The invention relates to supertwist liquid-crystal displays (SLCDs) having very short response times and good steepnesses and angle dependencies, and to the novel nematic liquid-crystal mixtures used therein, which are distinguished in that they comprise at least one compound of the formula IA and at least one compound of the formula IB and/or at least one compound of the formula IC in which Ra, Rb, Rc, Rd, Re, Z, L, q and c have the meaning given.

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 novel nematic liquid-crystal mixtures used therein.

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 lower 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 have hitherto been 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 electro-optical characteristic line in SLCDs, the liquid-crystal mixtures should have relatively large values for K 3 /K 1 and relatively small values for / .

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. High 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 (XGAs), 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.

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, in particular at low temperatures, and very good steepnesses.

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.

Particularly, it has been found that advantages are achieved if nematic liquid-crystal mixtures are used which comprise compounds of the formula IA

in combination with compounds of the formula IB

and/or with compounds of the formula IC

in which

R a and R b , independently of one another, are alkyl or alkoxy having 1 to 7 carbon atoms or alkenyl or alkenyloxy having 2 to 7 carbon atoms, where at least one of the radicals R a and R b is alkenyl or alkenylbxy having 2 to 7 carbon atoms,

R c is an alkenyl group having 2 to 7 carbon atoms,

R d and R e , independently of one another, are an alkyl or alkoxy group having 1 to 12 carbon atoms or an alkenyl group having 2 to 12 carbon atoms, in which, in addition, one or two non-adjacent CH 2 groups may be replaced by O , CH CH , CO , OCO or COO in such a way that O atoms are not linked directly to one another,

L is H or F,

Z is CH 2 CH 2 or a single bond, and

c is 0 or 1.

The use of the compounds of the formulae IA in combination with IB and/or IC in the mixtures for SLCDs according to the invention produces

high steepness of the electro-optical characteristic line

low temperature dependence of the threshold voltage and

very fast response times, in particular at low temperatures.

The compounds of the formulae IA in combination with IB and/or IC significantly shorten, in particular, the response times of SLCD mixtures while simultaneously increasing the steepness and retaining the low temperature dependence of the threshold voltage.

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.

The invention thus also includes liquid-crystal displays having

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 pre-tilt angle between the longitudinal axis of the molecules at the surface of the outer plates and the outer plates of from about 0 degrees 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 22.5 and 600 ,

a nematic liquid-crystal mixture consisting of

a) 0-90% by weight of a liquid-crystalline component A consisting of one or more compounds having a dielectric anisotropy of greater than 1.5;

b) 15-80% 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) if desired, 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 of the formula IA

in which

R a and R b are alkyl or alkoxy having 1 to 7 carbon atoms or alkenyl or alkenyloxy having 2 to 7 carbon atoms, where at least one of the radicals R a and R b is alkenyl or alkenyloxy having 2 to 7 carbon atoms, and

Z is CH 2 CH 2 or a single bond,

component B simultaneously comprises at least one compound of the formula IB

in which

R c is an alkenyl group having 2 to 7 carbon atoms,

R d is an alkyl or alkoxy group having 1 to 12 carbon atoms or an alkenyl group having 2 to 12 carbon atoms, in which, in addition, one or two non-adjacent CH 2 groups may be replaced by O , CH CH , CO , OCO or COO in such a way that O atoms are not linked directly to one another, and

c is 0 or 1,

and/or the liquid-crystal mixture simultaneously comprises at least one compound of the formula IC:

in which

R e is an alkyl or alkoxy group having 1 to 12 carbon atoms or an alkenyl group having 2 to 12 carbon atoms, in which, in addition, one or two non-adjacent CH 2 groups may be replaced by O , CH CH , CO , OCO or COO in such a way that O atoms are not linked directly to one another, and

L is H or F, and

q is 0 or 1.

The invention also relates to corresponding liquid-crystal mixtures for use in SLCDs, in particular in medium- and low-multiplexed SLCDs.

