Supertwist liquid-crystal displays (SLCDs) with outstanding properties are obtained if the nematic liquid-crystal mixtures used therein comprise at least one compound selected from the formulae 1A and 1B ##STR1## and at least one compound of the formula 1C ##STR2## in which R.sup.a is alkyl, alkoxy, alkenyl or alkenyloxy having 1 to 12 carbon atoms, PA1 R.sup.b is alkyl or alkoxy having 1 to 5 carbon atoms, PA1 Z is --COO--, --CH.sub.2 CH.sub.2 -- or a single bond, and PA1 L.sup.a, L.sup.b, L.sup.c, L.sup.d, L.sup.e, L.sup.f, L.sup.g, and L.sup.h in each case independently of one another are H or F, PA1 with the proviso that the 1,4-phenylene rings carry not more than 2 fluorine atoms per ring, PA1 R.sup.3 is an alkenyl group having 2 to 7 carbon atoms, PA1 R.sup.4 is R.sup.a or R.sup.3 and PA1 c is 0 or 1.

The invention relates to supertwist liquid-crystal displays (SLCDs) or 
supertwisted nematic (STN) displays having very short response times and 
good steepnesses and angle dependencies, and to the new nematic 
liquid-crystal mixtures used therein. 
BACKGROUND OF THE INVENTION 
SLCDs as defined in the preamble are known, for example from EP 0 131 216 
B1; DE 34 23 993 A1; EP 0 096 070 A2; M. Schadt and F. Leenhouts, 17th 
Freiburg Congress on Liquid Crystals (8.-10.04.87); K. Kawasaki et al., 
SID 87 Digest 391 (20.6); M. Schadt and F. Leenhouts, SID 87 Digest 372 
(20.1); K. Katoh et al., Japanese Journal of Applied Physics, Vol. 26, No. 
11, L 1784-L 1786 (1987); F. Leenhouts et al., Appl. Phys. Lett. 50 (21), 
1468 (1987); H. A. van Sprang and H. G. Koopman, J. Appl. Phys. 62 (5), 
1734 (1987); T. J. Scheffer and J. Nehring, Appl. Phys. Lett. 45 (10), 
1021 (1984), M. Schadt and F. Leenhouts, Appl. Phys. Lett. 50 (5), 236 
(1987) and E. P. Raynes, Mol. Cryst. Liq. Cryst. Letters Vol. 4 (1), pp. 
1-8 (1986). The term SLCD here covers any more highly twisted display 
element with a value for the twist angle of between 160.degree. and 
360.degree., such as, for example, the display elements of Waters et al. 
(C.M. Waters et al., Proc. Soc. Inf. Disp. (New York) (1985) (3rd Intern. 
Display Conference, Kobe, Japan), STN-LCDs (DE-A 35 03 259), SBE-LCDs 
(T.J. Scheffer and J. Nehring, Appl. Phys. Lett. 45 (1984) 1021), OMI-LCDs 
(M. Schadt and F. Leenhouts, Appl. Phys. Lett. 50 (1987), 236, DST-LCDs 
(EP-A 0 246 842) or BW-STN-LCDs (K. Kawasaki et al., SID 87 Digest 391 
(20.6)). 
SLCDs of this type are distinguished, in comparison to standard TN 
displays, by significantly better steepnesses of the electrooptical 
characteristic line and consequently better contrast values, and by 
significantly less angle dependence of the contrast. Of particular 
interest are SLCDs having very short response times, in particular also at 
relatively low temperatures. In order to achieve short response times, the 
rotational viscosities of the liquid-crystal mixtures were hitherto 
optimized using usually monotropic additives having relatively high vapour 
pressure. However, the response times achieved were not adequate for all 
applications. 
In order to achieve a steep electrooptical characteristic line in SLCDs, 
the liquid-crystal mixtures should have relatively large values for 
K.sub.33 /K.sub.11 and relatively small values for 
.DELTA..epsilon./.epsilon..sub..perp.. 
In addition to optimization of the contrast and the response times, further 
important requirements are made of mixtures of this type: 
1. A broad d/p window 
2. Hich long-term chemical stability 
3. High electrical resistance 
4. Low frequency and temperature dependence of the threshold voltage. 
The parameter combinations achieved are still far from. adequate, in 
particular for high-multiplex, but also for low- and medium-multiplex STNs 
(1/400). This is in some cases attributable to the fact that the various 
requirements are affected in opposite manners by material parameters. 
There thus continues to be a great demand for SLCDs, in particular for 
high-resolution displays (XGA), having very short response times and at 
the same time a large operating temperature range, high characteristic 
line steepness, good angle dependence of the contrast and low threshold 
voltage which meet the abovementioned requirements. 
SUMMARY OF THE INVENTION 
The invention has an object of providing SLCDs which do not have the 
abovementioned disadvantages, or only do so to a lesser extent, and at the 
same time have very good response times. 
It has now been found that this object can be achieved if nematic 
liquid-crystal mixtures are used which comprise at least one compound 
selected from the formulae IA and IB 
##STR3## 
in which R.sup.a is alkyl, alkoxy, alkenyl or alkenyloxy having 1 to 12 
carbon atoms, 
R.sup.b is alkyl or alkoxy having 1 to 5 carbon atoms, 
Z is --COO--, --CH.sub.2 CH.sub.2 -- or a single bond, and 
L.sup.a, L.sup.b, L.sup.c, L.sup.d, L.sup.e, L.sup.f, L.sup.g and L.sup.h 
in each case independently of one another are H or F, 
with the proviso that the 1,4-phenylene rings carry not more than 2 
fluorine atoms per ring, 
and at least one compound of the formula IC 
##STR4## 
in which 
______________________________________ 
R.sup.3 is an alkenyl group having 2 to 7 carbon 
atoms, 
R.sup.4 is R.sup.a or R.sup.3, and 
c is 0 or 1. 
