WO2019110473A1

WO2019110473A1 - Liquid-crystal medium

Info

Publication number: WO2019110473A1
Application number: PCT/EP2018/083283
Authority: WO
Inventors: Nils Greinert; Matthias Bremer; Patrick SUESS; Christian Schoenefeld; Jochen SIEBERLING; Renate SEEGER; Anna Lisa HAWLITSCHEK
Original assignee: Merck Patent Gmbh
Priority date: 2017-12-04
Filing date: 2018-12-03
Publication date: 2019-06-13
Also published as: TW201925437A; DE112018006182T5

Abstract

The present invention relates to a liquid crystal (LC) medium comprising polymerizable compounds, to a process for its preparation, to its use for optical, electro-optical and electronic purposes, in particular in LC displays, and to LC displays comprising it.

Description

Liquid-crystal medium

The present invention relates to a liquid crystal (LC) medium comprising polymerizable compounds, to a process for its preparation, to its use for optical, electro-optical and electronic purposes, in particular in flexible LC displays, and to LC displays comprising it.

Background of the Invention

Recently liquid crystal (LC) mixtures have been developed for the realization of flexible substrate based LC displays. These LC mixtures contain reactive polymer precursors that allow the formation of polymer walls in the display, which help to maintain the gap distance of the LC layer. This technology thus enables manufacturing of free form and robust displays by using LC materials.

Free form LC displays can either have a permanent shape other than the flat shape of rigid flat panel displays, for example a curved shape, or can even have flexible shape. The simplest form of the first type are curved TVs that have been developed in the recent past and offer the viewer an enhanced viewing experience. Thereby it is possible to provide displays which are not only shaped in one but in two dimensions, and which can be used for example as car dashboards or advertising screens.

Flexible displays, another type of free form displays, have also been developed, and have been proposed for example for use in mobile phones or smart watches utilizing the advantages of flexibility. Further potential applications are foldable or Tollable mobile phones, as well as extra-large screens for presentations or home entertainment, which, due to their size, require to be Tollable or foldable for being transported or stowed.

Advantageously such devices are based on plastic substrates instead of rigid glass substrates as used in conventional, unflexible LC displays.

Another display concept,’unbreakable’ displays, are also based on plastic substrates and refers to a display design featuring particular robustness, durability, and resistance against mechanical impact. One problem that should be solved is that mobile devices have an elevated risk of being dropped accidentally or becoming otherwise damaged during their normal use. In view of the high value of these devices, a solution to this problem would be highly desirable.

There is thus a great demand for free form or unbreakable LC displays.

One of the main technical challenges of LC displays with flexible substrates is that a constant LC layer thickness is critical for proper device operation. A proper combination of defined LC layer thickness and LC material properties ensures that the pixels can be switched between a black state and light transmitting state. In case of a varying layer thickness, unwanted interference with the gap distance between the substrates can result in visible optical defects. It should therefore be ensured that the LC layer thickness is not altered by the bending or the lack of rigidity of flexible plastic substrates.

In conventional LC displays with rigid glass substrates, usually spacer particles are added to the LC layer in order to define and maintain a constant layer thickness. A possible solution for free form displays is to adapt this concept by incorporating supporting structures, like for example polymer walls, that can both resist compression and bind the two substrates together. A suitable manufacturing process is to prefabricate the polymer wall structures, spread the LC mixture on the substrate, and subsequently close the panel with the top substrate. Potential problems with this approach are for example that spreading of the LC mixture is obstructed by the support structures, and that bonding to the top substrate might not be sufficient.

An alternative solution is to create the polymer wall structures by means of a photolithographic process after the display has been assembled. This is schematically illustrated in Fig. 1 showing a polymer wall formation process. Fig. 1 (a) shows an LC mixture consisting of LC host molecules (rods), polymerizable monomer (dots), and photo-initiator (not shown). As shown in Fig. 1 (b) the LC mixture is filled into the display, or the LC mixture is spread on a first substrate and a second substrate applied on top, and UV radiation (indicated by the arrows) is applied through a photomask. Polymerization induced phase separation takes place, as a result of which polymer walls are formed in irradiated regions according to the mask pattern as shown in Fig. 1 (c), while the LC phase of the LC host molecules (rods) in the pixel area is restored. The principle of creating polymer walls by this method for LC display applications is a known technique that has been described in the literature and has been suggested for use in a variety of display modes.

For example, US6130738 and EP2818534 A1 disclose an LC display that comprises polymer walls formed from one or two polymerizable monomers that are contained in the LC host mixture.

However, the currently used LC mixtures and monomers for use in flexible LC displays with polymer wall formation do still have several drawbacks and leave room for further improvement.

For example, it was observed that the polymerizable compounds and LC media used in prior art do often show insufficient phase separation between the polymer walls and the LC molecules of the LC host mixture. This leads on the one hand to the undesired inclusion of LC molecules in the polymer walls, and on the other hand to increased amounts of polymer molecules dissolved or dispersed in the LC host mixture, both of which can negatively influence the display performance. Thus, LC molecules trapped in the polymer wall can lead to reduced transparency and contrast of the display, a deterioration of the electrooptical response due to formation of domains with different switching speed, and decreased adhesion of the polymer walls to the substrates. On the other hand, undesired amounts of polymer molecules in the LC host mixture can negatively affect the LC mixture properties.

Moreover, it was observed that the thickness of the polymer walls is often not constant but varying, which can lead to non-uniform pixel size. Besides the polymer walls do often still not show sufficient stability against mechanical pressure on the one hand and sufficient elasticity on the other hand. Also, the polymer walls are often too thick, which reduces transparency and contrast of the display.

Another problem observed with hitherto used materials is that they do not always fulfil the requirement of good phase separation, thus leading to increased polymerization time, and high degree of crosslinking, thus leading to poor wall stability especially under mechanical stress.

Another problem arises from the fact that the monomers used for polymer wall formation typically comprise polymerizable groups that are polymerized by radical UV photopolymerization.

However, there are various LC display modes wherein the LC medium contains compounds or additives which are not stable to the UV radiation applied for radical UV photopolymerization. These displays are therefore not easily compatible with the polymer wall technology.

One example for such a display mode is the polymer stabilized (PS or PSA) mode. In displays of the PSA mode the LC medium contains a small amount of polymerizable mesogenic compounds or reactive mesogens, which are polymerized after the LC medium is filled into the display cell, typically while a voltage is applied to the display electrodes, and do thereby generate or stabilize a specific alignment of the LC molecules. These reactive mesogens are usually selected from compounds that are polymerized by radical UV photopolymerization. Therefore, when using such an LC medium in displays with polymer walls, it is difficult to control polymerization of the monomers forming the polymer walls on the one hand, and polymerization of the reactive mesogens stabilizing the alignment on the other hand, independently from each other.

Another example for such a display mode is the Guest-Host (GH) mode. In these displays the LC medium contains a dichroic dye which is reoriented together with the LC molecules when applying a voltage to the display, so that the display can be switched between states with different transmission and/or colour. Such displays are used for example in smart windows.

However, the dyes typically used in GH mode displays are often unstable against free radicals. Therefore, when using such an LC medium in displays with polymer walls, the dye can be damaged during polymerization of the monomers forming the polymer walls. It is therefore desirable to have available improved LC mixtures and

monomers for use in flexible LC displays which can overcome the drawbacks of materials used in prior art as described above.

The present invention is based on the object of providing novel suitable materials, in particular LC host mixtures comprising polymerizable monomers, for use in flexible LC displays with polymer walls, which do not have the disadvantages indicated above or do so only to a reduced extent.

In particular, the invention is based on the object of providing LC media comprising polymerizable monomers, which enable the formation of polymer walls in a time- and cost-effective manner, and which are suitable for mass production. The formed polymer walls should show clear phase separation from the LC host mixture, without or with a reduced amount of defects or LC molecules trapped in the polymer wall, and without or with a reduced amount of polymer molecules dissolved in the LC host mixture. Also, the polymer walls should show constant thickness, high elasticity, high stability against mechanical pressure, and good adhesion to the substrates.

Another object of the invention is to provide improved LC host mixtures for flexible displays which should show high specific resistance values, high VHR values, high reliability, low threshold voltages, short response times, high birefringence, show good UV absorption especially at longer wavelengths, allow quick and complete polymerization of the monomers contained therein, and reduce or prevent the occurrence of image sticking in the display.

Another object of the invention is to provide LC displays with polymer walls that show high transparency in the addressed state, good contrast, high switching speed and a large operating temperature range. Another object of the present invention is to provide an improved technical solution for enabling LCD technology for free form and unbreakable plastic substrate based LC displays. Another object of the invention is to provide polymerizable LC media for the manufacturing of LC displays with polymer walls, which enable at the same a good phase separation and a high degree of crosslinking.

Another object of the present invention is to provide LC media which enable the use of the polymer wall technology in display modes, like for example the PS mode or GH mode, which utilize materials that are sensitive to free radicals, such as dyes or reactive mesogens. Thereby it is possible to extend the range of polymer wall displays available to the expert. The above objects have been achieved in accordance with the present invention by materials and processes as described and claimed hereinafter.

Thus, it has surprisingly been found that at least some of the above-mentioned objects can be achieved by using an LC medium which comprises one or more monomers that are polymerizable by cationic polymerization, and further comprises a cationic polymerization initiator, for example a photoacid generator (PAG). Such an initiator upon its activation, for example by illumination, does not produce free radicals but forms strong acids releasing protons, for example by proton photodissociation, which initiate the cationic polymerization of the monomers.

It is therefore possible to add to the LC medium according to the present invention further monomers or reactive mesogens with acrylate or

methacrylate groups which are, under the usually applied conditions, not capable of undergoing cationic polymerization but to radical polymerization, and do therefore not, or only at a small extent, participate in the cationic polymerization of the monomers forming the polymer walls. It is also possible to add to the LC medium a dichroic dye which may be unstable against free radicals but has higher stability stable against the cationic initiator (like for example the PAG). The LC displays containing an LC medium according to the present invention can therefore also be operated in the PSA or GH mode. It has also been surprisingly found that the polymerizable compounds contained in the LC medium can also be used to form spacers to maintain a constant cell gap between the substrates of the LC display. This can support or even replace the spacer materials that are normally used in prior art.

Summary of the Invention

The invention relates to a liquid crystal (LC) medium comprising a) a polymerizable component A) comprising one or more polymerizable compounds comprising one or more

polymerizable groups that are capable of undergoing cationic

polymerization, a cationic photoinitiator, preferably selected from photoacids (PAs) and photoacid generators (PAGs), optionally a stabiliser, b) a liquid-crystalline component B), hereinafter also referred to as "LC host mixture", which comprises, and preferably consists of, one or more mesogenic or liquid-crystalline compounds.

The invention furthermore relates to an LC medium comprising, in addition to components A) and B) as described above and below, a second

polymerizable component C) comprising one or more polymerizable compounds comprising one or more polymerizable groups that are capable of undergoing radical polymerization.

The invention furthermore relates to an LC medium comprising, in addition to components A) and B) as described above and below, one or more dyes, preferably selected from dichroic dyes. The liquid-crystalline component B) of an LC medium according to the present invention is hereinafter also referred to as "LC host mixture", and preferably contains LC compounds that are selected only from low-molecu- lar-weight compounds which are unpolymerizable, and optionally contains further additives like stabilisers or chiral dopants.

The invention furthermore relates to an LC medium or LC display as described above and below, wherein the polymerizable compounds, or the compounds of component A), are polymerized by cationic polymerization.

The invention furthermore relates to a process for preparing an LC medium as described above and below, comprising the steps of mixing an LC host mixture or LC component B) as described above and below, with one or more polymerizable compounds or component A) as described above and below, and optionally with further LC compounds and/or additives.

The invention further relates to the use of LC medium in LC displays, preferably in flexible LC displays. The invention furthermore relates to an LC display comprising an LC medium as described above and below.

The invention furthermore relates to an LC display comprising polymer walls obtainable by cationic polymerization of one or more polymerizable

compounds or a polymerizable component A) as described above and below, or comprising an LC medium as described above and below.

The invention furthermore relates to an LC display comprising spacers obtainable by cationic polymerization of one or more polymerizable

The LC display according to the present invention is preferably a flexible LC display, and preferably a TN, OCB, IPS, FFS, posi-VA, VA or UB-FFS display. In another preferred embodiment the LC display according to the present invention is a display of the polymer stabilized alignment (PSA) mode, preferably a flexible LC display, and preferably a PS-TN, PS-OCB, PS-IPS, PS-FFS, PS-posi-VA, PS-VA or PS-UB-FFS display.