The compounds of the formulae IA, IB and IC are known and are prepared by methods known per se, as described in the literature (Houben-Weyl, Methoden der organischen Chemie Methods of Organic Chemistry , Georg-Thieme-Verlag, Stuttgart), to be precise under reaction conditions which are known and suitable for said reactions. Use can also be made here of variants which are known per se, but are not mentioned here in greater detail.

In preferred compounds of the formula IA, one of the radicals R a or R b is an alkenyl group having 2 to 5 carbon atoms, while the other is alkyl or alkoxy having 1 to 5 carbon atoms. The radical R a is particularly preferably vinyl, 1E-propenyl, 1E-butenyl, 3E-butenyl or 3E-pentenyl, while the radical R b is preferably alkyl or alkoxy, in particular methyl, ethyl, n-propyl, n-pentyl, methoxy, ethoxy, n-propoxy, n-butoxy, n-pentoxy or n-hexyloxy.

Preference is furthermore given to compounds of the formula IA in which the radical R b is particularly preferably 3E-butenyl or 3E-pentenyl, while the radical R a is preferably alkyl or alkoxy, in particular methyl, ethyl, n-propyl, n-pentyl, methoxy, ethoxy, n-propoxy, n-butoxy, n-pentoxy or n-hexyloxy.

Z in the compounds of the formula IA is preferably CH 2 CH 2 .

The formula IA includes the following preferred compounds:

in which R a1 and R b2 , independently of one another, are H, methyl, ethyl or n-propyl, in particular H or methyl, and R b1 and R a2 , independently of one another, are alkyl or alkoxy having 1 to 7 carbon atoms, in particular methyl, ethyl, n-propyl, n-pentyl, n-heptyl, methoxy, ethoxy, n-propoxy, n-butoxy, n-pentoxy or n-hexyloxy. R b1 and R a2 are very particularly preferably methyl, ethyl, n-propyl or n-pentyl.

The compounds of the formulae IA1, IA3 and IA4 are particularly preferred.

The formula IB includes the following compounds:

in which R c and R d are as defined for the formula IB. Particular preference is given to compounds of the formulae IB1 and IB2 in which R c is 1E-alkenyl or 3E-alkenyl having 2 to 7 carbon atoms.

Particularly preferred compounds of the formula IB1 are those of the sub-formulae IB1-1 to IB1-5

in which R c1 and R d1 are each, independently of one another, H, CH 3 , C 2 H 5 or n C 3 H 7 .

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 IB1-1 and IB1-5 in which R c1 and R d1 each have the same meaning.

Particularly preferred compounds of the sub-formula IB2 are those of the sub-formulae IB2-1 and IB2-2:

in which R c1 and R d1 are each, independently of one another, as defined under the compounds of the formulae IB1-1 to IB1-5.

Particular preference is given to liquid-crystal displays according to the invention in 10 which component B comprises at least one compound selected from the formulae IB1-4, IB2-1 and IB2-2.

Particularly preferred compounds of the sub-formula IB2 are those in which R d is an alkyl group having 1 to 8 carbon atoms, and R c is 1E-alkenyl or 3E-alkenyl having 2 to 7 carbon atoms.

Preferred compounds of the formula IC are those in which R e is alkyl or alkoxy having 1 to 7 carbon atoms, and L is H. q is preferably 0.

The formula IC includes the following compounds:

in which R e is as defined above.

Particular preferred are those where, R e is n-propyl, n-pentyl or n-heptyl.

Component A preferably comprises compounds of the formulae II and/or III

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 2 groups may be replaced by O , CH CH , CO , OCO or COO in such a way that O atoms are not linked directly to one another,

independently of one another

L 1 to L 6 are each, independently of one another, H or F,

Z 1 is COO , CH 2 CH 2 or a single bond,

Z 2 is CH 2 CH 2 , COO , C C or a single bond,

Y is F or Cl

a is 1 or 2, and

b is 0 or 1,

where compounds of the formula IC are excluded from the scope of the formula II.

Preferred compounds of the formula II conform to the sub-formulae lha to IIh:

in which R, L 1 , L 2 and L 3 are as defined above.

The compounds IIa to IIf are preferred.

Particular preference is given to mixtures which comprise one or more compounds of the following sub-formulae:

in which R is as defined above.