______________________________________ 
The use of compounds of the formulae IA and/or IB and IC in the mixtures 
for SLCDs according to the invention produces, in particular, very fast 
response times. 
Furthermore, the mixtures according to the invention are distinguished by 
the following advantages: 
they have low viscosity, 
they have low temperature dependence of the threshold voltage and the 
operating voltage, and 
they effect long storage times of the display at low temperatures.

Upon further study of the specification and appended claims, further 
objects and advantages of this invention will become apparent to those 
skilled in the art. 
The invention thus includes a liquid-crystal display containing 
two outer plates which, together with a frame, form a cell, 
a nematic liquid-crystal mixture of positive dielectric anisotropy which is 
present in the cell, 
electrode layers with alignment layers on the insides of the outer plates, 
a pretilt angle between the longitudinal axis of the molecules at the 
surface of the outer plates and the outer plates of from about 1 degree to 
30 degrees, and 
a twist angle of the liquid-crystal mixture in the cell from alignment 
layer to alignment layer with a value of between 100.degree. and 
600.degree., 
a nematic liquid-crystal mixture consisting of 
a) 10-65% by weight of a liquid-crystalline component A consisting of one 
or more compounds having a dielectric anisotropy of greater than +1.5; 
b) 20-90% by weight of a liquid-crystalline component B consisting of one 
or more compounds having a dielectric anisotropy of between -1.5; and 
+1.5; 
c) 0-20% by weight of a liquid-crystalline component D consisting of one or 
more compounds having a dielectric anisotropy of below -1.5; and 
d) an optically active component C in such an amount that the ratio between 
the layer thickness (separation of the outer plates) and the natural pitch 
of the chiral nematic liquid-crystal mixture is from about 0.2 to 1.3, 
characterized in that the liquid-crystal mixture comprises at least one 
compound selected from the formulae IA and IB 
##STR5## 
in which R.sup.a is alkyl, alkoxy, alkenyl or alkenyloxy having 1 to 12 
carbon atoms, 
R.sup.b is alkyl or alkoxy having 1 to 5 carbon atoms, 
Z is --COO--, --CH.sub.2 CH.sub.2 -- or a single bond, and 
L.sup.a, L.sup.b, L.sup.c, L.sup.d, L.sup.e, L.sup.f, L.sup.g and L.sup.h 
in each case independently of one another are H or F, 
with the proviso that the 1,4-phenylene rings carry not more than 2 
fluorine atoms per ring, 
and component B comprises at least one compound of the formula IC 
##STR6## 
in which 
______________________________________ 
R.sup.3 is an alkenyl group having 2 to 7 carbon 
atoms, 
R.sup.4 is R.sup.a or R.sup.3, and 
c is 0 or 1. 
______________________________________ 
The invention also relates to corresponding liquid-crystal mixtures for use 
in SLCDs. 
Preferred compounds of the formulae IA and IB are those compounds in which 
Z is a single bond and/or the 1,4-phenylene groups are substituted by not 
more than 2 fluorine atoms. 
Particularly preferred compounds of formulae IA and IB are those compounds 
in which Z is a single bond and one of the 1,4-phenylene groups is 
##STR7## 
or 
##STR8## 
Further particularly preferred compounds of formulae IA and IB are those 
compounds in which Z is a single bond, one of the substituents L.sup.a, 
L.sup.b, L.sup.c, L.sup.d, L.sup.e, L.sup.f, I.sup.g and L.sup.h is F and 
the others are H. Particular preference is extended to compounds of the 
formulae IA and IB in which Z is a single bond and L.sup.a, L.sup.b, 
L.sup.c, L.sup.d, L.sup.e, L.sup.f, L.sup.g and L.sup.h are H. 
Among the particularly preferred compounds of the formulae IA and IB 
particular preference is given to the compounds of subformulae IA1, IA2, 
IA3, IA4, IA5, IA6, IA7, IA8, IB1, IB2, IB3 and IB4 
##STR9## 
R.sup.a and R.sup.b are preferably straight-chain alkyl having 1 to 5 
carbon atoms, or straight-chain alkoxy having 1 to 5 carbon atoms. 
The formula IC embraces the following compounds 
##STR10## 
in which R.sup.3 and R.sup.4 possess the meaning indicated above. 
Preference is given to compounds of the formulae IC1 and IC2 in which 
R.sup.3 is 1E-alkenyl or 3E-alkenyl having 2 to 7 carbon atoms. 
Particularly preferred compounds of the formula IC1 are those of the 
subformulae IC1-1 to IC1-5. 
##STR11## 
in which R.sup.3a and R.sup.4a in each case independently of one another 
are H, CH.sub.3, C.sub.2 H.sub.5 or n-C.sub.3 H.sub.7 and R.sup.4b is 
n-alkyl having 1 to 8 carbon atoms. 
Particularly preferred compounds of the formula IC2 are those of the 
subformulae IC2-1 and IC2-2 
##STR12## 
in which R.sup.3a and R.sup.4b possess the meaning indicated under the 
compounds of the formulae IC1-1 to IC1-5. 
Particular preference is given to liquid-crystal displays according to the 
invention in which component B comprises at least one compound selected 
from the formulae IC1-4, IC2-1 and IC2-2. 
