EP3769152A1

EP3769152A1 - Liquid-chrystal display

Info

Publication number: EP3769152A1
Application number: EP19710711.3A
Authority: EP
Inventors: Fisher Chen; Sang-Kyu Lee; Gavin Hung (Chuan); Ming Chou Wu; Arnold CHANG (Jer-Wei)
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 2018-03-23
Filing date: 2019-03-20
Publication date: 2021-01-27
Also published as: CN111971618A; TWI837119B; WO2019180060A1; TW201940675A; CN111971618B

Abstract

The present invention relates to a method of manufacturing a liquid crystal display (LCD) of the polymer stabilized ultra fast (PS-UF) twisted nematic (TN) mode, to an LCD obtained by this method and to an LC medium used therein.

Description

Liquid-Crystal Display

The present invention relates to a method of manufacturing a liquid crystal display (LCD) of the polymer stabilized (PS) twisted nematic (TN) mode, to an LCD obtained by this method and to an LC medium used therein.

Background of the Invention

Currently used LCDs provide many good properties such as low weight, flatness, and wide viewing angle. However, the response time of state-of-the- art LCDs is often not fast enough, and therefore constitutes a barrier for their implementation in various novel applications such as gaming and virtual reality (VR). In order to enable color sequential technology a response time is required which is around 1 ms. If such fast response times could be realized, LCDs could become a low power consumption technology to enlarge the battery life time for mobile devices. LCD manufacturers of LCD are therefore investing high effort to reduce the response time of LCDs.

However, up to date no viable solution could be developed for an LCD mode with ultra fast response time that is also suitable for mass production. For example, currently used LCD modes such as TN, multidomain vertically aligned (MVA), in-plane switching (IPS), and fringe-field switching (FFS) mode could not fully meet the requirements of both fast response time and high transmittance due to their cell configuration. In order to reach this target, a new LCD mode is therefore necessary.

Recently, a solution to this problem has been proposed by using a short pitch TN LCD to achieve a fast response time. The TN LCD is doped with a chiral nematic LC material such that a shorter helical pitch (p) of the twisted nematic LC molecules is achieved, thereby enabling a faster decay response time (t_d).

However, when the ratio d/p of cell gap (d) over helical pitch (p) is larger than 0.5, the 270° super-twisted nematic (STN) LC director configuration is energetically more stable than the 90° TN LC director configuration of the short pitch length design, while the 90° TN configuration becomes unstable and transforms into the 270° STN configuration. Therefore, it is desired to keep a short pitch with d/p>0.5, but at the same time maintain the TN LC configuration which is needed to realize fast switching times.

In the literature it was reported that the 270° STN configuration can be changed to the 90° TN configuration by applying an electric voltage, and the 90° TN configuration can then be stabilized by photopolymerization, e.g. by formation of a polymer network in the LC medium, see K. Takatoh et al.,“Fast- response twisted nematic liquid crystals with ultrashort pitch liquid crystalline materials”, Liq. Cryst. 2012, 39, 715-720. It was also reported that the 90° TN configuration can be stabilized by the formation of polymer walls in the LC medium, see IDW 2014, LCT1 -2, "Polymer-Wall Stabilization of Ultra-Short- Pitch TN-LCDs". However, the stabilized TN LCDs as described therein have lower transmittance and/or lower contrast ratio and require higher driving voltage compared to a conventional, unstabilized TN LCD.

It was therefore an aim of the present invention to provide a method of manufacturing a TN LCD with fast response times, especially fast switch-off or decay time (t_d), while still maintaining a 90° TN LC director configuration, and at the same time achieve one or more of a low driving voltage, a high contrast ratio and a high transmittance. Another aim of the invention is to provide a TN LCD, especially a polymer stabilized (PS) TN LCD, obtained by this method which allows to achieve a fast response time and overcome the

disadvantages of the TN LCDs and PS-TN LCDs of prior art, like high driving voltage, low contrast ratio and low transmission. Other aims of the invention are immediately evident to the skilled person from the following description.

It was found that these aims can be achieved by providing a method of manufacturing a TN LCD as disclosed and claimed hereinafter. In particular it was found that it is possible to achieve a fast response time while maintaining a 90°TN LC director configuration, and still enable low driving voltage, high contrast ratio and high transmittance, by polymer stabilization of a TN LCD according to the method as described hereinafter even when using only a small amount of polymer. The display obtained by this method according to the invention is hereinafter also referred to as "polymer stabilized (ultra fast) twisted nematic LCD" or "PS(-UF)-TN LCD". Summary of the Invention

The invention relates to a liquid crystal display (LCD) of the polymer- stabilized twisted-nematic (PS-TN) mode comprising

a) a first substrate and a second substrate, the first substrate being

equipped with a first electrode layer and optionally a first alignment layer, the second substrate being equipped with a second electrode layer and optionally a second alignment layer,

b) a layer of a nematic LC medium containing a chiral additive and having positive dielectric anisotropy being dispensed between the first and the second substrate,

c) optionally a first polarizer on the side of the first substrate facing away from the LC layer and a second polarizer on the side of the second substrate facing away from the LC layer, said polarizers preferably being oriented such that their transmission planes for plane-polarized light are at right angles (crossed nicols),

wherein the longitudinal axes of the LC molecules are oriented parallel or tilted relative to the planes of the substrates, and the chiral additives induce in the LC molecules of the LC medium a helical twist along an axis

perpendicular to the substrates with a given pitch p, and

wherein layer of the LC medium has a thickness d, and the ratio d/p is ³0.5, preferably >0.5, very preferably from 0.6 to 0.8, and

wherein the twist angle of the helical twist of the LC molecules is from 60 to 120°, preferably from 80 to 100°, very preferably 90°, and

wherein the display further comprises a polymer layer deposited on one or both of said first and second electrode or, if present, on one or both of said first and second alignment layer,

wherein said polymer layers are formed from one or more polymerizable mesogenic compounds, which are contained in the LC medium at a concentration <3%, preferably from 0.05 to <3%, and which are polymerized in situ after the LC medium has been dispensed between the two substrates. The invention further relates to a method of manufacturing an LCD of the PS- TN mode comprising the steps of

a) providing a first substrate and a second substrate, the first substrate being equipped with a first electrode layer and optionally with a first alignment layer, the second substrate being equipped with a second electrode layer and optionally with a second alignment layer,

wherein the first and/or the second substrate are preferably equipped with fixing means, preferably a sealant material and/or spacers, fixing the first and second substrate at a constant distance relative to each other and with their planes parallel to each other,

b) dispensing a layer of a nematic LC medium having positive dielectric anisotropy between the first and the second substrate, such that the LC medium is in contact with the first and second alignment layer if these layers are present,

wherein the LC medium comprises, preferably consists of,

A) a liquid crystal component A (hereinafter also referred to as "LC host mixture") comprising, preferably consisting of, mesogenic or liquid- crystalline molecules,

B) a polymerizable component B comprising, preferably consisting of, one or more polymerizable mesogenic compounds (hereinafter also referred to as "reactive mesogens"),

C) one or more chiral additives, preferably selected from chiral dopants,

D) optionally one or more further additives, preferably selected from polymerization initiators, stabilizers and self-aligning additives, wherein the concentration of the polymerizable mesogenic compounds in the LC medium is <3%, preferably from 0.05 to <3%, and

wherein the longitudinal axes of the LC molecules are oriented parallel or tilted relative to the planes of the substrates, and the chiral additive induces in the LC molecules of the LC medium a helical twist along an axis perpendicular to the substrates with a given pitch p, and

wherein layer of the LC medium has a thickness d, and the ratio d/p is ³0.5, preferably >0.5, very preferably from 0.6 to 0.8, and wherein the twist angle of the helical twist of the LC molecules induced by the chiral additive is >210°, preferably from 210 to 330°, more preferably from 240 to 300°, very preferably 270°,

c) applying a voltage to the first and second electrodes such that the twist angle of the helical twist of the LC molecules is reduced to <150°, preferably to a range from 60 to 120°, more preferably from 80 to 100°, very preferably to 90°,

d) after applying the voltage or while applying the voltage, polymerizing the

Ί Q polymerizable mesogenic compounds of the polymerizable component B of the LC medium between the first and second substrate, preferably by exposure to UV radiation, thereby stabilizing the twisted nematic configuration of the LC medium with the reduced twist angle of step c), and

15 e) optionally subjecting the LC medium to a second polymerization step, preferably by exposure to UV radiation, without applying a voltage to the first and second electrodes, thereby polymerizing any polymerizable compounds which have not reacted in step d),

f) optionally providing a first polarizer on the side of the first substrate facing

20

away from the LC layer, and a second polarizer on the side of the second substrate facing away from the LC layer, wherein said polarizers are preferably oriented such that their transmission planes for plane-polarized light are at right angles (crossed nicols).

25

The invention further relates to an LC display obtained by the method as described above and below.

The invention further relates to an LC medium for use in an LC display as described above and below.

30

Brief Description of the Drawings

Fig. 1 exemplarily and schematically illustrates the structure of a PS-UF TN- LC display according to the present invention. Fig. 2a-c exemplarily show suitable and preferred driving schemes for applying a voltage in the process step c) of the present invention.

Fig. 3 shows the transmittance vs. voltage curves of display test cells containing mixtures according to Example 1 of the present invention.

Fig. 4a-c show the transmittance vs. voltage curves of display test cells containing mixtures according to Example 1 of the present invention at different temperatures.

Fig. 5 shows the transmittance vs. voltage curves of display test cells containing mixtures according to Example 2 of the present invention.

Fig. 6 shows the transmittance vs. voltage curves of display test cells containing mixtures according to Example 3 of the present invention.

Fig. 7 shows the transmittance vs. voltage curves of display test cells containing mixtures according to Example 4 of the present invention. Fig. 8 shows the transmittance vs. voltage curves of display test cells containing mixtures according to Example 5 of the present invention.

Terms and Definitions As used herein, the terms "active layer" and "switchable layer" mean a layer in an electrooptical display, for example an LC display, that comprises one or more molecules having structural and optical anisotropy, like for example LC molecules, which change their orientation upon an external stimulus like an electric or magnetic field, resulting in a change of the transmission of the layer for polarized or unpolarized light.

As used herein, the terms "twist" and "twist angle" are understood to refer to an orientation where the longitudinal axis of the LC molecules of the LC medium are substantially parallel to the plane of the nearest substrate of the display cell, and are twisted along a helical axis that is perpendicular to the plane of the substrate. As used herein, the terms "tilt" and "tilt angle" are understood to refer to an orientation where the longitudinal axis of the LC molecules of the LC medium form an angle with the plane of the nearest substrate of the display cell.

As used herein, the term "director" or "LC director" is understood to mean the average direction of the long molecular axes of the LC molecules.

As used herein, the terms "reactive mesogen" and "RM" will be understood to mean a compound containing a mesogenic or liquid crystalline skeleton, and one or more functional groups attached thereto which are suitable for polymerization and are also referred to as "polymerizable group" or "P".

Unless stated otherwise, the term "polymerizable compound" as used herein will be understood to mean a polymerizable monomeric compound.

The wording as used above and below that the LC medium comprises "a polymer obtained by polymerizing a polymerizable component B" or "a polymer obtained by polymerizing one or more polymerizable compounds" is to be understood to cover both the embodiment where the polymer remains partially or completely dispersed in the LC medium, and the embodiment where the polymer precipitates from the LC medium and forms a polymer layer on one or both of the substrates, or on one or both of the alignment layers or electrode structures deposited thereon.

As used herein, the term "low-molecular-weight compound" will be

understood to mean to a compound that is monomeric and/or is not prepared by a polymerization reaction, as opposed to a "polymeric compound" or a "polymer".

As used herein, the term "unpolymerizable compound" will be understood to mean a compound that does not contain a functional group that is suitable for polymerization under the conditions usually applied for the polymerization of the RMs.

The term "mesogenic group" as used herein is known to the person skilled in the art and described in the literature, and means a group which, due to the anisotropy of its attracting and repelling interactions, essentially contributes to causing a liquid-crystal (LC) phase in low-molecular-weight or polymeric substances. Compounds containing mesogenic groups (mesogenic com- pounds) do not necessarily have to have an LC phase themselves. It is also possible for mesogenic compounds to exhibit LC phase behaviour only after mixing with other compounds and/or after polymerization. Typical mesogenic groups are, for example, rigid rod- or disc-shaped units. An overview of the terms and definitions used in connection with mesogenic or LC compounds is given in Pure Appi. Chem. 2001 , 73(5), 888 and C. Tschierske, G. Pelzl, S. Diele, Angew. Chem. 2004, 116, 6340-6368.

The term "spacer group", hereinafter also referred to as "Sp", as used herein is known to the person skilled in the art and is described in the literature, see, for example, Pure Appi Chem. 2001 , 73(5), 888 and C. Tschierske, G. Pelzl, S. Diele, Angew. Chem. 2004, 116, 6340-6368. As used herein, the terms "spacer group" or "spacer" mean a flexible group, for example an alkylene group, which connects the mesogenic group and the polymerizable group(s) in a polymerizable mesogenic compound.

Above and below,

denote a trans-1 ,4-cyclohexylene ring, and

denote a 1 ,4-phenylene ring.

Above and below "organic group" denotes a carbon or hydrocarbon group.

"Carbon group" denotes a mono- or polyvalent organic group containing at least one carbon atom, where this either contains no further atoms (such as, for example, -CºC-) or optionally contains one or more further atoms, such as, for example, N, O, S, B, P, Si, Se, As, Te or Ge (for example carbonyl, etc.). The term "hydrocarbon group" denotes a carbon group which

additionally contains one or more H atoms and optionally one or more heteroatoms, such as, for example, N, O, S, B, P, Si, Se, As, Te or Ge. "Halogen" denotes F, Cl, Br or I.

-CO-, -C(=0)- and -C(O)- denote a carbonyl group, i.e.

A carbon or hydrocarbon group can be a saturated or unsaturated group.

Unsaturated groups are, for example, aryl, alkenyl or alkynyl groups. A carbon or hydrocarbon radical having more than 3 C atoms can be straight-chain, branched and/or cyclic and may also contain spiro links or condensed rings.

The terms "alkyl", "aryl", "heteroaryl", etc., also encompass polyvalent groups, for example alkylene, arylene, heteroarylene, etc.

The term "aryl" denotes an aromatic carbon group or a group derived therefrom. The term "heteroaryl" denotes "aryl" as defined above, containing one or more heteroatoms, preferably selected from N, O, S, Se, Te, Si and Ge.

Preferred carbon and hydrocarbon groups are optionally substituted, straight- chain, branched or cyclic, alkyl, alkenyl, alkynyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy and alkoxycarbonyloxy having 1 to 40, preferably 1 to 20, very preferably 1 to 12, C atoms, optionally substituted aryl or aryloxy having 5 to 30, preferably 6 to 25, C atoms, or optionally substituted alkylaryl, arylalkyl, alkylaryloxy, arylalkyloxy, arylcarbonyl, aryloxycarbonyl, arylcarbonyloxy and aryloxycarbonyloxy having 5 to 30, preferably 6 to 25, C atoms, wherein one or more C atoms may also be replaced by hetero atoms, preferably selected from N, O, S, Se, Te, Si and Ge.

