GB2310669A - Liquid-crystalline medium having positive dielectric anisotropy and an electro-optical liquid-crystal display containing such a medium - Google Patents

Abstract

There is provided both a liquid-crystalline medium (as defined below) and an electro-optical liquid-crystal display comprising a realignment layer (for realigning liquid crystals whose field exhibits a significant component parallel to the liquid-crystal layer) and containing a liquid-crystalline medium having positive dielectric anisotropy, the medium containing at least one mesogenic compound carrying a 3,4,5-trifluorophenyl group and/or at least one mesogenic compound of the formula I R 1 -(A 1 -Z 1 ) m -A 2 -R 2 ```(I) in which R 1 and R 2 are each, independently of one another, H, an alkyl or alkenyl radical of 1 to 15 carbon atoms which is unsubstituted or monosubstituted by CN or CF 3 or at least monosubstituted by halogen, it also being possible for one or more CH 2 groups in these radicals to be replaced, in each case independently of one another, by -O-, -S-, -CO-, -CO-O-, -O-CO- or -O-CO-O- in such a manner that oxygen atoms are not linked directly to one another, A 1 and A 2 are each, independently of one another, (a) a trans-1,4-cyclohexylene radical or a 1,4-cyclohexenylene radical in which one or more non-adjacent CH 2 groups can also be replaced by -O- and/or -S-, (b) a 1,4-phenylene radical in which one or two CH groups can also be replaced by N, (c) a radical from the group consisting of 1,4-bicyclo 2.2.2octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl, where the radicals (a) and (b) can be substituted by one or two fluorines, Z 1 is -CO-O-, -O-CO-, -CH 2 O-, -OCH 2 -, -CH 2 CH 2 -, -CH=CH-, -C* identical with *C- or a single bond, furthermore also -(CH 2 ) 4 - or -CH=CH-CH 2 CH 2 -, and m is 1, 2 or 3.

Description

Electro-optical liquid-crystal display The invention relates to an electro-optical liquid crystal display comprising a realignment layer for realigning liquid crystals whose field exhibits 2 significant component parallel to the liqud-crystal layer and containing a liquid-crystalline medium having positive dielectric anisotropy, the medium containing at east one mesogenic compound carrying a 3,4,5-trifluorophenyl group and/or at least one mesoaenic compound of the formula I R1-(A1-Z1)m-A2-R2 (I) in which R and R2 are each, independently of one another, H, an alkyl or alkenyl radical of 1 to 15 carbon atoms which is unsubstituted or monosubstituted by CN or or3 or at least monosubstituted by halogen, it also being possible for one or more CH2 groups in these radicals to be replaced, in each case independently of one another, by -O-, -S-,

-CO-, -CO-O-, -O-CO- or -O-CO-O in such a manner that oxygen a atoms are not linked directly to one another, A1 and A2 are each, independently of one another, (a) a trans-1,4-cyclohexylene radical or 1,4-cyclohexenylene radical in which one or more non-adjacent CH2 groups can also be replaced by -0- and/or -S-, (b) a 1,4-phenylene radical in which one or two CH groups can also be replaced by , (c) a radical from the group consisting of 1,4-bicyclo[2.2.2]octylene, piperidine 1,4-diyl, naphthalene-2,6-d@yl, deca- hydronaphthalene-2,6-diyl and 1,2,3,4 tetrahydronaphthalene-2, 6-diyl where the radicals (a) and (b) can be substituted by one or two fluorines, Z1 is -CO-O-, -O-CO-, -CH2O-, -OCH2-, -CH2CH2-, -CH=CH-, -CC- or a single bond, furthermore also - (CH2)4- or -CH=CH-CH2CH,-, and m is 1, 2 or 3.

In customary liquid-crystal displays (TN, STN, OMI, AMD TN), the electrical fields for effecting realignment are for the most part generated perpendicular to the liquidcrystal layer.

International Patent Application WO 91/10936 discloses a liquid-crystal display in which the electrical signals are generated in such a manner that the electrical fields possess a significant component parallel to the liquid-crystal layer (IPS, in-plane switching) . The principles of operating such a display are described, for example, by R.A. Soref in Journal of Applied Physics, Vol. 45, No. 12, pp. 5466-5468 (1974).