Component A preferably comprises compounds of the formulae II and/or III 
##STR13## 
in which R is an alkyl, alkoxy or alkenyl group having 1 to 12 carbon 
atoms, in which, in addition, one or two non-adjacent CH.sub.2 groups may 
be replaced by --O--, --CH.dbd.CH--, --CO--, --OCO-- or --COO--, in such a 
way that O atoms are not linked directly to one another, 
##STR14## 
are each, independently of one another, 
##STR15## 
L.sup.1 to L.sup.6 are each, independently of one another, H or F, 
______________________________________ 
Z.sup.1 
is --COO--, --CH.sub.2 CH.sub.2 -- or a single bond, 
Z.sup.2 is --CH.sub.2 CH.sub.2 --, --COO--, --C.tbd.C-- or a single 
bond, 
Q is --CF.sub.2 --, --CHF--, --OCF.sub.2 --, --OCHF-- or a single bond, 
Y is F or Cl 
a is 1 or 2, and 
b is 0 or 1. 
______________________________________ 
Preferred compounds of the formula II conform to the subformulae IIa to 
IIh: 
##STR16## 
in which R, L.sup.1, L.sup.2 and L.sup.5 are as defined above. 
Particular preference is given to mixtures which comprise one or more 
compounds of the subformulae 
##STR17## 
in which R is as defined above. 
In a particularly preferred embodiment, component A additionally comprises 
compounds of the formulae AI to AIV: 
##STR18## 
in which R is an alkyl, alkoxy or alkenyl group having 1 to 12 carbon 
atoms, in which, in addition, one or two non-adjacent CH.sub.2 groups may 
also be replaced by --O--, --CH.dbd.CH--, --CO--, --OCO-- or --COO--, in 
such a way that O atoms are not linked directly to one another 
##STR19## 
and Q.sup.1 are each, independently of one another, 
##STR20## 
or a single bond. 
The mixtures according to the invention preferably comprise one or more 
polar compounds having a high clearing point selected from the group 
consisting of the compounds AIV1 to AIV4: 
##STR21## 
In the compounds AIV1 to AIV4, the 1,4-phenylene rings can also be 
laterally substituted by one or two fluorine atoms. Preferred compounds of 
this type are the compounds of the formulae AIV1-1, AIV1-2 and AIV1-3: 
##STR22## 
In the mixtures according to the invention which comprise compounds of the 
formulae AIV1 to AIV4, the proportion of these compounds is preferably 
from about 2 to 25%. 
Preferred compounds of the formula III conform to the subformulae 
IIIa-IIIv: 
##STR23## 
in which R is as defined above, and L.sup.3 and L.sup.4, independently of 
one another, are H or F. 
Of the compounds of the formulae IIIa to IIIv, particular preference is 
given to those in which L.sup.3 is F, furthermore those in which L.sup.3 
and L.sup.4 are F. 
In addition to one or more compounds of the formulae IA and/or IB and IC, 
preferred mixtures comprise one, two, three or more compounds of the 
formulae IIa, IIb, IIc, IIf, IIIb, IIId, IIIf, IIIh, IIIi, IIIs or IIIu, 
preferably one or more compounds of the formula IIIb, IIId, IIIh or IIIu, 
and from one to four compounds of the formulae IA and/or IB and Ic and 
from one to four compounds of the formulae IIa, IIb and/or IIc. 
In the preferred compounds of the subformulae to the formulae II and III 
mentioned above and below, R, R.sup.1 and R.sup.2, unless stated 
otherwise, are preferably straight-chain alkyl, alkenyl or alkoxy, in 
particular alkyl, having 1 to 12 carbon atoms, in particular having 1 to 7 
carbon atoms. 
Preference is furthermore given to mixtures which comprise one or more 
compounds of the subformula IIIb1 
##STR24## 
in which R is as defined in the formula III and is preferably alkyl having 
1 to 7 carbon atoms or alkenyl having 2 to 7 carbon atoms, in particular 
1E- or 3E-alkenyl having 2 to 7 carbon atoms. 
In the compounds of the formula IIIb1, R is particularly preferably vinyl, 
1E-propenyl, 1E-butenyl, 3E-butenyl, 3E-pentenyl, in particular vinyl. 
The individual compounds, for example of the formulae II and III or their 
subformulae, or alternatively other compounds which can be used in the 
SLCDs according to the invention, are either known or can be prepared 
analogously to known compounds. 
Preferred liquid-crystal mixtures comprise one or more compounds of 
component B, preferably from 30 to 75%. The compounds of ccmponent B are 
distinguished, in particular, by their low rotational viscosity values 
.gamma..sub.1. 
Component B preferably, in addition to one or more compounds of the formula 
IC, comprises one or more compounds selected from the group consisting of 
the compounds of the formulae IV1 to IV9: 
##STR25## 
in which R.sup.1 and R.sup.2 are as defined for R, provided that a 
compound of formula IV6 is not the same as a compound of formula IC 
contained in the mixture. 
Component B preferably additionally comprises one or more compounds 
selected from the group consisting of the compounds of the formulae IV10 
to IV24: 
##STR26## 
in which R.sup.1 and R.sup.2 are as defined for R, and the 1,4-phenylene 
groups in IV10 to IV12, IV23 and IV24 may each, independently of one 
another, also be monosubstituted or polysubstituted by fluorine, provided 
that a compound of formula IV16 is not the same as a compound of formula 
IC contained in the mixture. 
Particular preference is given to mixtures comprising one or more compounds 
of the following formulae: 
##STR27## 
in which R.sup.1# is as defined for R.sup.3, and R.sup.2# is 
straight-chain alkyl having 1 to 4 carbon atoms, 
In these compounds, R.sup.1# is particularly preferably vinyl, 
1E-propenyl, 1-butenyl, 2E-butenyl, 3-butenyl, 2E-pentenyl or 3E-pentenyl. 