In another preferred embodiment the LC display according to the present invention is a display of the self-aligned (SA) mode, preferably a flexible LC display, and preferably a SA-VA or SA-FFS display. The invention furthermore relates to an LC display comprising two

substrates, at least one which is transparent to light, an electrode provided on each substrate or two electrodes provided on only one of the substrates, and located between the substrates a layer of an LC medium as described above and below, wherein the polymerizable compounds are polymerized by cationic polymerization between the substrates of the display.

The invention furthermore relates to a process for manufacturing an LC display as described above and below, comprising the steps of filling or otherwise providing an LC medium as described above and below between the substrates of the display, and polymerizing the polymerizable compounds by cationic polymerization.

The displays according to the invention have two electrodes, preferably in the form of transparent layers, which are applied to one or both of the substrates. In some displays, for example in TN, OCB or VA displays, one electrode is applied to each of the two substrates. In other displays, for example in IPS, FFS or UB-FFS displays, both electrodes are applied to only one of the two substrates. The polymerizable compounds of the polymerizable component are preferably polymerized by cationic photopolymerization, very preferably by cationic UV photopolymerization, further preferably by thermal cationic polymerization. Brief Description of the Drawings Fig. 1 schematically illustrates the polymer wall formation process in displays according to prior art and according to the present invention.

Fig. 2-7 show polarization microscope images of test cells containing polymerizable mixtures P1 -P6 according to the invention after polymerization.

Terms and Definitions

Above and below, the term "free form display" will be understood to mean a display that has either a permanent shape other than a plane-parallel shape, like for example a curved shape, or a flexible display. The term "flexible display" will be understood to mean a display which is bendable without breaking, like for example a display having flexible plastic substrates instead of rigid glass substrates and not comprising any other rigid layers. The term "curved display" will be understood to mean a display which has top and bottom subtrates that are not plane-parallel but curved.

Above and below, the term "flat display with reduced touch Mura sensitivity" will be understood to mean a display wherein irregular luminosity variation defects, which are caused by touching the front screen of a display, are reduced.

Above and below, the term“bi- or polycyclic group” will be understood to mean a group that consists of two or more fused rings, i.e. rings that share at last one common atom (in contrast to rings that are connected via covalent bonds between atoms belonging to different rings), wherein fusion of the rings occurs a) across a sequence of atoms (bridgehead), like for example in

bicyclo[2.2.1]heptane (norbornane) or tricyclo[3.3.3.1]decane (adamantane), hereinafter also referred to as“bridged bi- or polycyclic groups”,

b) across a bond between two atoms, like for example in bicyclo[4.4.0]decane (decalin), hereinafter also referred to as“fused bi- or polycyclic groups” c) at a single atom (spiro atom), like for example in spiro[4.5]decane, hereinafter also referred to as“spirocyclic groups”. Unless indicated otherwise, the abbreviation "RM" is used above and below when referring to a reactive mesogen. Above and below, polymerizable compounds or RMs with one polymerizable reactive group are also referred to as "monoreactive", polymerizable compounds or RMs with two polymerizable reactive groups are also referred to as "direactive", and polymerizable compounds or RMs with three polymerizable reactive groups are also referred to as "trireactive".

Unless indicated otherwise, the expression "LC mixture" is used when referring to the LC host mixture (i.e. without the RMs or polymerizable compounds), while the expression "LC medium" is used when referring to the LC host mixture plus the RM(s) or polymerizable compounds.

Unless stated otherwise, the polymerizable compounds and RMs are preferably selected from achiral compounds.

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 "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.

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 or polymerizable compounds.

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 corn- 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, C -C20 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 CFI2 groups may each be replaced, independently of one another, by -C(R^S1)=C(R^S1)-, -CºC-, -N(R^S1)-, -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

R^S1 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-, -CO-O-, -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^s, are, for example, F, Cl, Br, I, -CN, -NO2, -NCO, -NCS, -OCN, -SCN, -C(=0)N(R^s)₂, -C(=0)Y^s, - C(=0)R^s, -N(R^s)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^s denotes FI, F, Cl, CN, or straight chain, branched or cyclic alkyl having 1 to 25 C atoms, wherein one or more non-adjacent CFI₂-groups are optionally replaced by -0-, -S-, -CO-, -CO-0-, -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 or Cl,

Y^s denotes halogen, preferably F.

"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, CH3, C2H5, OCHs, OC2H5, COCH3, COC2H5, COOCHs, COOC2H5, CFs, OCFs, OCFIF2, OC2F5, furthermore phenyl.

in which L has one of the meanings indicated above and r is 0, 1 , 2, 3 or 4.

A polymerizable group that is capable of undergoing cationic polymerization, and the groups P^x and P^y in formula I and its subformulae, are preferably selected from the group consisting of CFh=CW¹-0-, CH2=CW¹-,

and W² each, independently of one another, denote H or alkyl having 1 to 5 C atoms, preferably H, methyl, ethyl or n-propyl, very preferably H, and ki denotes 0 or 1 .

Very preferably the polymerizable groups that are capable of undergoing cationic polymerization, and the groups P^x and P^y in formula I and its subformulae, are selected from the group consisting of vinyloxy, vinyl, styrene, epoxy, oxetane, acetolactone, propiolactone, acetolactame, propiolactame, most preferably from vinyloxy.

The lactone and lactame groups are preferably selected from the group consisting of a-acetolacatone, b-propiolactone, a-acetolactame and b- propiolactame.

In another preferred embodiment of the present invention the polymerizable groups that are capable of undergoing cationic polymerization, and the groups P^x and P^y in formula I and its subformulae, are selected from the group consisting of saturated heterocylic groups having 3, 4 or 5 ring atoms and containing one or more hetero atoms selected from O, S, N and B. Very preferred polymerizable groups according to this preferred embodiment are aziridine, oxirane, thiirane, borirane, diaziridine, oxaziridine, dioxirane, azetidine, oxetane, thietane, diazetidine, dioxetane, dithiethane, pyrrolidine, tetrahydrofurane, tetrahydrothiopene, borolane, imidazolidine, oxazolidine, thiazolidine, dioxolane, dithiolane.

A polymerizable group, or group P¹·², which is capable of undergoing radical polymerization, is preferably selected from the group consisting of acrylate, methacrylate, fluoroacrylate, chloroacrylate and cyanoacrylate, very preferably from acrylate and methacrylate.

If Sp, Sp^x or Sp¹·² is different from a single bond, it is preferably selected of the formula Sp"-X", so that the respective radical P-Sp- conforms to the formula P-Sp"-X"-, wherein

Sp" denotes straight-chain ir branched alkylene having 1 to 40, preferably 1 to 20, C atoms, which is optionally mono- or polysubstituted by F, Cl, CN or P, and in which, in addition, one or more non-adjacent CFh groups may each be replaced, independently of one another, by -O-, - S-, -NH-, -N(R⁰)-, -Si(R°R⁰⁰)-, -CO-, -CO-0-, -O-CO-, -0-C0-0-, -S-CO- , -CO-S-, -N(R⁰⁰)-CO-O-, -0-CO-N(R°)-, -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-, -C0-, -COO-, -OCO-, -0-C00-, -CO-NR⁰-, -NR°- CO-, -NR°-CO-NR⁰⁰- or a single bond. Typical spacer groups Sp, Sp^x, Sp¹·² and -Sp"-X"- are, for example, -(CH₂)_PI-, -(CH₂CH₂0)qi-CH₂CH₂-, -CH₂CH₂-S-CH₂CH₂-, -CH₂CH₂-NH-CH₂CH₂- or -(SiR°R⁰⁰-O)_pi-, in which p1 is an integer from 1 to 20, q1 is an integer from 1 to 6, and R° and R⁰⁰ have the meanings indicated above. Particularly preferred groups Sp, Sp^x, Sp¹·² and -Sp”-X”- are -(CH₂)_PI-, -(CH₂)_PI- 0-, -(CH₂)_PI-0-C0-, -(CH₂)_PI-C0-0-, -(CH₂)_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

The LC medium according to the present invention is characterized in that it comprises one or more monomers that are polymerizable by cationic

polymerization, and further comprises a cationic polymerization initiator, for example a photoacid (PA) or photoacid generator (PAG). Such a PAG upon its activation, for example by illumination, does not produce free radicals but forms strong acids releasing protons, for example by proton photodissociation, which initiate the cationic polymerization of the monomers. It is therefore possible to add to the LC medium according to the present invention further monomers or reactive mesogens with acrylate or

methacrylate groups, which are not capable of undergoing cationic

polymerization but to radical polymerization, and do therefore not participate in the cationic polymerization of the monomers forming the polymer walls. It is also possible to add to the LC medium a dichroic dye which may be unstable against free radicals but is stable against the initiator (like for example the PA or PAG) used for cationic polymerization. The LC displays containing an LC medium according to the present invention can therefore also be operated in the PSA or GH mode.

Preferably, the polymerizable compounds of component A) are selected from compounds having one, two, three or four polymerizable groups, more preferably from compounds having one, two or three polymerizable groups, most preferably from compounds having one or two polymerizable groups.

Preferably component A) of the LC medium comprises one or more polymerizable compounds selected of formula I

P^x-Sp¹-(A¹-Z¹)_m-R^x I wherein the individual radicals, independently of each other, and on each occurrence identically or differently, have the following meanings

R^x -Sp²-P^y, H, F, Cl, -CN, 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-, -NR⁰-, -CO-, -C0-0-, -0-C0-, -O-CO- 0-, -C(R°)=C(R⁰⁰)-, -CºC- in such a manner that O- and/or S-atoms are not directly connected with each other, and wherein one or more H atoms are each optionally replaced by F or Cl,

P^x, P^y a polymerizable group that is capable of undergoing cationic

polymerization,

Sp¹, Sp² a spacer group or a single bond,

A¹ an aromatic, heteroaromatic, alicyclic or heterocyclic group having 4 to 25 ring atoms, which may also contain fused rings, and which is unsubstituted, or mono- or polysubstituted by L, Z¹ -0-, -S-, -CO-, -C0-0-, -OCO-, -0-C0-0-, -OCH₂-, -CH₂O-, -SCH₂-, - CH₂S-, -CF₂0-, -OCF₂-, -CF₂S-, -SCF₂-, -(CH₂)_{ni i}-, -CF₂CH₂-, - CH₂CF₂-, -(CF₂)ni 1-, -CH=CH-, -CF=CF-, -CºC-, -CH=CH-COO-, - OCO-CH=CH-, CR°R⁰⁰ or a single bond,

L F, Cl, -CN, -N0₂, -NCO, -NCS, -OCN, -SCN, -C(=0)N(R^q)₂,

-C(=0)Y^z, -C(=0)R^q, -N(R^q)₂, optionally substituted silyl, optionally substituted aryl or heteroaryl having 5 to 20 ring atoms, 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(R⁰)-, -O- , -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 FI atoms may be replaced by F, Cl, -CN, one or more of L may also denote P^x-Sp¹ -,

R^q FI, F, Cl, CN, or straight chain, branched or cyclic alkyl having 1 to 25 C atoms, wherein one or more non-adjacent CFI₂-groups are

optionally replaced by -O-, -S-, -CO-, -C0-0-, -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 or Cl,

R°, R⁰⁰ FI or alkyl having 1 to 20 C atoms,

Y^z halogen, preferably F or Cl, m 0, 1 , 2, 3 or 4, n11 1 , 2, 3 or 4.

Especially preferred are compounds of formula I and its subformulae wherein R^x denotes -Sp²-P^y. Further preferred are compounds of formula I and its subformulae wherein R^x is different from -Sp²-P^y. Preferably R^x in these compounds is selected from the group consisting of primary alkyl or alkoxy having from 1 to 12, preferably 1 to 6 C atoms, secondary alkyl or alkoxy having from 3 to 15, preferably 3 to 10 C atoms, or tertiary alkyl or alkoxy having from 4 to 18, preferably 4 to 12 C atoms.

Very preferably P^x and P^y in formula I and its subformulae are selected from the group consisting of vinyloxy, vinyl, styrene, epoxy, oxetane, acetolactone, propiolactone, acetolactame, propiolactame, most preferably from vinyloxy.

