IMPROVED LIQUID CRYSTAL MIXTURE

Abstract: An improved twisted nematic liquid crystal display device operating in the high multiplex mode, having a high contrast and containing a liquid crystal mixture which has a ratio of the elastic constants K3/K1 as small as possible but not more than 0.9 and a ratio of DELTA epsilon / epsilon ORTHOGONAL of at most +0.3 and comprises at least three liquid crystal materials: (a) at least 10 wt% of a first liquid crystal material comprising at least one of liquid crystal compounds represented by general formula (I), wherein R1 represents a group R or OR; and R2 represents R or OR; R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH2 groups may be replaced by -O- and/or -CH=CH-, two oxygen atoms not being directly attached to one another, A is 1,4-phenylene or trans-1,4-cyclohexylene, Z<1> is -CO-O-, -O-CO-, -CH2-O-, -OCH2-, -CH2CH2- or a single bond, Q<1> is 1,4-phenylene or trans-1,4-cyclohexylene, and m is 0, 1, or 2, (b) less than 10 wt% of a second liquid crystal material comprising one or more liquid crystal compounds having a distinct positive dielectric anisotropy ( DELTA epsilon >/= +3); and, (c) less than 90 wt% of a third liquid crystal material comprising at least one liquid crystal compound having a negative or substantially 0 dielectric anisotropy, wherein (1) the first liquid crystal material comprises at least one of liquid crystal compounds represented by general formulae (Ib) to (Ii), and/or (2) the third liquid crystal material comprises at least one liquid crystal compound represented by general formulae (IIId) to (IIIh), (III6) to (III15) and/or (III16) and (III17).

Description: Improved Liquid Crystal Mixture The invention relates to the improvement of a twisted nematic liquid crystal display device operating in the high multiplex mode with a very high contrast and with a particularly steep electro-optical characteristic. The device is operating in the first Gooch and Tarry trans¬ mission minimum. The invention furthermore relates to new liquid crystal dielectrics which have a ratio of the elastic constants K 3 /K.. as small as possible but not more than 0.9 and a ratio of Δε/εJ_ of at most 0.3. Such, dielec¬ trics are used in the matrix.type liquid crystal display devices driven by time sharing according to the invention. The properties of nematic or nematic-cholesteric liquid- crystalline materials are utilized for liquid-crystal display elements in order to effect significant changes in their optical properties, such as light transmission, light scattering, birefringence, reflectance or color, under the influence of electric fields. The functioning of display elements of this type is based here, for example, on the phenomena of dynamic scattering, the deformation of aligned phases or the Schadt-Helfrich effect in the twisted cell. Among these usual types of liquid-crystal display ele¬ ments, especially those based on the twisted nematic cell (TN cell) have gained particular importance recently, because they can be operated with relatively low ' con¬ trol voltages which can be readily made available even by small batteries. Moreover, these display elements have hitherto been the best which can be constructed as matrix display elements, which allow the presentation of a high information density without an intolerably large number of control lines, lead-ins and lead-outs. When used in practice, however, the TN cell, in parti¬ cular in the form of matrix display elements, still raises considerable difficulties. These include above all the more or less pronounced dependence of the con- trast on the angle of observation and the restricted multiplexing capacity. Conventional dielectrics for TN cells have a ratio of the elastic constants K-/K-. of approximately 1.2-1.3 and Δε/εJ_ above 1.0. Such conventional liquid crystal compositions are widely used in commercial twisted nematic display devices and disclosed in many references, e.g. Published Unexamined Japanese Patent Applications No. 56-105 510 and 56-105 511 and U.S. Patent 4,285,829. In these compositions, design is made based on the con- cept that the proportion of liquid crystal compounds having a distinct positive dielectric anisotropy generally is 30 % or more. These compositions are characterized in that the threshold voltages are in the range of 1 to 2 volts in most cases. It has now been surprisingly found that when values of Δε/εJ_ and K,/K-. of liquid crystal dielectrics become extremely small in time sharing-driven liquid crystal display devices, response speed and γ property (the sharp¬ ness in voltage-luminance property) are markedly improved in such a range of d.Δn that does meet the requirements for the first Gooch and Tarry minimum. The liquid crystal dielectrics are most suited for use in liquid crystal dis¬ play devices operating in the high multiplex mode and having a surprisingly improved contrast. It is an object of the invention to provide improved display devices, in which both a markedly improved con¬ trast, and, simultaneously, also a high response speed are ensured by operating the display elements in the first transmission minimum according to Gooch and Tarry. Upon further study of the specification and appended claims, further objects and advantages of this inven¬ tion will become apparent to those skilled in the art. It has now been found that, with a suitable choice of the liquid crystal parameters, it is possible, surprising¬ ly, to obtain the desired properties by operating the display elements in the first transmission minimum. A subject of the invention, therefore, is the improve¬ ment of a twisted nematic liquid crystal display device operating in the high multiplex mode and having a high contrast, wherein the liquid crystal dielectric has a ratio of the elastic constants K.