R.sup.2# is particularly preferably methyl, ethyl or propyl, in 
particular methyl or ethyl. Particular preference is given to mixtures 
comprising compounds of formula IV12a and compounds of formula IC2-1 or 
IC2-2 wherein R.sup.3a a is H, CH.sub.3, C.sub.2 H.sub.5 or n-C.sub.3 
H.sub.7 and R.sup.4b is n-alkyl having 1 to 8 carbon atoms. 
Component B preferably additionally, in addition to component IC, comprises 
one or more compounds selected from the group consisting of the compounds 
of the formulae IV25 to IV31: 
##STR28## 
in which R.sup.1 and R.sup.2 are as defined for R, and L is F or H. The 
1,4-phenylene groups in IV25 to IV31 may also each, independently of one 
another, be monosubstituted or polysubstituted by fluorine. 
Particular preference is given to compounds of the formulae IV25 to IV31 in 
which R.sup.1 is alkyl and R.sup.2 is alkyl or alkoxy, in particular 
alkoxy, in each case having 1 to 7 carbon atoms. Preference is furthermore 
given to compounds of the formulae IV25 and IV31, in which L is F. 
In the compounds of the formulae IV1 to IV31, R.sup.1 and R.sup.2 are 
particularly preferably straight-chain alkyl or alkoxy having 1 to 12 
carbon atoms. 
Component B optionally comprises one or more compounds selected from the 
group consisting of the compounds of the formulae VI and VII: 
##STR29## 
in which C.sub.r H.sub.2r+1 is a straight-chain alkyl group having up to 9 
carbon atoms. 
In a further preferred embodiment, component B additionally comprises one 
or more compounds from the group of compounds of the formulae VIII and IX 
##STR30## 
in which R.sup.1 and R.sup.2 are as defined above, provided that the 
compounds of formula VIII or IX are different from those of formula IC, in 
a given mixture. 
Furthermore preferred liquid-crystal mixtures comprise at least one 
component selected from the group consisting of the compounds of the 
formulae X to XIV: 
##STR31## 
in which Hal is F or Cl, L is H or F, and R is as defined above, in 
particular alkyl having 1 to 12 carbon atoms. 
The liquid-crystal mixtures optionally comprise an optically active 
component C in such an amount that the ratio between the layer thickness 
(separation of the outer plates) and the natural pitch of the chiral 
nematic liquid-crystal mixture is greater than 0.2. For the component, a 
multiplicity of chiral dopants, some commercially available, is available 
to the person skilled in the art, for example such as cholesteryl 
nonanoate, S-811 from Merck KGaA, Darmstadt, FRG, and CB 15 (BDH, Poole, 
UK). The choice of dopants is not crucial per se. 
The proportion of the compounds of component C is preferably from 0 to 10%, 
in particular from 0 to 5%, particularly preferably from 0 to 3%. 
In a particularly preferred embodiment, the mixtures according to the 
invention comprise from about 5 to 35%, in particular from 5 to 25%, of 
liquid-crystalline tolan compounds. This enables smaller layer thicknesses 
to be used, significantly shortening the response times. The tolan 
compounds are preferably selected from group T consisting of the compounds 
of the formulae T1 and T2: 
##STR32## 
in which 
##STR33## 
formula T2, 
______________________________________ 
d is 0 or 1, 
______________________________________ 
L.sup.1 to L.sup.6 are each, independently of one another, H or F, 
______________________________________ 
Q is --CF.sub.2 --, --CHF--, --OCF.sub.2 --, --OCHF-- or a single 
bond, 
Y is F or Cl, 
Z.sup.4 is --CO--O--, --CH.sub.2 CH.sub.2 -- or a single bond, and 
R.sup.1 and R.sup.2 are each as defined above. 
______________________________________ 
R.sup.1 and R.sup.2 are each as defined above. 
Preferred compounds of the formula T1 conform to the subformulae T1a and 
T1b 
##STR34## 
in which R.sup.1 is as defined above, L.sup.1 to L.sup.4 are each, 
independently of one another, H or F, and Q-Y is F, Cl or OCF.sub.3, in 
particular F or OCF.sub.3. 
Preferred compounds of the formula T2 conform to the subformulae T2a to T2g 
##STR35## 
in which R.sup.1, R.sup.2 and Z.sup.4 are as defined above, and L.sup.1 to 
L.sup.6 are each, independently of one another, H or F. 
Particularly preferred compounds of the formula T2e are those in which one, 
two or three of the radicals L.sup.1 to L.sup.6 are F and the others are 
H, where L.sup.1 and L.sup.2 or L.sup.3 and L.sup.4 or L.sup.5 and L.sup.6 
are not both simultaneously F. 
The proportion of compounds from the group T is preferably from 5 to 30%, 
in particular from 5 to 25%. 
In a further particularly preferred embodiment, the mixtures according to 
the invention preferably comprise from about 5 to 20% of one or more 
compounds having a dielectric anisotropy .DELTA..epsilon. of less than 
-1.5 (component D). 
Component D preferably comprises one or more compounds containing the 
structural unit 2,3-difluoro-1,4-phenylene, for example compounds as 
described in DE-A 38 07 801, 38 07 861, 38 07 863, 38 07 864 or 38 07 908. 
Particular preference is given to tolans containing this structural unit, 
as described in International Patent Application PCT/DE 88/00133, in 
particular those of the formulae T2f and T2g. 