Further preferred carbon and hydrocarbon groups are C₁-C₂₀ alkyl, C₂-C₂₀ alkenyl, C2-C20 alkynyl, C3-C20 allyl, C₄-C2o alkyldienyl, C₄-C2o polyenyl, Ce- C₂₀ cycloalkyl, C₄-Cis cycloalkenyl, C6-C30 aryl, C6-C3o alkylaryl, C6-C30 arylalkyl, C6-C30 alkylaryloxy, C6-C3o arylalkyloxy, C₂-C30 heteroaryl, C₂-C30 heteroaryloxy.

Particular preference is given to C₁-C₁₂ alkyl, C₂-C₁₂ alkenyl, C₂-C₁₂ alkynyl, C6-C25 aryl and C2-C25 heteroaryl. Further preferred carbon and hydrocarbon groups are straight-chain, branched or cyclic alkyl having 1 to 20, preferably 1 to 12, C atoms, which are unsubstituted or mono- or polysubstituted by F, Cl, Br, I or CN and in which one or more non-adjacent CFh groups may each be replaced, independently of one another, by -C(R^X)=C(R^X)-, -CºC-, -N(R^X)-, -0-, -S-, - CO-, -CO-0-, -O-CO-, -O-CO-O- in such a way that O and/or S atoms are not linked directly to one another. R^x preferably denotes H, F, Cl, CN, a straight-chain, branched or cyclic alkyl chain having 1 to 25 C atoms, in which, in addition, one or more non-adjacent C atoms may be replaced by -O-, -S-, -CO-, -C0-0-, -O-CO-, -O-CO-O- and in which one or more FI atoms may be replaced by F or Cl, or denotes an optionally substituted aryl or aryloxy group with 6 to 30 C atoms, or an optionally substituted heteroaryl or heteroaryloxy group with 2 to 30 C atoms.

Preferred alkyl groups are, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, 2-methylbutyl, n-pentyl, s-pentyl, cyclopentyl, n-hexyl, cyclohexyl, 2-ethyl hexyl, n-heptyl, cycloheptyl, n-octyl, cyclooctyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, dodecanyl, trifluoromethyl, perfluoro- n-butyl, 2,2,2-trifluoroethyl, peril uorooctyl, perfluorohexyl, etc.

Preferred alkenyl groups are, for example, ethenyl, propenyl, butenyl, pentenyl, cyclopentenyl, hexenyl, cyclohexenyl, heptenyl, cycloheptenyl, octenyl, cyclooctenyl, etc.

Preferred alkynyl groups are, for example, ethynyl, propynyl, butynyl, pentynyl, hexynyl, octynyl, etc. Preferred alkoxy groups are, for example, methoxy, ethoxy, 2-methoxy- ethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, s-butoxy, t-butoxy, 2- methylbutoxy, n-pentoxy, n-hexoxy, n-heptoxy, n-octoxy, n-nonoxy, n- decoxy, n-undecoxy, n-dodecoxy, etc. Preferred amino groups are, for example, dimethylamino, methylamino, methylphenylamino, phenylamino, etc. Aryl and heteroaryl groups can be monocyclic or polycyclic, i.e. they can contain one ring (such as, for example, phenyl) or two or more rings, which may also be fused (such as, for example, naphthyl) or covalently bonded (such as, for example, biphenyl), or contain a combination of fused and linked rings. Heteroaryl groups contain one or more heteroatoms, preferably selected from O, N, S and Se.

Particular preference is given to mono-, bi- or tricyclic aryl groups having 6 to 25 C atoms and mono-, bi- or tricyclic heteroaryl groups having 5 to 25 ring atoms, which optionally contain fused rings and are optionally substituted. Preference is furthermore given to 5-, 6- or 7-membered aryl and heteroaryl groups, in which, in addition, one or more CH groups may be replaced by N,

S or O in such a way that O atoms and/or S atoms are not linked directly to one another.

Preferred aryl groups are, for example, phenyl, biphenyl, terphenyl,

[1 ,1 ':3',1 "]terphenyl-2'-yl, naphthyl, anthracene, binaphthyl, phenanthrene, 9,10-dihydro-phenanthrene, pyrene, dihydropyrene, chrysene, perylene, tetracene, pentacene, benzopyrene, fluorene, indene, indenofluorene, spirobifluorene, etc.

Preferred heteroaryl groups are, for example, 5-membered rings, such as pyrrole, pyrazole, imidazole, 1 ,2,3-triazole, 1 ,2,4-triazole, tetrazole, furan, thiophene, selenophene, oxazole, isoxazole, 1 ,2-thiazole, 1 ,3-thiazole, 1 ,2,3- oxadiazole, 1 ,2,4-oxadiazole, 1 ,2,5-oxadiazole, 1 ,3,4-oxadiazole, 1 ,2,3- thiadiazole, 1 ,2,4-thiadiazole, 1 ,2,5-thiadiazole, 1 ,3,4-thiadiazole, 6-membered rings, such as pyridine, pyridazine, pyrimidine, pyrazine, 1 ,3,5-triazine, 1 ,2,4- triazine, 1 ,2,3-triazine, 1 ,2,4,5-tetrazine, 1 ,2,3,4-tetrazine, 1 ,2,3,5-tetrazine, or condensed groups, such as indole, isoindole, indolizine, indazole,

benzimidazole, benzotriazole, purine, naphthimidazole, phenanthrimidazole, pyridimidazole, pyrazinimidazole, quinoxalinimidazole, benzoxazole, naphthoxazole, anthroxazole, phenanthroxazole, isoxazole, benzothiazole, benzofuran, isobenzofuran, dibenzofuran, quinoline, isoquinoline, pteridine, benzo-5, 6-quinoline, benzo-6, 7-quinoline, benzo-7, 8-quinoline, benzoisoquin- oline, acridine, phenothiazine, phenoxazine, benzopyridazine, benzopyrimi- dine, quinoxaline, phenazine, naphthyridine, azacarbazole, benzocarboline, phenanthridine, phenanthroline, thieno[2,3b]thiophene, thieno[3,2b]thiophene, dithienothiophene, isobenzothiophene, dibenzothiophene, benzothiadiazo- thiophene, or combinations of these groups.

The aryl and heteroaryl groups mentioned above and below may also be substituted by alkyl, alkoxy, thioalkyl, fluorine, fluoroalkyl or further aryl or heteroaryl groups.

The (non-aromatic) alicyclic and heterocyclic groups encompass both saturated rings, i.e. those containing exclusively single bonds, and also partially unsaturated rings, i.e. those which may also contain multiple bonds. Heterocyclic rings contain one or more heteroatoms, preferably selected from Si, 0, N, S and Se.

The (non-aromatic) alicyclic and heterocyclic groups can be monocyclic, i.e. contain only one ring (such as, for example, cyclohexane), or polycyclic, i.e. contain a plurality of rings (such as, for example, decahydronaphthalene or bicyclooctane). Particular preference is given to saturated groups. Preference is furthermore given to mono-, bi- or tricyclic groups having 5 to 25 ring atoms, which optionally contain fused rings and are optionally substituted. Preference is furthermore given to 5-, 6-, 7- or 8-membered carbocyclic groups, in which, in addition, one or more C atoms may be replaced by Si and/or one or more CH groups may be replaced by N and/or one or more non-adjacent CH2 groups may be replaced by -O- and/or -S-.

Preferred alicyclic and heterocyclic groups are, for example, 5-membered groups, such as cyclopentane, tetrahydrofuran, tetrahydrothiofuran, pyrroli- dine, 6-membered groups, such as cyclohexane, silinane, cyclohexene, tetrahydropyran, tetrahydrothiopyran, 1 ,3-dioxane, 1 ,3-dithiane, piperidine, 7-membered groups, such as cycloheptane, and fused groups, such as tetrahydronaphthalene, decahydronaphthalene, indane, bicyclo[1.1.1 ]- pentane-1 ,3-diyl, bicyclo[2.2.2]octane-1 ,4-diyl, spiro[3.3]heptane-2,6-diyl, octahydro-4,7-methanoindane-2,5-diyl. Preferred substituents are, for example, solubility-promoting groups, such as alkyl or alkoxy, electron-withdrawing groups, such as fluorine, nitro or nitrile, or substituents for increasing the glass transition temperature (Tg) in the polymer, in particular bulky groups, such as, for example, t-butyl or optionally substituted aryl groups.

Preferred substituents, hereinafter also referred to as "L", are F, Cl, Br,

I, -CN, -NO2, -NCO, -NCS, -OCN, -SCN, -C(=0)N(R^x)₂, -C(=0)Y¹, -C(=0)R^x, -N(R^x)₂, straight-chain or branched alkyl, alkoxy, alkylcarbonyl,

alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy each having 1 to 25 C atoms, in which one or more H atoms may optionally be replaced by F or Cl, optionally substituted silyl having 1 to 20 Si atoms, or optionally substituted aryl having 6 to 25, preferably 6 to 15, C atoms, wherein R^x denotes FI, F, Cl, CN, or straight chain, branched or cyclic alkyl having 1 to 25 C atoms, wherein one or more non-adjacent CFh-groups are optionally replaced by -0-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O- in such a manner that O- and/or S-atoms are not directly connected with each other, and wherein one or more FI atoms are each optionally replaced by F, Cl, P- or R-Sp-, and

Y¹ denotes halogen.

"Substituted silyl or aryl" preferably means substituted by halogen, -CN, R°, -OR⁰, -CO-R⁰, -CO-O-R⁰, -O-CO-R⁰ or -O-CO-O-R⁰, wherein R° denotes

FI or alkyl with 1 to 20 C atoms.

Particularly preferred substituents L are, for example, F, Cl, CN, NO₂, CFI3, C2H5, OCHs, OC2H5, COCHs, COC2H5, COOCHs, COOC2H5, CFs, OCFs, OCFIF₂, OC₂F₅, furthermore phenyl.

in which L has one of the meanings indicated above. The polymerizable group P is a group which is suitable for a polymerization reaction, such as, for example, free-radical or ionic chain polymerization, polyaddition or polycondensation, or for a polymer-analogous reaction, for example addition or condensation onto a main polymer chain. Particular preference is given to groups for chain polymerization, in particular those containing a C=C double bond or -CºC- triple bond, and groups which are suitable for polymerization with ring opening, such as, for example, oxetane or epoxide groups.

NH-, CH₂=CH-(C00)ki-Phe-(0)_k2-, CH₂=CH-(C0)_ki-Phe-(0)_k2-, Phe-CH=CH- , HOOC-, OCN- and W⁴W⁵W⁶Si-, in which W¹ denotes H, F, Cl, CN, CF₃, phenyl or alkyl having 1 to 5 C atoms, in particular H, F, Cl or CFI₃, W² and W³ each, independently of one another, denote FI or alkyl having 1 to 5 C atoms, in particular FI, methyl, ethyl or n-propyl, W⁴, W⁵ and W⁶ each, independently of one another, denote Cl, oxaalkyl or oxacarbonylalkyl having 1 to 5 C atoms, W⁷ and W⁸ each, independently of one another, denote FI, Cl or alkyl having 1 to 5 C atoms, Phe denotes 1 ,4-phenylene, which is optionally substituted by one or more radicals L as defined above which are other than R-Sp-, ki, k₂ and k₃ each, independently of one another, denote 0 or 1 , k₃ preferably denotes 1 , and k₄ denotes an integer from 1 to 10.

NH-, CH₂=CH-(C00)ki-Phe-(0)_k2-, CH₂=CH-(C0)_ki-Phe-(0)_k2-, Phe-CH=CH- and W⁴W⁵W⁶Si-, in which W¹ denotes H, F, Cl, CN, CF3, phenyl or alkyl having 1 to 5 C atoms, in particular H, F, Cl or CFI3, W² and W³ each, independently of one another, denote FI or alkyl having 1 to 5 C atoms, in particular H, methyl, ethyl or n-propyl, W⁴, W⁵ and W⁶ each, independently of one another, denote Cl, oxaalkyl or oxacarbonylalkyl having 1 to 5 C atoms, W⁷ and W⁸ each, independently of one another, denote H, Cl or alkyl having 1 to 5 C atoms, Phe denotes 1 ,4-phenylene, ki, k₂ and k₃ each, independently of one another, denote 0 or 1 , k₃ preferably denotes 1 , and k₄ denotes an integer from 1 to 10.

Very particularly preferred groups P are selected from the group consisting of CH₂=CW¹-CO-0-, in particular CH₂=CH-CO-0-, CH₂=C(CH₃)-C0-0- and CH₂=CF-CO-0-, furthermore CH₂=CH-0-, (CH₂=CH)₂CH-0-C0-,

O

o

(CH₂=CH)₂CH-0-, W²HC - CH - and W² (CH₂)_k1-0-

Further preferred polymerizable groups P are selected from the group consisting of vinyloxy, acrylate, methacrylate, fluoroacrylate, chloroacrylate, oxetane and epoxide, most preferably from acrylate and methacrylate.

If Sp is different from a single bond, it is preferably of the formula Sp"-X", so that the respective radical P-Sp- conforms to the formula P-Sp"-X"-, wherein

Sp" denotes alkylene having 1 to 20, preferably 1 to 12, C atoms, which is optionally mono- or polysubstituted by F, Cl, Br, I or CN and in which, in addition, one or more non-adjacent Chte groups may each be replaced, independently of one another, by -0-, -S-, -NH-, -N(R⁰)-, -Si(R°R⁰⁰)-, - CO-, -CO-0-, -O-CO-, -0-C0-0-, -S-CO-, -CO-S-, -N(R⁰⁰)-CO-O-, -O- CO-N(R⁰)-, -N(R°)-CO-N(R⁰⁰)-, -CH=CH- or -CºC- in such a way that O and/or S atoms are not linked directly to one another,

X" denotes -O-, -S-, -CO-, -C0-0-, -O-CO-, -0-C0-0-, -CO-N(R⁰)-, -N(R°)- CO-, -N(R°)-CO-N(R⁰⁰)-, -OCH2-, -CH2O-, -SCH2-, -CH2S-, -CF2O-, - OCF2-, -CF2S-, -SCF2-, -CF2CH2-, -CH2CF2-, -CF2CF2-, -CH=N-, - N=CH-, -N=N-, -CH=CR⁰-, -CY²=CY³-, -CºC-, -CH=CH-C0-0-, -O-CO-

CFI=CFI- or a single bond,

R° and R°° each, independently of one another, denote FI or alkyl having 1 to 20 C atoms, and

Y² and Y³ each, independently of one another, denote FI, F, Cl or CN.

X" is preferably -0-, -S-, -CO-, -COO-, -OCO-, -O-COO-, -CO-NR⁰-, -NR°- CO-, -NR°-CO-NR°°- or a single bond.

Typical spacer groups Sp and -Sp"-X"- are, for example, -(CFh)pi-,

-(CH₂CH20)qi-CH₂CH2-, -CH2CH2-S-CH2CH2-, -CH2CH2-NH-CH2CH2- or -(SiR°R⁰⁰-O)_pi-, in which p1 is an integer from 1 to 12, q1 is an integer from 1 to 3, and R° and R°° have the meanings indicated above.

Particularly preferred groups Sp and -Sp”-X”- are -(CFh)pi-, -(CFh)pi-O-, -(CFl₂)pi-0-C0-, -(CFl₂)pi-C0-0-, -(CFl₂)pi-0-C0-0-, in which p1 and q1 have the meanings indicated above. Particularly preferred groups Sp" are, in each case straight-chain, ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, octadecylene, ethyleneoxyethylene, methyleneoxybutylene, ethylenethioethylene, ethylene-N-methylimino- ethylene, 1-methylalkylene, ethenylene, propenylene and butenylene.