Sp¹ and Sp² in formula I and its subformulae preferably denote -(CFteJpi-, - (CH₂)_PI-0-, -(CH₂)_PI-0-C0- or -(CH₂)_PI-C0-0-, very preferably-(CH2)_Pi-, in which p1 is an integer from 1 to 20.

A¹ in formula I and its subformulae is preferably selected from,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 CFh groups may be replaced by O and/or S, 1 ,4-cyclohexenylene, bicyclo[1.1.1]pentane-1 ,3-diyl, bicyclo[2.2.2]octane-1 ,4-diyl, spiro[3.3]heptane- 2, 6-diyl, piperi-dine-1 ,4-diyl, decahydronaphthalene-2, 6-diyl, 1 ,2,3,4-tetrahydro- naphthal-ene-2, 6-diyl, indane-2,5-diyl or octahydro-4,7-methanoindane-2,5-diyl, where all these groups are unsubstituted or mono- or polysubstituted by L as defined above.

Very preferably A¹ in formula I and its subformulae is selected from 1 ,4- phenylene, naphthalene-2, 6-diyl and cyclohexane-1 ,4-diyl, which are

unsubstituted or mono- or polysubstituted by L as defined above.

Z¹ in formula I and its subformulae is preferably selected from -CO-0-, -OCO-, - OCH₂-, -CH2O-, -CF2O-, -OCF2-, -CF2S-, -(CH₂)nii-, -CH=CH-, -CF=CF-, -CºC-, -CH=CH-COO-, -OCO-CH=CH- or a single bond. In a first preferred embodiment of the present invention component A) of the LC medium comprises one or more compounds of formula I wherein m is > 1 , and is preferably 1 , 2 or 3, very preferably 2.

Preferred compounds of formula I of this first preferred embodiment are selected from the group consisting of the following subformulae:

in which P^x, P^y, Sp¹, Sp² and L are as defined in formula I Z² is -0-, -CO-, -C(R^yR^z)- or -CF₂CF₂-,

R^y, R^z independently of one another, denote H, F, CFI3 or CF3, Z³, Z⁴ are independently of each other -CO-O-, -O-CO-, -CFI₂0-, -

OCFI₂-, -CF₂0-, -OCF₂- or -(CH₂)_ni 1-, where n11 is 2, 3 or 4, r is 0, 1 , 2, 3 or 4, s is 0, 1 , 2 or 3, t is 0, 1 or 2.

Especially preferred are compounds of formula I3 and I4. In the compounds of formulae 11 to 116 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, N0₂, CFI3, C₂Fl5, C(CH₃)₃, CH(CH₃)2, CH₂CH(CH₃)C₂H₅, OCHs, OC₂H₅, COCHs, COC₂H₅, COOCFI3, COOC₂Fl5, CF3, OCF3, OCFIF₂, OC₂F₅ or P^x-Sp¹-, very preferably F, Cl, CN, CFI3, C₂Fl5, OCFI3, COCFI3, OCF3, more preferably F, Cl, CFI3, OCFI3, COCFI3, CF3 Oder OCF3, especially F or CFI3.

Further preferred are compounds of formulae 11 -116 comprising one or more, preferably one or two, most preferably one, substituent L that denotes P^x-Sp¹-. Very preferred compounds of formula 11-116 are selected from the following subformulae

wherein L and r have the meanings given in formula I. In a second preferred embodiment of the present invention component A) of the LC medium comprises one or more compounds of formula I wherein m is 0.

Preferred compounds of formula I of this second preferred embodiment are selected of the following formula:

P^x-Sp^x-R^x IA wherein P^x and R^x have the meanings given above, and Sp^x is straight chain or branched alkylene having 1 to 40 C atoms, wherein one or more non- adjacent CFte-groups are optionally replaced by -0-, -S-, -CO-, -CO-0-, -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 H atoms may be replaced by F, Cl, -CN or P^x. Preferred compounds of formula IA are selected from the group consisting of the following subformulae: P^x-(CHW^{1 1} )n2-(CH₂)n1-(CHW¹²)n3-H IA1

P^x-(CHW^{1 1} )n2-(CH₂)n1-(CHW¹²)n3-P^y IA2 P^X-(CH₂)n2-(CF₂)n1-(CH₂)n3-H IA3

P^X-(CH₂)n2-(CF₂)n1-(CH₂)n3-P^y IA4

(P^x-(CH₂)nl )n4CW^x _4-n IA5 wherein P^x, P^y are as defined in formula I, and the other individual radicals, independently of each other and on each occurrence identically or differently, have the following meanings W¹¹, W¹² H, F or Ci-Ci₂-alkyl,

W^x FI, OFI, or alkyl or alkoxy with 1 to 12 C atoms, preferably FI, OFI,

CH3, OCH3, or C₂H5 or OC₂H5, n1 an integer from 2 to 20, preferably from 3 to 16, n2, n3 0 or an integer from 1 to 6 n4 2, 3 or 4, and wherein in formula IA1 -IA5 in the group (CFI₂)_ni one or more of the CFI₂ groups, which are not directly connected to P^x or P^y, are optionally replaced by -O- or -CO-, and one or more of the FI atoms are optionally replaced by F or alkyl with 1 to 6 C atoms.

Very preferred compounds of formula IA are selected from the following subformulae

IA1 a

In a preferred embodiment of the present invention component A) of the LC medium comprises, preferably consists of, one or more polymerizable compounds, preferably of formula I or its subformulae, having exactly one polymerizable group or group P^x that is capable of undergoing cationic polymerization (monoreactive compounds). The concentration of these monoreactive compounds of formula I in the LC medium is preferably from 5 to 25%, very preferably from 11 to 20% by weight.

In another preferred embodiment of the present invention component A) of the LC medium comprises, preferably consists of, one or more polymerizable compounds, preferably of formula I or its subformulae, having exactly two polymerizable groups or groups P^{x y} that are capable of undergoing cationic polymerization (direactive compounds). The concentration of these direactive compounds of formula I in the LC medium is preferably from 5 to 15%, very preferably from 5 to 10% by weight.

In another preferred embodiment of the present invention component A) of the LC medium comprises one or more polymerizable compounds, preferably of formula I or its subformulae, having exactly three polymerizable groups or groups P^{x y} that are capable of undergoing cationic polymerization (trireactive compounds). The concentration of these trireactive compounds of formula I in the LC medium is preferably from 1 to 10%, very preferably from 2 to 5% by weight.

In another preferred embodiment of the present invention component A) of the LC medium comprises one or more polymerizable compounds, preferably of formula I or its subformulae, having exactly one polymerizable group or group P^x that is capable of undergoing cationic polymerization (monoreactive compounds), and further comprises one or more polymerizable compounds, preferably of formula I or its subformulae, having exactly two, three or four, very preferably two, polymerizable groups or groups P^{x y} that are capable of undergoing cationic polymerization (multireactive compounds). In this preferred embodiment the concentration of the monoreactive compounds of formula I in the LC medium is preferably from 5 to 20%, very preferably from 12 to 20% by weight, and the concentration of the multireactive compounds of formula I in the LC medium is preferably from 2 to 10%, very preferably from 3 to 8% by weight.

In the LC medium according to the present invention, the concentration of each individual polymerizable compound, preferably of formula I or its subformulae, is preferably from 1 to 25%, very preferably from 5 to 20% by weight.

In the LC medium according to the present invention, the total concentration of the polymerizable compounds, preferably of formula I or its subformulae, is preferably from 2 to 30%, more preferably from 3 to 25%, very preferably from 5 to 22%, most preferably from 10 to 20% by weight.

Particular preference is given to LC media wherein the polymerizable component A) comprises one, two or three polymerizable compounds, preferably of formula I or its subformulae. The polymerizable component A) additionally contains one or more polymerization initiators that are capable of initiating cationic polymerization. Suitable types and amounts of initiators are known to the person skilled in the art and are described in the literature. Preferably the initiator is a

photoinitiator. Such cationic polymerization initiators are commercially available.

Preferably the concentration of cationic polymerization initiator in the LC medium is from 0.001 to 5% by weight, very preferably 0.005 to 1 % by weight, most preferably 0.01 to 0.5% by weight. In a preferred embodiment of the present invention polymerizable component A) of the LC medium contains a cationic photoinitiator selected from photoacids (PA) and photoacid generators (PAGs).

The initiator, PA and PAG can be a ionic or non-ionic compound.

Preferred PAs and PAGs are those comprising a sulfonyloxyimino group, a sulfonium ion, e.g. a triphenylsulfonium ion, or an iodonium ion, e.g. a diphenyliodonium ion. Such PAs and PAGs are commercially available for example under the series Irgacure®, Irgacure® PAG, Irgacure® CGI or Irgacure® GSID (BASF).

Suitable and preferred PAs and PAGs of these types are those selected from the following formulae

Further preferred PAs and PAGs are those comprising a sulfonyloxyimino group as disclosed for example in WO 2016/043558 A1 . Examples of suitable and preferred PAs and PAGs of these types are those selected from the following formulae

P1

Such PAs and PAGs are commercially available for example from Fleraeus.

Another suitable and preferred initiator has the following formula

Very preferred initiators, PAs and PAGs are selected from Irgacure® 250, Irgacure® 261 , Irgacure® 270, Irgacure® PAG 103, Irgacure® PAG 108, Irgacure® PAG 121 , Irgacure® PAG 203, Irgacure® PAG 290, Irgacure® CGI 725, Irgacure® 1380, Irgacure® CGI 1907, Irgacure® GSID 26-1 (from BASF), and those of formulae P1 -P10 (from Heraeus).

Further preferably the LC medium comprises one or more stabilisers in order to prevent undesired spontaneous polymerization of the polymerizable monomers, for example during storage or transport. Suitable types and amounts of stabilisers are known to the person skilled in the art and are described in the literature. Particularly suitable are, for example, the commercially available stabilisers from the Irganox® series (Ciba AG), such as, for example, Irganox® 1076. Preferably the total concentration of the stabilisers in the LC medium is from 0.001 to 3% by weight, very preferably 0.01 to 1 % by weight, most preferably 0.05 to 0.5% by weight.

Further preferably the polymerizable component A) contains one or more photosensitizers. Example of suitable and preferred photosensitizers include isopropylthioxanthone (ITX) and thioxanthone.

Preferably the concentration of the photosensitizer in the LC medium is from 0.001 to 10% by weight, very preferably 0.01 to 5% by weight, most preferably 0.01 to 2% by weight.

Another preferred embodiment of the present invention relates to an LC medium comprising, in addition to components A) and B) as described above and below, a second polymerizable component C) comprising one or more polymerizable compounds comprising one or more polymerizable groups that are capable of undergoing radical polymerization.

Such an LC medium is suitable for use in a LC display of the PSA mode, or another mode where reactive monomers contained in the LC medium are polymerized by radical polymerization.

Preferred polymerizable compounds of component C) are those of formula R

P¹-Sp¹-(B¹-Z¹)_m-Sp²-P² R wherein Z¹, Sp¹, Sp² and m are as defined in formula I, and the other radicals, independently of each other, and on each occurrence identically or differently, have the following meanings P¹, P² a polymerizable group that is not capable of undergoing cationic

polymerization under the conditons applied for polymerization of the polymerizable compounds of component A), and is preferably capable of undergoing radical polymerization,

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

L^x F, Cl, -CN, -NO2, -NCO, -NCS, -OCN, -SCN, -C(=0)N(R^q)₂,

-C(=0)Y^z, -C(=0)R^q, -N(R^q)₂, optionally substituted silyl, optionally substituted aryl or heteroaryl having 5 to 20 ring atoms, or straight- chain or branched alkyl having 1 to 25 C atoms in which, in addition, one or more non-adjacent CH₂ groups may each be replaced, independently of one another, by -C(R°)=C(R⁰⁰)-, -CºC-, -N(R⁰)-, -O- , -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, one or more of L^x may also denote P¹-Sp¹- and R^q, R°, R⁰⁰, Y^z have one the meanings given in formula I.

Preferred compounds of formula R 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 CFI groups in these groups may be replaced by N, cyclohexane-1 , 4-diyl, in which, in addition, one or more non-adjacent CFI₂ groups may be replaced by O and/or S, 1 ,4- cyclohexenylene, bicyclo[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^x as defined above.

Very preferred compounds of formula R 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, all of which are optionally mono- or polysubstituted by L^x as defined above.