EP 0,588,568 discloses various possibilities of addressing such a display.

These IPS displays can be operated with liquidcrystalline materials which either have a positive or a negative dielectric anisotropy (Ask O)- . The existing materials exhibit high values of dielectric anisotropy, which are achieved in particular by using liquid crystals having terminal cyano groups. However, these compounds have an unfavourable effect on the resistance and the voltage holding ratio of the IPS display element. Moreover, using high proportions of polar compounds results in unfavourable viscosity values and high birefringences, which is unfavourable for many applications. Accordingly, the object was to disclose liquid-crystalline materials which are suitable for achieving relatively high voltage holding ratios, low birefringence and viscosity values and short switching times in IPS displays.

Surprisingly, this object was achieved by using liquidcrystalline materials which contain at least one compound carrying a 3,4,5-trifluorophenyl group and/or contain at least one mesogenic compound of the formula I.

Compounds of this type are disclosed, for example, in EP 0,132,553 and DE 2,636,684.

However, in these disclosures, there is no mention that the voltage holding ratio and the switching times of IPS displays can be improved by means of these substances.

Accordingly, the invention provides an electro-optical liquid-crystal display comprising a realignment layer for realigning liquid crystals whose field has a significant component parallel to the liquid-crystal layer and containing a liquid-crystalline medium having positive dielectric anisotropy, the medium containing at least one mesogenic compound carrying a 3,4,5-trifluorophenyl group and/or at least one mesogenic compound of the formula I Rl~(A}-z1) ~A2~R2 (I) in which R1 and R2 are each, independently of one another, H, an alkyl or alkenyl radical of 1 to 15 carbon atoms which is unsubstituted or monosubstituted by CN or CF3 or at least monosubstituted by halogen, it also being possible for one or more CH2 groups in these radicals to be replaced, in each case independently of one another, by -O-, -S-,

-CO-, -CO-O-, -O-CO- or -O-CO-O in such a manner that oxygen atoms are not linked directly to one another, A' and A2 are each, independently of one another, (a) a trans-1,4-cyclohexylene radical or 1,4-cyclohexenylene radical in which one or more non-adjacent CH2 groups can also be replaced by -0- and/or -S-, (b) a 1,4-phenylene radical in which one or two CH groups can also be replaced by N, (c) a radical from the group consisting of 1,4-bicyclo[2.2.2]octylene, piperidine 1,4-diyl, naphthalene-2,6-diyl, deca hydronaphthalene-2,6-diyl and 1,2,3,4 tetrahydronaphthalene-2,6-diyl, where the radicals (a) and (b) can be substituted by one or two fluorines, Z1 is -CO-O-, -O-CO-, -CH20- , -OCH2-, -CH2CH2-, -CH=CH-, -C#C- or a single bond, furthermore also -(CH2) 4 - or -CH=CH-CH2CH2-, and m is 1, 2 or 3.

Preferred embodiments are IPS displays where a) the medium contains at least one compound of the formula I, b) the medium contains at least one compound of the formula II

in which R3 has the meaning given for R1 and R2, A3 and A4 each have, independently of one another, the meaning given for A1 and A2, z2 and Z3 each have, independently of one another, the meaning given for zl, and n is 0, 1 or 2; c) the medium contains at least one compound of the formula III

in which R4 has the meaning given for R1, A5 and A6 each have, independently of one another, the meaning given for A1 and A2, Z4 and Z5 each have, independently of one another, the meaning given for Z1, o is 0, 1 or 2, and L1 is H, F or Cl, the medium contains at least one compound of the formula IV

in which R5 has the meaning given for R1, A7 and A8 each have, independently of one another, the meaning given for A1 and A2, z6 and Z each have, independently or one another, the meaning given for Zl, L2 and L3 are each, independently of one another, H or F, Q is a polyfluoroalkylene radical of the formula - (O)q-(CH2)r- (CF2)s in which q is 0 or 1, r is 0 or an integer between 1 and 6, s is an integer between 1 and 6, X is H, F or Cl, and p is 0, 1 or 2, e) the medium contains at most 10% of liquid crystals carrying cyano groups.