-/K-. as small as pos¬ sible but not more than 0.9 and a ratio of Δε/εJ_ of at most +0.3 and comprises at least three liquid crystal materials: (a) at least 10 wt% of a first liquid crystal material comprising at least one of liquid crystal compounds represented by general formula: N R K-(i0X >/D V-Hz ---R 13 (I ) . wherein R_ represents a group R or OR; and R 9 represents R or OR; R being in each case indepen¬ dently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH groups may be replaced by -O- and/or -CH=CH-, two oxygen atoms not being directly attached to one another, A is 1,4-phenylene or trans-l,4-cyclo- hheexxyylleennee,, ZZ 1 iiss --CCOO--00--,, --ι0-CO-, -CH 2 -0-, -OCH,-, -CHH--CCHH^^--oorr aa ssiinnggllee bboonndd,, QQ_ iiss 11,,44--pphheennyylleennee or trans-l,4-cyclohexylene, and m. is 0, 1 or 2, (b) less than 10 wt% of a second liquid crystal ma¬ terial comprising one or more liquid crystal com¬ pounds having a distinct positive dielectric aniso- tropy (Δε ≥ + 3); and, (c) less than 90 wt% of a third liquid crystal material comprising at least one liquid crystal compound having a negative or substantially 0 dielectric anisotropy, the improvement wherein (1) the first liquid crystal material comprises at least one of liquid crystal compounds represented by general formulae lb to Ii: wherein R-, represents a group Ror OR; and R- repre¬ sents R or OR; R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH~ groups may be replaced by -0- and/or -CH=CH-, two oxygen atoms not being directly attached to one another, and/or (2) the third liquid crystal material comprises at least one liquid crystal compound represented by the general formulae Illd to Illh, III6 to III15 and/or II116 and II117: R 15 -/ H )-COO- H VR 16 nig wherein R11, R13, R15 and R18 each independently represent R, and R 9 , R 10 , R 12 , R 14 , R 16 and R 17 each independently represent R or OR, R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH groups may be replaced by -0- or -CH=CH-, two oxygen atoms not being directly attached to one another 4 and A is 1,4-cyclohexenylen, / H >-CH 2 CH 2 - / H -< O )-R ,38 III10 R 41 - H -CH 2 CH -( 0 )-\ ° )-R 42 III12 wherein R 29 , R 31 , R 33 , R 35 , R 37 , R 39 , R 40 , R 41 43 4 5 46 47 48 R , R , R , R , and R*° each independently represent R, R 30 , R 32 , R 34 , R 36 , R 38 , R 42 and R 44 each independently represent R or OR, R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH 2 groups may be replaced by -0- or -CH=CH-, two oxygen atoms not being directly attached to one another, 4 and A is 1,4-cyclohexenylen, R 49 - H ' *- H VoOC-R 50 11116 wherein R 49, R50, R51 and R52 each represent R, R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH 2 groups may be replaced by -O- or -CH=CH-, two oxygen atoms not being directly attached to one another.' A further subject of the invention is a method of simultaneously minimizing the dependence of contrast on the angle of observation of an electro-optical display element based on a liquid crystal dielectric and of maximizing its multiplexing capacity by maximi¬ zing its steepness of its characteristic curve, com¬ prising operating the element in the first Gooch and Tarry transmission minimum, selecting a dielectric as outlined above. The construction of the liquid crystal display element according to the invention from polarizers, electrode base plates and electrodes with such a.surface treatment that the preferential orientation of the particular adjoining liquid crystal molecules is usually twisted by 90° from one electrode to the other, corresponds to the type of construction conventional for such display ele¬ ments. The concept of the conventional type of con¬ struction is here taken in a very wide sense and also comprises all the variations and modifications, known from the literature, of the twisted nematic cell, and in particular also matrix display elements. An essential difference between the display elements according to the invention and those hitherto conventional and based on the twisted nematic cell is, however, the choice of the liquid crystal parameters in the liquid crystal layer. Whereas, for example, the K„/K, ratio in the con¬ ventional liquid-crystalline phases for display elements of this type is at least > 0.8 and the Δε/εJ_ ratio is normally between 1.2 and 1.7, the ~~ y ~~ - \ ratio in the display elements according to the invention is ≤ 0.9 and Δε/εJ_ is ≤ 0.3. The K 3 /K-. ratio in the display ele¬ ments according to the invention preferably is 0.4 to 0.9 and Δε/εJ_ preferably is 0.4 to 0.3. Particularly ^.preferred dielectrics are those, wherein 3 /K, is 0.2 to 0.75 and Δε/ε | is 0.1 to 0.3. The parameters used to define the invention are fully known to skilled workers. The contemplated definitions are to be found in many publications, e.g. W.H. De Jeu, Physical Properties of Liquid Crystal Materials, Gordon and Breach 1980 and the brochure "Liquid Crystals, Measurement of the Physical Properties" of E. Merck, whose disclosures are incorporated by reference herein. The thickness of a liquid crystal layer of the display element according to the invention and/or the optical anisotropy Δn of the liquid crystal material are chosen such that λ d . Δn = - . 3 2 the value of 550 n , normally used for the maximum sensi¬ tivity of the human eye, being taken for the wavelength λ. The layer thicknesses of the display elements according to the invention can, for example, be within the range from 2 to 10 μm. Preferably, the smallest possible layer thicknesses are chosen, the lower limit of d being de¬ termined by the quality standards rrquired for mass pro¬ duction. A particularly preferred range of d is thus 3 to 8 μm, in particular 4 to 7 μm. Liquid-crystalline dielectrics, the material parameters of which are within the ranges according to the inven¬ tion, can be prepared from conventional liquid-crystalline base materials. Numerous such materials are known from the literature. The dielectrics used for the display elements according to the invention comprise (a) at least 10 wt% of a first liquid crystal material comprising at least one of liquid crystal compounds represented by general formula: wherein R 1 represents a group R or OR; and R 2 repre¬ sents R or OR; R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH_ groups may be replaced by -0- and/or -CH=CH-, two oxygen atoms not being directly attached to one another, A is 1,4-phenylene or trans-l,4-cyclohexylene, Z Z 1 iiss --CCOO--00--,, --O0--CO-, -CH 2 -0-, -OCH 2 -, -CH 2 CH 2 - or aa ssiinnggllee bboonndd,, QQ iiss 11,,44--pphheennyylleene or trans-l,4-cyclohexylene, and m is 0, 1 or 2, (b) less than 10 wt% of a second liquid crystal material comprising one or more liquid crystal compounds having a distinct positive dielectric anisotropy (Δε ≥ + 3); and, (c) less than 90 wt% of a third liquid crystal material comprising at least one liquid crystal compound having a negative or substantially 0 dielectric anisotropy, whereby (1) the first