Very preferred compounds of formula R are selected from the group consisting of the following formulae:

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

W02019/110473

PCT/EP2018/083283

-43-

-44 -

35

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 FI, F, Cl, CN 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(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 FI 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°, R°° H or alkyl having 1 to 12 C atoms,

R^y and R^z H, F, CHs or CFs,

X¹ , X², X³ -C0-0-, -O-CO- or a single bond,

Z² -0-, -CO-, -C(R^yR^z)- or -CF2CF2-,

Z³, Z⁴ -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 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, t 0, 1 or 2, x 0 or 1.

Especially preferred are compounds of formulae R2, R13, R17, R22, R23, R24 and R30.

Further preferred are trireactive compounds R15 to R30, in particular R17, R18, R19, R22, R23, R24, R25, R26, R30 and R31.

In the compounds of formulae R1 to R31 the group

wherein L on each occurrence, identically or differently, has one of the meanings given above or below, and is preferably F, Cl, CN, NO2, CFI3, C2FI₅, C(CH₃)₃, CH(CH₃)₂, CH₂CH(CH₃)C₂H5, OCHS, OC2H5, COCHs, COC2H5, COOCFb, COOC2FI₅, CF₃, OCF_3J OCFIF2, OC2F₅ or P¹-Sp¹-, very preferably F, Cl, CN, CFI₃, C2FI₅, OCFI₃, COCFI₃, OCF₃ or P¹-Sp¹-, more preferably F, Cl, CFI₃, OCFI₃, COCFI_{3 O}der OCF₃ , especially F or CFI₃.

Preferred compounds of formula R and its subformulae are those in which P¹, P² and P³ are selected from the group consisting of acrylate,

methacrylate, fluoroacrylate, chloroacrylate and cyanoacrylate, very preferably from acrylate and methacrylate. Further preferred compounds of formula R and its subformulae are those in which Sp¹, Sp² and Sp³ denote -(CFteJpi-, -(CH₂)_PI-0-, -(CH₂)_PI-0-C0- or - (CH₂)_PI-C0-0-, very preferably-(CH2)_Pi-, in which p1 is an integer from 1 to 20. Further preferred compounds of formula R are those in which at least one of Sp¹, Sp² and Sp³ is a single bond and at least one of Sp¹, Sp² and Sp³ is different from a single bond, and is preferably selected from -(CH2)_PI-, - (CFl₂)_Pi-0-, -(CFl₂)_Pi-0-C0- or -(CFl₂)_Pi-C0-0-, very preferably-(CFl2)_Pi-, in which p1 is an integer from 1 to 20.

Another preferred embodiment of the present invention relates to an LC medium comprising, in addition to components A) and B) as described above and below, one or more dyes, preferably selected from dichroic dyes. Such an LC medium is suitable for use in displays of the GH mode, which are for example used in smart windows.

The dyes are preferably organic compounds, particularly preferably organic compounds containing at least one condensed aryl or heteroaryl group. The LC medium preferably comprises at least two, particularly preferably at least three and very particularly preferably three or four different dyes.

If two or more dyes are present in the mixture, they are preferably selected such that their absorption spectra complement one another in such a way that essentially the entire visible spectrum of light is absorbed. The

impression of a black colour thus arises for the human eye. This is preferably achieved by using three or more different dyes, at least one of which absorbs blue light, at least one of which absorbs green to yellow light and at least one of which absorbs red light. Light colour here is defined in accordance with B. Bahadur, Liquid Crystals - Applications and Uses, Vol. 3, 1992, World

Scientific Publishing, section 11.2.1.

The total proportion of the dyes in the LC medium as a whole is preferably from 0.01 to 20%, more preferably from 0.1 to 15% and very preferably from 0.2 to 12% by weight. The proportion of each individual dye in the LC medium as a whole is preferably from 0.01 to 15%, more preferably from 0.05 to 12% and very preferably from 0.1 to 10% by weight.

The dyes present in the LC medium are preferably dissolved in the LC medium. The dyes are preferably influenced in their alignment by the alignment of the molecules of the LC medium mixture in the LC state.

The dyes are preferably selected from dichroic dyes, particularly preferably positively dichroic dyes. Positively dichroic is taken to mean that the dye has a positive degree of anisotropy R. The degree of anisotropy R is particularly preferably greater than 0.4, very particularly preferably greater than 0.5 and most preferably greater than 0.6. The degree of anisotropy R is determined as indicated in the working examples of the application text WO2015/154848. In an alternative embodiment, it may also be preferred for the dyes to be negatively dichroic. Negatively dichroic is taken to mean that the dye has a negative degree of anisotropy R.

The dyes present in the LC medium are preferably either all positively dichroic, or all negatively dichroic.

Furthermore preferably, the dyes in accordance with the present application absorb predominantly light in the UV-VIS-NIR region, i.e. in a wavelength range from 320 to 1500 nm. The dyes particularly preferably absorb predominantly light in the VIS region, i.e. in a wavelength range from 380 to 780 nm. The dyes particularly preferably have one or more absorption maxima in the UV-VIS-NIR region defined above, preferably in the VIS region, i.e. a wavelength of 380 nm to 780 nm. For applications in switchable windows, it may likewise be preferred for the dyes to have one or more absorption maxima in the NIR region, in particular between 780 nm and 1500 nm.

The dye is furthermore preferably selected from the dye classes indicated in B. Bahadur, Liquid Crystals - Applications and Uses, Vol. 3, 1992, World Scientific Publishing, section 11.2.1 , and particularly preferably from the explicit compounds shown in the table. The dyes are preferably selected from azo compounds, anthraquinones, methine compounds, azomethine compounds, merocyanine compounds, naphthoquinones, tetrazines, rylenes, in particular perylenes and terylenes, benzothiadiazoles, pyrromethenes and diketopyrrolopyrroles. Of these, particular preference is given to azo compounds, anthraquinones, benzo- thiadiazoles, in particular as disclosed in WO 2014/187529, diketopyrrolo- pyrroles, in particular as disclosed in WO 2015/090497, and rylenes, in particular as disclosed in WO 2014/090373.

Another preferred embodiment of the present invention relates to an LC medium comprising, in addition to components A) and B) as described above, one or more self-aligning (SA) additives. Such an LC medium is suitable for use in displays of the so-called“self-aligned” or“self-aligning” (SA) mode.

Thus, it was observed that unfavourable interaction of the polyimide alignment layer with certain compounds of the LC medium often leads to a reduction of the electrical resistance of the LC display. In such SA displays the alignment layers, which are usually present in LCDs to ensure specific initial alignment of the LC molecules, are omitted on one or both of the substrates. Instead, a self alignment agent is added to the LC medium that induces the desired alignment, for example homeotropic or planar alignment, in situ by a self assembling mechanism.

Suitable self-aligning additives are for example compounds having an organic core group and attached thereto one or more polar anchor groups, which are capable of interacting with the substrate surface, causing the additives on the substrate surface to align and induce the desired alignment also in the LC molecules.

Suitable self-aligning additives to induce homeotropic alignment are disclosed for example in US 2013/0182202 A1 , US 2014/0838581 A1 , US 2015/0166890 A1 and US 2015/0252265 A1. Preferred SA additives 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 RMs in the PSA process.

The LC medium preferably contains one or more SA additives in a

concentration of 0.1 to 2.5 %.

The SA mode can also be used in combination with the PSA mode. Thus, another preferred LC medium according to the present invention contains, in addition to components A) and B) as described above and below, a second polymerizable component C) comprising one or more polymerizable

compounds comprising one or more polymerizable groups that are capable of undergoing radical polymerization, and are preferably selected from formula R or its subformulae, and further contains one or more self-aligning additives as described above and below.

Besides the polymerizable component A) as described above, the LC medium according to the present invention comprises an LC component B), or LC host mixture, comprising one or more, preferably two or more LC compounds which are selected from low-molecular-weight compounds that are unpolymerizable. These LC compounds are selected such that they stable and/or unreactive to a polymerization reaction under the conditions applied to the polymerization of the polymerizable compounds. Preference is given to LC media in which the LC component B), or the LC host mixture, has a nematic LC phase, and preferably has no chiral liquid crystal phase. The LC component B), or LC host mixture, is preferably a nematic LC mixture. Preference is furthermore given to achiral polymerizable compounds, and to LC media in which the compounds of component A) and/or B) are selected exclusively from the group consisting of achiral compounds.

Preferably the proportion of the LC component B) in the LC medium is from 70 to 95% by weight.

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.

In a first preferred embodiment of the present invention, the LC medium contains an component B) or LC host mixture having a positive dielectric anisotropy De.

Such LC media are especially suitable for use in TN, OCB-, Posi-VA-, IPS- or FFS-displays or related modes using LC-materials with De>0.

The LC media and LC host mixtures according to this first preferred embodiment preferably have a positive dielectric anisotropy De from +2 to +30, particularly preferably from +3 to +20, at 20°C and 1 kHz.

Particularly preferred is an LC medium of this first preferred embodiment, wherein the liquid-crystalline component B) or LC host mixture 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,

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, 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-CFI=CFI or a single bond, very preferably COO or a single bond.

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

in which A²¹, A²², R²¹, X°, L²¹ and L²² have the meanings given in formula A, L²³ and L²⁴ each, independently of one another, are FI 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.

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.

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.

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

-61 -

35

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

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.

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.

Preferably component B) 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 and L³² 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.

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 .

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. 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.

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.

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.

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.

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. 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.

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.

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.

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.

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.

in which R³¹ is as defined in formula B2.

Alternatively to, or in addition to, the compounds of formula B1 and/or B2 component B) 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:

B3a

in which R³¹ is as defined in formula B3.

Preferably component B) of the LC medium comprises, in addition to the compounds of formula A and/or B, one or more compounds of formula 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:

35 wherein 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.

In another preferred embodiment of the present invention component B) of the LC medium comprises, in addition to the compounds of formula A and/or B, 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 R⁴¹ preferably denotes alkyl bedeutet, and in formula D1 R⁴² preferably denotes alkenyl, particularly preferably -(CH₂)₂-CH=CH-CH3, and in formula D2 R⁴² preferably denotes alkyl, -(CH₂)2-CH=CH₂ or -(CH₂)₂-CH=CH-CH₃.

In another preferred embodiment of the present invention component B) 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 Chte groups may be replaced by -0-, -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:

alkyl— ( H alkenyl E1

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, E3a1 and E6a1 .

In another preferred embodiment of the present invention component B) 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: denote

R²¹ 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,

Z²¹

-CFI2CFI2-, -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, g 0, 1 , 2 or 3. 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:

in which R²¹ is as defined in formula F1 . In another preferred embodiment of the present invention component B) of the LC medium comprises, in addition to the compounds of formula A and/or B, one or more compounds of formula G containing a cyano group.

on each occurrence, identically or differently

R⁵¹ alkyl, alkoxy, oxaalkyl or alkoxyalkyl having 1 to 9 C

Z⁵¹ -CH2CH2-, -COO-, trans- CH=CH-, trans- CF=CF-, -CH2O-

, -CF2O-, -CºC- or a single bond, preferably a single bond,

L⁵¹, L⁵² H or F,

0, 1 , 2 or 3.

Preferred compounds of formula G are selected from the following

subformulae

35

in which R⁵¹ is as defined in formula G and L¹ and L² are each, independently of one another, H or F. Very preferred are compounds of formula G1 , G2 and G5.

Preferred compounds of formula G1 -G9 are those wherein L⁵¹ and L⁵² are F.

Further preferred compounds of formula G1 -G7 are those wherein L⁵¹ is F and L⁵² is FI.

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

in which R⁵¹ is as defined in formula G.

In the compounds of formula G, G1-G7 and their subformulae, R⁵¹ is particularly preferably alkyl or alkoxy having 1 to 8 carbon atoms, or alkenyl having from 2 to 7 carbon atoms.

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

The concentration 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 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 LC host mixture comprises one or more compounds selected from the group consisting of formulae A1a2, A1 b1 , A1d1 , A1f1 , A2a1 , A2h1 , A2I1 , A2I2, A2k1 , B2h3, B2I1 , F1a. The proportion of these compounds in the LC host mixture is preferably from 4 to 40%, very preferably from 5 to 35%. c) The LC host mixture comprises one or more compounds selected from the group consisting of formulae C3, C4, C5, C9 and D2. The proportion of these compounds in the LC host mixture is preferably from 8 to 70%, very preferably from 10 to 60%. d) The LC host mixture comprises one or more compounds selected from the group consisting of formulae G1 , G2 and G5, preferably G1a, G2a and G5a. The proportion of these compounds in the LC host mixture is preferably from 4 to 40%, very preferably from 5 to 35%. e) The LC host mixture comprises one or more compounds selected from the group consisting of formulae E1 , E3 and E6, preferably E1 a, E3a and E6a, very preferably E1 a2, E1 a5, E3a1 and E6a1. The proportion of these compounds in the LC host mixture is preferably from 5 to 60%, very preferably from 10 to 50%.