Further preference is given to an IPS display where the pixels are addressed by an active matrix.

The invention also provides a liquid-crystalline medium having positive dielectric anisotropy which contains at least one compound carrying a 3,4,5-trifluorophenyl group, preferably a compound of the formula II, and at least one compound of the formula I, in particular one which contains - 20 to 60, preferably 15 to 40, % by weight of at least one compound of the formula I, - 10 to 60, preferably 20 to 50, % by weight of at least one compound of the formula II, - 0 to 20, preferably 5 to 15, % by weight of at least one compound of the formula III and - 0 to 40, preferably 20 to 30, % by weight of at least one compound of the formula IV.

Preferably, the liquid-crystalline medium according to the invention contains: - at least one compound selected from formulae IIa and IIb

- at least one compound selected from formulae IIIa, IIIb, IIIc and IIId

- at least one compound selected from formulae Ia, Ib and Ic

and, if desired, - at least one compound selected from formulae IVa and IVb

in which

and R1, R2, R3, R4, R5, L1, L2 und L3 each have the meaning given.

In a particularly preferred embodiment, the media according to the invention contain at least one compound of the formula IIa in which

and at least one compound of the formula IIa in which

In a further preferred embodiment, the media according to the invention contain at least one compound of the formula IIa and at least one compound of the formula IIb.

Further preference is given to media containing at least one compound of the formula IIIb in which L is F and

or those compounds of the formula IIIc in which L1 is H and

Particularly preferably, the media according to the invention contain a compound of the formula IIIa in which

and L1 is F.

Particular preference is given to media containing not more than 10%, in particular to those containing preferably 0 to 5% of liquid crystals carrying cyano groups.

Typically, the liquid-crystalline media according to the invention have a birefringence (An) of < 0.12, An is preferably between 0.06 and 0.1, in particular between 0.06 and 0.08.

Typically, the viscosity (at 200C) of the materials according to the invention is less than 30 mm2 s-1, in particular between 10 and 25 mm2 s-l. Typically, the specific resistivity of the materials according to the invention at 20DC is between 5 x 1010 and 5 x 1013 nxcm, particularly preferably the values are between 5 x 101i and 5 x 1012 Rxcm.

It has been found that a relatively small proportion of compounds of the formula II in a mixture with customary liquid-crystal materials, but in particular with one or more compounds of the formulae I, III and/or IV already leads to a significant increase in the holding ratio and to short switching times, while simultaneously giving rise to broad nematic phases having low smectic-nematic transition temperatures. In particular the use of compounds of the formula I enables the viscosity and the birefringence to be reduced, which is advantageous for certain applications. The compounds of the formulae I to IV are colourless, stable and readily miscible with one another and with other liquid-crystal materials.

The term "alkyl" covers straight-chain and branched alkyl groups having 1-7 carbon atoms, in particular the straight-chain groups methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groups having 2-5 carbon atoms are usually preferred.

The term "alkenyl" covers straight-chain and branched alkenyl groups having 2-7 carbon atoms, in particular the straight-chain groups. Suitable alkenyl groups are C2-C:-lE-alkenyl, C4-C7-3E-alkenyl, C5-C:-4-alkenyl, C-C,-5-alkenyl and C7-6-alkenyl, in particular C2-C7-1E- alkenyl, C4-C -3E-alkenyl and Cs-c7-4-alkenyl. Examples of preferred alkenyl groups are vinyl, lE-propenyl, lE-butenyl, lE-pentenyl, lE-hexenyl, lE-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 in general preferred.

The term "fluoroalkyl" preferably covers straight-chain groups containing terminal fluorine, i.e. fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoro- pentyl, 6-fluorohexyl and 7-fluoroheptyl. However, other fluorine positions are not excluded.

The term "oxaalkyl" preferably covers straight-chain radicals of the formula CnH2n+1-O-(CH2) in which n and m are each, independently of one another, 1 to 6.

Preferably, n is 1 and m is 1 to 6.