Preference is furthermore given to mixtures which comprise one or more compounds of the formula IIh in which L 2 is H and L 1 is H or F, in particular F.

In a particularly preferred embodiment, component A additionally comprises compounds of the formulae AI to AIV:

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 2 groups may be replaced by O , CH CH , CO , OCO or COO in such a way that O atoms are not linded directly to one another,

and Q 1 are each, independently of one another,

CH 2 CH 2 , CO O , O CO 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:

in which R is as defined above.

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:

in which R is as defined above.

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 sub-formulae IIIa-IIIv:

in which R is as defined above, and L 3 and L 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 4 is F, furthermore those in which L 3 and L 4 are F.

In addition to one or more compounds of the formulae IA with one or more compounds of the formulae IB and/or IC, preferred mixtures comprise one, two, three or more compounds of the formulae Ia, IIb, IIc, IIf, IIIb, IIId, IIIf, IIIh, IIIi, IIIm, IIIs, IIIt or IIIu, preferably one or more compounds of the formula IIIb, IIId, IIIh, IIIt or IIIu, and from one to four compounds of the formulae IA and IB and/or IC and from one to three compounds of the formulae IIa, IIb and/or IIc.

In the above- and below-mentioned preferred compounds of the sub-formulae to the formulae II and III, R, R 1 and R 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 sub-formula IIIb1

in which R 3 is alkenyl having 2 to 7 carbon atoms.

In the compounds of the formula IIIbl, R 3 is particularly preferably vinyl, 1E-propenyl, 1E-butenyl, 3E-butenyl or 3E-pentenyl, in particular vinyl.

The individual compounds, for example of the formulae II and III or their sub-formulae, 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 a plurality of compounds of component A. Component A preferably has a proportion of from 10 to 35% in the mixture as a whole.

Further preferred liquid-crystal mixtures comprise one or more compounds of component B. preferably from 30 to 70%. The compounds of component B are distinguished, in particular, by their low rotational viscosity values 1.

Besides one or more compounds of the formula IB, component B preferably comprises one or more compounds selected from the group consisting of the compounds of the formulae IV1 to IV9:

in which R 1 and R 2 are as defined for R, and R 4 and R 5 , independently of one another, are straight-chain alkyl or alkoxy having 1 to 7 carbon atoms.

Component Bs additionally comprises one or more compounds selected from the group consisting of the compounds of the formulae IV10 to IV24:

in which R 1 , R 2 , R 4 and R 5 are as defined for R, and the 1,4-phenylene groups in IV10 to IV19, IV23 and IV24 may each, independently of one another, also be monosubstituted or polysubstituted by fluorine.

Particular preference is given to mixtures comprising one or more compounds of the following formulae:

in which R 1 is as defined for R 3 , and R 2 is straight-chain alkyl having 1 to 4 carbon atoms.

In these compounds, R 1 is particularly preferably vinyl, 1E-propenyl, 1-butenyl, 3E-butenyl or 3E-pentenyl. R 2 , independently of one another if it occurs more than once, is particularly preferably methyl, ethyl or propyl, in particular methyl or ethyl.

Besides the compound IB, component B preferably additionally comprises one or more compounds selected from the group consisting of the compounds of the formulae IV25 to IV31:

in which R 1 and R 2 are as defined for R, and L is F or H. The 1,4-phenylene groups in the compounds 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 1 is alkyl and R 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 IV30, R 1 and R 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:

in which C r H 2r 1 is a straight-chain alkyl group having up to 9 carbon atoms.

In a further preferred embodiment, the liquid-crystal mixtures according to the invention, besides components A, B, C and D, additionally comprise one or more compounds selected from the group consisting of the compounds of the formulae VIII and IX

in which R 1 and R 2 are as defined above.

Preference is furthermore given to liquid-crystal mixtures comprising at least one component selected from the group consisting of the compounds of the formulae X to XIV:

in which Hal is F or Cl, L is H or F, and R is as defined above, in particular in which R is alkyl having 1 to 12 carbon atoms.