In a second preferred embodiment of the present invention, the LC medium contains an component B) or LC host mixture having a negative dielectric anisotropy De.

Such LC media are especially suitable for use in VA, IPS and UB-FFS displays or related modes using LC-materials with De<0.

The LC media and LC host mixtures according to this second preferred embodiment preferably have a negative dielectric anisotropy De from -0.5 to - 10, very preferably from -2.5 to -7.5, at 20°C and 1 kHz. Particularly preferred embodiments of an LC medium according to this second preferred embodiment are those of sections a)-z2) below: a) LC medium wherein the component B) or LC host mixture comprises one or more compounds selected from formulae CY and PY:

wherein a denotes 1 or 2, b denotes 0 or 1

R¹ and R² each, independently of one another, denote alkyl having 1 to

12 C atoms, where, in addition, one or two non-adjacent CFh groups may be replaced by -0-, -CH=CH-, -CO-, -OCO- or -COO- in such a way that O atoms are not linked directly to one another, preferably alkyl or alkoxy having 1 to 6 C atoms,

Z^x and Z^y each, independently of one another, denote -CH2CH2-,

-CH=CH-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -CO-O-, -O-CO-, -C₂F₄-, -CF=CF-, -CFI=CFI-CFl₂0- or a single bond, preferably a single bond,

L^{1 4} each, independently of one another, denote F, Cl, OCF3,

CFs, CHs, CH₂F, CHF₂.

Preferably, both L¹ and L² denote F or one of L¹ and L² denotes F and the other denotes Cl, or both L³ and L⁴ denote F or one of L³ and L⁴ denotes F and the other denotes Cl.

The compounds of the formula CY are preferably selected from the group consisting of the following sub-formulae:

in which a denotes 1 or 2, 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 2-6 C atoms, and (O) denotes an oxygen atom or a single bond. Alkenyl preferably denotes 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-.

Especially preferred are compounds selected from formulae CY2, CY8, CY10 and CY16.

The compounds of the formula PY are preferably selected from the group consisting of the following sub-formulae:

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 2-6 C atoms, and (O) denotes an oxygen atom or a single bond. Alkenyl preferably denotes CFh=CFI-, 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-.

Especially preferred are compounds selected from formulae PY2, PY8 PY10 and PY16. Preferably the concentration of the compounds of formula CY and PY and their subformulae in the LC medium is from 10 to 70% by weight, very preferably from 15 to 50% by weight. Preferably the concentration of the compounds of formula CY and its subformulae in the LC medium is from 2 to 40% by weight, very preferably from 3 to 30% by weight.

Preferably the concentration of the compounds of formula PY and its subformulae in the LC medium is from 2 to 50% by weight, very preferably from 3 to 40% by weight. b) LC medium wherein the component B) or LC host mixture comprises one or more mesogenic or LC compounds comprising an alkenyl group (hereinafter also referred to as "alkenyl compounds"), wherein said alkenyl group is stable to a polymerization reaction under the conditions used for polymerization of the polymerizable compounds contained in the LC medium.

Preferably the component B) or LC host mixture comprises one or more alkenyl compounds selected from formulae AN and AY

in which the individual radicals, on each occurrence identically or differ- ently, and 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 -0-, -CH=CH-, -CO- , -OCO- or -COO- in such a way that O atoms are not linked directly to one another,

Z^x -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-, -OCH2-,

-CO-O-, -O-CO-, -C₂F₄-, -CF=CF-, -CH=CH-CH₂0-, or a single bond, preferably a single bond,

L¹-⁴ H, F, Cl, OCFs, CFs, CHs, CH₂F or CHF₂, preferably H, F or Cl, x 1 or 2, z 0 or 1.

Preferred compounds of formula AN and AY are those wherein R^A2 is selected from ethenyl, propenyl, butenyl, pentenyl, hexenyl and heptenyl. In a preferred embodiment the component B) or LC host mixture comprises one or more compounds of formula AN selected from the following sub-formulae:

alkenyl— ( H >— ( H >— ( O )— alkyl AN6

alkenyl— ( H >— ( H >— ( O )— O-alkyl AN7

alkenyl— ( H >— ( O > - ( O )— alkyl AN8

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-.

Preferably the the component B) or LC host mixture comprises one or more compounds selected from formulae AN1 , AN2, AN3 and AN6, very preferably one or more compounds of formula AN1 .

In another preferred embodiment the component B) or LC host mixture comprises one or more compounds of formula AN 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, Chb or C2H5. In another preferred embodiment the component B) or LC host mixture comprises one or more compounds selected from the following sub- formulae:

Most preferred are compounds of formula AN1 a2 and AN1 a5.

In another preferred embodiment the component B) or LC host mixture comprises one or more compounds of formula AY selected from the following sub-formulae:

in which alkyl and alkyl^* each, independently of one another, denote a straight-chain alkyl radical having 1 -6 C atoms, "(O)" denotes an O- atom or a single bond, 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-. In another preferred embodiment the component B) or LC host mixture comprises one or more compounds of formula AY selected from the following sub-formulae:

in which m and n each, independently of one another, denote 1 , 2, 3, 4, 5 or 6, and alkenyl denotes 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-. Preferably the proportion of compounds of formula AN and AY in the LC medium is from 2 to 70% by weight, very preferably from 5 to 60% by weight, most preferably from 10 to 50% by weight. Preferably the LC medium or LC host mixture contains 1 to 5, preferably

1 , 2 or 3 compounds selected from formulae AN and AY.

In another preferred embodiment of the present invention the LC medium comprises one or more compounds of formula AY14, very preferably of AY14a. The proportion of compounds of formula AY14 or

AY14a in the LC medium is preferably 3 to 20% by weight.

The addition of alkenyl compounds of formula AN and/or AY enables a reduction of the viscosity and response time of the LC medium. c) LC medium wherein the component B) or LC host mixture comprises one or more compounds of the following formula:

in which the individual radicals have the following meanings:

R³ and R⁴ each, independently of one another, denote alkyl having 1 to

12 C atoms, in which, in addition, one or two non-adjacent Chte groups may be replaced by -0-, -CH=CH-, -CO-, -O-CO- or -CO-O- in such a way that O atoms are not linked directly to one another, z^y denotes -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-,

-OCH2-, -CO-O-, -O-CO-, -C₂F₄-, -CF=CF-, -CH=CH-CH₂O- or a single bond, preferably a single bond.

The compounds of the formula ZK are preferably selected from the group consisting of the following sub-formulae:

0

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 2-6 C atoms. Alkenyl preferably denotes 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-.

Especially preferred are compounds of formula ZK1 .

Particularly preferred compounds of formula ZK are selected from the following sub-formulae:

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

Most preferred are compounds of formula ZK1 a. d) LC medium wherein component B) or the LC host mixture additionally comprises one or more compounds of the following formula:

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

R⁵ and R⁶ each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent Chte groups may be replaced by -0-, -CH=CH-, -CO-, -OCO- or -COO- in such a way that O atoms are not linked directly to one another, preferably alkyl or alkoxy having 1 to 6 C atoms,

e denotes 1 or 2.

The compounds of the formula DK are preferably selected from the group consisting of the following sub-formulae:

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 2-6 C atoms. Alkenyl preferably denotes 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-. e) LC medium wherein component B) or the LC host mixture additionally comprises one or more compounds of the following formula:

in which the individual radicals have the following meanings:

with at least one ring F being different from cyclohexylene f denotes 1 or 2,

R¹ and R² each, independently of one another, denote alkyl having 1 to

12 C atoms, where, in addition, one or two non-adjacent CFh groups may be replaced by -0-, -CFI=CFI-, -CO-, -OCO- or -COO- in such a way that O atoms are not linked directly to one another, - i i e -

Z^x denotes -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-,

-OCH2-, -C0-0-, -0-C0-, -C₂F₄-, -CF=CF-, -CH=CH-CH₂O- or a single bond, preferably a single bond, L¹ and L² each, independently of one another, denote F, Cl, OCF3,

CFs, CHs, CH₂F, CHF₂.

Preferably, both radicals L¹ and L² denote F or one of the radicals L¹ and L² denotes F and the other denotes Cl.

The compounds of the formula LY are preferably selected from the group consisting of the following sub-formulae:

in which R¹ has the meaning indicated above, alkyl denotes a straight- chain alkyl radical having 1 -6 C atoms, (O) denotes an oxygen atom or a single bond, and v denotes an integer from 1 to 6. R¹ preferably denotes straight-chain alkyl having 1 to 6 C atoms or straight-chain alkenyl having 2 to 6 C atoms, in particular CH3, C2H5, n-C₃Fl₇, n-C₄H9, n-CsHn, 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-. f) LC medium wherein component B) or the LC host mixture additionally comprises one or more compounds selected from the group consisting of the following formulae:

in which alkyl denotes Ci-₆-alkyl, L^x denotes FI or F, and X denotes F, Cl, OCF3, OCFIF₂ or OCFI=CF₂. Particular preference is given to corn- pounds of the formula GG1 in which X denotes F. g) LC medium wherein component B) or the LC host mixture additionally comprises one or more compounds selected from the group consisting of the following formulae:

in which R⁵ has one of the meanings indicated above for R¹, alkyl denotes Ci-₆-alkyl, d denotes 0 or 1 , and z and m each, independently of one another, denote an integer from 1 to 6. R⁵ in these compounds is particularly preferably Ci-₆-alkyl or -alkoxy or C2-6-alkenyl, d is preferably 1 . The LC medium according to the invention preferably comprises one or more compounds of the above-mentioned formulae in amounts of > 5% by weight. h) LC medium wherein component B) or the LC host mixture additionally comprises one or more biphenyl compounds selected from the group consisting of the following formulae:

BP3

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 2-6 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-.

The proportion of the biphenyls of the formulae BP1 to BP3 in the LC host mixture is preferably at least 3% by weight, in particular > 5% by weight.

The compounds of the formula BP2 are particularly preferred.

The compounds of the formulae BP1 to BP3 are preferably selected from the group consisting of the following sub-formulae:

in which alkyl* denotes an alkyl radical having 1 -6 C atoms. The medium according to the invention particularly preferably comprises one or more compounds of the formulae BP1 a and/or BP2c. i) LC medium wherein component B) or the LC host mixture additionally comprises one or more terphenyl compounds of the following formula:

in which R⁵ and R⁶ each, independently of one another, have one of the meanings indicated above, and

each, independently of one another, denote

in which L⁵ denotes F or Cl, preferably F, and L⁶ denotes F, Cl, OCF3, CF3, CFI3, CFI2F or CFIF2, preferably F.

The compounds of the formula T are preferably selected from the group consisting of the following sub-formulae:

F F F F

R- ( ⁰ )— ( ⁰ )— ( ⁰ ) (0)C_mH_2m+1 T17

F F F F

R ( o ) ( O ) ( O ) (O)C m H 2m+1 T18

in which R denotes a straight-chain alkyl or alkoxy radical having 1 -7 C atoms, R* denotes a straight-chain alkenyl radical having 2-7 C atoms, (O) denotes an oxygen atom or a single bond, and m denotes an integer from 1 to 6. R^* preferably denotes CFh=CFI-, CFh=CFICFl2CFl2-, CH₃-CH=CH-, CH₃-CH₂-CH=CH-, CH₃-(CH₂)₂-CH=CH-, CH₃-(CH₂)₃- CH=CH- or CH₃-CH=CH-(CH₂)₂-.

R preferably denotes methyl, ethyl, propyl, butyl, pentyl, hexyl, methoxy ethoxy, propoxy, butoxy or pentoxy. The LC host mixture according to the invention preferably comprises the terphenyls of the formula T and the preferred sub-formulae thereof in an amount of 0.5-30% by weight, in particular 1 -20% by weight.

Particular preference is given to compounds of the formulae T1 , T2, T3 and T21 . In these compounds, R preferably denotes alkyl, furthermore alkoxy, each having 1 -5 C atoms.