Through a suitable choice of the meanings of R1 and R5, it is possible to modify the response times, the threshold voltage, the steepness of the transmission characteristics etc. as desired. For example, 1E-alkenyl radicals, 3E-alkenyl radicals, 2E-alkenyloxy radicals and the like usually lead to shorter response times, improved nematic tendencies, and a higher ratio of the elastic constants k33 (bend) and kll (splay) compared with alkyl or alkoxy radicals. 4-Alkenyl radicals, 3-alkenyl radicals and the like in general result in lower threshold voltages and smaller k33/k1l values compared with alkyl and alkoxy radicals.

In general, a group -CH2CH2- in Z1 or Z2 leads to higher k33/k1l values compared with a simple covalent bond.

Higher k33/k1l values make it possible, for example, to achieve flatter transmission characteristics in TN cells having a 90 twist (for obtaining grey hues) and steeper transmission characteristics in STN, SBE and OMI cells (higher multiplex ratio) and vice versa.

The optimum mixing ratio of the compounds of the formulae I and II S III + IV depends largely or. =he desired properties, on the choice of components o tne formulae I, II, III and/or IV and on the choice cf anv other components which may be present. Suitable mixing ratios within the abovementioned range can be easily determined from case to case.

The total amount of compounds of the formulae I to IV in the mixtures according to the invention is not critil.

Accordingly, the mixtures can contain one or more further components for optimizing various properties.

However, the observed effect on the holding ratio, the response times and the threshold voltage is generally the greater, the higher the total concentration of the compounds of the formulae II and III. The observed effect on the viscosity and the birefringence is generally the greater, the higher the total concentration of the compounds of the formula I.

In a particularly preferred embodiment, the media according to the invention contain compounds of the formula IV (preferably I and/or III) in which Q-X is OCF3 or OCHF2. A favourable synergistic effect with the compounds of the formula II leads to particularly advantageous properties.

Preferably, the liquid-crystalline media accordingXthe invention contain, in addition to one or more compounds of the formulae I, II, III and IV, 2 to 40, in particular 4 to 30 components, as further constituents.

Most preferably, these media contain, in addition to one or more compounds according to the invention, 7 to 25 components. These further components are preferably selected from nematic or nematogenic (monotropic or isotropic) substances, in particular from substances from the classes of azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl or cyclohexyl benzoates, phenyl or cyciohexyl cyclohexanecarboxylates, phenyl cyclohexyl cyclohexylbenzoates, phenyl or cyclohexv cyclohexylcyclohexanecarboxylates,cyclohexylphenyl benzoates, cyclohexylphenyl cyclohexanecarboxylates or cyclohexyl- phenyl cyclohexylcyclohexanecarboxylates, phenylcyclo- hexanes, cyclohexylbiphenyls, phenylcyclohexylcyclo- hexanes, cyclohexylcyclohexanes, cyclohexylcyclohexylcyclohexenes, 1,4-bis(cyclohexyl)benzenes, 4,4'-bis cyclohexyl) biphenyls, phenyl- or cyclohexylpyrimidines, phenyl- or cyclohexylpyridines, phenvl- or cvcac- hexyldioxanes, phenyl- or cyclohexyl-1,3-dithianes, 1,2-diphenylethanes, 1,2-dicyclohexylethanes, 1-phenyl2-cyclohexylethanes, 1-cyclohexyl-2-(4-phenylcyclohexyl) ethanes, 1-cyclohexyl-2-biphenylethanes, 1-phenyl2-cyclohexylphenylethanes, optionally halogenated stilbenes, benzyl phenyl ethers, tolans and substituted cinnamic acids. The 1,4-phenylene groups in these compounds may also be fluorinated.

The most important compounds suitable as further constituents of media according to the invention can be characterized by the formulae 1, 2, 3, 4 and 5: R'-L-E-R@ 1 R'-L-COO-E-R@ 2 R'-L-OOC-E-R" 3 R'-L-CH2CH2-E-R@ 4 R'-L-C#C-E-R@ 5 In the formulae 1, 2, 3, 4 and 5, L and E, which may be identical or different, are in each case, independently of one another, a bivalent radical from the group formed by -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-, -G-Phe-, -G-Cyc- and their mirror images, where Phe is unsubstituted or fluorine-substituted 1,4- phenylene, Oyc is trans-1,4-cyclohexylene or 1,4-cyclohexenylene, Pyr is pyrimidine-2,5-diyl or pyridine-2,5-diyl, Dio is 1,3-dioxane-2,5-diyffi and G is 2-(trans-1,4-cyclohexyl)ethyl, py-im dine-2,5- diyl, pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl.