liquid crystal material comprises at least one of liquid crystal compounds represented by general formulae lb to li: If R - -„R2 Z ig wherein R, represents a group R or OR; and R ? repre¬ sents R or OR; R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH 2 groups may be replaced by -O- and/or -CH=CH-, two oxygen atoms not being directly attached to one another, and/or (2) the third liquid crystal material comprises at least one liquid crystal compound represented by the general formulae Hid to Illh, II16 to II115 and/or II116 and II117: R 9 - ~ θ - 0 Illd t 13 -< H " -CH 2 CH 2 - H R 14 Illf R 15 H COO-/ H VR 16 Illg wherein R , R. , R and R 18 each independent¬ ly represent R, and R 9 , R 10 , R 12 , R 14 , R 16 and R 17 each independently represent R or OR, R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH_ groups may be replaced by -O- or -CH=CH-, two oxygen atoms not being directly attached to one an- other and A 4 i.s 1,4-cyclohexenylen, R 3 "3 5 - / H \ o- ' H \ ϋ-( ' H \ p-R 3--6 III9 R37 -( H >-CH 2 CH 2 -./H III10 R 47 - ΛT> - -coo- T - <T 48 I I I15 wherei . n _ R > 29 , _R31 , -R33 , -R,35 , D R37 , Ω R39 , , _R41 a~. ~ \ Λ ~ \ 46 4-7 4-ft R , R , R , R , and R ° each independently represen _t_ „R, ,R_,30, ,R,32, -,36 R , „R38, „R42 and R 44 each independently represent R or OR, R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH 2 groups may be replaced by -0- or -CH=CH-, two oxygen atoms not being directly attached to one an¬ other, 4 , and A is 1,4-cyclohexenylen, R,49-x H i- H δ-OOC-R5 ' 0 III16 wherein R 49, R50, R51 and R52 each represent R, R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH 2 groups may be replaced by -O- or -CH=CH-, two oxygen atoms not being directly attached to one another. Preferably the dielectric comprises at least one liquid crystal compound represented by the general formula la Preferably the second liquid crystal material comprises at least one of liquid crystal compounds represented by the general formulae Ila to lid: R- _ H ~ \ 0 >-CN . " lib X X being hydrogen or fluorine, Y being cyano, trifluoro- methoxy or fluorine, r being 0 or 1, and R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH 2 groups may be replaced by -0- or -CH=CH-, two oxygen atoms not being directly attached to one another. The third liquid crystal material comprises preferably liquid crystal compounds having a dielectric anisotropy of -1 to +1. Preferably the third liquid crystal material comprises at least one of liquid crystal compounds represented by the general formulae Ilia to IIIc; wherein R 3 represents R; and R4 represents R or OR 5 fi wherein R represents R; and R represents R or OR wherein R 7 represents R; and R8 represents R or OR; R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH_ groups may be replaced by -O- or -CH=CH-, two oxygen atoms not being directly attached to one another. Other preferred dielectrics are those, wherein the third liquid crystal material further comprises at least one of liquid crystal compounds represented by general formulae: R 19 -< H b- s O -/ O >-R 20 III1 \ / \ / wherein R 19 and R20 represent independently from one another R ,21 - H *-C .OO- / O _-- , 2222 R"--< H ? ,-R III2 wherein R 21 and R22 represent mdenpendehtly from one another R; wherein R 23 and R24 represent independently from one another R; wherein R and R represent independently from one another R; wherein represent independently from one another R; and n is 0 or 1; R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH 2 groups may be replaced by -O- or -CH=CH-, two oxygen atoms not being directly attached to one another. In the following tables appropriate liquid crystal com¬ pounds are shown with their physical properties. These compounds can be used for example for the display ele¬ ments according to the invention. Compounds of formulae la, lb, Ic, Ie, If and Ig are listed in Table 1. R preferably is n-alkyl having 2 3 to 9 carbon atoms. R preferably is ethyl, n-propyl or n-alkoxy having 5 to 9 carbon atoms. In addition pyrimidines of formula la are preferred wherein R 2 i.s methoxy. Table 1 Table 1 (continuation) Representative compounds of the second liquid crystal material (general formulae Ila to Ilh) with a distinct positive dielectric anisotropy are shown in Table 2. Table 2 As the liquid crystal compound having a negative or substantially 0 Δε value, there can be used liquid crystal compounds of phenylcyclohexane type represented by general formula Ilia (German Patent 26 36 684), phenyl cyclohexane carboxylates represented by general formula nib (German Patent 24 29 093), cyclohexyl cyclo- hexanes (USP 4,622,164) represented by general formula IIIc, biphenylcyclohexanes - formula nil - (Japanese Patent 1,311,608), phenyl cyclohexylcyclohexane carboxy- lates - formula IIΪ2 - (Japanese Patent 1,297,121), l-phenyl-2-cyclohexylcyclohexylethanes - formula II13 - (USP 4,606,845), cyclohexyl cyclohexylcyclohexane car¬ boxylates - formula II14 - (Japanese Patent 1,297,121), 4,4'-biscyclohexylbiphenyls (USP 4,331,552) and 4,4'- biscyclohexyl-2-fluorbiphenyls (USP 4,419,264) - for¬ mula III5 -. These liquid crystal compounds are low viscosity liquid crystal compounds for controlling viscosity, high temperature liquid crystal for raising N-I point and liquid crystals for suppressing smectic phases. As low viscosity liquid crystal compounds, there can be used liquid crystal compounds shown in Table 3 which show η of approximately 6 to 20 mPa.s. As high temperature liquid crystals, there can be used liquid crystal compounds shown in Table 4 having N-I point of approximately 130 to 330 °C. η is approximately 13 to 65 mPa.s. In all components of the liquid crystal compositions according to this invention R is preferable alkyl of 1 to 10 carbon atoms. A particularly preferred range is 1 to 5 carbon atoms. Table 3 (low viscosity LC compounds) Compound No./Structure Δε/εJ_ Δn mp. Clp. R --< HHV*-. OO " )>--ΪR >- \° >- R 7 R 8 Table 4 (high clearing point LC compounds) Compound No./Structure Δε/εJ_ Δn mp. Clp. Table 4 (continuation) _- - H V- x H 4--COO- H *-R^ ' .. / \ / At least one of the liquid crystal compounds shown in these Tables 3 and 4 or at least one of the compounds of general formulae Illd to Illh and III6 to III17 may be used for said third liquid crystal material. Preferred devices according to the invention are those, " wherein the liquid crystal dielectric