Further known compounds of component D are, for example, derivatives of 
2,3-dicyanohydroquinones or cyclohexane derivatives containing the 
structural unit 
##STR36## 
as described in DE-A 32 31 707 or DE-A 34 07 013 respectively. 
The liquid-crystal mixture according to the invention preferably comprises 
one or more compounds selected from group B1 consisting of compounds of 
the formulae B1I to B1IV: 
##STR37## 
in which R.sup.1, R.sup.2 and Z.sup.4 are as defined above and 
##STR38## 
provided that compounds of the formula B1III are different from compounds 
of the formula IC for a given mixture, and/or at least one compound 
selected from group B2 consisting of compounds of the formulae B2I to 
B2III: 
##STR39## 
in which 
__________________________________________________________________________ 
R is as defined above, 
Z.sup.5 is --CH.sub.2 CH.sub.2 --, --CO--O-- or a single bond, 
- Q.sup.2 
##STR40## 
__________________________________________________________________________ 
alkyl is an alkyl group having 1 to 9 carbon atoms, 
______________________________________ 
X is CN or F, and 
L is H or F, 
______________________________________ 
and/or at least one compound selected from group B3 consisting of compounds 
of the formulae B3I to B3III: 
##STR41## 
in which R.sup.1 and R.sup.2, independently of one another, are as defined 
above, 
Y is F or Cl, and 
##STR42## 
The proportion of the compounds from group B1 is preferably from 10 to 50%, 
in particular from 15 to 40%. Compounds of the formulae B1III and B1IV are 
preferred. 
Particularly preferred compounds of group B1 are those of the following 
subformulae: 
##STR43## 
in which 
______________________________________ 
R.sup.1a 
is CH.sub.3 --(CH.sub.2).sub.p --, CH.sub.3 --(CH.sub.2).sub.p 
--O--, 
CH.sub.3 --(CH.sub.2).sub.p --O--CH.sub.2 --, 
trans-H--(CH.sub.2).sub.q --CH.dbd.CH--(CH.sub.2 CH.sub.2).sub.s -- or 
trans-H--(CH.sub.2).sub.q --CH.dbd.CH--(CH.sub.2 CH.sub.2).sub.s 
--CH.sub.2 O--, 
R.sup.2a is CH.sub.3 --(CH.sub.2).sub.p --, 
p is 1,2,3 or 4 
q is 0,1,2, or 3, and 
s is 0 or 1. 
______________________________________ 
The proportion of the compounds of the abovementioned subformulae B1 IIIa 
and B1IIIb together with the compounds of the formula IC1 is preferably 
from about 5 to 45%, particularly preferably from about 10 to 35%. 
The proportion of the compounds of the subformula B1IVa or of the compounds 
of the formula B1IV is preferably from about 5 to 40%, particularly 
preferably from about 10 to 35%. 
In a particularly preferred embodiment, the mixtures simultaneously 
comprise compounds of the formulae B1 III and B1IV together with the 
compounds of the formulae IC1 and/or IC2, observing the total proportion 
for components from group B1. 
If compounds of the formulae B1I and/or B1III are present, R.sup.1 and 
R.sup.2 are preferably each, independently of one another, n-alkyl having 
1 to 7 carbon atoms or for compounds of formula B1I, additionally 
(trans)-n-alkenyl having 3 to 7 carbon atoms. Z.sup.4 is preferably a 
single bond. 
Preference is furthermore given to mixtures according to the invention 
which comprise one or more compounds of the formula B1IV in which 
##STR44## 
is 
##STR45## 
and R.sup.1 and R.sup.2 have one of the preferred meanings indicated 
above, and are particularly preferably n-alkyl having 1 to 7 carbon atoms. 
In all cases, the total proportion of components from group B1 is observed. 
The proportion of the compounds from group B2 is preferably from about 5 to 
45%, in particular from 5 to 20%. The proportion (preferred ranges) for 
B2I to B2III is as follows: 
B2I: from about 5 to 30%, preferably from about 5 to 15%, sum of B2II and 
B2III: from about 5 to 25%, preferably from about 10 to 20%. 
Preferred compounds from group B2 are shown below: 
##STR46## 
in which R.sup.1, R.sup.2, L and Z.sup.5 are as defined above. 
In these compounds, R.sup.1 is preferably n-alkyl having 1 to 7 carbon 
atoms or (trans)-n-alkenyl having 3 to 7 carbon atoms, Z.sup.5 is 
preferably a single bond, R.sup.2 preferably has the preferred meaning 
given above for R or is fluorine, and L is preferably fluorine. 
The mixtures according to the invention preferably comprise one or more 
compounds selected from the group consisting of B2Ic, B2IIa and B2IIIa in 
a total proportion of from about 5 to 35%. 
In a particularly preferred embodiment, the mixtures according to the 
invention, in addition to B2Ic, B2IIa and B2IIIa (L=F), comprise further 
terminally fluorinated compounds, selected, for example, from the group 
consisting of 
##STR47## 
and/or polar heterocyclic compounds selected from the group consisting of 
##STR48## 
in which R.sup.1 is preferably n-alkyl having 1 to 7 carbon atoms or 
(trans)-n-alkenyl having 3 to 7 carbon atoms, g is 1 or 2, h is 0 or 1, 
X.sup.0 is F, Cl, CF.sub.3, --OCF.sub.3 or --OCHF.sub.2, and L is H or F. 
The total proportion of all terminally fluorinated compounds is preferably 
from about 5 to 65%, in particular from about 15 to 40%. 
The proportion of compounds from group B3 is preferably from about 5 to 
30%, particularly preferably from about 10 to 20%. R.sup.1 is preferably 
n-alkyl or n-alkoxy, in each case having 1 to 9 carbon atoms. 