The terphenyls are preferably employed in LC media according to the invention if the Dh value of the mixture is to be > 0.1 . Preferred LC media comprise 2-20% by weight of one or more terphenyl compounds of the formula T, preferably selected from the group of compounds T 1

k) LC medium wherein component B) or the LC host mixture additionally comprises one or more quaterphenyl compounds selected from the group consisting of the following formulae:

wherein

R^Q is 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^Q is F, Cl, halogenated alkyl or alkoxy having 1 to 6 C atoms or halogenated alkenyl or alkenyloxy having 2 to 6 C atoms,

L^Q1 to L^Q6 independently of each other are H or F, with at least one of

L^Q1 to L^Q6 being F. Preferred compounds of formula Q are those wherein R^Q denotes straight-chain alkyl with 2 to 6 C-atoms, very preferably ethyl, n-propyl or n-butyl.

Preferred compounds of formula Q are those wherein L^Q3 and L^Q4 are F. Further preferred compounds of formula Q are those wherein L^Q3,

L^Q4 and one or two of L^Q1 and L^Q2 are F.

Preferred compounds of formula Q are those wherein X^Q denotes F or OCF3, very preferably F.

The compounds of formula Q are preferably selected from the following subformulae

wherein R^Q has one of the meanings of formula Q or one of its preferred meanings given above and below, and is preferably ethyl, n-propyl or n- butyl.

Especially preferred are compounds of formula Q1 , in particular those wherein R^Q is n-propyl.

Preferably the proportion of compounds of formula Q in the LC host mixture is from >0 to <5% by weight, very preferably from 0.1 to 2% by weight, most preferably from 0.2 to 1 .5% by weight. Preferably the LC host mixture contains 1 to 5, preferably 1 or 2 compounds of formula Q.

The addition of quaterphenyl compounds of formula Q to the LC host mixture enables to reduce ODF mura, whilst maintaining high UV absorption, enabling quick and complete polymerization, enabling strong and quick tilt angle generation, and increasing the UV stability of the LC medium.

Besides, the addition of compounds of formula Q, which have positive dielectric anisotropy, to the LC medium with negative dielectric anisotropy allows a better control of the values of the dielectric constants e and _±, and in particular enables to achieve a high value of the dielectric constant e while keeping the dielectric anisotropy De constant, thereby reducing the kick-back voltage and reducing image sticking.

I) LC medium wherein component B) or the LC host mixture additionally comprises one or more compounds of formula CC:

wherein

R^c denotes 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^c denotes F, Cl, halogenated alkyl or alkoxy having 1 to 6 C atoms or halogenated alkenyl or alkenyloxy having 2 to 6 C atoms, L^C1 , L^C2 independently of each other denote FI or F, with at least one of L^C1 and L^C2 being F.

Preferred compounds of formula CC are those wherein R^c denotes straight-chain alkyl with 2 to 6 C-atoms, very preferably ethyl, n-propyl or n-butyl.

Preferred compounds of formula CC are those wherein L^C1 and L^C2 are F.

Preferred compounds of formula CC are those wherein X^c denotes F or OCF3, very preferably F.

Preferred compounds of formula CC are selected from the following formula

wherein R^c has one of the meanings of formula CC or one of its preferred meanings given above and below, and is preferably ethyl, n- propyl or n-butyl, very preferably n-propyl.

Preferably the proportion of compounds of formula CC in the LC host mixture is from >0 to < 10% by weight, very preferably from 0.1 to 8% by weight, most preferably from 0.2 to 5% by weight.

Preferably the LC host mixture contains 1 to 5, preferably 1 , 2 or 3 compounds of formula CC.

The addition of compounds of formula CC, which have positive

dielectric anisotropy, to the LC medium with negative dielectric

anisotropy allows a better control of the values of the dielectric constants e and e_±, and in particular enables to achieve a high value of the dielectric constant e while keeping the dielectric anisotropy De constant, thereby reducing the kick-back voltage and reducing image sticking. Besides, the addition of compounds of formula CC enables to reduce the viscosity and the response time of the LC medium. m) LC medium wherein component B) or the LC host mixture additionally comprises one or more compounds selected from the group consisting of the following formulae:

in which R¹ and R² have the meanings indicated above and preferably each, independently of one another, denote straight-chain alkyl having 1 to 6 C atoms or straight-chain alkenyl having 2 to 6 C atoms.

Preferred media comprise one or more compounds selected from the formulae 01 , 03 and 04. n) LC medium wherein component B) or the LC host mixture additionally comprises one or more compounds of the following formula:

in which

R⁹ denotes H, CH3, C2H5 or n-CsFF, (F) denotes an optional fluorine substituent, and q denotes 1 , 2 or 3, and R⁷ has one of the meanings indicated for R¹, preferably in amounts of > 3% by weight, in particular > 5% by weight and very particularly preferably 5-30% by weight. Particularly preferred compounds of the formula FI are selected from the group consisting of the following sub-formulae:

in which R⁷ preferably denotes straight-chain alkyl, and R⁹ denotes CFI3, C2FI5 or n-C3Fl₇. Particular preference is given to the compounds of the formulae FI1 , FI2 and FI3. o) LC medium wherein component B) or the LC host mixture additionally comprises one or more compounds selected from the group consisting of the following formulae:

in which R⁸ has the meaning indicated for R¹, and alkyl denotes a straight-chain alkyl radical having 1 -6 C atoms. p) LC medium wherein component B) or the LC host mixture additionally comprises one or more compounds which contain a tetrahydronaphthyl or naphthyl unit, such as, for example, the compounds selected from the group consisting of the following formulae:

in which

R¹⁰ and R¹¹ each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent Chte groups may be replaced by -0-, -CH=CH-, -CO-,

-OCO- or -COO- in such a way that O atoms are not linked directly to one another, preferably alkyl or alkoxy having 1 to 6 C atoms, and R¹⁰ and R¹¹ preferably denote straight-chain alkyl or alkoxy having

1 to 6 C atoms or straight-chain alkenyl having 2 to 6 C atoms, and

Z¹ and Z² each, independently of one another, denote -C2H₄-,

-CH=CH-, -(CH₂)4-, -(CH₂)₃0-, -0(CH₂)₃-, -CH=CH-CH₂CH₂-, -CH₂CH₂CH=CH-, -CH₂O-, -OCH₂-,

-CO-0-, -o-co-, -C₂F₄-, -CF=CF-, -CF=CH-, -CH=CF-, -CH₂- or a single bond. q) LC medium wherein component B) or the LC host mixture additionally comprises one or more difluorodibenzochromans and/or chromans of the following formulae:

in which

R¹¹ and R¹² each, independently of one another, have one of the

meanings indicated above for R¹¹,

ring M is trans-1 ,4-cyclohexylene or 1 ,4-phenylene,

Z^m -C₂H₄-, -CH2O-, -OCH2-, -CO-O- or -O-CO-,

c is 0, 1 or 2,

preferably in amounts of 3 to 20% by weight, in particular in amounts of 3 to 15% by weight.

Particularly preferred compounds of the formulae BC, CR and RC are selected from the group consisting of the following sub-formulae:

in which alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1 -6 C atoms, (O) denotes an oxygen atom or a single bond, c is 1 or 2, and alkenyl and alkenyl* each, independently of one another, denote a straight-chain alkenyl radical having 2-6 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 particular preference is given to LC host mixtures comprising one, two or three compounds of the formula BC-2. r) LC medium wherein component B) or the LC host mixture additionally comprises one or more fluorinated phenanthrenes and/or dibenzofurans of the following formulae:

in which R¹¹ and R¹² each, independently of one another, have one of the meanings indicated above for R¹¹, b denotes 0 or 1 , L denotes F, and r denotes 1 , 2 or 3.

Particularly preferred compounds of the formulae PH and BF are selected from the group consisting of the following sub-formulae:

in which R and R' each, independently of one another, denote a straight-chain alkyl or alkoxy radical having 1 -7 C atoms. s) LC medium wherein component B) or the LC host mixture additionally comprises one or more monocyclic compounds of the following formula

wherein

R¹ and R² each, independently of one another, denote alkyl having 1 to

L¹ and L² each, independently of one another, denote F, Cl, OCF3,

CFs, CHs, CH₂F, CHF₂.

Preferably, both L¹ and L² denote F or one of L¹ and L² denotes F and the other denotes Cl,

The compounds of the formula Y are preferably selected from the group consisting of the following sub-formulae:

0,

in which, Alkyl and Alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1 -6 C atoms, Alkoxy denotes a straight-chain alkoxy radical having 1-6 C atoms, Alkenyl and Alkenyl* each, independently of one another, denote a straight-chain alkenyl radical having 2-6 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-.

Particularly preferred compounds of the formula Y are selected from the group consisting of the following sub-formulae:

Alkoxy Alkoxy Y6A

Alkoxy Alkoxy Y6B

wherein Alkoxy preferably denotes straight-chain alkoxy with 3, 4, or 5 C atoms. t) LC medium which, apart from the polymerizable compounds as

described above and below, does not contain a compound which con- tains a terminal vinyloxy group (-0-CH=CH2). u) LC medium wherein component B) or the LC host mixture comprises 1 to 8, preferably 1 to 5, compounds of the formulae CY1 , CY2, PY1 and/or PY2. The proportion of these compounds in the LC host mixture as a whole is preferably 5 to 60%, particularly preferably 10 to 35%.

The content of these individual compounds is preferably in each case 2 to 20%. v) LC medium wherein component B) or the LC host mixture comprises 1 to 8, preferably 1 to 5, compounds of the formulae CY9, CY10, PY9 and/or PY10. The proportion of these compounds in the LC host

mixture as a whole is preferably 5 to 60%, particularly preferably 10 to 35%. The content of these individual compounds is preferably in each case 2 to 20%. w) LC medium wherein component B) or the LC host mixture comprises 1 to 10, preferably 1 to 8, compounds of the formula ZK, in particular

compounds of the formulae ZK1 , ZK2 and/or ZK6. The proportion of these compounds in the LC host mixture as a whole is preferably 3 to 25%, particularly preferably 5 to 45%. The content of these individual compounds is preferably in each case 2 to 20%. x) LC medium in which the proportion of compounds of the formulae CY, PY and ZK in the LC host mixture as a whole is greater than 70%, pref- erably greater than 80%. y) LC medium in which the LC host mixture contains one or more

compounds containing an alkenyl group, preferably selected from formulae AN and AY, very preferably selected from formulae AN1 , AN3 AN6 and AY14, most preferably from formulae AN 1a, AN3a, AN6a and AY14. The concentration of these compounds in the LC host mixture is preferably from 2 to 70%, very preferably from 3 to 55%. z) LC medium wherein component B) or the LC host mixture contains one or more, preferably 1 to 5, compounds selected of formula PY1 -PY8, very preferably of formula PY2. The proportion of these compounds in the LC host mixture as a whole is preferably 1 to 30%, particularly preferably 2 to 20%. The content of these individual compounds is preferably in each case 1 to 20%. z1 ) LC medium wherein component B) or the LC host mixture contains one or more, preferably 1 , 2 or 3, compounds selected from formulae T1 , T2, T3 and T21 , very preferably from formula T2. The content of these compounds in the LC host mixture as a whole is preferably 1 to 20%. z2) LC medium in which the LC host mixture contains one or more,

preferably 1 , 2 or 3, compounds of formula BF1 , and one or more, preferably 1 , 2 or 3, compounds selected from formulae AY14, AY15 and AY16, very preferably of formula AY14. The proportion of the compounds of formula AY14-AY16 in the LC host mixture is preferably from 2 to 35%, very preferably from 3 to 30%. The proportion of the compounds of formula BF1 in the LC host mixture is preferably from 0.5 to 20%, very preferably from 1 to 15%. Further preferably the LC host mixture according to this preferred embodiment contains one or more, preferably 1 , 2 or 3 compounds of formula T, preferably selected from formula T1 , T2 and T3, very preferably from formula T2. The proportion of the compounds of formula T in the LC host mixture medium is preferably from 0.5 to 15%, very preferably from 1 to 10%.

In the LC medium according to the present invention, the use of an LC host mixture together with the use of a polymerizable component comprising a combination of a first, second and third polymerizable compound as described above leads to advantageous properties in LC displays. In particular, one or more of the following advantages could be achieved: - easy and quick formation of polymer walls by polymerization-induced phase separation of the polymer formed by the first and second

polymerizable compounds,

- formation of polymer walls with highly defined shape and constant

thickness,

- constant cell gap,

- high flexibility of the display cell in case plastic substrates are used,

- high resistance of the display cell against mechanical pressure, and low variation of the cell gap under pressure,

- good adhesion of the polymer walls to the substrates,

- low number of defects,

- reduced formation of domains with different electrooptical properties like response time or contrast,

- high transparency,

- good contrast,

- fast response times.