Detailed Description of the Invention In the method according to the present invention, a twisted nematic LC configuration is provided with an initially short pitch corresponding to an STN configuration, where d/p is >0.5 and the twist angle is in the range from 210 to 330°, preferably 270°.

This is achieved by adding a chiral dopant to the LC medium, which has a certain twisting power. The helical twisting power or HTP of a chiral dopant is a measure of its ability to induce a helical twist in a specific nematic LC medium. The HTP of a chiral dopant is an intrinsic property and can be defined by equation (1 )

HTP = (p c) ¹ (1 ) wherein p is the pitch of the induced helical twist, and c is the concentration c of the chiral dopant in the LC medium.

It is also possible to use two or more chiral dopants, for example in order to compensate for the temperature dependence of the HTP of the individual dopants and thus to reduce temperature dependence of the helical pitch.

During the manufacturing process, a defined voltage is then applied to the electrodes of the display. As a result the twist angle is reduced to a value corresponding to a TN configuration, like 90°.

According to K. Takatoh et al., Liq. Cryst. 2012, 39, 715-720, the change of the twist angle from 270° to 90° can be explained by the LC molecules changing from a twisted splay state (as in a STN configuration) to a twisted bend state (as in a TN configuration).

This voltage-induced TN configuration is metastable and would normally relax to the initial STN configuration after a certain time when the voltage is switched off. In the method according to the present invention, relaxation of the twist angle from the TN-LC to the STN-LC configuration is prevented by polymerizing the polymerizable compounds of component B, preferably by UV-photo- polymerization. Thereby the metastable TN configuration with the "unnaturally" low twist angle is preserved, despite the short pitch induced by the chiral dopant. The LC molecules in the LC medium are thus forced into a state where the twist is lower than the natural pitch of the LC medium as given by equation (1 ) above. In other words the the actual twist angle of the LC molecules does no longer correspond to the "natural" pitch of the helical twist induced by the chiral dopant and the d/p value of the display cell.

As a result of this method, a significant reduction of the response times can be achieved, compared to a display which is made from similar materials but wherein the amount of the chiral dopant is reduced so that the pitch is longer and the d/p value is lower and both are matching the reduced twist angle.

It was found that polymer stabilization of the low twist and advantageous effects of the PS-TN LCD according to the present invention, like fast rise and decay times, high transmittance and good contrast, can be achieved already by adding only a low amount of <3% of polymerizable mesogenic compounds to the LC medium.

It was also found that in the PS-TN LCD according to the present invention a substantial part of the polymer which is formed by the polymerizable

mesogenic compounds will phase-separate or precipitate from the LC medium and form a polymer layer on the substrates or electrodes, or the alignment layer provided thereon. This could be confirmed by microscopic measurements (like SEM or AFM) which show that the formed polymer mainly accumulates at the LC layer/substrate interface. Thereby especially the loss of transmittance LCDs compared to unstabilized TN LCDs could be reduced and high transmittance could be realized.

These are significant advantages that could not be expected from prior art like the publications cited above, where it is reported that certain minimum amounts of monomer are needed for the formation of either a polymer network or polymer walls in the LC medium, and that the polymer network or polymer walls in the LC medium cause a lower transmittance.

Preferably the LC medium used in the display according to the present invention comprises

A) a liquid crystal component A comprising mesogenic or liquid-crystalline molecules,

B) a polymerizable component B comprising one or more polymerizable mesogenic compounds,

C) one or more chiral additives, preferably selected from chiral dopants,

D) optionally one or more further additives, preferably selected from

stabilizers and polymerization initiators,

wherein the concentration of the polymerizable mesogenic compounds of component B in the LC medium is from 0.1 to <3% by weight.

The liquid-crystalline component A) of an LC medium as used in the display according to the present invention is hereinafter also referred to as "LC host mixture", and preferably contains only LC compounds that are selected from low-molecular-weight compounds which are unpolymerizable.

Preferably the component A or LC host mixture of the LC medium comprises one or more compounds selected from formula A and B

in which the individual radicals have, independently of each other and on each occurrence identically or differently, the following meanings: each, independently

of one another, and on each occurrence, identically or differently

R²¹ , R³¹ each, independently of one another, alkyl, alkoxy, oxaalkyl or alkoxyalkyl having 1 to 9 C atoms or alkenyl or alkenyloxy having 2 to 9 C atoms, all of which are optionally fluorinated,

X° F, Cl, halogenated alkyl or alkoxy having 1 to 6 C atoms or halogenated alkenyl or alkenyloxy having 2 to 6 C atoms,

Z³¹ -CH2CH2-, -CF2CF2-, -COO-, frans-CH=CH-, trans-

CF=CF-, -CFI2O- or a single bond, preferably -CFI2CFI2-, - COO-, trans- CFI=CFI- or a single bond, particularly preferably -COO-, trans- CFI=CFI- or a single bond,

L²¹ , L ²², L³¹ , L ³² each, independently of one another, FI or F,

L^s FI or CFI3, wherein preferably at least one of two groups L^s attached to the same benzene ring is FI,

9 0, 1 , 2 or 3. In the compounds of formula A and B, X° is preferably F, Cl, CF3, CFIF₂, OCFs, OCHF2, OCFHCFs, OCFHCHF2, OCFHCHF2, OCF2CH3, OCF2CHF2, OCF2CHF2, OCF2CF2CHF2, OCF2CF2CHF2, OCFHCF2CF3, OCFHCF2CHF2, OCF2CF2CF3, OCF2CF2CCIF2, OCCIFCF2CF3 or CH=CF₂, very preferably F or OCF3, most preferably F.

In the compounds of formula A and B and their subformulae, the rings

preferably denote

furthermore

In a preferred embodiment at least one of the compounds of formula A and B or their subformulae contains at least one ring

In the compounds of formula A and B, R²¹ and R³¹ are preferably selected from straight-chain alkyl or alkoxy with 1 , 2, 3, 4, 5 or 6 C atoms, and straight-chain alkenyl with 2, 3, 4, 5, 6 or 7 C atoms. In the compounds of formula A and B, g is preferably 1 or 2.

In the compounds of formula B, Z³¹ is preferably COO, trans-CH=CH or a single bond, very preferably COO or a single bond.

Preferably component A) of the LC medium comprises one or more compounds of formula A selected from the group consisting of the following formulae:

in which A²¹, R²¹, X°, L²¹, L²² and L^s have the meanings given in formula A, L²³ and L²⁴ each, independently of one another, are H or F, and X° is preferably F. Particularly preferred are compounds of formulae A1 and A2. Particularly preferred compounds of formula A1 are selected from the group consisting of the following subformulae:

in which R²¹, X°, L²¹ and L²² have the meaning given in formula A1 , L²³, L²⁴, L²⁵ and L²⁶ are each, independently of one another, FI or F, and X° is preferably F.

Further preferred are compounds of formula A1 a-A1 g wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom.

Very particularly preferred compounds of formula A1 are selected from the group consisting of the following subformulae:

in which R²¹ is as defined in formula A1.

Further preferred are compounds of formula A1 a1 -A1g1 wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom. Particularly preferred compounds of formula A2 are selected from the group consisting of the following subformulae:

in which R²¹, X°, L²¹ and L²² have the meaning given in formula A2, L²³, L²⁴, L²⁵ and L²⁶ each, independently of one another, are FI or F, and X° is preferably F. Further preferred are compounds of formula A2a-A2l wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom.

Very particularly preferred compounds of formula A2 are selected from the group consisting of the following subformulae:

in which R²¹ and X° are as defined in formula A2.

Further preferred are compounds of formula A2a1 -A2l2 wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom.

Particularly preferred compounds of formula A3 are selected from the group consisting of the following subformulae:

in which R²¹, X°, L²¹ and L²² have the meaning given in formula A3, and X° is preferably F. Further preferred are compounds of formula A3a-A3c wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom.

Particularly preferred compounds of formula A4 are selected from the group consisting of the following subformulae:

in which R²¹ is as defined in formula A4.

Further preferred are compounds of formula A4a wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom.

Preferably component A) of the LC medium comprises one or more compounds of formula B selected from the group consisting of the following formulae:

in which g, A³¹, A³², R³¹, X°, L³¹, L³² and L^s have the meanings given in formula B, and X° is preferably F. Particularly preferred are compounds of formulae B1 and B2.

Particularly preferred compounds of formula B1 are selected from the group consisting of the following subformulae:

in which R³¹, X°, L³¹ and L³² have the meaning given in formula B1 , and X° is preferably F.

Further preferred are compounds of formula B1 a-B1 b wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom.

Very particularly preferred compounds of formula B1 a are selected from the group consisting of the following subformulae: in which R³¹ is as defined in formula B1 .

Further preferred are compounds of formula B1 a1 -B1 a6 wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom.

Very particularly preferred compounds of formula B1 b are selected from the group consisting of the following subformulae: in which R³¹ is as defined in formula B1 .

Further preferred are compounds of formula B1 b1 -B1 b4 wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom.

Particularly preferred compounds of formula B2 are selected from the group consisting of the following subformulae:

in which R³¹, X°, L³¹ and L³² have the meaning given in formula B2, L³³, L³⁴, L³⁵ and L³⁶ are each, independently of one another, H or F, and X° is preferably F.

Further preferred are compounds of formula B2a-B2l wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom.

Very particularly preferred compounds of formula B2 are selected from the group consisting of the following subformulae: in which R³¹ is as defined in formula B2.

Further preferred are compounds of formula B2a1 -B2a5 wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom.

Very particularly preferred compounds of formula B2b are selected from the group consisting of the following subformulae in which R³¹ is as defined in formula B2.

Further preferred are compounds of formula B2b1 -B2b4 wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom.

Very particularly preferred compounds of formula B2c are selected from the group consisting of the following subformulae:

in which R³¹ is as defined in formula B2.

Further preferred are compounds of formula B2c1 -B2c5 wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom.

Very particularly preferred compounds of formula B2d and B2e are selected from the group consisting of the following subformulae:

in which R³¹ is as defined in formula B2

Further preferred are compounds of formula B2d1 and B2e1 wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom. Very particularly preferred compounds of formula B2f are selected from the group consisting of the following subformulae:

in which R³¹ is as defined in formula B2. Further preferred are compounds of formula B2f1 -B2f5 wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom.

Very particularly preferred compounds of formula B2g are selected from the group consisting of the following subformulae: in which R³¹ is as defined in formula B2.

Further preferred are compounds of formula B2g1 -B2g5 wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom.

Very particularly preferred compounds of formula B2h are selected from the group consisting of the following subformulae: in which R³¹ is as defined in formula B2.

Further preferred are compounds of formula B2h1 -B2h3 wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom.

Very particularly preferred compounds of formula B2i are selected from the group consisting of the following subformulae:

in which R³¹ is as defined in formula B2.

Further preferred are compounds of formula B2i1 and B2i2 wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom.

Very particularly preferred compounds of formula B2k are selected from the group consisting of the following subformulae:

in which R³¹ is as defined in formula B2. Further preferred are compounds of formula B2k1 and B2k2 wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom.

in which R³¹ is as defined in formula B2. Further preferred are compounds of formula B2I1 and B2I2 wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom.

Alternatively to, or in addition to, the compounds of formula B1 and/or B2 component A) of the LC medium may also comprise one or more compounds of formula B3 as defined above.

Particularly preferred compounds of formula B3 are selected from the group consisting of the following subformulae:

in which R³¹ is as defined in formula B3.

Further preferred are compounds of formula B3a and B3b wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom. Preferably component A) of the LC medium comprises, in addition to the compounds of formula A and/or B, one or more compounds of formula C

,41

R C

in which the individual radicals have the following meanings: each, independently of one another, and

on each occurrence, identically or differently

R⁴¹, R⁴² each, independently of one another, alkyl, alkoxy, oxaalkyl or alkoxyalkyl having 1 to 9 C atoms or alkenyl or

alkenyloxy having 2 to 9 C atoms, all of which are

optionally fluorinated,

Z⁴¹, Z⁴² each, independently of one another, -CH2CH2-, -COO-, trans-

CH=CH-, frans-CF=CF-, -CFI2O-, -CF2O-, -CºC- or a single bond, preferably a single bond, h 0, 1 , 2 or 3.

In the compounds of formula C, R⁴¹ and R⁴² are preferably selected from straight-chain alkyl or alkoxy with 1 , 2, 3, 4, 5 or 6 C atoms, and straight- chain alkenyl with 2, 3, 4, 5, 6 or 7 C atoms.

In the compounds of formula C, h is preferably 0, 1 or 2. In the compounds of formula C, Z⁴¹ and Z⁴² are preferably selected from COO, trans-CH=CH and a single bond, very preferably from COO and a single bond.

Preferred compounds of formula C are selected from the group consisting of the following subformulae:

wherein f is 0 or 1 , and R⁴¹ and R⁴² have the meanings given in formula C, and preferably denote each, independently of one another, alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy with 1 to 7 C atoms, or alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl with 2 to 7 C atoms.

Very preferred are compounds of formula C1 , C4, C5 and C9. Preferred compounds of formula C are selected from the group consisting of the following subformulae:

in which alkyl and alkyl^* each, independently of one another, denote a straight-chain alkyl radical having 1 -6 C atoms.

Especially preferred are compounds of formula C1 a, very preferably those selected from the following sub-formulae:

wherein the propyl, butyl and pentyl groups are straight-chain groups.

Most preferred are compounds of formula C1 a1 . In another preferred embodiment of the present invention component A) of the LC medium comprises, in addition to the compounds of formula A and/or B and/or C, one or more compounds of formula D in which A⁴¹, A⁴², Z⁴¹, Z⁴², R⁴¹, R⁴² and h have the meanings given in formula C or one of the preferred meanings given above.

Preferred compounds of formula D are selected from the group consisting of the following subformulae:

in which R⁴¹ and R⁴² have the meanings given in formula D and preferably denote alkyl.

Very preferred compounds of formula D are selected from the group consisting of the following subformulae:

D1 a

in which alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1 -6 C atoms, and alkenyl denotes a straight-chain alkenyl radical having 2-7 C atoms, preferably CH2=CH-, CH₂=CHCH₂CH₂-, CH₃-CH=CH-, CH₃-CH₂-CH=CH-, CH₃-(CH₂)₂-CH=CH-, CH₃-(CH₂)₃-CH=CH- or CH₃-CH=CH-(CH₂)₂-.

Most preferred compounds of formula D are selected from the group consisting of the following subformulae:

In another preferred embodiment of the present invention component A) of the LC medium comprises, in addition to the compounds of formula A and/or B, one or more compounds of formula E containing an alkenyl group in which the individual radicals, on each occurrence identically or differently, each, independently of one another, have the following meaning:

R^A1 alkenyl having 2 to 9 C atoms or, if at least one of the rings X, Y and Z denotes cyclohexenyl, also one of the meanings of R^A2,

R^A2 alkyl having 1 to 12 C atoms, in which, in addition, one or two non- adjacent CFte 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, x 1 or 2. R^A2 is preferably straight-chain alkyl or alkoxy having 1 to 8 C atoms or straight-chain alkenyl having 2 to 7 C atoms. Preferred compounds of formula E are selected from the following sub- formulae:

alke nyl— ( H >— ( H >— alke nyl E2

alkyl— ( O )— ( O )— alkenyl E3

in which alkyl and alkyl^* each, independently of one another, denote a straight-chain alkyl radical having 1 -6 C atoms, and alkenyl and alkenyl^* each, independently of one another, denote a straight-chain alkenyl radical having 2-7 C atoms. Alkenyl and alkenyl^* preferably denote CH2=CH-,

CH₂=CHCH₂CH₂-, CH₃-CH=CH-, CH₃-CH₂-CH=CH-, CH₃-(CH₂)₂-CH=CH-, CH₃-(CH₂)₃-CH=CH- or CH₃-CH=CH-(CH₂)₂-.