However, it is also possible to employ analogous compounds containing 
alkenyl or alkenyloxy groups. Compounds of the formula B3I are preferred. 
The terms "alkyl" and "alkoxy" in the definition of R.sup.a, R.sup.b, R, 
R.sup.1, R.sup.2 and R.sup.4 embrace straight-chain and branched alkyl and 
alkoxy groups, in the case of R.sup.a, R, R.sup.1, R.sup.2 and R.sup.4 
having 1-12, in the case of R.sup.b having 1-5 carbon atoms and especially 
the straight-chain groups. Particularly preferred alkyl and alkoxy groups 
are ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, 
pentoxy, hexoxy or heptoxy, and also methyl, octyl, nonyl, decyl, undecyl, 
dodecyl, methoxy, octoxy, nonoxy, decoxy, undecoxy or dodecoxy. 
The term "alkenyl" in the definition of R.sup.a, R, R.sup.1, R.sup.2, 
R.sup.3 and R.sup.4 covers straight-chain and branched alkenyl groups, 
having 2-12 carbon atoms in the case of R.sup.a, R, R.sup.1, R.sup.2 and 
R.sup.4 and having 2-7 carbon atoms in the case of R.sup.3, in particular 
the straight-chain groups. Particularly preferred alkenyl groups are 
C.sub.2 -C.sub.7 -1E-alkenyl, C.sub.4 -C.sub.7 -3E-alkenyl, C.sub.5 
-C.sub.7 -4-alkenyl, C.sub.6 -C.sub.7 -5-alkenyl and C.sub.7 -6-alkenyl, 
in particular C.sub.2 -C.sub.7 -1E-alkenyl, C.sub.4 -C.sub.7 -3E-alkenyl 
and C.sub.5 -C.sub.7 -4-alkenyl. Examples of preferred alkenyl groups are 
vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 
3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 
4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups having 
up to 5 carbon atoms are generally preferred. 
The term "alkenyloxy" in the definition of R.sup.a embraces straight-chain 
and branched alkenyloxy groups having 2-12 carbon atoms, especially the 
straight-chain groups. In particular it means vinyloxy, propyl-1- or 
-2-enyloxy, but-1-, -2- or -3-enyloxy, pent-1-, -2-, -3- or -4-enyloxy, 
hex-1-, -2-, -3-, -4- or -5-enyloxy or hept-1-, -2-, -3-, -4-, -5- or 
-6-enyloxy, and also oct-1-, -2-, -3-, -4-, -5-, -6- or -7-enyloxy, 
non-1-, -2-, -3-, -4-, -5-, -6-, -7- or -8-enyloxy, dec-1-, -2-, -3-, -4-, 
-5-, -6-, -7-, -8-, or -9-enyloxy, undec-1-, -2-, -3-, -4-, -5-, -6-, -7-, 
-8-, -9- or -10-enyloxy or dodec-1-, -2-, -3-, -4-, -5-, -6-, -7-, -8-, 
-9-, -10- or -11-enyloxy. 
The mixtures according to the invention comprise compounds of the formulae 
IA and/or IB and IC and preferably compounds from at least one of groups 
B1, B2 and B3. They preferably comprise one or more compounds from group 
B1 and one or more compounds from group B2 and/or B3. 
In a preferred embodiment, the liquid-crystalline media according to the 
invention comprise 3, 4, 5 or 6 compounds of the formulae IA and/or IB and 
IC; the content of these compounds is generally from 20 to 70% by weight, 
preferably from 40 to 70% by weight, based on the total. 
In a further preferred embodiment, the mixtures comprise 
one or more compounds of the following formulae 
##STR49## 
in which R.sup.1, R.sup.2 and L have the preferred meanings given under 
compounds of component B. The proportion of these compounds in the 
liquid-crystal mixtures is preferably from 0 to 45%, in particular from 5 
to 30%; 
one or more, in particular 1, 2, 3 or 4, compounds selected from the 
compounds of the formulae IIIb, IIId, IIIf, IIIh, IIIi, IIIs and IIIu; 
at least two compounds selected from the compounds of the formulae IIb1, 
IIb2, IIb3, IIc1 and IIc2. The proportion of these compounds in the 
liquid-crystal mixtures is preferably from 0 to 60% by weight, 
particularly from 10 to 45%; 
one or more compounds of the formula T1 or T2, in particular one or more 
compounds of the formula T2a and/or T2b, where the proportion of these 
compounds in the liquid-crystal mixtures is preferably from 0 to 25%, in 
particular from 1 to 15%. 
Further particularly preferred embodiments relate to liquid-crystal 
mixtures comprising 
a least two compounds of the formula AI or AII; 
one or more compounds in which R or R.sup.1 is a trans-alkenyl group 
o.gamma. trans-alkenyloxy group; 
one or more compounds selected from the following group: 
##STR50## 
in which R.sup.1 and R.sup.2 have the preferred meanings given under 
compounds of component B provided that compounds of the formula IV6 are 
different from those of formula IC for a given mixture. The 1,4-phenylene 
groups in the abovementioned compounds can also be substituted by 
fluorine; 
one or more compounds of the formulae 
##STR51## 
in which R, R.sup.1 and R.sup.2 are as defined above. 
In particular when used in SLCDs having high layer thicknesses, the 
mixtures according to the invention are distinguished by very low overall 
response times (t.sub.over =t.sub.on +t.sub.off). Low overall response 
times are an important criterion, in particular, in SLCDs :or use as 
displays in laptops in order to be able to display cursor movements 
without interference. 
The liquid-crystal mixtures used in the STN cells according to the 
invention are dielectrically positive with .DELTA..epsilon..gtoreq.1. 