One of the radicals L and E is preferably Cyc, Phe or Pyr. E is preferably Cyc, Phe or Phe-Cyc. The media according to the invention preferably contain one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which L and 5 are selected from the group consisting of Cyc, Phe and Pyr and simultaneously one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 n which one of the radicals L and E is selected from the group consisting of Cyc, Phe and Pyr and the other radical is selected from the group consisting of -Phe-Phe-, -Phe Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc- and optionally one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which the radicals L and E are selected from the group consisting of -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-.

In a smaller subgroup of the compounds of the formulae 1, 2, 3, 4 and 5, R' and R" are in each case, independently of one another, alkyl, alkenyl, alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy having up to 8 carbon atoms. This smaller subgroup will be referred to in the following as group A and the compounds will be designated by the partial formulae la, 2a, 3a, 4a and 5a. In most of these compounds, R' and R" are different from one another, one of these radicals usually being alkyl, alkenyl, alkoxy or alkoxyalkyl.

In another smaller subgroup o the compounds of the formulae 1, 2, 3, 4 and 5, referred to as group B, R" is -F, -C1, -NCS or -(O)iCH3-(k+1)FkCl1 where i is 0 or 1 and k+l is 1, 2 or 3. The compounds in which R" has this meaning are designated by the partial formulae lb, 2b, 3b, 4b and 5b. Particular preference is given to those compounds of the partial formulae lb, 2b, 3b, 4b and Sb in which R" is -F, -C1, -NCS, -CF3, -OCHF2 or -OCF,.

In the compounds of the partial formulae lb, 2b, 3b, 4b and 5b, R' has the meaning given for the compounds of the partial formulae la-5a and is preferably alkyl, alkenyl, alkoxy or alkoxyalkyl.

In a further smaller subgroup of the compounds of the formulae 1, 2, 3, 4 and 5, R" is -CN. This subgroup Fill be referred to in the following as group C and the compounds of this subgroup will accordingly be described by the partial formulae lc, 2c, 3c, 4c and 5c. In the compounds of the partial formulae ic, 2c, 3c, 4c and 5c, R' has the meaning given for the compounds of the partial formulae la-5a and is preferably alkyl, alkoxy or alkenyl.

Apart from the preferred compounds from groups A, B and C, other compounds of the formulae 1, 2, 3, 4 and 5 having other variants of the intended substituents are also common. All these substances are available by methods known from the literature or in analogy thereto.

The media according to the invention preferably contain, in addition to compounds according to the invention of the formula I, one or more compounds selected from group A and/or group B and/or group C. The weight proportions of the compounds from these groups in the media according to the invention are preferably as follows: group A: 0 to 90%, preferably 20 to 90%, in particular 30 to 90% group B: 0 to 80%, preferably 10 to 80%, in particular 10 to 65% group C: 0 to 10%, preferably 0 to 5%, in particular 0 to 2E, the sum of the weight proportions of the compounds from groups A and/or B and/or C present in the corresponding media according to the invention being preferably 5 to 90% and, in particular, 10% to 90%.

The media according to the invention preferably contain 1 to 40%, particularly preferably 5 to 30%, of compounds according to the invention. Further preference is given to media containing more than 40%, in particular 45 to 90%, of compounds according to the invention. The media preferably contain three, four or five compounds according to the invention.

The construction of the IPS display according to the invention corresponds to the conventional design for displays of this type, such as described in WO 91/10936 or EP 0,588,568. The term conventional design is here drawn widely and also covers all derivatives and modifications of the IPS display, in particular also, for example, matrix display elements based on poly-Si TFT or MIM.

However, an essential difference between the displays according to the invention and those which have been customary up to now is the choice of liquid-crystal parameters in the liquid-crystal layer.

The liquid-crystal mixtures which can be used according to the invention are prepared in a manner customary per se. As a rule, the desired amount of the components used in the 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 acetone, chloroform or methanol, and, after thorough mixing, to remove the solvent again, example by distillation.