comprises at least five components. Preferred embodiments are those, wherein the liquid crystal mixture is adjusted for a device, operating in the first Gooch and Tarry transmission minimum. - the liquid crystal mixture is adjusted for a device, wherein the electro-optical characteristic curve is at least as steep as that curve in the second such transmission minimum. the liquid crystal mixture is adjusted for a device, wherein the steepness of the characteristic curve in the first minimum is greater than that in the second minimum. the liquid crystal mixture shows ~~ 3 / ~~ -, of 0.4 to 0.9 and Δε/ε I is 0.4 to -0.3. - the liquid crystal mixture shows K 3 /K-. of 0.2 to 0.75 and Δε/εJ_ is 0.1 to 0.3. the liquid crystal mixture comprises at least five components. the first liquid crystal material comprises at least one of liquid crystal compounds represented by the general formula la the second liquid crystal material comprises at least one of liquid crystal compounds represented by the general formulae Ila to lid: X being hydrogen or fluorine, Y being cyano, tri- fluoromethoxy or fluorine, r being 0 or 1 and R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH 2 groups may be replaced by -O- or -CH=CH-, two oxygen atoms not being directly attached to one another. the third liquid crystal material comprises liquid crystal compounds having a dielectric anisotropy of -1 to +1. the third liquid crystal material comprises at least one of liquid crystal compounds represented by the general formulae Ilia to IIIc; wherein R 3 represents R; and R4 represents R or OR wherein R 5 represents R; and R6 represents R or OR 7 Q wherein R represents R; and R represents R or OR; R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH 2 groups may be replaced by -0- or -CH=CH-, two oxygen atoms not being directly attached to one another. the third liquid crystal material further comprises at least one of liquid crystal compounds represented by general formulae: 19 20 wherein R and R represent independently from one another R wherein R 21 and R22 represent indenpendently from one another R; wherein R 23 and R24 represent independently from one another R; wherein R and R represent independently from one another R; wherein R 27 and R28 represent independently from one another R; and n is 0 or 1; R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH 2 groups may be replaced by -O- or -CH=CH-, two oxygen atoms not being directly attached to one another. the formulation ratios of said first liquid crystal material, said second liquid crystal material and said third liquid crystal material are at least 30 wt%, less than 10 wt% and less than 70 wt%, respectively. the formulation ratios of said first liquid crystal material, said second liquid crystal material and said third liquid crystal material are 30 to 65 wt%, less than 5 wt% and 35 to 70 wt%, respec- tively. Preferred dielectrics are those, wherein the formula¬ tion ratios of said first liquid crystal material, said second liquid crystal material and said third liquid crystal material are at least 30 wt%, less than 10 wt% and less than 70 wt%, respectively. Particularly preferred dielectrics are those, wherein the formulation ratios of said first liquid crystal material, said second liquid crystal material and said third liquid crystal material are 30 to 65 wt%, less than 5 wt% and 35 to 70 wt%, respectively. Such dielectrics can additionally contain dyes and/or doping substances in the usual quantities, unless the liquid crystal parameters are thus taken out of the ranges according to the invention. Mixing of the liquid crystalline components to achieve the parameters discussed above can be routinely accom¬ plished by the usual preliminary orientation experi¬ ments taking into account the usual considerations. Some of the many publications, whose disclosures are incor¬ porated by reference herein, disclosing details of suitable materials include German Offenlegungsschrift 2,257,588; 2,306,738; 2,017,727; 2,321,632; European Published Application 0,126,883; USP 3,997,536; 4,062,798; 4,462,923; 4,389,329; 4,364,838; 4,066,570; 4,452,718; 4,419,262; 4,510,069; Japanese Published Applications 144,770/84; 144,771/84; 144,772/8443,961/83; D. Demus et al., Flϋssige Kristalle in Tabellen, VEB Deutscher Verlag fur Grundstoffindustrie, Leipzig 1974 and D. Demus et al., Flϋssige Kristalle in Tabellen II, VEB Deutscher Verlag fur Grundstoffindustrie, Leipzig 1984. All components are known or can be prepared in analogy to known compounds. Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limita¬ tive of the remainder of the disclosure in any way whatso- ever. In the tables 1-4 above and in the following exam¬ ples, all temperatures are set forth uncorrected in degrees Celsius; unless otherwise indicated, all parts and percentages are by weight. Example 1 A liquid crystalline phase consisting of 2 % 2-(3 ' ,4'-difluorobiphenyl-4-yl)-5-heptylpyrimidine, 11 % trans-l-p-propylphenyl-4-pentylcyclohexane, 9 % trans-l-p-ethoxyphenyl-4-propylcyclohexane, 7 % trans-l-p-butoxyphenyl-4-propylcyclohexane, 7 % 2-p-ethylphenyl-5-propylpyrimidine, 7 % 2-p-propylphenyl-5-propylpyrimidine, 5 % 2-p-pentyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-heptylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-heptylpyrimidine, 9 % l-[trans-4-(trans-propylcyclohexyl)-cyclohexyl]- 2-(p-methylphenyl)-ethane, 9 % 1-[trans-4-(trans-propylcyclohexyl)-cyclohexyl]- 2-(p-propylphenyl)-ethane, 9 % l-[trans-4-(trans-propylcyclohexyl)-cyclohexyl]- 2-(p-pentylphenyl)-ethane and 5 % 4-nonyl-4'-(trans-4-pentylcyclohexyl)-biphenyl has a clearing point of 60.6°, Δε = 0.6 and Δn = 0.127. Example 2 A liquid crystalline phase consisting of 2 % 2-p-fluorophenyl-5-hexylpyrimidine, 11 % trans-l-p-propylphenyl-4-pentylcyclohexane, 9 % trans-l-p-ethoxyphenyl-4-propylcyclohexane, 7 % trans-l-p-butoxyphenyl-4-propylcyclohexane, 7 % 2-p-ethylphenyl-5-propylpyrimidine, 7 % 2-p-propylphenyl-5-propylpyrimidine, 5 % 2-p-pentyloxyphenyl-5-hexylpyrimidme, 5 % 2-p-heptyloxyphenyl-5-hexylpyrimidme, 5 % 2-p-nonyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-heptylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-heptylpyrimidine, 9 % l-[trans-4-(trans-propylcyclohexyl ) -cyclohexyl] - 2- (p-methylphenyl ) -ethane , 9 % l- [trans-4- (trans-propylcyclohexyl ) -cyclohexyl] - 2- (p-propylphenyl ) -ethane, 9 % 1- [trans -4- (trans-propyl cyclohexyl) -cyclohexyl] - 2 - (p-pentylphenyl ) -ethane and 5 % 4-nonyl-4 ' -(trans-4-pentyl cyclohexyl )-biphenyl has a clearing point of 57.8° , Δε = 0.5 and Δn = 0.125. Example 3 A liquid crystalline phase consisting of 3 % trans-4-(trans-4-propylcyclohexyl)-l-methoxycyclo- hexane, 3 % trans-4-(trans-4-propylcyclohexyl)-l-propoxycyclo- hexane, 2 % 2-p-fluorophenyl-5-hexylpyrimidine, 11 % trans-l-p-propylphenyl-4-pentylcyclohexane, 9 % trans-l-p-ethoxyphenyl-4-propylcyclohexane, 7 % trans-l-p-butoxyphenyl-4-propylcyclohexane, 7 % 2-p-ethylphenyl-5-propylpyrimidine, 7 % 2-p-propylphenyl-5-propylpyrimidine, 5 % 2-p-pentyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-heptylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-heptylpyrimidine, 7 % 1-[trans-4-(trans-propylcyclohexyl)-cyclohexyl]- 2 -(p-propylphenyl)-ethane, 7 % l-[trans-4-(trans-4-propylcyclohexyl)-cyclohexyl]- 2-(p-meth lphenyl)-ethane, 7 % 1-[trans-4-(trans-propylcyclohexyl)-cyclohexyl]- 2-(p-pentylphenyl)-ethane and 5 % 4-nonyl-4 ' - (trans-4-pentylcyclohexyl )-biphenyl has a clearing point of 50.9°, Δε = 0.5 and Δn = 0.121. Example 4 A liquid crystalline phase consisting of 3 % 2-p-cyanophenyl-5-pentyl-l,3-dioxane, 10 % trans-l-p-propylphenyl-4-pentylcyclohexane, 9 % trans-l-p-ethoxyphenyl-4-propylcyclohexane, 7 % 2-p-ethylphenyl-5-propylpyrimidine, 7 % 2-p-propylphenyl-5-propylpyri idine, 6 % 2-p-ethylphenyl-5-heptylpyrimidine, 5 % 2-p-pentyloxyphenyl-5-heptylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-heptylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-heptylpyrimidine, 22 % trans-4-(trans-4-propylcyclohexyl)-l-(4-ethyl- phenyl)-cyclohexane and 11 % trans-4-(trans-4-propylcyclohexyl)-l-4-propyl- phenylcyclohexane has a clearing point of 56.5°, Δε = 1.3 and Δn = 0.132. Example 5 A liquid crystalline phase consisting of 3 % 2-p-cyanophenyl-5-pentyl-l,3-dioxane, 10 % trans-l-p-propylphenyl-4-pentylcyclohexane, 9 % trans-l-p-ethoxyphenyl-4-propylcyclohexane, 7 % 2-p-ethylphenyl-5-propylpyrimidine, 7 % 2-p-propylphenyl-5-propylpyrimidine, 6 % 2-p-(trans-4-propylcyclohexyl)-phenyl-5-heptyl- pyrimidine, 5 % 2-p-pentyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-heptylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-heptylpyrimidine, 11 % l-[trans-4-(trans-4-propylcyclohexyl-cyclohexyl]- 2-(p-methylphenyl)-ethane, 11 % l-[trans-4-(trans-4-propylcyclohexyl-cyclohexyl]- 2-(p-propylphenyl)-ethane and. 11 % l-[trans-4-(trans-4-propylcyclohexyl)-cyclohexyl]- 2-(p-pentylphenyl)-ethane has a clearing point of 67.6°, Δε = 1.3 and Δn = 0.129. Example 6 A liquid crystalline phase consisting of 3 % 2-p-cyanophenyl-5-pentyl-l,3-dioxane, 10 % trans-l-p-p opylphenyl-4-pentylcyclohexane, 9 % trans-l-p-ethoxyphenyl-4-propylcyclohexane, 7 % 2-p-ethylphenyl-5-propylpyrimidine, 7 " % 2-p-propylphenyl-5-propylpyrimi ine, 6 % 2-p-ethylphenyl-5-heptylpyrimidine, 5 % 2-[trans-4-(trans-4-butylcyclohexyl)-cyclohexyl]- 5-propylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-heptylpyrimidine, 5 % 2-[trans-4-(trans-4-butylcyclohexyl)-cyclohexyl]- 5-heptylpyrimidine, 11 % l-[trans-4-(trans-4-propylcyclohexyl)-cyclohexyl]- 2-(p-methylphenyl)-ethane, 11 % 1-[trans-4-(trans-4-propylcyclohexyl)-cyclohexyl]- 2-(p-propylphenyl)-ethane and 11 % 1-[trans-4-(trans-4-propylcyclohexyl)-cyclohexyl]- 2-(p-pentylpheny1)-ethane has a clearing point of 62.2°, Δε = 1.3 and Δn = 0.119. Example 7 A liquid crystalline phase consisting of 3 % 2-p-cyanophenyl-5-pentyl-l,3-dioxane, 10 % trans-l-p-propylphenyl-4-pentylcyclohexane, 9 % trans- ' l-p-ethoxyphenyl-4-propylcyclohexane, 7 % 2-p-ethylphenyl-5-propylpyrimidine, 7 % 2-p-propylphenyl-5-propylpyrimidine, 6 % 2-p-[trans-4-(trans-4-pentylcyclohexyl)-cyclohexyl] phenyl-5-heptylpyrimidine, 5 % 2-p-pentyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-heptylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-heptylpyrimidine, - se ¬ ll % 1-[trans-4-(trans-4-propylcyclohexyl)-cyclohexyl]- 2-(p-methylphenyl)-ethane, 11 % 1-[trans-4-(trans-4-propylcyclohexyl)-cyclohexyl]- 2-(p-propylphenyl)-ethane and 11 % 1-[trans-4-(trans-4-propylcyclohexyl)-cyclohexyl]- 2-(p-pentylphenyl)-ethane has a clearing point of 73.6°, Δε = 1.2 and Δn = 0.13. Example 8 A liquid crystalline phase consisting of 3 % 2-p-cyanophenyl-5-pentyl-l,3-dioxane, 10 % trans-l-p-propylphenyl-4-pentylcyclohexane, 9 % trans-l-p-ethoxyphenyl-4-propylcyclohexane, 7 % 2-p-ethylphenyl-5-propylpyrimidine, 7 % 2-p-propylphenyl-5-propylpyrimidine, 6 % 2-p-ethylphenyl-5-heptylpyrimidine, 5 % 2-p-pentylσxyphenyl-5-hexylpyrimidme, 5 % 2-p-heptyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-hexylpyrimidine, 5 % 2-(4'-octyloxybiphenyl-4-yl)-5-heptylpyrimidine, 5 % 2-(4'-methoxybiphenyl-4-yl)-5-heptylpyrimidine, 11 % 1-[trans-4-(trans-4-propylcyclohexyl)-cyclohexyl]- 2-(p-methylphenyl)-ethane, 11 % l-[trans-4-(trans-4-propylcyclohexyl)-cyclohexyl]- 2-(p-propylphenyl)-ethane and 11 % l-[trans-4-(trans-4-propylcyclohexyl)-cyclohexyl]- 2-(p-pentylphenyl)-ethane has a clearing point of 65.9°, Δε = 1.1 and Δn = 0.141. Example 9 A liquid crystalline phase consisting of 2 % 4-cyanophenyl p-pentylbenzoate, 11 % trans-l-p-propylphenyl-4-pentylcyclohexane, 9 % trans-l-p-ethoxyphenyl-4-propylcyclohexane, 7 % trans-l-p-butoxyphenyl-4-propylcyclohexane, 7 % 2-p-ethylphenyl-5-propylpyrimidine, 7 % 2-p-propylphenyl-5-propylpyrimidine, 5 % 2-p-pentyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-heptylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-heptylpyrimidine, 9 % l-[trans-4-(trans-propylcyclohexyl)-cyclohexyl]- 2-(p-methylphenyl)-ethane, 9 % l-[trans-4-(trans-propylcyclohexyl)-cyclohexyl]- 2-(p-propylphenyl)-ethane, 9 % 1-[trans-4-(trans-propylcyclohexyl)-cyclohexyl]- 2-(p-pentylphenyl)-ethane and 5 % 4-nonyl-4'-(trans-4-pentylcyclohexyl)-biphenyl has a clearing point of 59.8°, Δε = 0.7 and Δn = 0.126 Example 10 A liquid crystalline phase consisting of 2 % 2-p-trifluoromethoxyphenyl-5-heptylpyrimidine, 11 % trans-l-p-propylphenyl-4-pentylcyclohexane, 9 % trans- l -p-ethoxyphenyl-4-propylcyclohexane, 7 % trans-l-p-butoxyphenyl-4-propylcyclohexane, 7 % 2-p-ehtylphenyl-5-propylpyrimidine, 7 % 2-p-propylphenyl-5-propylpyrimidine, 5 % 2-p-pentyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-nonyloxlyphenyl-5-hexylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-heptylpyrimidine, 9 % l-[trans-4-(trans-propylcyclohexyl)-cyclohexyl]- 