The display manufacture process is known to the skilled person and is described in the literature, for example in US6130738 and EP2818534 A1.

The present invention also relates to a process for the production of an LC display as described above and below, comprising the steps of providing an LC medium as described above and below into the display, and polymerizing the polymerizable compounds in defined regions of the display.

Preferably the polymerizable compounds are photopolymerized by exposure to UV irradiation.

Further preferably the polymerizable compounds are photopolymerized by exposure to UV irradiation through a photomask. The UV radiation can be generated by a variety of light sources which are known to the skilled person, including but not limited to arc lamps, led lights, laser light sources, or others. The photomask is preferably designed such that it comprises regions that are transparent to the UV radiation used for photopolymerization, and regions that are not transparent to the UV radiation used for photopolymerization, and wherein the transparent regions form a pattern or image that

corresponds to the desired shape of the polymer walls. As a result the polymerizable compounds are only polymerized in those parts of the display that are covered by the transparent regions of the photomask, thus forming polymer walls of the desired shape. Alternatively to using a photomask, a light source can be used that emits light with an already shaped profile. Such profile can for example be generated by interference of two laser beams.

In a preferred embodiment of the present invention, the display is subjected to a second UV irradiation step, preferably without a photomask applied, after the first UV irradiation step as described above. Thereby it is possible to complete polymerization of monomers that were not or only partially polymerized in the first step. The second UV step can have an emission spectrum and/or intensity which is the same as that of the first step, or which is different from the first step.

Alternatively two applying two separate irradiation steps, the intensity is changed during UV exposure. Preferably, the intensity is gradually increased during UV exposure.

For example, an LC display according to the present invention can be manufactured as follows. Polymerizable compounds as described above and below are combined with a suitable LC host mixture. This resulting LC medium can then be included into the display by using conventional manufacturing processes. The resulting LC medium can be filled for example using capillary forces into the cell gap formed by two substrates.

Alternatively, the LC medium can be deposited as a layer onto a substrate, and another substrate is placed on top of the LC layer under vacuum in order to prevent inclusion of air bubbles. The LC medium is in either case located in the cell gap formed by the two substrates, as exemplarily illustrated in Fig. 1a. These substrates usually are covered by an alignment layer which is in direct contact with the LC medium. The substrates itself can carry other functional components like TFTs, black matrix, colour filter, or similar. Subsequently, polymerization induced phase separation is initiated by exposure of the LC medium, which is either in the nematic or the isotropic phase, to UV radiation with collimated light through a photomask, as exemplarily illustrated in Fig. 1b. This leads to the formation of polymer wall structures, restoration of the LC host, and alignment of the LC phase with the alignment layer, as exemplarily illustrated in Fig. 1c.

This process can advantageously utilize display manufacturing processes that are established in the industry. Thus, both the display filling process, for example by one-drop-filling (ODF), and the radiation initiated polymerization step after sealing the display, which is known for example from polymer stabilised or PS-type display modes like PS-VA, are established techniques in conventional LCD manufacturing.

A preferred 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 including a micro-slit pattern, 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,

an LC layer disposed between the first and second substrates and including an LC medium comprising a polymerizable component A) and a liquid-crystalline component B) as described above and below, wherein the polymerizable component A) is polymerized.

The LC display 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. The electrode structure can be designed by the skilled person depending on the individual display type. For example for VA displays a multi-domain orientation of the LC molecules can be induced by providing electrodes having slits and/or bumps or protrusions in order to create two, four or more different tilt alignment directions.

The first and/or second alignment layer controls the alignment direction of the LC molecules of the LC layer. For example, in TN displays the alignment layer is selected such that it imparts to the LC molecules an orientation direction parallel to the surface, while in VA displays the alignment layer is selected such that it imparts to the LC molecules a homeotropic alignment, i.e. an orientation direction perpendicular to the surface. Such an alignment layer may for example comprise a polyimide, which may also be rubbed, or may be prepared by a photoalignment method.

The substrate can be a glass substrate, for example in case of a curved display. The use of an LC medium according to the present invention in an LC display with glass substrates can provide several advantages. For example, the formation of polymer wall structures in the LC medium helps to prevent the so-called“pooling effect” where pressure applied on the glass substrates causes unwanted optical defects. The stabilizing effect of the polymer wall structures also allows to further minimize the panel thickness. Moreover, in bent panels with glass substrates the polymer wall structures enable a smaller radius of curvature.

For flexible LC displays preferably plastic substrates are used. These plastic substrates preferably have a low birefringence. Examples are polycarbonate (PC), polyethersulfone (PES), polycyclic olefine (PCO), polyarylate (PAR), polyetheretherketone (PEEK), or colourless polyimide (CPI) substrates.

The LC layer with the LC medium can be deposited between the substrates of the display by methods that are conventionally used by display

manufacturers, for example the one-drop-filling (ODF) method. The polymerizable component of the LC medium is then polymerized for example by UV photopolymerization. In case the polymerizable compounds are used as a replacement for spacer particles, the display manufacturing process preferably comprises the following steps:

In a first step, the LC medium containing the LC host and monomer precursor is applied to one of the two substrates, preferably by using one of the following deposition methods: one drop filling, ink jet printing, spin coating, slit coating, flexo printing, or a comparable method. The substrate in that instance may carry a colour filter, TFT devices, a black matrix, a polyimide coating, or other components typically found on a display substrate. The applied LC medium forms a thin, uniform film with the thickness of the targeted cell gap of the final device. In a second step, the applied film is subjected to UV radiation having an intensity profile. This profile is generated for example by irradiating through a photomask, lithography, contact lithography, proximity lithography, projection lithography, using laser interference, direct laser writing, or a comparable method. Irradiation of the film can either occour from either side of the substrate. In case of using a photomask, the mask can either placed on the substrate and the LC film is cured by the light passing through the substrate, or the mask is directly brought in close proximity to the LC film and the LC medium is cured directly.

In this second step, polymer wall structures are created that function as spacer.

Subsequently, the second substrate, which may also carry colour filter, TFT devices, a black matrix, a polyimide coating, or other components typically found on a display substarte, is place ontop of the first substrate so that the LC film comes to rest in between the two substrates.

A further irradiation is now optionally possible to convert unreacted

monomers, generate adhesion between the two substartes, and/or seal the edges of the display. The polymerization of the polymerizable compounds can be carried out in one step or in two or more steps. It is also possible to carry out the polymerization in a sequence of several UV irradiation and/or heating or cooling steps. For example, a display manufacturing process may include a first UV irradiation step at room temperature to produce a pretilt angle, and subsequently, in a second polymerization step to polymerize or crosslink the compounds which have not reacted in the first step ("end curing").

Upon polymerization the polymerizable compounds react with each other to a polymer which undergoes macroscopical phase-separation from the LC host mixture and forms polymer walls in the LC medium.

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.

Preferably the LC medium contains one or more polymerization initiators. The polymerizable compounds according to the invention are also suitable for polymerization without an initiator, which is accompanied by considerable advantages, such, for example, lower material costs and in particular less contamination of the LC medium by possible residual amounts of the initiator or degradation products thereof. The polymerization can thus also be carried out without the addition of an initiator. In a preferred embodiment, the LC medium contains a polymerization initiator.

The LC medium may also comprise one or more stabilisers or inhibitors in order to prevent undesired spontaneous polymerization of the RMs, for example during storage or transport. Suitable types and amounts of stabilisers are known to the person skilled in the art and are described in the literature. Particularly suitable are, for example, the commercially available stabilisers from the Irganox® series (Ciba AG), such as, for example, Irganox® 1076. If stabilisers 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. Preferably the LC medium according to the present invention does essentially consist of a polymerizable component A) and an LC component B) (or LC host mixture) as described above and below. However, the LC medium may additionally comprise one or more further components or additives.

The LC media according to the invention may also comprise further additives which are known to the person skilled in the art and are described in the literature, such as, for example, polymerization initiators, inhibitors,

stabilisers, sensitizers, surface-active substances or chiral dopants. These may be polymerizable or non-polymerizable. Polymerizable additives, polymerization initiators and sensitizers are ascribed to the polymerizable component or component A). Other non-polymerizable additives are ascribed to the non-polymerizable component or component B).

Preferred additives are selected from the list including but not limited to co- monomers, chiral dopants, polymerization initiators, inhibitors, stabilizers, surfactants, wetting agents, lubricating agents, dispersing agents,

hydrophobing agents, adhesive agents, flow improvers, defoaming agents, deaerators, diluents, reactive diluents, auxiliaries, colourants, dyes, pigments and nanoparticles.

In a preferred embodiment the LC media contain one or more chiral dopants, preferably in a concentration from 0.01 to 1 % by weight, very preferably from 0.05 to 0.5% by weight. The chiral dopants are preferably selected from the group consisting of compounds from Table B below, very preferably from the group consisting of R- or S-1011 , R- or S-2011 , R- or S-3011 , R- or S-4011 , and R- or S-5011. In another preferred embodiment the LC media contain a racemate of one or more chiral dopants, which are preferably selected from the chiral dopants mentioned in the previous paragraph.

Furthermore, it is possible to add to the LC media, for example, 0 to 15% by weight of pleochroic dyes, furthermore nanoparticles, conductive salts, preferably ethyldimethyldodecylammonium 4-hexoxybenzoate, tetrabutyl- ammonium tetraphenyl borate 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. Sub- stances 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.

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 of the above-mentioned compounds with one or more polymerizable compounds as defined above, and optionally with further liquid-crystalline compounds and/or additives. In general, the desired amount of the com- ponents used in lesser amount is dissolved in the components making up the principal constituent, advantageously at elevated temperature. It is also possible to mix solutions of the components in an organic solvent, for example in acetone, chloroform or methanol, and to remove the solvent again, for example by distillation, after thorough mixing. The invention furthermore relates to the process for the preparation of the LC media according to the invention.

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 following examples explain the present invention without restricting it. However, 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.

Preferred mixture components are shown in Tables A1 and A2 below. The compounds shown in Table A1 are especially suitable for use in LC mixtures with positive dielectric anisotropy. The compounds shown in Table A2 are especially suitable for use in LC mixtures with negative dielectric anisotropy.

Table A1

In Table A1 , 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

160

GP-n-CI GGP-n-CI

T3 n

Table A2

In Table A2, 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_mH2 m+i means Cm H2m+1 or OC mH2m+1

CB-n-Om

CY-n-Om

CCY-V-m

CCP-n-m

CY-n-m

CVC-n-m

CY-V-On

CPY-n-Om

COChrom-n-m

CNaph-n-Om

LYLI-n-m

COY-n-Om

PP-n-2V1

YY-nO-Om In a first preferred embodiment of the present invention, the LC media according to the invention, especially those with positive dielectric anisotropy, comprise one or more compounds selected from the group consisting of compounds from Table A1.

In a second preferred embodiment of the present invention, the LC media according to the invention, especially those with negative dielectric

anisotropy, comprise one or more compounds selected from the group consisting of compounds from Table A2.

Table B

Table B shows possible chiral dopants which can be added to the LC media according to the invention.

CM 44 CM 45

R/S-1011

The LC media preferably comprise 0 to 10% by weight, in particular 0.01 to 5% by weight, particularly preferably 0.1 to 3% by weight, of dopants. The LC media preferably comprise one or more dopants selected from the group consisting of compounds from Table B.

Table C

Table C shows possible stabilisers which can be added to the LC media according to the invention. Therein n denotes an integer from 1 to 12, preferably 1 , 2, 3, 4, 5, 6, 7 or 8, and terminal methyl groups are not shown.





The LC media preferably comprise 0 to 10% by weight, in particular 1 ppm to 5% by weight, particularly preferably 1 ppm to 1 % by weight, of stabilisers. The LC media preferably comprise one or more stabilisers selected from the group consisting of compounds from Table C.

In addition, the following abbreviations and symbols are used:

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

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,

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

|| 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,I) clearing point [°C],

gi 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 concentrations and ratios in the present application are quoted in per cent by weight, and preferably 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" for the present invention relates to the capa- citive 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).

Examples

A) Host Mixtures

The nematic LC host mixture N1 is formulated as follows.