Particular preference is given to liquid-crystal mixtures where 
.DELTA..epsilon..gtoreq.3 and very particularly to those where 
.DELTA..epsilon..gtoreq.5. 
The liquid-crystal mixtures according to the invention have favourable 
values for the threshold voltage V.sub.(10, 0, 20) and for the rotational 
viscosity .gamma..sub.1. If the value for the optical path difference 
d..DELTA.n is specified, the value for the layer thickness d is determined 
by the optical anisotropy .DELTA.n. In particular at relatively high 
values for d..DELTA.n, the use of liquid-crystal mixtures according to the 
invention having a relatively high value for the optical anisotropy is 
generally preferred since the value for d can then be chosen to be 
relatively small, which results in more favourable values for the response 
times. However, liquid-crystal displays according to the invention which 
contain liquid-crystal mixtures according to the invention having 
relatively small values for .DELTA.n are also characterized by 
advantageous values for the response times. 
The liquid-crystal mixtures according to the invention are furthermore 
characterized by advantageous values for the steepness of the 
electrooptical characteristic line and can be operated at high multiplex 
rates, in particular at temperatures above 20.degree. C. In addition, the 
liquid-crystal mixtures according to the invention have high stability and 
favourable values for the electrical resistance and the frequency 
dependence of the threshold voltage. The liquid-crystal displays according 
to the invention have a broad operating temperature range and good angle 
dependence of the contrast. 
The construction of the liquid-crystal display elements according to the 
invention from polarizers, electrode baseplates and electrodes with a 
surface treatment such that the preferential alignment (director) of the 
liquid-crystal molecules in each case adjacent thereto is usually twisted 
by a value of from 160.degree. to 720.degree. from one electrode to the 
next, corresponds to the structure which is conventional for display 
elements of this type. The term conventional structure here is broadly 
drawn and also includes all derivatives and modifications of the STN cell, 
in particular also matrix display elements, and display elements which 
contain additional magnets. 
The surface tilt angle at the two outer plates may be identical or 
different. Identical tilt angles are preferred. In STN displays, the 
pretilt angle is from 1.degree. to 30.degree., preferably from 1.degree. 
to 12.degree., in particular from 3.degree. to 10.degree.. 
The twist angle of the STN mixture in the display from alignment layer to 
alignment layer has a value of between 100.degree. and 600.degree., 
preferably between 170.degree. and 300.degree., in particular between 
180.degree. and 270.degree.. 
The liquid-crystal mixtures which can be used according to the invention 
are prepared in a manner which is known per se. In general, the desired 
amount of the components used in a lesser amount is dissolved in the 
components making up the principal constituent, expediently at elevated 
temperature. It is also possible to mix solutions of the components in an 
organic solvent, for example in acetone, chloroform or methanol, and, 
after mixing, to remove the solvent again, for example by distillation. 
The dielectrics may also contain further additives which are known to a 
person skilled in the art and are described in the literature. For 
example, 0-15% of pleochroic dyes may be added. 
The entire disclosure of all applications, patents and publications, cited 
above and below, and of corresponding German Application No. 197 33 522.5, 
filed Aug. 2, 1997 is hereby incorporated by reference. 
In the present application and in the examples below, the structures of the 
liquid-crystal compounds are indicated by acronyms, the transformation 
into chemical formulae taking place in accordance with tables A and B 
below. All radicals C.sub.n H.sub.2n+1 and C.sub.m H.sub.2m+1 are 
straight-chain alkyl radicals having n and m carbon atoms respectively. 
The alkenyl radicals have the trans-configuration. The coding in Table B 
is self-evident. In Table A, only the acronym for the parent structure is 
given. In individual cases, the acronym for the parent structure is 
followed, separated by a dash, by a code for the substituents R.sup.1, 
R.sup.2, L.sup.1, L.sup.2 and L.sup.3 : 
______________________________________ 
Code 
for R.sup.1, 
R.sup.2,L.sup.1, 
L.sup.2,L.sup.3 R.sup.1 R.sup.2 L.sup.1 L.sup.2 L.sup.3 
______________________________________ 
nm C.sub.n H.sub.2n+1 
C.sub.m H.sub.2m+1 
H H H 
nOm OC.sub.n H.sub.2n+1 C.sub.m H.sub.2m+1 H H H 
nO.m C.sub.n H.sub.2n+1 OC.sub.m H.sub.2m+1 H H H 
n C.sub.n H.sub.2n+1 CN H H H 
nN.F C.sub.n H.sub.2n+1 CN H H F 
nN.F.F C.sub.n H.sub.2n+1 CN H F F 
nF C.sub.n H.sub.2n+1 F H H H 
nOF OC.sub.n H.sub.2n+1 F H H H 
nCl C.sub.n H.sub.2n+1 Cl H H H 
nF.F C.sub.n H.sub.2n+1 F H H F 
nmF C.sub.n H.sub.2n+1 C.sub.m H.sub.2m+1 F H H 
nCF.sub.3 C.sub.n H.sub.2n+1 CF.sub.3 H H H 
nOCF.sub.3 C.sub.n H.sub.2n+1 OCF.sub.3 H H H 
n-Am C.sub.n H.sub.2n+1 --C.tbd.C--C.sub.m H.sub.2m+1 H H H 
n-Vm C.sub.n H.sub.2n+1 --CH.dbd.CH--C.sub.m H.sub.2m+1 H H H 
nV-Vm C.sub.n H.sub.2n+1 --CH.dbd.CH-- --CH.dbd.CH--C.sub.m H.sub.2m+1 
H H H 
______________________________________ 
The STN displays preferably contain liquid-crystalline mixtures composed of 
one or more compounds from Tables A and B. 