2-(p-methylphenyl)-ethane, 9 % 1-[trans-4-(trans-propylcyclohexyl)-cyclohexyl]- 2-(p-propylphenyl)-ethane, 9 % 1-[trans-4-(trans-prtopylcyclohexyl)-cyclohexyl]- 2-(p-pentylphenyl)-ethane and 5 % 4-nonyl- '-(trans-4-pentylcyclohexyl)-biphenyl has a clearing point of 58.2°, Δε = 0.6 and Δn = 0.125. Example 11 A liquid crystalline phase consisting of 1 % p-(trans-4-heptylcyclohexyl)-benzonitrile, 12 % trans-l-p-propylphenyl-4-pentylcyclohexane, 10 % trans-l-p-ethoxyphenyl-4-propylcyclohexane, 7 % trans-l-p-butoxyphenyl-4-propylcyclohexane, 7 % 2-p-ethylphenyl-5-propylpyrimidine, 7 % 2-p-propylphenyl-5-propylpyrimidine, 5 % 2-p-pentyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-nongloxyphenyl-5-hexylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-heptylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-heptylpyrimidine, 11 % l-[trans-4-(trans-4-propylcyclohexyl)-cyclohexyl] -2-(p-propylphenyl)-ethane, 10 % l-[trans-4-(trans-4-propylcyclohexyl)-cyclohexyl]' -2-(p-pentylphenyl)-ethane, and 10 % 1-[trans-4-(5- ropylpyrimidin-2-yl)-cyclohexyl]- 2-(trans-4-pentylcyclohexyl)-ethane has a clearing point of 60°, Δn = 0.12, Δε = +1.2, Δε/εl = 0.3, K.-/K.- = 0.82 and V , = 4,0 Volt. Example 12 A liquid crystalline phase consisting of 1 % 4,-heptyl-4'-cyanobiphenyl, 5 % 2-p-ethylphenyl-5-heptylpyrimidine, 5 % 2-p-methoxyphenyl-5-hexylpyrimidine, 5 % 2-p-methoxyphenyl-5-heptylpyrimidine, 5 % 2-p-methoxyphenyl-5-nonylpyrimidine, 5 % 2-p-pentyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-hexyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-heptylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-heptylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-nonylpyrimidine, 5 % 2-p-hexyloxyphenyl-5-nonylpyrimidine, 11 % 1-[trans-4-(5-propylpyrimidin-2-yl)-cyclohexyl]- 2-(trans-4-pentylcyclohexyl)-ethane_ 4 % p-(trans-4-propylcyclphexyl)-phenyl trans-4-(trans- 4-propylcyclohexyl)-cyclohexane carboxylate. 12 % trans-l-p-methoxyphenyl-4-propylcyclohexane, 6 % trans,trans-4-butanoyloxy-4-propylcyclohexylcyclo¬ hexane, 6 % trans,trans-4-hexanoyloxy-4-propylcyclohexylcyclo¬ hexane, has a clearing point of 60°, Δn = 0.13, Δε = +1.2, Δε/εJ_ = 0.3, ~~ z / ~~ - L = 0.7 and V . = 4,0 Volt. Example 13 A liquid crystalline phase consisting of 1 % 2-p-cyanophenyl-5-heptylpyrimidine, 5 % 2-p-ethylphenyl-5-heptylpyrimidine, 5 % 2-p-methoxyphenyl-5-hexylpyrimidine, 5 % 2-p-methoxyphenyl-5-heptylpyrimidine, 5 % 2-p-methoxyphenyl-5-nonylpyrimidine, 5 % 2-p-pentyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-hexyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-hexylpyrimidme, 5 % 2-p-heptyloxyphenyl-5-heptylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-heptylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-nonylpyrimidine, 5 % 2-p-hexyloxyphenyl-5-nonylpyrimidme, 11 % 1-[trans-4-(5-propylpyrimidin-2-yl)-cyclohexyl]- 2-(trans-4-pentylcyclohexyl)-ethane. 4 % p-(trans-4-propylcyclohexyl)-phenyl trans-4-(trans■ 4-propylcyclohexyl)-cyclohexane carboxylate. 12 % trans-l-p-methoxyphenyl-4-propylcyclohexane, 6 % trans,trans-4-butanoyloxy-4-propylcyclohexylcyclo- hexane, 6 % trans,trans-4-hexanoyloxy-4-propylcyclohexylcyclo- hexane, has a clearing point of 59°, Δn = 0.13, Δε = +1.2, Δε/εJ_ = 0.3, I , = 0.69 and V.. = 4,0 Volt. Example 14 A liquid crystalline phase consisting of 1 % 2-p-cyanophenyl-5-heptylpyrimidine, 12 % trans-l-p-methoxyphenyl-4-propylcyclohexane, 6 % trans, trans-4-butanoyloxy-4' -propylcyclohexyl- cyclohexane, 6 % trans, trans-4-hexanoyloxy-4' -propylcyclohexyl- cyclohexane, 5 % 2-(trans-4-ethylcyclohexyl)-5-heptylpyrimidine, 5 % 2-p-methoxyphenyl-5-hexylpyrimidine, 5 % 2-p-ρentyloxyρ enyl-5-hexylpyrimidine, 5 % 2-p-hexyloxyphenyl-5-hexylpyrimidme, 5 % 2-p-nonyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-methoxyphenyl-5-heptylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-heptylpyrimidme, 5 % 2-p-nonyloxyphenyl-5-heptylpyrimidine, 5 % 2-p-methoxyphenyl-5-nonylpyrimidine, 5 % 2-p-hexyloxyphenyl-5-nonylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-nonylpyrimidine, 5 %' 2- ( trans-4-heptyl cyclohexyl ) -5-hexyloxypyrimidine , 5 % 2-(trans-4-heptylcyclohexyl)-5-nonyloxypyrimidine, 11 % l-[trans-4-(5-propylpyrimidin-2-yl)-cyclohexyl]- 2-(trans-4-pentylcyclohexyl)-ethane 4 % p-(trans-4-propylcyclohexyl)-phenyl trans-4-(trans- 4-propylcyclohexyl)-cyclohexane carboxylate has a clearing point of 56°, Δn = 0.12, Δε = +1.2, Δε/εi = 0.3, K 3 K χ = 0.74 and V^ = 4,2 Volt. Example 15 A liquid crystalline phase consisting of 1 % 2-p-cyanophenyl-5-heptylpyrimidine, 12 % trans-l-p-methoxyphenyl-4-propylcyclohexane, 3 % 4-methoxy-4'-propylbiphenyl, 4 % trans-4-propylcyclohexyl trans-4-pentylcyclohexane carboxylate, 5 % trans-4-pentylcyclohexyl trans-4-pentylcyclohexane carboxylate, 4 % trans,trans-4-hexanoyloxy-4Ipropylcyclohecylcyclo- hexane, 5 % 2-p-ethylphenyl-5-heptylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-hexylpyrimidme , 5 % 2-p-pentyloxyphenyl-5-hexylpyrimidine , 5 % 2-p-hexyloxyphenyl-5-hexylpyrimidme, 5 % 2-p-nonyloxyphenyl-5-hexylpyrimidine , 5 % 2-p-methoxyphenyl-5-heptylpyrimidme, 5 % 2-p-heptyloxyphenyl-5-heptylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-heptylpyrimidine , 5 % 2-p-methoxyphenyl-5-nonylpyrimidine , 5 % 2-p-hexyloxyphenyl-5-nonylpyrimidine , 5 % 2-p-nonyloxyphenyl-5-nonylpyrimidine, 10 % 1-[trans-4-pentylcyclohexyl)-2-(4 • -ethyl-2'-fluoro- biphenyl-4-yl)-ethane and 6 % p-(trans-4-propylcyclohexyl)-phenyl trans-4-(trans- 4-propylcyclohexyl)-cyclohexane carboxylate has a clearing point of 59°, Δn = 0.13, Δε = 0.7, Δε/εχ = 0.2, Kg/I^ = 0.72 and V^ = 4,8 Volt. Example 16 A liquid crystalline phase consisting of 1 % 2-p-cyanophenyl-5-heptylpyrimidine., 12 % trans-l-p-methoxyphenyl-4-propylcyclohexane, 3 % 4-methoxy-4'- propylbiphenyl, 4 % trans,trans-4-hexanoyloxy-4'-propylcyclohexyl- cyclohexane, 4 % trans-4-propylcyclohexyl trans-4-pentylcyclo- hexanecarboxylate, 5 % trans-4-pentylcyclohexyl trans-4-pentylcyclo- hexanecarboxylate, 5 % 2-(trans-4-ethylcyclohexyl)-5-heptylpyrimidine, 5 % 2-p-pentyloxy phenyl-5-hexylpyrimidine, 5 % 2-p-hexyloxy phenyl-5-hexylpyrimidine, 5 % 2-p-nonyloxy phenyl-5-hexylpyrimidine, 5 % 2-p-methoxy phenyl-5-heptylpyrimidine, 5 % 2-p-heptyloxy phenyl-5-heptylpyrimidine, 5 % 2-p-methoxy phenyl-5-nonylpyrimidine, , 5 % 2-p-hexyloxy phenyl-5-nonylpyrimidine, 5 % 2-p-nonyloxy phenyl-5-nonylpyrimidine, 5 % 2-(trans-4-heptylcyclohexyl)-5-hexyloxypyrimidine, 5 % 2-(trans-4-heptylcyclohexyl)-5-nonyloxypyrimidine, 10 % l-[trans-4-pentylcyclohexyl)-2-(4'-ethyl-2'-fluoro- biphenyl-4-yl)-ethane and 6 % p-(trans-4-propylcyclohexyl)-phenyl trans-4-(trans- 4-propylcyclohexyl)-cyclohexane carboxylate has a clearing point of 56°, Δn = 0.12, Δε = +0.7, Δε/ε_L = 0.2, K 3 /K χ = 0.77 and V.