The dielectrics may also contain further additives < now to those skilled in the art and described literature. For example, 0-15% of pleochroic dyes chiral dopants can be added.

C denotes a crystalline phase, S a smectic phase, S smectic B phase, N a nematic phase and I the isotropic phase.

V10 denotes the voltage for 10% transmission (viewing direction perpendicular to the plate surface). ton denotes the switch-on time and t0f the switch-off time at an operating voltage corresponding to 2.5 times the value of V10. An denotes the optical anisotropy and nc the refractive index (both at 589 nm). AE denotes the dielectric anisotropy ( As = - #@ where #1 is the dielectric constant parallel to the longitudina molecular axes and El is the dielectric constant perpendicular thereto. The electro-optical data were measured in an IPS cell at 20 C unless expressly stated otherwise. The optical data were measured at 20 C unless expressly stated otherwise.

The IPS test cell used was one in accordance with WO 91/10936 of comb structure in which the electrodes and the electrode interspaces have a spacing of 20 Wm.

The layer thickness d of the liquid-crystal material is 5 Fm. The cell furthermore comprises: Starting twisting angle: 0 Alignment angle: 5 Surface tilt angle: 3 In the "switched-off" state, the cells are dark.

In the present invention and in the examples which follow, the structures of the liquid-crystal compounds are indicated by acronyms which can be transformed into chemical formulae with the aid of Tables A and B below.

All radicals CnH2n+1 and CmH2m+l are straight-chain alkyl radicals having n or m carbon atoms. The coding in Table B is self-explanatory. In Table A, only the acronym for the base structure is given. In individual cases, the acronym for the base structure is followed, separated by a hyphen, by a code for the substituents R1, R2, L1 and L2 Code for R1, R1 R2 L1 L2 R2, L1, L2 nm CnH2n+1 CmH2m+1 H H nOm CnH2n+1 OCmH2m+1 H H nO.m OCnH2n+1 CmH2m+1 H H n CnH2n+1 CN H H nN.F CnH2n+1 CN F H nF CnH2n+1 F H H nOF OCnH2n+1 F H H nCI C"Hs4 CI H H nF.F CnH2n+1 F F H nN.F.F CnH2n+1 CN P F nCF3 CnH2n+1 CF3 H H nOCF, CnH2n+1 OCF3 H H nOCF2 CnH2n+1 OCHF2 H H nS CnH2n+1 NCS H H rVsN CTH2@+1-CH=CH-C@H2s- CN H H rEsN CTH2@+1-O-C2H2s- CN H H nAm CnH2n+1 COOCmH2m+1 H H nF.F.F CnH2n+1 F F F nCI.F.F CnH2n+1 Cl F F nCF3.F.F CnH2n+1 CF3 F F nOCF3.F.F CnH2n+1 OCF3 F F nOCF2.F.F CnH2n+1 OCHF2 F F nOCF@.F CnH2n+1 OCF3 F H Table A:

Table B:

Even without any further explanations, it is assumed that a person skilled in the art can utilize the above description to the fullest extent. The preferred embodiments are therefore merely descriptive and should not be construed as limiting the disclosure in any way.

The complete disclosures of all applications, patent specifications and publications listed above and beicx and the corresponding applications P 19,503,507 of 03.02.1995, P 19,509,791 of 17.03.1995, P 19,528,104 of 01.06.1995, P 19,528,106 of 01.08.1995, P 19,528,107 of C..0e.1995 and P 19,537,802 of 11.10.1995 are incorporated in this application by reference.

Example 1 An IPS display contains a nematic mixture exhibiting clearing point +71 C An 0.0759 nO 1. 4793 viscosity (20 C) 16 mm2 S-1 and consisting of PCH-7F 9.00 PCH-302 4.0C CCH-35 5.00 CCH-303 6.0C CCH-50l 3.00 CCP-20CF3 6.00 CCP-30CF3 6.00 CCP-40CF3 6.00 CCP-5OCF3 6.00 ECCP-3F.F 5.00 ECCP-SF.F 5.00 CGU-2.F 4.00 CGU-3.F 4.00 CGU-5.F 4.00 CCP-2F.F.F 10.00 CCP-3F.F.F 12.00 CCP-5F.F.F. 5.00 and shows high contrast and short switching times.