Very preferred compounds of the formula E are selected from the following sub-formulae:

in which m denotes 1 , 2, 3, 4, 5 or 6, i denotes 0, 1 , 2 or 3, and R^b1 denotes H, CH₃ or C₂H₅. Very particularly preferred compounds of the formula E are selected from the following sub-formulae:

Most preferred are compounds of formula E1 a2, E1 a5, E6a1 and E6a2.

In another preferred embodiment of the present invention component A) of the LC medium comprises, in addition to the compounds of formula A and/or B, one or more compounds of formula F

in which the individual radicals have, independently of each other and on each occurrence identically or differently, the following meanings:

R²¹ , R³¹ each, independently of one another, alkyl, alkoxy, oxaalkyl or alkoxyalkyl having 1 to 9 C atoms or alkenyl or alkenyloxy having 2 to 9 C atoms, all of which are optionally fluorinated, x° F, Cl, halogenated alkyl or alkoxy having 1 to 6 C atoms or halogenated alkenyl or alkenyloxy having 2 to 6 C atoms,

Z²¹ -CH2CH2-, -CF2CF2-, -COO-, trans- CFI=CFI-, trans- CF=CF-, -CFI2O-, -CF2O-, -CºC- or a single bond, preferably -CF2O-,

L²¹ , L ²², L²³, L ²⁴ each, independently of one another, FI or F L^s Fl or CFI3, wherein preferably at least one of two groups L^s attached to the same benzene ring is FI,

9 0, 1 , 2 or 3. In the compounds of formula F and its subformulae, the rings

preferably denote

furthermore

In a preferred embodiment at least one of the compounds of formula F or its subformulae contains at least one ring

Particularly preferred compounds of formula F are selected from the group consisting of the following formulae:

in which R²¹, X°, L²¹ and L²² have the meaning given in formula F, L²⁵ and L²⁶ are each, independently of one another, FI or F, and X° is preferably F.

Very particularly preferred compounds of formula F1 -F3 are selected from the group consisting of the following subformulae:

35 in which R²¹ is as defined in formula F1 . Further preferred are compounds of formula F1 -F3 and F1 a-F3b wherein at least one of the fluorine-substituted benzene rings is additionally substituted by a methyl group in para-position to a fluorine atom. The proportion of the compounds of formula A and B in the LC host mixture is preferably from 2 to 60%, very preferably from 3 to 45%, most preferably from 4 to 35%.

The proportion of the compounds of formula C and D in the LC host mixture is preferably from 2 to 70%, very preferably from 5 to 65%, most preferably from 10 to 60%.

The proportion of the compounds of formula E in the LC host mixture is preferably from 5 to 50%, very preferably from 5 to 35%.

The proportion of the compounds of formula F in the LC host mixture is preferably from 2 to 30%, very preferably from 5 to 20%.

Further preferred embodiments of the present invention are listed below, including any combination thereof. a) The component A or LC host mixture comprises one or more

compounds of formula A and/or B with high positive dielectric anisotropy, preferably with De > 15. b) The component A or LC host mixture comprises one or more

compounds selected from the group consisting of formulae A1 a2 (CCQU), A1 b1 (ACQU), A1d1 (PUQU), A1fl (GUQU), A2a1 (APUQU), A2h1 (CDUQU), A2I1 (DUUQU), A2I2 (DGUQU), A2k1 (PGUQU), B2g2 (PGU), B2i1 (CPGU), B2h3 (CCGU), B2k1 (PPGU), B2I1 (DPGU), F1 a

(GUQGU). The proportion of these compounds in the LC host mixture is preferably from 4 to 40%, very preferably from 5 to 35%. c) The component A or LC host mixture comprises one or more

compounds selected from the group consisting of formulae C1 (CCH), C4 (PCH), C5 (CCP), C 7 (BCH), C9 (CBC) and D2 (PGP), preferably C1 a (CCH-nm), C4b (PCH-nOm), C5b (CCP-nOm), C7b (BCH-nOm), C9b (CBC-nmF), D2a (PGP-n-m) and D2b (PGP-n-mV). The proportion of these compounds in the LC host mixture is preferably from 5 to 60%, very preferably from 8 to 50%. d) The LC host mixture comprises one or more compounds selected from the group consisting of formulae E1 (CC-alkenyl), E3 (PP-alkenyl) and E6 (CCP-alkenyl), preferably E1 a (CC-n-Vm), E3a (PP-n-kVm) and E6a (CCP-Vn-m), very preferably E1 a2 (CC-3-V), E1a5 (CC-3-V1 ), E3a1 (PP-3-V), E3a3 (PP-1 -2V1 ) and E6a1 (CCP-V-1 ). The proportion of these compounds in the LC host mixture is preferably from 5 to 750%, very preferably from 10 to 65%.

Preferably the proportion of the LC component A) in the LC medium is from 95 to <100%, preferably from 95 to 97%, very preferably from 96 to 99%.

The LC component A), or LC host mixture, is preferably a nematic LC mixture.

The polymerizable mesogenic compounds of the polymerizable component B of the LC medium are preferably selected from formula I

R^a-B¹-(Z^b-B²)_m-R^b I in which the individual radicals, on each occurrence identically or differently, and each, independently of one another, have the following meaning:

R^a and R^b P, R-Sp-, H, F, Cl, Br, I, -CN, -N0₂, -NCO, -NCS, -OCN, -SCN,

SF5 or straight-chain or branched alkyl having 1 to 25 C atoms, in which, in addition, one or more non-adjacent CFI2 groups may each be replaced, independently of one another, by -C(R°)=C(R⁰⁰)-, -CºC-, -N(R⁰⁰)-, -0-, -S-, -CO-, -CO- O-, -O-CO-, -O-CO-O- in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more FI atoms may be replaced by F, Cl, Br, I, CN, P or R-Sp-, where, if B¹ and/or B² contain a saturated C atom, R^a and/or R^b may also denote a radical which is spiro-linked to this saturated C atom, wherein at least one of the radicals R^a and R^b denotes or contains a group P or P-Sp-,

P a polymerizable group,

Sp a spacer group or a single bond,

B¹ and B² an aromatic, heteroaromatic, alicyclic or heterocyclic group, preferably having 4 to 25 ring atoms, which may also contain fused rings, and which is unsubstituted, or mono- or polysubstituted by L,

Z^b -0-, -S-, -CO-, -CO-0-, -OCO-, -0-C0-0-, -OCH₂-, -CH₂O-,

-SCH2-, -CH2S-, -CF2O-, -OCF2-, -CF2S-, -SCF2-, -(CH₂)ni-, -CF2CH2-, -CH2CF2-, -(CF₂)ni-, -CH=CH-, -CF=CF-, -CºC-, -CH=CH-COO-, -OCO-CH=CH-, CR°R⁰⁰ or a single bond,

R° and R⁰⁰ each, independently of one another, denote FI or alkyl having 1 to

12 C atoms, m denotes 0, 1 , 2, 3 or 4, n1 denotes 1 , 2, 3 or 4,

L P, R-Sp-, OH, CH2OH, F, Cl, Br, I, -CN, -NO2, -NCO, -NCS, -

OCN, -SCN, -C(=0)N(R^x)₂, -C(=0)Y¹, -C(=0)R^x, -N(R^x)₂, optionally substituted silyl, optionally substituted aryl having 6 to

20 C atoms, or straight-chain or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxy- carbonyloxy having 1 to 25 C atoms, in which, in addition, one or more H atoms may be replaced by F, Cl, P or P-Sp-,

P and Sp have the meanings indicated above Y¹ denotes halogen,

R^x denotes P, R-Sp-, H, halogen, straight-chain, branched or cyclic alkyl having 1 to 25 C atoms, in which, in addition, one or more non-adjacent CFte groups may be replaced by -0-, -S-, -CO-, -CO-0-, -O-CO-, -O-CO-O- in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by F, Cl, P or R-Sp-, an optionally substituted aryl or aryloxy group having 6 to 40 C atoms, or an optionally substituted heteroaryl or hetero- aryloxy group having 2 to 40 C atoms.

Particularly preferred compounds of the formula I are those in which B¹ and B² each, independently of one another, denote 1 ,4-phenylene, 1 ,3- phenylene, naphthalene-1 ,4-diyl, naphthalene-2, 6-diyl, phenanthrene-2,7- diyl, 9,10-dihydro-phenanthrene-2,7-diyl, anthracene-2, 7-diyl, fluorene-2,7- diyl, coumarine, flavone, where, in addition, one or more CH groups in these groups may be replaced by N, cyclohexane-1 , 4-diyl, in which, in addition, one or more non-adjacent CFte groups may be replaced by O and/or S, 1 ,4- cyclohexenylene, bicycle[1 .1 .1 ]pentane-1 ,3-diyl, bicyclo[2.2.2]octane-1 ,4-diyl, spiro[3.3]heptane-2, 6-diyl, piperidine-1 ,4-diyl, decahydronaphthalene-2,6- diyl, 1 ,2,3, 4-tetrahydronaphthalene-2, 6-diyl, indane-2,5-diyl or octahydro-4,7- methanoindane-2,5-diyl, where all these groups may be unsubstituted or mono- or polysubstituted by L as defined above.

Particularly preferred compounds of the formula I are those in which B¹ and B² each, independently of one another, denote 1 ,4-phenylene, 1 ,3- phenylene, naphthalene-1 ,4-diyl or naphthalene-2, 6-diyl.

Very preferred compounds of formula I are selected from the following formulae:

in which the individual radicals, on each occurrence identically or differently, and each, independently of one another, have the following meaning: P¹, P², P³ a vinyloxy, acrylate, methacrylate, fluoroacrylate, chloro- acrylate, oxetane or epoxy group,

Sp¹, Sp², Sp³ a single bond or a spacer group where, in addition, one or more of the radicals P¹-Sp¹-, P¹-Sp²- and P³-Sp³- may denote R^aa, with the proviso that at least one of the radicals

P¹-Sp¹-, P²-Sp² and P³-Sp³- present is different from R^aa,

R^aa H, F, Cl, CN or straight-chain or branched alkyl having 1 to

25 C atoms, in which, in addition, one or more non-adjacent CFte groups may each be replaced, independently of one another, by -(R°)=C(R⁰⁰)-, -CºC-, -N(R°)-, -0-, -S-, -CO-, - CO-O-, -O-CO-, -O-CO-O- in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by F, Cl, CN or P¹-Sp¹-, particularly preferably straight-chain or branched, optionally mono- or polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12 C atoms (where the alkenyl and alkynyl radicals have at least two C atoms and the branched radicals have at least three C atoms),

R°, R⁰⁰ H or alkyl having 1 to 12 C atoms,

R^y and R^z H, F, CFb or CF3,

X¹, X², X³ -CO-O-, -O-CO- or a single bond, Z¹ -0-, -CO-, -C(R^yR^z)- or -CF2CF2-,

Z², Z³ -CO-O-, -O-CO-, -CH2O-, -OCH2-, -CF2O-, -OCF2- or -(CH₂)_n- , where n is 2, 3 or 4,

L F, Cl, CN or straight-chain or branched, optionally mono- or polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy hav- ing 1 to 12 C atoms,

L', L" H, F or Cl, r 0, 1 , 2, 3 or 4, s 0, 1 , 2 or 3,

0, 1 or 2,

0 or 1.

Very preferred are compounds of formulae M2, M10 and M13, especially direactive compounds containing exactly two polymerizable groups P¹ and P². Further preferred are compounds selected from formulae M15 to M31 , in particular from formulae M17, M18, M19, M22, M23, M24, M25, M26, M30 and M31 , especially trireactive compounds containing exactly three

polymerizable groups P¹, P² and/or P³.

In the compounds of formulae M1 to M31 the group

is preferably

wherein L on each occurrence, identically or differently, has one of the meanings given above or below, and is preferably F, Cl, CN, NO₂, CH3, C₂H₅, C(CH₃)₃, CH(CH₃)₂, CH₂CH(CH₃)C₂H5, OCHS, OC2H5, COCHs, COC2H5, COOCH₃, COOC₂H₅, CF₃, OCF_3J OCFIF₂, OC₂F₅ or R-Sp-, very preferably F, Cl, CN, CFI₃, C₂FI₅, OCFI₃, COCFI₃, OCF₃ or R-Sp-, more preferably F, Cl, CFI₃, OCFI₃, COCFI₃ Oder OCF₃ , especially F or CFI₃.

Preferred compounds of formulae M1 to M30 are those wherein P¹, P² and P³ denote an acrylate, methacrylate, oxetane or epoxy group, very preferably an acrylate or methacrylate group.

Further preferred compounds of formulae M1 to M31 are those wherein Sp¹, Sp² and Sp³ are a single bond.

Further preferred compounds of formulae M1 to M31 are those wherein one of Sp¹, Sp² and Sp³ is a single bond and another one of Sp¹, Sp² and Sp³ is different from a single bond.

Further preferred compounds of formulae M1 to M31 are those wherein those groups Sp¹, Sp² and Sp³ that are different from a single bond denote - (CFl₂)si-X"-, wherein s1 is an integer from 1 to 6, preferably 2, 3, 4 or 5, and X" is X" is the linkage to the benzene ring and is -0-, -O-CO-, -CO-O, -O-CO- O- or a single bond. Further preferred compounds of formula I are those selected from formulae RM-1 to RM-131 in Table D below, especially those selected from the group consisting of of formula RM-1 , RM-4, RM-8, RM-17, RM-19, RM-35, RM-37, RM-39, RM-40, RM-41 , RM-48, RM-51 , RM-52, RM-54, RM-57, RM-64, RM- 74, RM-76, RM-88, RM-91 , RM-102, RM-103, RM-109, RM-117, RM-120,

RM-121 and RM-122.

Particular preference is given to LC media comprising one, two or three polymerizable compounds of formula I.

Preference is further given to LC media in which the polymerizable

component B) consists exclusively of polymerizable compounds of formula I.

In another preferred embodiment component B) comprises, in addition or alternatively to the polymerizable compounds of formula I according to the preferred subformulae and subgroups as described above, one or more polymerizable mesogenic compounds which contain one or more

polymerizable groups and one or more polar anchor groups selected for example from hydroxy, carboxy, amino or thiol groups. These compounds can serve as self-aligning (SA) additives and are useful for SA mode displays according to the present invention. Suitable and preferred polymerizable mesogenic SA additives of this type are selected from compounds of formulae I or M1 to M31 wherein at least one group B¹, B², R^a, R^b, R^x, L, Sp, Sp¹, Sp², Sp³ or R^aa is substituted by a hydroxy, carboxy, amino or thiol group, preferably a hydroxy group. Further preferred polymerizable mesogenic SA additives of this type are selected from formula SA-9 to SA-34 in Table E.