CC-3-V 40.00 % cl.p. 81.5°C

CC-3-V1 8.00 % Dh 0.0827

PUQU-2-F 3.00 % De 9.4

PUQU-3-F 8.00 % e 12.8 APUQU-2-F 7.00 % yi 75 mPa s

APUQU-3-F 7.00 %

CCP-3-1 7.00 %

CCOC-3-3 5.00 %

CCOC-4-3 5.00 %

CDUQU-3-F 10.00 %

Monomers + Photoinitiators

Polymerizable Mixtures Polymerizable mixture preparation: Polymerizable LC media for polymer wall formation are prepared by mixing LC host, monomers and photoinitiator (PI) and then homogenizing the resulting mixture by heating above its clearing point.

The polymerizable mixture compositions are shown in Table 1 below.

Table 1

Polymer Wall Formation

Test Cells: The test cells comprise two glass substrates coated with ITO, which are kept apart by spacer particles or foils at a layer thickness of 3-4 microns and glued together by an adhesive (usually Norland, NEA 123). On top of the electrode layers polyimide alignment layers (Nissan SE-6514 or SE2414) are applied which are rubbed parallel or antiparallel.

Wall formation:

The test cells are filled with the LC medium and placed on a black, non- reflecting surface. A photomask is placed on top of the test cells and the sample is subjected to UV radiation (Hg/Xe arch lamp, LOT QuantumDesign Europe, LS0205). The UV radation is applied in a first step for 30min with 4mW/cm² intensity, and in a second step for 30min with 10mW/cm² intensity (both steps at 365+/-10nm FWHM). Radiation of the emission spectrum below 320nm is removed by a dichroic mirror. The photomask usually has a pattern of equidistant lines of the same thickness. The line thickness is 140 microns and the distance between the lines is 9 microns, unless stated otherwise.

Characterization: Samples are analyzed under a polarization microscope. The isotropic polymer walls can clearly be distinguished from areas containing birefringend LC. The width of the walls and inclusions of LC into the polymer walls, and defects in the pixel area caused by contamination of polymer, or misalignment of the LC caused by the wall formation process can be observed.

Residual monomer content: After exposurure through the photomask, the test cells are opened by cutting off the sealant frame and lifting off the top glass using a scalpel. The LC host and remaining monomer is washed down by applying 100pm Ethyl methyl keton p. A. (Merck KGaA, Art. -Nr.:

1.09708.2500). The fluid is collected in a glass bottle and passed on for analysis by gas chromatography (Agilent Technologies 6850, Detector:

FID/310°C, Injector: Split/300^o, Program: 100°-300 10 min, Gas: Helium/ const flow @ 2.5ml, column: VF-5ms, 30m, 0.25pm, Sample concentration.

~ 1 %).

Device Examples

Polymerizable LC mixtures M1 -M6 are each filled into a test cell and subjected to UV irradiation under a photomask as described above.

Fig. 2-7 show polarization microscope images of test cells prepared from polymerizable mixtures M1 -M6, respectively, after polymerization. The formed polymer walls can be seen as dark lines, which means that the pattern of the mask has been reproduced in the reactive mixture.

For the test cells with mixture M6 the residual concentration of each of the two monomers was measured after polymerization as follows:

The values are shown in Table 2 below:

Table 2 - Residual monomer content for M6

It can be seen that nearly all of the monomer of formula IA1d with a vinyloxy group was consumed by the cationic polymerization reaction, whereas only a small portion of the monomer of formula R0 with a methacrylate group reacted but the major part is still present in the mixture after the cationic polymerization reaction. This monomer can still be polymerized by radical photopolymerization, for example in a PSA process.

This demonstrates that the LC medium according to the present invention is suitable for LC displays utilizing both the polymer wall technology and the PSA mode.

Claims

1 . A liquid crystal (LC) medium comprising a polymerizable component A) comprising

one or more polymerizable compounds comprising one or more polymerizable groups that are capable of undergoing cationic polymerization,

a cationic polymerization initiator,

optionally a stabiliser,

and a liquid-crystalline component B), which comprises one or more mesogenic or liquid-crystalline compounds.

2. The LC medium of claim 1 , characterized in that the polymerizable groups in the polymerizable compounds of component A) are selected from the group consisting of vinyloxy, vinyl, styrene, epoxy, oxetane, acetolactone, propiolactone, acetolactame and propiolactame.

3. The LC medium of claim 1 or 2, characterized in that the cationic

polymerization initiator is selected from photoacids and photoacid generators.

4. The LC medium according to one or more of claims 1 to 3, character- ized in that component A) comprises one or more polymerizable compounds selected of formula I

R^x -Sp²-P^y, H, F, Cl, -CN, 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-, -NR⁰-, -CO-, - C0-0-, -0-C0-, -0-C0-0-, -C(R°)=C(R⁰⁰)-, -CºC- in such a manner that O- and/or S-atoms are not directly connected with each other, and wherein one or more H atoms are each optionally replaced by F or Cl,

P^x, P^y a polymerizable group that is capable of undergoing cationic polymerization,

Sp¹, Sp² a spacer group or a single bond,

A¹ an aromatic, heteroaromatic, alicyclic or heterocyclic group having 4 to 25 ring atoms, which may also contain fused rings, and which is unsubstituted, or mono- or polysubstituted by L,

Z¹ -0-, -S-, -CO-, -C0-0-, -OCO-, -0-C0-0-, -OCH₂-, -CH₂O-, - SCH₂-, -CH2S-, -CF2O-, -OCF2-, -CF2S-, -SCF2-, -(CH₂)nii-, - CF2CH2-, -CH2CF2-, -(CF₂)nii-, -CH=CH-, -CF=CF-, -CºC-, - CH=CH-COO-, -OCO-CH=CH-, CR°R⁰⁰ or a single bond,

L F, Cl, -CN, -NO2, -NCO, -NCS, -OCN, -SCN, -C(=0)N(R^q)₂, -C(=0)Y^z, -C(=0)R^q, -N(R^q)2, optionally substituted silyl, optionally substituted aryl or heteroaryl having 5 to 20 ring atoms, 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(R⁰)-, -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, -CN, one or more of L may also denote P^x-Sp¹ -,

R^q 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 or Cl, R°, R⁰⁰ H or alkyl having 1 to 20 C atoms,

Y^z halogen, preferably F or Cl, m 0, 1 , 2, 3 or 4, n1 1 1 , 2, 3 or 4. 5. The LC medium according to any of claims 1 to 4, characterized in that component A) comprises one or more polymerizable compounds selected from the group consisting of the following subformulae:

R^y, R^z independently of one another, denote H, F, CFb or CF3,

Z³, Z⁴ are independently of each other -CO-O-, -O-CO-, -CFI₂0-, - _ OCFI₂-, -CF₂0-, -OCF₂- or -(CH₂)_ni 1-, where n1 1 is 2, 3 or 4,

5 r is 0, 1 , 2, 3 or 4, s is 0, 1 , 2 or 3, 0

t is 0, 1 or 2.

6. The LC medium according to any of claims 1 to 5, characterized in that component A) comprises one or more polymerizable compounds of,- formula IA

P^x-Sp^x-R^x IA wherein P^x and R^x have the meanings given in claim 4, and Sp^x is5 straight chain or branched alkylene having 1 to 40 C atoms, wherein one or more non-adjacent CFI₂-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 may be replaced by F, Cl, -CN or P^x. 5

7. The LC medium according to any one of claims 1 to 6, characterized in that component A) comprises one or more polymerizable compounds selected from the group consisting of the following subformulae P^x-(CHW^{1 1} )n2-(CH₂)n1-(CHW¹²)n3-H IA1

P^x-(CHW^{1 1} )n2-(CH₂)n1-(CHW¹²)n3-P^y IA2

P^X-(CH₂)n2-(CF₂)n1-(CH₂)n3-H IA3

P^X-(CH₂)n2-(CF₂)n1-(CH₂)n3-P^y IA4

(P^X-(CH₂)nl )n4CW^X4_-n4 IA5 wherein P^x, P^y are as defined in claim 4, and the other individual radicals, independently of each other and on each occurrence identically or differently, have the following meanings

W¹¹, W¹² H, F or Ci-Ci₂-alkyl,

W^x H, OH, or alkyl or alkoxy with 1 to 12 C atoms, preferably H,

OH, CHs, OCHs, or C₂H₅ or OC₂H₅, n1 an integer from 2 to 20, preferably from 3 to 16, n2, n3 0 or an integer from 1 to 6, n4 2, 3 or 4, and wherein in formula IA1 -IA5 in the group (CH₂)_ni one or more of the

CH₂ groups, which are not directly connected to P^x or P^y, are optionally replaced by -O- or -CO-, and one or more of the H atoms are optionally replaced by F or alkyl with 1 to 6 C atoms.

8. The LC medium according to any one of claims 1 to 7, characterized in that component A) contains a cationic polymerization initiator selected from photoacids and photoacid generators.

9. The LC medium according to any one of claims 1 to 8, characterized in that component A) contains a cationic polymerization initiator comprising a sulfonyloxyimino group, a sulfonium ion, or an iodonium ion.

10. The LC medium according to any one of claims 1 to 9, characterized in that the concentration of each individual polymerizable compound of component A) in the LC medium is from 1 to 25% by weight.

11. The LC medium according to any one of claims 1 to 10, characterized in that the total concentration of the polymerizable compounds of component A) in the LC medium is from 2 to 30% by weight.

12. The LC medium according to any one of claims 1 to 11 , characterized in that.the concentration of the cationic polymerization initiator in the LC medium is from 0.001 to 5% by weight.

13. The LC medium according to any one of claims 1 to 12, characterized in component B) comprises one or more compounds selected from formulae A and B

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-, -CH2O- or a single bond,

L²¹, L ²², L³¹, L ³² each, independently of one another, FI or F g 0, 1 , 2 or 3.

14. The LC medium according to claim 13, characterized in that component B) comprises, in addition to the compounds of formula A and/or B, one or more compounds of formula C

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, h 0, 1 , 2 or 3.

15. The LC medium according to any one of claims 1 to 14, characterized in that component B) comprises one or more compounds selected from formulae CY and PY:

wherein a denotes 1 or 2 b denotes 0 or 1 ,

R¹ and R² each, independently of one another, denote alkyl having 1 to

12 C atoms, where, in addition, one or two non-adjacent CFh groups may be replaced by -0-, -CH=CH-, -CO-, -OCO- or -COO- in such a way that O atoms are not linked directly to one another,

Z^x and Z^y each, independently of one another, denote -CH2CH2-,

-CH=CH-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -CO-O-, -O-CO-, -C₂F₄-, -CF=CF-, -CFI=CFI-CFl₂0- or a single bond, L^{1 4} each, independently of one another, denote F, Cl, OCF3,

CFs, CHs, CH₂F, CHF₂.

16. The LC medium according to claim 15, characterized in that component B) comprises, in addition to the compounds of formula CY and/or PY one or more compounds of formula ZK

in which the individual radicals have the following meanings:

R³ and R⁴ each, independently of one another, denote alkyl having 1 to

12 C atoms, in which, in addition, one or two non-adjacent CH2 groups may be replaced by -0-, -CH=CH-, -CO-, -O-CO- or -CO-O- in such a way that O atoms are not linked directly to one another,

Z^y denotes -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-,

-OCH2-, -C0-0-, -0-C0-, -C₂F₄-, -CF=CF-, -CH=CH-CH₂O- or a single bond.

17. The LC medium according to any one of claims 1 to 16 characterized in that the polymerizable compounds are polymerized.

18. An LC display comprising an LC medium according to any one of claims

1 to 17.

19. The LC display of claim 18, which is a flexible or curved display.

20. The LC display of claim 18 or 19, which is a TN, OCB, IPS, FFS, posi-

VA, VA or UB-FFS display.

21. A process for the production of an LC display according to any one of claims 18 to 20, comprising the steps of providing an LC medium as defined in any one of claims 1 to 16 into the display, and polymerizing the polymerizable compounds in defined regions of the display.

22. The process of claim 21 , wherein the polymerizable compounds are

photopolymerized by exposure to UV irradiation.

23. The process of claim 22, wherein the polymerizable compounds are

photopolymerized by exposure to UV irradiation through a photomask.

24. A process of preparing an LC medium according to any one of claims 1 to 16, comprising the steps of mixing a liquid-crystalline component B) as defined in any one of claims 1 and 13-16, with one or more

polymerizable compounds, or with component A), as defined in any one of claims 1 to 12, and optionally with further LC compounds and/or additives.