The liquid-crystalline 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 of which are commercially available, is available to the person skilled in the art, for example such as cholesteryl nonanoate, S-811 from Merck KGaA, Darmstadt, and CB15 (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 further liquid-crystalline tolan compounds in addition to the compounds of the formula IA. 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:

d is 0 or 1,

L 1 to L 6 are each, independently of one another, H or F,

Y is F or Cl,

Z 4 is CO O , CH 2 CH 2 or a single bond,

R 4 is straight-chain alkyl or alkoxy having 1 to 7 carbon atoms, and

R 1 and R 2 are as defined above.

Preferred compounds of the formula T1 conform to the sub-formulae T1a and T1b

in which R 1 and R 4 are as defined above, L 1 to L 4 are H or F, and Q-Y is F, Cl or OCF 3 , in particular F or OCF 3 .

Preferred compounds of the formula T2 conform to the sub-formulae T2a to T2g

in which R 4 , R 2 and Z 4 are as defined above, and L 1 to L6 are H or F.

Particularly preferred compounds of the formula T2e are those in which one, two or three of the radicals L 1 to L 6 are F and the others are H, where L 1 and L 2 or L 3 and L 4 or L 5 and L 6 are not both simultaneously F.

The proportion of compounds from Group T is preferably from 0 to 30%, in particular from 5 to 30%, very particularly preferably 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 of less than 2 (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

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:

in which

R 1 , R 2 and Z4 are as defined above and

and/or at least one compound selected from Group 132 consisting of compounds of the formulae B2I to B2III:

in which

R is as defined above,

Z 5 is CH 2 CH 2 , CO O or a single bond,

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:

in which

R 1 and R 2 , independently of one another, are as defined above,

Y is F or Cl, and

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 from Group B1 are those of the following sub-formulae:

in which

q is 0, 1, 2 or 3, and

s is 0 or 1.

The proportion of the compounds of the abovementioned sub-formulae B1IIIa and B1IIIb together with the compounds of the formula IB1 is preferably from about 5 to 45%, particularly preferably from about 10% to 35%.

The proportion of the compounds of the sub-formula 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 B1III and B1IV together with the compounds of the formulae IB1 and IB2, where the total proportion for components from Group B1 is observed.

If compounds of the formulae B1I and/or B1III are present, R 1 and R 2 are preferably each, independently of one another, n-alkyl having 1 to 7 carbon atoms or (trans)-n-alkenyl having 3 to 7 carbon atoms. Z 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

and R 1 and R 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 B21 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:

in which R 1 , R 2 , L and Z 5 are as defined above.

In these compounds, R 1 is preferably n-alkyl having 1 to 7 carbon atoms or (trans)-n-alkenyl having 3 to 7 carbon atoms, Z 5 is preferably a single bond, R 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

and/or polar heterocyclic compounds selected from the group consisting of

in which R 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 0 is F, Cl, CF 3 , OCF 3 or OCHF 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 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 mixtures according to the invention comprise compounds of the formulae IA and of one of the formulae 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; the content of these compounds is generally from 10 to 60% by weight, preferably from 15 to 50% by weight, based on the mixture as a whole.

Preference is furthermore given to media whose content of compounds of the formula IC is from 5 to 60%, in particular from 15 to 35%.

In a further preferred embodiment, the mixtures comprise

one or more compounds of the following formulae

in which R 1 , R 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, III, IIIm, IIIs, IIIt and IIIu;

at least two compounds selected from the compounds of the formulae IIb1, IIb2, 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

at least two compounds of the formula AI or AII;

one or more compounds in which R is a trans-alkenyl group or trans-alkenyloxy group;

one or more compounds selected from the following group:

in which R 1 , R 2 , R 4 , R 5 and L have the preferred meanings, the meanings given above.

The 1,4-phenylene group in the abovementioned compounds may also be substituted by fluorine;

one or more compounds of the formulae

in which R, R 1 and R 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 total response times (t tot t on t off ). Low total response times are an important criterion, in particular, for SLCDs for use as displays in laptops in order to be able to display cursor movements without interference.