Preferably the proportion of the polymerizable compounds of component B) in the LC medium is from 0.05 to <3%, more preferably from 0.1 to 2.8%, very preferably from 0.1 to 2.5%, most preferably from 0.2 to 2.2%. In another preferred embodiment the proportion of the polymerizable compounds of component B) in the LC medium is <1.7%, more preferably from 0.1 to 1.0%, very preferably from 0.1 to 0.8%, most preferably from 0.1 to 0.5%. In addition to the component A and B, the LC medium preferably contains a component C comprising one or more optically active compounds, preferably selected from chiral dopants. The helical twisting power and amount of the dopant in the LC medium are preferably selected such that the ratio d/p in the display according to the present invention is ³0.5, very preferably from 0.5 to 1.2, more preferably from 0.55 to 1.0, most preferably from 0.6 to 0.8. The proportion of the chiral dopants in the LC medium is preferably from 0.01 to 6%, very preferably from 0.05 to 3%, more preferably from 0.1 to 0.5%.

Suitable and preferred chiral dopants are mentioned below in Table B.

Preferred chiral dopants are for example selected from R- or S-1011 , R- or S- 2011 , R- or S-3011 , R- or S-4011 , or R- or S-5011.

Preferably the twist angle of the helical twist induced in the LC medium by the chiral dopants (before applying a voltage) is from 210° to 330°, more preferably from 240 to 300°, most preferably 270°.

Preferably the pitch of the helical twist induced in the LC medium by the chiral dopants is from 2 to 10 mΐti, very preferably from 3 to 6 mΐti.

Preferably the ratio d/p in a display according to the present invention is ³0.5, very preferably from 0.5 to 1.2, more preferably from 0.55 to 1.0, most preferably from 0.6 to 0.8.

In another preferred embodiment the LC medium contains one or more polymerization initiators.

Suitable conditions for the polymerization and suitable types and amounts of initiators are known to the person skilled in the art and are described in the literature. Suitable for free-radical polymerization are, for example, the commercially available photoinitiators Irgacure651®, Irgacure184®,

Irgacure907®, Irgacure369® or Darocurel 173® (Ciba AG). If a polymerization initiator is added to the LC medium, its proportion is preferably from 0.001 to 1 % by weight, particularly preferably from 0.001 to 0.5% by weight. In another preferred embodiment the LC medium does not contain a

polymerization initiator.

In another preferred embodiment the LC medium contains one or more stabilizers. The use of stabilizers can prevent undesired spontaneous polymerization of the RMs, for example during storage or transport.

Suitable types and amounts of stabilizers are known to the person skilled in the art and are described in the literature. The LC media according to the present invention may, for example, also comprise one or more UV stabilizers, for example from the Tinuvin^® series from Ciba Chemicals, such as Tinuvin^® 770, or from the Irganox® series, such as Irganox® 1076 (all from BASF). Further suitable and preferred stabilizers are those selected from Table C below.

If stabilizers are employed, their proportion, based on the total amount of RMs or the polymerizable component (component A), is preferably 10- 500,000 ppm, particularly preferably 50-50,000 ppm. The LC medium according to the invention may also comprise further additives for example selected from the list including but not limited to antioxidants, free- radical scavengers, defoaming agents, wetting agents, lubricating agents, dispersing agents, hydrophobing agents, adhesive agents, flow improvers, deaerators, diluents, reactive diluents, auxiliaries, colourants, dyes, pigments and nanoparticles.

Furthermore, it is possible to add to the LC media, for example, 0 to 15% by weight of pleochroic dyes, conductive salts, preferably ethyldimethyldodecyl- ammonium 4-hexoxybenzoate, tetrabutylammonium tetraphenylborate or complex salts of crown ethers (cf., for example, Haller et al ., Mol. Cryst. Liq. Cryst. 24, 249-258 (1973)), for improving the conductivity, or substances for modifying the dielectric anisotropy, the viscosity and/or the alignment of the nematic phases. Substances of this type are described, for example, in DE-A 22 09 127, 22 40 864, 23 21 632, 23 38 281 , 24 50 088, 26 37 430 and 28 53 728.

In a preferred embodiment the LC medium comprises, preferably consists of,

A) a liquid crystal component A comprising one or more compounds

selected from formula A and B or their subformulae as defined above, one or more compounds selected from formula C and D or their subformulae as defined above, and optionally one or more compounds of formula E or their subformulae as defined above,

B) a polymerizable component B comprising one or more polymerizable mesogenic compounds of formula I as defined above, preferably selected from formulae M1 -M31 , very preferably selected from Table D,

C) one or more chiral additives, preferably selected from chiral dopants, very preferably selected from Table B,

D) optionally one or more further additives, preferably selected from

polymerization initiators, stabilizers, which are very preferably selected from Table C, and self-aligning additives, which are very preferably selected from Table E,

wherein the concentration of the polymerizable mesogenic compounds in the

LC medium is from 0.05 to <3%, and

wherein the concentration of the chiral additives is selected such that twist angle they induce in the LC medium is >210°, preferably from 210 to 330°, more preferably from 240 to 300°, very preferably 270°.

In another preferred embodiment the LC medium comprises, preferably consists of

A) a liquid crystal component A comprising one or more compounds

D) optionally one or more further additives, preferably selected from

wherein the concentration of the polymerizable mesogenic compounds in the

LC medium is from 0.05 to <3%, and

wherein the concentration of the chiral additives is selected such that the helical pitch they induce in the LC medium is from 2 to 10 mΐti, very preferably from 3 to 6 mΐti.

In another preferred embodiment the LC medium comprises one or more compounds selected from the following groups or any combination thereof:

1 ) One or more compounds selected from the group consisting of formula A2a1 , A2k1 , B2k1. These compounds can increase the dielectric anisotropy, the optical anisotropy and the operating temperature.

2) One or more compounds selected from the group consisting of formula A1d1. These compounds can increase the dielectric anisotropy and the optical anisotropy but decrease the operating temperature.

3) One or more compounds selected from the group consisting of formula A1 a2. These compounds can increase the dielectric anisotropy but decrease the operating temperature. 4) One or more compounds selected from the group consisting of formula C1 a, C1 b, E1 a. These compounds can decrease the viscosity and adjust the optical anisotropy but decrease the operating temperature.

5) One or more compounds selected from the group consisting of formula C4b. These compounds can decrease the viscosity but decrease the operating temperature.

6) One or more compounds selected from the group consisting of formula C7a, D2, E6. These compounds can decrease the dielectric anisotropy and the operating temperature.

7) One or more chiral dopants, preferably selected from Table B, very preferably from formulae R/S-1011 , R/S-2011 , R/S-3011 , R/S-4011 and R/S- 5011. These compounds induce a helically twisted structure and a twist angle in the layer with the LC molecules.

8) One or more reactive mesogens, preferably selected of formula I, very preferably from formulae M1 to M31 , more preferably from formulae RM-1 to RM-131 of Table D, most preferably from the group consisting of formulae RM-1 , RM-4, RM-8, RM-17, RM-19, RM-35, RM-37, RM-39, RM-40, RM-41 , RM-48, RM-51 , RM-52, RM-54, RM-57, RM-64, RM-74, RM-76, RM-88, RM- 91 , RM-102, RM-103, RM-109, RM-117, RM-120, RM-121 and RM-122. These compounds provide polymer stabilization that reduces the twist angle.

9) One or more stabilizers, preferably selected from Table C, very preferably from the following formulae

wherein n is 1 , 2, 3, 4, 5, 6 or 7, preferably 3,

10) One or more photoinitiators. These compounds initiate polymerization of the polymerizable compounds of component B and group 8 above.

11 ) One or more self-aligning additives. These compounds enable to omit the alignment layer.

12) One or more additives selected from antioxidants, UV absorbers, coloring materials, antifoaming agents.

The individual components of the preferred embodiments of the LC media according to the invention are either known or methods for the preparation thereof can readily be derived from the prior art by the person skilled in the relevant art, since they are based on standard methods described in the literature.

It goes without saying to the person skilled in the art that the LC media according to the invention may also comprise compounds in which, for example, H, N, O, Cl, F have been replaced by the corresponding isotopes like deuterium etc.

The LC media which can be used in accordance with the invention are prepared in a manner conventional per se, for example by mixing one or more LC compounds selected from formulae A to F or one or more corn- pounds of the above-mentioned preferred embodiments with each other and/or with further LC compounds and/or additives, like polymerizable compounds or RMs. In general, the desired amount of the components used in the smaller 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 ace- tone, chloroform or methanol, and to remove the solvent again, for example by distillation, after thorough mixing.

It goes without saying that, through a suitable choice of the components of the LC mixtures according to the invention, it is also possible for higher clearing points (for example above 100°C) to be achieved at higher threshold voltages or lower clearing points to be achieved at lower threshold voltages with retention of the other advantageous properties. At viscosities correspondingly increased only slightly, it is likewise possible to obtain mixtures having higher De and thus low thresholds. The MLC displays ac- cording to the invention preferably operate at the first Gooch and Tarry trans- mission minimum [C.H. Gooch and H.A. Tarry, Electron. Lett. 10, 2-4, 1974; C.H. Gooch and H.A. Tarry, Appl. Phys., Vol. 8, 1575-1584, 1975], where, besides particularly favourable electro-optical properties, such as, for example, high steepness of the characteristic line and low angle depend- ence of the contrast (German patent 30 22 818), lower dielectric anisotropy is sufficient at the same threshold voltage as in an analogous display at the second minimum. This enables significantly higher specific resistance values to be achieved using the mixtures according to the invention at the first minimum than in the case of mixtures comprising cyano compounds.

Through a suitable choice of the individual components and their proportions by weight, the person skilled in the art is able to set the birefringence neces- sary for a pre-specified layer thickness of the MLC display using simple routine methods. The LC media and LC host mixtures of the present invention preferably have a nematic phase range > 80 K, very preferably > 100 K, and preferably a rotational viscosity < 250 mPa s, very preferably < 200 mPa s, at 20°C.

The birefringence Dh of LC media and LC host mixtures according to the invention is preferably preferably from 0.07 to 0.15, particularly preferably from 0.08 to 0.15 at 20°C. The LC medium and LC host mixture have a positive dielectric anisotropy De. Preferably the LC medium and and the LC host mixture have a positive dielectric anisotropy De from +2 to +30, particularly preferably from +3 to +20, at 20°C and 1 kHz. The structure of the PS-UF TN-LC displays according to the present invention corresponds to the usual geometry for TN displays as described in the prior art cited at the outset.

The construction of the PS-UF TN-LC display according to the invention from polarisers, electrode base plates and surface-treated electrodes corresponds to the usual design for displays of this type. The term usual design is broadly drawn here and also encompasses all derivatives and modifications of the LC display, in particular including matrix display elements based on poly-Si TFTs or MIM.

A preferred PS-UF TN-LC display of the present invention comprises:

a first substrate including a pixel electrode defining pixel areas, the pixel electrode being connected to a switching element disposed in each pixel area, and optionally a first alignment layer disposed on the pixel electrode,

a second substrate including a common electrode layer, which may be disposed on the entire portion of the second substrate facing the first substrate, and optionally a second alignment layer,

- a layer of a nematic LC medium having positive dielectric anisotropy, which is dispensed between the first and second substrates and comprises a liquid crystal component A comprising, preferably consisting of, one or more mesogenic or liquid-crystalline molecules, and further comprises a component C comprising one or more chiral additives, and optionally comprises a component D comprising one or more further additives,

a polymer layer deposited on each of said first and second electrode or, if present, on each of said first and second alignment layer, wherein the polymer layers are formed from one or more polymerizable mesogenic compounds which are present in the LC medium at a concentration from 0.1 to <3%, and which are polymerized in situ after the LC medium has been dispensed between the two substrates,

optionally a first polarizer on the side of the first substrate facing away from the LC layer, and a second polarizer on the side of the second substrate facing away from the LC layer, said polarizers preferably being oriented such that their transmission planes for plane-polarized light are at right angles (crossed nicols).

Fig. 1 exemplarily and schematically illustrates the structure of a preferred PS-UF TN-LC display according to the present invention in the off-state or non-addressed state, i.e. without a voltage applied to the electrodes. The display (100) comprises a first substrate (110) and a second substrate (150), each being equipped with ITO electrodes (115, 155) and optional alignment layers (120, 160), preferably being both unidirectionally rubbed and arranged such their rubbing directions are at right angles, an LC medium (140) located between the two substrates wherein the LC molecules are aligned parallel or tilted relative to the substrates and helically twisted along an axis

perpendicular to the substrates, and polymer layers (130, 170) which are formed on the alignment layers (120, 160) by polymerization of the

polymerizable mesogenic compounds contained in the LC medium. The display further contains two polarizers (180, 190) sandwiching the display and being arranged so that their transmission planes for plane-polarized light are at 90° relative to each other (crossed nicols). The invention also relates to a method of manufacturing a liquid crystal display (LCD) of the polymer-stabilized twisted-nematic (PS-TN) mode comprising the steps of

wherein the LC medium comprises, preferably consists of,

A) a liquid crystal component (hereinafter also referred to as "LC host mix- ture") comprising, preferably consisting of, mesogenic or liquid- crystalline molecules,

C) one or more chiral additives, preferably selected from chiral dopants,

D) optionally one or more further additives, preferably selected from polymerization initiators, stabilizers and self-aligning additives, wherein the ratio of the polymerizable mesogenic compounds in the LC medium is <3%, preferably from 0.05 to <3%, and

wherein the longitudinal axes of the LC molecules are oriented parallel or tilted relative to the planes of the substrates, and the chiral additive induces in the LC molecules of the LC medium a helical twist along an axis perpendicular to the substrates with a given pitch p, and, wherein layer of the LC medium has a thickness d, and the ratio d/p is ³0.5, preferably >0.5, very preferably from 0.6 to 0.8, and

wherein the twist angle of the helical twist of the LC molecules induced by the chiral additive is >210°, preferably in the range from 210 to 330°, more preferably from 240 to 300°, very preferably 270°,

c) applying a voltage to the first and second electrodes such that the twist angle of the helical twist of the LC molecules is reduced to <150°, preferably to a range from 60 to 120°, preferably from 80 to 100°, very preferably to 90°,

d) after applying the voltage or while applying the voltage, polymerizing the polymerizable mesogenic compounds of the polymerizable component B of the LC medium between the first and second substrate, preferably by exposure to UV radiation, thereby stabilizing the twisted nematic configuration of the LC medium with the reduced twist angle of step c), and

e) optionally subjecting the LC medium to a second polymerization step, preferably by exposure to UV radiation, without applying a voltage to the first and second electrodes, thereby polymerizing any polymerizable compounds which have not reacted in step d),

f) optionally providing a first polarizer on the side of the first substrate facing away from the LC layer, and a second polarizer on the side of the second substrate facing away from the LC layer, wherein said polarizers are preferably oriented such that their transmission planes for plane-polarized light are at right angles (crossed nicols).

The substrates used in the display according to the present invention and in step a) of its manufacturing process are preferably glass substrates. For flexible LC displays preferably plastic substrates are used. These plastic substrates preferably have a low birefringence. Examples of suitable and preferred plastic substrates are polycarbonate (PC), polyethersulfone (PES), polycyclic olefine (PCO), polyarylate (PAR), polyetheretherketone (PEEK), or colourless polyimide (CPI) substrates. At least one substrate should be transmissive for the photoradiation used for polymerizing the polymerizable compounds used in the process according to the present invention. In case the substrates are equipped with alignment layers that are prepared by photopolymerization and/or photoalignment, at least one substrate should be transmissive for the photoradiation used for photopolymerization or

photoalignment of the alignment layer material or its precursor. The electrode layers can be designed by the skilled person depending on the individual display type. In the LC display according to the present invention the first and second substrate are each equipped with an electrode layer.