Example 2 An IPS display contains a nematic mixture exhibiting clearing point +80 C An [589 nm; 20 C] 0.0761 nO 1.4769 he [1 kHz; 20 OC] +5.0 viscosity (20 C) 16 mm2#S-1 and consisting of PCH-7F 8.00 % PCH-302 5.00 % CCH-301 12.00 % CCH-35 5.00 % CCP-20CF3 7.00 % CCP-30CF3 8.00 % CCP-40CF3 7.00 % CCP-50CF3 8.00 % BCH-2F.F 3.00 % BCH-3F.F 4.00 % ECCP-3F.F 7.00 % ECCP-5F.F 8.00 % OCP-2F.F.F 6.00 % CCP-3F.F.F 6.00 % CCP-5F.F.F 6.00 % and shows high contrast and short switching times.

Example 3 An IPS display contains a nematic mixture exhibiting clearing point +71 C An [589 nm; 20 C] 0.0843 nO 1.4861 A [1 kHz; 20 C] +6.3 viscosity (20 C) 16 mm2#S-1 and consisting of PCH-7F 8.00 % PCH-301 7.00 % PCH-302 6.00 % CCH-35 5.00 % CCP-20CF3 6.00 % CCP-30CF3 6.00 % CCP-40CF3 6.00 % CCP-50CF3 6.00 % ECCP-3F 6.00 % CGU-2-F 6.00 % CGU-3-F 3.00 % BCH-3F.F 5.00 % BCH-5F.F 4.00 % CCP-2F.F.F 10.00 % CCP-3F.F.F 11.00 % CCP-5F.F.F 5.00 % and shows high contrast and short switching times.

Example 4 An IPS display contains a nematic mixture exhibiting clearing point +70 C An [589 nm; 20 CC] 0.00846 nO 1.4855 ## [1 kHz; 20 C] +6.5 viscosity (20 C) 16 mm2#S-1 and consisting of PCH-7F 8.00 % PCH-301 7.00 % PCH-302 7.00 % CCH-35 3.00 % CCP-20CF3 6.00 % CCP-30CF3 6.00 % CCP-40CF3 6.00 % CCP-50CF3 6.00 % ECCP-3F.F 6.00 % ECCP-5F.F 3.00 % CGU-2-F 5.00 % CGU-3-F 4.00 % BCH-3F.F 4.00 % BCH-5F.F 4.00% CCP-2F.F.F 9.00 % CCP-3F.F.F 11.00% CCP-5F.F.F 5.00 % and shows high contrast and short switching times.

Example 5 An IPS display contains a nematic mixture exhibiting clearing point +96 C An [589 nm; 20 CC] 0.0859 nO 1.4795 ## [1 KHz; 20 C] +4.1 viscosity (20 C) 16 mm2 s- and consisting of CCH-301 9.50 % PCH-7F 7.00 % CCP-20CF3 7.00 % CCP-30CF3 8.00 % CCP-40CF3 5.00 % CCP-50CF3 5.00 % CCP-3F.F.F 8.00 % CCP-5F.F.F 4.00 % ECCP-3F.F 7.00 % PCH-302 10.00 % BCH-3F.F 7.00 % ECCP-3F 10.00 % CBC-33F 4.00 % CBC-53F 3.00 % CCH-35 5.50 % and shows high contrast and short switching times.

Comparative Example An IPS display contains a nematic mixture exhibiting clearing point 64 C An 0.0813 ## +12.0 and consisting of ME2N.F 4.00 ME3N.F 4.00 ME5N.F 10.00 ME7N.F 6.00 CCH-2 12.00 CCH-3 12.00 CCH-4 12.00 CCP-30CF3 6.00 CCP-50CF3 6.00 CH-33 3.00 CH-35 3.00 CCH-34 10.00 CCH-35 4.00 CCH-303 4.00 CCH-501 4.00 and shows a lower contrast, a higher holding ratio, a higher birefringence and a higher switching time than the display from Example 1.