The liquid-crystal mixtures used in the STN and TN cells according to the invention are dielectrically positive preferably with 1. Particular preference is given to liquid-crystal mixtures where 3 and very particularly to those where 5.

The liquid-crystal mixtures according to the invention have favourable values for the threshold voltage V 10/0/20 and for the rotational viscosity 1. If the value for the optical path difference d n is specified, the value for the layer thickness d is determined by the optical anisotropy n. In particular at relatively high values for d 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 an 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 electro-optical characteristic line and can be operated at high multiplex rates, in particular at temperatures above 20 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 base plates and electrodes having 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 to 720 from one electrode to the other corresponds to the structure which is conventional for display elements of this type. The term conventional structure is broadly drawn here and also includes all derivatives and modifications of the TN and 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. Preferred TN displays have pre-tilt angles between the longitudinal axis of the molecules at the surface of the outer plates and the outer plates of from 0 to 7 , preferably from 0.01 to 5 , in particular from 0.1 to 2 . In STN displays, the pre-tilt angle is from 1 to 30 , preferably from 1 to 12 , in particular from 3 to 10 .

The twist angle of the TN mixture in the cell has a value of between 22.5 and 170 , preferably between 45 and 130 , in particular between 80 and 115 . The twist angle of the STN mixture in the display from alignment layer to alignment layer has a value of between 100 and 600 , preferably between 170 and 300 , in particular between 180 and 270 .

The liquid-crystal mixtures which can be used according to the invention are prepared in a manner which is conventional 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, advantageously 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 the person skilled in the art and are described in the literature. For example, 0-15% of pleochroic dyes may be added.

In the foregoing and in the following examples, all temperatures are set forth uncorrected in degrees Celsius; and, unless otherwise indicated, all parts and percentages are by weight.

The entire disclosure of all applications, patents and publications, cited above or below, and of corresponding German application No. 119 20 406.3, filed May 4, 1999 is hereby incorporated by reference.

EXAMPLES

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 n H 2n 1 and C m H 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 hyphen, by a code for the substituents R 1 , R 2 , L 1 , L 2 and L 3 :

Code for R , R 1 R 2 , L 1 , L 2 , L 3 R 2 L 1 L 2 L 3 nm C n H 2n 1 C m H 2m 1 H H H nOm OC n H 2n 1 C m H 2m 1 H H H nO.m C n H 2n 1 OC m H 2m 1 H H H n C n H 2n 1 CN H H H nN.F C n H 2n 1 CN H H F nN.F.F C n H 2n 1 CN H F F nF C n H 2n 1 F H H H nOF OC n H 2n 1 F H H H nCl C n H 2n 1 Cl H H H nF.F C n H 2n 1 F H H F nmF C n H 2n 1 C m H 2m 1 F H H nCF 3 C n H 2n 1 CF 3 H H H nOCF 3 C n H 2n 1 OCF 3 H H H n-Am C n H 2n 1 C C C m H 2m 1 H H H n-AN C n H 2n 1 C C CN H H H n-Vm C n H 2n 1 CH CH C m H 2m 1 H H H nV-Vm C n H 2n 1 CH CH CH CH C m H 2m 1 H H H The TN and STN displays preferably contain liquid-crystalline mixtures composed of one or more compounds from Tables A and B.

TABLE A (L 1 , L 2 and L 3 H or F) TABLE B The examples below are intended to illustrate the invention without representing a limitation.

The following abbreviations are used:

cl.p. clearing point

t on time from switching on until 90% of the maximum contrast is achieved

t off time from switching off until 10% of the maximum contrast is achieved

V 10 threshold voltage characteristic voltage at a relative contrast of 10% (also abbreviated to V (10,0,20) )

V 90 characteristic voltage at a relative contrast of 90%

V op operating voltage

t ave t on + t off 2

d cell thickness

p pitch

Above and below, all temperatures are given in C. Percentages are percent by weight. The values for the response times and viscosities relate to 20 C., unless stated otherwise. The response time is, unless stated otherwise, the average value tave of the switch-on and switch-off times.

The SLCD is, unless stated otherwise, addressed in multiplex mode (multiplex ratio 1:240, bias 1:16).

Mixture Examples