ethane, 5 % of 4,4'-Bis-(trans-4-propylcyclohexyl)-2-fluoro- biphenyl, 5 % of 4,4'-Bis-(trans-4-pentylcyclohexyl)-2-fluoro- biphenyl, 5 % of 4-(trans-4-pentylcyclohexyl)-4'-(trans-4-propyl- cyclohexyl)-2-fluorobiphenyl has a clearing point of 88.4°, a transition point smectic- nematic < -20°, a viscosity of 29.9 mPa.s at 20°, and an optical anisotropy of 0.167. In a 6 mm thick, 180° twist angle STN cell doped with S811 such that d/p = 0.35 electro-optical measurements were taken using a white light source operating the cell in positive contrast mode, with parallel polarisers the input polariser being at an angle of 45° to the input director: 2.00 90,0,20 10,0,20 2.15 10,0,20 = 1.075 90,0,20 Example 9 A liquid crystal phase consisting of 25 % of l-(trans-4-ethylcyclohexyl)-2-(4'-ethyl-2'- fluorobiphenyl-4-yl)-ethane, 25 % of l-(trans-4-propylcyclohexyl)-2-(4'-ethyl-2'- fluorobiphenyl-4-yl)-ethane, 10 % of 4-ethyl-4'-cyanobiphenyl, 13 % of 4-pentyl-4'-cyanobiphenyl, 12 % of l-(trans-4-propylcyclohexyl)-2-(p-cyanophenyl)- ethane, 7.5 % of 4,4'-Bis-(trans-4-propylcyclohexyl)-2-fluoro- biphenyl and 7.5 % of 4-(trans-4-pentylcyclohexyl)-4'-(trans-4- propylcycldhexyl)-2-fluorobiphenyl has a clearing point of 88.9°, a transition point smectic- nematic of < -20°, a viscosity of 29.5 mPa.s at 20° and an optical anisotropy of 0.166. In a 6 μm thick, 180° twist STN cell with S811 dopant such that d/p = 0.35 electro-optical measurements were taken using a white light source operating the cell in positive contrast mode, with parallel polarisers the input polariser being at an angle of 45° to the input director: V 90 Example 10 A liquid crystal phase consisting of 9.1 % of l-(trans-4-propylcyclohexyl)-2-(4 » -ethyl-2*- fluorobiphenyl-4-yl)-ethane, 9.1 % of l-(trans-4-pentylcyclohexyl)-2-(4*-ethyl-2'- fluorobiphenyl-4-yl)-ethane, 9.1 % of l-(trans-4-propylcyclohexyl)-2-(4*-pentyl- 2'-fluorobiphenyl-4-yl)-ethane, 14.9 % of trans,trans-4-propyl-4'-propoxycyclohexyl- cyclohexane, 5.2 % of 2-p-cyanophenyl-5-propyl-l,3-dioxane, 5.0 % of 4-cyano-3-fluorophenyl p-propylbenzoate, 9.9 % of 2-fluoro-4-pentylphenyl trans-4-(trans-4- pentylcyclohexyl)-cyclohexane carboxylate, 22.6 % of l-(trans-4-propylcyclohexyl)-2-(p-cyanophenyl)- ethane, 5.0 % of 4,4'-Bis-(trans-4-propylcyclohexyl)-2-fluoro- biphenyl, 5.1 % of 4,4'-Bis-(trans-4-pentylcyclohexyl)-2-fluoro- biphenyl and 5.0 % of 4-(trans-4-pentylcyclohexyl)-4'-(trans-4-propyl- cyclohexyl)-2-fluorobiphenyl has a clearing point of 93.4°, a viscosity of 24.6 mPa.s at 20°, an optical anisotropy of 0.121 and shows good properties in supertwisted nematic devices.

Claims: Claims : 1. A liquid crystal phase for use in supertwisted nematic cells consisting of at least three com¬ ponents A, B and C, each of which contains one or more compounds, wherein component A has a viscosity of at most about 25 mPa.s at 20°, a clearing point of at most 130° and a dielectric anisotropy between about -2 and about +2, component B has a dielectric anisotropy above about +8, component C has a clear- ing point of more, than 130° and a dielectric aniso¬ tropy between about -2 and about +2, characterized in that component A contains at least one compound of the formula III in which R is alkyl of 1 to 12 C atoms, in which in addition one or two non- adjacent CH_ groups can be replac by 0 atoms, -CO-, -0-CO-, -CO-O- and/or -CH=CH- groups, R 2 has one of the me ϊaarnings of R 1 , F A 3 is -<£>- or -(ό>-l-<0>-, Z 1 is -CO-O- , -O-CO- or -CH„CH - , F Δ Cy is trans-l , 4-cyclohexylene , and Phe is 1 ,4-phenylene . 2. Liquid crystal phase according to claim 1, charac¬ terized in that component B contains at least one compound of the formula I in which R is alkyl of 1 to 12 C atoms, in which in addition one or two non- adjacent CH 2 groups can be re¬ placed by 0 atoms, -CO-, -O-CO-, -CO-O- and/or -CH=CH- groups, A° and A are each, independently of each other, Cy, Dio, Pyr or Phe, Z is -CO-O-, -0-CO-,-CH 2 -0-, -0-CH 2 - or a single bond, X 1 is F, Cl or -CN, X 2 is F or Cl, m is 0 or 1, Cy is trans-l,4-cyclohexylene, Pyr is pyrimidine-2,5-diyl or pyridine- 2,5-diyl, Dio is trans-l,3-dioxane-2,5-diyl and Phe is 1,4-phenylene. 3. Liquid crystal phase according to at least one of claims 1 and 2, characterized in that compound B contains at least one compound of the formula II R 1 -A 4 -Phe-CN II in which A is Cy, Cy-CH 2 CH 2 , Phe, Dio, Phe-COO, Cy-COO, Phe-Phe, Phe-COO-Phe, Cy-Phe-COO-Phe, Phe-Phe-COO-Phe, Cy-Cy, Cy-Cy-CH 2 CH 2 , Cy-CH 2 CH 2 ~Cy, Cy-Phe or Cy-COO-Phe and R , Cy and Phe have the meanings indicated above. 4. Liquid crystal phase according to at least one of claims 1 to 3, characterized in that component B contains at least one compound of the formula R 1 -^H)»-(H^-C and/or of the formula R 1 YHVCH 2 CH 2 - HVCN in which R has the meaning indicated above. 5. Liquid crystal phase according to at least one of claims 1 to 4, characterized in that component C contains at least one compound of the formula IV R 1 -A 2 -(Z 2 -A 2 ) 2 -R 2 IV m which Z 2 independently i.s -CO-O- or -0-CO-, A2 is Cy or Phe and R 1 and R2 independently have the meanings indicated above. 6. Liquid crystal phase according to at least one of claims 1 to 4, characterized in that component C contains at least one compound of the formulae R 1 -Cy-Phe-|-Phe-Cy-R 2 7. Use of liquid crystal phases according to claim 1, for supertwisted nematic electro-optical display elements. 8. Supertwisted nematic electro-optical display ele¬ ment, characterized in that it contains a phase according to claim 1.

Inventors: CHAMBERS MICHAEL KEVIN, SAGE IAN CHARLES, CHAMBERS, MICHAEL, KEVIN, SAGE, IAN, CHARLES
Applicants: MERCK PATENT GMBH, MERCK PATENT GESELLSCHAFT MIT BESCHRAENKTER HAFTUNG
Application year: 1988
Main classification: C09K19
IPC codes: C09K19