Further preferably, one of the first and second electrode layers is a pixel electrode defining pixel areas, the pixel electrode being connected to a switching element disposed in each pixel area and optionally including a micro-slit pattern, and the other of the first and second electrode layers is a common electrode layer, which may be disposed on the entire portion of the substrate facing the other substrate.

The first and/or second substrate may carry further layers or components including but not limited to a colour filter, TFT arrays, a black matrix, a polyimide coating, or other components typically found on a display

substrate.

Preferably at least one of the first and second substrates, more preferably each substrate, is equipped with an alignment layer which is usually applied on the electrodes such that it contacts the LC medium. The first and/or second alignment layer controls the alignment direction of the LC molecules of the LC layer. In the display according to the present invention the alignment layers are selected such that they impart to the LC molecules an orientation direction parallel or slightly tilted relative to the substrate. A suitable and preferred alignment layer comprises or consist of, for example, a polyimide, which may also be rubbed or prepared by a

photoalignment method. Solution processable alignment layer materials are preferred. These are preferably processed from solution in a solvent, preferably an organic solvent, like for example N-methylpyrrolidone, 2- butoxyethanol or y-butyrolactone.

In a preferred embodiment the alignment layer is formed by depositing a solution of an alignment layer material like for example polyimide, or a precursor thereof like for example a polyimide precursor, on the substrate, and optionally curing the alignment layer material or its precursor by exposure to heat and/or actinic radiation, for example UV radiation.

The alignment layer material, or precusor thereof, can be deposited on the substrate for example by coating or printing methods.

In case a solvent is used for deposition of the alignment layer material, it is preferably dried off or evaporated off after deposition. Solvent evaporation can be supported for example by applying heat and/or reduced pressure.

Preferred methods for curing the alignment layer are thermal curing and photocuring, very preferably photocuring. Photocuring is for example carried out by exposure to UV radiation. Suitable curing conditions can be selected by the skilled person depending on the precusor material used, based on his common knowledge and as described in the literature. In case of commercially available materials suitable processing and/or curing conditions are often provided together with the sales or sampling of the material.

In the display according to the present invention the alignment layers are preferably selected such that they impart to the LC molecules planar (or parallel) alignment, i.e. wherein the longitudinal axis of the LC molecules is parallel to the surface of the nearest substrate, and wherein the longitudinal axis of the LC molecules may also be slightly tilted relative to the surface of the substrate. Preferably the tilt angle of the longitudinal axis of the LC molecules located in proximity to the surface of a substrate relative to said substrate is from >0° to 20°, preferably from 0.1 ° to 20°, very preferably from 0.2° to 3.5°. In order to impart a preferred two-dimensional alignment direction of the LC molecules within the plane of the substrate, the alignment layers for example comprise an alignment layer material, for example a polyimide, which is unidirectionally rubbed or is prepared by a photoalignment method. Preferably the alignment direction, or the average orientation direction of the longitudinal axes of the LC molecules (also referred to as "director") in vicinity to the first and second substrates, are at right angles, i.e. at an angle of 90° relative to each other. Further preferably the alignment direction or LC director in vicinity to the first and second substrates is at an angle of 45° relative to the edges of the substrates.

This can be achieved for example by using a first and second alignment layer, for example comprising polyimide, which are both unidirectionally rubbed and which are arranged such that their rubbing directions are at right angles, and wherein the rubbing direction of the alignment layer corresponds to the alignment direction of the LC molecules. Alternatively this can be achieved by preparing the alignment layers by photoalignment using linearly polarized light, wherein the polarization direction of the polarized light corresponds to the alignment direction of the LC molecules.

The display according to the present invention preferably comprises a first and second alignment layer, preferably comprising polyimide, which are both unidirectionally rubbed and wherein the rubbing directions are at right angles to each other.

The display according to the present invention may comprise further elements, like a colour filter, a black matrix, a passivation layer, optical retardation layers, transistor elements for addressing the individual pixels, etc., all of which are well known to the person skilled in the art and can be employed without inventive skill. In step b) a layer of a nematic LC medium having positive dielectric anisotropy, and containing components A, B, C and optionally D as described above and below, is dispensed between the first and the second substrate, such that the LC medium is in contact with the first and second alignment layer in case such an alignment layer is present.

The LC medium can be dispensed or filled onto the substrates or into the display, respectively, by methods that are conventionally used by display manufacturers.

Preferably the LC medium is deposited onto the substrate by using one of the following deposition methods: one drop filling (ODF), ink jet printing, spin coating, slit coating, flexo printing, or a comparable method. A preferred method is ink jet printing.

Another preferred method is ODF method, preferably comprising the following steps b1 ) dispensing a droplet or an array of droplets of the LC medium on the first substrate, and b2) providing the second substrate on top of the first substrate with the dispensed droplets of the LC medium, preferably under vacuum conditions, causing the droplets of the LC medium to spread and form a continuous layer between the two substrates.

The applied LC medium forms a thin, uniform film with the thickness of the targeted final cell gap of the display.

Preferably the display according to the present invention comprises a fixing means, fixing the first and second substrate at a constant distance relative to each other and with their planes parallel to each other. Preferably the fixing means comprises a sealant material and a spacer material, in order to maintain a constant cell gap and LC layer thickness. Preferably the first and second substrate are fixed or glued together by the fixing means, for example a sealant material, that is provided on the substrates, preferably in the region close to the edges of the substrates. Preferably the sealant material is deposited onto the first substrate, or between the first and the second substrate, before the LC medium is dispensed between the first and the second substrate.

The sealant material is provided on the first substrate, or between the first and the second substrate, preferably in the region between the LC medium and the edges of the respective substrate. The sealant material is for example a crosslinked polymer which is formed from a curable polymer precursor. The sealant material is then cured, preferably after the first and second substrates are assembled to form an LC cell, but before

photopolymerization of the polymerizable compounds contained in the LC medium. Preferably said sealant material is cured by exposure to heat and/or photoradiation.

The spacer material for example consists of transparent glass or plastic beads. In a preferred embodiment the spacer is dispensed between the substrates together with the LC medium.

In another preferred embodiment, in order to maintain a constant cell gap and LC layer thickness, the display contains a spacer material, for example a photospacer, outside the LC layer, for example above the black matrix, and the LC layer does not contain a spacer material.

Suitable sealants and spacers are known to the skilled person and are commercially available.

In step c) a voltage is applied to the first and second electrodes such that the twist angle of the helical twist of the LC molecules in the LC layer is reduced from the range of 210 to 330°, preferably from 240 to 300°, very preferably 270°, as given by the LC layer thickness and the natural helical twist induced by the chiral dopant, to a range from 60 to 120°, preferably from 80 to 100°, very preferably to 90°. Suitable ways, conditions, parameters and driving schemes for applying a voltage to achieve the desired twist angle, which is then polymer stabilized, are well known to the person skilled in the art or described in the literature, for example in K. Takatoh et al., Liq. Cryst. 2012, 39(6), 715-720, and can be employed without inventive skill.

The selection of suitable voltages and driving schemes for applying a voltage also depends on the physical properties of the LC medium and the

collocation between the LC medium and the alignment layer.

In a preferred embodiment the applied voltage and driving scheme are selected such that the TN orientation with reduced twist angle as described above is stable for a given period of time, for example several (>1 ) seconds, several (>1 ) minutes or several (>1 ) hours. This allows to carry out polymerization step d) after step c), i.e. without any overlap in time.

Suitable and preferred driving schemes for applying a voltage in step c) are exemplarily depicted in Fig. 2a, 2b and 2c.

For example, suitable and preferred driving schemes for applying a voltage in step c) include, without limitation:

applying a square wave from +20V to -20V, with a frequency of 50 to 100 Hz, ^or

applying a square wave with a pulse height from 0V to +20V, with a pulse width from 50 to 150 ms, preferably 100ms, and a cycle length of 2 to 8s, preferably 5s for one pulse (see Fig. 2a),

or

applying a square wave with a pulse height from +20V to -20V, wherein each pulse contains one positive and one negative sub-pulse, with a pulse width from 50 to 150 ms, preferably 100ms, a cycle length of 5 to 15s, preferably 10s for one pulse, and a subcycle length from 2 to 8s, preferably 5s, for one sub-pulse (see Fig. 2b)

or applying a square wave with a pulse height from OV to +30V, with a pulse width of the first pulse from 1 to 10s, preferably 5s, and a pulse width of second and further pulses from 50 to 150 ms, preferably 100ms, and a pause between the pulses of 10 to 40s, preferably 30s (see Fig. 2c).

In step d) the polymerizable compounds of the polymerizable component B contained in the LC medium are then polymerized, or crosslinked (if a compound contains two or more polymerizable groups) by in-situ

polymerization in the LC medium between the substrates of the LC display, optionally while a voltage is applied to the electrodes for at least a part of the time of the polymerization process. In optional step e) the polymerizable compounds which have not completely reacted in step d) are polymerized or crosslinked by in-situ polymerization without applying a voltage. In step d) and e) the polymerizable compounds of the polymerizable component B are preferably polymerized by photopolymerization, very preferably by UV photopolymerization.

Upon polymerization the polymerizable compounds form a polymer or crosslinked polymer, which stabilizes the reduced twist angle of the LC molecules in the LC medium. Without wishing to be bound to a specific theory, it is believed that a significant part of the polymer which is obtained from the polymerizable compounds will phase-separate or precipitate from the LC medium and form a polymer layer on the substrates or electrodes, or the alignment layer provided thereon. Microscopic measurement data (like SEM and AFM) have confirmed that the polymer mainly accumulates at the LC layer/substrate interface.

Suitable and preferred polymerization methods are, for example, thermal or photopolymerization, preferably photopolymerization, in particular UV induced photopolymerization, which can be achieved by exposure of the polymerizable compounds to UV radiation.

The polymerization can be carried out in one step (step d) or in two or more steps (steps d and e or repetitions thereof) as described above and below. Step d) is hereinafter also referred to as "UV1 " step and step e) is hereinafter also referred to as "UV2" step.

In a preferred embodiment of the present invention the process for preparing the display comprises one or more of the following features:

- the polymerizable LC medium is exposed to UV light in a two-step process, including a first UV exposure step (step d or UV1 ) while or after, preferably after, applying a voltage to the electrodes, and further including a second UV exposure step (step e or UV2) to finish polymerization without applying a voltage to the electrodes,

- the polymerizable LC medium is exposed, preferably in the UV2 step, and optionally also in the UV1 step, to UV light generated by a UV lamp in the wavelength range from 300-380nm, preferably with an intensity of from 0.5 mW/cm² to 30 mW/cm², more preferably from 1 to 20 mW/cm²,

- the polymerizable LC medium is exposed to UV light having a wavelength of 340 nm or more, and preferably 400 nm or less.

The process of this preferred embodiment can be carried out for example by using the desired UV lamps or by using a band pass filter and/or a cut-off filter, which are substantially transmissive for UV light with the respective desired wavelength(s) and are substantially blocking light with the respective undesired wavelengths. For example, when irradiation with UV light of wavelengths l of 300-400nm is desired, UV exposure can be carried out using a wide band pass filter being substantially transmissive for wavelengths 300nm < l < 400nm. When irradiation with UV light of wavelength l of more than 365 nm is desired, UV exposure can be carried out using a cut-off filter being substantially transmissive for wavelengths l > 365 nm. "Substantially transmissive" means that the filter transmits a substantial part, preferably at least 50% of the intensity, of incident light of the desired wavelength(s). "Substantially blocking" means that the filter does not transmit a substantial part, preferably at least 50% of the intensity, of incident light of the undesired wavelengths. "Desired (undesired) wavelength" e.g. in case of a band pass filter means the wavelengths inside (outside) the given range of l, and in case of a cut-off filter means the wavelengths above (below) the given value of l.

The process of this preferred embodiment enables the manufacture of displays by using longer UV wavelengths, thereby reducing or even avoiding the hazardous and damaging effects of short UV light components.

The polymer obtained by polymerization of the polymerizable compounds of component B of the LC medium preferably forms a layer on one or both of the substrates, or on one or both of the alignment layers or electrode structures deposited thereon.

Preferably the polymerizable compounds of the polymerizable component B are polymerized while the voltage is applied at least during a part of the polymerization process, preferably during step UV1 as described above, in order to stabilize the reduced twist. However, it is also possible to achieve the desired orientation with reduced twist by carrying out polymerization, preferably the UV1 process step, after applying a voltage in step c). Thus, in a preferred embodiment of the present invention step d) (UV1 ) of polymerizing the polymerizable compounds of the polymerizable component B is carried out either simultaneously with step c) of applying a voltage, or step d) is carried out such that it overlaps at least partially with step c). In another preferred embodiment of the present invention step d) (UV1 ) of polymerizing the polymerizable compounds of the polymerizable component B is carried after step c) of applying a voltage.

In a preferred embodiment the display according to the present invention does not contain a polyimide alignment layer. In another preferred embodiment the display according to the present invention contains a polyimide alignment layer on one or both of the substrates.

In another preferred embodiment the LC medium according to the present invention contains a self-aligning (SA) additive, preferably in a concentration of 0.1 to 2.5 %. An LC medium according to this preferred embodiment is especially suitable for use in polymer stabilized SA (PS-SA) displays.

Preferred SA additives for use in this preferred embodiment are selected from compounds comprising a mesogenic group and a straight-chain or branched alkyl side chain that is terminated with one or more polar anchor groups selected from hydroxy, carboxy, amino or thiol groups.

Further preferred SA additives contain one or more polymerizable groups which are attached, optionally via spacer groups, to the mesogenic group. These polymerizable SA additives can be polymerized in the LC medium under similar conditions as applied for the polymerizable compounds of polymerizable component B. In another preferred embodiment an LC medium or a polymer stabilized SA- VA or SA-FFS display according to the present invention contains one or more self-aligning additives selected from Table E below.

Above and below, any SA additives comprised in the LC medium which contain a mesogenic group and one or more polymerizable groups, like those of formula SA-9 to SA-34 in Table E, are understood to be part of the polymerizable component B. The preferred compositions and concentration ranges given above and below for polymerizable component B and its ingredients are thus understood to include both RMs which are not SA additives, and RMs which are SA additives and contain one or more polar anchor groups selected for example from hydroxy, carboxy, amino or thiol groups.

The following examples are intended to explain the invention without limiting it. Above and below, percentage data denote per cent by weight; all temperatures are indicated in degrees Celsius.

Table A In Table A, m and n are independently of each other an integer from 1 to 12, preferably 1 , 2, 3, 4, 5 or 6, k is 0, 1 , 2, 3, 4, 5 or 6, and (0)C_mH_{2 m+i} means Cm H2m+1 or OC mH2m₊₁

CBC-nmF

CCH-n-Om, CC-n-Om CCH-n-m, CC-n-m GPQU-n-F GUQGU-n-F

Particular preference is given to liquid-crystalline mixtures which comprise at least one, two, three, four or more compounds from Table A.

Table B indicates possible dopants which are generally added to the mixtures according to the invention. The mixtures preferably comprise 0-10% by weight, in particular 0.001-5% by weight and particularly preferably 0.001 -3% by weight, of dopants.

Table B

C 15 CB 15

R/S-1011 Table C

Stabilizers which can be added, for example, to the mixtures according to the invention in amounts of 0-10% by weight are mentioned below.