TABLE A 
__________________________________________________________________________ 
(L.sup.1, L.sup.2, L.sup.3 ; each, independently of one another, H or 
__________________________________________________________________________ 
F) 
#STR52## 
#STR53## 
- 
#STR54## 
#STR55## 
- 
#STR56## 
#STR57## 
- 
#STR58## 
#STR59## 
- 
#STR60## 
#STR61## 
- 
#STR62## 
#STR63## 
- 
##STR64## 
__________________________________________________________________________ 
TABLE B 
__________________________________________________________________________ 
#STR65## 
#STR66## 
##STR67## 
#STR68## 
- 
#STR69## 
#STR70## 
- 
#STR71## 
- 
#STR72## 
- 
#STR73## 
- 
#STR74## 
- 
#STR75## 
- 
#STR76## 
- 
#STR77## 
- 
##STR78## 
__________________________________________________________________________ 
The examples below are intended to illustrate the invention without 
representing a limitation. 
The following abbreviations are used: 
______________________________________ 
S-N smectic-nematic phase transition temperature 
N-I nematic-isotropic phase transition temperature 
c.p. clearing point 
visc. rotational viscosity (mPa.s) 
.DELTA.n optical anisotropy (589 nm, 20.degree. C.) 
t.sub.on time from switching on until 90% of the 
maximum contrast is achieved 
t.sub.off time from switching off until 10% of the 
maximum contrast is achieved 
steepness ((V.sub.90 /V.sub.10) - 1) .multidot. 100% 
V.sub.10 threshold voltage = characteristic voltage at a 
relative contrast of 10% (also written for short as 
V.sub.(10,0,20)) 
V.sub.90 characteristic voltage at a relative contrast of 90% 
p pitch 
V.sub.op operating voltage 
t.sub.ave 
##STR79## 
______________________________________ 
Above and below, all temperatures are given in .degree. C. Percentages are 
percent by weight. The values for the response times and viscosities 
relate to 20.degree. C., unless stated otherwise. The response time is, 
unless stated otherwise, the average value t.sub.ave of the switch-on and 
switch-off times. 
The SLCD is, unless stated otherwise, addressed in multiplex operation 
(multiplex ratio 1:240, bias 1:16). 
Mixture examples 
______________________________________ 
Example A 
PCH-2 10.0% Clearing point [.degree. C.]: +105 
ME2N.F 3.0% .DELTA..epsilon. [1 kHz, 20.degree. C.]: +7.9 
ME3N.F 3.0% .DELTA.n [589 nm, 20.degree. C.]: +0.1351 
ME4N.F 5.0% STN 240.degree. 0.85 
CC-5-V 20.0% d .multidot. .DELTA.n [.mu.m]: 
CCP-V-1 15.0% V.sub.(10,0,20) [V]: 2.30 
CCP-V2-1 15.0% Steepness [%]: 7.1 
CCG-V-F 10.0% t.sub.ave [ms]: 189 
CPP-1V2-2 10.0% d/p: 0.53 
MPTP-3-2 9.0% 
Example B 
PCH-2 10.0% Clearing point [.degree. C.]: +106 
ME2N.F 3.0% .DELTA..epsilon. [1 kHz, 20.degree. C.]: +7.5 
ME3N.F 3.0% .DELTA.n [589 nm, 20.degree. C.]: +0.1341 
ME4N.F 5.0% STN 240.degree. 0.85 
CC-5-V 20.0% d .multidot. .DELTA.n [.mu.m]: 
CCP-V-1 15.0% V.sub.(10,0,20) [V]: 2.34 
CCP-V2-1 15.0% Steepness [%]: 6.9 
CCG-V-F 10.0% t.sub.ave [ms]: 222 
CPP-1V2-2 10.0% d/p: 0.53 
MPTGI-3-2 9.0% 
Example C 
PCH-2 10.0% Clearing point [.degree. C.]: +104 
ME2N.F 3.0% .DELTA..epsilon. [1 kHz, 20.degree. C.]: +7.8 
ME3N.F 3.0% .DELTA.n [589 nm, 20.degree. C.]: +0.1343 
ME4N.F 5.0% STN 240.degree. 0.85 
CC-5-V 20.0% d .multidot. .DELTA.n [.mu.m]: 
CCP-V-1 15.0% V.sub.(10,0,20) [V]: 2.29 
CCP-V2-1 15.0% Steepness [%]: 6.5 
CCG-V-F 10.0% t.sub.ave [ms]: 203 
CPP-1V2-2 10.0% d/p: 0.53 
MGTP-3-2 9.0% 
Example D 
PCH-2 10.0% Clearing point [.degree. C.]: +104 
ME2N.F 3.0% .DELTA..epsilon. [1 kHz, 20.degree. C.]: +8.1 
ME3N.F 3.0% .DELTA.n [589 nm, 20.degree. C.]: +0.1352 
ME4N.F 5.0% STN 240.degree. 0.85 
CC-5-V 20.0% d .multidot. .DELTA.n [.mu.m]: 
CCP-V-1 15.0% V.sub.(10,0,20) [V]: 2.23 
CCP-V2-1 15.0% Steepness [%]: 7.1 
CCG-V-F 10.0% t.sub.ave [ms]: 198 
CPP-1V2-2 10.0% d/p: 0.53 
GTMP-2-3 9.0% 
______________________________________ 
The preceding examples can be repeated with similar success by substituting 
the generically or specifically described reactants and/or operating 
conditions of this invention for those used in the preceding examples.