Claims (9)

1. Patent claims

   i. Electro-optical liquid-crystal display -comprising a realignment layer for realicning liquid crystals whose field exhibits a significant component parallel to the liquid crystal layer and - containing a liquid-crystalline medium having positive dielectric anisotropy, characterized in that the medium contains (a) at least one mesogenic compound carrying a 3,4,5-trifluorophenyl group and/or (b) at least one mesogenic compound of the formula I R1-(A1-Z1)m-A2-R2 in which K and R2 are each, independently of one another, H, an alkyl or alkenyl radical of 1 to 15 carbon atoms which is unsubstituted or monosubstituted by CN or CF3 or at least monosubstituted by halogen, it also being possible for one or more OH- groups in these radicals to be replaced, in each case independently of one another, by -O-, -S-,

   -CO-, -CO-O-, -G-CO- or -O-CO-Oin such a manner that oxygen atoms are not linked directly to one another, Al and A2 are each, independently of one another, (a) a trans-1,4-cyclohexylene radical or a 1,4-cyclohexenylene radical in which one or more non-adjacent CHn groups can also be replaced by -0- and/or -S-, (b) a 1,4-phenylene radical in which one or two CH groups can also be replaced by N, (c) a radical from the group consisting of 1,4-bicyclo[2.2.2]octylene, piperidine 1,4-diyl, naphthalene-2,6-diyl, deca hydronaphthalene-2,

   6-diyl and 1,2,3,4 tetrahydronaphthalene-2,6-dil, where the radicals (a) and (b) can be substituted by one or two fluorines, Z1 is -CO-O-, -O-CO-, -CH20-, -00H2-, -CH2CH2-, -CH=CH-, -C#C- or a single bond, furthermore also -(CH2)4- or -CH=CH-CH2CH2-, and m is 1, 2 or 3.
2. 2. Liquid-crystal display according to Claim 1, characterized in that the medium contains at east one compound of the formula II

   in which R3 has the meaning given for R-, A3 and A4 each have, independently of one another, the meaning given for A1 and A2, z2 and Z3 each have, independently of one another, the meaning given for Z, and n is 0, 1 or 2.
3. 3. Liquid-crystal display according to Claim. 1 or 2, characterized in that the medium contains at least one compound of the formula III

   in which L1 is H, F or Cl, R4 has the meaning given for R1, As and A6 each have, independently of one another, the meaning given for A: and A2, Z4 and Z5 each have, independently of one another, the meaning given for Z: and Z2, and o is 0, 1 or 2.
4. 4. Liquid-crystal display according to one of Claims 1 to 3, characterized in that the medium contains at least one compound of the formula IV

   in which R5 has the meaning given for R1, A' and A8 each have, independently of one another, the meaning given for A1 and A2, Z6 and Z7 each have, independently of one another, the meaning given for Z1, L2 and L3 are each, independently of one another, H or F, Q is a polyfluoroalkylene radical of the formula - (O)q- (CH2)r- (CF2)s in which q is O or 1, r is O or an integer between and 6, s is an integer between l and 6, X is H, F or Cl, and p is 0, 1 or 2.
5. 5. Liquid-crystal display according to one of Claims to 4, characterized in that the medium contains not more than 10% of liquid-crystalline compounds carring cyano groups.
6. 6. Display according to one of Claims 1 to 5, characterized in that the pixels are addressed by an active matrix.
7. 7. Liquid-crystalline medium having positive dielectric anisotropy and containing a composition according to Claims 1 to 5.
8. 8. Liquid-crystalline medium according to ClaIm 7, characterized in that it contains - 20 to 60, preferably 15 to 40, % by weight of at least one compound of the formula I, - 10 to 60, preferably 20 to 50, % by weight of at least one compound of the formula II, - O to 20, preferably 5 to 15, % by weight of at least one compound of the formula and - O to 40, preferably 20 to 30, % by weight cf at least one compound of the formula IV.
9. 9. Liquid-crystalline medium according to Claim 5 cr 8, characterized in that it contains: - at least one compound selected from formulate Ila and IIb

   - at least one compound selected from formulae IIIa, IIIb, IIIc and IIId

   - at least one compound selected from formulae Ia, Ib and Ic

   and, if desired, - at least one compound selected from formulae IVa and IVb

   in which

   and R1, R2, R3, R4, R5, L1, L2 und L3 each have the meaning given.