35



35 Table D Table D shows illustrative reactive mesogenic compounds which can be used in the LC media in accordance with the present invention.

-IIS-

RM-82

RM-83

RM-84

RM-85

RM-86

RM-87

RM-88

RM-89 RM-90

RM-91

RM-92

RM-93

RM-94 RM-95

RM-96

RM-97

RM-98

RM-99

RM-100

RM-105

RM-106

RM-107

RM-108

In a preferred embodiment, the mixtures according to the invention comprise one or more polymerizable compounds, preferably selected from the polymerizable compounds of the formulae RM-1 to RM-140. Of these, compounds RM-1 , RM-4, RM-8, RM-17, RM-19, RM-35, RM-37, RM-39, RM- 40, RM-41 , RM-48, RM-51 , RM-52, RM-54, RM-57, RM-64, RM-74, RM-76, RM-88, RM-91 RM-102, RM-103, RM-109, RM-1 17, RM-120, RM-121 and RM-122 are particularly preferred.

Table E

Table E shows self-alignment additives for vertical alignment which can be used in LC media for SA-VA and SA-FFS displays according to the present invention together with the polymerizable compounds of formula I:

134

In a preferred embodiment, the LC media, SA-VA and SA-FFS displays

according to the present invention comprise one or more SA additives

selected from formulae SA-1 to SA-34.

Examples The following examples explain the present invention without restricting it.

Flowever, they show the person skilled in the art preferred mixture concepts with compounds preferably to be employed and the respective con- centrations thereof and combinations thereof with one another. In addition, the examples illustrate which properties and property combinations are

accessible.

In addition, the following abbreviations and symbols are used: toff, td, Toff switch-off or decay time [ms] at 20°C

ton, tr, Ton switch-on or rise time [ms] at 20°C

d cell gap or LC thickness of the switchable LC layer [mΐti]

Vo, V_th threshold voltage, capacitive [V] at 20°C,

Vop operating voltage [V]

n_e extraordinary refractive index at 20°C and 589 nm,

n₀ ordinary refractive index at 20°C and 589 nm,

Dh optical anisotropy at 20°C and 589 nm,

e± dielectric permittivity perpendicular to the director at 20°C and 1 kHz,

S 1 1 dielectric permittivity parallel to the director at 20°C and 1 kHz,

De dielectric anisotropy at 20°C and 1 kHz,

cl.p., T(N,l) clearing point [°C],

yi rotational viscosity at 20°C [nnPa-s], Ki elastic constant, "splay" deformation at 20°C [pN],

K₂ elastic constant, "twist" deformation at 20°C [pN],

K₃ elastic constant, "bend" deformation at 20°C [pN]

Unless explicitly noted otherwise, all parameters and values as given above and below refer to a temperature of 20°C.

Unless explicitly noted otherwise, all concentrations and proportions in the present application are quoted in per cent by weight and relate to the corresponding mixture as a whole, comprising all solid or liquid-crystalline components, without solvents.

Unless explicitly noted otherwise, all temperature values indicated in the present application, such as, for example, for the melting point T(C,N), the transition from the smectic (S) to the nematic (N) phase T(S,N) and the clearing point T(N,I), are quoted in degrees Celsius (°C). M.p. denotes melting point, cl.p. = clearing point. Furthermore, C = crystalline state, N = nematic phase, S = smectic phase and I = isotropic phase. The data between these symbols represent the transition temperatures.

All physical properties are and have been determined in accordance with "Merck Liquid Crystals, Physical Properties of Liquid Crystals", Status Nov. 1997, Merck KGaA, Germany, and apply for a temperature of 20°C, and Dh is determined at 589 nm and De at 1 kHz, unless explicitly indicated otherwise in each case.

The term "threshold voltage (Vt_h, Vo)" for the present invention relates to the capacitive threshold (Vo), also known as the Freedericks threshold, unless explicitly indicated otherwise. In the examples, the optical threshold may also, as generally usual, be quoted for 10% relative contrast (V₁₀).

The term "operating voltage (V_op)" for the present invention relates to the voltage given by 2xVio and then choosing the next larger multiple of 0.5 V.

For example when V₁₀ = 4.8 V then V_op = 10 V, when V₁₀ = 5.2 V then V_op =

10.5 V, when V₁₀ = 5.6 V then V_op = 1 1 .5 V. Unless stated otherwise, the process of polymerizing the polymerizable compounds in the polymer stabilized displays as described above and below is carried out at a temperature where the LC medium exhibits a liquid crystal phase, preferably a nematic phase, and most preferably is carried out at room temperature (also abbreviated as "RT").

Unless stated otherwise, methods of preparing test cells and measuring their electrooptical and other properties are carried out by the methods as described hereinafter or in analogy thereto.

Example 1

The nematic LC host mixture N1 is formulated as follows:

CC-3-V 48.00% cl.p. + 76.2 °C

CC-3-V1 3.00% Dh 0.1404 (20°C)

PGP-2-3 10.00% De 2.9 (20°C)

PGP-2-4 10.00% eii/e± 5.73/2.88 (20°C)

PGP-2-2V 13.00% K3/K1 12.4/14.9 (20°C)

PGUQU-3-F 1.50% gi 52 mPa s (20°C)

PPGU-3-F 1.50% Vo 7.5 V

PGU-2-F 9.00%

CPGU-3-OT 2.00%

PP-1 -2V1 2.00%

Mixture A1 is prepared by adding to the LC host mixture N1 2.75% of the chiral dopant S-4011. The pitch of the mixture induced by the chiral dopant is 5 microns. Mixture B1 is prepared by adding to the LC host mixture N1 0.39% of the chiral dopant S-4011. The pitch of the mixture induced by the chiral dopant is 35 microns.

Mixture PS-A1 is prepared by adding to the Mixture A1 1.5 % of RM-51 , 0.5% of RM-1 , and 1 %, relative to the total concentration of RMs, of lrgacure®651. The pitch of the mixture induced by the chiral dopant is 5 microns.

TN test cell manufacture

TN test cells are prepared comprising two substrates of polished SL glass (Corning, thickness 1 .1 mm), which are equipped with ITO electrode layers (thickness 200 A, 10 Ohms/sq, 1 cm x 1 cm), rubbed polyimide alignment layers (JSR AL3046) with rubbing directions at 0° and 90° respectively, spacers to achieve a cell gap of 3.14 microns, and a sealant (XN-1500 from Mitsubishi Chemicals).

Each of mixtures N1 , B1 and PS-A1 is filled into a test cell.

PS-TN test cell manufacture The test cell with mixture PS-A1 is subjected to a two-step UV curing process, wherein in the first step a voltage is applied to the electrodes and in the second UV step no voltage is applied.

UV step 1 (UV1 ):

Fe/I lamp with 365nm filter, UV intensity 4.0 mW/cm ² with UV power detector Ushio UIT-250, UVD-S365; electric field (see Fig. 2a): pulse 5 s / period, pulse height 18 V, pulse width 100 ms. Irradiation time 300 s.

UV step 2 (UV2): Toshiba C type fluorescent lamp, green UV without 365 nm filter, UV intensity 0.5 mW/cm² with UV power detector Ushio UIT-250, UVD-S365, irradiation time 60 min. Twist Angle

The twist angle is measured with and AxoStep-Mueller Matrix Imaging Polarimeter (Brand: Axometrics) In the test cell with chirally doped mixture B1 the twist angle is measured to be -90.5°, which corresponds to an TN configuration, as expected from the low d/p value of 0.09.

In the test cell with chirally doped, polymer stabilized mixture PS-A1 the twist angle is measured to be -90.8°, which also corresponds to a TN

configuration, but is significantly lower than expected from the high d/p value of 0.62. This can be explained by the polymerization of the RMs under applied voltage which stabilizes the unusually low twist angle. This demonstrates that by applying the process according to the present invention it is possible to manufacture a polymer stabilized TN mode display with a high d/p value but a low twist angle.

E/O Performance, Response Times

The electrooptical performance (transmission vs. voltage) and response times of the test cells are measured with an LCD evaluation system (LCD- 5200, Otsuka electronics Co., Ltd). In addition, the response times are calculated for the individual mixtures by using the following equations wherein x_0ff is the decay time, gi is the rotational viscosity, d is the cell gap, p is the helical pitch, and K , K22 and K33 are the elastic constants for splay, twist and bend deformation, respectively.

Fig. 3 shows the e/o curves of the test cells with host mixture N1 (a), chirally doped mixture B1 (b) and chirally doped, polymer stabilized mixture PS-A1 (c). It can be seen that in the test cell with mixture PS-A1 the V/T curve is shifted to higher voltages due to the short pitch and polymer stabilization as expected, because a higher voltage is needed to overcome the orientation force of the surface polymer, compared to the test cell with undoped host mixture N1 and the test cell with mixture B1 having a lower d/p value. It can also be seen that the polymer stabilized mixture PS-A1 maintains a high transmittance and contrast ratio, which is an advantage compared to PS-TN displays as reported in prior art.

Fig. 4a-c show the e/o curves measured at 0°C, 10°C, 25°C, 35°C and 50°C (from right to left), respectively, for the test cells with undoped host mixture N1 (Fig. 4a), chirally doped mixture B1 (Fig. 4b) and polymer stabilized, chirally doped mixture PS-A1 (Fig. 4c), respectively. It can be seen that the e/o curves are shifted to lower voltages with increasing temperature. It can also be seen that the test cell with polymer stabilized mixture PS-A1 shows a significantly smaller shift of the e/o curve compared to the test cells with mixture N1 and B1 which are not polymer stabilized.

Table 1 shows the calculated response times.

Table 1 - Calculated Response Times

t_d reduction from N1 to PS-A1 : 39%

5

It can be seen that from the calculation a reduction of t_d 39% is expected when the d/p ratio is changed from 0 to 0.63.

Table 2 shows the measured response times.

10

Table 2 - Measured Response Times

t_d reduction from N1 to PS-A1 : 38%

It can be seen that the response times t_r, t_d and t_r+t_d are significantly reduced

Of)

from mixture N1 to mixture PS-A1 .

It can also be seen that the measured reduction of the decay time t_d (38%) is almost identical to the calculated value (39%). The small difference can be explained by the fact that polymer stabilization will influence the operating

26

voltage, and the operating voltage for the polymer stabilized mixture may still be optimized to further reduce the difference between calculated and measured response times.

Example 2

30

Mixture A2 is prepared by adding to the LC host mixture N1 2.75% of the chiral dopant S-401 1 . The pitch of the mixture induced by the chiral dopant is 5 microns.

35 Mixture PS-A2 is prepared by adding to the Mixture A2 2.0 % of RM-51 and 1 %, relative to the concentration of the RM, of lrgacure®651. The pitch of the mixture induced by the chiral dopant is 5 microns. Mixture B2 is prepared by adding to the LC host mixture N1 1.0% of the chiral dopant S-4011. The pitch of the mixture induced by the chiral dopant is 13.7 microns.

Mixture C2 is prepared by adding to the LC host mixture N1 0.39% of the chiral dopant S-4011. The pitch of the mixture induced by the chiral dopant is 35 microns.

TN, PS-TN test cell manufacture TN test cells with mixtures N1 , B2 and C2 and a PS-TN test cell with mixture PS-A2 are prepared as described in Example 1.

E/O Performance. Response Times The electrooptical performance (transmission vs. voltage) and response times of the test cells are measured as described in Example 1.

Fig. 5 shows (from left to right) the e/o curves of the test cells with undoped host mixture N1 , chirally doped mixture B2, chirally doped mixture C2, and chirally doped, polymer stabilized mixture PS-A2. It can be seen that in the test cell with mixture PS-A2 the V/T curve is shifted to higher voltages, compared to the test cell with host mixture N1 and the test cells with mixtures B2 and C2 having lower d/p value, for the reasons as discussed in Example 1. It can also be seen that the polymer stabilized mixture PS-A2 maintains a high transmittance and contrast ratio, which is an advantage compared to PS-TN displays as reported in prior art.

Table 3 shows the measured response times. Table 3 - Response Times

t_d reduction from N1 to PS-A2: 51 %

It can be seen that the response times t_d and t_r+t_d are significantly reduced from mixture N1 to mixture PS-A2.

Example 3

Mixture A3 is prepared by adding to the LC host mixture N1 0.25% of the chiral dopant R-501 1 . The pitch of the mixture induced by the chiral dopant is 5 microns.

Mixture PS-A3 is prepared by adding to the Mixture A3 1 .5 % of RM-91 , 0.5% of RM-1 and 1 %, relative to the total concentration of RMs, of lrgacure®651 . The pitch of the mixture induced by the chiral dopant is 5 microns.

Mixture B3 is prepared by adding to the LC host mixture N1 0.035% of the chiral dopant R-501 1 . The pitch of the mixture induced by the chiral dopant is 35 microns.

Mixture C3 is prepared by adding to the LC host mixture N1 0.09% of the chiral dopant R-501 1 . The pitch of the mixture induced by the chiral dopant is 13.6 microns.

RM-91

TN test cell manufacture

TN test cells with mixtures N1 , B3 and C3 are prepared as described in Example 1 , but wherein the cell gap is 2.95 microns.

PS-TN test cell manufacture

The test cell with mixture PS-A3 is subjected to a two-step UV curing process, wherein in the first step a voltage is applied to the electrodes and in the second UV step no voltage is applied.

UV step 1 (UV1 ):

Toshiba C type fluorescent lamp, green UV with 365 filter, UV intensity 0.5 mW/cm² with UV power detector Ushio UIT-250, UVD-S365; electric field (see Fig. 2b): each pulse containing one plus and one minus pulse, 10 s/ period, pulse height +/-18 V, pulse width 100 ms. Irradiation time 600 s.

UV step 2 (UV2):

Same lamp and UV intensity as used in step UV1 but without filter, irradiation time 60 min.

E/O Performance, Response Times

The electrooptical performance (transmission vs. voltage) and response times of the test cells are measured as described in Example 1.

Fig. 6 shows (from left to right) the e/o curves of the test cells with undoped host mixture N1 , chirally doped mixture B3, chirally doped mixture C3, and chirally doped, polymer stabilized mixture PS-A3, measured at 25°C. It can be seen that in the test cell with mixture PS-A3 the V/T curve is shifted to higher voltages due to the short pitch and polymer stabilization for the reasons as discussed in Example 1 and 2. It can also be seen that mixture PS-A3 maintains high transmittance and contrast ratio, which is an advantage compared to PS-TN displays as reported in prior art. Table 4 shows the measured response times. Table 4 - Response Times

It can be seen that the response times t_d and t_r+t_d are significantly reduced from mixture N1 to mixture PS-A3.

Example 4

Mixture A4 is prepared by adding to the LC host mixture N1 0.25% of the chiral dopant R-5011. The pitch of the mixture induced by the chiral dopant is 5 microns. Mixture PS-A4 is prepared by adding to the Mixture A4 1.5 % of RM-51 , 0.5% of RM-1 and 1 %, relative to the total concentration of RMs, of lrgacure®651. The pitch of the mixture induced by the chiral dopant is 5 microns.

Mixture B4 is prepared by adding to the LC host mixture N1 0.035% of the chiral dopant R-5011. The pitch of the mixture induced by the chiral dopant is 35 microns.

TN, PS-TN test cell manufacture

TN test cells with mixtures N1 and B4 and a PS-TN test cell with mixture PS- A4 are prepared as described in Example 3.