^ = 5,0 Volt. Example 17 A liquid crystalline phase consisting of 1 % 2-(3-fluoro-4-cyanophenyl)-5-heptylpyrimidine, 12 % trans-l-p-methoxyphenyl-4-propylcyclohexane, 7 % trans,trans-4-hexanoyloxy-4'-propylcyclohexyl- cyclohexane, 5 % trans-4-propylcyclohexyl trans-4-pentyl cyclohexane carboxylate, 5 % trans-4-pentylcyclohexyl trans-4-pentyl cyclohexane carboxy1ate, 5 % 2-p-propylphenyl-5-pen ylpyrimidine, 5 % 2-p-ethylphenyl-5-heptylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-hexyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-methoxyphenyl-5-heptylpyrimidine, 5 % 2-p-hepJtyloxyphenyl-5-heptylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-heptylpyrimidine, 5 % 2-p-methoxyphenyl-5-nonylpyrimidine, 5 % 2-p-hexyloxyphenyl-5-nonylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-nonylpyrimidine, 10 % 1-[trans-4-(5-propylpyrimidin-2-yl)-cyclohexyl]- 2-(trans-4-pentylcyclohexyl)-ethane 5 % p-(trans-4-propylcyclohexyl)-phenyl trans-4-(trans■ 4-propylcyclohexyl)-cyclohexane carboxylate has a clearing point of 60°, Δn = 0.12, Δε = +1.2, Δε/εJ_ = 0.3, ~~ 3 / ~~ - ι _ = 0.75 and V^ = 4,1 Volt. Example 18 A liquid crystalline phase consisting of 1 % 2-(3-fluoro-4-cyanophenyl)-5-heptylpyrimidine, 12 % trans-l-p-methoxyphenyl-4-propylcyclohexane, 7 % trans,trans-4-hexanoyloxy-4'-propylcyclohexyl- cyclohexane, 5 % trans-4-propylcyclohexyl trans-4-pentyl cyclohexane carboxylate, 5 % trans-4-pentylcyclohexyl trans-4-pentyl cyclohexane carboxy1ate, 5 % 2-(trans-4-ethylcyclohexyl)-5-heptylpyrimidine, 5 % 2-(trans-4-propylcyclohexyl)-5-pentylpyrimidine, 5 % 2-p-hexyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-hexylpyrimidine, 5 % 2-p-methoxyphenyl-5-heptylpyrimidine, 5 % 2-p-heptyloxyphenyl-5-heptylpyrimidine, 5 % 2-p-methoxyphenyi-5-nonylpyrimidine, 5 % 2-p-hexyloxyphenyl-5-nonylpyrimidine, 5 % 2-p-nonyloxyphenyl-5-nonylpyrimidine, 5 % 2(trans-4-heptylcyclohexyl)-5-hexyloxypyrimidine, 5 % 2(trans-4-heptylcyclohexyl)-5-nonyloxypyrimidine, 10 % 1-[trans-4-(5-propylpyrimidin-2-yl)-cyclohexyl]- 2-(trans-4-pentylcyclohexyl)-ethane 5 % p-(trans-4-propylcyclohexyl)-phenyl trans-4-(trans- 4-propylcyclohexyl)-cyclohexane carboxylate has a clearing point of 56°, Δn = 0.11, Δε = +1.1, Δε/εi = 0.3, K^/I - = 0.81 and V^ = 4,3 Volt.

Claims: Patent Claims: 1. In a twisted nematic liquid crystal display device operating in the high multiplex mode, having a high contrast and containing a liquid crystal mixture which has a ratio of the elastic constants K 3 /K 1 as small as possible but not more than 0.9 and a ratio of Δε/εJ_ of at most +0.3 and comprises at least three liquid crystal materials: (a) at least 10 wt% of a first liquid crystal material comprising at least one of liquid crystal compounds represented by general formula: wherein R, represents a group R or OR; and R 2 represents R or OR; R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH 2 groups may be replaced by -0- and/or -CH=CH-, two oxygen atoms not being directly attached to one another, A is 1,4- phenylene or trans-l,4-cyclohexylene, Z is -CO-0-, -0-CO-, -CH 2 -0-, -OCH 2 -, -CH 2 CH 2 - or a single bond, Q 1 is 1,4-phenylene or tranε-l,4-cyclohexylene, and m is 0, 1 or 2, (b) less than 10 wt% of a second liquid crystal material comprising one or more liquid crystal compounds having a distinct positive dielectric anis-otropy (Δε ≥ + 3) ; and, (c) less than 90 wt% of a third liquid crystal ma¬ terial comprising at least one liquid crystal compound having a negative or substantially 0 dielectric anisotropy, the improvement wherein (1) the first liquid crystal material comprises at least one of liquid crystal compounds represen¬ ted by general formulae lb to li: wherein R 1 represents a group R or OR; and R ? represents R or OR; R being in each case inde¬ pendently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non- adjacent CH 2 groups may be replaced by -O- and/or -CH=CH-, two oxygen atoms not being directly attached to one another, and/or (2) the third liquid crystal material comprises at least one liquid crystal compound represen¬ ted by the general formulae Illd to Illh, III6 to III15 and/or III16 and III17: RVO OVR 10 Illd ; - \ wherein R 11, R13, R15 and R18 each independent- ly represent R, and R 9 , R 10 , R 12 , R 14 , R 16 and R 17 each independently represent R or OR, R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH_ groups may be replaced by -0- or -CH=CH-, two oxygen atoms not being directly attached to one another and A 4 i•s 1,4-cyclohexenylen, R 37 -(H )-CH 2 CH 2 -< H »- 0 >-R 3 ' 8 III10 \ _/ III13 ,45 ■ -0- O >-ø-R46 11114 wherein R 29 , R 31 , R 33 , R 35 , R 37 , R 39 , R 40 , - R.41, D R43, -R.45, D R46, _R,47, and. „R48 eac.h m. d,epen- dently represent R, R 30 , R 32 , R 34 , R 36 , R 38 , R 42 and R44 each independently represent R or OR; R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH_ groups may be replaced by -O- or -CH=CH-, two oxygen atoms not being directly attached to one another, 4 and A is 1,4-cyclohexenylen, R 51 -/H H «-COO- 52 III17 wh .erei.n _R49, D R50, _R51 and, -R,52 eac.h represent. R, R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH ? groups may be replaced by -0- or -CH=CH-, two oxygen atoms not being directly attached to one another. 2. An improved liquid crystal mixture according to claim 1 in a device, operating in the first Gooch and Tarry transmission minimum. 3. An improved liquid crystal mixture according to claim 2 in a device, wherein the electro-optical characteristic curve is at least as steep as that curve in the second such transmission minimum. 4. An improved liquid crystal mixture according to claim 3 in a device, wherein the steepness of the characteristic curve in the first minimum is greater than that in the second minimum. 5. An improved liquid crystal mixture according to ccllaaiimm 11 iinn aa ddeevviiccee,, wwhh<erein K 3 /K_. is 0.4 to 0. and Δε/ε I is 0.4 to 0.3 6. An improved liquid crystal mixture according to ccllaaiimm 11 iinn aa ddeevviiccee,, wwhherein ~~ 3 / ~~ -, is 0.2 to 0.75 and Δε/ε I is 0.1 to 0.3 7. An improved liquid crystal mixture according to claim 1, wherein the liquid crystal mixture com- prises at least five components. 