E/O Performance. Response Times

The electrooptical performance (transmission vs. voltage) and response times of the test cells are measured as described in Example 1. Fig. 7 shows (from left to right) the e/o curves of the test cells with undoped host mixture N1 , chirally doped mixture B4 and chirally doped, polymer stabilized mixture PS-A4. It can be seen that in the test cell with mixture PS-A4 the V/T curve is shifted to higher voltages due to the short pitch and polymer stabilization for the reasons as discussed in Example 1 and 2. It can also be seen that mixture PS-A4 maintains high transmittance and contrast ratio, which is an advantage compared to PS-TN displays as reported in prior art. Table 5 shows the measured response times.

Table 5 - Response Times

t_d reduction from N1 to PS-A4: 37%

It can be seen that the response times t_d and t_r+t_d are significantly reduced from mixture N1 to mixture PS-A4.

Example 5

Mixture A5 is prepared by adding to the LC host mixture N1 0.25% of the chiral dopant R-501 1 . The pitch of the mixture induced by the chiral dopant is 5 microns.

Mixture PS-A5 is prepared by adding to the Mixture A5 1 .5 % of RM-51 , 0.5% of RM-1 and 1 %, relative to the total concentration of RMs, of lrgacure®651 . The pitch of the mixture induced by the chiral dopant is 5 microns.

Mixture B5 is prepared by adding to the LC host mixture N1 0.035% of the chiral dopant R-501 1 . The pitch of the mixture induced by the chiral dopant is 35 microns. TN, PS-TN test cell manufacture

TN test cells with mixtures N1 and B5 and a PS-TN test cell with mixture PS- A5 are prepared as described in Example 3.

E/0 Performance. Response Times

The electrooptical performance (transmission vs. voltage) and response times of the test cells are measured as described in Example 1 .

Fig. 8 shows (from left to right) the e/o curves of the test cells with undoped host mixture N1 , chirally doped mixture B5 and chirally doped, polymer stabilized mixture PS-A5. It can be seen that in the test cell with mixture PS-A4 the V/T curve is shifted to higher voltages due to the short pitch and polymer stabilization for the reasons as discussed in Example 1 and 2. It can also be seen that mixture PS-A5 maintains high transmittance and contrast ratio, which is an advantage compared to PS-TN displays as reported in prior art.

Table 6 shows the measured response times.

Table 6 - Response Times

t_d reduction from N1 to PS-A5: 38%

It can be seen that the response times t_d and t_r+t_d are significantly reduced from mixture N1 to mixture PS-A5.

The above results show that the process of the present invention enables to manufacture a PS-UF TN-LCD with a high d/p value while keeping a 90° TN configuration, and to achieve fast response times, especially a faster decay time, and lower temperature dependence of the e/o curves, while maintaining a reasonably low driving voltage, high contrast ratio and high transmittance.

Claims

1. An LC display comprising

a) a first substrate and a second substrate, the first substrate being equipped with a first electrode layer and optionally a first alignment layer, the second substrate being equipped with a second electrode layer and optionally a second alignment layer, b) a layer of a nematic LC medium containing a chiral additive and having positive dielectric anisotropy being dispensed between the first and the second substrate,

c) optionally a first polarizer on the side of the first substrate facing away from the LC layer and a second polarizer on the side of the second substrate facing away from the LC layer, said polarizers preferably being oriented such that their transmission planes for plane-polarized light are at right angles (crossed nicols), wherein the longitudinal axes of the LC molecules are oriented parallel or tilted relative to the planes of the substrates, and the chiral additive induces in the LC molecules of the LC medium a helical twist along an axis perpendicular to the substrates with a given pitch p,

wherein layer of the LC medium has a thickness d, and the ratio d/p is ³0.5, preferably >0.5, very preferably from 0.6 to 0.8,

wherein the twist angle of the helical twist of the LC molecules is from 60 to 120°, preferably from 80 to 100°, very preferably 90°, and wherein the display further comprises a polymer layer deposited on one or both of said first and second electrode or, if present, on one or both of said first and second alignment layer,

wherein said polymer layers are formed from one or more

polymerizable mesogenic compounds, which are contained in the LC medium at a concentration <3%, preferably from 0.05 to <3%, and which are polymerized in situ after the LC medium has been dispensed between the two substrates.

2. The display according to Claim 1 , characterized in that the twist angle of the helical twist of the LC molecules between the first and the second substrate is from 80 to 100°.

3. The display according to Claim 1 or 2, characterized in that the ratio d/p of the layer thickness d of the LC medium and the pitch p of the helical twist induced by the chiral additive is from 0.6 to 0.8.

4. The display according to one or more of Claims 1 to 3, characterized in that the the longitudinal axes of the LC molecules of the LC medium located at the surface of each substrate exhibit a tilt angle relative to said substrate from >0° to 20°,

5. The display according to one or more of Claims 1 to 4, characterized in that the first and second substrate are equipped with fixing means fixing the first and second substrate at a constant distance relative to each other and with their planes parallel to each other.

6. The display according to one or more of Claims 1 to 5, characterized in that the LC medium comprises one or more compounds selected from the following formulae:

of one another, and on each occurrence, identically or differently

R²¹, R³¹ each, independently of one another, alkyl, alkoxy, oxaalkyl or alkoxyalkyl having 1 to 9 C atoms or alkenyl or alkenyloxy having 2 to 9 C atoms, all of which are optionally fluorinated,

Z³¹ -CH2CH2-, -CF2CF2-, -COO-, frans-CH=CH-, trans-CF=CF-, -

CFI2O- or a single bond, preferably -CFI2CFI2-, -COO-, trans- CFI=CFI- or a single bond, particularly preferably -COO-, trans- CFI=CFI- or a single bond,

L²¹, L ²², L³¹, L ³² each, independently of one another, FI or F,

L^s H or CHs

9 0, 1 , 2 or 3.

7. The display according to one or more of Claims 1 to 6, characterized in that the LC medium comprises one or more compounds selected from the following formulae:

on each occurrence, identically or differently

R⁴¹, R⁴² each, independently of one another, alkyl, alkoxy, oxaalkyl or alkoxyalkyl having 1 to 9 C atoms or alkenyl or alkenyloxy having 2 to 9 C atoms, all of which are optionally fluorinated,

Z⁴¹, Z⁴² each, independently of one another, -CH2CH2-, -COO-, trans- CH=CH-, frans-CF=CF-, -CFI2O-, -CF2O-, -CºC- or a single bond, preferably a single bond, h 0, 1 , 2 or 3.

8. The display according to one or more of Claims 1 to 7, characterized in that the LC medium comprises one or more compounds selected from the following formula: in which the individual radicals, on each occurrence identically or differ- ently, each, independently of one another, have the following meaning:

R^A2 alkyl having 1 to 12 C atoms, in which, in addition, one or two non-adjacent CFh 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, x 1 or 2.

9. The display according to one or more of Claims 1 to 8, characterized in the polymerizable mesogenic compounds are selected of formula I

R^a-B¹-(Z^b-B²)_m-R^b I in which the individual radicals, on each occurrence identically or differ- ently, and each, independently of one another, have the following meaning:

R^a and R^b P, R-Sp-, H, F, Cl, Br, I, -CN, -N0₂, -NCO, -NCS, -OCN,

-SCN, SF₅ or straight-chain or branched alkyl having 1 to 25 C atoms, in which, in addition, one or more non-adjacent Chte groups may each be replaced, independently of one another, by -C(R°)=C(R⁰⁰)-, -CºC-, -N(R⁰⁰)-, -0-, -S-, -CO-, -CO- 0-, -0-C0-, -O-CO-O- in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by F, Cl, Br,

I, CN, P or R-Sp-, where, if B¹ and/or B² contain a saturated C atom, R^a and/or R^b may also denote a radical which is spiro-linked to this saturated C atom, wherein at least one of the radicals R^a and R^b denotes or contains a group P or P-Sp-,

P a polymerizable group,

Sp a spacer group or a single bond,

Z^b -0-, -S-, -CO-, -C0-0-, -OCO-, -O-CO-O-, -OCH₂-, -CH₂O-, -

SCH_2-, -CH2S-, -CF2O-, -OCF2-, -CF2S-, -SCF2-, -(CH₂)ni-, - CF2CH2-, -CH2CF2-, -(CF₂)ni-, -CH=CH-, -CF=CF-, -CºC-, - CH=CH-COO-, -OCO-CH=CH-, CR°R⁰⁰ or a single bond,

R° and R⁰⁰ FI or alkyl having 1 to 12 C atoms, m 0, 1 , 2, 3 or 4, n1 1 , 2, 3 or 4,

L P, R-Sp-, OH, CH₂OH, F, Cl, Br,

I, -CN, -NO2, -NCO, -NCS, -OCN, -SCN, -C(=0)N(R^x)₂, -C(= 0)Y¹, -C(=0)R^x, -N(R^x)₂, optionally substituted silyl, optionally substituted aryl having 6 to 20 C atoms, or straight-chain or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 25 C atoms, in which, in addition, one or more H atoms may be replaced by F, Cl, P or P-Sp-,

Y¹ halogen,

R^x P, R-Sp-, H, halogen, straight-chain, branched or cyclic alkyl having 1 to 25 C atoms, in which, in addition, one or more non-adjacent CFh groups may be replaced by -0-, -S-, -CO-, -CO-0-, -O-CO-, -O-CO-O- in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by F, Cl, P or R-Sp-, an optionally substituted aryl or aryloxy group having 6 to 40 C atoms, or an optionally substituted hetero- aryl or heteroaryloxy group having 2 to 40 C atoms.

10. The display according to one or more of Claims 1 to 9 characterized in that the polymerizable mesogenic compounds are selected from the following formulae:

35

in which the individual radicals, on each occurrence identically or differ- ently, and each, independently of one another, have the following meaning:

P¹, P², P³ a vinyloxy, acrylate, methacrylate, fluoroacrylate,

chloroacrylate, oxetane or epoxy group,

Sp¹, Sp², Sp³ a single bond or a spacer group where, in addition, one or more of the radicals P¹-Sp¹-, P¹-Sp²- and P³-Sp³- may also denote R^aa, with the proviso that at least one of the radicals P¹-Sp¹-, P²-Sp² and P³-Sp³- present is different from R^aa,

R^aa H, F, Cl, CN or straight-chain or branched alkyl having 1 to 25 C atoms, in which, in addition, one or more non- adjacent CFh groups may each be replaced, indepen- dently of one another, by -C(R°)=C(R⁰⁰)-, -CºC-, -N(R°)- , -0-, -S-, -CO-, -CO-0-, -O-CO-, -O-CO-O- in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by F, Cl, CN or P¹-Sp¹-, particularly preferably straight-chain or branched, optionally mono- or polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12 C atoms, where the alkenyl and alkynyl radicals have at least two C atoms and the branched radicals have at least three C atoms,

R°, R⁰⁰ H or alkyl having 1 to 12 C atoms,

R^y and R^z H, F, CFb or CF3,

X¹, X², X³ -CO-O-, -O-CO- or a single bond

Z¹ -0-, -CO-, -C(R^yR^z)- or -CF2CF2-,

Z², Z³ -CO-O-, -O-CO-, -CH₂O-, -OCH₂-, -CF₂O-, -OCF₂- or

-(CFl2)n-, where n is 2, 3 or 4,

L F, Cl, CN or straight-chain or branched, optionally

mono- or polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12 C atoms,

L', L" H, F or Cl, r 0, 1 , 2, 3 or 4, s 0, 1 , 2 or 3, t 0, 1 or 2, x 0 or 1 .

1 1 . The display according to one or more of Claims 1 to 10, characterized in that the polymerizable mesogenic compounds are polymerized by UV photopolymerization .

12. The display according to one or more of Claims 1 to 1 1 , characterized in that the LC medium comprises one or more chiral dopants.

13. The display according to one or more of Claims 1 to 12, characterized in that the LC medium comprises one or more additives selected from photoinitiators, stabilizers and self-aligning additives.

14. A method of manufacturing a display according to one or more of

Claims 1 to 13, comprising the following steps

a) providing a first substrate and a second substrate, the first substrate being equipped with a first electrode layer and optionally with a first alignment layer, the second substrate being equipped with a second electrode layer and optionally with a second alignment layer, wherein the first and/or the second substrate are preferably equipped with fixing means, preferably a sealant material and/or spacers, fixing the first and second substrate at a constant distance relative to each other and with their planes parallel to each other,

wherein the LC medium comprises, preferably consists of,

A) a liquid crystal component A comprising, preferably consisting of, mesogenic or liquid-crystalline molecules,

B) a polymerizable component B comprising, preferably consisting of, one or more polymerizable mesogenic compounds,

C)one or more chiral additives, preferably selected from chiral dopants,

wherein layer of the LC medium has a thickness d, and the ratio d/p is ³0.5, preferably >0.5, very preferably from 0.6 to 0.8, and wherein the twist angle of the helical twist of the LC molecules induced by the chiral additives is >210°, preferably from 210 to 330°, more preferably from 240 to 300°, very preferably 270°,

c) applying a voltage to the first and second electrodes such that the twist angle of the helical twist of the LC molecules is reduced to

<150°, preferably to a range from 60 to 120°, more preferably from 80 to 100°, very preferably to 90°,

e) optionally subjecting the LC medium to a second polymerization step, preferably by exposure to UV radiation, without applying a voltage to the first and second electrodes, thereby polymerizing any

polymerizable compounds which have not reacted in step d).

15. The method according to Claim 14, characterized in that the twist angle of the helical twist of the LC molecules between the first and the second substrate before application of a voltage in step c) is from 240 to 300°, and after application of a voltage in step c) is from 80 to 100°.

16. The method according to Claim 14 or 15, characterized in that

component A of the LC medium comprises one or more compounds as defined in one or more of Claims 6, 7 and 8.

17. The method according to any of Claims 14 to 16, characterized in that the polymerizable mesogenic compounds of component B of the LC medium are as defined in Claim 9 or 10.

18. An LC medium comprising

A) a liquid crystal component A comprising one or more compounds selected from formula A and B as defined in claim 6, one or more

5

compounds selected from formula C and D as defined in claim 7, and optionally one or more compounds of formula E as defined in claim 8,

B) a polymerizable component B comprising one or more

Ί Q polymerizable mesogenic compounds of formual I as defined in claim 9,

C)one or more chiral additives, preferably selected from chiral dopants,

D) optionally one or more further additives, preferably selected from 15

polymerization initiators, stabilizers and self-aligning additives, wherein the concentration of the polymerizable mesogenic

compounds of component B in the LC medium is from 0.05 to <3%, and

20 wherein the concentration of the chiral additives is selected such that the twist angle they induce in the LC medium is >210°, preferably from 210 to 330°, more preferably from 240 to 300°, very preferably 270°.

19. An LC medium comprising

A) a liquid crystal component A comprising one or more compounds selected from formula A and B as defined in claim 6, one or more compounds selected from formula C and D as defined in claim 7, and optionally one or more compounds of formula E as defined in claim 8,

B) a polymerizable component B comprising one or more

polymerizable mesogenic compounds of formual I as defined in claim 9,

C)one or more chiral additives, preferably selected from chiral dopants, D) optionally one or more further additives, preferably selected from polymerization initiators, stabilizers and self-aligning additives, wherein the concentration of the polymerizable mesogenic

compounds in the LC medium is from 0.05 to <3%, and