8. An improved liquid crystal mixture according to claim 1, wherein the first liquid crystal material comprises at least one of liquid crystal compounds represented by the general formula la 9. An improved liquid crystal mixture according to claim 1, wherein the second liquid crystal material comprises at least one of liquid crystal compounds represented by the general formulae Ila to lid: X R_/ o >-< 0 V-CN lid X being hydrogen or fluorine, Y being cyano, trifluoromethoxy or fluorine, r being 0 or 1 and R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH 2 groups may be replaced by -O- or -CH=CH-, two oxygen atoms not being directly attached to one another. 10. An improved liquid crystal mixture according to claim 1, wherein the third liquid crystal material comprises liquid crystal compounds having a di¬ electric anisotropy of -1 to +1. 11. An improved liquid crystal mixture according to claim 1, wherein the third liquid crystal material comprises at least one of liquid crystal compounds represented by the general formulae Ilia to IIIc; wherein R 3 represents R; and R4 represents R or OR R " '- . « . - COO _ / 0 ,-R 11lb \ c c. wherein R represents R; and R represents R or OR wherein R 7 represents R; and R8 represents R or OR; R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH„ groups may be replaced by -O- or -CH=CH-, two oxygen atoms not being directly attached to one another. 12. An improved liquid crystal mixture according to claim 1, wherein the third liquid crystal material further comprises at least one of liquid crystal compounds represented by general formulae: R - • - - / H t- / θ V θ \ -R 20 1111 wherein R 19 and R20 represent independently from one another R wherein R 21 and R22 represent mdenpendently from one another R; II 13 wherein R 23 and R24 represent independently from one another R; 1114 wherein R and R represent independently from one another R; wherein R 27 and R28 represent independently from one another R; and n is O or 1; R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH 2 groups may be replaced by -0- or -CH=CH-, two oxygen atoms not being directly attached to one another. 13. An improved liquid crystal mixture according to claim 1, wherein the formulation ratios of said first liquid crystal material, said second liquid crystal material and said third liquid crystal material are at least 30 wt%, less than 10 wt% and less than 70 wt%, respectively. 14. An improved liquid crystal mixture according to claim 8, wherein the formulation ratios of said first liquid crystal material, said second liquid crystal material and said third liquid crystal material are 30 to 65 wt%, less than 5 wt% and 35 to 70 wt%, respectively. 15. A method of simultaneously minimizing the dependence of contrast on the angle of observation of an- electro- optical display element based on a liquid crystal mixture and of maximizing its multiplexing capa¬ city by maximizing its steepness of its character- istic curve, comprising operating the element in the first Gooch and Tarry transmission minimum, selecting a mixture having a ~~ 3 / ~~ 1 ratio as small as possible but not more than 0.9 and a ratio of Δε/εJ_ of at most 0.3, said mixture comprises at least three liquid crystal materials: (a) at least 10 wt% of a first liquid crystal material comprising at least one of liquid crystal compounds represented by general formula: wherein R., represents a group R or OR; and R 2 represents R or OR; R being in each case inde¬ pendently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non- adjacent CH 2 groups may be replaced , by -O- and/or -CH=CH-, two oxygen atoms not being directly attached to one another, A is 1,4- phenylene or trans-1,4-cyclohexylene, Z is -CO-0-, -0-CO-, -CH 2 -0-, -OCH 2 -, -CH 2 CH 2 - or a single bond, O O iiss 11,,44--pphheennyyll€ene or trans-l,4-cyclohexyl- ene, and m is 0, 1 or 2, (b) less than 10 wt% of a second liquid crystal material comprising one or more liquid crystal compounds having a distinct positive dielec¬ tric anisotropy (Δε ≥ + 3); and, (c) less than 90 wt% of a third liquid crystal material comprising at least one liquid crystal compound having a negative or sub¬ stantially 0 dielectric anisotropy, and (1) the first liquid crystal material comprises at least one of liquid crystal compounds re¬ presented by general formulae lb to li: wherein R-, represents a group R or OR; and R 2 represents R or OR; R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH 2 groups may be replaced by -O- and/or -CH=CH-, two oxygen atoms not being directly attached to one another, and/or (2) the third liquid crystal material comprises at least one of liquid crystal compound repre¬ sented by the general formulae Illd to Illh, II16 to II115 and/or II116 and II117: wherein R 11, R13, R15 and R18 each independent¬ ly represent R, and R 9 , R 10 , R 12 , R 14 , R 16 and R 17 each independently represent R or OR, R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent OB groups may be replaced by -0- or -CH=CH-, two oxygen atoms not being directly attached to one an- 4 . other and A is 1,4-cyclohexenylen, R 33 -^) -^)-^^ III8 R 39 - HV ■ CH. ; CH 2 -0- -R 4 ° inn R 43 - H CH 2 CH 2 -< 0 ) - O >-R 44 III13 46 R45 -< " = )-(=)-(° /- ~ (W = -* III14 R 47 - - H )> -COO- -R 48 III15 wherein R 29 , R 31 , R 33 , R 35 , R 37 , R 39 , R 40 , 4.1 A ~ x Δ.~~ 46 47 Aft R , R , R , R , R , and R ° each independ¬ ently represent R, R 30 , R 32 , R 34 , R 36 , R 38 , R 42 and R44 each independently represent R or OR, R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH_ groups may be replaced by -O- or -CH=CH-, two oxygen atoms not being directly attached to one another, 4 , and A is 1,4-cyclohexenylen, wherein R 49, R50, R51 and R52 each represent R, R being in each case independently a straight chain alkyl group having up to 12 carbon atoms wherein one or two non-adjacent CH 9 groups may be replaced by -O- or -CH=CH-, two oxygen atoms not being directly attached to one another.

Inventors: OYAMA TAKAMASA, SCHEUBLE BERNHARD, OYAMA, TAKAMASA, SCHEUBLE, BERNHARD
Applicants: MERCK PATENT GMBH, MERCK PATENT GESELLSCHAFT MIT BESCHRAENKTER HAFTUNG
Application year: 1989
Main classification: C09K19
IPC codes: C09K19, G02F1